Fault diagnosis for HEX/reactor system via invertibility

A fault diagnosis approach is developed for pneumatic valve used in intensified HEX/reactor system. The pneumatic valve is viewed as an actuator subsystem interconnected with process subsystem in series. A condition of invertibility of the cascade system has been derived in [18], characterizing that effects of faults occurred in actuator subsystem are distinguishable by the global output uniquely. Using this idea, the fault diagnosis scheme proposed in this paper is based on local fault filtering, each subsystem is assigned to monitor one subsystem and provided a decision regarding its health. In particular, the connection point between the two subsystems is not accessible to measurements. An input estimator is then developed to estimate this unknown connection point only rely on the global system output. Different from [18], any information of the derivatives of the output vectors is not involved in the input estimation stage. For that, a high-gain second-order sliding mode observer is considered to exactly estimate the derivatives of the output vectors in a finite time. Numerical simulation examples are given to illustrate the effectiveness of the proposed methods.