  Conventional active magnetic bearing (AMB) systems use several separate
radial and thrust bearings to provide a 5 degree of freedom (DOF) levitation
control. This paper presents a novel combination 5-DOF active magnetic bearing
(C5AMB) designed for a shaft-less, hub-less, high-strength steel energy storage
flywheel (SHFES), which achieves doubled energy density compared to prior
technologies. As a single device, the C5AMB provides radial, axial, and tilting
levitations simultaneously. In addition, it utilizes low-cost and more
available materials to replace silicon steels and laminations, which results in
reduced costs and more convenient assemblies. Apart from the unique structure
and the use of low magnetic grade material, other design challenges include
shared flux paths, large dimensions, and relatively small air gaps. The finite
element method (FEM) is too computationally intensive for early-stage analysis.
An equivalent magnetic circuit method (EMCM) is developed for modeling and
analysis. Nonlinear FEM is then used for detailed simulations. Both permanent
magnets (PM) and electromagnetic control currents provide the weight-balancing
lifting force. During the full-scale prototype testing, the C5AMB successfully
levitates a 5440 kg and 2 m diameter flywheel at an air gap of 1.14 mm. Its
current and position stiffnesses are verified experimentally.
