Multi-group double-wire parallel wound coils and corresponding transformers

Abstract

The utility model provides a kind of multiple sets of double-wire parallel-wound coil and corresponding transformer, the coil is wound by two sets of primary and secondary side double-wire parallel-wound wire, the coil has four-layer structure, first layer and fourth layer are wound by first set of primary and secondary side double-wire parallel-wound wire, second layer and third layer are wound by second set of primary and secondary side double-wire parallel-wound wire, wherein immediately adjacent bone magnetic core middle column is first layer.The multiple sets of double-wire parallel-wound coil and corresponding transformer provided in the application increase the effective coupling area of primary and secondary side winding by discretizing arrangement and symmetrical distribution design of primary and secondary side winding, optimize magnetic motive force distribution, greatly reduce the leakage inductance of transformer.

Description

Technical Field

[0001] This utility model relates to the field of transformer technology, and in particular to a multi-set double-wire parallel-wound coil and a corresponding transformer. Background Technology

[0002] With the increasing popularity of new energy vehicles, the demand for DC charging piles is growing, and the power requirements for these piles are also increasing. As the core unit of a charging pile, the charging module faces ever-higher requirements for power density and efficiency. To improve the power density of the charging module, its frequency is becoming increasingly higher. As the core component inside the charging module, the transformer's transmission efficiency and heat dissipation have become key technical challenges.

[0003] In the high-frequency design of magnetic components, multi-strand wire is usually used to wind the transformer in order to reduce the loss of the transformer winding. However, after the multi-strand wire winding is completed, the gap between the wires is relatively large. Even if the primary and secondary sides are wound in parallel, the leakage inductance is at least greater than 2%, which affects the transformer performance. Utility Model Content

[0004] In view of this, the present invention provides a multi-set of double-wire parallel-wound coils and a corresponding transformer to solve at least one of the aforementioned problems.

[0005] To achieve the above objectives, the present invention adopts the following solution:

[0006] In one aspect, this application provides a multi-group double-wire parallel-wound coil, the coil comprising a four-layer structure, the first layer and the fourth layer being wound by a first group of primary and secondary double-wire parallel-wound conductors, the second layer and the third layer being wound by a second group of primary and secondary double-wire parallel-wound conductors, wherein the first layer is located immediately adjacent to the central column of the magnetic core.

[0007] As an embodiment of this application, the primary and secondary sides of the above-mentioned adjacent two layers of primary and secondary side double-wire parallel wires are arranged in opposite order.

[0008] As an embodiment of this application, the starting and exit positions of the first group of primary and secondary side double-wire parallel winding conductors and the second group of primary and secondary side double-wire parallel winding conductors are located on the same side or different sides of the winding area.

[0009] Secondly, this application provides a multi-group double-wire parallel-wound coil, the coil comprising a four-layer structure, the winding area being divided into a left half and a right half by an isolator located at the center of the axis, wherein the four layers of wire on the left half are wound by a first group of primary and secondary double-wire parallel-wound wires, and the four layers of wire on the right half are wound by a second group of primary and secondary double-wire parallel-wound wires.

[0010] As an embodiment of this application, the primary and secondary sides of the above-mentioned adjacent two layers of primary and secondary side double-wire parallel wires are arranged in opposite order.

[0011] As an embodiment of this application, the starting and exit positions of the first group of primary and secondary side double-wire parallel winding conductors are located at the first end of the winding area, and the starting and exit positions of the second group of primary and secondary side double-wire parallel winding conductors are located at the second end of the winding area.

[0012] Thirdly, this application provides a multi-group double-wire parallel-wound coil, the coil comprising a four-layer structure, the first to fourth layers being respectively wound by the first to fourth groups of primary and secondary double-wire parallel-wound conductors, wherein the first layer is located immediately adjacent to the central column of the magnetic core.

[0013] As an embodiment of this application, the primary and secondary sides of the above-mentioned adjacent two layers of primary and secondary side double-wire parallel wires are arranged in opposite order.

[0014] As an embodiment of this application, the starting position of the four sets of primary and secondary side double-wire parallel winding conductors is located at the first end of the winding area, and the exit position of the four sets of primary and secondary side double-wire parallel winding conductors is located at the second end of the winding area.

[0015] Fourthly, this application provides a transformer that includes the coil described above.

[0016] As one embodiment of this application, the transformer includes a frame, the coil is wound on the frame, and a plurality of openings are provided on the core of the frame that contacts the coil.

[0017] As can be seen from the above technical solution, the multiple sets of double-wire parallel windings and corresponding transformers provided in this application, by discretizing and symmetrically distributing the primary and secondary windings, increase the effective coupling area of ​​the primary and secondary windings, optimize the magnetomotive force distribution, and greatly reduce the leakage inductance of the transformer. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings:

[0019] Figure 1 This is a winding diagram of a multi-group double-wire parallel-wound coil provided in Embodiment 1 of this application;

[0020] Figure 2 This is a winding diagram of another multi-group double-wire parallel-wound coil provided in Embodiment 1 of this application;

[0021] Figure 3 This is a winding diagram of a multi-group double-wire parallel-wound coil provided in Embodiment 2 of this application;

[0022] Figure 4 This is a winding diagram of a multi-group double-wire parallel-wound coil provided in Embodiment 3 of this application;

[0023] Figure 5 This is an exploded view of the structure of a transformer provided in an embodiment of this application. Detailed Implementation

[0024] It should be noted that the term "comprising" and any variations thereof in the specification, claims, and accompanying drawings of this utility model are intended to cover non-exclusive inclusion. For example, a process, method / process, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods / processes, products, or devices.

[0025] In this invention, the terms "upper," "lower," "inner," "outer," "middle," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing this invention and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0026] Furthermore, in addition to indicating direction or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this utility model according to the specific circumstances.

[0027] Furthermore, the terms "setup" and "connection" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0028] Example 1

[0029] like Figure 1 The diagram shown is a winding schematic of a multi-group bi-wire parallel-wound coil provided in Embodiment 1 of this application. Figure 1 As can be seen, the coil is made of two sets of primary and secondary double-wire parallel-wound conductors, which are defined here as the first set of primary and secondary conductors and the second set of primary and secondary conductors, where 1 and 2 are the starting points of winding, and 3 and 4 are the exit points.

[0030] The first set of primary and secondary conductors is wound in a double-wire parallel manner, starting from the left side to form the first layer. This double-wire parallel winding involves twisting one primary conductor and one secondary conductor together like a twisted pair before winding. Then, the second set of primary and secondary conductors is wound in the same double-wire parallel manner, starting from the right side to form the second layer, and then the third layer is wound from left to right. Next, the first set of primary and secondary conductors is wound in the same double-wire parallel manner, starting from right to left to form the fourth layer. After this winding process, a four-layer coil is obtained, with the first layer immediately adjacent to the central core. The first and second sets of primary and secondary conductors can be wound on a frame or without a frame; this application does not limit this, but for ease of explanation, the following example will use winding on a frame.

[0031] In this embodiment, the coil is wound with two sets of primary and secondary double-wire parallel-wound conductors, which reflects the discretization of the winding. This embodiment decomposes the winding function of the entire transformer into two independent primary and secondary double-wire parallel-wound units (the first set and the second set). This discretization provides a basis for subsequent optimized arrangement. Specifically, the optimized arrangement in this embodiment is reflected in the stacking method of "first set - second set - second set - first set", forming an interlaced structure. In this structure, the first set of primary and secondary windings (in the first and fourth layers) sandwiches the second set of primary and secondary windings (in the second and third layers). This means that the magnetic field of the first set can couple with the second set from both the inner and outer sides, while the magnetic field of the second set can also couple with the first set from both the inner and outer sides. Compared with simply winding the primary side completely and then the secondary side, or performing only one-time primary and secondary side parallel winding, this multi-layered interlaced structure significantly increases the interface for the primary and secondary windings to contact and interact with each other in space, that is, it increases the coupling area. The magnetic flux can more effectively link the primary and secondary windings simultaneously, naturally reducing the "leakage flux" that fails to link them both, thus lowering the leakage inductance between the primary and secondary windings. Furthermore, the aforementioned structure possesses a physical property; this symmetrical arrangement helps achieve a symmetrical distribution of the magnetomotive force within the winding window. When multiple windings operate in parallel to share the total current (assuming these two sets are in parallel or have parallel sub-windings), the symmetrical magnetomotive force distribution means that the magnetic environments of each winding are similar, and their inductive reactance and leakage inductance will be closer. This helps balance the impedance between the parallel branches, thereby achieving a more uniform current distribution, i.e., ensuring current sharing. Uneven current sharing, on the other hand, can lead to overload of some windings, uneven heating, and affect transformer efficiency and lifespan.

[0032] Optionally, in the four-layer structure of the coil described above, the primary and secondary sides of the primary and secondary conductors on adjacent sides are arranged in reverse order. Specifically, for example... Figure 1As shown, the first layer is arranged in the pattern (primary edge, secondary edge), ..., (primary edge, secondary edge); the second layer is arranged in the pattern (secondary edge, primary edge), ..., (secondary edge, primary edge); the third layer is arranged in the pattern (primary edge, secondary edge), ..., (primary edge, secondary edge); and the fourth layer is arranged in the pattern (secondary edge, primary edge), ..., (secondary edge, primary edge). Of course, it is also possible to reverse the above order.

[0033] This reverse arrangement ensures that each primary-side conductor is surrounded as closely as possible by the secondary-side conductor (and vice versa), even between different layers. It makes it easier for magnetic field lines to close between the primary and secondary sides, reducing outward leakage paths. This meticulous arrangement allows for a further increase in coupling area, thus more effectively reducing leakage inductance.

[0034] Optionally, in the four-layer structure of the coil described above, the starting points and exit points of the two sets of primary and secondary side conductors are located on different sides of the frame. This arrangement greatly simplifies the coil pin handling, soldering to the PCB board, or connection to external circuits. This not only facilitates automated production but also makes the PCB layout simpler and reduces the area of ​​parasitic loops that may be formed by external connection lines. Of course, to meet special exit requirements, the starting points and exit points of the two sets of primary and secondary side conductors in this embodiment can also be located on the same side of the frame. In this case, only the starting point and sequence of the winding need to be adjusted. For details, please refer to [link to relevant documentation]. Figure 2 As shown, 1 and 2 are the starting points of the winding, and 3 and 4 are the exit points.

[0035] Example 2

[0036] like Figure 3 The diagram shown is a winding schematic of a multi-set double-wire parallel-wound coil provided in Embodiment 2 of this application. The coil is also wound by two sets of primary and secondary double-wire parallel-wound conductors, which are defined here as the first set of primary and secondary conductors and the second set of primary and secondary conductors, where 1 and 2 are the starting points of winding, and 3 and 4 are the exit points.

[0037] In this embodiment, the skeleton is physically divided into left and right halves by an isolator (e.g., an insulating partition) located at the center of its axis. Without a skeleton, the winding area is divided into left and right halves by the isolator located at the center of its axis. The first set of primary and secondary conductors is used to wind the four-layer conductor structure on the left half in a double-wire parallel winding manner, while the second set of primary and secondary conductors is used to wind the four-layer conductor structure on the right half in a double-wire parallel winding manner. This means that the entire coil is clearly divided into two independent but structurally similar winding regions axially, each region containing four layers of winding. Here, double-wire parallel winding means the same as in Embodiment 1, that is, a primary conductor and a secondary conductor are first joined together like a twisted pair before winding.

[0038] In this embodiment, the discretization of the transformer windings is reflected in the explicit allocation of the complete winding task to two physically isolated half-regions of the frame, with each half-region being handled by an independent primary and secondary side double-wire parallel winding unit (i.e., the first group or the second group). This optimized arrangement of axial segments concentrates the first group of windings and the second group of windings on the left and right half-sides of the frame, respectively, forming a compact four-layer structure.

[0039] Although different from the interlayer staggered arrangement in Embodiment 1, this embodiment aims to achieve tight coupling between the primary and secondary windings within a designated half-region by winding each set of primary and secondary windings (e.g., the first set) entirely in four layers on its designated half-region (e.g., the left half). The four-layer structure itself helps to increase the effective coupling area between the primary and secondary conductors in this region, thereby reducing the leakage inductance of the set of windings themselves. The presence of the isolator clearly defines the physical boundaries between the two sets of windings.

[0040] The frame is divided into symmetrical left and right halves by an isolator, and each side is wound with the same four-layer structure using a set of primary and secondary conductors. The first and second sets of primary and secondary conductors are identical in design (e.g., number of turns, wire diameter). This physically symmetrical layout helps to ensure that the magnetomotive force distribution of the entire transformer is as symmetrical as possible on both sides. When these two sets of windings need to operate in parallel to share the total current, this symmetry and their independent, compact windings help ensure that the two sets of windings have similar electrical parameters (e.g., inductive reactance, leakage inductance), thereby promoting a uniform current distribution between the two sets, ensuring current sharing, and avoiding localized overheating or efficiency reduction caused by uneven current distribution.

[0041] Optionally, in the four-layer conductor structure on the left side (and similarly in the four-layer conductor structure on the right side), the primary and secondary sides of adjacent layers of double-wire parallel conductors are arranged in reverse order. Specifically, if the first layer on the left side is arranged in the order of (primary side, secondary side), ..., (primary side, secondary side), then the second layer should be arranged in the order of (secondary side, primary side), ..., (secondary side, primary side), the third layer reverts to the (primary side, secondary side) order, and the fourth layer is in the (secondary side, primary side) order. The four-layer structure on the right side also follows the same reverse order rule for adjacent layers.

[0042] This reverse-order arrangement within each half-region ensures that each primary-side conductor in that region is surrounded as closely as possible by secondary-side conductors (and vice versa). This makes it easier for magnetic field lines to close between the primary and secondary sides of each pair, reducing outward leakage paths and thus further effectively reducing leakage inductance and improving coupling within their respective responsible half-regions.

[0043] Optionally, the starting and exit points of the first group of primary and secondary parallel-wound conductors are both located at the first end (e.g., the left end) of the bobbin (winding area), while the starting and exit points of the second group of primary and secondary parallel-wound conductors are both located at the second end (e.g., the right end) of the bobbin (winding area). This method of placing the exit points of the two windings at different ends of the bobbin physically separates the electrical connection points of the first and second groups, facilitating differentiation and management when connecting to external circuits (such as PCB boards). It avoids the wiring congestion or unnecessary bridging that can occur when all leads are concentrated at one end, and may help reduce potential capacitive coupling or electromagnetic interference between different groups of leads.

[0044] Example 3

[0045] like Figure 4 The diagram shown is a winding schematic of a multi-group double-wire parallel-wound coil provided in Embodiment 3 of this application. The coil is made of four groups of primary and secondary double-wire parallel-wound conductors, which are defined here as the first group, the second group, the third group and the fourth group of primary and secondary conductors, respectively. Among them, 1, 2, 3 and 4 are the starting points of winding, and 5, 6, 7 and 8 are the exit points.

[0046] The first layer of this coil is formed by winding a first set of primary and secondary double-wire parallel wires, the second layer by winding a second set of primary and secondary double-wire parallel wires, the third layer by winding a third set of primary and secondary double-wire parallel wires, and the fourth layer by winding a fourth set of primary and secondary double-wire parallel wires. The first layer is located immediately adjacent to the core shaft, followed by the second, third, and fourth layers sequentially outwards, with the first layer closest to the central post of the magnetic core. The term "double-wire parallel winding" here has the same meaning as in the previous embodiment, where a primary wire and a secondary wire are first twisted together like a pair of twisted wires before being wound.

[0047] In this embodiment, the discretization of the transformer winding is more fully realized, and the entire winding task of the coil is decomposed into four independent primary and secondary double-wire parallel winding units (i.e., the first group to the fourth group). The optimized arrangement is to layer them in order of group sequence: the first group constitutes the first layer, the second group constitutes the second layer, and so on.

[0048] Each layer consists of an independent primary and secondary double-wire parallel winding. The double-wire parallel winding itself ensures tight coupling between the primary and secondary wires within that layer, greatly reducing leakage flux within the group. These four internally tightly coupled primary and secondary unit layers are stacked sequentially, and the close contact between the layers allows for magnetic field coupling between the groups. Although this embodiment is not a sandwich structure like Embodiment 1, this orderly, group-based layered arrangement, combined with the double-wire parallel winding within each layer, still helps to increase the effective coupling of the primary and secondary windings in the entire coil structure, thereby reducing overall leakage inductance.

[0049] Furthermore, in this embodiment, by winding the four sets of primary and secondary conductors into independent layers, and ensuring that these four sets of conductors are identical in design (e.g., number of turns, wire diameter) to share the load, this clear layered structure helps achieve a more symmetrical magnetomotive force distribution. Each set occupies a complete layer in its radial position, which provides a structural basis for achieving impedance balance and uniform current distribution among the sets (especially in parallel applications), thus ensuring current sharing. The symmetrical magnetomotive force distribution and uniform current distribution can reduce unnecessary losses, prevent local overheating, and improve the overall efficiency and reliability of the transformer.

[0050] Optionally, in the four-layer structure of this coil, the primary and secondary sides of the bi-wire parallel-wound conductors in adjacent layers are arranged in reverse order. Specifically, if the order of the bi-wire parallel-wound conductor pairs in the cross-section of the first layer is (primary side, secondary side), ..., (primary side, secondary side), then the second layer should be (secondary side, primary side), ..., (secondary side, primary side), the third layer reverts to the order (primary side, secondary side), ..., (primary side, secondary side), and the fourth layer is (secondary side, primary side), ..., (secondary side, primary side). This fine arrangement of the relative positions of the primary and secondary sides within the bi-wire parallel-wound unit, which reverses between adjacent layers, can further optimize the magnetic field coupling between layers and reduce magnetic field distortion. It allows different groups of primary and secondary conductors to form a more detailed spatial interleaving, which helps to cancel some leakage magnetic field components at a more microscopic scale, thereby more effectively reducing overall leakage inductance and potentially improving current distribution at high frequencies, reducing AC losses.

[0051] Optionally, the starting points of the four sets of primary and secondary conductors are all located at the first end (e.g., the left end) of the bobbin winding area, while the exit points are all located at the second end (e.g., the right end) of the bobbin. This lead-in method, which sets the starting point of all windings at one end of the bobbin winding area and the ending point of all windings at the other end of the bobbin, has the following advantages: increased electrical clearance and improved insulation performance. Physically placing the "head" (starting point) and "tail" (exit point) of all windings at both ends of the bobbin can maximize the creepage distance and electrical clearance between them. This is beneficial for transformers that need to withstand higher operating voltages or pulse voltages, as it improves their withstand voltage level and insulation reliability.

[0052] Example 4

[0053] like Figure 5 The diagram shown is an exploded view of a transformer structure according to an embodiment of this application. Figure 5 As can be seen, the transformer includes: coil 10, frame 20, magnetic component 30 and base 40.

[0054] Coil 1 is any one of the coils in Embodiment 1, Embodiment 2 or Embodiment 3, and it is wound on the frame 20. It is responsible for realizing the transmission of electrical energy and the transformation of voltage.

[0055] The skeleton 20 is a cylindrical or square frame structure made of insulating material (such as engineering plastics). Its main function is to provide mechanical support for the coil 10, so that the wires can be wound regularly on it and maintain the shape of the winding and the interlayer / interturn insulation.

[0056] The center of the skeleton 20 is hollow. Optionally, in this embodiment, the sidewalls of the skeleton 20 may be provided with a number of window structures, which may be rectangular, circular or other various shapes.

[0057] Coil 10 generates heat during operation due to copper losses (heat generated by the resistance of the wires as current flows through them) and AC losses at high frequencies. If this heat cannot be effectively dissipated, the coil temperature will rise. The window structure on the side wall of the frame 20 directly exposes part of the coil surface or forms an air convection path between the frame's interior and the external environment. This makes it easier for the heat generated by the coil to be dissipated into the surrounding environment through thermal radiation and air convection. As a result of improved heat dissipation, the transformer can carry a larger current or operate at a higher power level under the same temperature rise limit. Although the weight reduction effect of a single window is negligible, if the window area is large or the number of windows is large, it can reduce the weight of the frame to a certain extent, contributing to the overall lightweight design.

[0058] Magnetic component 30 is a ferromagnetic material component that constitutes the magnetic circuit of the transformer, typically consisting of two symmetrically shaped ferrite cores (such as...). Figure 5 The image shows two E-type magnetic cores (though other shapes that can be joined to form a closed magnetic circuit, such as a combination of U-type and I-type cores, are also possible). The cores can use a concentrated air gap or a multi-segment air gap. The permeability of ferromagnetic materials drops sharply after the magnetic field strength exceeds a certain value, entering a saturation state, causing a sharp drop in inductance and preventing the transformer from functioning properly. Introducing an air gap is equivalent to inserting a high reluctance component into the magnetic circuit, requiring a higher magnetomotive force to reach the saturation flux density. Therefore, cores with air gaps can withstand larger DC bias currents or higher AC peak currents without easily saturating.

[0059] The base 40 is a metal or plastic piece with upwardly bent sidewalls and four upwardly protruding pin structures at the bottom. These pins are used to securely solder the transformer to the circuit board and connect to the pins of coil 1 to bring out the electrical connections of the transformer.

[0060] During assembly, as shown in the exploded view above, firstly, the wires of coil 10 are tightly wound around the central cylindrical portion of the frame 20, located between its upper and lower flanges, following the winding method described in the previous embodiment. Then, the magnetic component 30 is inserted into the frame 20 and surrounds the coil 10; the central hole of the frame 20 is used to insert the magnetic component 30. The two magnetic components 30 are joined together from the top and bottom (or sides, depending on the specific design of the magnetic core and frame) of the frame 20, fitting tightly. After assembly, the magnetic component 30 passes through the central hole of the frame and surrounds the frame portion containing the coil 10, forming a closed magnetic circuit. Finally, the transformer body, with coil 10, frame 20, and magnetic component 30 assembled, is mounted onto the base 40. The leads of coil 10 are connected to pins at the bottom of the base 40, thereby bringing out the electrical terminals of the transformer. The pins on the base 40 are ultimately used to solder the entire transformer to an external circuit board. Through these steps, these separate components are assembled into a complete transformer.

[0061] As can be seen from the above, the multiple sets of double-wire parallel-wound coils and corresponding transformers provided in this application, by discretizing and symmetrically distributing the primary and secondary windings, increase the effective coupling area of ​​the primary and secondary windings, optimize the magnetomotive force distribution, and greatly reduce the leakage inductance of the transformer.

[0062] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this utility model. It should be understood that the above descriptions are merely specific embodiments of this utility model and are not intended to limit the scope of protection of this utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the scope of protection of this utility model.

Claims

1. A multi-group double-wire parallel-wound coil, characterized in that, The coil comprises a four-layer structure. The first and fourth layers are wound by a first group of primary and secondary double-wire parallel-wound conductors, and the second and third layers are wound by a second group of primary and secondary double-wire parallel-wound conductors. The first layer is located immediately adjacent to the central column of the magnetic core.

2. The multi-group dual-filar pancake coil of claim 1, wherein, The primary and secondary sides of two adjacent layers of double-wire primary and secondary sides are arranged in opposite order.

3. The multi-group dual-filar pancake coil of claim 1, wherein, The starting and exit positions of the first group of primary and secondary side double-wire parallel winding conductors and the second group of primary and secondary side double-wire parallel winding conductors are located on the same side or different sides of the winding area.

4. A multi-group double wire-wound coil, characterized by, The coil has a four-layer structure. The winding area is divided into a left half and a right half by an isolator located at the center of the axis. The four layers of wire on the left half are wound by the first set of primary and secondary double wires wound together, and the four layers of wire on the right half are wound by the second set of primary and secondary double wires wound together.

5. The multi-group dual-filar pancake coil of claim 4, wherein, The primary and secondary sides of two adjacent layers of double-wire primary and secondary sides are arranged in opposite order.

6. The multi-group dual-filar pancake coil of claim 4, wherein, The starting and exit positions of the first group of primary and secondary side double-wire parallel winding conductors are located at the first end of the winding area, and the starting and exit positions of the second group of primary and secondary side double-wire parallel winding conductors are located at the second end of the winding area.

7. A multi-group double wire-wound coil, characterized by The coil has a four-layer structure. The first to fourth layers are respectively wound by the first to fourth groups of primary and secondary double wires. The first layer is located immediately adjacent to the central column of the magnetic core.

8. The multiple sets of bi-wire parallel-wound coils as described in claim 7, characterized in that, The primary and secondary sides of two adjacent layers of double-wire primary and secondary sides are arranged in opposite order.

9. The multi-group dual-filar pancake coil of claim 7, wherein, The starting position of the four sets of primary and secondary side double-wire parallel winding conductors is located at the first end of the winding area, and the exit position of the four sets of primary and secondary side double-wire parallel winding conductors is located at the second end of the winding area.

10. A transformer, characterized by The transformer includes multiple sets of bi-wire parallel-wound coils as described in any one of claims 1-9.

11. The transformer as described in claim 10, characterized in that, The transformer includes a frame, the coil is wound on the frame, and a number of openings are provided on the core of the frame that contacts the coil.

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