Full Study of a Precise and Practical Harmonic Elimination Method for Multilevel Inverters

Multilevel inverters have been widely used in medium and high voltage applications. Selective harmonics elimination for the staircase voltage waveform generated by multilevel inverters has been studied extensively in the last decade. Most published methods on this topic aimed at solving high-order multi-variable polynomial equation groups derived from Fourier series expansion. A totally different approach based on equal area criteria and harmonics injection in the modulation waveform is fully studied in this paper. Regardless how many voltage levels are involved, only four simple equations are involved in the basic method. The problems of the basic method are identified and discussed. A full set of solutions is proposed. The results of a case study with maximum five switching angles show that the proposed method can be used with excellent harmonics elimination performance for the modulation index range from 0.2 to 0.9.