An optimized design of bi-directional dual active bridge converter for low voltage battery charger

This paper proposes an optimized design of dual active bridge (DAB) converter for low voltage charger. Among various bi-directional DC/DC converters, DAB converter is a high efficiency buck and boost bi-directional DC-DC converter isolated by a high frequency transformer. Battery voltage varies according to the charging status of the battery and the parameters of the DC/DC converter are the same regardless of the battery voltage. When the battery voltage is high, the soft switching (ZVS) region is reduced compared to the low battery voltage. In this paper, variable switching frequency is adopted in order to maximize soft-switching (ZVS) region at the high battery voltage. The same power can be obtained at the same duty regardless of the battery voltage using the variable switching frequency. The proposed method is applied to a 5kW prototype dual active bridge converter, and the experimental results are analyzed and verified.