A simple method of tuning PID controllers for interval plant of cold rolling mill

The mathematical model (Interval Plant) of the web guide in rolling mill is controlled using PID controller. The given interval plant is approximated to first order plus time delay with integrator (FOPTDI) system. The equating Coefficient (EC) method proposed by Padmasree et. al. for design PID controllers for FOPTD systems is extended to FOPTDI systems. The equating coefficient method gives simple equations for the controller settings. This method is based on matching the coefficient of corresponding powers of s in the numerator and that in the denominator of the closed loop transfer function. Controllers are designed using two tuning parameter. The performance of the closed loop system is evaluated for both the original and the approximated model. The controllers are also tuned using Ziegler-Nichols technique (Z-N), Internal Model Control (IMC) and the performance are compared by simulation.