Improvement of Efficiency in Bidirectional DC-DC Converter with Dual Active Bridge Using GaN-HEMT

A prototype bidirectional isolated DC-DC converter with an output of 3.6 kW, using GaN-HEMTs, employing a planar transformer and operating at a maximum frequency of 400 kHz, was developed and evaluated. Typical circuits for bidirectional isolated DC-DC converters are the LLC resonant converter and the dual active bridge (DAB), both of which have the disadvantage of low efficiency at light loads. In this paper, GaN-HEMTs were used as a rectifier device to reduce DAB losses with natural commutation under light loads, utilizing their no reverse recovery loss characteristics. Zero-voltage switching was achieved using the transformer excitation current as a lagging phase current on the input side. As a result of the efficiency comparison between the LLC resonant converter and DAB under the same components and input/output conditions, higher efficiency was obtained in DAB under most conditions. The maximum efficiency was 98.6%.