Split Complementary Duty Modulation for Balanced Switching Loss in Bidirectional Resonant Converter

In conventional fixed-frequency bidirectional resonant converter, the upper switches at the primary side or the lower switches at the secondary side suffer from high heat due to the hard switching turn-OFF under buck or boost modes respectively in both power-flow directions. To balance the switching loss among the primary-side or secondary-side switches, we propose split complementary duty modulation for a fixed-frequency bidirectional resonant converter. The split complementary duty modulation enables the upper switches at the primary side or the lower switches at the secondary side to operate with the main duty and the complementary duty split by fixed duty ratio of 0.5 during two consecutive switching periods under buck or boost modes in both power-flow directions. Asymmetric current flows through the switches, so extra dead-time is required for the primary-side or secondary-side switches with weak zero-voltage switching current under buck or boost mode in both power-flow directions. The different minimum dead-times required for all the switches are analyzed in detail. Under the split complementary modulation, the resulting switching losses on the switches are well balanced. A 1.6-kW prototype with primary-side voltage range of 320–480 V and secondary-side voltage of 400 V is built to verify the effectiveness of the proposed switching modulation.