high frequency modeling of induction motor drives for

8/11/2019 High Frequency Modeling of Induction Motor Drives For

1/7

High Frequency M odeling

of

Induction Motor Drives for

EM1 and Overvoltage Mitigation Studies

L.

Arnedo and

K.

Venkatesan

Center for Power Electronic Systems

Electrical and Com pute Engineering Department

Unive rsity of Puerto Rico,Mayaguez C ampus

The present work deals with a comparative study of different

overvoltage mitigation techniques and

their

effect upon

the

COD

ducted EMI emissions in

an

nduction

motor

dlive system.

A

de-

tailed

PSplce model

of

the system has been developed

considering lumped parameter model

with 64

seclious for the

cable and high frequeucy models for the

IGBT

PWM nverter

and Induction motor.

Simulanon

results are compared

with

er-

perimental results.

Four

overvoltage mitigation techniques such

as

RLC

nverter

output

Nter, modified RLC inverter output

fX-

ter, RC Blter at motor te d n a l s and dv/dt control

are

consid-

e r e d

1.

IR0DUCTION

Advances

in power electronic switching devices such

as

Power MOSFETs and IGBTs have enabled high tequency

switching

operatious

and hence improved the performance of

PWM inverters for feeding induction motors. However these

new technologies have created new problems related to Elec-

tromagnetic interference (Emand over-voltages at the ter-

m i na l s

of electric ma chi es [I].

Presently EMC regulations are more stringent, imposing

additional design objectives for power electronic systems.

Some

forms

of filtering are required

for

the input and out-

put(s)

lines of

equipmen t However, the optimum design a p

poach is to minimize E M at the source of emission. This

reduces the size and volume of the filter and reduces the

p a -

sibility EMI being radiated internally to other sen sitive com-

ponents m the equipment.

When an induction motor is con nected to a PWM IGBT

inverter through a cable, over-voltage is caused at its termi-

nals w i g lectric s t r e ss

on

nter-- insulation

of

motor

windings.

There are a lso parasitic currents referred as cam -

mon mode (CM) and differential mode OM) currents flow-

ing through the parasitic capacitances of the inverter, cable

and m ot a. These high frequency currents create EMI prob-

lems in

the

system.

The frequency range o f interest for con-

ducted E M

n

power electronics

is

usually from IO KHz to

IO

MHZ

[Z].

The over-voltage phenomenon ha s destructive effectsupon

both cable and machine insulation system due the energy

. contained in the transient overshoot caused by voltage wave

reflection

at

the electric machine

terminals.

This phenomenon

is also directly related with the conducted EM . There exists a

close relationship hetween the over-voltage phenomenon and

the E M problem through the rise and

fall

times of the volt-

age pulses generated by the PWM Inverter. For voltage

.

.

pulses with short rise times the voltage at motor terminal and

the magnitude of the CM nd DM currents will increase and

for voltage pulses with large rise time the voltage at motor

terminal and the magnitude of the CM and DM urrents will

decrease [3]. The overvoltage mitigations techniques change

the rise and fall times of the incident pulses to cable or motor.

It is important that the EMI and over voltage characteris-

tics of the system must be analyzed and predicted in the d e

sign stage. The simulation model of the system taking into

account the noise cw en t paths would

he

useful

for imple

menting E M mitigation circuits in system design.

In this work, a PSpice model of an electrical drive system

that allows prediction of over voltage at the terminal of the

motor and conducted EMI in presence of long feeders is d e

vel& The m odel is used to study the effect

of

over-

voltage mitigation techniques upon conducted emissions.

11.

DEVELOPMENTOF SYSTEM

MODELXNP-SPICE

A. HFPWMInvener Model

For an accurate EMC model of the inverter it is necessary

to take into a w u n t the

HF

parasitic paths. Fig. 1shows he

HF quivalent circuit for one leg o fth e inverter [4].

~~~

( . c .

-

Fig 1

Fig. 1

Inverter

model for

EM1

studies

The most important parasitic paths of this circuit are: the

parasitic inductance

of

the emitter

Le

and the internal para-

sitic capacitances of the IGBT. The value of L s taken from

d a ic e datasheet and parasitic capacitances of IGBT are in-

cluded in the IGBT P-spice model. Stray inductances of the

connecting wires (I.,) have very small values and affect prin-

cipally the differential conducted emissions. For this study

0-7803-78l7-~3I l7 .~

ZW3

EEE 468


2/7

this inductance has been neglected because the P W M nverter

is enclosed in a package and the length of the conn ecting wire

is very small. The Stray capacitanceC, between the collector

and grounded heatsink is measured mth an impedance ana-

lyzer.

In

the

HF

range the equivalent circuit of the

DC

ink

ca-

pacitor consists of the series combina tion of capacitance , re-

sistance and inductance, as sh o w in fig.2

Ls

Rs

C s

- : -

Ca- bd-

FO

.

F .

2 . G

Fig.

2

High

kquency model ofDC

link capacitor

When the frequency ncreases the impedance of the capaci-

tor

decreases linearly at rate of -2OdEVdecade. Tb e im pedance

of the indu ctor increase until it

equals

that of the capacitor at

the point of resonance. At

t h i s

point the impedance

is %.

For

higher frequencies the impedance of the inductor increases at

rate

of

+20dB/decade. The im pedance of the DC link capaci-

tor bas a strong effect upon the d ifferential conducted

emis-

sions [4].

The parameters

of

the inverter used are given in append ix

B.

H

Cable m o d 1

The

transient phenomena of cables have been explained

in

detail using transmission

lie

theory

[ 5 ]

and different cable

model configurations used in studies of vo ltage reflection are

presented in

[a] In

P-spice program

although

there are circuit

simulation elements for transmission

lines,

the options

are

limited for multi-conductor cables. For o b t a i i g an ads

quate model of the cable for high fiq ue nc y studies software

Maxwell 2D xtractor is used.

The Maxwell 2D extractor

uses

finite element method to

compute the circuit parameter matrices such as inductance

and capacitance for any arbitrary multi-conductor transmis-

sion line. These circuit parameters depend upon the geometry

of the structure and the characteristics of the materials that

make up the s fmchue. Once computed, tbese circu it parame-

ters c nbe transformed into a P-spice s sub circuit forming the

lumned

A

reoresentation of the cable. In order

to

model aw

experimentally determined values closely agree with the cal-

culated values as

shown

in the same figure.

Fig. 3

Cable

on ode

impedance

C. Induclion

Motor model

A

motor model

as

s h o w in fig.4 suitable

for

low and bigh

frequencies is used

[SI.

The model is based

on

the expeainten-

tal observation of frequency

response

and an approximation

of the distributedHFmotor model presented in

[9]

wfiere

it

is

possible to identify three dominant capacitancesC,

Ci,

C, t

high teqnencies.

l l

Limp

m

odel

Fig.

4 Induaimmotor

model for

wide frequency

range

In above C

q i

and %representing phase

or

neutral

to

ground capacitance, phase

to

phase capacitance, phase to neu-

tral capacitance and eddy

loss resistor

are effective

at high

frequencies. Series impedance elements c onsisting of %, L

and C, are associated with phase to ground and neutral to

ground

currentpaths

at medium frequencies.

propriately the cable in a wide frequency range

64

umped

sections have been used [7]. Fig 3shows the variation of

common mode impedance with frequ ency as calcu lated for a

six meter SJ 4-14

AWG

cable using 64 lumped sections. The

The advantages of this model are that the parameters can

be determined by frequencyresponse tests and

the

model can

be used

for

over voltage and condu cted

EMI

studies. This can

be implemented in P-spice or Saber for analysis of inverter

fed induction motor drive systems.

469


3/7

I ll. S W AT IO N F OVR-VOLTAGE AND

E M

ble twe

SJ-4

14

AWG.

a 1/3 HP

three

Dhase 208

V

induc-

tion -motor and LISN' was modeled

;or low

and high

points ofmeasurements

are

indicated in

figure

,

effectivenessOf

the

n predicting over-voltages f i q e n c Y

studies,

Typical results =e given below, The

at motor terminals and conducted EMI in the system has been

verified

through

experimental results. An induction motor

Drive

system consisting

of

a

three

phase

PWM

inverter,

Ca-

Fig. 5 Complete Dri

Figure 6shows the simulated and experimental voltage

pulses at the inverter and motor erminals when the lengtb

of he cable connecting he inverter and motor s sixmeters

and the

rise

time

of

the inverter voltage pulse is 110 ns.

I*' _ ..,

BXP*ri .(

. ,

I

..

'*

-.&


4/7

VI

OVERVOLTAGEITIGATION ECHNIQUES

Conventional

Ourput

Filter

A

low-pass filter to reduce the d dd t

of

the inverter volt-

form

s passed

viaually

unchanged except

for

the delayed

rise and fall limes [IO]. Fig.

9

shows the inverter

output

il-

The developed models are

used

to analyze the effect of

over-vo ltage mitigation techniqu es such a s Inverter output

filter, motor terminal filter and dv/dt control upon con-

ducted emissions,

To

compare the effectiveness

of

these

age pulses is used at the inverter output The p m ave

...

a

strategies and their effect upon conducted emissions the

same induction motor drive system is studied with the in-

corporation of different types of filters

Fig.

9

Drive

System

Wim

Inverter

Output Filter

Figure.10 shows the line to line voltage at the inverter

and at motor terminals without and with filta. The rise

time of the inc ident pulse is 11Ons.

A

filter

has

been de-

signed to reduce the over-voltage at th e terminals of the

motor to

10%

of overshoot

and

increasing the rise tim e of

the incident pulses ffom 1 Ons to 32Ons. Although the fil-

ter reduces the overvoltage at motor terminals, there is no

significant reduction

in

the conducted

EMI

emissions up to

4 M H z as shown

in

Fig. 11;this is

because

the magnilude

of the ulmmon mode voltage is still the same.

Sf

m

u

a

Fig

-


5/7

Ill

Fig. 12 .r)rve system

with

modified invertet output

filter

...... ...... _i..... . in-&..................

.........

i

.....

. . . .

. . .

. . . .

. . .

. . . . .

\ . . . . .

....

...

.... ....

;.

....

..

.... i

....

i , : : I

1 ; : i $ i j

Fig.

13

Voltage at motm terminsls aud

EMI

conducted emis-

I

Y

*

a

*

2 1 1

a

e

W.

sions

using modified inverter output filter

RC

tennination

Filter

The motor terminal over-voltage

can he

educed with a

first order resistor-capacitor filter that is connected in par-

allel with the motor taminals [IO]. With

a

designed filter

the ova sho d pacentage is 14%. The total EMI emission

does

not change appreciably compared to a

system

without

filter. Fig. 14

shows

the voltage at the inverter, motor ter-

minal and the spectrum obtained througb simulation up to

5.2 MHz

.................

......... .....,..

...................

D

.- .

. . . .

_ __

.....

_

.....

......

....

2

Fig. 14.Voltage

at motor

terminals and

EMI

onducted emir

.2S6

P_

......

si using

RC

en&ation

DV/DT Control

In d d d t control the output voltage rate

can be

con-

trolled by adding pby%ically a small capacitor between the

IGBT gate to collector to increase the Miller capacitance

[12]. The inverter voltage rise tim e

cbanges d e n

capaci-

tor of

0.15

nF is placedbetween he gate and collector. The

inverter voltage rise time without dvldt control is 1Ions

whereas with dv/dt

control

it increases o

524ns.

The over-

shoot at motor tamina ls with a rise time of 52411s s

6%.

Fig.

15 shows

the voltage a t inverter terminals, at motor

terminals and

EMI

conducted emissions.

A

decrease

of

10

dBuV

in the total EMI emission s is

obtained.

412


6/7

V.

ONCLUSION

The use of RLC low pass inverter output filtes is al-

though effective to mitigate the over voltage at motor ter-

minals,

it does not have an appreciable effect in the

reduction of the total E M emissions. More reduction of

the total E M emission s is possible by inc reasing the value

of th e filter capacitor but thiswould increase the losses in

the filter.

Modified low pass RLC output filter represen ts an alter-

native to contro l effectively both the ov er voltage and

EMI

emission s without increasing significantly filter

losses.

A

reduction

of

both ovenoltage and EMI conducted muis-

sions is obtained.

The RC filter at motor term inals is a sim ple solution for

the ov er voltage control but it is an expensive solution due

to the high power losses in the filter and this technique

does not reduce the E M emissions.

Control with a capacitor placed between the collector

and gate of the IGBT educes the over voltage at motor

termina ls due to the decreased dv/dt of the inverter output

pulses. It is also effective in reducing conducted EMI

emissions.

The over voltage reduction techniques based upon low

pass filters have disadvantages such as the power

losses

in

the damping resistors of the filters, the lags introduced by

the filters and the sue of the filters in increasing the vol-

ume of the final product

Phase

Volts

Hcrtz

Input

ACKNOWLEDGEMENT

This work was supported primarily by the ERC

Program

of the National Science Foundation under Award EEC-

9131617.

APPENDIX

TABLE I

HIGH AND

MEDIUMFEQX

PNUMEIERS

FOR

%w OTOR

1

3

208i230

5otf.o

I

TABLE U

LOW FFSQuurcYP RI\METuIsFOn% Hp

MOTOR

I = 13.5 R L 4 . 4 2 0 6 H

L

.61R

Frenucncy-

60Hz

Lq-=L1-=20.95E-3H

J ~

= 0 . 0 0 1 5 1 5 k ~ z

TABLE m

PWM GBT INVERTERPUUMRERS

REFERENCES

[ ] Ron, .: Gokani. S. Clare,J : B r d e y ,U : hrirtopoulos. C.

Con-

ducted

demomagnetic

cmisdons in indudon motor drive systems

I. Time domain analysis and idmtificationof +mimrd moden Power

Electronicn,IEEETmnaaionr on, Volume: 13 Issue:

4

uly 1998

Pa ):

757 -767.

[Z]

Grmdi. G :

Corode,

D.;

Reggiani.

U: A

w&sb

o

c o n - md

d@erent iol-moL

HF m t componenD

in P W M nverier+d AC

molars PESC 98 Record 29th Annual

BEE, Voh :

2 17-22

Moy

1998 Pa&): 1146- 1151 wlZ

[3]

Skibinski.

G.L:

Kerbnon.RJ.; chlepzl,

D EM

embsbw

ofmod-

em

PWMAC driwr BEE bdusny Applicanbns Volume.. Imua: 6

NoWDec

1999 Pn ge(s): 47 -80

473


7/7

[4]

Grandi

1.

Man mari, U.

Rcggiani:

Effccts of

ow= cowma

para-

d t i o m-nats m

mnducted

EMI, Msnational zurish

Sympo-

sium

onEMC, zurich(CH),

18-20F e b m q 1997.

[SIChen,S. Qrmstionand

qpressim

ofmnduncd

EMI from

inverts-

fed m m rives Inhsmy Applications

Conference,

1999.

biny-

Founh

I AS nnualMeeting. Confsrsnce Record of hc 1999

lEEE,

Volume: 3, 1999Pa ): 1583 -1589 01.3.

[SI S.R

SCshadri

Fmbcmal of

Transmission line and clectmmag-

=tctc fields. Addisan weslcy

[6] kibinski, G ;

firbum,

R.;

L g p l e ,

D.: P m h . .;

Schlegel,

D. e-

flected

wave

modeling

techniques fm P W

C m n m

driver

A p

ptied Pow= ElectronicsConfeence

and Expositios

1998.

APEC

98

C c e

Raaedhgs 1998..Thirrcslth

bud Volume:

2,1998

Pap< :

IO21 -1029~1.2

[7]

Yong Tang;

Hcng a n ; &ag Wmg; Fongrao

Doi;

Shvmg Jiong.

T i a t i o n l i n

models

used

in mvdling

wave

audies

Tmsmis-

sion and

D i m i t i o n

Confcrmce, 1999 I EEE Volume: 2 1999

high frequency modeling of induction motor drives for

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