文献翻译-三种关于无刷电机控制器设计的解决方案

英汉互译ThreePieceSolutionForBrushlessMotorControllerDesignPreparedbyKimGauenandJadeAlberkrackUntilrecently,motorcontroldesignerswhowishedtotakeadvantageofthebrushlessDCmotorsuniqueattributeswerefacedwithadifficulttask.TherewerenocontrolIcsdesignedtodecodedatacomingfromHalleffectsensors,letaloneperformalltheancillaryfunctionssuchasforward/reverseselection,overcurrentshutdown,undervoltagelockout,overtemperatureshutdown,andsoforth.Usingdiscretecomponentstoincludethesefunctionswasanalternative,butdiscretesoftenconsumedfartoomuchcircuitboardarea,especiallyifthecontrolunitwastobeplacedinsidethemotorhousing.Figure1.ConstructionandDiagramoftheMPM3003,aThreePhaseBridgeThatisIdealforDrivingSmallBrushlessDCMotorsAnotherproblemareawastheinadequateperformanceoftheavailablepowertransistors.PowerbipolarswerentfavoredbecausetheycantbedrivendirectlyfromacontrolIC,andDarlingtonshaveon-statevoltagesthataresometimestoohigh.PowerMOSFETsseemedtobetheidealchoicesincetheyareeasytodrive,efficientandinexpensive.However,designersweresometimestroubledbytheirinabilitytowithstandstressescommoninpulsewidthmodulatemotorcontrollers.THEPOWERSTAGEThreerecentlyintroduceddevices,apowermoduleandtwolinearICs,combinetoovercomethelimitationsofthesemiconductorstoformasimpledesign,highperformancesystem.ThepowermoduleistheMPM3003,athreephasebridgehousedina12pinpowerpackage(Figure1).Itsthreeuppertransistorsare0.28ohmP-channelpowerMOSFETsandthethreelowerdevicesare0.15ohmN-channels.Allsixdeviceshavedrain-to-sourcevoltageratingsof60V.TherearethreeattributesthatmakethenewerMOSFETsmoreruggedthantheirpredecessors.First,theycanwithstandgreaterstressduringcommutationsoftheMOSFETsinternalsourcedraindiode.FirstgenerationMOSFETssometimesfailedwhentheirdiodeswereforcedthroughreverserecovery.(1)Second,thenewerMOSFETsarelesssusceptibletofailurecausedbybriefdraintosourceovervoltagetransients.Finally,theMOSFETsintheMPM3003haveminimumgate-to-sourcerupturevoltageratingsof40Vinsteadoftheindustrystandard20V.Agreaterrupturevoltagenotonlyimprovestolerancetoelectrostaticdischargeandunanticipatedgate-to-sourcevoltagespikes,butitalsoextendsthelifetimeofthegateoxideatalloperatingvoltages.TheMPM3003ssmallsizeandisolatedpackageareothermajorbenefits.ComparedwithmountingsixTO-220s,mountingtheMPM3003ismucheasierandrequiresabouthalfthefootprintarea.AsshowninFigure1,assemblybeginswithsolderingdicetoanickelplatedcopperleadframe,anartwellknownfromTO-220manufacturing.Theleadframehelpsreducethermalresistancebyservingasaheatspreader.Inaseparateassembly,analuminumheaderiscoveredwiththedielectric,anepoxyfilm.Tofacilitateattachingtheleadframeassemblytothealuminumheader,thecopperfoilontheepoxyfilmisetchedtoformislandsforthedice.Justbeforemolding,thealuminumheadersarebondedtothecopperfoil.Suchconstructiongiveslowthermalimpedanceandavoidsthebrittlenessandexpenseofaceramicisolationmaterial.Figure2.MC33035RepresentativeBlockDiagramTHEBRAINSThesystemhighlightedhereisbuiltwithMotorolasMC33035andasupportchip,theMC33039.TheyareexamplesofnewICsthatdramaticallysimplifythedesignofbrushlessmotorcontrolsystemsandreducerequiredcircuitboardareaandpartscount.Addedbenefitsareshorterdesigntimesandimprovedsystemperformance.TheMC33035isa24-pinlinearICthatcanoperateasthecontrolcenterforabrushlessDCmotorcontrolsystem.ThemaindutyoftheMC33035istodecodethesignalsfromtheHalleffectsensorsandgeneratelogicforelectronicallycommutatingthemotor.ThecommutationlogicisinternallyfedintothesixoutputdriversconsistingofthreeopencollectorNPNtransistorsthatdrivetheupperlegsofthebridgeandthreetotempoledriversthatcontrolthedevices.Theopencollectoroutputscansink50mA;withsomeadditionalcircuitrythisallowscontrolofeitherN-channelMOSFETsforhigherpowerapplicationsorP-channelMOSFETsifasimpleinterfaceisdesired.Sincethethreelowertotempoleoutputscansourceandsink100mA,theycandrivepowerMOSFETsdirectly.FAULTMANAGEMENTTheMC33035candetectandmanageseveraltypesoffaults.Acommonmethodofovercurrentdetectionistotiethesourcesofthelowerthreetransitorstogetherandreturnthemtothenegativesupplyrailthroughacurrentsenseresistor.Thesensevoltage,whichisproportionaltoloadcurrent,isfedintoacomparatoronboardtheMC33035.ThecomparatorthenfeedsanRSFlip-Flop,whichensuresthatonceanovercurrentconditionisdetected,theoutputdriversturn-offthepowertransistorstheremainderoftheoscillatorcycle.Withouttheinternalflip-floptheovercurrentprotectionloopwouldrapidlycycleOnandOffaboutthecomparatorsthreshold,causingexcessivepowertransistorheating.Inadditiontoovercurrentmanagement,theMC33035providesundervoltagelockoutsthatterminatethedrivetotheoutputtransistorsifanyofthreeconditionsoccur.ThefirstisinsufficientvoltagetooperatetheIC.ThesecondoccurswhenthereisinsufficientvoltagetodrivethepowerMOSFETgates.Finally,theoutputdriversturnoffthepowertransistorswhentheMC33035doesnotsustainitsonboard6.25Vreference.AninvalidsetofHalleffectsignalsorexcessivetemperaturewillcauseshutdown,too.Wheneveranyfaultconditionispresent,anNPNtransistorcapableofsinking16mApullstheFaultOutputpinlow.PotentialusesoftheFaultOutputincludealertingamicroprocessorofaproblem,lightinganLED,implementingasoftstartfeaturetolimitmotorstartupcurrents,orlatchingthesystemoffatthefirstsignofaproblemorafterafixeddelay.CONTROLFEATURESTheMC33035scircuitrycontainsallbutoneofthemajorelementsforclosedloopspeedcontrol.TheonlypiecelackingisonethatmonitorsmotorRPMandgeneratesasignalproportionaltomotorspeed,afunctionwhichtraditionallyhasbeenthedomainofatachometer.Onceprovidedwithamotorspeedsignal,theMC33035shighperformanceerroramplifieranditsinternaloscillatorformthelastmajorlinksinthecontrolloop.TheMC33035son-boardoscillatoroperatesatafrequencysetbyanexternalR-C.EachcyclecapacitorCT(Figure2)ischargedfromthereferenceoutputthroughresistorRTandthenrapidlydischargedthroughaninternaltransistor.Figure3showshowtheresultingsawtooth-shapedwaveformaffectsoutputpulsewidth.TheMC33035hastremendousflexibilitysinceitworkswellwithvariousHalleffectsensorspacingsandthemostcommonbrushlessmotorwindings.AnMC33035basedsystemcaneasilybealteredtodrivemotorswitheitherdeltaorwyeconnectedthreephasewindingswith60or120degreeHalleffectsensorspacing.Figure3.TheMC33035sPulseWidthModulatorTimingDiagramAcompanionIC,theMC33039,isalowcost,spacesavingalternativetoatachometer.AteachpositiveornegativetransitionoftheHalleffectsensorstheMC33039generatesapulsewithafixedontime.Theoutputsignalcanthenbefilteredtoobtainavoltageproportionaltomotorspeed.DesignofanMC33035/39basedsystemshouldbeginwithsettingthesystemtiming,whichoriginatesintheMC33039.ASSEMBLINGTHEPIECESSelectionoftimingcomponentsfortheMC33039isbasedonthedesiredmaximummotorRPM.Forthemotorusedinthisapplication(PittmanELCOM5112)therearetwoelectricaldegreesforeverymechanicaldegreesincethepermanentmagnetontherotorhastwopairsofpoles.Therefore,foreverymechanicalrevolutioneachHalleffectsensordeliverstwopulsesandthethreesensorsgeneratesixpulses.TheMC33039generates12,oneforeachrisingandfallingedge.Foragivenmaximummotorspeed,theoutputpulsewidthhasamaximumlimit.Ifweassumeamaximumdesiredspeedof5000RPM,whichisabout83revolutionspersecond,theMC33039willgenerate83x12,or1000pulsespersecond.The1kHzfrequencydictatesthatthemaximumpulsewidthmustbelessthan1ms.FromFigure4,whichistakenfromtheMC33039sdatasheet,onecandeterminethatR1andC1valuesof43kand22nFresultinapulsewidthof950s.TosetthesystemPWMfrequency,refertotheMC33035sdatasheet.ThereitshowsthatsettingR2andC2to5.1kand0.01Fgivesanominalpulsewidthmodulationfrequencyof24kHz,justabovetheaudiblerange.BothinputsandtheoutputoftheMC33035serroramplifierareaccessibletoaccommodatevariouscontrolmethods.Foropenloopcontrolyoucanfeedareferencesignalproportionaltodesiredspeedintotheerroramplifiersnon-invertinginput.Theerroramplifieristhenconfiguredasaunitygainvoltagefollowerbyconnectingitsinvertinginputtoitsoutput.TheerroramplifiersoutputisthencomparedtotheoutputoftheoscillatortoobtainaPWMsignalproportionaltodesiredmotorspeedunlessthecontrolloopisoverriddenbyanovercurrentorfaultcondition.ForclosedloopcontroloneapproachistofiltertheMC33039soutputwithalowpassfiltertogenerateavoltageproportionaltomotorspeedandfeedtheresultingsignalintotheinvertinginputoftheMC33035scomparator.Asignalproportionaltodesiredmotorspeeddrivesthenon-invertinginput,andtheratiooftheinputandfeedbackresistorsR3andR4controlgain.Inthisdesign,lowpassfilteringandgeneratingtheerrorsignalarecombinedbyusingfeedbackcapacitor,C3.Ideally,theintegrator/erroramplifiershouldproducearipplefreeoutputevenatlowmotorspeeds.Todosoatverylowspeedsreducessystemresponsetime,however.Componentvaluesmustbeadjustedaccordingtotherotorsandloadsinertiaandfriction.Inthisparticularapplicationthevalues1Mand0.1F(t=100ms)givegooddynamicresponseandstability.Whenmotorspeedfallsbelowthedesiredspeed,theMC33035extendstheoutputpulsewidthtothedrivetransistors.Whenmotorspeedisgreaterthanthedesiredspeed,thedutycycledecreases.However,iftheinputsignalabruptlydemandsamuchlowerspeed,thedutycyclecouldfalltozeroandthemotorwouldcoasttodesiredlowspeed.Therefore,sincetheMC33035hasnoprovisiontodynamicallybrakethemotorandthuscontrolrapiddeceleration,itisbestsuitedforapplicationswhichhavealargefrictionalloadorthosethatdonotrequireacontrolled,abruptdeceleration.TheschematicofaclosedloopbrushlessmotorcontrolsystemisshowninFigure5.ShowninFigure11isacompletedbrushlessmotorcontrol.Figure4.foutPulseWidthversusTimingResistorFigure5.RepresentativeBlockDiagramofMC33039三种关于无刷电机控制器设计的解决方案由KimGauen和JadeAlberkrack的设计近来，希望利用直流无刷电机特性的电机控制器设计者面临着一个很大的难题。没有控制信息系统的设计，它的解码数据来自霍尔效应传感器，它可以执行所有的辅助功能，例如正反转控制，过流停止，低压停止，过热关闭等许多功能。给它使用分立元件是一个可选折的办法，但是这些分立元件常常要占用很大的电路板面积，尤其是如果控制部件是被布置在电动机内部的情况下。另一个问题所在是有效功率晶体管的不够充分的性能。双极功率管不是有利的，因为它们不能被从开始控制的集成电路直接地驱动，还有用的达林顿管额定电压有时会太高。功率场效应晶体管似乎是个理想得选折，因为他们很容易被驱动，而且效率高，价格便宜。然而，设计者有时会因为它们而不能禁得住在脉冲宽度上调节电机控制器的重压而烦恼。图1.实物与MPM3003图解，一个理想的三相桥式直流无刷电机的驱动图功率模块三个最近引进的设计方案，一个功率模块和两个线性集成块，共同克服半导体的限制，形成一个简单的设计，高性能系统。功率模块是MPM3003，在十二脚的功率块内部是一个三相桥式驱动电路（如图1所示）。在它上面的是三个晶体管，是0.28欧姆的P沟道功率场效应晶体管，下面的三个是0.15欧姆的N沟道功率场效应晶体管。六只晶体管的漏源极额定电压均是60伏特。他们的三个外观使新出来的场效应晶体管比原来的管子更粗糙。一、在交换场效应管内部的二极管时，他们能承受更大的电压。二、新出来的场效应管受到小的瞬时的漏源电压时所导致的失败的影响。三、在MPM3003内部的场效应晶体管有个很小的栅源极断电压40伏，代替了工业标准20伏电压。一个大的断电压不仅可以改善静电流出和没有预知的栅源极电压接地，而且还可以延长常规运行电压下的晶体管的寿命。小型MPM3003的独立包装是它另一个主要的好处。与使用六对TO-220s相比较而言，使用MPM3003要更加容易并且只要一半的板面积。如图1所示，装配是从焊接的模子开始，连接在板子上面的镀铜上，这是个来自TO-220制造业的知名技术。此设计通过散热分布器减少热变电阻值。在一个独立的装配上，用铝覆盖绝缘材料，这是个环氧薄膜。要更容易的连接板面装配到铝片上，在环氧薄膜上的铜箔形成一个又一个单独的模块。在成型之前，铝与铜箔被结合在一起。这样的设计提供了低热量阻抗并且避免了陶瓷隔离材料的易碎性并降低了它的费用。图2MC33035的代表性结构图主体这里主要的系统是用摩托罗拉公司的MC33035和维持芯片MC33039。他们是显著简化无刷电动机控制系统和减少必需的电路板面积和零件个数的新的集成模块的例子。增加它的好处是有了更短的设计时间和被改进的系统性能。MC33035是作为直流无刷电机控制系统控制中心的一个24脚的线性集成电路模块。MC33035的主要任务是解码霍尔效应传感器的信号和电子换向马达产生的逻辑。换向逻辑内部是六个输出驱动器，它包括桥上部分的三个NPN场效应晶体管和三个控制装置的图腾柱驱动器。开放收藏品输出可达到50安培，如果想得到一个简单的接口，用一个另外的电路，它能控制大功率应用N沟道场效应，或者P沟道场效应经晶体管。因为三个较低的图腾柱输出能产生或降低100毫安，他们能直接的输出功率场效应管。错误的操作MC33035能查出并处理几个类型的错误。过载电流侦察的一个普通的方法是，将较低的三个晶体管的源极连在一起，通过直流感应电阻器使他们回到负电源。与过载电流成比例的感应电压，被反馈到MC33035上的比较器。比较器再供给RS双稳态多谐振荡器，它确保一旦有过载电流就被查出。输出驱动器支路功率晶体管使震荡器循环。没有内在的双稳态多谐震荡器，过电流保护回路就会在比较器的门限迅速的循环地开与关，导致过多的功率晶体管发热。除了过流管理之外，如果下面的三个情况中的任一个发生时，MC33035提供低压驱动使输出晶体管停止工作。一是用不足的电压操作集成电路。二是用不足的电压驱动功率场效应管的门极。三是，当MC33035不能承受它的6.25伏参考电压时，输出驱动器关断功率晶体管。无效的霍尔效应信号或过高的温度也将导致门关断。当任何一个错误的情况发生时，一个降低16安培的NPN晶体管能使出错的输出脚的电压变低。对错误输出的潜在的用途包括警告问题的微处理器，点亮发光二极管，实现一个平稳启动特征来限制电动机的启动电流，或者在出现问题时与在固定延迟以后，关闭系统。控制作用MC33035的电路几乎包含适合闭环速度控制的任一个主要元素。唯一的接合不足是电机可靠性能测定监控和产生一个与电机速度成比例的信号，它的主要功能是测出转速计的转动范围。一旦拥有了电机速度信号，MC33035的高性能误差信号放大器和它的内部振荡器型式对于操纵系统维持在主要的连接。MC33035上面的振荡器在隔开外部的R-C频率时运转起来。每个周期电容CT（如图2所示）被通过电阻RT的参考输出充满电，然后又通过内部晶体管迅速的放