An Enhanced Virtual Vector PWM Modulation Method

Abstract

The invention discloses an enhanced VSVPWM (virtual space vector pulse-width modulation) method. The method comprises steps as follows: space vectors are converted into virtual vectors through PWM, and the action time duty ratio of each virtual vector is calculated; duration per unit values of three-phase output voltage at states P and N are figured out according to the correspondence between the virtual vectors and actual space vectors; the duration per unit values of the three-phase output voltage at the states P and N are used as modulating waves respectively, and a three-phase switch state is obtained; small vector action time is adjusted according to the difference between voltage of two direct-current capacitors or the fluctuation magnitude of midpoint potential, and PWM output of an inverter is obtained. With the adoption of the method, the problem of virtual vector PWM midpoint potential cumulative deviation is solved, midpoint potential balance control can be realized within any modulation degrees, the low-frequency fluctuation of the midpoint potential can be completely eliminated, the anti-interference performance of a system is improved, sizes of the direct-current capacitors are reduced, and the output waveform quality is improved.

Description

technical field [0001] The invention relates to an enhanced virtual vector PWM modulation method. Background technique [0002] Three-level inverters are widely used in high-voltage and high-power occasions due to their advantages such as low voltage for switching devices and high-quality output waveforms. However, the inherent problem of unbalanced midpoint potential has obvious restrictions on the promotion of three-level inverter applications. In recent years, many scholars at home and abroad have done a lot of work on this problem. In terms of topology, a mixed-clamp three-level topology was proposed to realize the automatic balance of the midpoint potential; in terms of modulation methods, methods such as zero-sequence component injection and changing the action time of small vectors were proposed and achieved good results. [0003] In the midpoint potential imbalance problem, the fluctuation of the midpoint potential three times the fundamental frequency is called lo...

AI Technical Summary

Problems solved by technology

But these two methods belong to open-loop control, the anti-interference ability is poor, and the cumulative DC offset problem of the midpoint potential cannot be eliminated

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