A Multilevel Open-End Winding Six-Phase Induction Motor Drive Topology Based on Three Two-Level Three-Phase Inverters

This article presents a nine-leg (9L) multilevel inverter to drive an asymmetrical six-phase induction machine in an open-end winding (OEW) configuration. The system is based on three conventional two-level three-phase voltage source inverters (VSIs) with three, two, or one isolated dc links. A machine with two sets of 30 degrees shifted three-phase stator windings is considered. The article discusses the converters operating principles and proposes a simple space-vector pulse-width modulation (SV-PWM) and its implementation through equivalent level-shifted PWM (LS-PWM). Also, a comparative study is presented regarding the discussed 9L-OEW systems and two conventional drives: the six-leg two-level (6L), and the 12-leg OEW (12L-OEW) systems. The figures of merit were the number of components, required dc-link voltage, voltage and current harmonic distortions, torque ripple, and semiconductor losses. Simulations and experiments show results for a 1 HP machine. Finally, the article concludes that the characteristics of the 9L-OEW system using three isolated dc links fit between the 6L and 12L-OEW conventional systems.