Voltage harmonics generated by 3-level converters using PWM natural sampling

This paper presents a detailed analysis on how the independent choice of the branch carrier phase shift angles in 3-level three-phase converters using PWM natural sampling can offer some extra degrees of freedom to establish rules to optimize the line voltage harmonic content. The study developed in this paper is only valid for converters that can be considered as an association of independent 2-level cells, which are the floating capacitors and the H-bridges topologies. This paper shows how, in order to minimize the harmonic distortion, the choice of the modulation technique depends on the modulation index. For low values of the modulation index, the so-called three-phase modulation achieves the best results, while for high values (greater than 0.9) the so-called single-phase modulation reaches better results.