基于C51兼容微处理器单片机的PWM控制器设计.docx
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基于C51兼容微处理器单片机的PWM控制器设计.docx
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基于C51兼容微处理器单片机的PWM控制器设计
DesignofPWMControllerinaMCS-51CompatibleMCU
Author.Yue-LiHu,WeiWangMicroelectronicResearch&DevelopmentCenter
CampusP.O.B.221,149YanchangRd,Shanghai200072,China
Introduction
PWMtechnologyisakindofvoltageregulationmethodbycontrollingtheswitchfrequencyofDCpowerwithfixedvoltagetomodifythetwo-endvoltageofload.Thistechnologycanbeusedforavarietyofapplicationsincludingmotorcontrol,temperaturecontrolandpressurecontrolandsoon.InthemotorcontrolsystemshownasFig.1,throughadjustingthedutycycleofpowerswitch,thespeedofmotorcanbecontrolled.AsshowninFig.2,underthecontrolofPWMsignal,theaverageofvoltagethatcontrolsthespeedofmotorchangeswithDuty-cycle(D=t1/TinthisFigure),thusthemotorspeedcanbeincreasedwhenmotorpowerturnon,decreasedwhenpowerturnoff.
Fig.1:
TheRelationshipbetweenVoltageofArmatureandFig.2ArchitectureofPWMModule
Therefore,themotorspeedcanbecontrolledwithregularlyadjustingthetimeofturn-onandturn-off.Therearethreemethodscouldachievetheadjustmentofdutycycle:
(1)Adjustfrequencywithfixedpulse-width.
(2)Adjustbothfrequencyandpulse-width.(3)Adjustpulse-widthwithfixedfrequency.
Generally,therearefourmethodstogeneratethePWMsignalsasthefollowing:
(1)Generatedbythedevicecomposedofseparatelogiccomponents.Thismethodistheoriginalmethodwhichnowhasbeendiscarded.
(2)Generatedbysoftware.ThismethodneedCPUtocontinuouslyoperateinstructionstocontrolI/OpinsforgeneratingPWMoutputsignals,sothatCPUcannotdoanythingother.Therefore,themethodalsohasbeendiscardedgradually.(3)GeneratedbyASIC.TheASICmakesadecreaseofCPUburdenandsteadyworkgenerallyhasseveralfunctionssuchasover-currentprotection,dead-timeadjustmentandsoon.Thenthemethodhasbeenwidelyusedinmanykindsofoccasionnow.(4)GeneratedbyPWMfunctionmoduleofMCU.ThroughembeddingPWMfunctionmoduleinMCUandinitializingthefunction,PWMpinsofMCUcanalsoautomaticallygeneratePWMoutsignalswithoutCPUcontrollingonlywhenneedtochangeduty-cycle.Itisthemethodthatwillbeimplementedinthispaper.
Inthispaper,weproposeaPWMmoduleembeddedina8051microcontroller.ThePWMmodulecansupportPWMpulsesignalsbyinitializingthecontrolregisterandduty-cycleregisterwiththreemethodsjustmentionedabovetoadjustthedutycycleandseveraloperationmodestoaddflexibilityforuser.
ThefollowingsectionexplainsthearchitectureofthePWMmoduleandthearchitecturesofbasicfunctionalblocks.Section3describestwooperationmodes.Experimentalandsimulationresultsverifyingpropersystemoperationarealsoshowninthatsection.Dependingonmodeofoperation,thePWMmodulecreatesoneormorepulse-widthmodulatedsignals,whosedutyratioscanbeindependentlyadjusted.
ImplementationofPWMmoduleinMCU
OverviewofthePWMmodule
AblockdiagramofPWMmoduleisshowninFig.3.Itisclearlyfromthediagramthatthewholemoduleiscomposedoftwosections:
PWMsignalgeneratoranddead-timegeneratorwithchannelselectlogic.ThePWMfunctioncanbestartedbytheuserthroughimplementingsomeinstructionsforinitializingthePWMmodule.Inparticular,thefollowingpowerandmotioncontrolapplicationsaresupported:
•DCMotor
•UninterruptablelPowerSupply(UPS)
·ThePWMmodulealsohasthefollowingfeatures:
•TwoPWMsignaloutputswithcomplementaryorindependentoperation
•Hardwaredead-timegeneratorsforcomplementarymode
•DutycycleupdatesareconfigurabletobeimmediatedorsynchronizedtothePWM
Fig.3ArchitectureofPWMModule
Detailsofthearchitecture
PMWgenerator
Thearchitectureofthe2-outputPWMgeneratorshowninFig.4isbasedona16-bitresolutioncounterwhichcreatesapulse-widthmodulatedsignal.Thesystemissynthesizedbyasystemclocksignalwhosefrequencycanbedividedby4timesor12timesthroughsettingthevalueofT3MforPWM0orT4MforPWM1inthespecialregisterPWMCONasshowninFig.4.ToPWM0generator,theclockto16-bitcounterwillbepre-dividedby4timesbydefaultwhenT3Missettozero.Andtheclockwillbedividedby12timeswhenT3Missetto1.ThisisalsotrueforPWM1.TheotherbitsinPWMCONareexplainedindetailinTable1.
Fig.4BitMappingofPWMCON
Table1:
TheBitDefinitioninPWMCON
Channel-selectlogic
ThefollowFig.5showsthechannel-selectlogicwhichisusefulinComplementaryMode.Fromthisdiagram,itiscleartoknowthatsignalCPandCPWMcontrolthesourceofPWMHandPWML.Andthedetailsaboutthetwocontrolsignalswillbediscussedinthesection3,andthearchitectureofdead-timegeneratorwillalsobediscussedinsection5forthecontinuityofComplementaryMode.
Fig.5DiagramofChannel-selectLogic
OperationModeandSimulationResults
Thedesignhastwooperationmodes:
IndependentModeandComplimentaryMode.BysettingthecorrespondingbitCPWMinregisterPWMCONshowninFig.6usercanselectoneofthetwooperationmodes.WhenCPWMissettozero,PWMmodulewillworkinIndependentMode,whereas,PWMmodulewillworkinComplimentaryMode.Inthefollowingofthissection,thetwooperationmodewillbeexplainedrespectivelyindetailandthesimulationresultsofthePWMmodulefromtheSynoposysVCSEDAplatformwhichverifythedesignwillalsobeshown.
IndependentPWMOutputMode
AnIndependentPWMOutputmodeisusefulfordrivingloadssuchastheoneshowninFigure6.AparticularPWMoutputisintheIndependentOutputmodewhenthecorrespondingCPbitinthePWMCONregisterissettozero.Inthiscase,two-channelPWMoutputsareindependentofeachother.ThesignalonpinPWM0/PWMHisfromPWM0generator,andthesignalonpinPWM1/PWMLisfromPWM0generator.Theseparatecaseisachievedbythechannel-selectlogicshowninFig.6.ThePWMI/Opinsaresettoindependentmodebydefaultuponadvicereset.Thedead-timegeneratorisdisabledintheIndependentmode.ThesimulationresultisshowninFigure6asthefollowingFig.6Tr4andtr3arerunbitstoPWM0andPWM1,respectively.Actually,fromthisdiagram,PinP1[5]/P1[4]ofMCUisusedforPWMH/PWMLornormalI/O,alternatively.
Fig6theWaveformofPWMOutputsinIndependentMode
ComplementaryPWMOutputMode
TheComplementaryOutputmodeisusedtodriveinverterloadssimilartotheoneshowninFigure7.ThisinvertertopologyistypicalforDCapplications.InComplementaryOutputMode,thepairofPWMoutputscannotbeactivesimultaneously.ThePWMchannelandoutputpinpairareinternallyconfiguredthroughchannel-selectlogicasshowninFigure7.Adead-timemaybeoptionallyinsertedduringdeviceswitchingwherebothoutputsareinactiveforashortperiod.
Fig7:
TypicalLoadforComplementaryPWMOutputs
TheComplementarymodeisselectedforPWMI/OpinpairbysettingtheappropriateCPWMbitinPWMCON.Inthiscase,PSELisineffect.PWMHandPWMLwillcomefromPWM0generatorwhenPSELissettozero,whenthesignalsfromPWM1generatorisuseless,whereasPWMHandPWMLwillcomefromPWM1generatorwhenPSELissetto1,whenthesignalsfromPWM0generatorisuseless.IntheprocessofproducingthePWMoutputsinComplementaryMode,thedead-timewillbeinsertedtobediscussedinthefollowingsection.
Dead-timeControl
Dead-timegenerationisautomaticallyenabledwhenPWMI/OpinpairisoperatingintheComplementaryOutputmode.Becausethepoweroutputdevicescannotswitchinstantaneously,someamountoftimemustbeprovidedbetweentheturn-offeventofonePWMoutputinacomplementarypairandtheturn-oneventoftheothertransistor.The2-outputPWMmodulehasoneprogrammabledead-timewith8-bitregister.ThecomplementaryoutputpairforthePWMmodulehasan8-bitdowncounterthatisusedtoproducethedead-timeinsertion.AsshowninFigure8,thedeadtimeunithasarisingandfallingedgedetectorconnectedtoPWMsignalfromoneofPWMgenerator.ThedeadtimesisloadedintothetimeronthedetectedPWMedgeevent.Dependingonwhethertheedgeisrisingorfalling,oneofthetransitionsonthecomplementaryoutputsisdelayeduntilthetimercountsdowntozero.AtimingdiagramindicatingthedeadtimeinsertionforthepairofPWMoutputsisshowninFigure8a.
Fig8aDead-timeUnitBlockDiagram
Fig.8btheWaveformsofPWMOutputsinComplementaryMode
Conclusions
Inthispaper,wehavedesignedPWMmodulebasedonan8-bitMCUcompatiblewith8051family.Thedesigncangenerate2-channelprogrammableperiodicPWMsignalswithtwooperationmode,IndependentModeandComplementaryModeinwhichdead-timewillbeinserted.ThesimulationresultsontheEDAplatformhaveprovenitscorrectnessandusefulness.
基于C51兼容微处理器单片机的PWM控制器设计
作者:
Yue-LiHu,WeiWa单片机研究与开发中心学院P.O.B.221,149延长路,上海200072,中国
导言
PWM技术,是一种电压调节方法,通过控制具有固定电压的直流电源的开关频率来调整两端负荷电压。
这种技术能用于各种应用包括电机、温度、和压力的控制,等等。
在电机系统中的应用,如图1所示,通过调整电源开关的占空比,来控制电机的速度,如图2所示,平均电压通过改变占空比来控制电机的速度(在图中D=t1/T),这样当电机的电源打开时,它的速度加快,相反,当电源关闭时,速度下降。
图1PWM控制框图图2电压的电枢和占空比之间的关系
所以,通过定期地调整时间的开通和关断来控制电机的转速:
这儿有三种方法可以完成占空比的调整
(1)通过脉宽来调整频率;
(2)通过同时调整频率和脉宽;(3)通过频率来调整脉宽。
一般情况下,有四中方法可以产生PWM信号,正如以下:
(1)由独立逻辑元件组成的装置产生,这种是原始的方法,现在已被淘汰;
(2)通过软件产生,这种方法需要CPU持续操作代码来控制I/O口,以致于CPU不能做其他任何事。
所以,这种方法也渐渐被淘汰;(3)通过ASIC产生,ASIC减少了CPU的负担,并获得了稳定的工作,一般有几个功能,如电流保护、死区时间调整等等;然而
这种方法现在已被广泛用于许多场合;(4)通过单片机的PWM功能模块产生,只有当需要改变占空比的时候CPU失控,这样就不能产生PWM信号,否则通过在单片机里嵌入PWM功能模块,并使这功能初始化,单片机的PWM口也能自动产生PWM信号。
这种方法将在文章中讲述。
在本文中,我们建议在8051单片机里嵌入一个PWM模块。
该PWM模块,通过初始化控制寄存器和寄存器的占空比,可以支持PWM脉冲信号,用刚才提到的上述三种方法调整占空比和几个操作模式,以增加用户弹性。
以下这部分解释PWM模块和基本功能模块的结构。
第三部分描述两种操作模式。
这部分还讲述了实验和仿真的结果验证了合适的系统操作。
通过操作模式,PWM模块产生一个或更多的
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