Comparison of SVPWM and SPWM Techniques for Back to Back Converters in PSCAD

Transcription

1 , 35 Otoer, 03, Sn Frniso, USA Comprison of SVPWM nd SPWM Tehniques for Bk to Bk Converters in PSCAD Agustin Hernndez, Ruen Tpi, Memer, IAENG, Omr Aguilr, nd Ael Gri Astrt This rtile presents the simultion nd omprison etween the spe vetor pulse width modultion nd sinusoidl pulse width modultion tehniques for k to k onverters with deoupling ontrol strtegy, PSCAD/EMTDC for simultion purpose is used. Also, study of stedy stte nd trnsient performne hrteristis of the system is rried out for oth tehniques. The simultion results show tht the trnsient response is similr for oth shemes, nd the SVPWM tehnique hs the dvntge less hrmoni ontent, whih it is useful in pplitions tht require low hrmoni level for voiding overhets nd mlfuntion in sensitive systems. Index Terms Power eletronis, PSCAD simultor, PWM tehnique. I. INTRODUCTION OWER onverters re inresingly importnt in mny P pplitions res; in the eletri utility for exmple mny devies sed on power eletronis re used sine finer nd ever more intelligent ontrols re needed to improve the eletril grid performne in different voltge levels []. They re essentil for pplitions in emerging generting systems derived on renewle resoures. It must ensure roustness performne when re pplied in isolted opertion or when re onneted with the onventionl grid [3]. Their use is inresing in the industry for mhines regultion. Furthermore, onsumer mrket pplitions suh s remote generting systems nd qulity energy pplitions result in growing topi for nlysis nd improvement [4]. Eletril power genertion with wind nd solr s soure of power my e onsidered of the most promising renewle energy soures, ut the ontrol shemes re n importnt issue [56]. There re extensive frmeworks of vrious types of eletril mhines nd ontrols lgorithms tht hve een developed for wind genertor pplitions s re presented in [79]. Among the shemes of wind energy onversion systems (WECS), the Mnusript reeived June 7, 03; revised July 08, 03. This work ws supported in prt y PROMEP: Redes Temátis de Colorión under the projet titled: Fuentes de Energís Alterns. Agustin Hernández, Ruén Tpi nd Omr Aguilr re with the Engineering Deprtment t Polytehni University of Tulningo, Tulningo, Hidlgo, CO 4369, Mexio (orresponding uthors to provide phone: ; fx: ; emil: ruen.tpi, [omr.guilr]@upt.edu.mx). Ael Gri is with Mehtronis Deprtment t Polytehni University of Phu, Zempol, Hidlgo, CO 43830, Mexio (emil: el@upp.edu.mx). indution mhine nd permnent mgnet synhronous mhine re seen s promising elements for energy onversion. In ll ses k to k (BTB) rrngement sed on power eletronis is required to tke dvntge of the enefits [9]. BTB onverter is formed y two identil voltge soure onverters (VSC) onneted y ommon dlink. This topology presents severl dvntges in terms of power proessing nd llows idiretionl power flow with qusisinusoidl urrents. The lod n e tive, pssive or even nother network, in suh se hieve unity power ftor is possile if it is required. The dlink in the middle provides deoupling etween oth onverters; s result, they ould e driven independently. Therefore, it is possile to hve fst nd independent ontrol of tive nd retive power for oth onverters nd improve the system opertion []. To ttin simultneously these enefits is importnt to explore ontrol strtegies, whih llow otining the desired regultion. These devies hve s their min omponent voltge soure onverter, whih uses pulse width modultion (PWM) for ontrolling purposes. The swithing elements re power semiondutors tht operte t high frequenies. There re severl tehniques for ontrolling semiondutors onverter; eh one hs its own dvntges nd disdvntges. The sinusoidl PWM (SPWM) is mtured tehnology. In this method tringulr wve is ompred to sinusoidl wve. The spe vetor PWM (SVPWM) hs een inresingly used in lst dede. This modultion, insted of using seprte modultor for eh of the three phses, the omplex referene voltge vetor is proessed s whole. An ptitude for esy digitl implementtion is the notle feture of spe vetor modultion, whih n e esily implemented in digitl signl proessor (DSP) [3]. Moreover, suitle ontrol sheme is neessry to del with different operting onditions nd unertinties in the network due to the prmeters or lod vritions. This rtile presents the performne omprison of k to k onverter onneted to stndlone lod, where the SPWM nd SVPWM tehniques re pplied. The two shemes hrteristis nd the implemented methodology in PSCAD re presented. The simultion results show some differenes in the ehvior of oth tehniques. The system under study is k to k onverter nd is sujet to different operting onditions nd lod vritions. This work ddresses two min issues: ) first, it presents detil implementtion proedure of PWM tehniques in industril softwre nd; ) it relizes ehvior omprison for the nlysis system. ISBN: ISSN: (Print); ISSN: (Online)

2 , 35 Otoer, 03, Sn Frniso, USA II. ACDCAC CONVERTER MODEL The k to k onverter shown in Fig. is formed y two shred VSC with ommon DC us. Both onverters n operte s retifier or inverter depending on the power flow diretion nd the opertion is omplementry. The soure side onverter is designted s VSC nd the onverter onneted to the lod side s VSC. This topology presents severl dvntges in terms of power proessing nd llows idiretionl power flow with qusisinusoidl urrents. The ontrol ojetives whih re set for the BTB opertion depend on the pplition, for exmple: ) AC voltge; ) AC frequeny; 3) tive power; 4) retive power; nd 5) DC voltge regultion. Two ontrol tsks re ssigned to eh VSC nd how they llote n e ritrry. Fig. shows the BTB onverter ontrol struture. A. Soure side onverter ontrol The soure side onverter ojetive is to keep the dlink voltge onstnt. The vetor ontrol method is used with referene frme oriented long vetor position, enling independent ontrol of the tive nd retive power flowing etween the soure nd the onverter [4]. The PWM signls re otined y urrent regulted sheme, with dxis urrent used to mnipulte the dlink voltge nd the qxis urrent omponent to regulte the retive power. The referene vlues for the gridside onverter V d nd V q re estlished with ontroller, respetively. The equtions () nd () show the development ontrol sheme [56]. V d = V d ( ω e i q V d ) () V q = V q (ω e i d ) () where V d nd V q re referene voltge for the dxis nd qxis, respetively; ω e is the AC frequeny in the grid; is the indutne of soure side; i d nd i q re urrents of the dxis nd qxis; V d is voltge the soure in the dq0 frme. B. Lod side onverter ontrol The ontrol trgets n e hoie nd drivers depending on the pplition. For exmple, in distriuted genertion systems it is usul tht the ontrol lok inludes sheme for regulting the AC frequeny nd voltge. Therefore, in this rtile we re ontrolling the AC voltge nd frequeny vlues; lso DC link voltge regultion is required. The VSC must keep onstnt AC frequeny nd voltge vlues for different lod vriles. In this onverter the ontrol prolem is to determine the referene signl in the PWM ontrol sheme to llow the lod voltge trking the referene. The rrier signl is fixed in 5 KHz for 60 Hz lod. Hene, the needed mesurement is the threephse voltge t the onnetion point. For ontrol purpose dq0 onversion is employed nd its expression is the following, V dq0 = TV (3) where T is the trnsformtion mtrix. ( sin ( ωt ) sin ωt π 3 sin ωt π 3 T = os(ωt) os ωt π 3 3 os ωt π 3 ) The ngulr veloity is quired y phse lok loop (PLL) strtegy nd the error signl employed for otining the PWM referene signl tkes the form,! e(t) = V d _ ref V q _ ref! V d V q Defining the referene voltges, there re two seprte xes 90 eletril degrees. dxis is in phse with the referene vetor, wheres qxis is delyed 90 degrees respet to voltge, similrly, into dq omponent the urrent is deomposed. Therefore, v d _ ref =300V nd v q _ ref =0V. For otining the PWM referene signl in dq frme ontroller is inluded, fter tht, n inverse trnsform is pplied from dq to. To otin PWM signl for VSC ontrol omprison etween oth tehniques SPWM nd SVPWM is rried out., (4) (5) v v v R R R i i i VSC P = P C d v d VSC i i i L L L R R R Bk to Bk Lod V d ( ω ) e i q V d PWM PWM S V dq_ ref V V d_ ref V d _ ref T i q _ ref V q _ ref T S dq T V dq i ( ω e ) i d q Fig.. Bk to k onverter shemti digrm. ISBN: ISSN: (Print); ISSN: (Online)

3 , 35 Otoer, 03, Sn Frniso, USA III. PROGRAMMING PWM TECHNIQUES IN PSCAD A. SPWM implementtion Within the progrmming environment, the SPWM tehnique is developed using some loks tht hve lredy een designed in mster lirry. The onfigurtion of eh lok is sed on the mthemtil model. In Fig. the tringulr wve (rrier) is ompred with eh phse sinusoidl voltge, where the output vriles represent the pulses to swithing the power eletroni elements. The rrier signl opertes t 5 KHz nd is ompred with the modulted signls t 60 Hz [6]. Vrlf mgnitude Vrlf Thet Vret nd Vret phse Time TIME Vm g Vmg Thet Time Thet Thet Vmg lultion Vm g Ed Ed gt T T gt Vetor T T gt4 Swithing gt4 trnsition gt3 Duty D D gt3 pulse D D gt6 time yle D D gt6 D D genertion gt5 lultion gt5 gt gt (C) (A) (B) (E) (D) Fig. 3. SVPWM tehnique in PSCAD. Vref Vref Vref Fig.. SPWM pulse genertor sheme in PSCAD. B. SVPWM implementtion The SVPWM tehnique in PSCAD/EMTDC is rried out y five userdefined susystems, (A)(E). These re shown in Fig. 3. In susystem (A): t first the mgnitude (Vmg) nd phse ngle (Thet) re determined from the referene threephse voltge. To find out the setor, the rnge of lulted ngle vlue must e etween 0 nd π. The equtions (6) nd (7) re progrmming in this lok. V S = V S e jθ s (6) V S = V Sα V Sβ θ S = tn V Sβ V Sα gt gt4 gt3 gt6 gt5 gt (7) IV. SIMULATION RESULTS In order to verify the ontrol sheme ppliility for the k to k onverter the PSCAD softwre is used. To nlyze the results two ses re presented. Cse A nd B re desried elow. The system dt re: the voltge soure is 380 V operting t 60 Hz nd the lod to 5KW, 300 V. A. Cse In this se, initilly the system is intive; ll vriles hve vlue equl to zero, fter trnsient period they re stilized round of onstnt vlue t stedy stte. Through the feedk ontrol strtegy the DC voltge hieves, V DCref = 700V. Fig. 4 shows the DC voltge performnes when the SPWM nd SVPWM ontrol strtegies re pplied. These tehniques implemented y softwre determine the sequene nd durtion of the time on nd off the swithes. One n see tht the stedy stte nd trnsient responses hve similr hrteristis for oth lgorithms. The ontrol strtegy lso llows regulting the power ftor, whih must remin losed to one, thus the retive power is equl to zero. Fig. 5 exhiits tht the soure side onverter is operting t unity power ftor, sine the retive power trks the referene zero for oth modultion strtegies. The ontrol of the lod side onverter regultes the AC voltge nd frequeny. Fig. 6 presents the voltge performne in phse A, for oth lgorithms. The modultion tehniques show fst evolution, llowing tht the onverters re operted properly nd the interest vriles reh the desired stedy stte vlue with fst trnsient response. where V s is the mgnitude nd θ s is the phse ngle; (B): this susystem is designed to lulte the turnon time of two djent tive vetors nd the zero stte vetors; susystem (C): the trnsition time of tive nd zero vetors re lulted; (D): in this lok the duty yles genertion proedure is estlished; finlly, susystem (E): the swithing pulses for power eletroni devies re generted. The tehnique ws tken from [7]. Fig. 4. DC us voltge evolution. ISBN: ISSN: (Print); ISSN: (Online)

4 , 35 Otoer, 03, Sn Frniso, USA perturtions. The simultions of k to k struture under different operting onditions demonstrte the effetiveness nd roustness of PWM tehniques. Trnsient nd stedy stte response were nlyzed. Fig. 5. Retive power output in the soure side onverter. Fig. 8. Lod urrent when the lod is inresed. Fig. 6. Phse voltge output in lod side onverter. B. Cse The seond se illustrtes the system s evolution when the lod is inresing from 5 to 5 KW, t t = 0.5 s. One n see tht the trnsient period is short nd quikly response is exhiited efore the stedy stte ondition is hieved. The lod voltge ttins the referene vlue t 300V, efore nd fter the lod hnged, Fig. 7. By inresing the lod vlue, the urrent tkes new vlue nd it is estlished round 90A, Fig. 8. It is ler tht the trnsient response is similr for oth shemes nd the settling time is sme for two ses. The modultion tehniques disply very well performne llowing tht the onverters operte properly nd the interest vriles reh the desired stedy stte vlue. () () Fig. 9.FFT nlysis of phse urrent A: ) SPWM; ) SVPWM. Fig. 7. Lod voltge when the lod is inresed. The wveform distortion ording to FFT nlysis in Fig. 9 is exhiited. Using the SVPWM sheme the hrmoni urrent omponents of phse A is less tht with the SPWM tehnique. In generl, drive systems with low hrmoni ontent re etter thn tht with high ontent. The two ses vlidte the pproprite system evolution under ISBN: ISSN: (Print); ISSN: (Online) V. CONCLUSIONS This rtile developed the simultion nd omprison of spe vetor pulse width modultion nd sinusoidl pulse width modultion for k to k onverters with deoupling ontrol strtegy in PSCAD/EMTDC. Both stedy stte nd trnsient system performne re presented. The simultion results show the ontrol sheme effetiveness. The SPWM is simpler to implement thn SVPWM in the softwre. Very similr results re presented with oth ontrol lgorithms. However, the most ovious differene is displyed in the hrmoni urrent ontent. The

5 , 35 Otoer, 03, Sn Frniso, USA SVPWM hs dvntge of less hrmoni ontent with this sheme hs vlue of 3.66, wheres 6.05 with SPWM; it is useful priniplly to void mlfuntion of sensitive equipment y hrmoni exess, s well s, prolems of trnsformers nd wiring overheting. ACKNOWLEDGMENT This projet hs een prtilly funded y the CONACyT Mexio grnt CB6906 nd y the ECESTSEP (Espio Común de Eduión Superior Tenológi) Progrm under the moility sheme for students, nd ws supported y PROMEP: Redes Temátis de Colorión under the projet titled: Fuentes de Energís Alterns. REFERENCES [] Jun SegundoRmírez, Aurelio Medin, Modeling of FACTS devies Bsed on SPWM VSCs, IEEE Trns. on Power Delivery, Vol. 4, No. 4, pp. 8583, 009. [] Nrin G. Hingorni, Lszlo Gyugyi, Understnding FACTS, IEEE Press Editoril Bord, 000. [3] R. Mjumder, A. Ghosh, G. Ledwih, F. Zre, Control of Prllel Converters for Lod Shring with Semless Trnsfer Between Grid Conneted nd Islnded Modes, IEEE Power nd Energy Soiety Generl Meeting, 008. [4] Pedro RoneroSánhez, Enrique Ah, Jose Enrique Orteg Clderon, Viente Feliu, Aurelio GríCerrd, A Verstile Control Sheme for Dynmi Voltge Restorer for PowerQulity Improvement, IEEE Trns. on Power Delivery, Vol. 4, No., pp. 7784, 009. [5] Ho M. Nguyen, D. Surm Nidu, Advned Control Strtegies for Wind Energy Systems: An Overview, IEEE PES Power Systems Conferene Exposition (PSCE), 0. [6] Adrià JunyentFerré, Oriol GomisBellmunt, Andres Sumper, Mr Sl, Montserrt Mt, Modeling nd Control of the Douly Fed Indution Genertor Wind Turine, Simultion Modelling Prtie nd Theory, vol. 8, No. 9, pp , 00 [7] G.O. Cimu, C. Sudemont, B. Royns, nd M.M. Rdulesu, Control nd Performne Evlution of Flywheel EnergyStorge System Assoited to VrileSpeed Wind Genertor, IEEE Trns. Industril Eletronis, vol. 53, No. 4, pp , 006. [8] S. Niu, K.T. Chu, J.Z. Jing, nd C. Liu, Design nd Control of New DouleSttor CupRotor PermnentMgnet mhine for wind power genertion, IEEE Trns. Mgnetis, vol. 43, No. 6, pp , 007. [9] Yi Wng, Lie Xu, Coordinted Control of DFIG nd FSIGBsed Wind Frms Under Unlned Grid Conditions, IEEE Trns. Power Delivery, vol. 5, No., pp , 00. [0] S. Mishr, Y. Mishr, Fngxing Li, Z. Y. Dong, TSfuzzy Controlled DFIG sed Wind Energy Conversion Systems, IEEE Power Energy Soiety Generl Meeting, pp. 7, 009. [] F. M. Hughes, O. AnyLr, N. Jenkins, nd G. Str, Control of DFIGsed Wind Genertion for Power Network Support, IEEE Trns. Power Systems, vol. 0, No. 4, pp , 005. [] Jneth Allá, Vitor Cárdens, Emnuel Ross nd Ciro Nuñez.: Control System Design for Bidiretionl Power Trnsfer in Single Phse Bk to Bk Converter Bsed on the Liner Operting Region, Applied Power Eletronis Conferene nd Exposition (APEC), pp , 00. [3] Amit Kumr Gupt, Ashwin M. Khmdkone, A Spe Vetor PWM Sheme for Multilevel Inverters Bsed on TwoLevel Spe Vetor PWM, IEEE Trns. on Industril Eletronis, Vol. 53, No. 5, pp , 006. [4] R. Pen, J.C.J.C Clre, G.M. Asher, Douly fed indution genertor using ktok PWM onverters nd its pplition to vrilespeed windenergy genertion, IEE Proeedings Eletri Power Applitions, Vol. 43, No. 3, pp. 34, 996. [5] Jtin Nth Wni nd Artie W. Ng., Pths to sustinle energy, Inteh, hpter. 4, 00. [6] B. Wu, Y. Lng, N. Zrgri, S. Kouro, Power Conversion nd Control of Wind Energy systems, IEEE Press, hpter., 0. [7] Muyeen, S.M., Mnnn, M.A., Ali, M. H.: Simultion Tehnique nd Applition of Spe Vetor PWM method in PSCAD/EMTDC. In: Interntionl onferene on Informtion nd Communition Tehnology, ICICT (007). ISBN: ISSN: (Print); ISSN: (Online)