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 (AMB's) present one emerging bearing option with major advantages in terms of lifetime and rotational speed, and also favora bly integrate into high-speed flywheel systems, The Department of Defense C ombat Hybrid Power Systems (CHPS) program serves as an excellent case study for magnetic bearing applications on combat vehicles. Under the sponsorshi p of the CHPS program. The University of Texas at Austin Center for Electro mechanics (UT-CEM) has designed active magnetic bearing actuators for use i n a 5 MW flywheel alternator with a 318 kg (700 Ib), 20 000 rpm rotor. The flywheel alternator serves as a power supply for multiple systems on a mili tary vehicle, including mobility load leveling and weapons systems. Because of continuous duty requirements, magnetic bearings were chosen for this hi gh-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 compone nts. Accordingly, magnetic bearing actuators are required which share this ''inside-out" configuration, Because of inherent low loss and nearly linear force characteristics, UT-CF,M has designed and analyzed permanent magnet bias bearing actuators for this application. To verify actuator performance , a nonrotating bearing test fixture was designed and built which permits m easurement of static and dynamic force. An active magnetic bearing (AMB) co ntrol system was designed to provide robust, efficient magnetic levitation of the CHPS rotor over a ride range of operating speeds and disturbance inp uts, while minimizing the occurrence of backup bearing touchdowns. This pap er discusses bearing system requirements, actuator and controller design, a nd predicted performance; it also compares theoretical vs, measured actuato r characteristics.