Proactive Actuator Fault-Tolerance in Economic MPC for Nonlinear Process Plants

Abstract

This paper presents a scheme for proactive accommodation of incipient actuator faults in nonlinear process plants operated with economic model predictive control (EMPC). The control scheme implements a switching from nominal economic operations to a safe-transition mode when receiving a warning about an incipient fault in one of the actuators, thereby ensuring that the plant is proactively steered to a steady-state point where the suspect control actuator is inactive. Upon reaching this safe steady-state point, the faulty actuator can be safely disconnected and repaired without shutting down the plant, before the controller subsequently resumes nominal economic operation. To steer the plant to the safe steady-state point, we impose an $\ell_1$ penalty function in order to achieve dead-beat control and reach the steady state in finite time. We provide a lower bound on the penalty parameter to ensure exactness of the penalty function, and analyze stability and convergence properties of the proactive fault-tolerant EMPC scheme. We demonstrate application of the proposed scheme on a non-isothermal continuously stirred tank reactor.