Extended field weakening and overloading of high-torque density permanent magnet motors

The results of an extended field weakening and overloading test for two high-torque density permanent magnet (PM) motors with concentrated stator windings are presented in this paper. The two 45 kW motors were designed for continuous rated power of 45 kW between the rated speed of 1000 min^-1 and the maximum speed of 5000 min^-1. The concentrated stator winding determines a high harmonics content of the air gap field, thus segmented magnets were used for the rotor in order to reduce the rotor eddy current losses. The water jacket cooling of the stator gives at rated operation a thermal reserve of 30 K at 1000 min-1 to the Thermal Class F limit temperature for the first motor. Thus it is possible to increase the power for the rated speed up to 55.2 kW. The motor has due to the relatively high inductance a good field weakening capability. The measurements confirmed that the field weakening can be extended up to 5 times the rated speed with constant output power of 45 kW. The loss calculation is presented and the calculation results are compared with the measurement results.