Comparison of two concentrated winding topologies applied on an axial flux permanent magnet machine

Axial flux machines with internal stator and two outer rotor discs are either specified as N-S- or N-N-type, dependant on the flux path through the stator. While the N-S- type has to be equipped with tooth-wound coils, the N-N- type allows the application of core-wound coils. The main difference between these winding configurations is the alignment of the end turns. Since the stator of a N-N-machine requires additional space for a yoke, this drawback can be potentially balanced out by using core-wound coils. This paper gives an analytical approach in order to evaluate both stator types including the respective winding configurations. It is shown that tooth- and core-wound coils are subject to the same winding factor if the same number of slots per pole and phase (SPP) is chosen. Apart from that, a comparison of the stator losses under the supposition of identical stator volumes is drawn. The result reveals that the N-N- machine is likely to produce more iron and copper losses, if the SPP is near to 1/3, as it is compulsory for tooth-wound coils. Eventually, it is reasoned that the N-N-machine gets more competitive if core-wound coils with a SPP of about 1/6 are applied.