A method to improve the dynamic performance of moving average filter based PLL

5978IEEETRANSACTIONSONPOWERELECTRONICS,VOL.30,NO.10,OCTOBER2015

AMethodtoImprovetheDynamicPerformance

ofMovingAverageFilter-BasedPLL

JinyuWang,JunLiang,FengGao,Member,IEEE,LiZhang,andZhuodiWang

Abstract—Phase-lockedloop(PLL)techniqueiswidelyusedforsynchronizationapplications.Avarietyofmovingaverage?lter(MAF)-basedPLLshavebeenpresentedinrecentlypublishedlit-eratures.MAF-basedPLLcancompletelyeliminatetheeffectofunbalancedvoltage,characteristicharmonics,anddcoffset.Un-fortunately,theopen-loopbandwidthisdrasticallyreducedafterincorporatingMAFintothePLLstructure.Theproblemisana-lyzedindetailinthispaper,anditisprovedtobecausedbythelargeMAFwindowwidthwhichisdeterminedbythelowestorderhar-monic.Then,animprovedmethodnameddifferentialMAF-PLL(DMAF-PLL)isproposed.ThismethodcanrapidlyeliminatethelowestorderharmonictonarrowtheMAFwindowwidth.DMAF-PLLisrealizedbyincorporatingaspecialproportionalcomponentintotheMAF-basedPLL.Thespecialproportionalcomponentcanonlinechangeitsvalueaccordingtothefrequencyofinputsignal,anditwillnotintroducephaselag,soasnottodeterioratethesta-bilityofPLL.DMAF-PLLincreasestheopen-loopbandwidthandgreatlyimprovesthedynamicperformanceofMAF-basedPLL,anditiseasytobeimplementedwithlowcomputationalburden.DMAF-PLLcanbeusedinboththree-phaseandsingle-phasevolt-agesystems.Simulationandexperimentalresultsareincludedtovalidatetheeffectivenessandrobustnessoftheproposedmethod.IndexTerms—Bandwidth,dynamicresponse,gridsynchroniza-tion,movingaverage?lter,phase-lockedloop(PLL).

I.INTRODUCTION

INCEdistributedgenerationsystems,?exibleactransmis-sionsystems,activepower?lter,andVSC-HVDCsystemsareallconnectedtothegridthroughpowerconverters,oneofthemostimportantaspectsoftheircontrolstrategyistosynchro-nizetheconverterswiththeutilitygridatthepointofcommoncoupling(PCC).Forthisreason,thefundamentalpositivese-quencevoltageinformation(e.g.,phaseangleandfrequency)atthePCCmustbeobtainedquicklyandaccurately[1]–[6].

PLListhemaintechniqueusedtoobtainthevoltageinfor-mation.Inthepastfewyears,variouskindsofPLLshavebeenproposed.Themostwidelyusedoneisthesynchronousrotat-ingframePLL(SRF-PLL).SRF-PLLisextremelysimpleandcanbeusedinsingle-phase[7]–[9]andthree-phase[10]–[12]systems.Underidealgridconditionswithoutanyharmonic,un-balance,ordcoffset,SRF-PLLcanachieveafastandprecisedetectionofthephaseangleandfrequencyofthegridvoltage.

ManuscriptreceivedJuly17,2014;revisedOctober3,2014;acceptedDe-cember1,2014.DateofpublicationDecember18,2014;dateofcurrentversionMay22,2015.RecommendedforpublicationbyAssociateEditorM.Molinas.TheauthorsarewiththeKeyLaboratoryofPowerSystemIntelligentDispatchandControlofMinistryofEducation,ShandongUniversity,Jinan250061,China(e-mail:jinyu88330@126.com;liangjun@sdu.edu.cn;fgao@sdu.edu.cn;yzhangli@sdu.edu.cn;wangzhuodi@sdu.edu.cn).

Colorversionsofoneormoreofthe?guresinthispaperareavailableonlineathttp://ieeexplore.ieee.org.

DigitalObjectIdenti?er10.1109/TPEL.2014.2381673

S

Incasethegridvoltageisonlydistortedwithhigh-orderhar-monics,theSRF-PLLcanstillworkproperlybynarrowingtheloopbandwidthtoattenuatetheeffectofhigh-orderharmon-icsatthecostofreducingthePLLresponsespeed.However,theperformanceofSRF-PLLbecomesunacceptablewhentheutilityvoltageisunbalanced[13],[14].Inordertosolvethisproblem,lotsofimprovedversionsofSRF-PLLhavebeenpre-sentedinliteratures.In[15],doublesecond-ordergeneralizedintegrator-basedPLL(DSOGI-PLL)waspresented.

ThismethodisrealizedbyusingaDSOGIstructureoperat-ingintheαβ-frametoobtainthefundamentalpositivesequencecomponentfromtheunbalancedvoltage.Analternativemethod,adaptivenotch?(ANF)-basedPLL(ANF-PLL)waspresentedin[16],whichissimilartoDSOGI-PLLexceptitadoptsANFratherthanDSOGItoacquirethefundamentalpositivesequencecomponentfromtheunbalancedvoltage.AnenhancedPLL(EPLL)waspresentedforthesamepurposebyGhartemanietal.[17],[18].EPLLcanestimatethephaseangleandampli-tudeofinputsignalsatthesametimeandcouldreconstructthetargetedsignalseasily.EPLLpossessesaperfect?lteringcapa-bilitybutarelativelylowerresponsespeedcomparedtosomeothersynchronizationmethods.In[19],adecoupleddoublesyn-chronousreference-framePLL(DDSRF-PLL)waspresented.DDSRF-PLLusesdoublesynchronousframetransformationsandadecouplingnetworktodetectthepositiveandnegativesequencecomponents.In[20],amultiplecomplexcoef?cient?-basedPLL(MCCF-PLL)waspresentedbyGuoetal.Un-liketraditionalreal-coef?cient?,thecomplex-coef?cient?candistinguishthepositiveandnegativesequencesforthesamefrequency.In[21]and[22],delayedsignalcancellation(DSC)techniquewasintroducedintothePLLandDSC-PLLwaspre-sented.InDSC-PLL,theinputsignalsaredelayedonequarterofthefundamentalperiodtoproducea90°phaseshift,andthedelayedsignalsareaddedintotheinputonestoacquirethefundamentalpositivesequencecomponentfromtheunbalancedvoltage.ANFandleadcompensatorswereusedasloop?ltersinPLLstoeliminatetheeffectoftheunbalancedvoltagein[23]and[24],respectively.

ThoughtheaforementionedPLLscaneliminatetheeffectofunbalancedvoltage,mostofthemactastraditionallow-pass?l-terornotch?lter.Inhighlydistortedcase,thePLLshavetonar-rowthebandwidthtoattenuatetheharmonics,whichseriouslyreducestheirdynamicresponsespeed.Inordertoeliminatetheeffectoftheunbalancedvoltageandlow-orderharmonicswith-outreducingtoomuchofthedynamicresponsespeed,multiplereferenceframe-basedPLL(MRF-PLL)waspresentedin[25].TheMRF-PLLutilizestwosynchronousreferenceframesro-tatingatthesameangularspeedwithoppositedirectionsand

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