A Full bridge type series connected Modular Multilevel Converters for Medium Voltage Drive

This paper proposes a new MMC topology, in which, a "full-bridge" with four arms of cascaded full-bridge modules is applied for each phase and three phase legs are series connected in vertical direction to support the DC-link. The major advantages of proposed topology are as follows: (1) The total number of required submodules are reduced to 2/3 compared with traditional MMC topology. As a result, the volume of the converter shrinks significantly. Regarding the reduced voltage amplitude, an AC transformer is used to bring the voltage back into the normal amplitude in a three-phase Y-connection manner. (2) The second order harmonic is eliminated in the proposed unique configuration. Thus, the capacitor size is reduced and no more circulating current control loop is required. A detailed 20 MW simulation has been conducted and the related results of proposed topology have been presented. What’s more, The SM prototype and preliminary experiments are also demonstrated and analyzed.