8/7/2019 Starting of WRIM Using Choper

1/6

STARTING CONTROL OF WOUND-ROTOR INDUCTION MOTORSBY USING CHOPPER-CONTROLLED RESISTANCE IN ROTOR CIRCUIT* * **Chin S. Moo*, Chung C. Wei , Ching L. Huang , and Chao S. Chen* : Institute of Electrical Engineering** : Institute of Electrical Engineering

National Cheng Kung University, Taiwan, R.O.C.

National Sun Yat-Sen University, Taiwan, R.O.C.

Abst rac tThe s ta r t in g t ran s ie n t pe rfo rmance o f wound- ro to rknduction motors can be improved by using chopper-c o n t r o l l e d r e s i s t a n c e i n t h e r ot o r c i r c u i t . I n t h i spaper , th e t r a ns i en t behav iors o f induc t ion motorscon t ro l led by the p roposed scheme a re inve s t ig a ted . Tocont ro l th e s t a r t i ng per fo rmance o f th e wound- ro t o rinduc t ion motor under se vera l load co ndi t io ns andsystem requirements, maximum torque operation andl i m i t e d - c u r r e n t o p e r a t i o n a r e d i s c u s s e d . T he t r a n s i e n tcur r en t , speed , and to rqu e o f th e induc t ion motorshave been solved by computer s imulat ion, and verif ica-t io n o f these numer ica l s tud ies are a l so p rov ided f romexperimental tes ts .

I. INTRODUCl'IONDuring the s ta r t -u p o f induc t ion motors , ve ry l a rgec u r r e n t i s drawn. Hence, vo ltag e dip s and harmonicsar e introduc ed in t he power system. Moreover, t he highmechanical stress, which i s r e s u l t e d f r o m s t a r t i n gi n r u sh c u r r e n t , may c a u s e t h e f a i l u r e s o r r e d u c e t h el i f e - time of induc t ion motors . There fore , t he in rus hc u r r e n t s h o ul d b e c o n s t r a i n e d t o a c e r t a i n v a lu e l i m i -te d by th e power system. Up t o now, many methods haveb ee n pr o po s ed t o c o n t r o l t h e s t a r t i n g i n r u s h c u r r e n tof t he machine [I]- [5]. Among va rio us tec hniq ues , t h emethod of ro to r res i s tan ce con t ro l has been wide lyused f o r th e medium and la rg e wound-rotor ind uctionmotors , e spe c ia l l y when h igh s ta r t in g to rque is re-q u ir e d o r l on g s t a r t i n g p e r i o d s are encountered. It isf ou nd t h a t e x c e l l e n t s t a r t i n g p e rf or m an c e is obta inedby c o n t r o l l i n g t h e r o t o r r e s i s t a n c e p r o p e r l y. B e s i d es ,ad ju s tab le speed opera t io n can a l so be p rov ided by

this method.Convent iona l ly , ro to r res i s tance con t ro l scheme isachieved by connecting a set o f t h r e e - p h a s e r e s i s t o rt o t h e r o t o r c i r c u i t v i a s l i p ri n g s t o i n cr e as e t h er o t o r r e s i s t a n c e so t h a t t h e i n r u s h c u r r e n t is reducedan d t h e s t a r t i n g t o r q u e i s i n c r e a s e d d u r i n g t h es t a r t i n g p e r i od [5]. T h e r e s i s t o r i s des igned t o matcht h e l o a d c o n d i t i o n s i n t h e e n t i r e r u n- u p p er i o d .D urin t h i s p e ri o d, t h e r e s i s t o r s are s h o r t - c i r c u i t e ds tep $y s t ep to pe rmi t t he motor to come up t o th eo p e r a ti n g s p ee d u nd e r t h e c o n t r a i n t of t h e c u r r e n tl imi ta t ion and to rque requ i rement .Yith the advance in power semiconductor technology,th e rotor res is t an ce c on tro l scheme can be improved bys o l i d - state method. A t h r e e -p h a s e r e c t i f i e r b r id g e a nda chopper c i rcu i t are i n s e r t e d b et we en s l i p r i n g s o fth e induc t ion motor and th e ex te rna l r e s i s t o r as showni n Pig. 1 [6]- [8]. T h e e f f e c t i v e r o t o r r e s i s t a n c e c a nbe con t inuously con t ro l l ed by ad jus t ing t he du ty cyc leof the chopper c i r cu i t . As compared with the conven-t i o n a l c o n t r o l sc he me , t h e s o l i d - state method canoperate the machine more smoothly and may be easilymodif ied t o match the pa ramete r va r ia t io ns o f motorsand the changes of l o a d c o n d i t i o n s .

3-phase

I aooed-' ~ 9Fontrol1 t-1Fig . 1 Schemat ic d iagram of ro to r res i s tance con t ro lby solid- state method11. VARYING ROTOR PESISTANCE OF I N D U C T I O N MOTORSTheor e t ica l l y , wound- ro to r induc t ion motors can beopera ted wi th l imi ted - cur r en t o r h i g h e r s t a r t i n gt o r q u e by s e l e c t i n g a n a p p r o p r i a t e v a l u e of t h e r o t o rr e s i s t a n c e . As t h e r o t o r s p e ed s up , t h e e x t e r n a l re-s i s t a n c e i s decreased accord ing ly t o match th e oper -

a t ing requ i rements .The chopper in Pig . 1 is a power switching deviceopera ted as a r o t o r r e s i s t a n c e c o n t r o l l e r . By re gu -l a t i n g t h e d ut y c y c l e of t h e c h o pp e r , it i s p o s s i b l et o o b t a i n a n e q u i va l e n t r e s i s t a n c e of a value betweenz e r o a n d t h e e x t e r n a l r e s i s t a n c e . The du ty cyc le o fthe chopper is def ined as:

where T(on) i s t h e time i n t e r v a l o f t h e "o n" state,and T(ch) i s the the chopping per iod o f the chopper .The equ iva len t r es i s tance of t h e c h o p p e r c o n t r o l l e dr e s i s t o r is obta ined as [6]:Be q= (1- ) Re x (2 )B e c a u s e t h e c u r r e n t d i s t o r t i o n i s in t roduced by the

o p e r a t i o n o f t h e c ho p pe r a nd t h e r e c t i f i e r , it is veryd i f f i c u l t t o d e v el o p an e x a c t m o de l of i n d u c ti o nmotors with sol id- s t a t e c o n t r o l l e r . I n t h i s p a pe r, t h es impl i f i ed equ iva len t c i rcu i t mode l deve loped by Sen[6], [ as shown i n Fig . 2, is u se d t o p r e d i c t t h eo p e r a ti n g c h a r a c t e r i s t i c s o f t h e i n d u c t i o n m ot or s w it ha chopper con t ro l led res i s to r . Based on t h i s c i r c ui t ,a s a t i s f a c t o r y s i m u l a t i o n an d c o n t r o l o f t h e i n d u c t io nmotors can be made.

Pig. 2 Equiva len t c i r cu i t o f the induc t ion motor wi thc ho pp er - c o n t r o l l e d r e s i s t a n c e i n r o t o r c i r c u i tF igure 3 shows the cu rren t waveforms of th e rot or

c i r c u i t d u r in g t h e s t a r t i n g t r a n s i e n t p e ri o d. Ther o t o r c u r r e n t is assumed t o be s in uso i da l and th er e c t i f i e d c u rr e nt i s represen ted as:id(ut)=,@sin(ut)i d ( u t +n r / 3 ) = i d ( u t ) n=1,2,3;,

r/3 S u t S 2 r / 3and89CH2792-0/89/0000-2295$01.W 989 IEEE

8/7/2019 Starting of WRIM Using Choper

2/6

8/7/2019 Starting of WRIM Using Choper

3/6

2 C o r e s a t u r a t i o n i s n e g l e c t e d .31 Parameters of the machine remain constant through-4) Forward vo l tage d rops of the b r idge r ec t i f i e r and

Based on t h e s e a s s u m p t i o n s , t h e t r a n s i e n t p e r f o r -mance of induction motors is descr ibed by t h e f o l -lowing th ree equa t ions :1) Voltage equation

o u t the p rocess o f compute r s imula t ion .c h o p p e r t h y r i s t o r a r e n e g l e c t e d . ModeConductionDiodes

where p i s t h e d i f f e r e n t i a l o p e r t a t o r a nd[e ]=[esa esb eSc & a e r b e r c l[R]=diag[R~ R I R I R2+Req R2 +Re q R 2+ R e q][ i ]= [ i sas b i s c i r a i r b i r c ]

T

T

1 2 3 4 5 6 7 8 9 1 0 1 1 1 2D 1 D 1 D2 D2 D3 D3 D4 D4 D5 D5 D6 D6D2 D2 D3 D3 D4 D4 D5 D5 D6 D6 D1 D 1D3 D4 D5 D6 D 1 D2

P I =

Ls s , L , , L r r , L r n are th e s e l f and mutua l induc tancesof s t a t o r and ro to r phase wind ings respec t ive ly ; Ysris the mutual inductance between the s t a t o r a n d r o t o rphase windings when their magnetic axes are coinci-den t .

3) Mechanical motion equation

The numerical solut ions of these nonlinear equationscan be solved w i t h dig i ta l compute r [9 ] - [ l l ] . I n addi-t i on t o the commonly used simulat io n proce ss, the COPmutation st at us es of th e bridge diodes should be de-termined. For an idea l bz id e r e c t i f i e r , t h e r o t o rc i r c u i t w i l l be operated wit! only two phases. How-ever , th e commutat ion over laps o f the r ec t i f i e r b r idgeare in t roduced by the l eaka e reac tances o f the motor.Durin the commutation overfap periods th e r o t o r c u r -rent !lows i n a l l t h r e e p h a se s . T h e r e j o r e, the br idger e c t i f i e r w i l l . o t a l l y h a v e 1 2 p o s s i b l e c o n d uc t in gmodes as shown i n Table 1 [12]. The odd numbered modescorrespond to the n or ma l r e c t i f y i n g o p e r a t i o n s , w h i leeven ones correspond t o th e commutation ove rlap sbetween two odd numbered modes. The op er at in g seque ncew i l l b e e i t h e r i n os i t i ve sequence (1 ,2 ,3 ...) or i nnegative sequence [1,12,11.. .) . Figure 4 i l l u s t r a t e sthe c o r r e s p o n d i n g r o t o r e q u i v a l e n t c i r G u i t s f o r s u c -cessive operat ing modes 1, 2, and 3.

Mods.rc Lde

D2Re x

Mod-. 2Ld

I

Mode.3Fig . 4 Rotor c i rc u i t s fo r opera t ion Modes 1, 2, and 3Since the rot or c ir cu it of th e motor may be operatedw i t h ei th er two- phase conducting mode or th ree - phaseconducting mode, it i s necessary t o i d e n t i f y t h e in -st an ts when the chan e of op er at io n mode occurr ed. Thecommutation overlap %egins whenever the r ot or vol tag eof the non-conducting phase is g r e a t e r t h an t h a t ofthe conducting phase. A t this i n s t a n t , t h e o p e r a t i o nmode changes from twophase cond uctin g mode t o t hr ee -phase con ducti ng mode. The commutation ov er lap isaccomplished when one of th e thr ee ro tor cur ren ts isdecreased t o zero, and the operat ion mode changes fromthree- phase conducting mode t o t he suc ess ive two- phaseconducting mode.

V I . RESULTS OF COWPUTBP SIXULATIONSAND BXPEPIIENTAL TESTS

A 3-hp(motor A) and a 500-hp(motor B) induc t ionmotors a re se lec ted fo r compute r s imula t ion . The par-ameters of these two motors are shown i n Appendix.When the motors a re d i re c t ly s t a r te d wi th r a t e d l i n evo l tage , the ins tan taneous cur ren t s can reach soret ha n 6 t i m es t h e r a t e d c u r r e n t as shown i n Figs . 5 (a )and 6(a) . By maximum torque star t ing operat ion asi l l u s t r a t e d i n Figs. 5 b) and 6(b) , th e motors w i l l beaccelerated up much $a s t e r t h a n t h e m o to r w i th o u tcon t ro l , and the in rush cur re n t s can be reduced t o ava lue of abou t 4 times the ra ted cur ren t . There fore ,t h e d u r a t i o n an d ma n i t u d e of t h e t r a n s i e n t c u r r e n tc a n e f f e c t i v e l y b e a l l e v i a t e d . T h i s advantage is mores i g n i f i c a n t f o r t h e l a r e motor. Figures 7 an d 8 showthe comparisons of spe ef and torque fo r motors A and Brespec t ive ly . Moreover , because an ex te rna l r es i s ta nc ei s added t o the r o t o r c i r c u i t , t h e p o w e r f a c t o r c a na l s o be improved dur ing the s ta r t -u p per iod s as showni n Fig. 9.

2297

8/7/2019 Starting of WRIM Using Choper

4/6

Stator current (pu) Speed(pu11.2 I I0.8

0.4

0.0

-6 ' 10 0.8 I .6 2.4 3.2(a ) T ime (sec)

Stator current (pul1

30-3-6 ' 10 0.8 1.6 2.4 3.2

(b ) T 1m (secPig. 5 S t a r t i n g t r a n s i en t c u r r e n t of motor AtT,=lpu, J=O .1 Kg m2)a) without co nt ro l (b)maximum torque opera t ionS t a t o r current (pu)

w - - - --8 10 1 o 2.0 3.0 4.0(a) Timelsec)

Stator current (pu)

-6' I0 1 .o 2.0 3.0 4.0(bl TI ne (sec1Fig. 6 S t a r t i n g t r a n s i e n t c u r r e nt of motor Ea) without con trol (b)maxintum torqu e opera t ionT,=O, J=lOKg.mz)

0 0.8 1. 6 2.4 3.2(fd Time(sec1

Torque(pu)1

Torque Operatlon30 thout Control

-3 J 11 .o 0.6 0.2 -0.2(b) s1ip

Pig. 7 Comparisons of the t r ans ien t pe r fo rmance ofmotor A between maximum torque operation andd i r e c t s t a r t i n o p e r a t i o n ( a )s p e ed ( b )t o r q u e(T,=lpu, J=O.lfg-m2)Speed(pu1

0 0.8 1.8 2.4 3.2(a ) Tlme(sec)

Torque(pu)J4 MaxImum Torque Operatlon

0-4 J I1 .o 0.6 0.2 -0.2(b ) s1Ip

Pig. 8 Comparisons of t h e t r a n s i e n t p e rf o rm a nc e o fmotor B between maximum torque operation andd i r e c t s t a r t i n g op e r a t io n ( a ) s p e e d ( b )t o r q u e(T,=O, J=lOKg m2)On the other hand, when the motor is dr iven wi thl i m i t e d- c u r r e n t o p e r a t i o n , t h e s t a t o r c u r r e n t c a n bel imi ted wi th in a pre-determined value. P i u r e 10 i l l u s t r a t e s t h e c u r r e n t and torque waveforms o f motorA s t a r t e d by l i m i t e d - c u r r e n t o p e r a t i o n . F igure 11

shows the waveforms of the current and torque of t h esame motor wi th the conven t iona l ex te rna l ro to r resis-t a n c e c o n t r o l . T h e s t a t o r c u r r e n t is constrained belowt h r e e t i m e s t h e r a t e d c u r r e n t f o r bo th cases . It isfound that the waveforms of the cur ren t and to rquew i t h t h e s o l i d - s t a t e c o n t r o l l e r are much smoother thanthose of th e conventional scheme.2298

8/7/2019 Starting of WRIM Using Choper

5/6

Power Factor1 .0 1 I

0.0 1.0 0. 8 0.6 0.4 0. 2 0. 0SI i p

Fig. 9 Comparison of the power factor between maximumt o rq u e o p e r a t i on a nd d i r e c t s t a r t i n g o p e r a t i o nStator current (pu) 120-2-4 J 10 0.4 0. 8 1.2 1.6

(a) T i me (sec )Rotor current (pu)

I

-4 J 10 0.4 0.8 1.2 1.6(b ) T i me (sec)

Toque (pu)I

-2 10 0.4 0.8 1.2 1.6(C) T ime (sec)

Fig. 10 Trans ient performance of motor A with l imi ted-cur re n t o pera t ion by so l i d - s t a te method(T,=O , =O. Kgem2, I, 1 i 1 = 3 p ~ )T o v e r i f y t h e s i m u l a t i o n r e s u l t s , e x p e r i m e n t a l t e s t sare made on the motor A . Figure 12 shows the waveformsof t h e s t a t o r a nd r o t o r c u r r e n t s f o r t h e o p e r a t i o nwi thou t con t ro l , whi le F igs . 13 and 14 show the wave-forms of t he s t a to r and rot or c urr ent s with maximumtorque op era t ion and l imi ted- cur ren t o pera t io n res-pe ct iv ely . Comparing th e waveforms of Fig. 13 witht h o s e of Fig . 12 , th e run-up time and cur ren t of t h emotor with maximum torque operation are obvious lysmal le r than those o f t he motor wi thou t con t r o l .Figure 14 i l l u s t r a t e s t h a t s a t i s f a c t o r y results areo b t ai n e d by e x p e r i m e n ta l t e s t s f o r t h e i n d u c ti o n m o to r

w i th l i m i t e d - c u r r e n t o p e r a t i o n . B ec au se t h e a d d i t i o n a ll o s s i s introduced by the "on" s ta te r e s i s t a n c e o f t h er e c t i f i e r d i o d es a nd c ho pp er t h y r i s t o r , t h e s h o r t c i r -cu i t ope ra t ion by th e mechan ica l con tac t s i s recom-mended when the motor i s opera ted i n s t e a d y s t a t e .Stator current (pu)4 1 i20

-2-4 J I0 0.4 0.8 1.2 1.6

(a) T i me (sec )Rotor current (pu)4 1 1

-4 J I0 0.4 0. 8 1.2 1.6(bl Time hec )

Torque (pu)

-2 10 0.4 0.e 1.2 1.6(C ) Time (sec1

Fig. 11 Tra nsi ent performance of motor A with l imi ted-cur ren t ope ra t ion by conven t iona l c on t r o l method(T,=O, J=O.lKg.mz, 1, l i r n ) = 3 p u )

- -I L I0 . 0 5.0Time ( s e c )

Fig . 12 Trans ien t cur ren t waveforms wi thou t con t ro l(T,=O , J=O. Kg.rn2)2299

8/7/2019 Starting of WRIM Using Choper

6/6

I0.0 a 5. 0

-."I I3

I-W O

---0

aU

0

L - 1 10 . 0 a 5 .0Time (sec)

Fig. 13 Tra nsie nt curren t waveforms by ma x im um t o r q u eo pe ra t on (T,=O, J=O. 1KgSm2)

v ) W0. 0 a .O

0.0 5.0T i m (sec)Fig . 14 Transient current waveforms by l imited-c u r r e n t o p e r a t i o n(T,=O, J=O. Kgmm2, 11 1 i m ) =3PU)

VII. CONCLUSIONSI n t h i s p a p e r , t h e s t a r t i n g t r a n s i e n t ph en om en a ofthre e- phase wound- ro to r inducti on niotors w ith re ct i-f i e r c ho pp er c o n t r o l is presented. By properlyc o n t r o l l i n t h e d u ty c y c l e o f t h e c ho p pe r t o a d j u s tt h e e q u i va q e nt r o t o r r e s i s t a n c e , h i g h e r o u t p u t t o r q u ewi th lower s ta r t in g cur ren t can be ob ta ined . Prom t h eresults of computer s imulat ion and experimental tests,fo l lowing conc lus ions are summarized:1) By maximum torque operat ion, the avera e accelera-t i n g t o rq u e i s approx imate ly equa l to t f e breakdowntorque o f t he induc t ion motor f rom zero speed t othe speed at which th e chopper c i rc u i t is f u l l y. Moreover, t he problem of lar ge inr ush cu rren tion"c an a l s o b e a l l e v i a t e d .2) B ec au se t h e d i f f e r e n c e b e tw ee n t h e s t a r t i n g t o r q u eand breakdown torque is l a r g e r t h a n t h a t o f smallmotors, the start- up of l a rge in duc t io n motors canbe improved more si gn if ic an tl y by maximum to rq ueopera t on .

3 ) By l i m i t e d c u r r e n t o p e r a t io n , t h e in r u s h c u r r e n t i scons t ra ined to a c e r t a i n l e v e l s m o o t h l y d u r i n g t h es t a r t i n g p e r i od .4) The power factor of the induc t ion motors can beimproved by ei th e r maximum tor qu e op era tio n o rl i m i te d - c u r r e nt o p e r a ti o n d u ri n g t h e s t a r t i n gper iod .Appendix: Machines parametersHotor A : 3-Ep, 4-pole, 3-phase, 220V. 60Hz

R I Rz X i 1 2 X m0.605 0.795 1.13 1.13 23.37 (fl)

Hotor B : 500-Bp, 4-pole, 3-phase, 2300V, 60HzR I R 2 X i X Z X m

0.262 0.187 1.206 1.206 54.0 2 (fl)References

P . J . Col le ran and Y. E . Rogers, "Control ledS t a r t i n g of AC Induction Motors," I EEE Trans . ,In d. Appl., Vol. IA-19, pp.1014-1018, Nov./Dec.1983.A . 0. Staub and E. L . Owen, "Solid-State MotorC o n t r o l l e r s 'I I E EE Trans. , Ind. Appl. , Vol.IA-22, pp. 1113-1120, Nov./Dec. 1986.R. L . Hyde and T . R. B r i n n e r , " S t a r t i n gC h a r a s i e r i s t i c s o f E l e c t r i c S u bm e rg ib le O i l YellPumps,pp.133-144, Jan./Feb. 1986.P . J. Lawrenson and J. Y . Stephenson, "Note onInduction Machine Performance with A Var iab le -Frequency Supply," Proc. IEE, Vol. 113, NO . 10,Oct. 1966.R. V. Smeaton, Motor Application and llainteanceHandbook," Hcgraw- R i l l , 1986.P . C. Sen and K . E. J . Ma, "Rotor Chopper f o rInduction Motor Drive: TRC S t r a t e g y , " I E EETrans., Ind. Appl., Vol. IA-11, pp.43-49,Jan./Feb. 1975.P . C. Sen and K. E. J . Ma "Constant TorqueOperat ion of Ind uction Motors Usin Chopper inRotor Ci rcu i t ," I E EE T r a n s . , I n d . f p p l . ,Vol. IA-14, pp.408-414, Sep./Oct. 1978.S. A. Hahmoud, A. E . Lashin and S. A . Hassan,"Torque/Speed of Yound Rotor Induction MotorsUsing A DC Chopper Ci rcu it , " El ec tr ic Machine andPower System, Vol. 11, pp.25-39, 1986.P . C. Krause and C. E . Thomas, "Simulation ofSymmetrical Induction Machinery," I E EE T r a n s . ,Power App. Sy st ., Vol. 84, pp.1038-1053, 1965.A. K . Desarkar and C . J. Ber , " D i g i t a lSimulat ion of Three- Phase In8 uct ion Motors," I EEETrans. Power App. Syst., Vol. 89, pp.1031-1037,1970.S. T. Robertson and K.H. Eebbar, "A D i i ta1 Modelfo r Three- Phase In duc tio n Machines It I f E E Trans.Power App. Sy st ., Vol. 88, pp.1624-1632, 1969.J . E. Brown, B. L. Jones and P. Vas, "Analysis oft h e P e r i o d i c T r a n s ie n t S t a t e o f a S t a t i c KramerDrive," IE E Proc., Vol. 113, No. 1, Jan. 1986

I EEE Trans., Ind. Appl., Vol. IA-22,