New results on semiglobal output regulation of nonminimum-phase nonlinear systems

This paper deals with the design of an internal model-based output feedback controller for non-minimum phase systems with a semi-global domain of attraction. Under the assumption of linear internal model, we present a sufficient condition for the existence of an output feedback controller which is able to semi-globally and asymptotically stabilize the extended system given by the controlled plant and the internal model unit. In this paper we the take advantage of the design tool proposed by Byrnes et al. (1997) and Khalil (1998), and we show how to construct a dynamic uniform completely observable controller starting from a stabilizing controller of a suitably defined auxiliary system. For linear systems, it is shown that the existence of a stabilizing controller for the auxiliary system becomes also a necessary condition for the solution of the output regulation problem as it corresponds to the classical non-resonance condition between the modes of the exosystem and the zeros of the controlled plant.