Analytical Calculation of Inductances of Multiphase Axial Flux Machines With Yokeless Topology

This paper investigates calculation methods for the self and mutual inductances of multiphase yokeless and segmented armature (YASA) machines. Firstly, the airgap flux density produced by each phase is obtained using the winding function method, while the leakage flux density created inside the slots and in the slot-opening region is obtained from Ampère's Law. Secondly, two analytical models are proposed to determine the self and mutual inductances of YASA machines, one model based on winding functions and specific permeances and the other based on reluctance networks. Further, to validate the proposed analytical models, a prototype multiphase YASA machine was tested with three different phase numbers using different coil connections. The experimental results proved that the model based on winding functions and specific permeances provides better estimates for self-inductances than for mutual inductances between adjacent phases. In contrast, the model based on reluctance networks gives satisfactory estimates for self- and mutual inductances between adjacent phases. Finally, the experimental results revealed that the self-inductances and mutual inductances between adjacent phases of multiphase YASA machines are strongly influenced by the leakage fluxes, so they must be considered to precisely predict the transient behavior of the machine.