A Nine-phase Six-Terminal Fractional-Slot-Winding for Interior Permanent-Magnet Machines with Low Space Harmonics

This paper introduces a nine-phase six-terminal fractional slot concentrated winding layout suitable for Interior Permanent-Magnet (IPM) machine with a number of stator slots equals a multiple of nine. The winding layout when compared with a three-phase machine having the same slot/pole combination can effectively eliminate all air-gap flux sub harmonics. This highly reduces rotor core and magnet losses. Moreover, it offers a torque gain of approximately 2.5% over conventional three-phase winding layout. The proposed layout is investigated based on some well-known slot-pole combinations, namely, 9-slot/8-pole and 9-slot/10-pole, and a comparison is carried out with the conventional three-phase case assuming same stator and rotor dimensions. Being a multiphase winding, the proposed layout also offers a higher reliability-oriented design over the three-phase based systems. During a fault in one of the three-phase converters, the machine can steadily run at approximately half load with the faulty converter disconnected. The proposed winding is also compared with the well-known six-phase 12-slot/10-pole combination in terms of torque production, torque ripple, and induced eddy current losses.