Relay Identification Using Shifting Method for PID Controller Tuning

Milan Hofreiter

doi:10.3390/en14185945

Abstract

The aim of this study was to present a relay shifting method for relay feedback identification of dynamical systems suitable for PID controller tuning. The proposed technique uses a biased relay to determine frequency response points from a single experiment without any assumptions about a model transfer function. The method is applicable for open-loop stable, unstable, and integration processes, even with a delay, and regardless of whether they are oscillating or non-oscillating. The core of this technique was formed by the so-called relay shifting filter. In this study, the method was applied to a parameter estimation of a second-order time-delayed (SOTD) model that can describe, with acceptable accuracy, the dynamics of most processes (even with a transport delay) near the operating point. Simultaneously, a parameter setting for the PID controller was derived based on the model parameters. The applicability of the proposed method was demonstrated on various simulated processes and tested on real laboratory apparatuses.

Highlights

Relay feedback identification is popularly used for estimating model parameters
This approach has been increasingly explored in recent years due to the relay feedback method suggested by Åström and Hägglund [2] for PID controller tuning
The frequency points G(jω i ), i = 1, 2,· · ·, N are determined from one relay feedback test without any prior knowledge of the model

Summary

Introduction

Relay feedback identification is popularly used for estimating model parameters. In the relay feedback test, the period of oscillation and the amplitude of the process output were measured. Let us consider a time-invariant process that can be described by the frequency response function GP (jω) around its operating point, where j is the imaginary unit and ω is the angular frequency. The hysteresis helps reduce the effects of measurement noise by enabling noiseless control action and increases the period of oscillation. The experimental time corresponds to approximately 3 to 4 periods of Tp [13]

Objectives

Methods

Conclusion