Irreversible Demagnetization of Permanent Magnet in a Surface-Mounted Permanent Magnet Motor With Overhang Structure

The overhang structure is an effective solution to increase the performance of a surface-mounted permanent magnet (SPM) motor using a ferrite PM. If a ferrite PM, which can be demagnetized through a large armature reaction, is used for an SPM motor controlled by the field-weakening method, the ferrite PM can suffer from irreversible demagnetization. Moreover, if an SPM from the overhang structure is directly exposed to the armature reaction by the winding of the stator, a ferrite PM of an SPM motor could be partially demagnetized. Because of this, when the field-weakening method is used for the control of the SPM motor with the overhang structure, PMs are disadvantageous to the irreversible demagnetization. To solve these problems, a novel structure is proposed, which can increase the motor performance through the overhang structure without irreversible demagnetization in the overhang part.