Simultaneous actuator and sensor fault isolation of nonlinear systems subject to uncertainty

This work considers the problem of actuator and sensor fault isolation for nonlinear systems subject to uncertainty. The key idea is to detect and isolate faults by using a bank of filters, dedicated to each fault that captures the difference between the observed and expected behavior of system while allowing thresholds, cognizant of the uncertainty. To this end, high gain observer are first designed and the bounds on the estimation error, subject to the uncertainty, are established. Then the residuals are defined in a way that each is only sensitive to a subset of faults, with the thresholds accounting for the impact of the uncertainty. The fault isolability condition, characterizing the class of faults that are isolable by the proposed fault detection and isolation (FDI) scheme is rigorously derived. The effectiveness of the fault isolation framework subject to uncertainty and measurement noise is illustrated using a chemical reactor example.