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

This article 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 only has three concentrated coils that are wound alternately on six teeth of the stator and uses only one three-phase inverter for both the 2-DOF radial magnetic suspension and single-phase motor drive. The theoretical calculation and finite-element method analysis demonstrated that the proposed three-coil combined winding configuration generates a four-pole rotating field and a six-pole alternating field for generating the 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 at 7500 r/min. 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 r/min with 20 mN·m output is improved by 5% when compared with the separated winding owing to the copper loss reduction.