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英语原文
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IEEETRANSACTIONSONSUSTAINABLEENERGY,VOL.4,NO.1,JANUARY201331AMethodologyforTransforminganExistingDistributionNetworkIntoaSustainableAutonomousMicro-GridM.VenkataKirthiga,S.ArulDaniel,Member,IEEE,andS.GurunathanAbstract-Adistributionnetworkwithrenewableandfossil-basedresourcescanbeoperatedasamicro-grid,inau-tonomousornonautonomousmodes.Autonomousoperationofadistributionnetworkrequirescautiousplanning.Inthiscontext,adetailedmethodologytodevelopasustainableautonomousmicro-gridispresentedinthispaper.Theproposedmethodologysuggestsnovelsizingandsitingstrategiesfordistributedgener-atorsandstructuralmodificationsforautonomousmicro-grids.Theoptimalsitesandcorrespondingsizesofrenewableresourcesforautonomousoperationareobtainedusingparticleswarmop-timizationandgeneticalgorithm-basedoptimizationtechniques.Structuralmodificationsbasedonrankingofbuseshavebeenat-temptedforimprovingthevoltageprofileofthesystem,resultinginreductionofrealpowerdistributionlosses.Theproposedmethodologyisadoptedforastandard33-busdistributionsystemtooperateasanautonomousmicro-grid.Resultsconfirmtheusefulnessoftheproposedapproachintransforminganexistingradialdistributionnetworkintoanautonomousmicro-grid.IndexTerms-Distributedpowergeneration,loadflow,powergenerationplanning.NOMENCLATURERealpowerratingofthethgenerator.Maximumgenerationlimitonthethgenerator.Minimumgenerationlimitonthethgenerator.Reactivepowerratingofthethgenerator.Costcoefficientoftherenewableenergysourceatthethbus.Currentdrawnfromthesubstationfeeder.Realpowerlossinlinebetweenbusesand.Totalrealpowergeneratedinthesystem.Totalreactivepowergeneratedinthesystem.ManuscriptreceivedOctober20,2011;revisedFebruary06,2012;accepted.April16,2012DateofpublicationMay30,2012;dateofcurrentversionDe-cember12,2012.MVKirthigaandSADanielarewiththeDepartmentofElectricalandElectronicsEngineering,NationalInstituteofTechnology,Tiruchirappalli620015,India(e-mail:
mvkirthiga@nitt.edu;daniel@nitt.edu).S.GurunathanwaswithDepartmentofElectricalandElectronicsEn-gineering,NationalInstituteofTechnology,Tiruchirappalli,India,andis.nowwithWEGIndustriesofIndia(P)Ltd,Hosur635109,India(e-mail:
guru_gce2005@yahoo.co.in).Colorversionsofoneormoreofthefiguresinthispaperareavailableonlineathttp:
//ieeexplore.ieee.org.DigitalObjectIdentifier10.1109/TSTE.2012.2196771Maximumlimitonthebusvoltagemagnitude.Minimumlimitonthebusvoltagemagnitude.Magnitudeofthevoltageatthethbus.Maximumbusvoltagemagnitudeatthbusofthesystem.Minimumbusvoltagemagnitudeatthethbusofthesystem.,Totalrealpowerdemandinsummerandwinter,respectively.,Totalreactivepowerdemandinsummerandwinter,respectively.Numberofbusesinthedistributionsystem.Numberofdistributedgenerator(DG)locations(Sites).I.INTRODUCTIONINmodernpowerdistributionsystems,integratingsmallnonconventionalgenerationsourceshasbecomeattractive.Thesetechnologieshavelessenvironmentalimpact,easysiting,highefficiency,enhancedsystemreliabilityandsecurity,improvedpowerquality,loweroperatingcostsduetopeakshaving,andrelievedtransmissionanddistributioncongestion[1].Thedistributedgenerator(DG)unitsusedarehighlymodularinstructureaswellashelpfulinprovidingcontinuouspowersupplytotheconsumers.However,dependingontheratingandlocationofDGunits,thereisalsoapossibilityforvoltageswellandanincreaseinlosses.Inthisscenario,toexploitthecompletepotentialofdistributedgeneration,propersitingandsizingofDGsbecomeimportant.Thispaper,there-fore,attemptstodevelopasizingalgorithmthattransformsanexistingdistributionnetworktoasustainableautonomoussystem.Insuchanoperation,thegenerationandcorrespondingloadsofthedistributionnetworkcanseparatefromthefeedernetworkandformamicro-gridwithoutaffectingthetransmis-siongrid'sintegrity.Mostofthecurrentmicro-gridimplementationscombineloadswithsourcesplacedatfavorablesitesthatallowinten-tionalislandingandtrytouseutmosttheavailableenergy[2].Insuchanoperation,stablegenerationandvoltageprofilearenecessarytoindependentlysupplypowertocustomers[3].1949-3029/$31.00©2012IEEE
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32IEEETRANSACTIONSONSUSTAINABLEENERGY,VOL.4,NO.1,JANUARY2013Henceobtainingthenumberoflocations(sites)atwhichtheDGsareplacedbecomessignificant.Inearlierworks,algorithmsweredevelopedforoptimalsizingoftheDGunitsandtheypertaintononautonomousmodeofoperationofthemicro-grids.Haesenetal.proposedasizingalgorithmbasedonminimizingthelossesusinggeneticalgorithm(GA)[4].MallikarjunaproposedanotheralgorithmbasedonsimulatedannealingforoptimizingthesizeoftheDGsinamicro-grid[5].Optimalsizingbasedonthedetailedannualizedcostcalculationswasalsoproposed[6].Neverthe-less,noneoftheabovealgorithmshadconsideredautonomousoperationofthemicro-grids.Katiraeietal.Hasdiscussedabouttheautonomousopera-tionofmicro-gridsbutitpertainstoisolatedoperationofafewloadsonemergencyoperatingconditions[7].Liu[8]andNehrir[9]havealsohighlightedisolatedoperationofhybridrenewablesystems.Butalltheseearlierworksdonotinvesti-gateanyautonomousmicro-gridforalargerdistributionnet-workatmediumvoltagelevel,independentoftheutilitygrid.Sofar,amethodologyforoptimalsitingandsizingoftheDGsinanautonomousmicro-gridisnotreportedintheliterature.Inthiscontext,thispaperattemptstodevelopasizingalgo-rithmforanautonomousoperationofanexistingradialdistribu-tionnetwork,thusmakingitanisolatedsustainablemicro-grid.Theconstraintsincludedintheproposedsizingalgorithmarevoltagelimits,demand,andgeneratorratinglimits.Inadditiontosizing,thispaperfocusesonsitingoftheDGsandsuggestsaminimum-lossconfigurationforthenetwork.Therearemanyoptionsavailableforreducinglossesatthedis-tributionlevel:
reconfiguration,capacitorinstallation,loadbal-ancing,andintroductionofhighervoltagelevels[10],[11].Nevertheless,aheuristicapproachinchoosingthesitesfortheDGunitshasbeenattemptedinthispaperforautonomousmicro-grids.SouzaRibeiroetal.proposedanarchitectureforisolatedmicro-grids[12].Theyhaveproposedprogrammedswitchingofalreadyexistingswitchestoreconfigurethedistributionnetworkforstableoperationasmicro-grid.Twotypesofswitchesareusedinprimarydistributionsystemsviz.,sectionalizingswitches(normallyclosed)andTIEswitches(Normallyopen)[13],[14].Theseswitchesaredesignedforbothprotectionandconfigurationmanagementresultingincostminimization.OptimalreconfigurationofdistributionsystemswithDGshavealsobeendiscussedintheliterature[15]-[18]butcomplexoptimizationtechniqueshavebeenusedtoiden-tifytheoptimallocationofTIEswitchestoenableadditionalbranchesforreconfiguration.Moreover,noneoftheseworksonreconfigurationhadanobjectiveofautonomousoperationofadistributionnetworkasamicro-grid.Inthiscontext,reconfigurationofanexistingdistributionsystemhasalsobeenattemptedforperformanceimprovementofanautonomousmicro-grid.Rankingofthebusesbasedonmaximumloadablelimits(beyondwhichthevoltagelimitsviolationofbuseswasobserved)hasbeenemployedtoidentifythenodes.Basedonthisranking,additionalTIEbranchesaretobeconnected.Thestandard33-busdistributionsystemisusedforvalida-tionofthealgorithmsproposedandMATLABcodinghasbeendevelopedforimplementationoftheproposedalgorithm.Therestofthepaperisorganizedasfollows:
Methodologyforplanninganautonomousmicro-gridisrevealedinSectionII.OptimalsizingofDGsandtheoptimizationtechniquesusedareexplainedinSectionIII.SectionIVfocusesonthesignif-icanceofreconfigurationintheoperationofanautonomousmicro-grid.SectionVdepictsdiscussionsontheresultsinsup-portoftheproposedmethodologyanditsvalidation.Conclu-sionsofthepaperarepresentedinSectionVI.II.PLANNINGOFAUTONOMOUSMICRO-GRIDSItisevidentthattransformationofanexistingradialdistribu-tionsystemintoasustainableautonomousmicro-grid,requiresDGstobeintegratedintothenetwork.Theexactsizeofthesegeneratorsandtheoptimalplacementofthesameinthenet-workarenecessaryforitsautonomousoperation.Henceahi-erarchicalandpartiallyheuristicmethodologyisattemptedfordeterminingtheoptimalsitesandsizesofthegeneratorsandforreconfiguringthenetwork.A.OptimalNumberandLocationofDGUnitsItismandatorythatthetotaldemandandthesystemlossesneedtobesatisfiedbytheDGunitsconnectedtothedistribu-tionsystem.ForobtainingtheoptimalnumberofDGunitsandthecorrespondingsitesfortheDGplacements,thefollowingmethodologyisproposed.1)Anoptimizationproblemisformulatedforminimizingthedistributionlosses,includingtheconstraintsviz.,gener-atorratingconstraint,voltageconstraint,andpowerbal-anceconstraint.2)For""generatorunits,thenumberofdifferentpossiblecombinationsofsitesis,Whereisthetotalnumberofbusesinthedistributionsystem.3)Theparticleswarmoptimization(PSO)techniqueisthenemployedforminimizingtheoptimizationproblem,foreachofthecombinations,whereinitially""issetto1.4)Theoptimallocationscorrespondingtoth