Fault detection and isolation in nonlinear systems

In this paper the problem of fault isolation in non linear systems is considered. Faults are formulated as parameter changes and a novel definition of fault detent ability is introduced. This connects a fault with its effect on the output of the system under consideration. Based on this definition, a practical way to test the fault detectability is introduced. In this context, a general result about fault isolation is presented. The result is based on the decoupling of faults in order to obtain a set of structured residuals. A procedure to calculate the required decoupling transformations is proposed. These results relax the existence conditions required by early approaches and represent a generalisation of the existing result for linear to non linear systems. The existence conditions are examined and a design procedure for the feasible case is proposed. Numerical examples are used to show the proposed ideas.