Structural Analysis of Back-Iron for Axial-Flux PM High-Speed Machines

Back-iron plays a vital role in electrical machines as they are normally designed to complete the magnetic circuit. Although laminated steel sheets have been used in traditional machines, they are not appropriate for high-speed rotating structure since they are exposed to high centrifugal forces which may cause mechanical failure. Rigidity, mechanical integrity and robustness are important factors that must be taken into account while designing the back-iron. This paper presents the utilization of annulus disc type back-iron fitted at the back of PM rotor for high rotational speed. Structural integrity of the disc is investigated and realized by performing stress and modal analysis using ANSYS FE modeling. Moreover, natural frequencies, vibration mode shapes, and participation factors are extracted from the FE results. Back-iron size, hence weight is optimized without degrading the flux density levels. Analysis results showed the validity of the proposed back-iron design for the intended application. Stress and vibration analysis results showed safe design structure as stress levels are well below 350 MPa and natural frequencies are all above the operating frequency of 833 Hz.