Magnetic Suspension Characteristics of a Bearingless Brushless DC Motor

This paper presents magnetic suspension characteristics of a bearingless brushless DC motor. The winding distribution, the principle of suspension force generation, and the magnetic suspension control strategy have been proposed by the author. The rotational torque and suspension force have been analyzed by Finite Element Method (FEM) using a machine model. A prototype bearingless brushless DC motor was designed on the basis of the analyzed results by FEM. In this paper, the prototype machine is constructed and the rotor levitation tests are implemented to confirm the validity of the proposed magnetic suspension control method. From the observed waveforms of rotor displacements and suspension force commands, it is confirmed that the rotor shaft is stably suspended without the mechanical contacts. The proposed control method is valid to support the rotor shaft magnetically stably in the bearingless brushless DC motor.