公共接地?zé)o刷直流電機(jī)驅(qū)動(dòng)系統(tǒng)的FPGA實(shí)現(xiàn)-外文翻譯_第1頁(yè)
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附錄ACommon-groundedBLDCMDriveSystemBasedonFPGAPinghuaTang,TiecaiLiDepartmentofElectricalEngneeringHarbinIndustryofTechnologyharbin,Email:tphqh@163.com;AbstractThispaperproposedakindofcommon-groundedbrushlessDCmotor(BLDCM)drivesystembasedonfieldprogrammedgatearray(FPGA)control.Theproposedsystemhastwocharacteristics:oneisthattheformer60°ofeverydrivelagappliespulsewidthmodulation(PWM)andthelatter60°conductsconstantly(PWM_ONmodulation);theotheristhattherearenoisolatingopticalcouplersbetweencontrolcircuitanddrivecircuit.Sotheproposedsystemhassomeadvantagessuchasreducingrippleofelectromagnetictorque,simplifyingdrivecircuittoreducethedelayofsignals,andreducingthecostandbulkofdrivesystem.AprototypeisdesignedbasedonFPGAchip,andexperimentalresultsdemonstratedthevalidityofrelativetheory.IndexTerms-common-groundeddrive;BLDCM;FPGA;PWM_ONmodulationI.INTRODUCTIONBrushlessDCmotoriswidelyappliedinmoderncontrolsystembecauseofmanyadvantagessuchashighefficiency,highpowerdensity,goodspeedcharacteristicandsimplifiedcontroletc.[1-2].InordertocontrolBLDCMsystemeffectively,conventionaldriveschemeforBLDCMsystemisthat120°controlsignalswhichisoutputbycontrolcircuitareisolatedbyopticalcouplers,thendelivertodrivecircuitandcontrolthepowermaincircuit.SoconventionalBLDCMsystempresentssomedisadvantagessuchasbigelectromagnetictorqueripples,bigvolume,highcost,andsignalsdelaybyopticalcoupleretc.ThesedisadvantagesmakeconventionalBLDCMsystemnotbeenusedinsomeconditionswhichneedhighprecisionandhighstability[3-4].ToovercomethesedisadvantagesofconventionalBLDCMsystemtosomeextent,thispaperpresentsanovelBLDCMsystemwhichisappliedwithPWM_ONmodulationandcommon-groundeddrivescheme.Theproposedsystemhastwocharacteristics:oneisPWM_ONmodulationcontrolmodethattheformer60°ofeverydrivelagappliespulsewidthmodulation(PWM)andthelatter60°conductedconstantlyin120°period;theotheristhattherearenoisolatingopticalcouplersbetweencontrolcircuitanddrivecircuit.ThispaperdeducedmathematicsmodelofBLDCM,thenanalyzedoperationalprincipleofthePWM_ONmodulationcommon-groundeddriveschemewhichisusedtoBLDCMsystem,andsimulationanalysisabouttheproposedschemeispresented,finally,a120WBLDCMsystemprototypeisdevelopedbasedonFPGAchip,andexperimentalresultswereanalyzed.II.BLDCMMATHEMATICALMODELMostBLDCMdrivesarebasedontheactivecontroltothree-phaseinvertertoobtainsquare-wavecurrentofBLDCMneededinmoderntimes.TheBLDCMmathematicalmodelwhichinfersbelowinthisarticleincludesthree-phaseinverter.ThemathematicalmodelofBLDCMiscomposedoftwoparts,namelymechanicalequationandvoltageequation.Thispapermakesthefollowingthreesuppositionsbeforeintroducingthemathematicalmodel,asfollows:(1)Three-phasestatorwindingA,B,Cissymmetricalinspatialdistribution,thehigherharmoniccomponentofmagneticfieldisneglected.(2)Themagneticsaturationandthecoreloss(magnetichysteresisloss,eddycurrentloss)areneglected.(3)Theinfluencefactorsincludingtemperature,frequencyetc.onparametersofmotorarenotconsidered.Mechanicalmovementequationofelectricmachineisfixedandwon’tchangewiththecoordinatetransformation.BLDCMmechanicalmovementequationisasfollows:Te-Tl=J+B(1)whereTeiselectromagnetictorque,TLisloadtorque,Jisrotorandloadinertia,Bisfrictioncoefficient,ωisrotatingspeedofBLDCM.Takethethree-phasestatorvoltageasthestatevariable.Itsvoltagebalanceequationcanbeexpressedas(2):UaRaiaLaLabLaciaUb=Rbib+LbaLbLbcib+eb(2)UcRcicLcaLcbLcicecBecausetherotorispermanent-magnet,La,Lb,Lc,Lab,Lba,Lac,Lca,Lbc,Lcb,canbeconsideredasconstants,then,Ra=Rb=Rc=RsLa=Lb=Lc=LLab=Lba=Lac=Lca=Lbc=Lcb=M(3)ia+ib+ic=0Therefore,weobtainthePMBLDCMvoltageequationwhichisshownin(4):UaRsiaL-MiaeaUb=Rsib+L-Mib+eb(4)UcRsicL-MicecThetopologyofBLDCMmodelisobtainedfrom(4)andshowninFig.1.Fig.1TopologyofBLDCMmodelSo,mathematicalmodelofBLDCMcanbedescribedas(1)and(4).III.PWM_ONMODULATIONCOMMON-GROUNDEDDRIVESCHEMEAsthree-phaseinverterisconcerned,PWMcontrolschemeiswidelyappliedtocontrolthespeedandcurrentofBLDCMcontrolsystem.Therearefollowingcommon-usedPWMmodulationmodes:H_PWM&L_ON,H_ON&L_PWMandH_PWM&L_PWM.Thefirsttwokindsofmodescanberealizedsimplybuthasthedisadvantageofbigphasecurrentpulsationineveryelectriccycle.Thelastoneisstudiedalotforitsadvantageofreducingcurrentpulsation,butswitchinglossistoobig.However,thecontrolsystemswhichapplythemodulationsabove,thecontrolpartisisolatedwiththedrivepart.Thatistosay,thereareopticalcouplersbetweencontrolcircuitanddrivecircuit.Theopticalcouplersmustcausesignalsdelaytoworsecharacteristicofsystem.Ontheotherhand,thismethodwillaffectreliabilityofthedriverandenhancethecost.PWM_ONmodulationandcommongroundcontrolschemewillbeintroduced.A.PWM_ONmodulationThecircuittopologyofBLDCMisshowedinFigure1.Thetraditionalcontrolschemeisusingthree-phasesixconditionsand120degreeconductionmode.Toproduceaconstantelectromagnetictorque,itisrequiredtofeedrectangularcurrentsintheflatpositionoftheidealtrapezoidalbackEMF.However,thecommutationofphase-currentsrequiresafinitetimeduetotheinductanceofmachinewindings,andtorquepulsationmayoccuraccordingly.Someresearchdiscoveredthattorquepulsationsizeisrelatedwiththenoninvertingcommutationcurrentandchangeswiththemodulationmodes.Atpresent,themainkindsofPWMmodulationsare:theswitchesintheupper-halflagmodulatedandinthelower-halflag120degreeon(H_PWM),theswitchesinthelower-halflagmodulatedandintheupper-halflag120degreeon(L_PWM),switchesofboththeupperlagandthelowerlagmodulated(H_PWM-L_PWM),thefirst60degreePWMandlatter60degreeoninthebothupperandlowerswitches(PWM_ON),thefirst60degreeonandlatter60degreePWMinthebothupperandlowerswitchesandsoon.TheresearchshowsthatPWM_ONmodulationhastheadvantageofthesmallesttorquerippleandswitchesloss.ThetimingdiagramisshowninFig2.Fig.2TimingdiagramofPWM_ONcontrolsignalsTheelectromagnetictorqueofelectricalmachinecanbeexpressedwith(5):Te=(eaia+ebib+ecic)(5)Where,Terepresentselectromagnetictorque,pispolepairs,ωrepresentselectricalrotatingspeed,ea,ebandecrepresentphasebackelectromotiveforce,ia,ibandicrepresentphasecurrent.Whenelectricalmachineoperatesconventionalcontrolschemeandneglectsinfluenceofphaseconversion,theelectromagnetictorqueofelectricalmachinecanbeexpressedas(6):Te=2pkei(6)Where,kerepresentselectromagnetictimecoefficient,iiscurrentofsteadystate.InordertodescribethetorquerippleofphaseconversioncausingbyPWM_ONmodulation,thispaperwilltakeperiod[60°,120°]forexampletodeduceit.Threephasecurrentsshowedin(7)canbeobtainedaccordingthemathematicalmodelofBLDCM.ia(t)=i-(2ke+2Rsi+DU)tib(t)=(DU-ke)t(7)ic(t)=-i+(4ke+3Rsi+DU)tWhere,Uisbusvoltage,DisdutycycleofPWM.Accordingto(5)and(7),theelectromagnetictorqueofBLDCMsystemwithPWM_ONmodulationcanbedescribedby(8):Te=2pkei+[2UDt-8ket-6Rsit](8)Therippleofelectromagnetictorquecanbeexpressedas:ΔTeT=[8ket+6Rsit-2UDt](9)From(9),itisdefinitethattherippleofelectromagnetictorqueisdeterminedbyωandD.SotheminimalrippleofelectromagnetictorquecanbegotinsuitableconditionofωandD.B.Common-groundeddriveschemeTheopticalcouplerdriveschemeismostwidespreadusedatpresent.Thesampledcurrent,speedandpositionsignalstransmittothecontrolpartthroughopticalcouplers,andthentheoutputsignalspassthroughtheopticalcoupleragainandareamplifiedbydrivepart,lastcontroltheswitchesoftheinverter.Isolationschemeisshowedinfig.3.Opticalcouplerusedinthesystemcancausetimedelay,evenusinghighspeedopticalcouplerthetimedelayismorethan2us.Atthesametime,becausenoteveryopticalcouplerhasthesamecharacteristic,thecontrolsignalscannotbesynchronous.Thus,theperformanceofsystembecomesworse.Inthispaper,common-groundeddriveschemeisproposed.Opticalcouplersarenotusedbetweencontrolpartanddrivepart.Thentimedelayisreduced,sothedynamicandsteadyresponsecharacteristicsofsystemareimproved,andsystemcostisreduced.Thecommon-groundedclosedloopsystemisshowninFig.4.Thetransferfunctionofsystemcanbedescribedas(10).Fig.3BlockDiagramofisolatingdriveFig.4Blockdiagramofcommon-groundeddriveF(S)=(10)Where,G(s)istheopenlooptransferfunction.ThedrivesystemshowninFig3canbedescribedbytransferfunction(11)FG(S)=(11)Where,T1,T2isthetimedelayinthemainchannelandfeedbackchannelrespectively.Fig.5Contrastofstepresponsebetweencommon-groundeddriveandisolatingdriveSimulatethesystemaccordingto(10)and(11)whenbothT1andT2are2us.SimulationwaveformisshowninFig5.Thus,systemhasbetterperformanceifthecommongroundstrategyisused.UsingbothPWM_ONmodulationandcommon-groundeddriveschemeintheBLDCMsystemwillreducetorqueripple,timedelay,systemfaultandcostandsoon.IV.PWM_ONCOMMON-GROUNDEDBLDCMSYSTEMThispartintroducesthedigitalachievementoftheproposedschemebasedonFPGAchip.DigitalBLDCMsystemconsistsofFPGAchip,drivecircuit,three-phaseinverterandBLDCM.Thebasicoperatingprinciplecanbedescribedas:positionsignalsoutputfromBLDCMinputthedecoderandposition/velocityconverterdesignedinFPGA,theerrorthatvelocitycommandsubtractsthevelocityfeedbackwhichistheoutputofposition/velocityconverterisamplifiedbyPIDregulator,andinputPWMgenerator,positiondecoderoutputsix120°conductingsignalsaccordingtopositionsignalsatthesametime,PWMgeneratoranddecoderasanunitoutputssixPWM_ONcontrolsignals;sixcontrolsignalsareamplifiedbydrivecircuitastheinputofthree-phaseinverter,thesixpowerswitchesoperatePWM_ONstate.Theblockchartofdigitalcontrolsystemisshowedinfig.6.Fig.6BlockdiagramofconvertersystemPIDalgorithmiswidelyappliednotonlybecauseit`scontrolstructureissimpleandit`sparametersiseasilyregulated,butitcomprehendsadvantagesofPregulator,IregulatorandDregulator.ThetransferfunctionofPIDalgorithmins-domaincanbeexpressedas(12):HPID=KP(1++τDS)(12)TobeeasilyachievedbyFPGA,(12)mustbetransformedintodiscreteform.(12)canbeexpressedby(13)whichisinz-domain:HPID(z)=KP++(1-Z-1)(13)(13)canbediscretizedusingdifferenceequation(14):up(n)=Kpe(n)uI(n)=u[n-1]+KI(e[n]+e[n-1])(14)uD(n)=KD(e[n]-e[n-1])ThecircuitstructureofPIDalgorithmachievedbyFPGAisshowedinfig.7accordingto(14).Fig.7HardwarestructureofPIDalgorithmachievedbyFPGADrivecircuitconsistsofIR2130andrelativeperipheralcircuit.IR2130iskeycomponenttoachievecommon-groundeddrivescheme.IR2130hassomegoodcharacteristics:itcandrivethreeupperlegsandthreelowerlegswhichbearhighvoltage;itcanpreventcross-conductionbecauseofundervoltageandover-currentshutdown;themostimportantisthatitreceivescontrolsignalsandoutputtothree-phaseinverterdirectlywithoutisolatedcomponent,socommon-groundedschemeisachieved.Common-groundeddrivesimplifiescircuitdesign,reducessignalsdelayandauxiliarypowersupplies.SothecostofBLDCMsystemisreduces.……附錄B公共接地?zé)o刷直流電機(jī)驅(qū)動(dòng)系統(tǒng)的FPGA實(shí)現(xiàn)摘要提出了一種基于利用現(xiàn)場(chǎng)編程門(mén)陣列器進(jìn)行控制的公共接地永磁無(wú)刷直流電機(jī)驅(qū)動(dòng)系統(tǒng)。該系統(tǒng)具有兩大特點(diǎn):一是,前60°的每個(gè)驅(qū)動(dòng)滯后運(yùn)用脈寬調(diào)制,后60°不間斷的進(jìn)行脈寬調(diào)制(PWM);另一個(gè)是,控制電路與驅(qū)動(dòng)電路之間沒(méi)有光電耦合器進(jìn)行電氣隔離。所以,該系統(tǒng)具有一定的優(yōu)勢(shì),比如降低了電磁轉(zhuǎn)矩脈動(dòng)、簡(jiǎn)化了的驅(qū)動(dòng)電路使得信號(hào)的延遲變小、降低生產(chǎn)成本并且精簡(jiǎn)了大部分驅(qū)動(dòng)系統(tǒng)。基于一個(gè)FPGA芯片設(shè)計(jì)了一個(gè)原型,并且利用該原型進(jìn)行測(cè)試的實(shí)驗(yàn)結(jié)果證明了相關(guān)理論的正確性。關(guān)鍵詞公共接地驅(qū)動(dòng);無(wú)刷直流電機(jī);現(xiàn)場(chǎng)可編程門(mén)陣列;PWM_ON調(diào)制策略第一章引言由于無(wú)刷直流電動(dòng)機(jī)具有效率高,功率密度高,良好的速度特性和簡(jiǎn)化控制等諸多優(yōu)點(diǎn),被廣泛應(yīng)用于現(xiàn)代控制系統(tǒng)。為了有效地控制無(wú)刷直流電動(dòng)機(jī)系統(tǒng),傳統(tǒng)的無(wú)刷直流電機(jī)驅(qū)動(dòng)方案是使用被光電耦合器隔離的控制電路輸出的120°控制信號(hào),提供給驅(qū)動(dòng)電路并且控制電源主電路。因此,傳統(tǒng)的無(wú)刷直流電機(jī)系統(tǒng)出現(xiàn)了一些缺點(diǎn),如電磁轉(zhuǎn)矩脈動(dòng)大,體積大,成本高,和光耦合器造成的信號(hào)延遲等,這些缺點(diǎn)使傳統(tǒng)的無(wú)刷直流電機(jī)系統(tǒng)不能應(yīng)用在需要高精度,高穩(wěn)定等條件的環(huán)境下。為了在一定程度上克服上述常規(guī)無(wú)刷直流電動(dòng)機(jī)系統(tǒng)的缺點(diǎn),本文提出了一種新的無(wú)刷直流電機(jī)系統(tǒng),該系統(tǒng)應(yīng)用PWM_ON調(diào)制策略和共同接地驅(qū)動(dòng)器原理。設(shè)計(jì)的系統(tǒng)有兩個(gè)特點(diǎn):一是PWM_ON調(diào)制控制方式,在一個(gè)120°周期內(nèi),前60°的每個(gè)驅(qū)動(dòng)器滯后適用脈寬調(diào)制(PWM),而后者60°進(jìn)行不間斷脈寬調(diào)制;另一種是控制電路和驅(qū)動(dòng)電路之間不存在用于電氣隔離的光電耦合器。本文首先推導(dǎo)出了無(wú)刷直流電機(jī)的數(shù)學(xué)模型,然后分析了用于無(wú)刷直流電機(jī)系統(tǒng)的PWM_ON調(diào)制策略和共同接地驅(qū)動(dòng)器的工作原理,對(duì)提出的設(shè)計(jì)原理進(jìn)行仿真分析,最后,開(kāi)發(fā)了基于FPGA芯片的120W無(wú)刷直流電機(jī)系統(tǒng)原型,并對(duì)實(shí)驗(yàn)結(jié)果進(jìn)行分析。第二章無(wú)刷直流電機(jī)的數(shù)學(xué)模型在近代,大多數(shù)基于主動(dòng)控制的無(wú)刷直流電動(dòng)機(jī)驅(qū)動(dòng)器是由三相逆變電源提供無(wú)刷直流電機(jī)工作需要的方波的。本文接下來(lái)要推導(dǎo)的無(wú)刷直流電機(jī)的數(shù)學(xué)模型中包括三相逆變電源部分。無(wú)刷直流電機(jī)的數(shù)學(xué)模型由兩部分組成,即機(jī)械方程和電壓方程。本文在推導(dǎo)無(wú)刷直流電機(jī)的數(shù)學(xué)模型之前提出以下三個(gè)假設(shè),具體如下:(1)三相定子繞組A,B,C的空間分布是均勻?qū)ΨQ的,磁場(chǎng)的較高的諧波分量忽略不計(jì)。(2)磁飽和與鐵芯損失(磁滯損耗,渦流損耗)是忽略不計(jì)的。(3)環(huán)境因素如溫度,頻率等電機(jī)的參數(shù)忽略不計(jì)。電機(jī)的機(jī)械運(yùn)動(dòng)方程是固定的,也不會(huì)隨著坐標(biāo)變換而改變。無(wú)刷直流電機(jī)的機(jī)械運(yùn)動(dòng)方程如下:Te-Tl=J+B(1)TE是電磁轉(zhuǎn)矩,負(fù)載轉(zhuǎn)矩是TL,J是轉(zhuǎn)子和負(fù)載慣量,B是摩擦系數(shù),ω是無(wú)刷直流電機(jī)的轉(zhuǎn)速。將三個(gè)階段的定子電壓作為狀態(tài)變量。其電壓平衡方程可以表示為(2):uaRaiaLaLabLaciaub=Rbib+LbaLbLbcib+eb(2)ucRcicLcaLcbLcicec由于轉(zhuǎn)子是永磁體,La,Lb,Lc,Lab,Lba,Lac,Lca,Lbc,Lcb,可視為常數(shù),那么,Ra=Rb=Rc=RsLa=Lb=Lc=LLab=Lba=Lac=Lca=Lbc=Lcb=M(3)ia+ib+ic=0因此,我們得到了首相無(wú)刷直流電動(dòng)機(jī)的電壓方程,如(4)所示:UaRsiaL-MiaeaUb=Rsib+L-Mib+eb(4)UcRsicL-Micec無(wú)刷直流電機(jī)得拓?fù)淠P褪怯?4)得到的,其模型如圖1所示。圖1拓?fù)涞臒o(wú)刷直流電機(jī)模型因此,無(wú)刷直流電機(jī)的數(shù)學(xué)模型可以由(1)和(4)描述。第三章PWM_ON調(diào)制共同接地驅(qū)動(dòng)架構(gòu)作為三相逆變器而言,PWM控制方案被廣泛應(yīng)用于控制速度和目前的無(wú)刷直流電機(jī)控制系統(tǒng)。有以下常用的PWM調(diào)制模式:H_PWM&L_ON,H_ON&L_PWM和H_PWM&L_PWM。前兩種模式,實(shí)現(xiàn)起來(lái)非常簡(jiǎn)單,但缺點(diǎn)是,在每個(gè)電周期,相電流脈動(dòng)都很大。最后一種模式為了具有減少電流脈動(dòng)的優(yōu)勢(shì)而做了很多研究,但開(kāi)關(guān)損耗過(guò)大。然而,應(yīng)用于上述調(diào)制系統(tǒng)中的控制系統(tǒng),其控制部分與驅(qū)動(dòng)器部分是分離的。換句話說(shuō)就是控制電路和驅(qū)動(dòng)電路之間有起電氣隔離作用的光學(xué)耦合器。光學(xué)耦合器肯定會(huì)產(chǎn)生信號(hào)遲延,從而降低系統(tǒng)特性。另一方面,這種方法會(huì)影響驅(qū)動(dòng)器的可靠性同時(shí)提高生產(chǎn)成本。下面介紹PWM_ON調(diào)制策略和共同接地控制方案。A:PWM_ON調(diào)制策略無(wú)刷直流電機(jī)的電路拓?fù)淙鐖D1所示。傳統(tǒng)的控制方案是采用三相六拍和120度導(dǎo)電模式。不斷產(chǎn)生電磁轉(zhuǎn)矩,這就要求將理想梯形波在同一位置產(chǎn)生的電流反饋到EMF。不過(guò),由于機(jī)繞組電感和可能會(huì)產(chǎn)生的轉(zhuǎn)矩脈動(dòng),相電流的整流需要一定限度的時(shí)間。一些研究發(fā)現(xiàn),轉(zhuǎn)矩脈動(dòng)的大小與非逆變整流電流有關(guān),同時(shí)隨調(diào)制方式的改變而改變。目前,幾種主要的PWM調(diào)制有:上橋臂調(diào)制,下橋臂120度恒通(H_PWM);下橋臂調(diào)制,上橋臂120度恒通(L_PWM),上下橋臂同時(shí)調(diào)制(H_PWM-L_PWM),頭60度調(diào)制和后60度上下橋臂恒通(PWM_ON),頭60度和后60度上下橋臂都調(diào)制等。研究表明,PWM_ON調(diào)制具有最小轉(zhuǎn)矩脈動(dòng)和開(kāi)關(guān)損耗的優(yōu)點(diǎn)。時(shí)序圖如圖2所示。圖2PWM_ON控制信號(hào)時(shí)序電機(jī)的電磁轉(zhuǎn)矩可用(5)表達(dá):Te=(eaia+ebib+ecic)(5)其中,Te代表電磁轉(zhuǎn)矩,P是磁極對(duì),ω代表電機(jī)轉(zhuǎn)速,ea,eb和ec代表反饋電動(dòng)勢(shì),ia,ib和ic代表三相電流。當(dāng)電機(jī)運(yùn)行常規(guī)控制方案斌且忽略相移的影響,電機(jī)的電磁轉(zhuǎn)矩可表示為(6):Te=2pkei(6)這里,Te代表電磁時(shí)間系數(shù),i是穩(wěn)定狀態(tài)的電流。為了描述由pwm_on調(diào)制引起的相移而產(chǎn)生的轉(zhuǎn)矩脈動(dòng),本文將以[60°,120°]為例進(jìn)行推導(dǎo)。如(7)所示的三相電流,可以獲得建立無(wú)刷直流電機(jī)數(shù)學(xué)模型的依據(jù)。ia(t)=i-(2ke+2Rsi+DU)tib(t)=(DU-ke)t(7)ic(t)=-i+(4ke+3Rsi+DU)t這里,U是總線電壓,D是PWM的占空比。根據(jù)(5)和(7),使用PWM_ON調(diào)制的無(wú)刷直流電機(jī)系統(tǒng)的電磁轉(zhuǎn)矩,可以由(8)描述:Te=2pkei+[2UDt-8ket-6Rsit](8)電磁轉(zhuǎn)矩脈動(dòng)可以表示為:ΔTeT=[8ket+6Rsit-2UDt](9)從(9)可以看出,繞組的電磁轉(zhuǎn)矩是由ω和D所確定的.所以最小電磁轉(zhuǎn)矩脈動(dòng)可以ω和D作為條件獲得.B.共同接地驅(qū)動(dòng)器原理光耦隔離器驅(qū)動(dòng)原理是如今最普遍使用的驅(qū)動(dòng)原理。采樣電流,速度和位置信號(hào)通過(guò)光電耦合器傳送到控制部分,然后輸出信號(hào)也通過(guò)光耦合器,并被驅(qū)動(dòng)器放大,最后控制逆變器的開(kāi)關(guān)。電氣隔離原理如圖3所示。光電耦合器在系統(tǒng)中應(yīng)用會(huì)造成一段時(shí)間的延遲,即使使用高速光耦,所產(chǎn)生的時(shí)間延遲還是超過(guò)2us。與此同時(shí),由于不是每個(gè)光耦合器具有相同的特性,控制信號(hào)不能同步。因此,系統(tǒng)的性能變差。本文提出的共同接地驅(qū)動(dòng)方案??刂撇糠趾万?qū)動(dòng)部分之間不使用光纖耦合器進(jìn)行隔離。減少了延時(shí),因此,改善了系統(tǒng)特性中的動(dòng)態(tài)和穩(wěn)態(tài)響應(yīng),降低了系統(tǒng)成本。共同接地閉環(huán)系統(tǒng)如圖4所示。系統(tǒng)的傳遞函數(shù)可以用(10)來(lái)描述。圖3光耦隔離驅(qū)動(dòng)器系統(tǒng)框圖圖4共同接地驅(qū)動(dòng)系統(tǒng)框F(S)=(10)其中,G(s)是開(kāi)環(huán)的傳遞函數(shù)。圖3所示得驅(qū)動(dòng)系統(tǒng)可以用傳遞函數(shù)(11)描述FG(S)=(11)其中,T1,T2分別是前向通道和反饋通道的延時(shí)。圖5對(duì)比共同接地驅(qū)動(dòng)器和隔離驅(qū)動(dòng)器之間的階躍響應(yīng)根據(jù)(10)和(11)進(jìn)行系統(tǒng)仿真,設(shè)兩個(gè)T1和T2都是2us。仿真波形如圖5所示。由圖5可知,如果使用共地驅(qū)動(dòng)原理,系統(tǒng)將具有更好的性能。在無(wú)刷直流電機(jī)系統(tǒng)中,同時(shí)使用PWM_ON調(diào)制策略和共同接地驅(qū)動(dòng)原理將減少轉(zhuǎn)矩脈動(dòng),時(shí)間延遲,系統(tǒng)故障和成本等。第四章PWM_ON共同接地?zé)o刷直流電機(jī)系統(tǒng)這部分介紹了設(shè)計(jì)的系統(tǒng)基于FPGA芯片的數(shù)字化實(shí)現(xiàn)。數(shù)字無(wú)刷直流電機(jī)系統(tǒng)包括FPGA芯片、驅(qū)動(dòng)電路、三相逆變器和無(wú)刷直流電機(jī)。其基本工作原理可以被描述為:無(wú)刷直流電機(jī)輸出的位置信號(hào)輸入在FPGA芯片中設(shè)計(jì)的解碼器和位置/速度轉(zhuǎn)換器,誤差是速度指令減去位置/速度轉(zhuǎn)換器輸出的經(jīng)過(guò)PID控制器放大的速度反饋信號(hào),然后輸入到PWM信號(hào)發(fā)生器中,位置解碼器根據(jù)位置信號(hào)同時(shí)輸出六個(gè)120°驅(qū)動(dòng)信號(hào),PWM發(fā)生器和解碼器作為一個(gè)模塊的產(chǎn)生六個(gè)PWM_ON控制信號(hào);6個(gè)控制信號(hào)作為三相逆變器的輸入被驅(qū)動(dòng)器放大,六個(gè)電源開(kāi)關(guān)控制PWM_ON狀態(tài)。數(shù)字控制系統(tǒng)模塊圖如圖6所示。圖6轉(zhuǎn)換系統(tǒng)框圖PID算法被廣泛應(yīng)用不僅是因?yàn)樗目刂平Y(jié)構(gòu)簡(jiǎn)單、參數(shù)規(guī)范簡(jiǎn)單、易于理解,還因?yàn)樗吮壤{(diào)節(jié)、積分調(diào)節(jié)和微分調(diào)節(jié)的優(yōu)點(diǎn)。PID在S域的傳遞函數(shù)算法可以表示為(12)HPID=KP(1++τDS)(12)為了在FPGA芯片上實(shí)現(xiàn)PID調(diào)節(jié),(12)要轉(zhuǎn)變?yōu)殡x散形式。(12)在Z域可以由(13)表示:HPID(z)=KP++(1-Z-1)(13)(13)可以用離散差分方程(14)描述:up(n)=Kpe(n)uI(n)=u[n-1]+KI(e[n]+e[n-1])(14)uD(n)=KD(e[n]-e[n-1])由(14)得到的PID算法在FPGA上該實(shí)現(xiàn)的電路結(jié)構(gòu)如圖7所示。圖7硬件結(jié)構(gòu)PID算法的FPGA實(shí)現(xiàn)驅(qū)動(dòng)電路包括IR2130和其他周邊電路。IR2130是實(shí)現(xiàn)公共接地驅(qū)動(dòng)器原理的關(guān)鍵組成部分。IR2130有一些很好的特點(diǎn):它可以驅(qū)動(dòng)在高電壓環(huán)境下工作的三個(gè)上管和三個(gè)下管;它具有低壓和過(guò)流保護(hù),可以防止交叉?zhèn)鲗?dǎo);最重要的是,它沒(méi)有隔離器件,可以直接接收控制信號(hào)和三相逆變器的輸出信號(hào),至此,公共接地原理就可以實(shí)現(xiàn)了。公共接地驅(qū)動(dòng)器簡(jiǎn)化了電路設(shè)計(jì),降低了信號(hào)的延遲及輔助電源的供應(yīng)。因此降低了無(wú)刷直流電機(jī)系統(tǒng)的成本。

論大學(xué)生寫(xiě)作能力寫(xiě)作能力是對(duì)自己所積累的信息進(jìn)行選擇、提取、加工、改造并將之形成為書(shū)面文字的能力。積累是寫(xiě)作的基礎(chǔ),積累越厚實(shí),寫(xiě)作就越有基礎(chǔ),文章就能根深葉茂開(kāi)奇葩。沒(méi)有積累,胸?zé)o點(diǎn)墨,怎么也不會(huì)寫(xiě)出作文來(lái)的。寫(xiě)作能力是每個(gè)大學(xué)生必須具備的能力。從目前高校整體情況上看,大學(xué)生的寫(xiě)作能力較為欠缺。一、大學(xué)生應(yīng)用文寫(xiě)作能力的定義那么,大學(xué)生的寫(xiě)作能力究竟是指什么呢?葉圣陶先生曾經(jīng)說(shuō)過(guò),“大學(xué)畢業(yè)生不一定能寫(xiě)小說(shuō)詩(shī)歌,但是一定要寫(xiě)工作和生活中實(shí)用的文章,而且非寫(xiě)得既通順又扎實(shí)不可。”對(duì)于大學(xué)生的寫(xiě)作能力應(yīng)包含什么,可能有多種理解,但從葉圣陶先生的談話中,我認(rèn)為:大學(xué)生寫(xiě)作能力應(yīng)包括應(yīng)用寫(xiě)作能力和文學(xué)寫(xiě)作能力,而前者是必須的,后者是“不一定”要具備,能具備則更好。眾所周知,對(duì)于大學(xué)生來(lái)說(shuō),是要寫(xiě)畢業(yè)論文的,我認(rèn)為寫(xiě)作論文的能力可以包含在應(yīng)用寫(xiě)作能力之中。大學(xué)生寫(xiě)作能力的體現(xiàn),也往往是在撰寫(xiě)畢業(yè)論文中集中體現(xiàn)出來(lái)的。本科畢業(yè)論文無(wú)論是對(duì)于學(xué)生個(gè)人還是對(duì)于院系和學(xué)校來(lái)說(shuō),都是十分重要

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