Direct current tractive power supply system based on flexible direct current power transmission

The invention discloses a direct current tractive power supply system based on flexible direct current power transmission. The direct current tractive power supply system comprises a step-down transformer, a double-end active high-voltage direct current power transmission system and a buck chopper. The double-end active high-voltage direct current power transmission system is based on the modularized multi-level converter technology and comprises two converters which are completely symmetric and connected through a direct current power transmission cable. Each converter is connected with the three-phase alternating current through the step-down transformer. The input end of the buck chopper is connected with the direct current side of the double-end active high-voltage direct current power transmission system through a first switch assembly, and the output end of the buck chopper is connected with a traction system through a second switch assembly. The second switch assembly is interlocked with a third switch assembly, when a metro or a light rail operates, the second switch assembly is switched on, the third switch assembly is switched off, and when an electric locomotive operates, the third switch assembly is switched on, and the second switch assembly is switched off. The direct current tractive power supply system has the advantages of being low in cost, little in traction network voltage and electric energy loss, low in harmonic content, high in system power coefficient, wide in application range and the like.