Attitude Fault Tolerant Control Of Microsatellite Based On Disturbance Observer

With the development of space technology, the scientific task of satellites is becoming more and more diversified. The performance requirements of the satellite attitude control system are getting higher and higher. However, when the satellite is on orbit, it is influenced by the high vacuum and strong radiation, which causes the performance of the satellite attitude control system decline. Therefore, it is important to develop a class of anti-disturbance satellite attitude control methods. The precision and stability of the satellite attitude control system is not only related to the performance of sensors and actuators, but also related to the control algorithms used in the system. When the physical structure of the satellite is determined, the control algorithm is vital to the control performance of the satellite. Therefore, a class of anti-disturbance fault tolerance control methods should be designed to keep the stability and complete the desired tasks for satellite attitude control system with multiple disturbances and healthy or faulty actuator. The main work and contributions of this thesis are listed as follows:A composite fault tolerant control (FTC) method based on disturbance observer and adaptive control is proposed for microsatellite attitude control system (ACS) with actuator faults and multiple disturbances simultaneously. The disturbances in ACS can be divided into a modeled disturbance and a bounded equivalent disturbance. Disturbance observer and fault diagnosis observer are designed to estimate the vibration disturbances and faults of flywheels, respectively. An adaptive term is applied to compensate norm-bounded disturbance. Furthermore, a composite fault tolerant controller is constructed to reject the modeled disturbance, to accommodate the actuator faults, and to compensate the norm bounded disturbance. Compared with the robust FTC, this method removes the assumption that the norm bounded disturbance is bounded by a known constant.An anti-windup fault tolerant control method based on disturbance observer is proposed for the ACS with multiple disturbances and input constraints. Disturbance observer and fault diagnosis observer are designed to estimate the periodic vibration disturbance and additive faults of flywheels, respectively. Then, the periodic disturbance and fault of actuator are part of the control torque. The periodic disturbance and fault are considered as a whole in input saturation. The saturation part is described by the method of polyhedron. Lyapunov function analysis method is applied to prove the stability of the system. Compared with the general saturation control method based on disturbance observer, the estimated value of disturbance observer and fault diagnosis observer is added to the controller, and the saturation of the control input is considered as a whole.A non singular fast terminal sliding mode controller based on disturbance observer is proposed for ACS of microsatellite with partial loss of actuator and multiple disturbances simultaneously. For partial loss of actuator, the minimum value is not required, and is estimated online by the adaptive method. The proposed method is able to deal with constant and time varying actuator faults. Disturbance observer is used to estimate and reject the periodic disturbance of the actuator, which can improve the precision of ACS. By designing a non singular terminal sliding mode controller, the attitude control system can reach a steady state in a finite time. Compared with the common terminal sliding mode control method, the proposed method has the advantages of non singularity and high precision.The control methods in this thesis are simulated and verified. The simulation results show that the proposed anti-disturbance fault-tolerant control methods can improve the accuracy and stability of the ACS with anti-disturbance ability and robust performance. They have engineering application value.