高压静电发生器外文翻译中英文翻译外文文献翻译.docx

高压静电发生器外文翻译中英文翻译外文文献翻译.docx

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高压静电发生器外文翻译中英文翻译外文文献翻译

HighVoltagePowerSuppliesforElectrostaticApplications

CliffScapellati,VicePresidentofEngineering

Abstract

Highvoltagepowersuppliesareakeycomponentinelectrostaticapplications.Avarietyofindustrialandscientificapplicationsofhighvoltagepowersuppliesarepresentedforthescientist,engineer,specifieranduserofelectrostatics.Industrialprocesses,forexample,requiresignificantmonitoringofoperationalconditionsinordertomaximizeproductoutput,improvequality,andreducecost.Newadvancesinpowersupplytechnologyprovidehigherlevelsofmonitoringandprocesscontrol.Scientificexperimentscanalsobeinfluencedbypowersupplyeffects.outputaccuracy,stability,rippleandregulationarediscussed.Contributingeffectssuchasoutputaccuracy,stability,rippleandregulationarediscussed.

I.Introduction

Theuseofhighvoltageinscientificandindustrialapplicationsiscommonplace.Inparticular,electrostaticscanbeutilizedforavarietyofeffects.Broadlystated,electrostaticsisthestudyofeffectsproducedbyelectricalchargesorfields.Theapplicationsofelectrostaticscanbeusedtogeneratemotionofamaterialwithoutphysicalcontact,toseparatematerialsdowntotheelementallevel,tocombinematerialstoformahomogeneousmixtureandotherpracticalandscientificuses.Bydefinition,theabilityofelectrostaticeffectstodoworkrequiresadifferenceinelectricalpotentialbetweentwoormorematerials.Inmostcases,theenergyrequiredtoforceapotentialdifferenceisderivedfromahighvoltagesource.Thishighvoltagesourcecanbeahighvoltagepowersupply.Today'shighvoltagepowersuppliesaresolidstate,highfrequencydesigns,whichprovideperformanceandcontrolunattainableonlyafewyearsago.Significantimprovementsinreliability,stability,control,sizereductions,costandsafetyhavebeenachieved.Bybeingmadeawareoftheseimprovements,theuserofhighvoltagepowersuppliesforelectrostaticapplicationscanbenefit.Additionally,uniquerequirementsofhighvoltagepowersuppliesshouldbeunderstoodastheycanaffecttheequipment,experiments,processorproducttheyareusedin.

II.OperationalPrinciplesofHighVoltagePowerSupplies

AsimplifiedschematicdiagramofahighvoltagepowersupplyisshowninFig.1.Theinputvoltagesourcemayhaveawiderangeofvoltagecharacteristics.ACsourcesof50Hzto400Hzat<24Vto480Varecommon.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,insulationbreakdowniscommonplace.Theinverterrobustnessandcontrolloopcharacteristicsmustaccountforvirtuallyanycombinationofopencircuit,shortcircuitandoperatingloadconditions.Theseconcernsaswellasreliabilityandcost,mustbeaddressedintheHighVoltagePowerSupplyInvertertopology.

Thehighfrequencyoutputoftheinverterisappliedtotheprimaryofthehighvoltagestep-uptransformer.Properhighvoltagetransformerdesignrequiresextensivetheoreticalandpracticalengineering.Understandingofmagneticsdesignmustbeappliedalongwithmaterialandprocesscontrols.Muchofthespecificexpertiseinvolvesmanagingthehighnumberofsecondaryturns,andthehighsecondaryvoltages.Duetothesefactors,coregeometry,insulationmethodsandwindingtechniquesarequitedifferentthanconventionaltransformerdesigns.Someareasofconcernare:

volts/turnratingsofthesecondarywire,layertolayerinsulatingratings,insulatingmaterialdissipationfactor,windinggeometryasitisconcernedwithparasiticsecondarycapacitanceandleakageflux,impregnationofinsulatingvarnishtowindinglayers,coronalevelandvirtuallyallotherconventionalconcernssuchasthermalmargins,andoverallcost.

Thehighvoltagemultipliercircuitsareresponsibleforrectificationandmultiplicationofthehighvoltagetransformersecondaryvoltage.Thesecircuitsusehighvoltagediodesandcapacitorsina"chargepump"voltagedoublerconnection.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,andcommandrequirementsdictate.Thisisbestaccomplishedbyafeedbackcontrolloop.Fig.2showshowfeedbacksignalscanbeusedtoregulatetheoutputofthepowersupply.Conventionalregulationofvoltageandcurrentcanbeachievedbymonitoringtheoutputvoltageandcurrentrespectively.Thisiscomparedtoadesired（reference）outputsignal.Thedifference（error）betweenthefeedbackandreferencewillcauseachangeintheinvertercontroldevice.Thiswillthenresultinachangeofpowerdeliveredtotheoutputcircuits.

Inadditiontothevoltageandcurrentregulation,otherparameterscanbepreciselyregulated.ControllingoutputpoweriseasilyaccomplishedbyanXY=Zfunction,（VI=W）,andcomparingittothedesiredoutputpowerreference.Indeed,anyvariablefoundwithinOhm'slawcanberegulated,（resistance,voltage,currentandpower）.Inaddition,endprocessparameterscanberegulatediftheyareeffectedbythehighvoltagepowersupply（i.e.coatings,flowrates,etc.）.

III.HighVoltageRegulation

Theimportanceofaregulatedsourceofhighvoltageand/orconstantcurrentiscriticaltomostapplicationsinvolvingelectrostatics.Variationsinoutputvoltageorcurrentcanhavedirecteffectsontheendresultsand,therefore,mustbeunderstoodasasourceoferror.Inhighvoltagepowersupplies,thevoltagereferencesthatareusedtoprogramthedesiredoutputcanbeeliminatedasasourceofsignificanterrorbytheuseofhighlystablevoltagereferenceICs.Typicalspecificationsofbetterthan5ppm/Careroutine.Similarly,analogICs（opamps,A/DD/A's,etc.）.canbeeliminatedasasignificantsourceoferrorbycarefulselectionofthedevices.

Thereremainsonecomponent,uniquetohighvoltagepowersupplies,whichwillbethemajorsourceofstabilityerrors:

thehighvoltagefeedbackdivider.AsseeninFig.1,thehighvoltagefeedbackdividerconsistsofaresistivedividernetwork.Thisnetworkwilldividetheoutputvoltagetoalevellowenoughtobeprocessedbythecontrolcircuits.Theproblemofstabilityinthisnetworkresultsfromthelargeresistanceofthefeedbackresistors.Valuesof>100megOhmsarecommon.（Thisistoreducepowerdissipationinthecircuitandreducetheeffectsoftemperaturechangeduetoselfheating）.Thelargeresistanceandthehighvoltageratingrequiresuniquetechnologyspecifictohighvoltageresistors.Theuniquehighvoltageresistormustbe"paired"withalowvalueresistortoinsureratiotrackingunderchangesoftemperature,voltage,humidityandtime.

Inaddition,thehighvalueofresistanceinthefeedbacknetworkmeansasusceptibilitytoverylowcurrentinterference.Itcanbeseenthatcurrentsaslowas1X10-9amp