机械类文献翻译风电对电力系统角稳定性的影响Word格式文档下载.docx
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机械类文献翻译风电对电力系统角稳定性的影响Word格式文档下载.docx
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Thereisnodoubtthatwindpowerwillplayapredominantroleinaddingcleanandnonpollutingenergytothecountry’sgrid.However,asmorewindturbinesareconnectedtothegrid,theirimpactonthepowerqualityofservicespopulatedwithwindgenerationisbecomingmoreevident,soitisimportanttoanalyzethetransientstabilityofpowersystemincludingwindpowerstations[4].
Athree-phasefaultisappliedtoa14busIEEEtestsystem,andclearedbydisconnectingtheaffectedline.
Inthispaper,thefocusislimitedtodetermineCriticalClearingTime(CCT)fortheseveralcasesbyobservingthetransitbehaviorsimulationofatestsystemduringgridfaultsusingaMatlabpowersystemanalyzetoolbox(PSAT)[5].
Thestructureofthispaperisasfollows.First,thewindmodelisdescribedbriefly;
alsothewindturbineconceptsaredescribed.Then,thetestsystemandtheappliedmodelsarepresented.Theoscillationofagroupofgeneratorsduringafaultisanalyzedbyobservingthetransientbehaviorforfollowingcases:
A-Changingawindsourcelocates.
B-Differentgeneratortechnologies.
C-Increasinggraduallyarateofwindsourcespenetration.
Toconclude,theresultsareclarifiedonthebasisofexistingtheoriesandcomparisonbetweendifferentcasesinordertochooseabestcaseandavoidaworseone.WindModel
Windenergyistransformedintomechanicalenergybymeansofawindturbinewhoserotationistransmittedtothegeneratorbymeansofamechanicaldrivetrain.
Thewind-powerequation[6,7]isgivenby:
Pt=1/8ρπd2v3Cp
whereρistheairdensity,ristheturbineradius,νisthewindspeed,andCpistheturbinepowercoefficientwhichrepresentsthepowerconversionefficiencyanditisafunctionoftheratiooftherotortip-speedtothewindspeed,termedasthetip-speed-ratio(TSR).
Suchdisturbancesarethemostcommoninthegrid,thegriddisturbancesconsideredinthispaperareofshortduration,maximumafewhundredsofmilliseconds.Sincetheconsideredgriddisturbancesaremuchfasterthanwindspeedvariations,thewindspeedcanheassumedconstant.Therefore,naturalwindvariationsneednotbetakenintoaccount.Thewindspeedissettoaconstant15m/s.
TurbineModels
Therearemanydifferenttypesofwindturbinesinusearoundtheworld,eachhavingitsownlistofbenefitsanddrawbacks[8].Inthispapertwomaintypesofwindturbinesaretakenintoaccount:
•Aconstantspeedwindturbine(Fig.1a),whichconsistsofagridcoupledshort-circuitedinductiongenerator[9].Thewindturbinerotorisconnectedtothegeneratorthroughagearbox.Thepowerextractedfromthewindislimitedinhighwindspeedsusingthestalleffect.Noactivecontrolsystemsareused.
•Avariablespeedwindturbinewithwoundrotorinductiongenerator(Fig.1b)–doubly-fedinductiongenerator(DFIG).Therotorwindingissuppliedusingaback-to-backvoltagesourceconverter[10].Asinthefirstcase,thewindturbinerotoriscoupledtothegeneratorthroughagearbox.Inhighwindspeedsthepowerextractedfromthewindislimitedbypitchingtherotorblades.
Figure1a.Squirrelcageinductiongenerator
Figure1b.Doubly-fedinductiongenerator
TestSystem
ThetestsystemforthisstudyispresentedinFig.2,itisderivedfromIEEEtestsystem;
thisnetworkconsistsof14buses,5generators,11loadsand83branches.Thetransformersconnectinggeneratorstothegridareadjustedaccordingly.Windturbinesarethe2MWmachinesdescribedaboveinsection2.
Notethatthegeneratorsdonotrepresentasinglemachinebutagroupofstronglycoupledgeneratorsandforthistestsystemthetotalpowerisdividedasfollow:
Table1.Activepoweroftestsystemgenerators
GeneratorN°
1
2
3
4
5
Power(MW)
615
60
25
Thedisturbanceinvestigatedisathree-phaseshort-circuitonBusnumber2.Thisthree-phasefaultrepresentsthemostseveredisturbancefortransientstabilityproblems.
ItmustbenotedthatallsimulationsaredevelopedbyPSAT(version2.0.0β1).ResultsandDiscussions
ImpactofLocation
Inordertoassumetheimpactofthewindpowertoangularstabilityofpowersystem,weincludedathreephasesymmetricalfaultthenwecalculatetheCCTcorrespondingtoacasewithoutwindsourceandotherscaseswhereawindsourceisconnectedtotestsystembydifferentBuses.
Figure2.Basecase
WithoutaWindSource
TheBaseCaserepresentsthenormaloperationofthesystemwithoutanywindpowerconnectedtothesystem.Thecriticalfaultclearingtime(CCT)canbedeterminedusingtransientsimulations[3].Forthiscase,theresultisCCT=196ms.Fig.3showsthespeedgeneratorsincomparisonforafaultclearingtimeclosetothecriticalclearingtime.
InFig.3b,thefaultintroducedhasdurationoft=197ms,sothetimeisexceedingthestabilitylimitofCCT.
Figure3a.Rotorspeedofallgeneratorsatt=196ms
Figure3b.Rotorspeedofallgeneratorsatt=197ms
WithaWindSource
Afterthat,onewindturbinegeneratorisconnectedtosystemthroughatransmissionlineondifferentbusesforevaluatingtheireffecttotheangularstability.
Table2.Resultsfromthesimulationsfortheangularstabilityondifferentlocations
Busnumber
Bus1
Bus3
Bus8
Bus14
CCT(ms)
186
187
263
220
Comparedtothepreviouscasewhereanywindsourcewasconnected,theintegrationofwindsourcehasincreasedthetransitstabilitywhenitwasconnectedatBUS8orBUS14,butonthecontraryforcasesofBUS1andBUS3,sothereisnogeneralstatementpossible,ifwindgenerationimprovestransientstabilitymarginsoriftheimpactisrathernegative.Theanswerdependsonlocationofwindresourcesandtheproblemhastobeanalyzedindividuallyforeachcase.
EffectofTypeofGeneratorTechnology
Inordertodeterminetheeffectoftypeofgeneratortechnologytotransitbehaviorofgrid,twotypesofgeneratorsarestudiedwithkeepingthesamefaultandthesamelocationofwindsource.Case1:
FixedSpeed
Thecriticalfaultclearingtime(CCT)canbedeterminedusingtransientsimulations.Forthiscase,wherewindsourceisconnectedtoBusN°
3theresultisCCT=187ms.Fig.4showsthespeedrotorofallgeneratorsincomparisonforafaultclearingtimeclosetothecriticalclearingtime.
Figure4a.Rotorspeedofallgeneratorsatt=187ms
Case2:
VariableSpeed(DFIGTechnology)
ThefixedspeedgeneratoraddedtoBus3isnowdisconnectedandsubstitutedbyadoubly-fedinductiongenerator(DFIG)havingasamepower(2MW).Thus,thechangeinthetechnologycanbeconsideredandanalyzed.TheanalysisoftheCCTresultsinanincreasedstabilitylimitcomparedtoCase1withonlyfixedspeedgeneratorsinservice.ThetimeincreasestoCCT=216msasshowninfigure5.Thismeans,thatthetransientnetworkstabilityisenhancedwhenDFIGareconnectedinsteadoffixedspeedgenerator.
Figure5a.Rotorspeedofallgeneratorsatt=216ms
Figure5b.Rotorspeedofallgeneratorsatt=217ms
Table3.CCTfortwotypesofturbinetechnologyonseveralbuses
BusN°
8
14
CCTforfixedspeed(ms)
186
187
263
CCTforvariablespeed(ms)
286
216
300
227
Accordingtoresults,itisveryclearlythattheDFIGgeneratorincreasethecriticalclearingtime,consequentlythistypeofgeneratorpresentsbestperformancethanasquirrelcageinductiongeneratorconcerningtheangularstabilityofgridconnectedtowindpower,itisevidentthattheWindpowergenerationwithDFIGprovidesbetterperformanceforangularstabilityafterfaultclearanceowingtoitsabilitytocontrolreactivepower.
Effectofwindpenetration
Inthissection,theeffectofwindpowerontheoscillationsisinvestigatedbygraduallyincreasingtherateofwindsourcepenetrationwhileobservingthetransitbehaviorofsystem[11].
Table4.CCTfordifferentratesofwindpowerpene
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