Closed-Loop PI/PID Controller Tuning for Stable and Integrating Process with Time Delay

Abstract

The objective of this study is to develop a new online controller tuning method in closed-loop mode. The proposed closed-loop tuning method overcomes the shortcoming of the well-known Ziegler-Nichols (1942) continuous cycling method and it can be an alternative for the same. This is a simple method to obtain the PI/PID setting which gives the acceptable performance and robustness for a broad range of the processes. The method requires a closed-loop step set-point experiment using a proportional only controller with gain Kc0. On the basis of simulations for a range of first-order with time delay processes, simple correlations have been derived to give PI/PID controller settings. The controller gain (Kc/Kc0) is only a function of the overshoot observed in the set-point experiment. The controller integral and derivative time (τI and τD) is mainly a function of the time to reach the first peak (tp). The simulation has been conducted for a broad class of stable and integrating processes, and the results are compared with a recently published paper of Shamsuzzoha and Skogestad (2010).1 The proposed tuning method gives consistently better performance and robustness for a broad class of processes.