GENERATING REFERENCE CURRENT AND VOLTAGE CONTROL OF STATIC COMPENSATOR DURING VOLTAGE SAGS

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1 GENERATING REFERENCE CURRENT AND VOLTAGE CONTROL OF STATIC COMPENSATOR DURING VOLTAGE SAGS Thmeem Ansr R PG sholr, power systems engneerng, Dept. of eletrl nd eletrons engneerng J.J ollege of engneerng nd tehnology, Trhy-60009,Ind. nsr863@yhoo.om Astrt Voltge sgs nd nterruptons re generlly used y the fults suh s short ruts, energzton of the hey lods, strtng of the lrge motors,sngle lne to ground fults nd et. These sgs produed y oe uses wll nterrupt the system nd t hs to e mtgted mmedtely. Ths pper presents omplete ontrol sheme ntended for stt ompenstors opertng under these norml ondtons.stt synhronous ompenstors he een rodly employed for the proson of eletrl networ seres, whh nlude oltge regulton, networ lne, nd stlty mproement. Here the ontrol sheme noel rete urrent referene genertor loop. The rete power support for the system s the mn rter for the system stlzton.ths n e heed y shunt onnetng stt ompenstor n to system. The urrent referene genertor hs s mn feture the pty to supply the reured rete urrent een when the oltge drops n mpltude durng the oltge sg. Thus, sfe system operton s esly gurnteed y fxng the lmt reured urrent to the mxmum rted urrent.. Keywords Rete ompenston,stt ompenstor, Rete referene urrent genertor, Voltge sg. I.INTRODUCTION Modern power system omprses of omplex networs, where mny genertng sttons nd lod entres re nteronneted through long power trnsmsson nd dstruton networs [6]. Utlty dstruton networs, rtl ommerl opertons nd senste ndustrl lods ll suffer from rous types of outges nd nterruptons whh n led to sgnfnt fnnl loss, loss of produton, dle wor fores et. Tody due to the hngng trends nd restruturng of power systems, the onsumers re loong forwrd to the ulty nd rellty of power supply t the lod entres. A power ulty prolem s n ourrene mnfested s nonstndrd oltge, urrent or freueny tht results n flure or ms-operton of end use eupments. The mn uses of poor power ulty re hrmon urrents, poor power ftor, supply-oltge rtons, et. Rpd growth of nonlner lods leds to lots of power ulty prolems suh s hrmons, unlne operton nd exesse soure-end neutrl urrent n three-phse supplyng networs. Power flow s funton of trnsmsson lne mpedne, the mgntude of Mohmed Bdh Y Assote professor Dept. of eletrl nd eletrons engneerng J.J ollege of engneerng nd tehnology, Trhy-60009,Ind. sheee@gml.om the sendng nd reeng end oltges, nd the phse ngle etween the oltges. By ontrollng one or omnton of the power flow rguments, t s possle to ontrol the te, s well s the rete power flow n the trnsmsson lne. In the pst, power systems were smple nd desgned to e selfsuffent. Ate power exhnge of nery power systems ws rre s trnsmsson systems nnot e ontrolled fst enough to hndle dynm hnges n the system nd, therefore, dynm prolems were usully soled y hng generous stlty mrgns so tht the system ould reoer from ntpted opertng ontngenes. The STATCOM hs the lty to nrese/derese the termnl oltge mgntude nd, onseuently, to nrese/derese power flows n the trnsmsson lne. The renewle energy s the new energy growng soures whh s loted ner the lod entres.for the generton of the power wth the renewle energy the nllry seres he to e proded. The mn seres re the rete power reurement, oltge stlty. To mproe the oltge stlty rete power support s needed. For ll renewle energy the rete power ontrol s low. As the nstllton of the dstruted energy soures,there s need of ontrol the rete power. A STATCOM s shunt-onneted rete power ompenston dee tht s ple of genertng nd/or sorng rete power nd n whh the output n e red to ontrol the spef prmeters of n eletr power system. A STATCOM n supply the reured rete power under rous opertng ondtons, to ontrol the networ oltge tely nd thus, mproe the stedy stte stlty of the networ. It n e operted oer ts full output urrent rnge een t ery low oltge leels nd the mxmum r generton or sorpton hnges lnerly wth the utlty or system oltge. The norml opertng ondton of the STATCOM ws studed n [] [5].The operton nd ntegrton of the STATCOM n we networ ws nlyzed n [1].The oltge flututon wll led to the system nterrupton lso the deton n the oltge wll redue performne of the power eletron dees onneted to the networ. The ojete of the pper s to mtgte the ourrng of the oltge sg y gng the rete power

2 support to the system wth the help of STATCOM. The rete urrent referene genertor n generte the rete urrent when the system oltge redued.. II. STATIC COMPENSATOR Ths pper fouses the rete power support under the oltge sgs. The Stt ompenstor hs to fulfl rete power ontrol,rete referene urrent reurement durng oltge sgs. When there s fult, t hs to mtgte the fult y genertng the rete urrent. Fg. 1. STATCOM onneted to the nduton mhne nd the grd through trnsformer. The system under onsderton s sethed n Fg. 1 nd onssts of n Induton genertor dretly onneted to the grd through trnsformer, nd STATCOM onneted t the termnls of the nduton mhne. A.Grd Code Reurements The generton of power should remn onneted een n fulty grd ondtons nd lso to support the grd oltge. It should e onneted een n the short durton when the oltge sg re deep. It hs to supply the rete power durng oltge sg. Fgure shows the ehor of the Stt ompenstor.when there s oltge dp t the grd the rete power njeton wll nrese the root men sure lue of the system oltge durng the oltge sg. The nputs for the ontroller re the mesured phse oltges t the PCC, the urrents flowng nd the d-ln oltge d. Voltge nd urrent re trnsformed nto SRF lues. Seuene extrtor extrts the Voltges nto the symmetr omponents α nd β. The symmetr seuene extrtor s ey spet to hrterze the grd oltge. Mny seuene extrtors n e found n the lterture to extrt oltge sg nformton..the DC ln oltge s gng the te power support. The oltge sg ws deteted y the oltge support lo. Ths n e done y omputng the oltge rms n eh phse. When rms lues drop elow predefned threshold, the oltge support ontrol s tted. The oltge support lo dedes whh strtegy should e mplemented ordng to grd odes nd system lmttons. Then the oe nformton re gen to the referene urrent genertor. Ths referene urrent genertor genertes the referene urrent α -, β. Fnlly the referene urrents re ompred wth the urrents n the urrent loop nd then the duty yle re generted y the pulse wdth modultor to trgger the Stt ompenstor. The mn ojete of ths wor s to present method to rde through oltge sgs nd support the grd oltge. In three phse lned oltge sgs. the ontrol strtegy should e to rse the oltge n ll phses B. Chrtersts of Voltge sg A oltge sg s n norml ondton n the grd oltges,hrterzed y short-tme reduton n one or rous phses[8]. The uses of oltge sgs re Fg..Control dgrm of Stt Compenstor under fult ondton

3 mnly phse-to-ground short rut, phse-to-phse (to ground) short rut, nd the strt-up of lrge motor.the most wdely epted lssfton of oltge sgs s presented n [9].Poste seuene,negte seuene nd zero seuene oltges re three seuenes.of those zero seuenes re not onsdered Usng the lres trnsformton the seuenes omponents re extrted.the euton re follows The oe phse oltges re trnsferred to poste nd negte seuenes of β nd α.. (5) (6) The referene urrent loop s responsle for genertng referene urrent, expressed n (7) nd (8), ordng to the set ponts V d nd I s follows α = αp + α (7) β = βp + β (8) where αp, βp, α, β re the te nd rete urrent referenes, respetely. (1) () (3) (4) C. Voltge unlne ftor The rto of the poste seuene oltge to the negte seuene oltge t the pont of ouplng s nown s the unlned ftor. n (9) When the n lue s zero then the system oltge s lned otherwse the system s unlned.aordng to the lue of the Stt ompenstor ontrol rut re depended. D. Ate nd Rete referene urrent genertors The urrent suppled to the networ durng unlned oltge sgs n e hghly dstorted y hrmons. Seuene detetor, together wth the followng te urrent referenes [7], the hrmons of the urrent re strongly redued: p 3 p (10) p 3 p (11) Also the Rete referene urrent re (1 ) 1 (1 ) 1 Q Q (1) (13) Where s the rete element. re the onstnts for tht element Fg3.Smuln of Rete referene urrent genertor usng MATLAB

4 III.GENERATING REACTIVE REFERENCE CURRENT From the lres trnsformton the referene urrent s otned whh n e wrtten s I 3 n 1 os n mn 1 Q n 1 V (14) When the lue of re ether zero or 1.The oe euton (14) wll redued to I (15) V Q 3 Q s rete power, njeton of the rete urrent n ether poste or negte seuenes. When the lue of s 1,t n e njeted through poste seuene nd when s 0 t n e delered through negte seuene. Clerly the lue of should regulted etween 0 nd 1 By nsertng the euton (1) nd (13) n oe euton numer (14).The rete referene urrent euton s otned s n n ( 1 ) (1 )os mn (1 )os n (1 ) ( 1 ) mn n (1 ) I V I V (16) (17) Poste- nd negte seuene omponents of the PCC oltge re dretly otned t the output of the oltge seuene detetor, s shown n Fg..The two set pont I nd the ontrol gn should e hosen n order to fulfll spef ontrol ojete. The urrent set pont ontrol the rete power delered to the system,so the referene of the urrent set pont s to regulte the poste seuene oltge. When the oltge leel t the pont of ommon ouplng dereses, wll njet the desred oltge to the system. The negte seuene lue dereses y deresng the lue. Therefore the oordnted ontrol of poste nd negte seuene s employed. TABLE I PARAMETERS OF THE SYSTEM AND STATIC COMPENSATOR Symol Vlues V g Grd oltge 110 K f g Freueny 50 Hz R s Lne resstne 10 Ω L s Indutne 8 10 H V p, d Proportonl 0.3V V, d V p, + Controller Of V d Integrl ontroller Of V d Proportonl gn Of V + loop V, + Integrl gn Of V + V p, - loop Proportonl gn Of V - loop V,, - Integrl gn Of V - loop 15Vs 0.1V 15A/Vs 0.1V 0.A/Vs Phse oltges t the PCC for the seleted oltge sgs re shown n Fgs. 4 nd 5. Before the fult, the oltge n eh phse s round 415 V. The oltge leel s then onerted nto the per unt lue. At tme t = 0.4 s, the oltge sg ours n the Fg 4. Instntly, the oltge support strtegy s tted. Then t hnges from For ths tme perod the prmeter s set n order to mtgte the oltge sg.the flexle propertes of the proposed oltge support ontrol sheme. The proposed STATCOM ws tested wth oltge sg presented n [10].Also the oltge sg for the dfferent tme durton ws smulted Fg. 5 hs lrge stedy-stte mlne (see the tme nterl from 0.3 to 0.6 s) nd rle oltge profle durng the trnsent stte. For ths reson, the hosen oltge sg s good nddte to elute the performne of the proposed ontrol soluton n derse strngent networ ondtons. IV. EXPERIMENTAL RESULTS The expermentl ldton whh shows the theoretl explnton of ths pper. The smulton of ontrol rut of the rete referene frme s shown n Fg 3. Tle I lsts the ontrol prmeters of the system nd the Stt ompenstor tht fulfll ths reurement. The freueny of the system s ssumed to e 50Hz.The oltge t the PCC hs fst enough trnsent response nd error n stedy stte s redued sne the oltge seuene detetor hs enough tme to e updted. Tme(se) ()

5 Tme n seonds () () () Fg.5. Voltge t the grd when the sg ours durng tme perod ( )seonds. () Grd oltge when Sttom ws nte ()Compensted Grd oltge () Injeton of rete urrent. (d) Fg.4. Voltge t the grd when the sg ours durng tme perod ( )seonds. () Grd oltge when Sttom ws nte () Swthng perod of ontrol ruts ()Compensted Grd oltge (d) Injeton of rete urrent. () The swthng tme of the Stt ompenstor ws shown n fg 4().When the oltge sg ours t ny tme,oltge support detetor n Fg dedues the sg leel nd lso the durton of the sg. Durng tht tme nterl the njeton of the rete referene ws shown n Fgs 4(d) nd 5(). The sg our n the system s 0% (the oltge leel redues to 0.8pu) ws shown n Fg 4() nd Fg 5() shows tht the 30% of the system oltge dp lso ompenston of the oe mentoned oltge sg durton ws shown n Fg 4() nd Fg 5().The dfferent type of oltge sg wth the rous tme durton of the sg ws smulted n the MATLAB. Ths spefton defnes the onentonl sheme of rete power njeton y prodng the mnmum rete urrent tht must e njeted durng oltge sg s funton of the oltge t the PCC. The results shows tht mtgton of oltge sg y the njeton of the urrent through the Stt ompenstor ws effete. () V. CONCLUSION Results from rtl Sg nd gener shorter fult ndte the generl ppllty of the tehnue to dpt the STATCOM ontrol to the needs of the system durng reoery fter ny nd of ontngenes. Ths oltge ontrol sheme whh hs the hs the dntges of 1) oltge support durng sgs ) oltge regulton. Two dfferent senros he een expermentlly tested to llustrte the results of the proposed oltge support ontrol wth dfferent sg leel n the

6 rous tme durton. Seleted expermentl tests onfrm the theoretl fetures of ths ontrol lgorthm. To erfy nd proe the lty nd effeteness of the proposed oltge ontrol loop n stedy-stte nd dynm operton modes, smulton model ws reted.. The rete power support wth the help of the STATCOM ws smulted under dfferent oltge nd tme durton. Smulton results show the effeteness of STATCOM n te flterng nd flututons of oltge under rndomly ryng sg n e effetely redued.thus the sg ourred n the system ws mtgted lso AC oltge regulton nd power ftor of the trnsmsson lne lso mproed. REFERENCES [1] C. Hn, A. Hung, M. Brn, S. Bhtthry, W. Ltzenerger, L. Anderson, A. Johnson, nd A. A. Edrs, STATCOM mpt study on the ntegrton of lrge wnd frm nto we loop power system, IEEETrns. Energy Coners., ol. 3, no. 1, pp. 6 33, Mr [] M. Molns, J. A. Suul, nd T. Undelnd, Low oltge rde through of wnd frms wth ge genertors: STATCOM ersus SVC, IEEE Trns. Power Eletron., ol. 3, no. 3, pp , My 008. [3] K. L, J. Lu, Z. Wng, nd B. We, Strteges nd opertng pont optmzton of STATCOM ontrol for oltge unlne mtgton n three-phse three-wre systems, IEEE Trns. Power Del., ol., no. 1, pp , Jn [4] T. Lee, S. Hu, nd Y. Chn, D-STATCOM wth posteseuene dmttne nd negte-seuene ondutne to mtgte oltge flututons n hgh-leel penetrton of dstruted generton systems, IEEE Trns. Ind. Eletron., ol. 60, no. 4, pp , Apr. 013 [5] A. Yzdn, H. Sephnd, M. L. Crow, nd M. Ferdows, Fult deteton nd mtgton n multleel onerter STATCOMs, IEEE Trns. Ind. Eletron., ol. 58, no. 4, pp , Apr [6] J. M. Crrso, L. G. Frnuelo, J. T. Blsewz, E. Glán, R. C. Gusdo, M. A. Prts, J. I. León, nd N. Moreno- Alfonso, Power eletron systems for the grd ntegrton of renewle energy soures: A surey, IEEE Trns. Ind. Eletron., ol. 53, no. 4, pp , Jun. 006 [7] P. Rodrıute;guez, A. Tmus, R. Teodoresu, M. Lserre, nd F. Bljerg, Independent PQ ontrol for dstruted power generton systems under grd fults, n Pro. IEEE IECON, 006, pp [8] IEEE Reommended Prte for Montorng Eletr Power Qulty, IEEE Std , 1995 [9] M. Bollen, Chrterston of oltge sgs experened y three phse djustle-speed dres, IEEE Trns. Power Del., ol. 1, no. 4,pp , Ot [10] S. Cunde, R. Neumnn, M. Bollen, Z. Koolns, J. Vulet, A. Krole, S. Djo, K. n Reusel, nd K. Stomn, Immunty gnst oltge dps Mn reommendtons to steholders of the CIGRE/CIRED/UIE jont worng group C4.110, Int. J. Emerg. S., ol. 1, no. 4, pp , De. 011