2英文翻译.docx

2英文翻译.docx

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2英文翻译

英文

Designconsiderationsofmicroprocessor-controlledmultiphasebatterychargerwithfast-chargingstrategy.J.B.WangandC.Y.Chuang

Abstract:

Amicroprocessor-controlledmultiphasebatterycharger,toenhancecurrentutilisationofthepowersupplyunit（PSU）andalsoavoidovervoltageproblemsduringregenerativeperiods,ispresented.ThechargerconsistsofaPSUandthreesetsofindependentcurrent-controlledbuck-derivedconvertersthatadopttime-shiftedpulse-chargingcurrentcommands.Owingtothemultiphasepulse-chargingcurrentcontrolscheme,theoutput-currentutilisationofthePSUcanbeimprovedremarkably.Moreover,thenegativepulse-dischargingcurrentisrecycledbacktothenextphasepositivepulse-chargingcurrent,andthuscompensatesfortheovervoltageofthePSUduringthisperiod.AccordingtooutputvoltagespecificationofthePSU,maximumoutput-powerlimitation,dutyratioandcurrentripplesoftheoutputinductor,thedesiredoutputvoltageandmaximumamplitudeofthepulse-chargingcurrentcommandcanbedeterminedforthesmallcapacitysealedlead-acidbattery.Thedesignproceduresofthemultiphasebatterychargeraregiven.Finally,somesimulationandexperimentalresultstoshowtheovervoltageproblemofthePSU,duringnegativedischargingperiod,canbeimprovedsignificantlybytheproposedmultiphasebatterychargingscheme.

1Introduction

Batteriesarecommonlyusedincomputersystems,communicationssystemsandelectricalvehiclesaselectricalenergystorageelements.Althoughtherearemanykindsofbatteriesthatcanbeused,thelead-acidbatterycanaffordtostoreareasonableamountofelectricalenergyandisadoptedwidelyintheindustrialfield.Ingeneral,thelead-acidbatterycanbeclassifiedintwocategories:

thevalve-regulatedtypeandthesealedtype.Avalve-regulatedlead-acidbatteryisoftenusedastheback-uppowerofacommunicationsystem,inwhichthebatterybankconsistsofaseriesofbatterycells.Totakecareofthechargingconditionofeachbatterycell,anequalizationcontrolmethodisoftenusedtoextendthelifeofthebattery[1–3].Asthechemicalreactionofthecharginganddischargingprocessesofthelead-acidbatterywillagitatetheelectrolyteandproducehydrogengas,thiswillleadtoreductionoftheelectrolyteandthestored-energycapability.

Furthermore,theallowableusablelifeofthebatterycanbealsoreducedsignificantly,thereforeadelicatedesignedbatterymonitoringsystemmustbeusedtosupervisetheoperatingconditionofthebattery.Analternativemethodtoimprovethisproblemistouseasealedlead-acidbatterythathastheadvantagesofbeingmaintenance-freeanddoesnotrequireequalizationcontrol.Itisverysuitabletouseinanenclosurespacebecausenoleakageoccurs.

Howtoshortenthechargingtimeofasealedlead-acidbatteryandextenditsusablelifeisaimportantdesignproblemforacharger,andsotherearemanyfast-chargingschemesthathavebeenproposedtoimprovethisproblem[4–6].Amongthesechargingmethods,thepulse-chargingschemeisthemostattractiveinrecentyears.Useofthepulse-chargingmethodhastheadvantagesofreducingchargingtimeandextendingtheusedlifeofthebattery.Ingeneral,atypicalpulse-chargingcycleconsistsofapositivepulse-chargingcurrent,anegativepulse-dischargingcurrentandisfollowedbyaperiodofwaitingtime.Theaforementionedprocessesarerepeateduntilthebatteryisfullycharged.Therearemanytypesofpowerconvertersthatcanimplementthepulsechargingscheme[1–7],butthebuck-derivedconverteristhemosteffective.Inapreviousstudy[4],thedifferentpulse-chargingcurrentamplitudeandperiodshavebeenmeasuredandcomparedtoshowtheeffectivenessofthepulse-chargingmethod,whichcanreducechargingtimeandextendbatterylife.However,theenergyofthenegativedischargingcurrentisreleasedthroughadissipatedresistorand,thus,reducedtheefficiencyofthecharger.Toimprovethisproblem,nondissipatedandregenerativepulse-chargingcontrolmethodswereproposed[5,6].Bothmethodsusedthetopologyofthebuck-derivedconverter.Thebuckoperationisusednormallyinpositivepulse-chargingcurrentperiod,whileonthecontrary,theboostoperationistorecyclethedischargingpulseenergybacktothepowersupplyunit（PSU）.Owingtothenonisolatedbuck-derivedconverter,anisolatedPSUmustbeusedtoprovidepowertothedownstreamconvertersandestablishgalvanicisolationtoprimarycircuits,suchthatsafetyrequirementcanbemet.Unfortunately,theoutputvoltageofthePSUmayfluctuateduetothiskindofpulseloadcurrent.Inparticular,theregenerativenegativepulse-dischargingcurrentrecycledbacktothePSUwillcauseanovervoltage（OVP）problemtotriggerprotectioncircuitsandturn-offthePSU.Hence,ableedingresistorisoftenplacedattheoutputofthePSUtoimprovethisproblem,buttheefficiencyofthechargerwillbefurtherreduced,thereforethepracticaldesignconsiderationbetweenPSUandbuck-derivedconverterincorporatedwithfast-chargingschememustbestudiedindetail.

Themajorpurposeofthispaperisnotonlytostudytheovervoltageproblemrecycledbythenegativepulsedischargingcurrentofthebuck-derivedconvertertothePSU,butalsotoproposeamultiphasepulse-chargingschemetofurtherimprovethisproblemandincreasethecurrentutilisationofthePSU.2Microprocessor-controlledmultiphasebatterychargerFig.1showstheblockdiagramofthedesignedmicroprocessor-controlledmultiphasebatterychargerwhichconsistsofapowersupplyunit,threesetsofthecurrent-controlledbuck-derivedconverters,pulse-chargingcurrentcommandgeneratorandaPICmicroprocessor.Theisolatedpowersupplyunitisusedtoprovidebulkpowertodownstreambatterychargerwithpulse-chargingschemeandalsosupportagalvanicisolationtoprimarysidecircuitsduetothenonisolatedbuck-derivedconvertertopology.TheconfigurationofthePSUdepictedinFig.2consistsofapower-factor-correction（PFC）convertertoallowtheinputcurrentharmonicsothatitcanmeettheIEC61000-3-2,aforwardconverterprovidingmainoutputpowertochargersandaflybackconvertertobuildtheauxiliarypowersourcetothecontrolcircuits.Furthermore,themainoutputvoltageoftheforwardconverteris24V,whichcanprovideamaximumcurrentof15Athatisenoughforasmall-capacitysealedlead-acidbatterytoadoptthefast-chargingscheme.Toreducethesizeofthepowersupplyeffectively,theswitchingfrequencyofthisPSUisdesignedat70kHz,thereforetheformfactorofthisPSUcanbereducedtothesizeofanATX12Vpowersupplyofanordinarypersonalcomputer.WhentheACinputlinevoltageispresentedandgreaterthan85V,theflybackconverterstartsoperatingtobuildtheauxiliarypowersourceforthecontrolcircuits,andthenthePFCconverteroperatestoproducenominalbulkvoltage.Simultaneously,thePIC16F877microprocessorbeginstoinitialiseprogramsettingandcontrolI/Opins.Whenthemicroprocessordetectsthatthechargingcontrolsignalisactivated,thentheforwardconverterwillturn-onandprovide24Vand+12Vpowertothechargers.5candd.Inthiscondition,thePSUoperatingatno-loadconditioncorrespondstotheconverteratboostoperation,theenergyofthedischargingpulsecurrentisrecycledbacktotheoutputcapacitorofthePSUthroughtheboostinductorandQU.TheaccumulatedchargesoftheoutputcapacitorswillleadtoincreasetheoutputvoltageofthePSU,andthusmaytriggerovervoltageprotectiontoturn-offPSU.Ableedingresistorisfrequentlyaddedtoreleasethisenergywiththepenaltyoflosses.Finally,thepulse-chargingcurrentcommandgoesintoawaitingtimeTWandthenrepeatsnextfast-chargingcycleuntilthebatteryisfullycharged.Duringthewaitingperiod,thechargingcurrenttracksazero-currentcommand,andthusincreasestheswitchinglossesofthebuck-derivedconverter,thereforeadisablesignalisgeneratedfrommicroprocessortoturn-offthePWMsignalsofthebuck-derivedconverterduringwaitingperiod,andthusimprovestheefficiencyofthecharger.

3Designandanalysis

3.1Buck-derivedconverter

Thefirststeptodesignthemultiphasebuck-derivedconverterwithpulse-chargingmethod,asshowninFig.1,istodetermineareasonableoutputvoltageofthePSUandpulsechargingcurrentcommandbasedonthemaximumoutputpowerlimitation.SupposethevariationsoftheoutputvoltageofthePSUandbatteryvoltagearesmallduringtheswitchingintervalofthebuck-derivedconverterand,also,theequivalentserialresistanceoftheconverterissmallenoughtobeneglected,wecanfindthecurrentdeviationsoftheoutputinductorDiLduringbuckchargingandboostdischargingoperationasfollows

WhereVout,VBat,Dbuck,DboostandTsdenotetheoutputvoltageofthePSU,batteryvoltage,buckdutyratio,boostdutyratioandswitchingperiodofthebuck-derivedconverter,respectively.Obviously,alargeroutputinductorvaluewillreducethecurrentdeviationtolettheconverteroperatetocontinuecurrentmodeeasily.However,therewillexistalargercurrenttrackingerrorattherisingandfallingedgesofthepulse-chargingcurrent,duetoasmallercurrentslewrate,especiallywhenusingthelargeroutputinductancewillcontributealotofrecycledenergyduringthefallingedgeofthenegative-pulse-dischargingperiodandthusincreasetheoutputvoltageofthePSU.Ontheotherhand,theexcellentcurrenttrackingresponsecanbeobtainedbyusingasmalloutputinductor,butitalsoincreasesthecurrentrippleofthatinductor.Inthiscase,theeffectivechargingcurrentisreducedremark