Reduction in torque and suspension force ripples of an axial-gap single-drive bearingless motor

This paper investigates reduction in torque and suspension force ripples of an axial-gap type bearingless motor with one-degree-of-freedom (DOF) active positioning in the axial direction. This one-DOF controlled bearingless motor employs only one set of three-phase winding and one three-phase inverter, called a single-drive bearingless motor (SDBelM). The proposed axial-gap SDBelM combines a repulsive permanent magnetic coupling that stabilizes four-DOF radial and tilting motions. The suspension force and torque, which are regulated by the d- and q-axis currents, respectively, are theoretically derived considering the spatial harmonics of the flux density distribution induced from the permanent magnets. For reduction in torque and force ripples, we have proposed the improved magnet shape with the gap between the magnet pieces. The finite element method calculation shows that the proposed PM configuration is effective to reduce the torque and the suspension force ripples.