Magnetic Bearing Technology for Industrial Bearingless Motor Systems

This paper investigates combined radial axial magnetic bearing (CRAMB) technology as an enabling component for shafted bearingless motor systems. The unique requirements of high speed bearingless motors designed for significant power levels are used to guide a literature review on CRAMB designs. Fundamental bearing topology aspects are identified and compared. Based on the outcome of this review, a new CRAMB topology is proposed and developed to meet the needs of a bearingless motor. Key features of the proposed design include a three pole radial force stage (driven by a three phase motor drive) and utilization of an optimal bias flux that improves radial force density by approximately 15% (improved rotor dynamics). It is shown that compared to a conventional four pole side-by-side CRAMB, this topology decreases the bearing shaft length and requires two fewer power electronic switches (6 instead of 8).