Attitude Control Of A Three-Axis Stabilized Satellite

Satellite attitude control system is a multi-input multi-output coupled uncertain nonlinear system. For any on-orbit satellite, it is inevitable to be influenced by some kinds of disturbance torques. Furthermore, these disturbances are uncertain. This uncertainty makes 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 linear control method based on LQR is given in accordance with the attitude control problem with constant value disturbance. At first, we linearize the kinetic model of the satellite. Then we select state variables according to the requirements of parameters' form in the LQR method, design appropriate feedback gain to implement disturbance suppression and attitude control.According to the known form periodic disturbance torque, we can get the independent pitch loop equation and coupled roll/yaw loop equation after we simplify the established rigid satellite attitude kinetic model. And then we theoretically analyze the impact of known form periodic disturbance torque to the satellite attitude. We carry out a separate compensation design for the independent pitch loop. For the intercoupling roll/yaw loop,the reaction flywheels on this loop are used to make maximum compensation to the known form periodic disturbance torque in order to realize high-precision attitude control.According to the bounded uncertain disturbances, we design several controllers with robustness. First,we design a quaternion feedback nonlinear control law base on Lyapunov method and prove the correctness of the control law theoretically. Secondly,a sliding mode variable structure control law with good robustness and rapidity is designed. We use reverse hyperbolic tangent function to aviod the chattering problem in sliding mode variable variable structure control. Finally, we design a output feedback disturbance observer without angular rate in accordance with the control problem in the state of angular velocity sensor failure.