Self-Optimizing Control Structure Selection Based On Active Constraint Regions

AGUSTÍN BOTTARI; DAVID ZUMOFFEN; ALEJANDRO G. MARCHETTI

Santa Fe

Congreso; X Congreso Argentino de Ingeniería Química (CAIQ2019); 2019

Asociación Argentina de Ingenieros Químicos

In the process industries, the selection of controlled variables, manipulated variables, and setpoint values, directly impacts on the operation costs of the plant. Defining the mentioned variables determines a specific control structure. Since the process is affected by disturbances it may happen that, under the effect of disturbances, the implemented control structure takes the controlled plant to an operating point that violates the operating constraints, or to an economically suboptimal point. In order to optimally select the control structure and the setpoint values while paying attention to the satisfaction of operating constraints, different approaches have been proposed in the literature. Two of the main strategies are the back-off approach and self-optimizing control. Recently, Bottari et al. (2019) argued that the steady-state back-off approach based on minimizing the average cost can be seen as a global self-optimizing control strategy. This approach selects a fixed control structure with fixed setpoint values regardless of whether or not the set of active constraints of the optimization problem changes with the disturbance values. Based on this work, in the present paper we evaluate the economic improvement that can be achieved by changing the control structure and/or the setpoint values for different active constraint regions. The new formulations are applied to a forced-circulation evaporator, and the results show that an important economic benefit can be achieved.