Double-controller scheme for control of processes with dominant delay

A double-controller structure is proposed for control of processes with dominant time delay. In contrast to the Smith predictor, the proposed control scheme contains two controllers, a set point controller and a load controller, and a process model. With this structure, the setpoint and load responses of the closed-loop system are no longer coupled, and the two controllers can be separately designed to obtain good performance in both setpoint tracking and load rejections. Any errors resulting from the inevitable mismatch between the model and the process can be viewed as additional load disturbances, and are compensated by the load controller. The load controller is tuned to be insensitive to the model structure and parameters, to accommodate large model uncertainty, for which the standard Smith predictor may give poor regulatory performance and even fail to work. Extensive simulations show that the proposed scheme is superior to the Smith predictor in the presence of large uncertainty in process dynamics