Cooling fans are widely used in communication base station servers since they have a good balance between performance and cost. Cooling fan motors generally have an outer rotor structure because the fan can be directly mounted on the rotor. However, the outer-rotor-type motor has a low degree of freedom in design since the rotor core is thin. Therefore, most of the cooling fan motors have a surface permanent magnet (SPM) structure, and thus, it has ferrite magnets to prevent eddy current losses

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... in magnets and cannot use a reluctance torque. This paper presents a novel outer-rotor-type high-speed PM motor with a segmented-shaped rotor. It can efficiently use reluctance torque in addition to magnet torque, and reduce eddy current loss in magnets even though the rotor has sintered Nd-Fe-B magnets. The usefulness of the proposed motor is proved by comparing it with an inset PM motor using a three-dimensional finite element method (3D-FEM) and prototype tests.