电气工程及其自动化专业英语第三章.ppt

Chapter3PowerElectronicTechnology,Section2TheDC-DCConverters,Text,NewWordsandExpressions,Exercises,End,Transitionofpartofspeech,Section2TheDC-DCConverters,IntroductionTheDC-DCconverterconvertsaDCpowersourcetoanotherDCsourcewithdifferentterminalspecifications.TheDC-DCconverterschangeDCtoACfirstandthanchangeACbacktoDC.TheDCsourceisoftentheuncontrolledDCvoltagewithripplefromACtoDCrectifier.TheDC-DCconvertersarewidelyusedintheswitch-modepowersuppliesandDCmotordriveapplications.Someoftheseconverters,especiallyinpowersupplies,haveanisolationtransformer.,Section2TheDC-DCConverters,TheDC-DCconvertersarealsousedasinterfacesbetweentheDCsystemsofdifferentvoltagelevels.Thestep-downandstep-upvoltageconvertersarethetwobasicconvertertopologies.ThesearereferredastheBuckandBoostconvertersrespectively.Itmust,however,bekeptinmindthatastep-downvoltageconverterisalsoastep-upcurrentconverterandviceversabecausetheinputpowermustequaltheoutputpower.TheBuck-Boostconverterdoesbothsteppingupanddown,Section2TheDC-DCConverters,action.TheUKconverterisadualoftheBuck-Boostconverter.Alltheseconvertershavesingle,twoandfourquadrantvariationsintopologies.ThevoltagesourcedrivenDC-DCconvertsaremorepopularthanthecurrentdrivenconverters,hence,thissectionwillconcentrateonthevoltagedrivenconverters.Allconvertsuseeffectivefilteringonboththeinputandtheoutputtoreducetheaccomponentsfromgoingoutsidetheconverters.,Section2TheDC-DCConverters,BuckConverterTheBuckconverterisavoltagestep-downandcurrentstep-upconverter.ThetopologyisshowninFig.3-2.Thetwo-positionswitchissynthesizedfromaswitchandadiode.Theswitchisturnedonforatimeperiodicallyatarate1/Ts.,Fig.3-2Buckconvertertopology,Section2TheDC-DCConverters,AprominentapplicationoftheBuckconverterisaDCregulatedpowersupplyinwhichtheoutputvoltageisregulatedagainstthevariationsintheloadresistanceandtheinputvoltages.Thesepowersuppliesareusedincomputersandportableinstrumentsinthemedicalandcommunicationfield.TherearetwomodesofBuckconverteroperationsinwhichtheoutputcurrentwaveformiseithercontinuousordiscontinuousintimeoveraswitchingperiod.,Section2TheDC-DCConverters,Continuousconductionmode(CCM)Theidealcurrentsinkintheoutputrepresentsinfinitelylargeinductorinserieswiththeloadresistance.ThisisahypotheticalcircuitbutitsdiscussionprovidesagoodunderstandingoftheBuckconverteroperation.Thesteady-stateoperationconsistsoftwocircuitmodes,showninFig.3-3.,Fig.3-3Circuitmodesinsteady-stateoperation,Section2TheDC-DCConverters,Astheswitchisturnedoninmodel,thediodeisreversebiasedandthecurrentflowsthroughinductorintothevoltagesink.Afteratime,theswitchisturnedoff.Theinductorcurrentthenfreewheelsthroughthediodeasshowninthecircuitofmode2.ThesecondmodeisterminatedatTSwhentheswitchisturnedonagain.ThecurrentandvoltagewaveformsareshowninFig.3-4.Theaverageoutputvoltageis,Section2TheDC-DCConverters,or,(3-5),Fig.3-4Thecurrentandvoltagewaveforms,Section2TheDC-DCConverters,Discalledthedutyratio.ThedutyratioDisalsotheturnratiooftheequivalentDCtransformer.Theturnratiooftheequivalentdctransformercanbecontrolledelectronicallyinarangeof01.TheDCoutputvoltageisalinearfunctionoftheon-timeoftheswitch,thepulsewidth,andtheswitchingfrequency(inversefunctionoftheswitchingperiodTS).TheoutputvoltagecontrolusingpulsewidthisknownasthePWMcontrol.Theoutputvoltagecanalsobecontrolledbyswitchingfrequency.ThePWMcontrolismorepopular.,Section2TheDC-DCConverters,IfthedutyratioDismadealinearfunctionofuC,acontrolvoltage,(3-6),Theoutputvoltageisthenalinearfunctionofthecontrolvoltage.Thisisalsotheprincipleofswitch-modelinearamplifier.Thegainofthisamplifierisdeterminedbytheinputdcsourcevoltage.Neglectingthepowerlossesinthecircuitelements,wecouldusetheequationofthebalanceofpower,Section2TheDC-DCConverters,(3-7),whereISistheaveragecurrentfromtheDCsource.Hence,(3-8),AlthoughtheDCoutputvoltageissmallerthantheDCinputvoltage,theDCoutputcurrentislargerthantheinputDCcurrent(astep-upactionincurrent),Return,NewWordsandExpressions,ripplen.波纹，波度，微波rectifiern.整流器isolationtransformer隔离变压器interfacen.接口Buckconverter降压式变换器，降压式斩波器Boostconverter升压式变换器，升压式斩波器Buck-Boostconverter升/降式变换器，升/降式斩波器quadrantn.象限，四分之一圆周，九十度弧,NewWordsandExpressions,step-downa.降压的，降低的step-upa.升压的，升高的duala.二重的，对偶的filtern.;v.滤波，过滤periodicallyad.周期地portablea.手提的，轻便的，可携带的sinkn.换能器，变换器，散热器，汇点，收点，穴hypotheticala.假设的，假定的，有前提的,NewWordsandExpressions,dutyratio功率比，能量比turnratio匝数比PWMpulsewidthmodulation脉冲宽度调制switch-modepowersupplies开关电源,Return,TransitionofPartofSpeech,二、转换为汉语名词1、动词转换成名词英语中有些动词在翻译成汉语时很难找到相应的动词，这时可将其转译成汉语名词。(1)Theelectroniccomputerischieflycharacterizedbyitsaccurateandrapidcomputations.电子计算机的主要特点是计算准确而快速。(2)Anelectriccurrentvariesdirectlyastheelectromotiveforceandinverselyastheresistance.电流的变化与电动势成正比，与电阻成反比。,TransitionofPartofSpeech,(3)Thedesignaimsatautomaticoperation,easyregulation,simplemaintenanceandhighproductivity.设计的目的在于自动操作，调节方便，维护简易，生产率高。,TransitionofPartofSpeech,2、形容词转换成名词英语中有些形容词加上定冠词the表示某一类人或物，汉译时常译成名词。另外，英语中有些表示事物特征的形容词作表语时，往往可在其后加上“性”、“度”、“体”等词，译成名词。(1)Peoplearesomuchmoreflexibleandinventivethanrobots.人类比机器人更灵活而且更富有创造性。(2)Somepeoplethinktomorrowscomputerswillbeintelligent.有人认为未来的计算机就具有智能。,TransitionofPartofSpeech,2、形容词转换成名词(3)Infissionprocessesthefissionfragmentsareveryradioactive.在裂变过程中，裂变碎片具有强烈的放射性。,TransitionofPartofSpeech,3、代词转换成名词英语中的代词译成汉语，有时为了使译文规范，须转换为名词。(1)Radiowavesaresimilartolightwavesexceptthattheirwave-lengthismuchgreater.无线电波与光波相似，只不过无线电波的波长更长一些。(2)Thespecificresistanceofironisnotsosmallasthatofcopper.铁的电阻系数不如铜的电阻系数那样小。,TransitionofPartofSpeech,(3)Electricitymaybeproducedbyageneratorwhichisturnedbyamotorusinganyoftheotherformsofenergy.发电机可以发电，而发电机是由利用任何其他形式能量的原动机带动的。,TransitionofPartofSpeech,4、副词转换成名词英语中有些副词，在句子中用作状语，译成汉语时可根据具体情况转换成汉语的名词。(1)Thequalityoftheoperatingsystemdetermineshowusefulthecomputeris.操作系统的质量决定着计算机的应用效能。(2)Electromagneticwavestravelasfastaslight.电磁波传播的速度和光一样。.,TransitionofPartofSpeech,4、副词转换成名词(1)Theinstrumentisusedtodeterminehowfullythebatteriesarecharged.这种仪表用来确定电池充电的程度。(2)ThedeviceisshownschematicallyinFigure1.图1所示为这种装置的简图。,Return,Exercises,I.Choosethebestanswerintotheblank,1.TheDC-DCconverterconvertsinputtooutput.A.directcurrent,alternatingcurrentB.directcurrent,directcurrentC.alternatingcurrent,alternatingcurrentD.alternatingcurrent,alternatingcurrent,Exercises,I.Choosethebestanswerintotheblank,2.TheBuckisaconverter.A.voltagestep-upB.currentstep-downC.currentstep-upD.resistance3.ThePWMcontrolthatusestocontroltheoutputvoltageismorepopular.A.switchingfrequencyB.pulsewidthC.risetimeD.downtime,Exercises,I.Choosethebestanswerintotheblank,4.Thegainofswitch-modelinearamplifierisdeterminedbyvoltage,andtheoutputvoltageisalinearfunctionof.A.theoutputdc,thecontrolvoltageB.theinputdcsource,thecontrolvoltageC.theinputdcsource,theoutputvoltageD.theinputdcsource,thecontrolvoltage,Exercises,II.Answerthefollowingquestionsaccordingtothetext,1.WhichDC-D