Neutral Point Potential Balance Method of NPC Three-level Converter Combining Modulation Factor and Vector Selection

Due to the influence of DC side double capacitance parameters, load power factor, load symmetry and so on, there are inherent problems of potential imbalance in DC side capacitor midpoint of NPC converter. Therefore, aiming at the problem of neutral point potential imbalance, a neutral point potential balance control strategy combining modulation factor and vector selection is studied in the paper. Firstly, the method and process of space vector pulse width modulation (SVPWM) is studied, and the mechanism of neutral point potential imbalance is analyzed. Secondly, the neutral point potential is controlled by dynamically adjusting the action time of redundant small vectors and selecting the composite vector group. Finally, the effectiveness of the control method is verified by simulation. Compared with the modulation factor control method, this method can reduce the fluctuation range of neutral point potential by about 48%.