Comparison of Eddy Current Loss Calculation Techniques for Axial Flux Motors with Printed Circuit Board Windings

In slotless machines, the winding conductors are exposed to the magnetic air gap field, which causes additional eddy current losses, thus decreasing efficiency and affecting thermal utilization. This is the case, inter alia, for axial flux motors equipped with printed circuit board windings, where the winding is made of copper–fiberglass epoxy laminations and located in the air gap. The dominant influencing factors are primarily the width of the conducting tracks and the magnetic air gap flux density and frequency. The evaluation time is a crucial constraint when calculating thousands of different designs for design space exploration or performing multi-objective optimizations. Finite element simulations can achieve very precise results, but unlike semi-analytical approximation functions, they are very time-consuming and therefore not the method of choice for design space exploration. This publication provides a comprehensive overview of a selection of different eddy current loss calculation techniques that are applicable for rectangular tracks and round wire windings. A comparison of the calculated results for a finite element simulation is presented for a slotless axial flux machine with printed circuit board windings and rectangular tracks. The calculation time consumed is also compared. The current density distribution of planar conductors of air gap windings differs from that in electrical steel sheets. In contrast to the methods based on steel sheets, only the adapted methods for conductors in air gaps offer acceptable accuracy. A recommendation is provided for the method that offers the best balance between accuracy and computation time for the early-stage design of slotless axial flux machines.