Suspension force analysis of six-pole radial-axial magnetic bearing for energy storage flywheel

This paper proposes a six-pole radial-axial hybrid magnetic bearing (RAHMB) used in a flywheel system. The radial and axial bias fluxes are generated by one permanent magnet and the radial control coils are driven by a three-phase converter. So, it has the advantages of compact structure, low power consumption and simple driver. First, the work principle is introduced. Then, the mathematical model is built. The force-current characteristics with different eccentricities, the coupling between radial two degrees of freedom (DOF) and the coupling between radial and axial DOF are analyzed based on the analytical model. Finally, the analyses are validated by 3D finite element analysis in the Maxwell software. The results have shown that the coupling between radial and axial DOF is very small. However, the force-current curves of radial two DOFs turn out to be nonlinear and coupled with the increase of rotor eccentricity.