CN112068208A

CN112068208A - Foreign matter detection method and device

Info

Publication number: CN112068208A
Application number: CN202010804977.4A
Authority: CN
Inventors: 胡锦敏; 梁立科
Original assignee: Shenzhen Hertz Innovation Technology Co ltd
Current assignee: Shenzhen Hertz Innovation Technology Co ltd
Priority date: 2020-08-12
Filing date: 2020-08-12
Publication date: 2020-12-11

Abstract

The invention is suitable for the technical field of wireless charging, and provides a foreign matter detection method and a foreign matter detection device, wherein the method is applied to a wireless charging system, the wireless charging system comprises a foreign matter detection circuit arranged on a transmitting coil, the foreign matter detection circuit comprises an alternating current source, a current detection module, a resonant capacitor and a detection coil, the alternating current source is connected with the resonant capacitor, the resonant capacitor is connected with the detection coil in parallel, the current detection module is connected with the resonant capacitor, and the foreign matter detection method comprises the following steps: starting an alternating current source to enable the alternating current source to transmit electricity to the resonant capacitor; the control current detection module acquires the total actual current flowing through the resonance capacitor and the detection coil; judging whether the total actual current is greater than a threshold current or not; if yes, judging that foreign matters exist on the transmitting coil, and if not, judging that the foreign matters do not exist on the transmitting coil. The method is used for accurately and simply detecting whether foreign matters exist in the wireless charging system.

Description

Foreign matter detection method and device

Technical Field

The invention belongs to the technical field of wireless charging, and particularly relates to a foreign matter detection method and device.

Background

The wireless charging system is characterized in that the transmitting coil and the receiving coil transmit energy through a magnetic field to realize non-contact transmission of electric energy. Because the multifunctionality is good, the reliability is high, the flexibility is good, security and life are higher, in addition contactless, the characteristics of no wearing and tearing, the wireless power consumption demand of electronic equipment under the different conditions can be satisfied to the wireless charging technology, compromises the demand of information transmission function simultaneously.

Since metal generates heat by forming eddy current in an electromagnetic field, the metal existing between the transmitting coil and the receiving coil may cause a safety hazard in a wireless charging process. At present, the following two main methods for detecting metal foreign matters exist. One is to detect by detecting the induced voltage by using the magnetic field of the transmitting coil, and the other is to detect by the impedance angle by transmitting excitation by the transmitting coil itself. The former has simple circuit but limited precision, and the latter has complex circuit.

Disclosure of Invention

The embodiment of the invention provides a foreign matter detection method, which can detect foreign matters based on current change, is simple in implementation method and can ensure detection precision.

The embodiment of the invention is realized in such a way that a foreign object detection method is applied to a wireless charging system, the wireless charging system comprises a foreign object detection circuit arranged on a transmitting coil, the foreign object detection circuit comprises an alternating current source, a current detection module, a resonant capacitor and a detection coil, the alternating current source is connected with the resonant capacitor, the resonant capacitor is connected with the detection coil in parallel, the current detection module is connected with the resonant capacitor, and the foreign object detection method comprises the following steps: turning on the AC source to enable the AC source to transmit electricity to the resonant capacitor; controlling the current detection module to obtain the total actual current flowing through the resonance capacitor and the detection coil; judging whether the total actual current is greater than a threshold current or not; if so, judging that foreign matters exist on the transmitting coil or the receiving coil, and if not, judging that no foreign matters exist on the transmitting coil or the receiving coil.

Further, the ac source is provided with one, the current detection module is provided with one, the resonant capacitor is provided with one, the detection coils are provided with a plurality of sets, each set of the detection coils is provided with at least one, the resonant capacitor is respectively connected with each detection coil, and a first switch is provided between the resonant capacitor and each detection coil, the ac source is turned on, so that after the step of transmitting power from the ac source to the resonant capacitor, the method further comprises:

sequentially closing the first switches;

controlling the current detection module to obtain the total actual current flowing through the resonant capacitor and the detection coil specifically comprises:

and controlling the current detection module to acquire the total actual current flowing through the resonant capacitor and the detection coil when the first switch is closed every time.

Further, the ac source may be one, the current detection module may be plural, the resonant capacitor may be plural, the detection coil may be plural, the resonant capacitor may be provided corresponding to the current detection module and the detection coil, and a second switch may be provided between each of the resonant capacitor and the ac source, and after the step of turning on the ac source to transmit power from the ac source to the resonant capacitor, the method may further include:

sequentially closing the second switches;

and when the second switch is closed each time, the current detection module is controlled to acquire the total actual current flowing through the detection coil and the resonance capacitor corresponding to the detection coil.

Further, the ac source is provided with a plurality of ac sources, the current detection module is provided with a plurality of groups, each group of the current detection module is provided with at least one, the resonance capacitor is provided with a plurality of groups, each group of the resonance capacitor is provided with at least one, the detection coil is provided with a plurality of groups, each group of the detection coil is provided with at least one, the resonance capacitor is respectively provided with the current detection module and the detection coil, each ac source is correspondingly connected with each group of the resonance capacitor, a third switch is provided between each resonance capacitor and the corresponding ac source, and the ac source is turned on so that the ac source transmits power to the resonance capacitor after the step of transmitting power to the resonance capacitor, the method further comprises:

sequentially closing the third switches;

and when the third switch is closed every time, controlling the current detection module to acquire the total actual current flowing through the resonance capacitor and the detection coil.

Further, before the step of obtaining the total actual current flowing through the resonance capacitor and the detection coil, the method further includes:

adjusting the test excitation frequency of the alternating current source;

acquiring total test current flowing through the resonance capacitor and the detection coil;

and when the total test current is smaller than the threshold current, stopping adjusting the test excitation frequency, and taking the corresponding test excitation frequency when the adjustment is stopped as the actual excitation frequency loaded to the detection coil by the alternating current source.

Furthermore, the foreign object detection circuit further includes a voltage detection module and a detection resistor, the detection coil is connected in parallel with the resonance capacitor and then connected in series with the detection resistor, the detection resistor is connected with the voltage detection module, and the foreign object detection method further includes the following steps:

controlling the voltage detection module to obtain actual voltages at two ends of the detection resistor;

judging whether the actual voltage is greater than a threshold voltage or not;

if so, judging that foreign matters exist on the transmitting coil or the receiving coil, and if not, judging that no foreign matters exist on the transmitting coil or the receiving coil.

The embodiment of the present invention further provides a foreign object detection device applied to a wireless charging system, wherein the wireless charging system includes a foreign object detection circuit disposed on a transmitting coil, the foreign object detection circuit includes an ac source, a current detection module, a resonant capacitor and a detection coil, the ac source is connected to the resonant capacitor, the resonant capacitor is connected in parallel to the detection coil, the current detection module is connected to the resonant capacitor, and the foreign object detection device includes:

an ac source turning-on unit configured to turn on the ac source so that the ac source transmits power to the resonant capacitor;

the current acquisition unit is used for controlling the current detection module to acquire the total actual current flowing through the resonance capacitor and the detection coil;

a first judgment unit for judging whether the total actual current is greater than a threshold current;

and if the total actual current is judged to be larger than the threshold current, judging that foreign matters exist on the transmitting coil or the receiving coil, and if the total actual current is judged not to be larger than the threshold current, judging that the foreign matters do not exist on the transmitting coil or the receiving coil.

Still further, the alternating current source is provided with one, the current detection module is provided with one, the resonance capacitor is provided with one, the detection coils are provided with a plurality of groups, each group of the detection coils is provided with at least one, the resonance capacitor is respectively connected with each detection coil, and a first switch is arranged between the resonance capacitor and each detection coil, the foreign matter detection device further comprises:

a first switch closing unit for sequentially closing the first switches;

the current obtaining unit is specifically configured to control the current detection module to obtain a total actual current flowing through the resonant capacitor and the detection coil when the first switch is closed each time.

Further, the ac source is provided with one, the current detection module is provided with a plurality of current sources, the resonant capacitor is provided with a plurality of current sources, the detection coil is provided with a plurality of current sources, the resonant capacitor is provided corresponding to the current detection module and the detection coil, and a second switch is provided between each of the resonant capacitor and the ac source, the foreign matter detection apparatus further includes:

a second switch closing unit for sequentially closing the second switches;

the current obtaining unit is specifically configured to control the current detection module to obtain a total actual current flowing through the detection coil and the resonance capacitor corresponding to the detection coil when the second switch is closed each time.

Further, the alternating current source is equipped with a plurality ofly, current detection module is equipped with the multiunit, every group current detection module is equipped with at least one, resonance capacitance is equipped with the multiunit, every group resonance capacitance is equipped with at least one, the detection coil is equipped with the multiunit, every group the detection coil is equipped with at least one, resonance capacitance respectively with current detection module with the detection coil corresponds the setting, every alternating current source and every group resonance capacitance corresponds the connection, each resonance capacitance with correspond be equipped with the third switch between the alternating current source, foreign matter detection device still includes:

a third switch closing unit for sequentially closing the third switches;

the current obtaining unit is specifically configured to control the current detection module to obtain a total actual current flowing through the resonant capacitor and the detection coil when the third switch is closed each time.

Still further, the foreign matter detection apparatus further includes:

the frequency adjusting unit is used for adjusting the test excitation frequency of the alternating current source;

a test current acquisition unit for acquiring a total test current flowing through the resonance capacitor and the detection coil;

and the frequency determining unit is used for stopping adjusting the test excitation frequency when the total test current is smaller than a threshold current, and loading the corresponding test excitation frequency when the adjustment is stopped to the actual excitation frequency of the detection coil as the alternating current source.

Furthermore, the foreign object detection circuit further includes a voltage detection module and a detection resistor, the detection coil is connected in parallel with the resonant capacitor and then connected in series with the detection resistor, the detection resistor is connected with the voltage detection module, and the foreign object detection device further includes:

the voltage acquisition unit is used for controlling the voltage detection module to acquire actual voltages at two ends of the detection resistor;

a second judging unit, configured to judge whether the actual voltage is greater than a threshold voltage;

and if the actual voltage is judged to be greater than the threshold voltage, judging that foreign matters exist on the transmitting coil or the receiving coil, and if the actual voltage is judged not to be greater than the threshold voltage, judging that the foreign matters do not exist on the transmitting coil or the receiving coil.

Compared with the related art, the foreign matter detection method and the foreign matter detection device provided by the invention have the following beneficial effects: the foreign matter detection circuit only needs to contain an alternating current source, a current detection module, a resonant capacitor and a detection coil, the current detection module is used for obtaining the total actual current of the resonant capacitor and the detection coil, the actual current is compared with a threshold current, when the actual current is larger than the threshold current, the foreign matter is determined to exist in the wireless charging system, and when the actual current is not larger than the threshold current, the foreign matter is determined not to exist in the wireless charging system. Therefore, in the application, the foreign matter is detected based on the current change, the implementation method is simple, namely the implementation circuit is simple, and the detection result is accurate, so that whether the foreign matter exists in the wireless charging system can be accurately and simply detected.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description, serve to explain the principles of the invention.

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without inventive exercise.

Fig. 1 is a schematic flow chart of a foreign object detection method according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a foreign object detection circuit according to an embodiment of the present invention;

fig. 3 is a schematic structural diagram of another foreign object detection circuit according to an embodiment of the present invention;

FIG. 4 is a schematic flow chart illustrating another foreign object detection method according to an embodiment of the present invention;

fig. 5 is a schematic structural diagram of another foreign object detection circuit according to an embodiment of the present invention;

fig. 6 is a schematic structural diagram of another foreign object detection circuit according to an embodiment of the present invention;

FIG. 7 is a schematic flow chart illustrating another method for detecting foreign objects according to an embodiment of the present invention;

FIG. 8 is a schematic diagram of another foreign object detection circuit according to an embodiment of the present invention;

FIG. 9 is a schematic flow chart of another foreign object detection method according to an embodiment of the present invention;

FIG. 10 is a schematic flow chart illustrating another method for detecting foreign objects according to an embodiment of the present invention;

fig. 11 is a schematic structural diagram of another foreign object detection circuit according to an embodiment of the present invention;

FIG. 12 is a schematic flow chart illustrating another method for detecting foreign objects according to an embodiment of the present invention;

fig. 13 is a schematic structural diagram of a foreign object detection apparatus according to an embodiment of the present invention;

fig. 14 is a schematic structural diagram of another foreign object detection apparatus according to an embodiment of the present invention;

fig. 15 is a schematic structural diagram of another foreign object detection apparatus according to an embodiment of the present invention;

fig. 16 is a schematic structural diagram of another foreign object detection apparatus according to an embodiment of the present invention;

fig. 17 is a schematic structural diagram of another foreign object detection apparatus according to an embodiment of the present invention;

fig. 18 is a schematic structural diagram of another foreign object detection apparatus according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

In order to effectively explain embodiments of the present invention, the embodiments of the present application will be described in detail below with reference to the accompanying drawings.

The invention provides a foreign matter detection method, a foreign matter detection circuit applied to the foreign matter detection method only needs to comprise an alternating current source 11, a current detection module 12, a resonant capacitor 13 and a detection coil 14, the total actual current of the resonant capacitor 13 and the detection coil 14 is obtained through the current detection module 12, the actual current is compared with a threshold current, when the actual current is larger than the threshold current, the foreign matter is determined to be in a wireless charging system, and when the actual current is not larger than the threshold current, the foreign matter is determined not to be in the wireless charging system. Therefore, in the application, the foreign matter is detected based on the current change, the implementation method is simple, namely the implementation circuit is simple, and the detection result is accurate, so that whether the foreign matter exists in the wireless charging system can be accurately and simply detected.

Example one

As shown in fig. 1, the present application provides a foreign object detection method applied to a wireless charging system, the wireless charging system includes a foreign object detection circuit disposed on a transmitting coil, and normally, a metal foreign object exists above the transmitting coil and does not exist near a receiving coil, so that the foreign object detection circuit is disposed on the transmitting coil and does not need to be disposed on the receiving coil, as shown in fig. 2, the foreign object detection circuit includes an ac source 11, a current detection module 12, a resonant capacitor 13, and a detection coil 14, the ac source 11 is connected to the resonant capacitor 13, the resonant capacitor 13 is connected in parallel to the detection coil 14, the current detection module 12 is connected to the resonant capacitor 13, and the foreign object detection method includes the following steps:

s101, turning on the ac source 11, so that the ac source 11 transmits power to the resonant capacitor 13.

S102, controlling the current detection module 12 to obtain a total actual current flowing through the resonant capacitor 13 and the detection coil 14.

S103, judging whether the total actual current is larger than a threshold current or not. If so, judging that foreign matters exist on the transmitting coil or the receiving coil, and if not, judging that no foreign matters exist on the transmitting coil or the receiving coil.

Specifically, in the present application, a foreign object detection circuit is provided on a transmission coil of a wireless charging system in order to detect whether a metallic foreign object is present between the transmission coil and a reception coil. The foreign object detection circuit according to the present application is shown in fig. 2 and includes an ac source 11, a current detection module 12, a resonant capacitor 13, and a detection coil 14. The alternating current source 11 is connected with a resonant capacitor 13, the resonant capacitor 13 is connected with the detection coil 14 in parallel, one end of the current detection module 12 is connected with one end of the resonant capacitor 13, and the other end is connected with the alternating current source 11.

In the foreign object detection circuit, the resonance capacitor 13 is connected in parallel with the detection coil 14 to form a resonance circuit, and the resonance frequency is f_DThen this circuit should satisfy

The circuit impedance is

Where j is a complex unit and is a mathematical constant, f_DIs the resonant frequency, L_dTo detect the inductance of coil 14, C_dThe capacitance of the resonant capacitor 13. Since the resonant capacitor 13 is connected in parallel with the detection coil 14, in an ideal state, the circuit impedance Z can be regarded as infinite, that is, current detection is performedThe current detected by the module 11 should be 0A.

When a metal or a substance having a high magnetic permeability is placed on the transmitting coil or the receiving coil, the inductance value of the detecting coil changes due to the eddy current effect of the metal or the magnetic permeability of the magnetic material, i.e., L_DChange occurs, denoted as L_D', due to L_D' and C_DNo resonance, so that the circuit impedance Z will change significantly, and the current I in the circuit_DFrom 0A to I_D', i.e. the current at the position detected by the current detection module 11 changes from 0A to I_DThat is, it is determined that a metal or a high magnetic permeability material is present in the vicinity of the transmission coil or the reception coil, and it is noted that the metal does not include litz wires in the normal case of the transmission coil, and the high magnetic permeability material does not include a magnetic core which is normally present in the transmission coil.

In this embodiment, based on the above foreign object detection circuit, the foreign object detection method specifically includes:

s101, the ac source 11 is turned on so that the ac source transmits power to the resonant capacitor 13.

The ac source 11 supplies power to the foreign object detection circuit, so that when foreign object detection is required, the control device turns on the ac source 11 in the foreign object detection circuit, so that the ac source 11 supplies power to other devices in the circuit, for example, the resonant capacitor 13 and the resonant coil 14.

S102, the control current detection module 12 obtains the total actual current flowing through the resonant capacitor 13 and the detection coil 14.

That is, since the current of the foreign object detection circuit is changed when metal or a high magnetic permeability substance exists in the transmission coil or the reception coil, whether metal or a high magnetic permeability substance is placed on the transmission coil or the reception coil can be known by detecting the current of the foreign object detection circuit. At this time, the current detection module 12 may obtain the total actual current flowing through the resonant capacitor 13 and the detection coil 14.

S103, judging whether the total actual current is larger than the threshold current, if so, judging that foreign matters exist on the transmitting coil, and if not, judging that the foreign matters do not exist on the transmitting coil.

In this embodiment, after the current detection module 12 acquires the total actual current flowing through the resonant capacitor 13 and the detection coil 14, the acquired total actual current flowing through the resonant capacitor 13 and the detection coil 14 is compared with a threshold current to determine whether the total actual current is greater than the threshold current.

It should be noted that the threshold current is preset, and is set according to actual conditions, and may be 10mA, 5mA, and the like, which is not limited in this application.

Since the threshold current can ideally be set to 0A, but in practice should be larger than 0A, for example 10 mA. This is due to practical errors. For example, the resonance frequency of the detection coil 14 and the resonance capacitor 13 in an ideal state is 350kHz, but the excitation frequency provided by the actual power supply is 349.5kHz, the current cannot be 0A, and a small current is used.

After the total actual current flowing through the resonant capacitor 13 and the detection coil 14 is compared with the threshold current, if the total actual current flowing through the resonant capacitor 13 and the detection coil 14 is greater than the threshold current, it indicates that a metal or a high-permeability substance exists in the transmission coil, which causes the current of the foreign object detection circuit to increase, and at this time, it can be determined that a foreign object exists in the transmission coil. If the total actual current flowing through the resonance capacitor 13 and the detection coil 14 is not more than the threshold current, it can be determined that no foreign matter is present on the transmission coil.

In the embodiment of the present invention, the foreign object detection circuit is generally applied to the transmitting coil end, and since the transmitting coil end is disposed on the ground and the receiving coil end is disposed on the load (e.g., an automobile), foreign objects are likely to be present on the transmitting coil end. In the following description of the embodiments of the present application, a foreign object detection circuit is described as an example provided at the transmitting coil end.

Furthermore, if the foreign matter exists on the transmitting coil, the power supply can be turned off, the foreign matter signal is output to the user, and the user is electrified after removing the foreign matter. Alternatively, a foreign matter presence signal is output to a cleaning mechanism (e.g., a robot with a broom), which removes foreign matter and re-energizes upon detection of the removal of foreign matter.

In the embodiment of the invention, in the wireless charging system, the size of the transmitting coil is usually larger, so that the upper surface of the whole transmitting coil is difficult to cover by adopting a single foreign object detection coil, and higher detection precision is difficult to realize. A preferable method is that a plurality of foreign body detection coils are adopted and placed above the transmitting coil, so that the whole transmitting coil can be covered, the size of a single coil is reduced, the detection precision of the single coil can be improved, and the high-precision omnibearing foreign body detection is realized.

As described above, the first aspect of the plurality of foreign object detection coils is specifically as follows:

as shown in fig. 3, there may be one ac source 11, one current detection module 12, one resonant capacitor 13, multiple sets of detection coils 14, at least one detection coil 14, and a first switch 15 between the resonant capacitor 13 and each detection coil 14. In this case, after the step of turning on the ac power source 11 so that the ac power source 11 transmits power to the resonant capacitor 13 in step S101, as shown in fig. 4, the method further includes:

and S104, closing the first switch 15 in sequence.

Specifically, in the charging system, since it is difficult for a single detection coil 14 to cover the entire transmission coil due to the large size of the transmission coil, a plurality of sets of detection coils 14 may be provided such that the plurality of sets of detection coils 14 cover the radiation area of the entire transmission coil. At this time, a first switch 15 is disposed between each set of detection coils 14 and the resonant capacitor 13, and the detection of which detection coil 14 forms a resonant circuit with the resonant capacitor 13 can be controlled by controlling the on and off of the first switch 15, so as to detect whether a foreign object exists at the position of the emission coil corresponding to the detection coil 14.

Since it is necessary to detect whether a foreign object exists on the entire transmission coil, the first switch 15 may be closed in sequence, so as to sequentially connect each of the detection coils 14 in the plurality of detection coils 14 with the resonant capacitor 13.

At this time, the step S102 of controlling the current detection module 12 to obtain the total actual current flowing through the resonant capacitor 13 and the detection coil 14 specifically includes:

the control current detection module 12 acquires the total actual current flowing through the resonance capacitor 13 and the detection coil 14 each time the first switch 15 is closed.

That is, each time the first switch 15 is closed, the control current detection module 12 obtains the total actual current flowing through the resonant capacitor 13 and the detection coil 14 with the first switch 15 closed and turned on.

For example, referring to fig. 3, in the foreign object detection circuit, the resonant capacitor 13 is C_DIt is noted that the current detection module 12 is denoted by CT, and it is assumed that n sets of detection coils 14, each denoted by L, are provided in the foreign object detection circuit_D1-L_DnIt is indicated that, at this time, the detection coils 14 and the resonant capacitor C are in each set_DA first switch 15 is arranged between the two switches, T₁-T_nAnd marking. When detecting foreign objects, the first switch T may be first switched₁Closed, at this time, the coil L is detected_D1And a resonance capacitor C_DAre conducted. Controlling the current detection module CT to obtain the current flowing through the resonant capacitor C_DAnd the detection coil L_D1The actual current in between. It is determined whether the actual current is greater than a threshold current. If the current is larger than the threshold current, judging that foreign matters exist on the transmitting coil. If the current is not larger than the threshold current, judging that no foreign matter exists on the transmitting coil. In-pair detection coil L_D1After the judgment is finished, the first switch T is switched off₁. Then the first switch T is closed₂At this time, the coil L is detected_D2And a resonance capacitor C_DAre conducted. Similarly, the current detection module CT is controlled to obtain the current passing through the resonant capacitor C_DAnd the detection coil L_D1The actual current in between. It is determined whether the actual current is greater than a threshold current. If the current is larger than the threshold current, judging that foreign matters exist on the transmitting coil. If the current is not larger than the threshold current, judging that no foreign matter exists on the transmitting coil. In-pair detection coil L_D2After the judgment is finished, the first switch T is switched off₂. Then the first switch T is closed₃Closing the first switch T₃The following steps may refer to closing the first switch T₁And a first switch T₂The following steps are carried out in the following steps,and will not be described in detail herein. Through the above process, until the first switch T is closed_nComplete closing of the first switch T_nAnd (5) the following steps. Thereby completing the detection of whether the whole transmitting coil has foreign matters.

Optionally, when the foreign object detection circuit is used for the first time, when the first switch is closed each time, the closed branch circuit may be scanned separately first, the resonant frequency of the branch circuit is recorded, and in the subsequent work, when the branch circuit is closed again, the resonant frequency of the branch circuit is directly applied to the branch circuit, so as to improve the detection accuracy.

It should be noted that each set of detection coils 14 may include one detection coil, as shown in fig. 3. A plurality of detection coils may also be included as shown in fig. 5. In the above-mentioned detection process, one first switch is closed at a time, and of course, a plurality of first switches such as T may be closed at the same time₁₁～T_m1The current detection module 12 obtains the actual current flowing between the resonant capacitor 13 and the plurality of groups of detection coils 14 with the closed first switch turned on, and compares the actual current with the threshold current to determine whether the actual current is greater than the threshold current. If the actual current is not greater than the threshold current, then it is determined that there is no foreign object on the emitter coil, and a plurality of first switches, such as T, are closed₁～T_nAnd disconnecting and re-starting other first switches, and repeating the processes until all branch circuits are detected. A special case is that all the first switches are closed at once to perform the determination. The determination process is the same as the above determination process, and is not described herein again. The above-mentioned turning on of the plurality of first switches can improve the detection speed.

In the embodiment of the present invention, a second mode of implementing a plurality of foreign object detection coils is specifically as follows:

as shown in fig. 6, there may be one ac source 11, a plurality of current detection modules 12, a plurality of resonance capacitors 13, a plurality of detection coils 14, resonance capacitors 13 provided corresponding to the current detection modules 12 and the detection coils 14, respectively, and a second switch 16 provided between each resonance capacitor 13 and the ac source 11. At this time, after the step of turning on the ac source 11 so that the ac source 11 transmits power to the resonant capacitor 13 in step S101, as shown in fig. 7, the method further includes:

and S105, closing the second switch 16 in sequence.

Specifically, in the charging system, because the size of the transmitting coil is large, a single detection coil 14 is difficult to cover the whole transmitting coil, and therefore, multiple groups of detection branches can be arranged, each group of detection branches comprises a current detection module 12, a resonant capacitor 13 and a detection coil 14, wherein the resonant capacitor 13 is respectively arranged corresponding to the current detection module 12 and the detection coil 14. So that the sets of detection branches cover the entire radiation area of the transmission coil. At this time, a second switch 16 is arranged between each group of detection branches and the ac source 11, which detection branch is turned on can be controlled and detected by controlling the on and off of the second switch 16, and then whether a foreign object exists at the transmitting coil corresponding to the detection branch is detected.

Since it is necessary to detect whether a foreign object exists in the entire transmitting coil, the second switch 16 may be sequentially closed, so as to sequentially connect each of the plurality of sets of detecting branches to the ac source.

At this time, the step S102 of controlling the current detection module 102 to obtain the total actual current flowing through the resonant capacitor 13 and the detection coil 14 specifically includes:

each time the second switch 16 is closed, the control current detection module 12 acquires the total actual current flowing through the detection coil 14 and the resonance capacitor 13 corresponding to the detection coil 14.

That is, each time the second switch 16 is closed, the ac source 11 transmits the power excitation signal to the detection branch where the second switch 16 is turned on, so that the current detection module 12 in the detection branch obtains the total actual current flowing through the resonant capacitor 13 and the detection coil 14 in the detection branch.

For example, referring to fig. 6, n detection coils 14 are used in the foreign object detection circuit, each detection coil 14 is individually matched with the resonant capacitor 13 and the current transformer 12, and each detection coil 14 is switched by the second switch 16 to detect the excitation added to each detection coil, so as to determine whether a foreign object exists near the detection coil 14. Wherein, in FIG. 6, n resonant capacitors 13 are represented by C_D1-C_DnNote that CT is used for the current detection module 12₁-CT_nNote that detection coil 14 is designated by L_D1-L_DnDenoted, Q for the second switch 16₁-Q_nAnd marking.

At this time, the foreign object detection circuit includes n groups of detection branches, and each group of detection branches includes one resonant capacitor 13, one current transformer 12, and one detection coil 14. And each set of detection branches is connected to the ac source 11 via a second switch 16. When detecting foreign matters, the second switch Q can be firstly switched on₁Is closed, at this time, the second switch Q₁The ac source 11 is conducted with the first detection branch to detect the current CT in the first detection branch₁Detection coil L_D1And a resonant capacitor C_D1A power supply energizing signal is provided. Through current detection module CT₁Obtaining a current flowing through a resonant capacitor C_D1And the detection coil L_D1The actual current in between. It is determined whether the actual current is greater than a threshold current. If the current is larger than the threshold current, judging that foreign matters exist on the transmitting coil. If the current is not larger than the threshold current, judging that no foreign matter exists on the transmitting coil. In-pair detection coil L_D1After the judgment is finished, the second switch Q is switched off₁. Then the second switch Q is closed₂At this time, the second switch Q₂The ac source 11 is conducted with the second detection branch to detect the current CT in the second detection branch₂Detection coil L_D2And a resonant capacitor C_D2A power supply energizing signal is provided. Similarly, the current detection module CT₂Obtaining a current flowing through a resonant capacitor C_D2And the detection coil L_D2The actual current in between. It is determined whether the actual current is greater than a threshold current. If the current is larger than the threshold current, judging that foreign matters exist on the transmitting coil. If the current is not larger than the threshold current, judging that no foreign matter exists on the transmitting coil. In-pair detection coil L_D2After the judgment is finished, the second switch Q is switched off₂. Then the second switch Q is closed₃Closing the second switch Q₃Subsequent steps may refer to closing the second switch Q₁And a second switch Q₂A subsequent step, in which no longerThe description is given. Through the above process, until the second switch Q is closed_nComplete closing of the second switch Q_nAnd (5) the following steps. Thereby completing the detection of whether the whole transmitting coil has foreign matters.

It should be noted that, in the above detection process, multiple detection branches, such as 1-3 detection branches, may also be closed at the same time, and the actual current of each branch is read at the same time, and the judgment is performed according to the actual current of each branch, so as to accelerate the scanning speed.

In the embodiment of the present invention, a third way of implementing a plurality of foreign object detection coils is specifically as follows:

as shown in fig. 8, a plurality of ac sources 11 are provided, the current detection module 12 is provided with a plurality of sets, each set of the current detection module 12 is provided with at least one, the resonant capacitor 13 is provided with a plurality of sets, each set of the resonant capacitor 13 is provided with at least one, the detection coil 14 is provided with a plurality of sets, each set of the detection coil 14 is provided with at least one, the resonant capacitor 13 is respectively provided with the current detection module 12 and the detection coil 14, each ac source 11 is correspondingly connected with each set of the resonant capacitor 13, and a third switch 17 is provided between each resonant capacitor 13 and the corresponding ac source 11. In this case, after the step of turning on the ac power source 11 so that the ac power source 11 transmits power to the resonant capacitor 13 in step S101, as shown in fig. 9, the method further includes:

and S106, closing the third switch 17 in sequence.

Specifically, in the charging system, because the size of the transmitting coil is large, a single detection coil 14 is difficult to cover the whole transmitting coil, and therefore, a plurality of groups of detection circuits can be arranged, each group of detection circuits comprises at least one detection branch, wherein each detection branch comprises a current detection module 12, a resonant capacitor 13 and a detection coil 14, and the resonant capacitor 13 is respectively arranged corresponding to the current detection module 12 and the detection coil 14. So that the sets of detection circuits cover the entire radiation area of the transmission coil. Because the inductance of each detection coil 14 and the capacitance of the resonant capacitor 13 are deviated, the resonant frequency of each group of detection circuits is different, that is, when a plurality of detection circuits are scanned simultaneously, alternating current sources 11 with different frequencies are needed, and only one alternating current source 11 can exchange current with one frequency at the same time. Therefore, in the third implementation, a plurality of ac sources 11 may be provided to provide excitation at different frequencies, thereby solving the above-mentioned problem. At this time, one ac source 11 is provided for each group of detection circuits, and the detection branches in each group of detection circuits share one ac source 11. In each group of detection branches, a third switch 17 is arranged between the alternating current source 11 and the resonant capacitor 13, which detection branch is turned on can be controlled and detected by controlling the on and off of the third switch 17, and then whether a foreign object exists at a transmitting coil corresponding to the detection branch is detected.

Since it is necessary to detect whether a foreign object exists in the entire transmitting coil, the third switch 17 may be closed in sequence, so that each of the plurality of groups of detecting branches is sequentially conducted with the ac source.

each time the third switch 17 is closed, the control current detection module 12 acquires the total actual current flowing through the resonance capacitor 13 and the detection coil 14.

That is, each time the third switch 17 is closed, the ac source 11 transmits the power excitation signal to the detection branch where the third switch 17 is turned on, so that the current detection module 12 in the detection branch obtains the total actual current flowing through the resonant capacitor 13 and the detection coil 14 in the detection branch.

For example, referring to fig. 8, n sets of detection circuits are used in the foreign object detection circuit, and each set of detection circuit includes m sets of detection branches. One ac source 11 is provided for each set of detection circuits. M detection coils 14 are arranged in each detection branch, each detection coil 14 is independently matched with the resonant capacitor 13 and the current transformer 12, and each detection coil 14 is switched through the third switch 17 to realize the detection of the excitation added to each detection coil, so that whether foreign matters exist near the detection coil 14 or not is judged. In FIG. 8, U is used for the AC source 11 in the foreign matter detection circuit₁-U_nNote that the resonant capacitor 13 is C_D11-C_DmnNote that CT1 is used by current sense module 12₁-CTm_nNote that detection coil 14 is designated by L_D11-L_DmnDenoted S for the second switch 16₁₁-S_mnAnd marking.

In this case, the foreign object detection circuit includes n sets of detection circuits, and one ac source U is provided for each set of detection circuits_nAnd each group of detection circuits comprises m groups of detection branches, and each group of detection branches comprises a resonant capacitor 13, a current transformer 12 and a detection coil 14. And each group of detection branches is connected with the corresponding alternating current source 11 through a third switch 17. When detecting foreign objects, the third switch S may be first switched₁₁Is closed, at this time, the third switch S₁₁Will exchange the source U₁Is conducted with a first detection branch circuit in the first detection circuit so as to be a current detection module CT in the first detection branch circuit₁₁Detection coil L_D11And a resonant capacitor C_D11A power supply energizing signal is provided. Through current detection module CT₁₁Obtaining a current flowing through a resonant capacitor C_D11And the detection coil L_D11The actual current in between. It is determined whether the actual current is greater than a threshold current. If the current is larger than the threshold current, judging that foreign matters exist on the transmitting coil. If the current is not larger than the threshold current, judging that no foreign matter exists on the transmitting coil. In-pair detection coil L_D11After the judgment is finished, the second switch Q is switched off₁₁. Then the third switch Q is closed₂₁At this time, the third switch Q₂₁Will exchange the source U₁Is conducted with a second detection branch circuit in the first detection circuit so as to be a current detection module CT in the second detection branch circuit₂₁Detection coil L_D21And a resonant capacitor C_D21A power supply energizing signal is provided. Similarly, the current detection module CT₂₁Obtaining a current flowing through a resonant capacitor C_D21And the detection coil L_D21The actual current in between. It is determined whether the actual current is greater than a threshold current. If the current is larger than the threshold current, judging that foreign matters exist on the transmitting coil. If the current is not larger than the threshold current, judging that no foreign matter exists on the transmitting coil. In-pair detection coil L_D21After the judgment is finished, the third switch Q is switched off₂₁. Then the third switch Q is closed₃₁Closing the third switch Q₃₁The following steps may refer to closing the third switch Q₁₁And a third switch Q₂₁The following steps are not described again. Through the above process, until the third switch Q is closed_m1Complete closing of the second switch Q_m1And (5) the following steps.

After the detection of the first detection circuit is completed, the detection of the second detection circuit is performed, i.e. the third switch S is switched₁₂Is closed, at this time, the third switch S₁₂Will exchange the source U₂Is conducted with the first detection branch in the second detection circuit, thereby being the current detection module CT in the first detection branch₁₂Detection coil L_D12And a resonant capacitor C_D12Providing power supply excitation signal to control current detection module CT₁₂Obtaining a current flowing through a resonant capacitor C_D12And the detection coil L_D12The actual current in between. It is determined whether the actual current is greater than a threshold current. If the current is larger than the threshold current, judging that foreign matters exist on the transmitting coil. If the current is not larger than the threshold current, judging that no foreign matter exists on the transmitting coil. In-pair detection coil L_D12After the judgment is finished, the third switch Q is switched off₁₂. Then the third switch Q is closed₂₂. In closing the third switch Q₂₂Thereafter, referring to the third switch Q being closed₁₂The following steps until the third switch Q is closed_m2Complete closing of the second switch Q_m2The following steps thus complete the detection of the second detection circuit. Similarly, after the detection of the second detection circuit is completed, the detection of the third to nth detection circuits may be sequentially completed, and the specific steps are not described herein again with reference to the above process.

After the detection of the nth detection circuit is finished, the detection of whether foreign matters exist in the whole transmitting coil is finished.

It should be noted that, in the above process, only one detection branch in one detection circuit is used for detection at a time, and multiple detection branches may also be used for detection at the same time, for example, two, three, four, or all detection branches in one detection circuit are used for detection at the same time. It is also possible to perform the detection simultaneously by a plurality of detection circuits, for example, by one, two or four detection branches of two, three or four detection circuits. All detection branches in all detection circuits can also detect simultaneously. When a plurality of detection circuits are simultaneously detected, the detection circuits can be set by a user according to actual needs, and the application is not limited to this.

In the present application, as shown in fig. 10, before the step of acquiring the total actual current flowing through the resonant capacitor 13 and the detection coil 14 in step S102, the method further includes:

and S107, adjusting the test excitation frequency of the alternating current source 11.

Specifically, since there is a deviation between the different detection coil inductors 14 and a deviation between the capacitance values of the different resonant capacitors 13, which makes it difficult to ensure resonance, each detection circuit is scanned before the power is turned on to determine the resonance state of the circuit.

At this point, the test excitation frequency of the ac source 11 is adjusted for different detection circuits to provide power excitation signals of different resonant frequencies for the different detection circuits.

And S108, acquiring the total test current flowing through the resonance capacitor 13 and the detection coil 14.

Specifically, when the test excitation frequency of the ac source 11 is modulated by a value, whether the adjusted test excitation frequency is suitable or not needs to be detected, at this time, the ac source 11 may supply power to the resonant capacitor 13 and the detection coil 14 in the circuit by using the test excitation frequency, and the total test current flowing through the resonant capacitor 13 and the detection coil 14 is obtained by the current detection unit 12.

And S109, when the total test current is smaller than the threshold current, stopping adjusting the test excitation frequency, and taking the corresponding test excitation frequency when the adjustment is stopped as the alternating current source to load the actual excitation frequency of the detection coil.

Specifically, after the total test current flowing through the vibrating capacitor 13 and the detecting coil 14 is obtained, the total test current is compared with a threshold current, if the total test current is not greater than the threshold current, the adjustment of the test excitation frequency is stopped, the corresponding test excitation frequency when the adjustment is stopped is determined as the resonant frequency corresponding to the detecting circuit, and recording is performed so that the resonant frequency is adopted in the subsequent detection.

Through the above steps, the resonant frequency of the ac source 11 may be adjusted for different detection circuits so as to obtain a desired resonant frequency.

When the test excitation frequency of the ac source is actually adjusted, the microprocessor may be connected to a plurality of driver chips, and the plurality of driver chips may realize frequency modulation. Or when the maximum current of the foreign matter detection circuit does not exceed 100mA, the microprocessor can be not connected with the driving chip and directly realizes frequency modulation.

Further, as shown in fig. 11, the foreign object detection circuit further includes a voltage detection module 18 and a detection resistor 19, the detection coil 14 is connected in parallel with the resonant capacitor 13 and then connected in series with the detection resistor 19, and the detection resistor 19 is connected to the voltage detection module 18.

Specifically, the foreign object detection circuit may detect a voltage in addition to a current of the circuit. At this time, the foreign object detection circuit is provided with a detection resistor 19, the voltage of the foreign object detection circuit is obtained by acquiring the voltage at the two ends of the detection resistor 19, and whether foreign objects exist is judged according to the voltage.

In the foreign object detection circuit, the AC source 11 is excited by an externally applied voltage, L_DTo detect coil 14, C_DIs a resonant capacitor 13 connected in parallel with L_DBoth ends, with L_DResonance at a resonance frequency f_D，R_DFor detecting the resistance 19, are connected in series in the circuit. At this time, the foreign matter detection circuit satisfies

Wherein the content of the first and second substances,

the circuit impedance is:

flows through R_DThe current at the two ends is:

R_Dthe voltage at the two ends is: u shape_D＝I_D·R_D。

In an ideal state, when no metallic foreign matter is present, L_D、C_DParallel resonance, the circuit impedance Z is infinite, and the current in the loop is I_DIs 0, R_DThe voltage across is 0.

When a metal foreign body exists, the inductance value of the detection coil, namely L, is influenced due to the eddy current effect of the metal_DChange occurs, denoted as L_D', due to L_D' and C_DNo resonance, so that the loop impedance Z will change significantly, the current I in the loop_DFrom 0 to I_D′，R_DThe voltage at both ends is changed from 0 to U_D', i.e. detecting R_DAnd the voltage at two ends changes to realize the judgment on the existence of the metal foreign matters.

In this case, as shown in fig. 12, the foreign object detection method further includes:

in step S110, the voltage detection module 18 is controlled to obtain the actual voltage across the detection resistor 19.

Specifically, when detecting foreign objects, after the ac source 11 supplies power to the resonant capacitor 13 and the detection coil 14, the voltage detection module 18 monitors the detection resistor 19 to obtain the actual voltage across the detection resistor 19.

Step S111, judging whether the actual voltage is greater than a threshold voltage; if so, judging that foreign matters exist on the transmitting coil or the receiving coil, and if not, judging that no foreign matters exist on the transmitting coil or the receiving coil.

Specifically, the acquired actual voltage of the detection resistor 19 is compared with a threshold voltage, and if the actual voltage is greater than the threshold voltage, it is determined that a foreign object is present on the radiation coil. And if the actual voltage is not greater than the threshold voltage, judging that no foreign matter exists on the transmitting coil.

The threshold voltage is set in advance, and is ideally 0v, but in an actual circuit, the threshold voltage may be greater than 0v, and may be 10mV, for example.

Example two

The application provides a foreign matter detection device, as shown in fig. 13, be applied to wireless charging system, wireless charging system is including setting up the foreign matter detection circuit on transmission coil, and foreign matter detection circuit refers to fig. 2 and shows, including exchange source 11, current detection module 12, resonant capacitor 13 and detection coil 14, exchange source 11 with resonant capacitor 13 connects, resonant capacitor 13 with detection coil 14 is parallelly connected, resonant capacitor 13 is connected to current detection module 12. The foreign matter detection device includes:

an ac source turning-on unit 201 configured to turn on the ac source so that the ac source transmits power to the resonant capacitor;

a current obtaining unit 202, configured to control the current detection module to obtain a total actual current flowing through the resonant capacitor and the detection coil;

a first judgment unit 203, configured to judge whether the total actual current is greater than a threshold current;

In an embodiment of the present invention, referring to fig. 3, there is one ac source 11, there is one current detection module 12, there is one resonant capacitor 13, there are multiple sets of detection coils 14, there is at least one detection coil 14 in each set, the resonant capacitor 13 is connected to each detection coil 14, and a first switch 15 is disposed between the resonant capacitor 13 and each detection coil 14, and the foreign object detection apparatus, as shown in fig. 14, further includes:

a first switch closing unit 204 for sequentially closing the first switches 15.

The current obtaining unit 202 is specifically configured to control the current detecting module 12 to obtain a total actual current flowing through the resonant capacitor 13 and the detecting coil 14 each time the first switch 15 is closed.

Alternatively, in the embodiment of the present invention, as shown in fig. 6, one ac source 11 is provided, a plurality of current detection modules 12 are provided, a plurality of resonance capacitors 13 are provided, a plurality of detection coils 14 are provided, the resonance capacitors 13 are respectively provided corresponding to the current detection modules 12 and the detection coils 14, and a second switch 16 is provided between each resonance capacitor 13 and the ac source 11, and the foreign object detection apparatus further includes:

a second switch closing unit 205 for closing the second switches 16 in sequence.

The current obtaining unit 202 is specifically configured to control the current detecting module 12 to obtain a total actual current flowing through the detection coil 14 and the resonance capacitor 13 corresponding to the detection coil 14 each time the second switch 16 is closed.

Alternatively, in an embodiment of the present invention, referring to fig. 8, a plurality of ac sources 11 are provided, the current detection module 12 is provided with a plurality of sets, each set of the current detection module 12 is provided with at least one, the resonant capacitor 13 is provided with a plurality of sets, each set of the resonant capacitor 13 is provided with at least one, the detection coil 14 is provided with a plurality of sets, each set of the detection coil 14 is provided with at least one, the resonant capacitor 13 is respectively provided corresponding to the current detection module 12 and the detection coil 14, each ac source 11 is connected to each set of the resonant capacitor 13, a third switch 17 is provided between each resonant capacitor 13 and the corresponding ac source 11, and the foreign object detection apparatus further includes, as shown in fig. 16:

a third switch closing unit 206 for closing the third switches in sequence.

The current obtaining unit 202 is specifically configured to control the current detecting module to obtain a total actual current flowing through the resonant capacitor and the detecting coil each time the third switch is closed.

Further, as shown in fig. 17, the foreign object detection device further includes:

and the frequency adjusting unit 207 is used for adjusting the test excitation frequency of the alternating current source 11.

A test current obtaining unit 208 for obtaining a total test current flowing through the resonance capacitor 13 and the detection coil 14.

A frequency determining unit 209, configured to stop the adjustment of the test excitation frequency when the total test current is smaller than a threshold current, and load the corresponding test excitation frequency when the adjustment is stopped as the ac source to the actual excitation frequency of the detection coil.

Further, referring to fig. 11, the foreign object detection circuit further includes a voltage detection module 18 and a detection resistor 19, the detection coil 14 is connected in parallel with the resonant capacitor 13 and then connected in series with the detection resistor 19, the detection resistor 19 is connected to the voltage detection module 18, and the foreign object detection device, as shown in fig. 18, further includes:

a voltage obtaining unit 210, configured to control the voltage detection module 18 to obtain an actual voltage across the detection resistor 19.

A second determining unit 211, configured to determine whether the actual voltage is greater than a threshold voltage.

In this way, the foreign object detection circuit only needs to include the ac source 11, the current detection module 12, the resonant capacitor 13, and the detection coil 14, the current detection module 12 obtains the total actual current of the resonant capacitor 13 and the detection coil 14, compares the actual current with the threshold current, determines that a foreign object exists in the wireless charging system when the actual current is greater than the threshold current, and determines that a foreign object does not exist in the wireless charging system when the actual current is not greater than the threshold current. Therefore, in the application, the foreign matter is detected based on the current change, the implementation method is simple, namely the implementation circuit is simple, and the detection result is accurate, so that whether the foreign matter exists in the wireless charging system can be accurately and simply detected.

The preferred embodiments of the present disclosure are described in detail with reference to the accompanying drawings, however, the present disclosure is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present disclosure within the technical idea of the present disclosure, and these simple modifications all belong to the protection scope of the present disclosure.

It should be noted that, in the foregoing embodiments, various features described in the above embodiments may be combined in any suitable manner, and in order to avoid unnecessary repetition, various combinations that are possible in the present disclosure are not described again.

In addition, any combination of various embodiments of the present disclosure may be made, and the same should be considered as the disclosure of the present disclosure, as long as it does not depart from the spirit of the present disclosure.

Claims

1. A foreign matter detection method is characterized by being applied to a wireless charging system, wherein the wireless charging system comprises a foreign matter detection circuit arranged on a transmitting coil, the foreign matter detection circuit comprises an alternating current source, a current detection module, a resonant capacitor and a detection coil, the alternating current source is connected with the resonant capacitor, the resonant capacitor is connected with the detection coil in parallel, the current detection module is connected with the resonant capacitor, and the foreign matter detection method comprises the following steps:

turning on the AC source to enable the AC source to transmit electricity to the resonant capacitor;

controlling the current detection module to obtain the total actual current flowing through the resonance capacitor and the detection coil;

judging whether the total actual current is greater than a threshold current or not;

2. The foreign object detection method according to claim 1, wherein one ac source is provided, one current detection module is provided, one resonant capacitor is provided, a plurality of sets of the detection coils are provided, at least one resonant capacitor is provided for each set of the detection coils, the resonant capacitors are respectively connected to the detection coils, and a first switch is provided between the resonant capacitors and the detection coils, and the method further comprises, after the step of turning on the ac source to transmit the electric power from the ac source to the resonant capacitors:

sequentially closing the first switches;

3. The foreign object detection method according to claim 1, wherein one ac source is provided, a plurality of current detection modules are provided, a plurality of resonance capacitors are provided, a plurality of detection coils are provided, the resonance capacitors are provided corresponding to the current detection modules and the detection coils, respectively, and a second switch is provided between each of the resonance capacitors and the ac source, and the method further comprises, after the step of turning on the ac source to transmit power from the ac source to the resonance capacitors:

sequentially closing the second switches;

4. The foreign object detection method according to claim 1, wherein a plurality of ac sources are provided, a plurality of sets of current detection modules are provided, at least one current detection module is provided for each set, a plurality of sets of resonance capacitors are provided, at least one resonance capacitor is provided for each set, at least one detection coil is provided for each set, at least one resonance capacitor is provided for each set, the resonance capacitors are provided corresponding to the current detection modules and the detection coils, each ac source is connected corresponding to each set of resonance capacitors, a third switch is provided between each resonance capacitor and the corresponding ac source, and the step of turning on the ac source to transmit power from the ac source to the resonance capacitors further includes:

sequentially closing the third switches;

5. The foreign object detection method according to any one of claims 1 to 4, characterized in that, before the step of acquiring the total actual current flowing through the resonance capacitance and the detection coil, further comprising:

adjusting the test excitation frequency of the alternating current source;

6. The foreign object detection method according to any one of claims 1 to 4, wherein the foreign object detection circuit further includes a voltage detection module and a detection resistor, the detection coil is connected in series with the detection resistor after being connected in parallel with the resonance capacitor, and the detection resistor is connected to the voltage detection module, and the foreign object detection method further includes:

judging whether the actual voltage is greater than a threshold voltage or not;

7. The utility model provides a foreign matter detection device, its characterized in that is applied to wireless charging system, wireless charging system is including setting up the foreign matter detection circuit on transmitting coil, foreign matter detection circuit includes interchange source, current detection module, resonant capacitor and detection coil, interchange the source with resonant capacitor connects, resonant capacitor with detection coil is parallelly connected, resonant capacitor is connected to the current detection module, foreign matter detection device includes:

8. The apparatus according to claim 7, wherein there is one ac source, one current detecting module, one resonant capacitor, multiple sets of detecting coils, at least one resonant capacitor connected to each detecting coil, and a first switch provided between the resonant capacitor and each detecting coil, the apparatus further comprising:

a first switch closing unit for sequentially closing the first switches;

9. The apparatus according to claim 7, wherein there is one ac source, there are a plurality of the current detection modules, there are a plurality of the resonant capacitors, there are a plurality of the detection coils, there are a plurality of the resonant capacitors provided corresponding to the current detection modules and the detection coils, respectively, and a second switch is provided between each of the resonant capacitors and the ac source, the foreign object detection apparatus further comprising:

a second switch closing unit for sequentially closing the second switches;

10. The apparatus according to claim 7, wherein a plurality of ac sources are provided, a plurality of sets of the current detection modules are provided, at least one current detection module is provided for each set, a plurality of sets of the resonant capacitors are provided, at least one resonant capacitor is provided for each set, at least one detection coil is provided for each set, at least one resonant capacitor is provided for each set, the resonant capacitors are provided corresponding to the current detection modules and the detection coils, each ac source is connected to each set of the resonant capacitors, a third switch is provided between each resonant capacitor and the corresponding ac source, and the foreign matter detection apparatus further comprises:

a third switch closing unit for sequentially closing the third switches;

11. The apparatus according to any one of claims 7 to 10, wherein the foreign matter detection apparatus further comprises:

12. The apparatus according to any one of claims 7-10, wherein the foreign object detection circuit further comprises a voltage detection module and a detection resistor, the detection coil is connected in series with the detection resistor after being connected in parallel with the resonance capacitor, the detection resistor is connected with the voltage detection module, and the foreign object detection apparatus further comprises: