Comparative Analysis of High Torque Density PM Machines

High torque density PM machines have attracted more and more attention recently, especially for the low-speed, high-torque application. In this paper, three high torque density PM machines are analyzed and compared, namely 12-slot/10-pole SPM, 16-pole transverse flux PM and 12-slot/22-pole flux modulation PM machines, with the specification of 30 kNm/m3, To reveal the nature of high torque density of different topologies, saturation effect is neglected. Based on the Maxwell stress tensor (MST) method, the radial and tangential flux density and force distribution along the airgap are illustrated. The torque contribution from different field harmonics are also compared. It's shown that torque density of PM machines can be enlarged further by improving the tangential flux density, decreasing the phase difference between radial and tangential flux density, and integrating more working harmonics into one PM machine.