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外文翻译风力发电中的自我激励与谐波.doc

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外文翻译风力发电中的自我激励与谐波.doc

8SelfExcitationandHarmonicsinWindPowerGenerationE.Muljadi,C.P.ButterfieldNationalRenewableEnergyLaboratory,Golden,Colorado80401H.RomanowitzOakCreekEnergySystemsInc.,Mojave,California93501R.YingerSouthernCaliforniaEdison,Rosemead,California91770Traditionalwindturbinesarecommonlyequippedwithinductiongeneratorsbecausetheyareinexpensive,rugged,andrequireverylittlemaintenance.Unfortunately,inductiongeneratorsrequirereactivepowerfromthegridtooperate,capacitorcompensationisoftenused.Becausethelevelofrequiredreactivepowervarieswiththeoutputpower,thecapacitorcompensationmustbeadjustedastheoutputpowervaries.Theinteractionsamongthewindturbine,thepowernetwork,andthecapacitorcompensationareimportantaspectsofwindgenerationthatmayresultinselfexcitationandhigherharmoniccontentintheoutputcurrent.Thispaperexaminesthefactorsthatcontrolthesephenomenaandgivessomeguidelinesonhowtheycanbecontrolledoreliminated.1.IntroductionManyoftodaysoperatingwindturbineshavefixedspeedinductiongeneratorsthatareveryreliable,rugged,andlowcost.Duringnormaloperation,aninductionmachinerequiresreactivepowerfromthegridatalltimes.Themostcommonlyusedreactivepowercompensationiscapacitorcompensation.Itisstatic,lowcost.Differentsizesofcapacitorsaregenerallyneededfordifferentlevelsofgeneration.Althoughreactivepowercompensationcanbebeneficialtotheoveralloperationofwindturbines,weshouldbesurethecompensationisthepropersizeandprovidespropercontrol.Twoimportantaspectsofcapacitorcompensation,selfexcitationandharmonics,arethesubjectsofthispaper.2.PowerSystemNetworkDescriptionAdiagramrepresentingthissystemisshowninFig1.ThepowersystemcomponentsanalyzedincludethefollowingAninfinitebusandalonglineconnectingthewindturbinetothesubstationAtransformeratthepadmountCapacitorsconnectedinthelowvoltagesideofthetransformerAninductiongenerator9Fortheselfexcitation,wefocusontheturbineandthecapacitorcompensationonlytherighthalfofFig.Forharmonicanalysis,weconsidertheentirenetworkshowninFig.3.SelfExcitation3.1TheNatureofSelfExcitationinanInductionGenerator.Selfexcitationisaresultoftheinteractionsamongtheinductiongenerator,capacitorcompensation,electricalload,andmagneticsaturation.Thissectioninvestigatestheselfexcitationprocessinanoffgridinductiongenerator,knowingthelimitsandtheboundariesofselfexcitationoperationwillhelpustoeitherutilizeortoavoidselfexcitation.Fixedcapacitorsarethemostcommonlyusedmethodofreactivepowercompensationinafixedspeedwindturbine.Aninductiongeneratoralonecannotgenerateitsownreactivepoweritrequiresreactivepowerfromthegridtooperatenormally,andthegriddictatesthevoltageandfrequencyoftheinductiongenerator.Onepotentialproblemarisingfromselfexcitationisthesafetyaspect.Becausethegeneratorisstillgeneratingvoltage,itmaycompromisethesafetyofthepersonnelinspectingorrepairingthelineorgenerator.Anotherpotentialproblemisthatthegeneratorsoperatingvoltageandfrequencymayvary.Thus,ifsensitiveequipmentisconnectedtothegeneratorduringselfexcitation,thatequipmentmaybedamagedbyover/undervoltageandover/underfrequencyoperation.Inspiteofthedisadvantagesofoperatingtheinductiongeneratorinselfexcitation,somepeopleusethismodefordynamicbrakingtohelpcontroltherotorspeedduringanemergencysuchasagridlosscondition.Withtheproperchoiceofcapacitanceandresistorload,selfexcitationcanbeusedtomaintain10thewindturbineatasafeoperatingspeedduringgridlossandmechanicalbrakemalfunctions。3.2SteadyStateRepresentation.Thesteadystateanalysisisimportanttounderstandtheconditionsrequiredtosustainortodiminishselfexcitation.Asexplainedabove,selfexcitationcanbeagoodthingorabadthing,dependingonhowweencounterthesituation.Figure2showsanequivalentcircuitofacapacitorcompensatedinductiongenerator.Asmentionedabove,selfexcitationoperationrequiresthatthebalanceofbothrealandreactivepowermustbemaintained.Equation(1)givesthetotaladmittanceofthesystemshowninFig2SYMYRY0(1)whereSYeffectiveadmittancerepresentingthestatorwinding,thecapacitor,andtheloadseenbynodeMMYeffectiveadmittancerepresentingthemagnetizingbranchasseenbynodeM,referredtothestatorsideRYeffectiveadmittancerepresentingtherotorwindingasseenbynodeM,referredtothestatorsideEquation1canbeexpandedintotheequationsforimaginaryandrealpartsasshowninEqs.2and3(2)Fig.2Perphaseequivalentcircuitofaninductiongeneratorunderselfexcitationmode11Fig.3AtypicalmagnetizationcharacteristicSRstatorwindingresistanceLRLstatorwindingleakageinductanceRrotorwindingresistanceLRLrotorwindingleakageinductanceMLstatorwindingresistanceSoperatingslipoperatingfrequencyLRloadresistanceconnectedtotheterminalsCcapacitorcompensationSR阻抗

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