Hybrid direct current transmission system and control method thereof

The present invention provides a hybrid direct current transmission system and a control method thereof, which belongs to the field of power electronics. The system includes: the rectifier side circuit adopts a heterogeneous series topology structure, the high-voltage valve group adopts LCC to withstand high voltage levels, and the low-voltage valve group adopts MMC to establish and maintain the voltage stability of the grid connection point; the inverter side circuit adopts a distributed connection, wherein the high-voltage valve group adopts LCC, the low-voltage valve group adopts three parallel MMCs, and multiple inverters are distributedly connected to different AC circuits. The rectifier side is composed of LCC and MMC in series, and the inverter side is composed of three parallel MMCs and LCC in series that are distributedly connected to different AC circuits. In this way, the system can provide voltage support for the energy base, has AC and DC fault ride-through function, prevents phase change failure, and improves system stability. In addition, the distributed access method can also achieve flexible power distribution.