电气类外文翻译.docx

电气类外文翻译.docx

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电气类外文翻译

1、外文原文（复印件）

A:

TheUtilityInterfacewithPowerElectronicSystem

Introduction

Wediscussedvariouspowerlinedisturbancesandhowpowerelectronicconverterscanperformaspowerconditionersanduninterruptiblepowersuppliestopreventthesepowelinedisturbancesfromdisruptingtheoperationofcriticalloadssuchascomputersusedforcontrollingimportantprocesses,medicalequipment,andthelike.However,allpowerelectronicconverters（includingthoseusedtoprotectcriticalloads）canaddtotheinherentpowerlinedisturbancesbydistortingtheutilitywaveformduetoharmoniccurrentsinjectedintotheutilitygridandbyproducingelectromagneticinterference,Toillustratetheproblemsduetocurrentharmonicsihintheinputcurrentisofapowerelectronicload,considerthesimpleblockdiagramofFig.1-6A-1.Duetothefinite（non-zero）internalimpedanceoftheutilitysourcewhichissimplyrepresentedbyLsinFig.l-6A-1,thevoltagewaveformatthepointofcommoncouplingtotheotherloadswillbecomedistorted,whichmaycausethemtomalfunction.Inadditiontothevoltagewaveformdistortion,someotherproblemsduetotheharmoniccurrentsareasfollows:

additionalheatingandpossiblyovervoltages（duetoresonanceconditions）intheutility'sdistributionandtransmissionequipment,errorsinmeteringandmalfunctionofutilityrelays,interferencewithcommunicationandcontrolsignals,andsoon.Inadditiontotheseproblems,phase-controlledconverterscausenotchesintheutilityvoltagewaveformandmanydrawpowerataverylowdisplacementpowerfactorwhichresultsinaverypoorpowerfactorofoperation.

Theforegoingdiscussionshowsthattheproliferationofpowerelectronicsystemsandloadshasthepotentialforsignificantnegativeimpactontheutilitiesthemselves,aswellasontheircustomers.Oneapproachtominimizethisimpactistofiltertheharmoniccurrentsandtheelectromagneticinterference（EMI）producedbythepowerelectronicloads.Abetteralternative,inspiteofasmallincreaseintheinitialcost,maybetodesignthepowerelectronicequipmentsuchthattheharmoniccurrentsandtheEMIarepreventedorminimizedfrombeinggeneratedinthefirstplace.Both,theconcernsabouttheutilityinterfaceandthedesignofpowerelectronicequipmenttominimizetheseconcernsarediscussedhere.

GenerationofCurrentHarmonics

Inmostpowerelectronicequipment,suchasswitch-modedcpowersupplies,uninterruptiblepowersupplies（UPS）,andacanddcmotordrives,ac-to-dcconvertersareusedastheinterfacewiththeutilityvoltagesource.Commonly,aline-frequencydioderectifierbridgeasshowninFig.1-6A-2isusedtoconvertlinefrequencyacintodc.TherectifieroutputisadcvoltagewhoseaveragemagnitudeUdisuncontrolled.AlargefiltercapacitorisusedattherectifieroutputtoreducetherippleinthedcvoltageUd.ThedcvoltageUdandthedccurrentIdareunipolarandunidirectional,respectively.Therefore,thepowerflowisalwaysfromtheutilityacinputtothedcside.Theseline-frequencyrectifierswithafaltercapacitoratthedcsidewerediscussedindetailinothersection.

Aclassofpowerelectronicsystemsutilizesline-frequencythyristor-controlledac-to-dcconvertersastheutilityinterface.Intheseconverters,whichwerediscussedindetail,theaveragedcoutputvoltageUdiscontrollableinmagnitudeandpolarity,butthedccurrentIdremainsunidirectional.Becauseofthereversiblepolarityofthedcvoltage,thepowerflowthroughtheseconvertersisreversible.Aswaspointedout,thetrendistousetheseconvertersonlyatveryhighpowerlevels,suchasinhigh-voltagedctransmissionsystems.Becauseoftheveryhighpowerlevels,thetechniquestoffdterthecurrentharmonicsandtoimprovethepowerfactorofoperationarequitedifferentintheseconverters,asdiscussedinothersection,thanthosefortheline-frequencydioderectifiers.

Thedioderectifiersareusedtointerfacewithboththesingle-phaseandthethree-phaseutilityvoltages.Typicalaccurrentwaveformswithminimalfilteringwereshowninothersection.Typicalharmonicsinasingle-phaseinputcurrentwaveformarelistedinTable1-6A-1,wheretheharmoniccurrentsIhareexpressedasaratioofthefundamentalcurrentIl.AsisshownbyTable1-6A-l,suchcurrentwaveformsconsistoflargeharmonicmagnitudes.Therefore,forafiniteinternalper-phasesourceimpedanceLs,thevoltagedistortionatthepointofcommoncouplinginFig.1-6A-1canbesubstantial.ThehighertheinternalsourceinductanceLs,thegreaterwouldbethevoltagedistortion.

CurrentHarmonicsandPowerFactor

Aswediscussedinothersection,thepowerfactorPFatwhichanequipmentoperatesistheproductofthecurrentratioIl/IsandthedisplacementpowerfactorDPF:

InEq.（1-6A-I）,thedisplacementpowerfactorequalsthecosineoftheangleΦ1.ThecurrentratioIl/IsinEq.（1-6A-l）istheratioofthermsvalueofthefundamentalfrequencycurrentcomponenttothermsvalueofthetotalcurrent.Thepowerfactorindicateshoweffectivelytheequipmentdrawspowerfromtheutility;atalowpowerfactorofoperationforagivenvoltageandpowerlevel,thecurrentdrawnbytheequipmentwillbelarge,thusrequitingincreasedvolt-ampereratingsoftheutilityequipmentsuchastransformers,transmissionlines,andgenerators.Theimportanceofthehighpowerfactorhasbeenrecognizedbyresidentialandofficeequipmentmanufacturersfortheirownbenefittomaximizethepoweravailablefromawalloutlet.Forexamplefroma120V,15Aelectricalcircuitinabuilding,themaximumpoweravailableis1.8kW,providedthepowerfactorisunity.Themaximumpowerthatcanbedrawnwithoutexceedingthe15Alimitdecreaseswithdecreasingpowerfactor.Theforegoingargumentsindicatetheresponsibilityanddesirabilityonthepartoftheequipmentmanufacturersanduserstodesignpowerelectronicequipmentwithahighpowerfactorofoperation.ThisrequiresthatthedisplacementpowerfactorDPFshouldbehighinEq.（1-6A-I）.Moreover,thecurrentharmonicsshouldbelowtoyieldahighcurrentratioI1/IsinEq.（1-6A-1）.

B:

AThree-phasePre-converterforInductionHeatingMOSFET

BridgeInverters

Introduction

Highfrequencypowersupplies,basedonMOSFETbridgeinverters,arealreadywidelyusedforinductionheatingapplications.Theseunitsrequiredcinputvoltagesofabout400VtoallowefficientoperationoftheMOSFETsemployed.Thissupplyvoltageisusuallyobtainedbyusingathree-phaserectifierstage,appropriatesmoothingcomponentsorbyemployingthyristorphase-anglecontroltothemainssupply.Thiskindofmainsfrequencypowersupplyallowsoutputpowercontroloftheinductionheater,butitsuffersfromhighlydistortedinputcurrentwaveformswithalowpowerfactor.Newlegislationhasbeenproposedtolimitthemaximummagnitudeofharmonicsdrawnfromthemainssupplyanddifferentstrategieshavebeensuggestedtoreducemainspollution.

Investigationshavebeenmadetoreplacemainsfrequencypowersuppliesbyswitchedmodepre-converters.Switchedmodeconverterscanbedesignedtodrawsinusoidalinputcurrentsthusavoidingtheneedforlargeandexpensivemainsfrequencyfilters.Atthesametimetheseconvertersprovideoutputpowercontrolandimplementationofasmallsizehighfrequencyisolationtransformer.Powerfactorcorrectedthree-phaseac-dcswitchedmodeconvertersystemshaveusuallybeenobtainedusingthreeidenticalsingle-phaseconverterswithacommonoutputfilter.Thesesystemsovercomeproblemsofmainspollution,butsufferfromthedisadvantageofarelativelylargenumberofcomponentsandtheneedforcomplicatedcontrolandsynchronizationcircuits.Toreducecomponentcosts,astructurebasedonaboostconverterwiththree-phaseinputdioderectifierhasbeensuggested.However,whenoperateddirect-off-linefromathree-phase415Vmainssupply,thisstructureleadstohighoutputvoltagesabovelkV.

Inthispaper,anovelmethodtoachievepowerfactorcorrectionforthree-phaseactodcpowerconvertersisdescribed.Theproposedtopologyisbasedonthebuckconverterandallowsthereforeoutputvoltagestobebelowthemaximuminputvoltage.Theproposedtopologyutilizesathree-phasedioderectifieratthemainsinputandasingleactiveswitchingdevice.Theactiveswitchingdeviceoperatesunderzero-currentswitchingconditions,resultinginveryhighconverterefficienciesandlowRFIemissions.Zero-currentswitchingtechniqueallowssemiconductordevicestobeoperatedatmuchhigherswitchingfrequenciesandwithreduceddriverequirementscomparedwithconventionalswitchedmodeoperation.

Theproposedsingle-endedresonantconverterwiththree-phasedioderectifieroffersgoodopportunitiesformediumpower,actodcapplications.Itcombinessimplicityandeaseofcontrolwithhighconverterefficiencyandhighoutputpowercapabilities.Itwillbeshowninthepaper,thatthesecharacteristicsmaketheconverterverysuitableasadirectreplacementfortheconventionalmainsfrequencypowersupplyusedtosupplyinductionheatingMOSFETbridgeinverters.

GeneralDescription

AblockdiagramoftheproposedinductionheatingsystemisshowninFig.1-6B-1.Block1representsthepre-converterthatproducesthedcsupplyvoltagetofeedtotheRFMOSFETbridgeinverter.Itsoutputvoltageshouldbecontrollableoverawiderangetocontroltheoutputpoweroftheinverteranditmustbeabletooperatewithawiderangeofloadresistancetocompensateloadchangesoftheinductionheatinginverterstage.Thepre-convertershouldoperatedirect-off-linefromathree-phase415Vmainssupply,drawing