Because permanent magnet motors can save energy by about 20%, the use of permanent magnet motors is becoming more and more widespread nowadays. This article explains the influences of permanent magnets on the performance of permanent magnet motors, I hope it will help you.
What are the effects of permanent magnets on the performance of permanent magnet motors?
Image Source: Researchnester
The Thickness of Permanent Magnets
In the case of a fixed inner or outer magnetic circuit circle, when the thickness of the permanent magnet increases, the air gap decreases, and the effective magnetic flux increases. That means, under the same remanence, the no-load speed decreases, the no-load current decreases, and the maximum efficiency of the permanent magnet motor increases. However, there are also unfavorable aspects, such as the increase in commutation vibration of permanent magnet motors, and the relative steepening of the efficiency curve of permanent magnet motors.
The Width of Permanent Magnets
For brushless motor magnets distributed in dense rows, the total cumulative gap must not exceed 0.5 mm, too small will not be able to be installed, and too large will lead to magnet positioning misalignment, motor vibration increases, and efficiency decreases. The spacing width between each two magnets must be the same, otherwise, it will also cause the vibration of the permanent magnet motor. For brushed motors, there is a certain space between the magnets left for the mechanical commutation transition. To ensure the effect of permanent magnet motors, the manufacturers have a strict magnet installation process to ensure installation accuracy.
The Chamfer of Permanent Magnets
If the magnet is not chamfered, the edge magnetic field of the permanent magnet motor will increase sharply, resulting in permanent magnet motor pulse vibration. The larger the chamfer, the smaller the vibration.
However, chamfering generally has a certain loss of magnetic flux. Magnets with some specifications are chamfered to 0.8, and the loss of magnetic flux will reach 0.5 ~ 1.5%. For brushed motors, the remanence is relatively low, so the reduction of chamfer size is conducive to the compensation of remanence, but the pulse vibration of permanent magnet motors increases.
The Remanence of Permanent Magnets
For DC motors, under the same winding parameters, the higher the remanence, the lower the no-load speed, the lower the no-load current; the higher the maximum torque, the higher the efficiency of the highest efficiency point. This is because the running motors generate sufficient reverse-induced voltage with a relatively low speed, which reduces the algebraic sum of the electromotive force applied to the winding. The no-load speed and maximum torque are generally used as criteria for determining the magnet’s remanence.
Image Source: Stanfordmagnets& Arkival
The Coercivity of Permanent Magnets
During the operation of a motor, there is always the problem of temperature rise and reverse demagnetization. From the point of view of motor design, the higher the coercivity, the smaller the magnet thickness can be. But the magnet is useless beyond a certain coercivity because the other components of the motor cannot work stably at that temperature either. So as long as the coercivity can meet the design requirements, there is no need to waste resources.
The Squareness of Permanent Magnets
The squareness is the ratio of Hk and HcJ (Hk / HcJ). The value of squareness is between 0 ~1, The closer the squareness is to 1, the better. Usually, products with a squareness of more than 0.9 are considered qualified products.
The degree of squareness affects the flatness of the efficiency curve of the motor performance. Although at present the flatness of the efficiency curve of the motor is not listed as an important standard, it is very important for the motor in the natural road conditions. Because of the different road conditions, the motor can not always work at the maximum efficiency point, which is one of the reasons why some motors do not have a high maximum efficiency but have a long range.
A good motor should not only have a high maximum efficiency, but the efficiency curve should be as horizontal as possible, with the slope of efficiency reduction as small as possible. With the maturity of motor technology and standards, the flatness of the efficiency curve of motor performance will gradually become an important criterion, and the squareness of the magnet will also be an important factor affecting the performance of the motor.
Image Source: Hsmagnets & Indiamart
The Consistency of Permanent Magnets
Inconsistent Remanence | The inconsistent remanence will lead to the inconsistency of the magnetic flux of each magnetic field section, resulting in asymmetry of the torque and vibration.
Inconsistent Coercivity | When the coercivity of some magnet is too low, it is prone to demagnetization, resulting in the inconsistent magnetic flux of each magnet and the vibration of the motor. This effect is more significant for brushless motors