基于C51兼容微处理器单片机的PWM控制器设计.docx

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

基于C51兼容微处理器单片机的PWM控制器设计

——外文翻译

英文原文

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-timegeneratorwillalsobediscussedinsection5for