Analytical Prediction of Optimal Split Ratio for Fractional-Slot External Rotor PM Brushless Machines

The split ratio is one of the most important design parameters for permanent-magnet (PM) brushless machines. It has been optimized for maximum torque density with both internal rotor and tubular PM brushless machines in existing papers. This paper proposes an analytical model to determine the optimal split ratio for external rotor PM brushless machine having nonoverlapping winding. The influence of winding factor, tooth tip, and end winding on the split ratio is considered. The theoretical analyses are verified by finite element analysis and validated with experimental measurement.