Coil

Abstract

The invention provides a coil, and belongs to the technical field of magnets, and the coil is formed by winding a hollow pipeline with a preset thickness. Wherein the hollow pipeline is made of a conductive material, the pipe wall of the hollow pipeline is used for current flowing, and the hollow part of the hollow pipeline is used for heat dissipation. According to the invention, the current-carrying conductor and the cooling channel are integrated in the hollow conductive pipeline, and on the premise of not sacrificing the electrical performance, zero-distance efficient heat dissipation is realized, skin effect temperature rise is inhibited, the bottleneck of current-carrying density is broken through, an external heat dissipation structure is eliminated, and the weight and thickness of the system are reduced. Therefore, the power density, the reliability and the engineering applicability of the high-power wireless power transmission system are remarkably improved, and a feasible technical path is provided for high-power wireless charging in the fields of electric traffic, industrial automation and the like.

Description

Technical Field

[0001] This application relates to the field of magnet technology, and more particularly to a coil. Background Technology

[0002] Wireless power transfer technology, with its advantages of safety, convenience, and the ability to automate and intelligently charge, has shown great application potential in consumer electronics, robotics, industrial equipment, electric vehicles, and rail transportation. For example, providing wireless charging for electric vehicles (especially public transportation and freight vehicles) while they are in motion or stopped at stations significantly alleviates range anxiety, reduces battery demand (thereby lowering costs, weight, and resource consumption), and promotes the electrification of heavy vehicles and public transportation. As vehicle battery capacity continues to increase, consumers' demands for charging time are becoming increasingly stringent, making the development of high-power wireless power transfer systems imperative. Inductive wireless charging systems utilize the principle of electromagnetic induction to achieve "wireless" power transfer, enabling high-power transmission capabilities. A typical topology is shown below. Figure 1 As shown in (a), the core carrier of system energy transmission—the coupling mechanism—can be considered a loosely coupled transformer. Compared with traditional transformers, its primary and secondary magnetic cores are independent of each other and have no mechanical contact. A typical structure is shown in [image missing]. Figure 1 As shown in (b), the magnetic core enhances coupling and shields leakage magnetic field, while the shielding plate further enhances the electromagnetic shielding effect.

[0003] However, a significant bottleneck for high-power wireless power transfer systems is the design of their cooling systems. In high-power systems, traditional air cooling methods fail to meet system requirements due to air's low specific heat capacity, low thermal conductivity, and a sharp decline in cooling efficiency at high ambient temperatures. Dust and humid air can also negatively impact fan and radiator performance. In contrast, liquid cooling uses coolants (water, glycol solutions, insulating oil, fluorinated liquids, etc.) as the cooling medium, absorbing heat through cold plates, flow channels, or immersion, and then dissipating it into the environment through radiators (air-cooled or water-cooled). Because liquids (especially water) have a much higher specific heat capacity and thermal conductivity than air, they effectively handle high heat flux densities (such as power devices) and significantly reduce hotspot temperatures. For the same cooling capacity, the system volume is typically smaller than air-cooled systems. However, traditional liquid cooling requires separate piping, increasing system weight and volume, especially thickness. With ever-increasing power density requirements, this increased volume, especially thickness, significantly limits the applicability of wireless power transfer systems. Furthermore, high-power systems require thicker wires. Because wireless power transmission systems typically operate at high frequencies, reaching tens or even hundreds of kHz, the skin effect-induced losses are significant. Traditionally, wireless power transmission systems mostly use Litz wire, which is a coil made of several very thin wires twisted together. However, as power increases, the coil current often increases as well, requiring a corresponding increase in the wire cross-sectional area. Although thicker cables have a larger total cross-sectional area, the heat generated is mainly concentrated in the inner layer or areas of high current density (such as the shallow layer below the surface). The thermal conductivity of conductors is relatively limited, making it difficult for the heat generated internally to be effectively transferred to the conductor surface for dissipation, resulting in an internal temperature rise that is much higher than the surface temperature rise, forming hot spots. To ensure that the cable insulation material does not exceed its maximum allowable operating temperature (to prevent aging and breakdown) and to ensure the safety of joints and other connections, the temperature rise of the conductor must be limited. Therefore, the alternating current (current density) that can be safely carried per unit cross-sectional area must be reduced to avoid overheating. The thicker the cable (the larger the cross-section), the more pronounced this decrease in current-carrying capacity per unit area becomes, exhibiting a diminishing marginal return effect. The existence of marginal effects leads to thicker Litz wires used in the winding of coils in high-power systems, which will significantly increase the weight of the system and reduce its power density.

[0004] In summary, the existence of marginal effects in the existing schemes leads to thicker Litz wires used for winding coils in high-power systems, which significantly increases the weight and cost of the system and reduces the system power density. The separate design of the heat dissipation system and the current-carrying wires increases the system volume and further reduces the system power density.

[0005] Therefore, there is an urgent need for a new flow carrier and heat dissipation method to improve the system power density. Summary of the Invention

[0006] This application provides a coil to address the shortcomings of existing technologies where marginal effects result in thicker coils and larger system volumes.

[0007] This application provides a coil, which is wound from a hollow tube of a predetermined thickness; The hollow pipe is made of a conductive material, the pipe wall is used for current flow, and the hollow part of the hollow pipe is used for heat dissipation.

[0008] According to a coil provided in this application, cooling fluid is injected from one end of the hollow pipe, flows through the hollow part of the hollow pipe, and flows out from the other end for heat dissipation.

[0009] According to a coil provided in this application, the cooling fluid uses a cooling gas.

[0010] According to a coil provided in this application, the cooling fluid is a coolant.

[0011] According to a coil provided in this application, if the coolant is a conductive liquid, an insulating layer is sprayed onto the inner wall of the hollow pipe.

[0012] According to a coil provided in this application, the coolant is ethylene glycol.

[0013] According to a coil provided in this application, the flow direction of the cooling fluid is opposite to the flow direction of the current in the hollow pipe.

[0014] According to the coil provided in this application, the outer wall of the hollow tube is coated or wound with an insulating layer.

[0015] According to a coil provided in this application, the wall thickness of the hollow tube is determined based on the skin depth of the hollow tube.

[0016] According to a coil provided in this application, the outer diameter of the hollow tube is determined based on the system's heat dissipation capacity, the allowable temperature rise of the hollow tube material, the ambient temperature, and the flow rate.

[0017] This application provides a coil wound from a hollow tube of a predetermined thickness. The hollow tube is made of a conductive material, with its walls used for current flow and its hollow portion for heat dissipation. This application uses a hollow conductive tube as the current carrier. Firstly, heat does not need to pass through the entire conductor cross-section to dissipate, significantly reducing conductor temperature rise and resulting in more uniform temperature distribution. Hot spot temperatures are effectively controlled, overcoming the diminishing marginal return effect of traditional conductors due to poor internal heat dissipation. Secondly, the hollow portion of the hollow tube acts as a heat sink, achieving an integrated conductor-heat sink design, eliminating the need for a separate heat dissipation system. Compared to separate heat dissipation designs, this achieves lower thermal resistance and higher heat dissipation power density, making it particularly suitable for integrating high heat flux density power devices. Furthermore, the hollow structure significantly reduces conductor mass while maintaining the conductive cross-sectional area, and the cooling function is built into the coil body, eliminating the need for an external cooling module, reducing the overall system thickness and assembly space, thereby significantly improving the volumetric power density and mass power density of the wireless power transmission system. In summary, this application integrates the current-carrying conductor and cooling channel into a hollow conductive pipe, achieving zero-distance high-efficiency heat dissipation, suppressing skin effect temperature rise, breaking through the current-carrying density bottleneck, eliminating external heat dissipation structures, and reducing system weight and thickness without sacrificing electrical performance. This significantly improves the power density, reliability, and engineering applicability of high-power wireless power transmission systems, providing a practical and feasible technical path for high-power wireless charging in fields such as electric transportation and industrial automation. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in this application 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 some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 It is a typical topology and coupling mechanism of wireless power transmission systems in the prior art; Figure 2 This is one of the structural schematic diagrams of the coil provided in this application; Figure 3 This is the second schematic diagram of the coil structure provided in this application; Figure 4 This is the third schematic diagram of the coil structure provided in this application; Figure 5 This is the fourth schematic diagram of the coil structure provided in this application; Figure 6 This is a schematic diagram of the coil winding process provided in this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] It should be noted that in the description of the embodiments of this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. The terms "upper," "lower," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly, for example, they can be fixed connections, detachable connections, or integral connections; they can be mechanical connections or electrical connections; they can be direct connections or indirect connections through an intermediate medium; and they can be internal connections between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0022] The terms "first," "second," etc., used in this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class, without limiting the number of objects; for example, a first object can be one or more. Furthermore, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects have an "or" relationship.

[0023] The following is combined Figures 2-6 The coil provided in the embodiments of this application is described.

[0024] Figure 2 This is one of the structural schematic diagrams of the coil provided in this application, such as... Figure 2 As shown, the coil is made by winding a hollow tube of a predetermined thickness; The hollow pipe is made of a conductive material, the pipe wall is used for current flow, and the hollow part of the hollow pipe is used for heat dissipation.

[0025] It should be noted that, Figure 2 An exemplary structural diagram is shown. For descriptive purposes, the illustrated architecture is merely an example of a suitable environment and does not imply any limitation on the scope or functionality of this application. Nor should the coil be construed as a representation of... Figure 2 Any component shown or a combination thereof has any dependencies or requirements.

[0026] In this embodiment of the application, a hollow pipe refers to a tubular component with a continuous hollow inner cavity. Its cross-section can be circular, elliptical, rectangular, or other shapes suitable for optimizing fluid flow and electromagnetic properties. Furthermore, the outer and inner cross-sections of the hollow pipe can be the same or different. For example... Figure 3 The hollow pipe shown has a circular outer cross-section and a rectangular inner cross-section. For example... Figure 4 The hollow pipe shown has hexagonal outer and inner cross sections.

[0027] Here, the hollow tube is used to carry current, forming an energy transfer channel, and plays the same role as Litz wire and conductor.

[0028] Here, the preset thickness refers to the pipe wall thickness, which can be preset according to the system operating frequency, current magnitude, skin depth and mechanical strength requirements. It is usually slightly greater than or equal to the effective skin depth of high-frequency current. For example, at 50-200 kHz, the skin depth of copper is about 0.15-0.3 mm to ensure efficient current conduction and avoid waste of ineffective materials.

[0029] Specifically, hollow tubes are made of highly conductive materials (such as oxygen-free copper, aluminum, or copper alloys), and their walls form the main path for alternating current. Under high-frequency operating conditions (typically 20kHz-1MHz), due to the skin effect, the current mainly flows in a thin layer near the outer surface or between the inner and outer surfaces of the tube wall. By rationally designing the tube wall thickness, the entire tube wall can be placed in an effective conductive area, maximizing material utilization and avoiding the problem of ineffective conductivity in the central area of ​​traditional solid conductors.

[0030] Understandable, Figure 2 Although a disc-shaped double-layer coil is shown, the shape and number of layers of the coil winding are not limited in actual implementation. For example, a hollow tube can be bent, coiled, or stacked to form a single-layer or multi-layer coil, suitable for magnetic coupling mechanisms at the transmitting or receiving end. The winding shape of the hollow tube can include, but is not limited to, disc-shaped, rectangular, and polygonal shapes. Figure 5 The coil shown is wound in a rectangular shape.

[0031] In this embodiment, the hollow portion of the hollow pipe is exposed to air, increasing the specific surface area of ​​the hollow pipe and the air / coolant for heat dissipation.

[0032] Understandably, for low-power systems or systems with good heat dissipation, there is no need to inject coolant; natural cooling is sufficient. For high-power systems, coolant can be injected into the central control section of the hollow pipe to accelerate heat dissipation.

[0033] The coil provided in this application embodiment is wound from a hollow tube of a predetermined thickness. The hollow tube is made of a conductive material, its walls are used for current flow, and its hollow portion is used for heat dissipation. This application uses a hollow conductive tube as the current carrier. On one hand, heat does not need to pass through the entire conductor cross-section to dissipate, significantly reducing conductor temperature rise and making its distribution more uniform. Hot spot temperatures are effectively controlled, overcoming the diminishing marginal return effect of current carrying capacity caused by poor internal heat dissipation in traditional conductors. On the other hand, the hollow portion of the hollow tube serves as the heat sink, achieving an integrated conductor-heat sink design. No additional heat dissipation system is required. Compared to separate heat dissipation designs, this achieves lower thermal resistance and higher heat dissipation power density, making it particularly suitable for integrating high heat flux density power devices. Furthermore, the hollow structure significantly reduces conductor mass while maintaining the conductive cross-sectional area, and the cooling function is built into the coil body, eliminating the need for an external cooling module. This reduces the overall system thickness and assembly space, thereby significantly improving the volumetric power density and mass power density of the wireless power transmission system. In summary, by integrating the current-carrying conductor and cooling channel into a hollow conductive pipe, this application achieves zero-distance high-efficiency heat dissipation, suppresses skin effect temperature rise, overcomes current density bottleneck, eliminates external heat dissipation structure, and reduces system weight and thickness without sacrificing electrical performance. This significantly improves the power density, reliability, and engineering applicability of high-power wireless power transmission systems, providing a practical and feasible technical path for high-power wireless charging in fields such as electric transportation and industrial automation.

[0034] In an optional embodiment, cooling fluid is injected from one end of the hollow pipe, flows through the hollow portion of the hollow pipe, and flows out from the other end for heat dissipation.

[0035] In this embodiment, the hollow inner cavity of the hollow pipe serves as a cooling medium flow channel, through which liquid cooling media (such as deionized water, ethylene glycol aqueous solution, fluorinated liquid, insulating oil, etc.) or gaseous cooling media can be introduced. The cooling fluid flows through the inside of the pipe under the drive of the pump, directly absorbing the heat generated by Joule heating of the pipe wall. Since the cooling medium is close to the heat source (i.e., the flow-carrying pipe wall), the heat conduction path is extremely short, and the thermal resistance is significantly lower than that of traditional external radiator solutions. The coolant after absorbing heat can be cooled by an external radiator (such as an air-cooled heat exchanger or a secondary water-cooling circuit) and then circulated for reuse, forming a closed cooling system.

[0036] Specifically, the hollow tube constitutes the main body of the coil. The coil is wound from a continuous conductive tube (such as an oxygen-free copper tube) with a hollow inner cavity according to a predetermined geometry (such as a planar spiral, double D-shape, or solenoid). The tube wall thickness is designed to be slightly greater than the skin depth (e.g., 0.2-0.4 mm) based on the system operating frequency (e.g., 85 kHz) to ensure efficient conduction of high-frequency current. The tube material possesses high conductivity, good flexibility, and weld sealing properties. After the coil is wound, the first end of the hollow tube is connected to a cooling fluid inlet connector, and the second end is connected to an outlet connector. A cooling pump drives the cooling fluid to be injected from the inlet end, flowing along the entire length of the coil through the hollow inner cavity of the tube, and finally flowing out from the outlet end. The flow direction can be clockwise or counterclockwise, but it always maintains a unidirectional, continuous, and uninterrupted flow to avoid dead zones or stagnant areas. Furthermore, the flow direction of the cooling fluid and the current in the tube can be the same or different. When a high-frequency, high-current is applied to the coil, heat is generated in the tube wall due to the Joule effect. The heat is rapidly transferred to the inner surface of the tube wall through thermal conduction. The cooling fluid continuously contacts the inner surface of the tube wall during its flow, carrying away the heat through convection heat transfer. As the fluid flows along the tube, its temperature gradually increases, forming a temperature gradient along the tube. After the high-temperature fluid flows out, it enters an external radiator (such as an air-cooled heat exchanger or a secondary cooling circuit) to cool down, and then circulates back to the pump inlet, forming a closed liquid cooling circuit.

[0037] The coil provided in this application embodiment achieves complete overlap and dynamic coupling between the current path and the cooling path by injecting cooling fluid from one end of the hollow pipe, allowing it to flow through the hollow inner cavity and out from the other end. This enables efficient heat dissipation over the entire area, eliminates hot spots, and ensures uniform temperature distribution, further improving the coil's heat dissipation performance.

[0038] In an optional embodiment, the cooling fluid is a cooling gas.

[0039] In practical implementation, the coil is wound from a continuous conductive hollow tube (such as a copper or aluminum tube). The tube wall thickness is designed according to the skin depth of the high-frequency current (e.g., 0.2-0.4 mm for copper at 85 kHz) to ensure efficient conductivity. A closed or semi-closed hollow flow channel is formed inside the tube, serving as a passage for cooling gas. Cooling gas is forcibly injected from one end (inlet) of the hollow tube by an air pump or blower. The gas flows along the hollow part of the tube for the entire length of the coil, exchanging heat with the heated inner surface of the tube wall. The high-temperature gas after absorbing heat is discharged from the other end of the tube (outlet), which can be directly discharged into the environment or cooled by a heat exchanger and then recycled (closed system). The flow pattern is unidirectional, continuous, and through-flow forced convection, avoiding dead zones and local stagnation.

[0040] In this embodiment, the choice of cooling gas is not limited. For example, air, dry compressed air, nitrogen, helium, etc. can be used. Ordinary air is inexpensive and readily available, and is suitable for general power scenarios; dry compressed air or nitrogen can prevent moisture condensation and oxidation, and improve insulation reliability; although helium is expensive, its thermal conductivity is about 6 times that of air, and it is suitable for ultra-high power density or closed systems.

[0041] Preferably, the cooling gas is selected to meet the requirements of electrical insulation, chemical stability and non-corrosiveness.

[0042] The coil provided in this application uses gas for cooling, eliminating the risk of leakage. Even a slight leak will not affect the insulation. Furthermore, compared to liquid cooling, it eliminates the need for complex water quality management. The hollow tube coil is lighter and simpler than liquid cooling solutions, making it suitable for mobile platforms such as electric vehicles and drones. In addition, liquids may experience a decline in insulation performance due to aging, contamination, or microporous penetration during long-term operation, while gases have extremely high breakdown strength and self-restoring insulation properties, resulting in high reliability in high-frequency, high-voltage wireless power transmission systems.

[0043] In an optional embodiment, the cooling fluid is a coolant.

[0044] In practice, the coolant is forced into the pipe inlet by a magnetic pump or centrifugal pump, flowing unidirectionally along the entire length of the coil through the hollow inner cavity. After absorbing heat from the pipe wall, it flows out from the outlet. The high-temperature coolant at the outlet enters an external radiator (such as an air-cooled heat exchanger, water-to-water heat exchanger, or phase change heat dissipation module) for cooling before returning to the pump inlet, forming a closed-loop liquid cooling circulation system. The pipe ends are connected to external pipelines via rotary joints, quick-connect fittings, or welded flanges. High-reliability sealing structures (such as O-rings or metal seals) are used at the connections to ensure leak-free long-term operation.

[0045] Optionally, the entire system can integrate pressure sensors, temperature sensors, and flow meters to achieve closed-loop thermal management control.

[0046] The type of coolant is not limited here, and may include, but is not limited to, deionized water, ethylene glycol-water mixture, fluorinated liquid, insulating oil, etc.

[0047] Preferably, a liquid with high specific heat capacity and thermal conductivity, high electrical insulation (especially for high-voltage systems), good chemical stability (does not corrode pipes), and low viscosity (easy to pump) is selected as the coolant.

[0048] The coil provided in this application embodiment achieves physical integration and performance synergy of current carrying and heat dissipation functions by forcing a coolant with high thermal conductivity and high specific heat capacity through the hollow cavity of a conductive hollow pipe. This results in ultra-high heat dissipation efficiency, excellent temperature rise control, and breakthrough of current carrying bottleneck. It also increases AC current density and releases the potential of the conductor, providing core technical support for high-power wireless power transmission systems that combines high performance, high integration, and engineering feasibility. It is particularly suitable for cutting-edge application scenarios such as electric heavy trucks, buses, rail transit, and industrial automation.

[0049] In an optional embodiment, if the coolant is a conductive liquid, an insulating layer is sprayed onto the inner wall of the hollow pipe.

[0050] In practice, the coil is wound into a hollow tube made of highly conductive metal. The tube wall thickness is optimized based on the high-frequency skin effect to ensure efficient current conduction through the tube wall. A continuous hollow flow channel is formed inside the tube for coolant circulation. An insulating coating is sprayed or deposited on the inner wall surface of the hollow tube (i.e., the side in direct contact with the coolant).

[0051] The material of the insulating layer is not limited here, and may include, but is not limited to, parylene, aluminum nitride or alumina ceramic coating, modified epoxy resin or polyimide coating.

[0052] Preferably, the insulating layer material has high volume resistivity to ensure effective blocking of current leakage; high thermal conductivity (>1 W / m·K, preferably 3-10 W / m·K) to minimize additional thermal resistance; good adhesion and mechanical strength to withstand coolant erosion and thermal cycling stress; chemical stability, resistance to hydrolysis and oxidation, and insolubility in coolant; and thin layer to avoid significantly reducing the cross-sectional area of ​​the flow channel.

[0053] The coil provided in this application reduces leakage current by spraying an insulating layer on the inner wall of a hollow pipe, thereby allowing the safe use of a high-performance conductive coolant. This breaks through the traditional contradiction of "insulation = low thermal conductivity," expands the range of coolant options, and balances high heat dissipation performance with electrical isolation. In addition, the insulating layer acts as a dielectric barrier, increasing the partial discharge initiation voltage, preventing dielectric breakdown under high-frequency electric fields, and ensuring the electrical safety of high-voltage, high-frequency systems.

[0054] In an optional embodiment, the coolant is ethylene glycol.

[0055] In this embodiment, pure ethylene glycol or an ethylene glycol-water mixture is used as the cooling medium. The ethylene glycol solution is driven by a magnetic pump and injected from one end of the hollow pipe, flowing through the hollow inner cavity of the entire coil length. After absorbing Joule heat from the pipe wall, it flows out from the other end. The high-temperature coolant enters an air-cooled or liquid-cooled condenser to cool down, and then returns to the pump inlet, forming a closed-loop circulation circuit.

[0056] The coil provided in this application embodiment has a freezing point of ethylene glycol aqueous solution that can be lowered to below -35°C and a boiling point that can be raised to above 107°C, which significantly widens the system's operating temperature range and adapts to harsh environments. It is especially suitable for wireless charging stations deployed outdoors. At the same time, the higher boiling point allows for a higher coolant outlet temperature, increasing the heat exchange temperature difference, improving heat dissipation efficiency, or reducing the size of the heat sink.

[0057] In an optional embodiment, the cooling fluid flows in the opposite direction to the current flow in the hollow pipe.

[0058] In the specific implementation process, the coil is made of a continuous conductive hollow pipe wound in a spiral or multi-turn form. High-frequency alternating current flows into the coil from one end (designated as end A), is conducted along the pipe wall, and flows out from the other end (end B). Due to the skin effect, the current is mainly distributed in the thin layer of the pipe wall near the inner and outer surfaces. Joule heat is generated uniformly or nearly uniformly along the entire length of the pipe. Cooling fluid (such as ethylene glycol solution, deionized water, or fluorinated liquid) is injected from end B of the coil (current outlet end), flows through the hollow inner cavity of the hollow pipe, and flows out from end A (current inlet end). Therefore, the flow direction of the cooling fluid is completely opposite to the physical flow direction of the current, forming a countercurrent heat exchange configuration.

[0059] The coil provided in this application embodiment has a cold fluid inlet corresponding to a hot fluid outlet (high temperature zone) and a cold fluid outlet corresponding to a hot fluid inlet (low temperature zone). It maintains a higher and more uniform local temperature difference throughout the process, which improves the average heat transfer driving force of the entire coil and significantly enhances the heat dissipation capacity. Furthermore, in the case of countercurrent, the current outlet (hottest area) is always in contact with the low temperature coolant and is effectively cooled. The current inlet is in contact with the coolant that has absorbed heat and risen in temperature, but since there is less heat accumulation here (the temperature rise is small when the fluid first enters), the overall temperature rise is controllable.

[0060] In an optional embodiment, the outer wall of the hollow pipe is sprayed or wrapped with an insulating layer.

[0061] In some embodiments, a uniform coating is formed on the outer wall using a high-temperature resistant and highly insulating coating (such as polyimide PI, epoxy resin, silicone rubber, Parylene, etc.) through spraying, brushing, or dipping processes.

[0062] In other embodiments, insulating films (such as polyester film PET, polytetrafluoroethylene PTFE, Nomex paper, mica tape, etc.) are tightly wound around the outer surface of the pipe in a spiral or stacked manner.

[0063] In some embodiments, a multi-layered protective system is formed by combining a bottom adhesive, an intermediate insulating layer, and an outer wear-resistant sheath.

[0064] The performance requirements for the insulation layer here are the same as those for the insulation layer on the inner wall of the hollow pipe, and will not be repeated here.

[0065] The coil provided in this application embodiment achieves reliable inter-turn and ground electrical insulation through the outer wall insulation layer, ensuring the safe operation of the high-voltage high-frequency system, completely eliminating the risk of inter-turn short circuits and high-frequency arcs, and the outer wall insulation layer allows for compact coil winding, improving the coupling coefficient and power density.

[0066] In an optional embodiment, the wall thickness of the hollow pipe is determined based on the skin depth of the hollow pipe.

[0067] Under the influence of high-frequency alternating current, due to the eddy current effect generated by electromagnetic induction, the current tends to concentrate within a thin layer on the surface of the conductor; this phenomenon is known as the skin effect. The current density decreases exponentially with depth.

[0068] In this embodiment, the wall thickness of the hollow pipe is set to be slightly greater than the skin depth. If the wall thickness is much less than the skin depth, the conductor cross-sectional area is insufficient, the AC resistance is too high, and the loss increases dramatically. If the wall thickness is much greater than the skin depth (as in a traditional solid conductor), almost no current flows through the central area, resulting in material waste, increased weight, and higher costs. However, if the wall thickness is slightly greater than the skin depth (e.g., the wall thickness is 1.2 times the skin depth), the current flows effectively through the wall while avoiding ineffective material.

[0069] The coil provided in this application maximizes high-frequency conductivity, reduces AC resistance to the theoretical lower limit, minimizes losses, and avoids ineffective conductors by scientifically setting the wall thickness of the hollow tube to the optimal value based on the skin depth.

[0070] In an optional embodiment, the outer diameter of the hollow pipe is determined based on the system's heat dissipation capacity, the allowable temperature rise of the hollow pipe material, the ambient temperature, and the flow rate.

[0071] Here, the system heat dissipation requirement is the Joule heat generated by the coil at rated power; the allowable temperature rise is the difference between the conductor's maximum operating temperature and the ambient temperature; the ambient temperature is the reference temperature of the system deployment environment; and the cooling fluid flow rate is the maximum or economical flow rate that the pumping system can provide.

[0072] In the specific implementation process, a heat balance equation can be constructed and solved based on the above constraints to determine the optimal pipe outer diameter.

[0073] The coil provided in this application embodiment sets the outer diameter of the hollow pipe as a function of the system's heat dissipation capacity, allowable temperature rise, ambient temperature, and cooling flow rate. This ensures that the conductor temperature rise is strictly controlled within the material safety limits, achieving precise thermal management, avoiding waste of materials and pump power, reducing the total system cost, and improving the efficient use of resources.

[0074] In summary, the coil winding process is as follows: Figure 6 As shown, firstly, the coil current, thin-walled tube material, and manufacturing process are determined based on specific application requirements. Then, the tube wall thickness is determined based on the skin depth. The inner cross-sectional shape and dimensions of the pipe are determined according to the type of cooling fluid used and its heat dissipation capacity, and the outer cross-sectional shape and dimensions are also determined. After verifying the pipe's heat dissipation capacity and confirming it meets requirements, the coil is wound, completing the coil winding process. This application uses a hollow thin-walled tube as the flow carrier, effectively increasing the specific surface area for heat dissipation and increasing the flow rate per unit cross-sectional area. The flow carrier and coolant channel are reused, effectively reducing the system's weight and volume.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A coil, characterized in that, The coil is made by winding a hollow tube of a predetermined thickness; The hollow pipe is made of a conductive material, the pipe wall is used for current flow, and the hollow part of the hollow pipe is used for heat dissipation.

2. The coil according to claim 1, characterized in that, Cooling fluid is injected from one end of the hollow pipe, flows through the hollow part of the pipe, and flows out from the other end for heat dissipation.

3. The coil according to claim 2, characterized in that, The cooling fluid uses cooling gas.

4. The coil according to claim 2, characterized in that, The cooling fluid used is a coolant.

5. The coil according to claim 4, characterized in that, If the coolant is a conductive liquid, an insulating layer is sprayed onto the inner wall of the hollow pipe.

6. The coil according to claim 5, characterized in that, The coolant is ethylene glycol.

7. The coil according to claim 2, characterized in that, The direction of the cooling fluid flow is opposite to the direction of the current flow in the hollow pipe.

8. The coil according to any one of claims 1-7, characterized in that, The outer wall of the hollow pipe is coated or wrapped with an insulating layer.

9. The coil according to any one of claims 1-7, characterized in that, The wall thickness of the hollow pipe is determined based on the skin depth of the hollow pipe.

10. The coil according to any one of claims 1-7, characterized in that, The outer diameter of the hollow pipe is determined based on the system's heat dissipation capacity, the allowable temperature rise of the hollow pipe material, the ambient temperature, and the flow rate.

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