Disturbance observer-based sliding mode backstepping control for a re-entry vehicle with input constraint and external disturbance

Abstract

An attitude controller is designed for a reusable launch vehicle (RLV) during the re-entry phase with input constraint, model uncertainty and external disturbance. A control-oriented model with matched and unmatched uncertainty is first derived for the control design. To proceed, the control scheme is designed taking advantage of the robust stability property of sliding mode control, the compensation ability of the non-linear disturbance observer (DOB) technique and the systematic design procedure of the backstepping technique. An additional system, the states of which are used for controller design and stability analysis, is constructed to handle the input constraint. The time derivative of the virtual control input is considered as an uncertainty to eliminate the ‘explosion of terms’ problem inherent in backstepping control. Moreover, the proposed method alleviates the chattering problem of the traditional sliding mode backstepping control scheme. Stability analysis of the composite control scheme consisting of the designed controller and the DOB is performed via Lyapunov theory. Finally, simulation results are compared to show that the proposed method is able to achieve better tracking performance and tackles input constraints more effectively than an adaptive filter backstepping control scheme.