Temperature drift at low temperatures and development of bearingless motor

Abstract

　This paper proposes an axial type bearingless motor using zero power control as a low-cost magnetic bearing as-suming temperature drift at low temperatures. A bearingless motor is a motor that functions as a bearing and can support the rotor without contact. The proposed bearingless motor is a one-degree-of-freedom axial type bearingless motor that is actively controlled only in the axial direction of the rotor using an eddy-current displacement sensor. Other degrees of freedom are passively controlled with permanent magnet bearings. In addition, zero-power control is used to solve the problem of temperature drift, in which the output of the eddy-current displacement sensor changes depending on the temperature. As a result, a bearingless motor with only one eddy current displacement sensor and requiring no sensor calibration from room temperature to liquid nitrogen temperature has been developed, and its drive has been verified by experiments using liquid nitrogen.