Mechanical Field Weakening Techniques for an Axial Flux Machine

The electric machine for automotive applications should have a wide speed range. This paper describes the mechanical techniques to weaken the magnetic field of an axial flux permanent magnet machine in order to increase the machine’s speed range as well as reduce the iron losses. Three different techniques have been simulated and analyzed in this paper which are variable air gap, variable rotational offset of the double-sided magnet discs and variable reluctance of the rotor back iron using the changing of material characteristic. Results show that all these techniques can be used to weaken the magnetic flux in the air gap. Furthermore, the force, torque, EMF, and power also can either increase or decrease using these techniques. Compared with the other proposed techniques, the variable rotational offset of magnet discs offers the best options for mechanical field weakening in an axial flux permanent magnet machine as this technique requires less force.