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外文翻译风力发电中的自我激励与谐波.doc外文翻译风力发电中的自我激励与谐波.doc -- 5 元

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编号:201311171438436631    大小:1.96MB    格式:DOC    上传时间:2013-11-17
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8Self-ExcitationandHarmonicsinWindPowerGenerationE.Muljadi,C.P.ButterfieldNationalRenewableEnergyLaboratory,Golden,Colorado80401H.RomanowitzOakCreekEnergySystemsInc.,Mojave,California93501R.YingerSouthernCaliforniaEdison,Rosemead,California91770Traditionalwindturbinesarecommonlyequippedwithinductiongeneratorsbecausetheyareinexpensive,rugged,andrequireverylittlemaintenance.Unfortunately,inductiongeneratorsrequirereactivepowerfromthegridtooperate,capacitorcompensationisoftenused.Becausethelevelofrequiredreactivepowervarieswiththeoutputpower,thecapacitorcompensationmustbeadjustedastheoutputpowervaries.Theinteractionsamongthewindturbine,thepowernetwork,andthecapacitorcompensationareimportantaspectsofwindgenerationthatmayresultinself-excitationandhigherharmoniccontentintheoutputcurrent.Thispaperexaminesthefactorsthatcontrolthesephenomenaandgivessomeguidelinesonhowtheycanbecontrolledoreliminated.1.IntroductionManyoftoday’soperatingwindturbineshavefixedspeedinductiongeneratorsthatareveryreliable,rugged,andlowcost.Duringnormaloperation,aninductionmachinerequiresreactivepowerfromthegridatalltimes.Themostcommonlyusedreactivepowercompensationiscapacitorcompensation.Itisstatic,lowcost.Differentsizesofcapacitorsaregenerallyneededfordifferentlevelsofgeneration.Althoughreactivepowercompensationcanbebeneficialtotheoveralloperationofwindturbines,weshouldbesurethecompensationisthepropersizeandprovidespropercontrol.Twoimportantaspectsofcapacitorcompensation,self-excitationandharmonics,arethesubjectsofthispaper.2.PowerSystemNetworkDescriptionAdiagramrepresentingthissystemisshowninFig(1).Thepowersystemcomponentsanalyzedincludethefollowing:•Aninfinitebusandalonglineconnectingthewindturbinetothesubstation•Atransformeratthepadmount•Capacitorsconnectedinthelowvoltagesideofthetransformer•Aninductiongenerator9Fortheself-excitation,wefocusontheturbineandthecapacitorcompensationonlytherighthalfofFig.Forharmonicanalysis,weconsidertheentirenetworkshowninFig.3.Self-Excitation3.1TheNatureofSelf-ExcitationinanInductionGenerator.Self-excitationisaresultoftheinteractionsamongtheinductiongenerator,capacitorcompensation,electricalload,andmagneticsaturation.Thissectioninvestigatestheself-excitationprocessinanoff-gridinductiongenerator,knowingthelimitsandtheboundariesofself-excitationoperationwillhelpustoeitherutilizeortoavoidself-excitation.Fixedcapacitorsarethemostcommonlyusedmethodofreactivepowercompensationinafixed-speedwindturbine.Aninductiongeneratoralonecannotgenerateitsownreactivepower;itrequiresreactivepowerfromthegridtooperatenormally,andthegriddictatesthevoltageandfrequencyoftheinductiongenerator.Onepotentialproblemarisingfromself-excitationisthesafetyaspect.Becausethegeneratorisstillgeneratingvoltage,itmaycompromisethesafetyofthepersonnelinspectingorrepairingthelineorgenerator.Anotherpotentialproblemisthatthegenerator’soperatingvoltageandfrequencymayvary.Thus,ifsensitiveequipmentisconnectedtothegeneratorduringself-excitation,thatequipmentmaybedamagedbyover/undervoltageandover/underfrequencyoperation.Inspiteofthedisadvantagesofoperatingtheinductiongeneratorinself-excitation,somepeopleusethismodefordynamicbrakingtohelpcontroltherotorspeedduringanemergencysuchasagridlosscondition.Withtheproperchoiceofcapacitanceandresistorload,self-excitationcanbeusedtomaintain10thewindturbineatasafeoperatingspeedduringgridlossandmechanicalbrakemalfunctions。3.2Steady-StateRepresentation.Thesteady-stateanalysisisimportanttounderstandtheconditionsrequiredtosustainortodiminishself-excitation.Asexplainedabove,self-excitationcanbeagoodthingorabadthing,dependingonhowweencounterthesituation.Figure2showsanequivalentcircuitofacapacitorcompensatedinductiongenerator.Asmentionedabove,self-excitationoperationrequiresthatthebalanceofbothrealandreactivepowermustbemaintained.Equation(1)givesthetotaladmittanceofthesystemshowninFig(2):SY+'MY+'RY=0(1)whereSY=effectiveadmittancerepresentingthestatorwinding,thecapacitor,andtheloadseenbynodeM'MY=effectiveadmittancerepresentingthemagnetizingbranchasseenbynodeM,referredtothestatorside'RY=effectiveadmittancerepresentingtherotorwindingasseenbynodeM,referredtothestatorsideEquation1canbeexpandedintotheequationsforimaginaryandrealpartsasshowninEqs.2and3:(2)Fig.2Perphaseequivalentcircuitofaninductiongeneratorunderself-excitationmode11Fig.3AtypicalmagnetizationcharacteristicSR=statorwindingresistanceLRL=statorwindingleakageinductance'R=rotorwindingresistance'LRL=rotorwindingleakageinductance'ML=statorwindingresistanceS=operatingslip=operatingfrequencyLR=loadresistanceconnectedtotheterminalsC=capacitorcompensationSR=阻抗
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