3 - Hardware - Verification - of - a - Hpyer-Efficient - Kasper - APEC - 2015 - 01 - 图文

? 2015 IEEE

Proceedings of the 30th Applied Power Electronics Conference and Exposition (APEC 2015), Charlotte, NC, USA, March 15-19, 2015.

Hardware Verification of a Hyper-Efficient (98%) and Super-Compact (2.2kW/dm3) Isolated AC/DCTelecom Power Supply Module based on Multi-Cell Converter Approach

M. KasperC. W. ChenD. BortisJ. W. KolarG. Deboy

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HardwareVeri?cationofaHyper-Ef?cient(98%)andSuper-Compact(2.2kW/dm3)IsolatedAC/DCTelecomPowerSupplyModulebasedonMulti-Cell

ConverterApproach

MatthiasKasper?,Cheng-WeiChen?,DominikBortis?,JohannW.Kolar?andGeraldDeboy??PowerElectronicSystemsLaboratory,ETHZurich,Switzerland,Email:kasper@lem.ee.ethz.ch

?ElectricEnergyProcessingLaboratory,NationalTaiwanUniversity,Taipei,Taiwan

?In?neonTechnologiesAustriaAG,Villach,Austria

Abstract—Duetotheincreasingelectricitydemandofdatacentersdrivenbytheemergenceofcloudcomputingandbigdata,thefocusonthedevelopmentoftelecomanddatacenterpowersuppliesisshiftedtowardshighef?ciencies.Inthispaper,amulti-cellconverterapproachforatelecomrecti?ermodulebreakingthroughtheef?ciencyandpowerdensitybarriersoftraditionalsingle-cellconvertersystemsisshown.Thecom-prehensiveoptimizationoftheentiresystemwithrespecttoef?ciencyandvolumeisdescribedandtheappliedcomponentlossmodelsareexplained.Furthermore,thedesignofahardwaredemonstratorbasedontheoptimizationresultsispresentedandseveralimportantdesignaspectsareexplainedindetail.

LgConverter CellACDCACDCDCDCDCDCVout

Vg

vFB,totACDCACDCDCDC=??

VDC,iI.INTRODUCTION

Duetotheincreasingpopularityofcloudbasedinternet

servicesandthetrendaroundbigdata,theelectricityconsump-tionofdatacentershasgrowntremendouslyinthepastdecadeandisprojectedtogrowinthefutureevenfurther,e.g.around70%from2013to2020intheUSalone[1].Asaconsequence,datacentersarenowoneofthelargestconsumersofelectricityandthereforealsounderagrowing?nancialandpoliticalpressuretoincreasetheirenergyef?ciency.

Nowadays,conventionalsingle-phasetelecompowersuppliestypicallyconsistofaPFCrecti?erstageinconnectionwithanisolatedDC-DCconverterstageinordertogenerateanoutputvoltageof48Vforthesubsequentconversionstages.Therecti?erstageisusuallyaboost-typePFCconverterwithafullbridgedioderecti?er,thatcreatesconsiderableconductionlossesduetotheforwardvoltagedropsoftheemployeddiodes.Thishasinitiatedatrendtowardsbridge-lesstopologiesasanalternativetopology[2],[3].Oneexampleofahighlyef?cientpowersupplyfortelecomapplicationsisatriple-parallel-interleavedTCMPFCrecti?ersystem[4]incombinationwithadouble-parallel-interleavedphase-shiftedfull-bridgeisolatedDC-DCconverter(ratedpowerPout=3.3kW,outputvoltageVout=48V)featuringapowerdensityofρ=3.3kW/dm3andanef?ciencyofη=97%athalfoftheratedpower.Asshownin[5],thisconceptcurrentlypresentstheleadingedgetechnologyfortelecompowersupplies.

Anewandverydifferentapproachtowardsahyper-ef?cient

DCDC=??

Fig.1:Multi-celltelecompowersupplymodulewithinput-series

output-parallelconnectionoftheconvertercells.EachcellconsistsofafullbridgeAC-DCrecti?erinputstageandanisolatedDC-DCconvertercomprisingaphase-shiftedfull-bridgeconverter.

andsuper-compacttelecomrecti?erdesignbeyondthebarriersoftraditionalconverterconceptshasbeenpresentedin[6].Theapproachisbasedonamulti-cellconverterconceptwithseriesconnectionoftheconvertercellsattheinputsideandparallelconnectionattheoutputside(i.e.ISOP),asshowninFig.1.EachconvertercellformedbyanAC-DCrecti?erstageswhichisoperatedwithaTotem-PolemodulationandanisolatedDC-DCconverterstageconsistingofphase-shiftedfullbridgeconverter.Thismulti-cellISOPcon?gurationallowstosharetheinputvoltageamongtheconvertercellsandthusenablestheuseoflow-voltageratedsemiconductorsthroughouttheconvertercells.Accordingtothescalinglawsof[7]withthisapproachsigni?cantbene?tsintermsofreducedconductionandswitchinglossesandsmallervolumeofinductivecompo-nentsandheatsinks,amongothers,canbeachieved.Basedonthespeci?cationofTab.Ithesystemperformancetargetsthatshouldbereachedbyutilizingtheadvantagesofthemulti-cellconvertertopologyareanoutputpowerofPout=3.3kWwith

Tab.I:Speci?cationsofthemulti-celltelecomrecti?ermodule.

Parameter

VariableValue

NominalgridvoltageVgrid,RMS,nom230V/50HzGridvoltagerangeVgrid,RMS180V-270VRatedoutputpowerPout3.3kWNominaloutputvoltageVout,nom48VOutputvoltagerangeVout40V-60VTotalDC-linkvoltageVDC400V

Hold-uptime

Thold10ms@ratedpower

Switchingfreq.percellfsw

≥18kHz

EMIstandards

CISPRClassAandB

aconversionef?ciencyof98%atpartloadoperationandapowerdensityofρ=2.2kW/dm3.

Inthispaper,at?rsttheoptimizationandofthesystemisdiscussedindetailandtheresultsareanalyzedinSec.II.Afterwards,therealizationofthehardwaredemonstratorisdescribedinSec.IIIanddifferentdesignaspectsareaddressed.Finally,conclusionsaredrawninSec.IV.

II.SYSTEMOPTIMIZATIONANDRESULTS

In[7]acomprehensivesystemmodelingandoptimizationintermsofef?ciencyandpowerdensityoftheISOPmulti-celltelecomrecti?ermodulehasbeenpresented.InthisoptimizationallavailabledegreesoffreedomforthedesignoftheAC-DCandtheDC-DCconverterstageshavebeenconsideredsuchas

?SwitchingoftheAC-DCfrequencyrecti?er:Thestageeffectiveequalsswitchingtheswitchingfrequencyfre-quencyofasinglecellmultipliedbythenumberofcellsduetheinterleavedoperationoftherecti?erstages,i.e.fsw,eff=Ncells·fsw.Anaturallowerlimitoftheswitchingfrequencyofasinglecellcanbedeductedfromtherangeofaudiblefrequencywhichshouldbeavoidedbychoosingfsw≥18kHz.TheupperboundaryoffeasibleswitchingfrequenciescanbederivedbytheCISPREMIstandardsthatimposelimitsonharmonicsatfrequenciesabovefEMI≥150kHz[8].Asaconsequencetheswitchingfrequencypercellshouldbelimitedtofsw

?MOSFETsizeofthechipMOSFETssizeandisjunctionanimportanttemperatureparameter:Theforchipthetrade-offbetweenconductionandswitchinglosses[4],asgivenfortheAC-DCstagewhichisoperatedunderhard-switching.Furthermore,thethermalresistancebetweenthejunctionandthecaseofthesemiconductorchangeswiththechipsize,whichalsoin?uencesthedesignandvolumeoftheheatsink.

η / ?98.5N=798N=697.5N=8N=59796.5Selected Designρ / kW96dm3012345Fig.2:Pareto-optimal(ef?ciency/power-density)designsofthemulti-celltelecompowersupplymodulefordifferentnumbersofconvertercellsandadropoftheDC-linkvoltageduringthehold-uptimeofkDC,drop=20%.

?

DC-linkemployedcapacitorDC-linkrealizationcapacitors:offersThesizeantrade-offandtypebetweenofthetheoverallvolumeoftheDC-linkcapacitorsandthelossescausedbytheequivalentseriesresistance(ESR).Theseparameters,amongothers,aresubjecttoatrade-offbetweenthepower-densityandtheef?ciencyoftheentiresystem.Therefore,forallcombinationsofdesignparametersthesystemperformancehastobedeterminedbyemployingcomponentlossandvolumemodels.

Thevolumesoftheconverterdesignshavebeendeterminedbyconsideringthesumofallcomponentboxedvolumes,suchasthevolumeofthe?DC-linkInductivecapacitors?EMI?ltercomponents?sink.

components?HeatThevolumeofPCBsandcontrolelectronicshavenotbeenconsideredsincetheyarelayoutdependentandthusnotavail-ablefortheoptimization.Forthecalculationoftheconversionef?ciencyfollowinglosseshavebeenincluded:?AC-DCFull-bridgeMOSFETs

–Switchinglosses–Conductionlosses–Gatedrivelosses

?Phase-shiftedFull-bridgeMOSFETs

–Conductionlosses–Gatedrivelosses

?Synchronousrecti?erMOSFETs

–Conductionlosses

–Reverserecoverylosses–Gatedrivelosses?Inductivecomponents

–Corelosses

–Windinglosses(incl.HF-losses).

Inaddtion,thelossescausedbytheequivalentseriesresistanceoftheelectrolyticcapacitorsandconstantlossescausedbyauxiliaryandcontrolelectronicshavebeenincluded.Designspeci?clossessuchastheconductionlossesofthePCBhavebeenomittedinthecalculationastheyvarywiththelayout.Asaresultofthiscomprehensivesystemoptimizationaclear

η / ?98.59897.59796.59699.599.5kDC,drop=10 0@?.4599.499.3599.399.25kDC,drop=10 0@?98.59897.597kDC,drop=10 0@%ρ / kWdm325Full system01234599.2AC-DC Rectifier Stage0246896.5DC-DC Conversion Stage05101520Fig.3:ImpactofdifferentvaluesofthemaximumpermissibledropoftheDC-linkvoltageduringthehold-uptime,kDC,drop,ontheachievablePareto-optimalresultsoftheentiresystem,theAC-DCrecti?erstagesandtheDC-DCconverterstages.

optimumcanbefoundforthenumberofemployedconvertercellsatNopt=6.Eventhoughthescalinglawsderivedin[7]predictabetterperformancewithincreasingnumberofcells,externalandotherpracticalconstraintsoutweighthebene?tsofalargercellnumber,suchasEMIlimitingstandardsbeginningatfEMI=150kHz,thepackageresistanceofMOSFETs,andcommunicationandcontroloverhead.

Thetelecomsupplyisrequiredtofeatureahold-uptimeofThold=10ms(cf.Tab.Iforthefullsetofspeci?cations)whichnecessitateselectrolyticcapacitorswithineachcell.Thevoltagedropofthesecapacitorsduringthehold-uptimewasfoundtobeanotheroptimizationparametersthatexhibitsanoptimumatavalueofkDC,drop=20%.

ThePareto-optimalresultsofthesystemoptimizationareshowninFig.2forfullloadoperationatthenominalop-eratingpointfordifferentnumbersofconvertercellsandamaximumpermissibledropoftheDC-linkvoltageduringthehold-uptimeofkDC,drop=20%.

Thein?uenceofkDC,dropontheachievablesystemperformanceisdepictedinFig.3(a)fortheentiresystemandinFig.3(b)and(c)fortheAC-DCandDC-DCstage,respectively.InthecalculationstheelectrolyticDClinkcapacitorshavebeenallocatedtotheAC-DCconverter.

III.HARDWAREDEMONSTRATORDESIGN

Thedesignwhichisselectedforthehardwaredemonstratorwithacalculatedmaximumef?ciencyofη=98%at75%oftheratedoutputpowerandapowerdensityaboveρcalc=3kW/dm3ismarkedinFig.2.ThemainsystemparametersoftheselecteddesignarelistedinTab.II.ApictureoftheassembledprototypeisshowninFig.4whichfeaturesavolumeofVol=30.4cm·4.5cm·11cm=1.504dm3andthusanoverallpowerdensityofρsys=2.2kW/dm3.ThepowerdensityoftheprototypeislowerthanthecalculatedvaluesincethespacebetweenthecomponentsadverselyaffectstheachievablepowerdensityandthevolumeofthePCBandthecontrolboardshavenotbeenincludedinthecalculations.AdetailedbreakdownofthecalculatedlossesandvolumesisprovidedinFig.5forfullloadoperation.

Inthefollowingparagraphsdifferentdesignaspectsoftheconvertersystemaredescribedindetail.

Tab.II:MainsystemparametersoftheselecteddesignforthehardwaredemonstratorwithN=6convertercells.(Allvaluesgivenpercomponent,e.g.parallelMOSFETs,ifnototherwisenoted.)

AC-DCrecti?er

Switchingfrequencyfsw,cell=20kHz

BoostinductanceAMCC-4,2605SA1,36μH,5turnsMOSFETs2xBSC046N10NS3G,100V,4.6m?DC-linkcap.4xPanasonicECO-S1KA222CA,alum.elect.,

80V,2.2mF

EMI?lter

3stages,2xcommonmodechokes

(EPCOSR40coresT38,10turns),3x680nFDC-DCconverter

Switchingfrequencyfsw=200kHz

Transformerturnsratio7:7,ETD34/17/11,N87,EPCOS

litzwire(600x71μm)

Inductance

ETD34/17/11,N87,EPCOS,20.5μHPrim.MOSFETsBSC046N10NS3G,100V,4.6m?Sec.MOSFETs

BSC046N10NS3G,100V,4.6m?

Phase-shiftedfullbridgeconverter

Thephase-shiftedfullbridgeconverter(PSFB)withfullbridgesynchronousrecti?cation(SR)ischosenfortheisolatedDC-DCconverterstagesinceitallowstoachieveacomparablyhighef?ciencybyoperatingthesemiconductorsunderzero-voltageswitching(ZVS)andstillprovidesaneasywaytocontrolthepower?owbymeansofthephaseshiftbetweenthebridgelegsontheprimarysideataconstantswitchingfrequency.Foraproperoperationoftheconverter,however,certaindesignguidelineshavetobeconsidered[10].WhileZVScanbeachievedforthelagginglegoftheprimaryfullbridgeeasilybyutilizingboththeenergystoredintheoutputinductorandintheleakageinductorofthetransformer,theoperationoftheleadinglegwithZVSreliessolelyontheen-ergystoredintheleakageinductanceduringthefreewheelingphase

E=12

Lσ2Lσ(ILoad·ntr+Imag)

(1)Thisenergyhastobesuf?cienttocharge/dischargethepar-asiticoutputcapacitancesoftheMOSFETsintheleadingbridgeleg.AnenergyanalysisrevealsthatsoftswitchingcanonlybeachievediftheenergyELσislargerthantheenergywhichisfedbackintotheDCinputvoltageduringdischarge

Inductor

DC LinkCapacitorsControlBoard

PowerBoard

Transformer(a)

DC LinkCapacitors

SingleCell

Increasingtheleakageinductanceevenfurtherforabroaderrangeofloadcurrentsforsoftswitchingwouldintroducethedrawbackofalargerdutycyclelosscausedbythetimerequiredtoreversethecurrentintheleakageinductancefrom(?ILoad·ntrafo)to(+ILoad·ntrafo)orviceversa,thusrenderingitasanunpracticalsolution.

AnotherissueintheoperationofthePSFBisthevoltagering-ingatthesecondaryrecti?erMOSFETsafterthefreewheelingphase.TheringingiscausedbytheresonantcircuitcomprisingtheleakageinductanceLσofthetransformerandtheparasiticcapacitancesoftherecti?erMOSFETs(2·COSS)sincethevoltageacrosstheoutputrecti?erisdecoupledbytheoutputinductorfromtheoutputvoltageandthereforenotclampedtoa?xedvoltage(cf.Fig.6(b)).Theresonantfrequencyofthisresonantcircuitequals

??

(3)ωres=1/2CossLσn2trandthecharacteristicimpedanceamountsto

??

Zres=Lσn2tr/(2Coss).

EMIFilterRelayCurrent Sensor

BoostInductor

ControlBoard

PowerBoard

(4)

(b)

Fig.4:Multi-cellsingle-phaseAC-DCtelecomrecti?erprototypewith6convertercellsinISOPcon?gurationforaratedpowerof3.3kWandapowerdensityofρ=2.2kW/dm3:(a)singlecelland(b)fullsystem(30.4cm·11cm·4.5cm/12in·4.3in·1.8in).

ofthechargeequivalentcapacitanceofaMOSFET,i.e.

2.EC,sw=Coss,Qeq·VDC

(2)

Theworstcasevoltageovershootcanreachthevalueoftwice

thetransformedprimaryvoltageVSR,peak=2Vsec=2ntrVDC,asshowninFig.6(d).Inthecaseatthehand,theDC-busvoltageineachcellequalsVDC=VDC,tot/Ncells=400V/6=66Vandwithatransfomerturnsratioofntr=1theworstcasevoltagespikecouldreacharoundVSR,peak=133Vwhichwouldleadtothedestructionofthesynchronousrecti?cationMOSFETswithavoltageratingofVDS,max=100V.Sincethediodesintherecti?erMOSFETsarepronetoreverserecoveryeffects,thevoltagespikeincreasesdependingonthepeakreverserecoverycurrentIRRandcanbecalculatedas

??

(5)VSR,pk=VDCntr+(VDCntr)2+(ZresIRR)2Inorderlimitthevoltagespikealoss-lesssnubbercircuit

consistingofasnubbercapacitorCSnubandtwodiodesisaddedtotheconverter[11].Analternativesnubberthatworkswithanadditionaltransformerwindingcanbefoundin[12].Byintroducingthesnubbertheequivalentcircuitof

Intheprototypeathand,theleakageinductanceofthetrans-formerwasselectedtobeLσ=1μHbyadjustingthewindingarrangement.Thisallowstoachievesoft-switchingintheleadinglegatlevelsoftheoutputcurrentaboveILoad≥3.4A(i.e.30%)accordingto(1)and(2).

Auxiliary(3.0 W)

Inductors(8.1 W)AC/DCstageMOSFETs (11.8 W)DC-linkcapacitors (6.4 W)Auxiliary(3.0 W)

DC/DCstage

Boost ind.(0.9 W)MOSFETs(17.2 W)

Inductors(0.15 dm3)

AC/DCstageTransformers(15.2 W)

Transformers(0.21 dm3)DC-linkcapacitors (0.52 dm3)

DC/DCstage

Boost ind.(0.04 dm3)(a)(b)

EMI filter(0.08 dm3)

Fig.5:Calculatedbreak-downofthelosses(a)andthevolume(b)fortheselectedconverterdesignofthemulti-celltelecompowersupplymoduleatfullload.

Snubber circuitLσ1:nCsnubtrV+-v+DCSR-Vout(a)

n2trLσn2LCtrσsnubn+trV2C+DC

vSR-OSSntrVDCvSR-2COSSVout

(b)

(c)

Z i.ZresISRwithout withSnubberSnubberZres,snubISRvSR

VoutntrVDCVSR,pk,sbVSR,pk(d)

Fig.6:Phase-shiftedfullbridgeconverterwithover-voltagelimitingloss-lesssnubbercircuit[11]forthesecondaryrecti?erMOSFETs:(a)applicationofthesnubbercircuittotheconverter;(b)equivalentcircuitoftheresonantnetworkforthecasewithoutsnubber;(c)modi?edresonantnetworkforcasewithsnubberelements;(d)comparisonoftheresonanttrajectoriesforthecaseswithandwithoutsnubberelementsandtheirresultingvoltagepeaksVSR,pk,sbandVSR,pk,respectively.(Thein?uenceofthereverserecoverycurrentoftheMOSFETbodydiodesisnotshown.)

theresonantnetworkchangesasshowninFig.6(c)andtheresonantfrequencybecomes

??

fres,snub=1/Lσn2tr(2Coss+Csnub)(6)whiletheresonantimpedance??

becomes

Zres,snub=Lσn2tr/(2Coss+Csnub)

(7)

afterthevoltagevSRhasrisenabovetheleveloftheoutputvoltagVout.ThisisalsodepictedinFig.6(d)wherethesuddenchangeoftheresonantimpedanceleadstoadropinthevSR?Z·iplane.Themaximumvoltagespikecanthenbederivedasafunctionoftheoutputvoltagetobe

Vn??

SR,pk,sb=VDCtr+(VDCntr?Vout)2+(Zres,snubISR)2.(8)ThesnubbercapacitorischosentohaveavalueofCSnub=15nFwhichlimitstheworstcasevoltagespikeatthelowestoutputvoltageofVout,min=40VtoVSR,peak,snub=92Vwithoutconsideringthein?uenceofthereverserecoverycurrent.ForthematerialoftheceramicsnubbercapacitorstheC0G(NP0)dielectricischosensinceitprovidesastablecapacitancevalueundervaryingtemperatureandvoltage.Inorderminimizethereverserecoverycurrentsofthediodes,theconductiontimeofthediodesintheSRMOSFETsiskepttoaminimum(around10ns)byadjustmentsofthetimingsofthegatesignals[13].

Master Controller

VDC,tot,ref+-VDC,1VDC,1V??NVV+DC,2DC,iDC,totVi=1-mDC,NGu,1(s)u+grid-VDC,2ugridKmii+g,refgrid-+-VDC,N

ModulationmG(a)

i,1(s)iindexgridmV++DC,N--VoutGate signalsiPWM?outGi,3(s)iV+ref,cellDC,ref-G++u,2(s)iout,refSlave ControllersMaster Controller

VDC,1??NVDC,2VVDC,refii=1DC,iout,ref

Gi,2(s)Vout

Vout,ref

(b)

VDC,NNFig.7:Controlimplementationofthemulti-celltelecomrecti?er:(a)totalDC-busvoltagecontrollerandinputcurrentcontroller;(b)outputcurrentcontrollerandDC-linkvoltagecontroller.

Controlimplementation

Oneofthemainchallengesregardingthecontrolofmulti-cellconvertersingeneralistheunbalanceoftheDC-link

voltagesofthecell.Inordertoovercomethisproblemdifferentcontrolstrategieshavebeenproposed[14]–[18].ThebasicideabehindthoseconceptsistoperformvoltagebalancingcontroleitherbythecascadedH-bridgerecti?erortheisolatedDC-DCconverters.In[14]avoltagebalancecontrolispresentedwhichisbasedonthesingle-phasedq-controlfortherecti?er,andapowerbalancecontrolmethodtoregulatethepowertransferredthroughtheDC-DCconverterthatareconnectedinparallelattheiroutputs.ThisallowstoindividuallyadjustthepowertransferfromeachDC-linktotheoutputinordertobal-ancetheDC-linkvoltages.Incontrast,[15]presentsamethodtocontrolandbalancethevoltageoftheDC-linksbyoperatingtherecti?erstageswithamixtureoflowandhighfrequencyPWM.However,bothoftheaforementionedmethodsresultinrathercomplicatedcontrollerimplementationssincethevoltagebalancingrequiresadditionalcontrolloops.AsimplerwaytooperatetheISOPsystemispresentedin[16]whichusesacommon-duty-ratiocontrolmethodwhichreliesonthenaturalbalancingbehaviorofISOPmulti-cellconverters[17].However,thismethodisnotactivelybalancingtheDC-linkvoltages.Therefore,anymismatchbetweentheconverters,

CCM3CCM2CCM1LCM2LCM2LgCCVDM3DM2CDM1gvFB,totCCM3CCM2CCM1filter stage 3filter stage 2filter stage 1Fig.8:Schematicoftheemployed3-stagecommon-modeanddifferential-modeEMI?lter.

suchase.g.slightlydifferenttransformerterminalbehaviors,willleadtodifferentACvoltageripplesontheDC-linkcapacitorscausedbythepulsatingpowerofthemains.ThesedifferencesintheDC-linkvoltageswillgeneratecirculatingcurrentsattheparallelconnectedconverteroutputswhichde-creasestheef?ciencyofthesystem.Thus,thecontrolschemewhichisselectedfortheimplementationintheprototypehasatotaldc-linkvoltageregulatorontherecti?ersideinordertohaveaconstanttotaldc-linkvoltage(i.e.thesumofallDC-linkvoltages).Inaddition,eachcellpossessesindividualDC-linkvoltageandloadcurrentcontrolfortheisolatedDC-DCconverters[18].Fig.7showsthecontrolblockimplementationoftheentiresystem.Thecontrolloopscanbeimplementedasamaster-slavecontrolregimewherethesloweroutervoltagecontrolloopsareprocessedbythemastercellandthefasterinnercontrolloopslikethecurrentcontrollersarecomputedlocallyoneachcell.Thecommunicationbetweenthecellsisrealizedbytheserialperipheralinterface(SPI).EMIFilterDesign

ForthedesignoftheEMI?lterthein?uenceofthedifferential-modeandthecommon-modenoisehavetobeconsidered.The?lterdesigncanbeperformedindividuallyforthecommon-modeandthedifferential-modenoiseiftherequiredattentuationforeachcaseiscalculatedwithamarginofaround16dBtothelimits,i.e.6dBfortheworstcaseadditionofthetwonoisesignalsand10dBtoaccountforcomponenttolerances.

Inordertocalculatetherequiredattenuationforthedifferential-modenoise,the?rstharmonicthatfallsintotheEMIconstrainedspectrum(fEMI≥150kHz)isconsidered,sincetheamplitudeoftheharmonicspectrumofsquarewavevoltagedecreaseswith?20dBperfrequencydecade,whereasthe?lterattenuationincreaseswith?40·NsdBwithNsbeingthenumberof?lterstages.Forthecaseathand,the?rstharmonicintheconstrainedfrequencyrangeisattwicetheeffectiveswitchingfrequencyfsw,eff=120kHzoftheinter-leavedAC-DCstages,i.e.f?lt=240kHz.ThecompliancewithEMIstandardsisevaluatedbydeterminingthequasi-peakemissionlevelsoftheconverter.Thequasi-peakvoltageoftheharmonicatf?lt=240kHziscalculatedbyconsideringa9kHzbandaroundthatharmonicandbysynthesizingatimedomainsignalwhichisfedintothenon-linearquasi-peakdetectionnetwork[19]andresultsinaquasi-peaknoise

voltageoftheconverteratf?lt=240kHzofV?lt,qp=17.2Vand/orarequiredattenuationof92.8dBincludingthemarginpreviouslymentioned.Followingthe?ltervolumeoptimiza-tionguidelinespresentedin[20]thenumberof?lterstagesforaminimumvolumeanditsassociatedvolumecanbefoundatn?lt=3asshowninFig.8.Themaximumvalueofthetotaldifferentialmodecapacitanceislimitedbythemaximumallowablereactivepowerconsumptionofthe?lter.Thelimitwassetsuchthatapowerfactorofcosφ=0.9canbereachedabove10%ofthenominalpower.ThisleadstototaldifferentialmodecapacitanceofCDM,tot=2μF,whichmeanseachdifferentialmodecapacitanceamountstoCDM=660nF.ThisleadstodifferentialmodeinductancesofLDM=18μHinordertoachievetherequiredattenuationincombinationwiththeboostinductorLg.

Theprecisemodelingofthecommon-modenoiseischal-lengingsinceitrequirestheexactknowledgeofthestraycapacitancesofallelectricnodesintheconvertercellstotheground.Sincethisispracticallyimpossibletodetermineformulti-cellconvertersystems,anapproachaspresentedin[21]wasfollowedwhichdeducesanequivalentcircuitforthecommon-modenoise.Byapplyingaworst-caseapproximationandneglectingsmallcapacitancescomparedtolargerones,itcanbefoundthatduetothenatureoftheseriesconnectionoftheconverterinputsthemeasuredcommon-modevoltageatthelineimpedancestabilizationnetwork(LISN)dependsonwhichcelloftheseriesstackisswitching.So,forexampleeachtimethelowestcelloftheseriesstackswitches,alluppercellsarealsomovedinrespecttotheirpotentialtoground.Sincethecellsareoperatedinterleaved,thecommon-modevoltageresemblesastaircaselikevoltagewaveformwiththelevelsbeing

vNCM(i)=

cells?i

N·VcellsDC(9)fori∈[1,Ncells]wherei=1meansthatthelowestcellofthestackisswitchedandi=Ncellsmeanstheuppermostcellisswitched.Basedonthatvoltagewaveformthequasi-peakvoltagespectrumcanbederivedbymeansofsimula-tionsandtherequiredcommon-mode?lterattenuationcanbedeterminedtobe78dB.Themaximumallowabletotalcommon-mode?ltercapacitanceislimitedbythemaximumtotalleakagecurrenttoearth(e.g.3.5mARMS)whichleadstoCCM,tot=36nFandthusthevalueforeachcommon-modecapacitorisselectedasCCM=4.7nF.Usually,thesmallestcommon-mode?ltervolumeisobtainedbyutilizingthemaximumallowableamountofcommon-mode?lterca-pacitance[22].Asaresult,thecommon-modeinductancescanbedeterminedtobeLCM=1.6mH.Intheprotoype,theleakageinductanceofthecommon-modechokesisutilizedasdifferential-mode?lterinductances.

IV.CONCLUSION

Anewapproachtowardsahighlyef?cientandverycompacttelecomreciti?ermodulebeyondthelimitsofstate-of-the-artsystemsispresented.Thedegreesoffreedominthedesignprocedureofamulti-celltelecompowersupplymoduleinISOPcon?gurationareoutlinedandtheoptimizationprocess

isdescribedindetail.Theoptimizationresultsshowthataconverterdesignwithanef?ciencyofη=98%andapowerdensityofρ=2.2kW/dm3canbeachieved.TheresultsalsorevealanoptimumvalueofN=6forthenumberofconvertercellsandanoptimummaximumpermissibledropof20%theDC-linkvoltageduringthehold-uptime.Basedontheoptimizationresultsahardwaredemonstratorrealizationispresentedandspeci?cdesignaspectsareexplained.Firstmeasurementresultsverifytheoperationofthesystemandwillbesummarizedinfuturepublication.

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