22 kW bidirectional on-board charger for V2X applications based on LLLC and buck converters
摘要
This paper proposes a bidirectional 22 kW OBC for V2X applications. The proposed OBC employs a three-stage topology consisting of an AC–DC inverter stage and a DC–DC stage including a bidirectional LLLC resonant converter and buck converter. The LLLC converter incorporates a reverse auxiliary inductor on the primary side and exhibits voltage-gain characteristics identical to those of an LLC converter regardless of the power transfer direction. This allows a design used in the easily controllable below-resonance region to be applied in both directions so that it can cope with a wide range of bidirectional loads even under fixed input voltage conditions. A bidirectional buck converter, which regulates the current for both charging and discharging operations, employs a ZVT (zero voltage transition) circuit to achieve soft switching and suppress switching surges. A comparative analysis of hard-switching configurations using SiC-FET and GaN devices is also presented. To verify the proposed circuit, a prototype rated for a three-phase 380 VAC input and a battery voltage range of 180–482 V was designed and tested. The results confirmed the validity of the proposed approach, achieving an efficiency exceeding 95% under bidirectional rated conditions without the need for additional complex algorithms, such as input-voltage variation or variable-structure control.