Run-out compensation of eddy current displacement sensor for performance improvement of a bearingless motor with unequal-tooth-pitch core

A bearingless motor is defined as a motor with a magnetically integrated bearing function. A displacement sensor is used to control the rotor position. Eddy-current sensors are typically located outside the motor, resulting in a large motor size. This study proposes a bearingless motor with an unequal-tooth-pitch stator to reduce system size by increasing the tooth pitch of part of the stator and placing eddy-current displacement sensors between the teeth. However, since eddy-current sensors use magnetic flux to measure distance, they are affected by the motor flux, causing an apparent vibration with components of harmonic orders of rotational frequency called run-out. This paper reports the results of a levitation test of a 10-pole, 12-slot, two-axis actively positioned bearingless motor with an unequal-tooth-pitch core employing run-out compensation. The run-out compensation was applied to the measured displacement using a function with pre-identified parameters and a notch filter. The motor successfully levitated and rotated at 4000 rpm in the actual machine test.