High gain adaptive output feedback tracking control of uncertain nonlinear systems without relative degree restriction

In this paper, a design method of adaptive output feedback controller for nonlinear systems with higher order relative degree and some uncertainties in control input term is proposed. The controlled systems are rendered the systems with a relative degree of one by introducing two different virtual filters and applying a variable transformation. The actual control input is designed so that the virtual filter´s signal may become a high gain adaptive output feedback control signal using backstepping strategy. The proposed method is useful in the cases where only the output signals are available.