外文翻译风力发电中的自我激励与谐波.docx

外文翻译风力发电中的自我激励与谐波.docx

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外文翻译风力发电中的自我激励与谐波

Self-ExcitationandHarmonicsinWindPowerGeneration

E.Muljadi，C.P.Butterfield

NationalRenewableEnergyLaboratory,Golden,Colorado80401

H.Romanowitz

OakCreekEnergySystemsInc.,Mojave,California93501

R.Yinger

SouthernCaliforniaEdison,Rosemead,California91770

Traditionalwindturbinesarecommonlyequippedwithinductiongeneratorsbecausetheyareinexpensive,rugged,andrequireverylittlemaintenance.Unfortunately,inductiongeneratorsrequirereactivepowerfromthegridtooperate，capacitorcompensationisoftenused.Becausethelevelofrequiredreactivepowervarieswiththeoutputpower,thecapacitorcompensationmustbeadjustedastheoutputpowervaries.Theinteractionsamongthewindturbine,thepowernetwork,andthecapacitorcompensationareimportantaspectsofwindgenerationthatmayresultinself-excitationandhigherharmoniccontentintheoutputcurrent.Thispaperexaminesthefactorsthatcontrolthesephenomenaandgivessomeguidelinesonhowtheycanbecontrolledoreliminated.

1．Introduction

Manyoftoday’soperatingwindturbineshavefixedspeedinductiongeneratorsthatareveryreliable,rugged,andlowcost.Duringnormaloperation,aninductionmachinerequiresreactivepowerfromthegridatalltimes.Themostcommonlyusedreactivepowercompensationiscapacitorcompensation.Itisstatic,lowcost.Differentsizesofcapacitorsaregenerallyneededfordifferentlevelsofgeneration.

Althoughreactivepowercompensationcanbebeneficialtotheoveralloperationofwindturbines,weshouldbesurethecompensationisthepropersizeandprovidespropercontrol.Twoimportantaspectsofcapacitorcompensation,self-excitationandharmonics,arethesubjectsofthispaper.

2．PowerSystemNetworkDescription

AdiagramrepresentingthissystemisshowninFig

（1）.Thepowersystemcomponentsanalyzedincludethefollowing:

•Aninfinitebusandalonglineconnectingthewindturbinetothesubstation

•Atransformeratthepadmount

•Capacitorsconnectedinthelowvoltagesideofthetransformer

•Aninductiongenerator

Fortheself-excitation,wefocusontheturbineandthecapacitorcompensationonlytherighthalfofFig.Forharmonicanalysis,weconsidertheentirenetworkshowninFig.

3.Self-Excitation

3.1TheNatureofSelf-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-excitationcanbeusedtomaintainthewindturbineatasafeoperatingspeedduringgridlossandmechanicalbrakemalfunctions。

3.2Steady-StateRepresentation.

Thesteady-stateanalysisisimportanttounderstandtheconditionsrequiredtosustainortodiminishself-excitation.Asexplainedabove,self-excitationcanbeagoodthingorabadthing,dependingonhowweencounterthesituation.Figure2showsanequivalentcircuitofacapacitorcompensatedinductiongenerator.Asmentionedabove,self-excitationoperationrequiresthatthebalanceofbothrealandreactivepowermustbemaintained.Equation

（1）givesthetotaladmittanceofthesystemshowninFig

（2）:

++=0

（1）

where

=effectiveadmittancerepresentingthestatorwinding,thecapacitor,andtheloadseenbynodeM

=effectiveadmittancerepresentingthemagnetizingbranchasseenbynodeM,referredtothestatorside

=effectiveadmittancerepresentingtherotorwindingasseenbynodeM,referredtothestatorside

Equation1canbeexpandedintotheequationsforimaginaryandrealpartsasshowninEqs.2and3:

（2）

Fig.2Perphaseequ