For permanent magnet motor, the iron core is a very important part of the motor, for the selection of iron core materials, it is necessary to fully consider whether the permeability can meet the needs of the permanent magnet motor. Under normal circumstances, permanent magnet motors choose electrical steel as a iron core material, the main reason is that electrical steel has a better performance in terms of magnetic permeability. The selection of the motor iron core material has a very important impact on the overall performance of the permanent magnet motor and the cost control of the motor. When the permanent magnet motor is manufactured, assembled and formally operated, a certain stress will be formed on the iron core. The existence of stress will directly affect the permeability of the electrical steel sheet, resulting in different degrees of decline in magnetic permeability, the performance of the permanent magnet motor will be reduced, and will increase the motor loss.

In the design and manufacture of permanent magnet motors, the selection and utilization of materials are becoming more and more demanding, and even close to the limit standards and levels of material performance. As the iron core material of permanent magnet motors, electrical steel must meet very high accuracy requirements in related application technologies and accurate calculation of iron consumption, in order to meet actual needs.

The traditional motor design method used to calculate the electromagnetic characteristics of electrical steel is obviously inaccurate, because these conventional methods are mainly for conventional conditions, the calculation results will have a large deviation. Therefore, a new calculation method is needed to accurately calculate the magnetic permeability and iron loss of electrical steel under the condition of stress field, so that the application level of iron core materials is higher, and the performance indicators such as the efficiency of permanent magnet motor can reach a higher level.

From the point of view of the form of permanent magnet motor stator core stress, the sources of its formation include punching, riveting, lamination, casing interference assembly, etc., and the most significant impact area is the stress caused by casing interference assembly. For the rotor of permanent magnet motor, its stress sources mainly include thermal stress, centrifugal force, electromagnetic force, etc. Compared with ordinary motors, the normal speed of permanent magnet motor is relatively high, and at the same time, the magnetic insulation structure should be set in the core of the rotor. Therefore, centrifugal stress is the most important source of stress. The stator core stress caused by the interference assembly of the permanent magnet motor shell mainly exists in the form of compressive stress, which is concentrated in the yoke of the stator core of the motor, and the stress direction is circumferential.

The magnetic density change of the key parts of the permanent magnet motor is analyzed. Under the influence of saturation, the magnetic density of the rotor reinforcing bar and the magnetic separation bridge does not change much. The magnetic density of the stator and main magnetic circuit of the motor has a very significant change. This can also further explain the effect of iron core stress on the magnetic density distribution and magnetic permeability of the permanent magnet motor during operation.

Due to the effect of stress, the compressive stress of the stator yoke of permanent magnet motor will be relatively concentrated, the loss of this part is large, and the performance is significantly deteriorated. There is a large iron loss problem in the stator yoke of permanent magnet motor, especially the iron loss in the joint part of the stator tooth yoke will increase the most under the influence of stress. Through calculation, it is found that the iron consumption of permanent magnet motor increases by 40%-50% due to the influence of tensile stress, which is still quite astonishing, so it also causes a significant increase in the total loss of permanent magnet motor. Through the analysis, it can also be found that the motor iron loss is the main loss form of the stator core caused by the influence of compressive stress, for the motor rotor, the running state of the iron core in the centrifugal tensile stress state, not only will not increase the core loss, but also will have a certain improvement effect.

The magnetic susceptibility of the motor core deteriorates under the condition of iron core stress, and its shaft inductance will be reduced to a certain extent. Specifically, the magnetic circuit of the permanent magnet motor is analyzed. The shaft magnetic circuit mainly includes three parts: Air gap, permanent magnet and fixed rotor core, of which the permanent magnet is the most important part. For this reason, when the magnetic susceptibility of the permanent magnet motor core changes, the shaft inductance cannot be greatly changed. The axial magnetic circuit of permanent magnet motor composed of air gap and fixed rotor core is much smaller than that of permanent magnet. When the influence of iron core stress is fully considered, the magnetic susceptibility deteriorates and the shaft inductance decreases significantly. The influence of stress on magnetic properties of the permanent magnet motor core is analyzed. As the magnetic properties of the iron core of the motor decrease, the magnetic linkage of the motor decreases, and the electromagnetic torque of the permanent magnet motor also decreases.