Tracking differentiator design for the robust backstepping control of a flexible air-breathing hypersonic vehicle

This paper is concerned with the robust backstepping controller design for a flexible air-breathing hypersonic vehicle. Due to the extreme complexity of the vehicle dynamics, only the longitudinal model is adopted and rewritten as a feedback form for the backstepping design. Then, a new tracking differentiator (TD) is designed based on hyperbolic sine function to solve the problem of “explosion of term” in the traditional backstepping control. Furthermore, to enhance the controller׳s robustness, a new nonlinear disturbance observer is constructed using the proposed TD to estimate the model uncertainties and varying disturbances. More specially, owing to the measurement difficulties of angle of attack and flight-path angle in practice, the developed TD is utilized to reconstruct them based on the measurable states. Finally, several numerical simulations are given to demonstrate the effectiveness of the proposed control strategy.