Dynamic Modeling And Attitude Control For The Flexible Satellite

Modern spacecraft is increasingly showing the features of large-scale, low rigidity and large flexibility. In orbit maneuvering operation and when influenced by the environmental torque, the flexible appendages are easily excited vibration, which is last for a long time because of its low damping. Both antenna shape accuracy is reduced and the playload work is influenced by the elastic vibration,reducing the accuracy and stability of the satellite attitude. In this dissertation, the high-precision, high stability attitude control for a communications satellite is deeply studied,. the main contents are:A class of clusters satellite with the characteristic of center rigid body plus flexible appendages, its dynamic equations is derived on Lagrangian principle, and the flexible coupling coefficient of simplified solar panels are analyzed using assumed mode method and finite element method, respectively.In view of the vibration of the satellite accessories, positive position feedback and speed feedback method is used to design active vibration compensator which is based on piezoelectric ceramics, respectively. A comparison is made between this two methods. Numerical simulation shows, active vibration compensator can effectively eliminate the unstable poles of the satellite dynamics, inhibiting the attachment of vibration fastly.To achieve high accuracy, high stability of the satellite attitude precision, Active Disturbance Rejection Controller(ADRC) is designed. In order to suppress the vibration of antenna in small angle attitude maneuver, the transition process consist of two parabolic path angles is arranged. Error motion equation of the second order Extended State Observer(ESO) is derived. Damping ratio and bandwidth is proposed, the nature of the relationship between the state error coefficient and ESO dynamic characteristics is illustrated in physical sense. New configuration methods of ESO coefficients is proposed. All of this such as transition process and linearization via dynamic compensation,and using of non-linear control law guarantees the excellent quality of controller, and ADRC can effectively compensates disturbances and ensure rapidity, accuracy and stability of the attitude maneuver.Due to the robustness of sliding mode control, combined with the superiority ability of ESO to compensate disturbance dynamically, a sliding mode control law based on the ESO is designed. Considering the failure or satellite steady-state operation to extend the life of gyroscope, a third-order ESO is designed to estimate angular velocity and total interference. For the third-order ESO, error equations of motion is constructed, damping ratio and bandwidth is proposed and dynamic characteristics of error is analyzed, the stability and convergence of the error motion is discussed. The method of parameters configuration is proposed. Numerical simulation results show that the sliding mode control based on ESO achieves the same control accuracy with ADRC approximately.