Fractional converter for high efficiency high power battery energy storage system

A family of bidirectional fractional DC-DC converter for high voltage, high power battery energy storage system is proposed in this paper. The proposed converter has the benefits of low cost, high efficiency since it only processes part of the total converted power. One extra low voltage battery pack is needed; however, it can be from a different voltage rail or seamlessly integrated with the high voltage battery pack. System efficiency and battery capacity calculation methodologies are given in details. A proof-of-concept fractional converter based on GaN transistor was fabricated. Experimental results of a 1.2kW prototype are presented to validate the analysis. With the proposed converter, a peak equivalent efficiency of 99.63% in a wide input/output voltage range are achieved. It is shown that the fractional converter can greatly reduce the cost of energy storage system while achieve high efficiency and high power-density in potential applications.