毕业论文外文资料翻译逆变器.docx

毕业论文外文资料翻译逆变器.docx

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毕业论文外文资料翻译逆变器

Inverter

1Introduction

Aninverterisanelectricaldevicethatconvertsdirectcurrent（DC）toalternatingcurrent（AC）;theconvertedACcanbeatanyrequiredvoltageandfrequencywiththeuseofappropriatetransformers,switching,andcontrolcircuits.Solid-stateinvertershavenomovingpartsandareusedinawiderangeofapplications,fromsmallswitchingpowersuppliesincomputers,tolargeelectricutilityhigh-voltagedirectcurrentapplicationsthattransportbulkpower.InvertersarecommonlyusedtosupplyACpowerfromDCsourcessuchassolarpanelsorbatteries.

Therearetwomaintypesofinverter.Theoutputofamodifiedsinewaveinverterissimilartoasquarewaveoutputexceptthattheoutputgoestozerovoltsforatimebeforeswitchingpositiveornegative.Itissimpleandlowcostandiscompatiblewithmostelectronicdevices,exceptforsensitiveorspecializedequipment,forexamplecertainlaserprinters.Apuresinewaveinverterproducesanearlyperfectsinewaveoutput（<3%totalharmonicdistortion）thatisessentiallythesameasutility-suppliedgridpower.ThusitiscompatiblewithallACelectronicdevices.Thisisthetypeusedingrid-tieinverters.Itsdesignismorecomplex,andcosts5or10timesmoreperunitpowerTheelectricalinverterisahigh-powerelectronicoscillator.ItissonamedbecauseearlymechanicalACtoDCconvertersweremadetoworkinreverse,andthuswere"inverted",toconvertDCtoAC.Theinverterperformstheoppositefunctionofarectifier.

2Applications

2.1DCpowersourceutilization

AninverterconvertstheDCelectricityfromsourcessuchasbatteries,solarpanels,orfuelcellstoACelectricity.Theelectricitycanbeatanyrequiredvoltage;inparticularitcanoperateACequipmentdesignedformainsoperation,orrectifiedtoproduceDCatanydesiredvoltageGridtieinverterscanfeedenergybackintothedistributionnetworkbecausetheyproducealternatingcurrentwiththesamewaveshapeandfrequencyassuppliedbythedistributionsystem.Theycanalsoswitchoffautomaticallyintheeventofablackout.Micro-invertersconvertdirectcurrentfromindividualsolarpanelsintoalternatingcurrentfortheelectricgrid.Theyaregridtiedesignsbydefault.

2.2Uninterruptiblepowersupplies

Anuninterruptiblepowersupply（UPS）usesbatteriesandaninvertertosupplyACpowerwhenmainpowerisnotavailable.Whenmainpowerisrestored,arectifiersuppliesDCpowertorechargethebatteries.

2.3Inductionheating

InvertersconvertlowfrequencymainACpowertoahigherfrequencyforuseininductionheating.Todothis,ACpowerisfirstrectifiedtoprovideDCpower.TheinverterthenchangestheDCpowertohighfrequencyACpower.

2.4HVDCpowertransmission

WithHVDCpowertransmission,ACpowerisrectifiedandhighvoltageDCpoweristransmittedtoanotherlocation.Atthereceivinglocation,aninverterinastaticinverterplantconvertsthepowerbacktoAC.

2.5Variable-frequencydrives

Avariable-frequencydrivecontrolstheoperatingspeedofanACmotorbycontrollingthefrequencyandvoltageofthepowersuppliedtothemotor.Aninverterprovidesthecontrolledpower.Inmostcases,thevariable-frequencydriveincludesarectifiersothatDCpowerfortheinvertercanbeprovidedfrommainACpower.Sinceaninverteristhekeycomponent,variable-frequencydrivesaresometimescalledinverterdrivesorjustinverters.

2.6Electricvehicledrives

Adjustablespeedmotorcontrolinvertersarecurrentlyusedtopowerthetractionmotorsinsomeelectricanddiesel-electricrailvehiclesaswellassomebatteryelectricvehiclesandhybridelectrichighwayvehiclessuchastheToyotaPriusandFiskerKarma.Variousimprovementsininvertertechnologyarebeingdevelopedspecificallyforelectricvehicleapplications.[2]Invehicleswithregenerativebraking,theinverteralsotakespowerfromthemotor（nowactingasagenerator）andstoresitinthebatteries.

2.7Thegeneralcase

AtransformerallowsACpowertobeconvertedtoanydesiredvoltage,butatthesamefrequency.Inverters,plusrectifiersforDC,canbedesignedtoconvertfromanyvoltage,ACorDC,toanyothervoltage,alsoACorDC,atanydesiredfrequency.Theoutputpowercanneverexceedtheinputpower,butefficienciescanbehigh,withasmallproportionofthepowerdissipatedaswasteheat.

3Circuitdescription

3.1Basicdesigns

Inonesimpleinvertercircuit,DCpowerisconnectedtoatransformerthroughthecentretapoftheprimarywinding.AswitchisrapidlyswitchedbackandforthtoallowcurrenttoflowbacktotheDCsourcefollowingtwoalternatepathsthroughoneendoftheprimarywindingandthentheother.Thealternationofthedirectionofcurrentintheprimarywindingofthetransformerproducesalternatingcurrent（AC）inthesecondarycircuit.

Theelectromechanicalversionoftheswitchingdeviceincludestwostationarycontactsandaspringsupportedmovingcontact.Thespringholdsthemovablecontactagainstoneofthestationarycontactsandanelectromagnetpullsthemovablecontacttotheoppositestationarycontact.Thecurrentintheelectromagnetisinterruptedbytheactionoftheswitchsothattheswitchcontinuallyswitchesrapidlybackandforth.Thistypeofelectromechanicalinverterswitch,calledavibratororbuzzer,wasonceusedinvacuumtubeautomobileradios.Asimilarmechanismhasbeenusedindoorbells,buzzersandtattooguns.

Astheybecameavailablewithadequatepowerratings,transistorsandvariousothertypesofsemiconductorswitcheshavebeenincorporatedintoinvertercircuitdesigns

3.2Outputwaveforms

Theswitchinthesimpleinverterdescribedabove,whennotcoupledtoanoutputtransformer,producesasquarevoltagewaveformduetoitssimpleoffandonnatureasopposedtothesinusoidalwaveformthatistheusualwaveformofanACpowersupply.UsingFourieranalysis,periodicwaveformsarerepresentedasthesumofaninfiniteseriesofsinewaves.Thesinewavethathasthesamefrequencyastheoriginalwaveformiscalledthefundamentalcomponent.Theothersinewaves,calledharmonics,thatareincludedintheserieshavefrequenciesthatareintegralmultiplesofthefundamentalfrequency.

Thequalityofoutputwaveformthatisneededfromaninverterdependsonthecharacteristicsoftheconnectedload.Someloadsneedanearlyperfectsinewavevoltagesupplyinordertoworkproperly.Otherloadsmayworkquitewellwithasquarewavevoltage.

3.3Threephaseinverters

Three-phaseinvertersareusedforvariable-frequencydriveapplicationsandforhighpowerapplicationssuchasHVDCpowertransmission.Abasicthree-phaseinverterconsistsofthreesingle-phaseinverterswitcheseachconnectedtooneofthethreeloadterminals.Forthemostbasiccontrolscheme,theoperationofthethreeswitchesiscoordinatedsothatoneswitchoperatesateach60degreepointofthefundamentaloutputwaveform.Thiscreatesaline-to-lineoutputwaveformthathassixsteps.Thesix-stepwaveformhasazero-voltagestepbetweenthepositiveandnegativesectionsofthesquare-wavesuchthattheharmonicsthataremultiplesofthreeareeliminatedasdescribedabove.Whencarrier-basedPWMtechniquesareappliedtosix-stepwaveforms,thebasicoverallshape,orenvelope,ofthewaveformisretainedsothatthe3rdharmonicanditsmultiplesarecancelled

4History

4.1Earlyinverters

Fromthelatenineteenthcenturythroughthemiddleofthetwentiethcentury,DC-to-ACpowerconversionwasaccomplishedusingrotaryconvertersormotor-generatorsets（M-Gsets）.Intheearlytwentiethcentury,vacuumtubesandgasfilledtubesbegantobeusedasswitchesininvertercircuits.Themostwidelyusedtypeoftubewasthethyratron.

Theoriginsofelectromechanicalinvertersexplainthesourceoftheterminverter.EarlyAC-to-DCconvertersusedaninductionorsynchronousACmotordirect-connectedtoagenerator（dynamo）sothatthegenerator'scommutatorreverseditsconnectionsatexactlytherightmomentstoproduceDC.Alaterdevelopmentisthesynchronousconverter,inwhichthemotorandgeneratorwindingsarecombinedintoonearmature,withslipringsatoneendandacommutatorattheotherandonlyonefieldframe.TheresultwitheitherisAC-in,DC-out.WithanM-Gset,theDCcanbeconsideredtobeseparatelygeneratedfromtheAC;withasynchronousconverter,inacertainsenseitcanbeconsideredtobe"mechanicallyrectifiedAC".Giventherightauxiliaryandcontrolequipment,anM-Gsetorrotaryconvertercanbe"runbackwards",convertingDCtoAC.Henceaninverterisaninvertedconverter.

4.2Controlledrectifierinverters

Sinceearlytransistorswerenotavailablewithsufficientvoltageandcurrentratingsformostinverterapplications,itwasthe1957introductionofthethyristororsilicon-controlledrectifier（SCR）thatinitiatedthetransitiontosolidstateinvertercircuits.

ThecommutationrequirementsofSCRsareakeyconsiderationinSCRcircuitdesigns.SCRsdonotturnofforcommutateautomaticallywhenthegatecontrolsignalisshutoff.Theyonlyturnoffwhentheforwardcurrentisreducedtobelowtheminimumholdingcurrent,whichvarieswitheachkindofSCR,throughsomeexternalprocess.ForSCRsconnectedtoanACpowersource,commutationoccursnaturallyeverytimethepolarityofthesourcevoltagereverses.SCRsconnectedtoaDCpowersourceusuallyrequireameansofforcedcommutationthatforcesthecurrenttozerowhencommutationisrequired.TheleastcomplicatedSCRcircuitsemploynaturalcommutationratherthanforcedcommutation.Withtheadditionofforcedcommutationcircuits,SCRshavebeenusedinthetypesofinvertercircuits