A Bidirectional GaN-Based CLLC Converter for Plug-In Electric Vehicles On-Board Chargers

This paper presents a bidirectional CLLC converter solution for the dc-dc stage in plug-in electric vehicle (PEV) on-board battery chargers. The proposed architecture allows the converter to operate at resonance for the bidirectional constant-power (CP) load range with a variable bus voltage, while frequency modulation is employed for the constant-current (CC) load range in the grid-to-vehicle (G2V) mode with a fixed bus voltage, resulting in a limited bus voltage range. This enables the use of 650-V Gallium nitride (GaN) devices for the primary and secondary sides' switches. The design flow is presented and a 1-kW high-frequency prototype is implemented. GaN reverse conduction characteristics are investigated and employed for the high-frequency current rectification. The prototype operates with soft switching across the operational range, achieving an efficiency of up to 95.7%, with the resonant inductances integrated in the transformer.