Generalized Luenberger-like observer for nonlinear systems

In this paper, some previous results on Luenberger-like observer for nonlinear systems are extended to the case where the relative degree is not well defined. It is shown that if a nonlinear system has robust relative degree n, then there always exists a local nonlinear observer whose output converges exponentially to true states. The proposed method is applied to a ball and beam system to show the effectiveness of the method.