Self‐sustained low‐frequency oscillation and its suppression in a practical AC/DC distribution network

Abstract

A variety of power electronic equipment in AC/DC distribution networks causes oscillations with unknown origin. A self-sustained low-frequency oscillation appeared recently in a practical AC/DC distribution network in Tongli, Jiangsu Province, China. In this paper, the accident is introduced, and the oscillation phenomenon has been successfully reproduced by theoretical modelling. Based on the small signal model, the oscillation is well analysed and an additional controller is designed to suppress this low-frequency oscillation. The reason of the oscillation is related to the power and control parameters of buck converter; the system is critically stable within the linear system stability theory, namely, the leading eigenvalues of the small-signal system are on the imaginary axis. Meanwhile, a novel inhomogeneity phenomenon for oscillation amplitudes on different voltage-level DC buses, which are not proportional to their steady-state voltages, is found. This paper provides a new case study of self-sustained oscillations coming from a practical AC/DC distribution network and is of great significance for our understanding of oscillations in electric power engineering.