Active Magnetic Bearings for Energy Storage Systems for Combat Vehicles

Advanced energy storage systems for electric guns and other pulsed weapons on combat vehicles present significant challenges for rotor bearing design. Active magnetic bearings (AMBs) present one emerging bearing option with major advantages in terms of lifetime and rotational speed, and also favorably integrate into high-speed flywheel systems. The Department of Defense Combat Hybrid Power Systems (CHPS) program serves as an excellent case study for magnetic bearing applications on combat vehicles. Under the sponsorship of the CHPS program, The University of Texas at Austin Center for Electromechanics (UT-CEM) has designed active magnetic bearing actuators for use in a 5 MW flywheel alternator with a 318 kg (700 lb), 20,000 rpm rotor. The flywheel alternator serves as a power supply for multiple systems on a military vehicle, including mobility load leveling and weapons systems. Because of continuous duty requirements, magnetic bearings were chosen for this high-speed application to minimize losses and to enable the flywheel to meet a planned vehicle life of 15 to 25 years. To minimize CHPS flywheel size and mass, a topology was chosen in which the rotating portion of the flywheel is located outside the stationary components. Accordingly, magnetic bearing actuators are required which share this “inside-out” configuration. Because of inherent low loss and nearly linear force characteristics, UT-CEM has designed and analyzed permanent magnet bias bearing actuators for this application. To verify actuator performance, a non-rotating bearing test fixture was designed and built which permits measurement of static and dynamic force. An active magnetic bearing (AMB) control system was designed to provide robust, efficient magnetic levitation of the CHPS rotor over a wide range of operating speeds and disturbance inputs, while minimizing the occurrence of backup bearing touchdowns. This paper discusses bearing system requirements, actuator and controller design, and predicted performance; it also compares theoretical vs. measured actuator characteristics. Manuscript received December 21, 1999. Funding for this work was provided by the Department of Defense under contract #4500152859, Mod