Auxiliary capacitance concentrated type full-bridge MMC self-voltage-sharing topology based on equality constraints

Abstract

The invention provides an auxiliary capacitance concentrated type full-bridge MMC self-voltage-sharing topology based on equality constraints. The full-bridge MMC self-voltage-sharing topology is established by connecting a full-bridge MMC model with a self-voltage-sharing auxiliary loop. The full-bridge MMC model is electrically connected with a self-voltage-sharing auxiliary loop through 6N IGBT modules in the auxiliary loop; the IGBT modules are triggered, and the full-bridge MMC model and the self-voltage-sharing auxiliary loop form the auxiliary capacitance concentrated type full-bridge MMC self-voltage-sharing topology based on the equality constraints; the IGBT modules are stopped, the topology is equivalent to the full-bridge MMC topology. By means of the full-bridge MMC self-voltage-sharing topology, DC side failures can be clamped without depending on special voltage-sharing control; the capacitances and voltages of sub-modules can be balanced spontaneously on the basis of completing AC and DC energy conversion; meanwhile, the triggering frequencies and capacitance values of the sub-modules can be correspondingly reduced, and base-frequency modulation of MMC is achieved.

Description

Technical field [0001] The invention relates to the field of flexible power transmission, in particular to an auxiliary capacitor centralized full-bridge MMC self-balancing topology based on equation constraints. Background technique [0002] The modular multilevel converter MMC is the development direction of the future DC transmission technology. MMC adopts the sub-module (SM) cascade method to construct the converter valve, avoiding the direct series connection of a large number of devices, and reducing the number of devices. Consistency requirements, while facilitating capacity expansion and redundant configuration. As the number of levels increases, the output waveform is close to sine, which can effectively avoid the defects of low-level VSC-HVDC. [0003] The full-bridge MMC is composed of full-bridge sub-modules. The full-bridge sub-module is composed of four IGBT modules, one sub-module capacitor and one mechanical switch, which is flexible in operation and has DC fault c...

AI Technical Summary

Problems solved by technology

However, the design of this scheme destroys the modular characteristics of the sub-modules to a certain extent, and the capacitive energy exchange channel of the sub-modules is also limited to the phase, which fails to make full use of the existing structure of the MMC, and the introduction of three transformers complicates the control strategy. At the same time, it will also bring a large transformation cost

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