Robust fault detection of non-linear systems with unknown disturbances

In this paper a novel robust fault detection scheme for non-linear systems based on unknown input observer is proposed. The basic principle of unknown input observers is to decouple disturbances from the state estimation error. In the proposed method, the linear UIO design algorithm is extended to non-linear systems and then observer gain is obtained using unscented Kalman filter. In order to illustrate the efficiency of the proposed method, it is adopted to detect sensor faults of a highly non-linear dynamic system. The faulty behavior of output sensors in a jacketed continuous stirred tank reactor (CSTR) is investigated. A single full-order observer is designed to detect sensor faults in the presence of unknown inputs (disturbances). Simulation results show that disturbances and therefore, a certain degree of model uncertainties can be distinguished from a response to a sensor fault.