Metal Foreign Object Detection Coil Structure of Electric Vehicle Wireless Charging System

Abstract

The present invention proposes a metal foreign object detection coil structure for an electric vehicle wireless charging system. Considering that in an electric vehicle wireless power transmission system, since there is no direct physical contact between the transmitting end and the receiving end, metal foreign objects often enter the charging area between the two. Compared with the original solution, the advantage of the present invention is that the detection coil and the transmitting coil are decoupled, thereby eliminating the influence on the wireless charging energy transmission, and a relatively large self-inductance change rate of the detection coil is obtained at each position of the detection coil, thus obtaining excellent metal foreign object detection ability.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless charging for electric vehicles, and particularly relates to a metal foreign object detection coil structure for a wireless charging system of an electric vehicle. Background Art

[0002] Wireless Power Transfer (WPT) technology, as a technology that can transfer energy from a transmitting end to a load receiving end without direct contact of metal wires, has received increasing attention from researchers in recent years. Its main advantages are safety, reliability, and flexibility, achieving free charging and complete electrical isolation between the power supply and the load in a full sense, and has been widely applied in commercial fields such as electric vehicles and consumer electronics products.

[0003] Magnetic coupling wireless power transfer technology is the most mature and widely used in WPT. However, in actual applications, since there is no direct physical contact between the transmitting end and the receiving end, metal foreign objects often enter the charging area between the two. On the one hand, these metal foreign objects will change the parameters of the coupling mechanism of the wireless power transfer system, thereby reducing the power and efficiency of the system and affecting the normal operation of the system; on the other hand, the accidentally entered metal foreign objects will generate heat under the influence of the eddy current effect. Especially in the scenario of wireless charging for electric vehicles where high power requirements are relatively high, the charging power generally reaches dozens of kilowatts, and the eddy current effect is particularly significant. The heat generation phenomenon caused by metal foreign objects will be very serious, and even fires may occur, threatening the safety of personal and property. Therefore, Foreign Object Detection (FOD), as a technology that can improve the safety and reliability of wireless charging for electric vehicles, its importance is self-evident, and relevant standards have stipulated that FOD technology must be included in the wireless charging system of electric vehicles. In foreign object detection technology, metal object detection (MOD) is particularly important. Its basic principle is that a metal foreign object under the eddy current effect in the charging area can be equivalent to a series model of a resistor and an inductor. As shown in the attached drawings of the specification, Figure 1 under high-frequency excitation, the self-inductance of the detection coil will change with the intrusion of metal foreign objects, and whether there are metal foreign objects is judged by detecting the change in the self-inductance of the detection coil. Summary of the Invention

[0004] Considering that in the wireless power transfer system of electric vehicles, since there is no direct physical contact between the transmitting end and the receiving end, metal foreign objects often enter the charging area between the two. In order to make up for the defects and deficiencies of the existing technology, the present invention aims to provide a metal foreign object detection coil structure for a wireless charging system of an electric vehicle.

[0005] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0006] A metal foreign object detection coil structure for an electric vehicle wireless charging system, characterized in that: the detection coil is located above the transmitting coil; the structure of the detection coil is decoupled between the detection coil and the transmitting coil by connecting coils with opposite polarities in series.

[0007] Further, there are a total of 20 columns of the detection coils, and each column is composed of 16 mutually connected rectangular small coils in series; a single sub-detection coil is formed by connecting two small rectangular coils with opposite polarities in series, so that the magnetic fields of the two small rectangular coils cancel each other out to achieve decoupling;

[0008] Two of the sub-detection coils are connected in series to obtain a detection module composed of four small rectangular coils, and then a strip-shaped detection coil composed of 8 sub-detection coils connected in series is obtained, and the detection coil is formed by laying 20 of the strip-shaped detection coils.

[0009] Further, the detection coil is composed of two layers of detection coils, and the second layer of detection coils is used to eliminate the detection blind area of the first layer;

[0010] Assume that coils A, B, C, and D are four four-pole coils, which are respectively formed by connecting four single-pole coils in series with opposite polarities, and the polarities of adjacent two single-pole coils are opposite, thus realizing the decoupling of the four-pole coil and the transmitting coil; by arranging multiple four-pole detection coils from the outside to the inside, a first layer of detection coils composed of 8 rectangular coils on each side is obtained;

[0011] The second layer of detection coils is arranged above the detection blind area at the junction of four different four-pole coils to eliminate the blind spot, and a four-pole coil and the same decoupling structure as the first layer of detection coils are adopted.

[0012] Further, there are seven single-pole coils on each side of the second layer of detection coils, and the single-pole coils that cannot form a four-pole coil in the middle adopt a bipolar coil structure, and the decoupling with the transmitting coil is realized by connecting two single-pole coils with opposite polarities in series.

[0013] Compared with the prior art, the advantages of the present invention and its preferred solutions are that the decoupling between the detection coil and the transmitting coil is realized, thus eliminating the influence on the wireless charging energy transmission, and a relatively large self-inductance change rate of the detection coil is obtained at each position of the detection coil, thereby obtaining excellent metal foreign object detection ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The following further details the present invention in conjunction with the drawings and specific embodiments:

[0015] Figure 1Schematic diagram of the model of the detection coil for metallic foreign objects and the metallic foreign object in the prior art: (a) Layout schematic diagram; (b) Coupling circuit model;

[0016] Figure 2 Schematic diagram of the structure of the detection coil for metallic foreign objects proposed by the present invention: (a) Top view; (b) Simulation model in MAXWELL;

[0017] Figure 3 Schematic diagram of the structure of the detection coil for metallic foreign objects connected in reverse series according to the present invention;

[0018] Figure 4 Schematic diagram of different positions of the metallic foreign object placed on the structure of the detection coil according to the present invention;

[0019] Figure 5 Schematic diagram of the structure of the detection coil for metallic foreign objects proposed by the present invention: (left) Top view; (right) Simulation model in MAXWELL;

[0020] Figure 6 Schematic diagram of the decoupling principle of the first - layer detection coil of the structure of the present invention;

[0021] Figure 7 Schematic diagram of the decoupling principle of the second - layer detection coil of the structure of the present invention;

[0022] Figure 8 Schematic diagram of different positions of the metallic foreign object placed on the structure of the detection coil according to the present invention. Detailed implementation manners

[0023] To make the features and advantages of this patent more obvious and understandable, the following specifically gives 2 embodiments for detailed description as follows:

[0024] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0025] It should be noted that the terms used herein are only for describing the specific implementation manners and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0026] Embodiment 1

[0027] The structure of the detection coil for metallic foreign objects of the wireless charging system for electric vehicles proposed by the present invention is as Figure 2As shown, the detection coil is located above the transmitting coil. There are a total of 20 columns, and each column consists of 16 small rectangular coils connected in series with each other.

[0028] To eliminate the influence of the detection coil on the magnetic field of wireless power transfer, it is necessary to design the coil structure to decouple the detection coil from the transmitting coil. As Figure 3 shown, the symbol "x" in the figure indicates that the magnetic field direction is into the paper perpendicular to the paper surface, while the symbol "·" indicates that the magnetic field direction is out of the paper perpendicular to the paper surface. A single sub-detection coil is composed of two small rectangular coils with opposite polarities connected in series. In this way, the magnetic fields of the two small rectangular coils cancel each other out, achieving decoupling. Connecting two sub-detection coils in series can obtain a detection module composed of four small rectangular coils, and further a strip-shaped detection coil composed of 8 sub-detection coils connected in series can be obtained. Figure 2 The detection coil in

[0029] is formed by laying 20 such strip-shaped detection coils. Figure 2 A simulation model of the proposed structure is established. As Figure 4 shown, using a coin as a metallic foreign object, the self-inductance change rate of the detection coil and the coupling coefficient between the detection coil and the transmitting coil when the metallic foreign object is at different positions are obtained, as shown in Table I. The different positions where the metallic foreign object is placed on the detection coil are as

[0030] Table I Self-inductance change rate of the detection coil structure I and coupling coefficient between the detection coil and the transmitting coil when the metallic foreign object is at different positions

[0031]

[0032] As can be seen from Table I, at the 5 positions where foreign objects often appear, the detection coil has achieved decoupling from the transmitting coil, and the minimum self-inductance change rate of the detection coil is 2.98%, and the maximum reaches 4.41%.

[0033] Embodiment 2

[0034] The metallic foreign object detection coil structure II of the electric vehicle wireless charging system proposed by the present invention is as Figure 5 shown. This structure consists of two layers of detection coils. The main function of the second layer of detection coil is to eliminate the detection blind area of the first layer.

[0035] The decoupling principle of the first layer of detection coil is as Figure 6As shown, the symbol "x" in the figure indicates that the magnetic field direction is into the paper perpendicular to the paper surface, while the symbol "· " indicates that the magnetic field direction is out of the paper perpendicular to the paper surface. Coils A, B, C, and D are four quadrupole coils, which are respectively formed by connecting four monopole coils in series with opposite polarities. From the magnetic field direction in the figure, it can be seen that the polarities of adjacent two monopole coils are opposite, thus realizing the decoupling of the quadrupole coil and the transmitting coil. By arranging multiple quadrupole detection coils from outside to inside, a first-layer detection coil composed of 8 rectangular coils on each side can be obtained.

[0036] At Figure 6 the four points marked with numbers 1 to 4, the parameter changes of the coil are very small because these points are located at the junctions of four different quadrupole coils. It is difficult to detect metallic foreign objects at these points, so they are called detection blind spots. It is necessary to place a second-layer detection coil above these points to eliminate the blind spots. As Figure 7 shown, the coil A in the figure is the quadrupole coil placed above the Figure 6 four points marked, and its decoupling principle is the same as that of the first layer. The double-layer detection coil structure ensures that the metallic foreign object can be located in the central area of a quadrupole coil to obtain a larger self-inductance change rate.

[0037] Since there are seven monopole coils on each side of the second-layer coil, there will be a remaining monopole coil in the middle of the second layer that cannot form a quadrupole coil, so this coil will be designed as a bipolar coil. As Figure 7 shown by the bipolar coil in the middle, decoupling from the transmitting coil is achieved by connecting two monopole coils with opposite polarities in series. In this way, good detection effects are obtained at all points.

[0038] According to Figure 6 and Figure 7 , a simulation model of the proposed structure is established. As Figure 5 shown in the figure (right), the maximum coupling coefficient between the detection coil and the transmitting coil is only 0.35%, so the detection coil and the transmitting coil are decoupled. Taking the latest version of the one-yuan RMB as the metallic foreign object, the self-inductance change rate of the detection coil when the metallic foreign object is at different positions is obtained, as shown in Table II. The schematic diagrams of different positions where the metallic foreign object is placed on the detection coil are as Figure 8 shown.

[0039] Table II Self-inductance change rate of the detection coil structure II and coupling coefficient between the detection coil and the transmitting coil when the metallic foreign object is at different positions

[0040]

[0041] As can be seen from Table II, the self-inductance change rate of the first-layer coil is between 0.92% and 3.51%, and the self-inductance change rate of the second-layer coil is between 2.4% and 28.11%. In practical applications, it is sufficient that one of the two detection coils detects the presence of a metallic foreign object, which means that the metallic foreign object in Detection Coil Structure II can be easily detected.

[0042] As can be seen from the above two embodiments, compared with the existing solutions, the advantages of the present invention are as follows:

[0043] (1) Two different structures of the metallic foreign object detection coil for an electric vehicle wireless charging system are proposed.

[0044] (2) Decoupling between the detection coil and the transmitting coil is achieved, thus eliminating the influence on the energy transmission of the electric vehicle wireless charging system.

[0045] (3) A relatively large self-inductance change rate of the detection coil is obtained at each position of the detection coil, thus achieving excellent metallic foreign object detection ability.

[0046] The structure of the metallic foreign object detection coil for the electric vehicle wireless charging system proposed by the present invention can obtain two different preferred decoupling methods, both of which achieve decoupling between the transmitting coil and the detection coil, thus eliminating the influence on the energy transmission of the wireless charging system and obtaining excellent metallic foreign object detection ability.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention in any other form. Any person skilled in the art may use the disclosed technical content to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention still fall within the protection scope of the technical solution of the present invention.

[0048] This patent is not limited to the above best implementation mode. Anyone can obtain other various forms of the metallic foreign object detection coil structure for the electric vehicle wireless charging system under the inspiration of this patent. All equal changes and modifications made according to the scope of the patent application of the present invention shall fall within the coverage scope of this patent.

Claims

1. A metal foreign object detection coil structure for an electric vehicle wireless charging system, characterized in that: The detection coil is located above the transmitting coil; the structure of the detection coil decouples the detection coil from the transmitting coil by connecting coils of opposite polarities in series. Among them, The detection coil has a total of 20 columns, and each column is composed of 16 rectangular small coils connected in series; a single sub-detection coil is formed by connecting two small rectangular coils of opposite polarities in series, so that the magnetic fields of the two small rectangular coils cancel each other out to achieve decoupling. Two of the sub-detection coils are connected in series to obtain a detection module composed of four small rectangular coils, and then a strip-shaped detection coil composed of 8 sub-detection coils connected in series is obtained. The detection coil is formed by laying 20 of the strip-shaped detection coils. Or The detection coil is composed of two layers of detection coils, and the second layer of detection coils is used to eliminate the detection blind area of the first layer. Let coils A, B, C, and D be four quadrupole coils, which are respectively formed by connecting four monopole coils in series with opposite polarities. The adjacent two monopole coils have opposite polarities, thus achieving decoupling of the quadrupole coil from the transmitting coil; by arranging multiple quadrupole detection coils from the outside to the inside, a first layer of detection coils composed of 8 rectangular coils on each side is obtained. The second layer of detection coils is arranged above the detection blind area at the junction of four different quadrupole coils to eliminate the blind spot, and a quadrupole coil and the same decoupling structure as the first layer of detection coils are adopted.

2. The metal foreign object detection coil structure of the wireless charging system for electric vehicles according to claim 1, wherein: When the detection coil is composed of two layers of detection coils, each side of the second layer of detection coils has seven monopole coils, and the monopole coils that cannot form a quadrupole coil in the middle adopt a bipolar coil structure, and decoupling from the transmitting coil is achieved by connecting two monopole coils of opposite polarities in series.

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