Apparatus, system, and method for detecting foreign objects

Abstract

To provide a detection device, a detection system, and a detection method for detecting a foreign object.SOLUTION: A detection device (100) includes a detection mat (102) having a plurality of detection coils (106) and at least one pair of groups of the detection coils (106). One pair of these groups of detection coils (106) includes a first group of detection coils (106) and a second group of detection coils (106). The first group of detection coils (106) includes a first impedance value, and the second group of detection coils (106) includes a second impedance value. The detection device (100) includes one or more drive subsystems (112) and a comparison subsystem (114).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] Embodiments of the present specification relate to a detection device. More specifically, embodiments of the present specification relate to a detection device for detecting foreign objects in the operating environment of a certain system.

Background Art

[0002] Conventional wireless power transfer (WPT) systems operate based on the principle of inductive power transfer that wirelessly transmits energy from one device to another. Usually, in a WPT system, a primary power device such as a transmitter wirelessly transmits power to a secondary power device called a receiver. These transmitter and receiver each include respective coils that are operably placed in close proximity during the operation of the WPT system. When a current passes through the transmitter coil, a magnetic field is generated and an electromotive force is induced in the receiver coil, thereby wirelessly transmitting power from the transmitter to the receiver.

[0003] In such a WPT system, if there is any metal object such as a metal can or aluminum foil between the transmitter coil and the receiver coil during wireless power transfer, this metal object may be unnecessarily heated due to eddy currents. This may cause safety hazards such as fire safety problems. Also, there is a possibility that the efficiency of the wireless power transfer process is unexpectedly affected or the entire process is completely interrupted.

[0004] There are various methods for detecting foreign objects in a WPT system. These methods include detecting the presence of a foreign object based on the measured value of the power drawn from the primary coil due to the frequency variation of the current in the primary coil, or detecting the unbalanced difference between the current and voltage in the primary coil. Also, in some detection methods, there may be some delay in detecting a foreign object after wireless power transfer is started. During this time, power continues to be consumed by the foreign object, which will lead to power waste.

Summary of the Invention

[0005] In one embodiment, a detection device comprises a detection mat having a plurality of detection coils and at least one pair of detection coil groups, the pair of detection coil groups including a first and a second group of detection coils. The first group of detection coils includes a first impedance value, and the second group of detection coils includes a second impedance value. Furthermore, the detection device comprises one or more drive subsystems and one comparison subsystem. The drive subsystem is operably coupled to the detection mat and configured to energize at least one pair of detection coil groups. The comparison subsystem is operably coupled to the detection mat and configured to receive a differential current signal from at least one pair of detection coil groups, the comparison subsystem is configured to generate a control signal based on this differential current signal.

[0006] In another embodiment, a detection system comprises a detection device and a wireless power transmission (WPT) system. The detection device comprises a detection mat having a plurality of detection coils and at least one pair of detection coil groups, the at least one pair of detection coil groups comprising first and second groups of detection coils. The first group of detection coils comprises a first impedance value, and the second group of detection coils comprises a second impedance value. Furthermore, the detection device comprises one or more drive subsystems and one comparison subsystem. The drive subsystem is operably coupled to the detection mat and configured to excite at least one pair of detection coil groups. The comparison subsystem is operably coupled to the detection mat and configured to receive differential current signals from at least one pair of detection coil groups, the comparison subsystem is configured to generate control signals based on these differential current signals. The WPT system includes a primary power supply configured to supply power in the form of alternating current (AC) voltage signals. The WPT system further includes a transmitter unit having at least one transmitter coil, the transmitter unit is configured to receive AC voltage signals from the primary power supply. Furthermore, the transmitter unit is configured to generate a primary magnetic field in response to a received AC voltage signal, with the detection mat operably coupled to the transmitter unit. The WPT system further includes a receiver unit comprising at least one receiver coil and configured to receive at least a portion of the primary magnetic field generated by the transmitter unit. The WPT system further includes a control unit operably coupled to a detection device and configured to receive a control signal from the detection device and to control the power supply to the transmitter unit based on this control signal.

[0007] In yet another embodiment, a method includes utilizing a detection device comprising a detection mat having a plurality of detection coils and at least one pair of detection coil groups, wherein the pair of detection coil groups includes a first and a second group of detection coils. The first group of detection coils includes a first impedance value, and the second group of detection coils includes a second impedance value. The method further includes exciting at least one pair of detection coil groups and measuring a differential current signal from at least one pair of detection coil groups. Furthermore, the method includes generating a control signal based on the differential current signal and transmitting the control signal. [Brief explanation of the drawing]

[0008] These and other features and aspects of the present invention will be better understood by reading the following detailed description with reference to the accompanying drawings, where similar reference numerals throughout these drawings represent similar parts.

[0009] [Figure 1] This is a schematic diagram of an exemplary detection device for detecting the presence of foreign matter according to an aspect of this specification. [Figure 2A] This is a schematic diagram showing an exemplary pair of detection coils according to an aspect of this specification. [Figure 2B] This is a schematic diagram showing an exemplary pair of detection coils according to an aspect of this specification. [Figure 3A] This is a schematic diagram showing a part of a detection device comprising a pair of detection coils coupled to a drive subsystem, according to an aspect of this specification. [Figure 3B] This is a schematic diagram showing a part of a detection device comprising a pair of detection coils coupled to a drive subsystem, according to an aspect of this specification. [Figure 3C] This is a schematic diagram showing a part of a detection device having one or more drive subsystems coupled to a pair of detection coil groups, according to an aspect of this specification. [Figure 3D]This is a schematic diagram showing a part of a detection device having one or more drive subsystems coupled to a pair of detection coil groups, according to an aspect of this specification. [Figure 3E] This is a schematic diagram showing a part of a detection device having one or more drive subsystems coupled to a pair of detection coil groups, according to an aspect of this specification. [Figure 4] This is a schematic diagram of an exemplary detection system having a detection device for detecting the presence of foreign matter in the operating environment of a WPT system, according to an aspect of this specification. [Figure 5] This is a schematic diagram showing an exemplary comparative subsystem of a detection device according to an aspect of this specification. [Figure 6] This describes an exemplary method for detecting the presence of foreign matter in the operating environment of a WPT system, according to aspects of this specification. [Figure 7] This describes an exemplary method for detecting the presence of foreign matter in the operating environment of a WPT system, according to aspects of this specification. [Figure 8] This is a cross-sectional view of a detection mat according to an aspect of this specification. [Modes for carrying out the invention]

[0010] Embodiments of this specification relate to detection devices, detection systems, and methods for detecting foreign objects. In certain embodiments, the detection devices can be used to detect foreign objects in a wireless power transmission (WPT) system. As used herein, the term “foreign object” refers to an object that is conductive or has a detectable permeability and is not part of the system but is incidentally present in the operating environment of the system. Non-limiting examples of foreign objects include ferrous objects, tin cans, or other conductive or ferrous objects. For example, a can or a bunch of keys would be considered a foreign object in the operating environment of the WPT system.

[0011] As used herein, the term “primary magnetic field” refers to the magnetic field excited by a transmitter unit, such as the transmitter unit of this WPT system. The term “operating environment” is defined by the primary magnetic field within the system, where the primary magnetic field of the transmitter unit is detectably present and can detectably interact with foreign matter. For example, foreign matter present in the operating environment of this WPT system may experience a temperature increase due to its interaction with this primary magnetic field.

[0012] As used herein, the term "detection coil group" refers to a single detection coil or two or more coils, where each detection coil in each group is electrically coupled to one another. The term "pair of detection coil groups" refers to two such detection coil groups.

[0013] Some electric vehicles (EVs) and hybrid vehicles are charged using wireless power transmission (WPT) systems, or inductive power transmission. This WPT system primarily consists of two parts: a transmitter unit, which is part of the charging station, and a receiver unit located inside the electric vehicle (EV). The transmitter unit in the charging station is inductively coupled to the receiver unit in the EV. Typically, when the receiver coil in the EV is brought into the operating environment of the transmitter coil and power is supplied to the transmitter unit, power transmission between the transmitter unit's coil and the receiver unit's coil begins.

[0014] If a foreign object made of conductive material or steel material is accidentally located in the operating environment of this WPT, this foreign object may interact with the magnetic field generated by the transmitter unit. As a result, the foreign object may accidentally intercept the magnetic field and draw power from the transmitter unit through this field. Therefore, if the foreign object draws power in this way, it will result in wasted power and unnecessary heating of the foreign object. If this is not addressed in a timely manner or is not noticed, the temperature of the foreign object may rise to a level that makes handling dangerous and may also cause safety risks. Therefore, it is desirable to detect the presence of foreign objects in order to prevent wasted power and avoid risks in a hazardous environment.

[0015] Figure 1 shows a detection device 100 comprising a plurality of detection coils 106 and a detection mat 102 having at least one pair of the detection coils 106 (not shown in Figure 1). The at least one pair of the detection coils 106 includes a first group of detection coils 106 and a second group of detection coils 106, the first group of detection coils 106 having a first impedance value and the second group of detection coils 106 having a second impedance value. The detection device 100 further comprises one or more drive subsystems 112 operably coupled to the detection mat 102 and configured to energize at least one pair of the detection coils 106. Furthermore, the detection device 100 comprises a comparison subsystem 114 operably coupled to the detection mat 102 and configured to receive differential current signals from at least one pair of the detection coils 106. The comparison subsystem 114 is configured to generate control signals based on these differential current signals.

[0016] In certain embodiments, the detection device 100 is configured to detect the presence of foreign objects in the operating environment of a wireless power transfer (WPT) system (not shown in FIG. 1). When a foreign object is present in the operating environment of the present WPT system, it may cause fluctuations in the impedance values of one or more detection coils 106. The presence of foreign objects is confirmed using the fluctuations in the impedance values of the detection coils 106. The group of detection coils 106 will be described in more detail with reference to FIGS. 2A-2B and FIGS. 3A-3B.

[0017] Furthermore, the detection mat 102 may include several geometric positions, also referred to as "detection regions" 104. The detection regions 104 define discrete regions of the detection mat 102, and each detection region 104 includes one or more groups of detection coils 106. Note that the detection regions 104 may not be physically separated or isolated from each other, and here the detection regions 104 may be electrically insulated from each other. Also, the detection regions 104 may have a geometric or non-geometric shape.

[0018] The detection mat 102 may be a flexible mat, a shape-conforming mat, a rigid mat, or a plug-and-play type mat, a stand-alone type mat, or a combination thereof. Note that the surface area of the detection mat 102 may be greater than or equal to the surface area of the transmitter unit on which the detection mat 102 is disposed. The substrate of the detection mat 102 may be made of an electrically insulating material. The detection mat 102 may further include a mechanically wear-resistant material to withstand the operation of an electric vehicle thereon. The detection mat 102 may be further designed for outdoor use, and thus may be temperature-resistant or moisture-resistant, and may also be resistant to water ingress.

[0019] In some embodiments, the detection coil 106 may be disposed on the substrate of the detection mat 102, or may be embedded in the substrate of the detection mat 102 to ensure user safety and aesthetics. In some other embodiments, the detection coil 106 may be printed, molded, woven, or additively manufactured on the substrate of the detection mat 102.

[0020] The detection coil 106 is an electromagnetic coil. In the illustrated embodiment of FIG. 1, the detection coil 106 is used for illustrative purposes, but each detection coil 106 may include a spiral or other coil phase. Further, each detection region 104 may have one or more detection coils 106. In certain embodiments, the group of detection coils 106 may include various coil phases, shapes, and geometric arrangements of the detection coils 106. Non-limiting examples of the shape of the detection coil 106 include helical coils, spiral coils, and non-circular coils. The different detection coils 106 or groups of detection coils 106 provided on the detection mat 102 may have the same impedance value or different impedance values.

[0021] Each pair of groups of detection coils 106 is disposed at the same or different geometric positions on the detection mat 102 and includes two groups forming the pair of groups of detection coils 106. As an example, the two groups in this pair may be disposed in the same detection region 104 or in two different detection regions 104. Non-limiting examples include that the groups of detection coils 106 may be concentric coils, adjacent coils, or parallel arrangements of coils. Further, one or more groups of detection coils 106 may be disposed in a single plane or in two or more layers. The detection coils 106 within a group of detection coils 106 may be connected in series, in parallel, or in a combination of series and parallel connections.

[0022] In some embodiments, a pair of detection coils 106 includes concentric coils. In non-limiting examples, the inductance value of one of these two concentric coils is different from the inductance value of the other concentric coil. For example, the inductance value of one concentric coil of a pair may be represented by L, while the inductance value of the other concentric coil of a pair may be represented by nL.

[0023] The drive subsystem 112 includes one or more drive units and one drive controller. The drive subsystem 112 is operably coupled to the detection mat 102 and configured to energize one or more pairs of a group of detection coils 106. The drive subsystem 112 may be configured to energize a group of detection coils 106 designated in the detection device 100 intermittently or periodically, where the designated group of detection coils forms one or more pairs of a group of detection coils 106. The drive subsystem 112 may be configured to energize pairs of groups of detection coils 106 belonging to the same or different detection regions 104. In certain embodiments, the drive subsystem 112 may be configured to energize a group of detection coils 106 arranged symmetrically with respect to the primary magnetic field of the WPT system (not shown in Figure 1).

[0024] In one example, the drive subsystem 112 may be configured to simultaneously or sequentially energize groups of detection coils 106 in pairs. Additionally or alternatively, the drive subsystem 112 may be configured to simultaneously or sequentially energize two or more pairs of detection coils 106 in the detection mat 102. In one example, the drive subsystem 112 may be configured to scan the detection mat 102 for the presence of foreign objects. Detection of the presence of foreign objects may be completed before the wireless power transmission of a device (such as an EV) begins. Furthermore, detection of the presence of foreign objects may also be performed periodically or intermittently during the wireless power transmission process of the device (such as an EV).

[0025] As detailed in Figures 3A to 3E, for example, each pair of detection coils 106 may be coupled to its respective drive subsystem, and in another example, two or more pairs of detection coils 106 may be coupled to different drive units that share a common drive controller.

[0026] In some embodiments, the drive unit of the drive subsystem 112 is configured to supply a voltage signal to one or more groups of the detection coils 106, and the drive controller is configured to control the operation of the drive unit. To this end, the drive controller turns on the drive subsystem 112 to excite one or more groups of the detection coils 106, and turns off the drive subsystem 112 when it is not necessary to excite the groups of detection coils 106. In certain embodiments, the drive subsystem 112 includes one or more of the following: an inverter, a converter, a linear amplifier, an electronic switch, or a combination thereof. The switching operation of the drive subsystem 112 may be performed by electronic switches such as bidirectional switches or semiconductor switches, mechanical switches such as relays or contractors, or a combination thereof. In certain embodiments, the drive subsystem 112 may draw power from a primary power supply configured to supply power to the transmitter unit of the WPT system. Alternatively, the drive subsystem 112 may have a separate power supply, such as a battery, but not limited to these.

[0027] Furthermore, if foreign matter is present on the detection mat 102 during operation, it may be inductively coupled to one or more detection coils 106, thereby potentially affecting the resulting impedance values ​​in those particular groups of detection coils 106. In addition, the individual group-specific impedance values ​​of the detection coils 106 in the detection device 100 may also be the same or different when no foreign matter is present. Furthermore, the individual impedance values ​​of two groups in a pair of detection coils 106 may also be the same or different when no foreign matter is present. In some of these embodiments, the detection mat 102 further includes a compensator element (not shown in Figure 1) that is operably coupled to at least one of the pair of detection coils 106 to produce similar resulting impedance values ​​from each of the two groups in the pair of detection coils 106 when no foreign matter is present. In some other embodiments, a drive controller may be used to provide voltage compensation to one of the groups in the pair of detection coils 106. As an example, the drive controller of the drive subsystem 112 supplies different voltage signals to two groups in a pair of detection coils 106 so that, when no foreign matter is present, the two groups in the pair of detection coils 106 are driven by the same current with similar magnitude and phase.

[0028] The comparison subsystem 114 is operably coupled to the detection mat 102 and is configured to receive one or more differential current signals from the detection mat 102. The comparison subsystem 114 is configured to determine the detection voltage signal based on this differential current signal. Note that if no foreign matter is present, the value of this differential current signal may become very small and undetectable. Also, due to inductive coupling between the foreign matter and one or more detection coils 106, the value of the differential current signal may become a non-zero value that is detectable in the presence of foreign matter.

[0029] The detection device 100 may be a standalone device that can be used to detect the presence of foreign objects in a system such as, but not limited to, a WPT system. For this purpose, the detection device 100 may be used in conjunction with an existing WPT system to detect the presence of foreign objects before and / or during wireless power transmission. In addition to the detection mat 102, the drive subsystem 112, and the comparison subsystem 114, the detection device 100 may further include a communication unit (not shown in Figure 1) that enables the detection device 100 to communicate with the system in which it is used. For example, this communication unit may enable the detection device 100 to communicate with the WPT system in accordance with Society of Automotive Engineers (SAE) standards. This communication unit may be used to transmit a detection voltage signal to the control unit of the WPT system to determine whether to continue supplying power to the transmitter unit of the WPT system.

[0030] Advantageously, the detection device 100 according to this technology is configured to detect even relatively small foreign objects in the operating environment of the WPT system. For example, this foreign object may have a surface area of ​​2 square centimeters or more.

[0031] Referring to Figures 2A and 2B, in certain embodiments, one or more pairs of detection coils in a detection device may be energized to obtain a differential current signal from the detection mat, and this differential current signal is used to determine the presence or absence of foreign matter. Each of the two groups in these pairs of detection coils may contain one or more detection coils.

[0032] In certain embodiments, the first and second groups in a pair of detection coils are arranged symmetrically with respect to the primary magnetic field. Furthermore, the first and second groups in a pair of detection coils are arranged in the same geometric region on the detection mat. In some embodiments, the first and second groups in a pair of detection coils include structurally similar arrangements with respect to the detection coils. Also, in certain embodiments, the first and second impedance values ​​of these groups in a pair of detection coils are similar when no foreign matter is present in the operating environment of the WPT system. As used herein, similar impedance values ​​refer to impedance values ​​that have a variation of plus or minus 0.5% or less from each other. For example, the impedance value of the first group may be within minus 0.5% of the impedance value of the second group, where these first and second groups form a pair of detection coils.

[0033] In some other embodiments, these first and second impedance values ​​are different in the absence of foreign matter. In some of these embodiments, the detection mat may include a compensator element operably coupled to one of the first or second groups in a pair of detection coils to compensate for the difference in impedance values ​​between the first and second groups of detection coils 106. In some embodiments, these first and second impedance values ​​are different in the absence of foreign matter, and one or more drive subsystems further include a drive controller configured to supply different voltage signals to the first and second groups of detection coils such that, in the absence of foreign matter, the first and second groups in the pair of detection coils are driven by the same current with similar magnitude and phase.

[0034] As described with respect to Figure 2A, the detection coils in a particular pair of detection coils are arranged symmetrically with respect to the primary magnetic field and are therefore exposed to similar primary magnetic field strengths. As described with respect to Figure 2B, the groups in a pair of detection coils may be arranged in the same geometric region on the detection mat, and therefore these groups may have similar primary magnetic field strengths. In some embodiments, each group in a pair of detection coils has the same impedance value when there is no foreign matter in the operating environment of the WPT system. In some other embodiments, the two groups in a pair of detection coils have different impedance values. In these embodiments, the two groups in these pairs of detection coils may be supplied with a very small and undetectable amount of differential current in relation to a compensator element or with the assistance of a drive controller, however, in the presence of foreign matter, one or more detection coils in one of the groups belonging to these pairs of detection coils are electrically coupled with the foreign matter, changing the net impedance of the detection coil group, so that a difference occurs in the current drawn by the two groups in these pairs of detection coils. As a result, the differential current, which is the difference between the input current of one of the two groups in this pair and the input current of the other group in the same pair of detection coils, reaches a detectable value.

[0035] Figure 2A shows an exemplary detection mat 200 comprising multiple detection regions 202, each having a group 204 of detection coils 205. In this non-limiting illustrated embodiment, the detection mat 200 is shown having a 4x4 array in the detection region 202, and each detection region 202 is shown having four groups 204 of detection coils 205. However, the number of detection regions 202 in the detection mat 200 and the number of groups 204 in each detection region 202 may vary, and this is merely illustrative. Furthermore, in this illustrated example, the detection mat 200 is shown having 16 detection regions 202, but the number of detection regions 202 in a single detection mat such as the detection mat 200 may be one or more. Also, each group 204 may contain one or more detection coils 205. Furthermore, the spiral shape of the detection coil 205 in group 204 is illustrative, and the shape of the detection coil 205 may be circular, non-circular, spiral, helical, or a combination thereof, but is not limited thereto. The detection mat 200 may be placed on a transmitter unit (not shown in Figure 2A). In addition, the dotted circle 206 represents the transmitter coil of the transmitter unit located beneath the detection mat 200.

[0036] Any two groups 204 in the detection coils that are likely to be exposed to similar strengths of the primary magnetic field may be paired to form a pair of detection coil groups for detecting the presence of foreign matter. Several possible pairs of groups 204 of the detection coils 205 are represented by n-n'. For example, group 204 referred to by reference number 208 is arranged symmetrically with respect to the primary magnetic field of the transmitter coil 206 or transmitter unit and forms pair 212 of detection coil group 208. Similarly, group 210 is arranged symmetrically with respect to the primary magnetic field of the transmitter unit and forms another pair 214 of detection coil group 210. Other pairs of groups 204 of the detection coils 205 other than 212, 214, and n-n' are also possible.

[0037] In certain embodiments, when the detection mat 200 is placed on the transmitter unit, detection coils 205 in one or more pairs of groups 204 may be excited to detect the presence of foreign matter in the operating environment of the WPT system (not shown in Figure 2A). For example, one of the two pairs 212 or 214 may be excited by a drive subsystem. Furthermore, if the impedance values ​​of the two groups in these pairs of groups are different, a compensator element 218 may be operably coupled to at least one of the groups 204 in the pair of groups 204 of the detection coils 205 so that the resulting impedance values ​​from each of the two groups 204 in these pairs of detection coils 205 are similar when no foreign matter is present.

[0038] Figure 2B shows a detection mat 220 comprising a plurality of detection regions 224, each having two or more detection coils 222. The detection device 220 may be located on a transmitter unit (not shown in Figure 2B). In the illustrated embodiment, the dotted circles 225 represent the transmitter coils of the transmitter unit located beneath the detection device 220. Each region 224 also includes a plurality of concentric groups of detection coils 222 arranged in each detection region 224. It is conceivable within the scope of this application that there may be a greater number of detection coils 222 per region 224, or that the shape and dimensions of the detection coils 222 may differ, and the embodiment shown in Figure 2B is a representative embodiment presented for illustrative purposes only. The pairs 226 of groups 228 and 230 of detection coils 222 are formed in the manner shown. The individual groups 228 and 230 are arranged in the same geometric region such that the detection coils 222 of these groups 228 and 230 are exposed to similar primary magnetic field strengths.

[0039] Figure 3A shows a portion 300 of the detection device described herein. The portion 300 includes a pair of detection coils 304 and 306 302, arranged on the detection mat of the detection device. In the embodiments intended herein, both groups 304 and 306 of the detection coils 308 are excited by a single drive subsystem 310. The drive subsystem 310 includes a drive unit 311 and a drive controller 314. Both groups 304 and 306 of the detection coils 308 are excited using the single drive unit 311 of the drive subsystem 310. The drive unit 311 includes an inverter / converter 312, capacitors 309 and 311, and one or more compensator elements 315 and 317. The capacitance values ​​of capacitors 309 and 311 may be fixed or variable. The drive controller 314 of the drive subsystem 310 is configured to control the excitation voltage to the two groups 304 and 306 of the detection coils 308. As shown in the figure, the detection coils 308 in each group 304 and 306 may be coupled to each other in series, in parallel, or both. Capacitors 309 and 311 are coupled to these groups 304 and 306 and form a resonant circuit with the detection coils 308 of groups 304 and 306. Capacitors 309 and 311 help to regulate the current driven by the detection coils 308 and thus modify the strength of the magnetic field used to detect foreign objects on the detection mat of this detection device.

[0040] One or more detection coils 308 located near a foreign object may be electromagnetically coupled to the foreign object, and this inductive coupling may result in a variation in the value of the current drawn by the detection coils 308. In one embodiment, two groups 304 and 306 in a pair 302 of detection coils 308 may have detectably similar impedance values ​​when no foreign object is present. To detect the presence of a foreign object, the differential current signal of the pair 302 is calculated based on the feedback current signal I1318 of group 304 and the continuous current signal I2320 of group 306, or vice versa. In another embodiment, when no foreign object is present, if the two groups 304 and 306 have detectably different impedances, one or more compensator elements 315 and 317 are used to ensure that the currents drawn by these two groups are similar to those when no foreign object is present. Non-limiting examples of compensator elements 315 and 317 may include inductance, resistance, and capacitance in series, parallel, or both forms.

[0041] Figure 3B shows another embodiment in which part 330 of the detection device according to this specification comprises a pair of first group 334 and second group 336 of detection coils 338 arranged on the detection mat of the detection device. These two groups 334 and 336 are coupled to a drive subsystem 340. The drive subsystem 340 includes two drive units 342 and 344 configured to excite the first group 334 and the second group 336, respectively. These two drive units 342 and 344 include inverters 348 and 350, DC / DC converters 352 and 354, and capacitors 333 and 335. Although not shown, one or both drive units 342 and 244 may further include one or more compensator elements. Capacitors 333 and 335 coupled to these groups 334 and 336 form a resonant circuit with the detection coil 338 of groups 334 and 336, thereby regulating the current driven by the coil and thus assisting in regulating the strength of the magnetic field in the detection mat. Inverters 348 and 350 receive input from two DC / DC converters 352 and 354 that drive these two groups 334 and 336, which may have similar or different impedance values ​​in the absence of foreign matter.

[0042] The drive subsystem 340 further includes a drive controller 346, which may be configured to compensate for any difference in current values ​​between the first and second groups 334 and 336, even if there is a difference in impedance values ​​between the first and second groups 334 and 336. In embodiments where the impedance values ​​of these groups 334 and 336 are different, the drive controller 346 may be configured to adjust the current used to drive these two groups 334 and 336 in one or more ways. In one embodiment, the drive controller 346 may be configured to change the voltage signals V1 and V2 of the inverters 348 and 350 by controlling the DC / DC stage converters 352 and 354. In another embodiment, the duty cycle of the inverters 348 and 350 may be changed without changing the operating frequency of the inverters 348 and 350, so that the first and second groups 334 and 336 of the detection coil 338 are driven by the same current with similar magnitude and phase when no foreign matter is present. The differential current signal of the pair 332 is calculated based on the feedback current signal I1356 of the first group 334 and the continuous current signal I2358 of the second group 336, or vice versa.

[0043] Referring here to Figures 3C to 3E, Figures 3C to 3E illustrate embodiments of an operable coupling between a drive subsystem and a group of detection coils. During detection operation, these groups of detection coils are coupled to one or more drive subsystems of the detection system, drawing current from one or more drive units of this drive subsystem. If the impedance values ​​of both groups in a pair of these groups are similar, the differential current drawn by these two groups in the pair of detection coils will be negligible in the absence of foreign matter. However, if the impedances of the two groups in the pair of detection coils are different, the drive controller compensates one or both groups in the pair of detection coils to ensure that these two groups are driven by similar current signals in the absence of foreign matter. The drive controller further controls the excitation voltage, excitation frequency, and excitation time of the detection coils. The drive controller turns on the drive units to excite the groups of detection coils and turns off the drive units when it is not necessary to excite the groups of detection coils. The drive controller may use electronic circuits to control these drive units. Non-exclusive examples of electronic circuits include microcontrollers, field-programmable gate arrays (FPGAs), semiconductor devices, logic gates, device drivers, oscillators and timers, or combinations thereof.

[0044] Figure 3C shows a portion 360 of a detection device (not shown in Figure 3C), which has a drive subsystem 362 coupled to a plurality of detection coil groups 364 arranged on a detection mat. The drive subsystem 362 includes a plurality of drive units 368, each of which is coupled to a corresponding group 366 of detection coils. The drive subsystem 362 further includes a drive controller 370 that controls the operation of the drive units 368.

[0045] Figure 3D shows a portion 380 of a detection device (not shown in Figure 3D) having a drive subsystem 382 coupled to a plurality of 384 of a group 386 of detection coils arranged on a detection mat. The drive subsystem 382 includes a plurality of drive units 387. The drive subsystem 382 further includes a drive controller 389 that controls the operation of the drive units 387. Pairs of the detection coil group 388 are coupled to the drive subsystem 382 such that each pair 388 is coupled to a single drive unit 387.

[0046] Figure 3E shows a part 390 of the detection device (not shown in Figure 3E), which uses two drive subsystems 391 and 392 coupled to a plurality of 393 of a detection coil group 394. These detection coils are placed on a detection mat. Pairs 395 and 397 of the detection coil group 394 are coupled to drive subsystems 391 and 392, respectively. Drive subsystem 391 includes a drive unit 399 and a drive controller 401, and drive subsystem 392 includes a drive unit 403 and a drive controller 405.

[0047] Figure 4 shows an exemplary detection system 400 for detecting the presence of foreign matter in the operating environment 402 of the WPT system 404. The system 400 comprises a detection device 406 and the WPT system 404. The detection device 406 comprises a plurality of detection coils for detecting the presence of foreign matter in the operating environment 402 of the WPT system 404, and a detection mat 408 having at least one pair of detection coil groups.

[0048] The detection device 406 further comprises a drive subsystem 410. The drive subsystem 410 includes a drive unit 411 and a drive controller 412. Although not shown, the detection system 400 may comprise two or more drive subsystems 410. Furthermore, the drive subsystem 410 may comprise multiple drive units 411, or multiple drive controllers 412, or both. The drive subsystem 410 is operably coupled to the detection mat 408 and configured to excite two or more groups of detection coils in the detection mat 408. The detection device 406 further comprises a comparison subsystem 414, operably coupled to the detection mat 408 and configured to receive a differential current signal from the detection mat. Furthermore, the comparison subsystem 414 is configured to supply a control signal based on the differential current signal.

[0049] The WPT system 404 of the detection system 400 includes a primary power supply 418 configured to supply power to the transmitter unit 420 of the WPT system 404 in the form of an alternating current (AC) voltage signal. The transmitter unit 420 includes at least one transmitter coil (not shown in Figure 4). The transmitter unit 420 is configured to receive an AC voltage signal from the primary power supply 418 and to generate a primary magnetic field or operating environment 402 in response to the received AC voltage signal.

[0050] The detection mat 408 is operably coupled to the transmitter unit 420. Specifically, the detection mat 408 is positioned on the transmitter unit 420. In some embodiments, the detection mat 408 is positioned directly on the surface 422 of the transmitter unit 420. In some other embodiments, the detection mat 408 is positioned above the transmitter unit 408 so that the detection mat 408 is positioned within the operating environment of the WPT system 404. The detection mat 408 may be positioned and aligned with the transmitter coil of the transmitter unit 420. The detection mat 408 may be positioned so that the transmitter coil is positioned geometrically symmetrically with respect to the detection mat 408. Furthermore, the detection mat 408 may be a standalone mat 408, a plug-and-play mat, and may have one or more of the following structures: flexible, conformal, or rigid.

[0051] The WPT system 404 further includes a receiver unit 424 having at least one receiver coil configured to receive at least a portion of the primary magnetic field 402 generated by the transmitter unit 420. The receiver unit 424 may be located on the underside 426 of the device that needs to be charged. In the illustrated embodiment, the receiver unit 424 is located on the underside 426 of an electric vehicle (EV) 416 that is charged using the WPT system 404. The EV 416 may include an external power source such as a battery 417. The WPT system 404 further includes a control unit 426 which controls the operation of the primary power supply 418 and is operably coupled to a detection device 406. The control unit 426 receives a control signal from the detection device 406. The control unit 426 also controls the power supply from the primary power supply 418 to the transmitter unit 420 based on this control signal.

[0052] In certain embodiments, the detection device 406 includes a communication unit 428 operably coupled to a comparison subsystem 414 and configured to receive control signals from the comparison subsystem 414. Furthermore, this communication unit 428 is configured to communicate with a control unit 426 of the WPT system 404. In certain embodiments, this communication unit 428 can transmit control signals to the user of the EV 416 or the operator of each EV charging station, for example, by using a cellular network, to communicate the presence and / or absence of foreign objects.

[0053] The differential current signal received by the comparison subsystem 414 from the detection coil of the detection mat 408 is converted into a voltage signal called a detection voltage signal. In some embodiments, this detection voltage signal is compared to a threshold or threshold voltage signal. The threshold or threshold may be defined by the user, for example, based on the parameters and design of the detection device 406. If the value of the detection voltage signal is greater than the value of the threshold voltage signal, it indicates that the currents drawn by the two groups in the pair of detection coils are different, which indicates the presence of foreign matter in the operating environment of the WPT system 404. Alternatively, if the value of the voltage signal is less than or equal to the value of the threshold voltage signal, it indicates that the currents drawn by the two groups in the pair of detection coils are sufficiently similar, which indicates that there is no foreign matter in the operating environment of the WPT system 404, or that there is very small foreign matter (such as a coil) that will not adversely affect the operation of the WPT.

[0054] Furthermore, in embodiments where the value of the detection voltage signal is greater than the value of the threshold voltage signal, the control signal is transmitted by the detection device 406 to the WPT system 404 to stop the power supply to the transmitter unit 420. In some embodiments, the communication unit 428 communicates with the control unit 426, which then stops the power supply from the primary power supply 418 to the transmitter unit 420. In another embodiment, if the transmitter unit 420 consists of an array of coils, when the control signal is transmitted by the detection device 406 to the control unit 426, the control unit 426 energizes only a subset of the coil array in the transmitter unit 420, thereby avoiding the area where the foreign object is detected.

[0055] Figure 5 shows an exemplary comparison subsystem 500 operably coupled to a pair 502 of detection coil groups 504 and 506 of a detection mat. Note that the illustrated example in Figure 5 is a non-limiting example of measuring differential current, and other methods for measuring differential are also used herein, including, but not limited to, electronic circuits such as differential amplifiers, which sense individual currents and detect the difference between these individual currents. The differential current signal from the pair 502 can be obtained using a continuous current signal to one group and a feedback current signal from the other group in the pair of groups. In the illustrated embodiment, the differential current signal of the pair 502 of groups 504 and 506 is derived using a feedback current signal I1508 from group 504 and a continuous current signal I2510 from group 506.

[0056] When the two current signals 508 and 510 pass through the magnetic core 512, the difference between these current signals 508 and 510 generates a magnetic flux linkage within the core, thereby inducing a corresponding detection voltage signal, shown as a whole by reference number 516, in the electric winding 514 wound along the magnetic core 512. This detection voltage is proportional to the difference between current signals 508 and 510 under magnetically unsaturated core conditions and represents a measured value of the differential current between the two groups 504 and 506 in the pair 502 of the group.

[0057] The comparison subsystem 500 further includes a rectifier 518 that receives and rectifies the detected voltage signal. An optional filter 520 filters the voltage signal before sending it to the comparator 522. In one example, the filter 520 is configured to remove high-frequency components from the measurement. The comparator 522 compares the filtered voltage signal to a threshold voltage signal, and accordingly transmits a control signal to a WPT system, such as the WPT system 404 in Figure 4.

[0058] Figure 6 is a flowchart 600 of an exemplary method for detecting the presence of foreign objects in the operating environment of a system. In one example, the system may be a WPT system. In block 602, a detection device is utilized by placing a detection mat of the detection device on the transmitter unit of the WPT system. This detection mat may be placed directly on the transmitter unit, or it may be placed above the transmitter unit so as not to be in physical contact with the transmitter unit. The detection mat includes a plurality of detection coils and at least one pair of detection coil groups, the at least one pair of detection coil groups including a first group of detection coils and a second group of detection coils, the first group of detection coils including a first impedance value and the second group of detection coils including a second impedance value.

[0059] In block 604, at least one pair of detection coils is energized. In some embodiments, these groups in a pair may be arranged symmetrically with respect to the primary magnetic field. In some other embodiments, these groups in the pair are arranged in the same geometric position. In certain embodiments, these groups in the pair may be arranged in two different detection regions, which may be selected such that the two detection regions in the pair are arranged symmetrically with respect to the magnetic field of the transmitter unit.

[0060] In certain embodiments, two or more pairs of detection coils may be energized. In one example, different pairs of detection coils may be energized simultaneously to detect the presence of foreign matter. In one embodiment, these different pairs of detection coils may be selected so as to energize the entire surface of the detection mat to detect the presence of foreign matter. In some embodiments, different pairs may be energized in different instances over time. In another embodiment, two or more pairs may be energized simultaneously. In one embodiment, these different pairs may be energized in chronological order.

[0061] Furthermore, these pairs of groups may be excited before initiating the wireless power transmission operation of the WPT system to the receiver unit, and during the wireless power transmission operation of the WPT system. These pairs of groups may be excited intermittently or at periodic intervals. Also, the detection coils corresponding to various pairs of detection regions are excited over time in various instances. In addition, different voltage signals are supplied to the detection coils in these pairs of detection coils with different impedance values ​​so that, in the absence of foreign matter, the detection coils in these pairs of detection coils are driven by the same current with similar magnitude and phase.

[0062] In block 606, the differential current signal of the excited detection coil is determined. In one embodiment, this differential current signal is determined using the continuous current signal of one group in a pair of detection coils and the feedback current signal of the other group in the same pair of detection coils. In embodiments where two or more pairs are excited simultaneously, corresponding individual differential current signals may be determined to detect the presence of foreign matter. Based on these differential current signals, the presence or absence of foreign matter in the operating environment of the WPT system is determined.

[0063] Next, in block 608, a control signal is generated based on the differential current signal. In block 610, the generated control signal is transmitted. In one example, this control signal is transmitted to the control unit of the WPT system. In some embodiments, the power supply to the transmitter unit of the WPT system is continued, adjusted, or stopped based on the control signal received by the control unit of the WPT system.

[0064] Figure 7 is a method flowchart 700 of a method for controlling the power supply to the transmitter unit based on a control signal. In block 702, a detection voltage signal proportional to the differential current signal is generated, for example, using the electrical windings and magnetic core of the comparison subsystem. In block 704, the detection voltage signal is compared to a threshold. In some embodiments, this threshold may be a threshold voltage signal. This threshold voltage signal may be a predetermined voltage signal based on the specifications of this WPT system.

[0065] If the determination block 706 determines that the detected voltage signal is greater than the threshold voltage signal, a control signal is transmitted to the WPT system indicating that it will not start supplying power to the transmitter unit, but will adjust or stop it (block 708). Alternatively, if the determination block 706 determines that the detected voltage signal is less than the threshold voltage signal, either no communication will be made to the WPT system, or a control signal is transmitted to the WPT system indicating that it will continue or start supplying power to the transmitter unit (block 710).

[0066] This detection may be performed in real time or near real time. Near real-time detection may be performed such that a control signal is generated and transmitted within a few microseconds to a few milliseconds from the time detection is initiated. In certain embodiments, the detection mat may scan for any foreign objects at regular intervals, for example, once per second. When a foreign object is detected, a communication signal is sent to the transmitter unit.

[0067] Figure 8 is a cross-sectional view of a detection mat 800 according to an aspect of this specification. In some embodiments, the detection mat 800 may be a standalone structure that is detachably coupled to a transmitter unit, such as the transmitter unit 420 in Figure 4. In one example, the detection mat 800 may be a plug-and-play structure. The detection mat 800 includes a substrate 802 having one or more printed circuit boards (PCBs) 804. The substrate 802 may contain an electrical insulating material. In some embodiments, the substrate 802 itself may be a printed circuit board (PCB).

[0068] Furthermore, the group 806 of detection coils 808 may be arranged on the substrate 802. In one embodiment, the group 806 of detection coils 808 may be arranged on each PCB 804. In some embodiments, the detection coils 808 may be arranged on the substrate 802, or they may be embedded in the substrate 802 to ensure user safety and aesthetics. The detection coils 808 may also be printed on a flexible or conventional printed circuit board. In certain embodiments, the detection coils 808 may be printed on the substrate 808 or PCB 804, molded, woven, or additively manufactured. Since each detection coil 808 is small, it may be wound on a thin gauge wire.

[0069] A coating layer 810 may be placed on the detection coil 808. This coating layer 810 has a first surface 812 and a second surface 814. In certain embodiments, the detection coil 808 may be placed directly on the second surface 814 of the coating layer 810. In some of these embodiments, the detection coil 808 may not be placed on the PCB 804. Furthermore, a suitable electronic circuit 816 may be provided on the substrate 802 to enable the operation of coupling the detection mat 800 with the drive subsystem and comparison subsystem of the detection device.

[0070] The substrate 802 and the coating layer 810 may include a flexible material, a rigid material, or a combination thereof. The coating layer 810 includes a thermally conductive and electrically insulating (TCEI) material. In one embodiment, this TCEI material may include an elastomer or thermoplastic containing a wear-resistant filler. In one embodiment, these elastomers may be silicone rubber. These fillers may be TCEI fillers such as aluminum oxide, aluminum nitride, beryllium oxide, boron nitride, graphene oxide, silicon carbide, and silicon nitride. Similarly, these thermoplastics may be polyolefins, polycarbonates, poly(methyl methacrylate) (PMMA), and polyesters. In certain embodiments, the substrate 802 and the coating layer 810 may be foldable together with the detection coil 808. In one embodiment, the detection mat 800 may have a shape-conforming structure. To this end, when the detection mat 800 is placed on the transmitter unit, the detection mat 800 may be configured to conform in general to the slope and curves of the surface of the transmitter unit. In some embodiments, the covering layer 810 may form an enclosure around the substrate 802, the detection coil 808, and possibly around the electronic circuit 816.

[0071] In one embodiment, the detection mat 800 may be integrated with a standard SAE transmitter system. In certain embodiments, the dimensions of the detection mat 800 may be in the range of about 0.5 m to about 2.2 m. The detection mat 800 may be sized appropriately to cover the surface area of ​​the transmitter coil. In some examples, the length of the detection mat 800 may be in the range of about 0.5 m to about 2.2 m, and the width may be in the range of about 0.5 m to about 2.2 m. The thickness of the detection mat 800 may also be in the range of about 1 mm to about 20 mm. In one embodiment, the detection mat 800 may be a single, integrated structure. In another embodiment, the detection mat 800 may be formed by integrating separate individual components.

[0072] Advantageously, the apparatus, system, and method of this technology are simple in structure and require no complex assembly. Furthermore, this technology is highly sensitive and can detect the presence of foreign objects immediately after wireless power transmission begins. This helps minimize power waste. Embodiments of this specification provide a highly sensitive, simple, and accurate system for detecting foreign objects located within the operating environment of the WPT system. Moreover, the detection devices of this specification can be deployed in existing WPT systems with minimal or no modification or adjustment required. Advantageously, the apparatus, system, and method of this specification create a safe working environment during wireless power transmission of electric vehicles (EVs), which is achieved by stopping wireless power transmission of the EV or issuing an alarm when a foreign object is detected in the operating environment of the WPT system.

[0073] While only specific features of the present invention are illustrated and described herein, those skilled in the art will likely conceive of numerous modifications and changes. Therefore, it should be understood that the appended claims are intended to encompass all such modifications and changes that fall within the scope of the present invention.

Claims

1. A detection mat (102) having a plurality of detection coils (106) and at least one pair of the group of detection coils (106), wherein at least one pair of the group of detection coils (106) includes a first group of detection coils (106) and a second group of detection coils (106), the first group of detection coils (106) includes a first impedance value, and the second group of detection coils (106) includes a second impedance value, One or more drive subsystems (112) are operably coupled to the detection mat (102) and configured to energize at least one pair of the group of detection coils (106), A comparison subsystem (114) is operably coupled to the detection mat (102) and configured to receive differential current signals from at least one pair of the group of detection coils (106), wherein the differential current signals are obtained using a continuous current signal to one group of detection coils and a feedback current signal from the other group of detection coils in that pair, and the comparison subsystem (114) is configured to generate a control signal based on the differential current signals. A detection device (100) for detecting foreign objects, comprising the following:

2. The detection device (100) for detecting foreign matter according to claim 1, wherein the first and second groups of the detection coil (106) are arranged symmetrically with respect to the primary magnetic field of a wireless power transmission (WPT) system, and the detection device (100) is configured to detect the presence of foreign matter in the operating environment of the WPT system based on the differential current signal.

3. The detection device (100) for detecting foreign matter according to claim 1, wherein the first and second groups of the group of detection coils (106) include structurally similar arrangements with respect to the detection coils (106).

4. The detection device (100) for detecting foreign matter according to claim 1, wherein the first and second groups of the group of detection coils (106) are arranged in the same geometric region on the detection mat (102).

5. The detection device (100) for detecting foreign matter according to claim 1, wherein the first and second impedance values ​​are similar to each other.

6. The detection device (100) for detecting foreign matter according to claim 1, wherein the first and second impedance values ​​are different from each other, and the detection mat (102) is operably coupled to one of the first or second group of the detection coils (106) to further include a compensator element for compensating for the difference in impedance values ​​between the first and second group of the detection coils (106).

7. The detection device (100) for detecting foreign matter according to claim 1, wherein the first and second impedance values ​​are different from each other, and the one or more drive subsystems (112) further include a drive controller configured to supply different voltage signals to the first and second groups of detection coils (106) such that the first and second groups of detection coils (106) are driven by the same current having similar magnitude and phase.

8. The detection device (100) for detecting foreign matter according to claim 1, wherein the one or more drive subsystems (112) include two drive units coupled to the first and second groups of the detection coil (106), respectively, and at least one drive controller, the drive controller being coupled to the drive unit.

9. The detection device (100) for detecting foreign matter according to claim 1, wherein the plurality of detection coils (106) include a plurality of detection regions, and each of the plurality of detection regions includes one or more groups of the detection coils (106).

10. The detection device (100) for detecting foreign matter according to claim 9, wherein at least a portion of the one or more drive subsystems (112) is configured to be coupled to two or more detection regions among the plurality of detection regions.

11. A detection device (100) for detecting foreign matter according to claim 10, wherein the detection regions in the plurality of detection regions corresponding to pairs of detection regions include a structurally similar arrangement with respect to the detection coil (106).

12. The detection device (100) for detecting foreign matter according to claim 1, wherein the detection mat (102) is a flexible mat or a rigid mat.

13. The detection device (100) for detecting foreign matter according to claim 1, wherein the detection coils (106) within the group of detection coils (106) are connected in series, in parallel, or in a combination of series and parallel connections, and the plurality of detection coils (106) include concentric coils, adjacent coils, and parallel arrangements of coils, and the plurality of detection coils (106) are arranged in one or more layers.

14. The comparison subsystem (114) is An electric winding and a magnetic core are configured to receive differential current signals from the first and second groups of the detection coil (106) and generate a detection voltage signal based on the differential current signals. A comparator configured to generate the control signal by comparing the detected voltage signal with a threshold voltage signal, A detection device (100) for detecting foreign matter according to claim 1, including the above.

15. A detection device (406) for detecting foreign objects, A detection mat (408) having a plurality of detection coils (106) and at least one pair of the group of the detection coils (106), wherein at least one pair of the group of the detection coils (106) includes a first group of the detection coils (106) and a second group of the detection coils (106), the first group of the detection coils (106) includes a first impedance value, and the second group of the detection coils (106) includes a second impedance value, One or more drive subsystems (410) are operably coupled to the detection mat (408) and configured to energize at least one pair of the group of detection coils (106), A comparison subsystem (414) is operably coupled to the detection mat (408) and configured to receive differential current signals from at least one pair of the group of detection coils (106), wherein the differential current signals are obtained using a continuous current signal to one group of detection coils and a feedback current signal from the other group of detection coils in that pair, and the comparison subsystem is configured to generate a control signal based on the differential current signals. A detection device (406) for detecting foreign objects, which is equipped with A wireless power transmission (WPT) system, A primary power supply configured to supply power in the form of an alternating current (AC) voltage signal, A transmitter unit comprising at least one transmitter coil, wherein the transmitter unit is configured to receive the AC voltage signal from the primary power supply, and is configured to generate a primary magnetic field in response to the received AC voltage signal, and the detection mat (408) is operably coupled to the transmitter unit, A receiver unit comprising at least one receiver coil and configured to receive at least a portion of the primary magnetic field generated by the transmitter unit, A control unit which is operably coupled to the detection device, The detection device receives the control signal, and, A control unit configured to control the power supply to the transmitter unit based on the control signal, Wireless power transmission (WPT) systems including, A detection system (400) for detecting foreign objects, comprising the following:

16. The detection system (400) for detecting foreign matter according to claim 15, wherein the drive subsystem is configured to intermittently or periodically energize the detection device.

17. The detection system (400) for detecting foreign objects according to claim 15, wherein the detection device (406) further includes a communication unit configured to transmit the control signal to the control unit.

18. (602) Using a detection device comprising a plurality of detection coils and a detection mat having at least one pair of the group of detection coils, wherein at least one pair of the group of detection coils includes a first group of detection coils and a second group of detection coils, the first group of detection coils includes a first impedance value, and the second group of detection coils includes a second impedance value. Exciting at least one pair of the group of detection coils (604), Measuring (606) differential current signals from at least one pair of the group of detection coils, wherein the differential current signals are obtained using a continuous current signal to one group of detection coils and a feedback current signal from the other group of detection coils in that pair, Based on the differential current signal, a control signal is generated (608), Transmitting the aforementioned control signal (610), A method for detecting foreign matter, including (600).

19. The method for detecting a foreign object according to claim 18, further comprising controlling the power supply to the transmitter unit based on the control signal (700).

20. Based on the differential current signal, a detection voltage signal is generated (702), The detection voltage signal is compared with the threshold voltage signal to generate the control signal (704), A method for detecting foreign matter according to claim 19 (600), further comprising:

21. The method for detecting foreign matter according to claim 18 (600), wherein the excitation of at least one pair of the group of detection coils (604) includes the excitation of at least one pair of the group of detection coils intermittently or at periodic intervals.

22. The method for detecting foreign matter according to claim 18 (600), wherein the excitation of at least one pair of the group of detection coils (604) includes supplying different voltage signals to the group of detection coils in the pair of detection coils with different impedance values, such that the group in the pair of detection coils is driven by the same current having similar magnitude and phase.

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