A comparative analysis of permanent magnet-type bearingless synchronous motors for fully magnetically levitated rotors

• Published in: Journal of Applied Physics
• Main Authors: Charpentier, J. F., Lemarquand, G.
• Format: Article in Journal/Newspaper
• Language: English
• Published: AIP Publishing 1998
• Subjects: General Physics and Astronomy; North Pole; South Pole; South pole
• Online Access: http://dx.doi.org/10.1063/1.367540; https://pubs.aip.org/aip/jap/article-pdf/83/11/7121/10592080/7121_1_online.pdf

Radial instability of synchronous motors is important data to design magnetic bearings. Moreover, original motor structures must be proposed to decrease the instability. In this article, four structures with a permanent magnet rotor, six poles, and the same main mechanical dimensions are analyzed and compared. The first concerns a rotor with six tiles of permanent magnets radially magnetized and adhered to an iron core. The second is a rotor with six axial permanent magnets tangentially magnetized and separated by iron pole pieces, where the shaft is amagnetic. The third design proposes a rotor with six contiguous tiles of permanent magnets tangentially magnetized and an amagnetic shaft. In the fourth structure each north pole is made up of two contiguous tiles of permanent magnets tangentially magnetized in opposite direction and each south pole is made up of an iron pole piece. The shaft of this structure is amagnetic. The stator structure and the currents in stator windings produce a six poles flux distribution. A finite element method program is employed to study the forces and the torques. The four structures are designed to provide the same motor performance (torque). The radial instability is modeled by outcentering the rotor. The relationships between the radial force and the type of structure are analyzed. The result is that the third structure is the best solution for fully magnetically levitated rotors. It has a small instability and does not generate any disturbing force whose frequency is the double of the rotation frequency. This structure also has good properties to be used as a radial magnetic bearing.