Transformer structure for reducing eddy-current loss of fractional-turn LLC magnetic core

Abstract

The invention discloses a transformer structure for reducing eddy current loss of a fractional turn LLC magnetic core, which comprises a bottom plate, a central magnetic column is arranged on the bottom plate, four side magnetic columns are sequentially arranged on the outer side of the bottom plate along the circumferential direction, the four side magnetic columns are used as a loop of magnetic flux generated by the central magnetic column, the central magnetic column is elliptical, and the central magnetic column is cylindrical. A primary winding and a secondary winding are wound on the central magnetic column. The transformer structure is low in winding loss.

Description

Technical Field

[0001] This invention belongs to the field of transformer technology and relates to a transformer structure for reducing eddy current losses in fractional-turn LLC magnetic cores. Background Technology

[0002] Data centers are constantly seeking server power converters with more efficient power delivery and higher power density. LLC resonant converters, as DC-DC converters, have been extensively researched and applied. They possess unique advantages, enabling soft switching across the entire load range, including ZVS for the primary-side switch and ZCS for the synchronous rectifier. To address the issue of high winding losses in fractional-turn LLC transformers under heavy loads, MIT proposed a half-fractional-turn LLC transformer structure, such as... Figure 1 The principle is to divide the secondary winding into N equal segments, with each segment connected in parallel to the other end, sharing the magnetic flux generated by the primary winding. Each segment receives 1 / N of the primary magnetic flux, thus producing a fractional effect.

[0003] Fractional-turn transformers can be classified into half-turn, quarter-turn, etc., depending on the number of segments in the secondary winding. According to Faraday's law, the relationship between the cross-sectional area of ​​the transformer core and the number of segments in the secondary winding can be derived.

[0004] (1) in A e It is the cross-sectional area of ​​the magnetic core. N The number of segments in the secondary winding. B m It is the magnetic flux density in the magnetic core. f It is the operating frequency. When N When the value equals 1, this formula represents a traditional LLC transformer. It can be seen that when the magnetic flux density, frequency, and output voltage remain constant, the cross-sectional area of ​​a fractional-turn transformer is [a fraction of] that of a traditional transformer. N Eddy current loss is a part of the core loss; it is mainly caused by the current induced by the alternating magnetic field inside the core. Eddy current loss is proportional to the cross-sectional area of ​​the core.

[0005] (2) Where σ is the conductivity of the magnetic core. Combining equations (1) and (2), the cross-sectional area of ​​a fractional-turn transformer is [a fraction of] that of a conventional transformer. N Therefore, eddy current losses are also a factor of traditional transformers. NTherefore, fractional-turn transformers only focus on reducing winding losses, neglecting the improvement of core losses, which is detrimental to energy saving in data centers. Building upon previous work, this invention proposes a novel elliptical quarter-turn transformer structure. This structure significantly reduces eddy current losses in the core, alleviating the problem of high core losses in fractional-turn transformers and further improving converter efficiency.

[0006] CN109686538B discloses a transformer, comprising: a magnetic core, the magnetic core including: a first magnetic post and a second magnetic post; one end of the first magnetic post is coupled to one end of the second magnetic post, and the other end of the first magnetic post is coupled to the other end of the second magnetic post to form a ring; one or more sets of primary coils are wound on the first and second magnetic posts, the primary coils are connected to a primary switching circuit, and when the primary switching circuit supplies power to the primary coils, the coils form magnetic flux on the first and second magnetic posts, wherein the direction of the magnetic flux formed on the first and second magnetic posts is the same; secondary coils are wound on the first and second magnetic posts respectively; the secondary coils are used to induce current by sensing the magnetic flux on the first or second magnetic post, wherein the number of turns of the secondary coils is a fraction of turns. In this way, while reducing winding losses through fractional turns, the primary and secondary coils can be wound on both the first and second magnetic pillars. Furthermore, the primary coil can directly utilize the ring structure formed by the coupling of the first and second magnetic pillars to generate magnetic flux, facilitating the generation of induced current in the secondary coil. This structure provides a simpler magnetic pillar distribution structure for the core compared to existing technologies. In addition, the primary coil can be wound from any position on either the first or second magnetic pillar, avoiding excessively long ends compared to existing technologies and providing a better winding distribution and input / output channels. Moreover, the secondary coil is wound around the perimeter of each magnetic pillar, improving the utilization rate of the core window compared to existing technologies where the secondary coil is only wound on the central or two side magnetic pillars. Furthermore, since both the first and second magnetic pillars can simultaneously wind the primary and secondary coils, the problems of poor coupling and insufficient overlap that occur when the primary and secondary coils are wound on different magnetic pillars are avoided. It also avoids the problem of magnetic flux imbalance when the secondary coil is wound on the magnetic pillars on either side of the central magnetic pillar.

[0007] Because fractional-turn transformers have a relatively novel structure and differ slightly from traditional transformers in principle, there is no literature researching how to reduce core losses in fractional-turn transformers. However, there is literature researching methods for reducing core losses in traditional transformers, such as... Figure 2As shown. The literature [A. Nabih, F. Jin, R. Gadelrab, FC Lee and Q. Li, "Characterization and Mitigation of Dimensional Effects on Core Loss in High-Power High-Frequency Converters," in IEEE Transactions on Power Electronics, vol. 38, no. 11, pp. 14017-14036, Nov. 2023, doi: 10.1109 / TPEL.2023.3285633.] compares three structures that can reduce core loss: a hollow core structure, a laminated structure, and an elongated core structure. (a) is a hollow core. This is achieved by reducing the effective thickness of the core, thereby reducing the eddy current effect and minimizing the eddy current loss of the core. (b) is a laminated core, which is a structure in which multiple magnetic chips are bonded together by lamination. There are gaps between the magnetic chips, and these gaps act as significant resistors in the eddy current circuit, preventing the generation of eddy current effects. (c) To lengthen the magnetic core, eddy current losses are also reduced by decreasing the effective thickness of the core. The principle is similar to replacing copper wire windings with PCB windings in a transformer to reduce eddy current losses. The literature also provides loss simulation analysis for three structures, such as... Figure 3 As shown in the figure. To make the comparison more intuitive, the loss of a traditional circular magnetic core is used as a reference, allowing direct observation of the loss of each core structure. It can be seen from the figure that the laminated core exhibits the greatest reduction in eddy current loss. This is because it essentially blocks the path of eddy current flow. Theoretically, the finer the magnetic particles, the lower the eddy current loss. However, this structure is extremely difficult to manufacture, very expensive, and less reliable than a monolithic core. Secondly, the elongated core has the second lowest eddy current loss, boasting not only low eddy current loss but also excellent manufacturing process and cost. Considering both functionality and cost, the elongated core structure is the best way to reduce eddy current loss.

[0008] Transformer losses include core losses and winding losses. Core losses further include hysteresis losses and eddy current losses. Under heavy load conditions, winding losses dominate, while under light load conditions, core losses dominate. Figure 4 As shown. According to Faraday's law, the cross-sectional area of ​​a fractional-turn transformer is [a fraction of] the cross-sectional area of ​​a conventional transformer. N Therefore, eddy current losses are also a factor of traditional transformers. N The fractional-turn transformer focuses only on reducing winding losses, neglecting the increase in core losses, which is detrimental to energy conservation in data centers. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a transformer structure for reducing eddy current losses in fractional-turn LLC cores, which has lower winding losses.

[0010] To achieve the above objectives, the present invention discloses a transformer structure for reducing eddy current losses in fractional-turn LLC magnetic cores, comprising a base plate, a central magnetic column on the base plate, and four side magnetic columns arranged sequentially along the circumference on the outer side of the base plate, the four side magnetic columns serving as a loop for the magnetic flux generated by the central magnetic column, wherein the central magnetic column is elliptical in shape, and a primary winding and a secondary winding are wound on the central magnetic column.

[0011] Furthermore, the sum of the cross-sectional areas of the four side magnetic pillars is equal to the cross-sectional area of ​​the central magnetic pillar.

[0012] Furthermore, both the primary winding and the secondary winding are PCB windings.

[0013] Furthermore, the primary winding includes a first PCB winding and a second PCB winding, and the secondary winding includes a third PCB winding and a fourth PCB winding, wherein the third PCB winding, the first PCB winding, the second PCB winding and the fourth PCB winding are distributed sequentially from top to bottom.

[0014] Furthermore, the third PCB winding is divided into four winding segments, which are connected in parallel.

[0015] Furthermore, the fourth PCB winding is divided into four winding segments, wherein the four winding segments are connected in parallel.

[0016] Furthermore, both the first PCB winding and the second PCB winding include two turns, for a total of four turns.

[0017] Furthermore, the four-turn windings are connected in series.

[0018] Furthermore, the base plate has a rectangular structure.

[0019] Furthermore, four side magnetic pillars are respectively set at the four corners of the base plate.

[0020] The present invention has the following beneficial effects: In the transformer structure for reducing eddy current losses in fractional-turn LLC magnetic cores described in this invention, a central magnetic post is provided on the base plate, and four side magnetic posts are sequentially arranged circumferentially on the outer side of the base plate. These four side magnetic posts serve as the loop for the magnetic flux generated by the central magnetic post. The central magnetic post is elliptical in shape, and primary and secondary windings are wound on it, resulting in a thinner core and thus lower eddy current losses, thereby improving converter efficiency. It should be noted that this invention reduces the core thickness by ellipticalizing the traditional fractional-turn magnetic core. This is similar to the principle of replacing copper wire windings with PCB windings to reduce eddy current losses in windings; both methods weaken the eddy current effect and reduce eddy current losses by reducing the conductor thickness. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a structural diagram of a half-turn LLC converter and transformer. Figure 2 The diagrams show a comparison of magnetic core structures, where a is a traditional magnetic core structure; b is the structure of the central magnetic pillar 1; c is the structure of a multilayer magnetic core; and d is the structure of an elongated magnetic core. Figure 3 Simulation comparison of losses for different magnetic core structures; Figure 4 The diagrams show the loss distribution under different operating conditions: a) is the loss distribution under heavy load; b) is the loss distribution under light load. Figure 5 This is a diagram showing the distribution of the primary and secondary windings in this invention. Figure 6 This is a structural diagram of the central magnetic column 1 in this invention; Figure 7 The simulation comparison diagrams show the eddy current effect and loss in different magnetic cores. a represents a traditional magnetic core, and b represents the magnetic core of this application.

[0023] Among them, 1 is the central magnetic column, 2 is the side magnetic column, 3 is the first PCB winding, 4 is the second PCB winding, 5 is the third PCB winding, and 6 is the fourth PCB winding. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0026] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0027] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this invention generally indicates that the preceding and following objects have an "or" relationship.

[0028] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0029] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0031] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0032] refer to Figure 5 and Figure 6 The transformer structure for reducing eddy current losses in fractional-turn LLC magnetic cores according to the present invention includes a base plate, a central magnetic column 1 is provided on the base plate, and four side magnetic columns 2 are arranged sequentially along the circumference on the outer side of the base plate. The central magnetic column 1 is elliptical in shape, and a primary winding and a secondary winding are wound on the central magnetic column 1.

[0033] In this embodiment, the sum of the cross-sectional areas of the four side magnetic pillars 2 is equal to the cross-sectional area of ​​the central magnetic pillar 1, and the four side magnetic pillars 2 serve as the loop for the magnetic flux generated by the central magnetic pillar 1.

[0034] In this embodiment, both the primary winding and the secondary winding are PCB windings. Specifically, the primary winding includes a first PCB winding 3 and a second PCB winding 4, and the secondary winding includes a third PCB winding 5 and a fourth PCB winding 6. The third PCB winding 5, the first PCB winding 3, the second PCB winding 4 and the fourth PCB winding 6 are distributed from top to bottom.

[0035] In this embodiment, the third PCB winding 5 is divided into four winding segments, which are connected in parallel. The fourth PCB winding 6 is also divided into four winding segments, which are connected in parallel.

[0036] In this embodiment, both the first PCB winding 3 and the second PCB winding 4 include two turns of winding, for a total of four turns of winding, wherein the four turns of winding are connected in series.

[0037] In this embodiment, the base plate is a rectangular structure, and four side magnetic pillars 2 are respectively set at the four corners of the base plate.

[0038] It should be noted that this invention proposes a novel elliptical quarter-turn transformer structure, which significantly reduces eddy current losses in the core, alleviates the problem of high core losses in fractional-turn transformers, and further improves the efficiency of the converter, providing a reference method for reducing core losses in fractional-turn LLC transformers.

[0039] Simulation Experiment This experiment used Maxwell finite element simulation software to simulate the eddy current effect and eddy current loss of a traditional quarter-turn transformer core structure and the elliptical quarter-turn transformer core structure described in this invention. The simulation results are as follows: Figure 7 As shown. (Through) Figure 7 As can be seen, the traditional quarter-turn transformer core structure generates a severe eddy current effect in the central magnetic column 1, resulting in current accumulation. In contrast, the novel elliptical quarter-turn transformer core structure exhibits a uniform current distribution in the central magnetic column 1, and the current density is lower than that of the traditional structure, indicating that the eddy current effect is effectively suppressed. The eddy current loss of the novel elliptical quarter-turn transformer core structure is reduced by 0.93W, a reduction of 46.5%, compared to the traditional structure. This demonstrates the effectiveness of the proposed novel elliptical quarter-turn transformer core structure in reducing core eddy current losses.

[0040] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and disclosure of the invention. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the following claims.

[0041] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

[0042] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A transformer structure for reducing fractional-turn LLC magnetic core core-loss, characterized by, Includes a base plate, on which a central magnetic column (1) is provided, and four side magnetic columns (2) are arranged in sequence along the circumference on the outer side of the base plate. The four side magnetic columns (2) serve as the loop for the magnetic flux generated by the central magnetic column (1). The central magnetic column (1) is elliptical in shape, and a primary winding and a secondary winding are wound on the central magnetic column (1).

2. The transformer structure for reducing fractional-turn LLC magnetic core core-loss according to claim 1, characterized in that, The sum of the cross-sectional areas of the four side magnetic pillars (2) is equal to the cross-sectional area of ​​the central magnetic pillar (1).

3. The transformer structure for reducing fractional-turn LLC magnetic core core-loss according to claim 1, characterized in that, Both the primary and secondary windings are PCB windings.

4. The transformer structure for reducing fractional-turn LLC magnetic core core-loss according to claim 1, characterized in that, The primary winding includes a first PCB winding (3) and a second PCB winding (4), and the secondary winding includes a third PCB winding (5) and a fourth PCB winding (6), wherein the third PCB winding (5), the first PCB winding (3), the second PCB winding (4) and the fourth PCB winding (6) are distributed from top to bottom.

5. The transformer structure for reducing fractional-turn LLC magnetic core core-loss according to claim 1, characterized in that, The third PCB winding (5) is divided into four winding segments, which are connected in parallel.

6. The transformer structure for reducing fractional-turn LLC magnetic core core-loss according to claim 1, wherein, The fourth PCB winding (6) is divided into four winding segments, wherein the four winding segments are connected in parallel.

7. The transformer structure for reducing fractional-turn LLC magnetic core core-loss according to claim 1, characterized in that, The first PCB winding (3) and the second PCB winding (4) each include two turns of winding, for a total of four turns of winding.

8. The transformer structure for reducing the fractional-turn LLC magnetic core core-loss according to claim 7, characterized in that, The four turns of winding are connected in series.

9. The transformer structure for reducing a fractional-turn LLC magnetic core core-loss according to claim 1, characterized by, The base plate has a rectangular structure.

10. The transformer structure for reducing fractional-turn LLC magnetic core core-loss according to claim 9, characterized in that, Four side magnetic pillars (2) are respectively set at the four corners of the base plate.

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