Virtual space vector PWM with reduced CMV for three-level inverters under unbalanced DC-links

In this paper, a virtual space vector pulse width modulation (VSVPWM) scheme with reduced common-mode voltage (CMV) for three-level inverters under unbalanced DC links is studied. The virtual space vectors (VSVs) under unbalanced DC links, which do not charge or discharge the neutral point of the DC links, are constructed by basic space vectors with reduced CMV. The implementation of the proposed VSVPWM and asymmetric control of the DC-links are studied. When compared with the existing methods, the control accuracy of the unbalanced degree is improved. In addition, the proposed VSVPWM method results in a 35.4% reduction in the peak-to-peak of CMV relative to the conventional VSVPWM. In addition, it can obtain a smaller CMV in comparison with the existing CMV reduction method when the modulation index is smaller than 2/3. Simulation and experimental results indicate the effectiveness and advantages of the proposed scheme.