Estimation and rejection for disturbances using composite nonlinear observer

This paper considers the stabilization problem for a nonlinear system with composite uncertain disturbances using disturbance observer based control (DOBC) approach. Instead of only one type disturbance such as harmonic or constant disturbance is concerned, the composite disturbances estimated consist of two parts, the first is harmonic with known parameter, the second is supposed to be system uncertainty, and a conventional controller is integrated with the observer to stabilize the closed loop system. Stability analysis of the closed-loop system is established using Lyapunov approach, if the prior knowledge of second disturbance is known, asymptotic stable is obtained. The control method shows lower conservative and especially, it can be extended to compensate unmatched disturbance problem. Simulations on a missile autopilot system show that satisfactory performance and robustness can be achieved using the proposed approaches.