交流伺服电机的驱动技术.doc

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1、交流伺服电机的驱动技术TheamplifierforACthree-phasemotorsincludesapulse-widthmodulationcircuitforvoltage,current,andfrequencycontrol.Figure11-81showsanexampleofthistypeofamplifier.Fromthediagramyoucanseethatthiscircuitisdesignedspecificallyforathree-phasetrapezoidalmotor.Thetransistorsintheamplifierar

2、econnectedinanH-bridgeconfiguration.Themotorwindingsareconnectedasathree-phasewyewithnoexternalwiresconnectedtothewyepoint.ThistypeofmotorisalsocalledastarconnectionwhenitisusedwithbrushlessACservomotors.ThedrivelogicandPWMswitchingcontrollerisshowninthediagramasablockthatisidentifiedasalo

3、gicandPWMcircuit.Thisblockshowssixarrowspointingawayfromitandpointingtothetransistors.Thesearrowsrepresentthesixcircuitsforthebaseofeachofthesixtransistors.TheblockbelowthePWMcircuitrepresentsthecurrent-sensingpartoftheamplifier.Thissectionoftheamplifierusesarecirculatingchoppersystemtocon

4、trolthecurrentinamannerthatissimilartothechoppercircuitintheDCamplifier.Thesignalsforthissectionoftheamplifiercomefromthevoltagethatisdevelopedacrosstheseriesresistorsconnectedbetweenthetransistorsectionandthemotors.Asyouknow,theamountofcurrentflowingtothemotorwilldeterminetheamountofvolta

5、gedropacrosstheseresistors.Thisamplifierhasavelocityamplifierthatreceivestheoriginalcommandsignalfortheamplifierandthevelocityfeedback.Theopampprovidesanoutputthatrepresentsthedifference(error)betweenthecommandsignalandthefeedbacksignal.Theoutputofthevelocityampissenttothetorqueamp,whereit

6、iscombinedwiththefeedbackfromthecurrent-sensingblock.TheoutputfromthisopampissenttothelogicandPWMcircuitblockwhereitactsasthecommandsignal.Thepositionencoderprovidesthefeedbacksignalforthisblock.Thismeansthatthevelocityandpositionamplifiersareactuallyaclosed-loopsystemwithinaclosed-loopsys

7、tem.Thegainforeachoftheseamplifiersmustbetunedsothatthesystemhasthebesttorqueresponseandsmoothaccelerationanddeceleration.FIGURE11-81AnACservodriveamplifierspecificallydesignedtooperatewithanACtrapezoidalbrushlessservomotor. Thefeedbackmechanismisgenerallyabru