Reduction of Cogging Torque Due to Production Tolerances of Rotor by Using Dummy Slots Placed Partially in Axial Direction

A novel stator-core structure for reducing cogging torque due to production tolerances of a permanent-magnet (PM) motor is proposed. On the basis of the results of a theoretical investigation on cogging torque (due to production tolerances of the motors' rotor), a stator-core structure, in which dummy slots are partially configured in the axial direction, is proposed. The phase of the cogging torque component due to production tolerances can be reversed by appropriately designing the shape of the dummy slot. Consequently, by applying the proposed dummy-slot configuration, it is possible to eliminate the cogging torque. The results of 2-D and 3-D finite-element analyses, considering variations in the shape and position of the PMs, show the effectiveness of the proposed dummy-slot stator-core structure in reducing cogging torque. In addition, measurements of cogging torque of 12-slot/10-pole PM motors demonstrate that the proposed stator-core structure significantly reduces the cogging torque due to production tolerances while having almost no effect on the average torque and output power of the motors.