MPC has been utilized for process control within ABB for a long time, initially using third-party solutions from other vendors. Later, solutions were implemented using the ABB products Predict & Control, and Expert Optimizer. Typically MPC provides set points for the underlying cascaded PID controllers.
Common for these approaches has been that the MPC has been running on a separate server, which is not part of the DCS (distributed control system). Signal data is then normally exchanged with the DCS using OPC; measurements, consisting of PV and feed-forward (FF) variables, are sent to the MPC, and the MPC outputs, also called manipulated variables (MVs), are then sent to the DCS.
However, for these solutions to work, a number of additional signals need to be exchanged between the DCS and the MPC on the external server. These carry information, eg, about which level-1 PID controllers will accept a set point from the MPC and whether the output from the PID is saturated. It is also necessary to move data between the MPC and the operator displays. Further information that needs to be exchanged is the status of the MPC, where often a “heartbeat” signal is used to indicate that the external MPC is alive. All of this communication needs to be configured before the engineer has even started to deal with the control problem. This must also occur before deciding to add or remove signals from the MPC. There is no question that the threshold to use MPC has been substantial.