An Improved DC-DC Converter Based on MMC

DC power grid has been considered as a better choice for large-scale new energy grid connection and long-distance transmission, which can effectively improve the stability and reliability of power grid. High voltage DC-DC converter, as one of the key devices connecting different voltage levels of DC system, plays the role of voltage matching, power flow control, fault isolation and so on. The paper proposed an improved single-phase DC-DC converter based on modular multilevel converter(MMC). It is a DC/AC/DC system with the intermediate medium frequency transformer. DC input voltage is inverted by VSC to intermediate frequency AC voltage, and then boosted by transformer. Finally, stable DC voltage is output by MMC rectification. The low voltage side adopts constant reactive power control, while the high voltage side adopts constant AC voltage control. With the midfrequency transformer, larger ratio can be got. In addition, properly increasing the AC frequency can reduce the volume and loss of the transformer and other passive components used in the circuit. The proposed topology structure and control strategy is validated by MATLAB SIMULINK simulation.