Harmonic distortion minimization in multilevel converters for a wide range of modulation indexes

Switching speed and losses and minimum turn-on and turn-off time are known as the limitations of semiconductor switches in high power converters. In applications such as variable speed drives, FACTS and active filters, a wide range of voltage variations are desirable. Therefore switching techniques applying in high power multilevel converters must consider above mentioned problems to have a good power quality and optimal efficiency for a wide range of modulation indexes. This paper presents a modified modulation technique with a wide range of modulation indexes and minimized harmonic distortion at low indexes. This method can be easily implemented for different converter topologies and for any number of levels. Simulation results of a three-phase seven-level cascaded converter validate the theoretical analysis with reasonable agreement.