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Center for Advanced Electrical Machines and Drives (CAEMD) Huazhong University of Science & Technology, China Ronghai Qu & Dawei Li [email protected] High Torque Density Machines

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Page 1: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

Center for Advanced Electrical Machines and Drives (CAEMD) Huazhong University of Science amp Technology China

Ronghai Qu amp Dawei Li

RonghaiQuhusteducn

High Torque Density Machines

CAEMD Web httpwwwcaemdcn

Outline

High torque density (HTD) machines

- Introduction and Ways to achieve HTD

Flux modulation machines

- Principle Features Topologies and family members

Vernier machines Topologies Analysis Design Prototypes

Challenges and Opportunities

Conclusions

2

CAEMD Web httpwwwcaemdcn 3

Introduction

Torque density is a main research topic and important index of electrical machines from the first day

The Development of Electrical Machines

The torque density is improved by 40 times

CAEMD Web httpwwwcaemdcn

Reduction gearbox

High-speed machines coupled with reduction gearbox

Regular high-speed machine

Frequent maintenance

Break tooth at overload

Mechanical gears are widely used in mechanical transmission chains moving towards heavy loads and micro-precision

High Speed Motors with Gearbox

A Direct-drive machine is often a preferred solution

Gearbox makes the two rotors in physical contact resulting in vibration amp noise the need for lubricating grease and the risk of breaking teeth at overload condition

4

CAEMD Web httpwwwcaemdcn

High torque density is an required feature for direct-drive machines

2e i e

PeT D LΩ

= prop

Direct-drive

Regular Direct-Drive Machines

USA HTS motor 365MW 120RPM Alstom Advanced Induction Motor 20MW 180RPM

Problems in manufacture transportation maintenance

Bulky and heavy

Requires high torque at low speed

Increase torque density

CAEMD Web httpwwwcaemdcn

2[ ] cose e i e g gT K D L AB ABη φ= propClassic Torque Equation

Increase magnetic loading

Increase electric loading

Increase electric loading

Increase magnetic loading

Increase linearity of torque vs loading

Ways to Improve Torque Density

Optimizing aspect ratio

Increasing cooling capability

Superconducting wires

Increasing loading utilization

New technics

New materials

New topologies

Reducing armature reaction

6

CAEMD Web httpwwwcaemdcn 7

Peak power density 67kWkgPeak torque density16Nmkg

High efficient oil channel (direct cooling)rated current density 20Amm2

Increase the heat capacity

Reduce the thermal resistance

Winding Potting

Auxiliary Heat Path

Water Channel within the Slot

Direct Oil Cooling

Improved thermal performance

Advanced Cooling Solutions

H Li 2017 Advanced MotorampLord

M Galea 2012 Nottingham

S A Semidey 2014 GIT

Temperature 22 D Howey 2016 YASA Rated current density 246Am2

7

CAEMD Web httpwwwcaemdcn

Lightweight ironless-stator PM generators E Spooner etc 2005

Ironless Dual stator axial Flux motor F Caricchi etc 1996

Novel Mechanical Structures

Novel Structure motor S Engstroumlm S Lindgren 2007

Proposed Gear and high-speed generator

Conventional Direct drive

8

CAEMD Web httpwwwcaemdcn

Flux Path Seperation

Flux lines (PM field) Flux lines (armature field)

Aver

age

torq

ue (N

m)

Electric loading (Acm)

The flux paths of excitation and armature field are separated using the Halbach array magnets and the armature reaction is weakened

9

CAEMD Web httpwwwcaemdcn

Theory

Realization

Instance

SC materials can carry large current Nearly no loss under DC condition T

SC DC excitation Matching structure vacuum cooler refrigerator etc

σLDTe2

= BA=σ

Material cooling system

Copper no extra cooling 45-6

Copper forced air cooling 75-9

Copper liquid cooling

SC material liquid helium

10 MW wind generator SC generator compared to conventional generator volume decrease to 12 weight decrease to 13

High Electric Loading-Superconducting Machines

10

CAEMD Web httpwwwcaemdcn

Liu Y Noe M 2016

R Fair 2012

132MW Superconducting wind generator R QU et al 2015

Yubin Wang etc 2013

Superconducting wires are nice but not free

High Electric Loading-Superconducting Machines

11

CAEMD Web httpwwwcaemdcn

TpropABS AmdashElectric loading BmdashMagnetic loading SmdashAir gap area

A small PM motor nested inside a large PM motor The torque and power densities are boosted by doubling the air gap

surface area

bull Higher torque per volume bull Doubled airgap area amp weight bull Unchanged volume

bull Higher torque per volumeweight bull Doubled airgap area bull Coreless rotor bull Unchanged volume

High Torque Density Machine Topology I

12

CAEMD Web httpwwwcaemdcn

Dual-rotor radial flux two airgaps Ronghai Qu 2003

Dual-rotor axial flux two airgaps Ion Boldea 2011

Dual-stator radial flux two airgaps Tae-Uk Jung 2013

Radial amp Axial flux three airgaps Masafumi Namba 2017

High Torque Density Machine Topology I

13

CAEMD Web httpwwwcaemdcn 14

High Torque Density Machine Topology II

Transverse flux machine(TFM) H Weh 1986

pφa pφ φ=

pφpφ

a pNφ φ=

Equivalent model of PMSM amp TFM

The flux linkage of TFM is N times that of PMSM

The torque density of TFM is proportional to N

CAEMD Web httpwwwcaemdcn 15

Separated rotor TFM G Henneberge 1997

Double side TFM H Weh 1995

C-core TFM S M Husband 2003 R Qu T Lipo etc 2002

In recent years a few topologies with high torque density have been obtained and gain lots of attention

High Torque Density Machine Topology II

image1png

Magnet13

13

Winding13

13

Rotor Pole13

13

Stator Pole13

13

Shaft13

13

Frame13

13

13

CAEMD Web httpwwwcaemdcn

Flux Modulation Machines

For flux modulation machines their pole number of armature windings and excitation MMF are different (For special cases the two values can be same)

They have potential to be with high torque density so that they are very competitive

16

Flux Modulation a new way to improve torque density

CAEMD Web httpwwwcaemdcn

Stator

Ferromagnetic pole pieces

Magnets

Rotor

Regular PM machine Flux modulation PM machine

There are three components in a flux-modulation machine ie 1 flux modulator 2 armature and 3 excitation field exciters

Flux Modulation Machines

17

CAEMD Web httpwwwcaemdcn

MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

CAEMD Web httpwwwcaemdcn

Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

CAEMD Web httpwwwcaemdcn

Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

CAEMD Web httpwwwcaemdcn

Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

CAEMD Web httpwwwcaemdcn

Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

CAEMD Web httpwwwcaemdcn

Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

CAEMD Web httpwwwcaemdcn

Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 2: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Outline

High torque density (HTD) machines

- Introduction and Ways to achieve HTD

Flux modulation machines

- Principle Features Topologies and family members

Vernier machines Topologies Analysis Design Prototypes

Challenges and Opportunities

Conclusions

2

CAEMD Web httpwwwcaemdcn 3

Introduction

Torque density is a main research topic and important index of electrical machines from the first day

The Development of Electrical Machines

The torque density is improved by 40 times

CAEMD Web httpwwwcaemdcn

Reduction gearbox

High-speed machines coupled with reduction gearbox

Regular high-speed machine

Frequent maintenance

Break tooth at overload

Mechanical gears are widely used in mechanical transmission chains moving towards heavy loads and micro-precision

High Speed Motors with Gearbox

A Direct-drive machine is often a preferred solution

Gearbox makes the two rotors in physical contact resulting in vibration amp noise the need for lubricating grease and the risk of breaking teeth at overload condition

4

CAEMD Web httpwwwcaemdcn

High torque density is an required feature for direct-drive machines

2e i e

PeT D LΩ

= prop

Direct-drive

Regular Direct-Drive Machines

USA HTS motor 365MW 120RPM Alstom Advanced Induction Motor 20MW 180RPM

Problems in manufacture transportation maintenance

Bulky and heavy

Requires high torque at low speed

Increase torque density

CAEMD Web httpwwwcaemdcn

2[ ] cose e i e g gT K D L AB ABη φ= propClassic Torque Equation

Increase magnetic loading

Increase electric loading

Increase electric loading

Increase magnetic loading

Increase linearity of torque vs loading

Ways to Improve Torque Density

Optimizing aspect ratio

Increasing cooling capability

Superconducting wires

Increasing loading utilization

New technics

New materials

New topologies

Reducing armature reaction

6

CAEMD Web httpwwwcaemdcn 7

Peak power density 67kWkgPeak torque density16Nmkg

High efficient oil channel (direct cooling)rated current density 20Amm2

Increase the heat capacity

Reduce the thermal resistance

Winding Potting

Auxiliary Heat Path

Water Channel within the Slot

Direct Oil Cooling

Improved thermal performance

Advanced Cooling Solutions

H Li 2017 Advanced MotorampLord

M Galea 2012 Nottingham

S A Semidey 2014 GIT

Temperature 22 D Howey 2016 YASA Rated current density 246Am2

7

CAEMD Web httpwwwcaemdcn

Lightweight ironless-stator PM generators E Spooner etc 2005

Ironless Dual stator axial Flux motor F Caricchi etc 1996

Novel Mechanical Structures

Novel Structure motor S Engstroumlm S Lindgren 2007

Proposed Gear and high-speed generator

Conventional Direct drive

8

CAEMD Web httpwwwcaemdcn

Flux Path Seperation

Flux lines (PM field) Flux lines (armature field)

Aver

age

torq

ue (N

m)

Electric loading (Acm)

The flux paths of excitation and armature field are separated using the Halbach array magnets and the armature reaction is weakened

9

CAEMD Web httpwwwcaemdcn

Theory

Realization

Instance

SC materials can carry large current Nearly no loss under DC condition T

SC DC excitation Matching structure vacuum cooler refrigerator etc

σLDTe2

= BA=σ

Material cooling system

Copper no extra cooling 45-6

Copper forced air cooling 75-9

Copper liquid cooling

SC material liquid helium

10 MW wind generator SC generator compared to conventional generator volume decrease to 12 weight decrease to 13

High Electric Loading-Superconducting Machines

10

CAEMD Web httpwwwcaemdcn

Liu Y Noe M 2016

R Fair 2012

132MW Superconducting wind generator R QU et al 2015

Yubin Wang etc 2013

Superconducting wires are nice but not free

High Electric Loading-Superconducting Machines

11

CAEMD Web httpwwwcaemdcn

TpropABS AmdashElectric loading BmdashMagnetic loading SmdashAir gap area

A small PM motor nested inside a large PM motor The torque and power densities are boosted by doubling the air gap

surface area

bull Higher torque per volume bull Doubled airgap area amp weight bull Unchanged volume

bull Higher torque per volumeweight bull Doubled airgap area bull Coreless rotor bull Unchanged volume

High Torque Density Machine Topology I

12

CAEMD Web httpwwwcaemdcn

Dual-rotor radial flux two airgaps Ronghai Qu 2003

Dual-rotor axial flux two airgaps Ion Boldea 2011

Dual-stator radial flux two airgaps Tae-Uk Jung 2013

Radial amp Axial flux three airgaps Masafumi Namba 2017

High Torque Density Machine Topology I

13

CAEMD Web httpwwwcaemdcn 14

High Torque Density Machine Topology II

Transverse flux machine(TFM) H Weh 1986

pφa pφ φ=

pφpφ

a pNφ φ=

Equivalent model of PMSM amp TFM

The flux linkage of TFM is N times that of PMSM

The torque density of TFM is proportional to N

CAEMD Web httpwwwcaemdcn 15

Separated rotor TFM G Henneberge 1997

Double side TFM H Weh 1995

C-core TFM S M Husband 2003 R Qu T Lipo etc 2002

In recent years a few topologies with high torque density have been obtained and gain lots of attention

High Torque Density Machine Topology II

image1png

Magnet13

13

Winding13

13

Rotor Pole13

13

Stator Pole13

13

Shaft13

13

Frame13

13

13

CAEMD Web httpwwwcaemdcn

Flux Modulation Machines

For flux modulation machines their pole number of armature windings and excitation MMF are different (For special cases the two values can be same)

They have potential to be with high torque density so that they are very competitive

16

Flux Modulation a new way to improve torque density

CAEMD Web httpwwwcaemdcn

Stator

Ferromagnetic pole pieces

Magnets

Rotor

Regular PM machine Flux modulation PM machine

There are three components in a flux-modulation machine ie 1 flux modulator 2 armature and 3 excitation field exciters

Flux Modulation Machines

17

CAEMD Web httpwwwcaemdcn

MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

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Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 3: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn 3

Introduction

Torque density is a main research topic and important index of electrical machines from the first day

The Development of Electrical Machines

The torque density is improved by 40 times

CAEMD Web httpwwwcaemdcn

Reduction gearbox

High-speed machines coupled with reduction gearbox

Regular high-speed machine

Frequent maintenance

Break tooth at overload

Mechanical gears are widely used in mechanical transmission chains moving towards heavy loads and micro-precision

High Speed Motors with Gearbox

A Direct-drive machine is often a preferred solution

Gearbox makes the two rotors in physical contact resulting in vibration amp noise the need for lubricating grease and the risk of breaking teeth at overload condition

4

CAEMD Web httpwwwcaemdcn

High torque density is an required feature for direct-drive machines

2e i e

PeT D LΩ

= prop

Direct-drive

Regular Direct-Drive Machines

USA HTS motor 365MW 120RPM Alstom Advanced Induction Motor 20MW 180RPM

Problems in manufacture transportation maintenance

Bulky and heavy

Requires high torque at low speed

Increase torque density

CAEMD Web httpwwwcaemdcn

2[ ] cose e i e g gT K D L AB ABη φ= propClassic Torque Equation

Increase magnetic loading

Increase electric loading

Increase electric loading

Increase magnetic loading

Increase linearity of torque vs loading

Ways to Improve Torque Density

Optimizing aspect ratio

Increasing cooling capability

Superconducting wires

Increasing loading utilization

New technics

New materials

New topologies

Reducing armature reaction

6

CAEMD Web httpwwwcaemdcn 7

Peak power density 67kWkgPeak torque density16Nmkg

High efficient oil channel (direct cooling)rated current density 20Amm2

Increase the heat capacity

Reduce the thermal resistance

Winding Potting

Auxiliary Heat Path

Water Channel within the Slot

Direct Oil Cooling

Improved thermal performance

Advanced Cooling Solutions

H Li 2017 Advanced MotorampLord

M Galea 2012 Nottingham

S A Semidey 2014 GIT

Temperature 22 D Howey 2016 YASA Rated current density 246Am2

7

CAEMD Web httpwwwcaemdcn

Lightweight ironless-stator PM generators E Spooner etc 2005

Ironless Dual stator axial Flux motor F Caricchi etc 1996

Novel Mechanical Structures

Novel Structure motor S Engstroumlm S Lindgren 2007

Proposed Gear and high-speed generator

Conventional Direct drive

8

CAEMD Web httpwwwcaemdcn

Flux Path Seperation

Flux lines (PM field) Flux lines (armature field)

Aver

age

torq

ue (N

m)

Electric loading (Acm)

The flux paths of excitation and armature field are separated using the Halbach array magnets and the armature reaction is weakened

9

CAEMD Web httpwwwcaemdcn

Theory

Realization

Instance

SC materials can carry large current Nearly no loss under DC condition T

SC DC excitation Matching structure vacuum cooler refrigerator etc

σLDTe2

= BA=σ

Material cooling system

Copper no extra cooling 45-6

Copper forced air cooling 75-9

Copper liquid cooling

SC material liquid helium

10 MW wind generator SC generator compared to conventional generator volume decrease to 12 weight decrease to 13

High Electric Loading-Superconducting Machines

10

CAEMD Web httpwwwcaemdcn

Liu Y Noe M 2016

R Fair 2012

132MW Superconducting wind generator R QU et al 2015

Yubin Wang etc 2013

Superconducting wires are nice but not free

High Electric Loading-Superconducting Machines

11

CAEMD Web httpwwwcaemdcn

TpropABS AmdashElectric loading BmdashMagnetic loading SmdashAir gap area

A small PM motor nested inside a large PM motor The torque and power densities are boosted by doubling the air gap

surface area

bull Higher torque per volume bull Doubled airgap area amp weight bull Unchanged volume

bull Higher torque per volumeweight bull Doubled airgap area bull Coreless rotor bull Unchanged volume

High Torque Density Machine Topology I

12

CAEMD Web httpwwwcaemdcn

Dual-rotor radial flux two airgaps Ronghai Qu 2003

Dual-rotor axial flux two airgaps Ion Boldea 2011

Dual-stator radial flux two airgaps Tae-Uk Jung 2013

Radial amp Axial flux three airgaps Masafumi Namba 2017

High Torque Density Machine Topology I

13

CAEMD Web httpwwwcaemdcn 14

High Torque Density Machine Topology II

Transverse flux machine(TFM) H Weh 1986

pφa pφ φ=

pφpφ

a pNφ φ=

Equivalent model of PMSM amp TFM

The flux linkage of TFM is N times that of PMSM

The torque density of TFM is proportional to N

CAEMD Web httpwwwcaemdcn 15

Separated rotor TFM G Henneberge 1997

Double side TFM H Weh 1995

C-core TFM S M Husband 2003 R Qu T Lipo etc 2002

In recent years a few topologies with high torque density have been obtained and gain lots of attention

High Torque Density Machine Topology II

image1png

Magnet13

13

Winding13

13

Rotor Pole13

13

Stator Pole13

13

Shaft13

13

Frame13

13

13

CAEMD Web httpwwwcaemdcn

Flux Modulation Machines

For flux modulation machines their pole number of armature windings and excitation MMF are different (For special cases the two values can be same)

They have potential to be with high torque density so that they are very competitive

16

Flux Modulation a new way to improve torque density

CAEMD Web httpwwwcaemdcn

Stator

Ferromagnetic pole pieces

Magnets

Rotor

Regular PM machine Flux modulation PM machine

There are three components in a flux-modulation machine ie 1 flux modulator 2 armature and 3 excitation field exciters

Flux Modulation Machines

17

CAEMD Web httpwwwcaemdcn

MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

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Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

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Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

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Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

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Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

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Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

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0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

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13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

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2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

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Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 4: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Reduction gearbox

High-speed machines coupled with reduction gearbox

Regular high-speed machine

Frequent maintenance

Break tooth at overload

Mechanical gears are widely used in mechanical transmission chains moving towards heavy loads and micro-precision

High Speed Motors with Gearbox

A Direct-drive machine is often a preferred solution

Gearbox makes the two rotors in physical contact resulting in vibration amp noise the need for lubricating grease and the risk of breaking teeth at overload condition

4

CAEMD Web httpwwwcaemdcn

High torque density is an required feature for direct-drive machines

2e i e

PeT D LΩ

= prop

Direct-drive

Regular Direct-Drive Machines

USA HTS motor 365MW 120RPM Alstom Advanced Induction Motor 20MW 180RPM

Problems in manufacture transportation maintenance

Bulky and heavy

Requires high torque at low speed

Increase torque density

CAEMD Web httpwwwcaemdcn

2[ ] cose e i e g gT K D L AB ABη φ= propClassic Torque Equation

Increase magnetic loading

Increase electric loading

Increase electric loading

Increase magnetic loading

Increase linearity of torque vs loading

Ways to Improve Torque Density

Optimizing aspect ratio

Increasing cooling capability

Superconducting wires

Increasing loading utilization

New technics

New materials

New topologies

Reducing armature reaction

6

CAEMD Web httpwwwcaemdcn 7

Peak power density 67kWkgPeak torque density16Nmkg

High efficient oil channel (direct cooling)rated current density 20Amm2

Increase the heat capacity

Reduce the thermal resistance

Winding Potting

Auxiliary Heat Path

Water Channel within the Slot

Direct Oil Cooling

Improved thermal performance

Advanced Cooling Solutions

H Li 2017 Advanced MotorampLord

M Galea 2012 Nottingham

S A Semidey 2014 GIT

Temperature 22 D Howey 2016 YASA Rated current density 246Am2

7

CAEMD Web httpwwwcaemdcn

Lightweight ironless-stator PM generators E Spooner etc 2005

Ironless Dual stator axial Flux motor F Caricchi etc 1996

Novel Mechanical Structures

Novel Structure motor S Engstroumlm S Lindgren 2007

Proposed Gear and high-speed generator

Conventional Direct drive

8

CAEMD Web httpwwwcaemdcn

Flux Path Seperation

Flux lines (PM field) Flux lines (armature field)

Aver

age

torq

ue (N

m)

Electric loading (Acm)

The flux paths of excitation and armature field are separated using the Halbach array magnets and the armature reaction is weakened

9

CAEMD Web httpwwwcaemdcn

Theory

Realization

Instance

SC materials can carry large current Nearly no loss under DC condition T

SC DC excitation Matching structure vacuum cooler refrigerator etc

σLDTe2

= BA=σ

Material cooling system

Copper no extra cooling 45-6

Copper forced air cooling 75-9

Copper liquid cooling

SC material liquid helium

10 MW wind generator SC generator compared to conventional generator volume decrease to 12 weight decrease to 13

High Electric Loading-Superconducting Machines

10

CAEMD Web httpwwwcaemdcn

Liu Y Noe M 2016

R Fair 2012

132MW Superconducting wind generator R QU et al 2015

Yubin Wang etc 2013

Superconducting wires are nice but not free

High Electric Loading-Superconducting Machines

11

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TpropABS AmdashElectric loading BmdashMagnetic loading SmdashAir gap area

A small PM motor nested inside a large PM motor The torque and power densities are boosted by doubling the air gap

surface area

bull Higher torque per volume bull Doubled airgap area amp weight bull Unchanged volume

bull Higher torque per volumeweight bull Doubled airgap area bull Coreless rotor bull Unchanged volume

High Torque Density Machine Topology I

12

CAEMD Web httpwwwcaemdcn

Dual-rotor radial flux two airgaps Ronghai Qu 2003

Dual-rotor axial flux two airgaps Ion Boldea 2011

Dual-stator radial flux two airgaps Tae-Uk Jung 2013

Radial amp Axial flux three airgaps Masafumi Namba 2017

High Torque Density Machine Topology I

13

CAEMD Web httpwwwcaemdcn 14

High Torque Density Machine Topology II

Transverse flux machine(TFM) H Weh 1986

pφa pφ φ=

pφpφ

a pNφ φ=

Equivalent model of PMSM amp TFM

The flux linkage of TFM is N times that of PMSM

The torque density of TFM is proportional to N

CAEMD Web httpwwwcaemdcn 15

Separated rotor TFM G Henneberge 1997

Double side TFM H Weh 1995

C-core TFM S M Husband 2003 R Qu T Lipo etc 2002

In recent years a few topologies with high torque density have been obtained and gain lots of attention

High Torque Density Machine Topology II

image1png

Magnet13

13

Winding13

13

Rotor Pole13

13

Stator Pole13

13

Shaft13

13

Frame13

13

13

CAEMD Web httpwwwcaemdcn

Flux Modulation Machines

For flux modulation machines their pole number of armature windings and excitation MMF are different (For special cases the two values can be same)

They have potential to be with high torque density so that they are very competitive

16

Flux Modulation a new way to improve torque density

CAEMD Web httpwwwcaemdcn

Stator

Ferromagnetic pole pieces

Magnets

Rotor

Regular PM machine Flux modulation PM machine

There are three components in a flux-modulation machine ie 1 flux modulator 2 armature and 3 excitation field exciters

Flux Modulation Machines

17

CAEMD Web httpwwwcaemdcn

MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

CAEMD Web httpwwwcaemdcn

Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

CAEMD Web httpwwwcaemdcn

Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

CAEMD Web httpwwwcaemdcn

Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

CAEMD Web httpwwwcaemdcn

Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

CAEMD Web httpwwwcaemdcn

Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

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Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

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Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

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Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

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Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

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Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

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Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 5: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

High torque density is an required feature for direct-drive machines

2e i e

PeT D LΩ

= prop

Direct-drive

Regular Direct-Drive Machines

USA HTS motor 365MW 120RPM Alstom Advanced Induction Motor 20MW 180RPM

Problems in manufacture transportation maintenance

Bulky and heavy

Requires high torque at low speed

Increase torque density

CAEMD Web httpwwwcaemdcn

2[ ] cose e i e g gT K D L AB ABη φ= propClassic Torque Equation

Increase magnetic loading

Increase electric loading

Increase electric loading

Increase magnetic loading

Increase linearity of torque vs loading

Ways to Improve Torque Density

Optimizing aspect ratio

Increasing cooling capability

Superconducting wires

Increasing loading utilization

New technics

New materials

New topologies

Reducing armature reaction

6

CAEMD Web httpwwwcaemdcn 7

Peak power density 67kWkgPeak torque density16Nmkg

High efficient oil channel (direct cooling)rated current density 20Amm2

Increase the heat capacity

Reduce the thermal resistance

Winding Potting

Auxiliary Heat Path

Water Channel within the Slot

Direct Oil Cooling

Improved thermal performance

Advanced Cooling Solutions

H Li 2017 Advanced MotorampLord

M Galea 2012 Nottingham

S A Semidey 2014 GIT

Temperature 22 D Howey 2016 YASA Rated current density 246Am2

7

CAEMD Web httpwwwcaemdcn

Lightweight ironless-stator PM generators E Spooner etc 2005

Ironless Dual stator axial Flux motor F Caricchi etc 1996

Novel Mechanical Structures

Novel Structure motor S Engstroumlm S Lindgren 2007

Proposed Gear and high-speed generator

Conventional Direct drive

8

CAEMD Web httpwwwcaemdcn

Flux Path Seperation

Flux lines (PM field) Flux lines (armature field)

Aver

age

torq

ue (N

m)

Electric loading (Acm)

The flux paths of excitation and armature field are separated using the Halbach array magnets and the armature reaction is weakened

9

CAEMD Web httpwwwcaemdcn

Theory

Realization

Instance

SC materials can carry large current Nearly no loss under DC condition T

SC DC excitation Matching structure vacuum cooler refrigerator etc

σLDTe2

= BA=σ

Material cooling system

Copper no extra cooling 45-6

Copper forced air cooling 75-9

Copper liquid cooling

SC material liquid helium

10 MW wind generator SC generator compared to conventional generator volume decrease to 12 weight decrease to 13

High Electric Loading-Superconducting Machines

10

CAEMD Web httpwwwcaemdcn

Liu Y Noe M 2016

R Fair 2012

132MW Superconducting wind generator R QU et al 2015

Yubin Wang etc 2013

Superconducting wires are nice but not free

High Electric Loading-Superconducting Machines

11

CAEMD Web httpwwwcaemdcn

TpropABS AmdashElectric loading BmdashMagnetic loading SmdashAir gap area

A small PM motor nested inside a large PM motor The torque and power densities are boosted by doubling the air gap

surface area

bull Higher torque per volume bull Doubled airgap area amp weight bull Unchanged volume

bull Higher torque per volumeweight bull Doubled airgap area bull Coreless rotor bull Unchanged volume

High Torque Density Machine Topology I

12

CAEMD Web httpwwwcaemdcn

Dual-rotor radial flux two airgaps Ronghai Qu 2003

Dual-rotor axial flux two airgaps Ion Boldea 2011

Dual-stator radial flux two airgaps Tae-Uk Jung 2013

Radial amp Axial flux three airgaps Masafumi Namba 2017

High Torque Density Machine Topology I

13

CAEMD Web httpwwwcaemdcn 14

High Torque Density Machine Topology II

Transverse flux machine(TFM) H Weh 1986

pφa pφ φ=

pφpφ

a pNφ φ=

Equivalent model of PMSM amp TFM

The flux linkage of TFM is N times that of PMSM

The torque density of TFM is proportional to N

CAEMD Web httpwwwcaemdcn 15

Separated rotor TFM G Henneberge 1997

Double side TFM H Weh 1995

C-core TFM S M Husband 2003 R Qu T Lipo etc 2002

In recent years a few topologies with high torque density have been obtained and gain lots of attention

High Torque Density Machine Topology II

image1png

Magnet13

13

Winding13

13

Rotor Pole13

13

Stator Pole13

13

Shaft13

13

Frame13

13

13

CAEMD Web httpwwwcaemdcn

Flux Modulation Machines

For flux modulation machines their pole number of armature windings and excitation MMF are different (For special cases the two values can be same)

They have potential to be with high torque density so that they are very competitive

16

Flux Modulation a new way to improve torque density

CAEMD Web httpwwwcaemdcn

Stator

Ferromagnetic pole pieces

Magnets

Rotor

Regular PM machine Flux modulation PM machine

There are three components in a flux-modulation machine ie 1 flux modulator 2 armature and 3 excitation field exciters

Flux Modulation Machines

17

CAEMD Web httpwwwcaemdcn

MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

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Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

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Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

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Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

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Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 6: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

2[ ] cose e i e g gT K D L AB ABη φ= propClassic Torque Equation

Increase magnetic loading

Increase electric loading

Increase electric loading

Increase magnetic loading

Increase linearity of torque vs loading

Ways to Improve Torque Density

Optimizing aspect ratio

Increasing cooling capability

Superconducting wires

Increasing loading utilization

New technics

New materials

New topologies

Reducing armature reaction

6

CAEMD Web httpwwwcaemdcn 7

Peak power density 67kWkgPeak torque density16Nmkg

High efficient oil channel (direct cooling)rated current density 20Amm2

Increase the heat capacity

Reduce the thermal resistance

Winding Potting

Auxiliary Heat Path

Water Channel within the Slot

Direct Oil Cooling

Improved thermal performance

Advanced Cooling Solutions

H Li 2017 Advanced MotorampLord

M Galea 2012 Nottingham

S A Semidey 2014 GIT

Temperature 22 D Howey 2016 YASA Rated current density 246Am2

7

CAEMD Web httpwwwcaemdcn

Lightweight ironless-stator PM generators E Spooner etc 2005

Ironless Dual stator axial Flux motor F Caricchi etc 1996

Novel Mechanical Structures

Novel Structure motor S Engstroumlm S Lindgren 2007

Proposed Gear and high-speed generator

Conventional Direct drive

8

CAEMD Web httpwwwcaemdcn

Flux Path Seperation

Flux lines (PM field) Flux lines (armature field)

Aver

age

torq

ue (N

m)

Electric loading (Acm)

The flux paths of excitation and armature field are separated using the Halbach array magnets and the armature reaction is weakened

9

CAEMD Web httpwwwcaemdcn

Theory

Realization

Instance

SC materials can carry large current Nearly no loss under DC condition T

SC DC excitation Matching structure vacuum cooler refrigerator etc

σLDTe2

= BA=σ

Material cooling system

Copper no extra cooling 45-6

Copper forced air cooling 75-9

Copper liquid cooling

SC material liquid helium

10 MW wind generator SC generator compared to conventional generator volume decrease to 12 weight decrease to 13

High Electric Loading-Superconducting Machines

10

CAEMD Web httpwwwcaemdcn

Liu Y Noe M 2016

R Fair 2012

132MW Superconducting wind generator R QU et al 2015

Yubin Wang etc 2013

Superconducting wires are nice but not free

High Electric Loading-Superconducting Machines

11

CAEMD Web httpwwwcaemdcn

TpropABS AmdashElectric loading BmdashMagnetic loading SmdashAir gap area

A small PM motor nested inside a large PM motor The torque and power densities are boosted by doubling the air gap

surface area

bull Higher torque per volume bull Doubled airgap area amp weight bull Unchanged volume

bull Higher torque per volumeweight bull Doubled airgap area bull Coreless rotor bull Unchanged volume

High Torque Density Machine Topology I

12

CAEMD Web httpwwwcaemdcn

Dual-rotor radial flux two airgaps Ronghai Qu 2003

Dual-rotor axial flux two airgaps Ion Boldea 2011

Dual-stator radial flux two airgaps Tae-Uk Jung 2013

Radial amp Axial flux three airgaps Masafumi Namba 2017

High Torque Density Machine Topology I

13

CAEMD Web httpwwwcaemdcn 14

High Torque Density Machine Topology II

Transverse flux machine(TFM) H Weh 1986

pφa pφ φ=

pφpφ

a pNφ φ=

Equivalent model of PMSM amp TFM

The flux linkage of TFM is N times that of PMSM

The torque density of TFM is proportional to N

CAEMD Web httpwwwcaemdcn 15

Separated rotor TFM G Henneberge 1997

Double side TFM H Weh 1995

C-core TFM S M Husband 2003 R Qu T Lipo etc 2002

In recent years a few topologies with high torque density have been obtained and gain lots of attention

High Torque Density Machine Topology II

image1png

Magnet13

13

Winding13

13

Rotor Pole13

13

Stator Pole13

13

Shaft13

13

Frame13

13

13

CAEMD Web httpwwwcaemdcn

Flux Modulation Machines

For flux modulation machines their pole number of armature windings and excitation MMF are different (For special cases the two values can be same)

They have potential to be with high torque density so that they are very competitive

16

Flux Modulation a new way to improve torque density

CAEMD Web httpwwwcaemdcn

Stator

Ferromagnetic pole pieces

Magnets

Rotor

Regular PM machine Flux modulation PM machine

There are three components in a flux-modulation machine ie 1 flux modulator 2 armature and 3 excitation field exciters

Flux Modulation Machines

17

CAEMD Web httpwwwcaemdcn

MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

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Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

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Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

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1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

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Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

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Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

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Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

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0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

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13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

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2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

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Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 7: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn 7

Peak power density 67kWkgPeak torque density16Nmkg

High efficient oil channel (direct cooling)rated current density 20Amm2

Increase the heat capacity

Reduce the thermal resistance

Winding Potting

Auxiliary Heat Path

Water Channel within the Slot

Direct Oil Cooling

Improved thermal performance

Advanced Cooling Solutions

H Li 2017 Advanced MotorampLord

M Galea 2012 Nottingham

S A Semidey 2014 GIT

Temperature 22 D Howey 2016 YASA Rated current density 246Am2

7

CAEMD Web httpwwwcaemdcn

Lightweight ironless-stator PM generators E Spooner etc 2005

Ironless Dual stator axial Flux motor F Caricchi etc 1996

Novel Mechanical Structures

Novel Structure motor S Engstroumlm S Lindgren 2007

Proposed Gear and high-speed generator

Conventional Direct drive

8

CAEMD Web httpwwwcaemdcn

Flux Path Seperation

Flux lines (PM field) Flux lines (armature field)

Aver

age

torq

ue (N

m)

Electric loading (Acm)

The flux paths of excitation and armature field are separated using the Halbach array magnets and the armature reaction is weakened

9

CAEMD Web httpwwwcaemdcn

Theory

Realization

Instance

SC materials can carry large current Nearly no loss under DC condition T

SC DC excitation Matching structure vacuum cooler refrigerator etc

σLDTe2

= BA=σ

Material cooling system

Copper no extra cooling 45-6

Copper forced air cooling 75-9

Copper liquid cooling

SC material liquid helium

10 MW wind generator SC generator compared to conventional generator volume decrease to 12 weight decrease to 13

High Electric Loading-Superconducting Machines

10

CAEMD Web httpwwwcaemdcn

Liu Y Noe M 2016

R Fair 2012

132MW Superconducting wind generator R QU et al 2015

Yubin Wang etc 2013

Superconducting wires are nice but not free

High Electric Loading-Superconducting Machines

11

CAEMD Web httpwwwcaemdcn

TpropABS AmdashElectric loading BmdashMagnetic loading SmdashAir gap area

A small PM motor nested inside a large PM motor The torque and power densities are boosted by doubling the air gap

surface area

bull Higher torque per volume bull Doubled airgap area amp weight bull Unchanged volume

bull Higher torque per volumeweight bull Doubled airgap area bull Coreless rotor bull Unchanged volume

High Torque Density Machine Topology I

12

CAEMD Web httpwwwcaemdcn

Dual-rotor radial flux two airgaps Ronghai Qu 2003

Dual-rotor axial flux two airgaps Ion Boldea 2011

Dual-stator radial flux two airgaps Tae-Uk Jung 2013

Radial amp Axial flux three airgaps Masafumi Namba 2017

High Torque Density Machine Topology I

13

CAEMD Web httpwwwcaemdcn 14

High Torque Density Machine Topology II

Transverse flux machine(TFM) H Weh 1986

pφa pφ φ=

pφpφ

a pNφ φ=

Equivalent model of PMSM amp TFM

The flux linkage of TFM is N times that of PMSM

The torque density of TFM is proportional to N

CAEMD Web httpwwwcaemdcn 15

Separated rotor TFM G Henneberge 1997

Double side TFM H Weh 1995

C-core TFM S M Husband 2003 R Qu T Lipo etc 2002

In recent years a few topologies with high torque density have been obtained and gain lots of attention

High Torque Density Machine Topology II

image1png

Magnet13

13

Winding13

13

Rotor Pole13

13

Stator Pole13

13

Shaft13

13

Frame13

13

13

CAEMD Web httpwwwcaemdcn

Flux Modulation Machines

For flux modulation machines their pole number of armature windings and excitation MMF are different (For special cases the two values can be same)

They have potential to be with high torque density so that they are very competitive

16

Flux Modulation a new way to improve torque density

CAEMD Web httpwwwcaemdcn

Stator

Ferromagnetic pole pieces

Magnets

Rotor

Regular PM machine Flux modulation PM machine

There are three components in a flux-modulation machine ie 1 flux modulator 2 armature and 3 excitation field exciters

Flux Modulation Machines

17

CAEMD Web httpwwwcaemdcn

MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

CAEMD Web httpwwwcaemdcn

Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

CAEMD Web httpwwwcaemdcn

Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

CAEMD Web httpwwwcaemdcn

Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

CAEMD Web httpwwwcaemdcn

Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

CAEMD Web httpwwwcaemdcn

Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

CAEMD Web httpwwwcaemdcn

Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

CAEMD Web httpwwwcaemdcn

Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

CAEMD Web httpwwwcaemdcn

Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 8: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Lightweight ironless-stator PM generators E Spooner etc 2005

Ironless Dual stator axial Flux motor F Caricchi etc 1996

Novel Mechanical Structures

Novel Structure motor S Engstroumlm S Lindgren 2007

Proposed Gear and high-speed generator

Conventional Direct drive

8

CAEMD Web httpwwwcaemdcn

Flux Path Seperation

Flux lines (PM field) Flux lines (armature field)

Aver

age

torq

ue (N

m)

Electric loading (Acm)

The flux paths of excitation and armature field are separated using the Halbach array magnets and the armature reaction is weakened

9

CAEMD Web httpwwwcaemdcn

Theory

Realization

Instance

SC materials can carry large current Nearly no loss under DC condition T

SC DC excitation Matching structure vacuum cooler refrigerator etc

σLDTe2

= BA=σ

Material cooling system

Copper no extra cooling 45-6

Copper forced air cooling 75-9

Copper liquid cooling

SC material liquid helium

10 MW wind generator SC generator compared to conventional generator volume decrease to 12 weight decrease to 13

High Electric Loading-Superconducting Machines

10

CAEMD Web httpwwwcaemdcn

Liu Y Noe M 2016

R Fair 2012

132MW Superconducting wind generator R QU et al 2015

Yubin Wang etc 2013

Superconducting wires are nice but not free

High Electric Loading-Superconducting Machines

11

CAEMD Web httpwwwcaemdcn

TpropABS AmdashElectric loading BmdashMagnetic loading SmdashAir gap area

A small PM motor nested inside a large PM motor The torque and power densities are boosted by doubling the air gap

surface area

bull Higher torque per volume bull Doubled airgap area amp weight bull Unchanged volume

bull Higher torque per volumeweight bull Doubled airgap area bull Coreless rotor bull Unchanged volume

High Torque Density Machine Topology I

12

CAEMD Web httpwwwcaemdcn

Dual-rotor radial flux two airgaps Ronghai Qu 2003

Dual-rotor axial flux two airgaps Ion Boldea 2011

Dual-stator radial flux two airgaps Tae-Uk Jung 2013

Radial amp Axial flux three airgaps Masafumi Namba 2017

High Torque Density Machine Topology I

13

CAEMD Web httpwwwcaemdcn 14

High Torque Density Machine Topology II

Transverse flux machine(TFM) H Weh 1986

pφa pφ φ=

pφpφ

a pNφ φ=

Equivalent model of PMSM amp TFM

The flux linkage of TFM is N times that of PMSM

The torque density of TFM is proportional to N

CAEMD Web httpwwwcaemdcn 15

Separated rotor TFM G Henneberge 1997

Double side TFM H Weh 1995

C-core TFM S M Husband 2003 R Qu T Lipo etc 2002

In recent years a few topologies with high torque density have been obtained and gain lots of attention

High Torque Density Machine Topology II

image1png

Magnet13

13

Winding13

13

Rotor Pole13

13

Stator Pole13

13

Shaft13

13

Frame13

13

13

CAEMD Web httpwwwcaemdcn

Flux Modulation Machines

For flux modulation machines their pole number of armature windings and excitation MMF are different (For special cases the two values can be same)

They have potential to be with high torque density so that they are very competitive

16

Flux Modulation a new way to improve torque density

CAEMD Web httpwwwcaemdcn

Stator

Ferromagnetic pole pieces

Magnets

Rotor

Regular PM machine Flux modulation PM machine

There are three components in a flux-modulation machine ie 1 flux modulator 2 armature and 3 excitation field exciters

Flux Modulation Machines

17

CAEMD Web httpwwwcaemdcn

MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

CAEMD Web httpwwwcaemdcn

Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

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Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

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Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

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Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

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Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

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No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

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Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

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Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 9: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Flux Path Seperation

Flux lines (PM field) Flux lines (armature field)

Aver

age

torq

ue (N

m)

Electric loading (Acm)

The flux paths of excitation and armature field are separated using the Halbach array magnets and the armature reaction is weakened

9

CAEMD Web httpwwwcaemdcn

Theory

Realization

Instance

SC materials can carry large current Nearly no loss under DC condition T

SC DC excitation Matching structure vacuum cooler refrigerator etc

σLDTe2

= BA=σ

Material cooling system

Copper no extra cooling 45-6

Copper forced air cooling 75-9

Copper liquid cooling

SC material liquid helium

10 MW wind generator SC generator compared to conventional generator volume decrease to 12 weight decrease to 13

High Electric Loading-Superconducting Machines

10

CAEMD Web httpwwwcaemdcn

Liu Y Noe M 2016

R Fair 2012

132MW Superconducting wind generator R QU et al 2015

Yubin Wang etc 2013

Superconducting wires are nice but not free

High Electric Loading-Superconducting Machines

11

CAEMD Web httpwwwcaemdcn

TpropABS AmdashElectric loading BmdashMagnetic loading SmdashAir gap area

A small PM motor nested inside a large PM motor The torque and power densities are boosted by doubling the air gap

surface area

bull Higher torque per volume bull Doubled airgap area amp weight bull Unchanged volume

bull Higher torque per volumeweight bull Doubled airgap area bull Coreless rotor bull Unchanged volume

High Torque Density Machine Topology I

12

CAEMD Web httpwwwcaemdcn

Dual-rotor radial flux two airgaps Ronghai Qu 2003

Dual-rotor axial flux two airgaps Ion Boldea 2011

Dual-stator radial flux two airgaps Tae-Uk Jung 2013

Radial amp Axial flux three airgaps Masafumi Namba 2017

High Torque Density Machine Topology I

13

CAEMD Web httpwwwcaemdcn 14

High Torque Density Machine Topology II

Transverse flux machine(TFM) H Weh 1986

pφa pφ φ=

pφpφ

a pNφ φ=

Equivalent model of PMSM amp TFM

The flux linkage of TFM is N times that of PMSM

The torque density of TFM is proportional to N

CAEMD Web httpwwwcaemdcn 15

Separated rotor TFM G Henneberge 1997

Double side TFM H Weh 1995

C-core TFM S M Husband 2003 R Qu T Lipo etc 2002

In recent years a few topologies with high torque density have been obtained and gain lots of attention

High Torque Density Machine Topology II

image1png

Magnet13

13

Winding13

13

Rotor Pole13

13

Stator Pole13

13

Shaft13

13

Frame13

13

13

CAEMD Web httpwwwcaemdcn

Flux Modulation Machines

For flux modulation machines their pole number of armature windings and excitation MMF are different (For special cases the two values can be same)

They have potential to be with high torque density so that they are very competitive

16

Flux Modulation a new way to improve torque density

CAEMD Web httpwwwcaemdcn

Stator

Ferromagnetic pole pieces

Magnets

Rotor

Regular PM machine Flux modulation PM machine

There are three components in a flux-modulation machine ie 1 flux modulator 2 armature and 3 excitation field exciters

Flux Modulation Machines

17

CAEMD Web httpwwwcaemdcn

MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

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2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

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Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 10: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Theory

Realization

Instance

SC materials can carry large current Nearly no loss under DC condition T

SC DC excitation Matching structure vacuum cooler refrigerator etc

σLDTe2

= BA=σ

Material cooling system

Copper no extra cooling 45-6

Copper forced air cooling 75-9

Copper liquid cooling

SC material liquid helium

10 MW wind generator SC generator compared to conventional generator volume decrease to 12 weight decrease to 13

High Electric Loading-Superconducting Machines

10

CAEMD Web httpwwwcaemdcn

Liu Y Noe M 2016

R Fair 2012

132MW Superconducting wind generator R QU et al 2015

Yubin Wang etc 2013

Superconducting wires are nice but not free

High Electric Loading-Superconducting Machines

11

CAEMD Web httpwwwcaemdcn

TpropABS AmdashElectric loading BmdashMagnetic loading SmdashAir gap area

A small PM motor nested inside a large PM motor The torque and power densities are boosted by doubling the air gap

surface area

bull Higher torque per volume bull Doubled airgap area amp weight bull Unchanged volume

bull Higher torque per volumeweight bull Doubled airgap area bull Coreless rotor bull Unchanged volume

High Torque Density Machine Topology I

12

CAEMD Web httpwwwcaemdcn

Dual-rotor radial flux two airgaps Ronghai Qu 2003

Dual-rotor axial flux two airgaps Ion Boldea 2011

Dual-stator radial flux two airgaps Tae-Uk Jung 2013

Radial amp Axial flux three airgaps Masafumi Namba 2017

High Torque Density Machine Topology I

13

CAEMD Web httpwwwcaemdcn 14

High Torque Density Machine Topology II

Transverse flux machine(TFM) H Weh 1986

pφa pφ φ=

pφpφ

a pNφ φ=

Equivalent model of PMSM amp TFM

The flux linkage of TFM is N times that of PMSM

The torque density of TFM is proportional to N

CAEMD Web httpwwwcaemdcn 15

Separated rotor TFM G Henneberge 1997

Double side TFM H Weh 1995

C-core TFM S M Husband 2003 R Qu T Lipo etc 2002

In recent years a few topologies with high torque density have been obtained and gain lots of attention

High Torque Density Machine Topology II

image1png

Magnet13

13

Winding13

13

Rotor Pole13

13

Stator Pole13

13

Shaft13

13

Frame13

13

13

CAEMD Web httpwwwcaemdcn

Flux Modulation Machines

For flux modulation machines their pole number of armature windings and excitation MMF are different (For special cases the two values can be same)

They have potential to be with high torque density so that they are very competitive

16

Flux Modulation a new way to improve torque density

CAEMD Web httpwwwcaemdcn

Stator

Ferromagnetic pole pieces

Magnets

Rotor

Regular PM machine Flux modulation PM machine

There are three components in a flux-modulation machine ie 1 flux modulator 2 armature and 3 excitation field exciters

Flux Modulation Machines

17

CAEMD Web httpwwwcaemdcn

MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

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Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

CAEMD Web httpwwwcaemdcn

Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

CAEMD Web httpwwwcaemdcn

Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

CAEMD Web httpwwwcaemdcn

Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 11: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Liu Y Noe M 2016

R Fair 2012

132MW Superconducting wind generator R QU et al 2015

Yubin Wang etc 2013

Superconducting wires are nice but not free

High Electric Loading-Superconducting Machines

11

CAEMD Web httpwwwcaemdcn

TpropABS AmdashElectric loading BmdashMagnetic loading SmdashAir gap area

A small PM motor nested inside a large PM motor The torque and power densities are boosted by doubling the air gap

surface area

bull Higher torque per volume bull Doubled airgap area amp weight bull Unchanged volume

bull Higher torque per volumeweight bull Doubled airgap area bull Coreless rotor bull Unchanged volume

High Torque Density Machine Topology I

12

CAEMD Web httpwwwcaemdcn

Dual-rotor radial flux two airgaps Ronghai Qu 2003

Dual-rotor axial flux two airgaps Ion Boldea 2011

Dual-stator radial flux two airgaps Tae-Uk Jung 2013

Radial amp Axial flux three airgaps Masafumi Namba 2017

High Torque Density Machine Topology I

13

CAEMD Web httpwwwcaemdcn 14

High Torque Density Machine Topology II

Transverse flux machine(TFM) H Weh 1986

pφa pφ φ=

pφpφ

a pNφ φ=

Equivalent model of PMSM amp TFM

The flux linkage of TFM is N times that of PMSM

The torque density of TFM is proportional to N

CAEMD Web httpwwwcaemdcn 15

Separated rotor TFM G Henneberge 1997

Double side TFM H Weh 1995

C-core TFM S M Husband 2003 R Qu T Lipo etc 2002

In recent years a few topologies with high torque density have been obtained and gain lots of attention

High Torque Density Machine Topology II

image1png

Magnet13

13

Winding13

13

Rotor Pole13

13

Stator Pole13

13

Shaft13

13

Frame13

13

13

CAEMD Web httpwwwcaemdcn

Flux Modulation Machines

For flux modulation machines their pole number of armature windings and excitation MMF are different (For special cases the two values can be same)

They have potential to be with high torque density so that they are very competitive

16

Flux Modulation a new way to improve torque density

CAEMD Web httpwwwcaemdcn

Stator

Ferromagnetic pole pieces

Magnets

Rotor

Regular PM machine Flux modulation PM machine

There are three components in a flux-modulation machine ie 1 flux modulator 2 armature and 3 excitation field exciters

Flux Modulation Machines

17

CAEMD Web httpwwwcaemdcn

MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

CAEMD Web httpwwwcaemdcn

Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

CAEMD Web httpwwwcaemdcn

Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

CAEMD Web httpwwwcaemdcn

Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

CAEMD Web httpwwwcaemdcn

Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

CAEMD Web httpwwwcaemdcn

Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

CAEMD Web httpwwwcaemdcn

Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

CAEMD Web httpwwwcaemdcn

Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

CAEMD Web httpwwwcaemdcn

Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 12: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

TpropABS AmdashElectric loading BmdashMagnetic loading SmdashAir gap area

A small PM motor nested inside a large PM motor The torque and power densities are boosted by doubling the air gap

surface area

bull Higher torque per volume bull Doubled airgap area amp weight bull Unchanged volume

bull Higher torque per volumeweight bull Doubled airgap area bull Coreless rotor bull Unchanged volume

High Torque Density Machine Topology I

12

CAEMD Web httpwwwcaemdcn

Dual-rotor radial flux two airgaps Ronghai Qu 2003

Dual-rotor axial flux two airgaps Ion Boldea 2011

Dual-stator radial flux two airgaps Tae-Uk Jung 2013

Radial amp Axial flux three airgaps Masafumi Namba 2017

High Torque Density Machine Topology I

13

CAEMD Web httpwwwcaemdcn 14

High Torque Density Machine Topology II

Transverse flux machine(TFM) H Weh 1986

pφa pφ φ=

pφpφ

a pNφ φ=

Equivalent model of PMSM amp TFM

The flux linkage of TFM is N times that of PMSM

The torque density of TFM is proportional to N

CAEMD Web httpwwwcaemdcn 15

Separated rotor TFM G Henneberge 1997

Double side TFM H Weh 1995

C-core TFM S M Husband 2003 R Qu T Lipo etc 2002

In recent years a few topologies with high torque density have been obtained and gain lots of attention

High Torque Density Machine Topology II

image1png

Magnet13

13

Winding13

13

Rotor Pole13

13

Stator Pole13

13

Shaft13

13

Frame13

13

13

CAEMD Web httpwwwcaemdcn

Flux Modulation Machines

For flux modulation machines their pole number of armature windings and excitation MMF are different (For special cases the two values can be same)

They have potential to be with high torque density so that they are very competitive

16

Flux Modulation a new way to improve torque density

CAEMD Web httpwwwcaemdcn

Stator

Ferromagnetic pole pieces

Magnets

Rotor

Regular PM machine Flux modulation PM machine

There are three components in a flux-modulation machine ie 1 flux modulator 2 armature and 3 excitation field exciters

Flux Modulation Machines

17

CAEMD Web httpwwwcaemdcn

MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

CAEMD Web httpwwwcaemdcn

Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

CAEMD Web httpwwwcaemdcn

Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

CAEMD Web httpwwwcaemdcn

Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

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Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

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Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

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Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

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Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

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No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

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Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

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Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

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Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 13: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Dual-rotor radial flux two airgaps Ronghai Qu 2003

Dual-rotor axial flux two airgaps Ion Boldea 2011

Dual-stator radial flux two airgaps Tae-Uk Jung 2013

Radial amp Axial flux three airgaps Masafumi Namba 2017

High Torque Density Machine Topology I

13

CAEMD Web httpwwwcaemdcn 14

High Torque Density Machine Topology II

Transverse flux machine(TFM) H Weh 1986

pφa pφ φ=

pφpφ

a pNφ φ=

Equivalent model of PMSM amp TFM

The flux linkage of TFM is N times that of PMSM

The torque density of TFM is proportional to N

CAEMD Web httpwwwcaemdcn 15

Separated rotor TFM G Henneberge 1997

Double side TFM H Weh 1995

C-core TFM S M Husband 2003 R Qu T Lipo etc 2002

In recent years a few topologies with high torque density have been obtained and gain lots of attention

High Torque Density Machine Topology II

image1png

Magnet13

13

Winding13

13

Rotor Pole13

13

Stator Pole13

13

Shaft13

13

Frame13

13

13

CAEMD Web httpwwwcaemdcn

Flux Modulation Machines

For flux modulation machines their pole number of armature windings and excitation MMF are different (For special cases the two values can be same)

They have potential to be with high torque density so that they are very competitive

16

Flux Modulation a new way to improve torque density

CAEMD Web httpwwwcaemdcn

Stator

Ferromagnetic pole pieces

Magnets

Rotor

Regular PM machine Flux modulation PM machine

There are three components in a flux-modulation machine ie 1 flux modulator 2 armature and 3 excitation field exciters

Flux Modulation Machines

17

CAEMD Web httpwwwcaemdcn

MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 14: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn 14

High Torque Density Machine Topology II

Transverse flux machine(TFM) H Weh 1986

pφa pφ φ=

pφpφ

a pNφ φ=

Equivalent model of PMSM amp TFM

The flux linkage of TFM is N times that of PMSM

The torque density of TFM is proportional to N

CAEMD Web httpwwwcaemdcn 15

Separated rotor TFM G Henneberge 1997

Double side TFM H Weh 1995

C-core TFM S M Husband 2003 R Qu T Lipo etc 2002

In recent years a few topologies with high torque density have been obtained and gain lots of attention

High Torque Density Machine Topology II

image1png

Magnet13

13

Winding13

13

Rotor Pole13

13

Stator Pole13

13

Shaft13

13

Frame13

13

13

CAEMD Web httpwwwcaemdcn

Flux Modulation Machines

For flux modulation machines their pole number of armature windings and excitation MMF are different (For special cases the two values can be same)

They have potential to be with high torque density so that they are very competitive

16

Flux Modulation a new way to improve torque density

CAEMD Web httpwwwcaemdcn

Stator

Ferromagnetic pole pieces

Magnets

Rotor

Regular PM machine Flux modulation PM machine

There are three components in a flux-modulation machine ie 1 flux modulator 2 armature and 3 excitation field exciters

Flux Modulation Machines

17

CAEMD Web httpwwwcaemdcn

MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

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Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

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2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 15: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn 15

Separated rotor TFM G Henneberge 1997

Double side TFM H Weh 1995

C-core TFM S M Husband 2003 R Qu T Lipo etc 2002

In recent years a few topologies with high torque density have been obtained and gain lots of attention

High Torque Density Machine Topology II

image1png

Magnet13

13

Winding13

13

Rotor Pole13

13

Stator Pole13

13

Shaft13

13

Frame13

13

13

CAEMD Web httpwwwcaemdcn

Flux Modulation Machines

For flux modulation machines their pole number of armature windings and excitation MMF are different (For special cases the two values can be same)

They have potential to be with high torque density so that they are very competitive

16

Flux Modulation a new way to improve torque density

CAEMD Web httpwwwcaemdcn

Stator

Ferromagnetic pole pieces

Magnets

Rotor

Regular PM machine Flux modulation PM machine

There are three components in a flux-modulation machine ie 1 flux modulator 2 armature and 3 excitation field exciters

Flux Modulation Machines

17

CAEMD Web httpwwwcaemdcn

MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

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l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

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There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

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Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

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Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

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Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

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Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

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Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

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1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

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Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

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Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

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Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

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0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

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13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

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2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
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  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
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  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
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  • 幻灯片编号 30
  • 幻灯片编号 31
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  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
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Page 16: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

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Flux Modulation Machines

For flux modulation machines their pole number of armature windings and excitation MMF are different (For special cases the two values can be same)

They have potential to be with high torque density so that they are very competitive

16

Flux Modulation a new way to improve torque density

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Stator

Ferromagnetic pole pieces

Magnets

Rotor

Regular PM machine Flux modulation PM machine

There are three components in a flux-modulation machine ie 1 flux modulator 2 armature and 3 excitation field exciters

Flux Modulation Machines

17

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MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

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l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

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There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

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Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

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Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

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Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

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Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

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Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

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Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

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1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

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Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

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Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

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Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

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0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

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13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

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2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

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2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

CAEMD Web httpwwwcaemdcn

Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 17: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Stator

Ferromagnetic pole pieces

Magnets

Rotor

Regular PM machine Flux modulation PM machine

There are three components in a flux-modulation machine ie 1 flux modulator 2 armature and 3 excitation field exciters

Flux Modulation Machines

17

CAEMD Web httpwwwcaemdcn

MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

CAEMD Web httpwwwcaemdcn

Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

CAEMD Web httpwwwcaemdcn

Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

CAEMD Web httpwwwcaemdcn

Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

CAEMD Web httpwwwcaemdcn

Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

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Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

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Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

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Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 18: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

MMF

Flux modulator

Flux density

Space PWM

Flux Modulation Effect

0 40 80 120 160 200 240 280 320 360-05

-04

-03

-02

-01

00

01

02

03

04

05

Rotor position(deg)

-5 0 5 10 15 20 25 300

01

02

03

04

Order

Flux

den

sity

(T)

0 40 80 120 160 200 240 280 320 360-10

-08

-06

-04

-02

00

02

04

06

08

10

Rotor position(deg)

-5 0 5 10 15 20 25 300

05

1

15

Order

Flux modulator

Flux

den

sity

(T)

Flux

den

sity

(T)

Flux

den

sity

(T)

18

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

CAEMD Web httpwwwcaemdcn

Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

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0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

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Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

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Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

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Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

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Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

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No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

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Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

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Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 19: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn 19

Flux Modulation Effect

PrgTorqueDensity AB

Psprop A electrical loading

Bg magnetic loading

The flux modulation PM machine works as an integrator constituted of a magnetic gear and a regular PM machine

Ferromagnetic pole pieces work as a flux modulator to transform the speed of flux from Ω to PrPs Ω

Magnetic gear Flux modulation machine Regular machine

19

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

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Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

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Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

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Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

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Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 20: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

l hT Tβ= plusmn

hT

(1 )f hT Tβ= minus plusmn

Positivedirection Magnets

Low speed PM rotor

High speed Armature field

Ferromagnetic pole piece rotor

MMF

Flux modulator

Flux density distribution

Pe=11

Pa=1

Pf=12

Flux modulation PM machine

= sgn

0

sgn

(1 sgn )

re fe e

ra a f a

r re e a a

ee a

a

ef a

a

PP

T TPT TP

PT TP

Ω minusΩΩ= minus

Ω Ω minusΩ Ω + Ω = = = minus +

Features

Pe magnet pole pair number Pa armature winding pole pair Pf flux modulator pole pair

20

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

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2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

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Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

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Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 21: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

There are three components in a flux-modulation machine ie flux modulator armature and excitation field exciters

The pole number of the two MMFs is different and the flux modulation is requisite to work as a pole number transformer through air-gap permeance function

Among flux modulator armature and excitation fields only one component can be but not necessary stationary

Flux modulation machines

Stationary Flux Modulator

(SFM)

Stationary Excitation Field

(SEF)

Stationary Armature Field

(SAF)

All the three parts are Rotary

Features

General topology theory for flux modulation machine 21

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

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13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

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2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 22: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Stator

Flux modulatorMagnet

s

Rotor

Flux modulator

Rotor WindingWinding

Magnets Magnets

Flux modulator PM rotor

Stator WindingWinding

Vernier PM machine

Harmonic PM machine Transverse flux PM machine

Pf=Z

Pf=kZ

Pr=Z Pr Pole pairs of magnets Z Slot number

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Flux-Modulation Machines with SFM

22

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

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Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

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Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

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0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

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13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

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2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

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Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 23: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Magnets

Flux modulator rotor

Armature winding

Armature winding Magnets Armature

winding

Flux modulator rotor

Flux reversal machine

Flux switching PM machines

Flux modulator rotor

MagnetsStator

Winding

Stator Magnets

Winding

Flux-Modulation Machines with SEF I

Stator

Flux modulatorRotor

Magnets

Stationary magnet

23

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

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Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

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Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

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Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

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0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

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13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

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2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 24: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF II

Stator Magnets

Winding

2Pe=Z

StatorMagnets

ArmatureWinding

Stator Magnets

ArmatureWinding

DC-Field Winding

Hybrid excitation vernier reluctance machine

StatorMagnets

ArmatureWindingDC+AC

Hybrid excitation vernier reluctance machine with DC-bias current

Stator Magnets

ArmatureWinding

DC Field Winding

StatorMagnets

ArmatureWindingDC+AC

DC-bias

Time

CurrentSwitched reluctance machine

Dc-bias vernier reluctance machine

DC field winding is used to replace

the magnets

Stator excitation vernier reluctance machine or variable reluctance machine SRMampDC- bias vernier reluctance machine

Stator

Magnets

ArmatureWinding

DC field winding is used to partly replace

the magnets

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

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Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

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1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

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Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

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Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

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0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

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13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

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2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 25: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with SEF III

Brushless doubly fed machine

Flux modulator rotor

A

B C

Armature winding

Vernier reluctance machine

Flux modulator rotorArmature winding

Synchronous reluctance machine

AC field winding can be removed

Pe=Pa Pf=2Pa Pf=Zr+-Zs

Flux modulator rotor

Excitation winding

A

B C

CA

B

Armature winding

Pe=Pa Pf=2Pa Pf=Zr

AC field winding can be removed

Pf=Pe+-Pa Pf=Zr+-Zs

25

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Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

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Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

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Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

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Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

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0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

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2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 26: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Flux modulator rotorPM rotor

BrushDC armature winding

+

+- -

Flux modulator rotor

PM rotor

Stationary DC winding

Flux-modulation DC commutator machine

Flux-modulation coupling

Flux-Modulation Machines with SAF

26

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

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Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

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0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

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2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 27: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Winding A

Winding A1

Winding A

Dual Electrical ports Dual mechanical ports

1

A e f

A e

P P PP P

= minus=

Flux-Modulation Machines with Dual Ports

Single electrical ports Dual mechanical ports

27

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

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Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

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0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

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13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

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2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

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Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 28: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

1

1

1 1 1

sgn

(1 sgn )

sgn

mma A

A

mf A

A

m ma ma

m f A

A f m

A m

m m m f f f

A A A A A A

PT TP

PT TP

T T T

PP

f P f Pf P f P

=

= minus +

= +

Ω minusΩ= minus

Ω minusΩΩ = Ω

= Ω = Ω= Ω = Ω

Flux-Modulation Machines with Dual Ports

Speed relationship

Torque relationship

Flux modulation machine

Regular PM machine

Flux modulation machine with

dual ports

Flux modulation machine with

dual ports

Winding A1 Pole pair PA1

Winding A Pole pair PA

Pe=PA1 Pe=PA1

Winding A1

Pole pair PA1

Winding A1 Pole pair PA1

28

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

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13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

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2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 29: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Flux-Modulation Machines with Dual Ports

Converter

fΩrΩ

Grid

Flux modulator

PM rotor

Winding A

Winding A1

The flux modulation PM machine with dual ports can be used in HEV to replace one mechanical planetary gear one torque regular motor and one generator

This topology can also work as one type brushless DFIG 29

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

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Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

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Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 30: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Basic Theory for Flux Modulation Machines

General topology theory

Field analysis of flux modulation machine

Winding theory

Performance features

Basic theory

A new perspective ie flux modulation principle on the both flux modulation and regular machines is presented

30

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

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Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

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Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

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Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

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Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

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Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

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Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

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No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 31: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Field Analysis based on MMF-Permeance Model

c135

135 0 r

( ) cos( )

4 sin( ) cos( )2

s ci e si

rm e s e

i

F t F iP i t

B h i iP i t

θ θ ω

πα θ ωπ micro micro

=

=

= minus

= minus

sum

sum

αmh

MMF Fc

0

rm

r

B hmicro micro

0

rm

r

B hmicro micro

minus

Magnets

Magnet

Stator yoke

0

r mc

r

B hFmicro micro

=0

mm

r m

hRAmicro micro

=0

gr g

gRAmicro micro

=

hm

Rsy

Rry Rotor yoke

g2Rg

Fc

2Rm

2Rg

2Rm

Fc

Rsy

Rry

Airgap

0o 180o

MMF excited by magnets

31

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

CAEMD Web httpwwwcaemdcn

Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

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Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

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Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

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Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

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Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

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No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

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Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

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Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 32: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

0 1( ) cos( )s f s fP tθ θ ωΛ asymp Λ +Λ minusPermeance function

Field excited by magnets c

10

135 1351

135

( )= ( ) ( )cos( ) cos[( ) ( ) ]

2cos[( ) ( ) ]

2

g s s s

cici e s e e f s e f

i ici

e f s e fi

B t F tFF iP i t iP P i t

F iP P i t

θ θ θθ ω θ ω ω

θ ω ω= =

=

ΛΛ= Λ minus + minus minus minus

Λ+ + minus +

sum sumsum

Pole pair Speed Frequency Source Permeance Magnet MMF

iPe 2iπωe Pe 2iπωe Λ0 i th harmonic Pf-iPe 120iπ(ωe-ωf)( Pf -iPr) 2iπ(ωe-ωf) Λ1

Pf+iPe 120iπ(ωe+ωf)( Pf +iPr) 2iπ(ωe+ωf) Λ1

Field Analysis based on MMF-Permeance Model

32

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

CAEMD Web httpwwwcaemdcn

Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

CAEMD Web httpwwwcaemdcn

Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

CAEMD Web httpwwwcaemdcn

Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

CAEMD Web httpwwwcaemdcn

Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

CAEMD Web httpwwwcaemdcn

Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

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Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

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Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

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Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

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Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

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Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

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Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

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Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 33: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j a sj

b s j a sj

c s j a sj

sj wj

a

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Winding Function for balanced three-phase winding

Magnet Flux linkage 2

0

( ) ( )a g stk g s a s sr l B t N dπ

ψ θ θ θ= int

Flux Linkage Formula

33

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

CAEMD Web httpwwwcaemdcn

Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

CAEMD Web httpwwwcaemdcn

Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

CAEMD Web httpwwwcaemdcn

Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

CAEMD Web httpwwwcaemdcn

Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

CAEMD Web httpwwwcaemdcn

Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

CAEMD Web httpwwwcaemdcn

Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

CAEMD Web httpwwwcaemdcn

Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

CAEMD Web httpwwwcaemdcn

Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

CAEMD Web httpwwwcaemdcn

Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 34: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

2

1350

10

2

1350

0

[ ( ) ( ) ]

sin( ) ( ) sin[( ) ]2

[ ( ) ( ) ]

si

a g stk g s a s s ci g stki

e j e e f j e fPe Pf Pej i j iPa Pa Pa

b g stk g s b s s ci g stki

e j

de r l B t N d F r ldt

i N i t i N i t

de r l B t N d F r ldt

i N

π

π

θ θ θ π

ω ω ω ω ω ω

θ θ θ π

ω

=

= = plusmn

=

= minus =

ΛΛ + plusmn plusmn

= minus =

Λ

sumint

sum sum

sumint

1

2

1350

10

2 2n( ) ( ) sin[( ) sgn ]3 2 3

[ ( ) ( ) ]

2 2sin( ) ( ) sin[( ) sgn ]3 2 3

e e f j e fPe Pf Pej i j iPa Pa Pa

c g stk g s b s s ci g stki

e j e e f j e fPfj

i t j i N i t j

de r l B t N d F r ldt

i N i t j i N i t j

π

ω π ω ω ω ω π

θ θ θ π

ω ω π ω ω ω ω π

= = plusmn

=

=

Λminus + plusmn plusmn minus

= minus =

ΛΛ + + plusmn plusmn +

sum sum

sumint

Pe Pej i iPa Pa Pa= plusmn

sum sum

Back EMF Formula

34

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

CAEMD Web httpwwwcaemdcn

Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

CAEMD Web httpwwwcaemdcn

Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

CAEMD Web httpwwwcaemdcn

Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

CAEMD Web httpwwwcaemdcn

Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

CAEMD Web httpwwwcaemdcn

Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

CAEMD Web httpwwwcaemdcn

Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

CAEMD Web httpwwwcaemdcn

Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

CAEMD Web httpwwwcaemdcn

Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

CAEMD Web httpwwwcaemdcn

Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

CAEMD Web httpwwwcaemdcn

Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 35: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn 35

Torque Formula (1 sgn )

[ ( ) ( ) ( ) ( ) ( ) ( )] [ ]sgn

e

ae a a b b c c e f

e

a

PPT e t i t e t i t e t i t

PP

+= + + Ω minus Ω

1 1 132

eg stk s max c w

a

P r l N I F kP

Λ 1 1 132

e g axial s max c wP r L N I F k Λ 21 1 1

3=2

avg g stk s max c wa

ZT r l N I F kP

Λ

Magnets

Flux modulator rotor

Armature winding

Phase coil Stator

Magnet

Flux

Direction of rotation

Magnet

PM rotor PM rotor

B1 B2

Laxial

Transverse flux PM machine Flux switching PM machines

Winding

Magnets

Rotor

Vernier PM machine

There is an additional coefficient ie pole ratio in the torque formulas of flux modulation machine This offers flux modulation machines high torque density potential capability with limited current and magnetic loading

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

CAEMD Web httpwwwcaemdcn

Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 36: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

2

1PF=1 ( )s

m

L Iψ

+

Power Factor Formula

2

6 1 2

1 11

1 0

1PF15

11 ( )

2e a

end slotj

j k g stk

p p c

L LN I Ir l

N F NN

π= plusmn

=+

+sum+

Λ+

Λ

2

6 1 20

1 1 1

1PF15

21 ( )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sumΛ

2

6 1 2

1 1

1PF15

1 (1 )

end slotj

j k g stk

c

L LN I Ir l

F Nπ= plusmn

=+

+sum+

Regular PM machine

SFM flux modulation machine

SEF flux modulation machine

36

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

CAEMD Web httpwwwcaemdcn

Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

CAEMD Web httpwwwcaemdcn

Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

CAEMD Web httpwwwcaemdcn

Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

CAEMD Web httpwwwcaemdcn

Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

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Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

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Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

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Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

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Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 37: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations The vernier magnetic geared flux reversal flux switching and

transverse flux machines share same operation principle ie flux modulation principle

Therefore their winding configurations could be analyzed and designed by the same method ie the classical winding theory

So far some topologies still use specified winding theory especially for flux switching machines whose structures are different from regular machines and this introduces some barriers for researchers to further study those machines

No load flux

density analysis Armature

winding pole pair Decide the winding

configuration amp scheme

Since the pole number of armature winding and PM rotor is same in the regular PM machines this two steps are always neglected

37

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

CAEMD Web httpwwwcaemdcn

Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

CAEMD Web httpwwwcaemdcn

Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

CAEMD Web httpwwwcaemdcn

Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

CAEMD Web httpwwwcaemdcn

Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

CAEMD Web httpwwwcaemdcn

Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

CAEMD Web httpwwwcaemdcn

Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

CAEMD Web httpwwwcaemdcn

Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

CAEMD Web httpwwwcaemdcn

Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

CAEMD Web httpwwwcaemdcn

Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

CAEMD Web httpwwwcaemdcn

Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
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Page 38: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulations

1 1 11 2 2 2 2 2 3 2 2

1 1 14 2 2 5 2 2 6 2 2

( ) ( ) ( )

5sin(( ) ) sin(( ) ) sin( ) )

2 2 23 5 3

sin(( ) ) sin(( ) ) sin(( ) )2 2 2

g s s sr s

s s s

s s s

B t F t

Z Z ZB Z Z t B Z Z t B Z Z t

Z Z ZB Z Z t B Z Z t B Z Z t

θ θ θ

θ θ θ

θ θ θ

= Λ

= minus + minus Ω + minus minus Ω + minus + Ω

minus minus + Ω + + minus Ω minus + minus Ω

No-load airgap flux density for flux switching PM machines

Flux switching machine

Rotor Stator

PMs Windings

38

CAEMD Web httpwwwcaemdcn

Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

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Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

CAEMD Web httpwwwcaemdcn

Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

CAEMD Web httpwwwcaemdcn

Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

CAEMD Web httpwwwcaemdcn

Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

CAEMD Web httpwwwcaemdcn

Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

CAEMD Web httpwwwcaemdcn

Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 39: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Fortunately all the working flux harmonics of FSPM machines satisfy

1 1

1 23456

i jj

ZP k PP

i j i j

= plusmn

= ne

( )

1 1( ) ( )i jGCD Z P GCD Z P=

Summary Each of these harmonics is a slot harmonic of another In other words for FSPM machines the pole pair number of all the working harmonics can be used as the armature winding pole pair number to assign winding connection and check whether the windings of a stator and rotor slot combination is symmetrical or not

Winding Theory for Flux Modulation Machines

39

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

CAEMD Web httpwwwcaemdcn

Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

CAEMD Web httpwwwcaemdcn

Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

CAEMD Web httpwwwcaemdcn

Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

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14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

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End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

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Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

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Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

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Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

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Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 40: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Winding connection

determination

1

67

2

34

5

8

910

11

12

30o

Winding Theory for Flux Modulation Machines

14710

25811

36912

A

B

C

Direction of flux rotation

16=Z2+Z12

120O

14710

25811

36912

A

B

C

Direction of flux rotation

20=3Z12-Z2

120O

14710

36912

A

B

C

8=3Z12-Z2

25811 Direction of flux rotation

120O

14710

36912

A

B

C

28=3Z12+Z2

25811 Direction of flux rotation

120O

A 1210 statorrotor tooth FSPM machine

Star of slots of 1210 statorrotor tooth FSPM machine for different order working flux harmonics (a) 16th (b) 20th (c) 8th (d) 28th

(a) (b)

(c) (d)

40

CAEMD Web httpwwwcaemdcn

Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

CAEMD Web httpwwwcaemdcn

Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

CAEMD Web httpwwwcaemdcn

Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

CAEMD Web httpwwwcaemdcn

Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

CAEMD Web httpwwwcaemdcn

Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

CAEMD Web httpwwwcaemdcn

Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

CAEMD Web httpwwwcaemdcn

Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

CAEMD Web httpwwwcaemdcn

Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

CAEMD Web httpwwwcaemdcn

Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 41: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Winding configurations The slot per pole per phase and winding pitch of FSPM machines are

1

1

SPP=2

2

a

aa

ZmP

ZP

τ

=

Winding Theory for Flux Modulation Machines

41

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Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

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Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

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Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

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Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

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The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

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Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

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Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

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Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

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Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

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Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

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0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

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0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

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Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

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Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

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Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

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Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

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Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

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Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

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Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

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Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

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Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

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Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

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Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

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Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

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Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

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Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

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Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 42: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Winding type determination

Winding configurations of three-phase FSPM machines

Winding Theory for Flux Modulation Machines

Three-phase FSPM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

SPPge1 05ltSPPlt1

The fractional slot distributed winding and concentrated winding with two-slot pitch are naturally discovered for the FSPM machines after that the classical winding theory is used

42

CAEMD Web httpwwwcaemdcn

Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

CAEMD Web httpwwwcaemdcn

Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

CAEMD Web httpwwwcaemdcn

Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

CAEMD Web httpwwwcaemdcn

Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

CAEMD Web httpwwwcaemdcn

Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

CAEMD Web httpwwwcaemdcn

Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

CAEMD Web httpwwwcaemdcn

Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
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Page 43: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Winding type

+A

-A+B

-B

-C

-C

-C

-C

-A

+A

+B

-B

Nonoverlapping winding (Type1)

Overlapping winding (Type2)

Winding Theory for Flux Modulation Machines

613

614 Type 1

(Nonoverlapping)

614 Type 2 (Overlapping)

614 Type 3 (Full

pitch) Speed 1200RPM No of stator teeth 6 6 No of rotor teeth 13 14 Outer stator diameter 170mm Stack length 100mm Airgap length 2mm Outer rotor diameter 102mm Pole pitches (slot No) 1 1 2 3 Stator tooth width 85m

m 8mm

Magnet thickness 85mm

8mm

Stator back iron thickness

78mm

Slot area 6900mm2 Rotor pole arc 13 No of turns per phase 26 Magnet remanence 11T Relative recoil permeability

105

Rated current 32A 0 1 2 3 4 5 6 7 80

02

04

06

08

1

12

14

614 FSPM machine with overlapping winding614 FSPM machine with nonoverlapping winding

Order

Mag

nitu

de(V

)

43

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

CAEMD Web httpwwwcaemdcn

Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

CAEMD Web httpwwwcaemdcn

Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

CAEMD Web httpwwwcaemdcn

Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

CAEMD Web httpwwwcaemdcn

Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

CAEMD Web httpwwwcaemdcn

Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

CAEMD Web httpwwwcaemdcn

Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 44: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Winding Theory for Flux Modulation Machines

0 50 100 150 200 250 300 350-40

-30

-20

-10

0

10

20

30

40

1210 FSPM machine613 FSPM machine614 FSPM machine with tooth-coil winding614 FSPM machine with two slot pitches614 FSPM machine with full pitches

Back

EM

F(V)

Rotor position(elecdeg)0 1 2 3 4 5 6 7

0

5

10

15

20

25

30

35

1210 FSPM machine613 FSPM machine614 FSPM machine with nonoverlapping winding614 FSPM machine with two slot-pitch winding614 FSPM machine with overlapping

Order

Back

EM

F(V)

200 250 300 350 400 450 500 550 60010

20

30

40

50

60

70

80

90

100

613 FSPM machine614 type1 FSPM machine614 type3 FSPM machine

Stack length(mm)

Torq

ue(N

m)

0 20 40 60 80 100 120 140-10

0

10

20

30

40

50

60

70

80

90

614 type1 FSPM machine614 type3 FSPM machine

Q-axis current(A)

Torq

ue(N

m)

Phase back EMF of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Torque vs stack length waveforms of 613 and 614 FSPM machines with nonoverlapping and overlapping windings

Average torque vs iq in 614 FSPM machines with nonoverlapping and overlapping windings (Stack length is 200mm)

44

CAEMD Web httpwwwcaemdcn

Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

CAEMD Web httpwwwcaemdcn

Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

CAEMD Web httpwwwcaemdcn

Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

CAEMD Web httpwwwcaemdcn

Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

CAEMD Web httpwwwcaemdcn

Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

CAEMD Web httpwwwcaemdcn

Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 45: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Conditions for Symmetrical Phase Flux linkage Waveform

The airgap flux density produced by the even harmonics in Λr(θst) and magnet MMF is

1 21 11 3 1 2 2

0

0 2 2 2

3( ) [ sin( ) sin( )][ cos((2 2 ) 2 )

2 2 2cos(2 2 )]

s rg s c s c s s

s r s

Z ZgB t F F Z Z Z t

Z Z t

θ θ θ θmicro

θ

Λ Λ= + plusmn Ω

minusΛ Λ minus Ω

Winding Theory for Flux Modulation Machines

45

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

CAEMD Web httpwwwcaemdcn

Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

CAEMD Web httpwwwcaemdcn

Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

CAEMD Web httpwwwcaemdcn

Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

CAEMD Web httpwwwcaemdcn

Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

CAEMD Web httpwwwcaemdcn

Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 46: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

14710

25811

36912

A

B

C

4=Z2-Z12

120O 17

511

39

+A

+B

+C

14=2Z2-Z12

60O

410

28

612

+A

+C

+B1210 FSPM machine

2 2 1Z kt= plusmn

Winding Theory for Flux Modulation Machines Conditions for Symmetrical Phase Flux linkage Waveform

If t the greatest common factor of stator slots and pole pairs and Z1(mt) are odd the back EMF waveform of FSPM machines is asymmetrical

If Z1(mt) is even the number of spokes in star of slots is the integer multiple of 2m In order to get symmetrical back EMF waveform the number of stator and rotor teeth satisfy

46

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

CAEMD Web httpwwwcaemdcn

Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

CAEMD Web httpwwwcaemdcn

Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

CAEMD Web httpwwwcaemdcn

Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

CAEMD Web httpwwwcaemdcn

Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

CAEMD Web httpwwwcaemdcn

Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 47: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

The Vernier magnetic geared flux reversal flux switching and transverse flux machines share same operation principle ie flux modulation principle or magnetic gear effect

All these topologies can be transferred from the basic flux-modulation machine and classified into the flux-modulation machine family

The basic theory of the flux modulation machine has been presented The classical winding theory is successfully applicable to all flux modulation machines

Among these Flux modulation topologies Vernier PM machines are attracting more and more attentions due to its high torque density and simple mechanical structure

Flux Modulation Machines ndash Summary

47

CAEMD Web httpwwwcaemdcn

Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

CAEMD Web httpwwwcaemdcn

Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

CAEMD Web httpwwwcaemdcn

Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

CAEMD Web httpwwwcaemdcn

Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

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Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 48: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Vernier PM Machines Magnets

+A

A-

+A

A-

+B

+B

-B-B+C +C

-C-C

Stator

Rotor

NSNSNSNSN N

Rotor PM MMF

Airgap Permeance

Airgap Flux Density Fundamental Harmonic

S

Stator

Rotor

No load flux density distribution

Vernier PM machines have same mechanical structrue with that of traditional PM machines

Merits High torque density simple mechanical structure high efficiency and structure compactness

48

CAEMD Web httpwwwcaemdcn

Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

CAEMD Web httpwwwcaemdcn

Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

CAEMD Web httpwwwcaemdcn

Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

CAEMD Web httpwwwcaemdcn

Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 49: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Winding Configurations

Three-phase Vernier PM machines

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

3 1 23(Z )

=a

e a

e

a

Z k kGCD PZ P P

PPoleRatioP

= = +

=

pole ratio 21 1( )4 2

q

le

lt le

pole ratio 5123q

ge =

2 pole ratio 51( 1)2

q

lt lt

lt lt

For vernier machines

49

CAEMD Web httpwwwcaemdcn

Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

CAEMD Web httpwwwcaemdcn

Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

CAEMD Web httpwwwcaemdcn

Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
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Page 50: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Slot amp Pole Combinations

r sZ P P= plusmn ( 1 23) ( )

s r

s r s

P P mk kG C D P P P

plusmn = =plusmn

50

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

CAEMD Web httpwwwcaemdcn

Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

CAEMD Web httpwwwcaemdcn

Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
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Page 51: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Back-EMF

2

0

e= [ ( ) ( ) ]g stk g s s sd r L B t N ddt

π

θ θ θminus int 1 5 10 15 20 25 30 35 40Harmonics order

0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

13 5

13 5

13 5

( ) cos( )

2( ) cos( )32( ) cos( )3

2

a s j s sj

b s j s sj

c s j s sj

sj wj

s

N N jP

N N jP j

N N jP j

NN kj P

θ θ

θ θ π

θ θ π

π

=

=

=

= = minus = + =

sumsumsum

Win

ding

Fun

ctio

n Back EMF Analysis

The back-EMF is determined by the product of winding function and flux density harmonics

The order of flux density harmonics contributing to back-EMF harmonics is large in VPM machines

The back-EMF waveform of VPM machines should be sinusoidal

51

CAEMD Web httpwwwcaemdcn

Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

CAEMD Web httpwwwcaemdcn

Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 52: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Working Harmonics Vernier PM machines Regular PM machines

No of fundamental magnet MMF Pr Pr

No of airgap permeance Const Z 3Z Const

No of working harmonics Pr Z-Pr Z+Pr 3Z-Pr 3Z+Pr Pr

Frequency PrΩ2π PrΩ2π

12-slot 2-stator pole 22-rotor pole vernier PM machines

12-slot 2-stator pole 2-rotor pole regular PM machines

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40 45 50

Harmonics order0

01

02

03

04

05

06

07

Flux

den

sity

(T)

Harmonics

Working harmonics

Field Analysis

The flux density working harmonic is defined as the harmonics which contribute to the average torque

52

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

CAEMD Web httpwwwcaemdcn

Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
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Page 53: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

0 5 10 15 20 25 30 35 40 45 500

01

02

03

04

05

06

07

Flux

den

sity

(T) Working

harmonics

Harmonics

Harmonics order1 5 10 15 20 25 30 35 40

Harmonics order0

01

02

03

04

05

06

07

08

09

1

Win

ding

func

tion

pu

Harmonics for regular PM machine

Harmonics for VPM machine

0 2 4 6 8 10 12

-600

-400

-200

0

200

400

600

Back

-EM

F(V)

A sinusoidal Wave Phase A

Time(ms)

For the 22-rotor pole 12-stator teeth VPM machine

57111317191 23aiP =

The pole pair number of magnet field harmonics

The pole pair number of winding function harmonics

The EMF waveform of vernier PM machines is inherently sinusoidal even with the full pitch winding configuration

Other Features - Back EMF Harmonics

Ripple torque Average torque

Winding function Magnet field

25471 4923 71eiP =

53

CAEMD Web httpwwwcaemdcn

Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 54: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Other Features - Torque Ripple 1

0

10

+2( )

+2

Pr iPr Z Z iPriPs Ps Ps

Pr Z Pr Z PrPs Ps Ps

N N NTRI vernier i

N N N

minus +

minus +

ΛΛ=

ΛΛ

( + )

( + )

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

1(regular) iNTRI i

N=

12-slot 22-rotor pole vernier PM machines

12-slot 20-rotor pole vernier PM machines

18-slot 34-rotor pole vernier PM machines

16 1=123

( ) cos( 1)peak ripple ei

avg ei kk

T FTRI i tT F

ω= plusmn

= sum

VPM machineRegular PM machine

1 5 7 11 13 17 19 23 25 29Harmonics index

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 290

02

04

06

08

1

12

14

VPM machineRegular PM machine

Harmonics index

Tor

que

ripp

le In

dex

VPM machineRegular PM machine

0

02

04

06

08

1

12

14

Tor

que

ripp

le In

dex

1 5 7 11 13 17 19 23 25 29Harmonics index

54

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 55: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

0 40 80 120 160 200 240 280 320 360-80

-60

-40

-20

0

20

40

60

80

Measured 2D FEA

Rotor position(elecdeg)

Line

bac

k EM

F(V

)

Vernier PM Prototypes

Torque transducer

Gear box Prototype

Magnetic powder brake(mechanical Load)

VPM prototype

Commercial motor

Torque Nm 174 Efficiency 085 08 Stator diameter mm 124 Air-gap length mm 08 Magnet thicknessmm 3 32 Stack length 70 120 Active length mm (including end winding length)

160 150

Weight kg 122 145 Power factor 059 098

0 1 2 3 4 5 6 7 8 9

0

5

10

15

20

2D FEA Measured

Input current(A)

Tor

que(

Nm

)

Long end winding

55

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 56: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

End Winding Reduction

56

To reduce Long End Winding

New winding configuration

Dual rotor topologies

Novel stator structure With auxiliary teeth

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 57: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Different Winding Configurations

Three-phase Vernier PM machine

Overlapping winding Nonoverlapping winding

Integer slot distributed winding

Fractional slot distributed winding

Concentrated winding with two-slot pitch

SPPge1 SPP is a fraction SPP is an integer

Long end windings

ldquoNewrdquo type vernier PM machines are found

57

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 58: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Two Slot Coil Pitch Winding VPM Machines Slot pole combination

pole ratio 21 1( )4 2

q

le

lt le

pole ratio = 511171 23q

=

2 pole ratio 51( 1)2

q

lt lt

lt lt

18 slots Pr =12 Ps =6 18 slots Pr =14 Ps =4 18 slots Pr =15 Ps =3

A VPM machine with two slot coil pitch winding or tooth winding leads to low pole ratio and may be a cost-effective option

58

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 59: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Performance Comparison Z=24 Pr=19 Ps=5

0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (V

)

Elec Angle (degree)

slot opening ratio=058 slot opening ratio=013

3 123(Z )

=10866 ( 1)2 6r

s

r s

Ps

Z k kGCD PZ P P

ZkP

= = + gt hArr lt lt

The open slot topology

The half-closed slot topology

The open slot topology achieves ~11 larger EMF than the counterpart 59

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
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Page 60: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Slot-Pole Combinations

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

Optional Slot-Pole Combinations For VPM Machines (Z=Pr+Ps kw ge 086)

241010 24168 24195 24204

1

2

3

4

5678

910

11

12

13

14

15

16

1718 19 20

2122

23

24

60

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 61: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Back-EMF Comparison

Item 2410 24168 24195 24204 Stator outer diameter 248mm 248mm 248mm 248mm Stator inner diameter 85mm 85mm 85mm 85mm

Airgap length 10mm 10mm 10mm 10mm PM thickness 35mm 30mm 30mm 30mm PM pole arc 09 09 09 09

Slot opening ratio 013 058 058 058 Turns in series per phase 168 168 168 168 Rotating speed (RPM) 300 300 300 300

Magnet remanence 105T 105T 105T 105T 0 50 100 150 200 250 300 350

-300

-200

-100

0

100

200

300

back

-EM

F (k

V)

Elec Angle (degree)

24168 24195 24204 241010

Pole Ratio

Main Design Parameters

Main geometric parameters of the four topologies keep the same to make a relatively fair comparison

The back-EMF of the 24195 model is ~18 larger than that of the regular 241010 model while 24 lower than the 24204 case

61

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 62: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Output Torque and Power Factor

0 1 2 3 40

30

60

90

120

24168 24195 24204 2410

Torq

ue (N

m)

Time (ms)

Pole Ratio

0 20 40 60 80 1000

200

400

600

800

24168 24195 24204 241010

Ave

rage

Tor

que

(Nm

)

Phase current (A)

Pole Ratio

0 20 40 60 80 10000

02

04

06

08

10

24168 24195 24204 241010

Pow

er F

acto

r

Phase current (A)

Pole Ratio The average torque values of 24195 and 24168 models are ~18 higher and ~73 lower than that of the 2410 case respectively

62

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 63: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Prototype and Experiments

Back EMF waveform of the vernier PM machine with two slot pitch winding is also sinusoidal

It power factor is larger than 08 63

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 64: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Relationship between VPM and FSCW Machines

Pr=8 Pr=7 Pr=5

Open Slot Half Closed

Slot

Model Z Pr Slot type Ps Ps regular PrPs

1

12

5 Open slot 7 5 57

2 5 Half closed slot 7 5 57

3 7 Open slot 5 7 12

4 7 Half closed slot 5 7 12

5 8 Open slot 4 8 2

6 8 Half closed slot 4 8 2

0 2 4 6 8 10 12 140

1

2

3

4

times10(-4)

ΛZ

Airg

ap P

erm

eanc

e

Order

slot opening ratio=058 slot opening ratio=013

Λ0

Spectra of airgap permeance harmonics

64

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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  • 幻灯片编号 3
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Page 65: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

0

8

16

24

Torq

ue (N

m)

Half Closed Slot Opening Slot

1284 1275 1257PR=2 PR=14 PR=07

VPM and FSCW Machine Relationship

0

1

2

3

4

5

PR=07PR=14PR=2

Open SlotHalf Closed Slot

12571275

times10(-4)

k conv

+kve

r

Modulated part Regular part

1284

Predicted by analytical method Predicted by FEA

The fractional slot concentrated winding (FSCW) PM machines can also be regarded as one type flux modulation machine

The modulated part torque accounts for large proportion in the total torque of the FSCW PM machines

As the pole ratio increases the ratio of the modulated part torque to the total torque increases

65

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
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Page 66: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Non-overlapping Windings with Large Pole Ratio

Lap Winding Toroidal Winding Non-overlapping FSCW

s

Z 1 1q = = 2mP 4 2s

Zq = = 1232mP

End winding length is almost independent from slotpole combination

f f e aP Z P P P= = plusmn f e aP P P= plusmn

66

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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  • 幻灯片编号 64
  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
  • 幻灯片编号 68
  • 幻灯片编号 69
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Page 67: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Dual-Airgap Axial Flux VPM Machines Rotor core

Stator core

WindingMagnets

Rotor coreMachine topology

The rotor-stator-rotor structure makes toroidal windings applicable

Due to mirror symmetry of axial flux topology the analyzing process can be simplified by focusing on only one rotor and half the stator

67

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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  • 幻灯片编号 3
  • 幻灯片编号 4
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Page 68: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Other Optional Configurations

Different winding configurations

(a) (b)

(c) (d)

(a) (b)

Different slot shapes

Different PM configurations

68

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 69: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Geometric Parameters

Cylindrical view Flux distribution of the AFVPM machine

Symmetrical Axis

+A+A-C-C+B+B-A-A+C+C-B-B

-A-A+C+C-B-B+A+A-C-C+B+B

Stator yoke

N N N

N N NS S

S S

Rotor yoke

Rotor yoke

ghm

ws wp(r)

hys

hyr

hss

Lt

ws

wp(r)

Slot

Slot

Ri

Ro

N

N

S

S

N

Ri

Ro

θs

θs

Top view

The stator teeth on both sides work as flux modulators

Rectangular instead of trapezoidal slots are chosen for the proposed machine due to manufacturing difficulties

69

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 70: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Quasi-3D and 3D FEA

Item Analytical Quasi-3D 3D Avg Torque Nm 1103 1056 1061

Torque density kNmm3 339 327 326 Torque ripple - 05 23

Calculation time lt1s 40min 8hour

Sketch of Quasi-3D method Magnetic field plot of quasi-3D and 3D FEA

70

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 71: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Prototypes

Stator and rotor cores Stator with windings

PM rotor Prototype

71

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 72: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Experimental Test

Test bench

Oscilloscope

Torque transducer

Prototype

Dyno machine

Current probe

Three phase back-EMF waveforms

Average torque vs current

Performance comparison with different analyzing methods

72

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
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  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
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  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
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Page 73: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Mutli Working Harmonic Vernier PM machines

Cross section of the proposed vernier topology (APMV machine)

= 2fk Pτ π

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

k=13θ=30degtimesk

A+

A-B+

B-

C+

C-

A+

A-

B-

B+C-

C+

Rotor

Magnets

30o

Stator

Flux modulator

Cross section of regular topology

The flux modulator pitch is unequal to slot opening width

Regular vernier PM machine is a special case of APMV machine

The flux modulator pitch ratio is defined as

Z=6 Pf=12 Ps=2 Pr=10

73

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
  • 幻灯片编号 23
  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
  • 幻灯片编号 58
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  • 幻灯片编号 60
  • 幻灯片编号 61
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  • 幻灯片编号 63
  • 幻灯片编号 64
  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
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Page 74: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn 74

Permeance and Flux Density Harmonics

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order Pf

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08

Rotor positionmm

Order

Flux

den

sity

TFl

ux d

ensi

tyT

Pf-Pr

Pf

Regular vernier PM machine k=1 Airgap permeance Flux density

New working permeance harmonics are introduced

0 20 40 60 80 100 120 140 160 180 2001

2

3

4x 10

-5

Rotor position(mechdeg)

0 2 4 6 8 10 12 14 160

1

2

3x 10

-5

Order

Airg

ap p

erm

eanc

eAi

rgap

per

mea

nce

Pf05Pf

0 50 100 150 200 250-2

-1

0

1

2

0 2 4 6 8 10 12 14 16 18 200

02

04

06

08Rotor positionmm

Order

Pf-Pr Pr-Pf2 Pr+Pf2

Flux

den

sity

TFl

ux d

ensi

tyT

The APMV machine k=13 Airgap permeance Flux density

0

10

20

30

2014104 8

Bac

k-EM

F(V)

Harmonic Order

k=10 Semi-analytical k=10 FEA k=13 Semi-analytical k=13 FEA

2

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
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  • 幻灯片编号 31
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  • 幻灯片编号 34
  • 幻灯片编号 35
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  • 幻灯片编号 40
  • 幻灯片编号 41
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  • 幻灯片编号 43
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  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
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  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
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  • 幻灯片编号 56
  • 幻灯片编号 57
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  • 幻灯片编号 61
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  • 幻灯片编号 64
  • 幻灯片编号 65
  • 幻灯片编号 66
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  • 幻灯片编号 68
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  • 幻灯片编号 98
  • 幻灯片编号 99
Page 75: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Slot Pole Combinations Optional slot-pole combinations for the proposed APMV machine

r rcom

f r s

P PPRP P P

= =minus

1r

addf

r ff

PPRnP P

n

=minusminus

3 123(Z )s

Z k kGCD P

= =

35 0866r s wP P kge ge

1 23f r sP nZ P P n= = plusmn =

75

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 76: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Case Study on Four FEA Models Topology

Z=6 Pf =12 Pr =10 Ps =2 Z=6 Pf =18 Pr =16 Ps =2

Z=6 Pf =24 Pr =22 Ps =2 Z=12 Pf =24 Pr =19 Ps =5

Tooth width

Flux modulatorpitch

PM thickness

76

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
  • 幻灯片编号 23
  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
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  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
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  • 幻灯片编号 60
  • 幻灯片编号 61
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  • 幻灯片编号 63
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Page 77: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

No Load Condition Back EMF

0 60 120 180 240 300 360

-60-40-20

0204060

Phas

e B

ack-

EMF(

V)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

0 60 120 180-15

-10

-05

00

05

10

15

Airg

ap fl

ux d

ensi

ty(T

)

ElecAngle(Degree)

612102 model 618162 model 624222 model 1224195 model

Airgap Flux Density

0 1 2 3 4 5 6 7 8 9 100

10

20

30

40

50

60

Phas

e B

ack-

EMF(

V)

Harmonic

612102 model 618162 model 624222 model 1224195 model

0 2 4 6 8 10 12 14 16 18 20 22 2400

04

08

12

Harmonic

Airg

ap fl

ux d

ensi

ty(V

)

612102 model 618162 model 624222 model 1224195 model

The back EMF waveforms of the four models are sinusoidal

Additional flux density harmonics are introduced in the proposed machines

77

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
  • 幻灯片编号 23
  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
  • 幻灯片编号 58
  • 幻灯片编号 59
  • 幻灯片编号 60
  • 幻灯片编号 61
  • 幻灯片编号 62
  • 幻灯片编号 63
  • 幻灯片编号 64
  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
  • 幻灯片编号 68
  • 幻灯片编号 69
  • 幻灯片编号 70
  • 幻灯片编号 71
  • 幻灯片编号 72
  • 幻灯片编号 73
  • 幻灯片编号 74
  • 幻灯片编号 75
  • 幻灯片编号 76
  • 幻灯片编号 77
  • 幻灯片编号 78
  • 幻灯片编号 79
  • 幻灯片编号 80
  • 幻灯片编号 81
  • 幻灯片编号 82
  • 幻灯片编号 83
  • 幻灯片编号 84
  • 幻灯片编号 85
  • 幻灯片编号 86
  • 幻灯片编号 87
  • 幻灯片编号 88
  • 幻灯片编号 89
  • 幻灯片编号 90
  • 幻灯片编号 91
  • 幻灯片编号 92
  • 幻灯片编号 93
  • 幻灯片编号 94
  • 幻灯片编号 95
  • 幻灯片编号 96
  • 幻灯片编号 97
  • 幻灯片编号 98
  • 幻灯片编号 99
Page 78: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn 78

Parametersrsquo effect on Performance

06 07 08 09 10 11 12 13 14 15 160

10

20

30

40

50

60

415

343

31

Ph

ase

Bac

k-EM

F(V)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

201

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Cog

ging

Tor

que(

Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

Compared to the regular PMV machine gt20 back EMF improvement can be obtained by using the proposed topology

Pole ratio increase

The optimization of the flux modulator pitch ratio k could achieve significant back-EMF improvement

The optimal values of k for maximum back-EMF of the four models are different

For the topologies with 6 slots cogging torque varies greatly with the value of k while the cogging torque of the 1224195 case remains low

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 79: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

00 02 04 06 08 10

12

14

16

18

20

22

00 02 04 06 08 10

12

14

16

18

20

22

Time(Period)

Torq

ue(N

m)

Time(Period)

612102 k=1 618162 k=1 624222 k=1 1224195 k=1

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Flux modulator pitch ratio k

06 07 08 09 10 11 12 13 14 15 16

0

1

2

3

Toru

qe ri

pple

(Nm

)

Flux Modulator Ratio k

612102 model 618162 model 624222 model 1224195 model

The optimization of k could achieve more than 20 higher torque capability for each case

The pitch ratio has significant influence on torque ripple

79

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
  • 幻灯片编号 23
  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
  • 幻灯片编号 58
  • 幻灯片编号 59
  • 幻灯片编号 60
  • 幻灯片编号 61
  • 幻灯片编号 62
  • 幻灯片编号 63
  • 幻灯片编号 64
  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
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  • 幻灯片编号 94
  • 幻灯片编号 95
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  • 幻灯片编号 98
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Page 80: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Parametersrsquo effect on Performance

030 035 040 045 050 055 0600

4

8

12

16

20

Torq

ue(N

m)

Auxiliary tooth width ratio

k=070 k=086 k=102 k=118 k=134 k=150

05 10 15 20 25 30 35 40 458

10

12

14

16

18

20

22

612102 k=126 618162 k=114 624222 k=108 1224195 k=134

Torq

ue(N

m)

Magnet Thickness(mm)

Tooth width ratio Magnet thickness

The topology with 6 slot 12 auxiliary teeth 10 rotor pole pair 2 stator pole pair is chosen for further analysis

As k rises from 07 to 15 the optimal auxiliary tooth width ratio for maximum output torque gradually decreases

Increasing magnet thickness may result in torque reduction which is different from that of regular PM machines

80

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
  • 幻灯片编号 23
  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
  • 幻灯片编号 58
  • 幻灯片编号 59
  • 幻灯片编号 60
  • 幻灯片编号 61
  • 幻灯片编号 62
  • 幻灯片编号 63
  • 幻灯片编号 64
  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
  • 幻灯片编号 68
  • 幻灯片编号 69
  • 幻灯片编号 70
  • 幻灯片编号 71
  • 幻灯片编号 72
  • 幻灯片编号 73
  • 幻灯片编号 74
  • 幻灯片编号 75
  • 幻灯片编号 76
  • 幻灯片编号 77
  • 幻灯片编号 78
  • 幻灯片编号 79
  • 幻灯片编号 80
  • 幻灯片编号 81
  • 幻灯片编号 82
  • 幻灯片编号 83
  • 幻灯片编号 84
  • 幻灯片编号 85
  • 幻灯片编号 86
  • 幻灯片编号 87
  • 幻灯片编号 88
  • 幻灯片编号 89
  • 幻灯片编号 90
  • 幻灯片编号 91
  • 幻灯片编号 92
  • 幻灯片编号 93
  • 幻灯片编号 94
  • 幻灯片编号 95
  • 幻灯片编号 96
  • 幻灯片编号 97
  • 幻灯片编号 98
  • 幻灯片编号 99
Page 81: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Prototypes

Stator lamination Stator winding

PM rotor View of the prototype 81

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
  • 幻灯片编号 23
  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
  • 幻灯片编号 58
  • 幻灯片编号 59
  • 幻灯片编号 60
  • 幻灯片编号 61
  • 幻灯片编号 62
  • 幻灯片编号 63
  • 幻灯片编号 64
  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
  • 幻灯片编号 68
  • 幻灯片编号 69
  • 幻灯片编号 70
  • 幻灯片编号 71
  • 幻灯片编号 72
  • 幻灯片编号 73
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  • 幻灯片编号 77
  • 幻灯片编号 78
  • 幻灯片编号 79
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  • 幻灯片编号 86
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  • 幻灯片编号 90
  • 幻灯片编号 91
  • 幻灯片编号 92
  • 幻灯片编号 93
  • 幻灯片编号 94
  • 幻灯片编号 95
  • 幻灯片编号 96
  • 幻灯片编号 97
  • 幻灯片编号 98
  • 幻灯片编号 99
Page 82: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Experimental Test Results

0 1 2 3 4 5 6-300

-200

-100

0

100

200

300

FEAMeasured

Time ms

Back

EM

F V

1 2 3 4 5 6 72

4

6

8

10

12

14

16

18

20

22

FEAMeasured

Current A

Torq

ueN

m

21Nm104kg

14Nm1435kg

APMV machine

RegularPM machine

FEA predicted and measured line back-EMF

FEA predicted and measured torque-current waveforms

Comparison of weight and volume the prototype and regular PM machine

The experimental test results agree well with theoretical analysis and simulation study above

The torque density of the APMV prototype is 2Nmkg ie two times that of the regular PM machine

82

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
  • 幻灯片编号 23
  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
  • 幻灯片编号 58
  • 幻灯片编号 59
  • 幻灯片编号 60
  • 幻灯片编号 61
  • 幻灯片编号 62
  • 幻灯片编号 63
  • 幻灯片编号 64
  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
  • 幻灯片编号 68
  • 幻灯片编号 69
  • 幻灯片编号 70
  • 幻灯片编号 71
  • 幻灯片编号 72
  • 幻灯片编号 73
  • 幻灯片编号 74
  • 幻灯片编号 75
  • 幻灯片编号 76
  • 幻灯片编号 77
  • 幻灯片编号 78
  • 幻灯片编号 79
  • 幻灯片编号 80
  • 幻灯片编号 81
  • 幻灯片编号 82
  • 幻灯片编号 83
  • 幻灯片编号 84
  • 幻灯片编号 85
  • 幻灯片编号 86
  • 幻灯片编号 87
  • 幻灯片编号 88
  • 幻灯片编号 89
  • 幻灯片编号 90
  • 幻灯片编号 91
  • 幻灯片编号 92
  • 幻灯片编号 93
  • 幻灯片编号 94
  • 幻灯片编号 95
  • 幻灯片编号 96
  • 幻灯片编号 97
  • 幻灯片编号 98
  • 幻灯片编号 99
Page 83: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Armature only

Magnet only

Flux linkageamp

Inductance

2

1

1 ( )s

m

PowerFactorL Iψ

=

+

Regular PM machine Vernier PM machine00

05

10

15

20

25

Sync

hron

ous

Indu

ctan

ce(m

H)

The power factor of VPM machines with high pole ratio are much lower than that of regular PM machine

Regular PM Vernier PM

Power Factor of Vernier PM Machines

Pole ratio=11 83

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
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  • 幻灯片编号 10
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  • 幻灯片编号 12
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  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
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  • 幻灯片编号 35
  • 幻灯片编号 36
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  • 幻灯片编号 40
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  • 幻灯片编号 43
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  • 幻灯片编号 46
  • 幻灯片编号 47
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  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
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  • 幻灯片编号 55
  • 幻灯片编号 56
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  • 幻灯片编号 70
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  • 幻灯片编号 78
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Page 84: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Power Factor Analysis

Regular VPM machine with 11 pole ratio

There are almost only half magnets contributing to the flux per armature field pole pitch during one armature field pole

The other half magnets mainly produce flux leakage

The key method to improve power factor is that 1 increasing magnet flux linkage or 2 reducing inductance

84

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
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  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
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  • 幻灯片编号 15
  • 幻灯片编号 16
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  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
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  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
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  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
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  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
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  • 幻灯片编号 92
  • 幻灯片编号 93
  • 幻灯片编号 94
  • 幻灯片编号 95
  • 幻灯片编号 96
  • 幻灯片编号 97
  • 幻灯片编号 98
  • 幻灯片编号 99
Page 85: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Power Factor Improvement

Regular Vernier PM machine

Proposed PMV machine

The consequent pole is employed in the rotor and the Halbach array PMs in the stator slot opening are used to guide flux into the stator

This structure can reduce leakage flux

Parameters Value Unit Outer diameter 124 mm Stator inner diameter 744 mm Airgap length 05 mm Magnet thicknesss 3 mm SlotsPoles 1222 ndash Pole arc 09 ndash Slot depth 148 mm Slot opening width 136 mm Stack length 70 mm

Proposed PM machine

85

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
  • 幻灯片编号 23
  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
  • 幻灯片编号 58
  • 幻灯片编号 59
  • 幻灯片编号 60
  • 幻灯片编号 61
  • 幻灯片编号 62
  • 幻灯片编号 63
  • 幻灯片编号 64
  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
  • 幻灯片编号 68
  • 幻灯片编号 69
  • 幻灯片编号 70
  • 幻灯片编号 71
  • 幻灯片编号 72
  • 幻灯片编号 73
  • 幻灯片编号 74
  • 幻灯片编号 75
  • 幻灯片编号 76
  • 幻灯片编号 77
  • 幻灯片编号 78
  • 幻灯片编号 79
  • 幻灯片编号 80
  • 幻灯片编号 81
  • 幻灯片编号 82
  • 幻灯片编号 83
  • 幻灯片编号 84
  • 幻灯片编号 85
  • 幻灯片编号 86
  • 幻灯片编号 87
  • 幻灯片编号 88
  • 幻灯片编号 89
  • 幻灯片编号 90
  • 幻灯片编号 91
  • 幻灯片编号 92
  • 幻灯片编号 93
  • 幻灯片编号 94
  • 幻灯片编号 95
  • 幻灯片编号 96
  • 幻灯片编号 97
  • 幻灯片编号 98
  • 幻灯片编号 99
Page 86: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn 86

Power Factor Improvement

= +

Proposed machine Consequent pole Vernier PM machine

Flux reversal PM machine

Proposed machine

Regular vernier machine

The analysis results have shown that this machine could produce 956 larger back-EMF and 548 larger output torque

If the two machines had same torque density ie the current loading is smaller in the proposed machine its power factor is ~089

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
  • 幻灯片编号 23
  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
  • 幻灯片编号 58
  • 幻灯片编号 59
  • 幻灯片编号 60
  • 幻灯片编号 61
  • 幻灯片编号 62
  • 幻灯片编号 63
  • 幻灯片编号 64
  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
  • 幻灯片编号 68
  • 幻灯片编号 69
  • 幻灯片编号 70
  • 幻灯片编号 71
  • 幻灯片编号 72
  • 幻灯片编号 73
  • 幻灯片编号 74
  • 幻灯片编号 75
  • 幻灯片编号 76
  • 幻灯片编号 77
  • 幻灯片编号 78
  • 幻灯片编号 79
  • 幻灯片编号 80
  • 幻灯片编号 81
  • 幻灯片编号 82
  • 幻灯片编号 83
  • 幻灯片编号 84
  • 幻灯片编号 85
  • 幻灯片编号 86
  • 幻灯片编号 87
  • 幻灯片编号 88
  • 幻灯片编号 89
  • 幻灯片编号 90
  • 幻灯片编号 91
  • 幻灯片编号 92
  • 幻灯片编号 93
  • 幻灯片编号 94
  • 幻灯片编号 95
  • 幻灯片编号 96
  • 幻灯片编号 97
  • 幻灯片编号 98
  • 幻灯片编号 99
Page 87: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

The proposed DSSA VPM machine has two stators and one rotor which is sandwiched by the two stators

The rotor employs tangential-excitation spoke-array magnets

Dual-Stator Spoke-Array(DSSA) Vernier PM machine

DSSA VPM Topology

A+

-C

A-

-C

-C

-C

B+

B-

+B

B-

A+

A-

+A

+A

-C-C

+B

-A

+C

-B

-B

MagnetWinding

Stator Rotor

+C

-A

+B

87

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
  • 幻灯片编号 23
  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
  • 幻灯片编号 58
  • 幻灯片编号 59
  • 幻灯片编号 60
  • 幻灯片编号 61
  • 幻灯片编号 62
  • 幻灯片编号 63
  • 幻灯片编号 64
  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
  • 幻灯片编号 68
  • 幻灯片编号 69
  • 幻灯片编号 70
  • 幻灯片编号 71
  • 幻灯片编号 72
  • 幻灯片编号 73
  • 幻灯片编号 74
  • 幻灯片编号 75
  • 幻灯片编号 76
  • 幻灯片编号 77
  • 幻灯片编号 78
  • 幻灯片编号 79
  • 幻灯片编号 80
  • 幻灯片编号 81
  • 幻灯片编号 82
  • 幻灯片编号 83
  • 幻灯片编号 84
  • 幻灯片编号 85
  • 幻灯片编号 86
  • 幻灯片编号 87
  • 幻灯片编号 88
  • 幻灯片编号 89
  • 幻灯片编号 90
  • 幻灯片编号 91
  • 幻灯片编号 92
  • 幻灯片编号 93
  • 幻灯片编号 94
  • 幻灯片编号 95
  • 幻灯片编号 96
  • 幻灯片编号 97
  • 幻灯片编号 98
  • 幻灯片编号 99
Page 88: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Outer Stator

Magnet

Winding

Innerstator

The inner stator tooth has half teeth pitch displacement compared to the outer stator tooth

Magnet Field of DSSA VPM Machines

-05 -04 -03 -02 -01 00 01 02 03 04 0500

02

04

06

08

10

Back

-EM

F(p

u)

Relative position angleslot pitch angleInner stator

Outer stator

Aouter+

Aouter+

A+ A+

Aouter-

Aouter-

A-A-

mioα

1

2

34

5

6 7

8

910

11

12

12

34

5

6 78

910

11

12

O

Inner StatorOuter Stator

A A1 A2

B B1 B2

C C1 C2

0 10 20 30 40 50 60 70 80 90-002

-0015

-001

-0005

0

0005

001

0015

002

Outer statorInner stator

Time(ms)

Flux

link

age(

Wb)

15o

Relative position of two stators in the DSSA vernier PM machine

88

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
  • 幻灯片编号 23
  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
  • 幻灯片编号 58
  • 幻灯片编号 59
  • 幻灯片编号 60
  • 幻灯片编号 61
  • 幻灯片编号 62
  • 幻灯片编号 63
  • 幻灯片编号 64
  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
  • 幻灯片编号 68
  • 幻灯片编号 69
  • 幻灯片编号 70
  • 幻灯片编号 71
  • 幻灯片编号 72
  • 幻灯片编号 73
  • 幻灯片编号 74
  • 幻灯片编号 75
  • 幻灯片编号 76
  • 幻灯片编号 77
  • 幻灯片编号 78
  • 幻灯片编号 79
  • 幻灯片编号 80
  • 幻灯片编号 81
  • 幻灯片编号 82
  • 幻灯片编号 83
  • 幻灯片编号 84
  • 幻灯片编号 85
  • 幻灯片编号 86
  • 幻灯片编号 87
  • 幻灯片编号 88
  • 幻灯片编号 89
  • 幻灯片编号 90
  • 幻灯片编号 91
  • 幻灯片编号 92
  • 幻灯片编号 93
  • 幻灯片编号 94
  • 幻灯片编号 95
  • 幻灯片编号 96
  • 幻灯片编号 97
  • 幻灯片编号 98
  • 幻灯片编号 99
Page 89: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Magnet Field of DSSA VPM Machines

Rotor

Stator

The DSSA VPM machine can greatly improve the flux density with same magnet usage

The special structure heavily reduce magnet leakage flux

89

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
  • 幻灯片编号 23
  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
  • 幻灯片编号 58
  • 幻灯片编号 59
  • 幻灯片编号 60
  • 幻灯片编号 61
  • 幻灯片编号 62
  • 幻灯片编号 63
  • 幻灯片编号 64
  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
  • 幻灯片编号 68
  • 幻灯片编号 69
  • 幻灯片编号 70
  • 幻灯片编号 71
  • 幻灯片编号 72
  • 幻灯片编号 73
  • 幻灯片编号 74
  • 幻灯片编号 75
  • 幻灯片编号 76
  • 幻灯片编号 77
  • 幻灯片编号 78
  • 幻灯片编号 79
  • 幻灯片编号 80
  • 幻灯片编号 81
  • 幻灯片编号 82
  • 幻灯片编号 83
  • 幻灯片编号 84
  • 幻灯片编号 85
  • 幻灯片编号 86
  • 幻灯片编号 87
  • 幻灯片编号 88
  • 幻灯片编号 89
  • 幻灯片编号 90
  • 幻灯片编号 91
  • 幻灯片编号 92
  • 幻灯片编号 93
  • 幻灯片编号 94
  • 幻灯片编号 95
  • 幻灯片编号 96
  • 幻灯片编号 97
  • 幻灯片编号 98
  • 幻灯片编号 99
Page 90: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Reluctance Torque of DSSA VPM Machines

The spoke-array magnets introduce rotor anisotropy for DSSA VPM topology

The gamma angle varies from 0 to 30 degree the power factor would increase from 076 to 091with almost 2 torque improvement

0 5 10 15 20 25 30980

990

1000

1010

1020

1030

0 5 10 15 20 25 3007

075

08

085

09

095

0 5 10 15 20 25 3007

075

08

085

09

095

Power FactorTorque

gamma angle(deg)

Power FactorT

orqu

e(N

m)

gamma angle(deg)0 5 10 15 20 25 300

2

4

6

8

10

12

14

16

Rat

io o

f rel

ucta

nce

torq

ue

to m

agne

t tor

que

()

Variation of torque and power factor vs gamma angle

Variation of reluctance torquemagnet torque vs gamma angle

90

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
  • 幻灯片编号 23
  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
  • 幻灯片编号 58
  • 幻灯片编号 59
  • 幻灯片编号 60
  • 幻灯片编号 61
  • 幻灯片编号 62
  • 幻灯片编号 63
  • 幻灯片编号 64
  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
  • 幻灯片编号 68
  • 幻灯片编号 69
  • 幻灯片编号 70
  • 幻灯片编号 71
  • 幻灯片编号 72
  • 幻灯片编号 73
  • 幻灯片编号 74
  • 幻灯片编号 75
  • 幻灯片编号 76
  • 幻灯片编号 77
  • 幻灯片编号 78
  • 幻灯片编号 79
  • 幻灯片编号 80
  • 幻灯片编号 81
  • 幻灯片编号 82
  • 幻灯片编号 83
  • 幻灯片编号 84
  • 幻灯片编号 85
  • 幻灯片编号 86
  • 幻灯片编号 87
  • 幻灯片编号 88
  • 幻灯片编号 89
  • 幻灯片编号 90
  • 幻灯片编号 91
  • 幻灯片编号 92
  • 幻灯片编号 93
  • 幻灯片编号 94
  • 幻灯片编号 95
  • 幻灯片编号 96
  • 幻灯片编号 97
  • 幻灯片编号 98
  • 幻灯片编号 99
Page 91: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Torque Density of DSSA VPM Machines

The back-EMF waveform of the regular VPM machine is more sinusoidal than that of regular PM machine

The torque per active machine volume of natural cooling totally-enclosed DSSA VPM machine can reach 66 kNmm3

Back-EMF waveform

Time(ms)

Bac

k-E

MF

(V)

Regular vernier DSSA Linear loading in out airgap

Acm 220 120

Linear loading in inner airgap Acm 100

Torque Nm 1156 2000 Power factor 066 091 Magnet volumecm3 8646 801 Torque pu 1 173 Torque density kNmm3 38 66

91

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
  • 幻灯片编号 23
  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
  • 幻灯片编号 58
  • 幻灯片编号 59
  • 幻灯片编号 60
  • 幻灯片编号 61
  • 幻灯片编号 62
  • 幻灯片编号 63
  • 幻灯片编号 64
  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
  • 幻灯片编号 68
  • 幻灯片编号 69
  • 幻灯片编号 70
  • 幻灯片编号 71
  • 幻灯片编号 72
  • 幻灯片编号 73
  • 幻灯片编号 74
  • 幻灯片编号 75
  • 幻灯片编号 76
  • 幻灯片编号 77
  • 幻灯片编号 78
  • 幻灯片编号 79
  • 幻灯片编号 80
  • 幻灯片编号 81
  • 幻灯片编号 82
  • 幻灯片编号 83
  • 幻灯片编号 84
  • 幻灯片编号 85
  • 幻灯片编号 86
  • 幻灯片编号 87
  • 幻灯片编号 88
  • 幻灯片编号 89
  • 幻灯片编号 90
  • 幻灯片编号 91
  • 幻灯片编号 92
  • 幻灯片编号 93
  • 幻灯片编号 94
  • 幻灯片编号 95
  • 幻灯片编号 96
  • 幻灯片编号 97
  • 幻灯片编号 98
  • 幻灯片编号 99
Page 92: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Inner Stator

Outer StatorRotorShaft

ReforcingRing

The support structure example of rotor and inner stator use cantilever structural model

The rotor support should be manufactured by non-magnetic material to reduce the magnet end flux leakage

Auxiliary Mechanical Structure

92

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
  • 幻灯片编号 23
  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
  • 幻灯片编号 58
  • 幻灯片编号 59
  • 幻灯片编号 60
  • 幻灯片编号 61
  • 幻灯片编号 62
  • 幻灯片编号 63
  • 幻灯片编号 64
  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
  • 幻灯片编号 68
  • 幻灯片编号 69
  • 幻灯片编号 70
  • 幻灯片编号 71
  • 幻灯片编号 72
  • 幻灯片编号 73
  • 幻灯片编号 74
  • 幻灯片编号 75
  • 幻灯片编号 76
  • 幻灯片编号 77
  • 幻灯片编号 78
  • 幻灯片编号 79
  • 幻灯片编号 80
  • 幻灯片编号 81
  • 幻灯片编号 82
  • 幻灯片编号 83
  • 幻灯片编号 84
  • 幻灯片编号 85
  • 幻灯片编号 86
  • 幻灯片编号 87
  • 幻灯片编号 88
  • 幻灯片编号 89
  • 幻灯片编号 90
  • 幻灯片编号 91
  • 幻灯片编号 92
  • 幻灯片编号 93
  • 幻灯片编号 94
  • 幻灯片编号 95
  • 幻灯片编号 96
  • 幻灯片编号 97
  • 幻灯片编号 98
  • 幻灯片编号 99
Page 93: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Prototype

93

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
  • 幻灯片编号 23
  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
  • 幻灯片编号 58
  • 幻灯片编号 59
  • 幻灯片编号 60
  • 幻灯片编号 61
  • 幻灯片编号 62
  • 幻灯片编号 63
  • 幻灯片编号 64
  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
  • 幻灯片编号 68
  • 幻灯片编号 69
  • 幻灯片编号 70
  • 幻灯片编号 71
  • 幻灯片编号 72
  • 幻灯片编号 73
  • 幻灯片编号 74
  • 幻灯片编号 75
  • 幻灯片编号 76
  • 幻灯片编号 77
  • 幻灯片编号 78
  • 幻灯片编号 79
  • 幻灯片编号 80
  • 幻灯片编号 81
  • 幻灯片编号 82
  • 幻灯片编号 83
  • 幻灯片编号 84
  • 幻灯片编号 85
  • 幻灯片编号 86
  • 幻灯片编号 87
  • 幻灯片编号 88
  • 幻灯片编号 89
  • 幻灯片编号 90
  • 幻灯片编号 91
  • 幻灯片编号 92
  • 幻灯片编号 93
  • 幻灯片编号 94
  • 幻灯片编号 95
  • 幻灯片编号 96
  • 幻灯片编号 97
  • 幻灯片编号 98
  • 幻灯片编号 99
Page 94: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Simulation value Measured value Torque Nm 2000 Speed 30 RMS line current A

236 246

Power factor 085 083 Efficiency 90 85

TABLE Comparison of Simulation and Measured

Performance Indexes

PrototypeMagnetic powder brake

Torque transducer Thermo detector

0 5 10 15 20 25 300

500

1000

1500

2000

2500

Outp

ut T

orqu

e(Nm

)Phase Current (A)

Measured 2-D FEA

Power Factor Improvement

The DSSA VPM topology can greatly reduce the magnet flux leakage and all magnets contribute to the airgap flux density at same time The DSSA VPM topology exhibits high power factor

94

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
  • 幻灯片编号 23
  • 幻灯片编号 24
  • 幻灯片编号 25
  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
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  • 幻灯片编号 60
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  • 幻灯片编号 97
  • 幻灯片编号 98
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Page 95: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

High torque density sinusoidal back EMF waveform and smooth torque waveform are inherently features of vernier PM machines

By introducing additional working flux density harmonic further improvement of the torque density can be obtained

Regular vernier PM machines always suffer from low power factor

The dual stator spoke array (DSSA) vernier PM machine can heavily reduce the leakage flux and improve the working flux density by specific design on the rotor and relative position of the two stators

Power factor of the DSSA vernier PM machine can reach a comparable value with that of the regular PM machines and its torque density is larger than that of the regular veriner PM machine

Vernier Machines ndash Summary

95

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
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  • 幻灯片编号 73
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  • 幻灯片编号 97
  • 幻灯片编号 98
  • 幻灯片编号 99
Page 96: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Challenges and Opportunities

96

Flux modulation effect is found and developed and this may introduce significant influence on the electric machine and there are still many challenges to be overcome Low power factor It has been illustrated that the low power

factor is the common issue for flux modulation machines and lots of effort is going on this topic Some topologies have shown promising results but with either complex structure or low pole ratio (lower torque density) Reduction of Rotor losses The main field and rotor have

different mechanical speed and this introduces improvement of torque density and large rotor losses at same time

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
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  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
  • 幻灯片编号 58
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  • 幻灯片编号 60
  • 幻灯片编号 61
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  • 幻灯片编号 63
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  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
  • 幻灯片编号 68
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  • 幻灯片编号 70
  • 幻灯片编号 71
  • 幻灯片编号 72
  • 幻灯片编号 73
  • 幻灯片编号 74
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  • 幻灯片编号 76
  • 幻灯片编号 77
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  • 幻灯片编号 79
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  • 幻灯片编号 81
  • 幻灯片编号 82
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  • 幻灯片编号 86
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  • 幻灯片编号 88
  • 幻灯片编号 89
  • 幻灯片编号 90
  • 幻灯片编号 91
  • 幻灯片编号 92
  • 幻灯片编号 93
  • 幻灯片编号 94
  • 幻灯片编号 95
  • 幻灯片编号 96
  • 幻灯片编号 97
  • 幻灯片编号 98
  • 幻灯片编号 99
Page 97: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

There are few ways to improve machine torque density Flux modulation is another way to offer higher specific torque and offer more freedom to work with It is found that flux modulation principle can be used to analyze

not only flux modulation machines but regular machines In other words regular machines could be regarded as special cases of flux modulation machines Vernier machines as one type of flux modulation machines

can produce high torque density sinusoidal back EMF and much lower torque ripple Some VPM topologies can greatly reduce the magnet flux

leakage boost power factor further improve torque density and greatly reduce machine volume and cost There are a lot more flux modulation machine topologies to be

discovered more opportunity to improve performance

HUST Private information

Summary Conclusions

97

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
  • 幻灯片编号 3
  • 幻灯片编号 4
  • 幻灯片编号 5
  • 幻灯片编号 6
  • 幻灯片编号 7
  • 幻灯片编号 8
  • 幻灯片编号 9
  • 幻灯片编号 10
  • 幻灯片编号 11
  • 幻灯片编号 12
  • 幻灯片编号 13
  • 幻灯片编号 14
  • 幻灯片编号 15
  • 幻灯片编号 16
  • 幻灯片编号 17
  • 幻灯片编号 18
  • 幻灯片编号 19
  • 幻灯片编号 20
  • 幻灯片编号 21
  • 幻灯片编号 22
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  • 幻灯片编号 24
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  • 幻灯片编号 26
  • 幻灯片编号 27
  • 幻灯片编号 28
  • 幻灯片编号 29
  • 幻灯片编号 30
  • 幻灯片编号 31
  • 幻灯片编号 32
  • 幻灯片编号 33
  • 幻灯片编号 34
  • 幻灯片编号 35
  • 幻灯片编号 36
  • 幻灯片编号 37
  • 幻灯片编号 38
  • 幻灯片编号 39
  • 幻灯片编号 40
  • 幻灯片编号 41
  • 幻灯片编号 42
  • 幻灯片编号 43
  • 幻灯片编号 44
  • 幻灯片编号 45
  • 幻灯片编号 46
  • 幻灯片编号 47
  • 幻灯片编号 48
  • 幻灯片编号 49
  • 幻灯片编号 50
  • 幻灯片编号 51
  • 幻灯片编号 52
  • 幻灯片编号 53
  • 幻灯片编号 54
  • 幻灯片编号 55
  • 幻灯片编号 56
  • 幻灯片编号 57
  • 幻灯片编号 58
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  • 幻灯片编号 60
  • 幻灯片编号 61
  • 幻灯片编号 62
  • 幻灯片编号 63
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  • 幻灯片编号 65
  • 幻灯片编号 66
  • 幻灯片编号 67
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  • 幻灯片编号 70
  • 幻灯片编号 71
  • 幻灯片编号 72
  • 幻灯片编号 73
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  • 幻灯片编号 76
  • 幻灯片编号 77
  • 幻灯片编号 78
  • 幻灯片编号 79
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  • 幻灯片编号 81
  • 幻灯片编号 82
  • 幻灯片编号 83
  • 幻灯片编号 84
  • 幻灯片编号 85
  • 幻灯片编号 86
  • 幻灯片编号 87
  • 幻灯片编号 88
  • 幻灯片编号 89
  • 幻灯片编号 90
  • 幻灯片编号 91
  • 幻灯片编号 92
  • 幻灯片编号 93
  • 幻灯片编号 94
  • 幻灯片编号 95
  • 幻灯片编号 96
  • 幻灯片编号 97
  • 幻灯片编号 98
  • 幻灯片编号 99
Page 98: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn 98

1 D Li R Qu and T Lipo ldquoHigh power factor vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 50 no 6 pp 3664-3674 NovDec 2014

2 D Li R Qu J Li L Wu and W Xu ldquoAnalysis of torque capability and quality in vernier permanent magnet machinesrdquo IEEE Trans Ind Appl vol 52 no 1 pp 125-135

3 D Li T Zou R Qu and D Jiang ldquoAnalysis of fractional-slot concentrated winding PM vernier machines with regular open-slot statorsrdquo IEEE Trans Ind Appl vol 54 no 2 pp 1320ndash1330 MarApr 2018

4 T Zou D Li R Qu J Li and D Jiang ldquoAnalysis of a dual-rotor toroidal-winding axial-flux vernier permanent magnet machine IEEE Trans Ind Appl vol 53 no 3 pp 1920-1930 MayJune 2017

5 T Zou D Li R Qu D Jiang and J Li ldquoAdvanced high torque density PM vernier machine with multiple working harmonicsrdquo IEEE Trans Ind Appl vol 53 no 6 pp 5295ndash5304 NovDec 2017

6 T Zou D Li R Qu and D Jiang ldquoPerformance Comparison of Surface and Spoke-Type Flux-Modulation Machines with Different Pole Ratiosrdquo IEEE Trans Magn vol 53 no 6 pp 7402605 June 2017

7 T Zou D Li C Chen R Qu and D Jiang ldquoA multiple working harmonic PM vernier machine with enhanced flux modulation effectrdquo IEEE Trans Magn accepted for publication 2018

8 X Ren D Li R Qu and T Zou ldquoA Brushless Dual-mechanical-port Dual-electrical-port Machine with Spoke Array Magnets in Flux Modulatorrdquo IEEE Trans Magn vol 53 no 11 pp 8110706 Nov 2017

9 K Xie D Li R Qu and Y Gao ldquoA Novel Permanent Magnet Vernier Machine With Halbach Array Magnets in Stator Slot Openingrdquo rdquo IEEE Trans Magn vol 53 no 6 pp 1-5 June 2017

Selected Reference

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
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Page 99: High Torque Density Machines - Global Events · USA HTS motor 36.5MW 120RPM Alstom Advanced Induction Motor. 20MW 180RPM Problems in manufacture, transportation, ... SC materials

CAEMD Web httpwwwcaemdcn

Center for Advanced Electrical Machines amp Drives Huazhong University of Science and Technology

Ronghaiquhusteducn

  • High Torque Density Machines
  • 幻灯片编号 2
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