Rapid voltage-sharing method of cascaded multilevel converter

Abstract

The invention discloses a rapid voltage-sharing method for a cascaded multilevel converter, and the method comprises the steps: obtaining all switching tube drive signals of each submodule after a bridge arm reference voltage modulation wave signal of the cascaded multilevel converter is compared with a phase-shifting triangular carrier; and performing logic AND operation on the driving signals outputting the positive level in all the sub-modules, adding the driving signals outputting the positive level to obtain a positive level number output by the bridge arm, performing logic AND operationon the driving signals outputting the negative level in all the sub-modules, adding the driving signals outputting the negative level to obtain a negative level number output by the bridge arm, and outputting zero level by the remaining sub-modules; according to the number of the bridge arm positive and negative level output modules, carrying out sorting and voltage-sharing control, thereby finally achieving the effect of bridge arm capacitor voltage rapid equalization, and solving the problems that the carrier phase shift control voltage-sharing speed is low and the harmonic content of outputcurrent of a traditional sorting and voltage-sharing method is high when the number of sub-modules is small. According to the method, the capacitor voltage of the sub-module is rapidly balanced, thebridge arm is ensured to have high equivalent switching frequency, and the current harmonic content of the alternating current side is ensured to be low.

Description

technical field [0001] The invention relates to a sub-module voltage equalization method of a converter, in particular to a sub-module fast voltage equalization method of a cascaded multi-level converter. Background technique [0002] With the rapid development of smart distribution network and new energy and the continuous increase of DC load, requirements are put forward for the flexible control, reliability and multi-port access of AC and DC of the distribution network. Higher requirements were put forward. Due to the high voltage level of the distribution network and limited by the withstand voltage level of the current semiconductor switching devices, most of the existing high-voltage and high-power power electronic equipment adopts the structure of cascaded full-bridge or cascaded half-bridge, but each Each capacitor in a full-bridge or half-bridge module is independent of each other and suspended from each other, energy cannot be exchanged between sub-module capacito...

AI Technical Summary

Problems solved by technology

Among them, the switching frequency of the carrier stacked modulation strategy is high, resulting in large switching losses of the sub-modules, so it is rarely used

The carrier phase-shift modulation has been widely used because of its fixed switching frequency and high equivalent switching frequency, but when the sub-module capacitor voltage deviation is large, its balance speed is slow

The NLM method has simple control, low switching frequency, and good voltage equalization effect, but when the number of MMC modules is small, it will lead to high harmonic content in the output current

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