MMC CONVERTER

A modular multilevel converter (MMC) converter including an auxiliary sub-module provided between an upper converter arm and a lower converter arm of the MMC converter is provided. An MMC converter includes an auxiliary sub-module including: an energy storage unit storing a DC voltage in the sub-module; a first semiconductor switch connected to the energy storage unit; a second semiconductor switch connected to the first semiconductor switch; a third semiconductor switch connected to the second semiconductor switch; and a switching controller turning ON/OFF the first to third semiconductor switches, wherein a mid-point between the first and second semiconductor switches is connected to the sub-module of the upper converter arm, a mid-point between the second and third semiconductor switches is connected to a load connection terminal, and a mid-point between the third semiconductor switch and the energy storage unit is connected to the sub-module of the lower converter arm.