A Highly Integrated Permanent-Magnet-Biased Five-Degree-of-Freedom Magnetic Bearing for Flywheel Energy Storage Systems: Electromagnetic Design and Compensation-Winding Decoupling Performance

Abstract

Conventional five-degree-of-freedom (5-DOF) magnetic bearing supports often require a large axial span, while highly integrated magnetic circuits can introduce axial–radial flux coupling through shared return paths. This study proposes a compact permanent-magnet-biased 5-DOF magnetic bearing for flywheel energy storage systems, integrating two radial support sections and one axial support unit within a common stator. A series-opposed compensation winding is introduced to suppress axial-control-induced leakage into the radial branch. An electromagnetic design procedure considering leakage, ampere-turns, and magnetic-saturation constraints is evaluated using a three-dimensional magnetostatic finite-element model. At 6 A, the modeled axial and radial forces reach approximately 1.50 and 0.75 kN, respectively, while the maximum ferromagnetic flux density remains below 1.25 T. Under permanent-magnet-biased operation, the compensation winding reduces the peak radial-field deviation from approximately 161.5 to 1.7 mT, corresponding to approximately 99.0% suppression; the full-path RMS-deviation metric indicates approximately 93.1% suppression. Among the investigated configurations, the one with 50 turns provides the closest restoration to the bias-only radial field. Prototype tests demonstrate stable five-channel closed-loop static suspension, supporting physical realizability, but do not directly validate the predicted decoupling ratios.