Selective Harmonic Elimination PWM for Cascaded Multilevel Inverter Based Genetic Algorithm and Newton Raphson: a Comparison Study

Abstract

The Selective Harmonic Elimination Pulse Width Modulation technique (SHEPWM) is widely used for eliminating pre-selected lower order harmonics in multilevel inverters (MLI) output voltage with controlling the fundamental voltage component. The problem of roots solving of the set of transcendental nonlinear harmonic equations derived by Fourier analysis is addressed in many recent researches. The Newton Raphson (NR) method is limited used in case of multilevel inverter controlled by SHEPWM, due to the transcendental nature of the system set of equations and dependency of roots initial values. Modern optimization techniques such as Genetic Algorithm (GA) optimization are widely used in case of MLI controlled by SHEPWM. The main problem when using GA is how to find the switching angle patterns for a wide range of the modulation index (M). Which they eliminate pre-selected lower order harmonics and controlling the fundamental voltage component with minimum Total Harmonic Distortion (THD). In this paper a comprehensive study to obtain the required switching patterns which satisfy elimination pre-selected lower order harmonics at minimum THD from cascaded MLI output voltage controlled by SHEPWM was performed. The performance of cascaded multilevel inverter controlled by SHEPWM is compared based on calculating the required switching patterns using NR and GA methods. A significant improve in the obtained solution sets in a wide range of M in GA is achieved. In particular, it is shown that there are new solution sets which haven't been previously reported in literatures. Selected simulation and experimental results for 5, 7, 9 and 11 MLIs were reported to verify and to validate the theoretical findings.