Three-phase symmetric topology for self-balance of capacitor voltage of MMC (Modular Multilevel Converter) module

Abstract

The invention discloses a three-phase symmetric topology for self-balance of capacitor voltage of an MMC (Modular Multilevel Converter) module. A half-bridge type MMC topology comprises inner-phase module capacitor self-circuits and inter-phase subsidiary loops. An inter-phase self-voltage-sharing circuit consists of 6(N-1) clamping diodes; and in switching of modules, unbalanced voltage of capacitors of the modules automatically flows from an i module to an (i-1) module, wherein the value of i is 2-(N-1). Each of the inter-phase subsidiary loops consists of six subsidiary capacitors, six subsidiary IGBTs (Insulated Gate Bipolar Translator) and nine subsidiary diodes, and a first module of a per-phase upper bridge arm and a last module of a per-phase lower bridge arm form two triangles by the inter-phase subsidiary loops, thereby realizing free flow of inter-phase energy. According to the topology disclosed by the invention, the self-balance of the inner-phase and inter-phase energy is realized; all the modules adopt identical sub-modules, thereby keeping consistency of the modules; and the inter-phase subsidiary loops at the two ends form the triangles, thereby keeping the symmetry of the three-phase topology.

Description

[0001] Technical field: [0002] The invention belongs to the technical field of flexible direct current transmission, and in particular relates to a three-phase symmetrical MMC module capacitor voltage self-balancing topology. [0003] Background technique: [0004] The Modular Multilevel Converter (MMC) is the basic topology of the converter valve of flexible direct current transmission technology, which solves the problem of direct series-parallel connection of switching devices in traditional two-level converters in high-voltage and high-current applications. The problem. In terms of loss, the switching frequency is greatly reduced by adopting the sine wave modulation method approximated by the ladder wave. Compared with the high-frequency modulation of the traditional two-level converter, the loss is greatly reduced. After multiple sub-modules are cascaded, the stepped wave output is very close to a sine wave, and the waveform quality is high, which reduces the filter req...

AI Technical Summary

Problems solved by technology

[0009] The purpose of the present invention is to overcome the problem of three-phase asymmetry in the "equal-constrained auxiliary capacitor centralized half-bridge MMC self-balancing topology", and to provide a three-phase symmetrical MMC module capacitor voltage self-balancing topology. This topology can realize the self-equalization of the module capacitor voltage in the phase, the unbalanced energy circulation between the phases, and the topology structure is completely symmetrical

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