Analysis and effect of switching frequency and voltage levels on total harmonic distortion in multilevel inverters

Multilevel converter technology has emerged as a very important alternative in the area of high-power medium-voltage energy control. Several topologies for multilevel inverters have been proposed over the years; the most popular cascaded H-bridge apart from other multilevel inverters is the capability of utilizing different dc voltages on the individual H-bridge cells which results in splitting the power conversion amongst higher-voltage lower-frequency and lower-voltage higher-frequency inverters. Considering the cascaded inverter to be one unit, it can be seen that a higher number of voltage levels are available for a given number of semiconductor devices. In this paper multilevel converters with different voltage levels are considered and simulation results are presented in terms of total harmonic distortion (THD). Finally generalized expression for highest order harmonic based on switching frequency and number of levels is derived.