Robust Fault Detection Observer Design Using H∞ Techniques for Uncertain Unmanned Aircraft

This paper presents a new approach to the design of a robust observer-based fault detection scheme for diagnosing incipient faults, called H∞ robust fault detection observer (RFDO). It takes into account the robustness of the fault detection observer against disturbances and sensitivity to faults simultaneously. The approach has originated from the robust H∞ estimator which minimizes the effect of disturbance on the estimation error and subsequently on the diagnostic residual. The effect of faults on the diagnostic residual is maximised by the proper selection of the performance bound and the estimation weighting matrix of the H∞ robust estimator. Depending on the class of uncertainty modeling consideration, one or two Riccati equations are required for the H∞ estimator design. H∞ estimator can be designed to be robust against; disturbance only, disturbance and parameter uncertainty only, and disturbance and a large variety of modeling errors. The approach has been applied to a flight control system and the results show that the fault detection scheme designed can detect incipient faults effectively even in the presence of disturbances and modeling errors.