NPC型八开关三相逆变器输出电流不平衡的调制补偿算法

Output current unbalance compensation strategy for NPC eight switch three-phase inverters

三相三电平中性点钳位(NPC)逆变器在单桥臂故障后可以重构为八开关三相逆变器,但此时直流侧电容充放电会引起中性点电位波动,导致三相输出电流不平衡。为此,基于空间矢量脉冲宽度调制(SVPWM)算法提出一种电压矢量实时补偿策略。首先,基于八开关三相逆变器的工作原理,推导出直流侧中性点电位波动的机理及其引起输出电流不平衡的原因;然后,对中性点波动量进行陷波滤波,并通过设计比例控制器得到抑制输出不平衡的补偿量大小;接着用补偿后的电压矢量对SVPWM各扇区的矢量作用时间进行重构计算,实时更新电压矢量的作用时间。实验结果表明,该算法可以消除直流侧中性点电位波动引起的输出电流不平衡现象,且在负载和频率突变工况下具有良好的鲁棒性。

The three-phase three-level neutral-point-clamp(NPC) inverters could be reconstructed into eight-switch three-phase inverters(ESTPI) after a single-arm failure. However, the charging and discharging of the DC-link capacitors cause the neutral point potential fluctuation, resulting in unbalanced three-phase output current. Therefore, a real-time compensation strategy for voltage vector was proposed based on the space vector pulse width modulation(SVPWM) algorithms for balancing the output current. Firstly, based on the working principle of the ESTPI, the mechanism of the neutral point potential fluctuation was derived and the reason for the output current unbalance was analyzed. By means of the notch filter and proportional control, the compensation value for suppressing the output imbalance is obtained. The compensated voltage vector was used to reconstruct the vector action time of each sector and the compensated duty-ratio was calculated in real time. Experimental results show that proposed algorithm can eliminate the impact of neutral point potential fluctuation on the output current, which has superior robustness under transient load and frequency changes.