三相四线制三电平变流器的优化调制策略

传统三相四线制三电平电容中分式变流器三维空间矢量脉宽调制(3D-SVPWM)策略较为复杂且中点电位平衡算法对中点电位偏移的抑制不精确，尤其是在负载不平衡的情况下，中线电流全部流过直流侧中点造成中点电位偏移。针对以上问题，提出一种基于三相abc坐标系的简化3D-SVPWM方法，并基于该简化方法提出一种多相控制的中点电位平衡算法，根据中点电位偏移情况，将电位偏移量平均分配到具有中点电位平衡能力的相，使多相共同参与中点电位平衡控制，通过偏移量数学模型计算得到补偿该偏移量所需要的时间量，然后作用于三电平变流器的输出状态，从而达到平衡中点电位的目的。仿真分析和实验结果均表明优化调制策略具有良好的三相四线制三电平变流器中点电位平衡能力。

Optimal Modulation Strategy for Three-phase Four-wire Three-level Converter

The traditional three-dimensional space vector modulation(3D-SVPWM)strategy applied in three-phase four-wire three-level mid-point capacitor converter is complex, and the neutral-point potential balance scheme is not accurate for suppressing the neutral-point potential shift. Especially in the case of unbalanced load condition, the neutral current flows through the neutral-point of the DC-link, when will cause the neutral-point potential offset. To solve this problems a simplified 3D-SVPWM strategy based on three-phase abc coordinate system is presented and a neutral-point potential balance scheme based on the simplified method is proposed. According to the potential shift, the value of potential shift is averagely distributed to the phase with capability of balancing neutral-point potential to make multiple phases balance the neutral-point potential together. The value of time needed to compensate the shifted potential is calculated by the mathematical model, and then acts on the output state of the three-level converter to achieve the goal of balancing the neutral-point potential. Simulation analysis and experimental results show that the optimized modulation strategy has good performance on controlling the neutral-point voltage for three-phase four-wire three-level converter.