Coil Winding Losses: Decomposition Strategy

Precise modeling of the magnetic field in the coil wire of an electric machine often becomes a major challenge: with the high number of turns and small penetration depth, the number of degrees of freedom exceeds reasonable limits in any standard approximation method. Precise approximation, however, is critical, e. g., to reliable coil loss estimation. Hence, there is a call for specialized approximative methods. This paper presents a method for time-harmonic coil wire field computations in 2-D problems. We replace the coil by a lattice of polygonal plane fillers and span a low-dimensional function space on the polygon boundaries. The reliability of loss estimates requires accurate computations of the responses to the interface excitations of this space. The responses constitute a Dirichlet-to-Neumann map to efficiently couple plane fillers together and to a standard finite-element method (FEM) outside the coil regions. The outcome is significantly faster than the standard FEM alone. The results are still in good agreement.