Power inverter.docx

Power inverter.docx

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Powerinverter

Powerinverter

FromWikipedia,thefreeencyclopedia

"Inverter"redirectshere.Forthelogicgate,see Inverter（logicgate）.Forotheruses,see Inverter（disambiguation）.

Thisarticle needsadditionalcitationsforverification. Pleasehelp improvethisarticle by addingcitationstoreliablesources.Unsourcedmaterialmaybe challenged and removed. （October2011）

Aninverterforasolar-mountedfree-standingplantinSpeyer,alongsidetheRhine.

Overviewofthesolarinverters

A powerinverter,or inverter,isan electricalpowerconverter thatchanges directcurrent （DC）to alternatingcurrent （AC）.[1] Theinputvoltage,outputvoltage,andfrequencyaredependentondesign.

Staticinvertersdonotusemovingpartsintheconversionprocess.Someapplicationsforinvertersincludeconverting high-voltagedirectcurrent electricutility linepowertoAC,andderivingACfromDCpowersourcessuchas batteries.

Contents

  [hide] 

∙1 Types

o1.1 Outputwaveforms

▪1.1.1 Modifiedsinewave

▪1.1.2 Sinewave

o1.2 Resonance

o1.3 Gridtie

▪1.3.1 Solar

∙2 Applications

o2.1 DCpowersourceutilization

o2.2 Uninterruptiblepowersupplies

o2.3 Inductionheating

o2.4 HVDCpowertransmission

o2.5 Variable-frequencydrives

o2.6 Electricvehicledrives

o2.7 Airconditioning

o2.8 Electroshockweapons

∙3 Circuitdescription

o3.1 Basicdesigns

o3.2 Outputwaveforms

o3.3 Advanceddesigns

o3.4 Threephaseinverters

∙4 History

o4.1 Earlyinverters

o4.2 Controlledrectifierinverters

o4.3 Rectifierandinverterpulsenumbers

∙5 Seealso

∙6 References

o6.1 Generalreferences

∙7 Externallinks

Types[editsource | editbeta]

Staticinvertersuseswitchingdevicesarrangedinan Hbridge.Thelargeswitchingdevicesforpowertransmissionapplicationsinstalleduntil1970predominantlyused mercury-arcvalves.Invertersforconsumeruseaswellaspowertransmissionsystemscommissionedafter1970are solidstate.[2] Thesame Hbridge basicdesignisusedinsmaller-scaleconsumerdevicesaswell.[3]

Outputwaveforms[editsource | editbeta]

Aninvertercanproducesquarewave,modifiedsinewave,pulsedsinewave,orsinewavedependingoncircuitdesign.Thetwodominantcommercializedwaveformtypesofinvertersasof2007aremodifiedsinewaveandsinewave.

Therearetwobasicdesignsforproducinghouseholdplug-involtagefromalower-voltageDCsource,thefirstofwhichusesaswitching boostconverter toproduceahigher-voltageDCandthenconvertstoAC.ThesecondmethodconvertsDCtoACatbatterylevelandusesa line-frequency transformer tocreatetheoutputvoltage.[4]

Modifiedsinewave[editsource | editbeta]

Thewaveformincommerciallyavailablemodified-sine-waveinvertersisasquarewavewithapausebeforethepolaritytransition,whichonlyneedstocyclethroughathree-positionswitchthatoutputsforward,off,andreverseoutputatthepre-determinedfrequency.[4] Thepeakvoltageto RMS voltagedonotmaintainthesamerelationshipasforasinewave.TheDCbusvoltagemaybeactivelyregulatedorthe"on"and"off"timescanbemodifiedtomaintainthesameRMSvalueoutputuptotheDCbusvoltagetocompensateforDCbusvoltagevariation.

TheratioofontoofftimecanbeadjustedtovarytheRMSvoltagewhilemaintainingaconstantfrequencywithatechniquecalled PWM.Harmonicspectrumintheoutputdependsonthewidthofthepulsesandthemodulationfrequency.Whenoperatinginductionmotors,voltageharmonicsisnotofgreatconcern,howeverharmonicdistortioninthecurrentwaveformintroducesadditionalheating,andcanproducepulsatingtorques.[5]

MostACmotorswillrunonMSWinverterswithanefficiencyreductionofabout20%duetotheharmoniccontent.[dubious – discuss][6]

Aproposalsuggestedin PowerElectronics magazineutilizestwovoltagesasanimprovementoverthecommoncommercializedtechnologywhichcanonlyapplyDCbusvoltageineitherdirectionsorturnitoff.Theproposaladdsanadditionalvoltagetothisdesign.Eachcycleconsistsofsequenceas:

v1,v2,v1,off/pause,-v1,-v2,-v1.[7]

Sinewave[editsource | editbeta]

Asinewaveinverterproducesasinewaveoutput,witha totalharmonicdistortion under3%[citationneeded].Sinewaveinvertersaremorecomplexandhaveahighercostthanamodified-sine-wavetypeofthesamesize.[7]

Resonance[editsource | editbeta]

Mainarticle:

 Resonantinverter

Resonant invertersproducesinewaveswith LCcircuits toremovetheharmonicsfromasimplesquarewave.Typicallythereareseveralseries-andparallel-resonantLCcircuits,eachtunedtoadifferentharmonicofthepowerlinefrequency.Thissimplifiestheelectronics,buttheinductorsandcapacitorstendtobelargeandheavy.Itshighefficiencymakesthisapproachpopularinlarge uninterruptiblepowersupplies indatacentersthatruntheinvertercontinuouslyinan"online"modetoavoidanyswitchovertransientwhenpowerislost.

Acloselyrelatedapproachusesaferroresonanttransformer,alsoknownasa constantvoltagetransformer,toremoveharmonicsandtostoreenoughenergytosustaintheloadforafewACcycles.Thispropertymakesthemusefulin standbypowersupplies toeliminatetheswitchovertransientthatotherwiseoccursduringapowerfailurewhilethenormallyidleinverterstartsandthemechanicalrelaysareswitchingtoitsoutput.

Gridtie[editsource | editbeta]

Grid-tieinvertersaredesignedtofeedintotheelectricpowerdistributionsystem.Theytransfersynchronouslywiththelineandhaveaslittleharmoniccontentaspossible.Theyalsoneedameansofdetectingthepresenceofutilitypowerforsafetyreasons,soasnottocontinuetodangerouslyfeedpowertothegridduringapoweroutage.

Solar[editsource | editbeta]

Asolarinvertercanbefedintoacommercialelectricalgridorusedbyanoff-gridelectricalnetwork.Solarinvertershavespecialfunctionsadaptedforusewith photovoltaic arrays,includingmaximumpowerpointtrackingandanti-islanding protection.

Applications[editsource | editbeta]

DCpowersourceutilization[editsource | editbeta]

Inverterdesignedtoprovide115VACfromthe12VDCsourceprovidedinanautomobile.Theunitshownprovidesupto1.2amperesofalternatingcurrent,orenoughtopowertwosixtywattlightbulbs.

AninverterconvertstheDCelectricityfromsourcessuchas batteries, solarpanels,or fuelcells toACelectricity.Theelectricitycanbeatanyrequiredvoltage;inparticularitcanoperateACequipmentdesignedformainsoperation,orrectifiedtoproduceDCatanydesiredvoltage.

Micro-inverters convertdirectcurrentfromindividualsolarpanelsintoalternatingcurrentfortheelectricgrid.Theyaregridtiedesignsbydefault.

Uninterruptiblepowersupplies[editsource | editbeta]

An uninterruptiblepowersupply （UPS）usesbatteriesandaninvertertosupplyACpowerwhenmainpowerisnotavailable.Whenmainpowerisrestored,a rectifier suppliesDCpowertorechargethebatteries.

Inductionheating[editsource | editbeta]

InvertersconvertlowfrequencymainACpowertohigherfrequencyforusein inductionheating.Todothis,ACpowerisfirst rectified toprovideDCpower.TheinverterthenchangestheDCpowertohighfrequencyACpower.

HVDCpowertransmission[editsource | editbeta]

With HVDC powertransmission,ACpowerisrectifiedandhighvoltageDCpoweristransmittedtoanotherlocation.Atthereceivinglocation,aninverterina staticinverterplant convertsthepowerbacktoAC.Theinvertermustbesynchronizedwithgridfrequencyandphaseandminimizeharmonicgeneration.

Variable-frequencydrives[editsource | editbeta]

Mainarticle:

 variable-frequencydrive

A variable-frequencydrive controlstheoperatingspeedofanACmotorbycontrollingthefrequencyandvoltageofthepowersuppliedtothemotor.Aninverterprovidesthecontrolledpower.Inmostcases,thevariable-frequencydriveincludesa rectifier sothatDCpowerfortheinvertercanbeprovidedfrommainACpower.Sinceaninverteristhekeycomponent,variable-frequencydrivesaresometimescalledinverterdrivesorjustinverters.

VFDsthatoperatedirectlyfromanACsourcewithoutfirstconvertingittoDCarecalled cycloconverters.Theyarenowcommonlyusedonlargeshipstodrivethepropulsionmotors.

Electricvehicledrives[editsource | editbeta]

Adjustablespeedmotorcontrolinvertersarecurrentlyusedtopowerthe tractionmotors insome electric and diesel-electric railvehiclesaswellassome batteryelectricvehicles and hybridelectric highwayvehiclessuchasthe ToyotaPrius, BYDe6 and FiskerKarma.Variousimprovementsininvertertechnologyarebeingdevelopedspecificallyforelectricvehicleapplications.[8] Invehicleswith regenerativebraking,theinverteralsotakespowerfromthemotor（nowactingasagenerator）andstoresitinthebatteries.

Airconditioning[editsource | editbeta]

Mainarticle:

 Inverterairconditioning

Aninverter airconditioner usesa variable-frequencydrive tocontrolthespeedofthemotorandthusthecompressor.

Electroshockweapons[editsource | editbeta]

Electroshockweapons and tasers haveaDC/ACinvertertogenerateseveraltensofthousandsofVACoutofasmall9VDCbattery.Firstthe9VDCisconvertedto400–2000VACwithacompacthighfrequencytransformer,whichisthenrectifiedandtemporarilystoredinahighvoltagecapacitoruntilapre-setthresholdvoltageisreached.Whenthethreshold（setbywayofanairgaporTRIAC）isreached,thecapacitordumpsitsentireloadintoa pulsetransformer whichthenstepsituptoitsfinaloutputvoltageof20–60kV.Avariantoftheprincipleisalsousedin electronicflash and bugzappers,thoughtheyr