一种新的三电平NPC变换器中点电位平衡控制策略

摘要

NPC three-level converter has more advantages compared with traditional two level converter, but its special topology also brings neutral voltage imbalance. On the basis of simplified three-level space vector pulse width modulation (SVPWM)algorithm and the virtual space vector, a mixed strategy about controlling neutral voltage is put forward. Namely under the low modulation index environment, the simplified three-level space vector algorithm is chosen, and with reference to the actual situation of neutral voltage and neutral current to determine how to select overlapping sectors' affiliation or change switch vector sequences of seven section;under the high modulation index environment, the strategy of virtual space vector is used to suppress the excursion of neutral voltage. Finally, the model is built and simulatied in Matlab, the result proves that this control method can obviously suppress the excursion of neutral voltage under the low modulation index and high modulation index environment.%三电平 NPC 变换器相较传统两电平变换器来说具有较多优点，但其特殊的拓扑结构也带来了中点电位不平衡问题。在简化三电平SVPWM算法和虚拟空间矢量的基础上，提出一种将两者混合的中点电位控制方式。即在低调制度环境下，调用简化三电平空间矢量算法，并参照中点电位与中点电流的实际情况，确定怎样选择重叠扇区的归属或改变七段式开关矢量序列；在高调制度时则可利用虚拟空间矢量能够控制中矢量的优势来抑制中点偏移。最后在Matlab中建模并进行仿真，结果证明了这种控制方式能够在高低调制度区域明显抑制中点电位波动与偏移。