State Calculation, Analysis, and High-Precision Location Diagnostic Method for Irreversible Demagnetization in SPMSM

This work proposes an improved analytical model and a novel location method for irreversible demagnetization (ID). The analytical model accounts for the nonlinearities from the demagnetization curve and saturation, and it is suitable for any magnetization orientation; the ID location method is unaffected by saturation, ensuring high accuracy and low detection costs. First, to calculate the local state of the permanent magnet, an improved analytical model involving radial subdomain layering and tangential unit partition is established. Next, the new calculation method for the knee point of the exponential demagnetization curve and the ID iteration calculation method are presented. Additionally, the characteristics of the electromagnetic force density under any ID state are summarized using the magnetomotive force (MMF)-permeability method and verified using the proposed analytical model. It is found that nonuniform ID introduces new spatial and temporal components. Furthermore, a new method for locating ID faults is introduced, deriving the quantitative expression between MMF harmonics and back electromotive force harmonics from the perspective of the location principle. Based on this, an accurate method for determining fault interval parameters is proposed. Finally, all the conclusions are validated through the test results.