Maneuvering and Vibration Reduction of Three-axis Stabilized Flexible Spacecrafts Using Variable Structure Strategies with Improved Adaptation Law

摘要

This paper proposes a robust control algorithm for stabilization of a three-axis stabilized flexible spacecraft in the presence of model uncertainty, external disturbances and control input nonlinearities. This control algorithm is based on variable structure output feedback control design technique, and explicitly accounts for the control input nonlinearities in the stability analysis. Asymptotically and exponentially stable design methods are investigated for constructing the controller to stabilized uncertain system with input nonlinearities. The proposed two kind of the controller ensures the global reaching condition of the sliding mode of the spacecraft dynamics system. Moreover, in the sliding mode, the investigated dynamics system still bears the insensitivity to the uncertainties and disturbances as the system with linear input. An additional attractive feature of the control method is that the structure of the controller is independent of the elastic mode dynamics of the spacecraft, since in practice the measurement of flexible modes is not easy or feasible. It is also shown that an adaptive version of the proposed controller is achieved through releasing the limitation of knowing the bounds of the uncertainties and perturbations in advance. The adaptive variable structure output feedback control law results in substantially simpler stability analysis and improves overall response. In addition, a modified adaptation control law is given for the upper bound on the uncertainty to improve the adaptive performances such that a new controller is designed which can guarantee the boundedness of the closed-loop system and can be described as a combination of sliding mode control law and S-modification adaptive law. Numerical simulations show that the precise attitude control and vibration suppression can be accomplished using the derived controller for both cases with and without adaptive control.