Research On Disturbance Rejection Of Spacecraft Attitude Control

For any on-orbit satellite, it is inevitable to be influenced by parameter uncertainties and some kinds of disturbance torques. Furthermore, these disturbances are uncertain. Spacecraft attitude control system is a multi-input multi-output coupled uncertain nonlinear system. These uncertainties make the attitude control problem further complicated. Therefore, to accomplish attitude control mission, it is necessary to design attitude control laws with high robustness. On this background, this thesis investigated attitude control algorithms for satellite attitude control system in detail, from both theoretical and applicable aspects, and applied the proposed control schemes to certain satellite control system. The main contents of this thesis are as follows.A feedback linearization control scheme based on differential geometry theory for nonlinear systems is used to design the controller in accordance with the attitude tracking control problem with bounded uncertain disturbance. At first, we established the kinematics model of the spacecraft attitude tracking control. Then we designed the feedback linearization controller through coordinate transformation and state feedback depending on the precise tracking model, by which the tracking and the almost disturbance decoupling performances can be easily achieved. Lyapunov theory is employed to prove that the influence of disturbances on the L2 norm of output tracking error can be arbitrarily attenuated by changing some adjustable parameters in the controller, and that spacecraft attitude tracking system is globally uniformly ultimately bounded stable. Simulation results demonstrate the effectiveness and feasibility of the proposed control scheme.Considering the inertia parameters uncertainty for spacecraft attitude tracking control problem of disturbance rejection, a daptive fuzzy control is combined with feedback linearization control to constitute the hybrid controller, due to the feedback linearization controller based on the precise tracking model, unable to eliminate the error generated by parameter uncertainties and control the spacecraft attitude tracking system effectively. The parameter of the adaptive fuzzy control is adjusted on-line to compensate the attitude tracking error of the uncertain satellite. Simulation results show that precise attitude control is accomplished in spite of the uncertainty in the system.In view of the actual project requirements of controller of simple structure, high precision, and good robustness, a new kind of controller --ADRC, which based on the theory of nonlinear control, is designed. This controller does not depend on the accurate object model. It uses the extended state observer to estimate the system's state, model and interference. Furthermore, with the compounding of nonlinear state error feedback and disturbance compensation, it could achieve a good control of the plant. The simulation results demonstrate that the ADRC has good performance which are mainly represented by high control precision and quick response in solving the nonlinear and coupling spacecraft attitude tracking problem of uncertainties.