INFLUENCE OF AN ADVANCE CONTROL OF PHOTOVOLTAIC GENERATION SYSTEM ON FAULT RIDE THROUGH PERFORMANCE

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1 Proceedngs of the ASTED nternatonal Conference Power and Energy Systems (AsaPES 213) Aprl 1 12, 213 Phket, Thaland NFLUENCE OF AN ADVANCE CONTROL OF PHOTOVOLTAC ENERATON SYSTEM ON FAULT RDE THROUH PERFORMANCE 3 1, Mohd Zamr Che Wank 1, Lm Chaw Yh 3, Afda Ayob 3, Sbyanto Sbyanto, Ahmad Kaml Mat Hsn 2 1 Radzan Abdl Rahman, Azlan M. Hashm Mohd 1 reen Technology Secton, TNB Research Malaysa, 2 Smart rd Unt, TNB Research Malaysa 3 Dept.of Electrcal, Electroncs and Systems Engneerng, Unverst Kebangsaan Malaysa mzamr@tnbr.com.my ABSTRACT Ths paper presents a comparson stdy on photovoltac generaton system (PVS) performance between two dfferent types of power converson topologes n rdng throgh the grd falts va dgtal smlaton. n the frst topology, PV panels are connected drectly to a DCAC converter. n the second topology, DCDC converter s employed between PV panels and the DCAC converter. The second topology added complexty of control bt t overs more advantages. Both topologes are sbjected to grd falts; whch reslt n voltage sags at the pont of nterconnecton. Actve power, reactve power and total crrent from both PVS topologes are analysed and compared. The smlaton reslts show that PVS wth DCDC converter performs better where t retrn to steady state operaton faster after clearance of falts and also the devaton of otpt from steady state vale s less drng the recoverng perod. KEY WORDS Photovoltac generaton system (PVS), converter, falt rde throgh, grd falt 1. ntrodcton Photovoltac (PV) energy as a form of clean and renewable resorces has ganed sgnfcant attenton n recent years de to the cost ncrement and adverse envronmental mpacts of conventonal fossl fels [1]. Crrently, PV energy system s consdered as an optmm solton to the electrcty spply n most rral zones n developng contres [2, 3]. However the ncertantes n prodcng otpt power create a challenges n operatng a power system wth large nmber of PV [4]. PV applcaton s ganng a lot of attenton n the developng contry lke Malaysa. Feed n Tarff (FT) ntrodced n Malaysa n 211 [5] s a sgn that the government s seros n promotng PV as a new energy sorce n spportng Malaysan sstanable growth. The partcpant of FT program wll enjoy hgh tarff for each klowatthor nject to the grd. The ntrodcton of ths FT s an example of the ncentves provded by Malaysan overnment to ncrease PV applcaton for electrcty generaton. The targeted nstallaton of PV n Malaysa s abot 1, MW by 25 [12]. At ths tme electrcty from PV consttte 38% of the electrcty prodcton n the contry yearly. Ths amont s consdered sgnfcant and wth ths level of PV nterconnecton, there wll be a lot of techncal challenges n operatng Malaysan electrcty grd. Some of the challenges are expected nclded coordnatng protecton system, severe voltage flctaton and stablty of the electrcal grd [7]. n Malaysa, PVS are only reqred to energze the grd wthot any reqrement to drectly spport the power grd relablty. However, ths polcy s expected to change when massve PV penetraton takes place. For example, n developed contres lke ermany, PVS s reqred to provde voltage spport drng steady state operaton and crtcal perod [6]. An example of grd spport reqrement s falt rde throgh reqrement drng temporary falt and njecton of reactve crrent at the same moment. The prpose of ths spport ncldes to spport voltage recovery and to avod a large msmatch of generaton and load after the clearance of temporary falts. n ths paper, falt rde throgh characterstc and behavors of two dfferent PVS topologes are nvestgated throgh compter smlatons. The paper content s arranged as follow. n Secton 2, PVS technology s revewed. n Secton 3, the expected grd code reqrement s descrbed. n Secton 4, the performance of the PVS drng and jst after temporary falt s presented and dscssed. DO: /P

2 2. Photovoltac eneraton System A typcal PVS conssts of PV panels and power condtoner [7]. When the sn radaton ht the panel, electrcty s generated. The generated electrcty s n DC form. Before the electrcty s sable, t needs to be converted to AC form, and the converson s realzed by sng a power electronc (DCAC) converter. The otpt freqency from the power electronc converter s 5/6 Hz, and then electrcty s fed drectly to the load or to the grd system. ts DC crct. n ths topology, only one DCAC converter s tlzed. The power components that are controlled by ths converter are DC voltage (U DC ), actve power ( P ), reactve power (Q) and power factor (cos ϕ). Fgre 2. Photovoltac generaton system Type 1 Fgre 1. Photovoltac generaton system Type 1 [7] Electrc crrent generated by PV panel s lnearly dependng on the solar rradaton level and also nflenced by the cell temperatre. The followng eqaton relates PV crrent to the rradaton and temperatre [11]: The second PVS topology tlzes two power electronc converters. As shown n Fgre 3, the converter on the PV panel s sde s DCDC converter and the converter on the grd sde s DCAC converter. Wth ths arrangement, actve power and the DC voltage s controlled sng a DC DC converter whle the reactve power and power factor s controlled sng DCAC converter. where pv pv n K (1), T n pv,n [A] = the lght generated crrent at 25 C and 1W/m 2 T [K] = the dfferences of actal and nomnal temperatres [W/m 2 ] = the rradaton on the devce srface n [W/m 2 ] = the nomnal rradaton The crrent and voltage at the termnal of PV panel has a characterstc as shown n Fgre 1. SC s short crct crrent, V OC s open crct voltage, V mp s maxmm power voltage and mp s maxmm power crrent. Fgre 3. Photovoltac generaton system Type 2 (, SC ) (V mp, mp ) (V OC,) Fgre 1. PV panel V crve The smplest arrangement of PVS s depcted n Fgre 2 where the otpt of PV panels s drectly connected to The DCDC converter s sally tlsed for ntegratng of maxmm power pont trackng (MPPT) algorthm to extract maxmm power from PV arrays [8]. For grd connected applcatons, boost type of DCDC converter s perred where t step p the arrays voltage to a hgher voltage [9]. n most cases, DCDC converter s sed to average and control the DC lnk voltage to match the desred voltage by varyng the dty cycle. Whle both topologes are capable of carryng ther basc dty, whch s delverng the electrcty generated by PV to the grd, there are dfferences n term of power components performance and characterstcs when exposed to electrcal dstrbances wthn the grd system sch as lne falts. 33

3 3. Falt Rde Throgh Reqrement n a contry where PV ntegraton s sbstantal sch as n ermany, t s made mandatory that the PVS connected to medm voltage level mst reman connected to the grd drng falt transent even when the voltage at connecton s zero. Ths falt rde throgh reqrements s smlar to the reqrement mposed on mcrotrbne generaton system (MTS) [7] and fel cell generaton system (FCS) [1]. n any staton, PVS s not allowed to be dsconnected f the falt leads to a voltage level above the bondary lne 1 (the ble lne ndcated n Fgre 4). Between bondary lnes 1 and 2, PVS can only be dsconnected f the network operator agreed that the reconnecton can be performed after a maxmm of 2 seconds. At the same tme, reactve crrent need to be njected accordng to the characterstc shown n Fgre 5. Magntde and type of reactve crrent njecton depends on the voltage level. f the system voltage drops below 9%, capactve reactve crrent s njected. n contrast, f the system voltage rses beyond 11%, ndctve reactve crrent s njected. The amont of reactve crrent descrbed s added to the actal reactve crrent already sppled drng steady state operaton. The objectve of reactve crrent njecton, as depcted n Fgre 4, s to mprove the voltage recovery after the falt [6,1]. voltage lmtng crve U/U c 1% 7% 45% 3% 15% bondary lne 1 bondary lne 2 lowest vale of voltage band = 9% of U c Below the ble lne there are no reqrements on generators to reman grd connected tme n ms pont of falt Fgre 4. Falt rde throgh reqrement [6] 5 voltage spport (overexcted mode). reqred addtonal reactve crrent B / N mantenance of the voltage spport n dead (nderexcted accordance wth band mode) the characterstc after retrn to the voltage band over a frther 5 ms reactve crrent statc: k= (Q/N)/(U/UN)2,p.. rse tme < 2 ms Qmax n Fgre 5. Reactve spport reqrement [6] magntde lmtaton Fgre 6. nner crrent loop [7,1] These loops are derved based on the relatonshp between the voltage at converter termnal ( CON ) and voltage ( ) after the grd ndctor as depcted n Fgre 7. The voltage n abc coordnate s transformed to dq coordnate for flexblty of control. n dq coordnate, actve and reactve power can be controlled separately where d component correspond to actve power whle q component correspond to reactve power. 1 K p 1 st l l 1 K p 1 st Voltage drop / rse U/U n d q magntde lmtaton Presently most of the grd system connected wth PVS s not set to rde throgh temporary grd falts. So, f there s any change n the grd code, a qeston arses that s how to tne the PVS to adhere to the new reqrements?. Most of the modern power electroncs converter tlzes BT swtches where the plse sgnal s sppled by modlaton crct. The modlaton sgnal s generated based on erence voltage magntde and angle gven by crrent control loops. The crrent control loops are segmented to nner crrent loop and oter voltage loop, as depcted n Fgre 6 and Fgre 7. These two loops are smlar as those sed n the MTS [7] and FCS [1]. DC C CON l CON Fgre 7. Oter Voltage Loop [7] La Lb Lc 34

4 The relaton of converter and grd voltage s gven by d l CON (2) dt After transformaton to rotatng erence frame, n the postve drecton of grd voltage, DC DC 1 K p 1 st P PV FC magntde lmtaton d j q and for converter crrent (3) reactve crrent characterstc * CON j The real part of grd voltage s d d l dt l And the magnary part s q d l dt l (4) (5) (6) Fgre 8. Oter Voltage Loop [7,1] 4.1 Dynamc of PVS at Falt Condton Sngle lnetogrond (SL) falt and threephase falt were appled. Both types of falts were appled on PVS type 1 and PVS type 2. The falt resstance s 1 Ω and falt s appled at.8 s for the draton of 15 ms. The mpact of the falt on both PVS s compared and dscssed. The reslts are depcted n Fgre 9, Fgre 1, Fgre 11 and Fgre 12 respectvely. 4.2 Sngle Lnetorond Falt The voltage drops across ndctor are treated as an otpt of P controller and after manplaton and arrangement, the erence converter voltage are wrtten as K p K p st K p K p st l d l q n ths voltage orented erence frame dcomponent of converter crrent s correspondent to actve crrent and qcomponent of converter crrent correspond to reactve crrent. The reactve crrent njecton characterstc can be easly added to AC voltage loop as shown n green box n Fgre 8. The voltage at the pont of connecton s compared to the prefalt voltage and the dfferences s mltple by the gan k as detaled n Fgre Smlaton Reslt and Dscsson n order to analyze the dynamcs of the PVS, the modelng and smlaton s performed n MATLAB/SMPOWERSYSTEM [13]. PVS s modeled as a detal models consderng the swtchng of the power electronc devces. PVS as shown n Fgre 2 and Fgre 3 s connected to low voltage bs.4 kv. The falt s appled at the same.4 kv bs. (7) (8) Drng falt, the grd voltage wll dp as shown n Fgre 9 and Fgre 1. The voltage dp for both PVS systems s almost the same. However, total falt crrent from PVS type 1 s hgher than PVS type 2. The advantage of PVS type 2 s t can retrn to steady state operaton n a shorter tme after the falt s cleared. t s also seen that wth DCDC converter, there s no overshoot of actve power from PVS mmedately after the clearance of falt. 4.3 Three Phase Falt Fgre 11 and Fgre 12 depct the responses of PVS to a three phase falt at the pont of nterconnecton for 15 ms.. Techncally, the voltage shold become zero bt t s not the case here. Ths voltage s de to the crrent njected by PVS whch gves rse to voltage potental across ts grd ndctor. From the Fgre 12, t can be seen that the magntde of the nrsh crrent for PVS type 2 almost reached 8 p. of ts rated crrent whle the nrsh crrent for PVS type 1 s only 4 p.. of ts rated crrent. Actve power and reactve power drng falt for both systems s approxmately the same. After the falt s cleared, PVS type 2 reaches steady state at t =.97 s whch s faster compared wth PVS type 1. t s fond that the nclson of DCDC converter n DC crct mproves the performance n falt rde throgh bt t s fond there s large magntde of nrsh crrent 35

5 developed drng at the begnnng of the event. t s however nknown f the manfactrer already eqpped the nverter wth the relevant protectve devce to lmt the crrent. f the answer s no, then retrofttng s needed to the nstalled nverters f the new reqrements s codfed n the near ftre. From the Fgre 11, t s also seen that reactve power flows nto the nverter whle at that tme actve power s delvers beyond the nomnal vale of nverter. Ths occrrence happen between the clearance of falt and the system reachng steady state. Theoretcally t s happened as prodced by compter smlaton. However t s not known f ths occrrence cold happen n the real nverter and t shold be nvestgated. Fgre 11. Three PhaseFalt of PVS Type 1 Fgre 9. Sngle Lnetorond Falt of PVS Type 1 Fgre 12. Three PhaseFalt of PVS Type 2 Fgre 1. Sngle Lnetorond Falt of PVS Type 2 36

6 5. Conclson Ths paper presents a comparson stdy on PVS performance of two dfferent types of power converson topologes n rdng throgh the grd falts. n the frst type, PV panels s connected drectly to a DCAC converter before the grd connecton. n the second type, a DCDC converter s placed between PV panels and DC AC converter. Both types are sbjected to a temporary grd falts whch reslts n voltage dp at the pont of nterconnecton. Actve power, reactve power and total crrent form both PVS are compared. Even thogh the second PVS type adds complexty to ts control method bt t has some advantages.the smlaton reslts shows that PVS wth DCDC converter has two man benefts: (1) t redces the retrn to steady state tme after clearance of falts and (2) t lessen the devaton of otpt from steady state vale drng recoverng perod. References [1] T. J. Hammons, J. C. Boyer, S. R. Conners, M. Daves, M. Ells, M. Fraser, E. A. Holt, and J. Markard, "Renewable energy alternatves for developed contres," EEE Transacton on Energy Converson, vol. 15, pp , December 2. [2] C. Boccalett,. Fabbr, J.Marco, and E. Santn, "An Overvew on Renewable Energy Technologes for Developng Contres: the case of nea Bssa," n nternatonal conference on renewable energes and power qalty, Santander, Span, 28. [3] D. N. Nkwetta, M. Smyth, and V Van Thong, "Electrcty spply, rreglartes, and the prospect for solar energy and energy sstanablty n SbSaharan Afrca," Jornal of renewable and sstanable energy, vol. 2, p. 16, 23 March [4] Sbyanto, A. Mohamed, and M. Hannan, "ntellgent maxmm power pont trackng for PV system sng Hopfeld neral network optmzed fzzy logc controller," Energy and Bldngs, vol. 51, pp. 2938, 212. [5] Renewable Energy Act 211, Law of Malaysa, Act 725 [onlne] [6] Technsche rchtlne erzegngsanlagen am mttelspannngsnetz, BDEW Standard. [onlne]. Avalable : /ste/de/netze/mg/pdf2netzanschlss/technscherchtlnen/ BDEWRLEAamMSNetzJn28.pdf [7] Mohd Zamr Che Wank, 211, Smlaton and Management of Dstrbted eneraton: reen Energy ntegraton to Electrcal Power System, Lambert Academc Pblshng, Saarbreken, ermany. [8] Sbyanto, A. Mohamed, and H. Shareef, "Hopfeld Neral Network Optmzed Fzzy Logc Controller for Maxmm Power Pont Trackng n a Photovoltac System," nternatonal Jornal of Photoenergy, vol. 212, pp. 1 13, 212. [9] M. A. H. Z A han, A Mohamed and Sbyanto, "ThreePhase Photovoltac rdconnected nverter sng dspace DS114 Platform," n EEE PEDS 211, Sngapore, 211, pp [1] M.Z.C. Wank, A. Mohamed, A.F.A.Kadr,. Erlch, " Low voltage rde throgh capablty of fel cell generaton system connected to low voltage network," 211 EEE 1st Conference on Clean Energy and Technology (CET), 2729 Jne 211, Malaysa. [11] M.. Vllalva, J.R. azol and E. Rppert F, "Modelng and crct based smlaton of photovoltac arrays, Brazllan Jornal of Power Electroncs, vol. 14, No. 1, 29, pp: [12] SEDA, Natonal Renewable Energy Polcy and Acton Plan 29, [13] MATLAB/SMULNK/SMPOWERSYSTEM Docmentato, [onlne]. Avalable:http// 37