Global practical tracking by output-feedback for nonlinear systems with unknown growth rate

This paper is devoted to the global practical tracking by output-feedback for a class of uncertain nonlinear systems with only the tracking error measurable. Different from the closely related works, the systems have unmeasured states dependent growth with unknown constant rate, and the reference signal, as well as its first order derivative, has unknown bound. Mainly because of these, the tracking problem can hardly be solved by straightforwardly extending the existing results. In the paper, motivated by the related stabilization results, and flexibly using the ideas of universal control and dead zone, an adaptive output-feedback controller is designed to make the tracking error prescribed arbitrarily small after a finite time while keeping all the states of the closed-loop system bounded. A numerical example demonstrates the effectiveness of the theoretical results.