Stability Analysis of the “Train-Network” System for Electrical Railways Based on Harmonic Linearization

Abstract

With the increasing application of power electronic equipment in electrified railways, low-frequency oscillations resulting from impedance interactions between trains and the traction network (TN) have become a significant factor affecting system stability. In passenger–freight mixed railway systems, trains supplied by the same TN may adopt different converter control schemes, which further complicates system modeling and stability evaluation. To address this problem, a sequence-domain impedance model derived through harmonic linearization is established to characterize the impedance behaviour of both high-speed trains and freight trains. The validity of the proposed model is confirmed by the frequency sweep method. Subsequently, the generalized Nyquist stability criterion is employed to investigate how train converter control parameters influence system stability. The results indicate that the system achieves the best stability performance when the proportional gain kpi is set to 5 for freight trains and 7 for passenger trains. This study offers useful technical guidance for the extensive application of power electronic equipment in electrified railway systems and supports their safe and stable operation.