最新电气专业毕业外文翻译分析解析Word文件下载.docx

最新电气专业毕业外文翻译分析解析Word文件下载.docx

《最新电气专业毕业外文翻译分析解析Word文件下载.docx》由会员分享，可在线阅读，更多相关《最新电气专业毕业外文翻译分析解析Word文件下载.docx（12页珍藏版）》请在冰豆网上搜索。

期刊

文献、资料发表（出版）日期：

2010.3.25

院（部）：

信息与电气工程学院

专业：

电气工程与自动化

班级：

姓名：

学号：

指导教师：

翻译日期：

2011.3.10

外文文献：

Theobjectiveofthistopicistoprovidethedesignerwithapracticalreviewofloopcompensationtechniquesappliedtoswitchingpowersupplyfeedbackcontrol.Atop-downsystemapproachistakenstartingwithbasicfeedbackcontrolconceptsandleadingtostep-by-stepdesignprocedures,initiallyappliedtoasimplebuckregulatorandthenexpandedtoothertopologiesandcontrolalgorithms.SampledesignsaredemonstratedwithMathcadsimulationstoillustrategainandphasemarginsandtheirimpactonperformanceanalysis.

I.INTRODUCTION

Insuringstabilityofaproposedpowersupplysolutionisoftenoneofthemorechallengingaspectsofthedesignprocess.Nothingismoredisconcertingthantohaveyourlovinglycraftedbreadboardbreakintowildoscillationsjustasitsbeingdemonstratedtothebossorcustomer,butinsuringagainstthisunfortunateeventtakessomeanalysiswhichmanydesignersviewasformidable.Pathstakenbydesignengineersoftenemphasizeeithercut-and-tryempiricaltestinginthelaboratoryorcomputersimulationslookingfornumericalsolutionsbasedoncomplexmathematicalmodels.Whilebothoftheseapproachabasicunderstandingoffeedbacktheorywillusuallyallowthedefinitionofanacceptablecompensationnetworkwithaminimumofcomputationaleffort.

II.STABILITYDEFINED

Fig.1.Definitionofstability

Fig.1givesaquickillustrationofatleastonedefinitionofstability.Initssimplestterms,asystemisstableif,whensubjectedtoaperturbationfromsomesource,itsresponsetothatperturbationeventuallydiesout.Notethatinanypracticalsystem,instabilitycannotresultinacompletelyunboundedresponseasthesystemwilleitherreachasaturationlevel–orfail.Oscillationinaswitchingregulatorcan,atmost,varythedutycyclebetweenzeroand100%andwhilethatmaynotpreventfailure,itwillsultimatelimittheresponseofanunstablesystem.

AnotherwayofvisualizingstabilityisshowninFig.2.Whilethisgraphicallyillustratestheconceptofsystemstability,italsopointsoutthatwemustmakeafurtherdistinctionbetweenlarge-signalandsmall-signalstability.Whilesmall-signalstabilityisanimportantandnecessarycriterion,asystemcouldsatisfythisrtquirementandyetstillbecomeunstablewithalarge-signalperturbation.Itisimportantthatdesignersrememberthatallthegainandphasecalculationswemightperformareonlytoinsuresmall-signalstability.Thesecalculationsarebasedupon–andonlyapplicableto–linearsystems,andaswitchingregulatoris–bydefinition–anon-linearsystem.Wesolvethisconundrumbyperformingouranalysisusingsmall-signalperturbationsaroundalarge-signaloperatingpoint,adistinctionwhichwillbefurtherclarifiedinourdesignprocedurediscussion。

Fig.2.Large-signalvs.small-signalstability

III.FEEDBACKCONTROLPRINCIPLES

Whereanuncontrolledsourceofvoltage（orcurrent,orpower）isappliedtotheinputofoursystemwiththeexpectationthatthevoltage（orcurrent,orpower）attheoutputwillbeverywellcontrolled.Thebasisofourcontrolissomeformofreference,andanydeviationbetweentheoutputandthereferencebecomesanerror.Inafeedback-controlledsystem,negativefeedbackisusedtoreducethiserrortoanacceptablevalue–asclosetozeroaswewanttospendtheefforttoachieve.Typically,however,wealsowanttoreducetheerrorquickly,butinherentwithfeedbackcontrolisthetradeoffbetweensystemresponseandsystemstability.Themoreresponsivethefeedbacknetworkis,thegreaterbecomestheriskofinstability.Atthispointweshouldalsomentionthatthereisanothermethodofcontrol–feedforward.Withfeedforwardcontrol,acontrolsignalisdevelopeddirectlyinresponsetoaninputvariationorperturbation.Feedforwardislessaccuratethanfeedbacksinceoutputsensingisnotinvolved,however,thereisnodelaywaitingforanoutputerrorsignaltobedeveloped,andfeedforwardcontrolcannotcauseinstability.Itshouldbeclearthatfeedforwardcontrolwilltypicallynotbeadequateastheonlycontrolmethodforavoltageregulator,butitisoftenusedtogetherwithfeedbacktoimprovearegulator’sresponsetodynamicinputvariations.

ThebasisforfeedbackcontrolisillustratedwiththeflowdiagramofFig.3wherethegoalisfortheoutputtofollowthereferencepredictablyandfortheeffectsofexternalperturbations,suchasinputvoltagevariations,tobereducedtotolerablelevelsattheoutputWithoutfeedback,thereference-to-outputtransferfunctiony/uisequaltoG,andwecanexpresstheoutputasyGu

Withtheadditionoffeedback（actuallythesubtractionofthefeedbacksignal）

yGuyHG

andthereference-to-outputtransferfunctionbecomes

y/u=G/1+GH

IfweassumethatGH__1,thentheoveralltransferfunctionsimplifiesto

y/u=1/H

Fig.3.Flowgraphoffeedbackcontrol

NotonlyisthisresultnowindependentofG,itisalsoindependentofalltheparametersofthesystemwhichmightimpactG（supplyvoltage,temperature,componenttolerances,etc.）andisdeterminedinsteadsolelybythefeedbacknetworkH（and,ofcourse,bythereference）.NotethattheaccuracyofH（usuallyresistortolerances）andinthesummingcircuit（erroramplifieroffsetvoltage）willstillcontributetoanoutputerror.Inpractice,thefeedbackcontrolsystem,asmodeledinFig.4,isdesignedsothatG__HandGH__1overaswideafrequencyrangeaspossiblewithoutincurringinstability.WecanmakeafurtherrefinementtoourgeneralizedpowerregulatorwiththeblockdiagramshowninFig.5.Herewehaveseparatedthepowersystemintotwoblocks–thepowersectionandthecontrolcircuitry.Thepowersectionhandlestheloadcurrentandistypicallylarge,heavy,andsubjecttowidetemperaturefluctuations.Itsswitchingfunctionsarebydefinition,large-signalphenomenon,normallysimulatedinmoststabilityanalysesasjustatwostateswitchwithadutycycle.Theoutputfilterisalsoconsideredasapartofthepowersectionbutcanbeconsideredasalinearblock.

Fig.4.Thegeneralpowerregulator

IV.THEBUCKCONVERTER

Thesimplestformoftheabovegeneralpowerregulatoristhebuck–orstepdown–topologywhosepowerstageisshowninFig.6.Inthisconfiguration,aDCinputvoltageisswitchedatsomerepetitiverateasitisappliedtoanoutputfilter.ThefilteraveragesthedutycyclemodulationoftheinputvoltagetoestablishanoutputDCvoltagelowerthantheinputvalue.Thetransferfunctionforthisstageisdefinedby

tON=switchon-time

T=repetitiveperiod（1/fs）

d=dutycycle

Fig.5.Thebuckconverter.

Sinceweassumethattheswitchandthefiltercomponentsarelossless,theidealefficiencyof

Thisconversionprocessis100%,andregulationoftheoutputvoltagelevelisachievedby

controllingthedutycycle.ThewaveformsofFig.6assumeacontinuousconductionmode（CCM）

Meaningthatcurrentisalwaysflowingthroughtheinductor–fromtheswitchwhenitisclosed,

Andfromthediodewhentheswitchisopen.Theanalysispresentedinthistopicwillemphasize

CCMoperationbecauseitisinthismodethatsmall-signalstabilityisgenerallymoredifficult

toachieve.Inthediscontinuousconductionmode（DCM）,thereisathirdswitchconditioninwhichtheinductor,switch,anddiodecurrentsareall5-4zero.Eachswitchingperiodstartsfromthesamestate（withzeroinductorcurrent）,thuseffectivelyreducingthesystemorderbyoneandmakingsmall-signalstableperformancemucheasiertoachieve.Althoughbeyondthescopeofthistopic,theremaybespecializedinstanceswherethelarge-signalstabilityofaDCMsystemisofgreaterconcernthansmall-signalstability.

ThereareseveralformsofPWMcontrolforthebuckregulatorincluding,

•Fixedfrequency（fS）withvariabletONandvariabletOFF

•FixedtONwithvariabletOFFandvariablefS

•FixedtOFFwithvariabletONandvariablefS

•Hysteretic（or“bang-bang”）withtON,tOFF,andfSallvariable

Eachoftheseformshavetheirownsetofadvantagesandlimitationsandallhavebeensuccessfullyused,butsinceallswitchmoderegulatorsgenerateaswitchingfrequencycomponentanditsassociatedharmonicsaswellastheintendedDCoutput,electromagneticinterferenceandnoiseconsiderationshavemadefixedfrequencyoperationbyfarthemostpopular.

Withtheexceptionofhysteretic,allotherformsofPWMcontrolhaveessentiallythesame

small-signalbehavior.Thus,withoutmuchlossingenerality,fixedfSwillbethebasisforourdiscussionofclassical,small-signalstability.

Hystereticcontrolisfundamentallydifferentinthatthedutyfactorisnotcontrolled,perse.Switchturn-offoccurswhentheoutputripplevoltagereachesanuppertrippointandturn-onoccursatalowerthreshold.Bydefinition,thisis

alarge-signalcontrollertowhichsmall-signalstabilityconsiderationsdonotapply.Inasmallsignalsense,itisalreadyunstableand,inamathematicalsense,itsfastresponseisduemoretofeedforwardthanfeedback.

REFERENCES

[1]D.M.Mitchell,“DC-DCSwitchingRegulatorAnalysis”,McGraw-Hill,1988,

DMMitchellConsultants,CedarRapids,IA,1992（reprintversion）.

[2]D.M.Mitchell,“Small-SignalMathcadDesignAids”,（Windows95/98version）,e/j

BLOOMAssociates,Inc.,1999.

[3]GeorgeChryssis,“High-FrequencySwitchingPowerSupplies”,McGraw-HillBook

Company,1984.

[4]RayRidley,“AMoreAccurateC