Analysis and Mitigation of Demagnetization Issue in Stator Slot PM Machines

The Stator slot permanent magnet (PM) machine with PMs placed circumferentially in the slot openings is inherently fault-tolerant under the uncontrolled generator operation since the PM flux is short-circuited within the stator. However, as the PMs are placed in the slot openings and adjacent to the high-permeability iron core, the tangential flux component may cause partial demagnetization of magnets, especially under heavy load condition. In this paper, the influence of the rotor and stator tooth widths, the PM shape, the rotor tooth shape, and the tooth tips on the PM demagnetization is investigated. The results show that by shaping the PMs or moving the PMs away from the airgap without using tooth tip, the demagnetization problem can be solved without reduction in torque.