Advanced design and experiment of a micro flywheel energy storage system with a high temperature superconductor bearing

Abstract

A micro flywheel energy storage system has been developed using a high temperature superconductor bearing. In the previous paper, the micro flywheel was fabricated and successfully rotated 38,000 rpm in the vacuum chamber. However, there are the large drag torque because of the non-axisymmetric magnetic flux of the motor/bearing magnet and the eddy current loss in the planar stator, which makes short spin-down time as 20-30 sec and coefficient of friction as 0.15. This paper presents the design, fabrication and electromagnetic analysis of the flywheel to reduce the large drag torque. The advanced flywheel is made up of motor and bearing magnet, aluminium disk, and magnetic screening disk. The maximum rotational speed is up to 51,000 rpm and furthermore the spin-down time is about 3 hr 20 min in the vacuum condition. From these results, the coefficient of friction is calculated as 0.001-0.002.