Robust fault detection observers for nonlinear polynomial systems

This paper proposes a robust fault detection observer (RFDO) for classes of nonlinear models which consists of polynomial nonlinearities up to degree three and are structured in continuous state-space form. The observer and d etection signal are designed to be independent of unknown inputs. Sufficien t conditions are given, in an efficient compact form, for an RFDO (observer and signal) to exist. Several useable results on detectablility conditions are given and a numerical procedure is considered. The modelling of a hydr aulic rig system is considered. Design steps are shown in obtaining an RFDO which is sensitive to faults at certain nodal points. This RFDO forms part of a bank of three observers used in a fault isolation procedure which is tested on real input-output data.