Global practical tracking by output feedback for nonlinear time-delay systems with uncertain polynomial growth rate

In this paper, the problem of global practical tracking is investigated by output feedback for a class of nonlinear time-delay systems. Different from the existing results, the nonlinearities allow the linear and lower-order growth in unmeasured free-delay and time-delay states with uncertain polynomial growth rate. With the aid of the ideas of universal control and dead zone, we construct an adaptive high-gain observer with two monotone non-decreasing dynamic laws. By Lyapunov-Krasovskii theorem, we show that the control scheme of this paper can be used to deal with a class of uncertain nonlinear time-delay systems. Finally, an example is given to illustrate the usefulness of our result.