Implementation of model predictive control on cascade control

In chemical process control, the flow rate is usually set as the minor loop of cascade control for the other more important controlled variables such as temperature, liquid level and material component. At the same time, the flow rate is often the manipulated variable of model predictive control(MPC). In view of the implementation dilemma of downloading the manipulated variable of MPC while the flow rate control is set as minor loop of cascade control, two implementation methods of MPC were proposed. Firstly, the output of MPC is downloaded to the set-point of major loop through an one order inertia object. Secondly, the transfer function of flow rate to controlled variable of major loop is embedded into the predictive model of MPC. The control of the Shell heavy oil fractionator's benchmark problem has proved the feasibility of the two methods. They are simple in theory and easy to implement for commercial processes. © 2016, Chemical Industry Press. All right reserved.