A Composite Magnetic Design Method for Suppressing Eddy Current Loss of Leakage Flux in Nanocrystalline High-Frequency Transformers

Abstract

The present invention proposes a composite magnetic design method for suppressing eddy current losses caused by leakage flux in a nanocrystalline high-frequency transformer. This method is applicable to high-power DC / DC converters and includes separating the primary winding and the secondary winding from each other to make the nanocrystalline high-frequency transformer have a high leakage inductance; determining the main temperature rise area of the magnetic core of the high-power nanocrystalline high-frequency transformer through finite element simulation; sleeving a ferrite magnetic ring with a small thickness outside the above temperature rise area to control the leakage flux path and reduce the leakage flux passing through the nanocrystalline strip in the vertical direction; verifying the suppression effect of the ferrite magnetic ring sleeved outside the nanocrystalline magnetic core on eddy current losses by changing the thickness of the ferrite magnetic ring through finite element simulation; and determining the thickness of the ferrite magnetic ring by comprehensively considering the volume, leakage inductance, and losses. Without significantly changing the volume and leakage inductance of the nanocrystalline high-frequency transformer, the present invention significantly reduces the core losses.

Description

Technical Field

[0001] The present invention relates to high-power high-frequency power supply technology, and particularly to a composite magnetic design method for suppressing eddy current loss of leakage magnetic flux in a nanocrystalline high-frequency transformer. Background Art

[0002] High-frequency transformers undertake functions such as voltage conversion, energy transmission, and electrical isolation in isolated DC / DC converters. Nanocrystalline and ferrite are the main materials for high-frequency transformer cores. Compared with ferrite, nanocrystalline materials have the advantages of high saturation magnetic flux, high magnetic permeability, and low coercive force. Therefore, nanocrystalline materials have broad application prospects in high-power high-frequency transformers. The eddy current loss of the magnetic core is inversely proportional to the resistivity. Compared with ferrite, nanocrystalline has the disadvantage of relatively low resistivity, which easily causes a sharp increase in the eddy current loss of the nanocrystalline magnetic core. By reducing the thickness of the nanocrystalline strip, the eddy current loss of the main magnetic flux can be effectively suppressed. However, when the leakage inductance of the high-frequency transformer is large, it is difficult to reduce the eddy current loss induced by the leakage magnetic flux, and this part of the loss is mainly concentrated on the side of the magnetic core. Summary of the Invention

[0003] To solve the above technical problems, the present invention proposes a composite magnetic design method for suppressing eddy current loss of leakage magnetic flux in a nanocrystalline high-frequency transformer. The method includes the following steps:

[0004] Step 1, establish a nanocrystalline high-frequency transformer model with separated primary and secondary windings;

[0005] Step 2, model the 10 layers of nanocrystalline strips on the inner and outer sides of the magnetic core of the nanocrystalline high-frequency transformer according to the actual thickness;

[0006] Step 3, input a sinusoidal alternating current with an amplitude of 100 A as the primary excitation, connect a resistive load to the secondary side, and determine the area with excessive eddy current loss induced by the high-frequency leakage magnetic flux of the nanocrystalline magnetic core. This area with excessive eddy current loss is the main temperature rise area; this main temperature rise area is located in the edge strip of the nanocrystalline magnetic core;

[0007] Step 4, sleave a ferrite magnetic ring outside the above main temperature rise area;

[0008] Step 5, input the excitation as described in Step 3, and observe the decreasing trend of the leakage magnetic flux eddy current loss;

[0009] Step 6, verify the suppression effect of the ferrite magnetic ring sleeved outside the nanocrystalline magnetic core on the eddy current loss by changing the thickness of the ferrite magnetic ring;

[0010] Step 7, comprehensively consider the volume of the nanocrystalline magnetic core, the leakage inductance and loss of the high-frequency transformer, and determine the thickness of the ferrite magnetic ring.

[0011] Furthermore, the primary and secondary windings of the high-frequency transformer adopt a split winding to increase the leakage inductance; the turns ratio of the high-frequency transformer is 12:12.

[0012] Furthermore, the shape of the nanocrystalline magnetic core is a hollow cylinder, and its external dimensions can be uniquely determined by the inner diameter, outer diameter, and height. Its thickness is defined as half of the difference between the outer diameter and the inner diameter. The nanocrystalline magnetic core is wound by nanocrystalline tapes. The thickness of a single tape is about 20 μm. The leakage magnetic flux is generated by the leakage inductance, and its path perpendicularly passes through the nanocrystalline tapes, inducing eddy currents, namely leakage magnetic flux eddy currents. In the case of high leakage inductance, it is obtained through finite element simulation that the leakage magnetic flux eddy current loss is mainly concentrated near the inner and outer side surfaces of the hollow cylinder and decreases sharply with the increase in depth.

[0013] Furthermore, two ferrite magnetic rings are respectively sleeved on both sides of the nanocrystalline magnetic core. The outer diameter of the inner ferrite magnetic ring is slightly smaller than the inner diameter of the nanocrystalline magnetic core, and the inner diameter of the outer ferrite magnetic ring is slightly larger than the outer diameter of the nanocrystalline magnetic core. The height of the ferrite magnetic ring is equal to the height of the nanocrystalline magnetic core; it is used to control the path of the leakage magnetic flux and reduce the magnetic flux perpendicularly passing through the nanocrystalline tapes.

[0014] Furthermore, the total volume of the nanocrystalline magnetic core and the ferrite magnetic rings remains unchanged. By changing the thickness of the ferrite magnetic rings, the thickness of the nanocrystalline magnetic core is correspondingly changed, and the change in the total core loss is observed.

[0015] Furthermore, by increasing the thickness of the ferrite magnetic rings, the leakage inductance of the high-frequency transformer remains basically unchanged, and the leakage magnetic flux eddy current loss decreases. However, the size of the nanocrystalline magnetic core decreases under the same volume, and its performance deteriorates. Therefore, it is necessary to balance the relationship between the two, and the thickness of the ferrite magnetic rings is selected to be 2 mm.

[0016] Compared with the prior art, the remarkable advantages of the present invention are as follows: The three-dimensional finite element simulation is used to reflect the eddy current loss induced by the leakage magnetic flux in the nanocrystalline high-frequency transformer under high leakage inductance. By combining two materials with different magnetic permeabilities and conductivities, and using the method of sleeving the ferrite magnetic rings on the nanocrystalline magnetic core, without significantly changing the volume and leakage inductance of the nanocrystalline high-frequency transformer, by comparing the core losses at different thicknesses of the ferrite magnetic rings, the core loss is significantly reduced. Description of the Drawings

[0017] Figure 1 It is a schematic diagram of sleeving the ferrite magnetic rings on the nanocrystalline high-frequency transformer under high leakage inductance.

[0018] Figure 2 It is a diagram showing the relationship between the leakage magnetic flux eddy current loss of 10 layers of tapes on the inner side of the nanocrystalline magnetic core and the thickness of the ferrite magnetic rings.

[0019] Figure 3 It is a diagram showing the relationship between the leakage magnetic flux eddy current loss of 10 layers of tapes on the outer side of the nanocrystalline magnetic core and the thickness of the ferrite magnetic rings.

[0020] Figure 4It is a graph showing the relationship between the losses of nanocrystalline magnetic cores and ferrite magnetic rings and the thickness of the ferrite magnetic rings. Specific implementation manners

[0021] In order to make the objectives, technical solutions and advantages of the present application clearer and more understandable, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0022] The present invention proposes a composite magnetic design method for suppressing the eddy current loss of leakage flux in a nanocrystalline high-frequency transformer. Since the eddy current loss induced by the high-frequency leakage flux in the edge strip of the nanocrystalline magnetic core is too large when the high-frequency transformer has a high leakage inductance, which is likely to cause local high temperature. Therefore, for the eddy current loss of the leakage flux in the nanocrystalline magnetic core, ANSYS Maxwell electromagnetic simulation is used to locate the main loss area, and a ferrite magnetic ring is sleeved near this area to reduce the core loss.

[0023] To achieve the above object, the method includes:

[0024] The primary winding and the secondary winding are separated from each other, so that the nanocrystalline high-frequency transformer has a high leakage inductance;

[0025] The main temperature rise area of the magnetic core of the high-power nanocrystalline high-frequency transformer is determined by finite element simulation;

[0026] Outside the above temperature rise area, a ferrite magnetic ring with a small thickness is sleeved to control the leakage flux path and reduce the leakage flux passing through the nanocrystalline strip in the vertical direction;

[0027] By changing the thickness of the ferrite magnetic ring, the finite element simulation is used to verify the suppression effect of the ferrite magnetic ring sleeved outside the nanocrystalline magnetic core on the eddy current loss;

[0028] Considering the volume, leakage inductance and loss comprehensively, the thickness of the ferrite magnetic ring is determined.

[0029] Furthermore, the tight coupling or interleaved windings between the windings of the high-frequency transformer can reduce the leakage inductance, and the separated primary and secondary windings of the high-frequency transformer can increase the leakage inductance. To reduce the number of magnetic components, the leakage inductance of the high-frequency transformer can be used as the resonant inductance, so a high leakage inductance is required.

[0030] Furthermore, the shape of the nanocrystalline magnetic core is generally a hollow cylinder, and its outer dimensions can be uniquely determined by the inner diameter, outer diameter and height. Its thickness is defined as half of the difference between the outer diameter and the inner diameter. The nanocrystalline magnetic core is wound by nanocrystalline strips, and the strip thickness is about 20 μm. The leakage flux is generated by the leakage inductance, and its path vertically passes through the nanocrystalline strip, and the induced eddy current is the leakage flux eddy current. In the case of high leakage inductance, it can be obtained through finite element simulation that the leakage flux eddy current loss is mainly concentrated near the inner and outer side surfaces of the hollow cylinder and decreases rapidly with the increase of depth.

[0031] Furthermore, since the ferrite has a low conductivity, it can also be formed into a hollow cylinder. Two ferrite magnetic rings are respectively sleeved on both sides of the nanocrystalline magnetic core. The outer diameter of the inner ferrite magnetic ring is slightly smaller than the inner diameter of the nanocrystalline magnetic core, and the inner diameter of the outer ferrite magnetic ring is slightly larger than the outer diameter of the nanocrystalline magnetic core. The height of the ferrite magnetic ring is equal to the height of the nanocrystalline magnetic core. The purpose is to control the leakage magnetic flux path and reduce the magnetic flux vertically passing through the nanocrystalline strip.

[0032] Furthermore, using ANSYS Maxwell electromagnetic simulation software, while keeping the total volume of the nanocrystalline magnetic core and the ferrite magnetic ring unchanged, change the thickness of the ferrite magnetic ring and accordingly change the thickness of the nanocrystalline magnetic core, and observe the change of the total core loss.

[0033] Furthermore, by increasing the thickness of the ferrite magnetic ring, the leakage inductance of the high-frequency transformer remains basically unchanged, and the eddy current loss of the leakage magnetic flux decreases. However, the size of the nanocrystalline magnetic core decreases under the same volume, resulting in a performance decline. Therefore, it is necessary to balance the relationship between the two. Generally, the thickness of the ferrite magnetic ring is 2 mm.

[0034] As a specific implementation, draw a three-dimensional finite element model of the high-frequency transformer. The magnetic core material is nanocrystalline, and the shape of the magnetic core is a hollow cylinder. At both sides of the hollow cylinder, draw 10 layers of nanocrystalline strips respectively. The primary and secondary windings are separated from each other and wound around both sides of the magnetic core respectively to increase the leakage inductance. For the case of sleeving the ferrite magnetic ring, the magnetic core sleeving and winding methods are as Figure 1 shown.

[0035] Use ANSYS Maxwell eddy current field for electromagnetic simulation. The turns ratio of the high-frequency transformer is 12:12. The primary excitation is a sinusoidal alternating current with an amplitude of 100 A, and the secondary side is connected to a resistive load with a resistance value of 6 Ω. The thickness of a single-layer strip is 20 μm, and the other nanocrystalline magnetic core regions are a whole entity. The eddy current loss of the leakage magnetic flux is mainly concentrated in the strips of the above model. In the simulation, to distinguish the main core loss of the nanocrystalline main magnetic core from the eddy current loss of the leakage magnetic flux in the three-dimensional model, in the pre-processing, for the main magnetic core, only consider the core loss in the software calculation model; for the 10 layers of strips on both sides, only consider the loss brought by the eddy current effect and ignore the hysteresis loss; in the post-processing, to distinguish different loss sources, the core loss in the simulation results is the main core loss of the whole nanocrystalline magnetic core in the three-dimensional model, and the eddy current loss in the simulation results is the additional eddy current loss of the strips on both sides. When the ferrite magnetic ring is not sleeved, the inner diameter of the nanocrystalline magnetic core is 120 mm, the outer diameter is 200 mm, and the height is 50 mm. In addition, ferrite magnetic rings with thicknesses of 1 mm, 2 mm, 3 mm, 4 mm, and 5 mm are sleeved in turn, and the total core volume is maintained unchanged during the process. For the case of sleeving the ferrite, when calculating the loss of the ferrite magnetic ring, rely on the normal calculation of the core loss model in the simulation software.

[0036] When there is no ferrite magnetic ring sleeved and when a 1 - 5 mm ferrite magnetic ring is sleeved, the relationship diagram of the eddy current loss of the leakage magnetic flux of the inner 10 - layer strip of the nanocrystalline magnetic core with respect to the thickness of the ferrite magnetic ring is as follows Figure 2 shown. The relationship diagram of the eddy current loss of the leakage magnetic flux of the outer 10 - layer strip of the nanocrystalline magnetic core with respect to the thickness of the ferrite magnetic ring is as follows Figure 3 shown. In the two diagrams, the layer sequence represents the order in which the nanocrystalline strip penetrates from the edge of the magnetic core into the interior of the magnetic core. It can be seen from the figures that, on the one hand, as the strip penetrates deeper, the eddy current loss decreases rapidly. Therefore, when simulating, it is not necessary to draw all the strips, and the loss situation can be reflected by several layers at the edges on both sides of the nanocrystalline magnetic core; on the other hand, as the thickness of the ferrite magnetic ring increases, the eddy current loss of the leakage magnetic flux decreases effectively. When the thickness of the ferrite magnetic ring is within 2 mm, the loss reduction amplitude is relatively large. When the thickness of the ferrite magnetic ring exceeds 2 mm, the loss reduction amplitude slows down.

[0037] The leakage inductances of the high - frequency transformer when there is no ferrite magnetic ring sleeved and when a 1 - 5 mm ferrite magnetic ring is sleeved are 20.42 μH, 20.43 μH, 20.61 μH, 20.71 μH, 20.76 μH, 20.71 μH respectively, and its leakage inductance remains basically unchanged; the eddy current losses of the leakage magnetic flux are: 941.45 W, 290.72 W, 108.13 W, 53.32 W, 35.99 W, 26.97 W respectively; the core losses of the ferrite magnetic ring are: 28.54 W, 54.40 W, 65.00 W, 63.19 W, 58.79 W, 55.66 W respectively. As follows Figure 4 shown, as the thickness of the ferrite magnetic ring increases, the eddy current loss of the leakage magnetic flux decreases effectively, and the loss of the ferrite magnetic ring increases slightly. In comparison, the absolute value of the loss of the ferrite magnetic ring is much lower than the eddy current loss of the leakage magnetic flux. This shows that the present invention significantly reduces the core loss without significantly changing the volume and leakage inductance of the nanocrystalline high - frequency transformer.

[0038] The above - described embodiments only represent one implementation manner of the present application, and its description is relatively specific and detailed, but it should not be construed as a limitation to the scope of the invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A composite magnetic design method for suppressing eddy current losses of leakage magnetic flux in a nanocrystalline high-frequency transformer, characterized in that, The method comprises the following steps: Step 1, establish a nanocrystalline high-frequency transformer model with separated primary and secondary windings; Step 2, model the 10 layers of nanocrystalline tapes on the inner and outer sides of the magnetic core of the nanocrystalline high-frequency transformer according to the actual thickness; Step 3, input a sinusoidal alternating current with an amplitude of 100 A as the primary excitation, connect a resistive load to the secondary side, and determine the area with excessive eddy current loss induced by the high-frequency leakage magnetic flux of the nanocrystalline magnetic core. This area with excessive eddy current loss is the main temperature rise area; this main temperature rise area is located in the edge tapes of the nanocrystalline magnetic core; Step 4, sleave a ferrite magnetic ring on the outside of the above-mentioned main temperature rise area; Step 5, input the excitation as described in Step 3, and observe the decreasing trend of the eddy current loss of the leakage magnetic flux; Step 6, verify the suppression effect of the ferrite magnetic ring sleeved on the nanocrystalline magnetic core on the eddy current loss by changing the thickness of the ferrite magnetic ring; Step 7, comprehensively consider the volume of the nanocrystalline magnetic core, the leakage inductance and loss of the high-frequency transformer, determine the thickness of the ferrite magnetic ring. Keep the total volume of the nanocrystalline magnetic core and the ferrite magnetic ring unchanged, change the thickness of the ferrite magnetic ring, and accordingly change the thickness of the nanocrystalline magnetic core, and observe the change of the total core loss; Two ferrite magnetic rings are respectively sleeved on both sides of the nanocrystalline magnetic core. The outer diameter of the inner ferrite magnetic ring is slightly smaller than the inner diameter of the nanocrystalline magnetic core, and the inner diameter of the outer ferrite magnetic ring is slightly larger than the outer diameter of the nanocrystalline magnetic core. The height of the ferrite magnetic ring is equal to the height of the nanocrystalline magnetic core; it is used to control the leakage magnetic flux path and reduce the magnetic flux vertically passing through the nanocrystalline tapes; By increasing the thickness of the ferrite magnetic ring, the leakage inductance of the high-frequency transformer remains basically unchanged, and the eddy current loss of the leakage magnetic flux decreases. However, the size of the nanocrystalline magnetic core decreases under the same volume, and the performance deteriorates. Therefore, it is necessary to balance the relationship between the two, and select the thickness of the ferrite magnetic ring to be 2 mm; the shape of the nanocrystalline magnetic core is a hollow cylinder, and its external dimensions can be uniquely determined by the inner diameter, outer diameter and height. Its thickness is defined as half of the difference between the outer diameter and the inner diameter. The nanocrystalline magnetic core is wound by nanocrystalline tapes, and the thickness of a single layer of tape is 20 μm. The leakage magnetic flux is generated by the leakage inductance, and its path vertically passes through the nanocrystalline tapes, and the induced eddy current is the eddy current of the leakage magnetic flux. In the case of high leakage inductance, through finite element simulation, it is obtained that the eddy current loss of the leakage magnetic flux is mainly concentrated near the inner and outer vertical surfaces of the hollow cylinder and decreases rapidly with the increase of the depth.

2. A composite magnetic design method for suppressing eddy current losses of leakage flux in a nanocrystalline high-frequency transformer according to claim 1, characterized in that: The primary and secondary sides of the high-frequency transformer adopt separated windings to increase the leakage inductance; the turns ratio of the high-frequency transformer is 12:12.

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