外文翻译原文-双轴太阳跟踪器的设计与实现光学传感器基于光电传感器的单电机光伏系统

Sensors2013,13,3157-3168;doi:10.3390/s130303157sensorsISSN1424-8220/journal/sensorsArticleDesignandImplementationofaSunTrackerwithaDual-AxisSingleMotorforanOpticalSensor-BasedPhotovoltaicSystemJing-MinWang*andChia-LiangLuDepartmentofElectricalEngineering,St.JohnsUniversity,499,Sec.4,TamKingRoad,TamsuiDistrict,NewTaipeiCity25135,Taiwan;E-Mail:.tw*Authortowhomcorrespondenceshouldbeaddressed;E-Mail:.tw;Tel.:+886-2-2801-3131(ext.6529);Fax:+886-2-2801-1972.Received:31January2013;inrevisedform:3March2013/Accepted:4March2013/Published:6March2013Abstract:Thedualthreatsofenergydepletionandglobalwarmingplacethedevelopmentofmethodsforharnessingrenewableenergyresourcesatthecenterofpublicinterest.Solarenergyisoneofthemostpromisingrenewableenergyresources.Suntrackerscansubstantiallyimprovetheelectricityproductionofaphotovoltaic(PV)system.Thispaperproposesanoveldesignofadual-axissolartrackingPVsystemwhichutilizesthefeedbackcontroltheoryalongwithafour-quadrantlightdependentresistor(LDR)sensorandsimpleelectroniccircuitstoproviderobustsystemperformance.Theproposedsystemusesauniquedual-axisACmotorandastand-alonePVinvertertoaccomplishsolartracking.Thecontrolimplementationisatechnicalinnovationthatisasimpleandeffectivedesign.Inaddition,ascaled-downlaboratoryprototypeisconstructedtoverifythefeasibilityofthescheme.TheeffectivenessoftheSuntrackerisconfirmedexperimentally.Toconclude,theresultsofthisstudymayserveasvaluablereferencesforfuturesolarenergyapplications.Keywords:dual-axisSuntracker;photovoltaicpanel;feedbackcontroltheory;lightdependentresistor;stand-alonePVinverter;energygain1.IntroductionWiththerapidincreaseinpopulationandeconomicdevelopment,theproblemsoftheenergycrisisandglobalwarmingeffectsaretodayacauseforincreasingconcern.TheutilizationofrenewableOPENACCESSSensors2013,133158energyresourcesisthekeysolutiontotheseproblems.Solarenergyisoneoftheprimarysourcesofclean,abundantandinexhaustibleenergy,thatnotonlyprovidesalternativeenergyresources,butalsoimprovesenvironmentalpollution.Themostimmediateandtechnologicallyattractiveuseofsolarenergyisthroughphotovoltaicconversion.ThephysicsofthePVcell(alsocalledsolarcell)isverysimilartotheclassicalp-njunctiondiode.ThePVcellconvertsthesunlightdirectlyintodirectcurrent(DC)electricitybythephotovoltaiceffect1,2.APVpanelormoduleisapackagedinterconnectedassemblyofPVcells.InordertomaximizethepoweroutputfromthePVpanels,oneneedstokeepthepanelsinanoptimumpositionperpendiculartothesolarradiationduringtheday.Assuch,itisnecessarytohaveitequippedwithaSuntracker.Comparedtoafixedpanel,amobilePVpaneldrivenbyaSuntrackermayboostconsistentlytheenergygainofthePVpanel.SolartrackingisthemostappropriatetechnologytoenhancetheelectricityproductionofaPVsystem.Toachieveahighdegreeoftrackingaccuracy,severalapproacheshavebeenwidelyinvestigated.Generally,theycanbeclassifiedaseitheropen-looptrackingtypesbasedonsolarmovementmathematicalmodelsorclosed-looptrackingtypesusingsensor-basedfeedbackcontrollers35.Intheopen-looptrackingapproach,atrackingformulaorcontrolalgorithmisused.Referringtotheliterature610,theazimuthandtheelevationanglesoftheSunweredeterminedbysolarmovementmodelsoralgorithmsatthegivendate,timeandgeographicalinformation.Thecontrolalgorithmswereexecutedinamicroprocessorcontroller11,12.Intheclosed-looptrackingapproach,variousactivesensordevices,suchaschargecoupledevices(CCDs)1315orlightdependentresistors(LDRs)12,1619wereutilizedtosensetheSunspositionandafeedbackerrorsignalwasthengeneratedtothecontrolsystemtocontinuouslyreceivethemaximumsolarradiationonthePVpanel.Thispaperproposesanempiricalresearchapproachonthisissue.Solartrackingapproachescanbeimplementedbyusingsingle-axisschemes12,1921,anddual-axisstructuresforhigheraccuracysystems1618,2227.Ingeneral,thesingle-axistrackerwithonedegreeoffreedomfollowstheSunsmovementfromtheeasttowestduringadaywhileadual-axistrackeralsofollowstheelevationangleoftheSun.Inrecentyears,therehasbeenagrowingvolumeofresearchconcernedwithdual-axissolartrackingsystems.However,intheexistingresearch,mostofthemusedtwosteppermotors22,23ortwoDCmotors16,17,24,25toperformdual-axissolartracking.Withtwotrackingmotorsdesigns,twomotorsweremountedonperpendicularaxes,andevenalignedthemincertaindirections.Insomecases,bothmotorscouldnotmoveatthesametime5.Furthermore,suchsystemsalwaysinvolvecomplextrackingstrategiesusingmicroprocessorchipsasacontrolplatform.Inthiswork,employingadual-axiswithonlysingletrackingmotor,anattempthasbeenmadetodevelopandimplementasimpleandefficientcontrolscheme.ThetwoaxesoftheSuntrackerwereallowedtomovesimultaneouslywithintheirrespectiveranges.Utilizingconventionalelectroniccircuits,noprogrammingorcomputerinterfacewasneeded.Moreover,theproposedsystemusedastand-alonePVinvertertodrivemotorandprovidepowersupply.Thesystemwasself-containedandautonomous.ExperimentresultshavedemonstratedthefeasibilityofthetrackingPVsystemandverifiedtheadvantagesoftheproposedcontrolimplementation.Theremainderofthearticleisorganizedinthefollowingmanner:Section2describesthetrackingstrategiesofthedevelopedclosed-loopsolartrackingsysteminwhichasensor-basedfeedbackcontrollerisused.ThedetailedarchitectureoftheSuntrackerhardwareisproposedinSection3.InSensors2013,133159Section4,ascaled-downlaboratoryprototypeisbuiltandtested.Finally,themainconclusionsofthisworkaredrawninSection5.2.DevelopedClosed-LoopSolarTrackingSystemTheblockdiagramofthedevelopedclosed-loopsolartrackingsystemisillustratedinFigure1,describingthecompositionandinterconnectionofthesystem.Fortheclosed-looptrackingapproach,thesolartrackingproblemishowtocausethePVpanellocation(output)tofollowthesunlightlocation(input)ascloselyaspossible.Thesensor-basedfeedbackcontrollerconsistsoftheLDRsensor,differentialamplifier,andcomparator.Inthetrackingoperation,theLDRsensormeasuresthesunlightintensityasareferenceinputsignal.TheunbalanceinvoltagesgeneratedbytheLDRsensorisamplifiedandthengeneratesafeedbackerrorvoltage.TheerrorvoltageisproportionaltothedifferencebetweenthesunlightlocationandthePVpanellocation.Atthistimethecomparatorcomparestheerrorvoltagewithaspecifiedthreshold(tolerance).Ifthecomparatoroutputgoeshighstate,themotordriverandarelayareactivatedsoastorotatethedual-axis(azimuthandelevation)trackingmotorandbringthePVpaneltofacetheSun.Accordingly,thefeedbackcontrollerperformsthevitalfunctions:PVpanelandsunlightareconstantlymonitoredandsendadifferentialcontrolsignaltodrivethePVpaneluntiltheerrorvoltageislessthanapre-specifiedthresholdvalue.Figure1.Blockdiagramofthesolartrackingsystem.ThesystemtrackstheSunautonomouslyinazimuthandelevationangles.ThewholeworkingalgorithmsaresummedupintheflowchartsshowninFigures2and3.ThesunlightintensityfromfourdifferentdirectionsismeasuredbytheLDR-basedsensingcircuit.ThevoltagesvE,vW,vSandvNaredefinedasthesensingvoltagesproducedbytheeast,west,south,andnorthLDRsrespectively.InanattempttodrawmaximumpowerfromthePVpanel,theazimuthandelevationtrackingprocessescansimultaneouslyproceeduntilthePVpanelisalignedorthogonallytothesunlight.Thetrackerinstallationisnotrestrictedtothegeographicallocation.Sensors2013,133160Figure2.Flowchartoftrackingalgorithmforazimuthcontrol.Figure3.Flowchartoftrackingalgorithmforelevationcontrol.2ThWEVvv2ThNSVvvEWWEvvv3.2.ComparatorThemainfunctionofthecomparatoristoactasaswitchtoturnontherelayandrotatethemotor.Acomparatorisessentiallyanoperationalamplifier(op-amp)operatedinanopen-loopconfiguration,whichconvertsatime-varyinganalogsignalintoabinaryoutput.AsdepictedinthesecondpartofFigure4,thecomparatorisdesignedtocomparetheerrorvoltagewithtwothresholdvalues.Thethresholdvalueisdefinedastheinputvoltageatwhichtheoutputchangesstates.AsshowninFigure4,therearetwothresholdvalueswhicharegivenas:CCThVRRRV4341+=(3)(4342CCThVRRRV+=(4)TheoutputofthecomparatorisahighsaturatedstateVHoralowsaturatedstateVL.ThesaturatedoutputvoltagesVHandVLmaybeclosedtothesupplyvoltages+VCCandVCC,respectively.Thecomparatoroutputsarethenexpressedasfollows:Sensors2013,13316311forforThEWLThEWHPEVvVVvVv=(5)22forforThEWHThEWLPWVvVVvVv=(6)Thevoltagetransfercharacteristicsofthecomparatorwithidealop-ampsareshowninFigure6.Itisnotedthatthesensitivityforthetrackingsystemisdominatedbythethresholdvalues,whichareadjustedbythevariableresistorR4accordingtothetrackingaccuracy.AsR4decreases,thetrackingaccuracyincreases.However,thesystemtrackingresponsewillbecomeincreasinglyoscillatory.Figure6.Voltagetransfercharacteristicsoftheopen-loopcomparator.3.3.MotorDriverwithaRelayAsseeninthelastpartofFigure4,itisobservedthatthedesignedmotordriverwitharelayconsistsoftwoDarlingtonpairsthatprovideincreasedcurrentgainandactuatetherelay.IfthewestLDRisshaded,afeedbackerrorvoltagevEWisgenerated.WhenvEWVTh1VTh2,thecomparatoroutputsvPEandvPWgohighandlowsaturatedvoltagesrespectively.ThetransistorsQ1andQ2willthereforeconductandQ3andQ4areinthecutoffstate.ReferringtoFigure4,transistorsQ1andQ2operateintheforward-activemode,andtheinputcurrentorthebasecurrentofQ1is:RVVVIBEBEHB211=(7)whereVBEistheforward-biasedbase-emittervoltageofthebipolartransistor.Therefore,theoutputcurrentcanbewrittenas:121122111211211)1()1(BBBBCCOIIIIIII+=+=+=(8)Theparameters1and2arethecommon-emittercurrentgainofthebipolartransistors.Therelayisactivatedbytheoutputcurrentandnormally-opencontacta1closes.Inthiscase,thetrackingmotorrotatesclockwiseintheazimuthdirectionandthusthePVpanelmoveseastwardtofacetheSun.Morespecifically,theSuntrackerattemptstoadjustthePVpanelsuchthatallthevoltagesproducedbyLDRsarenearlyequalandbalance.Asaresult,thePVpanelisalmostperpendiculartothesunlightandhasahighenergygeneration.Sensors2013,1331643.4.Stand-AlonePVPowerSystemAstand-aloneoroff-gridPVpowersystemisdesignedtochargeDCpowergeneratedbyPVpanelintobatteryandconverttheDCelectricityintoACsourceforACappliances.Thestand-alonepowersystemisdepictedinFigure7.Theinverterchanges12VDCinputvoltageto120VACoutputvoltageusedtopowertheACmotorandprovidethepowersupply.ThemotorrotatesthePVpanel,andthepowersupplyprovidesaDCsourcetotheentirecircuit.Inotherwords,thedevelopedsystemhasanautonomousenergysupply.Figure7.Stand-alonePVpowersystem.4.ExperimentValidationToverifytheperformanceoftheSuntrackerandtoillustratethefeasibilityofthecontrolscheme,alaboratoryprototypeofthesolartrackingsystemwasbuiltandtested.ThisworkwasdoneinNewTaipeiCity,Taiwanon16May2012.Itwaspartlycloudyday.ThelatitudeofTaiwanis23.5degreesnorth,sothatthefixedpanelwasfacedthesouthatatiltangleof23.5degreeswithmaximumaveragesolarradiation.4.1.ExperimentTestsFigure8showstheexperimenttestsonthepolycrystallinePVpanelwiththeSuntrackerandwithafixedangle.Thephysicaldimensions(LWD)ofthePVpanelwere835mm518mm30mm.Thechosenuniquemotorforthisworkwasdual-axis117VACmotor(LILINPIH-303)withaspeedof6/sinpanand3/sintilt.Ithadtwodegreesoffreedomtomovethepanelintheazimuthangleandthealtitudeanglesimultaneously.Theworkemployedpaperlessrecorder(YOKOGAWAFX106)todisplaythereal-timemeasurementofthevoltageandcurrentgeneratedbyPVpanel.TheEarthrotates15degreeswithrespecttoitsaxisperhour,andtheSunmovesslowly26,28.Tominimizepowerconsumption,thetrackingmotorwasnotoperatedcontinuously.ThedevelopedsystemthusadoptedatimeschedulealgorithmtofollowtheSunabouteveryhalfanhourbyvaryingtheresistorR4.Sensors2013,133165Figure8.Actualphotographoftheexperimentalprototype.4.2.ExperimentResultsThemeasurementresultsofgeneratingvoltageandcurrentwaveformsforthefixedandtrackingPVsystemsareshowninFigures9and10,respectively.Inordertogiveaclearexplanationontheenergyproductivity,thegeneratinginstantaneouspowersofthebothsystemswerefurthercalculated.Figure11showsthetestresultswithpromisingoutcome.Figure9.MeasuredtimefunctionsofoutputvoltageandcurrentforfixedPVsystem.Sensors2013,133166Figure10.Measuredtimefunctionsofoutputvoltageandcurrentforsolartrackingsystem.Figure11.Comparisonofthegeneratingpowersforthetrackingandfixedsystems.4.3.PerformanceAnalysisAsshowninFigure11,theperformanceofthetrackingsystemwassignificantlylessatnoon.ItcouldbereasonedthatbothofthePVpanelsalmostfacedthesamedirection,butaslightdifferenceofangle.Theincreaseinpowerwasfocusedintheafternoon.Thegeneratingelectricalenergiesforthefixedandtrackingsystemswere95.52W-hand123.06W-h,respectively.Therefore,anextrayieldof(123.0695.52)/95.52=0.2883or28.83%energygenerationwasobtained.Theincreasedsolarenergywasconsistentwiththeexistingliterature18,23,27.Energygainisthemostimportantfactorinevaluatingatrackingsystem.Theenergygainmeanshowmuchthetrackingsystemincreasestheenergygeneratedcomparedwithafixedsystem.However,tocalculatethenetenergygainofthetrackingsystem,energyconsumptionoftherotatingmotorshouldbeconsidered.Themotorenergyconsumptionwas0.5W-h.Theenergygainofthetrackingsystemwas(123.0695.520.5)/95.52=0.2831or28.31%.ThepartlycloudydaywouldVoltage(V)Current(A)TrackingsystemFixedsystem35.0025.0020.0015.0010.005.000.0030.0011:0011:4012:2013:0013:4014:2015:0015:4016:2017:00Sensors2013,133167affecttheenergygeneration.Moreover,ifthetrackingfrequencywasadjustedreasonablyaccordingtoactualtrackingcondition,theimprovedelectricityproductioncanbefurtherenhanced.5.ConclusionsThepaperhaspresentedanovelandasimplecontrolimplementationofaSuntrackerthatemployedasingledual-axisACmotortofollowtheSunandusedastand-alonePVinvertertopowertheentiresystem.Theproposedone-motordesignwassimpleandself-contained,anddidnotrequireprogrammingandacomputerinterface.Alaboratoryprototypehasbeensuccessfullybuiltandtestedtoverifytheeffectivenessofthecontrolimplementation.Experimentresultsindicatedthatthedevelopedsystemincreasedtheenergygainupto28.31%forapartlycloudyday.Theproposedmethodologyisaninnovationsofar.Itachievesthefollowingattractivefeatures:(1)asimpleandcost-effectivecontrolimplementation,(2)astand-alonePVinvertertopowertheentiresystem,(3)abilitytomovethetwoaxessimultaneouslywithintheirrespectiveranges,(4)abilitytoadjustthetrackingaccuracy,and(5)applicabletomovingplatformswiththeSuntracker.Theempiricalfindingsleadustobelievethattheresearchworkmayprovidesomecontributionstothedevelopmentofsolarenergyapplications.References1.Shen,C.L.;Tsai,C.T.Double-linearapproximationalgorithmtoachievemaximum-power-pointtrackingforphotovoltaicarrays.Energies2012,5,19821997.2.Liu,K.H.Dynamiccharacteristicsandgraphicmonitoringdesignofphotovoltaicenergyconversionsystem.WSEASTrans.Syst.2010,10,239248.3.Nayak,S.R.;Pradhan,C.R.Solartrackingapplication.IOSRJ.Eng.2012,2,12781281.4.Lee,C.Y.;Chou,P.C.;Chiang,C.M.;Lin,C.F.Suntrackingsystems:Areview.Sensors2009,9,38753890.5.Rubio,F.R.;Ortega,M.G.;Gordillo,F.;Lopez-Martinez,M.Applicationofnewcontrolstrategyforsuntracking.Energ.Conv.Manage.2007,48,21742184.6.Blanco-Muriel,M.;Alarcon-Padilla,D.C.;Lopez-Moratalla,T.;Lara-Coira,M.Computingthesolarvector.SolarEnergy2001,70,431441.7.Chong,K.K.;Siaw,F.L.;Wong,C.W.;Wong,G.S.Designandconstructionofnon-imagingplanarconcentratorforconcentratorphotovoltaicsystem.RenewableEnergy2009,34,13641370.8.Grena,R.Analgorithmforthecomputationofthesolarposition.SolarEnergy2008,82,462470.9.Reda,I.;Andreas,A.Solarpositionalgorithmforsolarradiationapplications.SolarEnergy2004,76,577589.10.Sproul,A.B.Derivationofthesolargeometricrelationshipsusingvectoranalysis.Rene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