Transformer with Controlled Leakage Inductance
The multi-leg transformer design addresses cooling and adaptability issues in transformers by incorporating magnetic shunt material to adjust leakage inductance, resulting in improved cooling efficiency and adaptability in high-power and LLC applications.
Patent Information
- Application Number
- JP2024562266
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-05-23
- Filing Date
- 2023-05-01
- Publication Date
- 2025-06-17
AI Technical Summary
Transformers face challenges such as cooling issues in high-power applications, size concerns related to core gaps and fringing flux in LLC applications, and leakage inductance affecting adaptability, which current technologies struggle to adequately address.
A multi-leg transformer design featuring a core with multiple center posts, primary and secondary coils wound around these posts, and magnetic shunt material strategically placed between the coils to adjust leakage inductance, thereby improving adaptability and reducing the need for additional inductors.
The multi-leg transformer design enhances cooling efficiency, particularly in high-power applications, and allows for precise adjustment of leakage inductance, improving adaptability and reducing the complexity of LLC converter circuits.
Smart Images
Figure 2025518447000001_ABST
Abstract
Description
Technical Field
[0001] <Cross - Reference to Related Applications> This application claims the benefit of priority under 35 U.S.C.§ 119(e) to U.S. Provisional Patent Application No. 63 / 344,819, filed on May 23, 2022, the content of which is incorporated herein by reference in its entirety.
[0002] <Technical Field> The disclosed concepts generally relate to electrical components, and more specifically to transformers.
Background Art
[0003] Transformers face many design challenges. When using high - power transformers, cooling is a concern. As another example, in transformers used for LLC applications, the size of the core gap and fringing flux are concerns. Further, the leakage inductance of a transformer affects the adaptability of the transformer in certain applications, and this is compensated by adding inductors.
[0004] There is room for improvement in transformers.
Summary of the Invention
[0005] According to one aspect of the disclosed concepts, a multi - leg transformer comprises a core having a plurality of center posts, a primary coil wound around at least one of those center posts, a secondary coil wound around at least one of those center posts and spaced apart from the primary coil, and at least one magnetic shunt material disposed in one or more selected areas between the primary coil and the secondary coil.
[0006] According to one aspect of the disclosed concept, a method of fabricating a multi-leg transformer includes providing a core having one or more core legs, a primary coil wound around at least one of the core legs, and a secondary coil wound around at least one of the core legs and spaced apart from the primary coil, determining a desired level of leakage inductance for the multi-leg transformer, and adjusting the multi-leg transformer to the desired level of leakage inductance by placing at least one magnetic shunt material in one or more selected areas between the primary coil and the secondary coil.
[0007] According to one aspect of the disclosed concept, a bobbin for a multi-leg transformer having a core with a plurality of center posts, a primary coil wound around at least one of the center posts, a secondary coil wound around at least one of the center posts and spaced apart from the primary coil, and at least one magnetic shunt material disposed in one or more selected regions between the primary coil and the secondary coil includes a plurality of center portions corresponding to the plurality of center posts, each center portion being configured to have a coil of the primary coil or the secondary coil wound around it, at least one insulating barrier disposed between two of the plurality of center posts and configured to provide insulation between coils of the primary coil or the secondary coil, and at least one capture feature configured to assist the primary coil or the secondary coil in maintaining its shape around the center post.
Brief Description of the Drawings
[0008] A complete understanding of the disclosed concept can be obtained from the following description of the preferred embodiments, read in conjunction with the accompanying drawings.
[0009]
Figure 1A
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Figure 5C
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Figure 6C
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Figure 6D
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Figure 7A
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Figure 7B
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Figure 7C
DETAILED DESCRIPTION OF THE INVENTION
[0028] As used herein, directional terms such as left, right, front, back, up, down, and their derivatives are related to the orientation of the illustrated elements and are not intended to limit the scope of the claims unless otherwise specified in the claims.
[0029] As used herein, the term "some" means one or an integer greater than one (i.e., a plurality).
[0030] Various views of a multi-leg transformer 10 according to an exemplary embodiment of the disclosed concept are shown in FIGS. 1A through 1D. FIGS. 2A and 2B are additional views including cross-sectional views of the multi-leg transformer 10, and FIGS. 3 and 4 are exploded views of the multi-leg transformer 10.
[0031] The multi-leg transformer 10 includes an upper core 20 and a lower core 22, an upper bobbin portion 30 and a lower bobbin portion 32, a primary coil 40 and a secondary coil 42, and a shunt material 50. FIGS. 5A through 5D are additional views of the lower core 22, FIGS. 6A through 6D are additional views of the upper bobbin portion 30, and FIGS. 7A through 7C are additional views of the primary coil 40. It will be understood that the upper core 20 and the lower core 22 may be the same or similar, the upper bobbin portion 30 and the lower bobbin portion 32 may be the same or similar, and the primary coil 40 and the secondary coil 42 may be the same or similar.
[0032] In an exemplary embodiment of the multi-legged transformer 10, the upper core 20 and the lower core 22 constitute a multi-leg e-e or e-I core type structure having a plurality of center posts 24, 25, 26 and outer posts 27, 28 (shown in FIGS. 5A to 5D). However, it will be understood that cores having any number of two or more cores or center posts may be used. Also, it will be understood that the center posts 24, 25, 26 may have any shape, for example, but not limited to, circular, square, elliptical, rectangular, or other shapes without departing from the scope of the disclosed concept. The primary coil 40 is wound around the center post of the upper core 20, and the secondary coil 42 is wound around the center post of the lower core 22. However, it will be understood that the primary coil 40 and the secondary coil 42 may be exchanged without departing from the scope of the disclosed concept. Also, it will be understood that the primary coil 40 and the secondary coil 42 may be wound around any number of center posts or outer posts without departing from the scope of the disclosed concept. The upper bobbin portion 30 and the lower bobbin portion 32 are configured to facilitate winding and arranging the primary coil 40 and the secondary coil 42 around their corresponding core posts.
[0033] In an exemplary embodiment, the multi-leg transformer 10 is configured such that the primary coil 40 and the secondary coil 42 are spaced-apart flat windings. However, it will be understood that the windings of the primary coil 40 and the secondary coil 42 may be changed without departing from the scope of the disclosed concept. For example, but not limited to, the windings may be single-layer or multi-layer. The primary coil 40 and / or the secondary coil 42 may each have a single or multiple windings. In embodiments having multiple windings, those windings may be connected in series or in parallel to add design flexibility. Further, each winding may be any of various conductor styles, such as, for example, but not limited to, copper foil, litz wire, or other suitable conductor styles. Also, it will be understood that the windings may be single-strand or multi-strand without departing from the scope of the disclosed concept. In an exemplary embodiment of the disclosed concept, the shunt material 50 may be disposed in a selected portion of the space between the primary coil 40 and the secondary coil 42. The shunt material 50 may be, for example, but not limited to, a magnetic shunt material such as a ferrite material or a powdered iron alloy. In some exemplary embodiments, the shunt material 50 may be a plate of material. The selected portion where the shunt material 50 is disposed may be selected to adjust the characteristics of the multi-leg transformer 10 such as leakage inductance. That is, the shunt material 50 may be disposed in a volume that is larger or smaller than the volume between the primary coil 40 and the secondary coil 42 to adjust the leakage inductance of the multi-leg transformer 10 to a desired level. Adjustment of the leakage inductance is useful, for example, but not limited to, in transformer applications such as transformers used in LLC converters. Further, the ability to adjust the leakage inductance through the shunt material 50 obviates the need for a separate resonant inductor to control the leakage inductance element within the LLC circuit.
[0034] In some exemplary embodiments, the multi-leg transformer 10 is, for example, thin with short core legs and flat windings. Its low profile allows for better cooling, for example, by providing a larger core surface area for better cold plate cooling. The improved cooling is useful in high-power applications. In some exemplary embodiments, the multi-leg transformer 10 may be used, for example but not limited to, at 1 to 22 kW, and in some exemplary embodiments may be used in 4 to 7 kW applications. In some exemplary embodiments, the multi-leg transformer 10 may be used in an LLC converter, but the multi-leg transformer 10 may be used in other applications, such as but not limited to battery charging applications, and it will be understood that it may also be used as a distribution transformer for stepping down voltage in large-scale server applications.
[0035] In some exemplary embodiments, the gap between the core legs is made as small as possible so that the fringing flux is limited to a region with less fringing flux, allowing only limited interaction with the windings of the primary coil 40 and the secondary coil 42.
[0036] In some exemplary embodiments, the windings of the primary coil 40 and the secondary coil 42 are, for example but not limited to, flat windings of single wire or Litz wire. In some exemplary embodiments, the flat windings minimize proximity effect losses and allow for good coupling between the primary coil 40 and the secondary coil 42. The windings may be made in series, and the windings around the core legs and the adjacent windings around the adjacent core legs may have currents flowing in the same direction as indicated by the arrows showing the current flow in FIG. 7B. Currents flowing in the same direction in adjacent windings cancel out the magnetic flux generated by the currents. In an exemplary embodiment, to facilitate the adjacent windings having currents flowing in the same direction, the transition from one winding to the adjacent winding has a wire that proceeds from the outer edge of one winding to the inner edge of the adjacent winding, as shown, for example, in FIG. 7B. In some exemplary embodiments, to facilitate insulation of the winding transition and prevent short circuits under high voltage conditions, the bobbin may include features for wiring the wires to insulate from each other at the transition from one winding to another.
[0037] It will be understood that in some exemplary embodiments, the primary coil 40 and the secondary coil 42 may be wound in the same way, but they may be wound differently. It will be understood that the primary coil 40 and the secondary coil 42 may have the same or different number of turns. The primary coil 40 and the secondary coil 42 may be configured in a matrix such that the windings around each post can be connected in series or in parallel depending on the voltage and current requirements. In some exemplary embodiments, the primary coil 40 and the secondary coil 42 may be further configured as tapped windings to allow for the use of switching devices with lower voltage ratings. In some exemplary embodiments, the primary coil 40 and the secondary coil 42 may be shaped to better facilitate heat transfer and increase voltage insulation, or they may not be shaped in such a way.
[0038] It will be understood that the bobbin may be formed from any number of parts without departing from the scope of the disclosed concept. For example, in an exemplary embodiment, an upper bobbin portion 30 and a lower bobbin portion 32 are shown, but it will be understood that the upper bobbin portion 30 and the lower bobbin portion 32 may be combined or divided into any number of bobbin parts in various ways. Each of the upper bobbin portion 30 and the lower bobbin portion 32 includes a center portion corresponding to the center posts 24, 25, 26. Each of the primary coil 40 and the secondary coil 42 is wound around one of the center portions.
[0039] In some exemplary embodiments, the upper bobbin portion 30 and the lower bobbin portion 32 may include one or more capture features that assist in keeping the primary coil 40 and the secondary coil 42 flat and substantially helically around each of the posts. An example of the capture feature 34 is shown in FIG. 6C. The capture feature 34 may be, for example, but not limited to, a formed notch.
[0040] In some exemplary embodiments, the upper bobbin portion 30 and the lower bobbin portion 32 may further include an insulating barrier between the center coils, which can increase the insulation voltage of the outermost turns of each coil.
[0041] In some exemplary embodiments of the disclosed concept, the thickness, width, and / or length of the shunt material 50 may be changed to adjust the leakage inductance of the multi-legged transformer 10. The shunt material 50 may be disposed in any or all of the spaces between the center posts of the core and / or between the outer legs of the core.
[0042] Although specific embodiments of the disclosed concept have been described in detail, it will be understood by those skilled in the art that various modifications and alternatives to those details may be developed in light of the overall teachings of the present disclosure. Accordingly, the specific configurations disclosed are merely exemplary and do not limit the scope of the disclosed concept to be given by the full scope of the appended claims and their equivalents.
Claims
1. A multi-leg transformer (10), comprising a core (20, 22) having a plurality of center posts (24, 25, 26); a primary coil (40) wound around at least one of the plurality of center posts (24, 25, 26); a secondary coil (42) wound around at least one of the plurality of center posts (24, 25, 26) and spaced apart from the primary coil (40); and at least one magnetic shunt material (50) disposed in one or more selected regions between the primary coil (40) and the secondary coil (42).
2. The multi-leg transformer according to claim 1, wherein the at least one magnetic shunt material (50) comprises a plurality of pieces of magnetic shunt material.
3. The multi-leg transformer according to claim 2, wherein the plurality of pieces of the plurality of shunt materials comprise different types of magnetic shunt materials.
4. The multi-leg transformer according to claim 1, wherein the at least one magnetic shunt material (50) is composed of at least one of a ferrite material and an iron alloy.
5. The multi-leg transformer according to claim 1, wherein one or more selected regions are selected to adjust the leakage inductance of the multi-leg transformer.
6. The multi-leg transformer according to claim 1, wherein the core (20, 22) is a core composed of a plurality of components.
7. The multi-leg transformer according to claim 6, wherein the core composed of a plurality of components includes an upper core (20) and a lower core (22), and one of the primary coil (40) and the secondary coil (42) is wound around the center posts (24, 25, 26) of the upper core (40), and the other of the primary coil (40) and the secondary coil (42) is wound around the center posts (24, 25, 26) of the lower core (22).
8. A first bobbin (30) configured to facilitate winding and placement of the primary coil (40); A second bobbin (32) configured to facilitate winding and placement of the secondary coil (42); The multi-legged transformer according to claim 1, comprising:
9. The multi-legged transformer according to claim 8, wherein at least one of the upper bobbin (30) and the lower bobbin (32) includes at least one capture feature (34) configured to assist in maintaining the shape of the primary coil (40) or the secondary coil (42) around the center posts (24, 25, 26).
10. The multi-legged transformer according to claim 8, wherein at least one of the upper bobbin (30) and the lower bobbin (32) includes an insulation barrier configured to provide insulation between coils of the primary coil (40) or the secondary coil (42).
11. The multi-legged transformer according to claim 1, wherein at least one of the primary coil (40) and the secondary coil (42) has a flat winding.
12. The multi-legged transformer according to claim 1, wherein at least one of the primary coil (40) and the secondary coil (42) has a winding configured such that a current flowing through a first winding around a first center post (24) and a current flowing through an adjacent winding around an adjacent second center post (25) are in the same direction.
13. The multi-legged transformer according to claim 1, wherein at least one of the primary coil (40) and the secondary coil (42) has a single-wire or Litz-wire winding.
14. A method of manufacturing a multi-legged transformer (10), comprising: One or more core legs, a primary coil (40) wound around at least one of the one or more core legs, and a secondary coil (42) wound around at least one of the one or more core legs and spaced apart from the primary coil, and preparing a core (20, 22) having the same; Determining a desired level of leakage inductance of the multi-leg transformer (10); Adjusting the multi-leg transformer (10) to a desired level of leakage inductance by disposing at least one magnetic shunt material (50) in one or more selected regions between the primary coil (40) and the secondary coil (42); A method comprising:
15. A bobbin (30, 32) for a multi-leg transformer (10), The multi-leg transformer (10) has a core (20, 22) having a plurality of center posts (24, 25, 26), a primary coil (40) wound around at least one of the center posts (24, 25, 26), and a secondary coil (42) wound around at least one of the center posts (24, 25, 26) and spaced apart from the primary coil (40), and at least one magnetic shunt material (50) disposed in one or more selected regions between the primary coil (40) and the secondary coil (42); The bobbin (30, 32) is A plurality of center portions corresponding to the plurality of center posts (24, 25, 26), each center portion being configured to have a coil of the primary coil (40) or the secondary coil (42) wound around it; At least one insulating barrier disposed between two of the plurality of center posts (24, 25, 26) and configured to provide insulation between coils of the primary coil (40) or the secondary coil (42); At least one capture feature (34) configured to assist the primary coil (40) or the secondary coil (42) in maintaining its shape around the plurality of center posts (24, 25, 26); A bobbin comprising the same.