Global robust servomechanism theory for nonlinear systems in lower-triangular form

The aim of this paper is to provide a solution for the global robust servomechanism problem for a general class of nonlinear systems in lower-triangular form, which may include systems that are not locally exponentially stabilizable. In the considered setup, the output error is available for measurement together with a certain number of perturbed derivatives of the plant output. The design methods exploits an extended internal model which aims at reconstructing the steady-state trajectories together with the unique input that renders the error-zeroing manifold invariant. We show how, under suitable assumptions, it is possible to give a constructive solution exploiting the celebrated gain-assignment technique of Jiang, Teel and Praly (1995), using feedback from the partial state and the state of the internal model.