基于SG3525设计单相正弦波SPWM逆变电源外文翻译.docx
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基于SG3525设计单相正弦波SPWM逆变电源外文翻译.docx
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基于SG3525设计单相正弦波SPWM逆变电源外文翻译
外文文献
Switched-modepowersupply
Aswitched-modepowersupply(alsoswitching-modepowersupply,SMPS,orsimplyswitcher)isanelectronicpowersupplyunit(PSU)thatincorporatesaswitchingregulator.Whilealinearregulatormaintainsthedesiredoutputvoltagebydissipatingexcesspowerinapasspowertransistor,theswitched-modepowersupplyswitchesapowertransistorbetweensaturation(fullon)andcutoff(completelyoff)withavariabledutycyclewhoseaverageisthedesiredoutputvoltage.Itswitchesatamuch-higherfrequency(tenstohundredsofkHz)thanthatoftheACline(mains),whichmeansthatthetransformerthatitfeedscanbemuchsmallerthanoneconnecteddirectlytotheline/mains.Switchingcreatesarectangularwaveformthattypicallygoestotheprimaryofthetransformer;typicallyseveralsecondariesfeedrectifiers,seriesinductors,andfiltercapacitorstoprovidevariousDCoutputswithlowripple.
Themainadvantageofthismethodisgreaterefficiencybecausetheswitchingtransistordissipateslittlepowerinthesaturatedstateandtheoffstatecomparedtothesemiconductingstate(activeregion).Otheradvantagesincludesmallersizeandlighterweight(fromtheeliminationoflowfrequencytransformerswhichhaveahighweight)andlowerheatgenerationduetohigherefficiency.Disadvantagesincludegreatercomplexity,thegenerationofhighamplitude,highfrequencyenergythatthelow-passfiltermustblocktoavoidelectromagneticinterference(EMI),andaripplevoltageattheswitchingfrequencyandtheharmonicfrequenciesthereof.
Anoteaboutterminology
Althoughtheterm"powersupply"hasbeeninusesinceradioswerefirstpoweredfromtheline/mains,thatdoesnotmeanthatitisasourceofpower,inthesensethatabatteryprovidespower.Itissimplyadevicethat(usually)acceptscommercialACpowerandprovidesoneormoreDCoutputs.Itwouldbemorecorrectlyreferredtoasapowerconverter,butlongusagehasestablishedtheterm.
Classification
SMPScanbeclassifiedintofourtypesaccordingtotheinputandoutputwaveforms:
ACin,DCout:
rectifier,off-lineconverterinputstage
DCin,DCout:
voltageconverter,orcurrentconverter,orDCtoDCconverter
ACin,ACout:
frequencychanger,cycloconverter,transformer
DCin,ACout:
inverter
Inputrectifierstage
IftheSMPShasanACinput,thenthefirststageistoconverttheinputtoDC.Thisiscalledrectification.Therectifiercircuitcanbeconfiguredasavoltagedoublerbytheadditionofaswitchoperatedeithermanuallyorautomatically.Thisisafeatureoflargersuppliestopermitoperationfromnominally120voltor240voltsupplies.TherectifierproducesanunregulatedDCvoltagewhichisthensenttoalargefiltercapacitor.ThecurrentdrawnfromthemainssupplybythisrectifiercircuitoccursinshortpulsesaroundtheACvoltagepeaks.Thesepulseshavesignificanthighfrequencyenergywhichreducesthepowerfactor.SpecialcontroltechniquescanbeemployedbythefollowingSMPStoforcetheaverageinputcurrenttofollowthesinusoidalshapeoftheACinputvoltagethusthedesignershouldtrycorrectingthepowerfactor.AnSMPSwithaDCinputdoesnotrequirethisstage.AnSMPSdesignedforACinputcanoftenberunfromaDCsupply(for230VACthiswouldbe330VDC),astheDCpassesthroughtherectifierstageunchanged.It'showeveradvisabletoconsultthemanualbeforetryingthis,thoughmostsuppliesarequitecapableofsuchoperationeventhoughnothingismentionedinthedocumentation.However,thistypeofusemaybeharmfultotherectifierstageasitwillonlyutilizehalfofdiodesintherectifierforthefullload.Thismayresultinoverheatingofthesecomponents,andcausethemtofailprematurely.
Ifaninputrangeswitchisused,therectifierstageisusuallyconfiguredtooperateasavoltagedoublerwhenoperatingonthelowvoltage(~120VAC)rangeandasastraightrectifierwhenoperatingonthehighvoltage(~240VAC)range.Ifaninputrangeswitchisnotused,thenafull-waverectifierisusuallyusedandthedownstreaminverterstageissimplydesignedtobeflexibleenoughtoacceptthewiderangeofdcvoltagesthatwillbeproducedbytherectifierstage.Inhigher-powerSMPSs,someformofautomaticrangeswitchingmaybeused.
Inverterstage
TheinverterstageconvertsDC,whetherdirectlyfromtheinputorfromtherectifierstagedescribedabove,toACbyrunningitthroughapoweroscillator,whoseoutputtransformerisverysmallwithfewwindingsatafrequencyoftensorhundredsofkilohertz(kHz).Thefrequencyisusuallychosentobeabove20kHz,tomakeitinaudibletohumans.Theoutputvoltageisopticallycoupledtotheinputandthusverytightlycontrolled.Theswitchingisimplementedasamultistage(toachievehighgain)MOSFETamplifier.MOSFETsareatypeoftransistorwithalowon-resistanceandahighcurrent-handlingcapacity.Sinceonlythelaststagehasalargedutycycle,previousstagescanbeimplementedbybipolartransistorsleadingtoroughlythesameefficiency.Thesecondlaststageneedstobeofacomplementarydesign,whereonetransistorchargesthelastMOSFETandanotheronedischargestheMOSFET.Adesignusingaresistorwouldrunidlemostofthetimeandreduceefficiency.Allearlierstagesdonotweightintoefficiencybecausepowerdecreasesbyafactorof10foreverystage(goingbackwards)andthustheearlierstagesareresponsibleforatmost1%oftheefficiency.ThissectionreferstotheblockmarkedChopperintheblockdiagram.
Voltageconverterandoutputrectifier
Iftheoutputisrequiredtobeisolatedfromtheinput,asisusuallythecaseinmainspowersupplies,theinvertedACisusedtodrivetheprimarywindingofahigh-frequencytransformer.Thisconvertsthevoltageupordowntotherequiredoutputlevelonitssecondarywinding.Theoutputtransformerintheblockdiagramservesthispurpose.
IfaDCoutputisrequired,theACoutputfromthetransformerisrectified.Foroutputvoltagesabovetenvoltsorso,ordinarysilicondiodesarecommonlyused.Forlowervoltages,Schottkydiodesarecommonlyusedastherectifierelements;theyhavetheadvantagesoffasterrecoverytimesthansilicondiodes(allowinglow-lossoperationathigherfrequencies)andalowervoltagedropwhenconducting.Forevenloweroutputvoltages,MOSFETsmaybeusedassynchronousrectifiers;comparedtoSchottkydiodes,thesehaveevenlowerconductingstatevoltagedrops.
Therectifiedoutputisthensmoothedbyafilterconsistingofinductorsandcapacitors.Forhigherswitchingfrequencies,componentswithlowercapacitanceandinductanceareneeded.
Simpler,non-isolatedpowersuppliescontainaninductorinsteadofatransformer.Thistypeincludesboostconverters,buckconverters,andthesocalledbuck-boostconverters.Thesebelongtothesimplestclassofsingleinput,singleoutputconverterswhichutilizeoneinductorandoneactiveswitch.Thebuckconverterreducestheinputvoltageindirectproportiontotheratioofconductivetimetothetotalswitchingperiod,calledthedutycycle.Forexampleanidealbuckconverterwitha10Vinputoperatingata50%dutycyclewillproduceanaverageoutputvoltageof5V.Afeedbackcontrolloopisemployedtoregulatetheoutputvoltagebyvaryingthedutycycletocompensateforvariationsininputvoltage.Theoutputvoltageofaboostconverterisalwaysgreaterthantheinputvoltageandthebuck-boostoutputvoltageisinvertedbutcanbegreaterthan,equalto,orlessthanthemagnitudeofitsinputvoltage.Therearemanyvariationsandextensionstothisclassofconvertersbutthesethreeformthebasisofalmostallisolatedandnon-isolatedDCtoDCconverters.ByaddingasecondinductortheĆukandSEPICconverterscanbeimplemented,or,byaddingadditionalactiveswitches,variousbridgeconverterscanberealised.
OthertypesofSMPSsuseacapacitor-diodevoltagemultiplierinsteadofinductorsandtransformers.Thesearemostlyusedforgeneratinghighvoltagesatlowcurrents(Cockcroft-Waltongenerator).Thelowvoltagevariantiscalledchargepump.
Regulation
Afeedbackcircuitmonitorstheoutputvoltageandcomparesitwithareferencevoltage,whichissetmanuallyorelectronicallytothedesiredoutput.Ifthereisanerrorintheoutputvoltage,thefeedbackcircuitcompensatesbyadjustingthetimingwithwhichtheMOSFETsareswitchedonandoff.Thispartofthepowersupplyiscalledtheswitchingregulator.TheChoppercontrollershownintheblockdiagramservesthispurpose.Dependingondesign/safetyrequirements,thecontrollermayormaynotcontainanisolationmechanism(suchasopto-couplers)toisolateitfromtheDCoutput.Switchingsuppliesincomputers,TVsandVCRshavetheseopto-couplerstotightlycontroltheoutputvoltage.
Open-loopregulatorsdonothaveafeedbackcircuit.Instead,theyrelyonfeedingaconstantvoltagetotheinputofthetransformerorinductor,andassumethattheoutputwillbecorrect.Regulateddesignscompensatefortheparasiticcapacitanceofthetransformerorcoil.Monopolardesignsalsocompensateforthemagnetichysteresisofthecore.
Thefeedbackcircuitneedspowertorunbeforeitcangeneratepower,soanadditionalnon-switchingpower-supplyforstand-byisadded.
Transformerdesign
SMPStransformersrunathighfrequency.Mostofthecostsavings(andspacesavings)inoff-linepowersuppliescomefromthefactthatahighfrequencytransformerismuchsmallerthanthe50/60Hztransformersformerlyused.
Thereareseveraldifferencesinthedesignoftransformersfor50Hzvs500kHz.Firstlyalowfrequencytransformerusuallytransfers
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