Phase-Shifted Full Bridge DC/DC Power Converter …

1 Phase-ShiftedFull BridgeDC/DCPowerConverterDesignGuideAbst ractThe phaseshiftedfull Bridge (PSFB)converteris usedfor DC-DCconversionin variousapplications,forexamplein telecomsystemsto converta high voltagebus to an intermediatedistributionvoltage,typicall ycloserto well as isolationfromthe line voltage,sincethistopologyincludesa documentpresentsthe implementationdetailsof a digitallycontrolledPSFB systemimplementedonthe HVPSFBkit kit convertsa 400 VDC inputto a regulated12V DC outputand is ratedfor operationsup to (PCMC)and voltagemodecontrol(VMC)implementationsar e (ZVS)and varioussynchronousrectificationschemes, generatingcomplexgatedrivewaveforms,requ iredby thesecontrolschemes,and intelligenttimingcontrol,to optimizesystemperformanceunderchangingop eratingconditions, step by step guideto run and get familiarwith the HVPSFB projectis also systemefficiencyabove10%ratedload,novelP CMC waveformgenerationbasedon on-chip hardwaremechanisms,and simplesystemimplementationare the highlightsof this.

2 If you wouldlike to quicklyevaluatethis kit withoutgoingthroughthe implementationdetails,pleasefollowthe accompanyingquickstartguide( )insteadof IMPORTANTNOTICEat the end of this TI referencedesignaddressesauthorizeduse, intellectualpropertymattersand otherimportantdisclaimersand May 2014 Phase-ShiftedFullBridgeDC/DCPowerConvert erDesignGuideSubmitDocumentationFeedback Copyright 2014, (TI HV EVM)UserSafetyGuidelinesAlwaysfollowTI s setupand applicationinstructions,includinguse of all interfacecomponentswithintheirrecommende delectricalratedvoltageand electricalsafetyprecautionsto helpensureyourpersonalsafetyand thoseworkingaroundyou. ContactTI's ProductInformationCenterhttp:// warningsand instructionsfor followwarningsand instructionsmayresultin personalinjury,propertydamage,ordeathdue to electricalshockand termTI HV EVMrefersto an electronicdevicetypicallyprovidedas an openframed, isintendedstrictlyfor use in developmentlaboratoryenvironments,solely for qualifiedprofessionalusershavingtraining ,expertiseand knowledgeof electricalsafetyrisksin developmentand applicationof otheruse and/orapplicationare strictlyprohibitedby TexasInstruments.

3 If you are not suitablequalified,you shouldimmediatelystop fromfurtheruse of the HV WorkAreaSafety(a) Keepworkareacleanand orderly.(b) Qualifiedobserver(s)mustbe presentanytimecircuitsare energized.(c) Effectivebarriersand signagemustbe presentin the areawherethe TI HV EVMand its interfaceelectronicsare energized,indicatingoperationof accessiblehigh voltagesmay be present,for thepurposeof protectinginadvertentaccess.(d) All interfacecircuits,powersupplies,evaluati onmodules,instruments,meters,scopesand otherrelatedapparatususedin a developmentenvironmentexceeding50 Vrms/75 VDCmustbeelectricallylocatedwithina protectedEmergencyPowerOff EPOprotectedpowerstrip.(e) Use stableand nonconductiveworksurface.(f) Use adequatelyinsulatedclampsand wiresto attachmeasurementprobesand ElectricalSafetyAs a precautionarymeasure,it is alwaysa goodengineeringpracticeto assumethat the entireEVMmay havefully accessibleand activehigh voltages.

4 (a) De-energizethe TI HV EVMand all its inputs,outputsand electricalloadsbeforeperforminganyelectr icalor TI HV EVMpowerhas beensafelyde-energized.(b) Withthe EVMconfirmedde-energized,proceedwith requiredelectricalcircuitconfigurations, wiring,measurementequipmentconnection,an d otherapplicationneeds,whilestill assumingtheEVMcircuitand measuringinstrumentsare electricallylive.(c) AfterEVMreadinessis complete,energizethe EVMas :WHILETHEEVMIS ENERGIZED,NEVERTOUCHTHEEVMOR ITS ELECTRICALCIRCUITSAS THEYCOULDBE AT HIGHVOLTAGESCAPABLEOF PersonalSafety(a) Wearpersonalprotectiveequipment(for example,latexglovesor safetyglasseswith side shields)or protectEVMin an adequatelucentplasticbox with interlocksto safeuse:EVMsare not to be usedas all or part of a May 2014 SubmitDocumentationFeedbackCopyright 2014, Bridge (PSFB)DC-DCconvertersare usedfrequentlyto step downhigh DC busvoltagesand/orprovideisolationin mediumto high powerapplicationslike serverpowersupplies,telecomrectifiers,ba tterychargingsystems,and ,micro-controllershavebeenrestrictedto only performingsupervisoryor communicationstasksin high performingmicro-controllerdevices,it is now possibleto use micro-controllersforclosingcontrolloopsi n thesesystems,in additionto handlingthe digitalpowercontrolmeansthat functionsthat werepreviouslyimplementedin hardwarearenow implementedin additionto the flexibilitythis addsto the system,this implementadvancedcontrolstrategiesto optimallycontrolthepowerstageunderdiffer entconditionsand also PSFB converterconsistsof four powerelectronicswitches(like MOSFETsor IGBTs)

5 That forma full -bridgeon the primaryside of the isolationtransformerand dioderectifiersor MOSFET switchesforsynchronousrectification(SR)o n the topologyallowsall the switchingdevicestoswitchwith zerovoltageswitching(ZVS)resultingin lowerswitchinglossesand an work,ZVSfor switchesin the one leg of the full bridgeand zeroor low voltageor Low VoltageSwitchingfor switchesin the otherleg is achievedacrossthe completeload range,by changingdead-timesfor primaryside switchesbasedon load suchan isolatedtopology,signalrectificationis requiredon the systemswith lowoutputvoltageand/orhigh outputcurrentratings,implementingsynchro nousrectificationinsteadof dioderectificationachievesthe best possibleperformanceby this work,currentdoublersynchronousrectificat ionis implementedon the secondaryside with differentswitchingschemesto achieveoptimumperformanceundervaryingloa d DC-DCconvertersystemcan be controlledin variousmodeslike voltagemodecontrol(VMC),averagecurrentmo decontrol(ACMC)or peakcurrentmodecontrol(PCMC).

6 Implementingthesedifferentcontrolmodesfo r controllingthe samepowerstagetypicallyrequiresredesigni ngthe controlcircuitalongwithsomechangesto the microcontrollerbasedsystem,all thesemodescan be experimentedwith on the samedesignwith minimalor no systemisimplementedhereusingVMCand a highlydesiredcontrolschemefor powerconvertersbecauseof its inherentvoltagefeedforward,automaticcycl eby cyclecurrentlimiting,flux balancingand a PSFB systemrequirescomplexPWMwaveformgenerati onwith newapproachto this waveformgenerationis presentedusingTMS320F2802xand TMS320F2803x(TexasInstrumentsPiccoloseri es)microcontrollerswithoutrequiringany usedto provideappropriateslopecompensationthat guaranteesopenloop stabilityand eliminates/limitssub-harmonicoscillation sat the a micro-controller,the regulatedoutputvoltageis dependenton the amountofoutputvoltageripple,whichin turn is dependenton the relationis explainedin detailanddifferentsolutionsare efficiencygreaterthan90%downto 10%load is achievedwith May 2014 Phase-ShiftedFullBridgeDC/DCPowerConvert erDesignGuideSubmitDocumentationFeedback Copyright 2014, showsa simplifiedcircuitof a phaseshiftedfull , QB, QC and QDformthe full -bridgeon the primaryside of the transformerT1.

7 QA and QB are switchedat 50 % duty and180 degreeout of phasewith ,QC and QD are switchedat 50 % duty and 180degreeout of phasewith PWMswitchingsignalsfor leg QC QD of the full bridgearephaseshiftedwith respectto thosefor leg QA - QB. Amountof this phaseshift decidesthe amountofoverlapbetweendiagonalswitches,w hichin turn decidesthe amountof , D2providediodecurrentdoublerrectificatio non the secondary,whileLo and Co formthe providesassistanceto the transformerleakageinductancefor resonanceoperationwithMOSFET capacitanceand facilitatesZeroVoltageSwitching(ZVS).Not ethe two differentgroundsG1and G2 on the two sidesof transformerT1. Figure2 providesthe switchingwaveformsfor the A Phase-ShiftedFull BridgeCircuitFigure2. PSFBPWMW aveforms4 Phase-ShiftedFullBridgeDC/DCPowerConvert erDesignGuideTIDU248 May 2014 SubmitDocumentationFeedbackCopyright 2014, HVPSFBB oardFigure3 showsa simplifiedblockdiagramof the PSFB circuitimplementedon the , QB, QC and QD in Figure3 correspondto switchesQ1, Q4, Q2 and Q3 and Q6 are usedfor synchronousrectificationon the PSFBS ystemBlockDiagramThe controlalgorithmis implementedon a C2000microcontroller(MCU).

8 The MCUinteractswith thePSFB powerstageby way of feedbacksignalsand controlleris placedon thesecondaryside on this the placementof the controllerwith respectto the isolationboundaryis a crucialstep whendesigningan systemsthat havemultipleoutputrails or handlemanysignalsand controlloopson the secondaryside or communicatewith othersystemsin the application(on the secondary),placingthe controlleron the secondaryside is betweenPWMsignalsdrivingthe two legs of the full bridgedeterminesthe amountof energytransferredto the phaseshift is the DC conversionby controllingthis phaseshift so as to regulateand maintaintheoutputvoltageat the systemin differentoperationmodesrequiresgeneratin gcomplexPWMdrivewaveformsalongwith fast and efficientcontrolloop is madepossibleon C2000microcontrollersby advancedon-chipcontrolperipheralslike PWMmodules,analogcomparatorswithDACand slopecompensationhardwareand 12-bithigh speedADCscoupledwith an detaileddescriptionof the softwarealgorithmis providedin the May 2014 Phase-ShiftedFullBridgeDC/DCPowerConvert erDesignGuideSubmitDocumentationFeedback Copyright 2014, 400 VDC input(370 Vdcto 410 Vdcoperation),12V DC output Peakefficiencygreaterthan95%.

9 Above90%efficiencydownto 10%load 50 Amp(600 Watt)ratedoutput PhaseShiftedFull-BridgeCircuittopology 100 KHz switchingfrequency PeakCurrentModeControl(PCMC)with no externalsupportcircuitryfor PCMC function MultipleSynchronousRectification(SR)swit chingschemes AdaptiveZVS/LVSacrossthe completeload range EfficientGUI Interfacethat allowsfast & easysystemtuningfor optimalperformance Faultprotection:InputUV and OV, Over-current,OutputUV (CC/CPmode) Constantcurrent(CC)and constantpower(CP)functions OptionalVoltageModeControl(VMC)6 Phase-ShiftedFullBridgeDC/DCPowerConvert erDesignGuideTIDU248 May 2014 SubmitDocumentationFeedbackCopyright 2014,TexasInstrumentsIncorporatedHVPSFB 600W EVM - Efficiency606570758085909510026 12 18 24 30 37 43 49 55 61 67 73 79 85 91 98% Load% kit:(1)Notethat the auxiliarypoweris not includedin the EfficiencyVs.

10 Load(PCMCand VMCI mplementations)ALoad= 12 AALoad= 12 AFigure5. Activeto PassiveLeg Transitions(ZVS)Figure7. Passiveto ActiveLeg Transitions(LVS)SwitchingSwitchingFigure 6. PCMCT ransientResponse(0% to 80%Figure8. PCMCT ransientResponse(80%to 0%LoadStep)LoadStep)7 TIDU248 May 2014 Phase-ShiftedFullBridgeDC/DCPowerConvert erDesignGuideSubmitDocumentationFeedback Copyright 2014, switchingare achievedacrossthe morethan90%is obtainedfor all loadsgreaterthan10%ratedload,whilethe peakefficiencyis greaterthan95%.Outputpeakdeviationsof less than3% of ratedoutputand settlingtimesless than250usareachievedfor 80%step changein responselookslike a dampedfirst (TMS320F2802x)basedimplementationprovide san abilityto generate,and control,complexgatedrivewaveformsrequire dfor PCMCand VMCcontrolschemeswhilestill providinga levelofintelligenceuniqueto snapshotof the PCMCGUI includedin the softwarepackageaccompanyingthis separateGUI for VMCimplementationis also PCMCGUI8 Phase-ShiftedFullBridgeDC/DCPowerConvert erDesignGuideTIDU248 May 2014 SubmitDocumentationFeedbackCopyright 2014, Componentson the BoardFigure10 showskey HVPSFBD evelopmentKit9 TIDU248 May 2014 Phase-ShiftedFullBridgeDC/DCPowerConvert erDesignGuideSubmitDocumentationFeedback Copyright 2014, and Figure12 providethe schematicdiagramfor the Piccolo-Acontrollercardand the MS320F28027(Piccolo-A)