A self-balancing topology of the capacitor voltage of a three-phase symmetrical mmc module

Abstract

The invention discloses a three-phase symmetrical MMC module capacitor voltage self-balancing topology. The half-bridge MMC topology is composed of the in-phase module capacitance self-circuit and the interphase auxiliary circuit. The phase-to-phase self-balancing circuit is composed of 6 (N-1) clamping diodes. When the module is switched on and off, the unbalanced voltage of the module capacitor automatically flows from the i-th module to the i-1 module. The value of i is 2~ N-1. The phase-to-phase auxiliary circuit is composed of 6 auxiliary capacitors, 6 auxiliary IGBTs and 9 auxiliary diodes. The first module of the upper bridge arm of each phase and the last module of the lower bridge arm of each phase respectively form two triangles through the phase-to-phase auxiliary circuit to realize phase-to-phase Energy flows freely. This topology realizes energy self-balancing within phases and between phases; all modules use the same sub-module to maintain the consistency of the modules; the interphase auxiliary circuits at both ends form a triangle to maintain the symmetry of the three-phase topology.

Description

Technical field: [0001] 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. Background technique: [0002] 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 requirements. In ...

AI Technical Summary

Problems solved by technology

Its topology can basically realize the module energy balance between phases and phases, but the topology itself is asymmetrical, which destroys the symmetry of the three-phase system. Finally, phases A and C can achieve complete symmetry, which is quite different from phase B.

In addition, the sub-modules used in phase B and phase A and C in the topology are different, which is not conducive to modular production

Images