Global practical tracking control via output feedback for more general nonlinear systems.

This paper focuses on the issue of global practical tracking control by output feedback for uncertain nonlinear systems with unknown control coefficients and unknown reference signal. Unlike other tracking works, the upper and lower bounds of the unknown control coefficients in the studied nonlinear system are not required to be known, while the nonlinearities are bounded by the unmeasured states multiplying an unknown constant, the polynomial-of-output and the polynomial-of-input. Inspired by related works, an adaptive tracking controller based on a new dynamic high gain has been successfully constructed by combining the universal control idea and the concept of dead-zone with backstepping technique, which effectively handles the impacts of multiple uncertainties. The designed adaptive controller ensures that the state of the closed-loop system is globally bounded, and the tracking error of the system converges to any arbitrarily small range of the origin after a finite time. Finally, two numerical examples are provided to illustrate the effectiveness of the theoretical results.