Microstructure Design of Surface Permanent Magnet and Tooth Surface Stator in Brushless DC Motor with Low Rare Earth Material

Abstract

Permanent magnet (PM) brushless DC motors (BLDCMs) are widely applied in industrial drives. However, the price rising of rare earth resource resulted in country policy restriction, so it is detrimental for mass production of PM-BLDCMs. As a result, the design and manufacture tendency of PM-BLDCMs are smaller and slighter in adopting rare earth materials of PMs. Additional, the magnetic flux density of PMs are difficult to improve in the near future. The effective method is to decrease stator reluctance and to adjust magnetic flux distribution of the air gap in stator design. Hence, the surface permanent magnets (SPMs) and tooth surface stators (TSSs) are designed to improve the motor performance, and are calculated by finite-element analysis (FEA) software in this study. Various hemicycle groove microstructures of SPMs and TSSs for designing, analyzing and optimizing are considered to observe the magnetic field strength distribution and to reduce the cogging torque in PM-BLDCMs, and the FEA result can be regarded as important references of motor structure design. The cogging torque can be reduced 80.9% in SPM3-model and can be decayed 89.2% in TSS2-model versus original model separately, and the cogging torque of the optimal combination of SPM-BLDCM can be abated 62.4%. Furthermore, the usage amount of rare earth material volume in designed SPM-BLDCMs can be reduced 5.3% in average. Finally, a prototype of the SPM- BLDCM has been constructed to prove the simulation design.