Star and Delta‐Channel Modular Multilevel Converters

This chapters presents the operation and control of star‐channel MMC, building upon the passive (PC‐MMC) and active (AC‐MMC) cross‐connected modular multilevel converters used to overcome the technical issues in the conventional modular multilevel converter (MMC) during low or zero‐frequency operation. The conventional modular multilevel converter is modified into a star‐channel modular multilevel converter by interconnecting the converter legs using additional submodules in star configuration. The star‐channel provides a path for high‐frequency current components owing in the system and helps to minimize the capacitor voltage ripple during low‐frequency operation. The required number of submodules in the sub‐arms and star‐channels depends on the converter voltage rating. Generally, the star‐channel requires only 1 4 of the submodules in the main arms. In star‐channel MMC, each sub‐arm is equipped with an arm inductor, which mitigates the switching ripples and the inrush current. The star‐channel MMC requires twice the buffer inductors, but the equivalent (total) inductance remains same as that of the conventional MMC.