Robust output feedback control of polynomial growth nonlinear systems with measurement uncertainty

Even in the presence of uncertainty in both state and output equations, we prove that global asymptotic stabilization is still possible by output feedback for a family of uncertain nonlinear systems dominated by a triangular system with a polynomial output-dependent growth rate. In contrast to the linear growth requirement in the recent work the nonlinear perturbations in this paper are allowed to satisfy a linear growth condition with a polynomial output-dependent rate. To handle simultaneously the polynomial nonlinearities and unknown parameter in the system output, we propose a high-gain estimator with a dynamic gain that is updated online through a Riccati-type dynamic equation. Then, an estimator-based controller is designed by a recursive algorithm that makes it possible to assign the controller gains step by step. The globally stabilizing output-feedback controller developed in this paper is robust with respect to uncertainties in the system dynamics and output equations.