Recycling Flux-Leakage: A Novel Design Strategy for High Torque Density Permanent Magnet Motors

Conventionally considered as detrimental to torque density, flux-leakage contains components that can improve output capability. Due to the nonlinear permeability of the core material, flux-leakage flowing into the bridge is more beneficial than that flowing into the air. The useful component is defined as utilized flux-leakage (UFL), with the remainder termed nonutilized flux-leakage (NUFL). Building on this distinction, a novel motor design strategy named recycling flux-leakage is proposed. It is divided into three key steps: 1) inlet control; 2) path selection; and 3) outlet guidance. The inlet control step ensures that all flux-leakage enters the bridge. The path selection step minimizes the flux-leakage losses when passing through the bridge and maximizes the proportion of UFL. The outlet guidance step aims to guide partial UFL into the air-gap, converting it into a unique effective flux defined as the continuous pole flux (CPF). The proposed design strategy is applied to a conventional spoke-type motor. The resulting improved rotor features elements such as square barriers and L-shaped bridges. Through simulation and experimental verification, the proposed rotor can simultaneously improve PM utilization and torque density.