Modular converter architecture for medium voltage ultra fast EV charging stations: Global system considerations

Electric Vehicles (EVs) are expected to contribute significantly to the reduction of CO₂ emissions and other types of pollution within the next years. However, the concept of their ultra fast charging still poses demanding requirements, both in terms of the EV battery and the impact on the power grid. Towards this direction, emerging power electronics interfaces as well as energy storage technologies will play a significant role into making EV charging stations competitive with the existing gas station infrastructures. This paper focuses on the proposal of a power converter architecture, which aims for the interface between the three-phase medium voltage AC grid and the Electric Vehicle (EV) batteries. The transformerless AC/DC conversion stage motivates the choice of a suitable multilevel topology, namely the Cascaded H-Bridge Converter (CHB), where the medium voltage is split into several dedicated low voltage DC buses. At each of these levels, integrated stationary Battery Energy Storage Systems (BESS) play the role of power buffers, reducing thus the influence of the charging station on the distribution grid. The EV battery is then charged through parallel-connected isolated DC/DC converters, in order to achieve high currents and meet the standards for galvanic isolation.