Optimal output regulation of minimum phase nonlinear systems

This paper studies the design of an optimal stabilizing controller for output regulation of minimum phase nonlinear systems in the Lyapunov redesign framework of our earlier work [6], and investigates the asymptotic robustness properties of the overall feedback design, given that the optimal stabilizing controller itself possesses strong robustness properties by construction. The motivation comes from the flexibility of incorporating any stabilizing controller within the proposed framework, and we seek for control design methods that yield stabilizing controllers with some additional desirable properties like optimality, disturbance rejection and robustness in the presence of matched uncertainties e.g. static nonlinearities, uncertain parameters and the unmodeled fast dynamics. We exploit the optimal control design methods developed by Kokotovic and his co-researchers [3], [4], [7] for nonlinear systems, where it is shown that in addition to achieving the asymptotic stability of the system and minimizing a cost functional, the optimal feedback control guarantees stability margins which characterize the robustness properties.