Operational Characteristics of an IPM-Type Bearingless Motor With 2-Pole Motor Windings and 4-Pole Suspension Windings

A bearingless motor (BelM) integrates the characteristics of an electric motor and a magnetic bearing. Typically, a surface-mounted permanent magnet (SPM)-type BelM with a ring magnet magnetized in parallel is employed for high-speed operation. It is noteworthy that a carbon fiber bandage is needed to fix the ring magnet. However, when an SPM-type BelM is applied to a high-output motor, it becomes difficult to generate sufficient suspension force because of the wide magnetic gap arising from the carbon fiber bandage and the ring magnet. In addition, the manufacturing cost for the large-scale ring magnet and the carbon fiber bandage is high. Therefore, to realize a high-output and high-speed BelM at a low cost, we have focused on an interior permanent magnet (IPM)-type BelM with 2-pole motor windings and 4-pole suspension windings. Moreover, a rotor structure for suppressing suspension force ripple arising in the IPM-type BelM has been proposed based on a three-dimensional finite element analysis. In this study, a prototype of the IPM-type BelM with the proposed rotor structure is produced. Experiments with this prototype show that the proposed rotor structure is effective in reducing suspension-force ripple. Additionally, the operational characteristics of the prototype are shown in detail.