Micro flywheel energy storage system with axial flux machine

This paper presents the design and fabrication of the micro generator using flywheel energy storage system with high-temperature superconductor bearing. The micro generator is characterized by the three-phase axial flux permanent magnets. The axial flux permanent magnet machine has compact construction and high power density. The large diameter rotor with its high moment of inertia is proper as a flywheel. The planar stator is fabricated with 5-lines, 100 mum-width, and 50 mum-height for low eddy current loss and high current density. The flywheel rotates up to 51,000 rpm (3.4 [kHz]times60 [sec] / 4 [pairs of poles]) and stores the rotational kinetic energy of 337 J. The flywheel can rotate freely during 3 hr 20 min without input voltage and the coefficient of friction is calculated as 0.001-0.002. At maximum speed, the no-load three-phase electric output of the micro generator is 802 mVrms.