AC/DC fault ride-through and energy dissipation method for wind power flexible direct grid connection

Abstract

The invention discloses an AC/DC fault ride-through and energy dissipation method for wind power flexible direct grid connection. A system is mainly formed by a direct-drive permanent magnet synchronous generator, a full-power frequency converter, a hybrid MMC and a dissipative resistor. An AC and DC are controlled respectively through the hybrid MMC; during direct current faults, the MMC operatesnear a zero direct voltage through a negative input full-bridge sub-module, and DC fault ride-through can be achieved without needing to block MMC. In order to ensure the safety of a converter valveduring the fault, the dissipative resistor is used to absorb energy during the fault so that a wind farm is disconnected with a grid during the fault and still maintains normal operation.

Description

technical field [0001] The invention belongs to the technical field of power transmission and distribution of power systems, and more specifically relates to an AC / DC fault ride-through and energy dissipation method for wind power flexible direct grid connection. Background technique [0002] Since the 21st century, in order to reduce carbon emissions and reduce the proportion of coal-fired power generation, wind power has been widely used as the most competitive clean energy. In order to reduce the occurrence of "abandoned wind", inland wind power bases can be connected to the grid through long-distance overhead lines to transmit wind energy to the load center. The flexible DC transmission technology using Modular Multilevel Converter (MMC) has many technical advantages such as active and reactive power control decoupling, and can be connected to passive grids. It is an effective method and has been widely used in the industry since it was proposed. [0003] As the voltag...

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Problems solved by technology

In order to solve this problem, Song Qiang et al. proposed a scheme of adding dissipative resistance in sub-modules (Li Qi, Song Qiang, Liu Wenhua, et al. Coordinated control strategy for grid-connected fault ride-through of wind farms based on flexible HVDC transmission[J]. Power Grid Technology ,2014,38(7):1739-1745.), this scheme increases the complexity of the sub-module design and increases the manufacturing cost; Li Daoyang and others proposed a communication-based control strategy for reducing the output power of wind farms, which has Communication delay, slow action response (Li Daoyang, Yao Weizheng, Wu Jinlong, etc. DC fault ride-through cooperative control strategy applied to flexible DC access system of offshore wind farm[J]. Power Grid Technology, 2016,40(1):47 -54.)

It is also proposed to connect a dissipation resistor in parallel on the DC line to absorb wind power during a fault, but the required resistance value is too large, and the cost is high and the floor space is large

Furthermore, the above-mentioned existing solutions do not comprehensively analyze the AC / DC fault ride-through, fault energy dissipation, and sub-module internal overvoltage of the wind power flexible DC grid-connected system.

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