Analysis of Permanent Magnet Demagnetization during the Starting Process of a Line-start Permanent Magnet Synchronous Motor

Abstract

Neodymium (NdFeB) rare earth Permanent Magnets (PMs) are widely used in the manufacturing of Line-Start Permanent Magnet Synchronous Motors (LSPMSMs). During the initial startup of LSPMSMs, irreversible PM demagnetization often occurs. This research provides a thorough examination of the PM demagnetization process during the initiation of a 15-kW, 3000-rpm LSPMSM, which was converted from a squirrel-cage Induction Motor (IM) featuring a 3-bar PM. Utilizing Ansys/Maxwell2D software for simulations and conducting experiments, this study reveals that upon starting the LSPMSM, demagnetization occurs at the two outermost PM pairs. This leads to unstable motor operation at synchronous speed, significant current fluctuations, and a substantial decrease in performance. The findings suggest that to ensure effective LSPMSM operation, it is crucial to either restrict frequent restarts or select an appropriate PM type to prevent partially irreversible demagnetization, thereby enhancing power efficiency.