A control strategy based on of modular multi-level converters with coupled inductances

This paper introduces a novel structure of Modular multilevel converter (MMC) with a coupled and center-tapped inductance, and its operating principle is elaborated. The upper and lower bridge arms are strictly symmetric, therefore, their fundamental currents are in anti-phase, and then it turns out that the voltages on inductances are significantly reduced with using the coupled inductance, which effectively suppresses the circulating currents. A simulation analysis is conducted with a step reference waveform modulation strategy combined with the sorting method. An improved method of sorting voltages of capacitors is proposed for MMC, and theoretical analysis has shown that it not only contributes to the balance of charging and discharging of capacitors, but also can stabilize the DC current. At last MATLAB/Simulink simulation results of a MMC with 10 sub-modules in each phase, illustrated the advantages of adopting the coupled inductance and the validity of improved sorting method.