Control method for capacitor voltage optimization and equalization of modular multilevel converter submodule

Abstract

The present invention is mainly applied to the technical field of power electronics, and aims to provide a control method for capacitor voltage optimization and equalization of a modular multilevel converter submodule. The control method realizes balance control of capacitor voltage of a modular multilevel converter submodule by selecting different optimization algorithms, and mainly comprises thefollowing steps: calculating the number of submodules to be inputted based on a recent level approximation modulation strategy; sorting the submodules on each bridge arm of an MMC system according toa size from large to small; judging the calculated number N of the submodules and the currently inputted submodules n, and selecting different submodule switching modes under different conditions; and finding a submodule with the largest capacitor voltage and a submodule with the smallest capacitor voltage on the current bridge arm, comparing a difference between the submodules, and then selecting different optimization algorithms for switching the submodules. Based on an MMC technology of the present invention, on the premise of controlling the balance of the capacitor voltage of the submodules, the control method can also ensure that the system has a lower switching frequency, and reduces the loss of a power converter in the MMC system.

Description

technical field [0001] The invention relates to the technical field of power electronic converters, in particular to a control method for optimizing and equalizing capacitor voltages of sub-modules of modular multilevel converters. Background technique [0002] At present, the power electronic converter technology has been developed rapidly and has become the core device for power conversion in the power system, especially in the power supply, transmission and configuration of power. Since Professor R. Marquart of the Bundeswehr University in Munich in Germany proposed a modular multilevel converter (MMC) based on a half-bridge structure in 2002, it marked the arrival of conversion devices in the field of power electronics technology transmission. It is a major innovation. Its structure mainly adopts the power semiconductor device with low voltage level - IGBT power tube. Through the parallel connection of IGBT and capacitor to form the sub-module of MMC, it can form a high-...

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Problems solved by technology

The advantage of the traditional balance control method is that it is simple to implement, but the voltage equalization algorithm requires strict sequencing of the capacitor voltage values ​​of the sub-modules at each action moment of the system to control the opening or closing of each module. This frequent switching The action will inevitably increase the switching loss, so it is necessary to carry out corresponding research on the switching frequency of MMC

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