Medium-voltage DC electric railway systems: A review on feeding arrangements and power converter topologies

Medium-voltage DC (MVDC) electric railway systems have several advantages over conventional DC and AC railway electrification systems. These advantages include higher capacity, possibility of connecting to power networks at lower voltage, removal of neutral sections, smaller line voltage drops, and longer distances between traction power substations. This paper reviews in depth the arrangements for MVDC railway electrification systems proposed in the technical literature and the topologies used for high-power medium-voltage AC-DC converters. With reference to typical requirements of a MVDC railway electrification system, the pros and cons of the topologies are critically analysed. Moreover, this paper reviews the DC-DC power converter topologies for on-board power electronic traction transformers, required to interface the MVDC power supply with the traction motors. Finally, the review highlights the existing challenges of MVDC electric railway systems and the potential areas of future research.