Review of Improved Direct Torque Control Methodologies for Induction Motor Drives

Transcription

1 Rviw of Improvd Dirct Torqu Control Mthodologi for Induction Motor Driv P. R. Mankad * Dr. A. R. Chudaama School of Enginring, R. K. Univrity, Notch Intitut of Tchnology HJD Intitut-Kra Vadodara Abtract Dcoupld control of induction motor driv i poibl uing Dirct Torqu Control (DTC) mthod which i vry impl control tratgy compard to fild orintd control. In thi mthod dirct torqu control i achivd by lcting uitabl invrtr witching voltag vctor from a lookup tabl. But drawback of thi mthod i that it produc toqu rippl. Alo th witching frquncy of invrtr witch i not contant. Many mthod hav bn propod to addr th iu of DTC. Thi papr rviw variou mthodologi which ar uggtd to improv prformanc of baic DTC induction motor driv. Kyword DTC, DTCSVM, Induction motor driv, SVPWM I. INTRODUCTION Induction motor(im) ar workhor of th indutry. Ovr vnty prcntag of motor ud in indutry ar thr pha induction motor. Thy ar o popular bcau of impl contruction, robutn and maintnanc fr opration. Howvr, application whr motiv powr i rquird at variabl pd, DC motor wr th only altrnativ bfor a dcad or two.thy wr prfrrd bcau of a of control. Th raon for non lction of induction motor for variabl frquncy opration wa it complx control tructur. Dvlopmnt in fild of procor hav mad it poibl to implmnt advancd control tratgi for IM driv. Vctor control mthod i on of uch tratgi which control IM imilar to paratly xcitd DC motor [1]. Drawback of vctor control ar complx control chm and nitivity to paramtr variation [2].Attmpt wr mad to find a control chm which i l complx and giv good dynamic rpon for induction motor driv.dirct torqu control (DTC) i on of uch mthod which giv prformanc comparabl to vctor control with vry l complxity [3]. In claical DTC chm on voltag vctor i lctd out of ix activ and two zro voltag vctor gnratd by VSI. Th lction i don in uch a way that torqu and tator flux rmain within limit of two hytri band. Sytmatic application of thi tratgy rult into dcoupld control of IM without complx co-ordinat tranformation, currnt rgulator or PWM pul. Howvr, du to hytri band controllr for torqu and tator flux, rippl ar producd in torqu and tator currnt, alo witching frquncy i variabl.th problm ar mor riou at low pd with havy load [4]. Many mthod hav bn propod to addr th iu of convntional DTC chm. Thi papr rviw variou mthod uggtd to improv prformanc of claical DTC of IM driv. Mthod for prformanc improvmnt of claical DTC can b claifid in four catgori a: (1) DTC with modifid lookup tabl mthod (2) DTC with contant witching frquncy uing SVPWM (3) DTC with prdictiv control (4) DTC with nuro-fuzzy controllr [5-7]. Thi papr i organizd in th following ction. Sction II-claical DTC, ction III-problm with claical DTC, ction IV- DTC with modifid lookup tabl, ction V- DTC with SVPWM, ction-vi-dtc with fuzzy logic and ction VII- concluion. II. CLASSICAL DTC Th torqu dvlopd by induction motor i dirctly proportional to angl btwn tator flux vctor and rotor flux vctor a hown in following quation. Lm T = r in r (1) L L r Th rotor flux vctor alway follow tator flux vctor. By advancing th tator flux vctor in pha, angl incrad and o th torqu dvlopd incra. Similarly by rducing angl 2014, IJIRAE- All Right Rrvd Pag -393 r r can b, torqu can b rducd. In hort dirct torqu control i poibl jut by changing poition of tator flux vctor with rfrnc to rotor flux vctor. In claical DTC thi movmnt of tator flux i achivd by lction appropriat witching voltag vctor of VSI. Appropriat invrtr voltag pac vctor i lctd bad on tator flux rror and torqu rror uch that tator flux and torqu rmain within a hytri band. Fig.1 how ix activ and two non zro voltag pac vctor which ar poibl for two lvl VSI.

2 Figur 1Voltag pac vctor * * Complt block diagram of claical DTC chm i hown in Fig. 2, whr T and ar rfrnc torqu and rfrnc tator flux rpctivly. Torqu rror and tator flux rror ar procd by thr lvl and two lvl hytri band controllr to gnrat tatu ignal dt and d rpctivly. Bad on tatu of dt, d and ctor i, uitabl voltag witching pac vctor i lctd form lookup tabl to giv fat dynamic rpon and to maintain torqu rror and tator flux rror within hytri band. Tabl-I how th look-up tabl ud to gnrat witching voltag vctor of VSI. Figur 2 Block diagram of claical DTC chm Torqu, tator flux magnitud and th ctor in which tator flux vctor i placd at any intant can b timatd from tator voltag and tator currnt. Following quation ar ud to timat torqu, tator flux and ctor information. d q q =tan = (V R i ) dt (2) -1 d = (V R i ) dt (3) q 2 2 d q q d d q (4) (5) 3 P T diq qid (6) , IJIRAE- All Right Rrvd Pag -394

3 d 1-1 Tabl 1 Lookup tabl of DTC chm dt (1) (2) (3) (4) (5) (6) 1 V2 V3 V4 V5 V6 V2 0 V7 V0 V7 V0 V7 V0-1 V6 V1 V2 V3 V4 V5 1 V3 V4 V5 V6 V2 V1 0 V0 V7 V0 V7 V0 V7-1 V5 V6 V1 V2 V3 V4 Striking advantag of thi mthod i that it achiv dcoupld control of torqu and flux without complx coordinat tranformation or PWM ignal gnration. It only dpnd on tator ritanc hnc it i a robut control mthod. It giv dynamic rpon quit comparabl to vctor control but it ha om of th drawback which ar dicud in th following ction. III. PROBLEMS IN CLASSICAL DTC Torqu rippl ar producd bcau of u of hytri band controllr for torqu and flux. It alo rult into variabl witching frquncy. Alo a dicud in prviou ction, timation of tator flux i ndd for implmntation of claical DTC. Stator flux timation can b don uing voltag modl timation or currnt modl timation [8]. Currnt modl timation rquir pd nor and hnc gnrally not ud. Voltag modl timation u pur intgration which cau problm at low pd and caud flux drooping[9].alo at low pd, th tator ritanc drop can no longr b ignord, o a boot in tator flux i rquird. Now whn tator flux vctor chang th ctor, thr i no activ voltag vctor which guarant th incra in tator flux. A a rult thr i flux drop at om intanc. Thu at low pd and havy load locu of tator flux vctor cannot rmain circl and bcom mor lik hxagon, which cau harmonic in tator currnt. Rviw of variou mthod uggtd to addr th problm i includd in th following ction. IV. IMPROVED DTC WITH MODIFIED LOOKUP TABLE Modification in lookup tabl ar mainly aimd at rducing torqu rippl. Som of th mthodologi ar for low pd rang alo. A. Rduction of torqu rippl by incraing numbr of witching voltag vctor Thi mthod i alo known a dicrt pac vctor modulation(dsvm) [10]. Block diagram of th am i hown in Fig.3. Figur 3 Block diagram of Dicrt SVM-DTC 2014, IJIRAE- All Right Rrvd Pag -395

4 Hr convntional thr lvl hytri band controllr for torqu i rplacd by fiv lvl hytri comparator. Suitabl witching voltag vctor i lctd bad on tatu of torqu and flux controllr, valu of tator flux and th information about th ctor of tator flux vctor. Intad of allowing hytri band to chang witching voltag vctor, a ampling priod i ud which i dividd into $n$ part. Suitabl witching voltag vctor i lctd for ach part. Thi way numbr of witching voltag vctor ar mor compard to baic DTC. Mor numbr of witching voltag vctor mak it poibl to dign mor accurat witching lookup tabl. Gnrally n=3 giv good dynamic prformanc without much incra in complxity of th look-up tabl. Fig. 4 how incrad witching voltag vctor aftr dividing th ampling priod in thr qual part in ctor-i. Figur 4 Sctor of DSVM-DTC Uing thi tchniqu mor appropriat lookup tabl can b dignd for pcial rquirmnt uch a low pd, high pd and tarting. Hr improvd DTC i achivd without going for complx calculation or coordinat tranformation. Thi lad to rducd torqu rippl compard to convntion DTC chm. B. Modifid DTC for low pd rang Rduction in tator flux i caud by tator ritanc drop in ca of low pd. Thi happn bcau of lction of zro voltag vctor for long tim. Modifid DTC chm with nw lookup tabl or th on with mixing of dithr ignal in torqu and flux rror ar uggtd to improv opration of induction motor at low pd and havy load [11-12]. V. DTC WITH CONSTANT SWITCHING FREQUENCY On of th main drawback of hytri band controllr in ca of baic DTC chm i that it witching frquncy i variabl. Bcau of thi problm optimum u of powr lctronic dvic ud in invrtr i not poibl. In contant frquncy DTC, a voltag pul width modulator rplac witching lookup tabl. Clod loop control i achivd by rplacing hytri band controllr with PI, prdictiv or nuro-fuzzy controllr. Rfrnc tator voltag i gnratd by thi controllr and it i ralizd by PWM tchniqu known a pac vctor PWM or SVPWM [13-15]. A. Spac Vctor Pul Width Modulation (SVPWM) Baic In pac vctor modulation tchniqu, dird rfrnc voltag i gnratd by lction of activ and zro witching voltag vctor to hav volt-cond balanc in ampling priod T. 2014, IJIRAE- All Right Rrvd Pag -396

5 Figur 5 Rfrnc vctor gnration in SVM-DTC If rfrnc voltag V rf i to b gnratd in firt ctor at an angl with a-axi a hown in Fig. 5, witching voltag vctor V 1 and V 2 ar lctd for tim T 1,T 2 and zro voltag vctor for tim T 0 in uch a way that V T V * T V * T V * T (7) rf To gnrat in wav, locu of rfrnc voltag vctor hould b circl o th witching qunc in ctor-i for pac vctor modulation hall b V0V1V2V7-V7V2V1V0 and o on. Zro vctor tim T 0 for a ampling priod i dividd into half and altrnativly zro witching vctor V0 and V7 ar lctd for T 0 in uch a way that minimum witching i ndd. Thi wll dvlopd pac vctor modulation chm can b ud to rplac lookup tabl. Torqu rror and tator flux rror along with tator flux vctor angl information can b ud to gnrat dird rfrnc voltag vctor uing a PI or prdictiv or fuzzy controllr. Clod loop control mthod uing SVM for DTC ar dicud in nxt ction. B. DTCSVM with clod loop Flux Control In thi mthod rfrnc valu of tator flux rfrrd to rotor rfrnc fram i calculatd from command valu of rotor flux and torqu T.Thi rfrnc valu of tator flux i tranformd to tationary rfrnc fram and * r compard to timatd valu of tator flux. \ * Figur 6 Block diagram of SVMDTC with flux control Rfrnc voltag vctor i gnratd bad on rror btwn rfrnc tator flux, timatd tator flux and tator ritanc drop. Now pac vctor modulation tchniqu i ud to gnrat voltag qual to rfrnc voltag vctor. Thi way it giv clod loop control bad on flux and pac vctor modulation. Hr timation of tator flux and rotor flux both i to b carrid out o knowldg of all th motor paramtr i ndd. Hnc it bcom nitiv to paramtr variation. 2014, IJIRAE- All Right Rrvd Pag -397

6 C. DTCSVM with clod loop Torqu Control An altrnativ approach to DTCSVM i with clod loop torqu control a hown in Fig.(4).In thi mthod rfrnc torqu i compard with timatd torqu to gnrat in rotor rfrnc fram. From tator flux valu in rotor r rfrnc fram and r, valu of command valu of tator flux i gnratd in tationary rfrnc fram. Rfrnc voltag vctor for SVM i gnratd by comparing command valu and actual valu of tator flux. Figur 7 SVMDTC with torqu control Thi mthod giv bttr torqu rpon in dynamic a wll a tady tat. D. Prdictiv SVMDTC chm In prdictiv chm, torqu rror and tator flux rror ar prdictd from approximat machin quation [16].Bad on th prdictd rror, uitabl rfrnc voltag pac vctor i lctd in uch a fahion that rror i minimum for that ampling priod. For gnration of rfrnc voltag pac vctor from prdictd torqu and tator flux rror, a quadratic critrion i ud. Thi way lctd witching pac vctor i valid for th whol ampling priod and unncary witching i avoidd. In convntional DTC chm, th pac vctor lctd may b appropriat at th ampling intant but may not b appropriat for th whol ampling priod. Thu by avoiding unncary witching, torqu rippl can b rducd. E. Nuro-Fuzzy SVMDTC chm Anothr mthod to gnrat rfrnc voltag vctor for SVMDTC i uing artificial intllignc bad controllr [17]. In lat dcad, application of AI bad controllr ar uccfully don for control of driv and powr lctronic. Nuro-Fuzzy (NF) controllr i on uch AI bad controllr which combin advantag of both artificial nural ntwork and fuzzy logic. In NF-DTCSVM, rror ignal dt and d ar fd to NF controllr along with tator flux poition information. Rfrnc tator voltag vctor in polar co-ordinat i dcidd by NF controllr which i ud by SVM block. VI. FUZZY LOGIC DTC It i quit obviou that in ca of claical DTC, non of th invrtr tat i abl to gnrat voltag pac vctor which i prfctly uitabl to mak torqu rror and tator flux rror zro. Th raon of rippl in torqu or tator flux i that th rror ar not quantifid a mall mdium, larg, vry larg and o on. Thi typ of quantification i not poibl with hytri band controllr, but vry aily poibl for fuzzy logic bad ytm. In fuzzy logic DTC, torqu rror, tator flux rror and tator flux angl information ar convrtd into fuzzy variabl and thn fd to fuzzy controllr[18]. Switching voltag pac vctor i dcidd by fuzzy logic controllr bad on th fuzzy variabl. Slctd activ voltag vctor i applid for th tim jut nough to achiv torqu and flux a pr rfrnc valu. For rt of th tim of ampling priod, zro voltag vctor i applid. VII. CONCLUSION Claical DTC mthod i having many advantag lik inhrnt pd nor l control, dpndnc on tator ritanc only, no nd for currnt controllr and implicity with high prformanc. Th problm aociatd with claical DTC ar torqu rippl, variabl witching frquncy and infrior prformanc at low pd opration with havy load. Som of th mthod rportd to improv prformanc of claical DTC ar rviwd in thi papr. Modifid 2014, IJIRAE- All Right Rrvd Pag -398

7 lookup tabl mthod ar uitabl for a particular ca to rduc torqu rippl but thy do not guarant contant witching frquncy. Dicrt SVMDTC mthod i impl and ffctiv but it do not giv atifactory Prformanc for whol pd rang from low to abov ba pd which i th ca with application lik automobil or traction driv. SVMDTC mthod ar o far th bt mthod which giv rducd torqu rippl, contant witching frquncy but it involv complx computation which mak thi tratgy highly dpndnt on motor paramtr. Hnc uing thi mthod dfat vary purpo of lcting DTC ovr vctor control for induction motor driv. Othr mthod lik DTC with prdictiv controllr, nural ntwork or fuzzy logic alo rult in improvd prformanc compard to claical DTC but no ingl mthod i uitabl for wid rang pd control. Alo thy ar far mor complx compard to claical DTC. Thr i wid cop for a control tratgy bad on DTC which can giv improvd prformanc for wid rang of pd. REFERENCES [1] S Ptr Va, Snlorl vctor and dirct torqu control, 3rd d. Oxford univrity pr, 1998 [2] B. K. Bo, Powr lctronic and motor driv- advanc trnd, 3rd d. Elvir Publication, [3] I. Takahahi, T. Noguchi, A Nw quick-rpon and High-fficincy control tratgy of an induction Motor, IEEE Tranaction on Indutrial Application, IA-22(5): , Sptmbr/Octobr, [4] M. Dpnbrock, Dirct Slf Control (DSC) of invrtr fd induction machin, IEEE Tranaction on Powr lctronic, 3(4): , Octobr, [5] Giupp S. Buja, Marian P. Kazmirkowki, Dirct torqu control of PWMinvrtr fd AC motor - A urvy, IEEE Tranaction on Indutrial Elctronic, Vol. 51,No. 4, pp , IA-22(5): , Augut,2004. [6] Giupp S. Buja, Marian P. Kazmirkowki, Rviw of Dirct Torqu Control mthod for voltag ourc invrtr fd induction motor, Conf. Rc. IEEE-IAS, pp , [7] D. Caadi, G. Srra, A. Tani, and L. Zarri, Amnt of Dirct torqu control for induction motor driv, Bull. Pol. Ac.:Tch., vol. 54, no. 3,pp , [8] Phan Quoc Dzung, L Minh Phuong, Nguyn Xuan Bac, Dirct torqu control of induction motor with modi_d witching tabl for low cot invrtr, Intrnational Sympoium on Elctrical and Elctronic Enginring 2007,HCM City, Vitnam Oct 24, [9] Y. Li, J. Shao, B. Si, Dirct torqu contrl of induction motor for low pd driv conidring dicrt ffct of control and dad tim of invrtr,conf. Rc. IEEE-IAS Ann. Mting, pp , [10] D. Caadi, G. Srra, A. Tani, Implmntation of a dirct torqu control algorithm for induction motor bad on dicrt pac vctor modulation, IEEE Tranaction on Powr lctronic, Vol. 15, No.4, pp ,july, [11] R. K. Bahra,S. P. Da, Improvd dirct torqu control of induction motor with injction, Procding in nginring cinc, Indian Acadmy of cinc, Sadhana, Vol. 33, Part 5, pp , Octobr, [12] N. R. N. Idri and A. H. M. Yatim, An Improvd tator flux timation in tady tat opration of dirct torqu control of induction motor driv,ieee Tranaction on Indutrial Application, Vol. 38, no. 1, pp , [13] T. G. Habltr, F. Profumo, M. Patorlli, and L. M. Tolbrt, Dirct torqu control o induction machin uing pac vctor modulation,ieee Tranaction on Indutrial Application, Vol. 28, no. 5, pp ,1992. [14] Marion P., A comparion of Dirct Torqu Control Mthodologi for Induction Motor in Proc. IEEE Porto Powr Tch Confrnc PPT'01,Sptmbr, Porto, Portugal, [15] Snthil U., Hybrid Spac Vctor Pul Width Modulation Bad Dirct Torqu Controlld Induction Motor Driv,Proc. in conf. Rc. IEEE-IAS, pp , 2003 [16] N. K. Mohanty,R. Muthu, M. Snthil, A Survy on controlld a lctrical driv, Intrnational Journal on Elctrical and Powr Enginring, ISSN: , vol. 3, pp , [17] T. Prabu, S. Sampatkumar and R. Gunabalan,Advancd Dirct torqu control of induction motor, IEEE tranaction on Indutrial Elctronic,2011. [18] H. Hallh, M. Rahmani, B. Kimiaghalam, Dirct torqu controllr of induction motor wit fuzzy controllr,intrnational Confrnc on automation and ytm- Sol-Kora, Octobr 14-17,2008, pp , IJIRAE- All Right Rrvd Pag -399