Improving Torque Properties of Coreless Stator Axial Flux Permanent Magnet Motors Using Space-Time Harmonic Analysis

Without teeth-slot regulation of the magnetic field and windings, the coreless stator axial flux permanent magnet (AFPM) motor offers greater flexibility and versatility in design. However, this also reduces its torque output capability and increases its sensitivity to topology. In this article, a coreless stator AFPM motor is investigated, focusing on optimizing its torque characteristics from the perspective of spatial and temporal harmonic behavior. First, a harmonic model is developed to analyze and quantify the harmonic interactions mechanism that contribute to torque and torque ripple. Next, key harmonic components in the rotor magnetic field and stator winding are selectively enhanced or suppressed through targeted design of coil configuration, pole-arc distribution, and axial size ratios. Finally, the proposed optimization strategy is validated by 3-D finite element method (FEM) and prototype testing. The research provides a valuable methodology for analyzing and optimizing the design of coreless motors.