Output feedback control for output tracking of nonlinear uncertain systems

The problem of robust output via dynamic output feedback for nonlinear systems which are subject to both uncertainty in system functions and input noise is addressed. The notion of β-tracking, which refers to the property of the system output that it follows a reference trajectory within a β neighborhood in finite time, is adopted. With some matching conditions, a minimum phase condition, Lipschitz bounds, and some other mild assumptions, it is shown that, if β-tracking of a nominal system can be achieved via a linear-cone bounded state feedback controller, then similar tracking can be achieved for the nonlinear uncertain system via dynamic output feedback. The resulting controller is linear-cone bounded or can be purely linear with the tradeoff of high gain if desired. The approach presented utilizes and generalizes results on robust tracking an stabilization via state feedback and robust observer design via loop transfer recovery theory