Development and Evaluation of a PID Auto-Tuning Controller

This paper presents comparative studies regarding a recently developed extension of the widely used relay-feedback PID auto-tuner. The proposed method consists of two steps: process identification and controller design. First, a non-iterative procedure is suggested for identification of two points on the process Nyquist curve. A second-order-plus-dead-time model is obtained and then used for PID controller design based on the internal model principle (IMC). For the identification of the two points on the Nyquist curve a pure relay in the feedback loop (as used in standard auto-tuning) and a relay which operates on the integral of the error are used. The paper compares the performance of autotuning methods with experimental studies on a commercial auto-tuning PID controller - a Shimaden PID auto-tuner