Sector Vector Control Method for Suppressing Series Combined MMC Circulation

Abstract

The invention discloses a fan-shaped vector control method for suppressing the circulation of series combination MMCs. On the basis of the classic modular multi-level (MMC) series structure, the current relationship between the series combination MMC and the power supply is analyzed, and the result is obtained. The current between the series combined MMC and the power supply will superimpose the double switching frequency circulating current conclusion, based on which a sector vector control strategy is proposed. The present invention can suppress the circulating current of twice the switching frequency superimposed between the series combination MMC and the power supply, reduce the input current fluctuation, and at the same time verify the control strategy in the series-in-parallel-type MMC-H bridge DC / DC conversion model, Strong practicability, simple control and high reliability.

Description

technical field [0001] The invention relates to a field of modular multilevel converters and direct current conversion, in particular to a fan-shaped vector control method for suppressing the circulating current of series combined MMCs. Background technique [0002] Modular multilevel converter (MMC) is a new type of converter suitable for medium and high voltage applications. This structure has great advantages. Compared with cascaded bridge multilevel topology, it has a common DC bus and good Four-quadrant working performance and other characteristics. The structure of each sub-module is relatively simple, easy to control, and can be expanded infinitely, especially suitable for high-voltage and large-capacity fields. [0003] With the rise of flexible DC transmission in recent years, the DC distribution network will continue to develop in the future. As an important part of DC distribution network, high-voltage and high-power DC / DC converters are being studied in depth. ...

AI Technical Summary

Problems solved by technology

[0005] However, for the series combined MMC on the DC side, a large number of literatures have not yet analyzed the relationship between the series MMC and the DC side current.

In fact, the modular multi-level sub-module (SM) contains a capacitor. According to the characteristics of the capacitor itself, the energy stored in the capacitor fluctuates, and the energy fluctuation frequency is twice the switching frequency. Therefore, the combined MMC and power supply side The current will be superimposed with the current of twice the switching frequency. With the increase of the number of SM modules connected in series, the double frequency circulating current will continue to increase, which will cause the peak-to-peak value of the input current to increase, thus requiring higher current-carrying capacity of the equipment.

[0006] The traditional method is to increase the size of the inductance on the power supply side. A large inductance can suppress the double frequency circulating current, but increasing the inductance will increase the size and cost of the system, and will also have a certain impact on the input side voltage.

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