Three-Coil Combined Winding Configuration for a 2-DOF Actively Controlled Bearingless Permanent Magnet Motor

Abstract

This study describes a simple combined winding configuration for a two-degrees-of-freedom (DOF) controlled bearingless motor with a six-slot/six-pole permanent magnet (PM) structure. This bearingless PM motor has only three concentrated coils that are wound alternately on six teeth of the stator and employs only one three-phase inverter for both the two-DOF radial magnetic suspension and single-phase motor drive. Theoretical calculation and finite element method (FEM) analysis demonstrated that the proposed three-coil combined winding configuration generates a four-pole rotating field and six-pole alternating field for generating radial suspension force and torque, respectively. To verify the proposed configuration, we built and tested an outer rotor bearingless PM motor with a diameter of 58 mm and a height of 5 mm. The rotor was successfully levitated and driven up to 7500 rpm. The calculated and measured results were compared for both the proposed combined winding configuration and the previously developed separated winding configuration. The measured motor efficiency of the prototype with the combined winding at 5000 rpm with 20 mNm output is improved by 5% due to the copper loss reduction when compared to that with the separated winding.