Mixed harmonic elimination and reduction technique for single phase nine level converters

This paper presents a procedure that works at fundamental frequency to compute switching angles in single phase 9-level converters to eliminate the third and odd triple harmonics and to reduce other low order harmonics, obtaining a low total harmonic distortion (THD). The DC voltages feeding the converter, that are equal, but variable, allow to obtain switching angles independent on modulation index. The proposed procedure consists in a minimization of THD by means of a suitable graphical procedure. It's mathematically demonstrated that the third and all odd multiple of the third harmonic are deleted. Simulation results, obtained by using Matlab/Simulink, are shown.