Disturbance observer–based dynamic surface control design for a hypersonic vehicle with input constraints and uncertainty

Abstract

This article presents the flight control problem of a flexible air-breathing hypersonic vehicle under input constraint and aerodynamic uncertainty. First, a control-oriented model is derived and decomposed into velocity subsystem and altitude subsystem, in which compounded disturbances are included to consider aerodynamic uncertainty and the effect of the flexible modes. Second, nonlinear disturbance observer technique is employed to estimate the compounded disturbance, where the estimation error converges to a compact set if the observer design parameters are chosen appropriately. Then, based on disturbance observer, a robust controller and a dynamic surface controller are developed, respectively, for the velocity subsystem and the altitude subsystem. Third, novel robust first-order filters are designed to overcome the “explosion of terms” problem induced by backstepping method. Additional systems are constructed to tackle input constraints. By rigorously Lyapunov stability proof, the designed control strategy can assure that tracking error converges to an arbitrarily small neighborhood around zero. Finally, simulations are performed to show the effectiveness of the presented control strategy.