Levitation force analysis for spherical permanent magnet bearingless motor

Abstract

This paper presents a synthesis method of magnetic levitation force in spherical permanent magnet (PM) motor, which overcomes the adverse impact of friction torque because there is no direct contact between the stator and rotor. Using the theorem of force translation, Lorentz force of a single coil is equivalent to a force and a moment of couple exerted on the rotor center, so the independent control on levitation force can be achieved. This paper analyzed the position change of stator coils in spherical coordinates when the eccentric rotor moves in three degrees-of-freedom (3-DOF), and then the control equation of levitation force is established. The required magnetic levitation force can be synthesized by controlling the stator currents. Simulation model in MATLAB is created, furthermore the relationships between coil currents and magnetic levitation force, eccentric deviation are studied. The results show that the synthesis method of levitation force is feasible and can provide a basis for control system design. © 2011 Springer-Verlag.