An improved modulation scheme for harmonic distortion reduction in modular multilevel converter

The modular multilevel converter (MMC) has recently attracted research attention in medium-voltage applications, such as MV drives and back-to-back systems. In such applications, the harmonic content of MMC´s output voltage and current is of particular importance and must be kept below permissible levels. This is typically done by increasing the switching frequency and/or by using an output filter stage. To lower the total harmonic distortion (THD) of the output voltage and current at the terminals, in this work, a new modulation scheme for MMC is presented. Using this modulation scheme, since the voltage and current harmonics are lowered at the converter terminals, the rating and hence the cost of the output filter required to achieve permissible THD level is reduced. Simulation results are provided to testify to the effectiveness of the proposed method.