Demagnetization Analysis and Magnet Design of Permanent Magnet Synchronous Motor for Electric Power Steering Applications

The demagnetization analysis method of permanent magnet synchronous motor (PMSM) used in electric power steering (EPS) system is studied, and the size of permanent magnet (PM) is optimized considering demagnetization performance and manufacturing cost in this paper. PMSM has the advantages of high torque density and high efficiency, which is suitable for EPS system. However, the PMs may demagnetize at a high temperature or by a larger reverse magnetic field, which will affect the torque characteristics or output power of the motor, eventually resulting in the failure to drive the load and also reducing the reliability of the EPS system. In order to deal with these problems, it is necessary to consider demagnetization in the analysis stage. In addition, EPS systems are sensitive to cost since PM material is expensive, so it is necessary to restrain irreversible demagnetization under the condition of minimizing the volume of PM. A demagnetization analysis method based on 2D and 3D finite element analysis (FEA) for PMSM in EPS systems is proposed and the size of PM is mainly designed. Based on the computation of the distribution of magnetic flux density on the surface of PM, the demagnetization risk is evaluated. The simulation and experiment results clearly show that the proposed PMSM design can meet the requirements of EPS system.