Abstract: The problem of unbalanced mid-point voltage of VIENNA rectifier will lead to unbalanced voltage stress on the two equalizing capacitors and the main switching device, resulting in the distortion of the input current waveform on the AC side, which greatly reduces the reliability of the system. To solve this problem, this paper studies the effect of the traditional three-level space vector modulation on the midpoint voltage of the VIENNA rectifier, so that an improved SVPWM control strategy is proposed to suppress the fluctuation of the midpoint potential. The combination of the three-phase current polarity on the input side further divides the traditional sector, and through the judgment of the new sector and the adjustment factor of the positive and negative small vectors, the effect of the middle vector is cancelled to achieve the midpoint balance. Finally, compared with the traditional SVPWM, it is verified by simulation that the midpoint potential and current fluctuations of the proposed control strategy are reduced from ±5 V and ±18 A to ±2.5 V and ±7.5 V respectively, which effectively suppresses the problem of midpoint voltage imbalance.

Key words: improved SVPWM control strategy, midpoint voltage unbalance, adjustment factor, VIENNA rectifier, positive and negative small vector