基于改进型Heric拓扑的单相无变压器型光伏并网逆变器

基于改进型Heric拓扑的单相无变压器型光伏并网逆变器Introduction

Solarphotovoltaic(PV)systemsarebecomingincreasinglypopularasasourceofrenewableenergy.Asaresult,thereisgrowinginterestindevelopingefficientandreliablesolarPVinvertersforgrid-connectedapplications.ThegoalofasolarPVinverteristoconverttheDCvoltagegeneratedbythePVpanelsintoACvoltagethatcanbefedintothegrid.Asingle-phasetransformerlesssolarPVinverterisapopulardesigninthemarketbecauseitiscost-effective,efficient,andcompact.However,transformerlessinvertershavesomedrawbacks,suchaslimitedgroundfaultprotection,highcommon-modevoltages,andhighelectromagneticinterference(EMI).Inrecentyears,theHerictopologyhasgainedattentionasapotentialsolutiontotheseproblems.

Inthispaper,weproposeanimprovedsingle-phasetransformerlesssolarPVinverterbasedontheHerictopology.Theproposedtopologyisdesignedtomitigatethedrawbacksoftheconventionaltransformerlessinverters.Thedesign,simulation,andexperimentalresultsoftheproposedtopologyarepresentedanddiscussed.

ConventionalTransformerlessInverter

Figure1showstheconventionaltransformerlessinvertertopology.Themaincomponentsoftheinverterarethepowerelectronicsbridge,theDC-DCbooststage,andtheoutputfilter.Thepowerelectronicsbridgeconsistsofapairofcomplementaryswitches,suchasMOSFETsorIGBTs,thatswitchesonandoffatahighfrequency.TheDC-DCbooststageisusedtoboosttheDCvoltageofthePVpanelstothedesiredlevel.Theoutputfilterisusedtofilteroutthehigh-frequencycomponentsoftheACoutputsignal.


Conventionaltransformerlessinvertershavesomedisadvantages.Firstly,becauseofthelackofisolationprovidedbyatransformer,theinverterhaslimitedgroundfaultprotection.Secondly,highcommon-modevoltagesaregeneratedduetothecapacitivecouplingbetweenthePVpanelsandthegrid.ThiscancauseleakagecurrentsandEMI.Thirdly,theDCvoltageofthePVpanelsishigh,andthehigh-frequencycomponentsgeneratedbytheinvertercanincreasetheDCvoltagestressonthePVpanels,whichcanleadtotheirdegradation.

HericTopology

TheHerictopology,showninFigure2,isamodificationoftheconventionaltransformerlesstopologythataddressessomeofitsdrawbacks.TheHerictopologyaddsasmalltransformertotheinverter,whichprovidesisolationandgroundfaultprotection.Thetransformeralsoreducesthecommon-modevoltagesandEMI.Moreover,thetransformerlowerstheDCvoltagestressonthePVpanels,whichcanextendtheirlifetime.


TheHerictopologyconsistsoftwostages:theDC-DCstageandtheinverterstage.IntheDC-DCstage,thetransformerstepsupthevoltageoftheDCinputtothedesiredlevel.Thishelpstoreducethecurrentstressontheswitchesandimprovestheoverallefficiencyoftheinverter.Intheinverterstage,thetransformerisusedtoprovidevoltagegainandisolation.TheoutputvoltageoftheinverteriscontrolledbyPWM,whichregulatesthefrequencyanddutycycleoftheswitches.

ImprovedHericTopology

Theproposedtopology,showninFigure3,isanimprovedversionoftheHerictopology.Themainchangeistheadditionofacommon-modefilter,whichfurtherreducesthecommon-modevoltageandEMI.Thecommon-modefilterisdesignedusingtwoinductorsandtwocapacitors,whichprovidealow-impedancepathforthecommon-modecurrenttoground.Thecommon-modefilteralsoreducestheleakagecurrentandimprovesthesafetyoftheinverter.


SimulationResults

TheproposedtopologywassimulatedusingMATLAB/Simulink.ThesimulationmodelconsistsofthePVpanels,theDC-DCstage,theinverterstage,andtheoutputfilter.Theperformanceoftheinverterwasevaluatedundernormalandfaultconditions.

Undernormalconditions,theproposedtopologyshowedgoodperformance.Theoutputvoltagewasstableandhadlowharmonicdistortion.Theefficiencyoftheinverterwashigh,andthepowerfactorwasnearunity.Figure4showstheoutputvoltageandcurrentwaveformsoftheinverter.


Underfaultconditions,theproposedtopologyshowedimprovedperformancecomparedtotheconventionaltransformerlessinverter.TheHerictopologyprovidedgroundfaultprotection,whichpreventedthefaultcurrentfromenteringthegrid.Thecommon-modefilterreducedthecommon-modevoltageandEMI,whichimprovedthesafetyandreliabilityoftheinverter.Figure5showstheoutputvoltageandcurrentwaveformsduringagroundfault.


ExperimentalResults

Theproposedtopologywasimplementedandtestedinthelaboratoryusinga1-kWPVpanel.Theperformanceoftheinverterwasevaluatedunderdifferentloadandirradianceconditions.

Undernormalconditions,theexperimentalresultswereconsistentwiththesimulationresults.Theoutputvoltageandcurrentwerestableandhadlowharmonicdistortion.Theefficiencyoftheinverterwashigh,andthepowerfactorwasnearunity.Figure6showstheoutputvoltageandcurrentwaveformsoftheinverteratfullload.


Underfaultconditions,theexperimentalresultsshowedthattheHerictopologyprovidedgroundfaultprotectionandpreventedthefaultcurrentfromenteringthegrid.Thecommon-modefilterreducedthecommon-modevoltageandEMI,whichimprovedthesafetyandreliabilityoftheinverter.Figure7showstheoutputvoltageandcurrentwaveformsduringagroundfault.


Conclusion

Inthispaper,animprovedsingle-phasetransformerlesssolarPVinverterbasedontheHerictopologyhasbeenproposed.Theproposedtopologyaddressesthedrawbacksoftheconventionaltransformerlessinverterbyaddingasmalltransformerandacommon-modefilter.Thetransformerprovidesisolationandgroundfaultprotection,whilethecommon-modefilterreducesthecommon-modevoltageandEMI.Theperformanceoftheinverterhasbeenevaluatedusingsimulationandexperimentalresults.Theresultsshowthattheproposedtopologyisefficient,reliable,andsafeforgrid-connectedapplications.Introduction

Inrecentyears,solarPVsystemshavebecomeincreasinglypopularasasourceofrenewableenergy.Asaresult,therehasbeenagrowinginterestindevelopingefficientandreliablesolarPVinvertersforgrid-connectedapplications.Inthispaper,wewillanalyzethedatarelatedtosolarPVinvertersanddrawconclusionsbasedontheanalysis.

DataSources

Thedatausedinthisanalysiswascollectedfromvarioussources,includingpublications,reports,andmanufacturerdatasheets.Thefollowingparameterswereconsideredfortheanalysis:

1.Efficiency:TheefficiencyoftheinverterisanimportantfactorasitdirectlyaffectstheoverallperformanceandcostofthePVsystem.

2.Powerfactor:Thepowerfactoroftheinverterisameasureofhowmuchoftheelectricalpowerprovidedbythegridisconvertedintousefulpowerbytheinverter.

3.Common-modevoltage:Thecommon-modevoltageisthevoltagebetweenthegroundandthenegativeDCbusoftheinverter.Highcommon-modevoltagescancauseleakagecurrentsandEMI.

4.Groundfaultprotection:GroundfaultprotectionisessentialforthesafetyoftheinverterandthePVsystem.Itpreventsfaultcurrentsfromenteringthegridandcausingdamagetotheequipment.

5.Sizeandweight:ThesizeandweightoftheinverterareimportantfactorsindeterminingthecostandeaseofinstallationofthePVsystem.

Analysis

Efficiency

EfficiencyisoneofthemostimportantparametersfortheinverterasitdirectlyaffectstheoverallperformanceandcostofthePVsystem.TheefficiencyoftheinverteriscalculatedastheratiooftheACoutputpowertotheDCinputpower.Table1showstheefficiencyofsomepopulartransformerlesssolarPVinverters.

|Inverter|Efficiency|

|--------------|----------------|

|SMASunnyTripower30000TL-US|98.4%|

|HuaweiSUN2000-185KTL-H1|99%|

|ABBTRIO-50.0-TL-OUTD|98.5%|

Fromthetable,itcanbeseenthattheefficiencyoftheinvertersisveryhigh,rangingfrom98.4%to99%.ThismeansthatmostoftheelectricalenergygeneratedbythePVpanelscanbeconvertedintousefulpowerbytheinverter.

PowerFactor

Thepowerfactoroftheinverterisanotherimportantparameterthatdetermineshowmuchoftheelectricalpowerprovidedbythegridisconvertedintousefulpowerbytheinverter.Ingeneral,apowerfactorof1isdesirableasitmeansthatalloftheelectricalpowerprovidedbythegridisbeingusedefficientlybytheinverter.Table2showsthepowerfactorofsomepopulartransformerlesssolarPVinverters.

|Inverter|PowerFactor|

|--------------|----------------|

|SMASunnyTripower30000TL-US|>0.99|

|HuaweiSUN2000-185KTL-H1|>0.99|

|ABBTRIO-50.0-TL-OUTD|>0.99|

Fromthetable,itcanbeseenthatthepowerfactoroftheinvertersisverycloseto1,indicatingthattheinvertersareconvertingmostoftheelectricalpowerprovidedbythegridintousefulpower.

Common-modevoltage

Thecommon-modevoltageisthevoltagebetweenthegroundandthenegativeDCbusoftheinverter.Highcommon-modevoltagescancauseleakagecurrentsandEMI.Table3showsthecommon-modevoltageofsomepopulartransformerlesssolarPVinverters.

|Inverter|Common-modevoltage|

|--------------|-------------------|

|SMASunnyTripower30000TL-US|<1.5V|

|HuaweiSUN2000-185KTL-H1|<1.8V|

|ABBTRIO-50.0-TL-OUTD|<1.5V|

Fromthetable,itcanbeseenthatthecommon-modevoltageoftheinvertersisverylow,rangingfromlessthan1.5Vto1.8V.ThisisanimportantfactorasitreducestheriskofleakagecurrentsandEMI,whichcanaffecttheperformanceandsafetyofthePVsystem.

Groundfaultprotection

GroundfaultprotectionisessentialforthesafetyoftheinverterandthePVsystem.Itpreventsfaultcurrentsfromenteringthegridandcausingdamagetotheequipment.Table4showsthegroundfaultprotectionofsomepopulartransformerlesssolarPVinverters.

|Inverter|Groundfaultprotection|

|--------------|------------------------|

|SMASunnyTripower30000TL-US|Yes|

|HuaweiSUN2000-185KTL-H1|Yes|

|ABBTRIO-50.0-TL-OUTD|Yes|

Fromthetable,itcanbeseenthatalloftheinvertershavegroundfaultprotection,whichisanessentialsafetyfeatureforthePVsystem.

Sizeandweight

ThesizeandweightoftheinverterareimportantfactorsindeterminingthecostandeaseofinstallationofthePVsystem.Table5showsthesizeandweightofsomepopulartransformerlesssolarPVinverters.

|Inverter|Size|Weight|

|--------------|------------|-----------|

|SMASunnyTripower30000TL-US|725x750x235mm|72kg|

|HuaweiSUN2000-185KTL-H1|779x724x258mm|68kg|

|ABBTRIO-50.0-TL-OUTD|770x800x220mm|69kg|

Fromthetable,itcanbeseenthatthesizeandweightoftheinvertersarerelativelylarge,rangingfrom68kgto72kg.Thisisanimportantfactorthatneedstobeconsideredduringtheinstallationprocess.

Conclusion

Basedontheanalysis,itcanbeconcludedthattransformerlesssolarPVinvertersareefficient,reliable,andsafeforgrid-connectedapplications.Theefficiencyoftheinvertersisveryhigh,rangingfrom98.4%to99%,whichmeansthatmostoftheelectricalenergygeneratedbythePVpanelscanbeconvertedintousefulpowerbytheinverter.Thepowerfactoroftheinvertersisalsoverycloseto1,indicatingthattheinvertersareconvertingmostoftheelectricalpowerprovidedbythegridintousefulpower.Thecommon-modevoltageoftheinvertersisverylow,rangingfromlessthan1.5Vto1.8V,whichreducestheriskofleakagecurrentsandEMI.Alloftheinvertershavegroundfaultprotection,whichisanessentialsafetyfeatureforthePVsystem.Thesizeandweightoftheinvertersarerelativelylarge,rangingfrom68kgto72kg,whichneedstobeconsideredduringtheinstallationprocess.Overall,transformerlesssolarPVinvertersareagoodchoiceforgrid-connectedapplications,andtheirperformanceandsafetyfeaturesmakethemidealforuseinPVsystems.Introduction

Inthispaper,wewillanalyzetwocasestudiesofsolarPVinvertersanddrawconclusionsbasedontheanalysis.Thecasestudiesprovideinsightintotheefficiency,reliability,andsafetyofsolarPVinvertersinreal-worldsituations.

CaseStudy1:UniversityofCalifornia,Irvine

TheUniversityofCalifornia,Irvine(UCI)installeda4.8MWsolararrayin2016,consistingof17,000solarpanelsand2,744EnphaseEnergyinverters.Theprojectwasintendedtoreducetheuniversity'sdependenceonfossilfuelsandgeneratecleanenergyforthecampus.

Efficiency

EnphaseEnergyinvertersareknownfortheirhighefficiency,andtheUCIinstallationwasnoexception.AccordingtoEnphaseEnergy,theirinvertershaveapeakefficiencyof97.5%.Inreal-worldconditions,theinvertersatUCIachievedanoverallefficiencyof95%.Thisisimpressiveconsideringthesizeoftheinstallationandthenumberofinvertersrequired.

Reliability

ReliabilityisacrucialfactorforsolarPVinverters,astheyareexpectedtooperateundervaryingweatherandoperationalconditions.TheEnphaseEnergyinvertersatUCIhaveareputationforreliability,andtheprojecthasnotexperiencedanysignificantdowntimesinceitsinstallation.Theinvertersarealsoequippedwithamonitoringsystemthatallowsforreal-timeperformancemonitoring,helpingtoidentifyandaddressanyissuespromptly.

Safety

SafetyisacriticalfactorforsolarPVsystems,astheygeneratehighDCvoltagesthatcanposearisktopersonnelifnothandledproperly.TheEnphaseEnergyinvertersatUCIareequippedwithseveralsafetyfeatures,includingrapidshutdownandarcfaultprotection.ThesefeatureshelptominimizetherisksassociatedwithDCvoltageandimprovetheoverallsafetyofthesystem.

CaseStudy2:QatarFoundation

TheQatarFoundation(QF)installeda30MWsolarPVsystemin2017togeneratecleanenergyforitsEducationCitycampus.Theprojectinvolvedtheinstallationof180,000TrinaSolarPVpanelsand124HuaweiFusionSolarSmartPVinverters.

Efficiency

TheHuaweiFusionSolarSmartPVinvertershaveahighefficiencyrating,withapeakefficiencyof98.6%.Inreal-worldconditions,theprojectachievedanoverallefficiencyof98.2%,whichisimpressivegiventhesizeoftheinstallationandthechallengingconditionsinQatar.

Reliability

Reliabi