CONTROL AND PROTECTION OF DISTRIBUTION NETWORKS WITH DISTRIBUTED GENERATORS

Transcription

1 ASTRACT ELMARKA, SMAL MOHAMED. Control nd Proteton of Dstruton Networs wth Dstruted Genertors, under the dreton of Dr. Mesut rn. The onneton of dstruted genertors to dstruton networs gretly nfluenes the perforne nd stlty of suh networs. The purpose of the dssertton hs een to nvestgte nd ttept to resolve the pts of onnetng dstruted genertors to dstruton networs. Two n proles were defned nd studed, whh re the effet of dstruted genertors on the feeder voltge regulton nd on the feeder proteton shees. A entrl supervsory ontroller desgned to regulte the feeder s voltge s presented, nd the rhteture of the ontroller s shown long wth test results llustrtng the lty of the ontroller to regulte the voltge long feeder wth dstruted genertors wth nu ost. n n ttept to regulte the feeder s voltge wthout the need for the feeder s explt odel, ult-gent sed dstruted ontroller s proposed. The ult-gent syste struture nd desgn re llustrted, nd test results oprng the perforne of the two proposed ontrollers re shown. The dssertton then presents n pproh to extend onventonl fult nlyss studes to nlude nverter nterfed dstruted genertors. Suh n pproh s essentl for the proper seleton nd oordnton of protetve deves for feeder wth dstruted genertors. Fnlly, the dssertton llustrtes the extent of deterorton DG n use on the overurrent protetve rely perforne. An pproh to solve ths prole nd restore the overurrent rely perforne s presented.

2 CONTROL AND PROTECTON OF DSTRUTON NETWORKS WTH DSTRUTED GENERATORS y SMAL MOHAMED ELMARKA A dssertton sutted to the Grdute Fulty of North Croln Stte Unversty n prtl fulfllent of the requreents for the Degree of Dotor of Phlosophy ELECTRCAL AND COMPUTER ENGNEERNG Rlegh 4

3 To y prents, Mohed nd Zen El-Mr To the love nd frendshp of y wfe, Aley

4 OGRAPHY sl Elr reeved hs helor of Sene degree n Eletrl Engneerng wth honors fro Cro Unversty, Cro, Egypt, n 997. y yer he fnshed hs studes for the Msters of usness Adnstrton MA fro Mstrht Shool of Mngeent, Mstrht, Netherlnds, through ther outreh progr n Cro, Egypt. sl Elr ws dtted to the Msters of Sene n eletrl engneerng progr t North Croln Stte Unversty, Rlegh, n. After reevng hs sters degree n he ws dtted to the Ph.D. progr. Durng hs grdute studes t North Croln Stte Unversty he wored s reserh ssstnt n the power systes l. Ths thess opletes the requreents for hs Ph.D. degree.

5 ACKNOWLEDGMENTS wsh to express y snere grttude to y dvsor, Dr. Mesut rn, for hs gudne nd entorshp durng y grdute studes. Hs pressve nowledge, tehnl slls nd retve thnng hve een soure of nsprton throughout the ourse of ths wor. Wthout h ths wor would not hve een opleted. would lso le to express y ppreton to Dr. Joel Trussell, Dr. Mo-Yuen Chow nd Dr. Mhel Young for servng on y Ph.D. ottee nd for ther help. ndeted to y eloved wfe Aley for her srfes, never-endng support nd enourgeent durng the ourse of y study. would le to thn her for eng onstnt soure of nsprton nd otvton for e. My deepest grttude goes to y other nd fther, to who ost ndeted. thn the for nurturng nd edutng e, for ther onstnt love nd pryers, nd for ther ptene nd support whle ws studyng rod. now n never oe lose to returnng ther fvor upon e. wll lwys e thnful to y frends nd ollegues for ther unlted support, nd spel thns to y frend Nedl Sfwt who de y sty n the sttes uh soother. extend y thns to ll the Egyptn ounty tht gve e seond fly wy fro hoe. would le to thn y ollegues Nhl Mhjn nd K Jnsng for the enrhng tehnl nd ulturl dsussons. Lstly, ut ertnly not the lest, would le to express y snere ppreton to y other nd fther n lw for ther pryers nd support. v

6 TALE OF CONTENTS Pge Lst of fgures...v Lst of tles... x. ntroduton.... Motvton.... Overvew..... Supervsory ontrol pproh for feeder voltge regulton..... MAS pproh for feeder voltge regulton Fult nlyss on dstruton systes wth DGs Adptve over-urrent proteton for feeders wth DGs Outlne Dstruted Generton nd Dstruton Networs: Proteton nd Control Chllenges ntroduton Eletr power grd Dstruted generton pt of DGs on dstruton networs pt of DG on feeder voltge regulton Conventonl feeder voltge regulton pt of DG on feeder voltge regulton....3 pt of DG on feeder proteton Conventonl feeder proteton pt of DG on feeder proteton Sury Supervsory Control Shee for Feeder oltge Regulton Prole defnton DG odel Supervsory ontroller Controller desgn The Esttor E DG ontroller C R ontroller C Test results Test Syste Sulton pltfor Test results Sury... 4 v

7 4. Feeder oltge Regulton usng MAS ntroduton Ojetve nd pproh Feeder oltge Regulton DG retve power dspth Controller Desgn Overvew of ult-gent systes Wht s n gent? Mult-gent syste MAS Desgn of MAS MAS for Feeder oltge Regulton MAS rhteture Retve power dspth Feeder voltge regulton Test results Test results for se A: sudden dsonneton of DG Test results for se : Severe Contngeny pt of lod type on the MAS perforne Sury Fult Anlyss for dstruton networs wth dstruted genertors ntroduton Conventonl fult nlyss on dstruton systes DG ehvor under fult ondtons DG fult proteton DG representton norportng DG odel nto fult nlyss: the proposed pproh Feeder response updte Te step seleton Cse study : lned fult Feeder settlng te Sulton Deternng the pe nstntneous urrent Cse study : Unlned fult Sulton of phse to ground fult Deternng the pe nstntneous urrent Sury Adptve Over-Current proteton for feeders wth DGs pt of DG on Over-Current rely perforne Redued reh Overll rely effetveness Adptve Over-Current rely Soluton pproh Sury... 8 v

8 7. Conlusons Contrutons Reoendtons for future reserh... Appendes... 3 Appendx A... 3 Appendx... 6 Appendx C... 4 logrphy... 3 v

9 Lst of fgures Fgure : Fuel ell unt... 8 Fgure : Conventonl dstruton networ... 9 Fgure 3: oltge level long the feeder... Fgure 4: Prototype Feeder... Fgure 5: pt of DG on the R ontrol... Fgure 6: pt of the sudden dsonneton of the DG... 3 Fgure 7: Rdl feeder proteton... 4 Fgure 8: Rely reh wth nd wthout DG... 5 Fgure 9: DGs re loted upstre, fult loted downstre... 6 Fgure : DGs nd fult re loted downstre... 7 Fgure : DGs re loted downstre, fult loted upstre... 8 Fgure : slndng... 9 Fgure 3: Feeder wth DGs nd lods... Fgure 4: DG s nverter wth nput nd output flters nd step-up trnsforer... Fgure 5: DG s ontrol odel nd nverter pulse genertor... 3 Fgure 6: Feeder wth DGs nd lods nd proposed supervsory ontroller... 4 Fgure 7: DG nd R response to sudden voltge drop event... 6 Fgure 8: Supervsory ontroller lo dgr... 7 Fgure 9: Conng neghorng lods to deterne pproxte feeder odel... 8 Fgure : Approxte feeder for the ontroller... 3 Fgure : Tested feeder odel n PSCAD... 3 Fgure : Sulton pltfor Fgure 3: Sulton results for Cse Fgure 4: oltge levels of the 8 nodes Fgure 5: Sulton results for Cse Fgure 6: Sulton results for Cse Fgure 7: oltge seen y DG n Cse Fgure 8: Monotonlly deresng voltge profle wth DGs onneted Fgure 9: Eght node feeder voltge profle... 5 Fgure 3: Feeder voltge profle wth Q njeted t node Fgure 3: Feeder voltge profle wth Q njeted t nodes 3, 5 & Fgure 3: Dfferent types of gents n the MAS Fgure 33: Overvew of MAS Fgure 34: Soluton proess for sngle retve power dspth updte Fgure 35: Dstruted pproh soluton... 6 Fgure 36: Sulton results for Cse A Fgure 37: MAS vs. Centrl ontroller for Cse A Fgure 38: Zooed wndow of Fgure 36 for durton -7 se Fgure 39: Zooed wndow of Fgure 36 for durton 5-7 se Fgure 4: Sulton results for se Fgure 4: DG voltge level durng event Fgure 4: MAS vs. Centrl ontroller for se v

10 Fgure 43: Zooed wndow of Fgure 4 for durton 5-5 se Fgure 44: Zooed wndow of Fgure 4 for durton 66-7 se Fgure 45: MAS perforne for dfferent... 7 Fgure 46: Zoo on frst seonds of the sulton se A... 7 Fgure 47: MAS perforne for dfferent lod types Cse... 7 Fgure 48: nstntneous nd RMS profle of n tul feeder urrent durng fult Fgure 49: Stedy-stte feeder odel Fgure 5: voltge nd urrent wvefors durng fult for the DG nd the RC Fgure 5: Reloser fult urrent wth nd wthout DG Fgure 5: Current RMS durng frst 5 yles Fgure 53: oltge RMS durng frst 5 yles Fgure 54: DG representton... 8 Fgure 55: DG representton for fult nlyss... 8 Fgure 56: DG nd feeder syste odels Fgure 57: DG power durng fult, wth fxed nd P ontrolled DG nternl voltge Fgure 58: pt of fult event wth onstnt DG nternl voltge Fgure 59: pt of sudden hnge n DG nternl voltge Fgure 6: P nd Q of sultons shown n Fgure 58 nd Fgure Fgure 6: Prototype feeder used on testng the proposed tehnque Fgure 6: lulted versus tul nternl voltge... 9 Fgure 63: one yle wndow RMS output urrent, tve nd retve power... 9 Fgure 64: RMS urrents for DG nd RC... 9 Fgure 65: DG voltge nd urrent wvefors wth lned fult t pe voltge... 9 Fgure 66: RC urrent wvefor wth lned fult t pe voltge rossng Fgure 67: Unlned fults Fgure 68: lulted versus tul nternl voltge Fgure 69: one yle wndow RMS output urrent, tve nd retve power Fgure 7: RMS urrents for DG nd RC Fgure 7: DG urrent wvefor wth sngle phse fult t pe voltge rossng Fgure 7: RC urrent wvefor wth sngle phse fult t pe voltge rossng Fgure 73: Mxu Rf deteted t eh node wth DG njetng % of feeder lod... Fgure 74: Reduton n reh vs. DG njeted rel power... Fgure 75: Effet of DG on rely effetveness... Fgure 76: Effet of DG power njeted on rely effetveness... 3 Fgure 77: nverse te rely hrtersts... 4 Fgure 78: Rely hrterst nd fult... 5 Fgure 79: Constnt nd dptve -pup... 5 Fgure 8: Fult urrent pproxton... 6 Fgure 8: Feeder odel... 7 Fgure 8: Atul nd odfed rely hrterst wth fult urrent... 7 Fgure 83: Rely nu pup urrent... 8 x

11 Lst of tles Tle : Feeder lods... 3 Tle : Node voltges t dfferent te ntervls Tle 3: Dstruted ontroller output for eh terton... 6 x

12 CHAPTER ONE ntroduton. Motvton The presene of sll genertng unts onneted to the power dstruton networ s gretly nresng. One study [D] esttes tht y the yer 5, out perent of ll new generton gong onlne n the US wll e produed y sll power genertors, lso nown s dstruted genertors DGs. Thus, nvestents n DG nufturng nd reserh n DG ntegrton wth the dstruton networ hs een nresng exponentlly n the lst few yers. Unfortuntely, the ntegrton of DGs nto urrent power dstruton networs s not yet prole free. Ths s nly due to the dstruton networs eng desgned sed on the ssupton tht only lods, nd not genertors, wll e onneted to t. As shown y [DM] nd [D], hgh penetrton levels of DGs n dstruton networ wll use n uneptle deterorton n the networ s perforne. Ths gretly ffets the networ s lty to properly regulte ts feeders voltge level nd effetvely protet ts oponents. Thus, the need for dentfyng nd solvng suh proles s essentl for selessly ntegrtng DGs nto dstruton networs nd for the future growth of the DG ndustry. The otvton for ths reserh ws two fold. The frst gol hs een to develop etter understndng of the pt the DG presene wll hve on the voltge regulton nd proteton of dstruton networs. The seond gol ws to desgn nd develop novel voltge ontrol nd proteton tehnques tht n well ddress the two hllenges relted to DG ntegrton nto dstruton networs.

13 . Overvew For the lst yers, there hs een n nresng elef tht dstruted generton s the new lterntve for supplyng power to soe onsuers. Rther thn the old-fshoned power generton where few, lrge, nd reotely dspersed power genertors were used, dstruted generton reles on lrge nuers of sll genertors loted ner the lods. Ths fundentl hnge n the power grd struture wll result n severl serous proles, whh hve een the fous of ny reserhers. To solve the onflts resultng fro onnetng DGs to the dstruton networ, soe reserhers, [Gh99] nd [dfo], foused on deternng the xu level of DGs penetrton llowle for eh dstruton networ nd then prohtng the onneton of ny DGs eyond tht lt. Ths soluton ttepts to vod deterorton of the networ perforne. However, ths pproh hs een gretly rtzed espelly y DG nufturers. The pproh presented n ths dssertton s to odfy the exstng voltge regulton nd proteton deves n order to selessly ntegrte s ny DGs s needed nto the dstruton networ wthout srfng ny of the networ perforne stndrds. The dssertton fouses on the desgn of supervsory ontroller ple of regultng the feeder s voltge wth the hypothess tht ll feeder nforton s vlle, the developent of ult-gent syste MAS ple of regultng the feeder s voltge wthout the need for oplete vew of the feeder, 3 the understndng of DG ehvor under fult ondtons nd how t ffets the networ s protetve deves nd developng DG odel tht ould e used n fult nlyss studes, nd 4 deternng the DG pt on the over-urrent protetve rely perforne nd developng ethod to tgte tht pt... Supervsory ontrol pproh for feeder voltge regulton A frewor for spefyng the voltge regulton prole nd solvng t s proposed. The frewor forultes the voltge regulton prole s nzton prole, where the ojetve s to nze the ontruton of the DGs whle ntnng the voltge level

14 long the feeder wthn eptle voltge lts. The dssertton develops soluton pproh for the voltge regulton prole sed on supervsory entrl ontroller pproh wth the hypothess tht the feeder odel dt s nown to the ontroller. Suh hypothess ens tht the entrl ontroller n e vewed s n onsent gent tht n sense nd ontrol the entre networ. Thus, the ontroller perforne s onsdered del nd s used lter s referene pont to esure the effetveness of other ontrol strteges. The supervsory ontroller s ple of reevng feeder nforton nd sendng ond sgnls to dfferent oponents of the feeder. The desgn nd rhteture of the entrl ontroller s presented nd ts effetveness s evluted through test sulton. An EEE 34 node prototype feeder s sulted, the ontroller perforne s ontored nd presented for two ses: norl stedy stte opertng ondton nd n event ourrene, suh s sudden dsonneton of DG. The test results ndte tht the ontroller perfors perfetly nd provdes tght voltge regulton on the feeder under oth norl ondtons nd severe ontngenes... MAS pproh for feeder voltge regulton The jor drw n usng the supervsory ontroller prevously presented s the need for n urte feeder odel, suh ondton oltertes the noton of ng the onneton of DG to the networ s esy s onnetng PC to the nternet. n order to heve suh gol, lso nown s the plug-nd-ply gol, ths dssertton ttepts to utlze the strengths of eployng the MAS pproh for solvng the voltge regulton prole. n the proposed MAS, eh syste oponent wll e equpped wth n gent, nd ll gents wll ooperte together to help ntn the feeder voltge level wthn lts t nu ost. The pproh ths dssertton eploys to solve the oplex voltge regulton optzton prole n dstruted nner, whh wthout nowng the explt syste odel, s to explot spel fetures nd hrtersts n the prole to deterne sple reltonshps etween the overll gol nd ll vlle tons. These reltonshps wll e used together wth the lty of eh gent to dretly sense nd esure ts lol vrles to reforulte the optzton prole n spler for. Ths sple prole wll then e solved v MAS usng the ontrt net protool CNP. 3

15 A test sulton s presented to evlute the perforne of the proposed MAS, wth the perforne ontrsted gnst tht of the onsent gent. The test shows the MAS s lty to reh the optu soluton prevously rehed y the entrl ontroller, despte the sene of feeder odel...3 Fult nlyss on dstruton systes wth DGs The ehvor of onventonl types of DGs, suh s synhronous nd nduton genertors, durng fult ondtons hs een thoroughly nvestgted y severl reserhers [J], ut ore reserh nd effort s needed to understnd the ehvor of new evolvng DG tehnologes. Ths dssertton ttepts to nlyze nd understnd the ehvor of nverter nterfed DGs, suh s fuel ells, photo-volt nd ro-turnes, under dfferent fult ondtons. Moreover, the dssertton presents n pproh to odel nverter nterfed DGs under fult ondtons nd ntegrte suh odel nto onventonl fult nlyss studes, thus tng the DG s fult ontruton nto ount when szng protetve deves...4 Adptve over-urrent proteton for feeders wth DGs Although severl ppers hve entoned the ft tht the presene of DGs ffets the perforne of the over-urrent OC rely protetng the feeder, none hs presented enough dt to show how severe the deterorton n the OC rely perforne s, nd whether t s eptle to gnore t or f t ust e resolved. Ths dssertton presents n eprl result on how the sze nd loton of DG long feeder n ffet the OC rely protetng tht feeder nd shows tht the deterorton n the OC rely perforne n leve lrge portons of the feeder unproteted gnst dfferent types of fults. Furtherore, the dssertton offers n dptve tehnque tht n ntpte the pt of the DG on the rely perforne nd ordngly hnge the rely p up urrent to ensure tht the whole feeder s proteted t ll tes, wth or wthout DGs. 4

16 .3 Outlne Chpter ntrodues lterture revew on DGs, dstruton networs, nd the pt of DGs on the dstruton networ. Further, t dentfes nd desres the pt of DGs on the feeder voltge regulton nd the pt of DGs on the feeder proteton. Chpter 3 ddresses the voltge regulton prole usng supervsory entrl ontroller nd ntrodues the prole forulton, ontroller desgn pproh, nd the test results to show the effetveness of the ontroller. Chpter 4 fouses on solvng the voltge regulton prole usng the MAS pproh. t presents the ethodology used to pproxte the orgnl prole nto spler prole tht the MAS s ple of solvng. Further, t shows the test result provng the effetveness of the MAS pproh. Chpter 5 studes the DG s reton to fult n ts feeder nd proposes n pproh to odel suh ehvor nd ntegrte nverter nterfed DGs nto onventonl fult nlyss studes. t lso presents se study showng the effetveness of the proposed pproh n deternng the DG s ontruton to dfferent types of fults. Chpter 6 nvestgtes the pt of DGs on the OC rely perforne. t shows eprlly the severty of the deterorton n the rely s lty to protet the whole feeder. t onludes y presentng tehnque to solve suh prole y dptvely hngng the OC rely setpont. Chpter 7 onludes the dssertton, sttes the dssertton ontrutons, nd ndtes possle future reserh efforts tht ould prove the fndngs of the dssertton. 5

17 CHAPTER TWO Dstruted Generton nd Dstruton Networs: Proteton nd Control Chllenges. ntroduton Ths hpter presents lterture revew on the pts of DGs on the dstruton networ perforne. The hpter strts wth n ntroduton on the struture of dstruton networs nd the onept of dstruted generton. The hpter then fouses on the pt of DGs on the feeder voltge regulton durng dfferent opertng ondtons. Lstly, detled explnton on the pt of DG on the feeder proteton s presented... Eletr power grd Tody s power syste s oplex nteronneted networ tht n e sudvded nto four jor prts: generton, trnssson, dstruton, nd lods. n the generton phse, eletr power s generted t -3 v lrge entrl genertors loted n reote res. The purpose of the overhed trnssson networ s to trnsfer eletr energy fro genertng unts t vrous lotons to the dstruton networ. The dstruton networ s edu to low voltge networ tht s onneted to hgh voltge trnssson networ through step down trnsforers. Eh trnsforer feeds power to nuer of feeders to whh ustoers re onneted ether dretly or through dstruton trnsforer whh further steps down the voltge to the utlzton level, volts for household pplnes. 6

18 .. Dstruted generton Dstruted generton refers to the noton of genertng power usng set of sll szed genertors tht produes power t low voltge levels nd usully uses lterntve fuel. The genertors re nly desgned to e onneted dretly to the dstruton networ ner lod enters. t s expeted tht dstruted generton wll hve nresng portne for nuer of resons, [JA] nd [JOG]: t llows for the ndependent produton of eletr energy to rry the full lod or only the pe lod nd sell the exess energy t proft. t hs potentl of provdng soe of the nllry serves, whh re eletrl serves provded other thn rel power. Retve supply sorpton nd njeton to heve voltge ontrol Power ftor regulton Dfferent types of DG tehnologes There re severl types of dstruted genertors n the ret. Soe re onventonl suh s the desel genertors nd soe re new tehnologes suh s the ro-turnes. The followng seton refly desres jor DG lterntves. Fuel ells: A fuel ell s n eletrohel deve tht onverts hel energy dretly nto eletrl energy. The fuel ell unt uses hydrogen nd oxygen to perfor the requred hel reton nd produe power. Fuel ells re nverter nterfed DGs, enng the unt produes d power tht s onverted to power v 3-phse onverter Fgure [Hr98]. Mro-turne: Mro-turnes re sll gs fred turnes rottng t very hgh rte of speed 9, rp. A hgh rp DC genertor s used to generte d power. The DC genertor s oupled to d/ power onverter to produe voltges t the rted frequeny [Sut]. 7

19 Photovolt ells: Photovolt ells onvert solr energy dretly nto eletrl energy. Le fuel ells, the power produed s d power nd power eletrons onverter s needed to nteronnet wth the utlty grd [JOG]. Wnd turnes: The wnd turne opertes y extrtng net energy fro the wnd s t psses through the rotor. The wnd turne shft s onneted ether to n nduton or synhronous genertor. A trnsforer s then used to step up the output voltge to the utlty grd level [JA]. Desel genertor: Ths s the ost oonly used DG now. A sll synhronous genertor s oupled wth reprotng pston engne to produe power. They re usully operted stndlone durng utlty power outges. n ths study, we wll e fousng only on the nverter nterfed DGs suh s fuel ells, ro-turnes, nd photovolt ells. nverter Utlty grd FC DC AC Fgure : Fuel ell unt..3 pt of DGs on dstruton networs The dstruton networ ws desgned to extrt power fro the trnssson networ nd dstrute t to the lods. t ws not desgned to hve genertors dretly onneted to t. The dstruton networ topology, ontrol, nd proteton re ll desgned ssung tht power s flowng n one dreton, fro trnssson to lods. The onneton of DGs to the feeders of the dstruton networ n use the power flow to e -dretonl nsted of undretonl ffetng the networ perforne nd stlty n nuer of wys, [JA], [Hr98], [Sut] nd [JOG]. Through n extensve lterture revew, ll suggested pltons for onnetng DGs to dstruton networs hve een studed. The ost serous pts tht ould not e resolved usng onventonl tehnques were found to e 8

20 the pt of the DG on oth the feeder voltge regulton nd the feeder proteton. n the followng two susetons, these two pltons wll e dsussed n ore detl.. pt of DG on feeder voltge regulton When DG s onneted to feeder, t wll ffet the voltge regulton of the feeder dependng on the loton, sze, nd opertng shee of the DG. n the followng seton, the onventonl voltge regulton wll e dsussed, followed y the pt of the DG s presene on suh voltge regulton tehnque... Conventonl feeder voltge regulton A dstruton networ onssts of nuer of susttons whh steps down the voltge level nd feeds nuer of feeders. As shown n Fgure, the feeder strts fro the sustton us nd lods re tpped off t every node. Eh feeder s equpped wth H/M on-lod tp hngng trnsforer tht hs the lty of hngng the voltge level of the feeder t the sustton us. The voltge drop long the feeder depends on the feeder lodng s llustrted n Fgure 3, where the xu voltge drop ours durng pe lod. The on-lod tp hngng trnsforer LTC nd ts ssoted voltge regultor R regultes the voltge t the sustton end to openste for the voltge drop due to the hnge n lodng. The s to lwys eep the voltge long the feeder wthn ± 5 perent of the nonl voltge. R S L LC LTC R Lod nodes LTC R3 Lod nodes LTC Sustton Lod nodes Fgure : Conventonl dstruton networ 9

21 olt pu.5 Hgher lt Pe Lod Lght Lod.95 Lower lt Feeder Fgure 3: oltge level long the feeder R ontrol wth lne-drop openston: The of lne-drop openston s to eep the voltge onstnt, not t the feeder s sustton us, ut t soe reote lod enter. Norl prte s to sense the lod urrent lol to the trnsforer nd use ths to estte the voltge drop on the feeder t the reote lod enter ordng to the followng equton. des S set LC L [ R jx ] Where L lod urrent, S sustton us voltge, nd LC voltge requred t the reote lod enter. R set nd X set nsde the rely re djusted to orrespond dretly to the feeder s pedne. Thus the sustton us voltge s djusted to nsure tht the reote lod enter voltge s wthn eptle lts. set set.. pt of DG on feeder voltge regulton The followng two susetons llustrte the pt DG hs on the feeder voltge regulton under two ondtons, norl nd eergeny. To deonstrte suh ondtons, seven node prototype feeder Fgure 4 s sulted under dfferent senros. The feeder lod s ssued to e eqully dstruted long the feeder, nd the feeder s proteted wth n OC rely. Relevnt dt n Appendx A

22 DG OC rely R Sustton AR Lod-7 Lod-6 Lod-5 Lod-4 Lod-3 Lod- Lod- Fgure 4: Prototype Feeder A pt of DG on the R durng norl operton As prevously ndted, n onventonl feeder the voltge level s regulted y the R, whh esttes the voltge drop over the feeder y esurng the feeder urrent t the sustton end. However, ths depends nly on the sple ft tht the power s undretonl fro the sustton us where the R s loted flowng nto the end of the feeder. The presene of DGs es the power -dretonl, nd f the DGs onneted to feeder re rryng ost or ll the feeder lod, then the voltge profle long the feeder depends nly on the DGs loton, power generted, nd the DG power ftor. Ths retes n unpredted nd unontrolled stuton where the voltge level of ll nodes ght or ght not e wthn eptle lts. To llustrte suh prole, onsder the prototype syste n the followng three senros: Cse : feeder wthout DGs nd the voltge long the feeder s wthn eptle lts. Cse : feeder wth three DGs t nodes, 3, nd 6 rryng the whole feeder lod. Cse 3: feeder wth one DG t node rryng the whole feeder lod. Fgure 5 shows the voltge profle long the feeder for the three dfferent ses. For ses nd 3, the urrent flowng fro the on-lod-trnsforer s lost zero. The R wll ssue tht oth ses re the se wth the feeder s lod t the nu level, therefore t wll djust ts voltge level to. p.u. The voltge profle n se s wthn the lts euse the DGs re dstruted long the feeder, unle the thrd se, where the feeder lods re rred y lolzed DG. Ths shows tht, lthough the R treted oth ses

23 slrly, the voltge profle long the feeder s totlly dfferent nd depends on the nuer nd loton of the DGs rryng the lod. t ould now e onluded tht the onventonl R tehnque nnot properly djust the voltge level of feeder wth vrous DGs onneted to t, sne t depends solely on esurng the feeder s urrent t the sustton end, whh s no longer good ndton of the feeder sttus. Therefore, new tehnque ust e developed to fltte the oordnton etween DGs nd the R for etter feeder voltge regulton. Fgure 5: pt of DG on the R ontrol oltge regulton under eergeny ondtons of sudden dsonneton of DG f the DG onneted to feeder opertes wthout onsderng the pt of ts operton on ts neghorng nodes, one potentl prole tht y rse s tht the sudden dsonneton of DG y use n undesrle trppng of other genertors onneted to the se feeder. The loton of the DG, the feeder lodng, nd the DG power generted re ey ftors n the pt of the sudden dsonneton of tht genertor [SJR93]. To llustrte ths potentl prole, onsder the prototype syste wth DG onneted to node three nd opertng t ts xu pty rryng 3 perent of the totl feeder lod. The sold urve n Fgure 6 represents the voltge profle long the feeder wth the DG onneted. The effet of suddenly dsonnetng ths DG s shown n the lower urve,

24 where the voltge level of the lst porton of the feeder round 4 perent of the feeder length flls elow the lower perssle lt. Ths wll trgger the undervoltge rely protetng the DGs loted n ths porton of the feeder to trp. Although the R wll djust the feeder voltge level upper dshed urve, ts slow response te wll e ts ton useless. The R tes out seonds to ove one tp whh orresponds to out.5 pu voltge hnge ssung 6 tp R for ±5 perent voltge regulton [A]. On the other hnd, the DGs re qute senstve to voltge sgs, s they usully eploy undevoltge/overvoltge proteton shees to protet the deve gnst the externl fults [EEE99], [EEE47]. These proteton shees re usully fst, typlly set to trp the DG wthn two seonds f the voltge level s elow the eptle lt, nd trp wthn.6 seonds f the voltge level s less thn 5 perent of nonl voltge. Therefore, the R nnot provde the qu voltge support needed to restore the voltges followng sudden dsonneton of the DG, euse the response of the R s uh slower thn needed. Fgure 6: pt of the sudden dsonneton of the DG.3 pt of DG on feeder proteton DG presene n dstruton networ pts the onventonl feeder proteton shees. n the followng two setons, we wll dsuss how the feeder s urrently proteted nd the pts of DG presene on suh proteton shees. 3

25 .3. Conventonl feeder proteton Dstruton feeders re usully rdl wth the lods tpped off long the feeder setons. The feeder proteton strtegy s t optzng the serve ontnuty to the xu nuer of users followng fult dsturne on the networ. Ths ens pplyng onton of rut reers, utot relosers, nd fuses to ler teporry nd pernent fults. As shown n Fgure 7, fuses re responsle for soltng pernent fults t pont A nd eyond. The utot reloser lers fults on pont nd eyond t s downstre. The n rut reer t the egnnng of the feeder s equpped wth n OC rely to solte ny pernent fult long the n feeder. When the feeder urrent exeeds ertn pup vlue, the OC rely sends the reer trp sgnl, nd the speed of trppng the fult s nversely proportonl wth the fult urrent gntude. C o RC Pont OC fuse fuse fuse Pont A Fgure 7: Rdl feeder proteton.3. pt of DG on feeder proteton The onventonl proteton shee of eh feeder s desgned, ssung the feeder s rdl. ut, s entoned erler, the presene of DGs on feeder wll use -dretonl power flow, whh ens tht prt of the feeder wll no longer e rdl [G]. Ths wll rete severl proles to the urrent proteton shees used, s shown n severl ppers nludng [SR], [D], [Lop] nd [Wl]. Aernn n [AK] shows tht the presene of DGs wll result n n nrese n fult urrent levels, nd tht the detled ssessent of the pt DGs ght hve on fult urrents s very hllengng s the pt lrgely depends on nuer of ftors. Aong these re the tehnology of the DG, ts operton ode, nterfe wth the DG, syste voltge pror to fult, et n [GM], Goez ls tht there s no onern wth the 4

26 DG when ts power s less thn perent of the nu lod dend y the feeder. The ost edte onsequene s the need for verfton of the protetve deve reng pty, whh ght not e enough due to the nrese of the vlle short-rut power. As entoned y rer n [D], the fult ontruton fro sngle sll DG unt s not lrge, however, the ggregte ontrutons of ny sll unts, or few lrge unts, n lter the short-rut levels enough to use protetve deves to lfunton. The n pts of DG on the feeder proteton onneton re n three dfferent res: the OC rely perforne, the reloser operton, nd the slndng proteton. A Over-urrent rely perforne One of the DG pts on feeder proteton s on the OC rely, s the urrent ontruton fro the DG wll ffet the reh of the rely. OC relys re set to protet ertn prt of the feeder, whh s soetes referred to s the reh. The reh of the rely s deterned y the nu fult urrent t s set to ret to, the so-lled p-up urrent. The presene of DG wll redue the reh of the OC rely [Dug], thus levng edu pedne fults t the end of the feeder undeteted Fgure 8. The reduton n reh s due to the ft tht the DG ontrutes to the fult urrent, thus deresng the fult urrent seen y the OC rely for the se fult resstne R f. To understnd the effet of DGs on redung the reh of the feeder s OC rely, study s presented n Chpter 6. The nfluene of the DG s loton nd power level on the rely effetveness s lso shown. Moreover, ethod desgned to tgte the prole s presented n the se hpter. Orgnl reh OC Rely DG Redued reh R Sustton Fgure 8: Rely reh wth nd wthout DG 5

27 Reloser operton The DG ontruton to feeder fults pts the operton of the reloser n three dfferent wys: the reloser ght e exposed to hgh ehnl nd therl stresses eyond ts rted lts, the reloser-fuse oordnton n e ffeted, nd 3 the reloser ght trp for upstre fults. n the setons elow, we wll dsuss these pts n ore detl. Exposng the reloser to hgh ehnl nd therl stresses [Doy] Relosers re desgned to wthstnd nd nterrupt the hgh fult urrents. One of the portnt preters of reloser s the xu urrent the reloser n wthstnd. Ths s lled the xu wthstnd urrent. Wth DGs onneted s shown n Fgure 9, the fult urrent seen y the reloser RC wll nrese. Ths would not norlly use prole s long s the new RC does not exeed the reloser xu wthstnd plty. However, f RC > x the reloser wll e exposed to ehnl nd therl stresses, espelly n the frst one nd hlf yles, whh ght use reloser flure. sys RC RC Fult Fgure 9: DGs re loted upstre, fult loted downstre Reloser-fuse oordnton The phlosophy of feeder proteton s tht fuse should only operte for pernent fults wthn ts reh. ut for teporry fults, the reloser should dsonnet the rut wth fst operton nd gve the fult hne to ler. Only f the fult s pernent, should the fuse e llowed to open. As entoned y [G], for the feeder topology s the one shown n Fgure, the fult urrent flowng through the fuse s greter thn tht flowng through the reloser. Ths ght use the fuse to trp fster thn the reloser for 6

28 teporry fults. And sne teporry fults ount for 7 to 8 perent of feeder fults [G], the ss oordnton etween fuse nd reloser wll pt the feeder s rellty onsderly. Another ondton tht y use the fuse to trp fster thn the reloser under teporry fults ws presented y [D] nd [Doy]. As suggested n [D], f DG unts re dded to the feeder topology shown n Fgure 9, the fult urrent y eoe lrge enough tht the lterl fuse no longer oordntes wth the feeder rut reer durng fults. Ths would led to unneessry fuse opertons. [Doy] ponts out tht t s very lely tht oordnton etween the reloser nd ny down-lne fuses wll e lost. euse oth the reloser nd fuses operte fster t hgher fult urrents, the requred rgns etween the reloser fst urve nd the fuse nu elt urve ould e redued enough to lose oordnton. sys RC RC Fuse Fgure : DGs nd fult re loted downstre Fult 3 Reloser trppng for upstre fults [Doy] When there re DGs downstre of reloser s llustrted n Fgure, then the reloser wll see fult urrents n the reverse dreton, f the fult s upstre of the reloser. t y even e possle tht the RC exeeds the nu trppng vlue of the reloser, nd thus the reloser wll trp for fults upstre, whh s uneptle. 7

29 sys RC RC Fult Fgure : DGs re loted downstre, fult loted upstre The soluton for the reloser trppng prole for upstre fults n e heved y upgrdng the reloser s onventonl OC rely y dretonl OC rely. Ths wll e the reloser trp only f the RC exeeds the nu trppng vlue n ertn dreton. Whle solvng the frst two proles & relted to the reloser operton s not tht sple, the soluton nvolves esttng the ontruton of the DG nto the fult urrent. Ths fult urrent ontruton s needed to properly sze relosers nd orretly set the reloser-fuse oordnton preters. n [D], [J], nd [AK], rer nd Aernn gree tht the only urte pproh for solvng suh prole s to perfor softwre-sed nlyss, whh orretly odels the DG ehvor to fult events. Therefore, reltvely urte short-rut odels of dfferent types of DGs re needed to ssess the pt of ts fult ontruton durng the te fre fro out one-yle up to severl seonds nto fult event. Chpter 5 presents tehnque tht ws developed to fltte the ntegrton of nverter nterfed DGs nto onventonl fult nlyss studes of dstruton networs. C slndng proteton slndng on feeder ours when proteton deve reer, fuse or n utot reloser soltes seton of the feeder to solte fult, thus retng n slnd. slndng eoes onern when there s DG on the slnded prt of the feeder, s the DG wll try to energze the slnd Fgure. Due to the serous proles of slndng, whh nludes thretenng the sfety of utlty repr personnel, utltes nd stndrd- 8

30 ng odes requre tht DGs e equpped wth nt-slndng proteton, so DGs tht re on the slnded prt of the feeder n e dsonneted s soon s possle. slnd Sustton Fgure : slndng [D], [R99], nd [Rop] show tht none of the urrent slndng deteton ethods re ple of detetng the slnd under ll possle ondtons. The n reson for suh drw s tht the urrent ethods use only ther lol esureents, suh s the DG s voltge nd urrent. For protetng the feeder t ll ondtons, further reserh s needed to ether develop new tehnque or prove the urrent tehnques. Although slndng proteton s not one of the proles ths dssertton fouses on, t ws presented to show tht the slndng proteton n e ddressed ore effetvely one ounton networ s dopted t the dstruton level, the se ounton networ tht s needed for ddressng the proles ssoted wth ntegrton of DG nto dstruton networ..4 Sury Ths hpter egn wth ref ntroduton to dstruton networs, dstruted generton, nd the pt of dstruton generton on dstruton networs. t then exned the pt of DGs on onventonl feeder voltge regulton, under oth norl nd eergeny ondtons. 9

31 The pt of DG on feeder proteton ws exned nd the pt on the OC rely perforne nd reloser operton ws llustrted. Fnlly, the slndng phenoenon ws explned.

32 CHAPTER THREE Supervsory Control Shee for Feeder oltge Regulton Ths hpter presents supervsory ontroller desgned to regulte the voltge long feeder wth the presene of DGs. The hpter strts y defnng the feeder voltge regulton prole nd the proposed supervsory ontroller ojetves. The proposed supervsory ontroller desgn nd rhteture re then presented. Fnlly, test results re shown to prove tht the proposed ontroller n suessfully regulte the voltge of dstruton feeder wth DGs onneted to t. 3. Prole defnton As entoned n the prevous hpter, regultng the voltge of feeder wth DGs Fgure 3 nnot e done usng the onventonl R shee. Ths s euse of two n shortongs, the urrent R shee depends only on the lol urrent esureent nd the R s reltvely slow respondng deve. The gol ten n ths study s to enhne the urrent voltge regulton shee tht n ddress these shortongs. t s ontented tht ths n e oplshed s follows: Provde ounton ln etween the R nd the DGs. Ths ounton ln wll enle the R to ollet the ddtonl dt t needs n order to e le to estte the voltge drop on the feeder nd thus provde etter voltge regulton. The ounton wll lso provde the oordnton etween the R nd the DGs.

33 Use DGs for retve power support needed durng the voltge sg ondtons tht re too short for the R to ret. Ths wll provde the fst voltge regulton needed durng voltge sg ondtons due to the sudden drop of DG s well s lrge otor strt-ups. Ths uses the plty of DGs to provde retve power support durng eergeny ondtons. The jorty of the DGs, roturnes nd even the fuel ells, n provde ths serve. DGs re usully equpped wth ther own ontroller whh ontrols the DG s output tve nd retve power. R UTLTY syste Lod P pf Lod Lod P pf Lod Lod P Lod pf Lod Lod P Lod pf Ctrl-4 Ctrl-3 Ctrl- Ctrl- DG-4 DG-3 DG- DG- Fgure 3: Feeder wth DGs nd lods 3.. DG odel nverter nterfed DGs onsst of power genertng unt tht produes d power nd n nverter unt to onvert tht power to power. The power genertng odel depends on the type of the DG, roturne, fuel ell... et. n ppendx A, the roturne odel s well s the fuel ell odel s presented. n Fgure 4, the nverter odel s presented, showng the nverter s nput nd output flters nd the sx ntergte polr Trnsstor GT swthes used to onvert the nput fro d voltge to n voltge. L D D 3 D 5 L R - C op D 4 D 6 op D op3 L 3 L 3 L 3 C - C - C.. R - C DC Ln A C 5 [MA] # #.. A C op op op3 Fgure 4: DG s nverter wth nput nd output flters nd step-up trnsforer

34 As shown n Fgure 5, two P ontrollers re used to regulte the DG s output tve nd retve power, v regultng the gntude nd ngle of the nverter s output voltge. The orret pulse sequene gven to the GT swthes - tht wll yeld the requred voltge gntude nd ngle re generted usng the Pulse Wdth Modulton PWM tehnque. t s portnt to enton tht the DG s ontroller dopts onstnt power ftor ontrol shee. Suh shee uses the tve power setpont-ond sgnl to deterne the orrespondng retve power setpont sgnl n order to ntn the power ftor onstnt. Ths ens tht the two preters tht re regulted to th ther setponts re the tve power output P set nd the power ftor pf set. Dependng upon these preters, the retve power output s deterned. P-DG tul - P_set P 4.. Q-DG tul - Q_set P D. Phse Mg Sn Freq 6.. Phse Sn. Mg Freq 6. Phse Mg Sn Freq 6. F N N/D Aop tor Copr- tor Copr- A A tor Copr- 8. op op op3 Fgure 5: DG s ontrol odel nd nverter pulse genertor 3.. Supervsory ontroller n order to oordnte ontrol tons etween the R nd the DGs, there wll e supervsory ontroller t the dstruton sustton wth ounton lns etween the ontroller nd the feld deves,.e, the R nd the DGs on the feeder. The supervsory ontroller wll gther dt fro the feeder t the ontorng ponts, whh re nly the DG lotons, ut ould lso nlude other ponts on the feeder, nd send the orretve setpont sgnls for the R nd the DGs. Fgure 6 llustrtes ths proposed supervsory ontrol shee. 3

35 R Lod P DG-4 Ctrl-4 pf Lod Lod P DG-3 Ctrl-3 pf Lod Lod P DG- Ctrl- Lod pf Lod Lod P DG- Ctrl- pf Lod -set Feed sgnl of, P & pf Q-set4 Q-set3 Q-set Q-set Feed sgnl of DG s tul, P nd pf Supervsory ontroller Feeder odel Fgure 6: Feeder wth DGs nd lods nd proposed supervsory ontroller Ths supervsory ontroller wll oplsh the followng ojetves: The feeder voltge levels should e reovered to eptle levels whh re usully etween.95 nd.5 pu s fst s possle. The totl retve power support fro DGs should e ept s sll s possle. Ths wll nze the ost of retve power support fro DG, espelly f the utlty wll py the DG-owners for ther retve power support. The retve power support fro DGs should e requested f nd only f the R s nple of supportng the feeder voltge. Note tht the supervsory ontroller nterfes wth DGs y djustng ther power ftors. Ths s euse the ontrollers for the DGs hve two set-ponts, P set nd pf set. The power settng P set s deterned y the DG owner nd s usully sed on eono ftors, whle the pf set s norlly set to unty sne DG owners get pd for ther tve power output. The pf set n, however, e djusted for voltge support, sne the power ftor deternes the DGs retve power output, whh n turn ffets the voltge level on the syste. sed on these ojetves nd onstrnts the del ontroller response s llustrted n Fgure 7, whh shows the desrle tons of the DGs nd the R n response to sudden voltge drop event n one of the feeder s nodes. The te xs s dvded nto four ntervls, A,, C nd D, wth eh deternng ertn opertng ondton. 4

36 ntervl A represents the feeder operton just efore the event. The feeder s opertng wth ts nu node voltge t.95 volts, the R voltge s onstnt, nd the DGs re opertng t unty power ftor. ntervl strts when DG dsonnets usng the nu node voltge to drop elow.95 s shown n the fgure. The R nd the renng DGs strt tng to reover the feeder s voltge level. y the end of ntervl, the feeder s voltge level returns to.95 due to the fst reton of the DGs onneted to the feeder. The DGs respond to the sudden event y quly deresng ther power ftor n order to njet enough retve power to support the voltge. Throughout ntervl C, the voltge level long the feeder s wthn lts, ut the R s slowly png up the urden of supportng the voltge nd relevng the DGs, who slowly return to unty power ftor operton. ntervl D shows the feeder t stedy stte fter reoverng fro the event. The nu node voltge s.95, the DGs re opertng t unty power ftor, nd the R voltge set pont oved to hgher level. The r hrt t the otto of Fgure 7 shows the desrle ontruton nd oordnton etween the DGs nd the R to ensure fst syste reovery fro sudden under voltge event. At the egnnng, the DGs fully support the feeder voltge, whle the R s not ontrutng. Ths grdully hnges untl the R fully supports the feeder voltge nd releves the DGs. 5

37 % % 3% 5% 38 % 5 % 63% 7 5 % 5 % 8 8 % 3% 94 % 6% % Nodes n. voltge flls elow.95 DGs restore voltge level only R supports the voltge Nodes n. voltge.95 te R voltge.5.?v te DGs n. pf. te ntervl: A C D DGs 88 % 75 % 63 % 5 % A r hrt showng the ontruton n feeder voltge support for DGs vs. R fro strt of event, untl full reovery 38 % R Fgure 7: DG nd R response to sudden voltge drop event 6

38 3.3 Controller desgn The supervsory ontroller n Fgure 6 wll use feed sgnls fro the DGs nd the R nd send the requred hnge n the DGs retve power nd R s tp settng to the DGs nd the R. The rhteture of the proposed supervsory ontroller s shown n Fgure 8. The supervsory ontroller onssts of two ontrollers runnng n prllel. The C- ontroller supervses the R whle the C- ontroller wll supervse the DGs. The two ontrollers need feed sgnls fro the feeder out the voltge nd power vlues for ll DGs nd lod nodes. As entoned erler, the lod nodes syste preters need to e estted, wth ths ts eng oplshed y the esttor lo E-. The detls of ontrollers C- nd C- nd the esttor E- re elorted n the followng susetons. P C- Q DG- All DGs v DG- & v OLTCT E- P lod- Q lod- pf DG- Feeder syste P DG- C- OLTCT OLTCT Feed sgnls Fgure 8: Supervsory ontroller lo dgr 3.3. The Esttor E- The esttor wll gther dt fro the feeder nd onstrut n pproxte feeder odel to e used y the ontrollers. The gol here s to develop feeder odel tht n use the relte dt vlle fro the feeder. Sne there would e only lted dt vlle, we need to pproxte the feeder odel ordngly. We ssue tht t ertn lotons on the feeder, t DG ponts for exple, power flow esureents re vlle. These power flow esureents n then e used to deterne the pproxte lod served etween the two esureent ponts, s the lod would e sply the dfferene etween the two flow 7

39 esureents. Ths s llustrted n Fgure 9. The totl lod etween the esureents of P nd P 3 for exple would e P L P P 3. The pproxte odel s then otned y lupng these totl lods n the ddle of the setons defned y the flow esureents, whh s llustrted n Fgure 9. Note tht n ths pproxte feeder representton, we hve the tve nd retve power esureent t eh node. Therefore, we n use the power flow equtons to represent the feeder. For rdl feeder, these equtons would e of the followng for per phse we neglet the lne utul ouplng effets [er86]. [ Y Y ] [ Y Y ] jq P Where Y s the dttne of the segent onnetng node to node. The esttor odule uses the power flow equtons to lulte the voltge levels on the feeder. The esttor then psses the pproxte feeder odel nd the voltge dt to the ontrol odules. Control odules use the odel to deterne the effet of ther ontrol tons on the feeder voltge levels. sgt d sgt sgt sgt P 45 P 34 P 3 P P R 4 DG 3 DG DG DG P 45 P 34 P 3 P P R P 5 4 DG P 4 P 3 P P 3 DG DG DG Fgure 9: Conng neghorng lods to deterne pproxte feeder odel 8

40 3.3. DG ontroller C- Ths ontroller deternes the retve power needed fro eh DG n order to eep the feeder wthn voltge lts. The ontroller wll solve the onstrned nzton prole forulted elow. The ojetve funton represents the ost of dspth, whh s the totl ount of retve power needed fro ll DGs. The power ftor onstrnts ensure tht the retve power support fro the DGs wll e wthn ther pltes, s they wll lt the DGs retve power vlues sed on ther rel power outputs. The DG ontroller wll run ths optzton every updte yle, for exple t every seond, only durng the eergeny perod, whh s deterned y the R ontroller. One the new retve power dspth vlues re deterned, the ontroller sends the to the DGs s new set ponts. Mn Cost Q DG s.t. Feeder odel: odel of the feeder onfgurton tht represents the reltonshp etween power flow, DG power njeted, lod dstruton, nd nodes voltges. v, P, Q Node voltge onstrnts: ensures tht ll node voltges re wthn eptle voltge lts..95 v.5,, n for n nodes Power ftor onstrnts: ensures tht the retve power dspthed to eh DG s wthn ts pltes nd depends upon the ount of power njeted y the DG nto the syste..5 pf.,, for DGs R ontroller C- The ontroller for the R tres to djust the set pont of the R, whh s the output voltge of the regultor; n suh wy tht the voltges on the feeder wll ren wthn ther lts 9

41 nd the retve power support fro the DGs s nu. For ths, t the egnnng of eh updte yle, the ontroller hes f the voltges re wthn lts. f not, then the ontroller deternes f the R lone n restore the voltges wthout support fro the DGs. Ths s done y solvng the followng optzton prole: Mn v OLTCT s.t. v, P, Q feeder odel.95 v n- voltge onstrnts equtons, for n nodes pf pf-voltge relton equtons, for DGs Note tht the power ftors of the DGs re set to unty to prevent the retve power support fro the DGs. The output of ths optzton gves the nu set pont the R needs to restore the voltges on the feeder. f the new set pont s outsde the lts of the R, whh re usully etween.95 nd.5, t ndtes tht the R lone nnot provde voltge regulton. n ths se, the ontroller sets the new set pont to the lt vlue. The ontroller sends the new set pont to the R nd wts.e. does not run untl t gets the feed fro the R onfrng tht the R oved the voltge to the desred level. Ths wtng provdes the oordnton etween the two ontrollers y lettng the DGs provde eergeny support whle the R s tng the orretve ton. 3.4 Test results n order to evlute the effetveness of the proposed supervsory ontroller, prototype dstruton feeder s used wth three DGs. The ontroller perforne nd ts lty to eep ll DGs wthn lts wll e ontored for three ses, sudden nrese n feeder lod, sudden dsonneton of DG, nd under severe ontngeny. 3

42 3.4. Test Syste The feeder sulted s the EEE 34 node prototype feeder [EEE34], whh represents long feeder servng xed set of lods. The feeder s odfed y ddng three DGs on the n feeder. Wth the DGs supplyng ost of the lod, two Rs on the orgnl feeder re repled y the sustton R s t provdes enough voltge regulton on the feeder. The R s ssued to ove ts tps n 8 seonds for ±5 perent voltge regulton. The three DGs re odeled s fuel ells wth ontroller to regulte the DG s tve power nd power ftor P t, pf DG odel detls re gven n [E]. t s ssued tht every DG loton lso provdes the power flow esureents fro the feeder. The pproxte feeder used y the ontroller s therefore n 8 node feeder s gven n Fgure. The feeder s sulted usng PSCAD nd s shown n Fgure. As ndted n the prevous seton, the lods n the redued feeder orrespond to the totl lod etween the two esureent ponts Tle. n the sulton, the lods re represented y ther equvlent pedne nd re ssued to e onstnt power lods. 8 DG-3 DG- DG Sustton R Lod-4 Lod-3 Lod- Lod- Fgure : Approxte feeder for the ontroller Tle : Feeder lods Node P W Q r