Generalized analytical approach of the calculation of the harmonic effects of single phase multilevel PWM inverters

Abstract

This paper introduces a generalized analytical approach for calculating the total harmonic distortion THD and its weighted value WTHD for multilevel PWM inverters. The calculation considers one single phase and it can apply to any number of levels of the inverter in general. Although the analysis is based on the assumption of a high number of pulses, the developed equations can also be applied for lower frequency ratios fs/f1. The analytical formulas require the characteristic parameters of the PWM only, which are the modulation factor m, the switching frequency fs, the fundamental frequency f1, the effective inductance L and the DC link voltage inverters with a number of levels N are considered. It must be noticed that some differences appear between the case of N odd and N even. Several parametric curves arc calculated to define the specifications of an inverter with N levels in order to fulfill the harmonic voltage recommendations trying to reduce the output signal filtering.