Practical tracking control of a class of uncertain nonlinear systems and unknown output function

This paper investigates the problem of global practical tracking control via dynamic output-feedback for a family of uncertain nonlinear systems with unknown output function. The nonlinear terms of the system under consideration are assumed to be bounded by an unknown parameter multiplied by a function of unmeasured states. Furthermore, contrary to the previous works, the system output is presented with a multiplicative unknown measurement noise. Based on a high-gain observer to reconstruct the unmeasured system states and handle the unknown output function, an adaptive output feedback controller is designed to guarantee the reference trajectory tracking. The boundedness of all the closed-loop signals is verified by Lyapunov analysis and the tracking errors are proved to be sufficiently small prescribed after a finite time. A practical example is given to illustrate the effectiveness of the proposed design scheme.