Research On Finite-time Control Method Based On Terminal Sliding Mode For Spacecraft Attitude

The attitude control system is an important part of the overall design of spacecraft. With the rapid development of space technology, it brings higher and higher requirement on the performance of aircraft attitude control system. However, structural nonlinearity, model parameter uncertainties, external disturbances makes spacecraft attitude system a class of complicated nonlinear uncertain system. Thus the research on its control strategy has important theoretical and practical value. Compare with the normal control mode which stabilizes in infinite time, the finite time control can make the system stability in finite time. And because of the finite time controller contains fractional power, the finite time control algorithm is more robust and anti-interference than other control algorithm. Based on the limited time control theory, this article design the control law for system in which the uncertainty upper bound known and unknown by using the terminal sliding mode control algorithm. Theory and simulation shows the design of its control law possess faster convergence properties.Firstly, this article describes the status of attitude control of spacecraft and finite time control theory. Then we introduce several typical kinematic and dynamic equations, and the characteristics of every description methods are discussed. By comparison, we use quaternion theory describe the attitude of spacecraft, then we establish the system model of the spacecraft and we have a deeper processing for the design of terminal sliding mode controller.Secondly, we design the control law for the system when the uncertainty upper bound is known by using non-singular terminal sliding mode control algorithm. We design stabilizing control law for spacecraft attitude based on non-singular terminal sliding mode control algorithm by using the coupling between kinematic and dynamic equations. Then we prove the attitude of spacecraft can calm to the target posture in finite time by finite time control theory.Finally, we design the control law for the system when the uncertainty upper bound is unknown. Based on the time-scale principle and the states of spacecraft are divided into slow subsystem corresponding to the quaternion and fast subsystem corresponding to the Angular velocity. Thus form both inner and outer control loop, with the outer loop tracking the given quaternion and the inner loop tracking the designed angular velocities. For the question that the uncertainty upper bound is unknown in the fast loop, we design a fuzzy disturbance observer with adaptive parameter which can enable estimate approach to uncertainties, and terminal sliding mode controller is designed on this basis. We prove the aircraft attitude can converge to the target posture in a finite time by finite time control theory. The simulation results show that the system can calm to the target posture in finite time using designed algorithm when the uncertainty upper bound is unknown.