采用VSC- HVDC连接的电压质量改进的风电场传输网

ImprovementofVoltageQualityinConnectionofWindFarmstoTransmissionNetworkUsingVSC-HVDCHanif.Livani1Javad.Rouhi1,2Saeed.Lesan1Hossein.Karimi-Davijani11DepartmentofElectricalandComputerEngineering,BabolUniversityofTechnology,Iran2MemberofAdministrativeCouncilofCigreABSTRACT:Thispaperstudiespossibleimprovementsofvoltagequalityinconnectionof40MWwindfarmtotransmissionnetworkusingVSC-HVDClink.The40MWwindfarmincludes20individual2MWpermanentmagnetsynchronousgenerators.Thevoltageatthetransmissionnetworkterminalshouldbere-establishedwithminimizedpowerlossesduringwindspeedfluctuationsandaftertheclearanceofgridsidefaults.ThispaperemphasizesonamodifieddecouplingcontrolstrategywhichisimplementedinVSC-HVDCconverterstoobtainvariablespeedoperationandvoltagestabilizationinwindfarmnetworkandtransmissionnetworkrespectively.SimulationsusingPSCAD/EMTDCareperformedtostudybehaviorofwindfarm,transmissionvoltageanddcvoltagefordifferentchangesinwindspeedandthree-phasefaultanda20%voltagesagontransmissionnetwork.Thesimulationresultsconfirmtheconnectionmethodandthemodifieddecouplingcontrolstrategy.1.IntroductionBecauseofsomechallengessuchasconventionalenergysourcesconsumption,pollution,globalclimatechangeandsecurityofenergysupply,significanteffortshavebeenmadetodeveloprenewableenergysourcessuchaswindenergy.Windpowerisgrowingwitha20%annualgrowthrateforthepastfiveyearsandthegrowthrateisfasterthananyotherrenewableenergysources[1].Itispredictedthatby2020upto12%oftheworld'selectricitywillbesuppliedfromwindpower[2]Intermsofwindpowergenerationtechnology,asaresultofnumeroustechnicalbenefits(higherenergyyield,reducingpowerfluctuationsandimprovingvarsupply)themodernMW-sizewindturbinesalwaysusevariablespeedoperationwhichisachievedwithasystemofconverters[3].Theseconvertersaretypicallyassociatedwithindividualgeneratorsandtheycontributesignificantlytothecostsofwindturbines.Betweenvariablespeedwindturbinegeneratorsdoublyfedinductiongenerators(DFIGs)andpermanentmagnetsynchronousgenerators(PMSGs)withprimaryconvertersareemergingasthepreferredtechnologies[4].OntheotherhandifHVDC(HighVoltageDCCurrent)linkisused,thewindpowerwillbetransmittedthroughtwoconverterssets,firstthroughturbinesandthenthroughHVDCtransmissionlink.Inordertoreducenumberofconvertersandsavingincostsandsimplicityofcontrol,thePMSGsintheanalysishavenoprimaryconvertersinthemselves[4].Asaresultoflarge-scalewindpowergeneration,interconnectinglargewindfarmstopowergridsandtherelevantinfluencesonthehostgridsneedstobecarefullyinvestigated.Windfarmsarenowrequiredtocomplywithstringentconnectionrequirementsincluding[5]:reactivepowersupport,transientrecovery,systemstabilityandvoltage/frequencyregulation.WindfarmscanbeconnectedtoelectricalnetworksusingeitherACorDClinks.AlthoughAClinkshassomeadvantages,suchaslowcost,provedtechnologyetc,therearesomedisadvantagesforwindfarminterconnectionvialongAClines,amongwhicharelargeamountofcapacitivereactivepower,synchronousoperationofwindfarmsandtheACgrid,andpropagationoffluctuationsinvoltageandfrequencyduetothevariationsinwind[4].ThereforeHVAC(HighVoltageAlternativeCurrent)connectionisaneconomicsolutionformediumrangewindfarms(uptoafewhundredMW)withtransmissiondistancessmallerthan5075km[2].Hence,fordistancesover50km,HVDCtransmissionoffersmanyadvantagesincomparisonwithACconnection:thepowerflowisfullydefinedandcontrolled,cablepowerlossesaremuchlower,sendingandreceivingendfrequenciesareindependent,andtransmissiondistanceisnotdeterminedbycablechargingcurrents[2].978-1-4244-2501-3/08/$20.00©2008IEEEInrecentyears,withthedevelopmentofpowerelectronics,Voltagesourceconverter(VSC)basedHVDC(VSC-HVDC)transmissionlink,usingself-commutatedvalves(IGBTs,IGCTsandGTOs)hasbeenanactiveplayerinelectricitytransmissionanddistribution,andtherearealsosomesignificantadvantages,whichmakeitsuitablefortheconnectionofwindfarmstotransmissionnetworks[6,7]:(i)IGBTvalvecanswitchoffandonimmediately,(ii)thereisnocommutationfailureproblem,(iii)notelecommunicationrequiredbetweentwostationsofHVDCsystem,(iv)Activeandreactivepowercanbecontrolledindependently,(v)reactivepowercompensationnotrequired,(vi)onlysmallfilterisrequiredtofilterhighfrequencysignalfromPWM.In[4]activeandreactivepowerdecouplingcontrolisappliedtoVSC-HVDCtoachievevariablespeedoperationofwindgenerators,butbasicrequirementssuchastransientrecoveryandvoltageregulationofthegridaren’tinvestigated.In[6]coordinatedcontrolofvoltagesourceconverterbasedHVDCandwindturbinesequippedwithdoubly-fedinductiongeneratorsareintroduced,butthefocusismoreonthevariablefrequencyoperationoftheDFIGwindfarm.In[5]anapproximatelinearcontrolstrategyisappliedtotheVSC-HVDClink.TheobjectiveofthispaperistoproposeamodifieddecouplingcontrolforVSC-HVDCconverterstoachievevariablespeedoperationofPMSGwindturbinesinwindfarmandalsotoimprovevoltagequalityandtransientstabilityintransmissionnetworkduringwindspeedfluctuationsandaftertheclearanceoftransmissionnetworksideshort-circuitfault.SectionIIdescribesthewindfarmandtheVSC-HVDCsystems,andthecontrolstrategiesaredescribedinsectionsIIIand