Comparison of Demagnetization Characteristic between Radial and Parallel Magnetization in Surface-Mounted PM Machines

This article compares the irreversible demagnetization characteristics between parallel and radial magnetization patterns in surface-mounted PM (SPM) machines. The results show that, in internal rotor SPM machines, parallel magnetization shows worse demagnetization than radial magnetization. However, when demagnetization level is not high, parallel magnetization has larger post-demagnetization average torque. As demagnetization level increased, radial magnetization can show larger post-demagnetization average torque. Then some key factors influencing the comparisons of post-demagnetization average torque between two magnetization patterns are investigated, including PM height, pole-arc to pole-pitch ratio, PM temperature and pole numbers. In addition, opposite rules are found in external rotor SPM machines. Finally, experiments are conducted to verify the theoretical analysis.