Modular Multilevel Converter and Cycloconverter Based Machine Drive Systems

The modular multilevel converter (MMC) becomes attractive in the medium- and high-power application with high modularity. In this paper, the MMC and cycloconverter based machine drive system is proposed. The six-phase MMC is used as the grid-side converter, which produces six-phase medium-frequency ac voltage for the machine side converter. The six-phase to three-phase cycloconverter is used as the machine-side converter, which converts the medium-frequency ac voltage to the low-frequency ac voltage to drive the machine. In addition, the corresponding control for the grid-side converter and the machine-side converter are also proposed. The proposed MMC and cycloconverter based machine drive system can effectively realize the control for the high-voltage, high-power and low-speed machine. What is more, the SM capacitance is significantly reduced owing to the medium-frequency ac output voltage of the MMC. The simulation studies of the proposed MMC and cycloconverter based machine drive system and control are conducted with a detailed PSCAD/EMTDC model, and the results show their effectiveness.