Dual-frequency metal foreign body detection system and control method for wireless charging system

Abstract

The present invention relates to the field of wireless power transmission technology, and specifically discloses a dual-frequency metal foreign body detection system for a wireless charging system and a control method thereof. A dual-frequency excitation circuit is provided to generate a low-frequency magnetic field and a high-frequency magnetic field, a dual-frequency detection circuit is provided to detect a low-frequency sampling voltage and a high-frequency sampling voltage under the low-frequency magnetic field and the high-frequency magnetic field, a signal processing circuit is provided to filter, amplify and rectify the low-frequency sampling voltage and the high-frequency sampling voltage to obtain a low-frequency detection signal and a high-frequency detection signal, a processor is provided to analyze the low-frequency detection signal and the high-frequency detection signal to determine whether there is a ferromagnetic or non-ferromagnetic metal foreign body, and a plurality of pairs of excitation coils L corresponding to each other are provided. e With detection coil L d , thereby dividing the foreign body detection area into multiple sub-areas, making it easier to determine the location of metal foreign bodies and achieve all-round metal foreign body detection; setting the excitation coil L e , detection coil L d It is decoupled from both the transmitting coil and the receiving coil, achieving isolation from the wireless charging system.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless power transmission, and in particular to a dual-frequency metal foreign body detection system for a wireless charging system and a control method thereof. Background Art

[0002] During the wireless charging process of electric vehicles, the presence of metal foreign objects in the magnetic field will generate eddy current effects and magnetization effects, affecting the electrical parameters of the coupling mechanism such as self-inductance and mutual inductance, causing the system to malfunction and even posing a risk of fire. The eddy current effect generated by metal foreign objects increases with the increase of the magnetic field frequency, while the magnetization effect is not affected by the detection magnetic field frequency. The eddy current effect and the magnetization effect have opposite effects on the detection magnetic field. For non-ferromagnetic metal foreign objects, the eddy current effect is the main effect, and high-frequency detection sensitivity is higher. For ferromagnetic materials, the eddy current effect has less impact than the magnetization effect under low-frequency magnetic field detection, and the detection sensitivity is higher. Existing single-frequency metal foreign object detection systems cannot avoid detection failure caused by the offset of eddy current effect and magnetization effect. Summary of the Invention

[0003] The present invention provides a dual-frequency metal foreign body detection system for a wireless charging system and a control method thereof, which solves the technical problem of how to avoid the occurrence of single-frequency detection failure and further improve the sensitivity and detection accuracy of metal foreign body detection.

[0004] To solve the above technical problems, the present invention provides a dual-frequency metal foreign body detection system for a wireless charging system. The wireless charging system is provided with a transmitting coil and a receiving coil. The key points of the dual-frequency metal foreign body detection system are as follows: the dual-frequency metal foreign body detection system includes a controller and a dual-frequency excitation circuit, a dual-frequency detection circuit, and a signal processing circuit connected to the controller;

[0005] The dual-frequency excitation circuit includes a dual-frequency voltage generating circuit, a dual-frequency resonant circuit and a plurality of excitation coils L e The dual-frequency voltage generating circuit is used to generate an AC output voltage of a low-frequency component and a high-frequency component, and the dual-frequency resonant circuit is used to resonate at low frequency and high frequency to make the working excitation coil L e Generate low-frequency magnetic field and high-frequency magnetic field;

[0006] The dual-frequency detection circuit includes a plurality of detection coils L d , and a plurality of the detection coils L d A dual-frequency sampling circuit is connected in parallel, and the dual-frequency sampling circuit includes a low-frequency sampling circuit and a high-frequency sampling circuit. The detection coil L d For receiving the excitation coil L e The low-frequency magnetic field and high-frequency magnetic field generated by the low-frequency sampling circuit are used to work with the detection coil L dResonance under low frequency magnetic field obtains low frequency sampling voltage, and the high frequency sampling circuit is used to work with the detection coil L d Resonate under high frequency magnetic field to obtain high frequency sampling voltage;

[0007] The signal processing circuit includes a low-frequency signal processing circuit connected to the low-frequency sampling circuit and a high-frequency signal processing circuit connected to the high-frequency sampling circuit, wherein the low-frequency signal processing circuit is used to filter, amplify and rectify the low-frequency sampling voltage to obtain a low-frequency detection signal, and the high-frequency signal processing circuit is used to filter, amplify and rectify the high-frequency sampling voltage to obtain a high-frequency detection signal;

[0008] Multiple excitation coils L e , multiple detection coils L d Fully cover the transmitting coil and the receiving coil, the excitation coil L e , detection coil L d decoupled from both the transmitting coil and the receiving coil;

[0009] The controller is used to sequentially control the excitation coils L of the first, second to nth detection areas at the first, second to nth moments in sequence. e , detection coil L d Working, n is the excitation coil L e And detection coil L d The first, second to nth detection areas are combined into a full coverage area of ​​the transmitting coil and the receiving coil;

[0010] The controller is also used to determine whether there is a metal foreign object based on the low-frequency detection signal and the high-frequency detection signal, and when a metal foreign object exists, determine whether the metal foreign object is a ferromagnetic metal foreign object or a non-ferromagnetic metal foreign object and determine the location of the metal foreign object.

[0011] Preferably, the dual-frequency resonant circuit includes a capacitor C e , inductor L1 and capacitor C1, capacitor C e The inductor L1 and capacitor C1 are connected in series with each of the excitation coils L e In series, capacitor C e Also connected to the dual-frequency voltage generating circuit, multiple excitation coils L e in parallel.

[0012] Preferably, the capacitor C e , inductor L1, capacitor C1 and excitation coil L e satisfy:

[0013]

[0014] Among them, f tis the operating frequency of the wireless charging system, f s is the foreign body low frequency detection frequency, f h is the foreign body high frequency detection frequency, ω t 、ω s 、ω h f t 、f s 、f h The corresponding angular frequency.

[0015] Preferably, the plurality of excitation coils L e Arranged in array, each of the excitation coils L e Use bipolar coil;

[0016] Multiple detection coils L d With multiple excitation coils L e Using the same array arrangement, each of the detection coils L d With the excitation coil L e The same bipolar coil; the transmitting coil and the receiving coil are both unipolar coils;

[0017] Multiple excitation coils L e Placed on the transmitting coil, multiple detection coils L d Opposite to the plurality of excitation coils L e superior.

[0018] Preferably, the dual-frequency resonant circuit and each excitation coil L e There are excitation switches connected to the controller in series, and the controller controls all the excitation switches in a time division multiplexing manner;

[0019] In each of the detection coils L d A detection switch connected to the controller is connected in series with the dual-frequency sampling circuit, and the controller controls all detection switches in a time division multiplexing manner.

[0020] Preferably, the controller controls the plurality of excitation coils L by controlling the on and off of the excitation switch and the detection switch. e With multiple detection coils L d Working in pairs, the excitation coils L facing each other are e and the detection coil L d As a pair.

[0021] Preferably, the low-frequency sampling circuit includes an inductor L h , capacitor C h , capacitor C ds and sampling resistor R ds , inductance L h, capacitor C h Parallel resonance forms high frequency f h The wave blocking circuit, capacitor C ds With high frequency f h The wave blocking circuit is connected in series so that the detection coil L d The low frequency sampling circuit forms a frequency of f s series resonant circuit; the sampling resistor R ds The voltage at both ends is the low-frequency sampling voltage;

[0022] The high frequency sampling circuit includes an inductor L s , capacitor C s , capacitor C dh and sampling resistor R dh , inductance L s , capacitor C s Parallel resonance forms a low frequency f s The wave blocking circuit, capacitor C s With low frequency f s The wave blocking circuit is connected in series so that the detection coil L d The high frequency sampling circuit as a whole forms a frequency of f h series resonant circuit; the sampling resistor R dh The voltage across both ends is the high-frequency sampling voltage.

[0023] Preferably, the inductor L h , capacitor C h , capacitor C ds and sampling resistor R ds satisfy:

[0024]

[0025] Inductor L s , capacitor C s , capacitor C dh and sampling resistor R dh satisfy:

[0026]

[0027] Preferably, the dual-frequency voltage generating circuit adopts bipolar SPWM modulation, and its AC output voltage is expressed as:

[0028]

[0029] Among them, V in is the DC voltage source size, a s is the modulation wave amplitude, ω s is the modulation wave angular frequency, ω h is the carrier angular frequency, J kis the k-order Bessel function, m is the order of the Fourier series, when m is odd, k is even, when m is even, k is odd, t represents the time, and θ represents the phase angle of the harmonic.

[0030] The present invention also provides a control method for the dual-frequency metal foreign body detection system of the wireless charging system, the key of which is to include the following steps:

[0031] S1, at the first, second to nth moments in sequence, sequentially control the excitation coils L of the first, second to nth detection areas e , detection coil L d Work;

[0032] S2. Compare the low-frequency detection signal and high-frequency detection signal generated at each moment with the preset low-frequency detection threshold and high-frequency detection threshold respectively. If the low-frequency detection signal or the high-frequency detection signal exceeds the detection threshold, it is determined that a metal foreign object exists. If the low-frequency detection signal increases or the high-frequency detection signal decreases, it can be determined that the metal foreign object is a ferromagnetic metal foreign object. Otherwise, the foreign object is determined to be a non-ferromagnetic metal foreign object.

[0033] The dual-frequency metal foreign body detection system and control method of the wireless charging system provided by the present invention are provided with a dual-frequency excitation circuit to generate a low-frequency magnetic field and a high-frequency magnetic field, a dual-frequency detection circuit to detect the low-frequency sampling voltage and the high-frequency sampling voltage under the low-frequency magnetic field and the high-frequency magnetic field, a signal processing circuit to filter, amplify and rectify the low-frequency sampling voltage and the high-frequency sampling voltage to obtain a low-frequency detection signal and a high-frequency detection signal, a processor to analyze the low-frequency detection signal and the high-frequency detection signal to determine whether a metal foreign body exists, and when a metal foreign body exists, determine whether the metal foreign body is a ferromagnetic metal foreign body or a non-ferromagnetic metal foreign body and determine the location of the metal foreign body, and provide multiple pairs of excitation coils L corresponding to each other. e With detection coil L d , thereby dividing the foreign body detection area into multiple sub-areas, making it easier to determine the location of metal foreign bodies and achieve all-round metal foreign body detection; setting the excitation coil L e , detection coil L d The present invention is decoupled from both the transmitting coil and the receiving coil, achieving isolation from the wireless charging system. Compared with the existing technology, the present invention has the following beneficial effects:

[0034] 1) It realizes the detection of metal foreign bodies in the whole area, eliminates the blind area of ​​magnetic field detection and solves the failure of single-frequency detection;

[0035] 2) It realizes independent operation with the wireless charging system and has high anti-interference performance;

[0036] 3) It has strong applicability and can be applied to all electric vehicle wireless charging systems or other wireless charging systems that require metal foreign body detection;

[0037] 4) The detection sensitivity of the wireless charging system to all types of metal foreign objects in the detection area is improved with high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a structural diagram of a dual-frequency metal foreign body detection system for a wireless charging system provided by an embodiment of the present invention;

[0039] Figure 2 A pair of excitation coils L provided in an embodiment of the present invention e and detection coil L d Specific circuit diagram of dual-frequency excitation circuit and dual-frequency detection circuit during operation;

[0040] Figure 3 1 is a diagram showing the relationship between the amplitudes of the fundamental wave and carrier component of the bipolar SPWM output voltage provided by an embodiment of the present invention;

[0041] Figure 4 The embodiment of the present invention provides n pairs of excitation coils L e and detection coil L d A diagram showing the connection relationship between the dual-frequency resonant circuit and the dual-frequency sampling circuit;

[0042] Figure 5 In the two detection cycles provided by the embodiment of the present invention, n pairs of excitation coils L e and detection coil L d Turn-on timing diagram;

[0043] Figure 6 This is a waveform diagram of the excitation loop current and dual-frequency detection signal provided by an embodiment of the present invention;

[0044] Figure 7 This is a curve diagram of the dual-frequency detection signal changes before and after the metal foreign body is introduced, provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0045] The following describes the embodiments of the present invention in detail with reference to the accompanying drawings. The embodiments are provided for illustrative purposes only and are not to be construed as limiting the present invention. The accompanying drawings are provided for reference and illustration only and do not constitute a limitation on the scope of protection of the present invention. Many changes may be made to the present invention without departing from the spirit and scope of the present invention.

[0046] In order to meet the requirements of independent operation and blind spot detection of metal foreign body detection system in wireless charging scenarios, avoid the occurrence of single frequency detection failure, and further improve the sensitivity and detection accuracy of metal foreign body detection, the embodiment of the present invention first provides a dual-frequency metal foreign body detection system for wireless charging system. The structure of the system is as follows: Figure 1 As shown. In a pair of excitation coils L eand detection coil L d When working, the specific circuits of the dual-frequency excitation circuit and the dual-frequency detection circuit are as follows: Figure 2 As shown. n pairs of excitation coils L e and detection coil L d The connection relationship between the dual-frequency resonant circuit and the dual-frequency sampling circuit is as follows: Figure 4 As shown. In two detection cycles, n pairs of excitation coils L e and detection coil L d The turn-on timing is as follows Figure 5 shown.

[0047] like Figure 1 As shown in FIG, a dual-frequency metal foreign body detection system provided in this embodiment includes a controller and a dual-frequency excitation circuit, a dual-frequency detection circuit, and a signal processing circuit connected to the controller. Figure 1 As shown, the system consists of a primary side and a secondary side. The primary side consists of a DC power supply, a high-power inverter, a transmitting coil, and its compensation circuit, while the secondary side consists of a receiving coil, its compensation circuit, and a load circuit. Taking the electric vehicle wireless charging system as an example, the primary side refers to the ground side, and the secondary side refers to the vehicle side.

[0048] like Figure 1 、 Figure 2 、 Figure 4 As shown, the dual-frequency excitation circuit includes a dual-frequency voltage generation circuit, a dual-frequency resonant circuit and n excitation coils L e (Excitation coil group, including excitation coil L E1 To L En , the i-th excitation coil is represented by L Ei ), the dual-frequency voltage generating circuit is used to generate an AC output voltage of a low-frequency component and a high-frequency component, and the dual-frequency resonant circuit is used to resonate at low frequency and high frequency to make the working excitation coil L e Generate low-frequency magnetic field and high-frequency magnetic field.

[0049] The dual-frequency voltage generation circuit includes an SPWM control circuit and a full-bridge inverter circuit. The SPWM control circuit adopts a bipolar modulation method. The harmonic component in the output voltage of the full-bridge inverter circuit is the highest at the carrier frequency. The SPWM control circuit uses bipolar modulation, and the sinusoidal modulation wave u s With the triangular carrier u h The switching signal is obtained by comparison, and the controller (DSP28335) outputs the switching signal, which is then controlled by the drive circuit to switch the full-bridge inverter circuit on and off, thereby achieving the output of AC voltage. According to the Fourier decomposition formula, the expression of the AC output voltage when bipolar SPWM modulation is obtained is:

[0050]

[0051] Among them, V in is the DC voltage source size, a s is the modulation wave amplitude, ω s is the modulation wave angular frequency (the corresponding modulation frequency is the low frequency f s ),ω h is the carrier angular frequency (the corresponding modulation frequency is high frequency f h ). J k is the k-th order Bessel function, and m is the order of the Fourier series. When m is odd, k is even, and when m is even, k is odd. That is, when m = 1, 3, 5, ..., k = 2, 4, 6, ...; when m = 2, 4, 6, ..., k = 1, 3, 5, ..., t represents the time, and θ represents the phase angle of the harmonic. Figure 3 This is the amplitude relationship diagram of the bipolar SPWM output voltage fundamental wave and carrier component. Figure 2 , single-phase inverter circuit in bipolar modulation mode, different modulation degrees a s The amplitude of the fundamental and carrier components of the output voltage, and the reasonable setting of the modulation index can obtain the ideal dual-frequency voltage amplitude.

[0052] The output voltage of the full-bridge inverter circuit contains the fundamental frequency f s Component and carrier frequency f h component, through the dual-frequency resonant circuit, the excitation circuit is at the frequency f s and f h Resonance occurs under the condition that the excitation coil generates a dual-frequency magnetic field.

[0053] like Figure 1 、 Figure 2 As shown, the dual-frequency resonant circuit includes a capacitor C e , inductor L1 and capacitor C1, capacitor C e After the parallel inductor L1 and capacitor C1 are connected in series with each excitation coil L e In series, capacitor C e It is also connected to a dual-frequency voltage generating circuit, multiple excitation coils L e In parallel. Capacitor C e , inductor L1, capacitor C1 and excitation coil L e satisfy:

[0054]

[0055] Among them, f t is the operating frequency of the wireless charging system, f s is the foreign body low frequency detection frequency, f h is the foreign body high frequency detection frequency, ω t 、ω s 、ω h f t 、f s 、fh The corresponding angular frequency. The parallel resonant frequency of the compensation capacitor C1 and the compensation inductor L1 is designed to be f t , to achieve wave blocking of power signals.

[0056] like Figure 1 、 Figure 2 、 Figure 4 As shown, the dual-frequency detection circuit includes n detection coils L d (Detection coil group, including detection coil L D1 To L Dn , the i-th detection coil is represented by L Di ), and n detection coils L d The parallel dual-frequency sampling circuit includes a low-frequency sampling circuit and a high-frequency sampling circuit. The working detection coil L d For receiving the excitation coil L e The low-frequency magnetic field and high-frequency magnetic field generated by the low-frequency sampling circuit are used to work with the detection coil L d Resonance in the low frequency magnetic field obtains the low frequency sampling voltage, and the high frequency sampling circuit is used to work with the detection coil L d The high-frequency sampling voltage is obtained by resonance in a high-frequency magnetic field.

[0057] like Figure 1 、 Figure 2 、 Figure 4 As shown, the low-frequency sampling circuit includes an inductor L h , capacitor C h , capacitor C ds and sampling resistor R ds , inductance L h , capacitor C h Parallel resonance forms high frequency f h The wave blocking circuit, capacitor C ds With high frequency f h The wave blocking circuit is connected in series so that the detection coil L d The overall frequency formed by the low-frequency sampling circuit is f s Series resonant circuit; sampling resistor R ds The voltage across the two ends is the low-frequency sampling voltage. Based on the resonance relationship, the inductor L h , capacitor C h , capacitor C ds and sampling resistor R ds satisfy:

[0058]

[0059] like Figure 1 、 Figure 2 、 Figure 4 As shown, the high-frequency sampling circuit includes an inductor L s , capacitor Cs , capacitor C dh and sampling resistor R dh , inductance L s , capacitor C s Parallel resonance forms a low frequency f s The wave blocking circuit, capacitor C s With low frequency f s The wave blocking circuit is connected in series so that the detection coil L d The overall frequency formed by the high-frequency sampling circuit is f h Series resonant circuit; sampling resistor R dh The voltage across the two ends is the high-frequency sampling voltage. s , capacitor C s , capacitor C dh and sampling resistor R dh satisfy:

[0060]

[0061] like Figure 4 As shown, in the dual-frequency resonant circuit with each excitation coil L e There are excitation switches connected to the controller in series, and the controller uses time division multiplexing to control all the excitation switches;

[0062] In each detection coil L d A detection switch connected to a controller is connected in series between the dual-frequency sampling circuit, and the controller controls all detection switches in a time-division multiplexing manner.

[0063] like Figure 5 As shown, n excitation coils L e Array arrangement, each excitation coil L e Use bipolar coils. n detection coils L d With n excitation coils L e Using the same array arrangement, each detection coil L d With the excitation coil L e Same bipolar coil; both the transmitting coil and the receiving coil use unipolar coils (which can realize the transmitting coil, receiving coil and detection coil L d , Excitation coil L e decoupling between them, so that the detection system and the charging system can operate independently).

[0064] like Figure 1 As shown, multiple excitation coils L e Placed on the transmitting coil, multiple detection coils L d Opposite to multiple excitation coils L e superior.

[0065] like Figure 5As shown, the controller controls the on and off of the excitation switch and the detection switch to control the multiple excitation coils L e With multiple detection coils L d Working in pairs, the excitation coils L facing each other e and detection coil L d As a pair.

[0066] like Figure 1 As shown, the signal processing circuit is mainly composed of a low-pass filter circuit and a band-pass filter circuit and their respective amplification and rectification circuits. Both the low-pass filter circuit and the band-pass filter circuit use a fourth-order filter design. The low-pass filter circuit filters out f s Interference signal, bandpass filter circuit filters out f h Interference signal. The filtered signal is output as a low-frequency detection signal U through the same-direction amplifier circuit and rectifier circuit. DS and high frequency detection signal U DH The dual-frequency detection signal is compared with the threshold voltage to determine whether a metal foreign object has invaded.

[0067] Based on the above system, an embodiment of the present invention further provides a control method for a dual-frequency metal foreign body detection system of a wireless charging system, that is, a control process of a processor, which specifically includes the following steps:

[0068] S1, at the first, second to nth moments in sequence, sequentially control the excitation coils L of the first, second to nth detection areas e , detection coil L d Work;

[0069] S2. Compare the low-frequency detection signal and high-frequency detection signal generated at each moment with the preset low-frequency detection threshold and high-frequency detection threshold respectively. If the low-frequency detection signal or the high-frequency detection signal exceeds the detection threshold, it is determined that a metal foreign object exists. If the low-frequency detection signal increases or the high-frequency detection signal decreases, it can be determined that the metal foreign object is a ferromagnetic metal foreign object. Otherwise, the foreign object is determined to be a non-ferromagnetic metal foreign object.

[0070] The controller activates the switch (S E1 -S En ) control the excitation coil group (L E1 -L E n ) is connected to the excitation circuit and detected by the switch (S D1 -S Dn )Control detection coil group (L D1 -L Dn) and the dual-frequency sampling circuit. At the same time, only one set of corresponding excitation coil and detection coil switches are turned on to detect metal foreign objects. The coil groups are turned on in a cycle until a metal foreign object is found. The system shuts down and reports the detection coil number where the metal foreign object is located. The coil number can be used to determine the location of the metal foreign object.

[0071] The present invention uses a bipolar excitation coil for active excitation to detect foreign objects. The detection coil also uses a bipolar coil to eliminate the blind spot of the magnetic field detection at the symmetrical center of the unipolar coil. The dual-frequency detection can eliminate the detection failure caused by the offset of the eddy current effect and magnetization effect of some metal foreign objects in single-frequency detection.

[0072] The eddy current effect generated by metallic foreign objects increases with increasing magnetic field frequency, while the magnetization effect is unaffected by the detection magnetic field frequency. The eddy current effect and the magnetization effect have opposite effects on the detection magnetic field. For non-ferromagnetic metallic foreign objects, the eddy current effect primarily affects them, resulting in higher detection sensitivity at high frequencies. For ferromagnetic materials, the eddy current effect is less influential than the magnetization effect at low-frequency magnetic fields, leading to higher detection sensitivity. Therefore, dual-frequency detection can effectively improve detection sensitivity.

[0073] The following experimental verification is carried out.

[0074] The DC voltage of the dual-frequency detection system is V in =10V, modulation wave frequency f s =8.5kHz, carrier frequency f h =850kHz, the modulation index is 0.2. The parameters of the dual-frequency resonant circuit are L1=496uH, C1=6.8uF, C e =700nF; low frequency sampling circuit parameters L h =14.7uH, C h =2.4nF, C ds =11.9uF, sampling resistor R ds =1Ω; high-frequency sampling circuit parameter L s =14.7uH, C s =23.8uF, C dh =2.4nF, sampling resistor R dh =1Ω. Equivalent inductance of the excitation coil L e =4.87uH, detection coil equivalent inductance L d =14.74uH.

[0075] Figure 6 The excitation circuit current I when the system is working e , the filtered dual-frequency sampling voltage U s and U h .from Figure 6It can be seen that this system uses SPWM modulation technology to achieve the generation and reception of dual-frequency detection magnetic fields.

[0076] Figure 7 The dual-frequency detection voltage changes when different materials of metal invade. Figure 7 It can be seen that the dual-frequency detection system can significantly improve the sensitivity of detecting various metal foreign objects.

[0077] from Figure 6 、 Figure 7 It is not difficult to see from the experimental results that the dual-frequency metal foreign body detection system and control method of the electric vehicle wireless charging system proposed in the embodiment of the present invention realize independent operation, eliminate the detection blind area, avoid the occurrence of single-frequency detection failure, and further improve the sensitivity and detection accuracy of metal foreign body detection.

[0078] In summary, the dual-frequency metal foreign body detection system and control method of the wireless charging system provided by the embodiment of the present invention are provided. A dual-frequency excitation circuit is provided to generate a low-frequency magnetic field and a high-frequency magnetic field. A dual-frequency detection circuit is provided to detect the low-frequency sampling voltage and the high-frequency sampling voltage under the low-frequency magnetic field and the high-frequency magnetic field. A signal processing circuit is provided to filter, amplify and rectify the low-frequency sampling voltage and the high-frequency sampling voltage to obtain a low-frequency detection signal and a high-frequency detection signal. A processor is provided to analyze the low-frequency detection signal and the high-frequency detection signal to determine whether there is a metal foreign body, and when a metal foreign body is present, determine whether the metal foreign body is a ferromagnetic metal foreign body or a non-ferromagnetic metal foreign body and determine the position of the metal foreign body. Multiple pairs of excitation coils L corresponding to each other are provided. e With detection coil L d , thereby dividing the foreign body detection area into multiple sub-areas, making it easier to determine the location of metal foreign bodies and achieve all-round metal foreign body detection; setting the excitation coil L e , detection coil L d The present invention is decoupled from both the transmitting coil and the receiving coil, achieving isolation from the wireless charging system. Compared with the existing technology, the present invention has the following beneficial effects:

[0079] 1) It realizes the detection of metal foreign bodies in the whole area, eliminates the blind area of ​​magnetic field detection and solves the failure of single-frequency detection;

[0080] 2) It realizes independent operation with the wireless charging system and has high anti-interference performance;

[0081] 3) It has strong applicability and can be applied to all electric vehicle wireless charging systems or other wireless charging systems that require metal foreign body detection;

[0082] 4) The detection sensitivity of the wireless charging system to all types of metal foreign objects in the detection area is improved with high accuracy.

[0083] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A dual-frequency metal foreign body detection system for a wireless charging system, wherein the wireless charging system is provided with a transmitting coil and a receiving coil, and is characterized in that: The dual-frequency metal foreign body detection system includes a controller and a dual-frequency excitation circuit, a dual-frequency detection circuit, and a signal processing circuit connected to the controller; The dual-frequency excitation circuit includes a dual-frequency voltage generating circuit, a dual-frequency resonant circuit and a plurality of excitation coils. L e The dual-frequency voltage generating circuit is used to generate an AC output voltage of a low-frequency component and a high-frequency component, and the dual-frequency resonant circuit is used to resonate at low frequency and high frequency to make the excitation coil work L e Generates low-frequency magnetic field and high-frequency magnetic field; the dual-frequency resonant circuit includes a capacitor C e ,inductance L 1 and capacitor C 1. Capacitor C e Inductor in parallel L 1 and capacitor C 1 is connected in series with each of the excitation coils L e Series, capacitor C e Also connected to a dual-frequency voltage generating circuit, multiple excitation coils L e parallel connection; capacitor C e ,inductance L 1. Capacitor C 1 and excitation coil L e satisfy: ， in, f t is the operating frequency of the wireless charging system, f s The low frequency detection frequency of foreign matter, f h The foreign body high frequency detection frequency, 、 、 They are f t 、 f s 、 f h The corresponding angular frequency; The dual-frequency voltage generating circuit adopts bipolar SPWM modulation, and its AC output voltage is expressed as: ， in, V in is the DC voltage source size, a s is the modulation wave amplitude, ω s is the modulation wave angular frequency, ω h is the carrier angular frequency, J k for k Bessel function of order, m is the order of the Fourier series, when m When odd k is an even number, when m Even number k is an odd number, t Indicates the moment, Indicates the phase angle of the harmonic; The dual-frequency detection circuit includes a plurality of detection coils L d , and a plurality of the detection coils L d A parallel dual-frequency sampling circuit, the dual-frequency sampling circuit includes a low-frequency sampling circuit and a high-frequency sampling circuit, the working detection coil L d For receiving the excitation coil L e The low-frequency magnetic field and high-frequency magnetic field generated by the low-frequency sampling circuit are used to work with the detection coil L d Resonate under the low frequency magnetic field to obtain the low frequency sampling voltage, the high frequency sampling circuit is used to work with the detection coil L d Resonate under high frequency magnetic field to obtain high frequency sampling voltage; The signal processing circuit includes a low-frequency signal processing circuit connected to the low-frequency sampling circuit and a high-frequency signal processing circuit connected to the high-frequency sampling circuit, wherein the low-frequency signal processing circuit is used to filter, amplify and rectify the low-frequency sampling voltage to obtain a low-frequency detection signal, and the high-frequency signal processing circuit is used to filter, amplify and rectify the high-frequency sampling voltage to obtain a high-frequency detection signal; A plurality of the excitation coils L e , a plurality of the detection coils L d Fully cover the transmitting coil and the receiving coil, the excitation coil L e , detection coil L d decoupled from both the transmitting coil and the receiving coil; The controller is used to sequentially n Time, control the first, second to n Excitation coil in the detection area L e , detection coil L d Work, n For the excitation coil L e and detection coil L d The number of first, second to n The detection area is combined into the full coverage area of ​​the transmitting coil and the receiving coil; The controller is also used to determine whether there is a metal foreign object based on the low-frequency detection signal and the high-frequency detection signal, and when a metal foreign object exists, determine whether the metal foreign object is a ferromagnetic metal foreign object or a non-ferromagnetic metal foreign object and determine the location of the metal foreign object.

2. The dual-frequency metal foreign body detection system for a wireless charging system according to claim 1, characterized in that: A plurality of the excitation coils L e Arranged in array, each of the excitation coils L e Use bipolar coil; A plurality of detection coils L d With multiple excitation coils L e Using the same array arrangement, each of the detection coils L d With the excitation coil L e The same bipolar coil; the transmitting coil and the receiving coil are both unipolar coils; A plurality of the excitation coils L e Placed on the transmitting coil, multiple detection coils L d Opposite to the plurality of excitation coils L e superior.

3. The dual-frequency metal foreign body detection system for a wireless charging system according to claim 2, characterized in that: In the dual-frequency resonant circuit and each excitation coil L e There are excitation switches connected to the controller in series, and the controller controls all the excitation switches in a time division multiplexing manner; In each of the detection coils L d A detection switch connected to the controller is connected in series with the dual-frequency sampling circuit, and the controller controls all detection switches in a time division multiplexing manner.

4. The dual-frequency metal foreign body detection system for a wireless charging system according to claim 3, characterized in that: The controller controls the plurality of excitation coils by controlling the on and off of the excitation switch and the detection switch. L e With multiple detection coils L d Working in pairs, the excitation coils facing each other L e and the detection coil L d As a pair.

5. The dual-frequency metal foreign body detection system for a wireless charging system according to claim 4, characterized in that: The low-frequency sampling circuit includes an inductor L h ,capacitance C h ,capacitance C ds and sampling resistor R ds ,inductance L h ,capacitance C h Parallel resonance forms high frequency f h The wave blocking circuit, capacitor C ds With high frequency f h The wave blocking circuit is connected in series so that the detection coil L d The frequency formed by the low-frequency sampling circuit is f s The series resonant circuit; the sampling resistor R ds The voltage at both ends is the low-frequency sampling voltage; The high frequency sampling circuit includes an inductor L s ,capacitance C s ,capacitance C dh and sampling resistor R dh ,inductance L s ,capacitance C s Parallel resonance forms low frequency f s The wave blocking circuit, capacitor C s With low frequency f s The wave blocking circuit is connected in series so that the detection coil L d The high frequency sampling circuit as a whole forms a frequency of f h The series resonant circuit; the sampling resistor R dh The voltage across both ends is the high-frequency sampling voltage.

6. The dual-frequency metal foreign body detection system for a wireless charging system according to claim 5, characterized in that: inductance L h ,capacitance C h ,capacitance C ds and sampling resistor R ds satisfy: ， inductance L s ,capacitance C s ,capacitance C dh and sampling resistor R dh satisfy: 。 7. The control method of the dual-frequency metal foreign body detection system of the wireless charging system according to any one of claims 1 to 6, characterized in that: Including steps: S1, in the order of first, second to n Time, control the first, second to n Excitation coil in the detection area L e , detection coil L d Work; S2. Compare the low-frequency detection signal and high-frequency detection signal generated at each moment with the preset low-frequency detection threshold and high-frequency detection threshold respectively. If the low-frequency detection signal or the high-frequency detection signal exceeds the detection threshold, it is determined that a metal foreign object exists. If the low-frequency detection signal increases or the high-frequency detection signal decreases, it can be determined that the metal foreign object is a ferromagnetic metal foreign object. Otherwise, the foreign object is determined to be a non-ferromagnetic metal foreign object.

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