Disturbance observer based control for a class of nonlinear systems with uncertain exosystem

A novel type of control scheme is proposed for a class of nonlinear systems subject to disturbance. The disturbance is generated by an exogenous system with uncertainty, which can represent the harmonic signals with modeling perturbations. A nonlinear disturbance observer is constructed for the estimation of the disturbance. The effectiveness of the method depends on the characteristics of external additional disturbance δ(t) which result from the perturbations and uncertainties in the exogenous system. More precisely, the assumptions of δ(t) ∈ L₂[0, ∞) and/or δ(t) ∈ L_∞[0, ∞) can result in different consequents. Numerical simulations are given to demonstrate the effectiveness of the proposed control schemes.