A discrete double-controller scheme for delayed processes with both load and set-point disturbances

Abstract

Using a double-controller strategy and a design approach related to Dahlin’s controller, a new sampled data control scheme is presented that is suitable for handling both set-point change and load disturbances. 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. The control scheme is applicable to processes that can be approximated by first-order plus time delay dynamics. For set-point changes, the set-point controller is a generalized Dahlin controller that has an extra tuning parameter T_LC and has more ‘exibility and more robustness than Dahlin’s controller. For load disturbances, the load controller is also a generalized Dahlin controller and shows a significant improvement over the performance of Dahlin’s controller. The new double-controller scheme also alleviates a difficult compromise that the generalized Dahlin controller makes between the set-point tracking performance and load rejection performance. A simulation study is used to evaluate the performance of this new double-controller scheme in the presence of noise and model errors, and to compare it to Dahlin’s controller and the generalized Dahlin controller. The results show that the proposed double-controller scheme is superior to both Dahlin’s controller and the generalized Dahlin controller.