Development And Evaluation Of A PID Auto-Tuning Algorithm Based On Relay FeedBack

Abstract

A method for automatic tuning of the PID controllers, usually called auto-tuning, is presented. The method is based on a frequency domain model of the process to be controlled and uses a single point on the Nyquist curve. The identification of this point is performed using a relay connected in a feedback loop with the process, forcing the process output to oscillate. The controller design is based on the dominant closed-loop poles method. No apriori information on the process parameters is required. Simulations compare the proposed method with two other tuning methods: Ziegler-Nichols method and internal model method applied to PID control. A variant using two points on the Nyquist curve is also presented. Some experimental results are shown for auto-tuning control of a thermal process.