Medium-voltage bidirectional direct-current power transmission system and control method thereof

Disclosed is a medium-voltage bidirectional direct-current power transmission system. The medium-voltage bidirectional direct-current power transmission system comprises a converter I, a converter II,a controller I, a controller II, an isolation switch and a direct-current connection line; the medium-voltage bidirectional direct-current power transmission system is characterized in that the current converter I is connected with an alternating-current power grid through the isolation switch, and the converter II is connected with an alternating-current power grid on the other side through theisolating switch; the converter I is connected with the converter II through the direct-current connection line; the controller I is electrically connected with the converter I, and the controller IIis electrically connected with the converter II; all the converter units adopt the same two-level or three-level three-phase structure; the converter units can be replaced with each other, so that maintenance is simple; the con