Optimal split ratio for permanent magnet brushless motors

Split ratio, i.e. the ratio of stator bore diameter to stator outer diameter, can significantly influence the torque capability and efficiency of permanent magnet brushless motors. It has been shown that the optimal split ratio for maximum specific output torque can be derived analytically. In this paper, the optimal split ratio is systematically investigated for both permanent magnet brushless AC and DC motors having overlapping or non-overlapping windings, accounting for the influence of rectangular or sinusoidal airgap flux distributions, tooth-tips and end-windings.