Design and manufacturing of axial flux permanent magnet machines for electric vehicle applications

This paper presents the design and prototyping of an open-slot, 18-slot, 12-pole, Axial-Flux, Permanent-Magnet (AFPM) machine that meets the typical requirements of electric vehicles. A multiphysics design approach was used to consider mechanical and thermal constraints during the design stage. The electromagnetic design is based on a combination of 2D and 3D Finite Element Analysis (FEA) approaches. Segmenting the rotor and optimizing the rotor disc material reduces rotor losses. This provides a balanced compromise between eddy current losses and manufacturing costs. The designed machine was manufactured and tested on a test bench under both no-load and load conditions. Experimental results, such as Back Electromotive Force (Back EMF), torque as a function of current, magnet temperature, and torque and power versus speed curves, are compared with simulation results. The impact of the manufacturing process on performance, especially iron losses, is investigated. For this purpose, the iron losses are assessed using the stator yoke of the axial flux machine in both the torus configuration test and an Epstein frame. These specific iron losses are then used to evaluate iron losses via 3D FEA. Several configurations are tested to evaluate different no-load losses, such as mechanical losses, magnet losses, rotor holder losses, and stator iron losses, as well as AC losses due to the proximity effect caused by the external magnetic field generated by the rotation of the magnets, in order to compare the calculated iron losses obtained by 3D FEA with the measured ones. Rotor losses in the magnet and rotor holder are evaluated by measuring the rotor temperature using an infrared sensor.