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1、英文资料ThecontraltechniquesdrivesandcontralshandbookChapterA4Torque,speedandpositioncontrolA4.1GeneralprinciplesA4.1.1TheidealcontrolsystemManyapplicationsexistwheresomethinghastobecontrolledtofollowareferencequantity.Forexample,thespeedofalargemotormaybesetfromalow-powercontrolsignal.Thiscanbeach
2、ievedusingavariable-speeddriveasdescribedinthefollowing.Ideally,therelationshipbetweenthereferenceandthemotorspeedshouldbelinear,andthespeedshouldchangeinstantlywithchangesinthereference.AnycontrolsystemcanberepresentedasinFigureA4.1b,withaninputreferencesignal,atransferfunctionFandanoutput.For
3、thesystemtobeideal,thetransferfunctionFwouldbeasimpleconstant,sothattheoutputwouldbeproportionaltothereferencewithnodelay.FigureA4.1Variable-speeddriveandmotorA4.1.2Open-loopcontrolUnfortunately,thetransferfunctionofmanypracticalsystemsisnotaconstant,andsowithoutanyformoffeedbackfromtheoutputto
4、correctforthenon-idealnatureofthetransferfunction,theoutputdoesnotfollowthedemandasrequired.Usinganinductionmotorsuppliedbyasimpleopen-loopvariable-speeddriveasanexample,thefollowingillustratessomeunwantedeffectsthatcanoccurinpracticalsystems:Speedregulation.Theoutputofasimpleopen-loopdriveisaf
5、ixedfrequencythatisproportionaltothespeedreference,andsothefrequencyappliedtothemotorremainsconstantforaconstantspeedreference.Thespeedofthemotordropsasloadisappliedbecauseoftheslipcharacteristicofthemotor,andsothespeeddoesnotremainattherequiredlevel.Instability.Itispossibleundercertainloadcond
6、itionsandatcertainfrequenciesforthemotorspeedtooscillatearoundtherequiredspeed,eventhoughtheappliedfrequencyisconstant.Anothermajorsourceofinstabilityinrotating12mechanicalsystemsislow-losselasticcouplingsandshafts.Non-linearity.Therearemanypossiblesourcesofnon-linearity.If,forexample,themotori
7、sconnectedtoagearbox,thespeedattheoutputofthegearboxcouldbeaffectedbybacklashbetweenthegears.Variationswithtemperature.Someaspectsofthesystemtransferfunctionmayvarywithtemperature.Forexample,theslipofaninductionmotorincreasesasthe
