A Novelty Proposal of Grid-Forming Multi-Cell DC-AC Converter for Single-Phase Railway Catenary Systems

One of the main problems related to single-phase AC railway electrification is the unbalance generated in the three-phase supply grid. This issue does not exist in case of DC electrification. The aim of this paper is to present a novelty topology for generating 25kV AC from the exisiting 3kV DC catenary, avoiding the generation of unbalances in the distribution grid. The system is proposed as a completely scalable solution, with multiple Grid-Forming DC/AC converters, whose control is based on the single phase Virtual Synchronous Machine concept. One of the main advantages of this approach is that all converters in the system provide support to the voltage and frequency. Besides, there is no need for any higher level controller and communication system. With a proper power control design, the power amount delivered by each converter, with respect to the total value demanded by the loads, can be established.