Identification of First Order Plants by Relay Feedback with Non-symmetrical Oscillations

Abstract

The paper deals with the approximation of the systems with dominant first order dynamics by the Integrator Plus Dead Time (IPDT) model. They are attractive especially in control of unstable plants, where an open-loop identification may not be applied. This paper updates a previously published contribution based on analysis of the non-symmetrical oscillations with possible offset arising typically under relay control that has been improved to prevent computational errors in the case of a negligible disturbances, when the relay on and off times are nearly equal over one control period. The analytical results are followed by the experiments with several laboratory plant models. The obtained model parameters are used to tune disturbance observer based controllers to illustrate the performance of the proposed method in real applications.