MMC-based bipolar flexible direct-current power grid short circuit and ground fault current prediction method

A flexible DC and current prediction technology, applied in the direction of power transmission AC network, emergency protection circuit devices, electrical components, etc., can solve the problems of flexible DC power grid fault protection, fast fault current rise speed, and wide range of influence, etc., to achieve easy expansion , simple modeling, good adaptability

Active Publication Date: 2020-06-05
WUHAN UNIV
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Problems solved by technology

[0005] The purpose of the present invention is based on the low damping characteristics of the flexible DC power grid. When the DC power grid fails, the fault current has no zero-crossing point, the fault current rises fast and has a wide range of influence, and proposes an accurate, An Efficient Prediction Method to Solve the Fault Protection Problem of Flexible DC Grids

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  • MMC-based bipolar flexible direct-current power grid short circuit and ground fault current prediction method
  • MMC-based bipolar flexible direct-current power grid short circuit and ground fault current prediction method
  • MMC-based bipolar flexible direct-current power grid short circuit and ground fault current prediction method

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Embodiment Construction

[0050] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0051] The present invention is applicable to the prediction of short-circuit and ground fault currents in multi-terminal bipolar flexible DC power grids. In the following embodiments, only a four-terminal bipolar flexible DC power grid is used as an example for illustration, but the present invention is not limited to four-terminal situations. Such as figure 1 As shown, each converter station is composed of a positive MMC and a negative MMC, the transmission line is an overhead line, and the metal return line constitutes a neutral line. MMC1 and MMC4 are transmitting end MMCs with rated power of 3000MW and 1500MW respectively, MMC2 and MMC3 It is the receiving end MMC, the rated power is 3000MW and 1500MW respectively, MMC1, MMC3, MMC4 adopt constant active power control, MMC2 adopts constant DC voltage control, the grid voltage level is ±500kV, and the number of sub-m...

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Abstract

The invention provides an MMC-based bipolar flexible direct-current power grid short-circuit and grounding fault current prediction method, which comprises the following steps: in a sub-module capacitor discharge stage before MMC locking, enabling an MMC to be equivalent to an RLC series branch; based on the influence of alternating current feed-in, an MMC adopting a constant active power controlmode is established as an equivalent circuit in which a current source and an RLC series branch are connected in parallel; considering a bipolar short-circuit fault and a monopole grounding fault of the flexible direct-current power grid, and building an equivalent circuit model of the direct-current power grid in a fault state; and based on the direct-current power grid equivalent circuit model,establishing a flexible direct-current power grid state-space equation and solving to obtain branch current and MMC equivalent sub-module capacitor voltage when the direct-current power grid fails. The fault current of the bipolar flexible direct-current power grid based on the MMC under the conditions of the bipolar short-circuit fault and the single-pole grounding fault is predicted, the methodis reliable and high in precision, and the discharge rule of the MMC is disclosed.

Description

technical field [0001] The invention belongs to the technical field of flexible direct current transmission, and in particular relates to a short-circuit and ground fault current prediction method for a bipolar flexible direct current grid based on MMC. Background technique [0002] The flexible DC grid based on Modular Multilevel Converter (MMC) is an effective means to accept large-scale renewable energy, and it is one of the important development directions of the future grid. Since the high penetration of renewable energy requires long-distance flexible transmission of electric energy, flexible DC transmission technology using overhead lines is a trend in the development of power grids. In addition, flexible DC power grids with bipolar structures have advantages in operability, reliability, flexibility and It has great advantages in scalability. For example, the Zhangbei ±500kV four-terminal flexible DC power grid demonstration project built in my country adopts a half-br...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H02J3/36H02H7/26
CPCH02H7/268H02J3/36Y02E60/60
Inventor 刘开培徐祎槐青朱蜀李可欣秦亮
Owner WUHAN UNIV
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