6.2ACtoACfrequencyconversioncircuit6.2交交變頻電路Item6AlternatingCurrentconversioncircuit項(xiàng)目六交流變換電路TeachingResourcesDatabaseof

NationalVocationalEducationPowerSupplyTechnologyBilingualcourses.Powerelectronicstechnology電力電子技術(shù)交流變換電路：把交流電能的參數(shù)（幅值、頻率、相位）加以轉(zhuǎn)換的電路。ACconversioncircuit:Acircuitthatconvertstheparameters(amplitude,frequency,phase)ofACenergy.交流電力控制電路ACpowercontrolcircuit

交一交變頻電路（直接變頻電路）ACtoACfrequencyconversioncircuit(directfrequencyconversioncircuit)維持頻率不變改變輸出電壓的幅值。Changetheamplitudeoftheoutputvoltagewhilekeepingthefrequencyconstant.

將電網(wǎng)頻率的交流電直接變換成較低頻率的交流電直接變頻的同時也可實(shí)現(xiàn)電壓變換。Thevoltageconversioncanberealizedbydirectlyconvertingthealternatingcurrentofthenetworkfrequencyintothealternatingcurrentofthelowerfrequency.分類Classification6.2ACtoACfrequencyconversioncircuit交交變頻電路

交－交變頻電路是不通過中間直流環(huán)節(jié)而把電網(wǎng)頻率的交流電直接變換成不同頻率（低于交流電源頻率）交流電的變流電路。AC-ACfrequencyconversioncircuitisnotthroughtheintermediateDClinkandthenetworkfrequencyofACdirectlyintodifferentfrequency(lowerthantheACpowersupplyfrequency)ACconvertercircuit.

主要用于大功率交流電動機(jī)調(diào)速系統(tǒng)。ItismainlyusedforhighpowerACmotorspeedregulationsystem.

1）定義Definition2）應(yīng)用Application圖6.4.2單相交流輸入時交－交變頻電路的波形圖Figure6.4.2Waveformdiagramofac-acfrequencyconversioncircuitwithsingle-phaseacinput6.2ACtoACfrequencyconversioncircuit交交變頻電路PositivegroupworksNegativegroupblocks1.電路結(jié)構(gòu)和工作原理Circuitstructureandworkingprinciple

◆1）電路結(jié)構(gòu)Circuitstructure

由具有相同特征的兩組晶閘管整流電路（正組整流器和反組整流器）反并聯(lián)構(gòu)成；Itiscomposedoftwogroupsofthyristorrectifiercircuits(positivegrouprectifierandnegativegrouprectifier)whichhavethesamecharacteristicsinreverseparallel.圖6.4.1單相輸出交－交變頻電路Fig.6.4.1Single-phaseoutputAC-ACfrequencycircuit

◆2）工作原理Workingprinciple

圖6.4.2單相交流輸入時交－交變頻電路的波形圖Fig.6.4.2Waveformdiagramofac-acfrequencycircuitwithsingle-phaseacinput

正組整流器工作，反組整流器被封鎖，負(fù)載端輸出電壓為上正下負(fù)；Thepositivegrouprectifierworks,thenegativegrouprectifierisblocked,andtheoutputvoltageoftheloadendispositiveandnegative.

負(fù)組整流器工作，正組整流器被封鎖，負(fù)載端得到輸出電壓上負(fù)下正；Thenegativegrouprectifierworks,thepositivegrouprectifierisblocked,andtheoutputvoltageattheloadendispositiveandnegative.

以低于電源的頻率切換正反組整流器的工作狀態(tài),在負(fù)載端就可獲得交變的輸出電壓；（如圖6.4.2）Byswitchingtheworkingstateofthepositiveandnegativerectifieratafrequencylowerthanthepowersupply,thealternatingoutputvoltagecanbeobtainedattheloadend.(Figure6.4.2)晶閘管的開通與關(guān)斷必須采用無環(huán)流控制方式，防止兩組晶閘管橋同時導(dǎo)通；TheopeningandturningoffofthyristormustbecontrolledbynocirculationtopreventthesimultaneousconductionoftwothyristorBridges.6.2ACtoACfrequencyconversioncircuit交交變頻電路PositivegroupworksNegativegroupblocksPositivegroupworksNegativegroupblocksPositivegrouprectifierNegativegrouprectifierAcinputAcinput3）電路控制特點(diǎn)Circuitcontrolcharacteristics

（1）一個周期內(nèi)控制角a固定不變時，輸出電壓為含有大量的諧波矩形波,(如圖6.4.2)對電機(jī)的工作很不利WhenthecontrolAngleAisfixedwithinacycle,theoutputvoltageisarectangularwavecontainingalargenumberofharmonics,which(asshowninFig.6.4.2)isveryunfavorabletothemotor圖6.4.2單相交流輸入時交－交變頻電路的波形圖Fig.6.4.2Waveformdiagramofac-acfrequencyconversioncircuitwithsingle-phaseacinput

圖6.4.3交－交變頻電路的波形圖（a變化）Fig.6.4.3waveformdiagramofAC-ACfrequencyconversioncircuit(variationofA)

（2）為了讓輸出電壓波形接近正弦波，可按正弦規(guī)律對a進(jìn)行調(diào)制。Inordertomaketheoutputvoltagewaveformclosetosinewave,acanbemodulatedaccordingtosinusoidallaw.

正組工作的半個周期內(nèi)讓控制角a按正弦規(guī)律從90°逐漸減小到0°，然后逐漸增加到90°。正組整流電流的輸出電壓的平均值就按正弦規(guī)律變化，從零增大到最大,然后從最大減小到零。Duringthehalfcycleofthepositivegroup,letthecontrolAngleAdecreasegraduallyfrom90°to0°andthengraduallyincreaseto90°accordingtothesinelaw.Theaveragevalueoftheoutputvoltageofthepositivegrouprectifiercurrentchangessinusoidally,increasingfromzerotomaximum,andthendecreasingfrommaximumtozero.反組工作的半個周期內(nèi)采用上述同樣的控制方法，就可以得到接近正弦波的輸出電壓。如圖6.4.3Theoutputvoltageclosetosinewavecanbeobtainedbyusingthesamecontrolmethodmentionedaboveinhalfacycleofreversegroupoperation.Asshowninfigure6.4.36.2ACtoACfrequencyconversioncircuit交交變頻電路1.電路結(jié)構(gòu)和工作原理Circuitstructureandworkingprinciple

PositivegroupworksNegativegroupblocksPositivegroupworksNegativegroupblocksoutputvoltageAverageoutputvoltage2.變頻電路的工作過程（電感性負(fù)載）Workingprocessoffrequencyconversioncircuit(inductiveload)

對于電感性負(fù)載，輸出電壓超前電流。Forinductiveloads,theoutputvoltageleadsthecurrent.

一個周期可以分為六個階段Acyclecanbedividedintosixstages

第一階段：輸出電壓過零，u0為正，i0<0，反組整流器工作在有源逆變狀態(tài)，正組整流器被封鎖；Thefirststage:theoutputvoltagecrosseszero,u0ispositivei0<0,thereversegrouprectifierworksintheactiveinverterstate,andthepositivegrouprectifierisblocked;圖5.4.1單相輸出交－交變頻電路Fig.5.4.1single-phaseoutputAC-ACfrequencyconversioncircuit

圖5.4.4交-交變頻電路電感性負(fù)載時的輸出電壓和電流波形Fig.5.4.4OutputvoltageandcurrentwaveformsofanAC-ACfrequencyconversioncircuitunderinductiveload

6.2ACtoACfrequencyconversioncircuit交交變頻電路ACinputACinputNegativegrouprectifierPositivegrouprectifier

第二階段：電流過零。為無環(huán)流死區(qū)。Thesecondstage:currentcrossingzeroisnocirculationdeadzone.

第三階段：i0>0，u0>0。正組整流器工作在整流狀態(tài)，反組整流器被封鎖。Thethirdstage:i0>0，u0>0.Thepositivegrouprectifierworksinthestateofrectification,andthenegativegrouprectifierisblocked.6.2ACtoACfrequencyconversioncircuit交交變頻電路2.變頻電路的工作過程（電感性負(fù)載）Workingprocessoffrequencyconversioncircuit(inductiveload)圖6.4.4交-交變頻電路電感性負(fù)載時的輸出電壓和電流波形Fig.6.4.4OutputvoltageandcurrentwaveformsofanAC-ACfrequencyconversioncircuitunderinductiveload

圖6.4.1單相輸出交－交變頻電路Fig.6.4.1single-phaseoutputAC-ACfrequencyconversioncircuit

PositivegrouprectifierNegativegrouprectifierACinputACinput

第四階段：i0>0，u0<0。正組整流器工作有源逆變狀態(tài)，反組整流器仍被封鎖；Stage4:i0>0，u0<0.Thepositivegrouprectifierworksintheactiveinvertingstate,andthenegativegrouprectifierisstillblocked.

第五階段：電流為零，為無環(huán)流死區(qū)；Stage5:thecurrentiszeroandthereisnocirculationdeadzone;

第六階段：i0<0,u0<0，反組整流器工作在整流狀態(tài)，正組整流器被封鎖；Stage6:i0<0,u0<0，thereversegrouprectifierworksinthestateofrectification,andthepositivegrouprectifierisblocked;6.2ACtoACfrequencyconversioncircuit交交變頻電路2.變頻電路的工作過程（電感性負(fù)載）Workingprocessoffrequencyconversioncircuit(inductiveload)圖6.4.4交-交變頻電路電感性負(fù)載時的輸出電壓和電流波形Fig.6.4.4OutputvoltageandcurrentwaveformsofanAC-ACfrequencyconversioncircuitunderinductiveload

圖6.4.1單相輸出交－交變頻電路Fig.6.4.1single-phaseoutputAC-ACfrequencyconversioncircuit

ACinputACinputPositivegrouprectifierNegativegrouprectifier

小結(jié)：Summary

1、哪組整流器電路工作是由輸出電流決定，而與輸出電壓極性無關(guān)；Whichsetofrectifiercircuitworkisdeterminedbytheoutputcurrent,andhasnothingtodowiththepolarityoftheoutputvoltage;2、變流電路是工作在整流狀態(tài)還是逆變狀態(tài)，則是由輸出電壓方向和輸出電流方向的異同決定；Whethertheconvertercircuitworksinrectificationstateorinverterstateisdeterminedbythesimilaritiesanddifferencesbetweenthedirectionofoutputvoltageandthedirectionofoutputcurrent.

6.2ACtoACfrequencyconversioncircuit交交變頻電路2.變頻電路的工作過程（電感性負(fù)載）Workingprocessoffrequencyconversioncircuit(inductiveload)圖6.4.4交-交變頻電路電感性負(fù)載時的輸出電壓和電流波形Fig.6.4.4OutputvoltageandcurrentwaveformsofanAC-ACfrequencyconversioncircuitunderinductiveload

圖6.4.1單相輸出交－交變頻電路Fig.6.4.1single-phaseoutputAC-ACfrequencyconversioncircuit

PositivegrouprectifierNegativegrouprectifierACinputACinput三相輸出交－交變頻電路ThreephaseoutputAC-ACfrequencyconversioncircuit

由三組輸出電壓相位各相差1200的單相交－交變頻電路組成。Itiscomposedofthreegroupsofsingle-phaseAC-ACinvertercircuitswithoutputvoltageandphasedifferenceof1200.

電路接線形式主要有兩種：Therearetwomainformsofcircuitwiring:

1）公共交流母線進(jìn)線方式Publiccommunicationbusentrymode

2）輸出星形聯(lián)結(jié)方式Outputstarconnectionmode

交－交變頻器主要用于交流調(diào)速系統(tǒng)中，實(shí)際使用的主要是三相交－交變頻器。AC-ACfrequencyconverterismainlyusedinACspeedcontrolsystem,theactualuseismainlythree-intersection-ACfrequencyconverter.

6.2ACtoACfrequencyconversioncircuit交交變頻電路1.公共交流母線進(jìn)線方式Publiccommunicationbusentrymode圖6.4.7公共交流母線進(jìn)線方式的三相交－交變頻電路原理圖Fig.6.4.7SchematicdiagramofthreephaseAC-ACfrequencyconversioncircuitofpublicacbusinputmode

由三組彼此獨(dú)立的，輸出電壓相位相互錯開120

0的單相交-交變頻電路組成。Itiscomposedofthreeindependentsingle-phaseACinvertercircuitswithoutputvoltageandphasestaggeredby120

0.

電源進(jìn)線通過進(jìn)線電抗器接在公共的交流母線上。ThepowerintakeisconnectedtothecommonACbusthroughtheintakereactor.

電源進(jìn)線端公用,故三相單相變頻電路的輸出端必須隔離，為此，交流電動機(jī)的三個繞組必須拆開，同時引出六根線。Theinputlineofthepowersupplyiscommon,sotheoutputendofthethree-phasesingle-phasefrequencyconversioncircuitmustbeisolated.Forthis,thethreewindingsoftheACmotormustbedisassembledandsixwiresdrawnatthesametime.

主要用于中等容量的交流調(diào)速系統(tǒng)。MainlyusedinmediumcapacityACspeedcontrolsystem6.2ACtoACfrequencyconversioncircuit交交變頻電路三相輸出交－交變頻電路ThreephaseoutputAC-ACfrequencyconversioncircuit

2.輸出星形聯(lián)結(jié)方式Outputstarconnectionmode

圖6.4.8輸出星形聯(lián)結(jié)方式的三相交－交變頻電路原理圖Fig.6.4.8SchematicdiagramofthreephaseAC-ACfrequencyconversioncircuitwithoutputstarconnectionmode

三組的輸出端和電動機(jī)的三個繞組都是星形聯(lián)結(jié)；Theoutputendofthethreegroupsandthethreewindingsofthemotorareallstarconnection;

電動機(jī)中點(diǎn)和變頻器中點(diǎn)接在一起，電動機(jī)只引三根線即可；Themidpointofthemotorandthemidpointofthefrequencyconverterareconnectedtogether,andthemotoronlyleadsthreelines.

三組單相變頻器連接在一起，其電源進(jìn)線必須隔離，所以分別用三個變壓器供電；Threegroupsofsingle-phasefrequencyconvertersareconnectedtogether,andthepowersupplylinemustbeisolated,sothreetransformersarerespectivelyusedforpowersupply;

由于變頻器輸出中點(diǎn)不和負(fù)載中點(diǎn)相聯(lián)結(jié)，所以在構(gòu)成三相變頻器的六組橋式電路中，至少要有不同相的兩組橋中的四個晶閘管同時導(dǎo)通才能構(gòu)成回路，形成電流；Becausetheoutputmidpointofthefrequencyconverterisnotconnectedwiththeloadmidpoint,sointhesixgroupsofbridgecircuitofthethree-phasefrequencyconverter,atleastfourthyristorsinthetwogroupsofdifferentphasesofthebridgeshouldconductatthesametimetoformacircuitandformacurrent;

同一組橋內(nèi)的兩個晶閘管靠雙脈沖保證同時導(dǎo)通。兩組橋之間依靠足夠的脈沖寬度來保證同時有觸發(fā)脈沖。TwothyristorsinthesamesetofBridgesareoperatedsimultaneouslybydoublepulses.ThepulsewidthbetweenthetwoBridgesissufficienttoensuresimultaneoustriggeringpulses.6.2ACtoACfrequencyconversioncircuit交交變頻電路三相輸出交－交變頻電路ThreephaseoutputAC-ACfrequencyconversioncircuit

交－交變頻電路輸出頻率上限的限制ThelimitontheupperlimitoftheoutputfrequencyofAC-ACfrequencyconversioncircuit

輸出頻率升高時，輸出電壓一個周期內(nèi)電網(wǎng)電壓的段數(shù)就減少，所含的諧波分量就要增加從而使輸出電壓波形畸變。Whentheoutputfrequencyincreases,thenumberofsegmentsofthenetworkvoltageinonecycleoftheoutputvoltagewilldecrease,andtheharmoniccomponentcontainedwillincrease,thusdistortingtheoutputvoltagewaveform.

一般的，交流電路采用6脈波的三相橋式電路時，最高輸出頻率不高于電網(wǎng)頻率的1/3～1/2。電網(wǎng)頻率為50HZ，交－交變頻電路的輸出上限頻率約為20Hz。Generally,whentheACcircuitusesthethree-phasebridgecircuitwith6pulsewaves,thehighestoutputfrequencyisnothigherthan1/3~1/2ofthegridfrequency.Thegridfrequencyis50Hz,andtheoutputupperlimitfrequencyoftheAC-ACinvertercircuitisabout20Hz.6.2ACtoACfrequencyconversioncircuit交交變頻電路

交－交變頻器的優(yōu)缺點(diǎn)AdvantagesanddisadvantagesofAC-ACinverter

優(yōu)點(diǎn)Advantages

只有一次變流，且使用電