Cascade converter valve, DC power transmission system and control method thereof

Abstract

The invention discloses a cascade converter valve, a DC power transmission system and a control method thereof. The cascade converter valve is provided with a high voltage valve group and a low voltage valve group which are connected in series in the DC side. The high voltage valve group is a first converter. The low voltage valve group comprises a second converter and a third converter which areconnected in parallel. At least one of the converters is a hybrid multilevel output converter. The AC side of the first converter and the AC side of the third converter are connected in parallel through a transformer to form the first AC end of the cascade converter valve. The AC side of the second converter forms the second AC end of the cascade converter valve. The cascade converter valve has multiple working modes and AC system access modes, high-voltage, high-capacity and long-distance DC power transmission and receiving AC network hierarchical access and asynchronous partition interconnection can be simultaneously realized under the premise of reducing the total manufacturing cost and area occupation of the DC system and thus the system stability and reliability can be enhanced. The cascade converter valve is suitable for the electric power system of multiple DC feed-in points.

Description

technical field [0001] The invention belongs to the technical field of electric power transmission and distribution, and more specifically relates to a cascaded converter valve, a direct current transmission system and a control method thereof. Background technique [0002] Since the 21st century, with the increasingly prominent environmental problems, in order to reduce carbon emissions and reduce the proportion of coal-fired power generation, it is necessary to develop and utilize renewable energy on a large scale. my country's new energy bases are characterized by dispersal, remote distribution, and strong volatility, and are distributed inversely with the load center, leading to an increasing demand for large-capacity long-distance transmission of electric energy. The grid-connected high-voltage AC transmission system has inherent defects such as high cost and serious stability problems. The conventional high-voltage DC transmission technology based on grid commutation ...

AI Technical Summary

Problems solved by technology

[0008] Aiming at the above defects or improvement needs of the prior art, the present invention provides a cascaded converter valve, a DC system and a control method thereof, which solve the problem of existing AC-DC transmission while realizing high-voltage and large-capacity long-distance DC transmission. Due to the lack of asynchronous partitioning of the AC system in the system, when the AC-DC fault occurs under the multiple DC feed-in of the receiving-end power grid, the AC-DC transmission system is unstable or the technical problem of decoupling occurs

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