Simple robust output-feedback controller for uncertain nonlinear systems

A robust output-feedback controller is designed by using observer plus backstepping procedure to solve the tracking problems of a class of uncertain nonlinear systems. In the design procedure, three techniques are applied: a) a single filter whose dynamic order is the same as the system order is constructed; b) a normalization signal is introduced; c) positive nonlinear functions that are used to generate the normalization signal and to construct nonlinear damping terms can be chosen freely. The designed controller has a very simple structure and can be applied to track much broader classes of reference signals. It can guarantee the global boundness of all closed-loop signals and make the output tracking error arbitrarily small. The technique c) may provide the designer possibility to find a better choice of positive nonlinear functions for our controller to achieve similar tracking performance with less control effort.