Multi-agent based protection system for distribution system with DG

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1 Multi- bsd protction systm for distribution systm with DG JIN SHAGN, NENGLING TAI, QI LIU Dprtmnt of Elctricl Powr Enginring Shnghi JioTong Univrsity NO.800, DongChun Rod, Shnghi CHINA Abstrct: - This ppr introducs th bsic structur of multi- bsd protction systm for distribution systm with DGs. Th ntir systm consists of intllignt s nd communiction systm. Intllignt s cn b dividd into thr lyrs, th bottom lyr, th middl lyr nd th uppr lyr. Th dsign of th in diffrnt lyr is nlyzd in dtil. Communiction systm is th bridg of multi- systm (MAS). Th trnsmission mod, slctiv communiction nd othr principls r discussd to improv th trnsmission fficincy. Finlly, som vlutions r proposd, which provids th dsign of MAS with rfrnc. Ky-Words: - multi-; protction; distribution systm; DG; communiction 1 Introduction Th nvironmntl problms hv rousd worldwid ttntion, nd th nrgy crisis is gtting mor nd mor srious. With th dvlopmnt of rnwbl sourcs nd its controlling tchnology, numbr of distributd gnrtions (DG) hv bn connctd to th distribution systm, which provids nw mthod to sv th limitd nrgy nd rduc crbon dioxid missions. Howvr, DGs lso bring som problms. Protction coordintion is on of th most importnt problms. Thr r lots of rsrchs tht nlyz th problms from diffrnt spcts [1-4]. Th ky point is tht, thr is only singl powr supply in th originl systm, but DGs dd nw powr supplis to th grid, which mk it into complx multi powr supplis ntwork. Th nw powr supplis will significntly ffct th powr flow. Whn fult occurs, thy will provid dditionl currnt to th fult point, which will grtly ffct th rlibility of protction. Sinc th originl protction of distribution systm is no longr s rlibl s bfor, thr r mny improvd mthods proposd to solv this problm. It is vry convnint to disconnct th DG unit whn fult occurs [4]. And most stndrds for DG lso rquir lik this (IEEE-Std ). In this cs, DG will not ffct th fult currnt. Howvr, for th systm with lrg DG pntrtion lvl, it will not support th grid voltg nd frquncy during nd immditly ftr th fult. Rstricting th cpcity nd ccss point of DG is nothr mthod [5-7]. Thn th influnc of DGs is grtly rducd. But this will grtly stunt th dvlopmnt nd ppliction of DG. Th fult currnt limitr (FCL) hs lso bn populr for whil [8]. Thr r lso mny othr mthods tht proposd to improv th originl protction schm to mk th protction systm mor rlibl [9-12]. Howvr, ll ths mthods hv som limittion. Thy my hv solvd th problms in som dgr, but, thy r not systmic nd ffctiv nough. Th protction schm should b modifid whn th structur of th systm chngs. Th multi- tchnology ws first pplid to th powr systm in th rly 1990s. And thr r lots of rsrchs ftr tht, such s optiml powr flow lgorithm, powr mrkt, voltg controlling nd so on. Th protction systm bsd on multi ws proposd not long go. It hs bn studid lot rcntly. Howvr, th influncs of DGs to th protction of distribution systm hv rrly bn nlyzd bfor [13-14]. Th dtild dsign of MAS hs not bn introducd ithr [15-16]. This ppr prsnts n ffctiv nd xtnsibl schm. Th bsic structur of MAS is introducd, th dsign of th s nd communiction systm r nlyzd. 2 Structur of MAS Th multi- systm is composd of diffrnt intllignt s, which cooprt with othrs s individul units. Any lctricl lmnt tht contins ncssry informtion cn b rprsntd s n lmnt, such s th lin brkr, E-ISSN: X 201 Volum 14, 2015

2 trnsformr nd so on. Thr r lso intgrtd s, thy do not collct informtion from crtin lmnt dirctly, but collct informtion from othr s nd drw conclusions. Fig. 1 shows th schmtic digrm of typicl distribution systm nd th corrsponding protction systm. MV B5 B6 B7 CESS Lod B1 B2 B3 B4 Lod trnsmission btwn diffrnt s. It s of grt importnc to dsign both of thm proprly. 3 Intllignt Agnts In ordr to rliz th function of diffrnt lvls nd mk th structur of MAS clr, th whol MAS cn b dividd into thr lyrs, th bottom lyr, th middl lyr nd th uppr lyr, s shown in Fig.2. Uppr lyr Cntrl Agnt PV CCHP () Schmtic digrm of distribution systm Middl lyr Agnt 1 Agnt 2 PV Distribution Systm Elctricl quntitis Othr informtion CCHP Elctricl quntitis Othr informtion CESS Elctricl quntitis Othr informtion Switch tims Currnt Voltg Frquncy Lod Instructions B1 B2 B3 B4 Unit1 Unit2 (b) Structur of corrsponding MAS Fig.1 Digrm of distribution systm nd MAS Th distribution systm in sub-grph () consists of two fdr lins nd thr nrgy sourcs, th Photovoltic (PV), Combind Cooling Hting nd Powr (CCHP), nd Composit Enrgy Storg Systm (CESS). In sub-grph (b), th svn orng boxs (B1 to B7) rprsnt th brnch s. which gthr informtion from th distribution systm dirctly. Th thr blu boxs rprsnt DG s, which gthr th rl-tim informtion of DGs. Th two grn llipss rprsnt th rgionl s, which r th middl sgmnts btwn trminl s nd cntrl. Th rd llips rprsnts th cntrl. Th rrows rprsnt th informtion flow, two-wy rrow mns two-wy flow. Th rrows cn b considrd to mk up th communiction systm. According to th structur introducd bov, thr r minly two spcts for th implmnttion of MAS. On spct is th dsign of vrious kinds of s. Th othr is th construction of communiction systm. Th two spcts r both vry importnt, nd thy influnc ch othr t th sm tim. Th modl of ffcts th structur of communiction systm. Mnwhil, th rstriction of communiction limits th informtion B5 B6 B7 Cntrl Unit Bottom lyr Agnt 1 Agnt 2 Agnt 3 Agnt 4 Fig.2 Hirrchy chrt of s All th trminl s tht dirctly intrct with th distribution systm (including diffrnt DGs), mk up th bottom lyr. s tht connct bottom lyr nd th uppr lyr mk up th middl lyr. Th cntrl gthrs informtion of th ntir systm, nd it forms th uppr lyr. Thr lyrs ply diffrnt rols. Agnts r dsignd ccording to th functionl rquirmnts. 3.1 s Th s for brkrs, lins, DGs nd othr lmnts in th bottom lyr r clssifid s trminl s. Thy not only gthr informtion from th powr systm, but lso work s ctutors. Th tripping, rclosing, lod shdding nd othr instructions r ll implmntd through thm. Sinc thir functions r complictd, th modl should b wll dsignd. Fig.3 shows th structur of th brnch. Th brnch is th intgrtion of lin nd brkr. Sinc th brkr provids th lin with protction nd th lin provids th rly with informtion, th two s r closly rltd with ch othr. Thus thy r intgrtd to rduc th invstmnt nd mk th communiction btwn thm sir. As shown in Fig.3, th dshd box rprsnts for th brnch. Dt collction modul is rsponsibl for th dt cquisition from th snsors, which dirctly msur th lctricl qulitis of th powr systm. Th dt prprocss modul will fulfill th dt convrsion nd filtring, Thn, th dt with prscribd formt will b stord in th dtbs. Th nlysis modul rds th dt from th dtbs nd conducts th fult nlysis [15]. If th brkr should ct to clr th fult, th E-ISSN: X 202 Volum 14, 2015

3 instruction will b snt out. Th ction will lso b rcordd in th dtbs. Onc th instruction is succssfully xcutd, th will gt th nw sttus. Th dt is bi-dirctionl port connctd to th dtbs. Th will communict with othr s through this port. Snsors Dt collction modul Dt prprocss Instructions Brkr s b t D Elctricl dt Stting vlu of protction Othr prmtrs Anlysis modul c rf t in t D Brnch Fig.3 Structur of brnch Dtbs is th cor of th, ll th lctricl dt collctd from th powr systm r stord hr, such s th sttus, th stting vlus of protction, nd othr prmtrs tht rltd to th lin nd th quipmnt (.g. rly, brkr). Th modl of th dtbs will dirctly ffct th fficincy of th. Fig.4 shows th structur of th dtbs modl. Brnch ID #1 proprty Brkr sttus Anlog proprty St vlu Powr (rl) Currnt (rl) Voltg (rl) Frquncy (rl) St vlu 1 Tripping vlu (rl) St vlu 2 Othr prmtrs Dly (rl) Switching tims (intgr) Lngth of lin (rl) Thrml stbl currnt (rl) Fig.4 Structur of dtbs modl Thr r mor dtils in th prcticl modl. Ech proprty hs its sub-proprtis. For xmpl, if th Brkr sttus shows tht th brkr is closd, thr is sub-proprty to tll whthr th currnt strtus is norml stt, rclosing or mnul oprtion. Bsids, th nlog proprtis (currnt, voltg) should b stord sprtly ccording to t n g r th O phs, b nd c. St vlu is concrnd with th protction principl nd th sttus of DGs. Svrl groups of st vlu r stord for diffrnt situtions. Bsids th brnch nlyzd bov, thr r lso trnsformr, busbr nd so on. Th dsign of this kind of is similr with th brnch. Th dsign of DG is lso similr, lthough th intrnl control of DG is vry complx, only th xtrnl informtion is th ky for protction systm. Th xtrnl informtion prsntd by DG is littl diffrnt from tht of th ordinry lmnt, but th dsign id is th sm. In word, th should collct informtion from th powr systm, tk nlysis, nd communict with othr. 3.2 s s ply th rol s gtwy. Thy do not connct with th distribution systm dirctly, but collct informtion from crtin r through svrl trminl s. Th informtion is prprocssd hr. Th xisting of rgionl s cn void th dt flood. Although ch rgionl covrs crtin r, djcnt rs should ovrlp with ch othr to nsur th comprhnsivnss nd rlibility of th protction systm. Sinc th rgionl s xchng informtion widly with othrs, its dtbs, lgorithm, nd th whol structur r ll vry importnt. Th structur of rgionl is shown in Fig.5. Adjcnt rgionl Agnt Informtion snding Informtion Informtion collction Agnt 1 Cntrl Agnt Dtbs Agnt 2 Instruction Exprt Systm Instruction Agnt 3 Function modul1 lgorithm nlysis unit Critrion... Function modul2 lgorithm nlysis unit Critrion Fig.5 Structur of rgionl Whn th rgionl is to b dsignd, th function of th is dfind t first. Thn, th informtion rquird nd th instructions snt out E-ISSN: X 203 Volum 14, 2015

4 r confirmd. Th dtbs nd s r dsignd ccording to this. Dtbs lys solid foundtion for th function moduls. For diffrnt function moduls, it s vry importnt to choos propr lgorithm to chiv th function quickly nd ccurtly. Sinc th influncs of DGs to th protction systm r complictd, MAS should b dptiv in diffrnt situtions. Howvr, th spd of onlin dptiv systm cn hrdly mt th rquirmnt of protction. But th possibl running sttus of DGs in crtin distribution systm r fixd, which provids possibility to build n offlin dptiv systm. An xprt systm is built to support th offlin dptiv systm. Whn th running sttus of th ntwork chngs, th xprt systm will provid pproprit protction knowldg, including protction configurtion, coordintion, stting vlus nd so on. Th knowldg s wll s th rltim informtion will b rd by th function modul. Thn, th nw protction schm cn b figurd out nd instructions will b snt to th trminl s. 3.3 Cntrl s Sinc MAS hs good bilitis of informtion intrction nd controlling [16], bsids working s protction systm, it is lso rsponsibl for th optiml oprtion of th ntir systm. Som kinds of DG hv rndom powr output, such s PV wind turbin nd CCHP. Ful cll nd CESS r flxibl units, which cn b djustd s sourc or lod. Sinc th cntrl cn obtin th informtion of th ntir systm, it s bl to rrng th running of ch DG to chiv th optiml nd stbl running of distribution systm. DG s will implmnt th instructions. Th concrt implmnttions r crrid out by th controlling modul insid of DG, which is not concrnd by MAS. Onc th voltg or frquncy of th distribution systm is bnorml, th cntrl cn mk djustmnts by controlling th ctiv nd rctiv powr of DGs, trnsfrring lod or vn shdding lod to kp th systm stbl. Th gol of cntrl involvs th ntir distribution systm. Th informtion it rquirs minly coms from th rgionl s. Nturlly, only th conclusiv nd ncssry mssgs ftr prprocssing r snt hr. Sinc th controlling trgt of cntrl is complx, th lgorithm is much mor complictd. Diffrnt lgorithms r pplid undr diffrnt situtions. Using pproprit lgorithms for diffrnt ppliction is of grt significnc. 4 Communiction Systm Communiction systm is th bridg of MAS. Th trnsmission mod, fficincy, synchroniztion, cost nd informtion scuritis r importnt spcts to vlut th systm. Thy not only chllng th communiction tchnology, but lso put forwrd highr dmnds on th configurtion schm of MAS. 4.1 Trnsmission mod Using propr trnsmission mod will significntly improv th prformnc of MAS. Thr r thr communiction mods tht commonly usd, dirct communiction, rdio communiction, nd blckbord systm. Dirct communiction is pplid for th sitution, in which both sids know ch othr in dvnc. Rdio communiction nbls on to brodcst informtion to ll th mmbrs in th sm group, vn without knowing th ddrss. Blckbord systm is cntrlizd controlling systm, in which ll th group mmbrs uplod thir informtion to public r nd th othrs cn shr th informtion s thy nd. Th thr mods r pplid in diffrnt situtions ccording to thir chrctristics. s dirctly contct with th powr systm. Thy dmnd littl of informtion nlysis. So, it s unncssry for thm to communict widly with othrs. Thy only communict with djcnt s, which is fixd nd rgulr. It s bttr to us dirct communiction. s lso snd informtion to rgionl. Sinc ch rgionl covrs crtin r, it will b dtrmind which fw trminl s r in this r. In turn, ths trminl s will clrly know thir communiction objct. So, it s lso suitbl to us dirct communiction. Thr r lots of trminl s in bottom lyr, dirct communiction rducs th cost nd mk th communiction mor sf nd ffctiv. A rgionl is th cor of th crtin r. Bsids rciving informtion from th trminl s, it lso snds instructions to thm. Sinc thr is mor thn on trminl in th group, th instructions my b snt to ny on of thm. It s bttr to us rdio communiction, thn, ll th s in this group cn rciv th informtion nd th instruction will b xcutd by th corrspondd on ftr furthr confirmtion. s lso E-ISSN: X 204 Volum 14, 2015

5 communict with th othr s in th sm lyr. Blckbord systm is pplid in this sitution. All th rgionl s put thir informtion in th public r. Othrs cn sily gt wht thy nd for th furthr nlysis. Bcus th public r is ccssibl for ll th rgionl s, it rquirs strong fult tolrnc. Whn th mssgs uplodd by diffrnt s r in conflict, only th right on or th on with highr priority will b rcordd. Th conclusions md by th rgionl s should b snt to th cntrl, which is similr to th informtion trnsmission from trminl to rgionl. Th dirct communiction is suitbl in this cs. Th cntrl gts informtion from ll th rgionl s for globl optimiztion. Th rsults nd instructions will thn b snt to th rgionl s by rdio communiction. Th communiction mods btwn diffrnt objcts in MAS r listd in Tb.1. Tb. 1 Communiction mod of MAS Sndr Rcivr Cntrl Cntrl Dirct Rdio Dirct Blckbord Rdio Dirct 4.2 Slctiv communiction In ordr to sv costs nd incrs spd, th communiction systm should b ffctiv. Whn th communicts with othrs, th objcts should b slctiv. In th bottom lyr, trminl communicts with djcnt s. As shown in Fig.1, lin B7 is fr from lin B4, whthr brkr B7 should ct or not lmost hs nothing to do with lin B4. So it s unncssry to connct B7 with B4. On th contrry, lin B1 nd B2 r djcnt, which mk thm closly rltd. It s vry importnt to cquir th informtion of th djcnt lin to mk fult nlysis. So th two s r connctd to shr th informtion. Th informtion trnsfrrd should lso b slctiv. For th communiction btwn trminl s, th brkr sttus nd currnt informtion is usful for th othrs, whil th voltg nd switch tims r uslss. It s of mor importnc to mk it slctiv whn th trminl s snd informtion to th rgionl s nd th rgionl s snd informtion to th cntrl. s nd cntrl gt lrg mount of informtion from mor thn on, it must b nsurd tht only th informtion ncssry for th furthr nlysis r rcivd. Wht s mor, cntrl is mor likly to rciv th nlysis rsults from th rgionl s to chiv th rpid nlysis of optimiztion oprtion. 4.3 Principls Thr r som othr principls tht should b followd to improv th fficincy nd rduc th cost of th communiction systm. Firstly, th tsk of locl should b rrngd rsonbly. Sinc ll th s r intllignt, thy should crry out nlysis s much s possibl within thir cpbility. This will rduc th informtion trnsmission from th sourc. Scondly, it s bttr to trnsport sttus informtion instd of nlog informtion. For xmpl, dirctionl ovrcurrnt protction nds currnt dirction s critrion, whil low voltg strt ovrcurrnt protction nds th vlu of voltg. Dirction cn b sily rprsntd by sttus proprty, which tks up only 1 byt. But th vlu of voltg tks up mor mmory nd it s mor dmnding on th synchroniztion of informtion. Th trnsmission of sttus informtion is sir nd mor rlibl [17]. Th trnsmission distnc should b s short s possibl. A trminl should snd informtion to th nrst rgionl rthr thn th othr on. Mnwhil, trminl s do not snd informtion dirctly to cntrl. Th informtion is snt to rgionl nd prprocssd to gt simplifid conclusions. Th conclusions will thn b snt to th cntrl. 5 Conclusion Th dsign of MAS cn b mor flxibl on th prmis of rlibility. An xcllnt MAS implmnttion should t lst mt four rquirmnts s following: First of ll, it must stisfy th rlibility, snsitivity, rpidity, slctivity rquirmnts of protction nd chiv th optiml controlling of th distribution systm. Scond, th moduls of MAS should b stndrdizd to nsur th comptibility of diffrnt systms nd good sclbility to th xpnsion of grid. E-ISSN: X 205 Volum 14, 2015

6 Third, th construction nd running of MAS should b conomicl. Fourth, th informtion scurity should b gurntd. Th four rquirmnts dfin th optiml gols nd provid th dsign of MAS with rfrnc. Gnrlly, th futur protction of distribution systm should b intllignt bsd on th multi tchnology nd th communiction ntwork. With th dvlopmnt of DGs nd its controlling tchnology, communiction ntwork for DGs should b built to chiv th optiml running of powr systm. This will lso ly foundtion for th multi- bsd protction systm nd mks it n inxorbl trnd. Rfrncs: [1] Yun Cho, Wu Gng, Protction tchnology for distributd gnrtion systms, Powr Systm Protction nd Control, Vol.37, No.4, pp, [2] Ardito, D, Conti, Stfni, Mssin, N., Nicotr, S. Oprting conflicts in distribution ntworks protction with distributd gnrtion, WSEAS Trnsctions on Circuits nd Systms. Vol.4, No.9,2005, pp [3] Mäki, Kri, Rpo, Smi, Järvntust, Prtti. Protction coordintion to mt th rquirmnts of blinding problms cusd by distributd gnrtion, WSEAS Trnsctions on Circuits nd Systms. Vol.4, No.7,2005, pp [4] Morrn, J., Hn, S.W.H. Impct of distributd gnrtion units with powr lctronic convrtrs on distribution ntwork protction, IET 9th Intrntionl Confrnc on Powr Enrgy, & Industry Applictions, UK, 2008 [5] Wng Jinghi, Ti Nngling. Pntrtion lvl prmission of DG in distributd ntwork considring rly protction, Procdings of th CSEE, Vol.30, No.10,2010, PP [6] Fng Xik, Ti Nngling. Rsrch on th impct of DG cpcity on th distribution ntwork currnt protction nd countrmsur, Powr Systm Protction nd Control, Vol.38, No.14, 2010, pp [7] Li Jinyong, Hung Wi, Xi Xing. Pntrtion lvl clcultion with considrtions of phs-to-phs short circuit fult, Automtion of Elctric Powr Systms, Vol.32, No , pp [8] YE Lin, LIN Ling-zhn. Suprconducting Fult Currnt Limitr Applictions in Elctric Powr Systms, Procdings of th CSEE, Vol.20, No.5, 2000, pp.1-5 [9] Lin Xi, Lu Yuping, Wng Linh. Nw Currnt Protction Schm Considring Distributd Gnrtion Impct, Automtion of Elctric Powr Systm, Vol.32, No.7,2008, pp [10] Zhng Ynxi. Nw Schms of Fdr Protction for Distribution Ntworks Including Distributd Gnrtion, Automtion of Elctric Powr Systm, Vol.33, No.9, 2009, pp [11] Li Yongli, Jin Qing, Li Botong. Appliction of invrs-tim ovrcurrnt protction bsd on low voltg cclrtion in Micro-Grid, Journl of Tinjin Univrsity, Vol.44, No.10, 2011, pp [12] Sun Jinglio, Li Yongli. Study on Adptiv Currnt Instntnous Trip Protction Schm for Distribution Ntwork with Invrtr Intrfcd DG, Automtion of Elctric Powr Systm, Vol.33, No.6,2009, pp [13] Rnn Giovnini, Knnth Hopkinson, A Primry nd Bckup Cooprtiv Protction Systm Bsd on Wid Ar Agnts, IEEE Trnsctions on Powr Dlivry, Vol.21, No.7,2006 pp [14] Wng Huifng, H Bntng, Shi Hongyu, Applictions of multi-agnt tchnology in protction systm, Elctric Powr Automtion Equipmnt. Vol.27, No.10, 2007, pp [15] K.K. Li, W.L. Chn, Xingjun Zng, Agntbsd slf-hling protction systm, IEEE Trnsctions on Powr Dlivry, Vol.21, No.1, 2006, pp [16] I. Zbt nd M. Montzri, Implmnting Cooprtiv Agnt-bsd Protction nd Outg ngmnt Systm for Powr Distribution Ntwork Control, 4th Intrntionl Powr Enginring nd Optimiztion Conf, Mlysi, [17] Sun Hui, Liu Qinjin, Powr Distribution Ntwork Protction nd Control Using Ms, Procdings of th CSU-EPSA. Vol.23, 2011, pp E-ISSN: X 206 Volum 14, 2015