Unified Power Quality Conditioner (UPQC) with Voltage Dips and Over-voltages Compensation Capability

Transcription

1 Unfed Powe Qualty Condtone UPQC wth oltage Dps and Oe-oltages Compensaton Capablty ícto M. Moeno, Albeto Pgazo, Maco Lsee and Antono Dell Aqula Depatamento de Electonca y Computadoes Unesdad de Cantaba Ada. de los Castos s/n, 394 Santande Span Tel.: , fax: , e-mal: moeno@uncan.es, pgazoa@uncan.es Dpatmento d Elettotecnca ed Elettonca Poltecnco d Ba a Oabona 4, 75 Ba taly Tel.: , fax: , e-mal: lsee@eee.og, dellaqu@polba.t Abstact Unfed powe qualty condtones UPQCs allow the mtgaton of oltage and cuent dstubances that could affect senste electcal loads whle compensatng the load eacte powe. Dese contol technques hae been poposed to ealuate the nstantaneous output oltage of the sees acte powe flte of the UPQC but, n most cases, these contolles only can compensate a nd of oltage dstubance. Ths pape poposes a new dgtal contolle fo UPQCs whch allows the load cuent hamoncs and eacte powe to be compensated at the gd sde whle aodng the effect of oltage dps, oe-oltages and oltage hamoncs on the local loads. The contolle chaactestcs can be establshed on-lne wthout changng ts basc stuctue. The pefomance of the poposed contolle has been ealuated though smulaton tests. Keywods: UPQC, oltage dps, oe-oltages, oltage hamoncs, cuent hamoncs, eacte component.. ntoducton Unfed powe qualty condtones UPQCs consst of combned sees and shunt acte powe fltes APFs fo smultaneous compensaton of oltage and cuent dstubances and eacte powe. They ae applcable to powe dstbuton systems, beng connected at the pont of common couplng PCC of loads that geneate hamonc cuents. Dese topologes has been poposed n lteatue fo UPQCs n sngle-phase confguatons,.e. two GBT half bdges [] o multleel topologes [], but ths pape focus on the commonly employed geneal stuctue depcted n fgue [3]. As can be seen, the powe conetes shae a dc-bus and, dependng on the functonaltes, employ an solaton tansfome sees APF o an nductance shunt APF as oltage o cuent lns. Sees APF Fg.. Hadwae stuctue of a UPQC. Shunt APF PCC The sees APF must compensate the souce oltage dstubances, such as hamoncs, dps o oe-oltages, whch mght deteoate the opeaton of the local load whle the shunt APF attenuates the undesable load cuent components hamonc cuents and the fundamental fequency component whch contbutes to the eacte load powe. Moeoe, the shunt APF must contol the dc-bus oltage n ode to ensue the compensaton capablty of the UPQC [4]. These functonaltes can be caed out by applyng dese contol stateges whch can opeate n the tme doman, n the fequency doman o both [5]. Tme doman methods, such as pq o dq based methods [6]-[8], allow the fast compensaton of tme-aant dstubances but mae moe complex the selecte compensaton. n ths sense, fequency doman methods ae moe flexble but the dynamcal esponse s slowe. Ths pape poposes a new contol technque fo UPQCs based on a Kalman flteng appoach. The poposed method opeates both n the tme and fequency domans allowng the selecte compensaton of oltage and cuent hamoncs wth fast dynamcal esponses. Moeoe, the mpact of dps and oe-oltages can be attenuated by applyng the poposed contolle RE&PQJ, ol., o.6, Mach 8

2 Fg.. Geneal stuctue of UPQC contolles. Functonal stuctue of UPQC The basc functonaltes of a UPQC contolle ae depcted n fgue. The oltage compensaton C and cuent njecton C efeence sgnals, equed fo compensaton puposes, ae ealuated fom the nstantaneous measuements of the souce oltage S, the dc-bus oltage dc and the load cuent L. These efeence sgnals ae compaed to the measued feedbac sgnals and and appled to the decoupled oltage and cuent contolles, whch ensue that the compensaton sgnals coespond to the efeence ones. The gate sgnals of the powe conetes ae obtaned by applyng pulse wdth modulatos to the contolle outputs. The powe conetes swtch at hgh fequency geneatng a PWM output oltage waefom whch must be low-pass flteed L, R and C n case of sees APF and L y C fo the shunt APF. Swtches S, S and S 3 contol the compensaton status of the UPQC. The oltage contolle can be mplemented n thee ways. Feedbac stuctues allow a good statonay esponse whle fowad stuctues geneate quc esponses dung oltage tansents. Feed-fowad stuctues allows both behaos beng moe used [9]. The geneaton of the efeence sgnal depends stongly on the compensaton objectes: oltage dps, oe-oltages o oltage hamoncs. The ms alue of the gd oltage can be measued to detect oltage dps and oe-oltages, once detected, the PLL used to synchonze the compensaton sgnal must be fozen not appled to the oltage sgnal to mantan the peous phase. When the load oltage hamoncs ae the compensaton objecte, a epette contolle can be appled to mtgate the effect of all oltage hamoncs [9]. n ths case the efeence sgnal s geneated nsde the oltage contolle and doesn t allow selecte hamonc compensaton, both n hamonc ode and hamonc magntude. output flte desgn []. P contolles hae been wdely appled but, due to the fnte gan at the fundamental gd fequency, they can ntoduce steady state eos. Ths can be soled by means of genealzed ntegatos []. Fuzzy logc and atfcal neual netwos A has been also poposed as cuent contolles n case of multple hamonc fequences n the efeence cuent sgnal [][3]. 3. Poposed Technque fo the Estmaton of the Compensaton Refeence Sgnals A. Refeence oltage estmaton The stuctue of the poposed algothm fo estmaton of C can be seen n fgue 3. A statonay fame dscete Kalman flte estmates the nstantaneous alues of each gd oltage hamonc, [4]. These oltage hamonc components ae used to establsh the pesence of a oltage dstubance compang the measued alues and the establshed confguaton alues. oltage dps and oe-oltages ae detected usng the gd oltage fundamental hamonc component, the ampltudes of othe measued oltage hamonc components ae ealuated to establsh the pesence of hamonc dstoton to be compensated. Once a cetan oltage dstubance s detected, the sees APF of the UPQC s swtched-on usng S, S and S 3. The efeence sgnal * at each equed fequency s obtaned as dffeence of the measued oltage hamonc components and the establshed confguaton alues. The dscete Kalman flte uses a statonay fame oltage sgnal model, then, each oltage hamonc component at tme nstant can be descbed as: Beng: x Ax w Dffeent appoaches hae been poposed fo cuent contol of gd-connected oltage souce conetes. Hysteess contolles ae mplemented by means of M L smple analog ccuts but, as dawbac, the spectum of O M the output cuent s not localzed, whch complcates the x M A M O n L M n n 95 RE&PQJ, ol., o.6, Mach 8

3 Fg. 3. Refeence oltage estmato. Whee and coespond espectely to the n-phase and the n-quadatue components of the fundamental fequency oltage hamonc of ode, w s the sgnal model nose ecto and M s defned as: M ωts sn ωts sn ωts ωts Beng ω the angula fequency of the fundamental gd oltage hamonc component and T S the samplng tme of the poposed dscete algothm. The appled ecuse dscete Kalman flteng loop coesponds to equatons [5]: P xˆ G P xˆ AP P G Axˆ xˆ C T T CP C R C P G Q Cxˆ whee P s the estmaton of pocess coaance matx at tme nstant usng ts alue at tme nstant -, Q - s the aance matx assocated to ecto w, G s the Kalman gans matx at tme nstant, ecto C, usng ths sgnal model, s defned as: C R s the aance matx of the oltage measuement eo and x ˆ s the pedcton of oltage hamonc components n the statonay fame at tme nstant usng the estmaton at tme nstant - x ˆ. The ampltude of the fundamental oltage hamonc component at nstant s ealuated as: A T S L 9 Fg. 4. Refeence cuent estmato. whch s compaed wth the equed load oltage. When a oltage dp o oe-oltage s detected the ecuse Kalman flte s fozen at the fundamental fequency and the descbed flteng loop s educed to 7 at the fundamental hamonc component, usng peously buffeed alues of and. The compensaton efeence sgnal at the fundamental fequency s obtaned as: R * R whee R s the equed load oltage ampltude. The compensaton efeences fo hghe ode hamonc components of s ae only appled when the establshed confguaton leels ae eached. These sgnals ae obtaned as: R * whee R s the confguaton ampltude of the oltage hamonc wth ode >. Fnally, the complete compensaton efeence sgnal at nstant can be obtaned usng: * C 3 Whee each * depends on the establshed confguaton leel R, allowng the selecte compensaton of oltage dstubances B. Refeence cuent estmaton The pocess to obtan C s shown n fgue 4. A dscete Kalman flte usng a statonay fame s appled to the load cuent L n ode to obtan ts hamonc and eacte components. The compensaton leels fo these components can be establshed usng the confguaton leels bloc depcted n the fgue. The estmaton of the hamonc cuent efeences s caed out accodng to n * 96 RE&PQJ, ol., o.6, Mach 8

4 the pocess descbed n the peous secton and, hence, ths secton only descbes the estmaton of the load cuent component whch contbutes to the eacte powe. t must be consdeed that the dc-bus oltage s contolled by means of a cuent consumpton at the fundamental gd fequency, whose ampltude s detemned though a P contolle, and n-phase wth the souce oltage. Snce the contolle executes smultaneously both Kalman flteng loops appled to load cuent and oltage sgnals, the flte efeence fames wll be synchonzed. Unde ths condton the phasos coespondng to oltage and cuent sgnals ae shown n fgue 5. Consdeng the outputs of the Kalman flteng loops at the fundamental pulsaton,, and : whee : 8 9 Due to the fact that: the nstantaneous alues of the snus and nus of can be obtaned as a functon of,, and : 3 As a consequence, the magntude of the cuent component whch contbutes to the eacte powe at the fundamental gd fequency can be ealuated each samplng nteal as a functon of the Kalman flteng outputs: 4 n ode to obtan the efeence cuent whch matches the nstantaneous alues of the cuent component contbutng to the eacte powe at the fundamental gd fequency, a untay ecto n phase wth must be appled to 4 : 5 The pecentage of the eacte powe at the fundamental gd fequency that can be compensated can be adjusted by ncludng a facto [,] n 5: 6 4. Smulaton Results The poposed algothm has been tested n smulaton, usng the SmPoweSystems BlocSet fom MatLab, accodng to fgue. The dc oltage efeence of the UPQC has been establshed at 4dc, the output flte of the oltage compensato conssts of a low-pass flte wth L 3 mh, R. Ω and C 3 µf whle the cuent ln of the cuent compensato has been modeled by applyng L mh and R.8 Ω. The nomnal powe of the oltage njecton tansfome s A wth a pmay and magnetzaton mpedances of L p.7mh, R p 35mΩ, L m 5mH and R m 8Ω. The souce oltage contans a 5Hz 35 sgnal and a 5 th hamonc of 5%. A dode ectfe wth a RC load C L µf, R L 3Ω has been used as local load. The efeence estmaton technque has been appled usng T S 56 μs as samplng tme, the load cuent sgnal has been modeled though the fst odd hamoncs whle st, 3 d, 5 th, 7 th and 9 th oltage hamoncs has been consdeed n case of the gd oltage sgnal. Fg. 6 shows the cuent compensaton capabltes of the poposed UPQC contolle. The oltage sgnal at the load temnals s shown n fg. 6.a. As can be seen, the sees sn sn sn sn sn sn sn sn sn ea ea,, sn Fg. 5. Repesentaton of oltage and cuent phasos n the synchonzed statonay efeence fames 97 RE&PQJ, ol., o.6, Mach 8

5 load Tme s a load 5 souce cuent A Tme s 3 b load souce Cuent specta A Fequency Hz c Fg. 6. oltage waefom at the load temnals, b load and souce cuent waefoms wth shunt compensaton only 3 d, 5 th and 7 th cuent hamoncs and c load and cuent specta Souce oltage Load oltage Tme ms Tme ms Fg. 8. Souce and load oltage waefoms fo a 4% oltage dp. 5 Gdsde waefoms p.u. Gdsde waefoms p.u. souce souce Tme s a souce souce Tme s b Fg. 7. oltage and cuent waefom sgnals at the gd sde a wthout eacte powe compensaton and b wth eacte powe compensaton. acte flte compensates the 5 th oltage hamonc esultng on a pue snusodal sgnal at the load sde. The cuent consumpton of the tested non-lnea load and the souce cuent wth selecte shunt compensaton s shown n fg. 6.b. As can be seen the waefom qualty mpoes due to the compensaton of 3 d, 5 th and 7 th cuent hamoncs. The sgnal specta can be compaed though fg. 6.c. As can be seen, the souce cuent consumpton at the fundamental fequency nceases due to the fact that the sees compensato s opeatng and the contbuton of 3 d, 5 th and 7 th cuent hamoncs to the load acte powe has been shfted to the fundamental gd fequency at the gd sde. Moeoe, the ntal load cuent THD s educed fom 3.3% wthout shunt compensaton to 35.9 % at the gd sde. n ode to mpoe the souce cuent THD, moe hamonc components of the load cuent waefom should be compensated by adjustng the selected confguaton leels. Fom the load oltage and cuent specta, the phase dsplacement between the oltage waefom at the load temnals and the souce cuent, both at the fundamental gd fequency, s.7º laggng fg. 7.a.. The powe facto can be mpoed by ncludng n the shunt Souce oltage Load oltage Tme ms Tme ms Fg. 9. Souce and load oltages when a 3% oe-oltage s appled compensaton tagets the load cuent component at the fundamental gd fequency whch contbutes to the eacte powe fg. 7.b.. n ths case, the dsplacement angle has been educed to.º mantanng the hamonc cuents compensaton capablty. The behao of the poposed UPQC contolle has been also tested unde oltage dp/oe-oltages. Fg. 8 shows the obtaned esults n case of a oltage dp s appled at t ms wth a oltage ampltude educton up to 95. The esponse tme, ncludng the oltage dp detecton tme and the contolle esponse, s less than one cycle at the fundamental fequency whch confms the appopate behao of the poposed UPQC contol technque fo the compensaton of oltage dps. Fgue 9 shows the obtaned smulaton esults when a 3% oe-oltage s appled at ms. As can be seen, once the oe oltage s detected, the UPQC acts educng the load oltage ampltude to the load nomnal oltage and the dynamcal esponse taes 3 ms. Ths demonstates that the poposed contolle allows a popely compensaton of oe-oltages. Fnally, the oltage hamonc compensaton capablty of a UPQC contolled usng the poposed estmaton 98 RE&PQJ, ol., o.6, Mach 8

6 oltage Tme ms Ampltude Fequency Hz Fg.. Souce and load oltage waefoms and specta fo the % compensaton of the 5 th oltage hamonc. efeence technque s shown n fgue. A gd oltage s wth a 5% of 5 th hamonc component s appled. The toleance leel fo the 5 th oltage hamonc 5 R s fxed to fo fully compensaton. The obtaned esults show that the poposed contol technque allows the % mtgaton of the 5 th oltage hamonc component. 5. Conclusons A new dgtal contol technque whch apples a dscete Kalman flte to geneate the compensaton efeence sgnals n UPQC has been pesented and tested n smulaton. The stuctue of the poposed efeence oltage and cuent estmato allows the compensaton of the eacte powe at the fundamental gd fequency, oltage and cuents hamoncs smultaneously and mtgates oltage dps and oe-oltages. Moeoe, the dstubance compensaton leels can be confgued allowng a moe flexble opeaton. The pefomance of the poposed contolle has been ealuated though dynamcal and steady-state smulaton tests. Refeences [] A. as and A. Emad, Dffeent topologes fo snglephase unfed powe qualty condtones, n Poc. Of 38th EEE ndusty Applcatons Socety Annual Meetng, ol., -6 Octobe 3. pp s L s L [] L. M. Tolbet, F. Z. Peng and T. G. Habetle, A multleel conete-based unesal powe condtone, EEE Tansactons on ndusty Applcatons, ol. 36, no, Mach/Apl. pp [3] G. Benyse, mpoement n the qualty of deley of electcal enegy usng powe electoncs. Spnge. London. 7. [4] H. Aag, E. H. Watanabe and M. Aedes, nstantaneous Powe Theoy and Applcatons to Powe Condtonng. Wley-EEE Pess. Apl 7. [5] M. Foghan and S. Afshana, Onlne waelet tansfom-based contol stategy fo UPQC contol system, EEE Tansactons on Powe Deley, ol., no., Januay 7. pp [6] H. Fujta and H. Aag, The unfed powe qualty condtone: the ntegaton of sees- and shunt-acte fltes, EEE Tansactons on Powe Electoncs, ol. 3, no., Mach 998. pp [7] D. Gaoac,. Katc and A. Rufe, Powe qualty compensaton usng unesal powe qualty condtonng system, EEE Powe Engneeng Reew, Decembe. pp [8] B. Han, B. Bae, H. Km and S. Bae, Combned opeaton of unfed powe-qualty condtone wth dstbuted geneaton, EEE Tansactons on Powe Deley, ol., no., Januay 6. pp [9] Y. H. Cho and S. K. Sul, Contolle desgn fo dynamc oltage estoe wth hamoncs compensaton functon, n Poc. of 39 th AS Annual Meetng, ol. 3, Octobe 4. pp [] D. G. Holmes and T. A. Lpo, Pulse wdth modulaton fo powe conetes : pncples and pactce. Wley-EEE Pess. 3. [] X. Yuan, W. Me, H. Stemmle and J. Allmelng, Statonay-fame genealzed ntegatos fo cuent contol of acte powe fltes wth zeo steady-state eo fo cuent hamoncs of concen unde unbalanced and dstoted opeatng condtons, EEE Tansactons on ndusty Applcatons, ol. 38, no., Mach-Apl. pp [] C.. Bhende, S. Msha and S. K. Jan, TS-fuzzycontolled acte powe flte fo load compensaton, EEE Tansactons on Powe Deley, ol., no. 3, July 6. pp [3] J. H. Mas and T. C. Geen, Pedcte tansentfollowng contol of shunt and sees acte powe fltes, EEE Tansactons on Powe Electoncs, ol. 7, no. 4, July. pp [4]. Moeno and J. Baos, Applcaton of Kalman flteng fo Contnuous Real Tme Tacng of Powe System Hamoncs, EE Poc.- Gene. Tansm. Dstb. ol. 44, no., Januay 997. pp RE&PQJ, ol., o.6, Mach 8