Address for Correspondence

Transcription

1 Research Paper YNAMIC VOLTAGE RETORER YTEM FOR POWER QUALITY IMPROVEMENT M. Balamuruan, T.. akumaran 2 Address for Correspondence Research cholar, epartment of EEE, Anna Unersty, Chenna, Taml Nadu, Inda. 2 Professor and ean, PG tudes, Aruna Collee of Enneern, Truannamala, Taml Nadu, Inda. ABTRACT ynamc Voltae Restorers (VRs) are ted to the power rd throuh powerfrequency transformers. In ths study, the desn of ode Clamped Multleel Inerter based dynamc oltae restorer (VR) s presented and offered to perform the fast fault detecton. A noel control method for VR s amed wth a carrer modulated PWM nerter. The proposed control system s smple to desn and has excellent oltae compensaton capabltes. The suested method for oltae sa/swell detecton can detect dfferent forms of power dsturbances faster than conentonal detecton methods. To obtan acceptable propertes such as transent oershoot, settn tme, and steadystate error. By ths, t s expected that the result of dsruptons on the output of proposed VR could be contracted for both symmetrcal and asymmetrcal oltae sa condtons usn MATLAB/ mulnk software. To reduce power nterruptons, ths study offers a new Zeta conerter based VR system. Ths proposed stratey can quckly access the oltae sa and swell under transent condton. KEYWOR: ynamc Voltae Restorer, Power Qualty, Voltae a/well, Zeta Conerter, Multleel Inerter. INTROUCTION Power qualty s the measure, analyss, and chane of a load bus oltae, to keep up that oltae to be snusodal at ealuated oltae and frequency. The phenomena assocated wth power qualty are real stochastc eents n the sense that n many cases are appearn and dsappearn arbtrarly. Thus, the power qualty measure s more than a mere measurement of an electrcal parameter;.e. It s necessary to record them oer an enouh lon tme nteral. To reduce the enormous amount of data by recordn and to analyze seeral electrcal parameters oer an extended perod, some recordn lmts are set. If these lmts are exceeded, the montorn nstruments ealuate the senste data and record just the substante data of the applcable ssues. There are dfferent reasons for montorn power qualty. The most snfcant cause s the economc damae created by electromanetc phenomena n crtcal process loads. Effects on equpment and process operatons can nclude malfunctons, damae, process dsrupton, and other anomales. Wth dstrbuton power systems, the man fnancal losses Moreoer, power qualty problems are connected wth oltae sa [], [2]. Recently, eneretc oltae restorer (VR) systems hae demonstrated promse n prodn a monetary alueeffecte resoluton for lowoltae (LV) systems [3]. nce nsulated ate bpolar transstors hae proressed snfcantly, and at the same tme, the cost and physcal sze of the conerters n the VR structures are reduced [4], []. On the other hand, unnterruptble power supples, whch are seen as an alternate to reulatn and een off the load oltae, hae become ery costly [6], [7]. Conentonal VRs are connected to the utlty rd throuh bulky powerfrequency transformers. Ths connecton has some demerts such as hh cost, lare sze, relately hh losses, saturaton, and start up nrush current [8] []. Besdes, the resstance of the transformer causes a oltae drop and ncreases load oltae harmoncs, especally when the load s nonlnear [9]. To reduce the cost and sze of the VRs n LV systems, transformerless VRs hae been proposed [8]. Ths approach not only adds to the number of swtches and needs solated capactors for each phase n a threephase system but also charn crcutry should mplement for each phase. These problems cast doubt oer the costeffcent aspect and operaton enhancement of the tradtonal structures. As a soluton, a current applcaton for VR system, where load oltae harmoncs are also compensated, has been proposed [9]. Thus, effecte usae of the seres transformer s obtaned [9]. Because ths VR system rejects the ffth and seenth oltae order harmoncs, hhfrequency harmoncs should pass throuh the rdconnected transformer. Ths approach dd not consder the passband lmtaton of the rdconnected transformer for hhfrequency harmoncs. Also, hhorder harmoncs ncrease losses n the rdconnected transformer. In [], an Hbrde cascaded multleel nerter has been mplemented to enhance the oltae leel wthout usn a transformer. Ths topoloy s relately complex, and the number of power swtches s consderable. o, n ths topoloy, cost ncreases and relablty decreases. A multleel cascadedtype VR, able to connect to the rd wthout a transformer, s proposed n []. The multleel VR can support a spread sa duraton compared to the twoleel VR. Also, harmoncs are studed, reardn the number of oltae leels produced by the VR system. It has been shown that reduced swtchn losses at the cost of ncreasn the number of swtches and ther assocated dre and control systems are obtaned. Ths approach cannot address the requrements of LV applcaton, where lowcost, smallsze, and lowweht systems are requred. Recently, an nterphase AC AC topoloy for snlephase sa compensaton has been proposed n [2]. Ths costeffcent topoloy enjoys small sze snce t has no storae dece. Howeer, t cannot compensate symmetrcal oltae sas. The concept of hhfrequencylnk VR for a snlephase system has been proposed [3], [4]. The ncorporaton of the transformer nto the conerter brns snfcant mproements such as substantal san n sze and weht. Therefore, the cost may also be reduced. o, ths VR s sutable for protecton of deces such as computers and medcal equpment [7]. Further nestatons of ths approach hae been deeloped n [] to compensate oltae sa n a threephase system wth a peak oltae of about 7 V. A sutable control stratey has been desned to aod hard swtchn, especally n cycloconerter. Unfortunately, the output of each phase cannot be controlled. A new concept of ode Clamped Multleel Inerter combned wth Zeta

2 conerter formed a VR s proposed n ths paper. The performance of VR depends on the effcency of control technque of swtchn the multleel nerter and zeta conerter. In ths artcle, PI controller and Multcarrer PWM control method are used to compensate oltae sa/swell. 2. YNAMIC VOLTAGE RETORER The seres oltae controller s connected n seres wth the protected load as shown n F.. Normally the connecton s establshed a a transformer, but forms wth drect connecton a power electroncs as well exst. The resultn potental dfference at the load bus bar equals the totalty of the rd oltae and the njected oltae from the VR. upply ZL Injecton Transformer V VR I Vs Flter Load Vactual Control unt 7 Leel CMLI Zeta conerter Vref ode Brde Rectfer F. chematc representaton of combned zeta conerter and CMLI based VR control system The crcut on the lefthand sde of the VR represents the Theenn equalent crcut of the system. The system mpedance Z th depends on the fault leel of the load bus. When the system oltae (V th ) drops, the VR njects a seres oltae VVR throuh the njecton transformer so that the desred load oltae mantude VL can be sustaned. The seres njected oltae of the VR can be wrtten as, usually hae a hh transfer oltae an and also produce hh nsulaton on both sdes. The an of the Zeta conerters always depends on the transformer s turn rato N, whch can be thousand tmes. The zeta conerter s a transformer based conerter wth a lowpass flter. Its output oltae rpple alue s small [89]. The crcut daram of zeta conerter s shown n F.2. VVR VL Zth IL Vth () Where, P V L s the desred load oltae Z th s the load mpedance C L I L s the load current C f 2 C V th s the system oltae durn fault condton N Tx The load current IL s F.2. Crcut daram of zeta conerter P L J Q The output oltae s en by, L I L (2) k VL Vo NVn (3) k The man use of the VR s to compensate oltae Where N s the turn rato of the transformer, and k sas and swells apart performn the chores such as s the conducton duty cycle k= t on /T. harmonc compensaton, reducton of transent n 2.2 ode Clamped Multleel Inerter oltae and fault current lmtaton [67]. VR s a The eneral structure of the multleel nerter s to seres connected custom power dece. Its prmary synthesze a snusodal oltae from seeral leels of purpose s the protecton of senste loads from any oltaes typcally obtaned from capactor oltae oltae dsturbances except oltae output. The sources. Multleel nerters are ben consdered for proposed VR system conssts of an njecton an ncreasn number of applcatons due to ther transformer, zeta conerter, flter, oltae source hh power capablty assocated wth lower output conerter and control & protecton system. F. harmoncs and lower commutaton losses. Multleel shows the formal representaton of proposed zeta nerters hae become an effcent and practcal conerter based VR control system. soluton for ncreasn power and reducn 2. Zeta Conerter harmoncs of AC load. The most commonly used A zeta conerter s a fourth order nonlnear system multleel topoloy s the dode clamped nerter, n ben that, about enery nput, t can seem as a buckboostbuck conerter and about the output, t can be whch the dode s used as the clampn dece to clamp the dc bus oltae so as to achee steps n the seen as a boostbuckboost conerter. mlar to the output oltae. Thus, the man concept of ths EPIC C/C conerter topoloy, the ZETA nerter s to use dodes to lmt the power deces conerter topoloy prodes a poste output oltae oltae stress. The oltae oer each capactor and from an nput oltae that ares aboe and below the each swtch s Vdc. An n leel nerter needs (n) output oltae. The ZETA conerter also needs two oltae sources, 2(n) swtchn deces and (n) nductors and a seres capactor sometmes called a (n2) dodes. By ncreasn the number of oltae flyn capactor. Unlke the EPIC conerter, whch leels, the qualty of the output oltae s mproed, s confured wth a standard boost conerter, the and the oltae waeform becomes closer to a ZETA conerter s set up from a buck controller that snusodal waeform. F. 3 shows the mulnk dres a hhsde NMOFET. Zeta conerters model of seen leel ode Clamped Inerter. VR

3 F. 3 mulnk model of seen leel ode Clamped Inerter 2.3 Injecton Transformer Its basc purpose s to step up the AC low oltae suppled by the nerter to the requred oltae. In the case of three phase VR type, three snle phase njecton transformers are commonly employed. The maxmum oltae sa the VR can compensate depends manly on the ratn of the nerter and the njecton transformer. The purpose of the njecton transformer s to nject the oltae suppled by the fltered zeta conerter based VI [2]. The njecton transformer wndn rato wll ncrease the prmary sde current, dependn upon the functonn of the zeta conerter based nerter. 2.4 Harmonc Flter A passe low pass flter conssts of an nductor and capactance. It can be located ether on the hh oltae sde or the nerter sde of the njecton transformer. It s appled to stran out the swtchn harmonc components of the njected oltae. By puttn the flter on the nerter sde, the hher order harmoncs are preented from nfltratn nto the transformer; thereby t reduces the oltae stress on the njecton transformer. When the flter s located on the hh oltae sde, snce harmoncs can penetrate nto the hh potental sde of the transformer, a hher ratn transformer s needed. The role of the flter s to stran out the selfenerated harmoncs enerated by VR, whch s composed of power electronc deces. The prmary use of the harmonc flter s to presere the harmonc oltae content to an acceptable leel, whch s produced by the zeta conerter fed multleel nerter. 2. Controller A proportonalnteral (PI) controller dres the plant to be controlled wth a wehted sum of the error ( the dfference between the actual sensed output and desred setpont) and the nteral of that alue. An adantae of a proportonal plus nteral controller s that ts nteral term causes the steadystate error to be zero for a step nput. The PI controller nput s an actuatn snal whch s the dfference between V L * and V L. The load oltae mantude s compared wth a reference oltae. uty cycle control technque s appled for zeta conerter swtchn to enerate a C oltae equalent to three phase quantty whch s to be fed throuh oltae source nerter at the load ends. The nput oltae of zeta conerter s taken out from the transmsson lne and run throuh the dode brde rectfer. PI controller s used wth zeta conerter to keep the electrc potental at the load termnals [2 22]. 3. Pulse Wdth Modulaton Control In the proposed CMLI topoloy, a leel based multcarrer PWM stratey s mplemented to frn the ate termnals of the MOFET to obtan the current waeform of seenleel dode clamped nerter. Multcarrer PWM stratey s a comparson of a reference waeform, wth ertcally shfted carrer snals. In multcarrer PWM technque, m tranular carrers are used for m leel nerter output oltae or current. In ths proposed seenleel topoloy sx tranular carrers are appled. The carrer waeforms hae same ampltude A C and frequency f C. mlarly, the reference waeforms hae frequency f ref and an ampltude A ref. At eery nstant, the response of the comparson s decoded to enerate the correct swtchn sequences on the output of the nerter. The frequency modulaton ndex (m f ) and ampltude modulaton ndex (m a ) are calculated n equaton () and (2) [232]. fc mf (4) f ref A ref ma () (m )A c In the leel shfted Multcarrer PWM Phase sposton (P), Phase Opposte sposton (PO), Alternate Phase sposton (APO) stratees are used. 3. Phase sposton (P) Ref, Carrer Tme () F. 4 Multcarrer PWM waeform (P waeform Phase sposton (P), where all tranular carrers aboe and below the zero reference are n phase. F. 3 shows the responses of P wth sne reference and F. 4 shows the responses of P wth snusodal reference. The responses of ths stratey shown for ma =.9, mf = 4.

4 4. VR COMPENATION F. shows the operaton of the VR that njects a controlled oltae enerated by the zeta conerter fed seen leel dode clamped nerter n seres to the system oltae usn an njectn transformer. The zeta conerter reulates the C oltae by aryn duty rato control usn PI controller. AC Man ode Brde Rec tfer Injecton Transformer CMLI P Cf N 2 Tx C L C Zeta conerter Load F.. Compensaton prncple of zeta conerter based VR system een leel dode clamped nerter used to conert the C oltae to AC oltae wth the elmnaton of harmoncs to compensate the power qualty dsturbances, such as oltae sa and swell. urn normal operatn condton, the VR njects ery low oltae to make up for the oltae drop n the njecton transformer and dece losses and drop. When sa/swell occurs n the dstrbuton system [26], the combned zeta conerter and CMLI based VR system ether njects/absorbs requred control oltae to presere output oltae to the load sde. The swtchn pattern of the seen leel CMLI can be nerted durn sa/swell condtons. The VR system s capable of eneratn or absorbn reacte power. In the proposed system the acte power njecton of the VR must be proded by combned zeta conerter and CMLI, whch s connected to the same system. The response tme of VR s ery small, and t s lmted by the power electroncs deces apart from the oltae sa/swell detecton tme.. IMULATION REULT AN ICUION MATLAB software s employed for obtann the smulatons. A threephase, power dstrbuton system confuraton s smulated usn Math Works Matlab/mulnk to study the effecteness and response of suested VR control stratey undersupply dsturbances (Lneround fault). Combned zeta conerter and CMLI based VR s connected n seres wth a lne for compensaton. The PI controller controls Zeta conerter by aryn the duty rato. Here VR system s connected n seres to the dstrbuton network by usn an njecton transformer. The VR operaton s based on three phase oltae source nerter wth LC output flter to remoe hhfrequency oltae components. An nducte nature RL load (R=KΩ, L =mcroh) s consdered for a ratn of the proposed scheme. F.6 shows the mulnk model of the proposed system and combned zeta conerter and CMLI based VR. The smulaton results are presented to proe the possblty of the proposed system. [n3] RL2 [out3] screte, Ts = e s. poweru n3 [n2] RL [out2] n2 RL [n] [out] out Ph C Ph B Ph A n Tx out2 out3 InOut [dra] T Ref InOut Ref2 InOut C Tx Ra Rb Rc Tmer Ref [drb] T Tx2 C2 [drc] [drc] ref ref Out Out2 R Y B N ubsystem2 C3 Out2 2. sa >= InOut Ref3 Measurement ubsystem 2. swell wtch Controlled Voltae ource n out u K T Abs Gan2 T F. 6 Oerall mulnk representaton of combned zeta conerter and CMLI based VR 2 2 Voltae n Volts Tme () F. 7 mulated seen leel CMLI output oltae

5 3 2 Input Voltae (V) Tme () F. 8 mulated nput oltae wth presence of swell condton 3 2 Load Voltae (V) Tme () F. 9 mulated load oltae compensated durn swell condton.3.2 Input Current (A) Tme () F. mulated nput current wth presence of swell condton.3.2 Load Current (A) Tme () F. mulated load current compensated durn swell condton 3 2 Input Voltae (V) Tme () F. 2 mulated nput oltae wth presence of sa condton

6 3 2 Load Voltae (V) Tme () F. 3 mulated load oltae compensated durn sa condton.3.2 Input Current (A) Tme () F. 4 mulated nput current wth presence of sa condton.3.2 Load Current (A) Compensaton Voltae (V) Tme () F. mulated load current compensated durn sa condton Compensaton Current (A) Tme () F. 6 Compensated oltae and current enerated by VR for R phase

7 Compensaton Voltae (V) Compensaton Current (A) Tme () F. 7 Compensated oltae and current produced by VR for Y phase Compensaton Voltae (V) Compensaton Current (A) Tme () F. 8 Compensated oltae and current produced by VR for B phase F. 7 shows the smulated seen leel CMLI output oltae. From the fure 7, t s clear that the dode clamped nerter produced seen leel output waeform. F. 8 shows the smulated nput oltae waeform wth the presence of a swell condton, the swell occurred at the perod of. sec to.2 sec. F. 9 shows the smulated waeform of load oltae compensated durn swell condton. The swelled oltae 2.V s compensated by the VR system combned wth Zeta conerter and CMLI. mlarly, the current waeform durn swell condton and compensated current waeform durn swell condton are shown n F. and respectely. F. 2 shows the smulated nput oltae waeform wth the presence of sa condton; the sa occurred at the perod of.3 sec to.4 sec. F. 3 shows the smulated waeform of load oltae compensated durn sa condton. The sa oltae 2.V s compensated by the VR system combned wth Zeta conerter and CMLI. mlarly, the current waeform durn sa condton and compensated current waeform durn sa condton are shown n F. 4 and respectely. F. 6 shows the compensated oltae and current enerated by VR for R phase. mlarly, the compensated oltae and current produced by VR for Y phase and B phase are shown n F.7 and 8 respectely. 6. CONCLUION In ths work, a fast response and cost effecte based ynamc Voltae Restorer (VR) s proposed for compensatn the problems of oltae sa and swell condton n dstrbuton systems, the effecteness of VR usn PI controller and Multcarrer PWM stratey s establshed for the nonlnear load. The response of the zeta conerter at C sde and the

8 performance of seen leel dode clamped nerter at AC oltae sde are performed well. The conerted oltae s properly njected nto the power system throuh njecton transformer. Other knds of controllers lke the fuzzy controller and adapte PIfuzzy controller may be employed n the VR compensaton scheme n future. REFERENCE. J. V. Mlanoc and Y. Zhan, Global mnmzaton of fnancal losses due to oltae sas wth FACT based deces, IEEE Trans. Power el., Vol. 2, No., pp , T. C. de Olera, J. M. de Caralho Flho, R. C. Leborne, and M. Bollen, Voltae sas: Valdatn shortterm montorn by usn lonterm stochastc smulaton, IEEE Trans. Power el., Vol. 24, No. 3, pp , Yan Gao, A. Q. Huan,. Krshnaswam, J. Rchmond, and A.K.Aarwal, Comparson of statc and swtchn characterstcs of 2V4HCBJT and 2VIGBT, IEEE Trans. Ind. Appl., Vol. 44, No. 3, pp , P.T. Chen, J.M. Chen, and C.L. N, esn of a statefeedback controller for seres oltaesa compensators, IEEE Trans. Ind. Appl., Vol. 4, No., pp , 29.. A. Cetn and M. Erms, VCbased TATCOM wth selecte harmonc elmnaton, IEEE Trans. Ind. Appl., Vol. 4, No. 3, pp., T. Jmch, H. Fujta, and H. Aka, esn and expermentaton of a dynamc oltae restorer capable of snfcantly reducn an enery storae element, IEEE Trans. Ind. Appl., Vol. 44, No. 3, pp , J.. Barros and J. F. la, Multleel optmal predcte dynamc oltae restorer, IEEE Trans. Ind. Electron., Vol. 7, No. 8, pp , B. H. L,.. Cho, and. M. Vlathamuwa, Transformerless dynamc oltae restorer, IEE Proc. Gener., Transm., strb., Vol. 49, No. 3, pp , M. J. Newman,. G. Holmes, J. G. Nelsen, and F. Blaabjer, A dynamc oltae restorer (VR) wth selecte harmonc compensaton at medum oltae leel, IEEE Trans. Ind. Appl., Vol. 4, No. 6, pp , 2... Wan, G. Tan, K. Yu, and J. Zhen, Modeln and control of a noel transformerless dynamc oltae restorer based on Hbrde cascaded multleel nerter, n Proc. Int. Conf., Power yst. Technol., pp. 9, 26.. A. M. Massoud,. Ahmed, P. N. Enjet, and B. W.Wllams, Ealuaton of a multleel cascadedtype dynamc oltae restorer employn dscontnuous space ector modulaton, IEEE Trans. Ind. Electron., Vol. 7, No. 7, pp , ubramanan and M. K. Mshra, Interphase AC AC topoloy for oltae sa supporter, IEEE Trans. Power Electron., Vol. 2, No. 2, pp. 4 8, H. Hossen, M. B. B. harfan, M. abah, A. Y. Goharrz, and G. B. Gharehpetan, Bdrectonal power electronc transformer based compact dynamc oltae restorer, n Proc. Power Enery oc. Gen. Meetn, pp., H. ree and N. Mohan, Hhfrequencylnk cycloconerterbased VR for oltae sa mtaton, n Proc. Power Modulator ymp., Conf. Rec. of the 24th Int., pp. 97, 2.. H. ree and N. Mohan, Voltae sa mtaton usn a hhfrequency lnk cycloconerterbased VR, n Proc. 26th Conf. IEEE Ind. Electron. oc., Vol., pp , O. Rosl and A.R. Nasrudn Modeln and mulaton for Voltae as/wells Mtaton Usn ynamc Voltae Restorer (VR)", 28 Australasan Unerstes Power Enneern Conference (AUPEC'8). 7. A.L. Fawz Modeln and mulaton of ynamc Voltae Restorer (VR) Based on Hysteress Voltae Control, Proceedns of 33rd Annual Conference of the IEEE Industral Electroncs ocety (IECON) No. 8, 27, Tape, Tawan. 8. N. Mohan, T.M. Undeland, and W.P. Robbns, Power Electroncs: Conerters, Applcatons, and esn, 3rd edton, John Wley & ons, New York, F.L. Luo and H. Ye Adanced C/C Conerters CRC PRE Boca Raton London New York Washnton,.C C. Zhan, V.K. Ramachandaramurthy, A.Arulampalam, C.Ftzer,.Kromlds, M.Barnes, N.Jenkns, ynamc oltae restorer based on Voltae space ector PWM control, IEEE Transactons on Industry Applcatons, Vol. 37, No.6,, pp. 8863, No./ec N.Katole Research cholar: epartment of Electrcal Enneern. G.H.Rason Collee of Enneern Napur, Maharashtra, Inda. Analyss and Mtaton of Balanced Voltae a wth the Help of Enery torae ystem ICETET pp. 3732, H.P. Twar and unl Kumar Gupta ynamc Voltae Restorer aanst Voltae a Internatonal Journal of Innoaton, Manaement, and Technoloy, ol., No. 3, pp , B. P. McGrath, et. al., Multcarrer PWM stratees for Multleel Inerters, IEEE Transacton on Industral Electroncs, Vol. 49, pp , R. Bowes, New snusodal pulse wdth modulated nerter, Insttute of Electrcal Enneern, Vol. 22, pp , M. A. Boost and P.. Zoas, tateoftheart Carrer PWM Technques: A Crtcal Ealuaton, IEEE Transactons on Industry Applcatons, Vol. 24, pp.27 28, M A Hannan and A Mohamed, Modeln and Analyss of a 24 Pulse ynamc Voltae Restorer n a strbuton ystem, tudent Conference on Research and eelopment proceedns, hah Alam, Malaysa, pp. 929, 22.