Investigation of integrated winding configuration for a two-DOF controlled bearingless PM motor using one three-phase inverter

This paper describes a simple integrated winding configuration for a two-degrees-of-freedom (DOF) controlled bearingless motor with 6-slot/6-pole surface-mounted permanent magnet (SPM) structure. This bearingless SPM motor has only three concentrated coils, wound alternately in the stator's 6 slots, and employs only one three-phase inverter for both two-DOF radial magnetic suspension and motor drive. The theoretical calculation and finite element method analysis have verified that the proposed integrated winding generates the 4-pole revolving field for radial suspension force generation and 6-pole alternating field for torque generation. This bearingless motor works as a single-phase SPM motor with effective use of cogging torque. An outer rotor type bearingless motor with a diameter of 58 mm and a height of 7 mm is built and tested. The rotor is successfully levitated and driven up to 6000 rpm. The peak-to-peak value of the rotor's radial displacement during rotation is smaller than 50 μm.