Magnetic slot wedge design for high power permanent magnet traction motors

Cogging torque is a major concern in permanent magnet (PM) motors, and some people have done many works on it [1], [2]. Magnetic wedge application for axial flux machine is mentioned in [3], but different with pre-formed radial flux PM machines, the tooth width of that machine is constant in the direction of the flux. In high power electrical machines with integral-slot distributed-winding, parallel slot is usually used to improve the slot fill factor. And in the traction application, the optimization split ratio of the PM motors is usually about 0.6, and slot number is not very much, these will lead to tooth tip much narrower than the tooth bottom, and the flux density in the tooth tips of the motor may higher than 2T at rated working condition. In this situation, magnetic slot wedge will reduce the saturation in the tooth tip, this advantage could counteract the torque reduction caused by slot leakage. So it is possible to decrease cogging torque, torque ripple and without torque reduction by employing magnetic slot wedge. In this paper, different designs of slot wedge have been done to reduce the cogging torque and torque ripple, at the same time, output torque capability has been analyzed. And then, since slot wedge needs to bear the weight of winding and magnetic force, mechanical analysis has been done to demonstrate the mechanical strength of the slot wedge.