A NEW APPROACH TO CLOSED-LOOP AUTOTUNING FOR PROPORTIONAL-INTEGRAL-DERIVATIVE CONTROLLERS

A simple method for the autotuning of proportional-integral-derivative (PID) controllers which keeps the PID controllers In a closed loop is proposed. A limit cycle is generated through setpoint relay to extrac t relevant information about the process dynamics. Ziegler-Nichols tun ing formulas based on the reaction curve method and the ultimate gain and ultimate period method are used to calculate the PID parameters. E xtensive simulations have shown that the proposed method is accurate a nd needs not. to switch off the existing controller.