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1、交流伺服電機的驅(qū)動技術(shù)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
