Rotor demagnetization diagnosis in five-phase surface-mounted permanent magnet generators under time-varying conditions

Multiphase Permanent-Magnet Generators 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 rotor magnets is crucial for improving the reliability of the generators. 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 generators under Time-varying conditions. In this context, the classical application of Fourier analysis for processing the back-emf induced in the α-β planes fails as the fault components intended to be monitored to assess the magnets status are spread in a bandwidth proportional to the speed variation. In this paper, a simple and effective method based on Wavelet Transform analysis of the back-emf induced in the α-β planes is presented, that allows the diagnosis of rotor demagnetization for multiphase surface-mounted permanent magnet generator under speed-varying conditions. 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.