Magnetomechanics of internal-dipole, Halbach-array motor/generators

The magnetomechanical behavior of internal-dipole, Halbach-type magnet arra ys is analyzed for application as a motor/generator (M/G) with an energy-st orage flywheel that is suspended by low-stiffness bearings. Scaling laws fo r the maximization of torque are derived as a function of geometry, The opt imal geometry is relatively insensitive to gap and stator design and occurs approximately at a ratio of inner to outer diameter of the array of 0.8. V alues are found for the angular extent of each phase of the stator coil tha t minimize the stiffness. The negative stiffness of the internal-dipole arr ay is calculated for several manufacturable configurations and is shown to provide an upper limit on the available torque of the M/G according to the positive stiffness of the bearings. Experimental results are reported for a n internal-dipole array used as a M/G for a flywheel suspended by a bearing consisting of a permanent-magnet assembly levitated over an array of high- temperature superconductors. Results show that the system is stable and tha t idling losses are low.