开关电源外文翻译Word下载.docx

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Modeling,Simulation,andReductionofConductedElectromagneticInterferenceDuetoaPWMBuckTypeSwitchingPowerSupplyI

A.Farhadi

Abstract:

UndesiredgenerationofradiatedorconductedenergyinelectricalsystemsiscalledElectromagneticInterference（EMI）.HighspeedswitchingfrequencyinpowerelectronicsconvertersespeciallyinswitchingpowersuppliesimprovesefficiencybutleadstoEMI.Differentkindofconductedinterference,EMIregulationsandconductedEMImeasurementareintroducedinthispaper.CompliancywithnationalorinternationalregulationiscalledElectromagneticCompatibility（EMC）.PowerelectronicsystemsproducersmustregardEMC.ModelingandsimulationisthefirststepofEMCevaluation.EMIsimulationresultsduetoaPWMBucktypeswitchingpowersupplyarepresentedinthispaper.ToimproveEMC,sometechniquesareintroducedandtheireffectivenessprovedbysimulation.

IndexTerms:

Conducted,EMC,EMI,LISN,SwitchingSupply

I.INTRODUCTION

FASTsemiconductorsmakeitpossibletohavehighspeedandhighfrequencyswitchinginpowerelectronics

.Highspeedswitchingcausesweightandvolumereductionofequipment,butsomeunwantedeffectssuchasradiofrequencyinterferenceappeared

.Compliancewithelectromagneticcompatibility（EMC）regulationsisnecessaryforproducerstopresenttheirproductstothemarkets.ItisimportanttotakeEMCaspectsalreadyindesignphase

.ModelingandsimulationisthemosteffectivetooltoanalyzeEMCconsiderationbeforedevelopingtheproducts.Alotofthepreviousstudiesconcernedthelowfrequencyanalysisofpowerelectronicscomponents

.DifferenttypesofpowerelectronicsconvertersarecapabletobeconsideredassourceofEMI.TheycouldpropagatetheEMIinbothradiatedandconductedforms.LineImpedanceStabilizationNetwork（LISN）isrequiredformeasurementandcalculationofconductedinterferencelevel

.InterferencespectrumattheoutputofLISNisintroducedastheEMCevaluationcriterion

.NationalorinternationalregulationsarethereferencesfortheevaluationofequipmentinpointofviewofEMC

.

II.SOURCE,PATHANDVICTIMOFEMI

Undesiredvoltageorcurrentiscalledinterferenceandtheircauseiscalledinterferencesource.Inthispaperahigh-speedswitchingpowersupplyisthesourceofinterference.

Interferencepropagatedbyradiationinareaaroundofaninterferencesourceorbyconductionthroughcommoncablingorwiringconnections.Inthisstudyconductedemissionisconsideredonly.Equipmentsuchascomputers,receivers,amplifiers,industrialcontrollers,etcthatareexposedtointerferencecorruptionarecalledvictims.Thecommonconnectionsofelements,sourcelinesandcablingprovidepathsforconductednoiseorinterference.Electromagneticconductedinterferencehastwocomponentsasdifferentialmodeandcommonmode

A.Differentialmodeconductedinterference

Thismodeisrelatedtothenoisethatisimposedbetweendifferentlinesofatestcircuitbyanoisesource.RelatedcurrentpathisshowninFig.1

.Theinterferencesource,pathimpedances,differentialmodecurrentandloadimpedancearealsoshowninFig.1.

B.Commonmodeconductedinterference

Commonmodenoiseorinterferencecouldappearandimposebetweenthelines,cablesorconnectionsandcommonground.Anyleakagecurrentbetweenloadandcommongroundcouldbemodeledbyinterferencevoltagesource.

Fig.2demonstratesthecommonmodeinterferencesource,commonmodecurrentsIcm1andIcm2andtherelatedcurrentpaths

.Thepowerelectronicsconvertersperformasnoisesourcebetweenlinesofthesupplynetwork.Inthisstudydifferentialmodeofconductedinterferenceisparticularlyimportantanddiscussionwillbecontinuedconsideringthismodeonly.

III.ELECTROMAGNETICCOMPATIBILITYREGULATIONS

Applicationofelectricalequipmentespeciallystaticpowerelectronicconvertersindifferentequipmentisincreasingmoreandmore.Asmentionedbefore,powerelectronicsconvertersareconsideredasanimportantsourceofelectromagneticinterferenceandhavecorruptingeffectsontheelectricnetworks

.Highlevelofpollutionresultingfromvariousdisturbancesreducesthequalityofpowerinelectricnetworks.Ontheothersidesomeresidential,commercialandespeciallymedicalconsumersaresosensitivetopowersystemdisturbancesincludingvoltageandfrequencyvariations.ThebestsolutiontoreducecorruptionandimprovepowerqualityiscomplyingnationalorinternationalEMCregulations.CISPR,IEC,FCCandVDEareamongthemostfamousorganizationsfromEurope,USAandGermanywhoareresponsiblefordeterminingandpublishingthemostimportantEMCregulations.IECandVDErequirementandlimitationsonconductedemissionareshowninFig.3andFig.4

Fordifferentgroupsofconsumersdifferentclassesofregulationscouldbecomplied.ClassAforcommonconsumersandclassBwithmorehardlimitationsforspecialconsumersareseparatedinFig.3andFig.4.FrequencyrangeoflimitationisdifferentforIECandVDEthatare150kHzupto30MHzand10kHzupto30MHzrespectively.Complianceofregulationsisevaluatedbycomparisonofmeasuredorcalculatedconductedinterferencelevelinthementionedfrequencyrangewiththestatedrequirementsinregulations.InunitedEuropeancommunitycomplianceofregulationismandatoryandproductsmusthavecertifiedlabeltoshowcoveringofrequirements

IV.ELECTROMAGNETICCONDUCTEDINTERFERENCEMEASUREMENT

A.LineImpedanceStabilizationNetwork（LISN）

1-Providingalowimpedancepathtotransferpowerfromsourcetopowerelectronicsconverterandload.

2-Providingalowimpedancepathfrominterferencesource,herepowerelectronicsconverter,tomeasurementport.

VariationofLISNimpedanceversusfrequencywiththementionedtopologyispresentedinFig.7.LISNhasstabilizedimpedanceintherangeofconductedEMImeasurement

VariationoflevelofsignalattheoutputofLISNversusfrequencyisthespectrumofinterference.Theelectromagneticcompatibilityofasystemcanbeevaluatedbycomparisonofitsinterferencespectrumwiththestandardlimitations.ThelevelofsignalattheoutputofLISNinfrequencyrange10kHzupto30MHzor150kHzupto30MHziscriterionofcompatibilityandshouldbeunderthestandardlimitations.Inpracticalsituations,theLISNoutputisconnectedtoaspectrumanalyzerandinterferencemeasurementiscarriedout.Butformodelingandsimulationpurposes,theLISNoutputspectrumiscalculatedusingappropriatesoftware.

ForasimplefixedfrequencyPWMcontrollerthatisappliedtoaBuckDC/DCconverter,itispossibletoassumetheerrorvoltage（ve）changesslowwithrespecttotheswitchingfrequency,thepulsewidthandhencethedutycyclecanbeapproximatedby

（1）.Vpisthesawtoothwaveformamplitude.

A.PWMwaveformspectralanalysis

Thenormalizedpulsetrainm（t）ofFig.8representsPWMswitchcurrentwaveform.ThenthpulseofPWMwaveformconsistsofafixedcomponentD/fs,inwhichDisthesteadystatedutycycle,andavariablecomponentdn/fsthatrepresentsthevariationofdutycycleduetovariationofsource,referenceandload.

AsthePWMswitchcurrentwaveformcontainsinformationconcerningEMIduetopowersupply,itisrequiredtodothespectrumanalysisofthiswaveforminthefrequencyrangeofEMIstudies.ItisassumedthaterrorvoltagevariesaroundVewithamplitudeofVe1asisshownin

（2）.

fmrepresentsthefrequencyoferrorvoltagevariationduetothevariationsofsource,referenceandload.Theinterceptionoftheerrorvoltagevariationcurveandthesawtoothwaveformwithswitchingfrequency,leadsto（3）forthecomputationofdutycyclecoefficients

MaximumvariationofpulsewidtharounditssteadystatevalueofDislimitedtoD1.IneachperiodofTm=1/fm,therewillber=fs/fmpulseswithdutycyclesofdn.Equation（4）presentstheFourierseriescoefficientsCnofthePWMwaveformm（t）.WhichhavethefrequencyspectrumofFig.9.

B-EquivalentnoisecircuitandEMIspectralanalysis

ToattaintheequivalentcircuitofFig.6thevoltagesourceVsisreplacedbyshortcircuitandconverterisreplacedbyPWMwaveformswitchcurrent（Iex）asithasshowninFig.10.

ThetransferfunctionisdefinedastheratiooftheLISNoutputvoltagetotheEMIcurrentsourceasin（5）.

Thecoefficientsdi,ni（i=1,2,…,4）correspondtotheparametersoftheequivalentcircuit.RcandLcarerespectivelytheeffectiveseriesresistance（ESR）andinductance（ESL）ofthefiltercapacitorCfthatmodelthenon-idealityofthiselement.TheLISNandfilterparametersareasfollows:

CN=100nF,r=5Ω,l=50uH,RN=50Ω,LN=250uH,Lf=0,Cf=0,Rc=0,Lc=0,fs=25kHz

TheEMIspectrumisderivedbymultiplicationofthetransferfunctionandthesourcenoisespectrum.SimulationresultsareshowninFig.11.

VI.PARAMETERSAFFECTIONONEMI

A.DutyCycle

ThepulsewidthinPWMwaveformvariesaroundasteadystateD=0.5.TheoutputnoisespectrumwassimulatedwithvaluesofD=0.25and0.75thatareshowninFig.12andFig.13.EvenharmonicsareincreasedandoddonesaredecreasedthatisdesiredinpointofviewofEMC.OntheotherhandthenoiseenergyisdistributedoverawiderrangeoffrequencyandthelevelofEMIdecreased

.

B.Amplitudeofdutycyclevariation

ThemaximumpulsewidthvariationisdeterminedbyD1.TheEMIspectrumwassimulatedwithD1=0.05.SimulationsarerepeatedwithD1=0.01and0.25andtheresultsareshowninFig.14andFi