A Control Strategy Based on UTT and ISCT for 3P4W UPQC

Transcription

1 Interntonl Journl of Electrcl nd Electroncs Engneerng 5: 011 A Control Strtegy Bsed on UTT nd ISCT for P4W UPQC Ysh Pl, A.Swrup, nd Bhm Sngh Astrct Ths pper presents noel control strtegy of threephse four-wre Unfed Power Qulty (UPQC) for n mproement n power qulty. The UPQC s relzed y ntegrton of seres nd shunt cte power flters (APFs) shrng common dc us cpctor. The shunt APF s relzed usng thee-phse, four leg oltge source nerter (VSI) nd the seres APF s relzed usng three-phse, three leg VSI. A control technque sed on unt ector templte technque (UTT) s used to get the reference sgnls for seres APF, whle nstntneous sequence component theory (ISCT) s used for the control of Shunt APF. The performnce of the mplemented control lgorthm s eluted n terms of power-fctor correcton, lod lncng, neutrl source current mtgton nd mtgton of oltge nd current hrmoncs, oltge g nd swell n three-phse four-wre dstruton system for dfferent comnton of lner nd non-lner lods. In ths proposed control scheme of UPQC, the current/oltge control s ppled oer the fundmentl supply currents/oltges nsted of fst chngng APFs currents/oltges, there y reducng the computtonl dely nd the requred sensors. MATLAB/Smulnk sed smultons re otned, whch support the functonlty of the UPQC. MATLAB/Smulnk sed smultons re otned, whch support the functonlty of the UPQC. Keywords Power Qulty, UPQC, Hrmoncs, Lod Blncng, Power Fctor Correcton, oltge hrmonc mtgton, current hrmonc mtgton, oltge g, swell I. INTRODUCTION ECAUSE of the pplcton of sophstcted nd more B dnced softwre nd hrdwre for the control systems the power qulty hs ecome one of the most mportnt ssues for power electroncs engneers. Wth gret dnc ment n ll res of engneerng, prtculrly, n sgnl processng, control systems, nd power electroncs, the lod chrcterstcs he chnged completely. These nonlner lods drw non-lner current nd degrde electrc power qulty. The qulty degrdton leds to low power-fctor, low effcency, oerhetng of trnsformers nd so on [1]. Moreoer, n cse of the dstruton system, the oerll lod on the system s seldom found lnced, whch cuse excesse neutrl currents n three-phse four-wre dstruton system. Idelly, oltge nd current weforms re n phse, power fctor of lod equls unty, nd the recte power consumpton s zero; ths stuton enles the most effcent trnsport of cte power, ledng of the chepest dstruton system. Reltng to power qulty ssues, the desgners of power qulty condtoner systems re requred to follow the recommendtons of some world-wde ccepted stndrds lke IEEE , IEC , IEC recommended prctce nd requrements for hrmonc control n electrc power systems. Ysh Pl s wth N.I.T,Kurukshetr, (e-ml: ysh_pl1971@yhoo.com) In the pst, the solutons to mtgte these dentfed power qulty prolems were through usng conentonl psse flters. But ther lmttons such s,fxed compenton, resonnce wth the source mpednce nd the dffculty n tunng tme dependence of flter prmeters he gnted the need of cte nd hyrd flters[]-[4]. Under ths crcumstnce, new technology clled custom power emerged [5], [6], whch s pplcle to dstruton systems for enhncng the rellty nd qulty of the power supply. The Unfed Power Qulty Condtoner (UPQC) s one of the est solutons to compente oth current nd oltge relted prolems, smultneously [7-9]. As the UPQC s comnton of seres nd shunt cte flters, two cte flters he dfferent functons. The seres cte flter suppresses nd soltes oltge-sed dstortons. The shunt cte flter cncels current-sed dstortons. At the me tme, t compentes recte current of the lod nd mproes power fctor. There re mny control strteges reported n the lterture to determne the reference lues of the oltge nd the current of three-phse four-wre UPQC, the most common re the p-q-r theory[10],modfed sngle-phse p-q theory[11], synchronous reference frme(srf) theory[1], symmetrcl component trnsformton [1],nd unt ector templte (UVT) technque [14] etc. Aprt from ths one cycle control (OCC) [15] (wthout reference clculton) s lso used for the control of-phse, 4-wre UPQC. Ths pper presents -phse, 4-wre UPQC for n mproement of dfferent power qulty prolems. A control technque sed on UTT s used to get the reference sgnls for seres APF, whle ISCT s used for the control of Shunt APF. The proposed control technque s cple of extrctng most of the lod current nd source oltge dstortons successfully. The seres AF s controlled to elmnte supply oltge hrmoncs nd oltge regulton gnst oltge g nd swell whle, the shunt APF s controlled to llete the supply current from hrmoncs, negte sequence current, recte power nd lod lncng. The performnce of the proposed system s demonstrted through smulted weforms usng SPS Mtl/Smulnk enournment. The UPQC confgurton nd the lod under consderton lod re dscussed n Secton II. The control lgorthm for UPQC s dscussed n Secton III. The SIM POWER SYSTEM (SPS), Mtl/ Smulnk sed smulton results re dscussed n Secton IV nd fnlly Secton V concludes the pper. II. SYSTEM DESCRIPTION The system under consderton for three-phse four-wre dstruton system s shown n Fg.1.The UPQC s connected efore the lod to mke the source nd the lod oltge free 145

2 Interntonl Journl of Electrcl nd Electroncs Engneerng 5: 011 from ny dstortons nd t the me tme, the recte current drwn from source should e compented n such wy tht the currents t source sde s, would e n phse wth utlty oltges. Prosons re mde to relze oltge hrmoncs, oltge g nd swell n the source oltge y swtchng on/off the three-phse rectfer lod, R-L lod nd R-C lod respectely. The UPQC, relzed y usng two oltge source nerters s shown n Fg.. One ctng s shunt APF (Acte Power Flter), whle the other s seres APF. The shunt APF s relzed usng thee-phse, four leg oltge source nerter (VSI) nd the seres APF s relzed usng three-phse, three leg VSI. Both the APFs shre common dc lnk n etween them. The four-leg VSI sed shunt cte flter s cple of suppressng the hrmoncs n the source currents, negte sequence of source current, lod lncng nd power-fctor correcton. The mplemented control lgorthm conssts mnly of the computton of three-phse reference oltges of lod oltges ( l, l nd lc), nd the reference currents for the source current (, s nd sc). Three-phse four-wre supply s sc sn R-C Lod for swell nj R,L Rs,Ls Rsc,Lsc nj njc s sc sn Rectfer Lod for Hrmoncs R-L Lod for g Three-Phse Four- Wre UPQC Fg. 1 System under consderton Cdc Bck to Bck VSI shshc sh l l lc ln l l shn lc ln Iner nd Nonlner lod Fg. UPQC Block Dgrm The oltge t the source sde efore UPQC, the lod oltge t lod, the oltge njected y seres APF nd the dc lnk oltge etween two nerters re represented y s, L, nj nd V dc respectely. Wheres, the current on the source sde, totl current drwn y ll the lods nd the current njected y shunt APF re represented y s, l, nd sh respectely. The lod under consderton s comnton of lner nd non-lner lods. Sngle-phse lggng power-fctor lod s tken s lner lod, where s three-phse dode rdge rectfer wth resste lod on dc sde s consdered s non-lner lod. The lues of the crcut prmeters nd lod under consderton re gen n Appendx. III. CONTROL STRATEGY OF SERIES APF The seres s controlled n such wy tht t njects oltges ( f, f nd fc ), whch cncel outs the dstortons present n the supply oltges (, s nd sc ), thus mkng the oltges t PCC ( l, l nd lc ) perfectly snusodl wth the desred mpltude. In other words, the sum of supply oltge nd the njected seres flter oltge mkes the desred oltge t the lod termnls. The control strtegy for the seres APF s shown n Fg.. Snce, the supply oltge s dstorted, phse locked loop (PLL) s used to chee synchronzton wth the supply oltge [14].Three-phse dstorted supply oltges re sensed nd gen to PLL whch genertes two qudrture unt ectors (snwt,coswt).the n-phse sne nd cosne outputs from the PLL re used to compute the supply n phse,10 ο dsplced three unt ectors (u,u u c ) usng eqn.(1) s: u 1 0 (1) 1 sn θ = u cos θ u 1 c The computed three n-phse unt ectors then multpled wth the desred pek lue of the PCC phse oltge (V lm), whch ecomes the three-phse reference PCC oltges s: l u = () l Vlm u lc u c The desred pek lue of the PCC oltge under consderton s 8V (=415sqrt ()/sqrt()).the computed oltges from reference oltges from eqn.() re then gen to the hysteress controller long wth the sensed three phse PCC oltges( l, l nd lc ).The output of the hysteress controller s swtchng sgnls to the sx swtches of the VSI of seres APF. The hysteress controller genertes the swtchng sgnls such tht the oltge t PCC ecomes the desred snusodl reference oltge. Therefore, the njected oltge cross the seres trnsformer through the rpple flter cncels out the hrmoncs, oltge g or swell present n the supply oltge. Desred Lod Voltge l l lc Mgntude l k Phse X s k Locked sc k Loop k=1/vm 10 phse shft -10 phse shft l X lc X Hystress Voltge Controller Fg. Control Scheme of Seres APF usng UTT Gte Pulses of VSI 146

3 Interntonl Journl of Electrcl nd Electroncs Engneerng 5: 011 IV. CONTROL STRATEGY OF SHUNT APF The control lgorthms for shunt APF conssts of the generton of -phse reference supply currents (, s nd sc).the control lgorthm sed on ICST for shunt APF s shown n Fg.4. The symmetrcl component trnsformton mtrx cn e ppled to nstntneous oltges nd currents. We cn then defne the nstntneous symmetrcl component of oltges s: = () 1 1 s 1 sc l l lc + s+ sc+ P=( + l +s + l + sc+ lc ) Aerge Vlue + + P loss Compute Reference Source Currents o s sc s sc sn Hysteress Current Controller Gte Pulses of Fourleg VSI Fg. 4 Control Scheme of Shunt APF usng ISCT Smlrly, we cn defne the nstntneous symmetrcl component of currents. The prmry ojecte of the control lgorthm shown n Fg.7 s to otned lnced source currents. Therefore reference source currents cn e consdered s: + s + sc = 0 (4) From the power fctor consderton, the phse ngle etween 1 nd 1 s Φ then: + + = { } { } φ 1 K tn K where K 1 = 1 = tn c 1 ( ), c ( ) K K K 4 + φ s sc 1 1 = c K = s, s sc sc K = 4 Solng the oe equtons we get ( c β c ) + ( c β ) s+ ( β c ) sc = 0 (5) where tn φ β =. For power-fctor correcton β=0, the source currents re to e n phse wth the source oltges. It mples tht the recte power demnd of the lod s suppled y the shunt APF of the UPQC. The prme ojecte of the control lgorthm s to supply the lod cte power nd the losses of the UPQC n power-fctor correcton mode:, + s + csc = plg + p (6) loss where, p lg fltered erge lod cte power usng mong erge flter clculted from lod power p l = + l + s + l + sc + lc where, +, s+ nd sc+ re the poste sequence of the threephse source oltges clculted s per equton(). The cte lod power s clculted y mong erge flter wth ergng tme of hlf cycle of the source frequency. The mpltude of the P loss s the output of DC us oltge PI controller for self supportng us of the UPQC whch cn e expressed s; I d = Id( n 1) + K pd{ Vde Vde ( n 1) } + KdVde (7) where Vde = Vdcr Vdc denotes the error n V dc clculted oer reference lue of V dc. nd erge lue of V dc.k pd nd K d re proportonl nd ntegrl gns of the dc us oltge PI controller. After solng eqn.4, 5nd 6 the reference source currents cn e otned s: = β p + p { ( c ) }( lg loss) A ( c ) plg + ploss ( ) p + p / s = β / sc = c β lg loss / A =,, cv { }( ) A { }( ) A where = In ths proposed control lgorthm, the sensed(, s nd sc ) nd reference source currents(, s nd sc) re compred n hysteress current controller to generte the swtchng sgnls to the swtches of the shunt APF whch mkes the supply currents snusodl, lnced n n- phse wth the oltge t PCC. Hence the supply current contns no hrmoncs or recte power component. The source neutrl current s compented to fllow reference sgnl of zero mgntude y swtchng the fourth leg of the VSI, through the hysterss controller. By dong ths, the supply neutrl current cn e elmnted. In ths control scheme, the current control s ppled oer the fundmentl supply currents nsted of the fst chngng APF currents, therey reducng the computtonl dely nd numer of requred sensor. In ddton to ths, the lod or the flter neutrl current re not sensed, therey reducng the computtonl dely. V. RESULTS AND DISCUSSION The proposed control scheme hs een smulted usng MATLAB/ Smulnk nd ts Sm-Power System toolox. The performnce of UPQC s eluted n terms of oltge nd current hrmoncs mtgton, lod lncng, power-fctor correcton nd mtgton of oltge g nd swell under dfferent lod condtons. A. Performnce of UPQC for lod lncng nd powerfctor correcton Fg. 5 shows the response of UPQC wth lner lggng power-fctor lod for power-fctor correcton nd lod lncng. The shunt APF s put nto operton t 0.1 sec. 147

4 Interntonl Journl of Electrcl nd Electroncs Engneerng 5: 011 Fg.5 (e) shows tht fter 0.1 sec the source oltge nd source current n phse re exctly n phse. At t=0. sec the lod s chnged from three phse to two phse to mke the lod unlnced nd restored to three-phse lnced lod t t=0. sec. Durng ths perod, current 19.A RMS ( ln ) flows n the neutrl conductor s shown n Fg.5 (g). Ths current s compented for y the fourth leg of the shunt APF, thus reducng the supply neutrl current ( sn ) to zero s depcted n Fg.5 (f). It s lso osered from Fg.5 (h) tht durng unlnced lod operton, the dc oltge s mntned to ts reference lue. order to demonstrte the response of UPQC for lod lncng, power fctor correcton nd current hrmonc mtgton, the lod under consderton s comnton of three-phse dode rdge rectfer wth resste lod nd two sngle phse lggng power fctor lod n phse nd only. Becuse of ths unlnced lod, current 17.50A RMS ( ln ) flows n the neutrl conductor s shown n Fg.6 (g). Ths current s compented for y the fourth leg of the shunt APF, thus reducng the supply neutrl current ( sn ) to zero s depcted n Fg.6 (f). It s osered tht the supply currents re lnced, snusodl nd n-phse wth the oltges s s shown n Fg.6 (). Fg. 5 Performnce of UPQC for lod lncng nd power fctor correcton Fg. 6 Performnce of UPQC for lod lncng, power fctor correcton nd current hrmonc mtgton B. Performnce of UPQC for lod lncng, power-fctor correcton nd current hrmonc mtgton Fg.6. shows the response of UPQC for power-fctor correcton, lod lncng nd current hrmonc mtgton. In Fg. 7 Performnce of UPQC for lod lncng, power fctor correcton, current nd oltge hrmonc mtgton C. Performnce of UPQC for lod lncng, power-fctor correcton, current nd oltge hrmonc mtgton Fg.7 shows the response of UPQC for lod lncng, power fctor correcton, oltge hrmonc mtgton nd current hrmonc mtgton. In order to erfy the effecteness of control lgorthm for oltge hrmonc mtgton, three-phse dode rdge rectfer wth resste lod on dc sde s swtched on t 0.05 sec. Becuse of ths the oltge cross the lod ecomes dstorted. To sulze the shunt APF nd seres APF performnce nddully, oth APF s re put nto operton t dfferent nstnt of tme. At tme t 1 =0.1 sec, shunt APF s put nto operton frst. It s osered from Fg.7 (d) tht the supply currents re lnced; snusodl nd n-phse wth the oltges een under nonsnusodl utlty oltge. The source current THD n phse c s mproed form % to 4.6 %. At tme t =0.5 sec the seres APF s put nto the operton. The seres APF strts compentng oltge hrmoncs mmedtely y njectng out of phse hrmonc oltge, mkng the lod oltge t lod dstorton free. The oltge njected y seres APF s shown n Fg. 7(c). Here lod oltge THD s mproed form 5.8 % to.47 %. The hrmonc spectr of the source current nd the lod oltge n phse c wth compenton nd wthout 148

5 Interntonl Journl of Electrcl nd Electroncs Engneerng 5: 011 compenton re shown n Fg. 8. Becuse of unlnced lod, current 18.69A RMS ( ln ) flows n the neutrl conductor s shown n Fg.7 (). Ths current s compented for y the fourth leg of the shunt APF, thus reducng the supply neutrl current ( sn ) to zero s depcted n Fg.7 (h). trnsformers, equl to the dfference etween the reference lod oltge nd supply oltge, s shown n Fg.10 (c). The lod oltge profle n Fg.10 () shows the UPQC s effectely mntnng the lod us oltge t desred constnt leel. Fg.10 () shows tht current ( ln ) flows n the neutrl conductor, whch s compented for y the fourth leg of the shunt APF, thus reducng the supply neutrl current ( sn ) to zero s depcted n Fg.10 (h). Fg.8 () - () Source current nd Lod oltge wthout compenton Fg.8(c) - (d) Source current nd Lod oltge wth compenton D. Performnce of UPQC for lod lncng, power-fctor correcton, current nd oltge g mtgton The smulton results for oltge g compenton re shown n Fg. 9. There re four nstnts; t 1, t, t nd t 4. At tme t 1 =0.10 s, the shunt APF s put nto the operton nd ts operton s s dscussed preously. At tme t =0.5 s, seres APF s put nto operton. Now 10 kw, 40 Kr (nducte) lod s swtched on t t=0.5 s nd swtched off t t=.045 sec. Becuse of ths g s deeloped on the system t tme t =0.5 s. Ths g lsted tll tme t 4 =0.45 s, s shown n Fg. 9 (). After tme t 4 =0.45 s, the system s gn t norml workng condton. Durng ths oltge g condton, the seres APF s prodng the requred oltge y njectng n phse compentng oltge equls to the dfference etween the reference lod oltge nd supply oltge, s shown n Fg. 9 (c). The lod oltge profle n Fg. 9 () shows tht UPQC s mntnng t t desred constnt oltge leel t lod een durng the g on the system such tht the lods cnnot see ny oltge rton. Becuse of unlnced lod, current ( ln ) flows n the neutrl conductor s shown n Fg.9 (). Ths current s compented for y the fourth leg of the shunt APF, thus reducng the supply neutrl current ( sn ) to zero s depcted n Fg.9 (h). E. Performnce of UPQC for lod lncng, power-fctor correcton, current nd oltge swell mtgton At tme t 1 =0.10 s, the shunt APF s put nto the operton nd t tme t =0.0 s, seres APF s put nto operton. A swell s now ntroduced on the system y swtchng on 10 kw, 40 Kr (cpcte) from tme t =0.5 s to t 4 =0.45 s, s shown n Fg. 10. Under ths condton the seres APF njects n out of phse compentng oltge n the lne through seres Fg.9 Performnce of UPQC for lod lncng, power fctor correcton, current hrmonc nd oltge g mtgton Fg.10 Performnce of UPQC for lod lncng, power fctor correcton, current hrmonc nd oltge swell mtgton F. Performnce of UPQC for sudden lod chnge In order to show the response of UPQC for sudden lod chnge the lod cross the dc sde of the rectfer s ncresed t t=0.5 s. It s osered from Fg.11() tht n ddton to the lod lncng, power fctor correcton nd current hrmonc mtgton, the UPQC controller cts mmedtely wthout ny dely n the operton nd gn the new stedy stte. It s lso 149

6 Interntonl Journl of Electrcl nd Electroncs Engneerng 5: 011 osered from Fg. 11 (f) tht there s smll dp n dc oltge t t=0.5 s, ut dc lnk s le to regulte the dc oltge to ts preous lue. Fg.1 () shows tht current ( ln ) flows n the neutrl conductor, whch s compented for y the fourth leg of the shunt APF, thus reducng the supply neutrl current ( sn ) to zero s depcted n Fg.11 (h). Fg. 11 Performnce of UPQC durng sudden lod chnge VI. CONCLUSION The proposed control scheme sed on UTT nd ISCT for the three-phse four-wre UPQC hs een ldted through smulton results, usng MATLAB softwre long wth smulnk nd sm-power system toolox. The performnce of the UPQC hs een osered to e tsfctory for rous power qulty mproements lke lod lncng; source neutrl current mtgton, power-fctor correcton, oltge nd current hrmonc mtgton, mtgton of oltge g nd swell. The source current THD s mproed from % to 4.6 %, whle the lod oltge THD s mproed form 5.8 % to.47 %. In ddton to ths the performnce of UPQC hs een found tsfctory durng trnsent condtons.the system prmeters used re s follows: REFERENCES [1] E.W.Gunther nd H.Meht, A surey of dstruton system power qulty, IEEE Trns. on Power Delery, ol.10, No.1, pp.-9, Jn [] B. Sngh, AL.K. Hddd nd A. Chndr, A reew of cte flters for power qulty mproement, IEEE Trns. on Ind. Electron, ol.46, pp , [] H Akg, New trends n cte Flters for power condtonng, IEEE Trns. on Ind. Appl., 1996,, pp [4] B.Sngh,V. Verm,A. Chndr nd K. Al-Hddd, Hyrd flters for power qulty mproement, Proc. IEE on Generton, Trnsmsson nd Dstruton, ol.15,pp.65-78,my005. [5] Arndm Ghosh, Gerrd Ledwch, Power Qulty Enhncement Usng Custom Power Deces,Kulwer Interntonl Seres n Engneerng nd Computer Scence, 00. [6] N. G. Hngorn, Introducng custom power,proc. IEEE Spectrum, ol., pp.41-48, June1995. [7] M. Aredes, K. Heumnn, nd E. H. Wlndle, An unerl cte power lne condtoner, IEEE Trns. Power Del., ol. 1, no., pp , Apr [8] H. Fujt nd H. Akg, The unfed power qulty condtoner: the ntegrton of seres- nd shunt-cte flters, IEEE Trns. Power Electron., ol. 1, no., pp. 15, Mr [9] B. Hn, B. Be, H. Km, nd S. Bek, Comned operton of unfed power-qulty condtoner wth dstruted generton, IEEE Trns. Power Del., ol. 1, no. 1, pp. 0 8, Jn [10] Tn Zhl, L Xun, Chen Jn, Kng Yong nd Dun Shnxu, A drect control strtegy for UPQC n three-phse four-wre system, Proc. IEEE Conf. on Power Electron. nd Moton Control 006,ol.,pp.1-5. [11] V.Khdkkr nd A. Chndr, A Noel Structure for Three-Phse Four- Wre Dstruton System Utlzng Unfed Power Qulty Condtoner (UPQC),IEEE Trns. Industry Applctons,ol.45,pp ,009. [1] L.Xun,Zhu. Guorong,Dun. Shnxu nd Chen Jn Chen, Control Scheme for Three-Phse Four-Wre UPQC n Three-Phse Sttonry Frme, Procd.IEEE/IECON 007, pp , 007. [1] A.Ghosh, A.K. Jndl nd A. Josh, A unfed power qulty condtoner for oltge regulton of crtcl lod us, Proc. IEEE Power Eng. Socety Generl Meetng, June 004, ol.1, pp [14] B.Sngh nd Venkteswrlu, A Smplfed Control Algorthm for Three- Phse Four-Wre Unfed Powe Qulty Condtoner, Journl of Power Electroncs,ol.10, No.1,Jnury010. [15] G.Chen, Y. Chen nd K.M. Smedley, Three-phse four-leg cte power qulty condtoner wthout references clculton, Procd. IEEE APEC '04, ol.1, pp , 004. APPENDIX Supply oltge nd lne mpednce: 415 V L-L, f=50 Hz, R s =0.1ohm, L s =1.5mH Flter:R=7ohm,C=5µF DC us cpctnce: C dc =000µF Trnsformer: 50MVA, 58kV/1kV Lods: Two sngle-phse lner lod of 1KW, 8KVr n phse nd only nd Three-Phse Rectfer Lod R=50 ohm on dc sde. 150