Highly Efficient EV Battery Charger Using Fractional Charging Concept with SiC Devices

This paper describes the implementation of the fractional power conversion concept for use in an on-board charger for Electric Vehicles (EV). High gain step up topologies are required and an efficiency analysis of the full bridge boost converter is made. A comparison of many power devices including Si, GAN and SiC devices concludes that SiC devices are well suited for this application. Using loss equations and battery charging characteristics the converter is optimized for low loss in a full battery charge cycle. Switching-average methods model the small signal characteristics and a PI controller is implemented. The fractional charging configuration results in a very high current gain. A 100 kHz prototype was tested on a 300 V EV battery, achieving a converter efficiency of 97.6%. For a 400 V battery the charger can charge 4 kW at more than 98% efficiency. The power density of the charger is 3.6 kW/L.