Extended disturbance observer based terminal sliding mode control for reentry vehicles

This paper presents an extended nonlinear disturbance observer and novel double loop nonsingular terminal sliding mode control for reentry vehicles with time-varying unmatched disturbance. Firstly, the Lyapunov theorem is employed to design the extended nonlinear disturbance observer, where the state variables are extended to observe the disturbances and their changing rates simultaneously. The motion of reentry vehicle is separated into inner loop of angle and outer loop of angular rate, and a nonsingular terminal sliding mode control laws based on novel sliding mode is developed. The disturbance can be efficiently compensated and the tracking error is guaranteed to converge to zero in finite time. Simulation results and comparisons illustrate the effectiveness of the control strategy.