KR101854788B1 - Wireless power transmission apparatus for detecting metal object and operating method thereof - Google Patents

Abstract

A wireless power transmission apparatus according to the present invention includes a transmission pad for transmitting wireless power in a magnetic field manner, a metal object detection (MOD) pad disposed on the transmission pad and having detection coils for detecting a metal object, and an MOD circuit electrically connected to the detection coils. The detection coils are arranged in a space symmetrical structure, and at least one pair of the detection coils may be cross-connected.

Description

TECHNICAL FIELD [0001] The present invention relates to a wireless power transmission apparatus for detecting a metal object, and a method of operating the same. [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless power transmission apparatus for detecting a metal object and an operation method thereof.

Various charging methods are used to charge the battery of the electric vehicle. There are a charging method (plug-in method) in which a cable of a charger installed in a charging station is directly connected to a vehicle, a method in which electromagnetic induction generated by a primary coil and a secondary coil And a non-contact charging method (wireless charging method) using the phenomenon. In recent wireless charging systems, a power is supplied from a power supply coil embedded in a road to a current collecting coil of an electric vehicle by using a magnetic induction action to charge the battery.

Metal object detection (MOD) is an essential technology for commercialization along with vehicle's wireless charging technology. In the case of wireless charging, a strong magnetic field is generated between the current collecting device and the power feeding device. When there is a thin conductor such as gum paper, the risk of fire increases, the power transmission efficiency and efficiency are reduced by changing the resonant frequency of the power system, If the same creature is located near the charging device, a strong magnetic field above the ICNIRP guideline may cause harm to living organisms such as stimulation of the central nervous system by induced currents in the body .

Korea Registered Patent: 10-1703995, Published on October 25, 2016 Title: FOD / LOD device for electric vehicle rapid transit device. US registered patent: US 9,614,395, published on June 30, 2016 Title: Wireless charging system and foreign metal object detection method for the system. United States Patent: US 9,410,823, published on Jan. 16, 2014 Title: Systems, methods, and apparatus for detection of metal objects in a predetermined space.

It is an object of the present invention to provide a wireless power transmission apparatus for detecting a metal object and an operation method thereof.

A wireless power transmission apparatus according to an embodiment of the present invention includes: a transmission pad for transmitting wireless power in a magnetic field manner; A metal object detection (MOD) pad disposed on the transmission pad and having sense coils for sensing a metal object; And a MOD circuit electrically connected to the sense coils, wherein the sense coils are arranged in a space-symmetrical structure, and at least one pair of the sense coils can be cross-connected.

In an embodiment, the MOD pad may be implemented as a printed circuit board (PCB) formed of at least one layer having the sense coils.

In an embodiment, at least another pair of the sense coils may be connected in a space-symmetric structure.

In an embodiment, the sense coils may be connected directly to the MOD circuit.

In an embodiment, it may further comprise at least one switch for selectively connecting the sense coils to the MOD circuit.

In one embodiment, a first multiplexer for selecting any one of the sense coils; A second multiplexer for selecting another one of the sense coils; And a variable resistor for determining a variable resistor according to the output of the first multiplexer and the output of the second multiplexer.

In an embodiment, the variable resistor may operate as a zero-voltage regulator that sets the voltage of the corresponding sense coil among the sense coils to 0V.

In one embodiment, the MOD circuit comprises: a low-pass filter for removing noise of an output signal of the zero-voltage regulator; A rectifier for rectifying a signal of the low-pass filter; And an amplifier for amplifying the output of the rectifier.

In an embodiment, the MOD circuit may further comprise a zero point adjusting circuit for generating a zero point voltage of the at least one sensing coil pair cross-connected.

An operation method of a wireless power transmission apparatus according to an embodiment of the present invention includes: generating wireless power in a transmission pad; And detecting metal objects using the sense coils disposed on the transmission pad, wherein the sense coils are arranged in a space-symmetrical structure, and at least one pair of the sense coils can be cross-connected.

In an embodiment, the method may further include searching for the sense coils to initialize a metal object detection (MOD) circuit.

In an embodiment, the step of searching for the sense coils may include connecting the sense coils to the MOD circuit through a sequential switching operation.

In an embodiment, the step of searching for the sense coils may further comprise setting a zero point voltage of the sense coils using a variable resistor.

A wireless power transmission apparatus and an operation method thereof according to an embodiment of the present invention can detect a metal object without a dead zone by arranging the sense coils in a space symmetrical manner and by providing at least one pair of sensing coils crossed each other.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. However, the technical features of the present embodiment are not limited to the specific drawings, and the features disclosed in the drawings may be combined with each other to constitute a new embodiment.
1 is an exemplary illustration of a vehicle wireless power system 10 in accordance with an embodiment of the present invention.
2 is an exemplary diagram illustrating a wireless power transmission apparatus 100 according to an embodiment of the present invention.
FIG. 3 is a diagram illustrating an exemplary strength of a magnetic field of a transmission pad 140 according to an embodiment of the present invention.
4 is a diagram illustrating an exemplary distribution of the magnetic fields of the plurality of sense coils included in the MOD pad 150 according to the embodiment of the present invention.
5 is a view for explaining that a dead zone always exists when detecting a metal at the center of the plurality of sense coils of the MOD pad 150 according to the embodiment of the present invention.
FIG. 6 is an exemplary view showing the crossing of adjacent sense coils to remove the dead zone shown in FIG. 5;
FIG. 7 is a diagram illustrating an exemplary MOD circuit 160 according to an embodiment of the present invention.
FIG. 8 is a diagram illustrating an exemplary MOD circuit 160a according to another embodiment of the present invention.
9 is a view showing one of the cases in which the initial value of the induction voltage of the MOD coils is not 0 when the magnetic field is deflected when the vehicle is not matched.
FIG. 10 is a diagram illustrating an exemplary MOD circuit 160a according to another embodiment of the present invention.
11 is a diagram illustrating an exemplary zero-point circuit according to an embodiment of the present invention.
FIG. 12 is a view showing an exemplary metal detection result according to the MOD circuit of the present invention.
13 is a diagram showing the intensity of a magnetic field in a transmitting pad and a receiving pad.
FIG. 14 is a view illustrating an exemplary detection coil search process according to an embodiment of the present invention. Referring to FIG.
15 is a flowchart illustrating an exemplary operation of a wireless power transmission apparatus according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG.

The present invention is capable of various modifications and various forms, and specific embodiments are illustrated in the drawings and described in detail in the text. It is to be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but on the contrary, is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms.

The terms may be used for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as a second component, and similarly, the second component may also be referred to as a first component. It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

Other expressions that describe the relationship between components, such as "between" and "between" or "neighboring to" and "directly adjacent to" should be interpreted as well. The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise.

In this application, the terms "comprises" or "having" are intended to specify the presence of stated features, integers, steps, operations, components, parts, or combinations thereof, wherein one or more other features, , Steps, operations, components, parts, or combinations thereof, as a matter of course. Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries should be construed as meaning consistent with meaning in the context of the relevant art and are not to be construed as ideal or overly formal in meaning unless expressly defined in the present application .

1 is an exemplary illustration of a vehicle wireless power system 10 in accordance with an embodiment of the present invention. Referring to FIG. 1, a vehicle wireless power system 100 includes a wireless power transmission apparatus 100 installed on a road and a wireless power receiving apparatus 200 that receives wireless power transmitted from the wireless power transmission apparatus 100 and is attached to the vehicle.

In an embodiment, the wireless power transmission apparatus 100 may be implemented to transmit wireless power in a magnetically inductive manner. It should be understood, however, that the wireless power transmission scheme of the present invention is not limited thereto. The wireless power transmission apparatus 100 of the present invention can transmit wireless power in various manners other than the magnetic induction method, for example, a self-resonant method.

On the other hand, in the case of a wireless power transmission system using a magnetic field, the temperature may suddenly rise when a metal is exposed to a magnetic field. This may lead to problems such as ignition, device damage, and user image. Therefore, in general, the wireless power transmission apparatus 100 includes a metal object detection (MOD) circuit for detecting a metal, and determines whether or not wireless power is supplied during metal detection. For example, the metal object detection circuit can interrupt the wireless power supply operation upon metal detection and notify the user of the related fact.

2 is an exemplary diagram illustrating a wireless power transmission apparatus 100 according to an embodiment of the present invention. 2, the wireless power transmission apparatus 100 includes a power supply 110, a power factor correction (PFC) and inverter 120, a compensation circuit 130, a transmission pad 140, a MOD pad 150, MOD circuit 160 as shown in FIG.

The power supply 100 may be implemented as an AC voltage source. The alternating current can be converted into the direct current while passing through the rectifying part. In another embodiment, the voltage source may be a DC voltage source.

 The PFC and inverter 120 may include a PFC circuit and an inverter. The PFC circuit may be implemented to reduce the phase difference between the direct current voltage and the direct current that is taken from the power source 100. That is, the PFC circuit can increase the power efficiency by canceling the reactive power. Further, the inverter can be implemented so as to convert the direct current outputted from the power factor compensator into an alternating current. The inverter may include a plurality of switches. These switches can control the current flowing in the transmission coil by PWM (pulse width modulation) control. The air-gap between the transmit coil and the receive coil can be seen as a large transformer.

The compensation circuit 130 may include a capacitor or an inductor to compensate for the reactive power of the transmission pad 140.

The transmit (TX) pad 140 may be implemented to include a transmit coil that generates a magnetic field corresponding to the radio power.

The MOD pad 150 may be disposed above the transmission pad 140 or below the reception pad 240, and may be implemented to include an MOD coil. Here, the MOD coil can be used to detect a metal object in a magnetic field. A voltage may be induced in the MOD coil of the MOD pad 150 by the magnetic field generated at the transmission pad 140. [ If there is no metal, the MOD coil may have a voltage of 0 V. On the other hand, if there is metal, an induced voltage other than 0 V can be measured on the MOD coil.

In an embodiment, the MOD pad 150 may be implemented as a printed circuit board (PCB) formed of at least one layer.

A typical MOD coil is implemented with an overlapped coil structure and a non-overlapped coil structure. In the case of an overlapped coil structure, only one voltage can be measured by using a coil of a twisted structure. Two layers of printed circuit boards are needed because of the use of twisted contacts. In the case of an overlapped coil structure, there are blind spots, and a plurality of layers are required to eliminate such blind spots. Also, in the case of a non-overlapped coil structure, since two coils are used, a process of measuring / comparing two voltages is required. By using two coils, only one layer of the printed circuit board is required. In the case of the non-overlapped coil structure, a blind spot exists when two adjacent coils are selected.

The MOD circuit 160 is electrically connected to the MOD coil and can be implemented to detect metal objects in the magnetic field. In an embodiment, the MOD circuit 160 may be disposed under the transmission pad 140. [ On the other hand, it should be understood that the arrangement of the MOD circuit 160 is not limited thereto.

Further, when the MOD circuit 160 detects a metal object, the MOD circuit 160 can transmit the detection signal to the PFC and the inverter 120. [ The PFC and inverter 120 may stop power transmission in response to the detection signal.

Meanwhile, the wireless power receiving apparatus 200 may be configured to receive the wireless power generated in the wireless power transmission apparatus 100. [ 2, the wireless power receiving apparatus 200 includes a battery 210, a rectifier and a battery management system (BMS) 220, a compensation circuit 230, and a receive (RX) pad 240 . The wireless power receiving apparatus 200 may be included in an electric vehicle (EV).

FIG. 3 is a diagram illustrating an exemplary strength of a magnetic field of a transmission pad 140 according to an embodiment of the present invention. Referring to FIG. 3, the magnetic field generated in the transmission pad 140 may be distributed in a symmetrical manner.

4 is a diagram illustrating a distribution of magnetic fields of a plurality of sense coils included in the MOD pad 150 according to an embodiment of the present invention. Referring to FIG. 4, since the magnetic field generated in the transmission pad 140 is bilaterally symmetric, the voltage induced in each of the uniformly arranged sense coils may also be symmetrical. A relatively constant voltage value is induced in a large area in the center of the sense coil.

5 is a view for explaining that a dead zone always exists when detecting a metal at the center of the sense coils 151, 152, 153 and 154 of the MOD pad 150 according to the embodiment of the present invention.

FIG. 6 is an exemplary view showing the crossing of adjacent sense coils to remove the dead zone shown in FIG. 5; 6, the central sense coil m and the sense coil m + 2 are electrically cross-connected, and the sense coil m -1 and the sense coil m +1 can be electrically cross-connected . That is, at least one pair of sense coils may be cross-connected. Where m is a natural number.

When spatially adjacent patterns are selected, the voltage variation due to the eddy current at the center point is the same for each coil, so that detection is impossible. To avoid this, the sense coils may be selected and connected at an intersection by dropping the space (symmetrical structure in one example). In the central portion, the detection coils may be physically dropped because there is a problem that the amount of change can not be detected even in the presence of the metal.

Other sensing coils may be connected in a space-symmetrical manner. 6, the sense coils 1 and the sense coils 2m are electrically connected to each other, the sense coils 2 and the sense coils 2m-1 are electrically connected to each other, and the sense coils 3 And the sense coils 2m-2 may be electrically connected to each other.

On the other hand, the shape of each of the sense coils 1 to 2m shown in Fig. 6 is rectangular. However, the shape of the sensing coil of the present invention will not be limited thereto. It should be understood that the sense coils of the present invention can be implemented in various polygonal shapes.

The sense coils according to the embodiment of the present invention may include at least one sense coil pair including a pair of sense coils connected at an intersection in the central portion and at least one sense coil pair connected with remaining space symmetrically.

The MOD pad 150 according to the embodiment of the present invention can detect a metal in all areas of the transmission pad 140 without a dead zone as a single layer.

FIG. 7 is a diagram illustrating an exemplary MOD circuit 160 according to an embodiment of the present invention. 7, the MOD circuit 160 may include a zero-voltage regulator 161, a low pass filter (LPF) 162, a precision rectifier 163, and an amplifier 164.

The zero-voltage regulator 161 can be implemented to set the voltage of the corresponding sense coil to 0V by using a variable resistor. The voltage induced in the sense coils may not be symmetrical depending on the position of the transmission pad 140 even if there is no metal. The zero-voltage regulator 161 can set the voltage of the sense coil to 0 V in order to detect a metal object.

A low pass filter (LPF) 162 may be implemented to remove noise caused by the switching process of the inverter. The low-pass filter 162 may further include a shield cable. The shielded cable serves to protect the signal from noise or electromagnetic interference (EMI).

The precision rectifier 163 can be implemented to accurately rectify the output signal of the low-pass filter 162. Since the signal generated by the metal object is smaller than the threshold voltage of the diode, it is impossible to rectify it from a normal diode rectifier.

The amplifier 164 may be implemented to amplify the output signal of the precision rectifier 163.

Meanwhile, the MOD circuit 160 of FIG. 7 may be directly connected to the plurality of sense coils. However, it should be understood that the present invention is not limited thereto. The MOD circuit of the present invention can be connected to the sense coils through a multiplexer.

FIG. 8 is a diagram illustrating an exemplary MOD circuit 160a according to another embodiment of the present invention. Referring to FIG. 8, the MOD circuit 160a may further include a multiplexer 166 as compared to that of FIG. The multiplexer 166 may selectively connect the sense coils to the MOD circuit 160. [

The multiplexer 166 receives the sense voltages V (1), V (2), ..., V (k), ..., V (n) from the plurality of sense coils 1 to n, (V1, V2) among the sense voltages V (1), V (2), ..., V (k), ..., V (n) (160) may receive voltages (V1, V2) from multiplexer (166) and generate a zero voltage.

9 is a view showing one of the cases in which the initial value of the induction voltage of the MOD coils is not 0 when the magnetic field is deflected when the vehicle is not matched. Referring to FIG. 9, a distance deviated from the matching position of the transmitting coil and the receiving coil is referred to as an alignment deviation. By using the metal object detection method of the present invention, the position of the receiving coil can be changed so that the misalignment is minimized.

10 is a diagram illustrating an exemplary MOD circuit 160b according to another embodiment of the present invention. Referring to FIG. 10, MOD circuit 160b may be implemented to add multiplexers MUX1 and MUX2 and a digital variable resistor as compared to it 160a shown in FIG.

The first multiplexer MUX1 is connected to one end of each of the sense coils, and can output the voltage of the selected sense coil. In an embodiment, the first power source Va may be connected between one end of each of the sense coils and the ground terminal. The second multiplexer MUX2 is connected to the other end of each of the sense coils, and can output the voltage of the selected sense coil. In an embodiment, the second power supply Vb may be connected between one end of each of the sense coils and the ground terminal. The digital variable resistor has one end receiving the output voltage of the first multiplexer (MUX1) and the other end receiving the output voltage of the second multiplexer (MUX2).

The MOD circuit 160b includes an amplifier OPM having a positive voltage terminal (+) connected to the distribution terminal of the variable resistor and a negative voltage terminal (-) connected to the bias voltage Ra, A capacitor Cb connected between the output terminal of the diode D and the ground terminal and a feedback resistor Rb connected between the output terminal of the diode D and the negative voltage terminal of the amplifier OPM can do. Here, the output voltage V0 is outputted from the output terminal of the diode D. Here, the distribution stage of the variable resistance means a point where the variable resistance is digitally distributed. The zero point voltage (V _{0, diff} ) may be output at the distribution stage. On the other hand, it should be understood that the configuration of the MOD circuit 160b shown in FIG. 10 is merely one embodiment without limiting the present invention.

Also, the middle portion of the spatially symmetric coil may be crossed-connected. The crossing portion may be implemented by at least one switch, or may be manufactured as a printed circuit board (PCB) in the form of a cross connection.

11 is a diagram illustrating an exemplary zero-point adjusting circuit according to an embodiment of the present invention. Referring to FIG. 11, the zero point voltage (V _{0, diff} ) can satisfy the following equation.

Where V1 is a first voltage, V2 is a second voltage, R1 is a first resistor, and R2 is a second resistor. The variable resistor may comprise R1 and R2. The first voltage V1 may be the output voltage of the first multiplexer MUX1 shown in Fig. The second voltage V2 may be the output voltage of the second multiplexer MUX2 shown in Fig.

FIG. 12 is a view showing an exemplary metal detection result according to the MOD circuit of the present invention. As a result of the experiment according to the height of the metal of 40 mm x 40 mm x 1 mm, referring to Fig. 9, it is possible to detect all rotation angles of the detectable metal up to 4 cm.

13 is a diagram showing the intensity of a magnetic field in a transmitting pad and a receiving pad. Referring to FIG. 10, the wireless power transmission apparatus of the present invention can detect a metal object in the entire region of a transmission pad.

14 is a view illustrating an example of a detection coil search process of the MOD circuit according to the embodiment of the present invention. Start from the set point k = 1 (S110). The MOD coil includes a plurality of sense coils, and the MOD circuit 160 can be connected to these and implemented to process signals. Each of the plurality of sense coils may be 1: 1 mapped to the MOD circuit 160 sequentially through an electronic switch. In the mapped state, a zero point is performed using a variable resistor, and the corresponding reference value can be stored. it is possible to determine whether k is n (S120). If k is not n, it is searched from the previous set point and the k value is increased by 1 (S130). Thereafter, step S120 is performed. That is, all of the processes of connecting the sense coils and adjusting the reference values and storing the values may be repeated using the switch. On the other hand, if k is n, the metal detection operation of the MOD circuit will be performed. The metal detection operation of the MOD circuit means that after the above-described initialization process is completed, the existence of the metal object is continuously monitored through the switch operation. The final output value can indicate the presence of a metallic object by comparing the voltage value with a reference value.

15 is a flowchart illustrating an exemplary operation of a wireless power transmission apparatus according to an embodiment of the present invention. Referring to FIG. 15, an operation method of the wireless power transmission apparatus is as follows. Wireless power may be generated at the transmission pad of the wireless power transmission apparatus (S210). A metal object may be detected during wireless power transmission using sense coils disposed on the transmit pad (S220). Wherein the sense coils are arranged in a space-symmetrical configuration, and at least one pair of the sense coils can be cross-connected.

The MOD pad according to an embodiment of the present invention may include one or more sense coils for detecting a metal. In the embodiment, the sense coils may be square, triangular, circular or the like.

In the embodiment, the sense coil bundle is disposed horizontally and vertically and is position-detectable. In the embodiment, any two of the sense coils may be selected for gain adjustment. Where any two coils may be contiguous or non-contiguous.

The MOD circuit according to the embodiment of the present invention can select two sense coils through connection of a multiplexer and a physical circuit.

In the embodiment, the MOD pad can be designed in a symmetrical structure. In an embodiment, if the MOD pad is bilaterally symmetric, metal detection may be possible crossing the sense coils at the center.

The MOD circuit according to an embodiment of the present invention may include a device for gain adjustment. In the embodiment, a variable resistance, a width adjustment, and a software method can be applied to the gain adjustment.

In the embodiment, the MOD circuit can deal with uneven distribution of vehicle alignment, vehicle effect, and magnetic field. In an embodiment, the MOD circuit may implement an algorithm for initialization time optimization to detect metal.

In practice, the MOD circuit may include a device for reducing the switching noise of the inverter. For example, MOD circuit can be applied low-pass filter, shield pattern. In an embodiment, the MOD circuit may comprise circuitry for accurately measuring the MOD coil voltage having a small amplitude.

The steps and / or operations in accordance with embodiments of the present invention may be performed in different orders, in parallel, or in other embodiments for other epochs or the like, as may be understood by one of ordinary skill in the art It can happen at the same time.

Depending on the embodiment, some or all of the steps and / or operations may be performed on one or more non-transitory computer-readable media, including instructions, programs, interactive data structures, At least some of which may be implemented or performed using one or more processors. The one or more non-transitory computer-readable media can be, by way of example, software, firmware, hardware, and / or any combination thereof. Further, the functions of the "module" discussed herein may be implemented in software, firmware, hardware, and / or any combination thereof.

One or more non-transitory computer-readable media and / or means for implementing / performing one or more operations / steps / modules of embodiments of the present invention may be implemented as application-specific integrated circuits (ASICs), standard integrated circuits, But are not limited to, controllers that perform appropriate instructions, including microcontrollers, and / or embedded controllers, field-programmable gate arrays (FPGAs), complex programmable logic devices (CPLDs) .

The above-described contents of the present invention are only specific examples for carrying out the invention. The present invention will include not only concrete and practical means themselves, but also technical ideas which are abstract and conceptual ideas that can be utilized as future technologies.

10: Vehicle wireless power system
100: Wireless power transmission device
200: Wireless power receiving device
110: Power supply
120: PFC and inverter
130: compensation circuit
140: transmission pad
150: MOD pad
160, 160a, 160b: MOD circuit
210: Battery
220: Rectifier and BMS
230: compensation circuit
161: Zero-voltage regulator
162: Low-pass filter
163: Precision rectifier
166: Multiplexer

Claims (13)

A wireless power transmission apparatus comprising:
A transmission pad for transmitting wireless power in a magnetic field manner;
A metal object detection (MOD) pad disposed on the transmission pad and having sense coils for sensing a metal object; And
And a MOD circuit electrically connected to the sense coils,
Wherein the sense coils are arranged in a space-symmetrical configuration, at least one pair of the sense coils is cross-
And at least another pair of the sense coils is connected in a space-symmetric structure. The method according to claim 1,
Wherein the MOD pad is implemented as a printed circuit board (PCB) formed of at least one layer having the sense coils. delete The method according to claim 1,
Wherein the sense coils are directly connected to the MOD circuit. The method according to claim 1,
And at least one switch for selectively coupling the sense coils to the MOD circuit. The method according to claim 1,
A first multiplexer for selecting any one of the sense coils;
A second multiplexer for selecting another one of the sense coils; And
And a variable resistor for determining a variable resistance in accordance with the output of the first multiplexer and the output of the second multiplexer. The method according to claim 6,
And the variable resistor operates as a zero-voltage regulator that sets the voltage of the corresponding sense coil among the sense coils to 0V. 8. The method of claim 7,
The MOD circuit comprises:
A low-pass filter for removing noise of an output signal of the zero-voltage regulator;
A rectifier for rectifying a signal of the low-pass filter; And
And an amplifier for amplifying the output of the rectifier. 8. The method of claim 7,
The MOD circuit comprises:
And a zero point adjustment circuit for generating a zero point voltage of the at least one sensing coil pair cross-connected. A method of operating a wireless power transmission apparatus comprising:
Generating wireless power at the transmit pad; And
Detecting a metal object using the sense coils disposed on the transmission pad,
Wherein the sense coils are arranged in a space-symmetrical configuration, at least one pair of the sense coils is cross-
And at least another pair of the sense coils are connected in a space-symmetric manner. 11. The method of claim 10,
Further comprising the step of searching for said sense coils to initialize a metal object detection (MOD) circuit. 12. The method of claim 11,
Wherein the searching for the sense coils comprises:
And connecting the sense coils to the MOD circuit through a sequential switching operation. 12. The method of claim 11,
Wherein the searching for the sense coils comprises:
And setting the zero point voltage of the sense coils using a variable resistor.

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