Application of superconducting magnetic bearings to a 10 kWh-class flywheel energy storage system

Radial type superconducting magnetic bearings have been developed for a 10 kWh-class flywheel energy storage system. The bearings consist of an inner-cylindrical stator of YBCO bulk superconductors and an outer-rotor of permanent magnets. The rotor is suspended without contact via the pinning forces of the bulk superconductors that are arranged such that the c-axis of each superconductor is aligned parallel to the radial direction of the cylinder. In this paper, we describe the implementation of the stator part and report the SMB test results, namely that the rotor was successfully rotated at up to 7,500 rpm. Thus we succeeded in energy storage of 2.24 kWh.

I. Introduction

A flywheel energy storage system is one of the most important energy-saving technologies. Although this system has already been used in various fields [1], the use has been limited to short-term storage within a few minutes due to the high rotation energy loss caused by mechanical bearings. In contrast to these conventional mechanical bearings, superconducting magnetic bearings (SMBs) involve much lower rotation loss since the flywheel rotor is suspended without contact via the pinning forces of bulk superconductors. Fig. 1. Schematic view of the 10 kWh-class flywheel energy storage test system developed in this project.