Fault detection and condition monitoring

A strand of work pioneered by the group has explored the use of sliding mode observers for Fault Detection and Isolation. The novelty of this approach lies in the ability of sliding mode observers to reconstruct un-measurable signals in the process being monitored by appropriate scaling and filtering of the so-called 'equivalent output error injection'. (This represents the average value the nonlinear term in the observer has to take in order to maintain a sliding motion). This is a unique property of sliding mode observers, and emanates from the fact that the introduction of a sliding motion forces the outputs of the observer to exactly track the plant measurements. This estimation approach is quite different from typical residual generation methods for fault detection in which the residual signals are dynamic weightings of the fault signals. Reconstruction approaches attempt to capture both the magnitude and 'shape' of the faults, and as a result both detection and isolation are handled simultaneously to some extent. Furthermore, the fact that the faults are reconstructed, allows the possibility of using the reconstructions to compensate for the fault effects - for instance by directly 'correcting' the output of a faulty sensor. These ideas have been investigated for fault detection (and fault-tolerant control) of a civil aircraft within the context of the GARTEUR Action Group on Fault Tolerant Control FM-AG16 and the EU FP7-funded ADDSAFE project.