Nonlinear augmented state observer-based adaptive output feedback anti-disturbance control for nonlinear systems with non-harmonic multiple uncertainties

In this paper, a novel output feedback anti-disturbance control method is carried out for a class of nonlinear systems subject to non-harmonic multisource disturbances. By using a nonlinear exogenous system, a class of non-harmonic disturbances possessing complex and nonlinear characteristics are taken fully into consideration. Based on a nonlinear damping term, we establish an adaptive augmented state observer that can achieve robust asymptotic disturbance estimation for the system states, the harmonic disturbances and the non-harmonic disturbances. By fusing the augmented state observer and a state-feedback controller, a robust adaptive output feedback anti-disturbance control structure is constructed. The boundness of the combined controller–observer system is derived on the basis of Lyapunov analysis. Furthermore, aiming at the intense non-harmonic disturbances, the proposed method is extended and a new output feedback controller is obtained. The effectiveness of the proposed scheme is demonstrated through experimental studies on a practical example.