Double-controller scheme for separating load rejection from set-point tracking

In the design of a conventional feedback control system, a difficult compromise has to be made between the set-point tracking performance and load rejection performance. A novel double-controller scheme is proposed in this paper to alleviate this compromise. This control scheme has two controllers, a set-point controller and a load controller, which result in the separation of the load response from the set-point response in a closed-loop system. These two controllers can be designed independently to achieve good system performance for both set-point tracking and load rejection. Also, good robustness of the double-controller scheme to variations in system dynamics can be obtained by properly designing the load controller. The proposed scheme is applied to two difficult problems, setpoint tracking in the presence of process uncertainty and control of a process with dominant time delay. The results show that the proposed double-controller scheme is superior to a conventional single controller system.