Robust Nonlinear Attitude Control Algorithms Research For Flexible Spacecraft

With the development of aerospace technology, attitude control problem of flexible spacecraft has received considerable attention and comprehensive investigation ever since the fifties of the last century. Attitude control system of spacecraft is a coupling and uncertain nonlinear system with multi-input and multi-output. In order to accomplish the attitude control missions, the control law should have robust capability to attenuate disturbances and be able to adapt to parameters. Under this background, the robust control algorithms of flexible spacecraft are deeply studies on theory and application for the attitude control system of spacecraft in the dissertation, which is funded by the Research Fund for the Doctoral Program of Higher Education of China Item—"Large flexible multi-bodies structure spacecraft active vibration control technology"(20050213010) and National Natural Science Foundation of China—"Study on Active Vibration Control of Flexible Spacecraft"(60774062). The main contents of this dissertation are as follows:A robust control scheme based on dynamic output feedback control is proposed for the attitude control problem of a flexible spacecraft in the presence of parametric uncertainty, external disturbances. Firstly, the controller design of state feedback is proposed for the dynamic model of flexible spacecraft; Furthermore, the robust dynamic output feedback method is proposed. Moreover, an adaptive attitude controller is presented to decrease the conservativeness and the stability of the system is analyzed via Lyapunov method. The designed controller is independent with the model parameters, i.e., it is independent with the inertial parameters of flexible spacecraft, and it doesn't have to know the upper bound of the out disturbance torque. Numerical simulations are performed to show that rotational maneuver and vibration suppression are accomplished in spite of the presence of disturbance torque and parametric uncertainty.A robust control algorithm for stabilization of a flexible spacecraft is investigated in the presence of parametric uncertainty, external disturbances and control input saturation/dead-zone nonlinearity. Firstly, the design process of the variable structure output feedback controller for a class of uncertain system is presented. Furthermore, the existent condition of sliding and the asymptotically and exponentially stable design methods are proposed for constructing the controller to stabilize uncertain system. Moreover, the developed controller is achieved through adaptive variable structure output feedback control without the limitation of knowing the bounds of the uncertainties and perturbations in advance and the existence of the sliding surfaces is analyzed via Lyapunov method. The simulation results show that the precise attitude control and vibration suppression can be accomplished using the derived controller for both cases with and without adaptive control, and it is robust to the uncertainty of the parameters.For the large angle attitude maneuvering problem of flexible with inertia parameter uncertainty, disturbances, a hybrid robust active control scheme is presented combined with the active vibration suppression technique based on piezoelectric materials. Firstly, based on T-S fuzzy control technique, a robust fuzzy attitude control scheme is given, in which the asymptotic stability is shown using a Lyapunov analysis. For actively suppressing the induced vibration, strain rate feedback control methods are provided by using piezoelectric materials as additional sensors and actuators such that the vibration can be damping down quickly. Secondly, a hybrid robust control method based on fuzzy logic compensator is provided. Compared with the T-S fuzzy controller, it has less computation cost. Thirdly, another hybrid robust control method is proposed based on sliding and active vibration control technique. In addition, to avoid chattering, pulse-width pulse-frequency (PWPF) modulation is adopted for the thruster control, which makes the thrusters to be operated in a close to linear manner and also can suppress the relatively large amplitude vibrations excited by, for example, rapid maneuver. The simulation results demonstrate the feasibility and effectiveness of the proposed method.A robust active control approach is presented for the attitude tracking control and vibration damping of a spacecraft with actor dynamics. Firstly, based on the sliding mode control (SMC) and backstepping technique, a new attitude tracking controller is derived to control the attitude motion of spacecraft, the stability of the system is analyzed via Lyapunov method and the reaction wheel dynamics is also considered from the real applications point of view. The whole design process is divided into two steps: the first step is to use sliding control technique to design suppositional adaptive variable structure controller; and the second step is to design attitude tracking controller based on SMC and backstepping technique. Numerical simulations are performed to show that both tracking maneuver and vibration suppression can be accomplished effectively.