A robust disturbance decoupling approach to fault detection in process systems

The authors describe a robust scheme for use in the role of fault detection in sensors and actuators of process systems. The fault detection scheme is designed to be insensitive to disturbances, while being sensitive to faults. The authors present the robust fault detection approach based on eigenstructure assignment in the discrete-time domain. By assigning the left eigenvectors of the observer orthogonal to the disturbance, robust (disturbance decoupling) fault detection is achievable. The approach has been applied to an 11th-order nuclear reactor system. A reduced-order model is used to approximate this system and modeling errors are considered as disturbances acting on the reduced-order model contained in the observer. The work involves the development and use of a method for estimating the disturbance direction. The robust fault detection scheme design uses this direction as that of the direction of unknown input acting on a fourth-order model. Simulation results show that the scheme can detect soft or incipient faults efficiently