Activeinvertercircuit5.2有源逆變電路TeachingResourcesDatabaseof

NationalVocationalEducationPowerSupplyTechnologyBilingualcourses.Powerelectronicstechnology電力電子技術(shù)Item5InverterCircuit項(xiàng)目五逆變電路Activeinvertercircuit5.2有源逆變電路用途：有源逆變電路常用于直流可逆調(diào)速系統(tǒng)、交流繞線轉(zhuǎn)子異步電動(dòng)機(jī)串級(jí)調(diào)速及高壓直流輸電等場(chǎng)合。Purpose:activeinvertercircuitiscommonlyusedinDCreversiblespeedregulationsystem,ACwindingrotorasynchronousmotorcascadespeedregulationandhighvoltageDCtransmissionetc..定義：當(dāng)交流側(cè)接在電網(wǎng)上，即交流側(cè)接有電源時(shí)，稱為有源逆變。有源逆變電路是將直流電功率返送回電網(wǎng)。Definition:whentheACsideisconnectedtothegrid,thatis,whentheACsideisconnectedtothepowersupply,itiscalledactiveinverter.

Activeinvertercircuitisdirectcurrentpowerbacktothegrid.有源逆變電路的基本原理

Thebasicprincipleofactiveinvertercircuit一、電能的交換

Exchangeofelectricalenergy對(duì)于整流電路而言，當(dāng)其滿足一定的條件，則可工作于有源逆變狀態(tài)。將這種既可工作在整流狀態(tài)又可工作在逆變狀態(tài)的整流電路稱為變流電路。Asfortherectifiercircuit,whenitmeetscertainconditions,itcanworkintheactiveinverterstate.

Thiskindofrectifiercircuitwhichcanworkinboththerectifierstateandtheinverterstateiscalledtheconvertercircuit.Activeinvertercircuit5.2有源逆變電路圖aM電動(dòng)運(yùn)轉(zhuǎn)，EG>EM，電流Id從G流向M，M吸收電功率。Fig.A

Melectricoperation,EG>EM,currentIDflowsfromGtoM,whereMabsorbselectricalpower.RΣ為主回路總電阻。由于Id和EG同方向，與EM反方向，因此G輸出電功率PG=EG·Id，電能由G流向M，M吸收功率PM=EM·Id，再轉(zhuǎn)變?yōu)闄C(jī)械能，RΣ上是熱耗。Risthetotalresistanceofthemaincircuit.BecauseIdandEGarethesamedirection,andtheEMintheoppositedirection,sotheelectricaloutputPG=EG·Id,powerflowfromGtoM,MabsorbedpowerPM=EM·Id,thentransformedintomechanicalenergy,RΣisheatloss.圖b回饋制動(dòng)狀態(tài)，M作發(fā)電運(yùn)轉(zhuǎn)，此時(shí)，EM>EG，電流反向，從M流向G。故M輸出電功率，G則吸收電功率，M軸上輸入的機(jī)械能轉(zhuǎn)變?yōu)殡娔芊此徒oG。Fig.BFeedbackbrakingstate,Mforpowergenerationoperation,atthistime,EM>EG,thecurrentflowsintheoppositedirection,fromMtoG.

Therefore,Moutputselectricpower,Gabsorbselectricpower,andthemechanicalenergyinputonaxisMisconvertedintoelectricenergyandsentbacktoG.圖c兩電動(dòng)勢(shì)順向串聯(lián)，向電阻R供電，G和M均輸出功率，由于R一般都很小，實(shí)際上形成短路，在工作中必須嚴(yán)防這類事故發(fā)生。Fig.CTwoelectrodynamicforcesareconnectedinseriestosupplypowertotheresistorR,andbothGandMareoutputpower.AsRisgenerallyverysmall,shortcircuitisactuallyformed,andsuchaccidentsmustbestrictlypreventedinthework.Activeinvertercircuit5.2有源逆變電路由上述分析，可以得出如下結(jié)論：

Fromtheaboveanalysis,thefollowingconclusionscanbedrawn:①兩電源同極性相連時(shí)，電流總是從電勢(shì)高的流向電勢(shì)低的。電流大小取決于電勢(shì)差和回路電阻。Whenthetwopowersourcesareconnectedwiththepolarity,thecurrentalwaysflowsfromthehighpotentialtothelowpotential.Themagnitudeofcurrentdependsonthepotentialdifferenceandcircuitresistance.②與電流同方向的電動(dòng)勢(shì)輸出功率，而與電流反方向的電動(dòng)勢(shì)吸收功率。Theelectromotiveforceisoutputinthesamedirectionasthecurrent,whiletheelectromotiveforceisabsorbedintheoppositedirectionofthecurrent.③兩電源反極性相連時(shí)形成短路，應(yīng)嚴(yán)防發(fā)生。Whenthetwopowersourcesareconnectedtotheoppositepolarity,theyformshortcircuit,whichshouldbestrictlyprevented.Activeinvertercircuit5.2有源逆變電路圖2直流卷?yè)P(yáng)系統(tǒng)Fig.2DCwinchsystem(a)提升重物；(b)放下重物

(a)Liftingheavyobjects;(b)Laydowntheweight二、電能的交換：有源逆變電路的工作原理

Powerexchange:Howactiveinvertercircuitswork

Activeinvertercircuit5.2有源逆變電路

1．整流工作狀態(tài)Rectifyingworkingstate（0＜α＜π/2）對(duì)于單相全控整流橋，當(dāng)控制角α在0～π/2之間的某個(gè)對(duì)應(yīng)角度觸發(fā)晶閘管時(shí)，上述變流電路輸出的直流平均電壓為Ud=Udocosα，因?yàn)榇藭r(shí)α均小于π/2，故Ud為正值。在該電壓作用下，直流電機(jī)轉(zhuǎn)動(dòng)，卷?yè)P(yáng)機(jī)將重物提升起來(lái)，直流電機(jī)轉(zhuǎn)動(dòng)產(chǎn)生的反電勢(shì)為ED，且ED略小于輸出直流平均電壓Ud，此時(shí)電樞回路的電流為Forthesingle-phasefullycontrolledrectifierbridge,whenthethyristoriscontactedatacontrollingangleαbetween0andπ/2,theaverageDCvoltageoftheabove-mentionedconvertercircuitisUd=Udocosα.Sinceαislessthanπ/2atthistime,Udispositive.

Undertheactionofthisvoltage,theDCmotorrotatesandthewinchliftstheheavyobject.ThebackpotentialgeneratedbytherotationoftheDCmotorisED,andEDisslightlylessthantheoutputDCaveragevoltageUd.Atthistime,thecurrentofthearmatureloopisActiveinvertercircuit5.2有源逆變電路2.中間狀態(tài)Intermediatestate（α=π/2）當(dāng)卷?yè)P(yáng)機(jī)將重物提升到要求高度時(shí)，自然就需在某個(gè)位置停住，這時(shí)只要將控制角α調(diào)到等于π/2的位置，變流器輸出電壓波形中，其正、負(fù)面積相等，電壓平均值Ud為零，電動(dòng)機(jī)停轉(zhuǎn)（實(shí)際上采用電磁抱閘斷電制動(dòng)），反電勢(shì)ED也同時(shí)為零。此時(shí)，雖然Ud為零，但仍有微小的直流電流存在，有關(guān)波形如圖(b)所示。注意，此時(shí)電路處于動(dòng)態(tài)平衡狀態(tài)，與電路切斷、電動(dòng)機(jī)停轉(zhuǎn)具有本質(zhì)的不同。

Whenthewinchtoliftweightsintorequiredheight,naturallytobeinapositiontostop,thenaslongasthedispatchcontrolAnglealphatoequaltothepositionofPI/2,inverteroutputvoltagewaveform,itspositiveandnegativeareaareequal,theaveragevoltageUdiszero,themotorstalling(actuallyusestheelectromagneticbrakepowerbrake),backemfEDiszeroatthesametime.

Atthispoint,althoughtheUdiszero,asmallDCcurrentstillexists,andtherelatedwaveformisshowninFig.(b).

Notethatthecircuitisinastateofdynamicbalance,whichisfundamentallydifferentfromcuttingoffthecircuitandstoppingthemotor.圖3直流卷?yè)P(yáng)機(jī)系統(tǒng)的電壓電流波形Figure3DCwinchsystemofvoltageandcurrentwaveform(a)整流；(b)中間狀態(tài)；(c)有源逆變(a)Rectification;(b)Theintermediatestate;(c)ActiveinverterActiveinvertercircuit5.2有源逆變電路3．有源逆變工作狀態(tài)Activeinvertingworkingstate（π/2＜α＜π）上述卷?yè)P(yáng)系統(tǒng)中，當(dāng)重物放下時(shí)，由于重力對(duì)重物的作用，必將牽動(dòng)電機(jī)使之向與重物上升相反的方向轉(zhuǎn)動(dòng)，電機(jī)產(chǎn)生的反電勢(shì)ED的極性也將隨之反相。如果變流器仍工作在α＜π/2的整流狀態(tài)，從上面曾分析過(guò)的電源能量流轉(zhuǎn)關(guān)系不難看出，此時(shí)將發(fā)生電源間類似短路的情況。為此，只能讓變流器工作在α＞π/2的狀態(tài)，因?yàn)楫?dāng)α＞π/2時(shí)，其輸出直流平均電壓Ud為負(fù)，出現(xiàn)兩電源極性同時(shí)反向的情況，此時(shí)如果能滿足ED＞Ud，則回路中的電流為Intheabovewinchsystem,whentheheavyobjectislowered,duetotheeffectofgravityontheheavyobject,themotorwillbedriventorotateintheoppositedirectiontotheliftingoftheheavyobject,andthepolarityofthebackelectricpotentialEdgeneratedbythemotorwillalsoreversephaseaccordingly.

Iftheconverterisstilloperatinginthestateofα<π/2rectification,itisnotdifficulttoseefromtheaboveanalysisofthepowersupplyenergyflowrelationship,atthistimewilloccurasimilarshortcircuitbetweenthepowersupply.

Forthisreason,theconvertercanonlyoperateinthestateofα>π/2,becausewhenα＞π/2,itsoutputDCaveragevoltageUdisnegative,andthepolarityofthetwosupplysourcesisreversedatthesametime.Atthistime,ifED＞Udbesatisfied,thecurrentintheloopisActiveinvertercircuit5.2有源逆變電路電流的方向是從電勢(shì)ED的正極流出，從電壓Ud的正極流入，電流方向未變。顯然，這時(shí)電動(dòng)機(jī)為發(fā)電狀態(tài)運(yùn)行，對(duì)外輸出電能，變流器則吸收上述能量并饋送回交流電網(wǎng)去，此時(shí)的電路進(jìn)入到有源逆變工作狀態(tài)。

ThedirectionofthecurrentisfromthepositivepoleofthepotentialED,andfromthepositivepoleofthevoltageUD,withoutchangingthedirectionofthecurrent.Obviously,atthistime,themotorrunsinthepowergenerationstateandoutputselectricenergytotheoutside,andtheconverterabsorbstheaboveenergyandfeedsitbacktotheACgrid.Atthistime,thecircuitenterstheactiveinverterworkingstate.上述三種變流器的工作狀態(tài)可以用圖3所示波形表示。圖中反映出隨著控制角α的變化，電路分別從整流到中間狀態(tài)，然后進(jìn)入有源逆變的過(guò)程。

TheworkingstatesoftheabovethreeconverterscanberepresentedbythewaveformshowninFig.3.AsthecontrolAngleαchanges,thecircuitmovesfromrectificationtointermediatestateandthenintoactiveinverter.圖3直流卷?yè)P(yáng)機(jī)系統(tǒng)的電壓電流波形Fig.3VoltageandcurrentwaveformofDCwinchsystem(a)整流；(b)中間狀態(tài)；(c)有源逆變(a)Rectification;(b)Theintermediatestate;(c)ActiveinverterActiveinvertercircuit5.2有源逆變電路

上述晶閘管供電的卷?yè)P(yáng)系統(tǒng)中，當(dāng)重物下降，電動(dòng)機(jī)反轉(zhuǎn)并進(jìn)入發(fā)電狀態(tài)運(yùn)行時(shí)，電機(jī)電勢(shì)ED實(shí)際上成了使晶閘管正向?qū)ǖ碾娫?。?dāng)α＞π/2時(shí)，只要滿足Ed＞|u2|，晶閘管就可以導(dǎo)通工作，在此期間，電壓Ud大部分時(shí)間均為負(fù)值，其平均電壓Ud自然為負(fù)，電流則依靠電機(jī)電勢(shì)ED及電感Ld兩端感應(yīng)電勢(shì)的共同作用加以維持。正因?yàn)樯鲜龉ぷ魈攸c(diǎn)，才出現(xiàn)了電機(jī)輸出能量，變流器吸收并通過(guò)變壓器向電網(wǎng)回饋能量的情況。Intheabovementionedthyristorpoweredwinch

system,whentheweightdropsandthemotorreversesandentersthegeneratingstate,theelectricpotentialofthemotorED,actuallyactsasthepowersourcetoenablethethyristorforwardtooperate.

Whenα＞π/2,aslongasmeetEd＞|u2|,thyristorconductionwork,duringthisperiod,mostofthetimevoltageUdarenegative,Udnatureisnegative,theaveragevoltagepotentialEDandinductorcurrentdependonthemotorworktogethertomaintainLdinducedpotentialonbothends.

Justbecauseoftheaboveworkingcharacteristics,themotoroutputenergy,converterabsorptionandthroughthetransformerbacktothegridenergysituation.Activeinvertercircuit5.2有源逆變電路二、有源逆變的條件

ActivecontravariantconditionsActiveinvertercircuit5.2有源逆變電路從上述分析可歸納出產(chǎn)生逆變的條件有二：Fromtheaboveanalysis,itcanbesummedupthattherearetwoconditionsforinversion:①外部條件：要有直流電動(dòng)勢(shì)，其極性與晶閘管的導(dǎo)通方向一致，其值應(yīng)大于直流側(cè)平均電壓；Externalconditions:tohavetheDCelectromotive