A Study on the Design Method of Spoke-Type PMSMs for Reducing Cogging Torque and Axial Force

In spoke-type permanent magnet synchronous motors (PMSMs), an asymmetric rib structure has been investigated as a method to reduce cogging torque. However, such rotor asymmetry tends to an increase in the axial force, which limits its applicability in precision and low-vibration systems. To overcome this limitation, this study proposes a new motor design method that introduces a skew factor as an additional design variable. The skew factor, defined as the ratio of the skewed region to the total stack length, enables simultaneous control of cogging torque and axial force by adjusting the degree of asymmetry along the rotor stack. Using parametric modeling and finite element analysis (FEA), the combined effects of the asymmetric rib and skew factor were investigated, and an optimized motor structure achieving balanced cogging torque and axial force characteristics was derived. The proposed design approach provides an effective method for simultaneously considering cogging torque and axial force in spoke-type PMSMs.