Low frequency ring current suppression method of modularized multilevel converter under carrier stacked pulse width modulation

Abstract

The invention relates to a low frequency ring current suppression method of a modularized multilevel converter under carrier stacked pulse width modulation. According to the low frequency ring currentsuppression method, on the premise that the output voltage level of a phase bridge arm is strictly equal to the level of a target waveform, a pulse distribution mode of a fixed route of an original state machine is improved reasonably, an appropriate redundant state is used adequately at a level moment affecting a ring current, changes of the ring current are always limited within the reasonablerange, the magnitude of low frequency ring current caused by capacitor voltage fluctuation of unit modules is suppressed effectively, and switch current stress of the unit modules is lowered. Meanwhile, according to the low frequency ring current suppression method, on the premise of not generating narrow pulses, uniformity and minimality of switching motions of the unit modules are maintained tothe maximum extent, and balance of capacitor voltage of the unit modules is not affected. In addition, according to the low frequency ring current suppression method, limiting frequency bands are appropriate to make sure that loss increasing of the unit modules is not caused by the frequent switching motions of the unit modules.

Description

technical field [0001] The invention belongs to the technical field of high-voltage and high-power power electronics, and mainly relates to a method for suppressing low-frequency circulating current of a modular multilevel inverter under carrier stack pulse width modulation. Background technique [0002] In recent years, due to its modularity, scalability, and redundancy, modular multilevel converters can be directly connected to high-voltage DC, and can use the public DC side to flexibly exchange power without affecting the AC system. received extensive attention from industry and academia. Therefore, the modular multilevel converter is not only applicable to HVDC transmission systems, but also suitable for medium and high voltage motor drives and medium voltage active filtering and other occasions. [0003] In these applications, the number of unit modules in each bridge arm of a modular multilevel converter usually does not exceed 20. Therefore, in order to obtain a more...

AI Technical Summary

Problems solved by technology

[0004] However, when this optimal modulation method is applied to a modular multilevel converter, because its influence on the low-frequency circulating current cannot be reflected in the modulated signal, the traditional low-frequency circulating current suppression strategy based on sub-module modulation signal correction will no longer be effective. Applicable, but the final pulse distribution must be redesigned to have low-frequency circulating current suppression

Images