Principle and Design of a Novel Lorenz Force Type Bearingless Motor with Single-Axis Actively Regulated Capability

This paper proposes a novel Lorenz-force-type bearingless motor with single-axis actively positioned functionality. The novel motor consists of two slotless surface-mounted permanent magnet (SPM) motors, which have six skewed coils for each motor to constitute 3-phase windings and are in tandem along axial direction so as to achieve actively regulated axial motion. Additionally, two repulsive permanent magnet bearings (RPMBs) are used to passively stabilize radial- and tilting movements of the rotor. The slotless stator iron is employed for arrangement of the skewed coils in toroidal form. Compared with state-of-the-art single-axis actively controlled bearingless motors utilizing field weakening or strengthening effect of d-axis current to regulate axial movement, perhaps suffering irreversible demagnetization of permanent magnets especially at the time of start-up, the merit of this proposed motor is beneficial to prevent the demagnetization risk of permanent magnets. To verify the novel concept, firstly, theoretical analysis is carried out for modeling back electromagnetic force (back-EMF), axial force, drive torque. Followed by the analytical model, a detailed design process by integration of analytical method and finite element analysis (FEA) for the structural parameters are revealed. At last, 3-D FEA is performed to validate the correctness of analytical model, design process as well as to evaluate the performance of proposed motor.