Fixed-Time Sliding Mode Disturbance Observer-Based Nonsmooth Backstepping Control for Hypersonic Vehicles

TLDR

The study proposes a fixed‑time SMDO‑based robust backstepping cruise‑tracking controller that achieves closed‑loop finite‑time convergence for flexible air‑breathing hypersonic vehicles by compensating flexibility, model uncertainties, and external disturbances. The controller employs a fixed‑time SMDO, nonsmooth backstepping, and specially designed nonsmooth filters to generate virtual control derivatives, with a Lyapunov analysis proving finite‑time convergence of the closed‑loop system. The approach achieves disturbance‑observation convergence independent of initial errors and, as shown by numerical simulations, outperforms conventional methods in tracking performance.

Abstract

This paper presents a novel fixed-time sliding mode disturbance observer (SMDO)-based robust backstepping cruise tracking control scheme with closed-loop finite-time convergence for flexible air-breathing hypersonic vehicles (FAHVs). In order to enhance the control system's robustness, a fixed-time SMDO is designed to compensate for the flexibility effects, model uncertainties, and external disturbances in FAHVs. In consequence, fixed convergence time of disturbance observation is achieved independently of initial estimation errors. Furthermore, velocity and altitude continuous finite-time tracking controllers are constructed by incorporating the SMDO and nonsmooth backstepping technique. To solve the problem of "explosion of complexity" in the conventional backstepping approach, nonsmooth filters are specifically constructed to generate the derivatives of virtual control laws. A Lyapunov-based stability analysis is conducted to show the finite-time convergence of the closed-loop FAHV control system. Finally, several representative numerical simulations are given to illustrate the effectiveness and superiority of the proposed control strategy.