ACTIVE VIBRATION SUPPRESSION IN SPACECRAFT STRUCTURES BASED ONLQG-CONTROLLER AND KALMAN-OBSERVER

摘要

Within the scope of the frame contract betweenDeutsches Zentrum für Luft- und Raumfahrt e.V.(DLR) and IABG mbH, an applicable controlmethodology for active vibration suppression on aflexible spacecraft structure was designed,implemented, and experimentally verified. The mainobjective of active vibration suppression is to reducethe structural vibrations due to unknown, externalperturbations. A practical application is thestabilization of on-board science payload of earthobservation satellites. According to this application,four piezo-electric actuators were attached to aflexible structure at dedicated positions to introducethe artificial attenuation. The objective was not todesign a new control strategy but to provide apracticable design guide for existing controlmethods which may efficiently be realized in astraight forward manner. In order to find the mostsuitable control strategy to be used in representative,low damped structure applications, several controlalgorithms, in particular. Modal FilteringTechniques (Spatio-Temporal-Filtering) and theLQG (Linear-Quadratic-Gaussian) were investigatedwith respect to performance and robustness. Thecontrol design methodology was based on a highfidelity mathematical model of an existingspacecraft experimental structure, obtained by finiteelement modelling and applying model orderreduction methods in the modal space. This modelwas supplemented by appropriate actuator andsensor models, and validated experimentallyutilizing modal analysis techniques. Prior to theimplementation and experimental validation,numerical simulations of open and closed loopbehaviour using MATLAB/Simulink? wereperformed. The model-based LQG control approachin conjunction with a Kalman filter turned out to bemost suitable with respect to controller-performance, applicability, and stability. In severaliterative steps, the controller design was adapted tothe dynamic properties of the spacecraft trussstructure CEM-3 2, 3, which was provided by NASALangley Research Center. Finally, the applicabilityof the control system was verified in a real worldexperiment on the CEM-3 test bed by using piezo- electric actuators and a configurable dSPACE?controller hardware. As a major result of thisexperimental verification step, attenuations of up to -30dB for the main target modes in the frequencyrange of 20 - 70 Hz were achieved. This paper givesa brief overview on the methodology which wasused to develop and to implement a controller for anactive structural damping. Further on, the difficultiesoccurred during control loop synthesis and theresults achieved are addressed.