Cascode GaN FET 기반 EV용 V2x DAB 컨버터의 경부하 효율 분석

Abstract

In this paper, the light-load efficiency of cascode gallium nitride (GaN) FET-based V2x dual active bridge (DAB) converters for electric vehicles(EVs) is analyzed. High efficiency and high power density are required when an on-board charger(OBC) is used in EVs. To this and a zero voltage switching (ZVS) topology, such as that observed in DAB converters, is widely applied. As for the converter requiring current enough to achieve the ZVS condition of the efficiency characteristics vary depending on whether ZVS operated or not. Therefore, in this study, the efficiency in the hard switching section is improved by applying a cascode GaN FET to a DAB converter. The ZVS characteristic is analyzed by considering the parasitic output capacitance of the switching device. Compared to the Si device, the cascode GaN FET with low parasitic output capacitance realizes ZVS under a lower load condition. To verify this, a load test is performed by applying it to a 3-kW DAB converter. The experimental results confirm that ZVS is achieved when the cascode GaN FET is applied. Moreover, a shorter dead time can be applied owing to excellent dv/dt and di/dt characteristics, which improves the overall efficiency. In conclusion, the use of GaN FET in DAB converters can improve efficiency at light loads.