Fast Charging of Electric Vehicles Using a Multi-Winding Transformer

A medium voltage grid connected fast charging architecture for electric vehicles is proposed in this paper. The proposed architecture uses a custom designed multi-winding transformer that has one primary winding and several isolated secondary windings. The secondary windings are connected in such a manner that they form two group. One group consists of a delta connected winding and two delta polygon connected windings such that the line voltages of these winding has a shift of ±20° with respect to line voltage of the primary winding. These three secondary windings are connected to three-phase bridge rectifiers, whose outputs are cascaded to form a necessary part of an 18-pulse converter. The cascade connection of DBRs forms a combined DC bus for fast charging of electric vehicles. Irrespective of number of charging vehicles, grid current drawn by this converter has a very low THD. The second group consists of delta connected secondary which is connected to voltage source converter. The voltage source converter is connected to large battery energy storage and allows bidirectional power flow between grid and battery energy storage,power flow from battery energy storage to vehicles connected to the combined DC bus. The proposed architecture provides a low cost fast charger that has bidirectional power flow capability and uses well-established multi-winding transformer for electric vehicles.