Title: Utilization of Multiple Planar Search Coils for Diagnosing Imbalance Irreversible Demagnetization Faults in PMSMs along the z-Axis 

Authors: Jun-Hyuk Im, Member, IEEE, Jun-Kyu Kang, Student, IEEE, and Jin Hur, Fellow, IEEE

will be published in IEEE Transactions on Industry Applications

Abstract— Permanent magnet motors with magnets installed on the rotor are widely employed in various fields due to their excellent efficiency and output density. However, magnets are susceptible to irreversible demagnetization faults, where their magnetic properties degrade due to stresses such as external magnetic fields and high temperature condition. Irreversible demagnetization faults can deteriorate motor performance and even lead to catastrophic failures like control failures. Furthermore, due to the uneven distribution of stresses, such as heat and magnetic flux, on the motor magnets, irreversible demagnetization faults exhibit non-uniformity along the z-axis direction. Therefore, there is a need to study diagnostic techniques for irreversible demagnetization faults. Various diagnostic techniques have been proposed; however, most of them cannot provide diagnostics for individual magnet segments. In this paper, we introduce a fault diagnosis technique using planar search coils attached to the surface of the motor's stator. The planar search coils can be fabricated in various shapes, allowing for the arrangement of multiple coils along the z-axis of the motor to acquire signals based on the flux crossing each coil. This technique is validated through finite element analysis and experiments. As a result, it is confirmed that the proposed technique allows for fault diagnosis in both the non-excited and excited states using the acquired signals.