A Fixed-time Sliding-mode Control Method for Hypersonic Vehicle

A fixed-time terminal sliding mode controller for the attitude control problem of hypersonic vehicle in the reentry gliding phase is proposed，in the presence of external disturbances，model uncertainty，and input saturation constraints. Firstly，a more accurate fixed convergence time upper bound is proposed for the fixed-time super-twisting second-order sliding-mode disturbance observer. Then，an improved variable exponential coefficient fast non-singular multivariable terminal sliding-mode surface is constructed. Furthermore，based on the fixed-time observer and the improved sliding-mode surface，a non-singular terminal sliding-mode controller is proposed to enable the hypersonic vehicle model to achieve attitude control in fixed-time under external disturbances，uncertain model parameters，and input saturation constraints. Its fixed-time stability before and after observer convergence is demonstrated. The proposed method can effectively avoid input saturation without introducing additional measurements. Finally，the effectiveness of the proposed control method is verified by numerical simulation. © 2024 Chinese Society of Astronautics. All rights reserved.