Axial flux PM machine design with optimum magnet shape for constant power region capability

Unlike radial flux machines, slotted axial flux machine has a particular airgap flux distribution which is a function of the machine diameter. Due to the rectangular slot geometry, stator teeth present a trapezoidal geometry with small tooth width close to the shaft, increasing as the diameter becomes larger. This fact introduces an uneven airgap flux distribution if a constant flux source, such as rectangular PM, is utilized to magnetize the machine. As a result, flux density over the stator tooth becomes irregular, inductance parameters are a function of the stator diameter and saliency varies according to machine load. All these effects degrade machine power capability for low and rated load. In this paper, a novel axial flux PM machine with tangential magnetization is presented. An analytic and numerical study is carried out to consider stator tooth geometry and its effect over machine saliency ratio.