Design of an actuator being both a permanent magnet synchronous motor and a magnetic suspension

An original structure of a bearingless motor is theoretically proposed. Using an octopolar permanent magnet synchronous motor, the four active radial axes of a magnetic suspension are generated by supplying some coils of the motor circuit with additional control currents. Following a given sequence, these control currents have to be modified depending on the rotor position in order to give a force that is independent of the rotor position. The most appropriate command strategy is described and theoretically validated. The working principle does not disturb the generated motor torque and the functioning of the actuator. The electric drive of this bearingless actuator is studied and the principal drawbacks are discussed.