Research On Fault Diagnosis And Fault Tolerant Control For Spacecraft Attitude Control System

With the development of space missions, the structure and function of the spacecraft is becoming more and more complicated. Meanwhile, the number of sensors and actuators increases continuously. However, due to some objective factors, such as the standard of machining and techniques, and cost control, the probability of fault occurrence in spacecraft also increases. As a result of that, the reliability of the spacecraft system will decrease. Fault detection and diagnosis(FDD) and fault-tolerant control(FTC) is a new way in promoting the reliability and safety of spacecraft. In this dissertation, the FDD and FTC technique for spacecraft attitude control system are studied preliminarily. The main contributions are included as follows.An FDD algorithm based on the sliding mode observer is investigated. Firstly, the principle of FDD based on the sliding mode observer is introduced, and the design method of Walcott-Zak observer is presented. Secondly, based on the Walcott-Zak observer model, a fault detection observer based on the nonlinear attitude dynamics is designed, and the residual signal is used to detect the actuator fault. In order to judge the fault type and estimate the severity of actuator fault on-line, a fault reconfiguration algorithm is investigated without the external disturbance, and the fault reconfiguration is accomplished based on the principle of equivalent injection.A fault reconfiguration algorithm based on the adaptive sliding mode observer is studied. When spacecraft operates on the orbit, the effects of the external disturbance could not be ignored. Thus, based on the attitude dynamics with disturbances, a fault reconfiguration algorithm based on the adaptive sliding mode observer is designed. By introducing the adaptive method, the algorithm can estimate the actuator fault on-line. Moreover, the influence of the external disturbance can be eliminated with the discontinuous term produced by the sliding mode method. Consequently, the actuator fault can be reconfigured precisely.An adaptive fault tolerant controller based on the adaptive terminal sliding mode is discussed. Considering that the upper bounds of the external disturbance are known and the actuator hardware is redundant, an active fault tolerant control method based on the terminal sliding mode surface is designed. This method not only can ensure the capability of fault tolerant, but also can guarantee that the system states convergent to the equilibrium point in finite time. However, the conventional terminal sliding mode surface is very sensitive to the initial system errors. Moreover, the inertia matrix is time-varying and the upper bounds of the external disturbance are not always easy to obtain. Thus, an adaptive terminal sliding mode fault tolerant controller is discussed. By introducing the technique of adaptive parameter adjusting, this controller not only has the capability of fault-tolerant, but also owns the robustness for the disturbances.A passive fuzzy fault tolerant controller based on the terminal sliding mode is developed. Considering that the information of the actuator faults is unknown, an adaptive fuzzy terminal sliding fault tolerant controller is designed. By employing the fuzzy approximate technique, the problem of unknown nonlinear system dynamics is explicitly addressed in the controller design. Meanwhile, by employing the adaptive method to estimate the upper bounds of the approximate errors and the external disturbances, the controller gets rid of the actuator fault information. Moreover, the fast terminal sliding mode surface accelerates the convergent rate of closed-loop system and promotes its robustness for the initial errors.The FDD and FTC methods presented in this dissertation have the favorable robustness for different actuator faults and can accomplish the fast and high precision attitude control missions, and these methods can promote the reliability of spacecraft. The conclusions in this dissertation can provide references and technique supports for further research in this field.