Output-based disturbance rejection control for nonlinear uncertain systems with unknown frequency disturbances using an observer backstepping approach

This paper is concerned with the output feedback control design for a class of nonlinear uncertain systems subject to multiple sources of disturbances including model uncertainties, unknown constant disturbances, harmonic disturbances with unknown frequency and amplitude. The total disturbances and uncertainties are delicately represented by a compact exogenous model first. By incorporating the adaptive internal model principle, a set of dynamic estimators are developed for both state and disturbance observations. By means of observer backstepping technique, a composite output feedback controller is constructed based on the disturbance and state estimations. The stability of the closed-loop system is rigorously established based on Lyapunov stability criterion. A missile roll stabilization example is finally investigated to validate the effectiveness of the proposed control approach.