Output feedback control for nonlinear systems with uncertainties on output functions and growth rates

This paper investigates the output feedback control for nonlinear systems with unknown output functions and unknown growth rates, where the unknown output functions are Lipschitz continuous and the unknown growth rates are time-varying. To deal with this challenging control problem, a time-varying observer is designed and a time-varying scaling transformation is introduced, which can avoid using the derivative information of the output function and can effectively compensate the unknown time-varying growth rate. Then, by combining the time-varying scheme, the backstepping method and the certainty equivalence principle, an output feedback controller is designed to guarantee the boundedness of the closed-loop system states and the global convergence of the original system states. Finally, two simulation examples are given to show the effectiveness of the control scheme.