中文摘要：

利用多电平逆变器载波之间在竖直方向的位移和水平方向的位移这两个自由度，从理论上进一步研究了二极管箝位型多电平逆变器的三类新型PWM方法：COPWM—A、COPWM-B和COPWM-C。通过双重傅立叶变换及其相关性质，理论上定量分析和计算了三类调制方法输出电压的谐波分量。根据COPWM-A、COPWM-B和COPWM—C三类调制方法线电压的谐波分量理论表达式，可以得出三类调制方法的理论频谱，并给出了三类PWM方法的特点。通过对三类PWM方法谐波性能的比较，得出了COPWM-A调制方法输出线电压的谐波性能最优的结论。根据线电压的谐波分量理论表达式，获得了载波之间竖直方向的交叠量、幅值调制度和多电平逆变器谐波件能指标之间的规律。

英文摘要：

Three kinds of novel PWM methods are researched theoretically in the paper, which utilizes vertical offsets among carriers of the CFD and horizontal offsets among carriers of the CFD. Harmonics of the COPWM-A, COPWM-B and COPWM-C can be calculated with the Double Fourier analysis. Analytical spectrum can be obtained and the harmonic characteristics of the COPWM-A, COPWM-B and COPWM-C are given in the paper. Through the comparison among the three methods, the COPWM-A method shows the best harmonic characteristics. According to the summation Fourier series of three kinds of methods, the relationships among the harmonic performance, vertical offsets and modulation index are obtained in the paper.