Structural Design for Post-Assembly Magnetization of Low-Speed High-Torque PMSM in Consideration of Eddy Current Effect

Low-speed high-torque permanent magnet synchronous machines (PMSMs) are widely used in heavy industrial production, whereas the bulky prototype size poses challenges for assembly. This paper presents a 400kW low-speed high-torque spoke-type PMSM equipped with integrated magnetizing coils for post-assembly magnetization (PAM) to improve assembly performance. Magnetic equivalent circuit models show that the magnetization effect can be optimized by manipulating the eddy currents within machine components, without an influence on machine operation. An analytical model is then developed, accurately evaluating the eddy current effects from the perspective of effective magnetic permeability. To enhance the PAM effect, conventional aluminum alloy spacers are replaced by epoxy glass laminate spacers, and an aluminum alloy plate is introduced in the airgap above the PM to be magnetized. This method has a harmless impact on machine performance, including mechanical and thermal concerns. The finite element simulation validates that this method significantly improves the magnetization saturation state and evenness in the magnetized PM, enhances the consistency of all PMs in different positions, and mitigates the adverse effect on subsequently magnetized PMs in this step-by-step magnetization. The shielding effect of the aluminum alloy plate also protects the armature windings from high induced voltage during PAM. Finally, a prototype is fabricated, and the magnetization saturation state along with the surface flux density of post-assembly magnetized PMs are experimentally measured, validating the effectiveness of the proposed magnetization method.