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The rapid economic development has promoted the further formation of the specialization trend of the permanent magnet motor industry and put forward higher requirements for motor-related performance, technical standards, and product operation stability. To achieve development, the relevant performance must be strengthened from all aspects, so that the overall quality and performance indicators of the motor can reach a higher level.
For permanent magnet motors, 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 magnetic permeability can meet the working needs of permanent magnet motors. Usually, permanent magnet motors choose electrical steel as the core material. The main reason is that electrical steel performs better in terms of magnetic permeability.
The choice of motor 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 officially operated, a certain stress will be formed on the iron core. The existence of stress will directly affect the magnetic permeability of the electrical steel sheet, resulting in varying degrees of decline in the magnetic permeability, which will reduce the performance of the permanent magnet motor and increase the loss of the motor.
In the design and manufacture of permanent magnet motors, the requirements for the selection and utilization of materials are getting higher and higher, even approaching the limit standards and levels of material performance. As the core material of permanent magnet motors, electrical steel, in the relevant application technology and accurate calculation of iron loss, etc. must meet very high precision requirements in order to meet actual needs.
It is obviously inaccurate to calculate the electromagnetic characteristics of electrical steel by the traditional motor design method used in the past, because these conventional methods are mainly aimed at conventional conditions, and the calculation results will have large deviations. Therefore, a new calculation method is needed to accurately calculate the magnetic permeability and iron loss of electrical steel under stress field conditions, so that the application level of core materials will be higher, and the efficiency and other performance indicators of permanent magnet motors will reach a higher level.
The researchers focused on the influence of core stress on the performance of permanent magnet motors, combined with experimental analysis, and discussed the related mechanisms of the stress magnetic properties and stress iron loss properties of permanent magnet motor core materials. There are many sources of stress that affect the stress of the iron core under the working conditions of permanent magnet motors, and various stress sources present many completely different properties.
From the perspective of the stress form of the stator core of the permanent magnet motor, the sources of its formation include punching, riveting, lamination, and interference assembly of the casing, etc., and the largest and most significant area of influence is the stress effect caused by the interference assembly of the casing. For the permanent magnet motor rotor, the stress sources it bears mainly include thermal stress, centrifugal force, electromagnetic force, etc. Compared with ordinary motors, the permanent magnet motor has a relatively high speed under normal conditions, and at the same time, it is necessary to set a magnetic isolation structure at the rotor core.
Therefore, centrifugal stress is the most important source of stress. The stator core stress caused by the interference assembly of the permanent magnet motor casing mainly exists in the form of compressive stress, and its action point is concentrated on the yoke of the stator core of the motor, and the stress direction is tangential to the circumference. The nature of the stress formed by the centrifugal force of the permanent magnet motor rotor is tensile stress, which acts almost entirely on the iron core of the rotor, its maximum centrifugal stress acts on the place where the magnetic isolation bridge of the permanent magnet motor rotor meets the reinforcing rib, which makes this part prone to performance degradation.
The magnetic density changes in the key parts of the permanent magnet motor are analyzed. Under the influence of saturation, the magnetic density of the motor rotor ribs and magnetic isolation bridges does not change much. There are very significant changes in the magnetic density of the motor stator and the main magnetic circuit. This can also further explain the effect of core stress on the magnetic density distribution and magnetic permeability of the permanent magnet motor during operation.
Due to stress, the compressive stress on the yoke of the stator of the permanent magnet motor will be relatively concentrated, the loss of this part will be large, and the performance will significantly deteriorate. The loss is affected by the stress to increase the most. Through calculation, it is found that the iron loss of permanent magnet motors increases by 40%-50% due to the influence of tensile stress. This increase is quite amazing, so it also causes a significant increase in the total loss of permanent magnet motors. Through the analysis, it can also be found that the iron loss of the motor is the main loss form of the stator core caused by the influence of compressive stress. For the motor rotor, the iron core is under the centrifugal tensile stress state in the running state, which not only will not increase the iron core loss but will also have a certain improvement effect.
The magnetic induction performance of the motor core deteriorates under the condition of core stress, and its shaft inductance will decrease to a certain extent. Specifically, the magnetic circuit of the permanent magnet motor is analyzed. The shaft magnetic circuit mainly includes three parts: the air gap, the permanent magnet and the stator and rotor core. Among them, The permanent magnet is the most important part. For this reason, when the magnetic induction performance of the permanent magnet motor core changes, it cannot cause a large change in the shaft inductance.
The shaft magnetic circuit part composed of the air gap of the permanent magnet motor and the stator and rotor core is much smaller than the reluctance of the permanent magnet. The influence of the core stress is fully considered, and the magnetic induction performance deteriorates, and the shaft inductance will be significantly reduced. The influence of the stress-magnetic properties of the permanent magnet motor core is analyzed. As the magnetic induction performance of the motor core decreases, the flux linkage of the motor decreases, and the electromagnetic torque of the permanent magnet motor will also decrease.
