Elimination/Mitigation of Output Voltage Harmonics for Multilevel Converters Operated at Fundamental Switching Frequency using Matlab's Genetic Algorithm Optimization

This paper deals with the optimization of the output voltage waveform of a multilevel converter operated with fundamental frequency switching. For a high number of output voltage levels, nearest-level control is typically used, whereas an optimized waveform can be presumably used to eliminate a selection of low order harmonics. A nonlinear optimization problem for any kind of multilevel inverter, operating in a single or three-phase arrangement, is formulated. It is shown that the set of nonlinear equations, defining this optimization problem, cannot be numerically solved, if the number of output voltage levels is higher than nine. Thus, an optimization algorithm, e.g., Matlab's genetic algorithm, should be used instead. Based on the concept of the weighted THD, it is shown that an optimized waveform has no effect on the output current's quality of a single phase multilevel converter. However, considering an ungrounded three-phase system, the content of the to be eliminated harmonic components is shifted towards the triplen harmonics and, consequently, the expected current quality, based on the WTHD, can be significantly improved.