The invention relates to a compact modularized multi-level tripolar direct-current
power transmission system, wherein according to the
system, tripolar direct-current
power transmission is achieved. The
system comprises a rectification side subsystem, direct-current circuits and an inversion side subsystem, wherein the rectification side subsystem, the direct-current circuits and the inversion side subsystem are sequentially connected. The direct-current circuits include three wires, namely, a first-pole direct-current circuit, a second-pole direct-current circuit and a third-pole direct-current circuit. The rectification side subsystem and the inversion side subsystem respectively comprises a converter
transformer and a converter, each converter is a four-phase eight-bridge-arm modularized multi-
level converter, the middle point of a first phase, the middle point of a second phase and the middle point of a
third phase of the converter are respectively connected with an auxiliary side of a winding of the converter
transformer, the middle point of the fourth phase of the converter is connected with the third-pole direct-current circuit through a
smoothing reactor, the positive pole of the converter is connected with the first-pole direct-current circuit through the
smoothing reactor, and the negative pole of the converter is connected with the second-pole direct-current circuit through the
smoothing reactor. Compared with the prior art, the system has the advantages that the occupied area of a converter
station is small and the overall modification cost is low.