正弦脉宽调制-毕业设计外文文献翻译

《正弦脉宽调制-毕业设计外文文献翻译》由会员上传分享，免费在线阅读，更多相关内容在学术论文-天天文库。

1、24.437PowerElectronicsSinusoidalPulsewidthmodulationTheswitchesinthevoltagesourceinverter(SeeFig.1)canbeturnedonandoffasrequired.Inthesimplestapproach,thetopswitchisturnedonIfturnedonandoffonlyonceineachcycle,asquarewavewaveformresults.However,ifturnedonseveraltimesinacycleanimprovedhar-monic

2、profilemaybeachieved.Fig1:SimpleVoltageSourcedInthemoststraightforwardimplementation,generationofthedesiredoutputvoltageisachievedbycomparingthedesiredreferencewaveform(modulatingsignal)withahigh-frequencytriangu-lar‘carrier’waveasdepictedschematicallyinFig.2.Dependingonwhetherthesignalvoltag

3、eislargerorsmallerthanthecarrierwaveform,eitherthepositiveornegativedcbusvoltageisappliedattheoutput.Notethatovertheperiodofonetrianglewave,theaveragevoltageappliedtotheloadisproportionaltotheamplitudeofthesignal(assumedconstant)duringthisperiod.Theresultingchoppedsquarewaveformcontainsarepli

4、caofthedesiredwaveforminitslowfre-quencycomponents,withthehigherfrequencycomponentsbeingatfrequenciesofanclosetothecarrierfrequency.Noticethattherootmeansquarevalueoftheacvoltagewaveformisstillequaltothedcbusvoltage,andhencethetotalharmonicdistortionisnotaffectedbythePWMprocess.Theharmoniccom

5、ponentsaremerelyshiftedintothehigherfrequencyrangeandareautomati-callyfilteredduetoinductancesintheacsystem.WhenthemodulatingsignalisasinusoidofamplitudeAm,andtheamplitudeofthetriangularcarrierisAc,theratiom=Am/Acisknownasthemodulationindex.Notethatcontrollingthemodulationindexthereforcontrol

6、stheamplitudeoftheappliedoutputvoltage.Withasufficientlyhighcarrierfrequency(seeFig.3drawnforfc/fm=21andt=L/R=T/3;T=periodoffunda-mental),thehighfrequencycomponentsdonotpropagatesignificantlyintheacnetwork(orload)duethepresenceoftheinductiveelements.However,ahighercarrierfrequencydoesresultin

7、alargernumberofswitchingspercycleandhenceinanincreasedpowerloss.Typicallyswitchingfrequenciesinthe2-15kHzrangeareconsideredadequateforpowersystemsapplications.Alsointhree-phasesystemsitisadvisabletousessothatallthreewaveformsaresymmetric.Fig2