Incipient Actuator Fault Handling in Nonlinear Model Predictive Control

Abstract

This paper presents a reconfigurable nonlinear model predictive control (NMPC) scheme for handling of incipient actuator faults in nonlinear plants. The scheme seeks to ensure recoverability from an incipient actuator fault in plants where the input redundancy is insufficient to stabilize the faulty system at the nominal operating point, thereby requiring transition to a safe control-invariant set. To this end, the proposed scheme takes into account an estimate of the decrease in remaining actuator capacity from the time of detection of an incipient actuator fault, and minimizes the required control input to steer the plant to the safe set. We provide conditions for stability and fault recoverability of the proposed scheme, and demonstrate its applicability on a numerical example with two CSTRs in series.