AFPM (Axial flux Permanent Magnet) AC generators have airgap surface perpendicular to the rotating axis and the airgap generates magnetic fluxes parallel to the axia. The rotor is in the form of a disc attached with a permanent magnet (Nd-Fe-B). The generator has two rotors on each side of the fixer. The advantage of AFPM generator is that it performs efficient cooling and can be manufactured in slim styles. The number of permanent magnets increase by two rotors on each side of the fixer coil. Therefore, the two sides of the conductor can be used concurrently to allow designing of high-efficiency generators. Also, the two disc-type rotors with permanent magnets play an additional role as fans to ease the exhaustion of heat generated from the coil of the fixer. Therefore, more electric current can pass through limited-capacity wiring.
As the rotors of the AFPM generator are outer-rotors, they can be directly attached for direct drive without any gears. High-energy permanent magnets using Nd-Fe-B structures allowed formation of relative large airgaps to make the production of coreless types possible. The noted advantages of coreless type is the relatively high density in the volume of coil and less loss of energy from the cogging torque.
The other advantage of AFPM generator is that it can have multi poles and multi stator by using big diameters and short axes structurally. As the fixer does not have a core, the density/volume of coil can be increased. The epoxy used for the fixer needs to have the mechanical characteristics of the core, so must be high in solidity and strong against heat. It also allows small-scale lightweight designs and results in lower cost in certain applications by reducing the overall weight of the generator.