Selective harmonic elimination for multilevel inverters with unbalanced DC inputs

Selective harmonics elimination for the staircase voltage waveform generated by multilevel inverters has been widely studied in the last decade for medium and high voltage applications. Most published methods on this topic are used for balanced multilevel inverters with the same DC voltage magnitude. In the proposed method, equal area criteria and harmonics injection are used for totally unbalanced multilevel inverters. Regardless of how many voltage levels are involved, only four modified equations are proposed in the basic method. To eliminate the harmonic components in unbalanced conditions, the problems of the basic method are discussed for a wide range of modulation indices. Then, a full set of solutions is proposed based on the combination of optimal PWM and the four-equation based method for a wide range of modulation indices in unbalanced conditions.