Abstract: When three-level neutral point clamped (NPC) inverters work at over-modulation phase, the middle vector leads to fluctuation of the neutral-point voltage, which cannot be well controlled by common neutral-point voltage balance control techniques. Aimed to solving this issue, a new virtual vector method is proposed to be applied in over-modulation. The characteristic of this method is to use the virtual middle vector instead of the combination of the original vector and the reference vector. Simulation results demonstrate that the new method can effectively mitigate fluctuation of neutral-point voltages in the process of modulation. So the method is feasible to be used in the future.
