Disturbance observer based robust backstepping control design of flexible air-breathing hypersonic vehicle

This study presents a new controller that is integrating sliding mode control method, a backstepping technique with disturbance observer (DO) for the flexible air-breathing hypersonic vehicle (FAHV). A control-oriented model (COM) is firstly established based on the engineering background of FAHV, and the COM is decomposed into a velocity subsystem and an altitude subsystem, then controllers and the DO are designed for them. The developed sliding mode surface with exponential form can accelerate the convergence speed of the sliding mode state. Furthermore, the time derivative of the virtual control inputs is seen as uncertainty, and the DO is used to estimate it, so the problem of 'explosion of terms' is avoided. Then the stability of the closed-loop system is proved by Lyapunov theory, the tracking error of velocity converges to the random neighbourhood around zero, and the tracking error of altitude is asymptotic stable. Lastly, the compared simulation result is shown to verify that the proposed control method has better tracking performance than that of an adaptive backstepping controller.