Inductance Calculation and Analysis of Axial-Flux Slotless Surface-Mounted Permanent Magnet Machine With Equidirectional Toroidal Winding

For the purpose of improving torque density of Axial-flux slotless surface-mounted permanent magnet (AFSSPM) machines, an equidirectional toroidal winding (EDTW) structure is proposed in previous research and applied. Due to the special winding layout of EDTW changing the flux distribution, the winding inductance of the EDTW-AFSSPM machine requires specific analysis to estimate the performance of flux-weakening capability, power factor, etc. In this paper, the winding inductances of the EDTW-AFSSPM machine are calculated and analyzed. First, to facilitate the analysis of inductances, winding layout and flux distribution of AFSSPM machines with EDTW and traditional TW are compared. Second, the flux density at the stator surface of two AFSSPM machines is obtained by the image method, and then the inductance parameters of two machines are calculated. At the same time, end-winding inductance and core saturation are considered to improve the calculation accuracy. Third, the flux density and inductances obtained by the analytical model and the three-dimensional finite element method (3D-FEM) are compared. Finally, a prototype of the EDTW-AFSSPM machine is developed and tested to further validate the analytical results of inductances.