A Boundary-Preserving Non-Conformal Mapping for Radial Rotor Eccentricity in Finite Element Simulations of Electrical Machines

Detailed field solutions obtained by the finite element method (FEM) for electrical machines come at a large computational cost. By introducing a novel non-conformal mapping (NCM), which transforms a rotor-centric air-gap domain to a rotor-eccentric air-gap domain, the computational cost and discretization error associated with remeshing are avoided. In contrast to the existing NCM approaches, the proposed solution preserves the boundaries of the air-gap domain concerning a change in rotor eccentricity. Resultingly, the interpolation error at the domain intersections with the FEM stator and rotor models is minimized, limited only by a moving band, which allows the rotation of the rotor. A general validation of a rotor-eccentric induction motor using the novel NCM is performed. Thereafter, a thorough comparison between the NCM and remeshing in terms of mesh quality and computational cost is made. For rotor eccentricities below 90% of the air gap, mesh quality is found to be in line with reference methods. Moreover, due to the efficient mapping and the sole requirement of a single moving band to accommodate rotor rotation, the NCM results in a 50% reduction of the total computation time compared with remeshing and a 12% reduction compared with a recent reference NCM.