基于SHEPWM的三电平NPC逆变器中点电压波动抑制方法研究

Suppression method of neutral point potential fluctuation for three-level NPC inverter based on SHEPWM

针对基于传统特定谐波消除调制(SHEPWM)的三电平NPC逆变器的中点电压波动问题,分析了相电压中基波与三次谐波对中点电压波动的影响。建立了中点电压与三次谐波含量之间的关系,提出了基于三次谐波定量控制的改进SHEPWM方法,通过引入三次谐波控制方程重构SHEPWM开关角求解方程,并在此基础上以最大化程度抑制中点电压波动为目的,推导出了最优的三次谐波含量,在Matlab/Simulink平台上搭建了2 MW/3 k V逆变器并网模型,对改进SHEPWM方法的中点电压波动抑制效果进行了测试。研究结果表明:利用基于三次谐波最优含量控制的改进SHEPWM方法,能有效抑制中点电压的低频波动,提高NPC逆变器输出性能,降低直流环节电容。

Aiming at the neutral point potential fluctuation of three-level NPC inverter based on traditional selective harmonic elimination pulse width modulation（ SHEPWM）,the influence of the fundamental and 3-order harmonic on the neutral point potential fluctuation was analyzed,the relationship between the neutral point potential and 3-order harmonic content was established,an improved SHEPWM method based on the3-order harmonic quantitative control was presented,the solving equation of SHEPWM switching angle was reconstructed by introducing the controlling equation of 3-order harmonic,and on the basis of this,the optimal 3-order harmonic content was deduced for the purpose of maximally suppressing the neutral point potential fluctuation. The grid-connected 2 MW/3 k V inverter model was built on the Matlab/Simulink platform,and the voltage fluctuation suppression effect of the improved SHEPWM method was tested. The results indicate that the improved SHEPWM method based on the 3-order harmonic optimal content control can effectively suppress the low frequency fluctuation of the neutral point potential,which is significant to improve the output performance and to reduce the DC-link capacitance of three-level NPC inverter.