High Torque Density Design For Direct Drive PM Machine Using Hybrid Pole Rotor

The torque density of traditional consequent-pole permanent magnet (PM) (CPM) machines is difficult to improve unless PM materials with higher remanence density are used. Therefor, a novel hybrid-pole permanent magnet (HPM) rotor is designed in this paper. The staggered PM sequence enhances the magnetic field aggregation ability and the utilization rate of PM materials, which enables HPM machine to meet the requirements of high torque density direct drive application. In addition, the electromagnetic performances of the proposed machine, including the open-circuit airgap flux density, back EMF, cogging torque, average torque, overload capacity, and efficiency, were compared with traditional machines. It is demonstrated that the utilization ratio of PM in HPMM can be increased by up to 17%, and the torque density is comparable to spoke-type permanent magnet (STPM) machine.