中文摘要：

特定谐波消除脉宽调制（SHEPWM）技术在逆变器脉宽调制（PWM）控制,尤其是在高压大容量多电平逆变器控制方面备受关注.利用三角余弦函数倍角关系,将七电平逆变器多波段SHEPWM消谐方程组转换为代数多项式组的形式,然后利用Matlab中Solve函数得到全调制比下的所有解.经分析,绘制了总谐波畸变率（THD）最小值随调制比变化的曲线及对应的消谐开关角度轨迹.仿真和实验证明,利用该方法求取的开关角度解正确可行,并且具有高效、快速等优点,对开关角度合理选取及改善多电平逆变输出电压质量很有意义。

英文摘要：

The selective harmonic elimination pulse with modulation（SHEPWM） control method gets more and more at- tention in PWM control of inverters, especially in high capacity multilevel inverters＇ controlling.This paper converter the SHE model, nonlinear equations into algebraic equations, which is for seven-level inverter, obtain all the solutions using solve function.Then the THD under each group of switching angles has been calculated and angles distribution has been analyzed,then draw a cure for the lowest THD versus m and the track of switching angles.The study of simu- lation and experiment certificate the angles worked out by the opposed method are correct and valid, which has a cer- tain significance in choosing switching angle improving the quality of output waveforms in multilevel inverters.