A Reversible Substation for MVDC Railway Electrification System

In order to improve the efficiency of railway lines electrified in 1.5 kV or 3 kV DC, the implementation of a Medium Voltage DC (MVDC) feeder-wire seems a relevant solution. This feed-wire, installed on the contact-line poles, allows the connection of renewable energy sources and storage systems. Thus, it is envisaged to use a reversible substation to interconnect the MVDC feed-wire and the AC public grid. When the traffic on the railway line is low, the reversible substation can provide both active and reactive power to support the three-phase utility grid. Consequently, this paper proposes a reversible MVDC substation based on three-level voltage source inverters. The different operating modes of the substation are first presented and illustrated by simulation results. The last part of the paper deals with the robustness of the reversible substation to withstand short-circuits on DC side.