Advanced design and experiment of a small-sized flywheel energy storage system using ahigh-temperature superconductor bearing

Abstract

A small-sized flywheel energy storage system has been developed using a high-temperaturesuperconductor bearing. In our previous paper, a small-sized flywheel was fabricatedand successfully rotated at 38 000 rpm under a vacuum condition. However, alarge drag torque was present because of the non-axisymmetric magnetic fluxof the motor/bearing magnet and the eddy current loss in the planar stator,resulting in a short spin-down time of 20–30 s and a coefficient of friction of 0.15.This paper presents the design, fabrication and electromagnetic analysis of the flywheel inorder to reduce the large drag torque. The advanced flywheel designed for solvingthe non-axisymmetric magnetic flux problem comprises eight motor magnetsand a single bearing magnet, a magnetic screening disc, and an aluminium discwhich is 50 mm in diameter and 5 mm in thickness. The eddy current loss in theplanar stator is minimized by reducing the contact area between the planar statorand the motor magnets. The maximum rotational speed increases 1.3 times to51 000 rpm and the spin-down time increases 600 times to 3 h 20 min. On the basisof these results, the coefficient of friction decreases 100 times to 0.001–0.002.