AAS_98-063_HIGH_FIDELITY_MATHEMATICAL_MODELING_OF_REACTION_WHEEL_PERFORMANCE.pdf

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1、-AAS98-063IDGHFIDELITYMAmEMATICALMODELINGOFREACTIONWHEELPERFORMANCEBillBialke*Ac~uratemathematicalmodelsofcomponentsareanessentialelementofattitudecontrolsystemdesign,analysis,andsimulation.Thispaperpres~ntsadetailedmathematicalmodelofareactionwheel,cont

2、ainingrelationshipsforpredictingreactiontorquesanddragtorques,powerconsumptionanddisturbances.PerformancecoefficientsareincludedforITHACO'sTypeAandTypeBreactionwheels.Disturbancesfromreactionwheelscontributetospacecraftpointingjitterandpotentiallygenerat

3、emicrophonicsinpayloadinstruments.Definitionsandquantitativeexamplesareprovidedforthevarioustypesofreactionwheeldisturbancesduetosourcessuchasflywheelimbalance,bearingstiction,bearingtorquenoiseandmotortorquerippleandcogging.INTRODUCTIONReactionwheelsare

4、momentumexchangedeviceswhichprovidereactiontorquetoaspacecraftandstoreangularmomentum.Mathematicalmodelingofthesedevicescancons.istmerelyofanapplicationofNewton'slaws'.butadditionaltermsareincludedheremtoassessperformancebeyondthenominalspeedrange,andasa

5、fun~tJOnoftemperatureandbusvoltage.Inaddition,reactionwheeldisturbancetermsarederivedforassessingspacecraftjitter..Areactionwheelconsistsofarotatingflywheel,typicallysuspendedon?allbeanngs,anddrivenbyaninternalbrushlessDCmotor:Ac~tawayviewofatypicalITHAc

6、areactionwheelisshowninFigure1.Amotordnverdeliverscommutatedcurrenttothemotorproportionaltoaninputvoltagecommandedbytheuser.Figure1CutawayViewofITHACOReactionWheel-------------ITHACOSpaceSystems.Inc.,950DanbyRoad.Suite100.Ithaca.NewYork14850.483NEARLYIDE

7、ALREACTIONWHEELAfundamentalblockdiagramofanearlyidealreactionwheelisshowninFigure2.Thesoleinputisatorquecommandvoltagewhichcontrolsmotorcurrent,andthusmotortorque.Frictiontorqueistheonlylosswhichissubtractedfromthemotortorque.Anidealreactionwheelwouldhav

8、enofrictiontorque,thusthediagramrepresentsa'nearly'idealwheel.ReactionTorquet------~rzTorqueCommandVolttlgeFigure2NearlyIdealReactionWheelBlockDiagramTheangularmomentumstoredintheflywheel,Hz,istheproductoftheflywheelinerti