overview electrical machines and drives - tu delft ... the future 19 armature reaction • section...

1Challenge the future

Overview Electrical Machines and

Drives

• 7-9 1: Introduction, Maxwell’s equations, magnetic circuits

• 11-9 1.2-3: Magnetic circuits, Principles

• 14-9 3-4.2: Principles, DC machines

• 18-9 4.3-4.7: DC machines and drives

• 21-9 5.2-5.6: IM introduction, IM principles

• 25-9 Guest lecture Emile Brink

• 28-9 5.8-5.10: IM equivalent circuits and characteristics

• 2-10 5.13-6.3: IM drives, SM

• 5-10 6.4-6.13: SM, PMACM

• 12-10 6.14-8.3: PMACM, other machines

• 19-10: rest, questions

• 9-11: exam

2Challenge the future

DC Machines

• Introduction, construction (4.2)

• Principle of operation and basic calculations (4.2)

• air gap flux density (1.1)

• armature turn voltage and commutation (4.2.2)

• armature windings (4.2.3)

• total armature voltage (4.2.4)

• torque (4.2.5)

• magnetisation curve (4.2.6)

• Armature reaction, interpoles, compensating winding (4.3)

• Characteristics, means to control speed (4.4)

• DC machine drives (4.5)

• PMDC machines / PCB machines (4.6, 4.7)

3Challenge the future

Assumptions for calculations

• steady state (mechanical and electrical)

• the air gap is so small that the flux density does not change in

radial direction

• the air gap is so small that the flux density crosses the air gap

perpendicular

• iron losses are negligible

• the magnetic permeability of iron is infinite

4Challenge the future

Air gap flux density

• The field winding around one pole has Nf turns and carries a

current If

• Calculate the air gap flux density between the poles and the rotor

5Challenge the future

Flux density

g

ffg l

INB 0µ

=

ffgg INlH 22 =

d dm mC S

H s J n Aτ⋅ = ⋅∫ ∫∫� �� �

�

6Challenge the future

Flux density

• Sketch flux linkage of a turn on the rotor

• Calculate the maximum voltage induced in turn from Faraday’s law

7Challenge the future

Armature turn

voltage

vlBlrBt

lrBt

lrB

rBt

l

AnBtt

eeS

t

)(2)(2d

d)(

d

d)(

d)(d

d

dd

d

d

d

θωθ

θπθθθ

θθ

λ

πθ

θ

==

+−=

−=

⋅==

∫

∫∫+

��

At θ=0, the flux linkage is minimum

8Challenge the future

Commutator as

rectifier

9Challenge the future

Commutation

Commutating coil in interpolar region: no induced voltage

10Challenge the future

Armature windings

• English: turn, coil, winding

• Dutch: winding, spoel, wikkeling

11Challenge the future

Mechanical and electrical angles

2e m

pθ θ=2e m

pω ω=

12Challenge the future

DC Machines

• Introduction, construction (4.2)

• Principle of operation and basic calculations (4.2)

• air gap flux density (1.1)

• armature turn voltage and commutation (4.2.2)

• armature windings (4.2.3)

• total armature voltage (4.2.4)

• torque (4.2.5)

• magnetisation curve (4.2.6)

• Armature reaction, interpoles, compensating winding (4.3)

• Characteristics, means to control speed (4.4)

• DC machine drives (4.5)

• PMDC machines / PCB machines (4.6, 4.7)

13Challenge the future

Armature voltage

)(2 θω Blre mt =

)(2 θω Blre mt =

)(2

d)(d/2

0

θπθθπ

Brlp

rBlAnBp

==⋅=Φ ∫∫∫��

mt

pe ω

πΦ=

mamta Ka

Npe

a

NE ωω

πΦ=Φ==

An armature winding has N turnswith a parallel pathsand therefore N/a series-connected turnsFor the turn voltage, we found

The average is lower:

Flux per pole

Using this, the turn voltage is given by

Therefore

14Challenge the future

Voltage and torque from power

balance

d

da

a a m

IU RI L K

tω= + + Φ

Cu f mechP P P P= + +

2 d

da

a a a a a m

IP UI RI I L I K

tω= = + + Φ

Power balance:

Therefore

mecha a

m

PT K I

ω= = Φ

15Challenge the future

Electromagnetic torque from Lorenz

a

IlBlIBF a

cc )()( θθ ==

a

IrlBrFT a

cc )(θ==

aa

c Ia

p

a

IrlBT Φ==

πθ

2)(

aaac IKIa

NpTNT Φ=Φ==

π2

aaaamm IEIKTP =Φ== ωω

Lorenz force gives the same result as power balance.

16Challenge the future

Magnetic circuit

Which part saturates first?Why?

17Challenge the future

Magnetization curve

Why is this not a straight line?Why does it not start from zero?

18Challenge the future

DC Machines

• Introduction, construction (4.2)

• Principle of operation and basic calculations (4.2)

• Armature reaction, interpoles, compensating winding (4.3)

• Characteristics, means to control speed (4.4)

• DC machine drives (4.5)

• PMDC machines / PCB machines (4.6, 4.7)

19Challenge the future

Armature reaction

• Section 4.3 (Sen) has the title “DC generators”

• DC machines are hardly used as generators

• The operating principles are the same in motoring and

generating

• Therefore, we only look at constructional aspects of DC

machines discussed in 4.3, which are present in DC motors as

well as in DC generators:

• compensating winding (Dutch: compensatiewikkeling)

• interpoles (Dutch: hulppolen)

• Both are related to armature reaction

20Challenge the future

Armature reaction

21Challenge the future

Consequences

armature

reaction

• Saturation

• Commutation problems

22Challenge the future

Compensation winding

• Saturation problem reduced

• Expensive; only applied in machines that are often heavily loaded.

Why in these machines?

23Challenge the future

Interpoles

Armature reaction

produces a flux

density in the

interpolar region, so

that a voltage is

induced in the

commutating coil.

This voltage opposes

commutation.

Interpoles reverse the

direction of this flux

density to induce a

voltage that

accelerates

commutation.

24Challenge the future

DC Machines

• Introduction, construction (4.2)

• Principle of operation and basic calculations (4.2)

• Armature reaction, interpoles, compensating winding (4.3)

• Characteristics, means to control speed (4.4)

• Connections of DC machines

• Separately excited DC machine

• Series connected DC machine

• DC machine drives (4.5)

• PMDC machines / PCB machines (4.6, 4.7)

25Challenge the future

Connections of DC machines

26Challenge the future

Separately excited DC machines

How to control speed?

Calculate no-load speed and stall torque.

Φ= ama KE ωaa IKT Φ=

aaat EIRU +=

Pole flux does not depend on armature voltage and load

2)( Φ−

Φ=

Φ−

Φ=

a

a

aa

aa

am K

TR

K

U

K

IR

K

Uω

27Challenge the future

Torque speed characteristic

• Where are motor, generator and plugging operation?• Speed control by means of

• Voltage control: what happens if the voltage is increased?• Field control: what happens if the current is increased?• Resistance control: old-fashioned

28Challenge the future

Voltage control

29Challenge the future

Field control

Are the characteristics of (c) parallel?

30Challenge the future

Series DC machine (universal motor)

What happens to the speed when the torque is zero?

21 aaaa IKKIKT =Φ=aIK1=Φ Neglecting saturation!

31Challenge the future

Series DC motor

11

t am

aa

U R

K KK K Tω = ± −

21

2

12

1 )( maa

taaaaa KKR

UKKIKKIKT

ω+==Φ=

maa

ta KKR

UI

ω1+=

maaaamaaaaaat IKKIRKIREIRU ωω 1+=Φ+=+=

21 aaaa IKKIKT =Φ=

aIK1=Φ

32Challenge the future

DC machines

• Introduction, construction (4.2)

• Principle of operation and basic calculations (4.2)

• Armature reaction, interpoles, compensating winding (4.3)

• Characteristics, means to control speed (4.4)

• DC machine drives (4.5)

• Ward-Leonard system

• Power electronics (Rectifier, Chopper)

• Closed loop control

• PMDC machines / PCB machines (4.6, 4.7)

33Challenge the future

Overview Electrical Machines and

Drives

• 7-9 1: Introduction, Maxwell’s equations, magnetic circuits

• 11-9 1.2-3: Magnetic circuits, Principles

• 14-9 3-4.2: Principles, DC machines

• 18-9 4.3-4.7: DC machines and drives

• 21-9 5.2-5.6: IM introduction, IM principles

• 25-9 Guest lecture Emile Brink

• 28-9 5.8-5.10: IM equivalent circuits and characteristics

• 2-10 5.13-6.3: IM drives, SM

• 5-10 6.4-6.13: SM, PMACM

• 12-10 6.14-8.3: PMACM, other machines

• 19-10: rest, questions

• 9-11: exam