A new type of flywheel energy storage system uses a magnetic suspension where the axial load is provided solely by permanent magnets, whereas active magnetic bearings are only used for radial stabilization. This means that the permanent magnet bearing must provide all the axial damping. Furthermore, it must have as low a negative radial stiffness as possible to reduce the workload on the radial active magnetic bearings. Many different mathematical models for determining force, stiffness, and damping of permanent magnet bearings are available in the literature. This work will further develop the most applicable analytical and numerical methods in order to make them directly implementable for designing permanent magnet thrust bearings for flywheel energy storage systems. The outcome is a fast and efficient method for determining force, stiffness, and damping when the bearing setup contains magnetic materials with relative permeability higher than one as well as when it does not. The developed method is validated against numerical and experimental results with good agreement.
Dual air-gap axial flux permanent magnet machines for flywheel energy storage systems
