Actuator and sensor fault isolation of nonlinear process systems

This work considers the problem of isolating actuator and sensor faults in nonlinear process systems. The key idea of the proposed method is to exploit the analytical redundancy in the system through state observer design. To this end, we consider subsets of faults, and design state observers that use information of inputs and outputs only subject to faults in each subset. We then design residuals using the process model and state estimates such that each residual is only sensitive to the corresponding subset of faults. The occurrence of faults in a subset is detected if the corresponding residual breaches its threshold. With the ability of detecting the occurrence of faults in a subset, faults can be isolated using a bank of residuals and a logic rule. The proposed method enables differentiation between and isolation of actuator and sensor faults while explicitly accounting for system nonlinearity. The effectiveness of the fault isolation design subject to plant-model mismatch and measurement noise is illustrated using a chemical reactor example.