An Analysis Study on Mutual Protection Cooperation Characteristics of Electric Vehicles Power Systems under Regenerative Braking Operations

Energy consumption in urban railway operations is primarily attributed to traction power and facility electricity. Electricity used for passenger amenities, lighting, and ancillary systems constitutes over 95% of total operational energy, with train traction alone accounting for approximately 70%. In domestic urban rail networks, about 80% of the system consists of underground sections, where the lack of natural lighting further intensifies electricity demand. Following a transitional phase that employed a combination of resistance, chopper, and VVVF (Variable Voltage Variable Frequency) control, the system has now achieved full adoption of VVVF technology. This study investigates the effectiveness of train regenerative braking and energy storage systems (ESS), alongside their influence on catenary voltage and power system performance, using data from two main substations and one depot substation operated by a domestic railway company. Based on these analyses, the paper assesses the appropriateness of protective coordination settings between rolling stock and the traction power system. The findings suggest that the inverter low-voltage protection setting for overhead lines (850V±10%) in VVVF-based electric vehicles requires reassessment. Furthermore, enhancing the capacity of surge arresters (S/A) is recommended to improve substation energy efficiency, stabilize overhead line voltage, and reinforce system protection. Finally, the study emphasizes the need for continued research into the reuse of energy storage systems and highlights the importance of technical advancements by rolling stock manufacturers to minimize voltage control deviations, ensuring reliable operation of inverter-based voltage reduction systems at a DC overhead line voltage of 1,800V.