A Zero-Dynamics Re-Design Approach to Problems of Nonlinear Output Regulation

In this paper we deal with the problem of output regulation for nonminimum-phase nonlinear systems. The main goal is to provide a unifying framework in which a number of results recently proposed on the subject can be framed. The underlying idea is to formulate a design paradigm based on zero-dynamics re-design which allows one to adopt high-gain techniques as key stabilization tool. By drawing inspiration from results known in a linear setting, two possible zero-dynamics redesign techniques will be explored: the first is based on the design of a feed-through compensator aiming to achieve nice asymptotic properties of the zero-dynamics by dynamical input-error re-design. The second is based on design techniques of time-varying fast controllers which extend, to a nonlinear setting, robust zero-assignment techniques known for linear systems as "vibrational feedback".