太阳能并网发电系统的仿真研究英文翻译Word文档下载推荐.docx

太阳能并网发电系统的仿真研究英文翻译Word文档下载推荐.docx

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J.M.A.Myrzik,andM.Calais,Member,IEEE

Abstract:

Thispaperpresentsanoverviewonrecentdevelopmentsandasummaryofthestate-of-the-artininvertertechnologyforsingle-phasegridconnectedphotovoltaic（PV）systems.TheinformationprovidedincludesdetailsoncommerciallyavailableEuropeanstringandmoduleintegratedPVinverters,theirefficiency,pricetrendsandmarketshare.Thisreviewisgivenforinvertersforapowerlevelupto6kW.Furthermore,thepaperdealswiththerecentdevelopmentsofnewinvertertopologiesandPVsystemconceptsanddiscussespossiblefuturetrends.IndexTerms-Invertersgridconnectedphotovoltaicpowersystems.

Ⅰ.INVERTERS,GRIDCONNECTEDPHOTOVOLTAICSYSTEMSINTRODUCTION

Thegridconnectedphotovoltaic（PV）marketinEuropeisaprosperingmarketwithgrowthratesof40%andmore.Particularly,subsidyprogramsandchangesintheenergylawsofseveralEuropeancountries（forexampleGermany）andtheEuropeanUnionhavepushednewdevelopmentsforgridconnectedPVsystemsoverthelastthreeyears.Growingdemand,butalsoadvancementsinsemiconductortechnologyandmagneticmaterialssuchashighfrequencyinductorcores,hashadasignificantimpactonPVinvertertopologiesandtheirefficiencies,ontheimprovementofthecontrolcircuitsandonthepotentialofcostreduction.

Pricereductionandefficiencyimprovementswerethemaingoals15yearsagowhenthePVgridconnectedsystemsbecamemorewidelyavailable.OverthelastdecadepricesforPVinvertershavedroppedby50%whilemaximumefficienciesincreasedfrom94toabove97%.Althoughpricereductionandefficiencyimprovements（especiallyatpartload）remainimportantgoalstoday,electromagneticcompatibility,reliability,safetyandmonitoringfunctionsarereceivingmoreandmoreattention.

Thispaperaimstogiveanoverviewonsingle-phasegirdconnectedPVinvertersavailableontheEuropeanmarketandtooutlinefuturetrendsinthisrapidlydevelopingtechnology.Thepaperisorganizedasfollows.SectionⅡdescribesPVsystemdesignsanddiscussessafetyaspectsconcerningtransformerlesstopologies.Thensomecommerciallyavailableinvertertopologiesarepresentedanddiscussedandanoverviewonmarketshares,priceandefficiencydevelopmentsisgiven.SectionⅢoutlinesnewdevelopmentsincludingnewsystemdesignssuchthe‘team’and‘Multi-string’inverterconceptanddiscussesnewtransformerlesstopologies.SectionⅣsummarisesthemainfindingsanddevelopments.

Ⅱ.COMMERCIALLYAVAILABLEINVERTERTOPOLOGIES

A.SystemsDesignAspects

Beforediscussinginvertertopologieswefirstdefinethreeinverterfamilies,whicharerelatedtospecificPVsystemdesigns:

centralinverters,moduleintegratedormoduleorientatedinvertersandstringinverters.

Inthemiddleofthe1980’sthemarketforPVgridconnectedsystemsdevelopedwithcentralinvertersofseveralkilowattsinsizebeingthemostcommon.ThetopologiesoftheseinverterswerebasedoninvertersusedinthedrivesystemindustryandwerenotoptimisedforthePVapplication.Beginningofthe1990’s,resultsofresearchprograms,suchasthe1000RoofPrograminGermany,highlightedtechnologydeficienciesanddrawbacksofsystemswithcentralinvertersbecameapparent.Theseincluded:

·

MismatchinglossesbyusingMaximumPowerPoint（MPP）controlforalargegroupofPVmodules;

LossesandriskofelectricalarcinDCwiring;

Poorexpandabilityandadaptabilitytocustomers’requirements,duetolittleornodesignflexibility.

Inordertoavoidtheseproblems,amodularsystemtechnologywasintroduced.Additionaladvantagesofamodularsystemconceptare:

Costreductionsandreliabilityimprovementsbyusingsimilarcomponents;

Simplersystemdesignandinstallationbycombiningstandardunits;

Simplerfaultfinding.

ThesmallestpossiblegridconnectedPVsystemunitisaPVmodulewithamodule-integratedinverter.Inthiscase,mismatchinglossesareminimised,sinceloadmatchingfortheindividualPVmoduleisachievedthroughitsinverter.Additionally,DCwiringisminimised.However,therearedrawbacksconcerningefficiencyduetothelowpowerratingsinvolvedandreplacementsincaseofinverterfaultsmaybedifficultandexpensive.Also,costperwattremainshighunlessmass-productionispossible.

Withthepressuretoincreasesystemefficiencieswhilesimultaneouslyreducingcosts,thestringorientatedorstringinverterwasintroducedonthemarketinthemid1990’s.StringinvertersaredesignedforasystemconfigurationofonestringofPVmodulesandcanbeseenasacompromisebetweenmoduleintegratedandcentralinverterconcepts.

Advancementsinsemiconductorandfiltercomponentshaveleadtoinverterefficiencyimprovementsbutwithmaximumefficienciesforstringinvertersrangingtodayfrom94toabove97%,thereislittleroomforfurtherimprovement.PVinvertercompaniesthereforeseemtobefocusingmoreonefficiencyimprovementsandcostreductionthroughnewPVsystemsconceptssuchastheteamconceptandmaster-slaveconcept,whicharediscussedinmoredetailinSectionⅢ.Theseconceptscombinetheadvantagesofthestringtechnologywiththelowercostsolutionofthecentralinverters.Furthergoalsaretoincreasetheoverallsystemefficiency,toreducetheharmonicdistortionsandtoenhancemonitoringfeatures.

B.Aretransformerlessinvertersariskforcustomers?

Inthepastfewyearsthemarketsharefortransformerlessinvertershassteadilyincreased.Topologieswithouttransformergenerallyhavehigherefficienciesandmaybecheaperthancomparableinverterswithtransformers.BotharecrucialadvantagestomakePVsystemsmorecompetitivewithtraditionalgeneration.Themaindisadvantage,however,isthedirectconnectionofthePVarraytothegridwithoutgalvanicisolation.DependingontheinvertertopologythismaycausefluctuationsofthepotentialbetweenthePVarrayandground.Thesefluctuationsmayhavesineorsquarewavebehavioratgridfrequencyorevenswitchingfrequency.Theygeneratetwoeffects:

1.ThesurfaceofthePVarrayformsacapacitor,withrespecttoground,whichisenergisedbythefluctuatingpotential.Aperson,connectedtogroundandtouchingthePVarray,mayconductthecapacitivecurrenttoground,causinganelectricalhazardtothepersoninvolved.

2.ThevoltagefluctuationsgenerateelectricandmagneticfieldsaroundthePVarray（electromagneticinterference）.

Theseriousnessoftheseeffectshasbeenanareaofconcernandcontroversialdiscussionoverthepastyears.MeanwhiledifferentstudiesshowthattheimpactofPVsystemswithtransformerlessinvertersonelectromagneticinterferenceisusuallynegligibleanddoesnotposeahazard.However,withrespecttocapacitivecurrentscertainrecommendationsoninverterandPVsystemdesignshouldbefollowedtopreventdangerouscurrentlevels.

ArecentpaperfromtheFraunhoferInstituteforSolarEnergySystemsinGermanydiscussestheelectricalhazardincaseofapersontouchingthesurfaceofaPVarray.ThecapacitancebetweenthepointofcontactandasinglePVmodulehasbeencalculatedtorangebetween100-400pF.ForthesinglePVmodulecase,anddependingonthetransformerlesstopologyandtheappliedswitchingmethod,acurrentofmax.0.2mAcouldflowthroughthehumanbody.WhenconsideringlargerPVarrayswithungroundedstructures,themaximumpossiblecurrentincreasesasthesurfaceareaofthePVarrayincreases.ThecapacitanceforlargerungroundedPVarrayshasbeenfoundtobe50-150nF/kWforglass-facedmodulesandupto1uF/kWforthin-filmmodules.CurrentsofseveralmAcanthenoccur.However,itisimportanttonote,thatbygroundingthePVarraystructuretherespectiveparasiticcapacitanceisreducedandwiththistheassociatedhazardouscurrent.Additionally,thetypeoftransformerlesstopologyandtheappliedswitchingschemeinfluencethemagnitudeandtypeofvoltagefluctuationatthePVarraywithrespecttoground.Adetaileddiscussionoftheseisgiveninandsomeexamplesonrecommendedtopologiesandswitchingschemesarepresentedinthefollowing.WhenfollowingtherecommendationsongroundingthePVarraystructure,topologyandswitchingschemechoice,alongwiththeuseofClassⅡequipment,transformerlessPVsystemdonotpresentanincreasedhazardcomparedtoPVsystemswithtransformers.

C.InverterTopologies

APVinverterhastofulfillthreemainfunctionsinordertofeedenergyfromaPVarrayintotheutilitygrid:

1.Toshapethecurrentintoasinusoidalwaveform;

2.ToinvertthecurrentintoanACcurrent;

3.IfthePVarrayvoltageislowerthanthegridvoltage,thePVarrayvoltagehastobeboostedwithafurtherelement.

Thewaythesethreefunctionsaresequencedwithinaninverterdesigndeterminesthechoiceofsemiconductorandpassivecomponentsandconsequentlytheirlosses,sizesandprices.ThissectionpresentsdifferentinvertertopologiesavailableontheEuropeanmarketandgivesanoverviewontheirmarketshares,efficienciesandpricedevelopmentsoverthelastdecade.ThissectioncontinuesandexpandsonapreviousdiscussionofPVinvertertopologiespresentedin.

Fig.1TransformerlessPVinverterwithseveralconversionstagesincludingbooststage

PVsystemsusingmoduleintegratedormodule-orientedinvertershavepeakpowerratingsofusuallylessthan500WandconsistofonetoafewPVmodules.Consequently,DCvoltagelevelsarelowandtoreachgridvoltagelevelsthemoduleintegratedinvertertopologiesrequireavoltageboostingelementwithintheenergyconversionchainfromD