Transformer and its applicable on-board charger DC-DC conversion device

Abstract

The present application provides a transformer and a DC-DC conversion device of an on-board charger suitable for the transformer. The transformer comprises a magnetic core, a winding area, a primary winding and a secondary winding. The magnetic core comprises a first cover plate, a second cover plate and a winding column, wherein the winding column is arranged between the first cover plate and the second cover plate. The winding area is arranged on the winding column and comprises a plurality of winding units. The primary winding is wound in part of the winding units to form a primary winding of the transformer, and the secondary winding is wound in another part of the winding units to form a secondary winding of the transformer. The primary winding and the secondary winding are at least partially interleaved in the plurality of winding units. The number of winding layers in each winding unit along the axial direction of the winding column is less than or equal to two.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, and in particular to a transformer and a DC-DC conversion device for a vehicle charger. BACKGROUND

[0002] With the continuous development of electric vehicle OBC (on-board charger) technology and the continuous progress of wide band gap switching devices, high frequency is one of the inevitable trends of development. The advantage of high frequency is to make the OBC module small and light. The volume and weight of the OBC module are mainly determined by the passive components (such as magnetic components, capacitors, etc.) and other mechanical components, so reducing the volume and weight of the passive components is crucial to the miniaturization and lightness of the OBC, and the increase of switching frequency can effectively reduce the volume and weight of inductors, transformers and capacitors within a certain range.

[0003] However, although the increase of switching frequency relatively reduces the size of magnetic components (such as inductors and transformers), it may also cause a certain degree of overall efficiency decline and heat dissipation difficulties. Furthermore, in order to further reduce the size and improve the efficiency, integrated magnetic components are often used, but the integration of components may make heat dissipation more difficult.

[0004] For example, LLC and Boost SRC are the most common DC-DC circuit topologies of OBC modules, and the resonant cavity of LLC and Boost SRC contains at least two magnetic components, i.e. resonant inductors and transformers. In the prior art, the following two design methods are mostly used for resonant inductors and transformers.

[0005] In the first method, as shown in Figure 1 , the traditional resonant inductor and transformer are independent in structure and can be packaged together. In the second method, as shown in Figure 2A and Figure 2B , the resonant inductor and transformer are integrated together by using a multi-slot structure, in which the resonant inductor and transformer share part of the magnetic circuit.

[0006] However, the volume and weight of the magnetic components in the first method are difficult to be further reduced, and the heat dissipation of the coils in the inner layer and the winding columns tightly wrapped by the coils is also difficult. As for the multi-slot structure of the second method, the surface area exposed to the heat dissipation material is small, so the heat dissipation is also relatively difficult. In addition, in the above two methods, for example, Figure 2B , the integrated magnetic components of the resonant inductor and transformer have multiple layers of coils along the axial direction in the winding area, for example, greater than or equal to 3 layers, and each layer has a large number of turns. The coils of each layer are tightly attached to each other, making it even more difficult for the innermost coil, the winding column and the magnetic core to dissipate heat.

[0007] In the prior art CN105869828B, etc., a multi-slot transformer including a plurality of winding spaces is disclosed. Heat generated by the coils is guided to the heat dissipation shell of the transformer and taken away by the refrigerant by filling a heat-conducting medium (such as heat-dissipating glue, etc.) in the winding space and in thermal contact with at least part of the coils. However, the integrated multi-slot transformer has many turns in its winding space, and the number of coil layers is also large. Its heat dissipation performance is one of its shortcomings, especially when the power and operating frequency of the OBC power supply are further improved. The arrangement of the winding will have an increasingly adverse effect on heat dissipation. Therefore, how to develop a transformer and its applicable vehicle-mounted charger DC-DC conversion device that can improve the above-mentioned known technology is a pressing need at present. SUMMARY

[0008] The purpose of the present application is to provide a transformer and its applicable vehicle-mounted charger DC-DC conversion device. Through the winding and arrangement of the primary coil and the secondary coil of the transformer in the present application, the volume and weight of the transformer can be effectively reduced while the high conversion efficiency of the OBC is taken into account, and the heat dissipation effect is significantly improved.

[0009] To achieve the above-mentioned purpose, the present application provides a transformer, which comprises a magnetic core, a winding area, a primary coil and a secondary coil. The magnetic core comprises a first cover plate, a second cover plate and a winding column, wherein the winding column is arranged between the first cover plate and the second cover plate. The winding area is arranged on the winding column and includes a plurality of winding units. The primary coil is wound in part of the winding units to form the primary winding of the transformer, and the secondary coil is wound in another part of the winding units to form the secondary winding of the transformer. The primary coil and the secondary coil are at least partially interleaved in the plurality of winding units. The number of winding layers in each winding unit along the axial direction of the winding column is less than or equal to two. The winding layout of less than or equal to two layers can significantly enhance the thermal contact and heat exchange between the coil and the heat dissipation material in each winding unit.

[0010] To achieve the above-mentioned purpose, the present application further provides a vehicle-mounted charger DC-DC conversion device applying the above-mentioned transformer, which comprises a primary circuit, the above-mentioned transformer and a secondary circuit. The primary circuit is used for receiving a first direct current voltage. The transformer includes a primary winding and a secondary winding which are magnetically coupled to each other, wherein the primary winding is electrically coupled to the primary circuit. The secondary circuit is electrically coupled to the secondary winding of the transformer and is used for outputting a second direct current voltage.

[0011] The transformer and the DC-DC conversion device of the vehicle charger suitable for the transformer provided by the application can effectively reduce the size of the transformer and strengthen heat dissipation while taking into account the high conversion efficiency of the OBC, and are especially suitable for high-frequency operation, such as but not limited to 400k-1MHz. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 and Figure 2A is a structural schematic view of a resonant cavity magnetic element in the prior art vehicle charger.

[0013] Figure 2B is a structural schematic view of the resonant cavity magnetic element in along the section OO' in Figure 2A

[0014] Figure 3A is a three-dimensional structural schematic view of the transformer of the first embodiment of the application.

[0015] Figure 3B and Figure 3C is a structural schematic view of the transformer in along the section AA' in Figure 3A

[0016] Figure 4A is a three-dimensional structural schematic view of the transformer of the second embodiment of the application.

[0017] Figure 4B and Figure 4C is a structural schematic view of the transformer in along the section BB' in Figure 4A

[0018] Figure 5A is a three-dimensional structural schematic view of the transformer of the variation of Figure 4A

[0019] Figure 5B is a structural schematic view of the transformer in along the section CC' in Figure 5A

[0020] Figure 6A is a three-dimensional structural schematic view of the transformer of the variation of Figure 4A

[0021] Figure 6B is a structural schematic view of the transformer in along the section DD' in Figure 6A

[0022] Figure 7A is a three-dimensional structural schematic view of the transformer of the variation of Figure 4A

[0023] Figure 7B is a three-dimensional structural schematic view of the transformer of the variation of Figure 7A ​​​​​​​​Fig. 1 is a perspective structural schematic view of a transformer according to an embodiment of the present application.

[0024] Figure 8A Fig. 2 is a structural schematic view of the transformer along a cross section EE' according to the embodiment of the present application. Figure 4A

[0025] Figure 8B Fig. 3 is a structural schematic view of the transformer along a cross section FF' according to the embodiment of the present application. Figure 8A

[0026] Figure 9 Fig. 4 is a perspective structural schematic view of a variation of the transformer according to the embodiment of the present application. Figure 10 Figure 4A Fig. 5 is a structural schematic view of the variation of the transformer along a cross section GG' according to the embodiment of the present application.

[0027] Reference signs are as follows:

[0028] 1: Transformer

[0029] 2: Magnetic core

[0030] 21: First cover plate

[0031] 22: Second cover plate

[0032] 23: Winding column

[0033] M: Axial direction

[0034] 11: Winding region

[0035] 12: Winding unit

[0036] 121: First winding unit

[0037] 122: Second winding unit

[0038] 123: Third winding unit

[0039] P: Primary coil

[0040] P1: First primary coil

[0041] P2: Second primary coil

[0042] P3: Third primary coil

[0043] S: Secondary coil

[0044] S1: First secondary coil

[0045] S2: Second secondary coil

[0046] S3: Third secondary coil

[0047] 3: Housing

[0048] 31: Side surface

[0049] ​​​32: Bottom

[0050] 33: Storage space

[0051] 4: Cover

[0052] 13: Winding skeleton

[0053] OO', AA', BB', CC', DD', EE', FF': Cross-sections Detailed Implementation

[0054] Some typical embodiments embodying the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can be varied in different ways without departing from the scope of the invention, and the descriptions and illustrations herein are for illustrative purposes only and not intended to limit the invention.

[0055] Figure 3A This is a three-dimensional structural diagram of the transformer according to the first embodiment of the present invention. Figure 3B and Figure 3C for Figure 3A A schematic diagram of the transformer along section AA'. (See diagram below.) Figure 3A , Figure 3B and Figure 3C As shown, the transformer 1 of the present invention includes a magnetic core 2, a winding region 11, a primary winding, and a secondary winding. The magnetic core 2 includes a first cover plate 21, a second cover plate 22, and a winding post 23, wherein the winding post 23 is disposed between the first cover plate 21 and the second cover plate 22. The winding region 11 is disposed on the winding post 23, and the winding region 11 includes three winding units 12, wherein the winding unit 12 can be regarded as a subspace in the winding region 11. The primary winding is wound in a portion of the winding units 12 to form the primary winding of the transformer 1, and the secondary winding is wound in another portion of the winding units 12 to form the secondary winding of the transformer 1. The number of winding layers in each winding unit 12 along the axial direction M of the winding post 23 is one layer. In some embodiments, the number of winding layers in the winding unit 12 along the axial direction M of the winding post 23 may also be two layers. In one embodiment, as Figure 7A and Figure 7B As shown, the first primary coil P1 and the third primary coil P3 both have two winding layers along the axial direction M of the winding post 23. In other words, the second winding unit 122 and the third winding unit 123 both have two winding layers along the axial direction M of the winding post 23. In another example, as... Figure 8A and Figure 8BAs shown, the second primary coil P2 has two winding layers along the axial direction M of the winding post 23. In other words, the first winding unit 121 for winding the second primary coil P2 has two winding layers along the axial direction M of the winding post 23. Furthermore, the present invention is not limited to this. Those skilled in the art can vary the number of winding layers in each winding unit 12 according to actual applications. However, the number of winding layers along the axial direction M of the winding post 23 in each winding unit 12 is less than or equal to two layers. Due to the special arrangement of the coil layers in the winding unit 12, the total heat generated in each winding unit 12 is reduced during operation, and each coil layer can exchange heat with the outside, increasing the heat exchange area. Therefore, the heat generated in each winding space coil can be effectively dissipated.

[0056] In one embodiment, the winding area includes multiple winding units. Figure 4A This is a three-dimensional structural diagram of the transformer according to the second embodiment of the present invention. Figure 4B and Figure 4C for Figure 4A A schematic diagram of the transformer along section BB', where... Figure 3A , Figure 3B and Figure 3C Components and parts with the same structure and function are represented by the same reference numerals, and therefore will not be described again here. See this embodiment. Figure 4B As shown, the winding region 11 has five winding units 12. However, the present invention is not limited thereto, and those skilled in the art can vary the number of winding units according to actual applications.

[0057] In one embodiment, the primary coil and the secondary coil are at least partially interleaved within all the plurality of winding units 12; in other words, the winding units 12 for winding the primary coil and the winding units 12 for winding the secondary coil are at least partially interleaved.

[0058] In some embodiments of this implementation, such as Figure 3B As shown, the multiple winding units 12 within the winding region 11 may include multiple first winding units 121 and a second winding unit 122. The primary coil includes a first primary coil P1 and a second primary coil P2. The first primary coil P1 is wound in the second winding unit 122 of the second winding space, and the second primary coil P2 is wound in the corresponding first winding unit 121 within the first winding space, forming a primary winding. The secondary coil S is wound in the corresponding first winding unit 121 within the first winding space, forming a secondary winding. For example, when viewed from the front... Figure 3B From the perspective of the first primary coil P1, the secondary coil S and the second primary coil P2 are wound sequentially from top to bottom in the corresponding winding unit 12.

[0059] In other embodiments, such as Figure 3CAs shown, the secondary winding includes a first secondary winding S1 and a second secondary winding S2. The first secondary winding S1 is wound in the second winding unit 122 of the second winding space, and the second secondary winding S2 is wound in the corresponding first winding unit 121 in the first winding space, forming a secondary winding. The primary winding P of the primary winding is wound in the corresponding first winding unit 121 in the first winding space, forming a primary winding. For example, when viewed from the front... Figure 3C From the perspective of the first secondary coil S1, the primary coil P and the second secondary coil S2 are wound sequentially from top to bottom in the corresponding winding unit 12.

[0060] In some embodiments, such as Figure 4B As shown, the multiple winding units 12 within the winding region 11 may include multiple first winding units 121, a second winding unit 122, and a third winding unit 123. The primary winding includes a first primary winding P1, a second primary winding P2, and a third primary winding P3. The first primary winding P1 and the third primary winding P3 are respectively wound in the second winding unit 122 of the second winding space and the third winding unit 123 of the third winding space. The second primary winding P2 is wound in the corresponding first winding unit 121 within the first winding space, forming a primary winding. Furthermore, the secondary winding includes a first secondary winding S1 and a second secondary winding S2. The first secondary winding S1 and the second secondary winding S2 are respectively wound in the corresponding first winding unit 121 within the first winding space, forming a secondary winding. Furthermore, the first winding unit 121 for winding the first secondary coil S1 and the first winding unit 121 for winding the second secondary coil S2 are respectively located on opposite sides of the first winding unit 121 for winding the second primary coil P2. For example, when viewed from the front... Figure 4B From the perspective of the first primary coil P1, the first secondary coil S1, the second primary coil P2, the second secondary coil S2, and the third primary coil P3 are wound sequentially from top to bottom in the corresponding winding unit 12.

[0061] In other embodiments, such as Figure 4CAs shown, the secondary side coils include a first secondary side coil S1, a second secondary side coil S2 and a third secondary side coil S3. The first secondary side coil S1 and the third secondary side coil S3 are wound in the second winding space second winding unit 122 and the third winding space third winding unit 123 respectively, and the second secondary side coil S2 is wound in the corresponding first winding unit 121 in the first winding space, forming a secondary winding. In addition, the primary side coils include a first primary side coil P1 and a second primary side coil P2, and the first primary side coil P1 and the second primary side coil P2 are wound in the corresponding first winding unit 121 in the first winding space, forming a primary winding. Furthermore, the first winding unit 121 for winding the first primary side coil P1 and the first winding unit 121 for winding the second primary side coil P2 are respectively located on the opposite sides of the first winding unit 121 for winding the second secondary side coil S2. For example, in the perspective view, the first secondary side coil S1, the first primary side coil P1, the second secondary side coil S2, the second primary side coil P2 and the third secondary side coil S3 are sequentially wound in the corresponding winding unit 12 from top to bottom. Figure 4C

[0062] The primary and secondary side coils of the transformer 1 are wound in the winding unit 12 to form the primary winding and the secondary winding. In particular, in the first winding unit 121, the interlaced winding of part of the primary side coils and the secondary side coils or part of the secondary side coils and the primary side coils can realize the strong coupling between the primary winding and the secondary winding in the first winding unit 121, so as to reduce the loss of the transformer and obtain good conversion efficiency in the high frequency working environment. However, the present application is not limited thereto, and the arrangement order of the primary side coils and the secondary side coils wound in the winding unit 12 can be changed according to actual needs by those skilled in the art.

[0063] In an embodiment, a plurality of first winding units form a first winding space, and a second winding unit forms a second winding space. Any two adjacent first winding units have a first spacing, and the maximum spacing between any two adjacent first winding units is a first spacing. The second winding space and the first winding space have a second spacing, and the second spacing is greater than the first spacing.

[0064] In the present embodiment, as shown in Figure 3A , Figure 3B and Figure 3C , in the first embodiment, the winding unit 12 includes two first winding units 121 and one second winding unit 122, wherein all the first winding units 121 form a first winding space, and the second winding unit 122 forms a second winding space. Any two adjacent first winding units 121 have a first spacing, and the second winding space and the first winding space have a second spacing, and the second spacing is greater than the first spacing. ​

[0065] In the second embodiment shown in Figure 4A , Figure 4B and Figure 4C , the winding unit 12 of the transformer 1 further comprises a third winding unit 123. The third winding unit 123 forms a third winding space, and the second winding space and the third winding space are respectively located on the opposite sides of the first winding space. The third winding space has a third spacing with the first winding space, wherein the second spacing is less than or equal to the third spacing.

[0066] In addition, preferably, when the ratio of the second spacing to the first spacing is greater than or equal to 3, better leakage inductance, i.e. the integration effect of the resonance inductance in the transformer, and further enhanced heat dissipation effect of the winding can be obtained. The first spacing may, for example but not limited to, be any value between 0.01mm and 2mm, and the second spacing may, for example but not limited to, be greater than or equal to 4.5mm. However, the present application is not limited thereto, and the first spacing and the second spacing can be changed according to actual needs by those skilled in the art.

[0067] In addition, in the embodiments shown in Figure 4B , the turn ratio of the first primary coil P1, the second primary coil P2 and the third primary coil P3 is 5:2:5, i.e. the number of turns of the first primary coil P1 and the third primary coil P3 is equal. However, in practice, it is not limited thereto, and those skilled in the art can change the number of turns of the coils in each winding unit according to actual needs. For example, in the embodiments shown in Figure 5A and Figure 5B , the turn ratio of the first primary coil P1, the second primary coil P2 and the third primary coil P3 is 4:4:4, i.e. the number of turns of the first primary coil P1, the second primary coil P2 and the third primary coil P3 is equal. In addition, for example, in the embodiments shown in Figure 6A and Figure 6B , the turn ratio of the first primary coil P1, the second primary coil P2 and the third primary coil P3 is 3:5:4, i.e. the number of turns of the first primary coil P1, the second primary coil P2 and the third primary coil P3 is not equal. However, the number of turns of the primary and secondary coils in each winding unit is not limited thereto in practice, and those skilled in the art can also change the number of turns of the secondary winding in each winding unit according to actual needs.

[0068] In addition, in the present embodiment, since the second spacing can be used to provide the leakage inductance of the transformer 1 as the main part of the resonance inductance, there is a certain relationship between the ratio of the second spacing to the first spacing and the turn ratio of each primary coil (or secondary winding). In Figure 6BIn the illustrated embodiment, the turns ratio of the primary winding to the secondary winding is 12:10, and the turns ratio of the first primary coil P1, the second primary coil P2, and the third primary coil P3 is 3:5:4. If the third spacing is set to be equal to or approximately equal to the second spacing, the ratio of the second spacing to the first spacing needs to be 9 / 1 to obtain the desired leakage inductance of the transformer 1. In the embodiments shown in Figure 5B and Figure 4B the ratio of the second spacing to the first spacing is set to be 7 / 1 and 5 / 1, respectively, to obtain the same leakage inductance of the transformer 1. In the following, the case where the number of turns of the first primary coil P1 and the third primary coil P3 is equal is taken as an example, and the relationship between the leakage inductance of the transformer 1 and the first spacing, the second spacing, and the number of turns of the primary coil is shown as follows:

[0069]

[0070] where L is the leakage inductance of the transformer 1, A is the window area of L, L is the window width of L, A is the second spacing, B is the first spacing, X is the length of the coil in the axial direction M of the winding post 23, N is the number of turns of the first primary coil P1 or the third primary coil P3, and N is the number of turns of the second primary coil P2. k e k g k px pz

[0071] In addition, in the embodiments shown in Figure 4B , Figure 5B and Figure 6B the turns ratio of the primary winding to the secondary winding is 12:10, and in the embodiment shown in Figure 7B the turns ratio of the primary winding to the secondary winding is 24:10. The turns ratio of the transformer is not limited thereto, and can be changed according to actual needs by those skilled in the art, and in other embodiments can also be any engineering required turns ratio.

[0072] In an embodiment, as shown in Figure 9 the transformer 1 further comprises a housing 3, wherein the housing 3 has at least one side surface 31 and a bottom surface 32. The side surface 31 stands on the bottom surface 32 and forms a containing space 33 together with the bottom surface 32. The magnetic core 2, the primary winding, and the secondary winding of the transformer 1 are located in the containing space 33. In some embodiments, the transformer 1 further comprises a cover 4, which is configured to seal the magnetic core 2, the primary winding, and the secondary winding in the containing space 33 by being coupled with the housing 3.

[0073] ​​​​​​​In some embodiments of this implementation, the transformer 1 further includes a heat dissipation material, wherein the heat dissipation material is at least partially filled in the accommodating space 33, and further, the heat dissipation material is filled in the spaces corresponding to the first spacing, the second spacing (and the third spacing), and the heat dissipation material is at least partially in thermal contact with the primary winding, the secondary winding and the magnetic core, thereby dissipating the heat generated by the primary winding, the secondary winding and the magnetic core of the transformer.

[0074] In some embodiments of this implementation, the transformer 1 further includes a winding bobbin 13. Figure 4A and Figure 4B For example, the winding frame 13 has a hollow channel and multiple slots. The hollow channel is structured to accommodate the winding post 23, so that the winding frame 13 is fitted onto the winding post 23. The multiple slots of the winding frame 13 form various winding units 12 for winding corresponding coils. Heat dissipation material is filled within the accommodating space 33, including the areas corresponding to the first, second, and third spacings, and within the winding units 12, and is at least partially in thermal contact with the coils and magnetic cores wound in the winding units 12. However, in some other embodiments, the transformer 1 may not include the winding frame 13, such as... Figure 10 exemplify Figure 4A The three-dimensional structure of transformer 1 when the winding bobbin 13 is omitted. Figure 10 In the illustrated embodiment, the coil can be supported and fixed by a heat-dissipating material (e.g., thermal adhesive) and disposed on the winding post 23, respectively, so as to be located in the corresponding winding unit 12. In practice, the method of supporting and fixing the coil and the heat-dissipating material are not limited thereto, and those skilled in the art can also make changes according to actual needs.

[0075] The transformer 1 of the present invention is applicable to a DC-DC converter (not shown) for an on-board charger. The DC-DC converter includes a primary circuit, a transformer 1, and a secondary circuit. The primary circuit receives a first DC voltage. The transformer 1 includes a primary winding and a secondary winding magnetically coupled to each other, wherein the primary winding is electrically coupled to the primary circuit, and the transformer 1 can be any of the transformers shown in the foregoing embodiments. The secondary circuit is electrically coupled to the secondary winding of the transformer 1 and outputs a second DC voltage.

[0076] When the on-board charger operates under single-phase AC power supply conditions, taking a nominal DC voltage of 400V as an example (the actual operating voltage is not limited to this, and there may be a deviation of + / -35%), in some embodiments, the turns ratio of the primary winding to the secondary winding in transformer 1 can be, for example, 12:10, and the DC-DC conversion device can adopt, for example... Figure 4B , Figure 5B or Figure 6BThe transformer 1 shown in the above-mentioned patent applications. In the case of a first DC voltage nominal value of 400 V, the number of winding layers along the axial direction M of the winding post 23 in each winding unit 12 for winding the primary coil is equal to one, but is not limited thereto.

[0077] When the on-board charger operates under the condition of three-phase power frequency AC power supply, taking a first DC voltage nominal value of 800 V as an example (the actual working voltage is not limited thereto, and there can be a deviation of + / - 35%), in some embodiments, the turn ratio of the primary winding and the secondary winding in the transformer 1 can be, for example, 24:10, and the DC-DC conversion device can adopt, for example, the transformer 1 shown in the above-mentioned patent applications. In the case of a first DC voltage nominal value of 800 V, the number of winding layers along the axial direction M of the winding post 23 in each winding unit 12 for winding the primary coil is equal to one and / or two, but is not limited thereto. Figure 7B

[0078] In summary, the present application provides a transformer and a DC-DC conversion device of an on-board charger suitable for the transformer. Through the winding and arrangement of the primary coil and the secondary coil of the transformer in the present application, the size of the transformer can be effectively reduced while the high conversion efficiency of the OBC is taken into account, and the heat dissipation is strengthened. The present application is particularly suitable for high-frequency operation, for example, but not limited to, 400 k-1 MHz.

[0079] It should be noted that the above-mentioned is only a preferred embodiment for illustrating the present application, and the present application is not limited to the described embodiments, the scope of the present application is determined by the appended claims. The present application can be modified by those skilled in the art, but all modifications are not out of the scope of the appended claims.​

Claims

1. A transformer comprising: a magnetic core comprising a first cover plate, a second cover plate and a limb, wherein the limb is disposed between the first cover plate and the second cover plate; and a winding region disposed on the limb, the winding region comprising a plurality of winding units; and a primary winding and a secondary winding, wherein the primary winding is wound in some of the winding units to form a primary winding of the transformer, and the secondary winding is wound in another some of the winding units to form a secondary winding of the transformer, wherein the primary winding and the secondary winding are at least partially interleaved in the plurality of winding units; and a number of winding layers in each of the winding units along an axial direction of the limb is less than or equal to two; wherein the plurality of winding units comprises a plurality of first winding units and a second winding unit, the plurality of first winding units form a first winding space, the second winding unit forms a second winding space, any two adjacent first winding units have a first spacing therebetween, the second winding space and the first winding space have a second spacing therebetween, and the second spacing is greater than the first spacing, wherein the plurality of first winding units are provided with at least part of the primary winding and at least part of the secondary winding.

2. The transformer of claim 1, wherein, The plurality of winding units further comprises a third winding unit, the third winding unit forms a third winding space, wherein the second winding space and the third winding space are respectively located on opposite sides of the first winding space, the third winding space and the first winding space have a third spacing therebetween, and the second spacing is less than or equal to the third spacing.

3. A transformer as claimed in claim 1 or 2, characterised in that, The ratio of the second spacing to the first spacing is greater than or equal to 3.

4. The transformer of claim 3, wherein, The second spacing is greater than or equal to 4.5 mm.

5. The transformer of claim 4, wherein, The first spacing is any value between 0.01 mm and 2 mm.

6. The transformer of claim 1, wherein The primary winding comprises a first primary winding and a second primary winding, wherein the first primary winding is wound in the second winding space, and the second primary winding is wound in the corresponding first winding unit in the first winding space.

7. The transformer of claim 1, wherein The secondary winding comprises a first secondary winding and a second secondary winding, wherein the first secondary winding is wound in the second winding space, and the second secondary winding is wound in the corresponding first winding unit in the first winding space.

8. The transformer of claim 2, wherein, The primary winding comprises a first primary winding, a second primary winding and a third primary winding, wherein the first primary winding and the third primary winding are wound in the second winding space and the third winding space respectively, and the second primary winding is wound in the corresponding first winding unit in the first winding space.

9. The transformer of claim 8, wherein, The secondary winding includes a first secondary coil and a second secondary coil, the first secondary coil and the second secondary coil are respectively wound in the corresponding first winding units in the first winding space, and the first winding units for winding the first secondary coil and the first winding units for winding the second secondary coil are respectively located on opposite sides of the first winding units for winding the second primary coil.

10. The transformer of claim 8, wherein, The number of turns of the first primary coil and the third primary coil is equal.

11. The transformer of claim 8, wherein, The number of turns of the first primary coil, the second primary coil and the third primary coil is equal.

12. The transformer of claim 2, wherein, The secondary winding includes a first secondary coil, a second secondary coil and a third secondary coil, wherein the first secondary coil and the third secondary coil are respectively wound in the second winding space and the third winding space, and the second secondary coil is wound in the corresponding first winding units in the first winding space.

13. The transformer of claim 12, wherein, The primary winding includes a first primary coil and a second primary coil, the first primary coil and the second primary coil are respectively wound in the corresponding first winding units in the first winding space, and the first winding units for winding the first primary coil and the first winding units for winding the second primary coil are respectively located on opposite sides of the first winding units for winding the second secondary coil.

14. The transformer of claim 1 or 2, wherein The spacing between any two adjacent first winding units is equal.

15. The transformer of claim 1, wherein, Further comprising a housing, the housing has at least one side and a bottom, the side stands on the bottom, and the side and the bottom together form a containing space; the magnetic core, the primary winding and the secondary winding are located in the containing space.

16. The transformer of claim 15, wherein, Further comprising a heat dissipation material, the heat dissipation material is at least partially filled in the containing space and at least partially in thermal contact with the primary winding, the secondary winding and the magnetic core.

17. The transformer of claim 15, wherein, The transformer further comprises a winding skeleton, wherein the winding skeleton has a hollow channel and a plurality of wire slots, the hollow channel is arranged to accommodate the winding column so that the winding skeleton is sleeved on the winding column, and the plurality of wire slots form the plurality of winding units.

18. The transformer of claim 1, wherein, Further comprising a heat dissipation material, the heat dissipation material is filled in the plurality of winding units for supporting and fixing the coils wound in the plurality of winding units, and at least partially in thermal contact with the coils wound in the plurality of winding units and the magnetic core.

19. The transformer of claim 1, wherein, The turns ratio of the primary winding and the secondary winding is 12:10 or 24:

10.

20. A DC-DC conversion device for an on-board charger, characterized by, The DC-DC conversion device comprises: a primary circuit for receiving a first direct current voltage; a transformer comprising a primary winding and a secondary winding magnetically coupled to each other, wherein the primary winding is electrically coupled to the primary circuit; and a secondary circuit electrically coupled to the secondary winding of the transformer for outputting a second direct current voltage, wherein the transformer is configured as the transformer of claim 1.

21. The DC-to-DC conversion device for use in a vehicle charger of claim 20, wherein, The first direct current voltage is 400V, and the turns ratio of the primary winding and the secondary winding is 12:

10.

22. The DC-to-DC conversion device for use in a vehicle charger of claim 21, wherein, The number of winding layers along the axial direction of the winding column in each of the winding units for winding the primary winding coil is equal to one layer.

23. The DC-to-DC conversion device for use in a vehicle charger of claim 20, wherein, The first direct current voltage is 800V, and the turn ratio of the primary winding and the secondary winding is 24:

10.

24. The DC-to-DC conversion device for use in a vehicle charger of claim 23, wherein, The number of winding layers along the axial direction of the winding column in each of the winding units for winding the primary winding coil is equal to one layer and / or two layers.

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