A review on PID tuning rules for SOPTD inverse response processes

Most widely used controllers in industries are of PID type. Availability of a number of PID tuning rules for various processes in the literature make difficult for the users to get familiar with all of them. Inverse response processes with time delay frequently occur in chemical process industries. These are difficult to control due to right half plane (RHP)zeros. Although advance control techniques are available but PID controllers because of simplicity and robustness have been used to control these processes. In this work, four PID tuning methods available in literature for underdamped second-order plus time delay (SOPTD) inverse response processes are studied. The study has been done for wide range of positive-zero time constant to time-lag constant ratios and time delay to time-lag constant ratios. Three of them are based on IMC theory having different types of approximations for time delay term and the fourth one on direct synthesis approach (i.e. on desired closed loop specifications). To evaluate the performance of PID controllers, a systematic approach was adopted. Tuning rules suitability according to the regions of applicability are highlighted. Finally work done is concluded with some recommendations.