Design of Concentrated Flux Type Synchronous Motor to Prevent Irreversible Demagnetization

Abstract

IPMSM using rare earth materials utilize various areas with high power density and a wide speed range. However, as these materials can only be found in limited areas and quantities, use of machines with rare earth materials will decrease. To solve this problem, various types of machines have been studied with rare earth free elements. In particular, the ferrite permanent magnet (PM) is used for substituting rare earth elements. However, this PM has disadvantages of residual flux density and coercive force in comparison with rare earth elements. Therefore, a new type design is required to use ferrite PM. In the paper, a concentrated flux synchronous motor using ferrite PM is designed to obtain similar power density compared to the flat type interior PM synchronous motor. However, an instantaneous current in the stating or locked rotor condition may cause a tremendous external demagnetizing field for PM. Therefore, a structure can be considered for preventing the demagnetization of ferrite PM at low temperature. This paper deals with the analysis for preventing irreversible demagnetization characteristics of the motor. Finally, the result and effect is discussed to improve a model applied structure for preventing demagnetization.