Active radial magnetic bearing for an ultra-high speed motor

The miniaturization trend of electric machines increases the demand for higher rotational speeds to provide a desired mechanical power level at decreased size. To push the limits of rotor miniaturization, new concepts for an ultra-high speed motor are researched, which employs sub-millimeter size rotors and is capable of achieving rotational speeds above 25 million rotations per minute (Mrpm). The rotor is supported by means of a frictionless active magnetic bearing, which counteracts the gravitational force in vertical direction. Due to the low damping of the rotor, a magnetic bearing is also required in horizontal direction for to fully stabilize it. The respective system model, position sensor system and controller design for such a magnetic bearing are outlined in this study. Experimental results demonstrate an increased horizontal damping of the rotor by a factor of more than 100.