电子电路英文文献及翻译A sensorless and simple controller for VSC based HVDC systems.docx

电子电路英文文献及翻译A sensorless and simple controller for VSC based HVDC systems.docx

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电子电路英文文献及翻译AsensorlessandsimplecontrollerforVSCbasedHVDCsystems

英文文献原文

AsensorlessandsimplecontrollerforVSCbasedHVDCsystems

Abstract:

Voltagesourceconverterhigh-voltagedirectcurrent（VSC-HVDC）isanewpowertransmissiontechnologypreferableinsmallormediumpowertransmission.Inthispaperwediscussanewcontrolsystembasedonspacevectormodulation（SVM）withoutanyvoltagelinesensors.Usingdirectpowercontrol（DPC）SVMandanewdoublesynchronousreferenceframephase-lockedloop（DSRF-PLL）approach,thecontrolsystemisresistanttothemajorityoflinevoltagedisturbances.Also,thesystemresponsehasacceleratedbyusingafeedforwardpowerdecoupledloop.TheoperationofthiscontrolstrategywasverifiedinaSIMULINK/MATLABsimulationenvironment.Tovalidatethiscontrolsystem,a5kV·Aprototypesystemwasconstructed.Comparedtotheoriginalcontrollers,thecurrenttotalharmonicdistortion（THD）,theactiveandreactivedeviationsandtheDCvoltageovershootwereloweredby2.5%,6.2%and8%,respectively.Therectifierpowerfactorintheworstconditionwas0.93andtheDCvoltagesettlingtimewas0.2s.

Keywords:

Voltagesourceconverterhigh-voltagedirectcurrent（VSC-HVDC）,Spacevectormodulation（SVM）,Directpowercontrol（DPC）,HVDCLight

1INTRODUCTION

Voltagesourceconverterhigh-voltagedirectcurrent（VSC-HVDC）,controlledbypulsewidthmodulation（PWM）,cansupplypowertobothactiveandpassiveelectricalsystems.TheintroductionofVSCandPWMmakespossiblefastandflexiblecontrolofpowerflowandmoreconvenientoperationofpowersystems.Besides,thisadvancement,comparedwithconventionalHVDC,mitigatesharmonicsinACcurrentandACvoltagegreatlyandimprovespowerfactorsoftheconnectedACsystems（LiGKetal.,2005）.VSC-HVDCorHVDCLight,inrecentyears,havesuccessfullybeencommerciallycommissionedinsuchfieldsassupplyingpowertoremoteisolatedloads,empoweringurbancenters,connectingdistributedgenerationsources,linkingtwoasynchronouselectricalpowersystems,improvingpowerquality,andsoon（Asplund,2000;Lietal.,2003）.

TheadvantagesofaVSCbasedHVDCsystemare（Asplund,2000）:

（1）onlyasmallfilterisrequiredtofilterhighfrequencysignalcomponents;

（2）thereisnocommutationfailureproblem;（3）reactivepowercompensationisnotrequired;（4）thereisnorestrictiononmultiplein-feeds;etc.

TherearevariouscontrolmethodsforVSCbasedHVDCsystems.Zhangetal.（2002）usedtheinversesteadystatemodelcontrollertotracetheoperatingpointandadoptedtwodecoupledcontrollingloopstoeliminatethesteadystatedeviation.Chenetal.（2004）proposedasteady-statecontrollerdesignschemebasedondq0-axis.Zhangetal.（2002）andChenetal.（2004）assumedthatthetwoterminalsofVSC-HVDChavebeenconnectedtoaninfinitebussystem.ButoneterminalofVSC-HVDCmaybeconnectedtoageneratorand,asinAsplundetal.（1997）,anHVDCLightsystemconnectsthegenerator（suchasanoffshorewindfarm）tothegrid.ThesestrategiesfocusoncontroloftheHVDCsystemitselfanddonotconsidertheinteractionbetweenACandDCsystems.Huetal.（2004）presentedanoptimalcoordinatedcontrolstrategybetweenthegeneratorexcitationandVSC-HVDC,whereasthederivationofcontrollawiscomplicated.Huetal.（2005）appliedageneticalgorithm（GA）tooptimizeparametersofthecontrollerafterdeterminingthem.OoiandWang（1991）andZhangandXu（2001）usedaphaseandamplitudecontrol（PAC）techniqueforVSCbasedHVDCapplications.LiGIetal.（2005）proposedanonlinearcontrolforanHVDCLightsystem.Thesemethodshaveusedvoltageandcurrentsensors.

Adirectpowercontrol（DPC）strategybasedonvirtualflux,calledVF-DPC,providessinusoidallinecurrent,lowerharmonicdistortion,asimpleandnoise-robustpowerestimationalgorithmandgooddynamicresponse（Rahmatietal.,2006）.However,theVF-DPCschemehasthefollowingwell-knowndisadvantages（Malinowskietal.,2001;2004）:

（1）variableswitchingfrequency（difficultiesofLCinputfilterdesign）,

（2）highsamplingfrequencyneededfordigitalimplementationofhysteresiscomparators,（3）necessityforafastmicroprocessorandA/Dconverters.

Therefore,thereisnotendencytoimplementVF-DPCinindustry.Alltheabovedrawbackscanbeeliminatedwhen,insteadoftheswitchingtable,spacevectormodulation（SVM）isapplied.

DPCisamethodbasedoninstantaneousdirectactiveandreactivepowercontrol（Malinowskietal.,2004）.InDPCtherearenointernalcurrentcontrolloopsandnoPWMmodulatorblock.Moreover,theturn-onandturn-offcommandsofthestaticswitchesoftheconvertersaregeneratedbySVM.Useofspacevectormodulationcauseslowercurrentharmonics,relativelyhighregulationandstabilityofoutputvoltageandobtainsahighermodulationfactorrelativetosinusoidalmodulation（Malinowskietal.,2004）.Also,itcaneasilybeimplementedinaDSPbasedsystem.

Doublesynchronousreferenceframephase-lockedloop（DSRF-PLL）basedonVFcausesthiscontrolsystemtoberesistanttothemajorityoflinevoltagedisturbances.Thisassuresproperoperationofthesystemforabnormalandfailuregridconditions.

InthispaperanewcontrolstrategyisproposedforVSC-HVDC.Inthisstrategy,thereactivepowerandoutputDCvoltageintherectifierstationandthereactiveandactivepowersintheinverterstationarecontrolled,separately.Also,theDPCrectifierequations（Malinowskietal.,2004）havebeendevelopedfortheinverter.Formoreaccuracyinhighpower,thesecondorderparameterisincludedintherectifierandtheinverterequations.Activeandreactivepowerfeedforwarddecouplingareusedforacceleratingthesystemresponse.Finally,DPCisappliedtotherectifierandinverterstationsofVSC-HVDC.

TheoperationofthiscontrolstrategyisverifiedinaSIMULINK/MATLABsimulationenvironmentforsteadystate,activeandreactivepowervariations,single-line-to-groundfaultsandunbalancedsourcesattherectifierandtheinverterstations.Also,thiscontrolstrategyisappliedtoa5kV·Aprototypesystemwhichisverificationthatthiscontrolstrategyhasafastresponseandstrongstability.

2CONTROLofVSCBASEDHVDCSYSTEM

2.1VSCbasedHVDCsystem

VSC-HVDCinvolvestwovoltagesourceconverterswiththesameconfiguration,linkingwithadctransmissionlineorcable（Fig.1）.Therearefourcontrolvariablesrepresentedby

and

forthissystem.Inthispaper,arectifierstationischosentocontrolDC-busoutputvoltageofrectifier（

）.Also,reactivepower（

）andinverterstationaresettocontrolactivepower（

）andalsoreactivepower（

）.Rcistheequivalentresistanceofthetransmissioncableandcanbepracticallyneglected.Thuswemaywrite

.

Fig.1AphysicalmodelforaVSCbasedHVDCsystem

2.2Virtual-fluxestimatorforrectifierandinverter

Fromtheeconomicalpointofview,andforsimplicity,morereliabilityandseparationofpowerstageandcontrol,AClinevoltagesensorsarereplacedbyafluxestimator（Malinowskietal.,2004）.

ThebasicmodelofaVSCstationisshowninFig.2.IfDa,Db,andDcarethedutycyclesofSa,Sb,andScsignals,respectively,UdcistheconverterDCvoltage,anduLαanduLβarelinevoltageinα-βcoordinates,thentherelatedfluxofACvoltage,

canbewrittenas（Malinowskietal.,2004）

（1）

Also,theconvertervoltageequationsinα-βcoordinatesare:

（2）

（3）

Fig.2Basicmodelofavoltagesourceconverter

2.3Directpowercontrol

Activeandreactivepowerintherectifierandtheinverterstationsareestimatedusingthelinecurrentvectors

andestimatedvirtualflux

inα-βcoordinates（Malinowskietal.,2004）:

（4）

（5）

2.4Rectifiercontroldesign

ThefullcontrolalgorithmoftheproposedcontrolsystemispresentedinFig.3.TheDPC-SVMusesclosed-looppowercontrol.Intherectifierstation,referencereactivepower（qrefr）issettozeroforunity-power-factoroperation.Inanidealcase,theactivepowerintherectifierstationandtheactivepowerintheinverterstationareequal,andnostorageelementsareneeded.Nevertheless,inrealsystemsdifferencesbetweentheseactivepowersareinevitable,andthesedifferencesareabsorbedbytheDClinkcapacitorandarereflectedinfluctuationsoftheDClinkvoltage.Thus,thereferenceactivepower（prefr）atthesideoftherectifieristhesumoftheouterproportional-integral（PI）dcvoltagecontrollerandestimatedactivepowerintheinverterstation（pi）.

Fig.3ControlschemeforaVSCbasedHVDCsystemwiththerectifierandinverterstations

Accordingtothecurrentdirection,thelinevoltageuLrcanbeexpressedasthesumoftheinductorvoltageuIr,theresistorvoltageuRrandtherectifiervoltageuSr（Rahmatietal.,2006）:

（6）

ByconsideringEq.

（1）,theestimatedvirtualfluxesare:

（7）

（8）

2.5Invertercontroldesign

Intheinverterstation,referencereactivepower（qrefi）andreferenceactivepower（prefi）aresettonetworkdemand.Accordingtothecurrentdirection,theinvertervoltageuSicanbeexpressedasthesumoftheinductorvoltageuIi,theresistorvoltageuRiandthelinevoltageuLiatthesideoftheinverter.Theestimatedvirtualfluxesare（Rahmatietal.,2006）:

（9）

（10）

3CONCLUSION

ThispaperproposesanewmethodforcontrollingaVSCbasedHVDCsystemwhichhasbeenconnectedbetweentwodistributionsystemswithdifferentfrequencies.Thismethodiseffectiveindampingsystemoscillationsquickly,andenhancespowerqualitywhenpowerflowisreversed.VFandDSRF-PLLcausethiscontrolsystemtoberesistanttothemajorityoflinevoltagedisturbances