  Permanent magnet-assisted synchronous reluctance motors (PMSynRM) have a
significantly higher average torque than synchronous reluctance motors. Thus,
determining an optimal design results in a multi-material topology optimization
problem, where one seeks to distribute ferromagnetic material, air and
permanent magnets within the rotor in an optimal manner. This study proposed a
novel density-based distribution scheme, which allows for continuous
magnetization direction instead of a finite set of angles. Thus, an
interpolation scheme is established between properties pertaining to magnets
and non-linear materials. This allows for new designs to emerge without
introducing complex geometric parameterization or relying on the user's biases
and intuitions. Toward reducing computation time, Nitsche-type mortaring is
applied, allowing for free rotation of the rotor mesh relative to the stator
mesh. The average torque is approximated using only four-point static
positions. This study investigates several interpolation schemes and presents a
new one inspired by the topological derivative. We propose to filter the final
design for the magnetization angle using K-mean clustering accounting for
technical feasibility constraints of magnets. Finally, the design of the
electrical motor is proposed to maximize torque value.
