Design of an Axial-Flux Permanent Magnet machine for an in-wheel direct drive application

This paper concerns the optimization and comparison of six different axial-flux permanent magnet (AFPM) machine topologies for an in-wheel direct drive application. The objective of the optimization is to reach maximum power density, which is of essence for an in-wheel motor. The machine topologies are optimized using the 3D analytical charge model in combination with a thermal equivalent circuit model for calculation of the temperature rise and thermal dependency of the main electromagnetic losses. All investigated AFPM machine topologies are variations of the internal stator twin external rotor AFPM machine. The resulting designs are compared based on their power density, weight, efficiency, and permanent magnet volume. The distributed winding topology with a quasi-Halbach magnet arrangement shows the best performance within the optimization problem.