An optimization design method for nanocrystalline high-frequency transformer with low eddy current loss

Abstract

The present invention proposes an optimization design method for a nanocrystalline high-frequency transformer with low eddy current loss, including determining the main temperature rise area of ​​a high-power nanocrystalline high-frequency transformer by finite element simulation; cutting grooves in the nanocrystalline strip in the above-mentioned temperature rise area to block the eddy current loop induced by the high-frequency leakage flux on the surface of the nanocrystalline strip, increase the equivalent resistance, and reduce the leakage flux eddy current loss; by changing the number of cutting layers, the finite element simulation is used to verify the inhibitory effect of cutting the outer layer of the strip on the eddy current loss. The present invention effectively reduces the eddy current loss of the magnetic core and improves the energy conversion efficiency without significantly changing the volume and leakage inductance of the nanocrystalline high-frequency transformer.

Description

Technical Field

[0001] The invention relates to a high-power high-frequency power supply technology, and in particular to an optimization design method for a low-eddy-current loss nanocrystalline high-frequency transformer. Background Art

[0002] The high-frequency transformer is one of the most important electrical components of the isolated DC / DC converter. It undertakes the functions of voltage conversion, energy transmission and electrical isolation. The volume and weight of the high-frequency transformer core account for the vast majority of the volume and weight of the DC / DC converter. Its performance is very important for the entire power transmission system. For the resonant DC / DC converter, a resonant inductor needs to be connected in series on the primary side to achieve soft switching of the switching device and reduce the switching loss of the device. The transformer's own leakage inductance, which is large enough, can be used as a series resonant inductor to reduce the number of components and improve the power density of the converter. Nanocrystalline alloy materials provide a technical basis for the miniaturization and lightweight of power electronic instruments and equipment due to their high saturation flux, high magnetic permeability, low coercive force, low high-frequency loss and high Curie temperature. However, the conductivity of nanocrystalline alloys is very high, and they will induce strong eddy currents under a changing magnetic field, which poses potential thermal problems. During the operation of the nanocrystalline high-frequency transformer, part of the leakage flux Bs passes vertically through the nanocrystalline strip and forms a leakage flux eddy current Js on the plane of the nanocrystalline strip. This eddy current loss cannot be ignored. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides an optimization design method for a nanocrystalline high-frequency transformer with low eddy current loss. When the leakage inductance of the nanocrystalline high-frequency transformer is large, the leakage flux eddy current loss induced by the high-frequency leakage flux on the edge strip of the core is too large, which can easily cause local high temperature and even burn the core. Therefore, the distribution area of ​​the leakage flux eddy current loss is determined for the leakage flux eddy current loss of the nanocrystalline core, and grooves are cut on several layers of the edge strip in the above area by mechanical means to reduce the core loss.

[0004] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] A method for optimizing the design of a low eddy current loss nanocrystalline high-frequency transformer comprises the following steps: using finite element simulation to determine the main temperature rise area of ​​a high-power nanocrystalline high-frequency transformer; cutting grooves in the main temperature rise area to block the eddy current loop induced by the high-frequency leakage magnetic flux on the surface of the nanocrystalline strip, thereby increasing the equivalent resistance and reducing the leakage magnetic flux eddy current loss; and verifying the inhibitory effect of cutting the outer nanocrystalline strip on the eddy current loss by changing the number of cutting layers. The method comprises the following steps:

[0006] Step 1: Establish a model of a toroidal nanocrystalline high-frequency transformer with completely separated and transposed windings;

[0007] Step 2: Model the 10 layers of nanocrystalline ribbons on the inner and outer sides of the magnetic core of the donut-shaped nanocrystalline high-frequency transformer using a set of concentric rings according to the actual thickness;

[0008] Step 3: Input excitation to the primary side, that is, input a sinusoidal voltage source with an amplitude of 1000V at 40kHz, and connect a resistor to the secondary side to determine the distribution area of ​​the leakage flux eddy current loss induced by the high-frequency leakage flux on the surface of the nanocrystalline strip at the edge of the magnetic core. The distribution area is the main temperature rise area. The main temperature rise area is at the intersection of the two ends of the primary winding and the secondary winding, and is symmetrical up and down. The leakage flux eddy current loss on the upper and lower sides is much greater than the leakage flux eddy current loss in the middle.

[0009] Step 4: cutting a plurality of grooves into the multilayer nanocrystalline ribbon at the edge of the magnetic core in the main temperature rise region;

[0010] Step 5: Input the excitation as described in step 3 and observe the downward trend of leakage flux eddy current loss;

[0011] Step 6: Expand the grooving range to cover the entire circumference of the nanocrystalline ribbon and increase the number of grooving to accommodate windings at different winding positions.

[0012] Furthermore, the separation and transposition of the primary and secondary windings of the single-phase nanocrystalline high-frequency transformer can increase the leakage inductance of the transformer to provide a front-stage resonant inductor of the DC / DC resonant converter, thereby achieving the purpose of soft switching of the switch tube.

[0013] Furthermore, the outer diameter of the magnetic core of the annular nanocrystalline high-frequency transformer is 200 mm, the inner diameter is 120 mm, the height is 50 mm, the thickness of a single layer including interlayer insulation is 20 μm, and the stacking coefficient is 0.8.

[0014] Furthermore, during the finite element simulation modeling in step 2, 10 layers of nanocrystalline ribbons are drawn on both sides of the circular ring of the magnetic core of the circular nanocrystalline high-frequency transformer, with a thickness of 16 μm and an interlayer insulation thickness of 4 μm.

[0015] Furthermore, in step 4, when finite element simulation modeling is performed, the width of the cutting groove at the main temperature rise area of ​​each layer of nanocrystalline ribbon is 4 mm, the number of grooves on each side is 7, and they are symmetrically distributed along the fourth groove, and the distance between two adjacent grooves is 10°. In order to prevent the grooving from causing part of the nanocrystalline ribbon to fall off, the grooving does not penetrate the nanocrystalline ribbon, that is, the area with smaller eddy current loss in the middle of the leakage magnetic flux is retained. The width of this area is 10 mm, and the cutting depth is 1 to 6 layers.

[0016] Furthermore, the circular nanocrystalline high-frequency transformer is a single-phase transformer with a turns ratio of 12:12, and the primary winding and the secondary winding are completely separated and symmetrically wound on half of the magnetic core. Ignoring the high-frequency AC loss of the winding, the winding cross-section is a 4mm*4mm rectangle, and the winding axis is 6mm away from the magnetic core.

[0017] Compared with the prior art, the present invention has the following significant advantages: it improves the finite element simulation modeling method of nanocrystalline high-frequency transformers, uses a 3D model to reflect the eddy currents induced by leakage flux on the edge strip of the nanocrystalline magnetic core, determines the main distribution area of ​​the eddy currents, and uses a method of cutting grooves on the edge strip of the magnetic core to effectively reduce the eddy current losses of the magnetic core leakage flux and improve the energy conversion efficiency without significantly changing the volume and leakage inductance of the nanocrystalline high-frequency transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of a high frequency transformer.

[0019] Figure 2 It is a schematic diagram of modeling the edge strip of the magnetic core.

[0020] Figure 3 This is the current density diagram of the outermost strip.

[0021] Figure 4 It is a schematic diagram of strip grooving.

[0022] Figure 5 This is the current density diagram after the outermost strip is grooved.

[0023] Figure 6a This is a graph showing the relationship between the loss and the number of cut layers after the 10 layers of strip on the inner side of the core are slotted.

[0024] Figure 6b This is a graph showing the relationship between the loss and the number of cut layers after the 10 layers of strip on the outside of the core are slotted.

[0025] Figure 7 It is a schematic diagram of grooving used in engineering. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with 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.

[0027] This embodiment is a method for optimizing the design of a nanocrystalline high-frequency transformer with low eddy current loss. Figure 1 As shown in the figure, a three-dimensional nanocrystalline high-frequency transformer model is drawn in ANSYS Maxwell. The transformer is a single-phase transformer with a turns ratio of 12:12. To increase the leakage inductance, the primary winding and the secondary winding are completely separated and symmetrically wound on half of the magnetic core. Ignoring the high-frequency AC loss of the winding, the winding cross-section is a 4mm*4mm rectangle, and the winding axis is 6mm away from the magnetic core.

[0028] like Figure 2As shown, for the magnetic core, most of it is a solid body, and 10 layers of nanocrystalline strips are drawn on each side of the ring, with a thickness of 16μm and an interlayer insulation thickness of 4μm. The primary excitation is a sinusoidal alternating current with an amplitude of 1000V, and a 6Ω resistor is connected to the secondary side. In the simulation, in order to distinguish the main core loss from the eddy current loss of the strip leakage flux on both sides, only the core loss of the main core is considered in the pre-processing, and only the eddy current effect is considered for the 10 layers of strips on both sides; in the post-processing, in order to distinguish different loss sources, the core loss in the software is the main core loss of the large entity in the model, and the eddy current loss in the software is the eddy current loss of the leakage flux of the strips on both sides.

[0029] Under normal circumstances, for the separated winding structure, the leakage flux is concentrated at the place where the two phase windings are close to each other, and crosses the outer strip to form eddy currents, such as Figure 3 As shown. Figure 3 It can be seen from the figure that the eddy current distribution in a single layer of strip is very uneven, which will lead to local overheating. Therefore, it is only necessary to suppress the eddy current at the location with higher current density. The eddy current is concentrated at the location with larger leakage flux, and most of it is located at the upper and lower sides of the strip. Therefore, the present invention considers blocking the eddy current loop in this part, that is, cutting the strip into several grooves in this part, thereby increasing the eddy current loop resistance, reducing the current density, and reducing the eddy current loss.

[0030] As a specific implementation method, the present invention takes into account both the computer solution speed and the actual production process when modeling. Figure 4 As shown in the figure, the width of the cutting groove in the main temperature rise area of ​​each layer of nanocrystalline ribbon is 4mm, the number of grooves on each side is 7, and they are symmetrically distributed along the 4th groove, and the distance between two adjacent grooves is 10°. In order to prevent the grooving from causing part of the nanocrystalline ribbon to fall off, the grooving does not penetrate the nanocrystalline ribbon, that is, the area with small eddy current loss in the middle of the leakage magnetic flux is retained. The width of this area is 10mm, and the cutting depth is 1 to 6 layers.

[0031] Taking the cutting depth of 1 layer as an example, the current density of the outermost strip is as follows: Figure 5 As shown, the value range is Figure 3 Same, compared Figure 3 The method proposed in the present invention can significantly reduce the current density, that is, the loss is significantly reduced.

[0032] The total eddy current loss of the leakage flux without slot cutting and slot cutting 1 to 6 layers are 643.54W, 528.65W, 443.92W, 371.01W, 319.67W, 282.67W, and 257.18W, respectively, and the leakage inductance is 20.42μH, 20.44μH, 20.48μH, 20.52μH, 20.55μH, 20.59μH, and 20.59μH, respectively. The present invention effectively reduces the eddy current loss of the leakage flux while ensuring that the leakage inductance is large enough. The eddy current loss of the leakage flux of each layer without slot cutting and slot cutting 1 to 6 layers is as follows Figure 6a , Figure 6b , the loss of the cut part is almost the same, but the more layers are cut, the greater the loss of the uncut part. But in general, the more grooves are cut, the lower the loss.

[0033] The simulation results show that the method proposed in the present invention can significantly reduce the core loss. In practical applications, sufficient and thin slots can be cut on the outer layers of the core to further suppress the generation of eddy currents. Figure 7 As shown. However, it should be noted that the area occupied by the slots should be as small as possible to prevent leakage flux from directly passing through the upper slots and directly affecting the lower strip; the slot depth should not be too deep to avoid reducing the relative magnetic permeability; the teeth left after slotting should not be too thin to avoid falling off. In general, the appropriate number of slots and layers should be selected according to the size of the core.

[0034] In summary, the present invention targets the eddy current loss of the nanocrystalline magnetic core leakage flux and is based on cutting grooves in the strip at the edge of the magnetic core. Under the premise of not significantly changing the volume and leakage inductance of the nanocrystalline high-frequency transformer, the eddy current loss of the magnetic core is effectively reduced and the energy conversion efficiency is improved.

[0035] The above-described embodiment only expresses one implementation method of the present application, and its description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present application, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of this application shall be based on the attached claims.

Claims

1. A method for optimizing the design of a nanocrystalline high-frequency transformer with low eddy current loss, characterized in that: Finite element simulation is used to determine the main temperature rise area of ​​a high-power nanocrystalline high-frequency transformer; a nanocrystalline strip is grooved in the main temperature rise area to block the eddy current circuit induced by the high-frequency leakage flux on the surface of the nanocrystalline strip, increase the equivalent resistance, and reduce the leakage flux eddy current loss; by changing different cutting layers, the finite element simulation is used to verify the inhibitory effect of cutting the outer nanocrystalline strip on the eddy current loss; the specific steps include: Step 1: Establish a model of a toroidal nanocrystalline high-frequency transformer with completely separated and transposed windings; Step 2: Model the 10 layers of nanocrystalline ribbons on the inner and outer sides of the magnetic core of the donut-shaped nanocrystalline high-frequency transformer using a set of concentric rings according to the actual thickness; Step 3: Input excitation to the primary side, that is, input a sinusoidal voltage source with an amplitude of 1000V at 40kHz, and connect a resistor to the secondary side to determine the distribution area of ​​the leakage flux eddy current loss induced by the high-frequency leakage flux on the surface of the nanocrystalline strip at the edge of the magnetic core. The distribution area is the main temperature rise area. The main temperature rise area is at the intersection of the two ends of the primary winding and the secondary winding, and is symmetrical up and down. The leakage flux eddy current loss on the upper and lower sides is much greater than the leakage flux eddy current loss in the middle. Step 4: cutting a plurality of grooves into the multilayer nanocrystalline ribbon at the edge of the magnetic core in the main temperature rise region; Step 5: Input the excitation as described in step 3 and observe the downward trend of leakage flux eddy current loss; Step 6: Expand the grooving range to cover the entire circumference of the nanocrystalline ribbon and increase the number of grooving to accommodate windings at different winding positions.

2. The method for optimizing the design of a low eddy current loss nanocrystalline high frequency transformer according to claim 1, characterized in that: During the operation of the annular nanocrystalline high-frequency transformer, leakage flux is distributed in the gap between the air and the nanocrystalline strip, and part of the leakage flux Bs passes vertically through the nanocrystalline strip to form leakage flux eddy current Js on the plane of the nanocrystalline strip.

3. The method for optimizing the design of a nanocrystalline high-frequency transformer with low eddy current loss according to claim 1, characterized in that: The outer diameter of the magnetic core of the annular nanocrystalline high-frequency transformer is 200 mm, the inner diameter is 120 mm, the height is 50 mm, the thickness of a single layer including interlayer insulation is 20 μm, and the stacking coefficient is 0.

8.

4. The method for optimizing the design of a low eddy current loss nanocrystalline high frequency transformer according to claim 3, characterized in that: In the step 2, finite element simulation modeling is used to draw 10 layers of nanocrystalline strips on both sides of the ring of the magnetic core of the ring-shaped nanocrystalline high-frequency transformer, with a thickness of 16 μm and an interlayer insulation thickness of 4 μm.

5. The method for optimizing the design of a nanocrystalline high-frequency transformer with low eddy current loss according to claim 1, characterized in that: In the step 4, finite element simulation modeling is used, the groove width in the main temperature rise area of ​​each layer of nanocrystalline strip is 4 mm, the number of grooves on the upper and lower sides of each side is 7 respectively, symmetrically distributed along the 4th groove, and the distance between two adjacent grooves is 10°; in order to prevent the groove from causing part of the nanocrystalline strip to fall off, the groove does not penetrate the nanocrystalline strip, that is, the area with smaller leakage flux eddy current loss in the middle is retained, the width of this area is 10 mm, and the cutting depth is 1 to 6 layers.

6. The method for optimizing the design of a nanocrystalline high-frequency transformer with low eddy current loss according to claim 1, characterized in that: The annular nanocrystalline high-frequency transformer is a single-phase transformer with a turns ratio of 12:

12. The primary winding and the secondary winding are completely separated and symmetrically wound on half of the magnetic core. Ignoring the high-frequency AC loss of the winding, the winding cross-section is a 4mm*4mm rectangle, and the winding axis is 6mm away from the magnetic core.

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