  Hybrid-excited electrical machines aim to combine the advantages of permanent
magnet machines (high efficiency and torque density) with those of separately
excited machines (ease of flux-weakening at high speed). These machines are of
interest to electric vehicles, and only parametric approaches are available in
the literature for their optimization. This work proposes a more general
topology optimization methodology by extending the formalism of density
methods. The difficulty lies in integrating the numerous natures of materials
(conductors, permanent magnets, ferromagnetic material, air...) without
strongly deconvexifying the optimization problem, which leads to non-physical
results with unsatisfactory performance. To address this issue, a recursive
material interpolation is introduced. The hybrid-excited rotors optimized by
this approach are compared with those of existing techniques, demonstrating a
clear superiority of the recursive interpolation.
