Hybrid Offshore Wind Farm DC Converter

Abstract

The hybrid offshore wind farm DC converter of the present invention includes: a diode rectifier, the AC side of the diode rectifier is connected to the wind farm internal network, and the DC side of the diode rectifier is connected to the high-voltage DC; the auxiliary converter and the auxiliary converter are respectively connected to Wind farm internal network and high-voltage DC connection; the auxiliary converter includes: modular multilevel converter, the AC side of the modular multilevel converter is connected to the wind farm internal network through a transformer; sub-module string, sub-module string One end of the sub-module string is connected to the modular multilevel converter, and the other end is connected to the high-voltage direct current transmission line; the filter circuit, the other end of the sub-module string is connected to the high-voltage direct current transmission line through the filter circuit. The invention has the following beneficial effects: compared with MMC converters with complete voltage levels, the invention can greatly reduce the number of sub-modules and IGBTs, and reduce system cost. It can actively establish the internal network voltage of the wind farm during the start-up phase of the wind farm, provide the start-up power of the wind farm, and realize the black start of the wind farm.

Description

technical field [0001] The invention belongs to the technical fields of flexible direct current transmission and power electronics in power systems, and relates to a converter topology applied to direct current transmission in offshore wind farms, in particular to a hybrid direct current converter for offshore wind farms. Background technique [0002] The flexible DC transmission technology based on the Modular Multilevel Converter (MMC) develops rapidly. MMC uses sub-modules to construct high-voltage and large-capacity AC / DC converters, which have the advantages of low harmonics and low loss, and become a DC power transmission technology. The most attractive converter topology in power transmission technology. However, with the increase of the voltage level, the number of MMC sub-modules has increased significantly. For a DC transmission system with a voltage level of several hundred kilovolts, the MMC converter needs to be composed of thousands of sub-modules. The control ...

AI Technical Summary

Problems solved by technology

However, with the increase of the voltage level, the number of MMC sub-modules has increased significantly. For a DC transmission system with a voltage level of several hundred kilovolts, the MMC converter needs to be composed of thousands of sub-modules. The control system is very complicated, and the converter The volume and weight are relatively large, and the manufacturing cost of the converter is relatively high

For DC transmission applications in offshore wind farms, offshore platform construction costs are high, further increasing system costs

[0003] The diode rectifier is low in cost and does not require a control system, which can greatly reduce the cost, volume and weight of the converter, but the use of diode rectifiers faces great technical challenges

[0005] Existing literature 2, authors: Ramon B, Salvador A, Johel R, et al. "Distributed Voltage and Frequency Control of offshore Wind Farms Connected with a Diode-Based HVDC Link[J]". IEEE Transactions on Power Electronics, 2010, 25( 12): 2095-3105. This technology adopts the diode rectifier scheme. Since the diode rectifier cannot actively establish the voltage of the wind farm internal network, it is necessary to design a special wind power converter control strategy

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