設(shè)計(jì)直流脈寬調(diào)速電動(dòng)機(jī)系統(tǒng)的機(jī)械特性

1、1.1直流電動(dòng)機(jī)pwm控制系統(tǒng)原理。pwm控制技術(shù)一直是變頻技術(shù)的核心技術(shù)之一。它通過分辨率計(jì)數(shù)器的使用，方波的占空比被調(diào)制用來對(duì)一個(gè)具體模擬信號(hào)的電平進(jìn)行編碼。principleofdemotorPWMcontrolsystem.PWMcontroltechnologyhasbeenoneofthecoretechnologyoffrequencyconversiontechnology.Itthroughtheuseofresolutioncounter,thesquarewavedutyratioismodulatedtoencodeaspecificanalogsignallevel.

2、直流電動(dòng)機(jī)pwm控制系統(tǒng)有可逆和不可逆系統(tǒng)之分。可逆系統(tǒng)是指電動(dòng)機(jī)可以正反兩個(gè)方向旋轉(zhuǎn)；不可逆系統(tǒng)是指電動(dòng)機(jī)只能單方向旋轉(zhuǎn)。對(duì)于可逆系統(tǒng)，又可分為單極性驅(qū)動(dòng)和雙極性驅(qū)動(dòng)兩種方式。這里只研究雙極性驅(qū)動(dòng)。DcmotorPWMcontrolsystemcanbereversibleandirreversiblesystems.Reversiblesystemisreferstothemotorcanbepositiveandnegativetwodirection;Irreversiblesystemreferstothemotorcanonlysingledirection.Forreversib

3、lesystemandcanbedividedintosinglepolardrivinganddoublepolardrivingintwoways.Hereonlythebipolardrive.h型雙極性可逆pwm驅(qū)動(dòng)系統(tǒng)控制原理。h”型是雙極性驅(qū)動(dòng)電路的一種，也稱為橋式電路。如圖1所示。其電路是由四個(gè)開關(guān)管和四個(gè)續(xù)流二極管組成，單電源供電。四個(gè)開關(guān)管分為兩組，v1和v4為一組，v2和v3為另一組。同一組的開關(guān)管同步導(dǎo)通或關(guān)斷，不同組的開關(guān)管的導(dǎo)通和關(guān)斷正好相反。hbipolarreversiblePWMdrivesystemcontroltheory.Htypeisoneofthebi

4、polardrivecircuit,alsoknownasthebridgecircuit.Asshowninfigure1.Thecircuitismadeupoffourswitchtubeandfourofthefly-wheeldiode,singlepowersupply.Fourswitchtubeisdividedintotwogroups,v1andv4asagroup,v2andv3foranothergroup.Thesamesetofsynchronousconductionorshutofftheswitchtube,differentgroupofconduction

5、andshutofftheswitchtubeofjusttheopposite.在每個(gè)pwm周期里，當(dāng)控制信號(hào)vi1高電平時(shí)，開關(guān)管v1和v4導(dǎo)通，此時(shí)vi2為低電平，因此v2和v3截止。電樞繞組承受從a到b的正向電壓；當(dāng)控制信號(hào)vi1為低電平時(shí)，開關(guān)管v1和v4截止，此時(shí)vi2為高電平，因此v2和v3導(dǎo)通，電樞繞組承受從b到a的反向電壓，這就是所謂的“雙極”IneachPWMcycle,whenthecontrolsignalvi1highelectricityatordinarytimes,switchtubev1andv4conduction,vi2atthistimeforthelo

6、wlevel,thereforethev2andv3.Thearmaturewindingunderthepositivevoltagefromatob;Vi1whenthecontrolsignalforlowelectricityatordinarytimes,switchtubev1andv4as,vi2forhighlevelrightnow,sothev2andv3conduction,armaturewindinginheritfrombtoareversevoltage,thisistheso-calledbipolar.可見，雙極性可逆pwm驅(qū)動(dòng)時(shí)，電樞繞組所承受的平均電壓取決

7、于占空比a大小。當(dāng)a=0時(shí)，u0=-us，電動(dòng)機(jī)反轉(zhuǎn)，且轉(zhuǎn)速最大；當(dāng)a=1時(shí)，u0=us，電動(dòng)機(jī)正轉(zhuǎn)，轉(zhuǎn)速最大；當(dāng)時(shí),a=1/2時(shí)u0=0,電動(dòng)機(jī)不轉(zhuǎn)，但電樞繞組中仍然有交變電流流動(dòng)，使電動(dòng)機(jī)產(chǎn)生高頻振蕩，這種振蕩有利于克服電動(dòng)機(jī)負(fù)載的靜摩擦，提高動(dòng)態(tài)性能。Visible,bipolarreversiblePWMdriver,thearmaturewindingoftheaveragevoltagedependsonthesizeofdutyratioalpha.Whenalpha=0u0=-us,motorreversal,andthemaximumspeed;U0whenalpha=1=u

8、s,motoristurned,themaximumspeed;When,whenalpha=1/2u0=0,motordoesnotturn,butthereisstillaalternatingcurrentinthearmaturewindingflow,makethemotorproduceshighfrequencyoscillation,theoscillationisbeneficialtoovercomethemotorloadstaticfriction,improvethedynamicperformance.2調(diào)速系統(tǒng)的設(shè)計(jì)2speedcontrolsystemdesig

9、n對(duì)于一個(gè)控制系統(tǒng)而言，最關(guān)鍵的是控制器的設(shè)計(jì)，控制器設(shè)計(jì)的好壞關(guān)系到控制系統(tǒng)性能的優(yōu)劣?？刂破饕髮?shí)時(shí)性強(qiáng)，通用性強(qiáng)，具有較強(qiáng)的智能，在滿足性能指標(biāo)的前提下應(yīng)盡可能的簡(jiǎn)單。Foracontrolsystem,thekeyisthedesignofcontroller,thecontrollerdesignisgoodorbadisrelatedtothemeritsofthecontrolsystemperformance.Controllerrequiresstrongreal-timeperformance,strongcommonality,strongintelligence,inm

10、eettheunderthepremiseofperformanceindicatorsshouldbeassimpleaspossible.pi控制器相當(dāng)于在系統(tǒng)中增加了一個(gè)位于原點(diǎn)的開環(huán)極點(diǎn)，同時(shí)也增加了一個(gè)位于s左半平面的開環(huán)零點(diǎn)。位于原點(diǎn)的極點(diǎn)可以提高系統(tǒng)的型別，以消除或提高系統(tǒng)的穩(wěn)態(tài)誤差，改善系統(tǒng)的穩(wěn)態(tài)性能。而增加釀酒設(shè)備的負(fù)實(shí)零點(diǎn)則用來提高系統(tǒng)的阻尼度，緩和pi控制器極點(diǎn)對(duì)系統(tǒng)穩(wěn)定性產(chǎn)生的不利影響。只要積分時(shí)間常數(shù)ti足夠大，pi控制器對(duì)系統(tǒng)穩(wěn)定性的不利影響可大為減弱。在控制系統(tǒng)中，pi控制器主要用于改善控制系統(tǒng)的穩(wěn)態(tài)性能2。PIcontrollerisequivalenttoin

11、thesystemaddsanopen-looppolesarelocatedattheorigin,butalsoaddedainslefthalfplaneoftheopen-loopzeros.Polecanimprovethesystemoftheorigin,inordertoeliminateorimprovethesteady-stateerrorofthesystem,improvethesteady-stateperformanceofthesystem.Andincreasethenegativerealzeroisusedtoimprovethesystemdamping

12、,moderatePIcontrollerpoleshaveadverseeffectsonsystemstability.Aslongastheintegraltimeconstanttiislargeenough,thenegativeimpactofthePIcontrolleronthesystemstabilitycanbegreatlyreduced.Inthecontrolsystem,controlsystemofPIcontrollerismainlyusedtoimprovethesteadystateperformance2.閉環(huán)調(diào)速系統(tǒng)的轉(zhuǎn)速和電流調(diào)節(jié)器都米用pi調(diào)節(jié)器

13、。米用pi調(diào)節(jié)器的自動(dòng)控制系統(tǒng)。ClosedloopspeedregulationsystemofspeedandcurrentregulatorUSESPIregulator.AutomaticcontrolsystemofPIregulator.從傳遞函數(shù)看，自動(dòng)調(diào)節(jié)系統(tǒng)為：Fromthetransferfunctionofautomaticregulatingsystemfor:=wp1(s)=kpkp+B(2)S=wp1KPKP+s=s(s)=(2)u1可分成比例部分ulp，和積分部分uli，其中，比例部分和偏差成正比積分部分同偏差的積分有關(guān)，把兩部分加起來，就是調(diào)節(jié)器的輸出信號(hào)u1。

14、U1u1pproportioncanbedividedintoparts,andintegralpartofu1i,amongthem,theproportionisproportionaltothedeviationintegralpartsassociatedwithdeviationintegral,addtwopartstogether,isthecontrolleroutputsignalu1.當(dāng)偏差信號(hào)&是階躍信號(hào)時(shí)，比例部分會(huì)突然加大，而積分部分則按線性增長(zhǎng)，經(jīng)過一定時(shí)間后，u1輸出達(dá)到限幅值。而實(shí)際系統(tǒng)中，偏差信號(hào)&只是一開始突跳，隨著輸出信號(hào)use的增長(zhǎng)，偏差信號(hào)&便逐漸降低

15、，u1是否能夠升到限幅值，就要看u1的增長(zhǎng)和&的衰減哪一方更快。如果調(diào)節(jié)對(duì)象的時(shí)間常數(shù)遠(yuǎn)大于調(diào)節(jié)器的時(shí)間常數(shù)，則&下降較慢，由于調(diào)節(jié)器的積分作用，海吉布盡管在下降，u1仍繼續(xù)增長(zhǎng)，在&衰減到零以前u1還來得及升到限幅值3。如果調(diào)節(jié)對(duì)象的時(shí)間常數(shù)較小，則&衰減較快，當(dāng)積分量還來不及把u1抬高到限幅值以前，&已經(jīng)衰減到零，u1也就不能再增長(zhǎng)，這時(shí)積分器不會(huì)飽和。Whenepsilonzerodeviationsignalisstepsignal,proportionalpartwillsuddenlyincrease,whileintegralpartaccordingtothelineargro

16、wth,afteracertaintime,theproductoutputreacheslimitvalues.Andpracticalsystem,thedeviationsignalrelay,epsilonisjustthebeginning,asthegrowthoftheoutputsignalofusc,epsilonzerodeviationsignalwillreducegradually,u1canrisetothelimitingvalue,dependsonthegrowthofu1andepsilonattenuationwhichoneisfaster.Iftime

17、constantofregulatingobjectthancontrollertimeconstant,theslowertheepsilonisreduced,duetotheeffectofintegrationoftheregulator,inspiteofthedrop,u1isstillcontinuetogrow,beforetheepsilondecaytozerou1stillcanrisetothelimitingvalue3.Iftheadjustingobjectsmallertimeconstant,theepsilondecayquickly,whentheprod

18、uctcomponentcouldu1beforepushinguptothelimitingvalue,epsilonhasdecaytozero,u1alsocantagaingrowth,theintegratorwillnotsaturated.在動(dòng)態(tài)過程中，pi調(diào)節(jié)器輸出電壓u1是否飽和對(duì)系統(tǒng)的輸出波形很有影響。若u1一旦飽和，只有&變負(fù)，即useusr時(shí)，才有可能使它退出飽和，因此必然超凋。Intheprocessofdynamic,PIregulatoroutputvoltageu1issaturatedoutputwaveformhasinfluenceonthesystem.

19、Ifu1oncesaturated,onlyepsilonbecomesnegative,namelytheuscusr,islikelytomakeitoutofsaturation,thereforethedepth.3直流脈寬調(diào)速系統(tǒng)的機(jī)械特性Themechanicalpropertiesof3dcpulsewidthspeedregulationsystem由于采用了脈寬調(diào)制，嚴(yán)格地說，即使在穩(wěn)態(tài)情況下，脈寬調(diào)速系統(tǒng)的轉(zhuǎn)矩和轉(zhuǎn)速也都是脈動(dòng)的4。所謂穩(wěn)態(tài)，是指電動(dòng)機(jī)的平均電磁轉(zhuǎn)矩和負(fù)載轉(zhuǎn)矩相平衡的狀態(tài)，機(jī)械特性是平均轉(zhuǎn)速和平均轉(zhuǎn)矩(電流)的關(guān)系。Withpulsewidthmodulat

20、ion,strictlyspeaking,evenundersteadystateconditions,pulsewidthspeedregulationsystemofpulsationoftorqueandrotationalspeedarealso4.Steadystate,referstotheaverageelectromagnetictorqueandloadtorqueofmotorphaseequilibriumcondition,mechanicalcharacteristicsistheaveragespeedandaveragetorque(current).采用不同形式的pwm變換器，系統(tǒng)的機(jī)械特性也不一樣。對(duì)于雙極式控制的可逆電路，電流的方向是可逆的，無論是重載還是輕載，電流波形都是連續(xù)的，因而機(jī)械特性關(guān)系式比較簡(jiǎn)單。UsingdifferentformsofPWMconverter,mechanicalpropertiesofthesystemisalsodifferent.Forbipolarreversibletypecontrolcircuit,thecu