三电平PWM变流器不对称运行中点电压波动研究

摘要

The neutral-point voltage fluctuation of three-level converter is only related to applied modulation method and three-phase current. Its unbalanced control strategy for DC-voltage harmonics suppression is analyzed and the neutral-point voltage fluctuation during single- and dual-phase voltage drops is respectively studied with standard SVPWM and VVS-SVPWM(Virtual Vector Synthesis SVPWM) technologies. Theoretical analysis shows that,the neutral-point voltage fluctuation decreases when the absolute value of power factor increases. Along with the decrease of drop ratio,it increases during single-phase voltage drop while it decreases then increases during dual-phase voltage drop. Under same conditions,VVS-SVPWM technique has better control performance of neutral-point voltage balance than standard SVPWM. Simulative results verify the correctness of theoretical analysis.%三电平变流器的中点电压波动只与变流器采用的调制技术和三相电流有关.分析了三电平变流器应用抑制直流母线电压谐波的不平衡控制策略,采用标准SVPWM技术与虚拟矢量合成SVPWM(VVS-SVPWM)技术,分别在单相电压跌落与两相电压跌落情况下研究了中点电压波动规律.理论分析表明,2种SVPWM技术的中点电压平衡控制能力随功率因数绝对值的增大而增大;单相电压跌落时,中点电压波动随电压跌落比的减小而增大;两相电压跌落时,中点电压波动随电压跌落比的减小,先减小后增大;而且在同样的条件下,WS-SVPWM技术具有更好的中点电压平衡控制能力.仿真结果证明了理论分析的正确.