Enhancement of Electromagnetic Supporting Force in Aerodynamic Bearing-Equipped SPMSMs

A high speed surface mounted permanent magnet synchronous motor (SPMSM) equipped with aerodynamic bearings is studied in this paper. Controllable electromagnetic supporting force (EMSF) is produced by the motor armature windings, while electromagnetic torque being simultaneously generated, in order to dilute dry friction in the air bearings before reaching the lift-off speed of the bearings. In this paper, a new method to increase the EMSF density and reduce the EMSF ripples is proposed. Firstly, generation principles of the EMSF and its ripples are introduced. Then, by analyzing the difference between the conventional electromagnetic torque design and the EMSF design, a new method is proposed, increasing the equivalent air gap magnetic permeability to enhance the EMSF density. Then, according to the analysis results of the air gap field spatial harmonic components affecting the EMSF ripples, shaping of the permanent magnets (PMs) and rotor core is conducted. This shaping method is founded on the analytical approach interpreting the influence of rotor parameters on the spatial magnetic field distribution. Utilizing the design method proposed in this paper, an SPMSM system capable of generating controllable EMSF is developed. Finite element analysis (FEA) and experimental study are carried out to demonstrate the improvement in EMSF density and the reduction in EMSF ripples, thereby proving the feasibility of the design method proposed.