逆变器外文文献及翻译.docx
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逆变器外文文献及翻译
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,SCRshavebeenusedinthetypesofinvertercircuitsde