Fault-tolerant control of nonlinear systems: fault-detection and isolation and controller reconfiguration

This work considers the problem of implementing fault-tolerant control on a multi-input multi-output nonlinear system subject to multiple faults in the control actuators and constraints on the manipulated inputs. We design output-feedback fault-detection and isolation filters and output-feedback controllers via a combination of state-feedback fault-detection and isolation filters and controllers, and state estimators. The fault-detection and isolation filters essentially capture the difference between fault-free evolution of the system and the true evolution of the system to detect and isolate faults in the control actuators. The state estimates are used in devising the reconfiguration rule that determines which of the backup control configurations should be implemented in the closed-loop system. Specifically, a configuration is chosen that 1) does not use the failed control actuator, and 2) guarantees stability of the closed-loop system starting from the system state at the time of the failure (this is ascertained via the use of feedback controllers that provides an explicit characterization of the output-feedback stability region). The implementation of the fault-detection and isolation filters and reconfiguration strategy is demonstrated on a chemical reactor network example