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calculation and analysis of permanent magnet eddy current loss fault with magnet segmentation.

by:Maghard      2020-02-24
1.
Introduction with the development of power electronic devices and the improvement of motor control technology, permanent synchronous motor has attracted more and more attention for its high efficiency, wide speed regulation and high power density.
However, with the increase of power density, how to raise the motor temperature within the allowable limit value is a problem worth considering.
Reducing the temperature rise of the motor should start from two aspects: how to improve the cooling capacity of the motor and how to reduce the loss of the motor.
Because the speed of the permanent synchronous motor is fast and the carrier frequency is large, the current loss is large.
In order to reduce the eddy current loss of permanent materials, the researchers conducted a lot of research. 1-5].
In many studies, the axial surface cutting method of permanent materials is widely accepted.
On the basis of previous research, this paper studies the eddy current loss of the internal permanent synchronous motor.
Internal permanent synchronous motor with rated power of 2 is adopted.
2 KW as an example, a threedimensional (3D)finite-
The unit model is established.
Theoretical calculation and analysis of permanent eddy current loss fault are carried out from the two aspects of spatial harmonic and time harmonic respectively;
At the same time, limited-
The element method is verified by analytical method.
One of the main problems of the NdFeB permanent synchronous motor is the thermal demagnetized due to the permanent eddy current loss.
In particular, the permanent servo motor is mainly used for magnetic power (MMF)
Rich in harmonic content]6].
Therefore, reducing the eddy current loss of permanent is getting more and more attention. In this case, the axial part of the pole is used to reduce the eddy current loss of permanent [1]7-9].
It is widely used by motor designers.
There are two reasons for Eddy current loss of permanent [10-12].
One is the distribution of slotted stator and stator windings caused by uneven magnetic dynamic potential distribution and spatial harmonics.
The second is the non-sinusoidal time harmonic of the stator current caused by the inverter power supply.
Permanent eddy current loss can be used 【P. sub. mag]= [Sum up (k)][J. sup. 2. sub. k]/[sigma]dV. (1)2.
Analysis and calculation of eddy current loss of permanent in internal permanent motor assume that there is an infinite length of nd iron boron permanent ;
The external magnetic field moves flat on the surface in the z-directionaxis;
The eddy current at a certain point in permanent can be decomposed into two vortex density perpendicular to each other;
Can be 【J. sub. e]= [sigma]U/L, (2)where [J. sub. e]
Is the vortex density, a is the conductivity of the permanent material, U is the voltage between nodes in the calculation unit, and L is the distance between nodes in the calculation unit.
As shown in Figure 1, suppose the electric potential difference between two points on both sides of the permanent block is [U. sub. 1], [U. sub. 2].
It can be set to [for ease of calculation [U. sub. 1]=[U. sub. 2]= U.
The potential difference of the permanent in the thickness direction is ignored again.
The total voltage of 4 points on the surface of a permanent consisting of both ends of the loop is 2U (t)= d[phi](t)
/Can be expressed in B (t)= [B. sub. 0]+ [B. sub. a], (4)where [B. sub. 0]
Static magnetic density and [B. sub. a]
It is the dynamic magnetic flux caused by the stator winding current. [B. sub. a]
It is considered to be a non-sine periodic function;
Triangle series]B. sub. a]
Decomposed into Fourier series :[B. sub. a]= [[infinity]. Sum up (n=1)]([a. sub. n]cosn[omega]t + [b. sub. n]sin n[omega]t), (5)where [a. sub. n]and [b. sub. n]
Is the amplitude of the dynamic magnetic flux generated by the harmonic component of armaturecurrent in the permanent . Then, [
Non-reproducible mathematical expressions], (6)[
Non-reproducible mathematical expressions]. (7)
Valid value of U (t)is [
Non-reproducible mathematical expressions]. (8)
According to the formula (7)
, Obtained the vortex density in the permanent :[
Non-reproducible mathematical expressions], (9)where [h. sub. m]
It is the length of the permanent magnetized direction, so the eddy current loss power density of the permanent can be obtained :[P. sub. e]= [J. sup. 2. sub. e]/[sigma]= [[pi]. sup. 2][f. sup. 2][sigma][h. sup. 2. sub. m]x [[infinity]. Sum up (n=1)][n. sup. 2]([a. sup. 2]+[b. sup. 2])/2. (10)
Eddy current loss density is [W. sub. e]= [[pi]. sup. 2]f[sigma][h. sup. 2. sub. m]x[[infinity]. Sum up (n=1)][n. sup. 2]([a. sup. 2]+[b. sup. 2])/2. (11)
The eddy current loss density of permanent is integral, and the eddy current loss in permanent can be obtained. 3.
Effect of polar section on permanent eddy current loss fault generated by spatial harmonics basic parameters of internal permanent synchronous motor with rated power of 2.
2 KW of this article is shown in Table 1.
The 3D model of the motor is established by finite element method.
Element analysis software.
In order to save the computing resources, combined with the circulation magnetic field distribution, a unit of the motor is modeled and calculated.
Figure 2 shows that 3D is limited
An element grid model of A 2.
2 KW permanent synchronous motor.
In order to maintain the consistency of grid division every time, a 3D model is established by insulating boundary conditions and zero excitation.
Under the noload condition, the eddy current loss of the permanent divided into different segments is calculated.
The results are shown in Figures 3 and 2.
From Figure 3, the vortex line is cut off by the axial part of the permanent and is formed locally in the magnetic pole part.
Compared to Table 2, the mean value of eddy current loss increases with the increase of the number of poles. 4.
The effect of polar section on the permanent eddy current loss generated by time harmonics the permanent eddy current loss is mainly generated by time harmonics. Literature [13]
The results show that the eddy current loss is maximum when the axial length of the permanent is equal to 2.
3 times the penetration depth.
A permanent for penetration depth can be defined as the depth of the magnetic field acting inside the permanent .
As the depth increases, the magnetic field strength decreases exponentially.
The penetration depth can be calculated [14-17][delta]= 1 / [Square root ()[pi]f[mu][sigma])], (12)where [delta]
It is the penetration depth of permanent , f is the sine frequency ,[mu]
Absolute penetration rate and [sigma]isconductivity.
Figure 4 is the current waveform measured by the inverter power supply test at the rated frequency. The eddy current loss generated by the 37 times harmonic in the permanent is not only not reduced, but also increased. 5.
2. Calculation of faults and analysis of results.
2 KW permanent synchronous motor, the permanent eddy current loss caused by spatial harmonics increases, while the number of segments decreases, and the permanent eddy current loss caused by time harmonics does not increase with the reduction of the number of segments.
The reason why the permanent eddy current loss generated by harmonics and 37 harmonics increases with the decrease of the number of segments is that the 37 harmonic current amplitude is small, and the permanent eddy current loss is large by the basic waveform current.
Why does the permanent eddy current loss caused by spatial harmonics increase with the reduction of the number of segments?
The first reason is that the axial split magnetic pole is equivalent to the oblique pole, and the gap magnetic density waveform is improved;
Another reason is that the segmented pole blocks the formation of the vortex ring, so the permanent eddy current loss decreases with the increase of the number of segments.
The excitation source provided by the inverter contains a large number of harmonic components and a higher harmonic amplitude.
The penetration depth of the low subharmonic is greater than the length of the magnetic direction, so it is not considered.
However, the penetration depth of higher-order harmonics is small and the skin effect is very strong. Therefore, the permanent eddy current loss generated by time harmonics will have a maximum value. 6.
Conclusion The permanent eddy current loss caused by spatial harmonics increases with the decrease of the number of segments, and the permanent eddy current loss caused by time harmonics does not increase with the decrease of the number of segments.
Therefore, when designing the motor, especially the design of the high-speed motor, first, reduce the eddy current loss in the by using the magnetic parts segmentation, considering the output current waveform of the inverter, and pay attention to the ratio between the extremely axial length and the penetration depth of the current high harmonic waveform.
Finally, it is also necessary to consider the compromise between the cost of segmented magnetic poles and the magnitude of reducing current losses;
The number of segments is generally no more than 4. 10.
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Li Bing and Li Ming College of Engineering, Bohai University, Jinzhou 121013, China Communications should go to Li Bing;
Libinger521 @ 163.
Received on January 16, 2016;
Accept the academic editor of April 5, 2016: Chen Wen Title: Figure 1: Potential difference on the surface of permanent magnets.
Description: 3D section diagram of Figure 2: 2.
2 KW permanent synchronous motor (
1 is the stator, 2 is the winding, 3 is the permanent , 4 is the rotor).
Description: Figure 3 :(a)
Eddy current density of permanent . (b)
Vortex density of two-
Permanent segment. (c)
Three-current density
Permanent segment. (d)
Vortex density of four-
Permanent segment. (e)
Eddy density-
Permanent segment. (f)
Vortex density of six-
Permanent .
Description: Figure 4: measured current waveform of inverter.
Description: Figure 5: Harmonic analysis of output current of inverter.
Description: Figure 6: Eddy current loss of permanent at different stages.
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