A rotor design of a permanent magnet-type bearingless motor considering demagnetization

The characteristics of a surface-mounted permanent magnet-type bearingless motor have reported by the authors. Thin permanent magnets are employed to generate radial forces efficiently. However, thin permanent magnets have a crisis of demagnetization because not only q-axis fluxes but also additional radial force fluxes exist in the motor magnetic field. The maximum q-axis and radial force currents limited by the demagnetization have been already made clear for a particular machine configuration using the finite element method. However, these results are not theoretically verified. In this paper, a limitation of demagnetization is analytically derived. The maximum current is found as a parameter of a permanent magnet thickness.