Investigation of Different Winding Configurations and Displacements of a Nine-Phase Permanent-Magnet-Synchronous Motor With Unbalanced AC Winding Structure

Integral-slot electrical machines require modifications and optimization of both stator and rotor to maximize the machine performance. In addition, sub-harmonics in magneto-motive force distributions is an important issue in motors with fractional-slot concentrated windings. These additional sub- and super-harmonics increase iron losses, which becomes an even bigger challenge in high speed/frequency applications. A permanent-magnet (PM) motor with unbalanced winding (UBW) and unconventional slot numbers is a good option for applications that require smooth torque output and low back electromotive force voltage harmonics. In this paper, different winding configurations and displacements of an unconventional nine-phase PM motor with both balanced fractional-slot winding and UBW structures have been investigated. The focus has been on 117-slot with 12-pole (for the balanced winding motor) and 36-pole (for the UBW motor) combinations. Motor prototypes with UBW configurations have been manufactured. The finite-element analyses results have been validated with experimental results and it is shown that such unconventional slot/pole combinations can be a good option for some high-power applications.