Multilevel Selective Harmonic Elimination for an Asymmetric Converter

Abstract

A novel Multilevel Selective Harmonic Elimination technique is presented for a 27-Level cascaded converter that follows the 9:3:1 ratio. The mathematical model of the AC waveform in the frequency domain allows to calculate the firing angles of the power cells in order to eliminate all the non-triple odd harmonics below the 51th order. Due to high nonlinearity of the resulting system, multiple solutions may be obtained and therefore three cases are presented in order to minimize the main distortion indexes found in literature. The proposed technique allows to eliminate 16 low order harmonics using the 27 nonredundant states of the converter. The proposal is validated using software simulations in time and frequency domains and evaluated with different merit indexes in order to compare its performance with other existing modulation algorithms. Keywords—Selective Harmonic Elimination, Asymmetric Multilevel Converters, Total Harmonic Distortion.