Capacitor voltage fluctuation suppression method of modular multi-level converter under low frequency and low voltage

Abstract

The invention relates to a capacitor voltage fluctuation suppression method of a modular multi-level converter under a low frequency and a low voltage. Under unbalanced control, an upper bridge arm and a lower bridge arm take turns; and one bridge arm mainly outputs an alternating-current voltage and an alternating current and the other bridge arm mainly outputs a direct-current voltage instead of an alternating current. On the basis of alternate switching, the module capacitor voltage difference of the three-phase upper and lower bridge arms can be suppressed well. With the method, a problem that the module capacitor voltage fluctuation is too large at the low frequency band when the modular multi-level converter is used for driving the motor can be solved; and thus a negative effect on a load due to a high-frequency injection method can be eliminated. According to the method, changing of a hardware circuit is not required; the low-frequency-band working performance of the modular multi-level converter can be improved substantially; the application range in the industry is wide; and practicability is high.

Description

technical field [0001] The invention relates to a low-frequency low-voltage driving technology of a modular multilevel converter, in particular to a control method for reducing capacitor voltage fluctuations in the low-frequency and low-voltage section of a modular multilevel converter. Background technique [0002] The modular multilevel converter obtains high voltage output by cascading (voltage superposition) and using conventional grade power modules. Since its appearance, modular multilevel converters have been applied in many fields, such as high-voltage direct current transmission, medium-voltage DC / DC converters, and medium-voltage motor drives. Theoretical analysis proves that the harmonic performance of the output voltage of the modular multilevel converter is better than that of the conventional H-bridge cascaded multilevel converter using a phase-shifting transformer structure. At present, some manufacturers have launched corresponding modular multilevel frequen...

AI Technical Summary

Problems solved by technology

The main problem with this method is that the injection of high-frequency components will affect the insulation design of the motor. At the same time, to completely offset the voltage fluctuations of the upper and lower bridge arms, the injected common-mode voltage must reach the DC bus voltage, and the injected current must be When the load current is large, it will obviously bring difficulties in the design of the converter, which makes the converter need to increase the voltage and current level and increase the cost of the converter

Images