A low-loss planar transformer winding structure and converter

Abstract

The present invention discloses a low-loss planar transformer winding structure and a converter, which includes a transformer core and windings wrapped inside the transformer core. The windings include five layers of primary windings and four layers of secondary windings. From the top layer to the bottom layer, the first layer, the third layer, the fifth layer, the seventh layer, and the ninth layer are the primary windings, and the second layer, the fourth layer, the sixth layer, and the eighth layer are the secondary windings. An insulating layer is disposed in a fitting manner between each layer of the primary windings and each layer of the secondary windings; the first layer, the fifth layer, and the ninth layer of the primary windings are connected in parallel, the third layer and the seventh layer of the primary windings are connected in parallel, and the second layer, the fourth layer, the sixth layer, and the eighth layer of the secondary windings are connected in parallel. The present invention fully suppresses the skin effect and the proximity effect at high frequencies and reduces the loss of the planar transformer.

Description

Technical Field

[0001] The present invention belongs to the field of switching power supplies, and particularly relates to a low-loss planar transformer winding structure and a converter. Background Art

[0002] In the field of switching power supplies, high efficiency and high power density have always been the goals pursued by converters. Traditional converters use vertical windings as inductors or transformers, but the vertical winding type has a large volume. Using a printed circuit board (PCB) as the inductor or transformer winding can greatly reduce the volume of the magnetic component. However, using a PCB winding type, that is, a planar magnetic component, will bring higher losses to the converter. For isolated converters, planar transformers will generate a large amount of losses. Especially under high turns ratio and high current power conditions, the losses of planar transformers may be close to or even exceed half of the total losses.

[0003] To reduce the losses of planar transformers, one method is to use a matrix transformer. Essentially, a matrix transformer obtains more parallel windings by increasing the volume of the transformer, thereby achieving a smaller AC resistance of the winding to reduce copper losses. In addition, since the volume of the magnetic core is increased and the magnetic fluxes partially cancel each other out, the iron losses can also be reduced. However, using a matrix transformer will increase the difficulty of circuit board layout. If there are a large number of parallel windings, additional connection terminals may be required to achieve connections such as signals, power supplies, and power, thereby reducing the power density and integration of the converter. Another method is to directly use multi-layer windings in parallel to reduce copper losses. Since only the number of layers of the PCB is increased, the overall volume of the converter hardly changes, and copper losses can be reduced while keeping the iron losses and power density unchanged.

[0004] However, when multi-layer windings are in parallel, the skin effect and proximity effect at high frequencies become non-negligible. The influence of the magnetic field of the winding itself and the magnetic field of adjacent windings makes the AC resistance much larger than that in DC. To fully utilize the benefits of multi-layer windings in parallel, it is necessary to suppress the skin effect and proximity effect as much as possible to reduce the copper losses of the winding. In the existing transformer structures, most of them design the number of layers of the primary and secondary windings to be equal and fully interleave them. Although the fully interleaved structure has a weaker proximity effect and lower overall copper losses compared to the non-interleaved structure, according to the winding AC loss model, this structure does not achieve the lowest AC resistance, and there is still room for further reduction of the AC resistance. How to construct a winding structure that achieves the lowest AC resistance has become the key to reducing the losses of transformer windings. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the present invention provides a low-loss planar transformer winding structure and a converter, which fully suppress the skin effect and proximity effect at high frequencies and reduce the losses of planar transformers.

[0006] To solve the above technical problems, the present invention is realized through the following technical solutions:

[0007] A low-loss planar transformer winding structure includes a transformer core and a winding wrapped inside the transformer core. The winding includes five primary windings and four secondary windings. From the top layer to the bottom layer, the first layer, the third layer, the fifth layer, the seventh layer, and the ninth layer are the primary windings, and the second layer, the fourth layer, the sixth layer, and the eighth layer are the secondary windings. An insulating layer is disposed in contact between each primary winding and each secondary winding; the first layer, the fifth layer, and the ninth layer of primary windings are connected in parallel, the third layer and the seventh layer of primary windings are connected in parallel, and the second layer, the fourth layer, the sixth layer, and the eighth layer of secondary windings are connected in parallel.

[0008] Further, the thickness of the first layer and the ninth layer of primary windings is h1, and the thicknesses of the third layer, the fifth layer, and the seventh layer of primary windings and the second layer, the fourth layer, the sixth layer, and the eighth layer of secondary windings are h2, where:

[0009] h1 = 1.57δ

[0010] h2 = 3.14δ

[0011] In the formula, δ is the skin depth of the current in the winding when the transformer is working.

[0012] Further, the winding is a PCB winding. The first layer, the fifth layer, and the ninth layer of primary windings are connected in parallel through vias, the third layer and the seventh layer of primary windings are connected in parallel through vias, and the second layer, the fourth layer, the sixth layer, and the eighth layer of secondary windings are connected in parallel through vias.

[0013] Further, the difference between the window width of the transformer core and the width of the winding is not greater than 0.5 mm.

[0014] Further, the transformer core is made of ferrite material.

[0015] Further, the primary winding and the secondary winding are made of copper material.

[0016] Further, the transformer turns ratio is 2:1.

[0017] A converter includes the low-loss planar transformer winding structure described above.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects:

[0019] A low-loss planar transformer winding structure disclosed by the present invention, by designing the parallel connection of the primary windings on the first layer, the fifth layer and the ninth layer, the parallel connection of the primary windings on the third layer and the seventh layer, and the parallel connection of the secondary windings on the second layer, the fourth layer, the sixth layer and the eighth layer, a current of 0.5 unit is generated on the primary windings of the first layer and the last layer, and a current of 1 unit is generated on the remaining layers. By using the overlap of the primary and secondary windings, a magnetomotive force of up to 0.5 unit and a proximity effect factor of 0.5 are constructed on all intermediate layer windings, so as to fully suppress the skin effect and proximity effect of the intermediate layer windings. The transformer winding structure proposed by the present invention can fully suppress the proximity effect and skin effect suffered by the intermediate layer windings, realizing the lowest loss of the intermediate layer windings and the extremely low loss of the overall transformer windings.

[0020] Furthermore, the present invention realizes the minimum AC resistance of all intermediate layers and the extremely low loss of the overall transformer windings by controlling the thickness of the winding layers.

[0021] In order to make the above objects, features and advantages of the present invention more obvious and understandable, the following specifically enumerates preferred embodiments and, in conjunction with the accompanying drawings, makes a detailed description as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the specific embodiments of the present invention, the following will briefly introduce the drawings required for use in the description of the specific embodiments. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0023] Figure 1 is a schematic diagram of a low-loss planar transformer winding structure of the present invention;

[0024] Figure 2 is a sectional view of a low-loss planar transformer winding structure of the present invention;

[0025] Figure 3 is a comparison diagram of current distribution and magnetic field intensity between a low-loss planar transformer winding structure of the present invention and a traditional transformer winding structure;

[0026] Figure 4 is a comparison diagram of the winding losses of each layer between a low-loss planar transformer winding structure of the present invention and a traditional transformer winding structure;

[0027] Figure 5 is a diagram of the relationship between the magnetomotive force and current of each layer of a low-loss planar transformer winding structure of the present invention.

[0028] In the figure: 1 - transformer core; 2 - winding; 201 - primary winding; 202 - secondary winding; 203 - insulating layer; 3 - via hole. Detailed implementation manners

[0029] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] As a specific implementation manner of the present invention, as Figure 1 and Figure 2 shown, a low-loss planar transformer winding structure includes a transformer core 1 and a winding 2 wrapped inside the transformer core 1. The winding 2 includes five layers of primary windings 201 and four layers of secondary windings 202. Specifically, from the top layer to the bottom layer, the first layer, the third layer, the fifth layer, the seventh layer and the ninth layer are the primary windings 201, and the second layer, the fourth layer, the sixth layer and the eighth layer are the secondary windings 202. An insulating layer 203 is disposed between each layer of primary winding 201 and each layer of secondary winding 202 in a fitting manner.

[0031] The primary windings 201 of the first layer, the fifth layer and the ninth layer are connected in parallel to form the first-turn primary winding; the primary windings 201 of the third layer and the seventh layer are connected in parallel to form the second-turn primary winding; the secondary windings 202 of the second layer, the fourth layer, the sixth layer and the eighth layer are connected in parallel to form the first-turn secondary winding. The transformer turns ratio of the planar transformer winding structure of the present invention is 2:1.

[0032] Preferably, the winding 2 is a PCB winding. The primary windings 201 of the first layer, the fifth layer and the ninth layer are connected in parallel through vias 3, the primary windings 201 of the third layer and the seventh layer are connected in parallel through vias 3, and the secondary windings 202 of the second layer, the fourth layer, the sixth layer and the eighth layer are connected in parallel through vias 3.

[0033] As Figure 2 shown, in the present invention, the winding is wrapped inside the transformer core, and within the plane of the transformer core window, the winding width w2 should be filled as much as possible to be close to the transformer core window width w1 to ensure that the magnetic field in the space where the winding is located only exists in the horizontal direction. Preferably, the difference between the window width of the transformer core 1 and the width of the winding 2 is not greater than 0.5 mm.

[0034] As Figure 2 shown, in the present invention, the thickness of the primary windings 201 of the first layer and the ninth layer is denoted as h1, and the thicknesses of the primary windings 201 of the third layer, the fifth layer and the seventh layer and the secondary windings 202 of the second layer, the fourth layer, the sixth layer and the eighth layer are denoted as h2. Then:

[0035] h1 = 1.57δ

[0036] h2 = 3.14δ

[0037] Wherein, δ is the skin depth of the current in the winding during the operation of the transformer.

[0038] In the present invention, the transformer core 1 is made of ferrite, and the primary winding 201 and the secondary winding 202 are made of copper.

[0039] The technical solution of the present invention will be analyzed and described in more detail below in combination with simulation examples.

[0040] Figure 3 It shows the comparison of the current distribution and the magnetic field strength distribution on the marked imaginary axis of the transformer winding structure proposed by the present invention and the traditional transformer winding structure at 1 MHz in the COMSOL electromagnetic field simulation. The amplitude of the primary current is 1 A, the amplitude of the secondary current is 2 A, and the skin depth is 66 μm at 1 MHz. Figure 3 Among them, (a) is the current distribution of the traditional transformer winding structure, and the copper thickness of each layer of the winding is 207 μm. (c) is the current distribution of the transformer winding structure proposed by the present invention. The copper thickness of the top and bottom windings is 104 μm, and the copper thickness of the middle layer winding is 207 μm. Compared with the traditional transformer winding structure, the transformer winding structure proposed by the present invention is less affected by the skin effect and the proximity effect, so the current distribution is more uniform and the loss is lower. Figure 3 Among them, (b) and (d) are the x-direction magnetic field strength distributions on the imaginary axis of the traditional transformer winding structure and the transformer winding structure proposed by the present invention respectively. The magnetic field strength distribution further verifies that the transformer winding structure proposed by the present invention reduces losses by reducing the skin effect and the proximity effect. The maximum magnetic field strength of the transformer winding structure proposed by the present invention is 1 / 2 of that of the traditional transformer winding structure. According to the Dowell model, the ratio of the AC resistance to the DC resistance under one-dimensional conditions is:

[0041]

[0042] Wherein, ξ = h / δ, m is a factor characterizing the degree of influence of the skin effect and the proximity effect on each layer of the primary and secondary windings, and is the ratio of the magnetic field strength below each layer of the primary and secondary windings to the change in the magnetic field strength above and below.

[0043]

[0044] For all layers of the traditional transformer winding structure, m = 1. For the transformer winding structure proposed by the present invention, m = 1 for the top and bottom layers, and m = 0.5 for the middle layer. When m = 0.5, the winding has the minimum AC resistance. Therefore, the transformer winding structure proposed by the present invention can fully suppress the proximity effect and the skin effect suffered by the middle layer winding, realizing the lowest loss of the middle layer winding and the extremely low loss of the overall transformer winding.

[0045] Figure 4 Among them, (a) further shows the copper thickness conditions of each layer of winding required by the transformer winding structure proposed by the present invention. The copper thickness for the winding to achieve the lowest AC resistance varies with the m value, where curve 1 corresponds to m = 1, curve 2 corresponds to m = 0.667, and curve 3 corresponds to m = 0.5. When m = 1, the winding can achieve the minimum loss at a copper thickness equal to 1.07 times the skin depth. When m = 0.5, the winding can achieve the minimum loss at a copper thickness equal to 3.14 times the skin depth, and when m = 0.5, the lowest loss is only about 1 / 2 of that when m = 1. Figure 4 Among them, (b) shows the comparison of the losses of each layer between the transformer winding structure proposed by the present invention and the traditional transformer winding structure in the above embodiment. The loss of the first layer of the transformer winding structure proposed by the present invention is only about 1 / 4 of that of the traditional transformer winding structure, the loss of the middle layer is only about 1 / 2 of the traditional structure, and the overall loss is only 0.48 of the traditional transformer winding structure. Therefore, it can be seen that the transformer winding structure proposed by the present invention has extremely small losses.

[0046] Figure 5 It shows the current and magnetomotive force distribution of each layer of winding. The first layer and the ninth layer have a current of 0.5 units, and the remaining layers have a current of 1 unit. The magnetomotive force of the primary winding of the first layer changes from 0 to 1 unit of magnetomotive force. The magnetomotive force of the secondary windings of the second, fourth, sixth, and eighth layers changes from 1 to -1 unit of magnetomotive force. The magnetomotive force of the primary windings of the third, fifth, and seventh layers changes from -1 to 1 unit of magnetomotive force. The magnetomotive force of the ninth layer of winding changes from -1 to 0 unit of magnetomotive force.

[0047] Finally, it should be noted that the above-described embodiments are only specific embodiments of the present invention, used to illustrate the technical solutions of the present invention, rather than limiting them. The protection scope of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that any person skilled in the art within the technical scope disclosed by the present invention can still modify the technical solutions recorded in the foregoing embodiments or can easily think of changes, or perform equivalent replacements for some of the technical features; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A low-loss planar transformer winding structure, characterized in that, It includes a transformer core (1) and windings (2) wrapped inside the transformer core (1). The windings (2) include five layers of primary windings (201) and four layers of secondary windings (202). Starting from the top layer to the bottom layer, the first layer, the third layer, the fifth layer, the seventh layer, and the ninth layer are the primary windings (201), and the second layer, the fourth layer, the sixth layer, and the eighth layer are the secondary windings (202). An insulating layer (203) is disposed in contact between each layer of the primary windings (201) and each layer of the secondary windings (202); the first layer, the fifth layer, and the ninth layer of the primary windings (201) are connected in parallel, the third layer and the seventh layer of the primary windings (201) are connected in parallel, and the second layer, the fourth layer, the sixth layer, and the eighth layer of the secondary windings (202) are connected in parallel; The thickness of the primary windings (201) of the first layer and the ninth layer is , and the thickness of the primary windings (201) of the third layer, the fifth layer and the seventh layer and the thickness of the secondary windings (202) of the second layer, the fourth layer, the sixth layer and the eighth layer are , where: Wherein, is the skin depth of the current in the winding during the operation of the transformer; The windings (2) are PCB windings. The first layer, the fifth layer, and the ninth layer of the primary windings (201) are connected in parallel through vias (3), the third layer and the seventh layer of the primary windings (201) are connected in parallel through vias, and the second layer, the fourth layer, the sixth layer, and the eighth layer of the secondary windings (202) are connected in parallel through vias.

2. The low-loss planar transformer winding structure according to claim 1, wherein The difference between the window width of the transformer core (1) and the width of the windings (2) is not greater than 0.5 mm.

3. A low-loss planar transformer winding structure according to claim 1, characterized in that, The transformer core (1) is made of ferrite material.

4. A low-loss planar transformer winding structure according to claim 1, characterized in that The primary windings (201) and the secondary windings (202) are made of copper material.

5. A low-loss planar transformer winding structure according to claim 1, characterized in that, The transformer turns ratio is 2:

1.

6. A converter, characterized in that, It includes a low-loss planar transformer winding structure according to any one of claims 1 to 4.

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