Integration of Scheduling and Control for Plants Controlled by Distributed MPC Systems

Increasingly dynamic market conditions have fueled efforts to integrate scheduling and control in recent years. While a large number of formulations have been proposed for different control systems, the integration of scheduling and control for plants controlled by distributed MPC systems has received scant attention. In this article, we present a framework for the integration of scheduling and control for plants controlled by distributed MPC systems. We also propose strategies to approximately model the distributed MPC action within the integrated problem formulation, reducing its complexity and computation time. The integrated problem is solved at the dynamic real-time optimization (DRTO) level, in a moving horizon fashion, to compute set-points assigned to the lower-level distributed MPC subsystems, whose formulation is kept intact. Case study results suggest that these strategies can significantly reduce the solution time of the closed-loop integrated scheduling and control problem without severely impacting plant performance. We demonstrate that the proposed integrated scheduling and control formulation can successfully coordinate the MPC subsystems to meet market demands of distinct product grades, even in the presence of plant–model mismatch.