LCC-MMC hybrid three-terminal high-voltage direct current transmission system and DC fault fast current limiting method thereof

Abstract

The invention discloses an LCC-MMC hybrid three-terminal high-voltage direct current transmission system and a DC fault fast current limiting method thereof. The LCC-MMC hybrid three-terminal high-voltage direct current transmission system comprises a transmitting end converter station LCC and receiving end converter stations, namely, two hybrid MMCs, and redesigns a control architecture of the existing hybrid direct current transmission system. The DC fault fast current limiting method provides a fault current limiting control strategy for the LCC and the MMCs, suppresses the magnitude of fault currents of the transmitting end LCC and the receiving end MMCs by adopting an additional control strategy during the system DC fault transient process, quickly suppresses the DC fault current whena DC fault occurs in the system, and protects current converter equipment. The LCC-MMC hybrid three-terminal high-voltage direct current transmission system and the DC fault fast current limiting method thereof realize the independent control of AC-DC control through AC-DC decoupling, enable each bridge arm to output a bridge arm output voltage reference value, and realize the control of AC and DC currents at the same time; and when a direct current fault occurs, the MMCs operate near a zero direct voltage through quickly switching the transmitting end LCC into an inverting state and negatively inputting full-bridge sub-modules of the receiving end hybrid MMCs, thereby realizing elimination of the DC fault current.

Description

technical field [0001] The invention relates to the technical field of power transmission and distribution in electric power systems, in particular to an LCC-MMC hybrid three-terminal high-voltage direct current transmission system and a fast current limiting method for direct current faults. Background technique [0002] Since the 21st century, with the increasingly prominent environmental problems, in order to reduce carbon emissions and reduce the proportion of coal-fired power generation, it is necessary to develop and utilize renewable energy on a large scale. my country's new energy bases are characterized by dispersal, remote distribution, and strong volatility, and are distributed inversely with the load center, leading to an increasing demand for large-capacity long-distance transmission of electric energy. The grid-connected high-voltage AC transmission system has inherent defects such as high cost and serious stability problems. Conventional high-voltage direct c...

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Problems solved by technology

[0007] The problem of the prior art is: for the above scheme of Tang Geng et al., although the fault current can be blocked when a DC fault occurs in the system, the diode group will generate a large power loss when the system is running in a steady state, which is not conducive to the system Economical operation, and for the LCC converter, it takes a long time to force the phase shift. During the phase shift process, the LCC will generate a high overcurrent, which will damage the thyristor components

For the above-mentioned scheme of Kong Ming et al., although the DC fault ride-through can be realized through the hybrid MMC, in the transient state of the DC fault, due to the slow drop of the DC voltage under the control of the hybrid MMC, the converter will still generate a large instantaneous fault current , which is not conducive to the safe operation of the converter equipment

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