Demagnetization diagnosis for five-phase surface-mounted permanent-magnet motor based on Wavelet Transform Analysis

Multiphase Permanent-Magnet Motors are an attractive alternative to induction machines for a variety of applications owing to their reliability and dynamic performance, suited for emerging applications such as automotive or traction systems. In this context, diagnosing the status of the motor magnets is crucial for improving the reliability of the machines. This paper is focused on the demagnetization of the rotor magnet trailing edges, due to large stator currents, in five-phase surface-mounted permanent magnet synchronous motors. The noninvasive detection method is based on the Wavelet Transform Analysis (WTA) of the back-emf induced in the a-β planes, and exploits the degrees of freedom of a multiphase motor drive. The proposed approach is validated by means of two dimensional (2-D) Finite Element Analysis (FEA) and numerical simulations. Moreover, a fault index, periodically calculated, is introduced to assess the healthy condition of the machine.