Verifying the calculation approach for radial suspension force based on the airgap flux density for SPM, consequent-pole, and bearingless AC homopolar motors

Abstract

In this paper, a calculation method is proposed for the radial suspension force of a bearingless motor with a surface-mounted permanent magnet (SPM) rotor, a consequent-pole permanent magnet (CPM) rotor, and a homopolar permanent rotor (HPM). The radial suspension forces are calculated mathematically and analytically using the airgap flux density. It was confirmed that the proposed radial force equations are practical to calculate the suspension force based on the airgap flux density. The CPM bearingless motor and bearingless AC HPM have salient pole rotors that interact with the 2-pole Magnetomotive force (MMF) to generate 6- and 10-pole components. As a result, the radial suspension force of the CPM bearingless motor is generated by 8- and 6-pole, and 8- and 10-pole magnetic flux, whereas the bearingless AC HPM produces the radial suspension force by DC and 2-pole components. The shaft torque, the suspension force, and efficiency were also compared for SPM, CPM bearingless motors, and bearingless AC HPM. Consequently, the torque value of the CPM bearingless motor is quite close to SPM bearingless motor. Moreover, the suspension force of the CPM bearingless motor is quite close to bearingless AC HPM.