Research of the demagnetization mechanism of line-start permanent magnet synchronous motor under operating condition of sudden reversal

Line-start permanent magnet synchronous motor (LSPMSM) has the advantages of high efficiency and power factor, compared with the electrically-excited motor, and is used in more and more applications. The reverse rotation of LSPMSM is caused by swapping two-phase voltages during the normal operation of three-phase LSPMSM, and it will cause large currents in stator windings and rotor bars, which may cause the irreversible demagnetization of permanent magnets. This paper calculates the variation of magnets´ minimum operating point, which is the minimum value of the projection of flux density in magnetization direction for all points of magnets, using two-dimensional finite-element method (2-D FEM), and analyzes the demagnetization characteristics of LSPMSM during the reverse rotation process. The influences of reverse time and initial load condition on the demagnetization of LSPMSM are studied, and some conclusions are drawn.