Implementation of predictive controllers as outer-loop controllers

This paper addresses the problem of implementing predictive controllers as supervisory control systems. In this configuration the manipulated variables calculated by the predictive controller are used as command signals for the actuators by the distributed control systems, which uses operator-tuned local PID controllers to act on the physical system. This structure presents the problem of loosening of performance if the inner-loop controllers are retuned. The paper presents a solution to this problem based on the use of an adequate two-degrees-of-freedom structure in the inner-loop that separates open and closed-loop properties. The application of this technique to the control of an industrial boiler is presented. By using this technique it is shown that the performance of the predictive control system is maintained despite re-tuning of the inner-loop controller.