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Overview
Dy-diffusion magnets can increase demagnetization resistance by distributing high coercive force on their magnet surfaces. Conversely, incomplete magnetization can reduce coercive force, resulting in parts where demagnetization is likely. Therefore, It is important to account for the effects of both Dy diffusion and incomplete magnetization.
The finite element method enables the definition of coercive force distribution and thermal demagnetization characteristics with incomplete magnetization. Motor performance at high temperatures can be evaluated using defined magnet characteristics.
In this example, the thermal demagnetization resistance of a motor is analyzed using Dy-diffusion magnets with a coercive force distribution under incomplete magnetization.
The finite element method enables the definition of coercive force distribution and thermal demagnetization characteristics with incomplete magnetization. Motor performance at high temperatures can be evaluated using defined magnet characteristics.
In this example, the thermal demagnetization resistance of a motor is analyzed using Dy-diffusion magnets with a coercive force distribution under incomplete magnetization.
Magnetization Material Determined from Demagnetization Data
Since the demagnetization characteristics after magnetization also depend on the temperature, prepare a characteristic table based on the applied magnetic field during magnetization and the temperature to be used after magnetization. As the applied magnetic field is not uniform in the magnet, each element has different demagnetization characteristics.
Fig. 1 shows the table of applied magnetic field-temperature-demagnetization characteristics.
Fig. 1 shows the table of applied magnetic field-temperature-demagnetization characteristics.
Dy-diffusion Magnet Coercive Force Distribution
The Dy-diffusion magnet maximum coercive force is distributed inside the magnet. Fig. 2 shows the coercive force distribution (complete magnetization) of a Dy-diffusion magnet used in this case study.
During incomplete magnetization, the coercive force distribution changes with the applied magnetic field.
During incomplete magnetization, the coercive force distribution changes with the applied magnetic field.
Magnetization Distributions
Fig. 3 shows the magnet magnetization distributions obtained by in-place magnetization at input currents of 25 kA and 45 kA. The smaller the input current, the smaller the magnetization of magnets from their center and outwards near the bridge .Incomplete magnetization results where the magnetization is small.
In addition to the effect of the magnitude of the magnetization, the Dy-diffused magnets are also affected by the coercive force distribution. Demagnetization is likely to occur where there is low coercive force and incomplete magnetization.
In addition to the effect of the magnitude of the magnetization, the Dy-diffused magnets are also affected by the coercive force distribution. Demagnetization is likely to occur where there is low coercive force and incomplete magnetization.
Torque
Fig. 4 shows the average torque when the magnet temperature is varied.
When the magnetization current is 25 kA, it can be seen that even at 100 deg C the torque is lower than with complete magnetization. From this, it is predicted that, compared with complete magnetization, a decrease in overall torque over the entire temperature range results from insufficient magnetization of the entire magnet due to incomplete magnetization at a magnetization current of 25 kA.
Magnetization characteristics will also change as temperature rises. Even with complete magnetization, when the temperature is 130 deg C or more, the torque decreases greatly and thermal demagnetization occurs. At the magnetization current of 45 kA, the torque up to 130 deg C is almost the same as that at complete magnetization, but when 130 deg C is exceeded, the torque decreases more than at complete magnetization. This is because with incomplete magnetization there is an area where demagnetization is large, thus at high temperature there is more demagnetization than with complete magnetization. From this the average torque is reduced.
When the magnetization current is 25 kA, it can be seen that even at 100 deg C the torque is lower than with complete magnetization. From this, it is predicted that, compared with complete magnetization, a decrease in overall torque over the entire temperature range results from insufficient magnetization of the entire magnet due to incomplete magnetization at a magnetization current of 25 kA.
Magnetization characteristics will also change as temperature rises. Even with complete magnetization, when the temperature is 130 deg C or more, the torque decreases greatly and thermal demagnetization occurs. At the magnetization current of 45 kA, the torque up to 130 deg C is almost the same as that at complete magnetization, but when 130 deg C is exceeded, the torque decreases more than at complete magnetization. This is because with incomplete magnetization there is an area where demagnetization is large, thus at high temperature there is more demagnetization than with complete magnetization. From this the average torque is reduced.
