Active Power Filtering by a Flying-Capacitor Multilevel Inverter with Capacitor Voltage Balance

Transcription

1 Active Power Filtering y Flying-Cpcitor Multilevel Inverter with Cpcitor Voltge Blnce JuneiHu,iZhng,S.J.Wtin School o Electronic nd Electricl Engineering, Univerity o eed, UK J.Hu@leed.c.u Atrct- A new control trtegy i developed or our-level lying cpcitor multilevel inverter to unction n ctive power ilter APF). hi employ pce vector modultion SVM) ccording to cpcitor voltge vlue t ech level. It lo pplie modiied predictive current control lw ting into ccount the derivtive o the reerence current. Simultion tudy h hown tht the propoed cheme led to high perormnce hrmonic current compention or oth tedy nd trnient tte opertion nd cpcitor voltge t ll level re well lnced. I. INRODUCION Active Power Filter APF) i ued to control rective power low nd eliminte hrmonic current in power ytem. hey re going to e indipenle or mintining high qulity power upply nd will ply n importnt role in the uture due to the increing integrtion o electric power genertor powered y renewle energy ource within the power ditriution inrtructure. Conventionl two-level inverter topology cnnot e pplied directly to high voltge power ditriution ytem which hve voltge level o ten o ilovolt ecue o limited device V/I rting nd high dv/dt. A vile pproch to high power converion i y contructing multilevel inverter, in prticulr, the lying cpcitor multilevel inverter FCMI) propoed y Meynrd, et l [1,, ]. he FCMI h een ued hunt power line conditioner nd lo uniied power low controller UPFC) [, 4]. he min chllenge in uing n FCMI n APF lie in otining t nd ccurte perormnce in hrmonic compention whilt mintining the voltge cro the loting or cell-cpcitor t the pproprite contnt level. rge cpcitor voltge wing my cue voltge tre cro device, conequently poor hrmonic control perormnce nd even inverter ilure. Hitherto ew pulihed wor hve ddreed thi iue. hi pper invetigte new control cheme or our-level FCMI unctioning hunt ctive power ilter. It employ predictive current controller, nd ue Spce Vector Modultion SVM) method to determine the inverter witching vector nd their correponding duty cycle [5], the propoed control trtegy h two novel eture: employing cpcitor voltge eedc ignl to determine the inverter witching vector nd equence, nd Incorporting the rte o chnge o the reerence current in the control lgorithm to improve the ccurcy in control t trnient current chnge. he propoed FCMI-APF h een imulted to eliminte the lod current hrmonic in mll power ytem upplying nonliner lod. he univerl progrm ytem EMP-AP Electromgnetic rnient Progrm Alterntive rnient Progrm.) h een ued to conduct thi tudy. he propoed control trtegy h led to good perormnce hrmonic elimintion, prticulrly or trnient opertion. he pper decrie the principle o the APF control cheme. he peciic SVM cheme or our-level lyingcpcitor multilevel inverter i preented. Simultion reult o the FCMI-APF controlling power ytem will e preented nd the eture o the method in comprion to the other pproche will e highlighted. II. HE SYSEM he power ytem imulted i hown in Figure 1. he threephe power ource i eprted rom the lod y the erie impednce S -R S. he nonliner lod i repreented y threephe thirted controlled rectiier upplying n R- lod, nd three-phe lod ilter chrcteried -R i ued. he APF i our-level including voltge level) lying-cpcitor multilevel inverter hown in Figure 1. It i hunt connected to the power line common coupling point CCP) on the lod ide through ilter etured -R. hi i necery or eliminting current ripple due to witching. Figure 1. Schemtic o the power ytem nd three-phe FCMI-ed hunt APF.

2 III. HE PREDICIVE CONRO PRINCIPE A i well nown the APF control cheme conit o two procee. he irt extrct the unwnted hrmonic component rom the meured lod current. hee re ten the reerence vlue or the econd prt which implement eedc control cheme or cnceling them rom the power line current. here re numer o method or the irt t, uch the intntneou rective power theory [7, 8]; however or implicity the ynchronou reerence rme lgorithm SRF) [9, 1] i pplied here. hi ume tht the three phe voltge o the imulted power ytem re lnced nd lrgely noie ree hence they re repreented pce vector rotting round ttionry reerence rme t the min requency. I the meured three-phe current vector i projected to - plne, phe loced to the rotting voltge vector, ccording to Pr trnormtion it cn e expreed i i p q in t co ti 1) co t in t i where i, i re the two orthogonl current component o the three phe current vector I in SRF, ip nd iq re deined intntneou ctive nd rective current repectively nd i the undmentl ngulr requency o the AC ytem. Both ip nd iq re compried o two component, the undmentl requency component trnormed to DC quntity nd the hrmonic component expreed elow ~ ) i p i p ip i ~ q iq iq Hrmonit current extrction Figure. Control ytem digrm Pridictive current control Uing low-p ilter hown in Figure we cn extrct the undmentl current. It equivlent AC quntity i,i,i c cn e derived y pplying invere Pr trnorm. hu the lod hrmonic current component cn e clculted ih i i ) ih i i i ch ic ic where i,i nd i c re the three phe lod current nd i h, i h nd, i ch re the hrmonic component. hee extrcted hrmonic current re pplied the reerence current or the APF control loop hown in Figure. he im o APF controller i to eliminte the hrmonic current component rom the lod current. A predictive current control lgorithm comining with the SVM cheme or FCMI i employed. he principle o predictive control cheme i well nown. Hving model o the ytem to e controlled it etimte the pproprite control ction to enle controlled vrile to ollow the deired vlue. In thi ppliction the model o the ytem i the R- impednce etween the inverter output nd power line common coupling point. he input nd output vrile re the inverter c terminl voltge nd current vector, repectively. hu the eqution expreing the reltionhip etween the input nd output vrile i given d i e V dt R i 4) where R nd re the line/ilter impednce etween inverter c terminl nd CCP, i i the inverter current vector equivlent to the compenting current upplied y the APF, e nd V re the voltge vector t CCP nd the inverter c terminl repectively. di dt i the rte o chnge o current etween two mple. During hort nd inite witching period, thi cn e pproximted y rtio o dierence term i i t K ) i t K ) 5) Sutituting i t ) with the etimted reerence current nd i t ) with the meured current vlue t th time intervl, the c ide voltge vectorv t next mple cn then e clculted : * V t ) e t ) i t ) R ) i t ) K S ) It i worth noting tht the ove lgorithm doe not wor well under operting condition where reerence current chnge rpidly. hi i due to the nturl dely in mpling tep cued y oth the reerence current nd inverter reerence voltge clcultion procee. hi eect i reveled in thi prticulr ppliction when the iring ngle o the three-phe rectiier ecome greter thn ; the ource current wveorm contin undeirle hrp piehowninfigure5.oovercomethideectthenew modiied lgorithm incorporte the rte o chnge o the reerence current t the current nd lt mple into Equ), uequently we hve * * * * V e t ) ) 1) i t R i t n i t i t m i t i t 7) where n nd m re the weighting ctor or newly dded term. Similr to dding derivtive term in P+I controller, thee term enle the controller reponding promptly to reerence current vrition. However they lo me the controller enitive to meurement noie, which my led the

3 ytem untle. hu it i importnt to tune m nd n ctor creully to chieve the deired trnient perormnce. S 9) where i the crrier period,, i the time intervl or V, nd re the time intervl or V, nd V, repectively, V i the trget output pce vector. he duty time eqution or ector 1 to re lited in le II, where i equl to nd M i the modultion index, deined the rtio etween the mgnitude o the modulting wveorm nd the crrier ignl. ABE I SPACE VECORS FOR A FOUR-EVE INVERER evel 1 evel V S V S V S ; ; 1; 1; 1 ; ; ; ; V V ; ; V ; 1; 1 1; ; ; ; Figure. Switching vector in multilyer hexgon 1; ; V 1 ; 1; 1 ; ; ; 1; V 1 ; ; 1 ; 1; V 1 1; ; IV. SPACE VECORS MODUAION SCHEME Once otining inverter voltge vector the SVM cheme i pplied to determine the witching vector nd clculte their correponding durtion. he method o vector election i decried elow ting our-level three-phe FCMI the exmple. In thi ce there re, in totl, 4 witching vector, ctive nd 4 ero one. he pred o thee vector within ounded three-lyer hexgon i hown in Figure. Selection o the witching vector t every mple intervl i ed on the loction o V re in the hexgon, which i coded ccording to the 54 mll tringle ee Figure ), ut lo importntly on the meured cpcitor voltge level. Ech o thee tringle h three djcent ctive witching vector. hoe o them connecting the middle nd low voltge level involve either cpcitor eing chrged y the power ource or the other eing dichrged through the lod. A loo-up tle i et up to tore the chrging nd dichrging eture o ll the witching vector. he vector re rrnged ccording to their lyer rom 1 to. A vector tle i etlihed with the phe leg output voltge level hown in le I. For exmple, the voltge o the our-level inverter phe leg output with repect to the negtive DC ril, V N, cn e yntheied to the ollowing voltge level: 1) For voltge level, V N = ) For voltge level 1, V N =V dc /. ) For voltge level, V N =V dc /. 4) For voltge level, V N =V dc. he tringle i ormed y tte vector V,,V, nd V.he ctive time or the tte vector cn e given y the ollowing ormule, V V V V 8) 1; 1; V 11 ; ; 1 ; ; ; 1; V 1 1; ; 1 ; ; ; 1; 1 V 11 1; ; ; ; ; ; 1 V 1 1; 1; ; ; 1; ; 1 V 11 ; 1; ; ; ; ; V ; ; 1 ;1 ; V 1 ; ; 1 ; ; V 1; ; 1 ; ; 1 V 1 ;1 ; evel ; ; V 1; 1; 1; ; V 1 ; 1; ; ; V ; 1; ; ; 1 V 1 ; ;1 V S V S V S V ;; V ;; V ;; V 1 ;1; V 1 ;;1 V 1 1;; V ;; V ;; V ;; V ;; V ;; V ;; V ;; V ;; V ;; V 1 1;; V 1 ;1; V 1 ;;1 Uing the cpcitor voltge eedc ignl we exmine the extent o relevnt cpcitor voltge devition rom their repective deired level. Suequently we determine the witching vector nd their equence o implementtion in the inverter pproprite or minimiing cpcitor voltge wing. he ove opertion i included in loc CV in Figure. Clcultion o the duty cycle or the elected vector i then ollowed indicted in loc CD/CS in the igure.

4 Sector, Phe n Angle, 1 < / / </ / < 4 < 4/ 5 4/ <5/ 5/ < ABE II FORMUAE FOR DUY CYCE CACUAION Vector V, V, Sector Duty Eqution M co 1) V M in V, V, M in 1) V M co ) 1) V, V, V V 1, V, V V, V, M in ) ) M co 1 ) M co ) 1) M in M co 1) V M in ) V, V, M in 1) 5 V M co ) 1) V, V, V V 1, V, V V, V, M in ) ) 5 M co 1 ) ; 7 M co ) 1) 4 M in 7 M co 1) 4 M in ) V V, 5 M in 1) V, M co ) 1) V V, V, V V 1, V, V 5 M in ) ) M co 1 ) 7 M co ) 1 ) M in 4 IV CAPACIOR VOAGE BAANCING CONRO Since there re two loting cpcitor in ech inverter lim, the voltge lnce o thee cpcitor ix o them) i ey iue or the ytem to operte deired. In thi wor, voltge eedc cheme i pplied. hi meure the cpcitor voltge t every mple intervl nd compred with their deired vlue. he error re pplied to determine the pproprite vector nd witching comintion t the correponding mple intervl. Epecilly or voltge level 1 nd, there re dierent witching comintion to chrge nd dichrge the cpcitor. For exmple i the voltge o C 1 i lower thn 1/ V DC y predeined error nd witch comintion will e choen uch tht it led to C 1 eing chrged, while the inverter output voltge ollow the deired vlue. On the other hnd i voltge o C 1 i higher thn deired, the witch comintion elected will cue it to dichrge through the lod. V. SIMUAION RESUS he ove decried control method h een pplied to the imulted power ytem hown in Figure 1. he voltge rting i et to V pe-pe, 5 H nd current rting 15A. he power line impednce vlue re deined R =.1 nd =.85mH. he lod reitnce R i. he lod input ilter prmeter re R r =.1 nd r =.mh. he reitnce nd inductnce o the APF ilter re.1 nd.8mh, repectively. he reult o imultion re hown in Figure 4-. In Figure 5, the modiied lgorithm i compred with the method when derivtive term re not ued. It i hown clerly tht the ltter led to pie on the pe point o current wveorm. In contrt, when uing the propoed method, thee pie re igniicntly ttenuted giving uperior current wveorm. he wveorm in Figure )-) re or trnient current repone with chnging rom to nd rom to. Figure ) nd d) how lod current, ) nd e) give APF compenting current repectively or oth vlue, nd c) nd ) re the power line current wveorm. Clerly t hrmonic compention h een chieved in oth ce uing the propoed control cheme. he perormnce o the propoed APF i tictory while the lying-cpcitor voltge t oth level 1 nd re well lnced hown in Figure 4. Figure 4 Blnced lying cpcitor voltge [] ile c1l4.pl4; x-vr t) c:ua -INSRA )Power line current with modiied lgorithm [] ile c1l4d.pl4; x-vr t) c:ua -INSRA )Power line current with conventionl lgorithm Figure 5: Simultion reult

5 [] ile c1l4ln.pl4; x-vr t) c:insra-x7a ) [] ile c1l4ln.pl4; x-vr t) c:x1a-x9a ) [] ile c1l4ln.pl4; x-vr t) c:ua c) INSRA [] ile c1l4ln.pl4; x-vr t) c:insra-x71a d) [] ile c1l4ln.pl4; x-vr t) c:uc -INSRC ) Figure rnient repone or rom to ; ) od current; ) APF current; c)compented ource current ; rnient repone or rom to d)od current; e) APF current; )Compented ource current VI. CONCUSION he pper preented n FCMI-APF or hrmonic compention. he predictive control cheme h incorported derivtive term nd SVM method or inverter witching control. Cpcitor voltge vlue re eedc to the control loop to it witching vector election t ech mple. Simultion reult h hown tht the propoed method i cple to give deired perormnce or oth tedy nd trnient opertion. REFERENCES [1] Meynrd,.A. nd Foch, H., "Dipoiti électronique de converion d'énergie électrique", French Ptent No B1, Filed 5th July 1991, Iued 9th Jnury 199. WO9/51A1, Electronic device or converting electricl energy ). [] Meynrd,.A. nd Foch, H., Multi-level chopper or high voltge ppliction, EPE Journl, Vol., No. 1, pp [] ing, Y.; Nwnp, C.O., A power-line conditioner ed on lyingcpcitor multilevel voltge-ource converter with phe-hit SPWM, Indutry Appliction, IEEE rnction on Vol., No. 4, pp [4]. Xu nd V.G. Agelidi, Flying cpcitor multilevel PWM converter ed UPFC, IEE Proc. Electr. Power Appl., Vol 149, No. 4, pp. 4-1 [5]. Xio,.Zhng, A Spce Vector-Bed Dedet Controller or Shunt Active power Filter ; EPE 97, pp [] Wtin, S.J.; Zhng,.; Multilevel pce vector PWM control cheme or lying-cpcitor inverter; PEMD 4, Vol. 1, pp:1-17 [7] H. Agi, Y. Knw, nd A. Ne, Generlied theory o the intntneou rective power in three-phe circuit, in Proc. I98 Int. Power Electronic Con, oyo, Jpn, 198, pp [8] Agi, H.; Active Hrmonic Filter ; Proceeding o the IEEE Volume 9, Iue 1, Dec. 5 Pge): [9] S. Bhttchry, M. Divn, nd B. Benerjee, Synchronou Reerence Frme Hrmonic Ioltor Uing Serie Active Filter, EPE 91, Vol.,pp. -5 [1] Bhttchry, S., Divn, D., Synchronou rme ed controller implementtion or hyrid erie ctive ilter ytem, IEEE/IAS Annul Meeting 1995, pp [] ile c1l4ln.pl4; x-vr t) c:x1a-x9a e)