Hybrid Electric Vehicles with Multilevel Cascaded Converter using Genetic Algorithm

Abstract

Multilevel converters as a novel kind of converters used in high voltage and high power application field, can generate near sinusoidal voltages with only fundamental frequency switching; and have almost no electromagnetic interference or common-mode voltage. This paper presents 11-level cascaded converter as an application for high-power and/or high-voltage hybrid electric vehicles (HEVs). The cascade inverter is a natural fit for large automotive all-electric drives because it uses several levels of dc voltage sources, which would be available from batteries or fuel cells. In the work presented here, it is shown how the switching times (angles) in a multilevel inverter can be chosen to achieve a required fundamental voltage and not generate or weaken the specific higher order harmonics. In this paper, a genetic algorithm (GA) optimization technique is applied to multilevel inverter to determine optimum switching angles for cascaded multilevel inverters for minimizing some predominant lower order harmonics via a cost function while maintaining the required fundamental voltage. This technique can be applied to multilevel inverters with any number of levels. By a Matlab program, the optimum switching angles are calculated offline to weaken the 5 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> , 7 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> , 11 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> and 13 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th </sup> harmonics to less than 0.5%. Then, these angles are used in a simulation and experimental hardware prototype, and the results show the superiority of the converters over two-level pulse width modulation-based drives