This paper presents transformerless multilevel converters as an application for high-power and/or high-voltage electric motor drives. Multilevel converters: 1) can generate nearsinusoidal voltages with only fundamental frequency switching; 2) have almost no electromagnetic interference or common-mode voltage; and 3) are suitable for large voltampere-rated motor drives and high voltages. 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. The back-to-back diode-clamped converter is ideal where a source of ac voltage is available, such as in a hybrid electric vehicle. Simulation and experimental results show the superiority of these two converters over two-level pulsewidthmodulation-based drives. Index Terms-Cascade inverter, common-mode voltage, diodeclamped inverter, electric vehicle, motor drive, multilevel converter, multilevel inverter.

In this paper, a genetic algorithm (CA) optimization technique is applied to multilevel inverter to determine optimum switching angles for cascaded multilevel inverters for eliminating some higher order harmonics while maintaining the required fundamental voltage. This technique can he applied to multilevel inverters with any number of levels; as an example in this paper, a 7-level inverter is considered, and the optimum switching angles are calculated oftline to eliminate the 5th and the 7th harmonics. Then, these angles are used in an experimental setup to validate the results.

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