Damping control strategy for reducing voltage unbalance in three-phase inverter

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2018ChinaInternationalConferenceonElectricityDistributionTianjin,17-19Sep.2018DampingControlStrategyforReducingVoltageUnbalanceinthree-phaseInverter1122DONGLEI,ZHANGTAO,PUTIANJIAO,CHENNAISHI1.NorthChinaElectricPowerUniversity，2.ChinaElectricPowerResearchInstituteoftreatment.Thedistributedpowergrid-connectedinverterinAbstract—Inviewofsingle-phaseandthree-phaseloadthemicro-gridhasthesamehardwarestructureandsimilarcoexistinlow-voltagedistributionnetwork,causingunbalanceofcontrolmethodwiththecompensationdevice.Ifanappropriatethethreephasevoltages,thispaperproposedadampingcontrolcontrolstrategyisadopted,theinverterwhichcancarryoutstrategybasedonthree-phaseinvertertoreducevoltageadditionalpowerqualityatthesametimeofoutputpower[8].unbalancefactor.ThemathematicalmodeloftheactivepowerdampingcontrolstrategyoftheinverterisestablishedbasedonAimingattheproblemofvoltageunbalancecompensationthesequentialcomponentmethod.Byanalyzingtheprincipleofforinverters,byusingthecurrentcommandsignalgeneratedbyactivepoweroutputandvoltageunbalancesuppression,theactivethenegativesequencereactive-conductancedroop-controlandreactivepowercooperativedampingcontrolstrategyforstrategy,whichcanreducethevoltageunbalance[9].In[10],threephaseinverterswasdeduced.Casestudiesarecarriedoutonaninvertervoltagecontrolstrategythatcanautomaticallya10busasymmetricdistributionnetwork.Theresultsverifythatcompensatefornegativesequencevoltageisproposed.In[11],thecontrolstrategyproposedoftheinverterinthispaperwhichcanrealizepoweroutputandreducethevoltageunbalanceofthe[12],amulti-functiongrid-connectedinvertercapableofnetwork.simultaneouslycompensatingforreactivepower,harmonicsandvoltageunbalanceinthemicro-gridisproposed.TheIndexTerms—low-voltagedistributionnetwork,three-phaseimproveddroopcontrolstrategyforthree-phaseinverteralsoinverter,thedampingcontrolstrategy,voltageunbalancefactorcanreducevoltageunbalance[13].In[14],[15]theinverteradoptsthree-phaseactivedampingcontrolstrategy,andtheunbalancedcurrentisadaptivelycompensatedaccordingtotheI.INTRODUCTIONmagnitudeoftheunbalancedvoltagecanreducethevoltageTHElow-voltagedistributionnetworksusethree-phaseandunbalance.However,thereactivepoweroutputanditsfour-wirepowersupplymode.Thecoexistenceofunbalancedcompensationcapabilityareignoredinthesesingle-phaseandthree-phaseloadwillinevitablyleadtopapers.three-phasevoltageimbalance[1],[2].AnunbalancedAimingatthree-phasefourwirelowvoltagedistributiondistributionsystemwillbesubjectedtomorelossesandheatingnetwork,thispaperproposedadampingcontrolstrategybasedeffects.Voltageunbalancecanalsohavenegativeeffectsononthree-phaseinvertertoreducevoltageunbalancefactor.equipmentsuchasinductionmotors,powerelectronicWhiletheinverteroutputsactiveandreactivepowertotheconvertersandadjustablespeeddrives[3].outside,theunbalancedcurrentcanbeadaptivelycompensatedByusingseriespowerqualityconditionertocompensateaccordingtotheunbalancedvoltagetoreducethevoltagenegativesequencevoltageinthesystemorusingparallelpowerunbalance.Finally,anexampleisgiventoillustratethequalityconditionertocompensateunbalancedcurrentcorrectnessandeffectivenessoftheproposedcontrolstrategy.introducedbyunbalancedload[4]-[7].Thesearealleffectivemeasurestoeliminatevoltageunbalance.ButtheyallneedII.DISTRIBUTEDGRIDCONNECTEDINVERTERadditionalcompensationdevices,whichwillincreasesthecostThedistributedgenerationisusuallyconnectedwithlowvoltagenetworkthroughinverter.TheconsideredinverterManuscriptreceivedJuly14,2018.ThisworkwassupportedinpartbythetopologyisdepictedinFig.1.Thephasea,b,andcshareaDCNationalKeyResearchandDevelopmentProgramofChinabus.AndtheDCbuscanbeafuelcell,aphotovoltaicpanelor(No.2017YFB0903300)andtheBeijingNaturalScienceFoundationanenergystoragedevice.Duetotheexistenceofasymmetric(No.3161002).DONGLei,associateprofessor,fromNorthChinaElectricPowerloads,thenegativesequencecurrentandthezerosequenceUniversity,Beijing,102206,China.(Emailaddress:hbdldl@126.com).currentflowthroughthelineimpedancewillcausevoltagedropZhangTao,mastergraduatestudent,fromNorthChinaElectricPowerthatwillresultthree-phasevoltageunbalance.BycontrollingUniversity,focusesonpowersystemanalysisoperationandcontrol.Telephonetheinverter,ifthisunbalancedcurrentcanbeeffectivelynumberis15501237366.(Emailaddress:Ztncepu639@126.com).CICED2018PaperNo.201804270000334Page1/5706

12018ChinaInternationalConferenceonElectricityDistributionTianjin,17-19Sep.2018compensated,thevoltageunbalanceoftheentirenetworkwillSZ1bereduceandthepowerqualityinsystemcanbeimproved.S1S3S5SVeqZload1LU111g1iauLaIdgaA1LiLbbU(a)PositivesequenceubLBdcNZ2SZ0SiLccuCcSSS246load11SeqZUSeqZloadcccU2V22gd0V00gdfffLdgdgnI2I0un(b)Negativesequence(c)ZerosequenceFig.1.ThreelegandfourwirevoltagesourceinvertertopologyFig.2.ThreesequencenetworkequivalentcircuitofdampingcontrolstrategyAccordingtothesymmetricalcomponenttheory,theAccordingtothecurrentdirectionshowninthefigure,asymmetricalthree-phasevoltagecandecomposethepositivenegativesequenceandzerosequencevoltagesatisfy:sequence,negativesequenceandzerosequencevoltage.TheZload||1/gZloadeq2,0dS2,0SvoltageunbalancefactorcanbeusedtomeasurethemagnitudeV2,0SloadU2,0SloadU2,0(3)Z(Z||1/g)Z(Z)2,02,0d2,02,0ofthethree-phasevoltageoffset.Theequationshowsthatthedampingcontrolstrategybyu2u22r2ipVUF2100%usingdampingconductancegdcanreducethenegativeu2u21r1i(1)sequenceandzerosequencevoltage,thentoreducethevoltage22unbalancefactorofthenetwork.uu0r0iVUF100%022Thekeytocontroltheactivepoweroutputoftheinverterisu1ru1ipthecontrolforthefundamentalconductanceg1.ThesequencewithVUF2andUVF0thenegativesequenceandzerocomponentsofvoltageandcurrentareconvertedintophasesequencevoltageunbalancefactor;u0,1,2randu0,1,2itherealandcomponentsinequation(2)areasfollows.imaginarypartsofunbalancedvoltagecomponents.1pppp2ppiug2gauggauggaa1db1dc1d3III.DAMPINGCONTROLSTRATEGYOFINVERTERi1a2ugpgpugp2gpaugpgp(4)ba1db1dc1dA.ActivePowerDampingControlStrategy31pp2ppppTheinverterwithactivedampingcontrolstrategycaniauggauggug2gca1db1dc1d3providecompensationcurrenttoreducevoltageunbalanceTheactivepoweroutputoftheinverterissatisfied:factorwhileitoutputstheactivepower.Thethree-sequence***PRe(uiuiui)(5)voltageandcurrentsatisfy:refaabbccigpuThefundamentalconductancecanbeobtainedby0d0igpusimultaneoustheequation(4)and(5).111(2)p3Prefigpug1c2d2u22uucos(2(/3))xxyxywithuanduthethreesequencevoltageandthethreexaxy0,1,20,1,2c2(6)psequencecurrentinjectedintothepowergridoftheinverter;g1uxuxuycos(xy2(/3))pxaxy2gthefundamentalconductance,controltheactiveoutputofthedc2pux2uxuycos(xy2(/3))inverter;gdthedampingconductance,controlthecompensatedxaxyunbalancedcurrenttothegrid.ItcanbeseenthatthenegativeInsummary,theactivedampingcontrolstrategybyusingpsequencecurrentandzerosequencecurrentvarywiththegdtocompensatetheunbalancedcurrent,achievethefunctionchangeofunbalancedvoltage.Thustheinverterwithactivepofreducingthevoltageunbalance.Byusingg1theinvertercandampingcontrolstrategycanadaptivelycompensatethecontroltheactivepoweroutput.unbalancedcurrentaccordingtothemagnitudeofvoltageunbalance.B.ActiveandReactivePowerCooperativeDampingControlStrategyThethree-sequenceequivalentcircuitofthedampingcontrolstrategyisshowninthefigureasfollows.Itisworthnotingthat,afterfurtheranalyzingtherelationshipbetweenthevoltage,currentandthepowerinequation(4),weCICED2018PaperNo.201804270000334Page2/5707

22018ChinaInternationalConferenceonElectricityDistributionTianjin,17-19Sep.2018foundthatthereactivepoweroutputfromeachphaseisnotzero,C.TheSolutionoftheModelbutthetotalreactivepowerofthethreephasesisalwaysequalStarttozeroregardlessofthevaluesoffundamentalanddampingconductance.Thatis,Settingiterationsnumberk0QQQ0(7)abcInotherwords,theactivedampingcontrolstrategyonlyCalculationtheinjectioncurrentoftheloadinjectsactivepowerintothegridwithoutreactivepower.Infact,nodei,ilithereisalargeamountofreactiveloadinthedistributionnetwork.Inordertomakefulluseofthecapacityoftheinverter,Calculationg1，gettheinjectioncurrentoftheitisnecessarytooutputactivepowerandreactivepowerattheinverterkk1sametime.Analogousactivepowerdampingcontrolstrategy,thereactivepowerdampingcontrolstrategiescanbederived:CalculationthebranchcurrentIiijgq00u0d0i0jgq0u(8)Updatenode111voltageForwardthenodevoltageU'UZIii1i1,iii00jgqu2d2Similarly,thereactivefundamentalconductancecanbeNkkobtainedas:Umax、max？3Qqrefg1c2ux2uxuycos(xy2(/3))Yxaxyc2(9)Stopuxuxuycos(xy2(/3))qxaxyFig.3.Solvingprocessofthreephasesdampingcontrolstrategy2gdc2ux2uxuycos(xy2(/3))ThedampingcontrolstrategybasedonDGgridconnectedxaxyinverterisproposedinthispaper,whichismainlyaimedatInsummary,anactiveandreactivepowercooperativethree-phasefour-wireasymmetricdistributionnetwork.Anddampingcontrolstrategyisproposedinthispaper.themodelcanbesolvedbyforwardandbackwardsubstitutioni0gd00u0method.Witheverystepintheiteration,thethree-phasei0g0u(10)111voltageoftheinverterchanges,causingachangeofg1.Theni00gdu2thethree-phasecurrentinjectedintothedistributionnetworkby2theinverteriscalculated.Eachiteration,thefundamentalpqWhere,thefundamentalconductanceg1g1jg1;thedampingconductancewillberecalculateduntilconvergenceisachieved.pqconductancegdgdjgd;andthedampingcontrolstrategyofthegrid-connectedinverterproposedinthispapercanoutputactiveIV.SIMULATIONRESULTSpowerandreactivepowertoimprovethenetworkpowerflow.InordertoverifythecorrectnessofthemodelproposedinInthemeantime,itcanalsoreducethevoltageunbalanceandthispaper.A10busdistributionnetworkasdepictedinFig.4isimprovethepowerqualityofthesystem.simulatedwitha380/220Visconsidered.Theimpedanceoftheline(a,b,c,n)conductorisZl=0.265+j0.078Ω/kmandthelengthofthelinebetweenadjacentnodesis40m.TheDGisconnectedtonode8andtheloaddataofeachnodeareshownintable1.12810PCCDGFig.4.Three-phaseandfour-wiredistributionnetworkwithinvertersTABLEILOADOFUNBALANCEDDISTRIBUTIONNETWORKNodePaQaPbQbPcQc100000021058463CICED2018PaperNo.201804270000334Page3/5708

32018ChinaInternationalConferenceonElectricityDistributionTianjin,17-19Sep.20183844252What’smorecase4addsreactivepoweroutputandreactive4533363dampingconductance,therefore,thevoltageunbalancefactor510584746746353ofeachnodeisalsorelativelymostsmall.7958463TABLEIII8000000NETWORKLOSSANDPOWEROUTPUT91165342Case1234101058453Ploss(kW)7.886.807.216.00Pref(kW)30303030A.ResultofDampingControlStrategyQref(kVar)020020Inordertoverifytheperformanceoftheproposedmodel,theTheactivepowerlossofthefourcasesisshownintable3.Itfollowingcasesaresetupforanalysis.canbeseenthatthedampingcontrolstrategyofinverterTABLEIIproposedinthispapercanoutputactivepowerandreactiveSUMMARYOFCONTROLVARIABLESUSEDINCASESTUDIESCasepQqpowertoimprovenetworkpowerflow.ByreducingthevoltagePrefgdrefgdunbalancefactor,theneutrallinelosscanbedecreased.Andit1√2√√cancomprehensivelyreducetheactivelossofthenetworkto3√√improvetheeconomicsofsystemoperation.4√√√√B.AdaptiveCompensationResultAnalysisWhere,theactivepowerPref=30kW;thereactivepowerThedampingcontrolstrategyofinverterproposedinthispqQref=20kVar;dampingconductancegd3,gd3.Thepapercancompensatetheunbalancedcurrentadaptivelyresultsofthesimulationareasfollows:accordingtothevoltageunbalancetoreducetheVUF.Then,adampingcontrolstrategyinverterisaddedtothenode5.Andtheresultsofthesimulationareasfollows:(a)zero-sequencevoltageunbalancefactor(a)zero-sequencevoltageunbalancefactor(b)negative-sequencevoltageunbalancefactorFig.5.Thevoltageunbalancefactorinfourcases(b)negative-sequencevoltageunbalancefactorComparisoncase1withcase2canbeseenthattheoutputFig.6.Thevoltageunbalancefactorintwoscenariospoweroftheinverterhasnoeffectonthevoltageunbalance.Asthepictureshows,incase1theDGisconnectedtonode8,Case3addsdampingconductancetocase1caneffectivelyincase2theDGisconnectedtonode5and8.Eachdampingreducethevoltageunbalancefactorofeachnodeofthenetwork.CICED2018PaperNo.201804270000334Page4/5709

42018ChinaInternationalConferenceonElectricityDistributionTianjin,17-19Sep.2018controlstrategyinverteradaptivelycompensatesthe[11]BULizhi,LIYongli,SUNGuangyuandJINWei,“Designofmulti-functionalgrid-connectedinverterbasedonmodifiedrepetitiveunbalancedcurrentaccordingtothevoltageunbalancewillnotcontrolalgorithm,”AutomationofElectricPowerSystem,vol.41,adverselyaffecttoeachother.Therefore,comparedwithcase1,pp.48-55,Jun.2017.thecase2hasasmallervoltageunbalancefactor.[12]LIShengwei,LIYongli,SUNJingliao,JINQiangandLIXuguang,“Apowerqualitycontrolalgorithmformicro-gridbasedoncontrolstrategyofinverterinterfaceddistributedgenerator,”PowerSystemTechnology,V.CONCLUSIONvol.34,pp.6-11,Aug.2010.Three-phaseloadasymmetrycanleadtothree-phasevoltage[13]LiuH,ZhouJ,LiPandWEIW,“Animproveddroopcontrolstrategyofthree-phaseinverterforgridvoltageunbalancecompensation,”inProc.unbalancewillhaveanegativeimpactonpowersupplysafety.3thInternationalFutureEnergyElectronicsConferenceandEcceAsia,ThispaperproposedanactiveandreactivepowercooperativeKaohsiung,2017,pp.3-7.dampingcontrolstrategyforthree-phasegrid-connected[14]MeersmanB,RendersB,DegrooteL,TineVandLievenV,“Three-phaseinverter-connectedDG-unitsandvoltageunbalance,”ElectricPowerinverter.Inwhichthestrategybyusingg1tocontrolthepowerSystemsResearch,vol.81,pp.899-906,Apr.2011.output,usinggdtoreducevoltageunbalance.Sothat,the[15]VandoornTL,VyverJVD,MeersmanB,ZwaenepoelBandinvertercanoutputactive/reactivepowerandreducetheVandeveldeL,“Phaseunbalancemitigationbythree-phasedampingvoltage-baseddroopcontrollersinmicrogrids,”ElectricPowerSystemsvoltageunbalancefactor.AnditcanimprovethepowerqualityResearch,vol.127,pp.230-239,Oct.2015.hasabetteroperatingresult.What’smore,thedampingcontrolDONGLeigraduatedfromTianjinUniversityinthefieldofpowersystemstrategyinverteradaptivelycompensatestheunbalancedautomation.NowsheisanassociateprofessorinNorthChinaElectricPowerUniversity,Beijing,China.Shefocusesonpowersystemanalysisoperationcurrentaccordingtothevoltageunbalanceandwillnotandcontrolandtheemailaddressishbdldl@126.com.adverselyaffecttoeachother.ThroughthecoordinatedZHANGTaoreceivedtheB.E.degreeinelectricalengineeringfromHefeioperationofmultipleinverters,thevoltageunbalanceoftheUniversityofTechnology,Hefei,China,in2016.HeiscurrentlypursuingtheM.E.degreeinelectricalengineeringatNorthChinaElectricPowerUniversity,networkwillbecomprehensivelyreduced.Beijing,China.HenowfocusesonpowersystemanalysisoperationandcontrolandtheemailaddressisZtncepu639@126.com.REFERENCES[1]ZHUJian,LUOHui,DENGWujun,WANGHongchun,andWUZhijun,“Multi-objectiveoptimizationschedulingofunbalancedlow-voltagemicrogridwiththree-phaseimbalance,”ElectricPowerConstruction,vol.38,pp.82-91,Feb.2017.[2]ZHOUXiaoping,CHENYandong,LUOAn,ZHOULeiming,LIMingshenandCHENZhiyong,“AHybridsingle-phase/three-phasemicrogridstructureanditsenergycoordinatedcontrolmethod,”ProceedingsoftheCSEE,vol.36,pp.6759-6768,Dec.2016.[3]NevesABFandFilhoADLF,“Effectsofvoltageunbalanceontorqueandefficiencyofathree-phaseinductionmotor,”inProc.16thInternationalConferenceonHarmonicsandQualityofQualityofPower,Bucharest,2014,pp.25-28.[4]DuanG,KaticVandRuferA,“PowerQualityProblemsCompensationWithUniversalPowerQualityConditioningSystem,”IEEETrans.PowerDelivery,vol.22,pp.968－976,Apr.2007.[5]SUYi,LEJian,LIUKaipei,TANTianyuan,LEIXiaoandCHENQingheng,“Designforanovellow-voltagecompensationdevicefitforruralpowergrid,”AutomationofElectricPowerSystem,vol.35,pp.88-92,Oct.2011.[6]YueY,MaF,LuoAandQianMX,“AcirculatingcurrentsuppressingmethodofMMCbasedSTATCOMfornegative-sequencecompensation”inProc.8thInternationalPowerElectronicsandMotionControlConference,Heifei,2016,pp.3566-3572.[7]Garcia-CerradaA，Pinzon-ArdilaOandFeliu-BatlleV,“ApplicationofaRepetitiveControllerforaThree-PhaseActivePowerFilter,”IEEETransactions.PowerElectronics,vol.22,pp.237-246,Jan.2007.[8]HeJandLiYW,“HybridVoltageandCurrentControlApproachforDG-GridInterfacingConvertersWithLCLfilters,”IEEETransactions.IndustrialElectronics,vol.60,pp.1797-1809,May.2013.[9]ZhouJie,LuoAn,ChenYandong,ZHOULeimingandHUANGYuan,“Voltageunbalancecompensationforlow-voltagemicrogridwithmultiparallellyconnectedinverters,”PowerSystemTechnology,vol.38,pp.412-418,Feb.2014.[10]WANGYichao,LUOAn,andJINGuobin,“Anunbalancedvoltagecompensationmethodforparallelinvertersinmicrogrids,”ProceedingsoftheCSEE,vol.35,pp.4956-4964,Oct.2015.CICED2018PaperNo.201804270000334Page5/5710