A Robust Output-Feedback Controller for a Class of 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 nonlinear uncertain systems. To make the design procedure and the controller structure simple, three techniques are applied: ① Only a linear observer is constructed to estimate the unknown states; ② A normalization signal is introduced. ③ A positive nonlinear function used to generate the normalization signal and a group of positive nonlinear functions used in the nonlinear damping terms are all chosen properly. The assumption made on the reference signals is much weaker than existing schemes, therefore the designed controller can be applied to track much broader classes of reference signals. The global boundness of all closed-loop signals can be guaranteed and the output tracking error can be made as small as possible if the design constants are chosen large enough.