Mixed type grid connected converter station for offshore wind power in serious connection

Abstract

The invention relates to a mixed type grid connected converter station for offshore wind power in serious connection, and belongs to the field of power conversion The mixed type grid connected converter station for offshore wind power in series connection is composed of a voltage source converter (VSC) and a line voltage commutated converter (LCC), wherein the VSC is in series connection with the direct current side of the LCC, and in parallel connection with the alternating current side of the LCC. The VSC adopts a modularized multi-level converter based on a half-bridge module, the direct current side voltage (UVSC) of the VSC is 0.5 UDC, the LCC adopts a thyristor converter with 12 pulses, the alternating current side voltage (ULCC) of the LCC is continuously adjustable from -0.5 UDC to 05 UDC, the converter statin is used for controlling the size of the direct current side current (Idc), and the output voltage (Udc) of the converter station is continuously adjustable from 0 to UDC. When the voltage of a grid falls, the VSC can provide reactive power to the LCC so as to reduce the probability of commutation failure of the LCC.

Description

technical field [0001] The invention relates to a hybrid grid-connected converter station for series direct current offshore wind power, which belongs to the technical field of power conversion. Background technique [0002] According to research, China's exploitable offshore wind energy resources are 750 million kilowatts, about three times that of land wind power; and offshore wind power is very close to the coastal load center, without the problem of long-distance transmission, and is easier to absorb. Therefore, abundant offshore wind energy resources, coupled with the feasibility of today's technology and the strong support of national policies, indicates that offshore wind farms will become the next rapidly developing energy market, and offshore wind power equipment will also usher in explosive growth. At present, high construction cost, high failure rate and high maintenance cost are important constraints to the development of offshore wind power. However, with the de...

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Problems solved by technology

[0005] At present, the collection and transmission of offshore wind power is carried out in the form of series DC. The voltage of the DC side of the grid-connected converter station on land must be continuously adjustable in a wide range to control the current in the DC circuit. It is currently available. There are two types of converters in China, one is the thyristor-based line voltage commutation converter, this kind of converter needs the assistance of grid voltage to commutate, when the grid fails, it is easy to cause commutation failure, and then result in converter latch-up; the other is a modular multilevel converter based on full-bridge sub-modules with full-bridge sub-modules whose DC side voltage can be continuously adjusted between positive and negative ratings , but the cost of this kind of converter is very high due to the use of the full-bridge sub-module, and the loss is also large. Since the series DC offshore wind power system does not require the negative voltage output of the grid-connected converter station, the Modular multi-level converters contain unnecessary redundancy, and these unnecessary redundancy will lead to higher construction costs and greater losses

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