Auto-tuning of phase lead/lag compensators

Abstract

In the tuning of phase lead/lag compensators, knowledge of specific points on the frequency response of the plant are required. Such points are specified by their frequency, gain and phase and are not readily available without an accurate model of the plant. Yet such information is important for any auto-tuning procedure to succeed. In this paper, relays with hysterisis are tuned to determine points on the frequency response of a plant with a user-specified gain, g0 or phase, φ0. On-line algorithms are developed to tune the operating point of the relay feedback system so that the resulting oscillations correspond to the frequency response of the plant with either gain, g0 or phase, φ0. Tuning involves setting either the amplitude of the relay or its hysterisis width. Improvement over the simple application of the describing function is also shown. The results are applied to the auto-tuning of phase lead and lag compensators. Simulations are presented to illustrate the auto-tuning procedures. © 2003 Elsevier Ltd. All rights reserved.