Air gap influence in axial flux machines with different excitation

Because of the constant progress regarding calculation methods, materials and production technologies, new opportunities for alternative machine concepts are offered, such as the concept of axial flux machines, which is under investigation in current research projects. Axial flux machines are well suited for applications, in which high torque densities are required in combination with a low axial motor length. To reduce costs of powerful axial flux machines, mostly used rare earth magnets could be replaced with alternative solutions, e.g. excitation coils. This paper deals with the elaboration of advantages and disadvantages of field coils in axial flux machines and the influence of the air gap size with different types of excitation.