Application of a robust nonlinear fault detection observer to a hydraulic system

This paper proposes a fault detection method for a fairly wide class of nonlinear systems based on a nonlinear observer. Various other methods proposed in the field are related to this method or are special cases of it. The observer is designed such that the error dynamics are independent of state, input, output and unknown disturbances. Necessary conditions are given for the observer to exist and to be robust with respect to an unknown input. Applications are made to a hydraulic system.