Bipolar direct current power transmission system with direct current failure self-elimination capacity

Abstract

The invention discloses a bipolar direct current power transmission system with a direct current failure self-elimination capacity. The bipolar direct current power transmission system comprises two current converters, wherein the positive end and the negative end of the first current converter are connected with the positive end and the negative end of the second current converter through two direct current power transmission lines respectively; each current converter consists of a positive electrode current conversion unit and a negative electrode current conversion unit which are connected in series with each other; and joints of the positive electrode current conversion units and the negative electrode current conversion units are grounded. By adopting a bipolar structure, a failed pole is generally required to be closed during direct current failure, so that a perfect pole is not influenced; and therefore, the reliability of the system is improved. A technology that the middle part is led out and grounded is adopted, so that stage construction and storage increase and extension of the system are facilitated; a single pole is put into operation, and then two poles are put into operation, so that the investment benefit can be developed early; furthermore, a grounding branch supplies a current backflow channel to the system under a single-pole loop running mode; and the current of the grounding branch is extremely low during balance running.

Description

Technical field [0001] The invention belongs to the field of power system transmission technology, and specifically relates to a bipolar DC transmission system with DC fault self-clearing capability. Background technique [0002] Modular Multilevel Converter (MMC) adopts the form of cascaded half-bridge sub-modules, which has low requirements for consistent triggering of devices and dynamic voltage equalization, good scalability, high output voltage waveform quality, low switching frequency, With many advantages such as low operating losses, it is the leader in the new generation of voltage source converter topology. The MMC-based high-voltage direct current transmission system (MMC-HVDC) is better than the traditional thyristor-based DC transmission system in the grid-connected situations of new energy sources such as photovoltaic, wind power and tidal power, ultra-large-scale urban power transmission and distribution, remote islands, isolated loads and passive network powe...

AI Technical Summary

Problems solved by technology

[0004] (1) Cannot effectively handle DC side faults

When a fault occurs on the DC side, the freewheeling diode connected in antiparallel to the full-control switching device constitutes an energy feed circuit that directly connects the fault point to the AC system, and must be cut off by tripping the AC circuit breaker. The disadvantage is that the mechanical response is slow (2 to 3 cycles are needed at the fastest), so auxiliary measures such as increasing the rated parameters of the equipment and configuring high-speed bypass switches are often required. Therefore, this topology is not suitable for overhead lines that are prone to temporary faults such as flashovers For power transmission, cable lines that are expensive but have a low failure rate are usually used, so at this stage MMC-HVDC is limited to cable transmission occasions, and the distance is relatively short and the cost is high;

[0005] (2) Difficulty in design and installation of grounding branch

[0008] Both of the above two existing technologies do not clearly point out that smoothing reactors should be installed on the DC side, so it is necessary to increase the parameters of the bridge arm reactors to suppress the rising rate of the fault current on the DC side; In the bipolar operation mode, once the DC line fails, bipolar outage is very likely to occur, that is, the entire system is out of service, and the system reliability is low

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