Local demagnetisation analysis of a permanent magnet motor

Irreversible demagnetisation of a permanent magnet (PM) at high temperature can be caused by the field distributions because of the stator currents. It can be prevented if the magnet thickness is sufficient. However local irreversible demagnetisation can occur even if the magnet thickness is sufficient. The local irreversible demagnetisation is varied according to the magnetic path. To analyse the cause of local irreversible demagnetisation, the authors introduced an interior PMSM (IPMSM), consisting of a V-shaped magnet and concentrated winding, and performed a parameter analysis of the magnetic field based on the barrier width and magnet position considerably related to the magnetic path using the finite-element method. On the basis of the results, the authors developed a model avoiding local irreversible demagnetisation. A maximum load test was performed after a thermal saturation test to confirm whether irreversible demagnetisation of the manufactured models occurred. Finally, to verify the validity of the finite-element analysis (FEA) results, the torque, efficiency, power factor and induced voltage of the manufactured model, which were obtained by FEA, were compared with the test results.