Inside-Out Configuration Active Magnetic Bearing Actuators

he University of Texas Center for Electromechanics (UT-CEM) has designed active magnetic bearing actuators for use in a 5 MW flywheel alternator with a 700 lb (318 kg), 20,000 rpm rotor, under the sponsorship of the Department of Defense Combat Hybrid Power Systems (CHPS) program. Because this machine incorporates an unusual inside-out topology (i.e., the rotating portion of the flywheel is located outside the stationary components), unique inside-out configuration magnetic bearing actuators are required. Permanent magnet bias bearings were chosen for this application because of inherent low power requirements, low power losses, and nearly linear current stiffness and positional stiffness. To verify performance, a bearing test fixture was designed and built which permits static and dynamic force measurement. This paper discusses bearing requirements, actuator design, predicted performance, and compares theoretical versus measured bearing characteristics. A companion paper discusses control issues for this unique magnetic bearing system [1].