Development and Investigation of Novel High Torque Density Magnet Surrounded Permanent Magnet Synchronous Machine

A new high-torque density axial radial flux permanent magnet machine (ARFPMM) known as a magnet-surrounded permanent magnet synchronous machine (MSPMSM) is proposed. This machine combines toroidal winding with magnet-surrounding technology to create a three-sided effective air gap, reducing the winding's ineffective ends and improving torque density. The optimized design of the MSPMSM is focused on the magnetic concentrating ring, stator split ratio, winding configuration, and pole-arc coefficient. A detailed mechanical design is presented to prevent axial movement of the stator, and further strength analysis of the machine is conducted. The temperature rise and heat dissipation problems of the MSPMSM are more complex than those of conventional machines due to their compact structure and high torque density. Existing experience cannot accurately predict the heat generation of the machine, and modeling with the 3D finite element method (FEM) is complex and time-consuming. A fast lumped parameter thermal network (LPTN) method for MSPMSMs is proposed to address this issue. Finally, a prototype is fabricated and tested on a self-developed experimental bench to verify the high torque density of the proposed machine and the accuracy of the proposed LPTN method. © 2025 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.