The rotor topology of slotless permanent-magnet brushless DC motor

The air-gap field in slotless permanent magnet motor is small. Based on the surface mounted permanent magnet, this paper compares the parallel magnetization with the radial magnetization by finite element calculation. The results show that parallel magnetization can provide larger air flux in the slotless motor. The large effective air gap makes the end leakage serious. In order to resolve this problem, this paper proposes a novel rotor topology structure adding end axial magnetization permanent magnet. Results from three-dimensional (3-D) finite-element analysis prove that the structure can have a significant effect on both reducing end leakage and increasing effective air flux.