Hybrid high-voltage direct current converter based on LCC and MMC and application of hybrid high-voltage direct current converter

Abstract

The invention discloses a hybrid high-voltage direct-current converter based on an LCC and an MMC and application thereof. The hybrid high-voltage direct-current converter comprises a thyristor-based LCC converter and a transformer connected with the LCC converter, and an MMC converter and a transformer connected with the MMC converter. The alternating current side of the thyristor-based LCC converter is connected to an alternating current system network through a transformer; the AC side of the MMC converter is also connected to the AC system network through the transformer, and the DC side of the MMC converter is connected to the high-voltage DC bus; the hybrid high-voltage direct-current converter is applied to a wind field starting stage, a wind field steady-state power generation / alternating-current system stable operation stage and a direct-current bus short-circuit fault. According to the invention, access starting requirements and bidirectional power transmission of weak power grids such as a wind power plant can be met; the full-bridge MMC connected with the LCC in parallel can actively establish alternating current side internal network voltage in the starting stage of weak power grids such as a wind field, provide starting power of the wind field and actively compensate reactive power and harmonic waves in the stable operation stage of an alternating current system.

Description

technical field [0001] The invention relates to the technical fields of flexible DC transmission and power electronic conversion in power systems, in particular to a hybrid high-voltage DC converter based on LCC and MMC and its application. Background technique [0002] The traditional high voltage direct current (High Voltage Direct Current, HVDC) system uses a thyristor-based line commutated converter (Line Commuted Converter, LCC) as the main converter of the converter station. This technology has low equipment cost, simple control, and It is very mature in the field of application, but there are some inherent shortcomings that cannot be ignored: 1) LCC uses a thyristor semi-controlled device, which cannot independently control active and reactive power, and will generate significant power on both the AC side and the DC side. Harmonic components often need to install reactive power compensation equipment and harmonic suppression devices during operation; 2) The AC side of...

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Problems solved by technology

[0002] The traditional high voltage direct current (High Voltage Direct Current, HVDC) system uses a thyristor-based line commutated converter (Line Commuted Converter, LCC) as the main converter of the converter station. This technology has low equipment cost, simple control, and It is very mature in the field of application, but there are some inherent shortcomings that cannot be ignored: 1) LCC uses a thyristor semi-controlled device, which cannot independently control active and reactive power, and will generate significant power on both the AC side and the DC side. Harmonic components often need to install reactive power compensation equipment and harmonic suppression devices during operation; 2) The AC side of the LCC needs a strong grid to provide commutation power, so it cannot actively establish wind power when connected to a weak grid such as an offshore wind farm. Intranet voltage, there is a risk of commutation failure; 3) The LCC-HVDC system needs to change the voltage polarity when the power flows in reverse, so generally it can only be used for point-to-point single-phase power transmission

However, with the increase of the voltage level, MMC also has certain defects, that is, in the high-voltage and high-power transmission system, the number of sub-modules required is large, the hardware cost is high, and each sub-module has an energy storage capacitor, which greatly increases The volume and weight of the converter station limit the application of the full MMC system in scenarios with tight land occupation such as offshore wind farms

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