The invention discloses a mixed MMC-based mixed
direct current power transmission system, comprising a rectifying converter
station and an inversion converter
station, wherein the inversion converter
station adopts a mixed MMC. The
direct current power transmission system has the active and reactive decoupling control capacity, can transmit power to a reactive network without the
phase change failure risk and has
direct current fault self-cleaning capacity; under the condition that a feeding end
alternating current system has a fault; the mixed MMC has the capacity of outputting a negative level by using a full-bridge submodule, the direct
current voltage output by the system can be reduced under the premise of ensuring the
controllability and stability of the system, the direct
current voltage can be matched with the direct
current voltage of a rectifying station, and the direct current power is maintained to be continuously transmitted; due to the optimization on the number of two types of submodules in the mixed MMC, the use number of power electronic components is greatly reduced and the
investment cost is reduced under the condition that the mixed modularized multi-
level converter meets the stable and transient operation demands of the direct current system.