A Novel Branch Energy Balancing Control Method for Modular Multilevel Matrix Converter Under Unbalanced System Conditions

The modular multilevel matrix converter (M3C) is a potential frequency converter for the low-frequency AC transmission. The energy distribution in the M3C affects the branch capacitor voltage and the normal operation of M3C, especially under unbalanced system conditions. This paper focuses on the branch energy balancing control method for M3C under unbalanced system conditions. First, the effect of unbalanced conditions on branch energy distribution is analyzed theoretically. Two forms of circulating current are proposed to cope separately with unbalanced conditions of grid side and low frequency side systems and the control method is designed accordingly. The effectiveness and precision of the proposed branch energy balancing control method are verified in the case of unbalanced system of grid side and low frequency side systems.