Arm voltage balancing control of modular multilevel resonant converter

Modular multilevel resonant converter is an promising candidate for high voltage applications since it has advantageous features, such as high efficiency, high voltage capability and easy fault-tolerant operation. However, the inequality of arm inductance in practice will lead to imbalance between the upper and lower arm voltages, which will induce large ripples in the circulating current and a dc bias on the voltage generated by modular circuits. To compensate for the voltage imbalance, effects of arm duty cycle changes on arm voltages are discussed. An arm voltage balancing control method is proposed: adjust arm duty cycle according to arm voltage deviation in every switching cycle. Simulation and experimental results are presented to validate the theoretical analysis and the proposed control method.