Bearingless segment motor with axial magnetized rotor magnets

One of the major advantages of magnetically levitated drives are the increased lifetime, the possibility of very high speeds and the feasibility to hermetically seal the rotor. Using a permanent magnet excited rotor disc three degrees of freedom can be passively stabilized by reluctance forces. Further decrease in complexity and costs can be realized by a segmented stator. This paper deals with the development and design of a special bearingless segment motor with axial magnetized rotor magnets that needs no back iron in the rotor. After theoretical derivations on the generation of bearing forces and motor torque a control scheme with current feeding power amplifier is presented. For the design of the geometry finite element simulations are applied to optimize the bearing forces, the motor torque per ampere and the reluctance forces. To verify the theoretical considerations a first prototype motor was built and put into operation.