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EuropeanAssociationfortheDevelopmentofRenewableEnergies,EnvironmentandPowerQuality(EA4EPQ)InternationalConferenceonRenewableEnergiesandPowerQuality(ICREPQ’12)SantiagodeCompostela(Spain),28thto30thMarch,2012ComparisonofmethodsforimplementingvirtualsynchronousmachineoninvertersYongChen1,RalfHesse2,DirkTurschner3andHans-PeterBeck41234InstituteofElectricalPowerEngineeringClausthalUniversityofTechnologyLeibnizstrasse28,38678Clausthal-Zellerfeld(Germany)1Phone:+0049-5323-72-3819,e-mail:yong.chen@tu-clausthal.de2Phone:+0049-170-5021628,e-mail:email@iehw.de3Phone:+0049-5323-72-2592,e-mail:dirk.turschner@tu-clausthal.de4Phone:+0049-5323-72-2570,e-mail:mendt@iee.tu-clausthal.deAbstractVirtualSynchronousMachinealsocalledVISMA[1]isacontrolalgorithmtomakeaninverteroperatedasaconventionalelectromechanicalsynchronousmachine.Itisapromisingsolutiontoovercometheproblemsofthegridstabilityandquality,whichhavebeenexacerbatedbyincreasingintegrationofdistributedgenerationunitsintothegrid.Comparedtotheconventionalpowerplants,inwhichthesynchronousmachinedominate,thedistributedgenerationunitshaveeithersignificantlysmallerornorotatingmassanddampingeffect.TheseweaknessescanbecompensatedbyusingtheVISMAconceptandthusthepowersystemqualitywillbeimproved.Furthermore,thepenetrationleveloftheDGsourceswon’tberestrictedanymore.UptonowtheVISMAwasimplementedbyusingavoltage-to-currentmodelonahysteresiscontrolledinverter[1][2][3].ThismethodwillbecalledVISMA-Method1here.SincethemostproductsofinvertersinthemarketarePWMcontrolled,theVISMA-Method1cannotbeeasilyappliedontheseinverters.Therefore,anewmethodisdevelopedtoimplementtheVISMAbyusingacurrent-to-voltagemodelonthecurrentlywidelyappliedPWMcontrolledinverter.ThisnewmethodiscalledVISMA-Method2inthispaperandwillbecomparedwiththeVISMA-Method1bysimulationresults.KeywordsVirtualSynchronousMachine(VISMA),inverter,hysteresiscontroller,pulse-widthmodulation(PWM),distributedgeneration(DG),stand-alonegrid,virtualrotatingmass,virtualdamping1.IntroductionThediffusingutilizationoftherenewableenergyresourcesisdrivenbythelimitedfossilenergystoreontheonehandandtheexacerbatedenvironmentalissuesaswellasenergypoliticsontheotherhand.Thediversityoftherenewableenergiesanditsstrongdependenceonthegeologicallocationandmeteorologicalsituationmakethechangethattheelectricitywillbegeneratedmoreandmorebysmalldistributedgeneration(DG)units.MostoftheseDGtechnologiesonlyconsidersupplyingmaximumpowerintothegridbuttakenthestabilityofthepowersystemnotintoaccount.Generally,afewsmall-sizeDGunitswillnotinfluencethesafeoperationofthepowernetworkinthepresenceoflargecentralizedpowerstationsthustheirinfluencescanbeneglected.ButwithalargernumbersofDGunitswithhighercapacities,theoveralldynamicsofpowersystemsaresignificantlyaffected[4].ThereforethesolutionstoimprovethepowersystemstabilityandatthesametimeensuretheincreasingintegrationoftheDGunitsarenecessary.Theconceptofvirtualsynchronousmachinedescribesanewtypeofgridfeedinginverter,whichoperateswithastoragesystementirelyasanelectromechanicalsynchronousmachine.ThebasicideaoftheVISMAbasesonreproducingthestaticanddynamicpropertiesofarealsynchronousmachineonapowerelectronicinterfacebetweenaDGunitandthegrid,inordertoinherittheadvantagesofasynchronousmachineinconsiderationofpowersystemstabilitysuchasadjustableactiveandreactivepower,dependenceofthegridfrequencyontherotorspeedandtheeffectoftherotatingmassanddampingwindingsaswellasstableoperationwithahighparallelismlevel.Fig.1illustratesthebasicideaoftheVISMA.Fig.1.BasicideaoftheVISMA.734RE&PQJ,Vol.1,No.10,April2012ThispaperpresentsfirstlytwomethodsforimpelmentingtheVISMAonaninverter.Thenthestaticanddynamicpropertiesofbothmethodsarecomparedbythesimulationresultsinaparalleloperationwiththestiffgrid.FuthermoreitisalsodisscussedthatwhetherbothVISMA-Methodsareabletobeoperatedinastand-alonegrid.Finallytherelavantconclusionsaredrawedattheendofthispaper.2.ImplementationMethodsoftheVISMAInthissectiontwomethodstoimplementtheVISMAonaninverterwillbediscussedhere.TheywillbecalledVISMA-Method1and2inthispaper.TheVISMA-Method1wasalreadypresentedin[1][2][3]andwillbeappliedasareferencehereforthecomparisonwiththeVISMA-Method2.A.VISMA-Method1:usingvoltage-to-currentmodelThecompleteVISMAfunctionalchainisshowninFig.2.Itstartswiththereal-timemeasurementofthegridvoltagetofeedthevirtualsynchronousmachinealgorithmontheprocesscomputeranddeliversthestatorcurrentsofthevirtualsynchronousmachineastheresultswhichpresentedasprocessvariables.Thefasthysteresiscontrolledinvertercarriesoverthecurrentsignalstodrivethesecurrentsatthegridimmediately.Fig.2.ConceptoftheVISMA-Method1.ThesynchronousmachinemodelusedinthismethodisshowninFig.3andwasintroducedin[5].Fig.3.BlockdiagramoftheVISMA-Model1.B.VISMA-Method2:usingcurrent-to-voltagemodelComparedwiththeVISMA-Method1,thecurrentswillbemeasuredintheVISMA-Method2andthereferencevoltagewillbecalculatedintheVISMA-Model2,andthensenttoapulse-widthmodulator,whichgeneratesswitchsignalsfortheinverter.TheinductorsLfundcapacitorsCfareusedtofiltertheharmoni