Evaluation of Multiphase Permanent Magnet Motors Using Winding Function Theory: Case Study of Fractional Slot Concentrated Windings

This paper presents an evaluation methodology for multiphase Permanent Magnet Synchronous Motors (PMSMs) using winding function theory. The study extends a previously developed space harmonic model and focuses on deriving comparative indicators for making decisions on slot, pole, and phase number combinations. Thus, it contributes a unified framework that integrates diverse performance indicators for the early-stage evaluation of multiphase motors, complemented by an experimental validation that defines the accuracy limits of such analytical models. Key performance metrics such as cogging torque harmonic order, torque ripple harmonic order, winding factor, inductance value, and inductance balance among harmonic planes are analytically derived and applied to two motor configurations: a Three-Phase (TP) and a Dual Three-Phase (DTP) motor, both with 24 slots and 10 pole pairs. Theoretical analysis reveals that the DTP winding offers improved torque capability, higher fundamental inductance ratio, and lower torque ripple, contributing to enhanced torque production and reduced airgap harmonic content. Experimental validation confirms the analytical predictions, demonstrating a 3.5% increase in torque and a 4–5% reduction in inductance for the DTP configuration. Additionally, vibration and torque ripple measurements show lower harmonic content in the DTP motor. While minor discrepancies existed between the analytical and experimental data, they were deemed within acceptable limits for a tool designed for preliminary comparative analysis rather than exact performance prediction. However, the analytical model was unable to predict the inductance balance across the various harmonic planes; addressing this would require a more complex model, which was beyond the scope of the current study. These findings underscore the effectiveness of winding function theory as a rapid design tool for evaluating multiphase motor windings.