Unbalance Compensation for Lorentz-force-type Self-Bearing Motor

A self-bearing motor is a combination of magnetic bearings and an electric motor, and many types of self-bearing motors have been proposed and developed. A Lorentz-force-type self-bearing motor consists of distributed wind- ings as a stator, and permanent magnets as a rotor. This motor does not have a stator core and slots, then, the structure of the motor becomes simple, and it allows miniaturization and cost reduction. However, the manufac- turing error of the distributed windings is not small, hence, the bearing force is affected by the rotating position of the rotor. This causes the rotor vibration, rotating losses, large stator current, and so on. To solve this problem, this paper introduces unbalance compensation for the position control of the rotor. The vibration synchronized with the rotation can be canceled by the integral feedback on the rotor coordinate system, and then, it is possible to reduce the vibration or motor current. The experimental results show that the unbalance compensation technique is effective for reducing motor currents.