Cogging torque reduction in an axial flux PM machine with extended speed range

Cogging torque is a source of vibration and noise in PM machines. This torque is proportional to the PM flux and the reluctance variation, and it is independent of the load current. In this paper, two methods for cogging torque reduction in an axial PM machine with field weakening capability is presented. The machine's rotor configuration considers two sections: one PM pole which provides the field excitation and one iron section in charge to providing low d-axis reluctance. Significant reduction of the cogging effects is achieved, by adjusting stator geometry and rotor pole configuration. 3D-FEA is used to demonstrate these improvements. Conclusions and design recommendations are presented for a 3 kW, 8-poles PM machine prototype