層疊式多單元變換器電容電壓平衡策略研究

層疊式多單元變換器電容電壓平衡策略研究摘要：

層疊式多單元變換器在電力電子領(lǐng)域的應(yīng)用越來越廣泛，但是由于每個(gè)單元間的耦合，導(dǎo)致電容充電和放電不平衡，嚴(yán)重影響了系統(tǒng)的可靠性和穩(wěn)定性。針對(duì)這一問題，本文提出了一種基于分時(shí)交替控制的電容電壓平衡策略。首先對(duì)層疊式多單元變換器進(jìn)行建模，分析電容充電和放電過程，確定了影響電容電壓平衡的主要因素。然后引入分時(shí)交替控制策略，通過協(xié)調(diào)各個(gè)單元間的充電和放電動(dòng)作，實(shí)現(xiàn)電容電壓的平衡。最后通過仿真和實(shí)驗(yàn)驗(yàn)證了所提出的策略的有效性。

關(guān)鍵詞：層疊式多單元變換器；電容電壓平衡；分時(shí)交替控制；可靠性；穩(wěn)定性。

Abstract：

Theapplicationofstackedmulti-cellconvertersinthefieldofpowerelectronicsisbecomingmoreandmorewidespread.However,duetocouplingbetweeneachcell,theimbalanceofcapacitorcharginganddischargingseriouslyaffectsthereliabilityandstabilityofthesystem.Inresponsetothisproblem,thispaperproposesacapacitorvoltagebalancingstrategybasedontime-sharingalternatingcontrol.Firstly,thestackedmulti-cellconverterismodeled,andthecapacitorcharginganddischargingprocessisanalyzedtodeterminethemainfactorsaffectingcapacitorvoltageimbalance.Then,thetime-sharingalternatingcontrolstrategyisintroducedtocoordinatethecharginganddischargingactionsbetweeneachcelltoachievecapacitorvoltagebalance.Finally,theeffectivenessoftheproposedstrategyisverifiedthroughsimulationandexperiment.

Keywords:Stackedmulti-cellconverter;Capacitorvoltagebalance;Time-sharingalternatingcontrol;Reliability;StabilityInstackedmulti-cellconverters,capacitorvoltageimbalanceisoneofthemainchallengesthataffectthereliabilityandstabilityofthesystem.Thisisbecausethevoltageimbalancecausesthecellswithhighvoltagetooperateinovervoltageconditions,whilethecellswithlowvoltagearesubjecttoundervoltageconditions.Theseextremeoperatingconditionsshortenthelifespanofthecellsandcancausesystemfailure.

Toaddressthisissue,athoroughanalysisofthechargingprocessisnecessarytoidentifythemainfactorsthatcontributetocapacitorvoltageimbalance.Theanalysisshouldconsidertheeffectsofthesystemparameters,suchasthecellcapacitance,theloadconditions,andtheswitchingfrequency,onthechargingprocess.

Oneeffectivestrategytoachievecapacitorvoltagebalanceisthetime-sharingalternatingcontrol,whichaimstocoordinatethecharginganddischargingactionsbetweeneachcell.Theprinciplebehindthisstrategyistoalternatethecharginganddischargingactionsamongthecellsperiodically.Specifically,duringthechargingphase,thecellwiththelowestvoltageischargedfirst,andthentheremainingcellsarechargedinaspecificsequence.Similarly,duringthedischargingphase,thecellwiththehighestvoltageisdischargedfirst,followedbytheremainingcells.

Thetime-sharingalternatingcontrolstrategyrequiresaprecisecontrolmechanismtoensureaccuratesynchronizationamongthecells.Acontrolalgorithmcanbedesignedtocalculatethecharginganddischargingtimesforeachcellbasedonitsindividualvoltagelevelandthesystemparameters.Thecontrollercanalsoadjusttheswitchingfrequencyanddutycycleoftheconvertertoachievethedesiredvoltagebalance.

Simulationandexperimentalresultshaveshownthattheproposedtime-sharingalternatingcontrolstrategyiseffectiveinachievingcapacitorvoltagebalanceinstackedmulti-cellconverters.ThestrategynotonlyimprovesthereliabilityandstabilityofthesystembutalsoprolongsthelifespanofthecellsInadditiontoachievingcapacitorvoltagebalance,thereareotherchallengesfacedbystackedmulti-cellconvertersthatneedtobeaddressed.Oneofthesechallengesisthethermalmanagementofthecells.Asthecellsarestackedcloselytogether,heatdissipationbecomesacriticalissue,especiallyforhighpowerapplications.Overheatingofthecellscannotonlyaffecttheperformanceoftheconverterbutalsoreducethelifespanofthecells.Therefore,effectivethermalmanagementstrategiesarenecessarytoensurethereliableoperationofstackedmulti-cellconverters.

Oneapproachtothermalmanagementistouseactivecoolingtechniquessuchasliquidoraircooling.Liquidcoolinginvolvescirculatingacoolantthroughaheatexchangerattachedtothecells,whileaircoolinginvolvesusingfanstoblowairoverthecells.Bothtechniquescaneffectivelydissipateheatfromthecellsbutrequireadditionalhardwareandcanincreasethecomplexityandcostofthesystem.

Anotherapproachistousepassivecoolingtechniquessuchasheatsinksorphasechangematerials(PCMs).Heatsinksaretypicallymadeofhighthermalconductivitymaterialssuchascopperoraluminumandareattachedtothecellstoenhanceheatdissipation.PCMsarematerialsthatabsorbandreleasethermalenergyduringaphasechange,suchasmeltingorfreezing.ByincorporatingPCMsintothedesignoftheconverter,excessheatgeneratedbythecellscanbeabsorbedandstored,therebyreducingthetemperatureofthecells.

Moreover,thedesignofthepowerstageoftheconverterisalsocrucialtotheperformanceandreliabilityofstackedmulti-cellconverters.Thepowerstageincludestheswitchingdevices,diodes,andinductors,whichareresponsibleforconvertingtheinputvoltagetothedesiredoutputvoltage.Theselectionandsizingofthesecomponentscanaffecttheefficiency,powerdensity,andthermalperformanceoftheconverter.

Toimprovetheefficiencyofstackedmulti-cellconverters,soft-switchingtechniquescanbeemployedtoreduceswitchinglosses.Soft-switchingtechniquesincludezerovoltageswitching(ZVS)andzerocurrentswitching(ZCS),whichcanminimizethevoltageandcurrentstressesontheswitchingdevicesandimprovetheoverallefficiencyoftheconverter.

Inconclusion,stackedmulti-cellconvertershaveshowngreatpromiseinhighpowerandhighvoltageapplications.However,achievingcapacitorvoltagebalanceandthermalmanagementremainmajorchallengesthatneedtobeaddressed.Theproposedtime-sharingalternatingcontrolstrategycaneffectivelybalancethecapacitorvoltages,whileactiveandpassivecoolingtechniquescanimprovethethermalperformanceofthesystem.Thedesignofthepowerstageandtheuseofsoft-switchingtechniquescanimprovetheefficiencyoftheconverter.Asthesechallengesareaddressed,stackedmulti-cellconvertersareexpectedtobecomeincreasinglypopularinawiderangeofapplicationsInadditiontothechallengesmentionedabove,thereareseveralotherareasthatneedtobeaddressedinordertofurtherimprovetheperformanceandreliabilityofstackedmulti-cellconverters.

Oneofthekeyissuesisthereliabilityofthecellsthemselves.Thecellsusedinstackedmulti-cellconvertersmaybesubjecttovarioustypesofdegradationovertime,suchascapacityloss,internalresistanceincrease,andvoltageimbalance.Thesefactorscanhaveasignificantimpactontheoverallperformanceandefficiencyofthesystem.Therefore,itisimportanttodeveloprobustcellmanagementalgorithmsthatcandetectandmitigateanydegradationinthecells,suchasbybalancingthevoltages,adjustingthecharginganddischargingrates,andmonitoringthecelltemperature.

Anotherareaofconcernistheelectromagneticinterference(EMI)generatedbytheconverter.Thehigh-frequencyswitchingoperationsofthepowerelectronicsdevicescancreateunwantedelectromagneticfieldsthatcaninterferewithotherelectronicdevicesandsystems.Thiscanleadtomalfunctionorevendamagetothesesystems.Therefore,itisimportanttodesigntheconverterwithappropriateelectromagneticcompatibility(EMC)measures,suchasshielding,filtering,andgrounding.Inaddition,itmaybenecessarytocomplywithcertaininternationalEMCstandards,suchastheCISPRorFCCregulations.

Moreover,thesafetyoftheconverterisalsoacriticalconsideration.Thehighvoltagesandcurrentsinvolvedintheconvertercanposeahazardtoboththeequipmentandtheoperators.Therefore,itisimportanttoimplementappropriatesafetyfeatures,suchasovercurrentprotection,overvoltageprotection,andshort-circuitprotection.Inaddition,safetystandardssuchastheUL,CE,orIECsafetystandardsmayneedtobefollowed.

Finally,costisalwaysaconcerninanypracticalapplication.Whilestackedmulti-cellconvertershavemanyadvantagesovertraditionalconverters,theycanalsobemoreexpensivetoproduceandmaintain.Therefore,itisimportanttodesignandoptimizetheconverterwithcostinmind,suchasbyusingcost-effectivematerials,minimizingthenumberofcomponents,andensuringhighefficiencytoreducethethermalmanagementcosts.

Inconclusion,stackedmulti-cellconvertershaveshowngreatpromiseinimprovingtheperformanceandefficiencyofpowerelectronicssystems.Howev