Exact reconstruction of actuator faults by reduced-order sliding mode observer

This paper presents an approach to the finite time detection and isolation of actuator faults in a class of nonlinear uncertain systems. After a suitable preliminary state transformation, devoted to put the system dynamics in an appropriate normal form, a reduced-order observer is designed which has an output injection term based on a second-order sliding mode control algorithm featuring global convergence properties. Thanks to the proposed observer, the reconstruction of the actuator faults can be performed exactly and in finite time directly from the observer output injection signal, i.e. without requiring any filtration. The effectiveness of the proposed method is shown by means of a simulation example.