Optimization Design of Bearingless Permanent-Magnet Slice Motor

The parameter and distribution of air-gap flux density determined by structures and methods of permanent-magnet rotor magnetization have effects on the performance of suspension forces and torque in a bearingless permanent-magnet slice motor (BPMSM) directly. In this paper, different rotor structures and magnetization methods are analyzed for the BPMSM. Based on the finite-element analysis, the optimum length ratio of rotor magnetic yoke d_r and l_r is calculated in different magnetizations to get the maximum flux density. Then the radial suspension forces with maximum air-gap flux density in different structures and rotor magnetizations are compared for the BPMSM. The simulation and experiment results show that the amplitude and sinusoidal characteristic of air-gap flux density are improved with parallel magnetized ring-shaped rotor. Furthermore, the BPMSM with parallel magnetized ring-shaped rotor is easily controlled and has a good suspension and speed regulation performance.