A Multi-Agent Solution to Distribution System Management by Considering Distributed Generators

Transcription

1 Pge of 0 IEEE PES Trnsctons on Power Systems A Mult-Agent Soluton to Dstrbuton System Mngement by Consderng Dstrbuted Genertors Abstrct A trdtonl dstrbuton networ crres electrcty from centrl power resource to consumers nd the power dsptch s controlled centrlly. Dstrbuted genertor (DG) emerge s n lterntve power resource to dstrbuton networs t smller nd dstrbuted scle whch wll brng benefts such s reduced voltge drop nd loss. However becuse most of hgh penetrton DGs re not utlty owned nd chrcterzed by hgh degree of uncertnty such s solr nd wnd the dstrbuton networ my perform dfferently from the conventonlly expected behvors. How to dynmclly nd effcently mnge the power dsptch n dstrbuton networ to blnce the supply nd demnd by consderng the vrblty of DGs nd lods becomes sgnfcnt reserch ssue. In ths pper multgent system (MAS) ws proposed to solve ths problem through ntroducng fve types of utonomous gents the electrcty mngement mechnsms the gent communcton ontology nd the gent cooperton strtegy. The smulton of the MAS by usng InterPSS JADE nd JUNE well demonstrtes the performnce of the system on dynmc supply nd demnd blnce by consderng both effcency nd economy. Index Terms Dstrbuton networ electrcty dsptch dstrbuted genertor mult-gent system I. INTRODUCTION A dstrbuton networ (DN) s the fnl stge n the delvery of electrcty to end users []. Typclly the bul generton s the only energy resource to DN nd the drecton of the power flow s strctly from the centrl generton to downstrem electrc components []. Conventonlly the DN s centrlly montored nd controlled nd the clsscl control technques focus more on verge lod nd demnd mngement [] []. Dstrbuted Genertor (DG) emerges s n lterntve power resources to DN t smller nd dstrbuted scle nd generlly locted close to the lods [] []. The ntroducton of DGs hs both dvntges nd dsdvntges []. On one hnd DGs cn supply power to the networ ner the lods wthout needng the trnsmsson system so s to sgnfcntly decrese the power loss nd cost nd shre the lods wth the centrl generton. Also DGs cn provde supports on voltge drop nd loss to DN durng pe lod []. On the other hnd most DGs cn only provde ntermttent power to the networ due to the ntermttent nture of the dstrbuted energy resources such s wnd nd sun. Also the utlty usully does not own the DGs nd hs dffculty n controllng ther outputs. Therefore wth n ncresng level of DG penetrton F. Ren nd M. Zhng re wth the School of Computer Scence nd Softwre Unversty of Wollongong Austrl eml:{frenmnje}@uow.edu.u D. Sutnto s wth the School of Electrcl Computer nd Telecom Unversty of Wollongong Austrl eml:soetnto@uow.edu.u Fenghu Ren Mnje Zhng nd Dnny Sutnto the DN my behve qute dfferently from the conventonl opertons. For exmple n PV pplctons durng noon tme when the PV s producng ts hghest output the resdentl lod my be t ts lowest whch results n power excess nd s trnsmtted bc to the substton ledng to voltge rse. Also the cloud pssng ssue n PV pplctons wll led to fst chnges of PV output wth hgh rmp rte. Furthermore wth hgh penetrton of DGs the power flow n dstrbuted networ my chnge from sngle drectonl flow to b-drectonl flow []. Therefore how to dynmclly nd effcently mnge the electrcty dsptch n DN to blnce the energy supply nd demnd by consderng the vrblty of DGs nd lods becomes n mportnt reserch ssue n power engneerng. The conventonl method my no longer be sutble for dong ths due to ts lmttons on flexblty communcton cooperton nd decson mng [] [] [0]. Mult-Agent Systems (MASs) hve been employed to solve mny power engneerng problems n recent yers nd re beng developed for rnge of pplctons ncludng system montorng nd fult dgnostcs [] [] system restorton [] [] system smulton [] [] nd system control [] []. In ths pper decentrlzed MAS s proposed to solve the dynmc electrcty dsptch problem n DN by consderng the vrbltes of DG s electrcty supply nd lod s demnd. The contrbutons of ths pper re tht: () t proposes fve types of gents to model the DN n n utonomous nd decentrlzed wy; () t proposes severl mechnsms to control the DGs nd other components to dynmclly blnce the electrcty supply nd demnd n the DN by consderng both effcency nd economy; nd () t descrbes the development nd mplement of the proposed MAS by usng InterPSS (Internet Technology Bsed Power System Smultor) JADE (Jv Agent Development Frmewor) nd JUNG (Jv Unversl Networ/Grph Frmewor) nd demonstrtes the smulton result. The orgnzton of ths pper s s follows. Secton II ntroduces the prncple nd the objectves of the proposed MAS. Secton III ntroduces three mjor mechnsms used n the MAS. Secton IV shows how to develop the MAS by usng JADE. Secton V demonstrtes the performnce of the proposed MAS through smulton nd Secton VI compres the proposed MAS wth some relted wor. Fnlly the concluson s gven n Secton VII.

2 IEEE PES Trnsctons on Power Systems Pge of Fg.. Interfce Lyer (JUNG) Multgent Lyer (JADE) SA Substton A. Prncple BA Bus Power System Lyer (InterPSS) GA FA Bus Feeder Genertor BA The three lyers vew of the proposed MAS. II. PRINCIPLE AND OBJECTIVE LA Lod Dfferent modelng strteges could be used to model DN [] [0]. Snce ths pper focuses on the electrcty dsptch problem n DN by consderng DGs fve types of gents re proposed to smulte the fve ey electrc components n DN.e. the substton the busbr the feeder the lod nd the DG. The rtonle of our desgn s to employ multgent technology to model ech of the ey components nd provde them wth the communcton nd decson mng bltes. Then these components cn me ndvdul decsons on locl power mngement bsed on locl nformton nd collectve decsons on regonl/globl power mngement through gent communcton nd cooperton. The proposed MAS contns three lyers.e. the power system lyer the multgent lyer nd the nterfce lyer. As shown n Fg. the lower power system lyer presents the physcl electrc components n DN the mddle mult-gent lyer hndles the communcton decson mng nd cooperton between the control gents of electrc components nd the upper nterfce lyer llustrtes the MAS. The mjor chrcterstcs of ech type of gents re ntroduced below. Substton Agent (SA): A SA represents secondry substton. It montors both the mgntude nd the drecton of electrcty through the substton. The SA hndles the power dsptch requests from other neghbor gents by consderng the cpcty of the substton nd the cble s lmt constrnt n-between them. Bus Agent (BA): A BA represents physcl busbr tht conducts electrcty between electrc components. The BA records nformton on the connected electrc components such s electrcty mgntude nd drecton cble s lmt constrnt nd the component s cpcty on power supply or consumpton. The BA decdes whether n power dsptch request cn be stsfed bsed on the nformton t hs nd order opertons on swtches to fulfll ts decson. Feeder Agent (FA): A FA represents physcl feeder whch delvers electrcty to downstrem components. The FA records the cble s lmt constrnt nd montors the current mgntude nd drecton on the cble. The FA checs the cble s trnsmsson blty to decde whether the requred power cn be delvered. In cse the electrcty drecton needs to be chnged the FA needs to hndle such procedure by communctng wth other gents long the feeder. Lod Agent (LA): A LA represents physcl lod whch consumes electrcty from the networ. Ech LA s ssgned prorty to ndcte ts sgnfcnce. If the lod needs to be chnged the LA wll contct the upstrem component to pply the power consumpton chnge. The LA s prorty s consdered by the upstrem BA n determnng how the LA s request s nswered. Generton Agent (GA): A GA represents physcl DG n the networ nd s lso ssgned prorty. The GA hndles the connectons nd dsconnectons of DG to the networ through communctng wth upstrem BA. Also the GA montors the power supply of the DG nd modfes the power supply under requests by consderng the DG s cpcty nd prorty. The proposed MAS hs the followng fetures by comprng wth clssc centrlzed power mngement systems: () the MAS employs the dstrbuted system structure whch mens tht gents re ssgned to dfferent components t dfferent loctons n DN. Therefore they re not ntegrted but seprted from ech other; () the decentrlzed mngement s employed by the MAS whch mens tht there s no centrl controller n the MAS nd gents wor utomtclly bsed on the nformton they receve from the correspondng electrc components nd neghbor gents. No gent n the system cn preset the globl nformton of the whole DN; () gents cn only notce nd communcte wth ther neghbor gents. Non-djcent gents do not now the exstence of ech other but the nformton cn stll be exchnged mong them through other gents n-between; nd (v) the MAS requres no dependency between gents nd the system rchtecture s extendble. Agents ply s plug nd operte component. B. Objectves The multobjectve pproch [] s employed to represent the objectves of the MAS whch re to () dynmclly blnce the power supply nd demnd n DN; () mxmze the power usge from DGs; nd () mnmze the power usge cost n DN. The restrctons such s cbles lmts electrc components lmts nd genertors power supply cpctes re lso consdered. Some relted MASs lso te the smlr consdertons nto ccount such s [] consders the cost mnmzton [] consders the voltge nd current lmtton nd [] consders the lod mxmzton. In ths pper we combne these consdertons together nd lso te the system blnce nd optmzton of DGs nto ccount. () Blnce Objectve: For ech component n DN we must ensure tht the power delverng to nd from re blnced p + + p j = p + p () j J + J where p + s the power generted by component p s the power consumed by component p j s the power delvered to from neghbor component j nd p s the power delvered from to nother neghbor component.

3 Pge of 0 IEEE PES Trnsctons on Power Systems () Usge Objectve: In order to decrese the burden on the bul genertons we wnt to mxmze the power usge from DGs. m mx p + () = where m s the totl number of DGs n DN. () Cost Objectve: We lso wnt to mnmze the power usge cost for DN. Frstly component s cost on consumng n unt electrcty s defned s follows: c = j J + pj cj j J + p j () where c j s the unt power prce from componentj. If component needs to further delver power to nother component then the cost s c = c +c cb where ccb s the cost on the cble between components nd. Then the cost objectve s formulted s: n mn c p () = where n s the totl number of components n the networ. The fulfllment of the objectves should not led to volton of opertng lmts of the components; hence severl constrnts re renforced. () Lmt on Cble: The current between components nd should be not greter thn the cble s crryng cpcty rtng to ensure tht the upper therml current lmt wll not be exceeded. I I mx () () Lmt on Genertor: For ech genertor the suppled power should be not greter thn ts cpcty. p + p +mx () () Lmt on Busbr: Ech bus s voltge must be lwys wthn ts voltge lmts. V mn V V mx () (v) Lmt on Component: Ech component lso hs current rtng lmt. I j I mx () j J+ III. AGENT MECHANISMS In ths subsecton we ntroduce three mechnsms used n the proposed MAS.e. connecton mechnsm dsconnecton mechnsm nd power mngement mechnsm. A. Connecton Mechnsm When new electrc component needs to connect to DN correspondng gent wll be frstly generted to represent the new component. Let be represented by fve-tuple < AID I mx S mx C mx P > nd n j =< AID j Sj mx Cj mx Ij mx A j I j P j > be s record on ts neghbor j (the explnton of nottons s gven by Tble I). Then f the component needs to connect to the DN through component j (represented by j ) the connecton process s gven s follows (see Fg. for the UML dgrm): Notton AID I mx S mx C mx P AID j Sj mx Cj mx Ij mx A j I j P j TABLE I THE EXPLANATION ON TATIONS. Explnton Agent s unque dentfcton the mxmum current llowed by the electrc component the mxmum power tht component cn supply the mxmum power tht component cn consume the unt electrcty prce supply neghbor gent j s dentfcton the mxmum power tht cn get through j the mxmum power tht j cn te from the mxmum current on the cble between components nd j the exstng power trnsferrng between components nd j the exstng current on the cble between components nd j the cost on delverng unt power from components j to Intlzton Send request for ds/connect Is ds/connect llowed? Termnte the process Agent Updte the neghbor gents record Set response to "" Agent Is ds/connect llowed? Reply the ds/connect request j Updte the neghbor gents record Inform other exstng nebhbor gents Set response to "" Fg.. The UML dgrm for ds/connecton mechnsm Step (): s creted to represent the electrc component nd s ntlzed ccordng to component. Step (): sends the connecton request nd ts nformton (.e. < AID S mx C mx P >) to j nd wts for j s response. Step (): j receves the request. If the connecton s not llowed j denes the connecton nd the procedure goes to Step (v). Otherwse the procedure goes to Step (v). Step (v): Frstly j cretes new neghbor gent record ccordng to the nformton sent by.e. n j =< AID S mx C mx Ij mx 00P + L j > (where L j ndctes the loss n the cble between components nd j) nd N j {n j } N j. Secondly j nforms other exstng neghbor gents bout ts updte on power supply nd demnd by sendng (S mx C mx ). Thrdly the neghbor gents updte ther record on j s electrcty supply nd demnd.e. Sj mx Sj mx +S mx nd Cj mx Cj mx +C mx. Lstly j reples s wth ts nformton.e. < AID j Sj mx + N j = Smx j Cmx j + N j = Cmx j P j >. Step (v): If receves refuse response the process s termnted. Otherwse cretes new neghbor gent record n j ccordng to the nformton sent by j.e. N {n j } N nd then connects to the DN. B. Dsconnecton Mechnsm An exstng electrc component my lso need to be dsconnected from DN. Let suppose tht gent wnts to dsconnect from the DN nd gent j s the upstrem

4 IEEE PES Trnsctons on Power Systems Pge of component then the dsconnecton process s gven s follows (see Fg. for the UML dgrm): Step (): ntlzes the process sends the dsconnecton request to j nd wts for j s response. Step (): j receves the request. If the dsconnecton s not llowed j denes the dsconnecton nd the procedure goes to Step (v). Otherwse the procedure goes to Step (). Step (): Frstly j nforms other neghbor gents bout ts updte on power supply nd demnd by sendng ( Sj mx Cj mx ). Secondly the neghbor gents updte ther record on j s power supply nd demnd.e. Sj mx Sj mx Sj mx nd Cj mx Cj mx Cj mx. Thrdly j deletes the record of from ts record set.e. N j N j /n j. Lstly j reples wth n greement. Step (v): If j denes the dsconnecton request the process s termnted. Otherwse wll deletes the record of j from ts record set.e. N N /n j nd then dsconnects from components j. C. Power Mngement Mechnsm If ny power unblnce occurs on ny component the power mngement mechnsm wll be ctvted to blnce the power supply nd demnd by consderng ll the objectves nd constrnts mentoned n Subsecton II-B. Let be the gent whch frstly notces n unblnce. Let N + ( N n m N + I m 0) be the set of s neghbor gents who get power from N ( N n m N I m < 0) be the set of s neghbor gents who send power to nd req ( = 0) be the mount of power tht wnts to chnge then there re two possble scenros.e. req < 0 ndreq > 0. Fg. llustrtes the UML dgrm for the mngement process nd the detl process s ntroduced s follows. ) When req < 0: ths scenro ndctes tht needs more req power. In order to stsfy the blnce objectve two possble solutons re consdered by.e. () seeng extr power from exstng supplers or (b) decresng output to exstng consumers (.e. lod sheddng). In order to mnmze the mpct on consumers wll see extr mount power req from ts exstng supplers frstly nd then perform the lod sheddng when necessry. Bsed on ths rule the followng procedures re performed: Step (): In order to stsfy the cost objectve the supplers wth lower prce wll be consdered frstly by to see the extr req power. rns ll supplers ccordng to the scendng order of ther supply prces. Let N r be the rned supplers nd gent be the frst gent n the rn. Frstly estmtes s power supply blty s S r = Smx S. If S r > req the request req (req pr ) (pr s s prorty) wll be sent to ; otherwse the request req ( S r pr ) wll be sent to nd leve the remnng S r req for the next suppler. Then wll remove from the set N r nd wt for s response. However f fls to receve ny response from wthn predefned tme perod wll bndon gettng power from by sendng cncelton nd rellocte the power req to the next suppler. Step (): my receve mny requests from dfferent gents. Therefore wll rn ll requests n queue Q by consderng the prorty of the requestor nd the tme they receved. A request wth the hgherest prorty wll be put n the front of the queue. For requests wth sme prorty the erler receved request wll be put n the front. For requests wth sme prorty nd tme lbel they wll be nserted nto the queue rndomly. Therefore once receves the request req from wll frstly nsert req nto the queue. Let us suppose tht lredy completes ll requests n front of req. If gent s GA or SA cn me decson on the request req wthout contctng other gents. In order to do tht frstly clcultes ts remnng supply blty to s S r = Smx j N + S j nd reples to ndcte the mount tht cn ctully supply.e. rsp = mn(s r req ) then the procedure goes to Step (). However f s BA or FA needs to contct other neghbors for s request. To do tht wll ntlze nother mngement process by seeng req mount of power from ts neghbors. Obvously such procedure wll be repeted untl GA or SA s found (see Subsecton III-D on the dscusson on the sclblty nd complexty). After receves ll responses from ts neghbor gents wll generte response to by combng ll the responses.e. rsp = m N rsp m. However f receves cncelton request from before the response rsp cn be generted wll lso send the cncelton to ts neghbors. Step (): receves s response. If s request cn be fully stsfed by.e. rsp = req then the procedure s termnted nd ll relted gents djust ther power ccordng to ther greements. Otherwse wll see for the remnng power req r rsp req r (where reqr s ntlzed s req ) from next vlble suppler n N r. Then steps () to () wll be repeted untl s request s fully stsfed (.e. req r = 0) or the rned lst N r becomes empty. For the ltter cse the procedure goes to Step (v). Step (v): Becuse cnnot get enough power from ts exstng supplers t hs to decrese output to exstng consumers (.e. lod sheddng). The lod sheddng strtegy employed n ths pper s smple.e. performng lod sheddng ccordng to the neghbor gent s prorty. Frstly rns ll consumers ccordng to the scendng order of consumers prortes. Let N +r be the rned consumers nd j be the frst gent. If s prorty s hgher thn j s then wll shed j s power by sendng request req j ( mn(a j req r )pr ) to j. Then removes j from set N +r nd the procedure goes to Step (v). However f the wtng perod s longer thn predefned perod wll shed j s lod wthout the response. Step (v): j wll nsert the request from to ts request queue Q j. Let us ssume tht req j s proceeded by j now. If j s LA the lod wll be shed on j drectly nd the procedure goes to Step (v). Otherwse f j s BA or FA j needs to contct other neghbors for s request. In order to do tht j wll ntlze nother mngement process by seeng the req mount of power from ts neghbors. After j receves ll responses from ts neghbor gents j wll reply wth the response rsp j = m N j rsp m nd the procedure goes to Step (v). However f j s lod ws shed by

5 No Pge of 0 IEEE PES Trnsctons on Power Systems r Rn N - ccordng to scendng order of prorty Send request req j to the next Agent j on the lst Agent j nserts request req j n ts queue nd hndle ll request orderly j replesrspj to drectly Is j LA Is req Stsfed Is the lst empty j strts nother process for req j nd replesrsp j r Rn N + ccordng to scendng order of prce Send request req to the next Agent on the lst Agent nserts request req j n ts queue nd hndle ll request orderly reples rsp to drectly Is GA or SA Is req Stsfed Is the lst empty strts nother process forreq nd replesrsp Fg.. The UML dgrm for power mngement before the response rsp j cn be generted j wll shed the sme mount of lod on ts consumers by consderng ther prortes. Step (v): receves j s response. If s request cn be fully stsfed by j.e.rsp j = req then the procedure s termnted nd ll relted gents djust ther power ccordng to ther greements. Otherwse wll see the remnng power req r rsp j req r from next vlble consumer n N +r. Then steps (v) to (v) wll be repeted untl s request s fully stsfed (.e. req r = 0) or no gent s prorty n the rned lst s lower thn s prorty. ) When req > 0: ths scenro ndctes hs extr power. Let P be the unt power prce provdng by. In order to stsfy the blnce objectve two possble solutons re consdered.e. () decresng power nput from exstng supplers or (b) delverng the extr power bc to the upstrem components. By consderng both the usge nd cost objectve the two optons should be combned.e. frstly tryng to decrese the power from supplers whose prce s hgher thn P nd then delverng the remnng extr power bc to the upstrem components. The procedures re s follows: Step (): rns ts supplers ccordng to the descendng order of supplers prces. Let N r be the rned supplers nd be the frst gent. If s prce s hgher thn s wll send the request req (mn(req A )pr ) to. Then removes from the lst nd the procedure goes to Step (). Otherwse f s prce s not hgher thn s prce the procedure goes to Step (v). However f cnnot receves s response wthn predefned perod wll cncel the request to nd contct the next suppler. Step (): Once receves the request to decrese ts power output to wll nsert the request to ts queue Q. Let us ssume tht request req s processed now. If s GA or SA t cn me the decson wthout contctng other neghbor gents. The ctul deducton on output mount wll be sent bc to s response.e. rsp. Then Agent Request req req <0 Process Termnted r Rn N + ccordng to scendng order of prce nd s the next Send request req to the upstrem Agent u Agent u nserts request req j n ts queue nd hndle ll request orderly The upstrem gent strts nother process u to send power to the networ 's prce hgher thn reples rsp to drectly Send requestreq to Agent nserts request req j n ts queue nd hndle ll request orderly Is GA or SA Is req Stsfed Is the lst empty strts nother process for req nd reples rsp the procedure goes to Step (). However f s BA or FA needs to contct ts neghbors for s request by ntlzng nother mngement process. Such procedure wll be repeted untl GA or SA s found. After receves ll responses from ts neghbor gents wll send request rsp = m N rsp m to. However f receves cncelton request from before the response cn be generted wll lso send the cncelton to ts neghbors. Step (): receves s response. If s request cn be fully stsfed by.e. rsp = req then the procedure s termnted nd ll relted gents djust ther power ccordng to ther greements. Otherwse wll deduce the remnng power req r reqr rsp (req r s ntlzed s req ) from next suppler n N r. Then Step () to Step () wll be repeted untl s request s fully stsfed (.e. req r = 0) or the frst suppler whose prce s not hgher thn P s met. For the ltter cse the procedure goes to Step (v). Step (v): wll send the request req (req rpr ) to ts upstrem gent.e. u. Then u wll strt nother power mngement procedure to meet s request by repetng Step () to Step (v). We ssume tht the extr power cn be sent bc to the substton eventully. Therefore u cn lwys fully stsfy s request. D. Dscusson on Sclblty nd Complexty It cn be seen tht the proposed power mngement mechnsm employs recursve strtegy to serch for power sources nd dsptch the pproprte power ccordngly. By comprng wth the conventonl centrlzed mngement the proposed mechnsm does not requre nowledge of the DN s whole nd cn me quc response bsed on locl nformton. However the proposed mechnsm wll hve hgher requrement on gents communcton blty. Ths wll not be sgnfcnt for smll rdl dstrbuton systems but further wor needs to be crred out to nvestgte ts mpct on very long dstrbuton systems.

6 IEEE PES Trnsctons on Power Systems Pge of In generl the proposed recursve mechnsm wll complete when () the power resources re found nd the power supply nd demnd re blnced; or () the procedure s bndoned becuse of tme restrcton. Usully by consderng norml rdl DN the number of tmes of recurson to send request from lod/dg to secondry bus s three (.e. lod/dg locl bus feeder secondry bus) then the secondry bus wll te n extr recurson (.e. secondry bus substton) to get response from substton or three extr recursons (.e. secondry bus feeder locl bus DG) to get response from nother DG on dfferent feeder. For n extreme complex cse when multple DGs nd the unblnced lod re locted on dfferent feeders n order to fulfll the usge nd cost objectves the secondry bus gent wll contct ll DG gents whch hve not reched ther mxmum power outputs before t contcts the substton gent. Therefore the totl number of recurson wll be the three tmes of the feeder s number n the DN. Of course f we consder to shre DGs from dfferent substtons the number of recurson wll lso ncrese exponentlly n order to get cheper power from other res. Therefore theoretclly these s no lmtton on the sclblty of the proposed mechnsm. But f we consder the prctcl ssues such s restrctons on tme nd communcton the effcency of the proposed mechnsm my be mpcted when the system scle s lrge. However such prctcl ssues n lrge scle DN wll lso be of concerned to other modern nd conventonl power mngement mechnsms. The complexty of the proposed mechnsms re gven below. Accordng to the UML dgrm n Fg. for both the ds/connecton mechnsm becuse needs to spend tme on ntlzng (one pss) exchngng messges wth j (two psses) nd updtng j s nformton (one pss); j needs to spend tme on exchngng messges wth (two psses) updtng s nformton (one pss) nd brodcstng ts updtng to other gents (n psses for the worst cse); nd other gents need to spend tme on updtng ther own nformton (n psses) so the complexty of the ds/connecton mechnsm s T(n) = n+ = O(n). Accordng to the UML dgrm n Fg. for the power mngement mechnsm the complexty of the cse req < 0 s more complex thn the cse req > 0 therefore the complexty of the whole mechnsm depends on the complexty of the cse req < 0. Let n s be the totl power source s number (ncludng ll DGs nd the substton) n l be the totl lod s number nd n bf be the totl number of buses nd feeders n DN then we should hve n = n s + n l + n bf. Accordng to the mechnsm when req < 0 n gent performs two steps.e. () seeng extr power nd () performng lod sheddng. For the frst step the gent wll frstly spend one pss on ntlzng the procedure. Although the exct nformton of the gent s neghbors s unnown (ncludng neghbor s number nd type) ech bus or feeder cnnot mmedtely me the fnl decson nd needs to ntlze other procedure. Therefore there wll be nother n bf psses (the worst stuton) for ntlzton. Also for ll the nvolved bus feeder substton nd DG gents ech of them wll spend three psses (.e. recevng messge Nme (Type) Power (C) Cost (C) Lmt (C) Lne (C) Neghbor (C) Ds/Connect (A) UpdteCost (A) UpdteLmt (A) ChngePower (A) TABLE II ONTOLOGY FOR AGENT COMMUNICATION Slot Nme (Type) from-power (Flot) to-power (Flot) from-cost (Flot) to-cost (Flot) lmt-power (Power) d (Strng) lmt (Lmt) power (Power) cost (Flot) nme (Strng) type (Strng) level (Strng) lne (Lne) cost (Cost) lmt (Lmt) type (Strng) level (Strng) lne (Lne) cost (Cost) lmt (Lmt) cost (Cost) lmt (Lmt) chnge (Flot) cost (Flot) mng decson nd replyng the messge) n order to response request. Therefore there wll be nother(n s +n bf ) psses (the worst stuton) whch results n the complexty of step one to + n bf + n s. For the lod sheddng step the nlyss s smlr s the frst step but we just replce the DGs nd the substtons wth the lods. Therefore the totl psses for the lod sheddng step (the worst stuton) s +n bf +n l. Eventully the complexty of the mechnsm s T(n) = (+n bf +n s )+(+n bf +n l ) = +n+n bf +n = O(n). IV. MAS DEVELOPMENT A. Jv Agent Development Frmewor (JADE) We employ the Jv Agent Development(JADE) Frmewor to mplement the proposed MAS. The communcton mong gents n JADE s crred out ccordng to FIPA-specfed Agent Communcton Lnguge (ACL) []. B. Agent Development In order to fulfll the communcton between djcent gents we defne the ontology tht gents must follow durng ther communctons n Tble II to ensure tht one gent s messges re understndble by others. Fve concept (C) ontologes e.g. Power Cost Lmt Lne nd Neghbor nd fve cton (A) ontologes e.g. Connect/Dsconnect Updte- Cost Updte-Lmt nd Chnge-Power re defned. The ctul wor tht n gent does s crred out n behvors. We defne sx gents behvors e.g. Connect Dsconnect Updte Cost Updte Lmt Chnge Power Supply nd Chnge Power Consumpton n Tble III. A detled explnton on how to develop gents by usng JADE cn be found n []. V. SIMULATION In ths secton we demonstrte the performnce of the proposed MAS through cse study. The smulton contns three lyers.e. () we employed InterPSS (Internet technology bsed Power System Smultor) to smulte DN []. InterPSS s n open-source Jv-bsed development project to enhnce power system desgn nlyss dgnoss nd operton; () we employed JADE on top of InterPSS to mplement the proposed MAS nd t s lned wth InterPSS to montor nd control the DN; nd () we employed JUNG

7 Pge of 0 IEEE PES Trnsctons on Power Systems TABLE III DESCRIPTION OF BEHAVIORS ASSOCIATED WITH AGENTS Behvors Send Messge Receve Messge Descrpton Connect performtve REQUEST ID connectprent sender Downstrem gent re- connect-prent sender Upstrem performtve AGREE/REFUSE ID cever Upstrem gent content (type gent recever Downstrem gent chld lne cost lmt) content (type prent lne cost lmt) Dsconnect performtve REQUEST ID dsconnect-prent sender Downstrem gent recever Upstrem gent content (type chld lne cost lmt) Updte Cost Updte Lmt Chnge Power Supply Chnge Power Consumpton performtve INFORM ID updtecost sender Neghbor gent recever Neghbor gent content (cost) performtve INFORM ID updtelmt sender Neghbor gent recever Neghbor gent content (lmt) performtve AGREE/REFUSE ID chnge-power-supply sender the gent recever neghbor gent content (power cost) performtve AGREE/REFUSE ID chnge-power-consumpton sender the gent recever neghbor gent content (power cost) Fg.. An InterPSS output showng the one-lne dgrm of dstrbuton networ. (Jv Unversl Networ/Grph Frmewor) [] on top of JADE to mplement the nterfce of the proposed MAS wth InterPSS. JUNG s free softwre lbrry tht provdes common nd extendble lnguge for the modelng nlyss nd vsulzton of dt tht cn be represented s grph or networ. In Fg. DN s smulted by usng InterPSS. The DN contns one substton two feeders fve buses sx lods nd one genertor. The lmts of power flow for substton bus nd feeder re set to 00 MW. The mxmum power supply blty for the substton s set to 00 MW nd s connected to 0 MW genertor resource. The power consumpton for ech lod s set to 0 MW nd we ssume tht ll lods consumpton nd the DG s supply cn chnge dynmclly n n unexpected wy. It s lso ssumed tht DG s power prce s cheper thn substton s power prce nd we set those two prces to $0 nd $0 respectvely. We set the length of ll cbles to m nd ssume tht the cost for delverng MW power on cble s $. Becuse ll lods nd DGs re dynmclly chnged the power dsptched by the DN s lso chnged ccordngly. Fg. shows moment when performtve AGREE/REFUSE ID dsconnect-prent sender Upstrem gent recever Downstrem gent content (type prent lne cost lmt) performtve INFORM ID updtecost sender Neghbor gent recever Neghbor gent content (cost) performtve INFORM ID updtelmt sender Neghbor gent recever Neghbor gent content (lmt) performtve REQUEST ID chngepower-supply sender neghbor gent recever the gent content (power cost) performtve REQUEST ID chngepower-consumpton sender neghbor gent recever the gent content (power cost) Sends connecton request to n upstrem gent; receves AGREE/REFUSE for successful/unsucessful result; exchnges nformton n predefned formt. Sends dsconnecton request to n upstrem gent; receves AGREE/REFUSE for successful/unsucessful result; exchnges nformton n predefned formt. Sends/receves/forwrds prce chnge nform to/from/to other neghbor gents. Sends/receves/forwrds lmt chnge nform to/from/to other neghbor gents. receves chnge power supply REQUEST from neghbor gent; reples AGREE f cn fully stsfy the request nd REFUSE f cnnot; reples ctul power supply chnge nd the new prce. receves chnge power consumpton REQUEST from neghbor gent; reples AGREE f cn fully stsfy the request nd REFUSE f cnnot; reples ctul power consumpton chnge nd the new prce. the Genertor provdes 0 MW to Bus nd the Substton provdes the remnng power (.e. 0 MW) to the networ. It s ssumed tht nother Genertor wnts to connect to the networ through Bus t ths moment. The Genertor s rted t 0 MW. In the followng we demonstrte the smulton of Genertor s connecton by usng our MAS. In Fg. (Messges (M) from to ) the communctons between gents for mplementng the Genertor s connecton re dsplyed nd re explned n below. (M) GA sends request nd self s nformton to BA for connecton. (M) BA reples GA s wth n greement nd lso sends self s nformton to GA. (M-) BA nforms FA nd LA bout ths updte. Then FA nd LA further nform ths updte to ther neghborng gents. Fnlly ths nformton s brodcsted n the networ. After GA ws connected t requests to supply 0 MW to the networ through BA mmedtely. In Fg. (messges from M to M) the communctons between gents for mplementng the power dsptch re dsplyed. The explntons re gven below. (M) GA requests to delver 0 MW to BA. (M) BA receves GA s request nd performs the power mngement.e. BA wll use GA s power to replce the power from FA to support LA (0 MW) nd delver the remnng power (0 MW) bc to FA (.e. the power flow drecton chnges). So BA further sends request to FA. (M) FA receves BA s request nd performs the power mngement.e. FA wll use BA s power to replce the power from BA to support BA (0 MW) nd delver the remnng power (0 MW) bc to BA (.e. the power flow drecton chnges). So FA sends request to BA. (M) BA receves FA s request nd performs the power mngement.e. BA wll stop the power supplyng (0 MW) to FA nd use the extr power (0 MW) from FA to support FA nd LA. Therefore BA wll decrese the power from SA by 0 MW nd BA sends ths request to SA. (M0) SA receves BA s request nd reples BA wth n greement to decrese

8 IEEE PES Trnsctons on Power Systems Pge of Fg.. Fg.. The gents communctons when GA s connected The smulted dstrbuton networ fter G s connecton. ts power supply by 0 MW. (M) BA receves SA s response nd reples FA wth n greement to te the extr 0 MW. (M) FA receves BA s response nd reples BA wth n greement to te the extr0 MW. (M) BA receves FA s response nd reples GA wth n greement to te the 0 MW. (M-) GA strts to supply power to the networ through BA nd ll relted gents rrnge ther power ccordng the greements mentoned bove. The smulton of the networ fter GA s connecton by usng JUNE s llustrted n Fg.. The results from the demonstrton show tht the proposed MAS s effectve n dynmclly executng power mngements n DN when the power supply nd/or demnd chnges. We lso employed the clsscl centrlzed mngement [] on the sme networ to repet the bove connecton nd power dsptch procedures. Accordng to [] the centrlzed mngement scheme should contn dstrbuton mngement system controller whch ccepts equpment sttus mesurements t selected loctons n dstrbuton networ. The controller would then use the globl nformton of the networ to estmte the best dsptchng soluton by consderng ech equpment s specfcton. In ths pper we lso follow ths well ccepted scheme n the smulton of the centrlzed mngement. The centrl controller s ssumed to be locted t the substton nd s mplemented by controller gent usng JADE. All lods nd DGs re selected s the mesurement ponts nd ther sttuses re reported to the controller gent drectly by locl montor gents. The communcton scheme between the centrl controller gent nd ll locl montor gents lso follows FIPA s ACL scheme. Comprng wth the proposed dstrbuted bus gent the centrl controller gent cts more les super bus gent wth the globl nformton nd control blty. For comprson purpose the objectves nd constrnts of the centrl controller gent re set to be the sme s the proposed MAS (see formuls ()-()). The optml soluton for the objectves cn be clculted drectly by the centrl controller gent wth the globl nformton nd then the controller gent djusts the substton s nd the DGs power output ccordngly. We eep both the decentrlzed nd centrlzed systems on runnng for hours fter GA s connecton nd let ll lods nd DGs dynmclly nd rndomly modfy ther consumptons nd supples respectvely. In Fg. we dsply the hstorcl record montored by InterPSS on Bus. The fluctuton dsplyed n Fg. s cused by the rndom chnge of lods consumpton nd DGs supply. We cn see tht the proposed MAS cn lwys blnce the supply nd demnd by consderng the economy. Then we summrze the tme (whch ncludes the tme of nformton exchnge between InterPSS nd JADE) spent by the two systems to respond to ll lods nd DGs requests n Tble IV. It cn be seen tht the verge response tme spent by the proposed decentrlzed system s only.% of the tme spent by the centrlzed system. Tht s becuse the centrlzed system needs to delver ll messges to the centrl controller gent for decson mng (.e. lrge mount of tme s consumed on communcton nd computton) whle the proposed decentrlzed system cn me the decson loclly. However the response tme spent by the proposed decentrlzed system on ech gent s request s mpcted by the gent s locton nd nerby components nd s not s consstent s the centrlzed system. Generlly the decentrlzed system spent less tme on nswerng the gents who hve energy

9 Pge of 0 IEEE PES Trnsctons on Power Systems Fg.. The hstorcl records of BA. TABLE IV TIME NEEDED OF THE PROPOSED MAS Centrlzed Tme (Sec) Decentrlzed Tme (Sec) Agent Mn Mx Avg Mn Mx Avg LA LA LA LA LA LA GA GA resources nerby such s LA LA nd LA but more tme on nswerng other gents who do not hve energy resources nerby such s LA LA nd LA. Also the decentrlzed system spent longer tme on nswerng DGs requests thn lods requests on verge. Tht s becuse the DGs requests hve hgher chnces to mpct the substton s power supply thn the the lods requests. VI. RELATED WORK Some gent-bsed systems were lredy mplemented by reserchers to provde supports on power system control nd mngement by consderng DGs. To lst few of them Pezesh et l. [] revewed the use of multgent systems to model the mpcts of hgh levels of photovoltc system n Perth Solr Cty project nd nvestgted the potentl problems cused by voltge regulton though gent-bsed smulton. The smulton results confrmed tht the usge of DGs could cuse problems such s over-voltge short crcut protecton desenstzton nd ncorrect operton n DN. Fnlly the pper suggested to employ more gents to montor nd control the lods the DGs the feeders nd the power qulty n DN whch s lso consstent wth our motvton. Frg nd El-Sdny [] studed the voltge regulton n unblnced dstrbuton feeders wth hgh penetrton of DGs. Ther reserch showed tht the trdtonl control technques ws no longer sutble for voltge regulton when DGs re consdered nd could cuse overvoltge nd/or undervoltge problem becuse of ncorrect opertons on voltge regultors. The resons behnd such ncorrect opertons were mnly becuse the regultor only employs one-wy communcton wth other components nd lcs of DGs nformton. Fnlly multgent systems wth three types of gents.e. regultor gent cpctor gent nd DG gent were proposed to solve ths ncoordnton problem through gent communcton nd cooperton. The power mngement problem studed by our pper hs smlr motvton s Frg nd El-Sdny s wor. But our proposed MAS consders more electrc components nd eventully optmzed the power mngement results by consderng both effcency nd economy. Mller et l. [] modeled the electrcty blnce problem between DGs nd lods s n optml dsptch problem nd solved the problem through mnmzng CO emssons of DN. Frstly fctor grph ws creted bsed on the structure of DN by consderng only DGs nd lods then the optml soluton ws clculted to set the electrcty output for ech genertor by trgetng the stsfcton of ll lods nd the mnmzton of ll DGs CO emssons. However ther wor only focused on the blnce problem between DGs supply nd lod demnds but other prctcl ssues such s economy electrcty delvery nd vrbltes of DGs nd lods re not consdered. Also t s not cler how ther proposed MAS ws mplemented nd operted to fulfl the systemc gols. Ko et l. [0] proposed MAS to mtch the electrcty supply nd demnd n electrcty networ by consderng the economcl optmzton. The electrcty supply nd consumpton devces were modeled by gents nd they communcted wth the SD-Mtcher gent to bd the electrcty prce. Through the coopertons between SD-Mtcher gents n dfferent herrchcl levels the prce greements between electrcty supplers nd consumers were creted. Fnlly contrct networ ws constructed bsed on physcl connectons between the electrc devces nd the prce greements were cheved. However ther wor focused more on the electrcty mret nd tred to cheve the economcl optmzton. Our wor presented more detls on electrc components mngement gents communcton gents cooperton nd MAS mplementton. Hung et l. [] proposed mret-bsed MAS to perform the utomtcl reconfgurton of rdl electrc shpbord power system. The ssues such s power cost nd lmtton on components were lso consdered. Through communcton wth neghbor gents the behvors such s swtchng between power supplers nd modfyng power supplyng could be utomtclly performed. However ther MAS focused on shpbord power system wth fxed electrcty networ whle our MAS pys ttentons on the DN by consderng DGs vrbltes. VII. CONCLUSION DG hs been consdered s supplementl energy resource to exstng electrcty networ nd cn provde ddtonl supports to solve the voltge drop nd energy loss problems. However the uncertnty of DG s locton nd the vrblty of DG s electrcty output hs cused serous systemc mngement problem to the exstng control technques. The conventonl control technques were no longer sutble to

10 IEEE PES Trnsctons on Power Systems Pge 0 of control n electrcty networ wth DGs due to ther lmttons on flexblty communcton cooperton nd decson mng. In ths pper multgent soluton ws proposed to solve the power dsptchng problem by consderng the vrbltes of DGs nd lods. Fve types of gent were proposed to model the ey electrc components n DN nd three system objectves were formulted to gurntee the system blnce s well s to optmze the system s effcency nd economy. Through the communcton nd cooperton between the proposed gents unexpected mblnces n the DN were effectvely resolved by consderng ll objectves. We lso ntroduced the detls on the MAS mplementton by usng InterPSS JADE nd JUNG nd demonstrted the good system performnce through the smulton. ACKWLEDGEMENT The uthors would le to cnowledge the fnncl support from the Austrln Reserch Councl (ARC) Lnge Scheme LP0 nd Trnsgrd Austrl for ths project. REFERENCES [] I. Bxevnos nd D. Lbrds Implementng Multgent Systems Technology for Power Dstrbuton Networ Control nd Protecton Mngement IEEE Trns. on Power Delvery vol. no. pp. 00. [] M. Nordmn nd M. Lehtonen Dstrbuted Agent-Bsed Stte Estmton for Electrcl Dstrbuton Networs IEEE Trns. on Power Systems vol. 0 no. pp. 00. [] H. Pezesh P. J. Wolfs nd M. Johnson Mult-Agent Systems for Modelng Hgh Penetrton Photovoltc System Impcts n Dstrbuton Networs n Proc. of Innovtve Smrt Grd Technologes As pp. 0. [] P. Vovos A. Kprs A. Wllce nd G. Hrrson Centrlzed And Dstrbuted Voltge Control: Impct on Dstrbuted Generton Penetrton IEEE Trns. on Power Systems vol. no. pp. 00. [] H. Wn K. L nd K. Wong Mult-Agent Applcton of Substton Protecton Coordnton wth Dstrbuted Genertors Europen Trns. on Electrcl Power vol. no. pp [] T. Acermnn G. Andersson nd L. Söder Dstrbuted Generton: A Defnton Electrc Power Systems Reserch vol. no. pp [] P. Brer nd R. Mello Determnng the Impct of Dstrbuted Generton on Power Systems. I. Rdl Dstrbuton Systems n Power Engneerng Socety Summer Meetng vol. pp [] H. Frg nd E. El-Sdny Voltge Regulton n Dstrbuton Feeders wth Hgh DG Penetrton: From Trdtonl to Smrt n Proc. of IEEE Power nd Energy Socety Generl Meetng pp. 0. [] M. Doyle Revewng the Impcts of Dstrbuted Generton on Dstrbuton System Protecton n Power Engneerng Socety Summer Meetng vol. pp [0] J. Ko C. Wrmer nd I. Kmphus PowerMtcher: Multgent Control n the Electrcty Infrstructure n Proc. of the fourth Int. conf. on Autonomous gents nd multgent systems pp. 00. [] R. Ryudu A Knowledge-bsed Archtecture for Dstrbuted Fult Anlyss n Power Networs Engneerng Applctons of Artfcl Intellgence vol. no. pp. 00. [] I. Bxevnos nd D. Lbrds Softwre Agents Stuted n Prmry Dstrbuton Networs: A Coopertve System for Fult nd Power Restorton Mngement IEEE Trns. on Power Delvery vol. no. pp. 00. [] F. Ren M. Zhng D. Soetnto nd X. Su Conceptul Desgn of A Mult-Agent System for Interconnected Power Systems Restorton IEEE Trns. on Power Systems vol. no. pp [] J. Soln S. Khushln nd N. Schulz A Mult-Agent Soluton to Dstrbuton Systems Restorton IEEE Trns. on Power Systems vol. no. pp [] M. Nordmn nd M. Lehtonen An Agent Concept for Mngng Electrcl Dstrbuton Networs IEEE Trns. on Power Delvery vol. 0 no. Prt pp [] C. Ln C. Chen T. Ku C. Ts nd C. Ho A Multgent-Bsed Dstrbuton Automton System for Servce Restorton of Fult Contngences Europen Trns. on Electrcl Power vol. no. pp. 0. [] S. McArthur E. Dvdson V. Ctterson A. Dmes N. Htzrgyrou F. Ponc nd T. Funbsh Mult-Agent Systems for Power Engneerng ApplctonsłPrt I: Concepts Approches nd Techncl Chllenges IEEE Trns. on Power Systems vol. no. pp. 00. [] M. Ppttnsomporn H. Feroze nd S. Rhmn Mult-Agent Systems n A Dstrbuted Smrt Grd: Desgn nd mplementton n Power Systems Conf. nd Exposton pp. 00. [] A. Sleem K. Heussen nd M. Lnd Agent Servces for Stuton Awre Control of Power Systems wth Dstrbuted Generton n IEEE Power nd Energy Socety Generl Meetng pp. 00. [0] M. Brn nd I. El-Mrb A Multgent-bsed Dsptchng Scheme for Dstrbuted Genertors for Voltge Support on Dstrbuton Feeders IEEE Trns. on Power Systems vol. no. pp. 00. [] M. Abdo Envronmentl/Economc Power Dsptch Usng Multobjectve Evolutonry Algorthms IEEE Trns. on Power Systems vol. no. pp. 00. [] K. Hung S. Srvstv D. Crtes nd L. Sun Mret-bsed Multgent System for Reconfgurton of Shpbord Power Systems Electrc Power Systems Reserch vol. no. pp [] K. Hung S. Srvstv D. Crtes nd M. Sloderbec Intellgent Agents Appled to Reconfgurton of Mesh Structured Power Systems n Int. Conf. on Intellgent Systems Applctons to Power Systems pp. 00. [] F. Bellfemne G. Cre nd D. Greenwood Developng Mult-Agent Systems wth JADE vol.. Wley 00. [] M. Zhou nd S. Zhou Internet Open-source nd Power System Smulton n IEEE Power Engneerng Socety Generl Meetng pp. 00. [] J. OMddhn D. Fsher P. Smyth S. Whte nd Y. Boey Anlyss nd Vsulzton of Networ Dt Usng JUNG Journl of Sttstcl Softwre vol. 0 no. pp. 00. [] S. Mller S. Rmchurn nd A. Rogers Optml Decentrlsed Dsptch of Embedded Generton n the Smrt Grd n Proc. of the Nneteenth Int. conf. on Autonomous Agents nd Multgent Systems pp. 0. chr for regon ten. BIOGRAPHIES 0 Dr. Fenghu Ren receved hs MCompSc-Res. nd Ph.D. from the Unversty of Wollongong n 00 nd 00 respectvely. He receved hs BCompSc from the Xdn Unversty n 00. Currently he s n Reserch Fellow n the School of Computer Scence nd Softwre Engneerng t the Unversty of Wollongong. Dr. Ren s n ctve resercher nd publshed reserch ppers. Hs reserch nterests nclude gent-bsed modelng smulton resonng nd lernng gent coordnton negotton nd optmzton. A/Prof. Mnje Zhng receved her BSc degree from Fudn Unversty Chn n nd her PhD degree from the Unversty of New Englnd Austrl n. Currently she s the Drector of Intellgent System Reserch Group n the Fculty of Informtcs t Unversty of Wollongong. Dr. Zhng hs publshed over 0 reserch ppers. Her reserch nterests nclude mult-gent systems gent-bsed smulton nd modelng n complex domns gentbsed mrt grds nd nowledge dscovery nd dt mnng. Prof. Dnny Sutnto receved hs B.Eng. nd Ph.D. from the Unversty of Western Austrl n nd respectvely. In 00 he joned the School of Electrcl Computer nd Telecommunctons Engneerng t the Unversty of Wollongong s the Professor of Power Engneerng. Dr. Sutnto hs publshed over 0 reserch ppers. Hs mn res of reserch re power system nlyss power system economcs voltge stblty hrmoncs power electroncs nd computer ded educton. He s currently the IEEE ndustry pplctons socety re