Research On Control Allocation Based Fault Tolerant Control For Over-actuated Satellite Attitude Control Systems

With the development of space technology, the structure of satellites is more and more complex,and the task of satellites is more and more difficult. As a result, it brings a high requirement of thestability and the control precision of satellites. In order to improve the stability and the reliability ofsatellite attitude control systems (SACS), satellites are often over-actuated. Avoiding to redesign thecontrol law when faults occur, it is necessary to investigate a fault tolerant control (FTC) methodbased on control allocation (CA) for over-actuated satellites. The thesis is derived from the InnovationFund of Nanjing University of Aeronautics and Astronautics. The research is to study FTCtechnologies based on CA for over-actuated satellites.Depending on the current task and the fault information, a FTC method based on CA is studied tosolve the CA problem for over-actuated satellites. In order to get the output movement of actuatorsfrom the desired control movement, the estimation of distribution algorithm (EDA) is applied. Theperformance of the proposed FTC method based on CA is demonstrated via simulation.In order to solve the tracking control problem for SACS in faulty case, a FTC method based on CAis studied. Firstly, a backstepping control law with disturbance observer is proposed for SACS, wherethere are inertia matrix uncertainty and external disturbance, and the stability of the closed-loopsystem is proved according to Lyapunov theory. Then a dynamic CA based on linear matrix inequality(LMI) method is designed to handle actuator faults, by which FTC can be realized without thereconfiguration of the baseline controller. Finally, the proposed FTC method is applied to aover-actuated satellite in the presence of faults in reaction wheels, and simulation results are presentedto demonstrate the effectiveness of the proposed method.Based on the T-S fuzzy model of SACS, a fuzzy robust control method is studied to handle the poleconstraints. Taking into account the installation matrix uncertainty which is caused by actuator faults,a fault tolerant control allocation method is proposed to solve the CA problem. The effectiveness ofthe proposed method is demonstrated by simulation results.