New Fast Terminal Sliding Mode and Its Application to Near Space Vehicles

To accelerate the convergence of a terminal sliding mode and avoid the singularity of the controller,an analysis for the cause of singularity in terminal sliding mode is presented in this paper.Based on Lie algebra,the nonsingular criterion is provided for the terminal sliding mode controller.Thereafter,two novel nonsingular fast terminal sliding modes are designed with convergence speed faster than that of a normal fast terminal sliding mode at any points.The formula of convergence time is derived.The new fast terminal sliding mode is combined with the dynamic sliding mode to eliminate chattering.Then,controllers are designed for the fast loop and slow loop of a near space vehicle.In order to improve the control effect,a nonlinear disturbance observer is used to approximate the compound disturbances.By means of the Lyapunov theorem,the system is proved to be stable.Finally,simulation is conducted.