Robust Adaptive Approximate Backstepping Control Design for a Flexible Air-Breathing Hypersonic Vehicle

Abstract

This paper presents a tracking control problem of a flexible air-breathing hypersonic vehicle with aerodynamic uncertainty. The flight control design is challenging because of heavily coupled propulsive, aerodynamic forces and flexibility effects. A control-oriented model is derived where the flexible dynamics are regarded as perturbations and the aerodynamic uncertainty is included. It does not need to be transformed into a linear parameterization formulation. Based on an analysis of it, it is decomposed into a velocity subsystem and an altitude subsystem. Then dynamic inversion and a sliding mode control are combined to design the controller of the velocity subsystem. In addition, the sliding mode control and adaptive control are incorporated into a backstepping control architecture to develop the controller for the altitude subsystem after it is transformed into approximately strict-feedback form. The upper bounds of the uncertain terms do not need to be known in advance. They are estimated online, and the estimated values are updated by adaptive laws. Time derivatives of virtual control inputs are taken as uncertain terms to eliminate the so-called explosion-of-terms problem in traditional backstepping control. Simulation results demonstrate the performance of the proposed control scheme, which achieves stable tracking of the reference trajectories.