Permanent Magnet Bias, Homopolar Magnetic Bearings for a 130 kW-hr Composite Flywheel

The Center for Electromechanics at the University of Texas at Austin is developing a power averaging flywheel battery for a high speed passenger locomotive as part of the Federal Railroad Administration’s Next Generation High Speed Rail Program. The flywheel rotor, which weighs 5100 lb, is designed to store 130 kW-hr of energy at a top design speed of 15,000 rpm. The vertical rotor, which runs in a vacuum, is supported by a 5 axis magnetic bearing system. The flywheel housing is gimbal mounted to isolate the vehicle chassis from the gyroscopic forces in this dynamic application. A high speed 2 MW motor-generator, which is outside the vacuum, is directly coupled to the flywheel with the use of a rotary vacuum seal. This paper discusses the design of the magnetic bearing actuators. There are two identical radial bearings and a double acting thrust bearing, each employing permanent magnet homopolar bias fields coupled with active control coils. The bearings employ permanent magnet homopolar bias fields. Some electromagnetic design analysis of the actuators is presented, along with test results for static electromagnetic fields measured within the bearing air gaps. Measured hysteresis loss in the radial bearing laminations is also presented. Analytical estimates of actuator bandwidth are compared to measurements. A preliminary build of the flywheel rotor (the design of which is discussed in a companion paper) has been successfully spin tested to 13,600 rpm with the use of a digital bearing controller. Performance of the position sensors, fiber optic for radial and eddy current for axial, has thus far been adequate.