A comparative study of methods for calculating ac winding losses in permanent magnet machines

In this study different methods of estimating the additional ac winding loss due to eddy currents at open-circuit are explored. A comparative study of 2D and 3D FEA, and hybrid numerical and analytical methods is performed in order to recommend feasible approaches to be employed. Axial flux permanent magnet (AFPM)machine case studies are included, namely a machine with open slots and a coreless configuration. These machine topologies are expected to present a substantial amount of ac winding loss, which would therefore need to be considered during optimal design. This study is one of the first ones to compare meticulous 3D FEA models with more approximate, but faster solution methods which can be employed in the optimization process. The study is comprehensive and includes other discussions relevant to the subject matter, including the selection of the number of turns, the effect of the conductor cross section shape, the placement of each turn for the two machines under study, and the meshing of the turns for FEA based methods. Furthermore, the paper also proposes a measurement method for additional open-circuit winding losses.