Study on low-frequency voltage fluctuation of traction power supply system introduced by multiple modern trains

As the modern trains have been widely adopted in China high-speed and heavy-haul railways, the low-frequency voltage fluctuation of traction network has been found frequently, which affects both traction power supply system (TPSS) and utility system seriously. In order to investigate such new phenomenon, this paper studies the formation mechanism and potential factors of the low-frequency fluctuation by comparing the results of the impedance-based and simulation methods. Firstly, the impedance-based model of the train-TPSS interaction system is presented with the consideration of concrete configurations. Then, the stability of interaction system under different conditions of system impedances has been studied based on the impedance-based stability analysis method. Besides, the low-frequency fluctuation and potential factors of the train-TPSS system have also been simulated on MATLAB/Simulink platform. The results of both theoretical and simulation analyses quantify the impacts of the equivalent output impedance of TPSS (e.g., catenary length, traction transformer capacity, etc.) and input impedance of the train (e.g., number, operation condition, control parameters, etc.) on low-frequency voltage fluctuations. Finally, the effectiveness of the proposed methods has been verified through sufficient field tests in China electrical railways. And the suppression suggestions are provided to improve the low-frequency voltage fluctuations.