A foreign matter detection device, method, and wireless charging system

Abstract

The embodiment of the present disclosure provides a foreign matter detection device, method and wireless charging system, the foreign matter detection device comprises a coil layer and a foreign matter detection circuit, the coil layer comprises a plurality of coil groups arranged in the same layer, each coil group comprises two detection coils arranged symmetrically, one end of the two detection coils with the same polarity is connected to each other, the other end with the same polarity is connected to the foreign matter detection circuit respectively, the foreign matter detection circuit is used for detecting an induced signal generated by each coil group in a detection magnetic field, and then whether there is foreign matter between the transmitting coil and the receiving coil coupled with each other is detected according to the induced signal, wherein the detection magnetic field is a magnetic field formed between the transmitting coil and the receiving coil. The embodiment of the present disclosure can quickly and accurately detect the metal foreign matter mixed in the wireless charging, improve the charging efficiency and charging safety, and has low cost.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of wireless charging, in particular to a foreign matter detection device, method and wireless charging system. BACKGROUND

[0002] In recent years, new energy vehicles have developed rapidly, further accelerating the development of wireless power transmission. Wireless power transmission mainly includes electromagnetic radiation type, electromagnetic wave type and electromagnetic induction type transmission methods. Among them, new energy vehicles use the most mature electromagnetic induction type wireless power transmission method. There are two ground end transmission schemes for electromagnetic induction type wireless transmission, including track type dynamic power transmission and fixed point type static power transmission. The track type transmission method can reduce the capacity and mass of the vehicle power battery and can achieve the purpose of charging while traveling, which has a very high effect on reducing the cost of the vehicle end. However, this scheme requires a large area of ground end track, which is not realistic for new energy vehicles just starting. Therefore, the fixed point type static wireless charging becomes the only choice for the current vehicle mass production charging.

[0003] In the current new energy vehicle wireless charging system, the presence of metal foreign matter in the charging path will have a considerable impact on the electromagnetic induction type static charging. When there is metal foreign matter between the transmitting coil and the receiving coil, it will affect the coupling coefficient between the coils and reduce the mutual inductance between the coils, causing the resonance point to change during transmission, reducing transmission efficiency and affecting charging time. On the other hand, the eddy current in the metal foreign matter will generate a large amount of heat due to long-term exposure to the alternating magnetic field, which may cause ablation to the ground end or vehicle end. In severe cases, it may also cause fire and explosion, which poses a great risk to charging safety.

[0004] The current foreign matter detection for wireless charging of new energy passenger vehicles is mostly divided into camera image processing and millimeter wave radar detection, resulting in a sharp increase in foreign matter detection cost. The image processing detection method requires reliable software processing, and the hardware and software costs are relatively high. Millimeter wave radar detection has high detection accuracy, but it cannot distinguish between metal and non-metal. Materials such as plastic and rubber that do not affect charging are also reported as foreign matter detection abnormalities, affecting the charging experience of users. SUMMARY

[0005] The purpose of the embodiments of the present disclosure is to provide a foreign matter detection device, method and wireless charging system that can quickly and accurately detect metal foreign matter mixed during wireless charging, improve charging efficiency and charging safety, and have a relatively low cost.

[0006] To solve the above technical problems, the embodiments of the present disclosure adopt the following technical solutions:

[0007] The foreign matter detection device comprises a coil layer and a foreign matter detection circuit, the coil layer comprises a plurality of coil groups arranged in the same layer, each coil group comprises two detection coils arranged symmetrically, one end of the two detection coils with the same polarity is connected to each other, and the other end with the same polarity is connected to the foreign matter detection circuit respectively, the foreign matter detection circuit is used for detecting an induced signal generated by each coil group in a detection magnetic field, and then detecting whether there is a foreign matter between the transmitting coil and the receiving coil according to the induced signal.

[0008] In some embodiments, the coil layer comprises a first coil layer and a second coil layer arranged in layers, the first coil layer comprises a plurality of first coil groups arranged in the same layer, each first coil group comprises two first detection coils arranged symmetrically, and the second coil layer comprises a plurality of second coil groups arranged in the same layer, each second coil group comprises two second detection coils arranged symmetrically, and the symmetry of the two second detection coils in the second coil group is different from the symmetry of the two first detection coils in the first coil group.

[0009] In some embodiments, the first detection coils of the first coil group and the second detection coils of the second coil group are arranged alternately, so as to divide the projection area of the first coil layer and the second coil layer into a plurality of detection areas.

[0010] In some embodiments, the two first detection coils in each first coil group are axisymmetric structures, and the two second detection coils in each second coil group are center-symmetric structures.

[0011] The present disclosure also provides a foreign matter detection method applied to a foreign matter detection device, the foreign matter detection device comprises a coil layer and a foreign matter detection circuit, the coil layer comprises a plurality of coil groups arranged in the same layer, each coil group comprises two detection coils arranged symmetrically, one end of the two detection coils with the same polarity is connected to each other, and the other end with the same polarity is connected to the foreign matter detection circuit respectively, and the method comprises:

[0012] Obtaining an induced signal generated by each coil group in the coil layer;

[0013] According to whether the induced signal is an abnormal induced signal, it is judged whether there is a foreign matter between the transmitting coil and the receiving coil.

[0014] In some embodiments, the method further comprises:

[0015] According to the abnormal induced signal, the position of the foreign matter is determined.

[0016] In some embodiments, the coil layer includes a first coil layer and a second coil layer arranged in a stack, a symmetry manner of a first detection coil in the first coil layer is different from a symmetry manner of a second detection coil in the second coil layer, the abnormal induction signal includes a first abnormal induction signal detected in the first coil layer and a second abnormal induction signal detected in the second coil layer, and the method further includes:

[0017] determining whether there is an overlapping region between the first detection region corresponding to the first abnormal induction signal and the second detection region corresponding to the second abnormal induction signal;

[0018] if there is the overlapping region, determining that there is the foreign matter and the foreign matter is located in the overlapping region.

[0019] In some embodiments, if there is no overlapping region, the method further includes:

[0020] changing an input signal of the foreign matter detection circuit, and obtaining an induction signal based on the changed input signal;

[0021] determining whether a change of the induction signal is proportional to a change of the input signal;

[0022] if the change is proportional, determining that there is the foreign matter and the foreign matter is located in a union region of the first detection region corresponding to the first abnormal induction signal and the second detection region corresponding to the second abnormal induction signal; and if the change is not proportional, determining that there is no foreign matter.

[0023] In some embodiments, the abnormal induction signal includes the first abnormal induction signal detected in the first coil layer or the second abnormal induction signal detected in the second coil layer, and the method further includes:

[0024] changing an input signal of the foreign matter detection circuit, and obtaining an induction signal based on the changed input signal;

[0025] determining whether the first abnormal induction signal and the second abnormal induction signal exist simultaneously in the induction signal obtained after the input signal is changed;

[0026] if the first abnormal induction signal and the second abnormal induction signal exist simultaneously, determining whether there is an overlapping region between the first detection region corresponding to the first abnormal induction signal and the second detection region corresponding to the second abnormal induction signal obtained after the input signal is changed; and if the first abnormal induction signal and the second abnormal induction signal do not exist simultaneously, changing the input signal of the foreign matter detection circuit again, and determining whether a change of an induction signal based on the changed input signal is proportional to a change of the input signal.

[0027] The disclosure also provides a wireless charging system, comprising a charging device and a power receiving device, the charging device is provided with a transmitting coil, the power receiving device is provided with a receiving coil which is coupled with the transmitting coil, and the foreign matter detection device in any of the above technical solutions is used to detect whether there is foreign matter between the transmitting coil and the receiving coil.

[0028] The disclosure also provides a foreign matter detection device, comprising a memory and a processor, the memory is used to store a computer program, and the processor is used to execute the foreign matter detection method in any of the above technical solutions when the computer program is called.

[0029] The disclosure also provides a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to implement the foreign matter detection method in any of the above technical solutions.

[0030] The foreign matter detection device, method and wireless charging system provided by the disclosure can quickly and conveniently detect whether there is foreign matter between the transmitting coil and the receiving coil by detecting the induced signal between the two ends of the detection coil connected to the foreign matter detection circuit, and the detection result is accurate and reliable, which can effectively improve the wireless charging efficiency and safety. In addition, only the structure of the detection coil needs to be designed, and the cost is low. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the disclosure or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments described in the disclosure, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0032] Fig. 1(a) is a schematic diagram of magnetic field distribution in the case of wireless charging without metal foreign matter;

[0033] Fig. 1(b) is a schematic diagram of magnetic field distribution in the case of wireless charging with metal foreign matter;

[0034] Figure 2 Fig. 1(b) is a schematic diagram of magnetic field distribution in the case of wireless charging with metal foreign matter;

[0035] Figure 3 Fig. 1(b) is a schematic diagram of magnetic field distribution in the case of wireless charging with metal foreign matter;

[0036] Figure 4Structure schematic diagram of the first coil layer and the second coil layer of the foreign matter detection device of the embodiment of the present disclosure after assembly;

[0037] Figure 5 Structure schematic diagram of the foreign matter detection circuit of the foreign matter detection device of the embodiment of the present disclosure;

[0038] Figure 6 Flow chart of the foreign matter detection method of the embodiment of the present disclosure;

[0039] Figure 7 Flow chart of the specific implementation of the foreign matter detection method of the embodiment of the present disclosure. DETAILED DESCRIPTION

[0040] Various aspects and features of the present disclosure are described herein with reference to the accompanying drawings.

[0041] It should be understood that various modifications can be made to the embodiments described herein. Therefore, the above description should not be construed as limiting, but merely as exemplification of the embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the present disclosure.

[0042] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and, together with the general description of the disclosure given above, and the detailed description of the embodiments given below, serve to explain the principles of the present disclosure.

[0043] These and other characteristics of the present disclosure will become apparent from the following description of the preferred forms given, by way of non-limiting example only, with reference to the attached drawings.

[0044] It should also be understood that, although the present disclosure has been described with reference to certain specific examples, various modifications thereof will be readily apparent to those skilled in the art and can be made without departing from the spirit of the present disclosure, as described by the claims.

[0045] The above and other aspects, features, and advantages of the present disclosure will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, when properly considered together.

[0046] Specific embodiments of the present disclosure are described hereinafter with reference to the accompanying drawings; however, it will be understood that the embodiments described are merely examples of the present disclosure, which can be implemented in numerous ways. Well-known and / or repeated functions and structures are not described in detail to avoid obscuring the present disclosure unnecessarily or superfluously. Therefore, the specific structural and functional details of the embodiments described herein are not intended to be limiting, but are merely to be used as a basis for the claims and representative basis for teaching one skilled in the art to employ the present disclosure in substantially any appropriate detailed structure.

[0047] The specification can use the phrases "in one embodiment," "in another embodiment," "in yet another embodiment," or "in other embodiments," which can refer to one or more embodiments according to the present disclosure.

[0048] A wireless power transmission (WPT) system mainly includes a wireless transmitting device and a wireless receiving device. The wireless transmitting device is installed on a charging device, and the wireless receiving device is installed on a powered device. The transmitting coil (TX) of the wireless transmitting device and the receiving coil (RX) of the wireless receiving device transmit energy in a battery induction manner. When the powered device is in the charging range (the position of the receiving coil corresponds to the position of the transmitting coil) of the wireless transmitting device and is powered on to start the wireless charging function, the transmitting coil can generate an alternating magnetic field between the transmitting coil and the receiving coil, and transmit energy through the alternating magnetic field. The receiving coil receives the energy transmitted by the transmitting coil, and the powered device can be charged.

[0049] The powered device can be an electric vehicle, a mobile terminal such as a mobile phone, a tablet computer, a wearable device (for example, a smart watch), or an electric robot. The charging device can be a wireless charging station for charging an electric vehicle, which is installed on the ground. The charging device can also be a portable or non-portable charger for charging a mobile terminal. The embodiments of the present disclosure do not specifically limit the types of the powered device and the charging device.

[0050] There is an air gap between the transmitting coil and the receiving coil, and thus foreign matter can enter. According to the principle of electromagnetic induction, as shown in FIG. 1(a), when there is no metal foreign matter between the transmitting coil and the receiving coil in the normal working state during wireless charging, the magnetic lines of force between the transmitting coil and the receiving coil are uniformly distributed, and the magnetic field intensity at the same radius position is the same. As shown in FIG. 1(b), when there is metal foreign matter between the transmitting coil and the receiving coil, the alternating electromagnetic field emitted by the ground end of the wireless charging will induce an alternating electric field in the metal foreign matter to form an eddy current, and the eddy current will also induce a magnetic field that is coupled with the magnetic field induced by the ground end transmitting coil to generate a distorted magnetic field, thereby causing the magnetic field intensity at the same radius position to be different.

[0051] According to the transmission power formula calculated according to the equivalent model, when the metal foreign matter is in the alternating magnetic field, the charging transmission efficiency is obviously reduced, and the charging efficiency is obviously reduced; and the metal foreign matter in the alternating magnetic field will generate eddy current, and the magnetic field generated by the eddy current will further reduce the coupling coefficient of the transmitting end and the receiving end, so that the leakage inductance of the transmitting end increases, the resonance point changes, and the transmission efficiency is negatively affected, which further affects the charging efficiency. In addition, the metal foreign matter will generate a large amount of heat due to long time in the alternating magnetic field, which may cause ablation to the ground end or the vehicle end during electric vehicle charging, and in serious cases, it may also cause fire and explosion, which has a great charging safety hazard.

[0052] Therefore, the embodiments of the present disclosure provide a foreign matter detection method, device and wireless charging system to improve the charging efficiency and safety of wireless charging. The embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0053] Figures 2 to 5 The structure of the foreign matter detection device of the embodiments of the present disclosure is shown in the structure diagram of the foreign matter detection device of the embodiments of the present disclosure, as shown in Figures 2 to 5 The foreign matter detection device provided by the embodiments of the present disclosure includes a coil layer and a foreign matter detection circuit, the coil layer includes a plurality of coil groups arranged in the same layer, each coil group includes two detection coils 1 arranged symmetrically, one end of the two detection coils 1 with the same polarity is connected to each other, the other end with the same polarity is connected to the foreign matter detection circuit respectively, the foreign matter detection circuit detects the induced signal generated by each coil group in the detection magnetic field, and then detects whether there is foreign matter between the transmitting coil and the receiving coil according to the induced signal, wherein the detection magnetic field is the magnetic field formed between the transmitting coil and the receiving coil.

[0054] Specifically, the two detection coils 1 in the same coil group arranged in the same layer are in an axial symmetric structure or a central symmetric structure. Since the transmitting coil has the same magnetic field strength in the same radius with the center as the radius in the circular area of the coil, the magnetic field strength at the axial symmetric area and the central symmetric position of the transmitting coil is also completely the same, and the two detection coils 1 in the same coil group are arranged in the axial symmetric or central symmetric structure, which facilitates the detection of metal foreign matter according to the symmetric detection coils 1.

[0055] Each coil group in the same coil layer is electrically connected to the foreign matter detection circuit, and the detection coils 1 in each coil group can generate an induced signal under the action of the environmental magnetic field between the transmitting coil and the receiving coil.

[0056] According to the Lenz law, in the alternating magnetic field without foreign matter, the induced voltages induced by the two detection coils 1 have the same time direction and the same voltage size. Therefore, in the present embodiment, one end of the two detection coils 1 with the same polarity (for example, the tail end in the clockwise direction,Figure 2 The ends with the same label a, b, c or d are connected together, and the other ends with the same polarity are connected to the positive and negative poles of the foreign matter detection circuit respectively, so that the two detection coils 1 generate induction signals with the same size and opposite directions when there is no foreign matter, so that the induction voltage between the unconnected ends of the two detection coils 1 is 0 (for example, between A1 and A2, between B1 and B2, between C1 and C2, and between D1 and D2), that is, the voltage detected by the foreign matter detection circuit is 0 when there is no metal foreign matter. When there is a foreign matter, the presence of the foreign matter in the detection area corresponding to any one of the two detection coils 1 will affect the magnetic field strength and the corresponding magnetic flux, so that the induction voltages of the two detection coils 1 are different, and the induction voltage between the unconnected ends of the two detection coils 1 is not 0, that is, the voltage detected by the foreign matter detection circuit is not 0 when there is a metal foreign matter. Therefore, in the embodiment of the present disclosure, whether there is a foreign matter between the transmitting coil and the receiving coil can be detected by detecting whether there is a voltage signal (whether the voltage is 0) between the unconnected ends of the two detection coils 1 through the foreign matter detection circuit, without considering the specific voltage value, and the detection is convenient and reliable.

[0057] It can be understood that the two ends of each detection coil 1 are positive and negative respectively. The ends with the same polarity of the two detection coils 1 are positive, and the other ends with the same polarity are negative. The tail end in the clockwise direction can be positive or negative. When the tail end in the clockwise direction is positive, the head end in the clockwise direction is negative. Of course, the ends with the same polarity of the two detection coils 1 can also be the tail end in the counterclockwise direction. The specific polarity and winding method are determined according to the needs, and the present disclosure is not specifically limited.

[0058] In the embodiment, the materials, winding methods (all wound in the clockwise direction) and number of turns of the detection coils 1 located in the same layer can be the same. The detection coil 1 can be wound into a U-shaped structure to form different detection areas.

[0059] In the embodiment, the induction current or power between the unconnected ends of the two detection coils 1 can also be detected, and whether there is a foreign matter can be determined according to the corresponding current or power change.

[0060] The foreign matter detection device provided by the embodiments of the present disclosure can quickly and conveniently detect whether there is a foreign matter between the transmitting coil and the receiving coil by detecting the induced signal between the two ends of the detection coil connected to the foreign matter detection circuit, and the detection result is accurate and reliable, which can effectively improve the wireless charging efficiency and safety; in addition, only the structure of the detection coil needs to be designed in the embodiments, and the cost is low.

[0061] The foreign matter detection device is arranged between the transmitting coil and the receiving coil, and the transmitting coil and the receiving coil are usually arranged in parallel and are matched in shape, for example, the transmitting coil and the receiving coil are circular structures arranged in parallel. Therefore, the coil layer can be laid between the transmitting coil and the receiving coil, and the center of the coil layer coincides with the center of the transmitting coil or the receiving coil.

[0062] In the coil layer, the detection areas formed by the detection coils 1 of different coil groups can cover the projection area of the transmitting coil or the receiving coil (the area of the detection area is greater than or equal to the area of the projection area), so as to detect the foreign matter in the area corresponding to the transmitting coil (the projection area of the transmitting coil in the direction of the receiving coil), and ensure the accuracy of the detection.

[0063] In the embodiments, as shown in Figures 2 to 4 The detection areas formed by different coil groups are circular areas matched with the shape and size of the transmitting coil.

[0064] The foreign matter detection device can be arranged on the charging side or the power receiving side. Since the same charging device can charge different power receiving devices, in order to facilitate installation and charging, and to reduce the cost, the foreign matter detection device can be arranged on the charging side, for example, the coil layer is installed above the transmitting coil of the charging device, and the foreign matter detection circuit is connected to the charging circuit of the charging device.

[0065] In some embodiments, as shown in Figure 2 The coil layer includes a first coil layer 10, and the first coil layer 10 includes a plurality of first coil groups arranged in the same layer, each of the first coil groups includes two first detection coils (101, 102) arranged in symmetry, and the two first detection coils are axisymmetric structures.

[0066] Specifically, as shown in Figure 2As shown, the first coil layer 10 may include four first coil groups: A, B, C, and D. In each first coil group, two first detection coils (101 and 102) are symmetrical along the Y-axis. The ends of the two first detection coils (101 and 102) with the same polarity are connected to each other, and the other ends with the same polarity are respectively connected to the foreign object detection circuit. For example, in the first coil group A, the clockwise tail ends of the two first detection coils (the ends labeled 'a' in both first detection coils) are connected to each other, and the clockwise head ends (the ends labeled A1 and A2 in both first detection coils) are respectively connected to the foreign object detection circuit. Detection can be achieved by detecting changes in the induced signal of the first coil group A (changes in the induced signal between ends A1 and A2). Figure 2 The detection area A, enclosed by the first coil group A, is used to detect whether there are foreign objects.

[0067] The structures of the first coil groups B, C, and D are similar to those of the first coil group A, and will not be described again here.

[0068] In some embodiments, such as Figure 3 and Figure 4 As shown, the coil layer may further include a second coil layer 20 stacked on top of the first coil layer 10. The second coil layer 20 includes multiple second coil groups arranged on the same layer. Each second coil group includes two second detection coils (201, 202) arranged symmetrically. The two second detection coils have a centrally symmetrical structure.

[0069] Specifically, such as Figure 3 As shown, the second coil layer 20 may include four second coil groups: E, F, G, and H. In each second coil group, two second detection coils (201 and 202) are arranged in a centrally symmetrical structure around the center of the second coil layer 20. The ends of the two second detection coils (201 and 202) with the same polarity are connected to each other, and the other ends with the same polarity are respectively connected to the foreign object detection circuit.

[0070] For example, in the second coil group E, the clockwise ends of the two second detection coils (the ends labeled 'e' in both second detection coils) are connected to each other, and the clockwise beginning ends (the ends labeled E1 and E2 in the two second detection coils, respectively) are connected to the foreign object detection circuit. Detection can be achieved by detecting changes in the induced signal of the second coil group E (changes in the induced signal between the ends E1 and E2). Figure 3 The detection area E, formed by the second coil group E, is used to check for foreign objects.

[0071] In this embodiment, the first coil layer 10 and the second coil layer 20 can perform foreign object detection respectively. The first coil layer 10 and the second coil layer 20 can also cooperate with each other to perform detection. When they cooperate with each other, they can not only detect whether there is a foreign object between the transmitting coil and the receiving coil, but also detect the location of the foreign object.

[0072] When the first coil layer 10 and the second coil layer 20 are used together, the first coil layer 10 and the second coil layer 20 are stacked one on top of the other, with one being the upper coil layer and the other being the lower coil layer.

[0073] like Figure 4 As shown, the first detection coils (101, 102) of the first coil group and the second detection coils (201, 202) of the second coil group are arranged alternately vertically to divide the projection areas of the first coil layer 10 and the second coil layer 20 into multiple detection areas. These multiple detection areas correspond to the projection area of ​​the transmitting coil (the area projected towards the receiving coil), allowing the position of the foreign object relative to the transmitting or receiving coil to be determined based on the detection area where the foreign object is located.

[0074] For example, in this embodiment, the first coil layer 10 and the second coil layer 20 are stacked together to work together, which can divide 16 different detection areas, namely AH, BH, BE, AE, AG, BG, BF, AF, CF, DF, DG, CG, CE, DE, DH, and CH. When a metal foreign object is in a different detection area, the corresponding upper and lower detection coils will simultaneously induce a voltage. Then, the detection coil that induces the voltage will be located at a specific position, thereby realizing the positioning of the metal foreign object and accurately determining its location. At the same time, the detection sensitivity of the foreign object can be effectively improved by using a double-layer coil to detect the foreign object.

[0075] It is understandable that using a single coil layer can roughly locate the position of a foreign object based on the detection area (inner side of detection coil 1) formed by each coil group. However, since there may also be induced signals in the outer detection area of ​​detection coil 1, and the outer detection area of ​​one detection coil 1 may be the inner detection area of ​​another detection coil 1, inaccurate positioning may occur. Therefore, in this embodiment, a detection coil structure composed of two coil layers is preferred when locating the position of a foreign object.

[0076] In specific implementation, the coil layer can also be a multi-layer coil layer structure, and the detection coils 1 of different layers are staggered up and down to divide more detection areas, so as to further improve the positioning accuracy. For example, the coil layer can be a three-layer coil layer structure, and the detection coils 1 of different layers are symmetrically arranged along different directions, the detection coils 1 of the upper coil layer are symmetric along the X axis, the detection coils 1 of the middle coil layer are symmetric along the Y axis, and the detection coils 1 of the lower coil layer are centrally symmetric.

[0077] As shown in Figure 5 In this embodiment, the foreign matter detection circuit is a voltage sensing circuit. Specifically, a 5V power supply is input to the positive electrode of the operational amplifier U1 through the RC filter circuit formed by the parallel connection of resistors R1, C2 and R2, the negative electrode of the operational amplifier U1 is connected to the output end of the operational amplifier to form a follower, and then a current is input to the positive electrode of the operational amplifier U2 through R3 current limiting, at the same time, the negative electrode of the operational amplifier U2 is connected to the output end of the operational amplifier U2 through R6, at this time, the two ends X1 and X2 of the input coil (a coil group formed by the connection of two detection coils 1) are connected to the positive electrode and the negative electrode of the operational amplifier U2 through resistors R4 and R5 to form a proportional amplifier, the induced signal of the input coil is amplified and output through the operational amplifier U2, at the same time, since U1 inputs a fixed current to U2 through R3, according to the virtual short and virtual open principle, there is still a fixed output current when there is no voltage difference between X1 and X2, which avoids system false alarm caused by zero offset; the output end of the operational amplifier U2 is connected to the current limiting resistor R7 and the diode D1, and then the alternating current (for example, alternating voltage) output by the operational amplifier U2 is rectified into direct current to facilitate reading, and then the detected induced voltage Vsen is filtered through the RC filter circuit formed by the parallel connection of C3 and R8 and output, so as to realize the detection of the induced voltage of the two ends of the coil group.

[0078] In this embodiment, the use of operational amplifiers U1 and U2 not only can accurately detect and output the induced voltage of the coil group (even a small change can be sensed), but also can avoid system false alarm caused by zero offset, and further improve the foreign matter detection accuracy.

[0079] Figure 6 A flow chart of a foreign matter detection method of the embodiment of the present disclosure is shown, as shown in Figure 6 The embodiment of the present disclosure provides a foreign matter detection method, which is applied to a foreign matter detection device, the foreign matter detection device includes a coil layer and a foreign matter detection circuit, the coil layer includes a plurality of coil groups arranged in the same layer, each coil group includes two detection coils 1 arranged symmetrically, one end with the same polarity of the two detection coils 1 is connected to each other, the other end with the same polarity is connected to the foreign matter detection circuit respectively, and the method includes the following steps.

[0080] S101: Acquire the induced signals generated by each coil group in the coil layer;

[0081] S102: Determine whether there is a foreign object between the transmitting coil and the receiving coil based on whether the sensing signal is an abnormal sensing signal.

[0082] Specifically, each coil group in the coil layer is connected to a foreign object detection circuit. After the foreign object detection circuit is powered on, it can detect the induced signal (e.g., induced voltage) at both ends of each coil group formed by connecting two detection coils 1 in real time using a voltage sensor, and determine whether the detected induced signal is an abnormal induced signal, thereby determining whether there is a foreign object between the transmitting coil and the receiving coil. The detected induced signal can be compared with a preset induced signal threshold to determine whether the induced signal is an abnormal induced signal. In this embodiment, as... Figure 7 As shown, the presence of an abnormal sensing signal can be determined by judging whether the magnitude of the induced voltage at both ends of each coil group (e.g., ends A1 and A2) exceeds the bias voltage threshold (whether the voltage difference between the two ends is 0). If it exceeds the threshold, the presence of a foreign object is confirmed (S1021); if it does not exceed the threshold, the absence of a foreign object is confirmed (S1022). Setting the preset sensing signal threshold to 0 allows for setting a uniform sensing signal threshold for each coil group, making detection convenient and quick.

[0083] In other embodiments, the presence of a foreign object can also be determined by judging whether the magnitude of the detected induced signal is within a preset range. For example, when the induced signal is an induced current, in order to avoid false alarms caused by zero bias in the foreign object detection circuit, there is always a certain induced current in the circuit. In this case, it can be determined whether the magnitude of the detected induced current is within a preset current range to determine whether a foreign object is present.

[0084] When a foreign object is detected between the transmitting coil and the receiving coil, a corresponding prompt message can be sent to the charging device and / or the powered device so that the user can disconnect the power and remove the foreign object in time; when there is no foreign object between the transmitting coil and the receiving coil, the charging device can be controlled to charge the powered device.

[0085] It is understandable that the aforementioned foreign object detection method can be performed before charging (e.g., activating only the transmitting coil of the charging device) or during charging (activating both the transmitting coil of the charging device and the receiving coil of the receiving device). Pre-charging foreign object detection can proactively prevent issues of low transmission efficiency and low security caused by the presence of foreign objects; in-charge detection can detect foreign objects that fall in during charging, thus preventing such issues as low transmission efficiency and low security.

[0086] In some embodiments, the method further comprises:

[0087] S103: determining the position of the foreign matter according to the abnormal induction signal.

[0088] When the foreign matter between the transmitting coil and the receiving coil is detected, the position of the foreign matter can be determined according to the arrangement mode (such as arrangement position and arrangement size, etc.) of the detection coil 1 in the coil layer of each coil group, so as to realize accurate positioning of the foreign matter and facilitate timely cleaning of the foreign matter.

[0089] In some embodiments, as shown in Figure 4 , the coil layer comprises a first coil layer 10 and a second coil layer 20 arranged in layers, the symmetry mode of the first detection coil (101, 102) in the first coil layer 10 is different from the symmetry mode of the second detection coil (201, 202) in the second coil layer 20, the abnormal induction signal comprises a first abnormal induction signal detected by the first coil layer 10 and a second abnormal induction signal detected by the second coil layer 20 at a preset time, as shown in Figure 7 , the method further comprises:

[0090] S201: determining whether there is an overlapping area between the detection areas corresponding to the first abnormal induction signal and the second abnormal induction signal;

[0091] S2021: if there is an overlapping area, it is determined that there is a foreign matter, and the foreign matter is located in the overlapping area.

[0092] In this step, after detecting the abnormal induction signal, the position of the foreign matter can be accurately determined according to the coil layer to which the abnormal induction signal belongs. If the abnormal induction signals detected at a preset time (at a certain time point or within a certain time period) belong to the induction signals of the first coil layer 10 and the second coil layer 20 respectively, it is determined whether there is an overlapping area between the detection areas corresponding to the first abnormal induction signal and the second abnormal induction signal belonging to different coil layers, if there is, it is determined that the foreign matter is located in the overlapping area (for example, DE area in Figure 4 ). The overlapping area can be one or more, for example, the overlapping area can be DE, DF, and BH areas in Figure 4 at the same time.

[0093] Further, as shown in Figure 7 , if there is no overlapping area (S2022), the method further comprises:

[0094] S301: changing the input signal of the foreign matter detection circuit, and obtaining an induction signal based on the changed input signal;

[0095] S302: determining whether the change of the induction signal is proportional to the change of the input signal;

[0096] S3031: If proportional, it is determined that there is a foreign object, and the foreign object is located in the union region of the first detection region corresponding to the first abnormal induction signal and the second detection region corresponding to the second abnormal induction signal; S3032: If not proportional, it is determined that there is no foreign object.

[0097] In this step, if there is no overlapping region between the detection regions corresponding to the first abnormal induction signal and the second abnormal induction signal belonging to different coil layers (for example, the first abnormal induction signal is detected in the DE region, and the second abnormal induction signal is detected in the DH region), the input signal can be changed by increasing or decreasing the input voltage of the foreign object detection circuit, and the induction signal of the above region after changing the input signal is obtained. The first abnormal signal and the second abnormal signal before and after changing the input voltage are compared with the change of the input signal, respectively, to determine whether the induction signal changes proportionally with the change of the input signal. If proportional, it is determined that the first abnormal induction signal and the second abnormal induction signal are both induction signals generated due to the presence of a foreign object, and the DE region corresponding to the first abnormal induction signal and the DH region corresponding to the second abnormal induction signal are the positions where the foreign object exists. If not proportional, it is determined that the first abnormal induction signal and the second abnormal induction signal are not induction signals generated due to the presence of a foreign object, and it is determined that this time may be a zero bias situation. At this time, the charging device can be controlled to normally work to charge the powered device. If one of the first abnormal signal and the second abnormal signal changes proportionally with the change of the input signal, it is determined that the detection region corresponding to the abnormal signal that changes proportionally has a foreign object, a corresponding prompt signal is generated, and the prompt signal is sent to the charging device or the powered device for foreign object existence prompt, and the charging device is controlled to be powered off, so that the user of the charging device or the powered device removes and cleans the foreign object.

[0098] In some embodiments, the abnormal induction signal includes a first abnormal induction signal detected by the first coil layer 10 or a second abnormal induction signal detected by the second coil layer 20 within a preset time, and the method further includes:

[0099] S401: Change the input signal of the foreign object detection circuit, and obtain the induction signal obtained based on the changed input signal;

[0100] S402: Determine whether the first abnormal induction signal and the second abnormal induction signal exist in the induction signal obtained after changing the input signal;

[0101] ​​​​​​​S4031: If the first abnormal induction signal and the second abnormal induction signal exist simultaneously, determine whether the detection regions corresponding to the first abnormal induction signal and the second abnormal induction signal after changing the input signal of the foreign object detection circuit exist an overlapping region; S4032: If the first abnormal induction signal and the second abnormal induction signal do not exist simultaneously, change the input signal of the foreign object detection circuit again, and determine whether the change of the induction signal based on the changed input signal is proportional to the change of the input signal.

[0102] In this step, after the detected abnormal induction signal belongs to the first coil layer 10 or the second coil layer 20, it is further determined whether the abnormal induction signal is an induction signal generated due to the existence of a foreign object. By changing the input signal (for example, increasing the input voltage) of the foreign object detection circuit in step S401, it is determined whether the changed induction signal is an abnormal induction signal, and whether the abnormal induction signal exists in the first coil layer 10 and the second coil layer 20 simultaneously. If so, it is determined by step S4031 whether the detection regions corresponding to the first abnormal induction signal and the second abnormal induction signal after changing the input signal exist an overlapping region, i.e., step S201 is entered. In a similar way to the above-mentioned simultaneous detection of abnormal induction signals in the first coil layer 10 and the second coil layer 20, it is further determined whether a foreign object exists, and when a foreign object exists, the position of the foreign object is determined according to whether an overlapping detection region exists.

[0103] In step S4031, if the detection regions corresponding to the first abnormal induction signal and the second abnormal induction signal existing simultaneously after changing the signal exist an overlapping region, it is determined that a foreign object exists, and the foreign object belongs to the overlapping region (S2021). If no overlapping region exists (S2022), the method further comprises:

[0104] S501: Determine whether the first abnormal induction signal and the second abnormal induction signal change proportionally with the change of the input signal in the foreign object detection circuit;

[0105] S5021: If the change is proportional, it is determined that a foreign object exists, and the foreign object is located in the detection region corresponding to the first abnormal induction signal or the second abnormal induction signal before the input signal is changed; S5022: If the change is not proportional, it is determined that no foreign object exists.

[0106] In step S4032, if the change of the induced signal based on the changed input signal is proportional to the change of the input signal (S4041), it is determined that there is a foreign object, and the foreign object is located in the detection area corresponding to the first abnormal induced signal or the second abnormal induced signal before the input signal is changed; if it is not proportional (S4042), it is determined that there is no foreign object. That is, when the first abnormal induced signal and the second abnormal induced signal are not detected at the same time after the input signal is changed, it is determined whether there is a foreign object by continuing to change the input signal.

[0107] In an embodiment, if the abnormal induced signal is detected in the D area of the first coil layer 10, and no abnormal induced signal is detected in the second coil layer 20, that is, only the first abnormal induced signal is detected. The first abnormal induced signal can be caused by the entry of a foreign object, or can be a disturbance caused by a zero bias condition. In order to accurately determine the type of the first abnormal induced signal, the input voltage is increased to determine whether the abnormal induced signal is detected at the same time in the first coil layer 10 and the second coil layer 20 (the first abnormal induced signal and the second abnormal induced signal exist at the same time). If the abnormal induced signal is detected at the same time, for example, the first abnormal induced signal is detected in the D area of the first coil layer 10, and the second abnormal induced signal is detected in the E area of the second coil layer 20, it is determined whether the first abnormal induced signal and the second abnormal induced signal overlap by step 4031. If there is an overlap area (DE area), it can be determined that there is a foreign object in the DE area. If there is no overlap area, step S501 is entered to continue to determine. The above steps S5021 (or S5022) are similar to the above steps S302 and S3031 (or S3032), which will not be described here. If the abnormal induced signal is not detected at the same time, that is, the first abnormal induced signal is still detected in the D area of the first coil layer 10, and the second abnormal induced signal is not detected in the second coil layer 20, it can be determined that the first abnormal induced signal detected in the D area of the first coil layer 10 before the input signal is changed is not an induced signal caused by the presence of a foreign object. At this time, the input signal of the foreign object detection circuit can be changed again by step S4032 to determine whether the detected induced signal changes proportionally with the change of the input signal. By changing the input signal twice, it can be accurately determined whether there is a foreign object.

[0108] It can be understood that, since the input signal is changed by increasing the input voltage in the embodiment, when the input voltage is not changed, the detection area where the first abnormal induced signal or the second abnormal induced signal is detected can still detect the abnormal induced signal after the input voltage is changed, that is, in the above step S4031, the first abnormal induced signal is still detected in the D area.

[0109] In a specific implementation, the initial input voltage can also be set higher, and then the input voltage is reduced to determine whether the induced signal changes proportionally with the change of the input voltage. When the input voltage is reduced to a lower level, the induced voltage is also reduced, i.e., the abnormal induced signal can disappear, and it cannot be determined whether it is caused by the presence of a foreign object or by a working error, etc. Therefore, to improve the accuracy of detection, in this embodiment, after detecting the presence of an abnormal induced signal, the input voltage is further increased to determine whether the abnormal induced signal is caused by the presence of a foreign object.

[0110] As shown in FIG. 1, the complete process of the foreign object detection method is specifically described by taking the charging of an electric vehicle as an example. Figure 7

[0111] When the local (charging side) charging device and the vehicle end (power receiving side) receive a start signal, the local transmitting coil is first started to work at a small working voltage, and the vehicle end receiving coil is kept in a closed state. At this time, since the local transmitting coil is connected to a small alternating voltage, an alternating magnetic field is induced in the detection coil 1. At this time, according to the strength of the magnetic field in the symmetric region of the two detection coils in the same coil group, it can be determined whether a metal foreign object exists.

[0112] When a metal foreign object exists in the charging area (between the transmitting coil and the receiving coil), the induced voltage in the detection coil 1 exceeds the bias threshold. At this time, it is detected whether the detection coil 1 whose induced voltage exceeds the bias threshold belongs to the upper and lower layers of coils respectively. If the detection coil 1 belongs to the upper and lower layers of coils (the first coil layer 10 or the second coil layer 20), it is further determined whether the two layers of coils have an overlapping region. If there is an overlapping region, it can be determined that a metal foreign object exists in the overlapping region. At this time, the local transmitting coil is disconnected from the power supply, and the vehicle control system (ECU) is reported, prompting the vehicle owner to remove the metal foreign object and prompting the vehicle owner that the accurate position area of the metal foreign object is the overlapping region. If there is no overlapping region, the output voltage of the transmitting coil (the input voltage of the foreign object detection circuit) is increased to detect whether the induced voltage increases proportionally under the condition of increased voltage. If it does, the local transmitting coil is disconnected from the power supply, and the vehicle control system (ECU) is reported, prompting the removal of the metal foreign object and prompting the vehicle owner that the accurate position area of the metal foreign object is the union area of the detection areas corresponding to the abnormal detection signals detected by the upper and lower layers of coils. If the detected induced voltage does not increase with the increase of the input voltage, it is determined that this is a zero bias situation, the vehicle end start receiving coil starts wireless charging, and whether the charging is completed is detected during the charging process. If it is not completed, the metal foreign object detection process is repeated to prevent the misentry of a metal foreign object during the charging process and affect the charging efficiency.

[0113] ​If only the single-layer coil (the detection coil in the first coil layer 10 or the second coil layer 20) detects an induced voltage exceeding the bias threshold after the bias, the output voltage of the transmitting coil is increased, and whether the induced voltage exceeding the bias threshold is induced in the detection coil belonging to the upper layer or the lower layer after the voltage is increased is detected. If so, the positioning detection process of the abnormal induced signal of the double-layer coil is jumped to. If only the single-layer coil still detects the induced voltage, whether the detected induced voltage is increased in proportion to the input voltage of the foreign object detection circuit is judged. If the detected induced voltage is increased in proportion to the input voltage, the ground end receiving coil is disconnected from the power supply, the vehicle control system (ECU) is reported, the vehicle owner is prompted to remove the metal foreign object, and the position of the metal foreign object is prompted to be the detection area corresponding to the abnormal induced signal detected by the single-layer coil. If the detected induced voltage is not increased with the increase of the input voltage, it is judged that the zero bias condition occurs at this time, the ground end starting receiving coil starts wireless charging, and whether the charging is completed is detected during the charging. If the charging is not completed, the metal foreign object detection process is repeated to prevent the metal foreign object from entering during the charging and affecting the charging efficiency.

[0114] The foreign object detection method provided by the embodiments of the present disclosure fully considers the induced signal generated by the wireless charging system itself during the foreign object detection process when the double-layer coil layer is used for foreign object detection. When the abnormal induced signal is detected, the input signal of the foreign object detection circuit is changed for multiple detection judgments, the foreign object can be accurately detected, the double-layer coil layer is cooperated with each other to accurately position the foreign object, the charging efficiency and the charging safety are effectively improved, and the cost is low.

[0115] It should be noted that the foreign object detected by the embodiments of the present disclosure is a metal foreign object, and the non-metal foreign object such as plastic and rubber which does not affect the charging does not need to be detected. The frequent foreign object detection prompt can be avoided, and the user experience is improved.

[0116] The embodiments of the present disclosure also provide a wireless charging system, which comprises a charging device and a power receiving device. The transmitting coil is arranged on the charging device, the receiving coil is arranged on the power receiving device and is coupled with the transmitting coil. The wireless charging system further comprises the foreign object detection device according to any one of the embodiments, which is used to detect whether the foreign object exists between the transmitting coil and the receiving coil.

[0117] The wireless charging system provided by the embodiments of the present disclosure corresponds to the foreign object detection device and the foreign object detection method of the above-mentioned embodiments. Any optional item in the foreign object detection device and the foreign object detection method embodiments is also applicable to the embodiments of the wireless charging system, which will not be described here.

[0118] The embodiment of the present disclosure further provides a foreign matter detection device, comprising a memory and a processor, the memory is used for storing a computer program; the processor is used for executing the foreign matter detection method in any of the above embodiments when the computer program is called.

[0119] The embodiment of the present disclosure further provides a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to implement the foreign matter detection method in any of the above embodiments.

[0120] The above description is merely preferred embodiments of the present disclosure and a description of the principles of the technology applied. Those skilled in the art should understand that the disclosed range of the present disclosure is not limited to the technical solutions formed by the specific combinations of the above technical features, and should also cover other technical solutions formed by any combinations of the above technical features or their equivalent features without departing from the above disclosed concept. For example, the technical solutions formed by replacing the above features with the technical features disclosed in the present disclosure (but not limited to) having similar functions.

[0121] In addition, although each operation is described in a specific order, this should not be understood as requiring the operations to be performed in the specific order shown or in a sequential order. In certain circumstances, multitasking and parallel processing can be advantageous. Similarly, although several implementation details are included in the above discussion, these should not be interpreted as limiting the scope of the present disclosure. Certain features described in the context of separate embodiments can also be combined in a single embodiment. Conversely, various features described in the context of a single embodiment can also be separated and implemented in multiple embodiments.

[0122] Although the subject matter has been described in language specific to structural features and / or methodological acts, it is to be understood that the subject defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

[0123] The above describes the embodiments of the present disclosure in detail, but the present disclosure is not limited to these specific embodiments, and those skilled in the art can make various modifications and embodiments on the basis of the concept of the present disclosure, and these modifications and embodiments should fall within the scope of the present disclosure.

Claims

1. A foreign matter detection device characterized by comprising: The coil layer comprises a plurality of coil groups arranged in the same layer, each coil group comprises two detection coils arranged symmetrically, one end of the two detection coils with the same polarity is connected to each other, the other end with the same polarity is connected to the foreign matter detection circuit respectively, the foreign matter detection circuit is used for detecting the induced signal generated by each coil group in the detection magnetic field, and then detecting whether there is foreign matter between the mutually coupled transmitting coil and receiving coil according to the induced signal, wherein the detection magnetic field is the magnetic field formed between the transmitting coil and receiving coil; the coil layer comprises a first coil layer and a second coil layer arranged in layers, the first coil layer comprises a plurality of first coil groups arranged in the same layer, each first coil group comprises two first detection coils arranged symmetrically; the second coil layer comprises a plurality of second coil groups arranged in the same layer, each second coil group comprises two second detection coils arranged symmetrically, and the symmetry mode of the two second detection coils in the second coil group is different from that of the two first detection coils in the first coil group; According to whether the induced signal is an abnormal induced signal, it is judged whether there is foreign matter between the mutually coupled transmitting coil and receiving coil; The abnormal induced signal includes a first abnormal induced signal detected in the first coil layer and a second abnormal induced signal detected in the second coil layer, and the foreign matter detection circuit is used for judging whether there is an overlapping area between the detection areas corresponding to the first abnormal induced signal and the second abnormal induced signal; if there is an overlapping area, it is determined that there is foreign matter, and the foreign matter is located in the overlapping area; If there is no overlapping area, the foreign matter detection circuit is also used for: Changing the input signal of the foreign matter detection circuit, obtaining the induced signal based on the changed input signal; Judge whether the change of the induced signal is proportional to the change of the input signal; If proportional, it is determined that there is foreign matter, and the foreign matter is located in the union area of the first detection area corresponding to the first abnormal induced signal and the second detection area corresponding to the second abnormal induced signal; if not proportional, it is determined that there is no foreign matter.

2. The foreign object detection device of claim 1, wherein The first detection coils of the first coil group and the second detection coils of the second coil group are arranged alternately, so as to divide the projection area of the first coil layer and the second coil layer into a plurality of detection areas.

3. The foreign object detection device of claim 1, wherein The two first detection coils in each first coil group are axisymmetric structure, and the two second detection coils in each second coil group are center symmetric structure.

4. A foreign matter detection method characterized by comprising: The method is applied to a foreign matter detection device, the foreign matter detection device comprises a coil layer and a foreign matter detection circuit, the coil layer comprises a plurality of coil groups arranged in the same layer, each coil group comprises two detection coils arranged symmetrically, one end of the two detection coils with the same polarity is connected to each other, the other end with the same polarity is connected to the foreign matter detection circuit respectively, the foreign matter detection circuit is used for detecting the induced signal generated by each coil group in the detection magnetic field, and then detecting whether there is foreign matter between the mutually coupled transmitting coil and receiving coil according to the induced signal, wherein the detection magnetic field is the magnetic field formed between the transmitting coil and receiving coil; the method comprises: Obtaining the induced signal generated by each coil group in the coil layer; determining whether there is a foreign object between the mutually coupled transmitting coil and receiving coil according to whether the induced signal is an abnormal induced signal; the coil layer comprises a first coil layer and a second coil layer stacked, a symmetric mode of the first detection coil in the first coil layer is different from a symmetric mode of the second detection coil in the second coil layer, and the abnormal induced signal comprises a first abnormal induced signal detected in the first coil layer and a second abnormal induced signal detected in the second coil layer within a preset time; the method further comprises: determining whether there is an overlapping area between detection areas corresponding to the first abnormal induced signal and the second abnormal induced signal; if there is an overlapping area, determining that there is a foreign object and the foreign object is located in the overlapping area; if there is no overlapping area, the method further comprises: changing an input signal of the foreign object detection circuit to obtain an induced signal based on the changed input signal; determining whether a change in the induced signal is proportional to a change in the input signal; if proportional, determining that there is a foreign object and the foreign object is located in a union area of a first detection area corresponding to the first abnormal induced signal and a second detection area corresponding to the second abnormal induced signal; if not proportional, determining that there is no foreign object.

5. The foreign object detection method according to claim 4, characterized by, the method further comprises: determining a position of the foreign object according to the abnormal induced signal.

6. The foreign object detection method according to claim 5, characterized by, the abnormal induced signal comprises a first abnormal induced signal detected in the first coil layer or a second abnormal induced signal detected in the second coil layer within a preset time, and the method further comprises: changing an input signal of the foreign object detection circuit to obtain an induced signal based on the changed input signal; determining whether the first abnormal induced signal and the second abnormal induced signal exist simultaneously in the induced signal obtained after changing the input signal; if the first abnormal induced signal and the second abnormal induced signal exist simultaneously, determining whether there is an overlapping area between detection areas corresponding to the first abnormal induced signal and the second abnormal induced signal obtained after changing the input signal; if the first abnormal induced signal and the second abnormal induced signal do not exist simultaneously, changing the input signal of the foreign object detection circuit again, and determining whether a change in an induced signal based on the changed input signal is proportional to a change in the input signal.

7. A wireless charging system comprising a charging device and a powered device, the charging device being provided with a transmitting coil, the powered device being provided with a receiving coil that is mutually coupled with the transmitting coil, characterized in that, further comprising the foreign object detection device according to any one of claims 1 to 3, for detecting whether there is a foreign object between the transmitting coil and the receiving coil.

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