Effect Analysis of Demagnetization of Permanent Magnet Synchronous Motor for Electric Drilling Tool on Air-gap Flux Density

Abstract Electric drilling tools have been developed in the field of drilling because of their high efficiency. As the core component of electric drilling tool, permanent magnet synchronous motor(PMSM) provides power for drilling tool. However, in the process of drilling, the permanent magnet of PMSM will appear demagnetization.The value of air-gap flux density affects the performance and efficiency of the motor directly. Demagnetization faults are divided into uniform demagnetization and local demagnetization.In order to study the influence of demagnetization of PMSM on the air-gap flux density, mechanism of permanent magnet is analyzed Firstly, and then establishing numerical model with analytical method. Finally, simulation motor demagnetization using finite element method(FEM) based on Maxwell. No-load and load operating state are analyzed under the two fault modes are considered in this paper, and compared with the healthy state of the motor. The analytical results show that when the demagnetization fault occurs in the motor permanent magnet, the air-gap flux density will decrease accordingly.The FEM method results show that with the increase of uniform demagnetization rate, the flux density of the air-gap almost decreases in proportion to the increase of demagnetization rate. The demagnetization of single pole permanent magnet has little effect on the magnetic density of the nearby permanent magnet, but it will lead to the imbalance of the whole electromagnetic field of the motor. The air-gap flux density can be used as a characteristic index to judge the fault of demagnetization.