RDC Converter for Battery Buffered Fast EV Charging

Current fast EV charging is facing challenges due to grid insufficiency and high operation costs. A battery-buffered fast EV charging is a possible solution to provide high charging power regardless of grid insufficiency. Besides, it can also reduce the operation costs of a fast-charging station. However, an additional DC/DC converter is needed for such a battery-buffered EV charging system. The efficiency of the state-of-the-art DC/ DC converter is limited. The DC/DC converter wastes lots of energy and needs an additional cooling system.
The reduced dissipation converter (RDC) converter using partial power processing idea is then proposed. It can significantly increase the efficiency and reduce the cost of the DC/DC conversion subsystem. Several DC/DC topologies have been analyzed. To provide sufficient regulation for wide voltage variations of electric vehicles, a multi-level DC/DC topology is proposed to provide wide voltage regulation as well as maintain partial power processing.
Regarding the efficiency and power density of the proposed topology in the RDC converter, a hardware optimization method is analyzed and illustrated to minimize the loss and volume of the RDC converter. A digital closed-loop control has been designed and implemented in the RDC converter.
Finally, a 20 kW RDC prototype has been built in the lab. Experiments show that the RDC converter can achieve 99.4% efficiency and about 5 kW/L power density. In addition, the output current ripple of the RDC converter is about 4% (less than 5% in CCS and CHAdeMO standards). Finally, the designed control system works stably at the steady state. The dynamic response experiments show that the control system performs well on overshot and tracking time, so as to provide effective and sufficient control for integration to the grid later on.