Converter voltage-sharing method based on nearest level approximation

Abstract

The invention relates to a converter voltage-sharing method based on nearest level approximation. The converter voltage-sharing method comprises the steps of: calculating a number N(t) of sub-modulesthat need to be triggered at a triggering moment by adopting a nearest level approximation modulation strategy, and acquiring a capacitor voltage sequence; setting a sub-module voltage-sharing recursive threshold RT, so as to determine a sorting method used by the voltage-sharing strategy at different numbers of recursive times; starting sub-module capacitor voltage recursive sorting, counting a number of recursive times, adopting a rapid sorting algorithm for sorting the sequence if the number of recursive times is less than a recursive threshold, otherwise, adopting a heap sorting algorithmfor sorting; and acquiring a sub-module capacitor voltage sequence after sorting, determining a current direction of a bridge arm, selecting the N(t) sub-modules with the lowest capacitor voltage to be put into charge if the current direction is a flow-in direction, and selecting the N(t) sub-modules with the highest capacitor voltage to be put into discharge if the current direction is a flow-outdirection.

Description

technical field [0001] The present invention relates to the technical field of electric power system control, and more specifically, relates to a voltage equalization method for a converter based on the nearest level approximation. Background technique [0002] With the rapid development of power electronics technology, flexible DC transmission technology based on modular multilevel converters has been widely used. Compared with traditional voltage source converters, modular multilevel converters have low manufacturing difficulty , small switching loss, less harmonic content and strong fault handling and control capabilities. State Grid Corporation of China plans to put into operation in 2018 the construction of the Chongqing-Hubei DC back-to-back DC project, which is currently the flexible DC project with the largest capacity and the highest voltage. The simulation of this project is also based on the modular multi-level technology. The research on this technology is curren...

AI Technical Summary

Problems solved by technology

The voltage equalization strategy should balance the two aspects of switching loss and voltage equalization at the same time. With the continuous progress of the voltage equalization sorting process, the IGBT must be switched multiple times in each control cycle, which will greatly increase the switching loss. The good operation of the project is unfavorable, and the traditional pressure equalization strategy needs to be optimized to achieve the two goals of smooth pressure equalization and loss reduction

Images