Duty-Ratio-Feedforward-for-Digitally-Controlled-Bo

108IEEETRANSACTIONSONINDUSTRIALELECTRONICS,VOL.52,NO.1,FEBRUARY2005Duty-RatioFeedforwardforDigitallyControlledBoostPFCConvertersDavidM.VandeSype,Member,IEEE,KoenDeGussemé,Member,IEEE,AlexP.M.VandenBossche,SeniorMember,IEEE,andJanA.Melkebeek,SeniorMember,IEEEAbstract—Whena“classical”currentcontrolschemeisapplied,thelinecurrentofaboostpower-factor-correction(PFC)converterleadsthelinevoltage,resultinginanonunityfundamentaldis-placementpowerfactorandinimportantzero-crossingdistortioninapplicationswithahighlinefrequency(e.g.,400-Hzpowersys-temsoncommercialaircraft).Toresolvethisproblem,acurrent-controlschemeisproposedusingduty-ratiofeedforward.Inthispaper,theinputimpedanceoftheboostPFCconverterforboththeclassicalcurrent-loopcontrollerandthecontrollerusingduty-ratiofeedforwardarederivedtheoretically.Acomparisonrevealstheadvantagesoftheproposedcontrolscheme:alowtotalharmonicdistortionofthelinecurrent,aresistiveinputimpedance,virtu-allynozero-crossingdistortion,andafundamentaldisplacementpowerfactorclosetounity.ThetheoreticalresultsobtainedareverifiedusinganexperimentalsetupofadigitallycontrolledboostPFCconverter.IndexTerms—Digitalcontrol,feedforwardsystems,inputimpedance,power-factorcorrection(PFC),totalharmonicdistor-tion(THD),zero-crossingdistortion.I.INTRODUCTIONINpower-factor-correction(PFC)convertersoperatinginthecontinuousconductionmode,thebehaviorofthecurrent-controlloopdetermineshowaccuratelytheinputcurrenttracksthedesiredwaveshape.Sincethebehaviorofthisloopisin-fluencedbytheimpedanceoftheelectromagneticinterference(EMI)filterandtheunknowntime-dependentlineimpedance,guaranteeingstabilityoftheconverterunderallcircumstancesisnotobvious.Forthe“classical”controlloopusingthemea-surementoftheinputvoltage,thisproblemisstudiedin[1]and[2].Wherethemethodpresentedin[1]providesageneralruleofthumb,amorerigorousmethodusingthestate-space-aver-agedmodelisdescribedin[2].Toincreasetherobustnessofthecurrent-controlloopagainstvariationsoftheimpedanceattheinputoftheconverter,theinsertionofalow-passfilterinthemeasurementcircuitoftheinputvoltageissuggested.Anotherpopular,morerecentcontrolmethodisthenonlinearcarrier(NLC)control.Thiscontrolmethoddistinguishesitselffromthe“classical”controlmethodbytheabsenceoftheinputvoltagemeasurement.ToobtainaresistiveinputinaboostPFCconvertereithertheswitchcurrent[3]orthediodecurrent[4]ManuscriptreceivedDecember23,2003;revisedJanuary27,2004.AbstractpublishedontheInternetNovember10,2004.Thispaperwaspresentedatthe2003IEEEAppliedPowerElectronicsConferenceandExposition,MiamiBeach,FL,February9–13.TheauthorsarewiththeElectricalEnergyLaboratory(EELAB),De-partmentofElectricalEnergy,SystemsandAutomation(EESA),GhentUniversity,B-9000Ghent,Belgium(e-mail:[e-mail];[e-mail];[e-mail];[e-mail]).DigitalObjectIdentifier10.1109/TIE.2004.841127arefirstintegratedandthencomparedtoanonlinearcarrier.Thiscontrolmethodcanalsobeappliedtoactiverectifiersbasedontopologiesdifferentfromtheboostconverter[5].In[6]agen-eralpulsewidthmodulatorisderivedthatallowsonetoeasilyimplementdifferentcontrolalgorithmswithoutinputvoltagemeasurementforvarioustopologiesofPFCconverters.Oneofthecontrollersfortheboosttopologypresentedin[6],whichcatchestheeyeduetoitssimplicity,wasderivedindependentlyin[7].ForthiscontrollertheswitchingwaveformsfortheswitchintheboostPFCconverterarederivedbyastraightforwardcom-parisonbetweentheinductorcurrentmeasurementandasaw-toothcarrier.Theamplitudeofthesawtoothwaveformisdeter-minedbytheoutputvoltagecontroller.Forreasonsofprice,thecontrolalgorithmsforsingle-phasePFCconvertersareinmostcasesimplementedasanalogcircuits[1]–[8].Withtheadventoffastdigitalsignalprocessors(DSPs)embeddingcontrolperipheralssuchaspulsewidth-modu-lation(PWM)generationunits,ADconverters,etc.(e.g.,TMS320C2XXfromTexasInstruments,ADSP-2199XfromAnalogDevices,andDSP56800fromMotorola),newandmorecomplicatedcontrolalgorithmsbecomefeasible.Forthenearfuture,astheratioprice/performanceofDSPsisexpectedtodecreasefurther,thereisafairchancethattheanalogcontrolcircuitswillbeabandonedinfavorofdigitalimplementations.ThistendencycanalsobeillustratedbytherecentinterestindigitalcontrolofPFCconverters[9]–[12].GeneraldesignissuesandpeculiaritiesforthedigitalcontrolofboostPFCconverterswerediscussedin[9]and[11].Sincethemeasuredcontrolsignalsinconvertersoftencontainasig-nificantrippleandhigh-frequencyoscillationsattheswitchinginstants,specialattentionmustbepaidtothesamplinginstantsindigitallycontrolledboostPFCconverters.Samplingalgo-rithmsthatguaranteehighfrequencyswitchingnoiseimmunityforboostPFCconvertersarepresentedin[10]and[12].Fig.1showsthecircuitdiagramemployed.Forthepurposeofdigitalcontrol,theanalogcontrolvariables(theinductorcurrent,theinputvoltageandtheoutputvoltage)mustbeconvertedintodigitalquantitiesbytheanalog-to-dig-italconverter.Theprocessofsensingthecontrolvariable,amplifyingthesensoroutputtotheappropriaterangeandtheanalog-to-digitalconversion,canberepresentedbyadivisionoftheanalogcontrolvariablesby