Fan-shaped vector control method capable of suppressing series connection combination type MMC ring current

Abstract

The invention discloses a fan-shaped vector control method capable of suppressing series connection combination type MMC ring current. On the basis of a classical modular multilevel converter (MMC) series connection structure, a relation between the series connection combination type MMC and a power supply is analyzed to obtain a theory that the current between the series connection combination type MMC and the power supply is overlaid with double switching frequency ring current, so that a fan-shaped vector control strategy is proposed. By virtue of the fan-shaped vector control method, the double switching frequency ring current overlaid between the series connection combination type MMC and the power supply can be suppressed and input current fluctuation can be reduced; and meanwhile, the control strategy is verified in a serial-in parallel-out type MMC-H bridge DC / DC conversion module, and high practicability, simple control and high reliability are shown.

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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