A Three-Pole DC Transmission System Topology Based on Modular Multilevel Converter

Abstract

The invention discloses a tri-pole direct current transmission system topology structure based on an MMC. The tri-pole direct current transmission system topology structure is characterized in that direct current transmission is performed in a tri-pole connecting mode, and each pole comprises a rectification-side converter transformer, a rectification-side converter, a rectification-side smoothing reactor, a direct current transmission line, an inversion-side smoothing reactor, an inversion-side converter and an inversion-side converter transformer group. The rectification-side converters and the inversion-side converters are in modular multi-level structures, sub-modules of different amounts are connected in series and in parallel to be adapted to requirements for different voltage classes and currents, and three transmission lines used in a tri-pole direct current system are cables or overhead lines. The tri-pole direct current transmission system topology structure is high in reliability and capable of meeting the requirement for changing alternating current lines into direct current lines, phase change failures on the inversion side can be avoided under the condition that an alternating current system breaks down, voltages on two sides of the alternating current system can be stabilized, a alternating current filtering and reactive compensation device is not needed, and good application values are provided.

Description

technical field [0001] The invention relates to the technical field of power transmission and distribution, in particular to a three-pole direct current transmission system for transforming an existing alternating current line into a direct current transmission line. Background technique [0002] With the sustained and rapid development of my country's economy, the contradiction of power demand has become increasingly prominent. On the one hand, the growth of power load exceeds the transmission capacity of the original AC transmission line, and it is difficult to obtain a new transmission corridor due to land resources constraints; The maximum thermal power that the wire can withstand is less, so it is necessary to adopt new technology to further tap the power transmission potential of the existing line. [0003] Compared with AC transmission, with DC transmission, the line current can reach the maximum thermal limit that the wire can withstand. In 2004, in the patent US67...

AI Technical Summary

Problems solved by technology

[0008] figure 1 The three-pole direct current transmission scheme in the paper adopts the conventional LCC-HVDC technology, so it also has the disadvantages of LCC-HVDC

If the AC system on the inverter side fails, it will cause commutation failures at the three poles of the DC at the same time, resulting in the interruption of the transmission power of the DC line, which poses a threat to the safety and stability of the receiving end system.

In addition, during the operation of the three-pole DC system, the magnitude of the current in each pole and the voltage polarity and current direction of pole 3 need to change rapidly according to a certain period, which will inevitably cause disturbance to the AC system at both ends.

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