电力电子技术

电力电子技术（PowerElectronicTechnology）Introducebasicideasaboutpowerelectroniccomponentssuchasthyristor（晶闸管）,4kindsofrectifyingcircuit（整流电路）,4kindsofpowerconverterincludingrectifier(AC-DC整流器),inverter[inˈvə:tə](DC-AC逆变器),ACvoltageregulator(AC-AC交流调压器),chopper(DC-DC直流斩波器).['tʃɒpə(r)]Thyristor:ThethyristorisasemiconductordevicewithfourlayersofP-Ntypematerial.ItconductswhentheGatereceivesacurrentpulse.最早出现与主要的一种是硅控整流器（SiliconControlledRectifier，SCR）(positivefeedback)Switchingcharacteristics开Inaconventionalthyristor,onceithasbeenswitchedonbythegateterminal,thedeviceremainslatchedintheon-state(i.e.doesnotneedacontinuoussupplyofgatecurrenttoconduct),providingtheanodecurrenthasexceededthelatchingcurrent(IL).Aslongastheanoderemainspositivelybiased,itcannotbeswitchedoffuntiltheanodecurrentfallsbelowtheholdingcurrent(IH).关AthyristorcanbeswitchedoffiftheexternalcircuitcausestheanodetobecomenegativelybiasedAC-DC（整流）:Arectifierisadevicethatconvertsalternatingcurrent(AC)todirectcurrent(DC).Thereare4kinsofveryimportantrectifier:singlephasehalf-wave（单相半波）,singlephasebridge（单相桥）,threephasehalf-wave（三相半波）,threephasebridge（三相桥）.Inhalfwaverectificationofasingle-phasesupply,eitherthepositiveornegativehalfoftheACwaveispassed,whiletheotherhalfisblocked.Becauseonlyonehalfoftheinputwaveformreachestheoutput,meanvoltageislower.Half-waverectificationrequiresasinglediodeinasingle-phasesupply,orthreeinathree-phasesupply.Rectifiersyieldaunidirectionalbutpulsatingdirectcurrent;half-waverectifiersproducefarmoreripplethanfull-waverectifiers,andmuchmorefilteringisneededtoeliminateharmonicsoftheACfrequencyfromtheoutput.半波整流halfwave桥式全波整流Ifyouarenotusingcenter-tappedtransformer,andonlyonesetofoutputcoil,youneedtousefourdiodesinordertodoafull-waverectifier.令峰值电压Peakvoltage为Vm，未做滤波filter时的AveragevoltageVdc=0.636Vm，FrequencyofACfrequencyof2timestheoriginal，每个二极管所承受的逆向峰值电压(PIV,PeakInverseVoltage)值是Vm。此种方式(如图)称为桥式整流，这四个二极管合称为桥式整流器：中心抽头式Forthesingle-phaseACpower，Ifthetransformeriscenter-tappedtype，Twobacktobackdiodes(cathodeconnectionreferstothecathodeoranodeconnectedtotheanode)mayformafull-waverectifier。未做滤波时的平均Vdc=0.636Vm，频率为原来频率2倍。每个二极管PIV值2Vm。Full-waverectificationtodoublethetransformersecondarywinding,lesssotoday.三相桥式整流器。Forathree-phasefull-wavedioderectifier,theideal,no-loadaverageoutputvoltageisIfthyristorsareusedinplaceofdiodes,theoutputvoltageisreducedbyafactorcos(α):Or,expressedintermsofthelinetolineinputvoltage:Where:VLLpeak,thepeakvalueofthelinetolineinputvoltages,Vpeak,thepeakvalueofthephase(linetoneutral)inputvoltages,α,firingangleofthethyristor(0ifdiodesareusedtoperformrectification)TheaboveequationsareonlyvalidwhennocurrentisdrawnfromtheACsupplyorinthetheoreticalcasewhentheACsupplyconnectionshavenoinductance.Inpractice,thesupplyinductancecausesareductionofDCoutputvoltagewithincreasingload,typicallyintherange10–20%atfullload.Theeffectofsupplyinductanceistoslowdownthetransferprocess(calledcommutation)fromonephasetothenext.Asresultofthisisthatateachtransitionbetweenapairofdevices,thereisaperiodofoverlapduringwhichthree(ratherthantwo)devicesinthebridgeareconductingsimultaneously.Theoverlapangleisusuallyreferredtobythesymbolμ(oru),andmaybe2030°atfullload.Withsupplyinductancetakenintoaccount,theoutputvoltageoftherectifierisreducedto:TheoverlapangleμisdirectlyrelatedtotheDCcurrent,andtheaboveequationmaybere-expressedas:Where:Lc,thecommutatinginductanceperphaseId,thedirectcurrent生成交流(这样的设备被称为交流发电机)的大多数设备生成三相交流为例，一个汽车交流发电机有六个里面作为为电池充电应用程式的全波整流二极管。可以作为计算的一个理想的全波整流的平均均方根输出电压：符号说明:Vdc,Vav-直流输出电压，平均电压Vp-峰值电压（半波中的）Vrms-输出的RMS(均方根值)电压，注;RMS值也称有效值e=~2.71828Half-waverectificationandfull-waverectifierDCoutputafter,arenotconstantDCvoltage.InordertogeneratestableACpowerrectifierdirectcurrent,theneedforfiltercircuitsmoothingtheoutputvoltage.Thesimplestfiltercircuitistheoutputoftherectifierwithacapacitortostoreelectricalenergy,通常称为滤波电容，即平滑电容（smoothingcapacitor）。butthesefiltercapacitorcannoteliminate[iˈlimineit]allripple['rɪpl]Three-phasehalf-waverectifiercircuitusing\o"Thyristor"thyristorsastheswitchingelements,ignoringsupplyinductanceThree-phasefull-wavethyristorrectifiercircuitusingacentre-tappedtransformer.中心抽头变压器Thisisequivalenttoasix-phasehalf-waverectifier.触发延迟角α：TriggerDelayAngle）3-phaseACinput,halfandfull-waverectifiedDCoutputwaveformsThree-phaseGraetzbridgerectifieratalpha=0°withoutoverlapThree-phaseGraetzbridgerectifieratalpha=0°withoverlapangleof20°Three-phasecontrolledGraetzbridgerectifieratalpha=20°withoverlapangleof20°Three-phasecontrolledGraetzbridgerectifieratalpha=40°withoverlapangleof20°DC-AC(逆变):Ainverterisadevicethatconvertsdirectcurrent(DC)toalternatingcurrent(AC).itcanbeusedforacmotordrivesandUPS（uninterruptiblepowersupplies）An\o"Uninterruptiblepowersupply"uninterruptiblepowersupply(UPS)usesbatteriesandaninvertertosupplyACpowerwhenmainpowerisnotavailable.Whenmainpowerisrestored,a\o"Rectifier"rectifiersuppliesDCpowertorechargethebatteries.半桥逆变器halfbridgeinverterV1V2turnsonalternately.ACoutputfrequencycanbechangedbychangingtheswitchingfrequencyofv1v2.开关旁一般需要并联续流\o"二极管"二极管Freewheelingdiode，以便在感性\o"负载"负载时起到续流作用。ifv1,v2turnonatthesametime,dcsourcewillbeshort.全桥逆变器fullbridgeinverter(图)全桥逆变器由各含两个开关的两个桥臂连接成正方形组成，输出端的两端分别位于两组开关的中点，相当于取两个半桥的电压差，因此可以得到正负双向的交流输出。Diagonal[daɪˈægənəl]devicealternatelyturn三相桥式逆变器threephasebridgeinverter(图)t1-6turnsoninturn,delay60degreeintime.Three-phasebridgeinvertercangetasetofequalamplitudeandfrequencyareequal,thephasedifferenceof120°electricalphase.Thereare2typesofinverter:1,Activeinverter（有源逆变）,convertDCtoAC,andsendtheACdirectlytothepowersystem.2,Reactiveinverter（无源逆变）,convertDCtoAC,andsendtheACtoelectricalequipments.AC-AC:ACvoltageregulator（交流调压）,changetheamplitudeofACvoltage,andthefrequencyarestillthesame.twothyristorsreversedparalledconnectedinseries任一相导通须和另一相构成回路，因此电流通路中至少有两个晶闸管，应采用双脉冲或宽脉冲触发。触发脉冲顺序和三相桥式全控整流电路一样，为VT1~VT6,依次相差60°。把相电压过零点定为开通角的起点，三相三线电路中，两相间导通时是靠线电压导通的，而线电压超前相电压30°，因此角的移相范围是0°~150°。☞根据任一时刻导通晶闸管个数以及半个周波内电流是否连续可将0°~150°的移相范围分为如下三段√0°≤<60°范围内，电路处于三个晶闸管导通与两个晶闸管导通的交替状态，每个晶闸管导通