Fault-Tolerant Control of Nonlinear Systems Subject to Sensor Data Losses

This work considers the problem of control of nonlinear process systems subject to input constraints and sensor faults (complete failure or intermittent unavailability of measurements). To clearly illustrate the importance of accounting for the presence of input constraints, we first consider the problem of sensor faults that necessitate sensor recovery to maintain closed-loop stability. We address the problem of determining, based on stability region characterizations for the candidate control configurations, which control configuration should be activated (reactivating the primary control configuration may not preserve stability) after the sensor is rectified. We then consider the problem of asynchronous measurements, i.e., of intermittent unavailability of measurements. To address this problem, the stability region (that is, the set of initial conditions starting from where closed-loop stabilization under continuous availability of measurements is guaranteed) as well as the maximum allowable data loss rate which preserves closed-loop stability for the primary and the candidate backup configurations are computed. This characterization is utilized in identifying the occurrence of a destabilizing sensor fault and in activating a suitable backup configuration that preserves closed-loop stability. The proposed method is illustrated using a chemical process example.