harmonic injection method for bridge arm multiplexing type MMC topology submodule capacity reduction

Abstract

The invention provides a harmonic injection method for bridge arm multiplexing type MMC topology submodule capacity reduction, and belongs to the technical field of high voltage. A modular multilevel converter (MMC) uses a large number of sub-modules to approach the voltage of a bridge arm, so that the size and the occupied area of the MMC are large. On the basis, from the two aspects of topology and control strategies, the harmonic injection method for bridge arm multiplexing type MMC topology submodule capacity reduction is provided, and light weight of the MMC is achieved. The harmonic injection method is characterized in that a part of full-bridge sub-modules are added to the bridge arm of the MMC, so that the MMC has certain overmodulation output capacity. Through a bridge arm multiplexing idea, the number of MMC bridge arm sub-modules with overmodulation capability is the same as the number of conventional half-bridge MMC bridge arm sub-modules, and a bridge arm multiplexing type MMC topology is obtained. Based on a control strategy level, the invention provides a method for determining the frequency doubling current injection quantity of the bridge arm. Based on the topology and control strategy level, the capacitance value of the bridge arm multiplexing type MMC sub-module capacitor can be greatly reduced.

Description

technical field [0001] The invention relates to the field of high-voltage technology, in particular to a method for injecting harmonics into bridge-arm multiplexed MMC topology sub-modules for capacity reduction. Background technique [0002] Modular Multilevel Converter (MMC) has become the preferred converter topology for flexible DC grids due to its advantages of no commutation failure, black start capability, and high modularity. [0003] At present, half-bridge MMCs are mostly used in flexible and straight projects. Because MMCs use a large number of sub-modules to approximate the bridge arm voltage, their volume and footprint are huge. The volume of the capacitor in the sub-module occupies a large proportion in the whole sub-module. Based on this, a bridge-arm multiplexed MMC topology sub-module reduction harmonic injection method is proposed, which can greatly reduce the capacitance value of the MMC sub-module. Realize the lightweight of MMC. SUMMARY OF THE INVENT...

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Problems solved by technology

[0004] Aiming at the problems of the large volume and occupied area of ​​the half-bridge MMC mentioned in the above background technology, the present invention proposes a bridge-arm multiplexed MMC topology sub-module derating harmonic from two perspectives of topology and control strategy. The wave injection method can greatly reduce the capacitance value of the MMC sub-module

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