Automatic Current Balancing Multi-Phase Recofigurable LLC Converter with Wide Voltage Gain Range for On-Board Battery Charger

On-board battery chargers need a large-current capacity isolated dc-dc converter with a wide voltage gain range as voltages of lithium-ion batteries vary depending on stage of charges. Although multi-phase LLC converters have been proposed to enhance input/output current capacities for large current applications, additional components and feedback control loops are necessary to actively balance multiple phase currents, resulting in increased system complexity and cost. Meanwhile, reconfigurable LLC converters have been proposed to widen voltage gain range, but conventional reconfigurable techniques cannot balance phase currents. This paper proposes an automatic current balancing multi-phase reconfigurable LLC converter with a wide voltage gain range. Phase currents in the proposed converter are automatically balanced thanks to the charge conservation of added flying capacitors. Furthermore, both primary- and secondary-side circuits are reconfigurable, achieving a wide voltage gain range. The experimental verification using a 1-kW prototype demonstrated the automatic current balancing capability and widened the voltage gain range.