Improved Coreless Axial Flux Permanent-Magnet Machine With Nonuniformly Distributed Winding

The windings of coreless axial flux permanent-magnet machine (CAFPM) are exposed to the rotor magnetic field, where each back electromotive force (EMF) harmonic is induced not only by several different spatial field harmonics but also by the winding distribution. In order to reduce the time harmonics of back EMF for CAFPM with nonoverlapping winding, one new winding structure with nonuniform distributed coils is proposed in this article, in which the coils are arranged in a nonuniform way with annular distribution in the stator. First, the relationship between uniform and nonuniform distributed windings is analyzed based on the phasor diagram of each coil EMF, and the analytical expression of back EMF under nonuniform distributed windings is established. Second, key performance indexes under different working states, such as no-load, are investigated by a 3-D finite-element analysis (FEA). Finally, comprehensive experiments are carried out to verify a related theoretical analysis, which demonstrates that the nonuniform distributed windings can effectively reduce the time harmonics and increase the working efficiency.