Tracking and disturbance rejection for passive nonlinear systems

In this paper, we apply internal model principle for plants that are passive nonlinear systems, to solve tracking of constant reference signal and disturbance rejection of a finite superposition of sine waves of arbitrary known frequencies. A desirable passivity property around an equilibrium (x0,u0) which generates y0is used to design the controller. The proposed controller is an LTI system, which assures that the state trajectories of the closed loop system is bounded and the error signal converges to zero.