Low cost and high efficiency of single phase photovoltaic system based on microcontroller.docx
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Low cost and high efficiency of single phase photovoltaic system based on microcontroller.docx
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Lowcostandhighefficiencyofsinglephasephotovoltaicsystembasedonmicrocontroller
Lowcostandhighefficiencyofsinglephasephotovoltaicsystembasedonmicrocontroller
LotfiKhemissia,
BrahimKhiaria,
RidhaAndoulsia,
AdnaneCherifb
aResearchCenterofEnergy(CRTEn),BorjCedriaScienceandTechnologyPark,HammamLif2050,Tunisia
bFacultyofSciencesofTunis,TunisElManarUniversity,2092Tunis,Tunisia
Received18June2010.Revised3December2011.Accepted21December2011.Availableonline2February2012. Communicatedby:
AssociateEditorArturoMoralesAcevedo.
http:
//dx.doi.org/10.1016/j.solener.2011.12.019,HowtoCiteorLinkUsingDOI
CitedbyinScopus(0)
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Abstract
Thispaperpresentsatheoreticalandpracticalstudyofasinglephasephotovoltaicconversionsystem.Itconsistsofastepdownconvertertochargeabatterywiththemaximumpoweravailablefromphotovoltaicgenerator(PVG)andasinglephasevoltagesourceinverter(VSI)toproduceastableACvoltage(220 V/50 Hz)withlowertotalharmonicdistortion(THD).AnewperturbandobservealgorithmisdesignedandimplementedinacheapermicrocontrollerPIC16F876wherethedutycycleperturbationandthesamplingperiodareselectedtoinsurethestabilityofthePVsystemaroundthemaximumpower.ThecontrolstrategyadoptedfortheinverteristheSelectiveHarmonicEliminatedPulseWidthModulation(SHEPWM).ThepulsesarecalculatedandtransferredonthePIC16F876memory.Withthistechnique,inverterlossesaredecreasedandtheoutputvoltageiseasilyfilteredwithasimplelowpassfilterproducingaperfectlysinewaveformvoltage.Thebatteryissizedtosupplyloadsinnon-sunnytimes.
Withoptimizationofitsvariouscomponents,theconventionalsinglephasePVsystemhasalowcost,highefficiencybutalsogoodpowerqualitywhichrepresentsagoodopportunitytouseitinmanystandalonephotovoltaicapplicationssuchashouseslighting.AnexperimentalsystemhasbeenmadetodemonstratetheefficiencyofthephotovoltaicsystemandtovalidatesimulationsdonebyMatlab–Simulinkenvironment.
Highlights
►WesimulateandtestalowcostandhighefficiencysinglephasePVsystem.►AnewMPPTalgorithmisimplementedonmicrocontrollertochargeabattery.►MPPTalgorithmParametersdependonthedynamicbehaviorofthePVsystem.►AsinglephaseVSIisimplementedwithgoodpowerqualityandreducedlosses.►ModularconfigurationallowingeasyprogrammodificationofthePVsystemconverters.
Keywords
Photovoltaicgenerator;
Buckconverter;
MaximumPowerPointTracking(MPPT);
Singlephaseinverter;
SelectiveHarmonicPulseWidthModulation;
Filter
Nomenclature
PVG
photovoltaicgenerator
VSI
voltagesourceinverter
THD
totalharmonicdistortion
SHEPWM
selectiveharmoniceliminatedpulsewidthmodulation
MPPT
maximumpowerpointtracking
PO
perturbandobservealgorithm
Iph
photocurrentofthephotovoltaicgenerator(A)
Is
cellreversesaturationcurrent(A)
K
Boltzman’sconstant(1.38 10−23 J K−1)
KT
temperaturecoefficientofthecell(55 e−4 K−1)
T
temperatureofthecellinKelvin(K),
G
irradiation(W/m2)
A
constantwithrespecttothetemperature(0.06 A K−3)
q
chargeoftheelectron(1.6 × 10−19 C)
Eg
bandgap(V)
B
idealityfactorofthejunction
ns
numberofcellsinseries
np
numberofcellsinparallel
Rs
cellseriesresistance(Ω)
Rsh
cellshuntresistance(Ω)
Varray
voltageofthearray(V)
Iarray
arraycurrent(A)
Voc
opencircuitvoltageofthePVG(V)
Isc
shortcircuitcurrentofthePVG(A)
Vmp
voltageatmaximumpowerofthePVG(V)
Imp
PVGcurrentatmaximumpower(A)
D(k)
dutycycleoftheDC/DCconverteratksampling
D0
dutycycleinitialization
I(k)
PVGoutputcurrentatksampling
V(k)
PVGvoltageatksampling
P(k)
PVGpoweratksampling
Δd
dutycycleperturbation
CCM
continuousconductionmode
L
inductanceoftheDC/DCconverter(H)
C
CapacitoroftheDC/DCconverter(F)
ΔiLmax
maximumpeaktopeakrippleoftheinductorcurrent(A)
ΔVsmax
maximumvalueofthepeak-to-peakrippleoutputvoltageoftheDC–DCconverter(V)
fs
switchingfrequency(Hz)
Cpv
inputcapacitor(F)
Dm
dutycycleatmaximumconverteroutputpower
Iom
DCcomponentoftheDC/DCoutputcurrentatmaximumoutputpower(A)
Rpm
PVarrayinternalresistanceatthemaximumpowerpoint(Ω)
Rpv
equivalentresistanceofthesimplifiedPVGmodel(Ω)
D
dutycycle
smallvariationofPVGvoltage,PVGcurrentandthedutycycleoftheconverter
io
smallvariationoftheDC/DCconverteroutputcurrent(A)
Cf
filtercapacitor(H)
Lf
filterinductance
ηMPPT
MPPTefficiency
Pactual
measuredpowerofthePVgenerator(W)
Pmax
maximumpowerthatthePVgeneratorcanproduceundergivenirradianceandtemperature(W)
Rds
onresistanceoftheMosfet(Ω)
PMosfet,loss
Mosfetlosses(W)
tr
risetime(s)
tf
falltime(s)
Qgate
reverserecoverycharge(C)
Vd
forwardvoltagedropofthediode(V)
Rcu
inductorresistance(Ω)
Pcore
inductorcorelosses(W)
1.Introduction
Duetorisingcostsofconventionalenergyandtheirlimitedresources,photovoltaicenergybecomesapromisingenergywithadvantagessuchastheabsenceofanypollutionandtheavailabilitywithmoreorlesslargequantitiesanywhereintheworld.Currently,thereisabiginterestinsolarenergyapplicationsespeciallyinregionswithfavorableclimaticconditions.Amongtheseapplicationswementionwaterpumpingandlightingespeciallyinisolatedsites.
TheaimofthispaperistodevelopaphotovoltaicapplicationthatprovidesastableACvoltage(220 V/50 Hz)fromnon-linearphotovoltaicgenerator(PVG)withhighefficiencyandlowcost.
Firstly,thephotovoltaicgeneratorrechargesabatterythroughabuckconvertercontrolledbyamicrocontroller16F876totrackthemaximumpowerfromthePVGwithanewperturbandobservealgorithm,thenasingle-phasevoltagesourceinverter(VSI)convertsthebatteryvoltage(24 V)toastableACvoltage(220 V/50 Hz)afterassociationwithasimplelowpassfilterandastep-uptransformer.Theinverterpulsesarecalculatedtoeliminate5th–9thorderharmonicsandthensavedinthePIC16F876memory.TheACphotovoltaicsystemasdesignedcanbeabestsolutionfordomesticapplicationssincetheircomponentsarewellsizedtodecreaselossesandthusdecreasingtheoverallpriceofthesystem.
In(AkkayaandKulaksiz,2004),authorshavedevelopedahighefficiencyACphotovoltaicsystembuttheyhaveusedasolartrackerbasedonasteppermotortoincreasetheefficiencyofthesystem,howeverthissolutionincreasestheoverallpricecomparingwiththeusesofmaximumpowerpointtracking(MPPT)algorithmstomatchthemaximumpowerofthePVGindependentlyoftheclimaticconditions.
Inliterature,severalalgorithmsaredevelopedtoextractthemaximumpowerpoint(MPP)fromthePVGsuchastheincrementalconductance(INC),PerturbandObserve(PO)andFuzzyLogic(FL)programsdifferinthestabilityoftheoperatingpointaroundtheoptimalpoint.(Lalounietal.,2009)proposesamethodbasedonafuzzycontrollertoextracttheMPPandsignificantlydecreasestheoscillationaroundtheoperatingpointhoweverthismethodrequiresanadvancedcontrolplatform.TheINCandthePOarethetwomostusedalgorithmsinpractice,thefirstismoreadaptedtoabruptclimaticchanges,butitrequiresalongercalculationtime.
InthePOalgorithmThePVGcurrentandvoltagearesensed,thenPVGpoweriscomputed,dependingonthesignofthedifferencebetweenPVGoutputpoweratksamplingandk + 1sampling,thedutycycleischanged,thenaPIcontrollerregulatestheoutputvoltageorcurrenttoreachitsreference.ThismethodcanbeimprovedbyusingamicrocontrollerwithPWMoutputs,inthiscasethecontrollerisomittedandthecontroloutputvariableisthedutycycle.(Koutroulisetal.,2001)usedthePOalgorithmonthecheapermicrocontrollerforbatterychargingapplicationinsteadofHuaetal.(1998)whereaDSPplatformwasusedtodeveloptheconverter;thePVoutputpowerisincreasedby15%.In(Albertoetal.,2009)anewbatterychargingbasedonmicrocontrollerisdeveloped,theoutputpowerisincreasedby25%andtheMPPTefficiencyreached95%.HoweverthismethodusedananalogcontroltoreachtheoptimalcurrentreferencewhichaffectstherapidityofthesystemtotracktheMPPinthecaseofsuddenclimaticvariations.In(Salasetal.,2005)authorspresentedabatterychargingapplicationwithamicrocontroller,onlythePVGcurrentwassensedthusdecreasingtheoverallprice,theefficiencywasincreasedby18.5%butthedutycycleperturbationneedstobequantifieddependingonthedynamicofthesystemtoimproveefficiencyandtoensureasystemstability.(Feimiaetal.,2005)presentedanoptimizationmethodofPOintermsofvariationofdutycycleandsamplingperiodandthusensuredagoodMPPtrackingevenasuddenchangeofirradiationoccurred(50 W/m2).InTarikDuru,2006amaximumpowertrackingbasedonImpp = f(Pmax)functionwasimplemented.ThisapproachneedspredeterminedexperimentalvaluesofPmaxandImppofthePVGfordifferentirradiances.WiththismethodtheimplementedcircuitmustbechangedoncethePVGmodulesconfigurationchanges,theoscillationsaroundthemaximumpowerpointareconsiderable.
InthispaperanewPOalgorithmisused.ThedutycycleperturbationandthesamplingperiodofPVGvoltageandcurrentareselecteddependingonthesystemstabilitywhileanewtestontheoutputpowerforcesthesystemtooperateneartheMPPifasuddenirradiationoccur(100 W/m2/s)thusd
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