CN116436172A - Wireless foreign matter detecting system that charges - Google Patents

Abstract

The invention discloses a wireless charging foreign matter detection system, which further comprises: a detection coil set having a plurality of coil units with an input port and an output port; the input port and the output port are respectively connected with a switch module, the switch module is provided with a single connection point and a plurality of connection points, and the excitation circuit is communicated with or disconnected from the coil unit through the switch module; the acquisition circuit acquires the electrical parameters of the ring unit during communication; the main controller is used for sending at least the working parameters of the excitation circuit to the acquisition circuit; a coil unit in communication with the excitation circuit, as a main coil unit, one or more coil units around the main coil unit, as main coil units, while being in communication with the acquisition circuit. Based on the coil units, one coil unit is used as a main coil unit, peripheral coil units form an auxiliary coil unit, the main coil unit generates an electromagnetic field, the auxiliary coil unit senses the electromagnetic field to generate an electric signal, and the electric signal of the auxiliary coil unit is monitored to realize the detection of foreign matters.

Description

Wireless foreign matter detecting system that charges

Technical Field

The invention relates to the field of wireless charging, in particular to a wireless charging foreign matter detection system.

Background

If metallic foreign matters exist on the power transmitting coil (namely, between the transmitting part and the receiving part) in the wireless charging process, the metallic foreign matters can generate heat due to the generated eddy current effect, so that the transmission efficiency of wireless charging is greatly reduced, and meanwhile, safety accidents such as combustion and the like can be possibly caused. The wireless charging system must be equipped with a metal foreign matter detection device to secure the safety of charging.

In the prior art, a power difference calculation mode is generally used to detect the foreign matters, that is, through the difference value between the receiving power and the transmitting power, whether the metallic foreign matters exist is judged. Still other methods employ temperature measurement, and if metallic foreign matter is present, the electromagnetic field heats it so that the foreign matter can be detected by temperature measurement.

Both schemes have hysteresis, so that foreign matters cannot be found timely and accurately, and the positions of the foreign matters cannot be determined.

Disclosure of Invention

The invention provides a wireless charging foreign matter detection system which can efficiently and rapidly detect and position foreign matters.

A wireless charging foreign matter detection system, further comprising: a detection coil group composed of a plurality of coil units, each coil unit having an input port and an output port; the number of the switch modules is twice that of the coil units, the input port and the output port are respectively connected with one switch module, the switch modules are provided with a single connection point and a plurality of connection points, and the single connection point is used for being connected with the input port or the output port; the multi-connection point is used for alternatively connecting the excitation circuit or the acquisition circuit; an excitation circuit which is communicated with or disconnected from the coil unit through the switch module and provides alternating current for the coil unit when being communicated; the acquisition circuit is communicated with or disconnected from the coil unit through the switch module and acquires the electrical parameters of the coil unit when the acquisition circuit is communicated with the coil unit; the main controller is respectively communicated with the detection coil group, the switch module, the exciting circuit and the acquisition circuit, and at least transmits working parameters of the exciting circuit to the acquisition circuit; wherein at most one coil unit is simultaneously communicated with the excitation circuit and serves as a main coil unit, and one or more coil units around the main coil unit serve as auxiliary coil units and are simultaneously communicated with the acquisition circuit.

Preferably, the multiple coupling points include: a first coupling point, a second coupling point, and a third coupling point; the acquisition circuit is divided into a first acquisition circuit and a second acquisition circuit; the first connection point is connected with the excitation circuit; the second connecting point is connected with the first acquisition circuit; the third junction is coupled to the second acquisition circuit.

Preferably, the first acquisition circuit and the second acquisition circuit comprise a filter circuit, a measurement circuit and a functional circuit.

Preferably, all of the coil units will sequentially serve as main coil units.

Preferably, the acquisition circuit obtains an electrical parameter of each of the auxiliary coil units and compares it with a predetermined reference value to determine whether or not there is a foreign object.

Preferably, the acquisition circuit obtains an excitation voltage of the excitation circuit, and also obtains an induced voltage of each auxiliary coil unit, so as to obtain a voltage difference between the excitation voltage and the induced voltage; the acquisition circuit obtains the excitation current of the excitation circuit, and also obtains the induction current of each auxiliary coil unit to obtain the phase difference between the excitation current and the induction current; and comparing the voltage difference with a reference voltage difference, comparing the phase difference with a reference phase difference, and judging that the foreign matter exists when one or both of the voltage difference and the reference phase difference exceed an allowable range.

Preferably, the auxiliary coil unit and the acquisition circuit form an acquisition loop, and a center frequency of a frequency bandwidth of the acquisition loop is configured as a frequency of the alternating current of the main coil unit; the frequency bandwidth comprises a lowest frequency and a highest frequency, and is different from the operating frequency of wireless charging power transmission.

The wireless charging foreign matter detection system is characterized in that a coil unit is used as a main coil unit, peripheral coil units form auxiliary coil units, the main coil unit generates an electromagnetic field, the auxiliary coil unit senses the electromagnetic field to generate an electric signal, and the electric signal of the auxiliary coil unit is monitored to realize the detection of foreign matters.

Drawings

FIG. 1 is a schematic diagram of a wireless charging foreign matter detection system according to the present invention;

FIG. 2 is a schematic diagram of a portion of a wireless charging foreign matter detection system according to the present invention;

fig. 3 is a schematic layout view of coil units in the wireless charging foreign matter detection system according to the present invention.

Detailed Description

Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative only and are not to be construed as limiting the invention.

The invention discloses a wireless charging foreign matter detection system, mainly a wireless charging transmitter, referring to fig. 1, the system is provided with a shell 0 (also called an external shell, wherein the shell 0 is divided into an upper part and a lower part, the upper part and the lower part are respectively shown by a reference numeral 0 in the figure), a working circuit and a transmitting coil 5 are arranged in the shell, and in addition, the system also comprises a detection coil group, an exciting circuit 2, an acquisition circuit 3 and a switch module 4, and the four parts can realize detection of metal foreign matters (whether the metal foreign matters exist or not and detection of the existence positions of the metal foreign matters). The system also comprises a transmitting end communication module and a master controller, and is used for transmitting information with the receiving end communication module. The main controller is used for controlling the wireless charging process and stopping wireless charging when abnormal conditions, such as metallic foreign matters, exist. The main controller is responsible for overall coordination control, and the transmitting end communication module is also in the control range of the main controller. Meanwhile, the master controller can also realize information sharing in all components in the system, for example, some working parameters of the exciting circuit 2 can be controlled and coordinated through the master controller, and the parameters can be shared to the acquisition circuit 3 through the master controller.

The material of the housing 0 is generally engineering plastic, and the housing 0 mainly plays a role in packaging and improving mechanical strength. The housing may be of a layered or layered structure, with the first layer in housing 0 providing the set of detection coils and the second layer providing the transmit coil 5. The first layer is here at the highest level, i.e. the detection coil assembly is arranged higher than the transmitter coil 5, the detection coil assembly being closer to the top than the transmitter coil 5. Meanwhile, the area covered by the detection coil group is a detection area required to be performed and can be larger than the area of the transmitting coil 5.

Besides the main components described above, a shield plate, a metal plate, etc. are included, which are in one layer with the transmitting coil 5 and are on the lower side of the transmitting coil 5.

The winding of the transmitting coil 5 is generally wound by a high-frequency litz wire, and a shielding plate is arranged below the winding and is generally made of nanocrystalline or ferrite and other high-permeability materials.

The shielding plate is also provided with a layer of aluminum metal plate, thereby further playing roles of electromagnetic field shielding and heat conduction.

As a transmitting end of the wireless energy, the transmitting coil 5 is coupled to the ac conversion circuit and controlled by the main controller. During wireless charging, the alternating current conversion circuit loads high-frequency alternating current to the transmitting coil 5, and then an alternating magnetic field for power transmission is generated above the transmitting coil 5. The ac conversion circuit, the master controller, etc. may be integrated in the housing structure, and in the application case of high-power wireless charging, the ac conversion circuit and the master controller may be independently disposed outside the housing due to volume, heat dissipation, etc. The receiving device with the receiving coil can be charged, and the winding of the receiving coil is of a plane coiled single-coil structure. When the receiving device is arranged above the transmitting end, the receiving device can be identified to start a wireless charging function, the receiving coil induces an alternating magnetic field above the transmitting coil 5 to generate alternating current, and the alternating current is converted by a direct current conversion circuit inside the receiving device to charge the receiving device.

The above-described detection coil group includes a plurality of coil units 1. Each coil unit 1 has an input port and an output port to which a switching module 4 is coupled, respectively. I.e. one coil unit 1, is provided with two switch modules 4, the number of switch modules 4 being seen to be twice that of the coil unit 1. Each switch module 4 has more than 1 coupling position, i.e. at least two coupling positions. The coupling position here means a position at which subsequent components can be coupled, excluding a position at which the switch module 4 is in an off state, that is, the switch module 4 also has an off position, which does not belong to the above-described at least two coupling positions, in which the corresponding coil unit 1 is not coupled with any other component.

Therefore, two switch modules 4 used by one coil unit 1 may be referred to as a double multi-position selector switch, and double refers to that the switch modules 4 are connected to both the input port and the output port of the coil unit 1, and the multi-position selector is at least two connection positions.

In general, in the coupling position, the corresponding coil unit 1 is coupled to the excitation circuit 2 in the first coupling position, and in the second coupling position, the corresponding coil unit 1 is coupled to the acquisition circuit 3.

As shown in fig. 2, the switch module 4 may have a structure in which one end is a single connection point 40 and the other end is a multi-connection point, and the single connection point 40 is connected to an input port or an output port of the coil unit 1, and the multi-connection point is connected to the acquisition circuit 3 or the excitation circuit 2. As shown in fig. 2, the switch module 4 has three multiple coupling points, namely three coupling positions, namely a first coupling point 41, a second coupling point 42 and a third coupling point 43. The first connection point 41 is connected to the excitation circuit 2, so that the corresponding coil unit is connected to the excitation circuit 2, the second connection point 42 and the third connection point 43 are connected to the acquisition circuit 3, respectively, and the corresponding coil unit is connected to the acquisition circuit 3.

In the same coil unit 1, its two switch modules 4 should be in the same coupling position. They may be internally linked or controlled by a master.

When they are both at the first coupling point 41, the corresponding coil unit 1 and the excitation circuit 2 form an excitation circuit, the excitation circuit 2 being able to apply an alternating current to the coil unit 1 as an excitation signal for the coil unit 1. When they are at non-first connection points, such as second connection points, the corresponding coil unit 1 and the acquisition circuit 3 form an acquisition loop, and the acquisition circuit 3 acquires the electrical parameters of the coil unit 1 and judges whether the metallic foreign matter exists according to the electrical parameters. The acquisition circuit 3 generally includes functional components (functional circuits) such as a filter (filter circuit) and a measurer (measurement circuit).

The excitation circuit 2 and the acquisition circuit 3 may be common to each coil unit 1. In general, a plurality of coil units 1 are not connected to the excitation circuit 2 and the acquisition circuit 3 at the same time, but are used sequentially one by one. One of the functions of the switching module 4 is thus to ensure that one acquisition circuit 3 is also coupled to only one coil unit 1 at a time, and that the same coil unit 1 is not coupled to both the excitation circuit 2 and the acquisition circuit 3.

Of course, in some cases where necessary, the excitation circuit 2 may communicate with a plurality of coil units 1 at the same time. While allowing the coil units 1 to operate. The coil units 1 which are simultaneously connected to the excitation circuit 2 are not generally adjacent in position.

In actual operation, generally, one coil unit 1 is connected to the excitation circuit 2, one or more coil units 1 around the coil unit 1 are used as a main coil unit 1A, for example, left, right, upper and lower coil units 1 are respectively connected to an acquisition circuit 3, and are used as auxiliary coil units 1B, so as to obtain electrical parameters of the auxiliary coil units 1B around, and then each coil unit 1 and the coil units 1 around the coil unit are sequentially connected in this way. That is, each coil unit 1 has an opportunity to become the main coil unit 1A in turn, and the coil units 1 around it become the auxiliary coil units 1B.

For better measurement, the detection dead zone is reduced, any two adjacent coil units 1 are overlapped, the coil units 1 are overlapped and are continuously arranged like tiles along one dimension direction, part of areas between one coil unit 1 and the next coil unit 1 are overlapped, and the area of the overlapped areas of all the adjacent coil units 1 is the same. The coil unit 1 in fig. 3 is merely an example, and is not limited to the structure of the coil unit. As shown in fig. 3, the coil units 1 overlap in one dimension of the lateral direction, and do not overlap in the longitudinal direction. Of course, this is only an example, and in other embodiments, there may be overlap in all directions, and this embodiment is to reduce the number and thus control the cost as a whole on the premise of meeting the requirements, in view of the number of coil units 1.

Referring to fig. 2, the detection coil sets share X sets of coil units 1, and, for example, a first set of coil units 1 is coupled with a switch module 4, and subsequently up to the X-th set of coil units 1, are coupled in the same manner.

As an example, the system comprises one excitation circuit 2 and two acquisition circuits 3 (first acquisition circuit 31 and second acquisition circuit 32), a first coupling position (coupling point 41) being coupled to both side ports of the excitation circuit 2, a second coupling position (coupling point 42) being coupled to both side ports of the first acquisition circuit 31, and a third coupling position (coupling point 43) being coupled to both side ports of the second acquisition circuit 32.

When the detection of the metal foreign matter is required, the corresponding coil unit 1 is taken as a main coil unit 1A, which is connected with the excitation circuit 2 to form an excitation loop, and at this time, the main coil unit 1A may be equivalent to one excitation coil (hereinafter, the main coil unit 1A may be referred to as an excitation coil). The auxiliary coil unit 1B therearound is equivalent to an induction coil (hereinafter, the auxiliary coil unit 1B may be referred to as an induction coil). An alternating current is applied to the exciting coil as an exciting signal, the alternating current generates an alternating magnetic field around the exciting coil, the peripheral auxiliary coil units 1B generate an induced current due to the existence of the alternating magnetic field, and the acquisition circuit 3 acquires electrical parameters to determine whether the metal foreign matter exists above the main coil units 1A. Then, excitation signals are sequentially applied to the coil units 1 at each position to form a main coil unit 1A, and the electric parameters of the peripheral auxiliary coil units 1B are respectively collected and judged, so that whether the metal foreign matters exist in the detection area can be known, and the positions where the metal foreign matters exist can be judged according to the positions of the coil units 1.

Specifically, the switch module 4, which connects one coil unit 1, is turned on to the first connection point 41 (i.e., the first connection position), so that the coil unit 1 serves as the main coil unit 1A, is turned on to the excitation circuit 2, and the output of the excitation circuit 2 is applied to both ends of the main coil unit 1A. At the same time, the second position or the third position is turned on by the switching module of two or more coil units 1 surrounding the coil unit 1 of the target position as the auxiliary coil unit 1B. For ease of understanding, we take two auxiliary coil units 1B as an example, where the switch module 4 of one auxiliary coil unit 1B is coupled to the second coupling point and the switch module 4 of the other auxiliary coil unit 1B is coupled to the third coupling point, so that the two auxiliary coil units 1B are respectively connected to the first and second acquisition circuits 31 and 32.

During operation, the connection relation of each coil unit 1 and the switch modules 4 of two or more peripheral coil units 1 is sequentially changed, the coil units 1 at different positions are used as main coil units 1A, alternating current is loaded as excitation signals, peripheral auxiliary coil units 1B can induce the excitation signals, the acquisition circuit 3 acquires the electrical parameters of the two or more auxiliary coil units 1B, then each coil unit 1 is sequentially used as main coil unit 1A, alternating current is loaded, the electrical parameters of the two or more peripheral auxiliary coil units 1B are respectively acquired, and the acquired electrical parameters of each auxiliary coil unit 1B are compared with a predetermined reference value.

The electrical parameters include some parameters of the main coil unit 1A acquired by the acquisition circuit 3 from the auxiliary coil unit 1B, as well as by other means, for example by means of which the electrical parameters loaded on the main coil unit 1A can be obtained by the master.

Preferably, these parameters include the acquisition circuit 3 obtaining the excitation voltage of the excitation circuit 2 (for example from the master, or alternatively, the excitation voltage is pre-fixed), and also obtaining the induced voltage of each auxiliary coil unit 1B, deriving the voltage difference between the excitation voltage and the induced voltage.

Further comprises: the acquisition circuit 3 obtains the excitation current of the excitation circuit 2 (for example, obtained from a master, or the excitation current is fixed in advance), and also obtains the induced current of each auxiliary coil unit 1B, and obtains the phase difference between the excitation current and the induced current.

And comparing the voltage difference with a reference voltage difference, comparing the phase difference with a reference phase difference, and judging that the metal foreign matter exists when one or both of the two exceeds an allowable range.

When more acquisition circuits 3 are provided, more peripheral coil units 1 can be acquired, i.e., more auxiliary coil units 1B are selected, and for example, upper and lower, left and right peripheral coil units 1 can be acquired at the same time. Of course, in some embodiments, even if only one acquisition single path 3 is used, the electric parameters of the plurality of auxiliary coil units 1B may be acquired, that is, the acquisition circuit 3 may also acquire the electric parameters of the plurality of auxiliary coil units 1B by means of time-sharing acquisition. But require sequential acquisitions and take more time. The collected electric parameters of different auxiliary coil units 1B can be compared with the corresponding reference values, and then the comparison results are compared with each other, so that misjudgment can be caused by failure of the coil or interference in detection when only one electric parameter of the auxiliary coil unit 1B is collected, and more electric parameters are collected with better detection reliability.

According to faraday's law of electromagnetic induction, when alternating current is applied to an exciting coil, the exciting coil generates an alternating magnetic field in a surrounding space, the presence of the alternating magnetic field causes a coil unit 1 which is closed around to generate induced current, a certain voltage difference and a certain phase difference exist between the exciting coil and the induced coil, and the voltage difference and the phase difference can be acquired in advance and are used as reference values of the voltage difference and the phase difference through compensation processing. Of course, the voltage difference and the reference value of the phase difference may be calculated by theory and then artificially given.

In addition, due to the different arrangement structure of the coil units 1, reference values acquired in advance or artificially given to the coil units 1 at different positions are generally different, for example, reference values of the left-right and up-down positions are different when serving as the auxiliary coil units 1B. During power transfer, the power transfer magnetic field also generates an induced current in the induction coil, and in order to reduce the influence of this on the detection of metallic foreign matter, the frequency of the alternating current applied in the excitation coil is set to be different from the operating frequency of the wireless charging power transfer, and the difference in such frequencies is of a large order, for example, the difference between kHz and MHz. The induction coil is configured to induce an alternating magnetic field generated by the excitation coil, the acquisition loop is configured to induce a magnetic field frequency which is the frequency of alternating current of the excitation coil, and the acquisition loop has a certain frequency bandwidth (frequency range) which can adapt to the change generated by the excited alternating magnetic field frequency in a certain range through impedance matching, and the center frequency of the frequency bandwidth is correspondingly configured to the frequency of the alternating current of the excitation coil. The frequency bandwidths, including the lowest frequency and the highest frequency, are also different from the operating frequency of wireless charging power transmission and have a large magnitude difference. Further, a filter (filtering circuit) is configured in the acquisition circuit to filter the influence of the wireless charging power transmission magnetic field on the induction coil.

When the metal foreign matter is in the alternating magnetic field generated by the exciting coil, the metal foreign matter can induce eddy current in the exciting coil, the eddy current can generate a secondary magnetic field, the induction coil senses the superposition of the alternating magnetic field generated by the exciting coil and the secondary magnetic field generated by the eddy current, the secondary magnetic field acts on the exciting magnetic field in a reaction mode, the induction voltage on the induction coil can be changed, the voltage difference between the excitation voltage and the induction voltage is changed, when the acquired voltage difference deviates from a reference value, the deviation of the acquired voltage difference exceeds the tolerance range allowed by the system, the existence of the metal foreign matter above the exciting coil can be judged, and the position of the coil unit 1 serving as the exciting coil is the position where the metal foreign matter exists.

Further, the induced current generated on the induction coil comprises the action of the secondary magnetic field generated by the eddy current, so that the phase of the induced current is changed, the phase difference between the exciting current and the induced current is changed, when the acquired phase difference deviates from the reference value and the deviation exceeds the tolerance range allowed by the system, the existence of the metal foreign matters above the exciting coil can be judged, and the position of the coil unit 1 serving as the exciting coil is the position where the metal foreign matters exist.

Because of the variety of the metal foreign matters, the physical parameters such as conductivity, magnetic conductivity and the like are different, the change of one of the voltage difference or the phase difference is very small under some conditions, and the metal foreign matters can not be found by only collecting the voltage difference or only collecting the phase difference, so that detection dead zones or erroneous judgment can be caused, and meanwhile, the defects can be overcome by collecting and comparing the voltage difference and the phase. On the other hand, the detection of the metal foreign matters occurs before the wireless charging is started, and in the power transmission process, as the magnetic field power of the wireless charging power transmission is larger than that of the magnetic field power generated by the exciting coil, the eddy current generated on the metal foreign matters is larger, and the voltage difference and the phase difference are more obvious than the change of the reference value.

When the metal object does not belong to the transmitting end or the receiving end of wireless charging, the metal object is equivalent to 'foreign matters' outside the wireless charging system. The metal foreign matter in the wireless charging power transmitting magnetic field may generate heat due to eddy effect, even ignite inflammables, and may cause loss of transmission power. When the metal foreign matters are found above the wireless charging transmitting end, the charging is stopped or not started, an alarm is sent out, and the standby detection state can be re-entered after the metal foreign matters are cleaned.

The invention can accurately detect the metal foreign matters and can avoid detection blind areas caused by parallel arrangement of the coil units 1; meanwhile, by switching the position of the coil unit 1 through the switch module 4, the coil unit is used as an exciting coil and an induction coil, and by setting corresponding frequency bands, the interference of factors such as wireless charging transmission magnetic fields and the like on detection of metal foreign matters is avoided.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims (7)

1. A wireless charging foreign matter detection system, characterized by further comprising:

a detection coil group consisting of a plurality of coil units (1), each coil unit (1) having an input port and an output port;

the number of the switch modules (4) is twice that of the coil units (1), the input port and the output port are respectively connected with one switch module (4), the switch modules (4) are provided with a single connection point (40) and multiple connection points, and the single connection point (40) is used for being connected with the input port or the output port; the multi-connection point is used for alternatively connecting the excitation circuit (2) or the acquisition circuit (3);

an excitation circuit (2) which is communicated with or disconnected from the coil unit (1) through the switch module (4) and supplies alternating current to the coil unit (1) when communicated;

the acquisition circuit (3) is communicated with or disconnected from the coil unit (1) through the switch module (4) and acquires the electrical parameters of the coil unit (1) when the coil unit is communicated with the coil unit;

the main controller is respectively communicated with the detection coil group, the switch module (4), the exciting circuit (2) and the acquisition circuit (3), and at least sends working parameters of the exciting circuit (2) to the acquisition circuit (3);

wherein at most one coil unit (1) is simultaneously communicated with the excitation circuit (2) and serves as a main coil unit (1A), and one or more coil units (1) around the main coil unit (1A) serve as auxiliary coil units (1B) and are simultaneously communicated with the acquisition circuit (3).

2. The wireless charging foreign matter detection system of claim 1, wherein,

the multiple coupling point includes: a first coupling point (41), a second coupling point (42) and a third coupling point (43);

the acquisition circuit (3) is divided into a first acquisition circuit (31) and a second acquisition circuit (32);

the first coupling point (41) is coupled to the excitation circuit (2);

-the second coupling point (42) is coupled with the first acquisition circuit (31);

the third junction (43) is coupled to the second acquisition circuit (32).

3. The wireless charging foreign matter detection system of claim 2, wherein,

the first acquisition circuit (31) and the second acquisition circuit (32) comprise a filter circuit, a measuring circuit and a functional circuit.

4. The wireless charging foreign matter detection system of claim 1, wherein,

all the coil units (1) will in turn act as main coil units (1A).

5. The wireless charging foreign matter detection system of claim 1, wherein,

the acquisition circuit (3) obtains an electrical parameter of each auxiliary coil unit (1B) and compares it with a predetermined reference value to determine whether or not there is a foreign matter.

6. The wireless charging foreign matter detection system of claim 5, wherein,

the acquisition circuit (3) obtains the excitation voltage of the excitation circuit (2) and also obtains the induction voltage of each auxiliary coil unit (1B) to obtain the voltage difference between the excitation voltage and the induction voltage;

the acquisition circuit (3) obtains the excitation current of the excitation circuit (2) and also obtains the induction current of each auxiliary coil unit (1B) to obtain the phase difference between the excitation current and the induction current;

and comparing the voltage difference with a reference voltage difference, comparing the phase difference with a reference phase difference, and judging that the foreign matter exists when one or both of the voltage difference and the reference phase difference exceed an allowable range.

7. The wireless charging foreign matter detection system of claim 1, wherein,

the auxiliary coil unit (1B) and the acquisition circuit (3) form an acquisition loop, the center frequency of the frequency bandwidth of the acquisition loop being configured as the frequency of the alternating current of the main coil unit (1A);

the frequency bandwidth comprises a lowest frequency and a highest frequency, and is different from the operating frequency of wireless charging power transmission.

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