Nonlinear steady-state tracking and disturbance rejection using static state feedback

In this paper, we consider the problem of steady-state tracking with disturbance rejection for nonlinear systems, using nonlinear static state feedback only. It is shown that, under certain conditions, a nonlinear static state feedback can be designed, such that in steady-state, the closed-loop system output equals the external (reference) input, and is not affected by the steady-state value of the disturbance. Furthermore, the output of the system follows the reference input, provided that the reference input and the disturbance are both slowly time-varying. This method is applied first to a simple second order system, then to an electric power generator system.