Numerical Series Based Switching Angle Calculation for Multilevel Inverters

Abstract

The output voltage of a multilevel inverter is a stair-case waveform. The quality of output voltage in multilevel inverter depend on the switching angles. In this paper, a simple method to compute the switching angles using a numerical series of natural numbers is presented. The series of triangular numbers, Fibonacci numbers, odd numbers, even numbers, and geometric series are used in switching angle calculation. Five different switching angle expressions corresponding to each numerical series are derived. From the analysis of the resulting quasi-square waveform, it is found that the odd number series method presented in this work produces an output voltage waveform with low total harmonic distortion. The results are shown for five level quasi-square waveforms. Based on the total harmonic distortion, the proposed methods are compared with the optimal switching angles that are reported in the literature. From the comparison, it is found that the total harmonic distortion in output voltage obtained by odd number series method is close to the minimum value reported in the literature. The method presented in this work computes switching angles without using complex algorithms and/or by solving non-linear equations.