Offshore wind power grid connection system based on full-bridge MMC DC-side serial connection and control method thereof

Abstract

The invention relates to an offshore wind power grid connection system based on full-bridge MMC DC-side serial connection and a control method thereof, and belongs to the technical field of offshore wind power grid connection. The grid connection system comprises a plurality of prime motors, a gear case, a wind power generator, an isolation transformer, a plurality of offshore platform devices composed of full bridge MMC, DC cables and a grid connection converter arranged on the land. The control method includes controlling amplitude of voltage at the full-bridge MMC AC side, controlling voltage at the full-bridge MMC DC side and controlling current at the DC side of the grid connection converter. High voltage is obtained through DC side serial connection, and the system and method are applicable to offshore wind power transmission. Converters and transformers are not needed in the system, the output power of the wind power generator can be controlled by adjusting the output voltage at the DC side of the full bridge MMC, and the current of a DC loop is controlled by the grid connection converter. The grid connection system and control method are simple for controlling, and easy to realize. The performance and extendibility are good.

Description

technical field [0001] The invention belongs to the technical field of offshore wind power grid connection, and in particular relates to an offshore wind power grid connection system based on full-bridge MMC DC side series connection and a control method thereof. Background technique [0002] With global warming, continuous increase in carbon dioxide emissions and the gradual depletion of traditional fossil energy, people are paying more and more attention to renewable energy, while the development technology of onshore solar and wind energy has been relatively mature and has been developed on a large scale. development, and offshore wind farms are very difficult to construct and maintain because they are far from the shore. For offshore wind farms far from the shore, DC transmission has become the only alternative power transmission solution. The method of collecting and converting the electric energy of the offshore wind farm is as follows: the wind generator adopts double...

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Problems solved by technology

However, due to the inherent shortcomings of the traditional AC-DC converter, the offshore wind farm with the DC side series structure is only in the preliminary research stage and has no practical value, and its performance does not meet the following requirements of the offshore wind farm: AC side current The distortion is small, the output voltage of the DC side can be adjusted arbitrarily from 0 to the maximum value, the converter technology is mature, the cost is low, the loss is small, the control is simple, and the reliability is high.

The voltage on the DC side of the thyristor-based phase-controlled rectifier can be adjusted arbitrarily, but the current distortion on the AC side is large, which has a significant impact on the performance and life of the offshore wind turbine; the wind power converter (VoltageSourceConvertor, VSC) based on the voltage source converter The distortion rate of the current waveform on the AC side is very small, but the voltage on the DC side cannot be adjusted arbitrarily, so it is not suitable for offshore wind farms connected in series on the DC side; the wind power converter (Current Source Convertor, CSC) AC based on a fully-controlled current source converter The side current waveform distortion rate is small, and the DC side voltage can be adjusted arbitrarily, but its technology is immature, and the loss is large, the control is difficult, and there are almost no other applications, and the research on CSC is also very limited, just staying in theory research stage

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