Research On Switching Based Fault Tolerant Control For Satellite Attitude Control Systems

To analyze the reconfigurability level of satellite attitude control systems (SACS) in the designphase, and to take fault tolerant control measures to cope with faults before any catastrophicconsequences, are effective ways to increase the reconfigurability level and fault-handling ability. Inthis paper, the reconfigurability of system is analyzed, and fault tolerant control approaches based onswitching control is designed for SACS. The key contributions are summarized as follows:The common actuator and sensor faults in the SACS are summarized. An approach to evaluatereconfigurability of SACS is provided with respect to actuator and sensor faults under a certainconfiguration. First, based on the common actuator configuration of SACS, controllability and controlenergy consumption of post-fault system are analyzed. And the smallest eigenvalue of controllabilityGramian is utilized to measure the level of reconfigurability. Then the relationship betweenobservability and reconfigurability is discussed from the system point of view considering a certainsensor configuration. Based on the analysis, an approach to assess the whole SACS’s reconfigurabilityis presented. Simulation results are given to demonstrate the effectiveness of the proposed approach.For the fault tolerant control of multiple fault scenarios, a supervisory fault tolerant control basedon switching is design for spacecraft attitude stabilization. The scheme that integrates FTC with faultdetection and isolation can cope with different actuator fault scenarios without any additional modelor filter. First, the faulty cases that bias fault or stuck fault occurs in each one of the actuators areconsidered. For each case, a fault tolerant controller is designed using sliding mode controlcorrespondingly. Then a supervisory switching among this family of pre-computed candidatecontrollers is presented, which starts from the time fault is detected and ends when the correctstabilizing controller is switched on. During the switching delay the attitude of spacecraft isguaranteed to be bounded. Simulation results illustrate the efficiency of the method.Consider complete failure of one actuator, an approach dealing with the attitude stabilization ofsatellite with two momentum wheels using switching controllers is designed. Under the restrictionthat the total angular momentum vector of the system is zero, the underactuated satellite equations arecontrollable but cannot be stabilized by any smooth feedback control law. Two nonlinear control lawsare designed to make the partial states input-to-state stable with respect to other partial states. Thenthe whole stability of system is ensured by the small gain theorem. A simulation example is presentedto illustrate the effectiveness of the proposed approach.