Changing between Active Constraint Regions for Optimal Operation: Classical Advanced Control versus Model Predictive Control

Abstract

Control structures must be properly designed and implemented to maintain optimality. The two options for the supervisory control layer are Advanced Control Structures (ACS) and Model Predictive Control (MPC). To systematically design the supervisory layer to maintain optimal operation, the constraints that can be given up when switching active constraint regions should be prioritized. We analyze a case study in which we control the temperature and the flow in a cooler with two degrees of freedom (DOF) represented by two valves, one for each of the two streams. Either valve can saturate and make a constraint active, forcing other constraints to be given-up, and thus changing the set of active constraints. We show that optimal or near-optimal operation can be reached with both ACS and MPC. We do a fair comparison of ACS and MPC as candidates for the supervisory layer, and provide some guidelines to help steer the choice.