| Abstract |
Future transmission and distribution grids will use power converters to enable interface with HVDC systems and the Modular Multilevel Converter (MMC) is a topology that is already employed in commercial systems. The MMC converter inherent the benefits and also the limitations of Voltage Source Converters, the more important one being the capability to only step-down voltage from the DC side to the AC side. In cases where voltage step up is required, a quasi Z-source network can be added to produce the quasi Z-source MMC. This paper proposes three modulation techniques for a quasi Zsource modular multilevel converter (qZS-MMC) to provide voltage boost capability. In addition, it will be shown that the qZS-MMC can handle the blocking of DC-faults and prevent the buildup of the resulting short-circuit currents which is essential in transmissions and distribution power grids. The relations of average shoot-through duty ratio, the average value of the sub-modules capacitor voltage and the peak value of the output voltage have been derived for each modulation technique. A comparison between these techniques has been presented. The simulation results presented in the paper confirm the validity of the proposed modulation techniques and capability for DC-fault blocking. |
