Adaptive practical output tracking control for a class of uncertain nonlinear systems

This paper investigates the problem of adaptive practical tracking control by output feedback for a class of uncertain nonlinear systems without zero dynamics. The uncertain nonlinear perturbed terms of the considered systems are assumed to satisfy a generalised condition which is more relaxed than the triangular-type condition. Furthermore, in contrast to the previous work in the literature, the upper bound of the nonlinearities is a polynomial function of the output, with an unknown growth rate, multiplied by some relaxed conditions of unmeasured states. Due to the presence of unknown parametric uncertainty, a dynamic output compensator with dynamically updated gains is explicitly constructed based on non-separation principle. In particular, we show that for any positive number γ, all the states of the closed-loop systems are globally bounded and the tracking error belongs to the interval [−γ, γ] after some positive finite time. A numerical example illustrates the efficiency of the method.