Nonlinear disturbance observer based robust backstepping control for a flexible air-breathing hypersonic vehicle

This paper presents a robust backstepping approach for a flexible air-breathing hypersonic vehicle in the longitudinal plane. The control design and stability analysis of the backstepping approach are based on a control-oriented model, which treats the flexible dynamics as dynamic perturbations. The backstepping method in this study utilizes a command filter to avoid the problem of "explosion of complexity" that occurs in the traditional backstepping method. To suppress the flexible dynamics and parameter uncertainties, a nonlinear disturbance observer is proposed to estimate these uncertainties during the tracking process. By introducing a group of virtual states, a Lyapunov-based stability analysis of the closed-loop system indicates that the tracking errors vanish asymptotically. A guideline for tuning the controller is given from a physical perspective to avoid exciting the flexible modes. This approach presents a good tracking performance with respect to both the flexible modes and parameter uncertainties. Simulation results of the full nonlinear model show the effectiveness of the proposed approach. (C) 2016 Elsevier Masson SAS. All rights reserved.