A FUZZY CONTROLLER FOR ENHANCEMENT OF POWER SYSTEM STABILITY WITH FACTS DEVICE

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1 JATIT. All righs rsrv. A FUZZY CONTROLLER FOR ENHANCEMENT OF POWER SYSTEM STABILITY WITH FACTS DEVICE K.R.SUDHA, K.Harinaha Ry Dparmn of Elcrical Enginring, Anhra Univrsiy,Visakhapanam Inia Dparmn of Elcrical Enginring,LBR Collg of Enginring,Mylavaram, Inia arsuhaa@gmail.com, kaapa_hari@yahoo.co.in ABSTRACT This papr prsns h sign of fuzzy conrollr for Unifi Powr Flow Conrollr o improv h ransin sabiliy prformanc of a powr sysm. Th fuzzy conrollr uss a numrical consun rul bas of h Takagi-Sugno yp, which can ihr linar or non linar-proucing conrol gain variaion ovr a vry rang. A fuzzy logic powr sysm sabilizr has bn vlop using sp an roor angl viaion as conrollr inpu variabls. Th un sabilizr has bn s by prforming non linar simulaions using a synchronous machin-infini bus mol. Inx Trms FACTS, Unifi Powr Flow Conrollr (UPFC), Fuzzy Powr Sysm Sabilizr (FPSS).. INTRODUCTION Powr sysms ar larg-scal, nonlinar, nonsaionary, mulivariabl, complx sysms isribu ovr larg gographical aras. Sysm-wi isurbancs in powr sysms ar a challnging problm for h uiliy inusry. Furhr, bcaus of nw consrains plac by conomical an nvironmnal facors, h rn in powr sysm planning an opraion is owar maximum uilizaion of xising lcriciy infrasrucur, wih igh opraing margins, an incras pnraion of rnwabl nrgy sourcs such as win powr. A fuzzyconrol approach for flxibl AC ransmission sysms (FACTS) bas on loa angl an iffrnc ar consir for sign of rul bas in is prsn in his papr. Unr ynamic coniions such as fauls, lin opnings, gnraor ripping an loa hrow off, c. prociv sysms ar sign wih mor mphasis on procing h uipmns han concrn o h sysm scuriy an sabiliy. Howvr, juicious us of ynamic conrols a gnraing sysms, xciaion/govrnor sysms, HVDC sysms, saic compnsaors an mor rcnly FACTS vics will hlp o mainain h sysm scuriy/sabiliy. In a ay-o-ay opraion i may b byon h opraor s scop o ak any conrol cision uring mrgncis an us various conrol vics. Th firs jusificaion is corrc, bu os no characriz h uniu naur of fuzzy sysms hory. In fac, almos all horis in nginring characriz h ral worl in an approxima mannr. For xampl, mos ral sysms ar non linar, bu w pu a gra al of ffor in h suy of linar sysm. A goo nginring hory shoul b prcis o h xn ha i characrizs h ky faurs of h ral worl an, a h sam im, i is rackabl for mahmaical analysis. In aspc, fuzzy sysms hory os no iffr from ohr nginring pracics.. SYSTEM MODEL For molling purpos, h horical analysis of h singl machin infini-bus sysm is consir for ransin sabiliy simulaions a h firs insanc. Th powr sysm an is ail circui mol ar shown in Fig.. Th synchronous gnraor is rprsn by a 3r orr machin mol an h gnraor xciaion sysm has a simpl auomaic volag rgulaor. ω = ω0 + ω = ( Pm P )/ M P = E f = ( E + E ( x x ) i ) i f0 = K + ( V V + u) rf f ( x x ) i i / τ / τ 0 33

2 JATIT. All righs rsrv. Unifi Powr Flow Conrollr is a mulifuncional flxibl ac ransmission (FACTS) vic wih is ponial applicaion in powr sysm for h powr flow conrol, volag conrol, ransin sabiliy improvmn an amping of oscillaions. In a powr sysm, h powr flow for a wo-bus sysm pns on h magniu of bus volags, hir phas iffrnc an h impanc of h ransmission lin. UPFC conrols h powr flow [-3] by conrolling on of h hr basic paramrs (volag, impanc or phas angl) of a ransmission lin or a combinaion of hs paramrs. UPFC consiss of wo volagsourc convrrs connc back-o-back hrough a common DC link capacior. On of h convrrs is connc in paralll wih ransmission lin hrough an xciaion ransformr whras h ohr in sris wih lin by a sris or boosing ransformr. Th sris an shun pars of UPFC can conrol powr flow an AC volag rspcivly, whn a consan volag is mainain across h DC link capacior. Lik ohr powr lcronic vics, UPFC is also a nonlinar, muli-inpu mulioupu an paramr snsiiv vic an hrfor sign of a clos loop conrollr is a challnging job. Fig.. UPFC Mol Sris Convrr: Th sris convrr injcs a variabl volag sourc an h shun convrr a variabl currn. Th simplifi rprsnaion of h iffrnial[3] an algbraic uaions for h gnraor, xciaion sysms ar givn. V = -V + Vb Sinδ x(i+is) V = -Vc + Vb Cosδ x(i+is) V = V + V V = V + V c c Shun Convrr: Th an -axs of h shun convrr ar chosn in such a way ha -axis volag coinci wih h rminal volag of h UPFC bus. Hnc h axs rprsnaion of h shun convrr is as shown.thus h irc an uaraur uaions of h shun convrs ar D = rs id xsiq+v Q = rs iq xsid Whn xprss in rms of h axs fix o roor of h synchronous gnraor h volag s, s ar s s sinδ = cosδ δ D cosδ sinδ v = an v = κρ V cos α = κρ V sin α C c D Q Shun convrr volag, E = + Th capacior volag ynamics[-4] is obain as Vc = i = i i c = i s Q D [ Vi D + Vi + Vcpi cp ]/ CVc + i + i s s For h ransin sabiliy nhancmn, h aciv volag componn is conroll using ihr h raciv powr viaion( Q) or volag viaion ( V ) a h bus no.. Th uaraur volag componn of h sris convrr is conroll by h ral powr viaion P a h bus-. Insa of using an ircly, a mor ralisic conrol is obain using h in-phas an uaraur volag componns [5], an wih h lin currn c I = i + i V V c = V = V cp cp i θ = an i V = V c crf sin θ V V c cr cos θ V cr cos θ sin θ C Q c 34

3 JATIT. All righs rsrv DESIGN OF FUZZY CONTROLLER FOR UPFC Fuzzy sysms ar o b prcisly fin an fuzzy conrol is a spcial kin of non linar conrol ha also will b prcisly fin. In ohr wors, alhough h phnomnon ha fuzzy sysms hory[9] characrisic may b fuzzy, hory islf is prcis. In h liraur, hr ar wo kins of jusificaion for fuzzy hory.in h liraur, hr ar wo kins of jusificaion for fuzzy hory. Thy ar.. Th ral worl is oo complica for prcis scripions o b obain; hrfor approximaion (fuzzinss) mus b inrouc in orr o obain a rasonabl, y rackabl mol.. As w mov ino informaion ra, human knowlg bcoms mor imporan. W n a hory o formula human knowlg is a sysmaic mannr an pu i ino nginring sysms, oghr wih ohr informaion lik mahmaical mol an snsory informaion. Th acion mol in PSS is bas on fuzzy logic applicaions. Th srucur of fuzzy logic PSS is show in figur. Conrol acion formaion inclus four sags. A)Ging h inpu valus of paramr viaion B)Fuzzificaion ( ransforming ino fuzzy form) of h inpus C)Drminaion of fuzzy conrol acion D)Dfuzzificaion (ransforming h linguisic valus ino uaniaiv form) of h conrol acion. Th riangular mmbrship funcion is us for boh inpu an an oupu. A funcion of a vcor, x, an pns on hr scalar paramrs a, b, an c, as givn by f ( xabc,,, ) Or, mor compacly, by 0, x a x, a x b b = c x, b x c c b 0, c x x a c a f( x, a, b, c) = max (min,, 0 ) b a c b Th paramrs a an c loca h f of h riangl an h paramr b locas h pak. Dgr of mmbrship LN MN SN ZE SP MP LP variaion of la Fig. Fuzzy mmbrship funcions Th vlopmn of h fuzzy logic approach hr is limi o h conrollr srucur an sign. Th scon rm of () is rplac wih a fuzzy logic rul-bas using h filr sp viaion an acclraion of h machin. Tha is h viaion from synchronous sp an acclraion of h machin ar h rror,, an rror chang. &, signals, rspcivly. For h conrollr h conrol oupu, u. is h sabilizing signal Vs. Each conrol rul R, is of h form: IF is Ai AND ė is bi THEN u is Ci Whr Ai, Bi an Ci ar fuzzy ss wih riangular mmbrship funcions as shown normaliz bwn - an. Ths sam fuzzy ss ar us for ach variabl of inrs: only h consan of proporionaliy is chang. Ths consans ar K, Kė an K for h rror. Error chang an conrol oupu, rspcivly. Th rror an rror changs ar classifi accoring o hs fuzzy mmbrship funcions moifi by an appropria consan. A spcific signal may hav non-zro mmbrship in mor han on s. Similarly, a spcific conrol signal may rprsn h conribuion of mor han on rul. Rul coniions ar join by using h minimum inrscion opraor so ha h rsuling mmbrship funcion for a rul is: 35

4 JATIT. All righs rsrv. V rf µ R,. = min µ Ai,(), µ Bi, Th suggs conrol oupu from rul I is h cnr of h mmbrship funcion C Ruls ar hn combin using h cnr of graviy mho o rmin a normaliz Conrol oupu U. ẹ LN MN SN ZE SP MP LP LN LP LP LP MP MP SP ZE MN LP MP MP MP SP ZE SN SN LP MP SP SP ZE SN MN ZE MP MP SP ZE SN MN MN SP MP SP ZE SN SN MN LN MP SP ZE SN MN MN MN LN LP ZE SN MN MN LN LN LN Fig 3. Fuzzy Rul Bas Tabl (LP=larg posiiv: MP= mium posiiv: SP=small posiiv; ZE=zro: SN=small ngaiv; MN=mium ngaiv; SN= small ngaiv) Th ia bhin h FLC[9] is o fuzify h conrollr inpus,hn infr h propr fuzzy conrol cision bas on fin ruls.th FLC oupu is hn prouc by fuzzifying his infrr conrol cision.fuzzyficaion is h procss of ransfrring h crisp inpu variabls o corrsponing fuzzy variabls. Sp ω an sp viaion ω ar fuzzifi accoring o mmbrship funcions shown in figur.. + V U pss AVR K + T s E f max E f min E f E f0 E f opraion an gnral cnroi fuzzifir mho is us for h oupu of h fuzzy conrollr 4. SIMULATION RESULTS Simulaion rsuls ar obain for h singlmachin infini-bus as shown in figur.9 o 0. Th UPFC conrol schm consiss of conrolling volag componns an by using ral an raciv powr viaions or ral powr an volag viaions. Th currn of h shun convrr is obain from h powr balanc uaions a vry conrol insan. Th following larg isurbanc cass ar consir for valuaing h prformanc of hs conrollrs. A h pr isurbanc coniion Th opraing lvl of h gnraor is hn chang o a high powr cas wih p.u., an p.u. an h sam faul is cra. Fig. 5 shows ransin rspons of h powr sysm for his opraing coniion wih ihr UPFC or h Fuzzy conrollr. Variaion of roor angl wih rspc o im is shown in fig.5.tim rspons is obsrv wih fuzzy conrollr. From h rspons, i can b ascrain ha h lcromchanical oscillaions ar amp vry uickly in cas of h nw conrollr proving is suprioriy ovr h convnional conrollrs us. Variaion of oscillaion shown in fig.5 givn opraring coniions wih an wihou fuzzy conrollr. roor angl roor angl - la wihou fuzzy wih fuzzy FPSS Inpu Signals im "" in scons Fig.5. Variaion of roor angl Fig.4. Propos FPSS conrol schm Th oupu variabls of h fuzzy infrnc sysm mus b convr ino numrical oupu. Using Zah s ruls for Variaion of sp angl wih rspc o im is shown in fig.6.tim rspons is obsrv wih fuzzy conrollr. 36

5 JATIT. All righs rsrv. sp sp - w wihou fuzzy wih fuzzy im "" in scons Fig.6. Variaion of sp 5. CONCLUSION In his papr h fuzzy logic sabilizr for Unifi Powr Flow Conrollr (UPFC) is prform. This conrol srucur uss boh convnional an FPSS. In paricular, using as inpu signal h sp viaion of machin an aciv powr of lin (whr Unifi Powr Flow Conrollr is connc) for fuzzy powr sysm sabilizr. Th simulaion rsuls obain on h singl machin wih fuzzy logic conrollr improvs powr sysm ynamic prformanc. By us of his mho no only h amping bhaviour bu also h ransin sabiliy is improv significanly. APPENDIX I ) Gnraor Daa x =.9, x=.6, x=0.7, τo=4.34s H=4s, x=0.3, K=50 τ = 0.s ) UPFC Daa Vcbas=3.3Kv, MVAbas = 00, C=5500µF Limis of UPFC aa in p.u. Vcp= ±0., Vcr= ±0. 3) Conrollrs aa Kpp = 0.3, Kip = 3, Kp = 0.5, Ki = ; Kpv = 0., Kiv = REFERENCES: [] K. R. Paiyar an A. M. Kulkarni, Conrol sign an simulaion of unifi powr flow conrollr, IEEE Trans. on Powr Dlivry, vol. 3, no. 4, pp , 998. [] S. Limyingcharon, U. D. Annakkag, an N. C. Pahalawahha, Fuzzy logic bas unifi powr flow conrollrs for ransin sabiliy improvmn, IEE Proc. -C, vol. 45, no. 3, pp. 5 3, 998. [3] P.K..Dash,S.Mishra,an G.Pana A Raial Basis Funcion Nural Nwork Conrollr for UPFC IEEE Trans. on Powr Sysms, vol. 5, no. 4, pp [4] L. Gyugyi, C. D. Schaur, S. L. Torgrson, an A. Eris, Th unifi powr flow conrollr: A nw approach o powr ransmission conrol, IEEE Trans. on Powr Dlivry, vol. 0, no., pp , 995. [5] M. Noroozian, L. Anguis, M. Ghanari, an G. Anrson, Improving powr sysm ynamics by sris-connc FACTS vics, IEEE Trans. on Powr Dlivry, vol., no. 4, pp , 997. [6] K. S. Narnra an K. Parhasarahy, Inificaion an conrol of ynamical sysms using nural nworks, IEEE Trans. on Nural Nworks, vol., no., pp. 4 7, Mar [7] K. G. Narnra, K. Khorasani, V. K. Soo, an R. V. Pal, Inllign currn conrollr for HVDC ransmission link, IEEE Trans. on Powr Sysms, vol. 3, no. 3, pp , Aug [8] M. Noorzian, G. Anrson, an K. Tomsovic, Robus, nar im-opimal conrol of powr sysm oscillaions wih fuzzy logic, IEEE Trans. on Powr Dlivry, vol., no., pp , 996. [9] S. Khanmohammai, Omi Ghari, Simulanous Coorina Tuning of Fuzzy PSS an Fuzzy FACTS Dvic sabilizr for Damping Powr Sysm Oscillaions in Muli Machin Powr Sysm IEEE Trans. on Powr Sysms 007 [0] Hingorani Narain G. Flxibl ac ransmission. IEEE Spcr 993:40 5. [] Eris A-A. Propos rms an finiions for flxibl ac ransmission sysms (FACTS). IEEE Trans Powr Dliv 997; (4): [] Gyugyi L. Unifi powr-flow conrol concp for flxibl ac ransmission sysm. IEEE Proc C 99;39 (4):

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