Hybrid offshore wind field DC converter

Abstract

A hybrid offshore wind field DC converter comprises the components of a diode rectifier, wherein the AC side of the diode rectifier is connected with a wind field internal network, and the DC side isconnected with high-voltage DC current; and an auxiliary converter which is connected with the wind field internal network and the high-voltage DC current, wherein the auxiliary converter comprises amodular multilevel converter of which the AC side is connected with the wind field internal network through a transformer; a sub-module string, wherein one end of the sub-module string is connected with the modular multilevel converter, and the other end is connected with a high-voltage DC power transmission line; and a filtering circuit, wherein the other end of the sub-module string is connectedwith the high-voltage DC power transmission line through the filtering circuit. Compared with a whole-voltage-grade MMC converter, the hybrid offshore wind field DC converter has the following beneficial effects: greatly reducing the number of submodules and IGBTs, reducing system cost, actively establishing wind field internal network voltage in a wind field starting period, supplying wind fieldstarting power and realizing black-start of the wind field.

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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