An inductive coupler for improving magnetic field coupling and resistance to axial misalignment

Abstract

This invention discloses an inductive coupler for improving magnetic field coupling and resisting axial displacement. The inductive coupler includes at least two primary coils and a secondary coil. The two ends of the secondary coil are flush and nested inside the primary coil. Adjacent primary and secondary coils are arranged at equal intervals around the center of the outer drill rod. Both primary and secondary coils carry a circular current with the same direction, and the central axis of the circular current is perpendicular to the central axis of the outer drill rod, thereby guiding the coupling magnetic field. This invention achieves enhanced internal magnetic field, application of S-S compensation circuit, reduced angular displacement during coupling mechanism rotation, strong resistance to axial displacement, and reduced influence of internal mutual inductance on the resonant frequency through optimized design of the square coil inductive coupler and series arrangement. These optimization measures improve the coupling capability between coils, reduce external interference and losses, and increase transmission efficiency and distance.

Description

Technical Field

[0001] This invention discloses an inductive coupler that improves magnetic field coupling and resists axial displacement, relating to the field of inductive coupler technology. Background Technology

[0002] Wireless power transfer (WPT) technology includes three methods: magnetic field induction, electric field induction, and microwave. Magnetic field induction has a shorter transmission distance but higher transmission efficiency; electric field induction is suitable for low-power and short-distance environments; microwave power transfer can reach distances of several kilometers, but requires precise positioning and suffers from significant energy loss. Compared to the other two methods, magnetic field induction coupling has some advantages in downhole wireless communication. For example, magnetic field transmission is not affected by electromagnetic interference in the oil well environment, thus exhibiting good anti-interference performance. Furthermore, magnetic field transmission can penetrate non-conductive media such as formations and wellbores, making it suitable for complex downhole environments. However, magnetic field induction coupling also has some limitations. For example, the transmission distance is relatively short, the transmission rate is low, and it is limited by environmental conditions such as the wellbore and formation. In addition, the energy attenuation of magnetic field transmission is significant, potentially requiring additional energy compensation measures.

[0003] To make magnetic field induction coupling applicable to oil well environments, researchers have designed several auxiliary magnetic field coupling devices. For example, patents (CN 1328473C) and (CN 101287888A) disclose an induction coupling device to improve the coupling effect of magnetic field induction. However, existing induction coupling devices all use a sequential arrangement of primary and secondary coils, resulting in a large distance between the coils and insufficient coupling, affecting energy transmission efficiency and distance. Furthermore, the couplers in existing technologies are susceptible to external magnetic field interference and losses, frequency drift, axial offset, and other factors, leading to poor transmission performance. Summary of the Invention

[0004] The purpose of this invention is to provide an inductive coupler that improves magnetic field coupling and resistance to axial offset, thereby enhancing the transmission performance of the inductive coupler.

[0005] To achieve the above-mentioned technical objectives and effects, the invention is implemented through the following technical solution:

[0006] An inductive coupler for improving magnetic field coupling and resisting axial displacement includes: an inductive coupler arranged on the inner surface of an outer drill pipe, characterized in that the inductive coupler includes at least two primary coils and secondary coils, the two ends of the secondary coils are flush and fitted inside the primary coils, and adjacent primary coils and secondary coils are arranged at equal intervals around the center of the outer drill pipe.

[0007] Furthermore, both the primary and secondary coils are filled with circular currents in the same direction, and the central axis of the circular currents is perpendicular to the central axis of the outer drill rod, thereby guiding the coupling magnetic field.

[0008] Furthermore, the distance between the primary and secondary coils is 8-12mm.

[0009] Furthermore, there are 4 primary coils and 2 secondary coils. Both primary and secondary coils are square coils. The circular current is reflected in the square coils, and the circuits of corresponding sides are reversed.

[0010] Furthermore, the square coil is wound using Litz wire.

[0011] Furthermore, both the secondary coil and the primary coil are connected in series.

[0012] Furthermore, the magnetic field coupling circuit formed by the primary coil and the secondary coil includes a primary coil, a primary compensation circuit, a secondary coil, and a secondary compensation circuit. The primary coil is connected to the primary resonant circuit, and the secondary coil is connected to the secondary compensation circuit. The system uses an SS compensation circuit to stabilize the resonant frequencies of both the primary and secondary sides at 50kHz.

[0013] Furthermore, the primary and secondary coils are powered by a DC power supply. The FPGA output pulse controls the inverter to convert the DC power into AC power with a frequency of 50kHz. The rectifier circuit converts the AC power into stable DC power for the load.

[0014] Furthermore, when the primary and secondary coils experience a 50mm axial offset, the system output power regulation rate is:

[0015]

[0016] Where P is the output power of the system when the coils are aligned, and P' is the output power of the system when the coils are axially offset.

[0017] Beneficial effects:

[0018] This invention optimizes the design of a square coil inductive coupler, combining it with a series arrangement to achieve enhanced internal magnetic field, the application of SS compensation circuitry, reduced angular offset during coupling mechanism rotation, strong resistance to axial offset, and reduced influence of internal mutual inductance on the resonant frequency. These optimizations improve the coupling capability between coils, reduce external interference and losses, and increase transmission efficiency and distance.

[0019] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0020] Figure 1This is a diagram of the existing WPT coupling mechanism described in an embodiment of the present invention;

[0021] Figure 2 This is a structural diagram of the inductive coupler described in an embodiment of the present invention;

[0022] Figure 3 This is a schematic diagram of the magnetic field coupling circuit described in an embodiment of the present invention;

[0023] Figure 4 This is a system block diagram of the wireless power transmission system described in an embodiment of the present invention;

[0024] Figure 5 This is a diagram showing the rate of change of mutual inductance between the square coil and the spiral coil when the coil undergoes axial displacement, as described in an embodiment of the present invention.

[0025] Figure 6 This is a prototype diagram of the WPT system in Embodiment 2 of the present invention;

[0026] Figure 7 This is a diagram showing the relationship between coil offset and output power according to an embodiment of the present invention; Detailed Implementation

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings.

[0028] Example 1

[0029] Currently, most downhole WPT coupling mechanisms use helical coils to ensure the stability of the system's output power when the coil rotates. However, during actual drill pipe operation, relative rotational motion and slight axial displacement occur between the outer and inner drill pipes, such as... Figure 1 As shown. In downhole wireless power transmission, the relative rotation and axial offset between helical coils affect the transmission effect, mainly in three aspects: changes in coupling distance, coil alignment error, and changes in the distance between coils.

[0030] To overcome the aforementioned problems, the applicant considered reducing the impact of offset on transmission performance by setting a more stable structure and improving coupling.

[0031] The inductive coupler described in this embodiment, which improves magnetic field coupling and resists axial displacement, is arranged on the inner surface of the outer drill pipe.

[0032] The inductive coupler includes at least two primary coils and a secondary coil. The two ends of the secondary coil are flush and nested inside the primary coil. Adjacent primary and secondary coils are arranged at equal intervals around the center of the outer drill pipe. Both the primary and secondary coils carry a circular current with the same direction, and the central axis of the circular current is perpendicular to the central axis of the outer drill pipe, thereby guiding the coupling magnetic field.

[0033] As can be seen from the structure described above, the inductive coupler of this embodiment uses a sleeve connection, and the central axis of the annular current is perpendicular to the central axis of the outer drill rod, thereby guiding the coupling magnetic field. This means that the primary and secondary coils have better axial load-bearing capacity. Compared with the prior art's arrangement with a large front-to-back gap, this coil has stronger resistance to axial displacement than ordinary helical coils.

[0034] In this embodiment, the inductive coupler is designed to optimize the axial load-bearing performance of the coil. By employing a sleeve connection, the central axis of the circular current is ensured to be perpendicular to the central axis of the outer drill pipe, thereby guiding the coupled magnetic field. This design provides better axial load-bearing capacity for both the primary and secondary coils, offering advantages over the previously used arrangement with significant spacing between them. Furthermore, the coil in this embodiment exhibits stronger resistance to axial displacement than ordinary helical coils, better meeting the requirements of specific applications.

[0035] In practice, the existing method of placing the primary and secondary coils together can result in a large distance between the coils, leading to insufficient coupling and affecting energy transfer efficiency and distance. Therefore, because the aforementioned embodiment has a nested structure, the spacing between the primary and secondary coils can be reduced, increasing the coupling between them. Higher coupling between the coils results in higher energy transfer efficiency and greater transmission distance.

[0036] In some embodiments, the distance between the primary and secondary coils is 8-12 mm. Preferably, the distance between the primary and secondary coils is 10 mm.

[0037] The applicant, taking into account the influence of various factors and combining the structure of the aforementioned embodiments, further proposes a preferred embodiment. In this preferred embodiment, there are 4 primary coils and 2 secondary coils. Both primary and secondary coils are square coils. The circular current is reflected in the square coils, and the circuits of corresponding sides are reversed.

[0038] The preferred embodiment structure reference Figure 2 In fact, the aforementioned structure can further reduce the problems of external magnetic field interference and loss. Specifically, there are two problems in magnetic field induction wireless power transmission: external magnetic field interference and magnetic field loss. External magnetic fields may interfere with coupled magnetic field communication, thereby affecting communication quality and stability; while magnetic field loss may lead to attenuation and energy loss of the coupled magnetic field, thereby reducing communication distance and transmission efficiency.

[0039] In this preferred embodiment, the current directions in the upper and lower portions of the square coil are opposite, which strengthens the internal magnetic field of the square coil and weakens the external magnetic field. This arrangement can reduce the interference and loss of the external magnetic field on the coil, thereby improving the coil's coupling capability and increasing energy transfer efficiency.

[0040] The hollowed-out center of the square coil reduces the overall weight of the coil, and the preferred winding of the coil with Litz wire reduces the skin effect at high frequencies.

[0041] In some embodiments, the secondary coil and the primary coil are connected in series. Specifically, the secondary coil is formed by two square coils laid at equal intervals on the outer surface of the inner drill pipe connected in series. This multi-coil series connection method can reduce the angular deviation of the coupling mechanism when it undergoes coaxial rotational motion, thereby maintaining the stability of power transmission.

[0042] Furthermore, due to the structural characteristics of square coils, the mutual inductance between series-connected square coils is relatively small, far less than the coil's self-inductance. This means that the internal mutual inductance between the primary and secondary coils will not significantly affect the circuit resonance, thus maintaining the stability of the resonant frequency. This helps improve the coupling capability between the coils, thereby improving the efficiency of wireless power transmission. In short, the mutual inductance between series-connected square coils is far less than the coil's self-inductance, therefore the internal mutual inductance between the primary and secondary coils will not affect the circuit resonance.

[0043] Based on the aforementioned preferred embodiments, the applicant has designed a detailed implementation process for the inductive coupler. In this embodiment, the magnetic field coupling circuit formed by the primary and secondary coils includes a primary coil, a primary compensation circuit, a secondary coil, and a secondary compensation circuit. The primary coil is connected to the primary resonant circuit, and the secondary coil is connected to the secondary compensation circuit. The system uses an SS compensation circuit to stabilize the resonant frequencies of both the primary and secondary sides at 50kHz.

[0044] Combination Figure 3 To understand its working principle, in one specific embodiment, the primary and secondary coils are powered by a DC power supply. The FPGA outputs pulses to control the inverter, which converts the DC power into AC power at a frequency of 50kHz. The rectifier circuit then converts the AC power into stable DC power for the load. See the specific implementation logic diagram below. Figure 4 .

[0045] Example 2

[0046] To prove the feasibility of the relevant content in Example 1, the applicant selected a preferred 10mm gap between the primary and secondary coils and tested it with the preferred embodiment in Example 1.

[0047] In this embodiment, the mutual inductance change rate is set as follows:

[0048]

[0049] Where M is the mutual inductance value when the coil does not shift axially, and M' is the mutual inductance value when the coil shifts axially.

[0050] When the coil undergoes axial displacement, the rate of change of mutual inductance between the square coil and the helical coil is as follows: Figure 5 As shown.

[0051] When the axial displacement of the drill pipe is slight, the rate of change of mutual inductance of the coupling coil is small. As the displacement increases, the rate of change of mutual inductance of the coupling coil gradually increases. After the axial displacement of the coil reaches 39mm, the rate of change of mutual inductance of the square coil is significantly lower than that of the ordinary helical coil, and its increasing trend gradually weakens, while the increasing trend of mutual inductance of the helical coil continues to strengthen with the increase of axial displacement. For specific experimental structure, please refer to [reference needed]. Figure 6 .

[0052] The relevant parameters are shown in Table 1.

[0053] Table 1

[0054]

[0055] The system output power was measured as the coupling coil gradually shifted axially by 50 mm from a point of no shift. The measurement results are as follows: Figure 7 As shown.

[0056] Based on the test results, the system output power adjustment rate is as follows when the coil experiences a 50mm axial offset:

[0057]

[0058] Where P is the output power of the system when the coils are aligned, and P' is the output power of the system when the coils are axially offset.

[0059] When the coupling coil is offset, the change in mutual inductance causes the system output power to be unstable. Experiments show that the output power decreases as the offset increases, but the trend of output power change gradually slows down. The system has good resistance to axial offset, which is basically consistent with the theoretical analysis.

[0060] The above are merely some of the embodiments of this application and are not intended to limit the application in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments shall still fall within the scope of protection of the technical solution of this application.

Claims

1. An inductive coupler for improving magnetic field coupling and resistance to axial displacement, wherein the inductive coupler is arranged on the inner surface of the outer drill pipe, characterized in that, The inductive coupler includes at least two primary coils and a secondary coil. The two ends of the secondary coil are flush and fitted inside the primary coil. Adjacent primary coils and secondary coils are arranged at equal intervals around the center of the outer drill rod. The primary coils are all filled with circular currents in the same direction, and the secondary coils are all filled with circular currents in the same direction. The central axis of the circular currents is perpendicular to the central axis of the outer drill rod, thereby guiding the coupling magnetic field. The distance between the primary and secondary coils is 8-12mm; There are 4 primary coils and 2 secondary coils. Both primary and secondary coils are square coils. The circular current is reflected in the square coils, and the current directions of corresponding sides are opposite. The square coil is wound using Litz wire; All primary coils are connected in series; all secondary coils are connected in series. The magnetic field coupling circuit formed by the secondary coil and the primary coil includes a primary coil, a primary compensation circuit, a secondary coil, and a secondary compensation circuit. The primary coil is connected to the primary resonant circuit, and the secondary coil is connected to the secondary compensation circuit. The system uses an SS compensation circuit to stabilize the resonant frequencies of both the primary and secondary sides at 50kHz. When the primary and secondary coils experience a 50mm axial offset, the system output power regulation rate is: ； in This represents the system's output power when the coils are aligned. This represents the system's output power when the coil undergoes axial displacement.

2. The inductive coupler for improving magnetic field coupling and resisting axial displacement according to claim 1, characterized in that, The primary and secondary coils are powered by a DC power supply. The FPGA output pulse controls the inverter to convert the DC power into AC power with a frequency of 50kHz. The rectifier circuit converts the AC power into stable DC power for the load.

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