A non-adaptive approach to the problem of tracking uncertain oscillations

This paper considers the problem of output regulation for nonlinear, possibly non-minimum phase, systems, in the presence of parameter-uncertain exosystems. The proposed result relies upon a framework recently proposed by the authors to deal with the presence of unstable zero dynamics in nonlinear output regulation. An interesting aspect of the theory presented in the paper is given by the fact that the internal model-based regulator is designed without using adaptation strategies as classically done in the literature on adaptive output regulation. Limits of performance linking the properties of the zero dynamics of the regulated plant and of the exosystem can be obtained as nice byproduct of the result.