Analysis of Selective Harmonic Elimination Pulse Width Modulation for a Three-Phase Multilevel-Inverter

The programmable pulse width modulation is gaining wider acceptance in the field of power inverter switching because of lower processing requirements. It allows the switching at pre-calculated values rather carrier comparison process. That facilitates adding fruitful modifications to the generated voltage. This study presents the analysis of applying Selective Harmonic Elimination Programmable Pulse Width Modulation (SHEPPWM) technique on a three-phase multilevel inverter. The inverter is constructed from three single-phase half-bridge inverters that can be connected in either star or delta. Different number of output voltage levels can be obtained based on the number and magnitude of DC sources. Genetic algorithms are used as a search technique to find-out the optimal switching angles of the inverter to reduce the total harmonic distortion (THD). The selection of these angles' search space is investigated to found out for rapid calculations that may be used for online optimization. The fast Fourier transform (FFT) is carried out at different values of modulation index. Typical case study is obtained for a three-phase 7-levels inverter supplying a static RL load. A special software utility is developed for this study. The results show the effectiveness of the optimization technique. In addition, they presents a good guide for switching angles' search space selection.