GA-Optimized Switching Angles for 13-level Asymmetrical Multilevel Inverter

Abstract

In this paper, the operating principle of a 13-level asymmetrical multilevel inverter (13L-AS-MLI) with three binary-based asymmetric DC voltage sources ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$V_{dc}$</tex> ) is presented. The 13L-AS-MLI is constructed using 8 active power semiconductor switches and it is able to generate a 13-levels output voltage waveform. Unlike the voltage waveform generated by 13-level symmetrical multilevel inverter (13L-S-MLI) in which all the voltage step sizes are equal in magnitude, the output voltage waveform produced by the 13L-AS-MLI consists of two different voltage step sizes, which are <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$V_{dc}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2V_{dc}$</tex> . The switching angles utilized by the 13L-AS-MLI are derived using selective harmonic minimization pulse-width modulation (SHMPWM) concept. A nature-inspired optimization algorithm known as genetic algorithm (GA) is applied in the SHMPWM to determine the optimum switching-angle solutions. The GA-based SHMPWM switching-angle computation has been formulated to retain the fundamental voltage component of the output voltage waveform, while minimize five selected undesired low-order harmonics. A PSIM simulation model is developed to validate the operating principle of the 13L-AS-MLI. The performance of the 13L-AS-MLI is evaluated and compared to that of a 13L-S-MLI. Simulation results show that the total harmonic distortion (THD) of the output voltage generated by the 13L-AS-MLI is more or less similar to that generated by the 13L-S-MLI, whilst at certain modulation indexes the THD of the output voltage generated by the 13L-AS-MLI is lower. It is worth to note that the 13L-S-MLI requires a total number of 14 active power semiconductor switches, whilst the 13L-AS-MLI has the advantage of requiring 43 % less power semiconductor switches to produce an output voltage waveform with quality nearly similar to that generated by the 13L-S-MLI.