A permanent magnet is a material with a stable magnetic field. It is widely used in the field of electric motors, and its performance directly affects the performance of electric motors.
Impact of Permanent Magnet’s Residual Magnetism
Residual magnetism refers to the degree of magnetization remaining in the magnet itself after the magnet is excited by an external magnetic field and the excitation source is removed. In DC motors, the level of residual magnetization directly affects parameters such as no-load speed, no-load current, and maximum torque of the motor.
Generally speaking, the higher the residual magnetization, the lower the motor’s no-load speed, with a corresponding reduction in the no-load current; concurrently, the maximum torque will increase, and the efficiency of reaching the maximum efficiency point will be higher. Therefore, when designing and selecting permanent magnets, the magnet’s residual magnetization standard should be reasonably determined according to the motor’s needs and performance requirements.
Impact of Coercivity
Coercivity refers to the magnet’s ability to resist demagnetization, i.e., the degree of influence of the external magnetic field on the magnet’s magnetization state. During motor operation, the level of coercivity directly affects the stability of the magnet and demagnetization issues.
Image Source: Wikipedia
Higher coercivity allows the magnet to achieve sufficiently stable magnetization in the direction of a smaller thickness while reducing the chance of reverse demagnetization; while lower coercivity requires a larger magnet thickness to maintain a stable magnetic field.
Therefore, when selecting permanent magnets, the appropriate degree of coercivity should be fully considered to meet the motor design conditions and experimental requirements.
Influence of Permanent Magnets’ Squareness
Squareness refers to the degree of regularity of the magnet surface, which affects the flatness of the efficiency curve in motor performance tests. The squareness of a magnetic material equals the ratio of the residual magnetization to the coercivity. Both the squareness and coercivity are two important performance indicators for hard ferrimagnetic materials. Although squareness is not currently listed as one of the significant indicators, it is crucial for the range of hub motors under real road conditions.
As motors cannot always operate at the point of maximum efficiency in real life, a good hub motor should not only have high maximum efficiency but should also maintain as horizontal an efficiency curve as possible.
In other words, the slope of the efficiency drop should be as small as possible. As the hub motor market, technology and standards mature, the flatness of the efficiency curve will become an increasingly important evaluation indicator.
Image Source: Orientalmotor
Impact of Performance Consistency
If there is inconsistency in the residual magnetization and coercivity of the permanent magnets, this can lead to asymmetric torque distribution and vibration problems, even if the performance of the individual motor is particularly good. Moreover, in brushless motors, the effect of coercivity inconsistency on motor performance is even more significant. Therefore, when manufacturing and selecting permanent magnets, attention should be paid to maintaining the consistency of their performance to enhance the motor’s stability and reliability.
The performance of magnet motors is closely linked to the permanent magnet for the motor. Factors such as residual magnetism, coercivity, squareness, and performance consistency all directly impact the motor’s speed, current, torque, efficiency, and stability.
Therefore, when designing, manufacturing, and selecting motors, the performance characteristics of permanent magnets should be fully considered to achieve the best motor performance matching. This will help improve the efficiency, reliability, and range of motors, promoting the development and application of motor technology.
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