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1、CHAPTER1.INTRODUCTION1.1BACKGROUNDMostelectronicequipmentissuppliedby50/60Hzutilitypower,andmorethan50%ofpowerisprocessedthroughsomekindofpowerconverters.Conventionally,mostofthepowerconversionequipmentemployseitherdioderectifierorthyristorrectifierwithabul
2、kcapacitortoconverterACvoltagetoDCvoltagebeforeprocessingit.Suchrectifiersproduceinputcurrentwithrichharmoniccontent,whichpollutethepowersystemandtheutilitylines.Powerqualityisbecomingamajorconcernformanyelectricalusers.Forexample,Fig.1.1(a)showsthecircuitd
3、iagramofadiode-capacitorrectifier,inwhichLKrepresentsthesourceimpedanceandCBisthebulkenergy-storagecapacitor.Figure1.1(b)showsthattheinputcurrentwaveformhasnarrowconductionangleandstrongdistortion.Tomeasurethequalityofinputpowerofelectricalequipment,powerfa
4、ctorisawidelyusedterm.Thepowerfactorofanoff-lineequipmentisdefinedastheproductoftwocomponents:thedisplacementfactorcosϕ,whichiscausedbythephasedifferencebetweenthefundamentalcomponentoftheinputcurrentandthesinusoidalinputvoltage,andthedistortionfactor,which
5、canbepresentedbythetotal-harmonic-distortion(THD)oftheinputcurrent[A1].Infact,thegreatestconcernoftheoff-linerectifier’simpactonthepowersystemisnotthedisplacementbetweenthevoltageandcurrent,buttheinputcurrentdistortionandcurrentharmonics,sincetheypollutethe
6、powersystemandcausesinterferenceamongoff-lineutilities.Tolimittheinputcurrentharmonicsdrawnbytheoff-lineequipment,severalinternationalregulations,suchastheIEC61000-3-2[A2]anditscorrespondingJapaneseregulation,haveChapter1.Introduction1beenproposedandjustenf
7、orcedthisyear.Thesespecificationshavepromptedmanypowersupplymanufacturerstointensifytheireffortstowardsfindingsimpleandcost-effectivesolutionsforcomplyingwiththespecifications.Asaresult,thetechniquesforreductionofinputcurrentharmonicsreductionhavebeenintens
8、ivelyintroducedandstudiedinrecentyears.Althoughthemainobjectiveisreallyinput-current-shaping(ICS),mostpeoplerefertheirworkaspower-factor-correction(PFC).Inthisdissertation,theterm“PFC”willbeusedtocompl
