System-level optimization of magnetically-levitated micro flywheel energy storage device

In this paper, we discuss an optimal design process of a micro flywheel energy storage system in which the flywheel stores electrical energy in terms of rotational kinetic energy and converts this kinetic energy into electrical energy when necessary. The flywheel is supported by two radial permanent magnet passive bearings. Permanent magnet passive bearings use the repulsive forces between two sets of permanent magnets so that contact-free rotation is possible. A set of voice coil actuator provides the axial stability, resulting in a complete magnetic levitation. A toroidally-wound BLDC machine which has high efficiency and little additional negative radial stiffness is used for motoring and generation. The optimization is carried out in two stages. The first stage is at the component level where separate optimizations for the bearings, actuator and BLDC machine are performed. System-level optimization determines axial sizes of these components and the placement in the system to have the maximum energy storage capacity.