Method and device for suppressing difference of capacitor voltage fluctuation of hybrid MMC sub-module

Abstract

The invention provides a method and device for suppressing difference of capacitor voltage fluctuation of a hybrid MMC sub-module. The method includes the steps: when a hybrid modular multilevel converter is running in a steady state through over-modulation, determining the third harmonic voltage correction according to the operating state of the system, then determining the circulating current suppression voltage correction, and finally determining the modulation wave voltage of the hybrid modular multilevel converter. The method and device for suppressing difference of capacitor voltage fluctuation of a hybrid MMC sub-module can suppress the difference of the capacitor voltage fluctuation of a full-bridge sub-module and a half-bridge sub-module of the hybrid modular multi-level converter, and at the same time, can reduce the fluctuation level of the capacitor voltage of the whole converter, and the light weight effect is obvious, and the hybrid modular multilevel converter can be running stably. The technical solution provided by the method and device for suppressing difference of capacitor voltage fluctuation of a hybrid MMC sub-module introduces the third harmonic voltage injection rate, and can effectively suppress the capacitor voltage fluctuation of the full-bridge sub-module and the half-bridge sub-module of the hybrid modular multi-level converter on the premise of maintaining the voltage of the DC bus and the transmission power unchangeable, and can reduce the sub-module capacitor voltage ripple level of the overall converter.

Description

technical field [0001] The invention relates to the technical field of flexible direct current transmission, in particular to a method and device for suppressing fluctuations in capacitance voltage fluctuations of hybrid MMC sub-modules. Background technique [0002] Flexible DC transmission is an important piece of equipment for building smart grids. Compared with traditional methods, flexible DC transmission has stronger technologies in island power supply, urban distribution network capacity expansion, AC system interconnection, and large-scale wind farm grid integration. The advantage is a strategic choice to change the development pattern of large power grids. Because the modular multilevel converter has the characteristics of easy expansion, good waveform and modular design, it is suitable for high-voltage and high-power occasions, and has attracted much attention in the field of flexible DC transmission. The hybrid MMC composed of half-bridge sub-modules and full-bri...

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Problems solved by technology

[0004] In order to overcome the deficiency of the increase in the fluctuation level of the capacitance voltage of the sub-module caused by the difference in the capacitance voltage fluctuation between the full-bridge sub-module and the half-bridge sub-module of the hybrid modular multi-level converter in the above-mentioned prior art, the present invention provides a The hybrid MMC sub-module capacitor voltage fluctuation suppression method and device, when the hybrid modular multilevel converter is running stably, determine the third harmonic voltage correction amount according to the system operating parameters, and then according to the hybrid modular multi-level converter The bridge arm current of the horizontal converter determines the correction value of the three-phase ci

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