Hypersonic vehicle attitude control based on new fast terminal sliding mode

To accelerate the convergence of a terminal sliding mode and avoid the singularity of the sliding mode controller, a new nonsingular fast terminal sliding mode, whose convergence speed is faster than that of the terminal sliding mode with double power functions at any point, is proposed according to an analysis of the cause of the singularity of the designed controller. The formula of convergence time is drived. Thereafter, a simpler nonsingular terminal sliding mode is designed. The nonsingular sliding mode controller is designed for the inner loop and outer loop of a hypersonic vehicle with an order filter by applying the new terminal sliding mode. In order to improve the control effect, two nonlinear observers are used to approximate the compound disturbances. The system including the inner loop and outer loop is proven to be stable in the finite time by means of the Lyapunov stability theorem. Finally, the performances and robustness are assessed through a hypersonic vehicle with model parameter perturbations.