Modeling and Simulation of Low Frequency Oscillation in Vehicle Network Coupling System Based on Modal Analysis Method

With the rapid development of China’s electrified high-speed railways, the number of EMUs (Electric Multiple Units) commissioned in the electrified railway network has increased significantly [1–3]. When multiple EMUs start under light-load conditions simultaneously in the traction network, low-frequency oscillations in the traction network voltage may occur. Therefore, this paper takes the CRH5 EMU as an example to model the vehicle-grid coupling system using the DQ impedance measurement method under a bilateral direct power supply mode with full parallel return lines. The node admittance matrix of the train connected to the bilateral power supply system is derived, and a small-signal analysis method is employed to establish the system mathematical model. Based on modal analysis, the influence of different factors on the low-frequency oscillations of the bilateral power supply system and the governing laws of the system’s key oscillation modes are investigated. Simulation results demonstrate that the proposed modeling method enables stability analysis of the vehicle-grid coupling system. This study thus holds significant practical implications for ensuring the safe and stable operation of the railway system and enhancing transportation efficiency.