Performance of a High Speed Motor Drive System Using a Novel Multi-Level Inverter Topology

This paper examines the performance of a novel multilevel six-switch three phase inverter drive for low-voltage high speed motor applications. Hard switched voltage source inverter topologies are limited in terms of switching frequency and therefore as the frequency modulation ratio decreases, the resulting increase in harmonic currents may cause excessive rotor heating or lead to larger than desired output reactors with a series voltage drop. The multi-level inverter structure offers an increased number of voltage levels, reduced dead-time effects and a significant reduction in harmonic content, resulting in a reduction of total losses compared to the standard six-switch three phase inverter. The harmonic reduction provided by the multilevel topology relative to the standard inverter is experimentally demonstrated with a 15 HP 18,000 rpm induction machine.