Voltage balancing method of high-voltage DC modular multilevel converter (MMC) in fundamental frequency modulation

Abstract

The invention discloses a voltage balancing method of a high-voltage DC modular multilevel converter (MMC) in fundamental frequency modulation. The voltage balancing method comprises the steps of S1, acquiring capacitor voltage of N sub-modules at the starting time of an i-th fundamental wave period, and selecting x first sub-modules with relatively large capacitor voltages and y second sub-modules with relatively small capacitor voltages in the N sub-modules, and using the residual sub-modules as third sub-modules; S2, controlling for making the capacitor voltages of the first sub-modules at the ending time of the current fundamental wave period smaller than the capacitor voltage of the first sub-modules at the starting time through a first driving signal, controlling for making the capacitor voltage of the second sub-modules at the ending time of the current fundamental wave period larger than the capacitor voltage of the second sub-modules at the starting time through a second driving signal, and controlling for making the capacitor voltage of the third sub-modules at the ending time of the current fundamental wave period equal with the capacitor voltage of the third sub-modules at the starting time; and S3, performing i=i+1, and returning to the S1. The voltage balancing method can remarkably reduce an ordering calculation load in operation of a system and is suitable for any modular multilevel converter in fundamental frequency modulation. When the number of sub-modules in a bridge arm increases, the voltage balancing method has a particularly remarkable advantage in reducing the ordering load.

Description

technical field [0001] The invention belongs to the technical field of power electronics, and in particular relates to a voltage equalization method of a high-voltage direct current MMC under fundamental frequency modulation. Background technique [0002] Due to the advantages of long transmission distance and small transmission loss, high-voltage direct current transmission has developed rapidly in recent years. However, unlike AC occasions, AC transformers cannot be used to connect DC grids of different voltage levels, and a high-voltage DC-DC power electronic converter is required as an intermediate isolation link. Modular multilevel converter (MMC) has obvious advantages over multilevel converters of other topologies in terms of scalability, flexibility, and fault redundancy, so it is the first choice for realizing high-voltage DC-DC conversion. [0003] The patent application publication number is CN 103280977 A, and the patent application document titled "An Isolated ...

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Problems solved by technology

[0005] Aiming at the defects of the prior art, the present invention provides a voltage equalization method of HVDC MMC under fundamental fre

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