An asymmetrical six-phase induction motor drive based on nine-arm Modular Multilevel Converter (9AMMC) with circulating current suppression

Asymmetrical six-phase (dual three-phase) induction motors have received significant attention in high power medium voltage drive applications. Normally, two three-phase voltage source converters are used to supply the six-phase motor. Multilevel inverters are preferred in medium voltage applications to provide a stepped output voltage waveform that not only reduces dv/dt stresses but also provides a better output current waveform. This also improves the machine torque quality and enhances the overall drive performance. Modular Multilevel Converter (MMC) is one of the promising converters in medium and high voltage applications. Instead of using two MMCs with six arms each to feed the six-phase motor, this paper proposes a new nine-arm MMC (9A-MMC) topology to drive such a motor. The proposed approach reduces the number of required dc capacitors, semiconductor devices and their gate driver circuits, which reduces system complexity and cost. The complete system analysis is presented along with the required filter to suppress the circulating currents, which is a critical issue in MMC converters, is also considered. Simulation results for the conventional and proposed systems are compared and results show the effectiveness of the proposed system.