Global Practical Tracking for Nonlinear Systems With More Unknowns via Adaptive Output-Feedback

This paper investigates the global practical tracking via adaptive output-feedback for a class of uncertain nonlinear systems. Essentially different from the closely related literature, the system under investigation possesses unknown time-varying control coefficients and a polynomial-of-output growth rate, and meanwhile, the system nonlinearities and the reference signal allow serious unknowns. For this, an adaptive observer is designed to reconstruct the system unmeasured states, where a new dynamic gain is introduced to compensate the serious unknowns in the system nonlinearities and the reference signal. Based on this and by backstepping technique, an adaptive output-feedback controller is successfully designed, such that all the states of the closed-loop system are bounded, and the tracking error will be prescribed sufficiently small after a finite time. A numerical simulation is provided to demonstrate the effectiveness of the proposed method.