Multi-Phase Reconfigurable LLC Resonant Converter with Passive Current Balancing and Wide Voltage Gain Range

Voltages of lithium-ion batteries for electric vehicles vary in the range of 100–420 V depending on their state-of-charge. On-board battery chargers need a large-current capacity isolated dc-dc converter with a wide voltage gain range. Although multi-phase LLC converters are a typical solution to enhance the current capacity, additional components and feedback control loops are necessary to balance phase currents, resulting in increased circuit complexity and cost. This paper proposes the multi-phase LLC resonant converter with passive current balancing capability and wide voltage gain range. Phase currents are passively balanced thanks to the charge conservation of added flying capacitors. Furthermore, reconfigurable primary- and secondary-side circuits achieve the voltage gain range twice wider than that of conventional converters. The experimental verification using a 1-kW prototype demonstrated the passive current balancing capability as well as widened voltage gain range.