Transient Stability Enhancement of Multimachine System Using UPFC

Transcription

1 Internatonal Journal of Innoate Studes n Senes and Engneerng Tehnology ISSN (Onlne) Volume: Issue: Noember 06 Transent Stablty Enhanement of Multmahne System Usng UPFC Maln Palt Assstant Professor, Eletral Engneerng Deartment, GIMT, Assam, Inda Abstrat: Flexble AC Transmsson Systems (FACTS) dees an be used for ower flow ontrol, oltage regulaton, enhanement of transent stablty and damng of ower osllatons. FACTS dees an be used as a seres ontroller, shunt ontrollers or by a ombnaton of both. The new generaton and most domnant onerters needed n FACTS ontrollers are the STATCOM, the Stat Synhronous Seres Comensator (SSSC) and the UPFC, whh are based on the oltagesoure nerters. The UPFC s a tyal FACTS ontroller layng a tal role as a stablty ad for small and large transent dsturbanes n an nteronneted ower system. The ontroller s desgned by P method. Comrehense omuter smulatons hae been arred out for stablty studes of SMIB and mult-mahne system wth UPFC. The aboe modelng wll be mlemented n mult-mahne system for transent stablty studes. Keywords: UPFC, P method, Custom ower soure, Transent stablty.. INTRODUCTION Stablzaton of a synhronous generator s undoubtedly one of the most mortant roblems n ower system ontrol. Power system stablzers (PSS) and Automat oltage regulators (AVR) are normally emloyed to dam out the eletromehanal osllatons as well as for the reoery of ost-fault bus oltage reoery. Howeer, t s well known that the erformanes of PSS and AVR are lmted sne ther desgns are rmarly based on lnear ontrol algorthms. In the eent of large faults, the nonlneartes of the system beome ery seere, thereby uttng lmtatons on the erformanes of lassal ontrol desgns. Fast rogresson n the feld of ower eletrons has great nfluene on the ower ndustry One dret outome of ts nfluene s the onet of Flexble AC Transmsson Systems (FACTS), whh mroes stablty to nrease usable ower transmsson aaty to ts thermal lmt. The famly of FACTS dees makes use of nsulated gate bolar transstors (IGBTs) n hgh ower onerter onfguratons that an be ontrolled to behae as three hase snusodal oltage soures, to rode fast ontrol of ate and reate ower through a transmsson lne. A ower eletron based system and other stat eument that rodes ontrol of one or more AC transmsson system arameters s alled FACTS ontroller. The famly of FACTS ontroller nludes the Stat Var Comensators (SVCs), Stat Synhronous Comensators (STATCOMs), Thyrstor Controlled Seres Comensators (TCSCs), the Stat Synhronous Seres Comensators (SSSCs), and the Unfed Power Flow Controllers (UPFCs). The uses of nonlnear loads are growng radly and ths knd of loads njets reate ower nto the ower system. Ths rojet resents a new and effete onet of FACTS ontrollers n order to ahee better reate as well as real ower omensaton than other onentonal ontrollers wth less omlexty. Lterature Reew In lterature arous modelng of and UPFC are roosed to sole the dfferent tye of roblem suh as oltage stablty enhanement, damng torsonal osllatons, ower system oltage ontrol, and ower system stablty mroement. The soluton roedures nlude urrent njeton as well as ower njeton method. Howeer both STATCOM and UPFC modelng are based on onentonal Fuzzy or PI ontrollers due to whh damng out of eletromehanal osllatons has not been redued and tme onsumton s more for tunng the gan arameters. Kalyan K. Sen, Staey, Er J [] modeled the FACTS dee UPFC usng EMTP smulaton akage. The UPFC s hang two soldstates VSI whh are onneted wth ommon d lnk aator. One s stat synhronous omensator (STATCOM) and a stat synhronous seres omensator (SSSC). Hngoran and Gyugy [], resented n the bas onet about FACTS dees. Ths aer dsusses all the Power Eletron dees, whh an be used to ontrol the bas ower system arameters (oltage, urrent and medane).the authors desrbe the bas onets of the roosed 06, IJISSET Page

2 Internatonal Journal of Innoate Studes n Senes and Engneerng Tehnology ISSN (Onlne) Volume: Issue: Noember 06 generalzed P and Q ontroller and omare t to the more onentonal but related ower flow ontrollers, suh as Thyrstor-ontrolled seres aator and Thyrstor ontrol hase angle regulator. Padyar and Kulkurn[] n, roosed a asade PI ontroller struture for shunt nerter of Unfed Power Flow Controller whh an be used for STATCOM. R.Mohan Mathur and Raj.K.Varma [4] n, resented the alatons of FACTS ontrollers n ower transmsson lne. They also resented about the FACTS dees used for transent stablty enhanement. P.Kundur[] n, resents detaled analyss about stablty. The author also learly exlans about the fators affetng transent stablty and also about the arous methods for enhanng transent stablty.. Objete The lterature reew reeals that there exsts a need for dynam modelng of FACTS dees wth sutable effete ontrollers, to dam out eletromehanal osllatons as well as to mroe the ower system stablty. To deelo MATLAB/SIMULINK model of UPFC for MMIB system to mroe the ower system stablty for a oen loo system. To deelo a MATLAB/SIMULINK model of UPFC wth roortonal ntegral ontroller for a losed loo system to mroe the ower system stablty to dam out eletromehanal osllatons.. POWER SYSTEM STABILITY. Introduton Power system stablty s defned as the roerty of ower system that enables t to reman n a state of oeratng eulbrum under normal oeratng ondtons and to regan an aetable state of eulbrum after beng subjeted to a dsturbane. It was reognzed as a roblem as far bak as the 90s at whh tme the haraterst struture of system onssted of remote ower lants feedng load entres oer long dstanes. These early stablty roblems, as a result of nsuffent synhronzng torue, were the frst emergene of transent nstablty. Transent stablty s the ablty of a ower system to reman n synhronsm when subjeted to large transent dsturbanes. These dsturbanes may nlude faults on transmsson elements, loss of load, loss of generaton, or loss of system omonents suh as transformers or transmsson lnes. Although many dfferent forms of ower system stablty hae emerged and beome roblemat n reent years, transent stablty stll remans a bas and mortant onsderaton n ower system desgn and oeraton. Whle t s true that the oeraton of many ower systems are lmted by henomena suh as oltage stablty or small-sgnal stablty, most systems are rone to transent nstablty under ertan ondtons or ontngenes and hene the understandng and analyss of transent stablty reman fundamental ssues. Also, we shall see later n ths hater that transent nstablty an our n a ery short tme-frame (a few seonds) leang no tme for oerator nterenton to mtgate roblems. It s therefore essental to deal wth the roblem n the desgn stage or seere oeratng restrtons may result. The ower system s a hghly nonlnear system that oerates n a onstantly hangng enronment loads, generator oututs, toology and key oeratng arameters hange ontnually. When subjeted to a transent dsturbane, the stablty of the system deends on the nature of the dsturbane as well as the ntal oeratng ondton. The dsturbane may be small or large. Small dsturbanes n the form of load hanges our ontnually, and the system adjusts to the hangng ondtons. The system must be able to oerate satsfatorly under these ondtons and suessfully meet the load demand.. Classfaton of Stablty Power system stablty s a sngle roblem; howeer, t s mratal to deal wth t as suh. Instablty of the ower system an take dfferent forms and s nfluened by a wde range of fators. Analyss of stablty roblems, nludng dentfyng essental fators that ontrbute to nstablty and desng methods of mrong stable oeraton s greatly faltated by lassfaton of stablty nto arorate ategores. These are based on the followng onsderatons:. The hysal nature of the resultng nstablty related to the man system arameter n whh nstablty an be obsered.. The sze of the dsturbane onsdered ndates the most arorate method of alulaton and redton of stablty.. The roesses and the tme san that must be taken nto onsderaton n order to determne stablty. 06, IJISSET Page

3 Internatonal Journal of Innoate Studes n Senes and Engneerng Tehnology ISSN (Onlne) Volume: Issue: Noember 06 Power system stablty may be broadly defned as that roerty of a ower system that enables t to reman n a state of oeratng eulbrum under normal oeratng ondtons and to regan an aetable state of eulbrum after beng subjeted to a dsturbane. Instablty n a ower system may be manfested n many dfferent ways deendng on the system onfguraton and oeratng mode. The stablty roblem has been one of mantanng synhronous oeraton. Power system stablty s a major roblem, howeer t s mratal to study t as suh. Instablty of a ower system an take dfferent forms and an be nfluened by a wde range of fators. Analyss of stablty roblems and formaton of methods of mrong stable oeraton are greatly faltated by the lassfaton of stablty nto arorate ategores. Physal nature of the resultng nstablty,. Sze of the dsturbane onsdered. Arorate method of alulaton and redton of stablty. Rotor Angle Stablty Rotor angle stablty s onerned wth the ablty of nteronneted synhronous mahnes of a ower system to reman n synhronsm under normal oeratng ondtons and after beng subjeted to a dsturbane. It deends on the ablty to mantan eual to restore eulbrum between eletromagnet torue and mehanal torue of eah synhronous mahne n the system. Instablty that may result ours n the form of nreasng angular swngs of some generators leadng to ther loss of synhronsm wth other generators. The rotor stablty roblem noles the study of eletromehanal osllatons nherent n ower systems. The fundamental fator s the manner n whh the ower oututs of synhronous mahnes ary as ther rotor angle hange. The mehansm by whh nteronneted synhronous mahnes mantan synhronsm wth one another s through restorng fores, whh at wheneer there are fores tendng to aelerate or deelerate one or more mahnes wth reset to other mahnes. Under steady-state ondtons, there s eulbrum between the nut mehanal torue and the outut eletral torue of eah mahne, and the seed remans onstant. If the system s erturbed, ths eulbrum s uset, resultng n aeleraton or deeleraton of the rotors of the mahnes aordng to the laws of moton of a rotatng body. If one generator temorarly runs faster than another, the angular oston of ts rotor relate to that of the slower mahne wll adane. The resultng angular dfferene transfers art of the load from the slow mahne to the fast mahne, deendng on the ower-angle relatonsh. Ths tends to redue the seed dfferene and hene the angular searaton. The ower-angle relatonsh, as dsussed aboe, s hghly nonlnear. Beyond a ertan lmt, an nrease n angular searaton s aomaned by a derease n ower transfer; ths nreases the angular searaton further and leads to nstablty. For any gen stuaton, the stablty of the system deends on whether or not the deatons n angular ostons of the rotors result n suffent restorng torues.. UNIFIED POWER FLOW CONTROLLER (UPFC). Defnton A ombnaton of a stat synhronous omensator (STATCOM) and a stat synhronous seres omensator (SSSC) whh are ouled a a ommon d lnk, to allow bdretonal flow of real ower between the seres outut termnals of the (SSSC) and the shunt outut termnals of the STATCOM, and are ontrolled to rode onurrent real and reate seres lne omensaton wthout an external eletr energy soure. The UPFC, by means of angularly unonstraned seres oltage njeton, s able to ontrol, onurrently or seletely, the transmsson lne oltage, medane, and angle or, alternately, the real and reate ower flow n the lne. The UPFC may also rode ndeendently ontrollable shunt-reate omensataton. The Unfed Power Flow Controller (UPFC) onet was roosed by Gyugy n 99.The UPFC was desed for the real-tme ontrol and dynam omensaton of a transmsson systems, rodng multfuntonal flexblty reured to sole many of the roblems fang the ower delery ndustry. Wthn the framework of tradtonal ower transmsson onets, the UPFC s able to ontrol, smultaneously or seletely, all the arameters affetng ower flow n the transmsson lne (.e., oltage, medane, and hase angle), and ths unue aablty s sgnfed by the adjete "unfed" n ts name.. Prnal of oeraton: The UPFC s the most ersatle FACTS ontroller deeloed so far, wth all enomassng aabltes of oltage regulaton, seres 06, IJISSET Page

4 Internatonal Journal of Innoate Studes n Senes and Engneerng Tehnology ISSN (Onlne) Volume: Issue: Noember 06 omensaton, and hase shftng. It an ndeendently and ery radly ontrol both real and reate ower flows n a transmsson lne. It omrses of two VSCs (Voltage Soure Conerter) ouled through a ommon d termnal. VSC s onneted n shunt wth the lne, through a oulng transformer; the other VSC s nserted n seres wth the transmsson lne through an nterfae transformer. The d oltage for both onerters s roded by a ommon aator bank. The seres onerter s ontrolled to njet a oltage n seres wth the lne. In ths roess, the seres onerter exhanges both real and reate ower wth the transmsson lne. Although the reate ower s nternally generated / absorbed by the seres onerter, the real-ower generaton / absorton s made feasble by the d-energy-storage that s the aator. 4. UPFC MODELING The UPFC s laed n a Transmsson network. A mahne system s onsdered wth non lnear load. A three hase fault s reated and the system s heked under arous ondtons. The oltage s generated at 0 kv, transmtted and then steed down at dfferent oltage leels based on nddual remses reurements. The UPFC s suosed to be nstalled at a lant whh s loated at a onsderable dstane from the transformer and there are some loads resent n between, reresented by eualent MW or MVA.. The UPFC s nstalled between bus B,.e. ont of onneton and load bus B The UPFC s nstalled n order to solate all the loads wthn the lant from any dsturbane from the soure sde. In addton to ths UPFC s atng as a harmon solator, reentng any urrent harmons gong towards ont of onneton from the lant sde. Fg. shows the bas blok dagram of the UPFC. realzed by usng two oltage soure nerters. One atng as a shunt ate ower flter (APF), whle the other as seres APF. Both the APFs share a ommon d lnk n between them. Eah nerter s realzed by usng sx IGBT swthes. The oltage at bus B before UPFC, the load oltage at load bus B, oltage njeted by seres APF and the d lnk oltage between two nerters. 4. UPFC CONTROLLER Fgure.: Bas UPFC onentonal dagram The shunt-onneted onerter s used manly to suly the real-ower demand of the seres onneted onerter, whh t deres from the transmsson lne tself. The shunt onerter mantans onstant oltage of the d bus. Thus the net real ower drawn from the a system s eual to the losses of the two onerters and ther oulng transformers. In addton, the shunt onerter funtons lke a STATCOM and ndeendently regulate the termnal oltage of the nteronneted bus by generatng absorbng a reuste amount of reate ower. Akag [7], roosed a theory based on nstantaneous alues n three-hase ower systems, wth or wthout neutral wre, and s ald for steady-state or transtory oeratons, as well as for gener oltage and urrent waeforms known as Instantaneous Power Theory or Ate-Reate (-) Theory whh onssts of an algebra transformaton (Clarke transformaton) of three-hase oltages n a-b- oordnates to α-β-0 oordnates, followed by the alulaton of the - theory nstantaneous ower omonents: 0 0 a b In three hase, three wre systems, there s no zero seuene omonent. If 0 and o are negleted, nstantaneous oltage (), and urrent hasor () an be defned from ther orresondng α and β omonents as follows: 06, IJISSET Page 4

5 Internatonal Journal of Innoate Studes n Senes and Engneerng Tehnology ISSN (Onlne) Volume: Issue: Noember 06 06, IJISSET Page 5 j j From () and (4), nstantaneous omlex ower an be defned as the rodut of the nstantaneous oltage hasor and omlex onjugate of nstantaneous urrent hasor gen n(5) S =. = ( α +j β )( α +j β ) = +j Where, P = α. α + β. β = α. β - β. α The nstantaneous omlex ower s useful. It an be aled for transent or steady-state analyss. The followng euaton s a omat form for the nstantaneous real and reate ower defnton and ts nerson: b ~ ~ Fg 4.: shunt urrent and oltage omensaton 4. Control Strategy for UPFC A UPFC ontroller an be desgned usng only the onet learned from the - theory and onet of nstantaneous aggregate oltage [4]. The funton ontrol blok dagram of ths UPFC ontroller s llustrated n Fgure 4 for the UPFC shunt onerter and Fgure 5 for the UPFC seres onerter. The nstantaneous aggregate alue s a orresondng alue between nstantaneous aggregate 0 b a The omensatng urrent on the αβ axes are determned as The nerse transformaton ges the nstantaneous referenes 0 b a Fg 4.: Control blok of shunt urrent omensaton. Fg 4.: Control Blok of Seres Conerter 5. SIMULATION RESULT Fgure 4. llustrates the smulaton of three hase fault ase of termnal oltage n the ower transmsson system. It an be seen that the haratersts of rotor angle of both the mahnes and the rotor osllatons hae beng damed by the use of UPFC when the system s subjeted to three hase fault. A three-hase fault reated for erod of 0.5 to 0.6seonds and maxmum Crtal Clearng Tme (CCT) s ealuated. When the UPFC was nluded nto the ower transmsson system, the load oltage was fulflled n the ranges of tmes, as shown n Fgure 4.4. In addton, the UPFC an rodue the omensatng oltage to the load, resultng n the termnal oltage beng mroed

6 Internatonal Journal of Innoate Studes n Senes and Engneerng Tehnology ISSN (Onlne) Volume: Issue: Noember 06 to the load oltage, as an be seen n Fgure 4.5. The UPFC suled reate ower rodes onstant bus oltage and meanwhle, the real ower s stll onstant. A. Crtal Clearng Tme The wthstandng aablty of a dee an be sad n terms of CCT. It s defned as the maxmum tme that a dee an wthstand on alaton of a fault. A threehase fault reated for erod of 0.5 to 0.6seonds and maxmum settlng tme s ealuated. Table I: Comarson of Settelng tme Dee Wthout UPFC Wth UPFC Table Column Head Fault Mahne Settlng tme n (Ses) LLL 9.95 LLG 6.5 LLLG 9.5 LLL 4.5 LLG.85 LLLG 4.0 Fg 4.4: LLG fault wth and wthout UPFC for mahne Table II: Crtal Clearng Tme Dee WITHOUT FACTS WITH UPFC Crtal learng tme (ses) 0 ms Nl 5 ms 87.6 Perentage nrease n t (%) 6. CONCLUSION Ths researh shows that mult mahne system subjeted to arous ower system dsturbanes and transent stablty of ower system s analysed usng FACTS dee UPFC (Unfed ower flow ontroller). Fg 4.5: LLLG fault wth and wthout UPFC for mahne The smulaton oututs reeals that UPFC settlng tme s between.5 to s. Thus the UPFC has a aablty of damng the rotor angle osllatons. Thus, FACTS dee UPFC lay a tal role n enhanng the transent stablty of an MMIB ower system. The UPFC shunt onerter suled reate ower nto the ontroller bus for regulated oltage bus. In ths study, the results showed that the UPFC an oerate and omensate oltage at bus ontroller radly and effently. REFERENCES [] Kalyan K. Sen, Er J. Staey, UPFC - Unfed Power Flow Controller Theory, Modelng, and Alatons, IEEE Transatons on Power Delery, Vol., No. 4, Otober 998. [] P.Kundur, Power system stablty and ontrol.tata Mgraw hll. Fg 4.6: LLL fault wth and wthout UPFC for mahne [] Mathur.R.M., Varma.R.K, Thyrstor based FACTS ontrollers for eletral transmsson systems, IEEE Press. 06, IJISSET Page 6

7 Internatonal Journal of Innoate Studes n Senes and Engneerng Tehnology ISSN (Onlne) Volume: Issue: Noember 06 [4] Kalyan K. Sen, Staey, Er J., UPFC unfed ower flow ontroller: theory, modelng and alatons, IEEE Transatons on Power Delery, Vol., No. 4, 998. [5] Ramnarayan Patel, T. S. Bhatt and D. P. Kothar, MATLAB/Smulnk-based transent stablty analyss of a multmahne ower system. [6] I. J. Nagrath and D. P. Kothar, Power system Engneerng (Tata MGraw-Hll, New Delh, 994). [7] Smulnk User s Gude (The Mathworks, Natk, MA, 999). [8] Had Saadat, Power System Analyss (MGraw- Hll, New York, 999). [9] Power System Blog set User s Gude (The Mathworks, Natk, MA, 998). [0] SIMULINK Model-Based and System-Based Desgn. [] Naran G.Hngoran,Laszlo Gyugy, for STATCOM, UPFC desgn Understandng of FACTS onets and tehnology. [] Dash P.K., Mshra S. and Lew A.C., Desgn of a Fuzzy PI Controller for Power System Alaton, Internatonal Journal of Intellgent and Fuzzy System, Vol.,. 9-4, 995. [] Wang H.F., Damng funton of Unfed Power Flow Controller, IEE. Pro. Gener. Transm. Dstrb., Vol.46, No ,999. [4] V. Khadkkar, A. Chandra, Alaton of UPQC to Protet a Senste Load on a Polluted Dstrbuton Network, 006 IEEE. [5] Mukhtr sngh, Vnod Khadkkar, Ambarsh Chandra, and Rajee K. Verma, Grd Interonnetons of Renuwable Energy Soures At Power Dstrbuton Leel Wth Power Qualty Imroement, IEEE transatons on Power Delery, Vol, 6, No., January 0 [6] Panumat Sanoung, Pasan Boonham and Boonyang Plangklang, Analyss and ontrol of UPFC for oltage omensaton usng ATP/EMTP, As. J. Energy En. 009, 0(04), [7] Akag, H., Watanabe, E.H. and Aredes, M. (007). Instantaneous Power Theory and Alatons to Power Condtonng, Wley-IEEE Press. AUTHOR'S BIOGRAPHY Maln Palt, workng as an Assstant Professor n Eletral Engneerng Deartment, Grjananda Chowdhury Insttute of Management and Tehnology, Azara, Assam. 06, IJISSET Page 7