A Step Wave Modulation Method for Sub-module Grouping of Modular Multilevel Converter

Abstract

The invention provides a step wave modulation method for grouping sub-modules of a modular multi-level converter, which includes the following steps: dividing the sub-modules in the commutation chain into N sub-module groups; rounding the reference voltages of the sub-module groups to obtain The rounded reference staircase wave voltage Vstair_wave; distribute the trigger pulse to the sub-modules inside the sub-module group; perform voltage equalization between the sub-module groups. In the present invention, the sub-modules are divided into N sub-module groups, and each sub-module group is regarded as a controllable voltage source. Step wave modulation is used in the sub-module groups, and the N sub-module groups use rounding corrections, which can achieve similar wave shift For the purpose of the phase, the appropriate voltage equalization control method is used for voltage stabilization control between the sub-module groups, which simplifies the complexity of the ladder wave modulation, and greatly reduces the requirements for the software and hardware of the modulation algorithm and the voltage equalization control algorithm.

Description

technical field [0001] The invention belongs to the technical field of power electronics, and in particular relates to a step wave modulation method for sub-module grouping of a modular multilevel converter. Background technique [0002] The traditional thyristor-based DC transmission system uses phase-controlled rectification to convert three-phase AC power into six-pulse or twelve-pulse DC power, but this DC power transmission system needs to absorb a large amount of reactive power, especially when the AC side is faulty case. The DC transmission system based on the voltage source converter (VSC-HVDC) is equivalent to a controllable voltage source, which can operate in four quadrants and realize the independent adjustment of active and reactive power on the AC side, which is of great significance for the formation of DC power grids. Since the modular multilevel converter adopts a modular design, each sub-module contains a large capacitor to clamp the voltage, and its volta...

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Problems solved by technology

However, when this kind of converter is applied to high-voltage and large-capacity occasions, a large number of sub-modules need to be connected in series, which makes the distribution of trigger pulses difficult, and the realization of the secondary system also becomes difficult or even unfeasible. Therefore, when the modular multilevel converter is applied to high-voltage and large-capacity occasions, it is necessary to reconsider the group control of many sub-modules to reduce the difficulty of trigger pulse distribution and make the secondary system easier to implement

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