Three-pole flexible direct current transmission system and method

摘要

The invention discloses a three-pole flexible direct current transmission system and method. Each of a rectification converter and an inversion converter is composed of a three-phase six-bridge-arm modularized multi-level converter. Two converter valves are arranged at a direct current side of a double-pole direct current system converter. the connection point of the upper and lower converter valves of the rectification converter and the inversion converter is connected with a pole 3 direct current line through a smoothing reactor, triggering of the converter valves is controlled, the pole 3 direct voltage polarity is changed periodically, and through modulation of current instructions of three poles, three-pole direct current transmission is achieved. Power can be transmitted by utilization of three wires, and the transmission system has characteristics of small converter station land occupation area, low total reconstruction cost, high reliability and the like. The transmission system is especially suitable for capacity increasing engineering of conversion from an alternating current line into a direct current transmission line in a power supply system of a large-size city with scant land resources and has good engineering application values.