Design of IMC filter for PID control strategy of open‐loop unstable processes with time delay

Abstract

AbstractA modified internal model control (IMC) filter has been proposed for the open‐loop unstable process with time delay and a further IMC–proportional‐integral‐derivative (PID) tuning rule is derived on the basis of the proposed IMC filter. Investigation of the IMC filter structure clearly demonstrates that a critically damped filter does not always provide satisfactory response and that this is probably due to lack of sufficient integral action. The conventional, critically damped filter is therefore replaced with a more general, second‐order IMC filter for improved integral action. The present investigation shows that for the most unstable processes, the underdamped IMC filter provides the desired integral action and improves the closed‐loop performance of the system except for the unstable processes with a strong lead term. An exhaustive simulation studies has been performed to show the advantage of the proposed method in both nominal and robust cases. By incorporating Kharitonov's theorem, closed‐loop time constant (λ) guidelines have been provided for the first‐order delayed unstable process (FODUP). Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.