Development and Test of a Dual-Stator, Spoke-Type Ferrite Permanent Magnet Motor with High Torque Performance for Direct-Drive Applications

The minimization or elimination of the use of rare earth magnets in electric motors has been recently recognized as a challenging problem due to the increased price and limited supply of rare earth magnetic materials. Before the emergence of new cost-effective magnetic materials with high properties, the development of rare-earth-free motors using ferrite magnets with improved motor topologies is appreciated. In the previous research, a dual-stator, spoke-type ferrite permanent magnet (PM) motor with the phase-group concentrated-coil (PGCC) windings has been reported to have high torque performance, including high torque density and low torque pulsations. However, the previous research mainly investigated the motor performance of the conceptual topologies by the aid of finite element method (FEM). In this paper, the dual-stator, spoke-type ferrite PM motor, designed based on the specifications of the referenced washer motor from LG electronics, is analyzed by considering the practical topology for manufactured prototype. To enhance torque density, the rotor-PM overhang structure, considering the length of stator end windings, is determined for the proposed motor. The effects of the misaligned angles between the outer and inner stators on motor performance are analyzed in detail. The contribution of the proposed motor with rotor-PM overhang structure is highlighted by comparing to the performance of the referenced washer motor at the washing speed case, utilizing a 3-D FEM. Finally, the performance of the proposed motor is verified by experimental test, which indicates the test results and simulation results have good agreement.