Axially Superimposed Windings with Different Radial Lengths to Increase Torque Capacity of Axial Flux Machines

This paper proposes a novel structure adopting combination of two sets of windings for axial flux permanent magnet (AFPM) machines in order to improve maximum output torque. A conventional AFPM machine is given as baseline design. Upon which, a new design with two windings is introduced. The two windings are axially superimposed with different radial lengths. The first winding takes less turns per phase to achieve a smaller inner diameter while the second winding has the reduced number of turns per phase to compensate the reduced current excitation for the original air-gap space. A new kind of stator is proposed to accommodate the two sets of windings. The two machines are compared from different aspects. The torque is significantly improved by extending the air-gap inward. Comparing with the conventional single winding, the design of superimposed windings allows different current excitations possible for different areas of air-gap.