Multilevel converters for large electric drives

This paper presents transformerless multilevel converters as an application for high-power and/or high-voltage electric motor drives. Multilevel converters: 1) can generate near-sinusoidal 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 ail-electric drives because it uses several levels of de 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 pulsewidth-modulation-based drives.