Permanent Magnet Motor
A permanent magnet motor is an electric motor that uses permanent magnet motor to generate the magnetic field required for operation. Unlike traditional electric motors, which use electromagnets created by passing current through coils of wire, permanent magnet motors have magnets embedded within their structure.
We primarily use the generation and preservation of magnetism in permanent magnet motor materials, like NdFeB. The most fundamental functional need for magnetic materials is this. How then can one quantify a magnet’s capacity to produce and maintain magnetism? Remanence Br, coercive force Hcb, intrinsic coercive force Hcj, and maximal magnetic energy product BH (max) are the four indications that we typically utilize.
You must first comprehend the demagnetization curve in order to fully comprehend the aforementioned symptoms. The magnetized permanent magnet motort must be able to endure the impact of several elements that are detrimental to magnetism while in operation since the permanent magnet material must first be magnetized. The magnet’s entire performance can be accurately represented by the demagnetization curve.
An example of a permanent magnet’s hysteresis loop is shown in the image above. The magnetization curve is located in the first quadrant, the demagnetization curve is located in the second quadrant, the reverse demagnetization curve is located in the third quadrant permanent magnet motor, and so on.
The applied magnetic field intensity H is shown by the abscissa, while the magnetic polarization intensity J and the magnetic induction intensity B are represented by the ordinate.
In short, the magnet’s internal magnetic field is represented by the magnetic polarization intensity J, and the magnet’s external and internal magnetic fields add up to form the magnetic induction intensity B.
The demagnetization curve is the source of the four magnetic performance parameters: remanence, coercive force, intrinsic coercive force, and maximum magnetic energy product.
The blue line in the above figure is known as the B-H demagnetization curve (the change curve of the magnetic induction intensity B and the external magnetic field H), and the red line is known as the J-H demagnetization curve (the change curve of the magnetic polarization intensity J and the external magnetic field H), also known as the intrinsic demagnetization curve permanent magnet motor.
Each magnetic domain is represented by a little box. A magnet is made up of numerous magnetic domains, and the arrow represents the C-axis of the direction of the magnetization that occurs spontaneously.
One way to conceptualize the magnetic domain is as a tiny magnet, a The arrow represents the C-axis of the direction of the magnetic domains’ spontaneous magnetization, which is made up of numerous magnetic domains. As illustrated in Figure 1, permanent magnets in a magnetically neutral state—basically, magnets that have not been magnetized—have most of their magnetic domains at the same coordinates permanent magnet motor, but their directions cancel each other out, making them invisible to the outside world.
When a magnetic field is applied along the magnetization direction, the magnetic domains gradually shift and rotate through the magnetic domain walls so that their C-axis directions point in the same direction, as shown in Figure 2 and Figure 3. This is the magnetization curve.
The corresponding magnetic polarization intensity value of the magnet when saturated magnetization is called is the saturation magnetic polarization intensity Js.
When the magnet is saturated and magnetized, the external magnetic field is removed. It can be seen from the figure that most of the magnetic domains still maintain the same direction. A small number of them rotate slightly but the main direction remains unchanged, as shown in Figure 4. In this way, the magnetic induction intensity and magnetic polarization of the magnet The intensity retains a high value.
This value is called the residual magnetic induction intensity Br or the residual magnetic polarization intensity Jr. The intuitive understanding is that after the external magnetic field is removed from the magnetized saturated permanent magnet motor,
the remaining magnetic induction intensity B or magnetic polarization intensity J of the magnet, when an external magnetic field is applied When H is 0, Br=Jr, we often use Br to describe it, which is what we most often call residual magnetism, the unit is Gs or T. The higher the Br, the stronger the magnetic induction intensity that can be retained, and the greater the potential to become a strong magnetic material.
When the applied external magnetic field increases in the opposite direction, the magnetic domains of the magnet gradually shift and rotate, as shown in Figure 5. When the magnetic field intensity reaches a certain value, the magnetic induction intensity B of the magnet drops to 0.
A simple understanding is that the magnetic field retained inside the magnet The magnetic field strength and the applied reverse magnetic field strength cancel each other out. At this time, the corresponding magnetic field strength value is called the magnetic coercivity Hcb (also written as bHc), and the unit is Oe or kA/m.
The magnetic coercivity Hcb is closely related to the inclination of the J-H demagnetization curve. If the magnetic domain of the magnet is difficult to shift or rotate in a short period of time, the J-H line will be very straight, so numerically Hcb will be infinitely close to the upper limit of Br and Hcb. It is Br, Hcb=Br.
This is an ideal situation, which means that there is no tendency for the magnetic domain to reverse before the reverse magnetic field intensity reaches Br numerically permanent magnet motor. In this way, the magnet is very stable, that is, the magnet is numerically sensitive to the reverse magnetic field. The initial state resistance to demagnetization is very strong below Br.
When the reverse magnetic field continues to increase, it reaches a critical value, and the reverse magnetic domain appears quickly, causing the magnetic polarization intensity of the magnet to quickly drop to 0. A simple understanding is that the magnetic field intensity retained inside the magnet drops to 0, as shown in Figure 6.
This The corresponding magnetic field strength value is called the intrinsic coercive force Hcj (also written as jHc), and the unit is Oe or kA/m.
The intrinsic coercive force is a physical quantity that reflects the magnet’s ability to resist demagnetization. The greater the intrinsic coercive force, the stronger the ability to resist demagnetization. To be precise, the stronger the ability to resist complete demagnetization permanent magnet motor.
Special attention needs to be paid here to the difference between Hcj and Hcb. When Hcj is numerically greater than Br, the limit value of Hcb is Br. When Hcj is numerically smaller than Br, the limit value of Hcb is Hcj.
The product of B and H corresponding to any point on the B-H demagnetization curve is called the magnetic energy product. The maximum value is the maximum magnetic energy product (BH)max. Theoretically, the maximum magnetic energy product (BH)max=½ Br².
The maximum magnetic energy product takes into account the residual magnetism. And the magnetic coercivity, its value represents the magnetic energy contained in the magnet, and can also reflect the initial inclination of the J-H line, in units of GOe or j/m³.
If the above four parameters are still difficult to understand, you can simply think of the magnet as a cup of water, magnetization is heating, residual magnetism is the heat of the water after stopping heating, demagnetization is like cooling the water, and Hcb is when the ambient low temperature reaches a When the value is high, it offsets the heat of the water and does not reflect heat as a whole permanent magnet motor.
Hcj is the ambient low temperature value required to completely reduce the heat of the water to 0. Below is a simplified version of the second quadrant diagram of the hysteresis loop, which can help you deepen your understanding of related concepts.
Bei den oben genannten magnetischen Parametern sollten wir in der Praxis auf folgende Punkte achten:
1. For magnets that require a strong magnetic field, we usually need to increase the remanence as much as possible to release more magnetism. However, it should be noted that this is without demagnetization permanent magnet motor .
If there is demagnetization, simply increasing the remanence may It is ineffective, and Hcj needs to be increased to reduce demagnetization permanent magnet motor. The simplest example is that for D10*1 disc-shaped magnets, the surface magnetism of 54H is higher than that of N54.
The reason is that the Hcj of 54H is higher, which can make its Br fully However, the Hcj of N54 is very low and cannot be maintained in a non-demagnetized state. No matter how high the Br is, it cannot fully exert its magnetism.
2. For magnets that require strong demagnetization resistance and stability, we usually need to increase Hcj, and also need the Hcb value to be as close as possible to Br.
3. For magnets that require good temperature resistance, we usually choose to increase Hcj, because the coercive force temperature coefficients of NdFeB permanent magnets with the same Hcj have little difference. The most direct effect of increasing Hcj is to make the inflection point of the B-H line as late as possible Appears or does not appear.
If the temperature stability requirements are strict permanent magnet motor, the Hcb requirements must also be considered and the slope of the B-H line should be reduced as much as possible to reduce the irreversible attenuation amplitude of the magnet.
