Investigation and Countermeasures for Demagnetization in Line Start Permanent Magnet Synchronous Motors

Line start permanent magnet synchronous motors (LSPMSM) may get demagnetized under some special conditions. The demagnetization is usually investigated with finite element analysis (FEA) by using the nominal properties of the magnets. However, the properties decay after the magnets have suffered the demagnetizing magnetic motive force (DMMF), causing spread of the demagnetization area. Therefore, it is proposed in this paper that iteration of FEA should be taken, considering the decaying of the magnets properties. Moreover, four rotor configurations are proposed, so as to enhance the anti-demagnetization capability. FEA with these four configurations proves that the comprehensive configuration with both dual squirrel cages and magnetic barriers on the rotor is rather effective to protect the magnets, but hardly deteriorates the motor operation performance under the rated condition.