An Improved Unevenly Distributed Winding Design to Optimize Winding Factor Families for Fractional Slot Concentrated Windings: The Fraternal Twin Machine Concept

This paper introduces the FRATERNAL TWIN MACHINE concept for Fractional Slot Concentrated Windings (FSCW), which alters the initial number of slots, resulting in a different visible topology to maximize the winding factor of the working harmonic while preserving the same harmonic families after optimization. The concept takes its name from the fact that, although they look different, the essence of the altered and unaltered windings is the same due to the identity in their phase spread. Despite offering advantages such as high torque density and simplified end connections, FSCW have relatively high torque ripple and limited performance due to the high space harmonic content in their magnetomotive force (MMF). Considering the winding factors of different harmonics, it is possible to achieve improvements by focusing on the winding function. In this study, a novel approach regarding this was developed and utilized for both existing and novel windings. Three relative three-phase windings with nine slots and different pole numbers are introduced and modified using the proposed method. Unconventional, unique winding solutions are obtained by analytical evaluation of different harmonic families to achieve improved harmonic spectra. Both the number of turns and slot position angles are processed with the proposed method, enabling stator core designs with unequal slot widths and different numbers of turns for a concentrated winding configuration. New solution sets serving increased winding factors for the related working harmonic components with a similar total harmonic distortion (THD) were obtained. The results were implemented in the designs, which led to an increased electromagnetic torque and almost the same torque ripple. Validation of the harmonic performances of proposed topologies and different slot/pole combinations by finite element analysis (FEA) is planned for future work.