A micro flywheel energy storage system with a high-temperature superconductor (HTS) bearing which is characterized by the diamagnetic effect and the flux pinning effect has been developed. The micro flywheel is made up of circumferential magnets for a motor/generator as well as concentric magnets for an HTS bearing and they are fitted into a 34-mm diameter and 3-mm thick aluminum disk. Mass and moment of inertia of the micro flywheel are 12.75 g and 1.84E-6 kgm~(2), respectively. For simplicity and miniaturization of the whole system, the micro flywheel directly takes torque from a planar stator, which consists of an axial flux type brushless DC motor/generator. The micro flywheel successfully rotated up to 38,000 rpm in vacuum condition as it is levitating above the stator with a gap of about 1 mm. However, there are some eddy current losses in the stator and non-axisymmetry in magnetic field causing large drag torque. In order to solve these problems, an improved magnet array in the flywheel including a Halbach array is proposed and 3D simulations have been conducted.
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