Selective harmonic mitigation technique for multilevel cascaded H-bridge converters

The increasing demand of energy and proliferation of non-linear loads have leaded to the appearance of new grid codes which limit the maximum acceptable harmonic levels. In this context, multilevel topologies are very attractive because can generate output waveforms with a low harmonic content using a low switching frequency. In this paper, the recently presented selective harmonic mitigation technique (SHMPWM) is adapted to a nine-level converter. Its flexibility is exploited to meet the EN 50160 and CIGRE WG 36-05 grid codes without any additional filtering system using 10 switching angles per quarter of period in a wide range of amplitudes of the fundamental harmonic from 0.70 to 1.22. Some results validating this technique applied to this topology are presented. A comparison with the well known selective harmonic elimination method is included showing the advantages of the SHMPWM technique.