Robust coupling-observer-based sliding mode control for flexible air-breathing hypersonic vehicles

This paper investigates the problem of nonlinear sliding mode control for flexible air-breathing hypersonic vehicles (FAHVs) with uncertainties. By modeling the flexible effects produced by the rigid-flexible coupling terms as a kind of disturbance and including in the new control-design model with multiple disturbances, a robust coupling observer is proposed to estimate these flexible effects. A novel composite hierarchical controller is also provided, which combines a robust coupling-observer-based compensator and a dynamic-inversion-based sliding mode controller. In addition, the uniformly ultimately boundedness of composite closed-loop system is confirmed by using Lyapunov theory. Simulation results on a full nonlinear model of FAHVs demonstrate that the proposed composite controller is more effective than traditional dynamic-inversion-based sliding mode controller.