Modeling of DC Railway Power Supply Systems Based on MMC

In this paper, design methodologies and topologies for modular multilevel converter (MMC), aimed at constructing (DC) railway power supply systems based on converter stations, are proposed. Traditional railway systems use railway vehicles that receive power through 25 kV AC supply lines and convert the single-phase AC 25 kV to DC 1.5 kV using 60 Hz transformers and converters. This process necessitates the use of large electrical components in the vehicles for the conversion from AC 25 kV to DC 1.5kV. The recent focus has been on configuring railway lines as DC ±20 kV and using bidirectional DC/DC converters to integrate with renewable energy sources through a DC multi-terminal topology, with the goal of extending the DC grid transmission and distribution system to railway systems. Urban railway vehicles operate with a 1.5 kV DC power supply system; thus, various topologies can be constructed for such DC power supply lines. In this paper, DC multi-terminal topologies for railway systems, consisting of an H-bridge-based three-phase monopolar AC/DC MMC converter and an isolated DC/DC MMC converter, are proposed. A parameter design methodology for MMC converters was suggested to implement the proposed DC multi-terminal topologies, and their active and reactive power control performance were verified through PSCAD simulation.