7-kW Bidirectional H-Bridge Flyback Converter for Onboard Chargers

In this paper, a bidirectional flyback converter with an H-bridge structure is proposed. Recently, LLC resonant converters are primarily used as DC–DC converters of unidirectional on-board chargers (OBCs), and CLLC and dual-active bridge (DAB) converters are mostly considered for bidirectional OBCs. However, in the case of CLLC and DAB for bidirectional chargers, issues such as difficulties in setting bidirectional gain and efficiency degradation owing to circulating currents have arisen. To address these issues, this paper suggests the feasibility of bidirectional operation of the flyback converter and overcomes the problem of high-voltage stress in the flyback converter through an active-clamped H-bridge structure. In addition, the proposed method applies a bidirectional symmetric structure and a simple PWM control method, which verifies the ease of designing bidirectional gain. The proposed circuit is implemented as a 7 kW prototype using Si-MOSFETs, operating at a switching frequency of 80 kHz, an input voltage of 400 V, and a battery voltage range of 100–450 V. The validity of the proposed circuit is verified through experimental results.