新型滾燙機結(jié)構(gòu)和控制系統(tǒng)設(shè)計外文翻譯

共共7頁第8頁譯文標題直流電機調(diào)速原文標題SpeedControlofDCMotor作者譯名國籍原文出處直流電動機調(diào)速控制摘要調(diào)節(jié)系統(tǒng)的特征在于能保持輸出功率的穩(wěn)定。不同的速度控制系統(tǒng)可以使用不同的制動系統(tǒng),在有高起、制動轉(zhuǎn)矩,快速響應和快速度調(diào)節(jié)范圍要求的直流調(diào)速系統(tǒng)中,采用的是電氣制動的方式。直流電機的速度控制取決于電樞電壓和磁通。要將轉(zhuǎn)速降為零,或者U=0或Φ=∞。后者是不可能的,因此只可通過電樞電壓的變化來降低轉(zhuǎn)速。要將轉(zhuǎn)速增加到較高值,可以增大U或減小Φ。關(guān)鍵詞直流調(diào)速反饋制動調(diào)節(jié)系統(tǒng)調(diào)節(jié)系統(tǒng)是一類通常能提供穩(wěn)定輸出功率的系統(tǒng)。例如,電機速度調(diào)節(jié)器要能在負載轉(zhuǎn)矩變化時仍能保持電機轉(zhuǎn)速為恒定值。即使負載轉(zhuǎn)矩為零,電機也必須提供足夠的轉(zhuǎn)矩來克服軸承的粘滯摩擦影響。其他類型的調(diào)節(jié)器也提供輸出功率,溫度調(diào)節(jié)器必須保持爐內(nèi)的溫度恒定,也就是說,即使爐內(nèi)的溫度散失也必須保持爐溫不變。一個電壓調(diào)節(jié)其也必須保持負載電流值變化時輸出電壓值恒定。對于任何一個提供一個輸出,例如,速度、溫度、電壓等的系統(tǒng),在穩(wěn)態(tài)下必須存在一個誤差信號。電氣制動在許多速度控制系統(tǒng)中,例如軋鋼機、礦坑卷揚機等這些負載要求頻繁地停頓和反向運動的系統(tǒng)。隨著減速要求,速度減小的比率取決于存儲的能量和所使用的制動系統(tǒng)。一個小型速度控制系統(tǒng),例如所知的伺服積分器,可以采用機械制動,但這對大型速度控制器并不可行因為散熱很難而且很昂貴?？尚械母鞣N電氣制動方法有1回饋制動。2渦流制動。3能耗制動4反接制動回饋制動雖然并不一定是最經(jīng)濟的方式,但卻是最好的方式。負載中存儲的能量通過工作電機,暫時以發(fā)電機模式運行,被轉(zhuǎn)化成電能并返回到電源系統(tǒng)中。這樣電源就充當了一個收容不想要的能量的角色。假如電源系統(tǒng)具有足夠的容量,在短時回饋過程中最終引起的端電壓升高會很少。在直流電機速度控制渥特-勒奧那多法中,回饋制動是固有的,但可控硅傳動裝置必須被排布的可以反饋。如果轉(zhuǎn)軸速度快于旋轉(zhuǎn)磁場的速度,感應電機傳動裝置可以反饋。由晶閘管換流器而來的廉價變頻電源的出現(xiàn)在變速裝置感應電機應用中引起了巨大的變化。渦流制動可用于任何機器只要在軸上安裝一個銅條或鋁盤并在磁場中旋轉(zhuǎn)它即可。在大型系統(tǒng)中,散熱問題是很重要的,因為如果長時間制動,軸、軸承和電機的溫度就會升高。在能耗制動中,存儲的能量消耗在回路電阻器上。用在小型直流電機上時電樞供電被斷開,接入一個電阻器,通常是一個繼電器、接觸器或晶閘管。保持磁場電壓,施加制動降到最低速。感應電機要求稍微復雜一點的排布,定子繞組被從交流電源上斷開,接到直流電源上。產(chǎn)生的電能繼而消耗在轉(zhuǎn)子回路中。能耗制動應用在許多大型交流升降系統(tǒng)中,制動的職責是反向和延長。任何電機都可以通過突然反接電源以提供反向的旋轉(zhuǎn)方向(反接制動)來停機。在可控情況下,這種制動方法對所傳動裝置都是使用的。它主要的缺點就是當制動等于負載存儲的能量時,電能被機器消耗了。這在大型裝置中就大大增加了運行成本。直流電機速度控制所有直流電機速度控制的基本關(guān)系都可由下式得出E∝ΦωU=E+IaRa各項就是她們通常所指的含義。如果IaRa很小,等式近似為U∝Φω或ω=U／Φ。這樣,控制電樞電壓和磁通就可影響電機轉(zhuǎn)速。要將轉(zhuǎn)速降為零,或者U=0或Φ=∞。后者是不可能的,因此只可通過電樞電壓的變化來降低轉(zhuǎn)速。要將轉(zhuǎn)速增加到較高值,可以增大U或減小Φ。后者是最可行的方法,就是我們通常所知道的弱磁場。在要求速度調(diào)節(jié)范圍寬的場合可綜合使用這兩種方法。使用晶閘管的單向速度控制系統(tǒng)一個單相晶閘管逆變器系統(tǒng)如圖1所示。讀者應該先忽略整流器BR2和它的相關(guān)電路(包括交流回路中的電阻器R),因為這部分只有在具有保護功能時才需要,將在下一節(jié)介紹。因為該電路是一個單向轉(zhuǎn)換器,只能在一個旋轉(zhuǎn)方向控制電機軸(系統(tǒng)的輸出)的速度。而且,回饋制動不能用于電機,在這種系統(tǒng)類型中,電機電樞可以通過電氣制動靜止(例如,當晶閘管門極脈沖反向時,電阻可通過一個繼電器或其他裝置連接到電樞上)。整流器BR1給并聯(lián)勵磁繞組提供一個穩(wěn)定電壓，產(chǎn)生穩(wěn)定的磁通。電樞電流由一個晶閘管控制，該晶閘管又由加在它們極上的脈沖控制。脈沖正向時（減小起動延時角）電樞轉(zhuǎn)速增加，門極脈沖反相時電樞轉(zhuǎn)速減小。速度參考信號可從人工操作的電位器上獲得，反饋信號或輸出轉(zhuǎn)速信號可從連接在電樞上的電阻器鏈R1R2上獲得。(嚴格的講,系統(tǒng)中反饋信號只有當電樞電組的壓降IaRa很小時,才與軸轉(zhuǎn)速成正比的電樞電壓成正比。用于補償IaRa壓降的方法將在閱讀材料中討論。)因為電樞電壓是從一個晶閘管上獲得的,該電壓包括一系列由電容器C濾波的脈沖。速度參考信號與電樞電壓信號極性相反,以確保施加的都是負反饋。直流電機裝置的一個特征就是需要供電的負載時電阻、電導的混合,并且在反電動勢二極管D確保當晶閘管陽極電勢低于前面敘述的電樞連接方式的上限時晶閘管電流應換向為零。在所示拖動系統(tǒng)中,當晶閘管處于斷開狀態(tài)時,其陽極電勢等于電機反電動勢。只有在瞬時電源電壓大于反向電勢的間隔時它才會導通。電機運行時晶閘管上峰值反向電壓大于峰值正向電壓。如圖所示,在晶閘管上串聯(lián)一個二級管,電路的反向關(guān)斷能力就會增強,所以允許使用低壓晶閘管。理想的波形是因為忽略了電樞電感、換向器紋波等因素的影響。典型的電樞電壓波形如圖所示。在該波形中，晶閘管在A點觸發(fā)，一直到B點電源電壓低于電樞反電動勢時導通。電樞電感的作用使晶閘管保持到C點飛輪二極管使電樞電壓反向之前導通。當電感能量消失（D點），電樞電流為零，電壓恢復到它的正常水平，這個暫態(tài)過程最后穩(wěn)定在E點。點E、F之前的紋波是由換向器引起的紋波。SpeedControlofDCMotorAbstractConditioningsystemischaracterizedinthatoutputpowertomaintainstability.Differentspeedcontrolsystemcanuseadifferentbrakesystem,highstartingandbrakingtorque,quickresponseandquickadjustmentrangeofdegreerequirementsofDCdrivesystem,theuseoftheelectricbrakingmode.DependsonthespeedcontrolofDCmotorarmaturevoltageandflux.Tozerospeed,orU=0orΦ=∞.Thelatterisimpossible,itonlychangesthroughthearmaturevoltagetoreducespeed.TospeedtoahighervaluecanincreaseordecreasetheUΦ.KeywordDCSpeedFeedbackBrakeRegulatorSystemsAregulatorsystemisonewhichnormallyprovidesoutputpowerinitssteady-stateoperation.Forexample,amotorspeedregulatormaintainsthemotorspeedataconstantvaluedespitevariationsinloadtorque.Eveniftheloadtorqueisremoved,themotormustprovidesufficienttorquetoovercometheviscousfrictioneffectofthebearings.Otherformsofregulatoralsoprovideoutputpower;Atemperatureregulatormustmaintainthetemperatureof,say,anovenconstantdespitetheheatlossintheoven.Avoltageregulatormustalsomaintaintheoutputvoltageconstantdespitevariationintheloadcurrent.Foranysystemtoprovideanoutput,e.g.,speed,temperature,voltage,etc.,anerrorsignalmustexistundersteady-stateconditions.ElectricalBrakingInmanyspeedcontrolsystems,e.g.,rollingmills,minewinders,etc.,theloadhastobefrequentlybroughttoastandstillandreversed.Therateatwhichthespeedreducesfollowingareducedspeeddemandisdependentonthestoredenergyandthebrakingsystemused.Asmallspeedcontrolsystem(sometimesknownasavelodyne)canemploymechanicalbraking,butthisisnotfeasiblewithlargespeedcontrollerssinceitisdifficultandcostlytoremovetheheatgenerated.Thevariousmethodsofelectricalbrakingavailableare:(1)Regenerativebraking.(2)Eddycurrentbraking.(3)Dynamicbraking.(4)Reversecurrentbraking(plugging)Regenerativebrakingisthebestmethod,thoughnotnecessarilythemosteconomic.Thestoredenergyintheloadisconvertedintoelectricalenergybytheworkmotor(actingtemporarilyasagenerator)andisreturnedtothepowersupplysystem.Thesupplysystemthusactsasa”sink”intowhichtheunwantedenergyisdelivered.Providingthesupplysystemhasadequatecapacity,theconsequentriseinterminalvoltagewillbesmallduringtheshortperiodsofregeneration.IntheWard-LeonardmethodofspeedcontrolofDCmotors,regenerativebrakingisinherent,butthyristordriveshavetobearrangedtoinverttoregenerate.Inductionmotordrivescanregenerateiftherotorshaftisdrivenfasterthanspeedoftherotatingfield.Theadventoflow-costvariable-frequencysuppliesfromthyristorinvertershavebroughtaboutconsiderablechangesintheuseofinductionmotorsinvariablespeeddrives.Eddycurrentbrakingcanbeappliedtoanymachine,simplybymountingacopperoraluminumdiscontheshaftandrotatingitinamagneticfield.Theproblemofremovingtheheatgeneratedissevereinlargesystemasthetemperatureoftheshaft,bearings,andmotorwillberaisedifprolongedbrakingisapplied.Indynamicbraking,thestoredenergyisdissipatedinaresistorinthecircuit.WhenappliedtosmallDCmachines,thearmaturesupplyisdisconnectedandaresistorisconnectedacrossthearmature(usuallybyarelay,contactor,orthyristor).Thefieldvoltageismaintained,andbrakingisapplieddowntothelowestspeed.Inductionmotorsrequireasomewhatmorecomplexarrangement,thestatorwindingsbeingdisconnectedfromtheACsupplyandreconnectedtoaDCsupply.Theelectricalenergygeneratedisthendissipatedintherotorcircuit.DynamicbrakingisappliedtomanylargeAChoistsystemswherethebrakingdutyisbothsevereandprolonged.DCMotorSpeedControlThebasisofallmethodsofDCmotorspeedcontrolisderivedfromtheequations:E∝ΦωU=E+IaRathetermshavingtheirusualmeanings.IftheIaRadropissmall,theequationsapproximatetoU∝Φωorω=U／Φ。Thus,controlofarmaturevoltageandfieldfluxinfluencesthemotorspeed.Toreducethespeedtozero,eitherU=0orΦ=∞.Thelatterisinadmissible;hencecontrolatlowspeedisbyarmaturevoltagevariation.Toincreasethespeedtoahighvalue,eitherUismadeverylargeorΦisreduced.Thelatteristhemostpracticalwayandisknownasfieldweakening.Combinationsofthetwoareusedwhereawiderangeofspeedisrequired.ASingle-QuadrantSpeedControlSystemUsingThyristorsAsingle-quadrantthyristorconvertersystemisshowninFig.1.ForthemomentthereadershouldignoretherectifierBR2anditsassociatedcircuitry(includingresistorRintheACcircuit),sincethisisneededonlyasaprotectivefeatureandisdescribedinnextsection.Sincethecircuitisasingle-quadrantconverter,thespeedofthemotorshaft(whichistheoutputfromthesystem)canbecontrolledinonedirectionofrotationonly.Moreover,regenerativebrakingcannotbeappliedtothemotor;inthistypeofsystem,themotorarmaturecansuddenlybebroughttorestbydynamicbraking(i.e.whenthethyristorgatepulsesarephasedbackto180o,aresistercanbeconnectedacrossthearmaturebyarelayorsomeothermeans).RectifierBR1providesaconstantvoltageacrosstheshuntfieldwinding,givingaconstantfieldflux.Thearmaturecurrentiscontrolledbyathyristorwhichis,inturn,controlledbythepulsesappliedtoitsgate.Thearmaturespeedincreasesasthepulsesarephasedforward(whichreducesthedelayangleoffiring),andthearmaturespeedreducesasthegatepulsesarephasedback.Thespeedreferencesignalisderivedfromamanuallyoperatedpotentiometer(shownattheright-handsideofFig.23.1),andthefeedbacksignaloroutputspeedsignalisderivedfromtheresistorchainR1R2,whichisconnectedacrossthearmature.(Strictlyspeaking,thefeedbacksignalinthesysteminFig.23.1isproportionaltothearmaturevoltage,whichisproportionaltotheshaftspeedonlyifthearmatureresistancedrop,IaRa,issmall.MethodsusedtocompensatefortheIaRadroparediscussedinReadingMaterial.)Sincethearmaturevoltageisobtainedfromathyristor,thevoltageconsistsofaseriesofpulses;thesepulsesaresmoothedbycapacitorC.Thespeedreferencesignalisoftheoppositepolaritytothearmaturevoltagesignaltoensurethatoverallnegativefeedbackisapplied.AfeatureofDCmotordrivesisthattheloadpresentedtothesupplyisamixtureofresistance,inductance,andbackEMFDiodeDinFig.1ensuresthatthethyristorcurrentcommutatestozerowhenitsanodepotentialfallsbelowthepotentialoftheupperarmatureconnection,inthemanneroutlinedbefore.Inthedriveshown,thepotentialofthethyristorcathodeisequaltothebackEMFofthemotorwhileitisinablockingstate.ConductioncanonlytakeplaceduringthetimeintervalwhentheinstantaneoussupplyvoltageisgreaterthanthebackEMF.InspectionofFig.2showsthatwhenthemotorisrunning,thepeakinversevoltageappliedtothethyristorismushgreaterthanthepeakforwardvoltage.Byconnectingadiodeinserieswiththethyristor,asshown,ther