参考文献及翻译.docx
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参考文献及翻译.docx
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参考文献及翻译
Agrid-connectedphotovoltaicpowerconversionsystemwithsingle-phasemultilevelinverter
ErsoyBeser
BirolArifoglu
SabriCamur
EsraKandemirBeser
DepartmentofElectricalEngineering,KocaeliUniversity,UmuttepeCampus,41380Kocaeli,Turkey
Received7May2010.Revised26September2010.Accepted28September2010.Availableonline20October2010. Communicatedby:
AssociateEditorNicolaRomeo.
http:
//dx.doi.org/10.1016/j.solener.2010.09.011,HowtoCiteorLinkUsingDOI
CitedbyinScopus(4)
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Abstract
Thispaperpresentsagrid-connectedphotovoltaic(PV)powerconversionsystembasedonasingle-phasemultilevelinverter.TheproposedsystemfundamentallyconsistsofPVarraysandasingle-phasemultilevelinverterstructure.First,configurationandstructuralpartsofthePVassistedinvertersystemareintroducedindetail.Toproducereferenceoutputvoltagewaves,asimpleswitchingstrategybasedoncalculatingswitchinganglesisimproved.Bycalculatedswitchingangles,thereferencesignalisproducedasamultilevelshapedoutputvoltagewave.Thecontrolalgorithmandoperationalprinciplesoftheproposedsystemareexplained.OperatingPVarraysinthesameloadconditionisaconsiderablepoint;thereforeasimulationstudyisperformedtoarrangethePVarrays.AfterdeterminingthenumberandconnectiontypesofthePVarrays,thesystemisconfiguredthroughthearrangementofthePVarrays.Thevalidityoftheproposedsystemisverifiedthroughsimulationsandexperimentalstudy.Theresultsdemonstratethatthesystemcanachievelowertotalharmonicdistortion(THD)ontheoutputvoltageandloadcurrent,anditiscapableofoperatingsynchronousandtransferringpowervalueshavingdifferentcharacteristictothegrid.Hence,itissuitabletousetheproposedconfigurationasaPVpowerconversionsysteminvariousapplications.
Keywords
Photovoltaic;
Photovoltaicpowerconversion;
Grid-connected;
Single-phasemultilevelinverter
Nomenclature
Ck
capacityofthekthcapacitorgroup(μF)
f
gridfrequency(Hz)
I
invertercurrent(A)
IPM
maximumpowercurrentvalue(A)
Ls
inductanceoftheselfinductor(H)
m
numberofthelevelmodules
n
outputlevelnumber
PLMk
powerofthekthlevelmodule(W)
Pref
referencerealpower(W)
P0
systemoutputpower(W)
Qk(t)
thekthswitchingsignal
Qref
referencereactivepower(VAr)
Rs
resistanceoftheselfinductor(Ω)
S
sumoftheenergyratios
t
instantaneoustimevalue(s)
tmax
maximumvalueofthesampletime(s)
tsample
valueofthesampletime(s)
Vb
voltageofthebaselevelmodule(V)
Vbus
busvoltage(V)
Vbusref
thereferencebusvoltage(V)
VCk
voltageofthekthcapacitorgroup(V)
Vg
gridvoltage(V)
Vmax
maximumvalueoftherequiredvoltage(V)
VPM
maximumpowervoltagevalue(V)
Vref
referencevoltage(V)
Vz
voltageoftheselfinductor(V)
V0
outputvoltage(V)
WCk
energyofthekthcapacitorgroup(J)
WLMk
energyofthekthlevelmodule(J)
XLs
reactanceoftheselfinductor(Ω)
Zs
impedanceoftheselfinductor(Ω)
Δt
timebetweentiandti+1(s)
δ
anglebetweenV0andVg(°)
δref
referenceanglebetweenVrefandVg(°)
θ
theanglebetweenRsandXLs(°)
φ
powerangle(°)
ω
angularspeed(rads−1)
1.Introduction
Recently,renewableenergyresourceshavebeenbecomingpopularduetothedecreaseoffuelsourcesandtheirdamagestotheenvironment.Asaresultofthenegativeeffectsofglobalwarmingandclimatechanges,theinterestofrenewableresourceshasbeenincreasedgradually.
Solarenergyisoneofthesealternativeenergyresources.Itisconvertedtotheelectricalenergybyphotovoltaic(PV)arrays.PVarraysdonotgenerateanytoxicorharmfulsubstancesthatpollutetheenvironment([Kangetal.,2005a] and [Kangetal.,2005b]).Anotherconsiderablefeatureofthemistherequirementoflowmaintenance.Dependingonthedevelopmentinphotovoltaictechnologies,theefficiencyofthePVarrayshasbeenimproved.Therefore,studiesonPVsystemshaveincreasedgradually.
PVsystemsareoccasionallyoperatedinstand-alonemodeandtheyfeedfixedloadsbystand-alonePVinverters([Myrzik,2001],[Kangetal.,2005a],[Kangetal.,2005b],[Daheretal.,2008],[Lalounietal.,2009] and [SaravanaIlangoetal.,2010]).PVsystemsarealsointerconnectedtothegrid.InterconnectingaPVsystemtothegridhasbeenthepopulardesigntrendandgrid-connectiontypesofPVinvertershavebeenproposed([Calaisetal.,1999],[Myrzik,2001],[Kuoetal.,2001],[Alonsoetal.,2003],[Yuetal.,2005],[Wuetal.,2005],[Patcharaprakitietal.,2005],[Leeetal.,2008],[Hassaineetal.,2009] and [Rahimetal.,2010]).ThereforevariouspowerelectronicstechnologiesareimprovedtoconvertthedctoacpowerforPVapplications.
Inaddition,itisimportanttooperatePVenergyconversionsystemsnearthemaximumpowerpointtoincreasetheoutputefficiencyofPVarrays([Kuoetal.,2001],[Alonsoetal.,2003],[Yuvarajanetal.,2004],[Yuetal.,2005],[Patcharaprakitietal.,2005] and [Leeetal.,2008]).Thus,powerelectronicsinvertersarerequiredformaximumpowerpointtracking(MPPT)algorithm,whichprovidesmaximumPVpower.TheyarealsoneededfortransferringthePVpowertoaloadortothegrid.
Multilevelinvertersaresuitablechoicesforrealizingthisobjective.Variousmultilevelinvertertopologieshavebeenintroducedandstudiedintheliterature.Themostconsiderableofthesetypesarethediodeclamped,theflyingcapacitor,thecascadedH-Bridge,themagneticcoupledandthefullbridgewithcascadedtransformersinverters.Theremarkablefeatureoftheseinvertersisgeneratinglessharmoniccomponentsonbothoutputvoltageandloadcurrent.Byincreasingthenumberofoutputlevels,thequalityoftheoutputvoltageandloadcurrentisincreasedstepbystep([Calaisetal.,1999],[Rodriguezetal.,2002],[Kangetal.,2005a],[Kangetal.,2005b],[Daheretal.,2008],[Rahimetal.,2010] and [Beseretal.,2010]).Duetotheproductionoflessharmoniccomponents,thePVpoweristransferredtotheloadortothegridinahigh-qualityformbymultilevelinverterstructures.
Relatedtothesedevelopments,thisstudypresentsaPVassistedmultilevelinvertersystemfortheconversionofPVpowertotheelectricalpower.TheproposedstructureoftheinvertersystemisquitesuitablefortheuseofPVarrays.Owingtotheuseofamultilevelinverterstructure,moresinusoidalshapedoutputvoltagewavesareobtained.Therefore,theTHDoftheoutputvoltageisconsiderablyreduced.PlacementofthePVarraysinthesystemisthesignificantpointofthestudybecauseofloadingthearraysinthesamecondition.Toaccomplishthis,asimulationstudyisperformedandthenumberandconnectiontypesofthePVarraysinthesystemaredetermined.AccordingtotheorderofthePVarraysaconfigurationisformedforthePVassistedinvertersystem.Thesystemissimulatedwhileoperatingsynchronousandtransferringvariouspowervalueshavingdifferentcharacteristicstothegrid.Thevalidityoftheproposedsystemisalsoverifiedthroughanexperimentalstudy.ThemeasuredTHDvaluesoftheoutputvoltageandcurrentarequitelow.ThesystemprovidesgoodperformanceasaPVenergyconversionsystem.
2.ProposedPVassistedsingle-phasemultilevelinvertersystem
2.1.Configurationandstructuralpartsoftheproposedsystem
Fig.1showsthebaseconfigurationoftheproposedPVassistedmultilevelinverter.ItconsistsofPVmodules,levelmodules(LM)andaconventionalH-Bridgemodule.Thebaseconfigurationofthemultilevelinvertergeneratesa7-levelshapedoutputvoltagewave.However,theproposedsystemcanbeeasilyexpandedandthenumberofoutputvoltagelevelsisincreasedbyaddinglevelmodulestothesystem(Beseretal.,2010).
Fig.1. ConfigurationoftheproposedPVassistedsingle-phasemultilevelinvertersystem.
Viewthumbnailimages
Theproposedinverterstructureprovidesanadvantageinpointofswitchingelementnumbercomparedtosomeinvertertypesintheliterature.Aswitchnumbercomparisonrelatedtooutputlevelnumber(n)ismadebetweendifferentinvertertypesinTable1.
Table1.Switchnumbercomparisonrelatedtooutputlevelnumber(n).
Invertertype
Switchnumber
Diodeclamped
2(n − 1)
Flyingcapacitor
2(n − 1)
CascadedH-Bridge
2(n − 1)
Magneticcoupled
4 log3(n)
Full-bridgewithcascadedtransformer
4 log3(n − 2) + 4
Proposed
2 log2(n + 1) + 2
Full-sizetable
ItcanbeseenfromTable1that60switchesareusedindiodeclamped,flyingcapacitorandcascadedH-Bridgeinverterstoobtain31-leveloutputvoltage.Themagneticcoupledinvertertypeuses12switchesandshapes27-levelvoltagewave.Thefullbridgewithcascadedtransformerinvertertypeuses16switchesandforms29-levelshapedoutputvoltage.However,theproposedinverterachieves31-leveloutputvoltagebyusingonly12switches.
Anotherconsiderablefeatureoftheproposedinverteristhatthesystemconfigurationallowsoperatingregenerative.Sothisfeatureprovidestotransferbothactiveandreactivepowertothegrid.
2.1.1.PVmodule
Fig.2showstheconfigurationofthePVmodule.ItcanbeseenfromFig.2thatitconsistsofPVarraysandacapacitorgroup.
Fig.2. ConfigurationofthePVmodule.
Viewthumbnailimages
Dependingontheincreaseoftheoutputlevelnumber,PVarraysaresuitablyconnectedseriallyandPVmoduleisexpandedaccordingtothenumberoflevelmodules.TheconfigurationoftheexpandedPVmoduleisshowninFig.3.
Fig.3. ConfigurationoftheseriallyconnectedPVarraysinthePVmo
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