外文资料翻译--高压静电电源应用.doc

1HighVoltagePowerSuppliesforElectrostaticApplicationsCliffScapellati,VicePresidentofEngineeringAbstractHighvoltagepowersuppliesareakeycomponentinelectrostaticapplications.Avarietyofindustrialandscientificapplicationsofhighvoltagepowersuppliesarepresentedforthescientist,engineer,specifieranduserofelectrostatics.Industrialprocesses,forexample,requiresignificantmonitoringofoperationalconditionsinordertomaximizeproductoutput,improvequality,andreducecost.Newadvancesinpowersupplytechnologyprovidehigherlevelsofmonitoringandprocesscontrol.Scientificexperimentscanalsobeinfluencedbypowersupplyeffects.outputaccuracy,stability,rippleandregulationarediscussed.Contributingeffectssuchasoutputaccuracy,stability,rippleandregulationarediscussed.I.IntroductionTheuseofhighvoltageinscientificandindustrialapplicationsiscommonplace.Inparticular,electrostaticscanbeutilizedforavarietyofeffects.Broadlystated,electrostaticsisthestudyofeffectsproducedbyelectricalchargesorfields.Theapplicationsofelectrostaticscanbeusedtogeneratemotionofamaterialwithoutphysicalcontact,toseparatematerialsdowntotheelementallevel,tocombinematerialstoformahomogeneousmixtureandotherpracticalandscientificuses.Bydefinition,theabilityofelectrostaticeffectstodoworkrequiresadifferenceinelectricalpotentialbetweentwoormorematerials.Inmostcases,theenergyrequiredtoforceapotentialdifferenceisderivedfromahighvoltagesource.Thishighvoltagesourcecanbeahighvoltagepowersupply.Todayshighvoltagepowersuppliesaresolidstate,highfrequencydesigns,whichprovideperformanceandcontrolunattainableonlyafewyearsago.Significantimprovementsinreliability,stability,control,sizereductions,costandsafetyhavebeenachieved.Bybeingmadeawareoftheseimprovements,theuserofhighvoltagepowersuppliesforelectrostaticapplicationscanbenefit.Additionally,uniquerequirementsofhighvoltagepowersuppliesshouldbeunderstoodastheycanaffecttheequipment,experiments,processorproducttheyareusedin.II.OperationalPrinciplesofHighVoltagePowerSupplies2AsimplifiedschematicdiagramofahighvoltagepowersupplyisshowninFig.1.Theinputvoltagesourcemayhaveawiderangeofvoltagecharacteristics.ACsourcesof50Hzto400Hzat24Vto480Varecommon.DCsourcesrangingfrom5Vto300Vcanalsobefound.Itiscriticalfortheusertounderstandtheinputvoltagerequirementasthiswillimpactoverallsystemuseanddesign.RegulatoryagenciessuchasUnderwritersLaboratory,CanadianStandardsAssociation,IECandothersarehighlyinvolvedwithanycircuitsconnectedtothepowergrid.Inadditiontopoweringthemaininvertercircuitsofthepowersupply,theinputvoltagesourceisalsousedtopowerauxiliarycontrolcircuitsandotherancillarypowerrequirements.Theinputfilterstageprovidesconditioningoftheinputvoltagesource.Thisconditioningisusuallyintheformofrectificationandfilteringinacsources,andadditionalfilteringindcsources.Overloadprotection,EMI,EMCandmonitoringcircuitscanalsobefound.Theoutputoftheinputfilteristypicallyadcvoltagesource.Thisdcvoltageprovidestheenergysourcefortheinverter.Theinverterstageconvertsthedcsourcetoahighfrequencyacsignal.Manydifferentinvertertopologiesexistforpowersupplies.Thehighvoltagepowersupplyhasuniquefactorswhichmaydictatethebestinverterapproach.TheinvertergeneratesahighfrequencyacsignalwhichissteppedupbytheHVtransformer.Thereasonforthehighfrequencygenerationistoprovidehighperformanceoperationwithreducedsizeofmagneticsandripplereductionstoragecapacitors.Aproblemiscreatedwhenatransformerwithahighstepupratioiscoupledtoahighfrequencyinverter.Thehighstepupratioreflectsaparasiticcapacitanceacrosstheprimaryofthehighvoltagetransformer.Thisisreflectedasa(Nsec:Npri)2function.Thislargeparasiticcapacitorwhichappearsacrosstheprimaryofthetransformermustbeisolatedfromtheinverterswitchingdevices.Ifnot,abnormallyhighpulsecurrentswillbepresentintheinverter.Anotherparameterwhichiscommontohighvoltagepowersuppliesisawiderangeofloadoperations.Duetothepresenceofhighvoltage,insulationbreakdownis3commonplace.Theinverterrobustnessandcontrolloopcharacteristicsmustaccountforvirtuallyanycombinationofopencircuit,shortcircuitandoperatingloadconditions.Theseconcernsaswellasreliabilityandcost,mustbeaddressedintheHighVoltagePowerSupplyInvertertopology.Thehighfrequencyoutputoftheinverterisappliedtotheprimaryofthehighvoltagestep-uptransformer.Properhighvoltagetransformerdesignrequiresextensivetheoreticalandpracticalengineering.Understandingofmagneticsdesignmustbeappliedalongwithmaterialandprocesscontrols.Muchofthespecificexpertiseinvolvesmanagingthehighnumberofsecondaryturns,andthehighsecondaryvoltages.Duetothesefactors,coregeometry,insulationmethodsandwindingtechniquesarequitedifferentthanconventionaltransformerdesigns.Someareasofconcernare:volts/turnratingsofthesecondarywire,layertolayerinsulatingratings,insulatingmaterialdissipationfactor,windinggeometryasitisconcernedwithparasiticsecondarycapacitanceandleakageflux,impregnationofinsulatingvarnishtowindinglayers,coronalevelandvirtuallyallotherconventionalconcernssuchasthermalmargins,andoverallcost.Thehighvoltagemultipliercircuitsareresponsibleforrectificationandmultiplicationofthehighvoltagetransformersecondaryvoltage.Thesecircuitsusehighvoltagediodesandcapacitorsinachargepumpvoltagedoublerconnection.Aswiththehighvoltagetransformer,highvoltagemultiplierdesignrequiresspecificexpertise.Inadditiontorectificationandmultiplication,highvoltagecircuitsareusedinthefilteringoftheoutputvoltage,andinthemonitoringofvoltageandcurrentforcontrolfeedback.Outputimpedancemayintentionallybeaddedtoprotectagainstdischargecurrentsfromthepowersupplystoragecapacitors.Thesehighvoltagecomponentsaretypicallyinsulatedfromgroundleveltopreventarcover.Theinsulationmaterialsvarywidely,buttypicalmaterialsare:air,SF6,insulatingoil,solidencapsulants(RTV,epoxy,etc.).Theinsulatingmaterialselectionandprocesscontrolmaybethemostimportantaspectofareliablehighvoltagedesign.Controlcircuitskeepallofthepowerstagesworkingtogether.CircuitcomplexitycanrangefromoneanalogI.C.toalargenumberofI.C.sandevenamicroprocessorcontrollingandmonitoringallaspectsofthehighvoltagepower.However,thebasicrequirementwhicheverycontrolcircuitmustmeetistopreciselyregulatetheoutputvoltageandcurrentasload,inputpower,andcommand4requirementsdictate.Thisisbestaccomplishedbyafeedbackcontrolloop.Fig.2showshowfeedbacksignalscanbeusedtoregulatetheoutputofthepowersupply.Conventionalregulationofvoltageandcurrentcanbeachievedbymonitoringtheoutputvoltageandcurrentrespectively.Thisiscomparedtoadesired(reference)outputsignal.Thedifference(error)betweenthefeedbackandreferencewillcauseachangeintheinvertercontroldevice.Thiswillthenresultinachangeofpowerdeliveredtotheoutputcircuits.Inadditiontothevoltageandcurrentregulation,otherparameterscanbepreciselyregulated.ControllingoutputpoweriseasilyaccomplishedbyanXY=Zfunction,(VI=W),andcomparingittothedesiredoutputpowerreference.Indeed,anyvariablefoundwithinOhmslawcanberegulated,(resistance,voltage,currentandpower).Inaddition,endprocessparameterscanberegulatediftheyareeffectedbythehighvoltagepowersupply(i.e.coatings,flowrates,etc.).III.HighVoltageRegulatio