Monitoring and diagnostics of a class of nonlinear systems using a nonlinear unknown input observer

In this paper we study a class of nonlinear systems with unknown inputs for which nonlinear observers with linearizable error dynamics in appropriate coordinates can be designed. Various conditions for accomplishing this task are stated. The observation scheme is then utilized as a mean for model based monitoring and failure diagnosis within the system. Selection of threshold value with reliability is discussed. Finally, the paper concludes with examples, illustrating applicability of the reported results in linear and nonlinear systems.