Comparative study of PID tuning methods for processes with large & small delay times

A series of simulations have been carried out to compare the PI and PID controller tunings of different tuning methods, namely Ziegler-Nichols(ZN), Cohen-Coon (CC), Chien-Hrones-Reswick(CHR) and minimum error criteria ISE, ISTE, ISTSE methods for various process models. Using simple first order plus time delay (FOPTD) and second order plus time delay (SOPTD) processes in a feedback control loop, simulations of system responses to setpoint changes were plotted and analyzed for speed of response, stability, and robustness of these tuning methods. It was found that minimum error criteria ISE, ISTE, ISTSE tuning methods, although they give a relatively slow response, were superior in stability and robustness in almost all cases. The minimum error tuning method is easy to implement and gives the desired results using MATLAB/Simulink effortlessly. It gives faster responses with less oscillation. This superiority is observed both for PI and PID controllers. On the other hand, ZN and CHR gave larger overshoots with longer settling time for PI and PID, while CC gives very sluggish response for PI controller. The ZN and CHR tuning methods have higher proportional gains and smaller integral time constants leading to very poor damping, thus they are only suitable for processes that operate deep within the stable region while for processes operating on the periphery of the stable region will be unsafe to tune using ZN and CHR tuning methods.