Torque density increase of multi-pole permanent magnet tooth-coil synchronous motors using the reluctance torque

Abstract:
The mechanical and magnetic analysis of different configurations of high torque 45 kW permanent magnet synchronous machines with tooth-coil stator structure and interior permanent magnet rotors is presented. The aim is to maximize the total torque in 16 pole motors by increasing the intrinsic reluctance torque. For a given magnet volume the torque may be increased by 40% with respect to surface mounted magnets. Two stators with q = 0.5 and 0.25 slots per pole and phase are calculated in combination with two rotors, including embedded V-shaped and flat I-shaped magnets. The mechanical rotor stress calculation is done at over-speed (1.2·5000 = 6000/min). For a high reluctance torque the air-gap is minimized, which causes increased rotor losses due to the space harmonics, so the maximum speed has to be limited to 3000/min to limit the harmonic rotor losses. Magnetic calculation results include torque, terminal voltage and losses at no-load and load conditions for rated speed 1000/min and maximum speed 3000/min. The sudden short circuit calculations are done to test the demagnetization limit of the magnets at 150 °C magnet temperature.