基于傅里叶级数拟合实现的三电平SHEPWM

Realization of Three-level SHEPWM Based on Fourier Series Fitting

在大功率场合,三电平中点箝位NPC (neutral point clamped)型逆变器需运行在较低的开关频率,此时传统调制方式(载波调制和空间矢量调制)不再适用,需采用特定谐波消除脉宽调制SHEPWM(specific harmonic elimination pulse width modulation)等其他调制方式。主要研究应用于三电平NPC的SHEPWM的实现方法,目前三电平SHEPWM的实现多采用多项式曲线拟合法,但当所需拟合的开关角曲线波动过大时,多项式曲线拟合法需进行分段拟合才可达到拟合精度的要求。为解决该问题,采用傅里叶级数拟合法来实现三电平SHEPWM的开关角曲线拟合。仿真结果表明,在满足拟合精度要求的同时,采用傅里叶级数拟合法,可降低曲线拟合的复杂性,且实现较为简便。最后,通过仿真及实验验证了傅里叶级数拟合法的可行性。

In high-power scenarios,the three-level neutral point clamped(NPC)inverter has to operate at a lower switching frequency,so the traditional modulation methods(e.g.,carrier pulse width modulation and space vector pulse width modulation)are no longer applicable,and other modulation methods such as specific harmonic elimination pulse width modulation(SHEPWM)are needed.The realization of SHEPWM which is applied to the three-level NPC inverter is studied.At present,the polynomial curve fitting method is mostly used in the realization of three-level SHEPWM.However,when the switching angle curve that needs to be fitted fluctuates too much,the polynomial curve needs to be piecewise fitted to meet the requirements of fitting accuracy.To solve this problem,Fourier series fitting is used to fit the switching angle curve of three-level SHEPWM.Simulation results show that Fourier series fitting can reduce the complexity in curve fitting while satisfying the requirements of fitting accuracy.In addition,its realization is relatively simple.Finally,the feasibility of the Fourier series fitting method was verified by simulation and experimental results.