Asymmetrical Combined Winding Arrangement for a Four-Phase Bearingless Motor

Conventional bearingless motors typically have two sets of independent windings in the stator for producing torque and suspension force, termed separated winding in this paper. However, several approaches to combine the suspension and motor windings into one set of winding, termed combined winding, have been investigated for torque density improvement. A theoretical calculation demonstrates that no suspension force can be generated at certain rotational angles when the four phases are symmetrically located, that is, all four phases are shifted every 90°. This study proposes a novel asymmetrical combined winding arrangement for a four-phase bearingless motor to enhance the torque, and one possible model is selected. The test results showed that the rotor was levitated and rotated up to 5000 rpm.