Metal foreign body detection circuit and wireless charging metal foreign body detection system without blind spots

Abstract

The present invention provides a metal foreign object detection circuit and a wireless charging metal foreign object detection system with no blind spots. The circuit includes four blind spot detection coils distributed in four quadrants. The first and third quadrant blind spot detection coils are connected to a first differential foreign object detection circuit; the second and fourth quadrant blind spot detection coils are connected to a second differential foreign object detection circuit. Both differential foreign object detection circuits are provided with differential amplifier circuits. One blind spot detection coil is connected to one input of the differential amplifier circuit via an overcompensated signal acquisition channel, while the other blind spot detection coil is connected to the other input of the differential amplifier circuit via an undercompensated signal acquisition channel. When the absolute value of the output voltage of the first differential foreign object detection circuit or / and the second differential foreign object detection circuit exceeds a preset threshold, a metal foreign object is detected. The effect is that the circuit can sensitively detect the entire area above the transmitting coil of the wireless charging system without any detection blind spots.

Description

Technical Field

[0001] The present invention relates to foreign object detection technology in the field of wireless charging technology, and in particular to a metal foreign object detection circuit and a wireless charging metal foreign object detection system without blind spots. Background Art

[0002] When an electric vehicle wireless charging system is operating, due to the strong electromagnetic coupling between the transmitting and receiving coils, any foreign metal object that enters or approaches this coupling area can alter the electrical parameters of the coupling mechanism, causing the system to deviate from its normal operating point, impacting its output power and transmission efficiency. The eddy current effect of foreign metal objects can cause them to heat up and potentially cause fires, posing a significant safety hazard.

[0003] Although the existing metal foreign body detection solution for wireless charging systems based on detection coils can detect metal foreign bodies relatively sensitively, the existence of detection blind spots means that this method still has certain safety risks. The blind spot elimination method of superimposing detection coils increases the system cost exponentially. Therefore, a new method is needed to eliminate the blind spots of metal foreign body detection systems at a lower cost. Summary of the Invention

[0004] In view of the above-mentioned defects, the primary purpose of the present invention is to provide a metal foreign body detection circuit to eliminate the detection blind area of ​​the existing system and make up for the deficiency of the detection blind area of ​​the differential structure foreign body detection coil.

[0005] To achieve the above objectives, the specific technical solutions adopted by the present invention are as follows:

[0006] A metal foreign object detection circuit, the key of which is that it includes four blind spot detection coils distributed in four quadrant planes, wherein the first quadrant blind spot detection coil and the third quadrant blind spot detection coil are connected to a first differential foreign object detection circuit; the second quadrant blind spot detection coil and the fourth quadrant blind spot detection coil are connected to a second differential foreign object detection circuit, and the first differential foreign object detection circuit and the second differential foreign object detection circuit are both provided with differential amplifier circuits, wherein one blind spot detection coil is connected to one input end of the differential amplifier circuit through an over-compensated signal acquisition channel, and the other blind spot detection coil is connected to the other input end of the differential amplifier circuit through an under-compensated signal acquisition channel. When the absolute value of the output voltage of the first differential foreign object detection circuit or / and the second differential foreign object detection circuit is higher than a preset threshold, it is judged that a metal foreign object is present.

[0007] When using a full-area foreign object detection coil group for detection, a detection blind spot appears at the midpoint of the coil due to its centrally symmetrical detection coil distribution and differential detection method. Therefore, a blind-area metal foreign object detection coil group is designed, and the two blind-area detection coil groups are respectively subjected to capacitor series overcompensation and undercompensation. When there is no metal foreign object near the blind-area metal foreign object detection coil, the induced voltage on the blind-area detection coil is the same. After filtering through the undercompensation circuit and the overcompensation circuit, sampling voltages with the same amplitude but different phases are output at both ends of the series resistor. After the sampling voltage is band-pass filtered and rectified, it is input to the differential amplifier circuit to output a metal foreign object detection voltage of zero. When a metal foreign object is present, the induced voltage on the blind-area detection coil has the same amplitude but a different voltage vector relative to the voltage when there is no foreign object. Therefore, after undercompensation and overcompensation, the output sampling voltage has different amplitudes. After band-pass filtering and rectification, the sampling voltage is input to the differential amplifier circuit to output a metal foreign object detection signal U. OA 、U OB , and compared with the preset voltage threshold to determine whether there is a metal foreign object in the blind spot.

[0008] Optionally, the over-compensation signal acquisition channel includes an over-compensation circuit, a band-pass filter circuit, and a rectifier filter circuit connected in sequence; the under-compensation signal acquisition channel includes an under-compensation circuit, a band-pass filter circuit, and a rectifier filter circuit connected in sequence.

[0009] Optionally, both the over-compensation circuit and the under-compensation circuit adopt a series capacitor compensation method.

[0010] Optionally, the four blind spot detection coils have the same structure.

[0011] Based on the above-mentioned metal foreign object detection circuit, another object of the present invention is to provide a wireless charging metal foreign object detection system without blind spots. The key point is that it includes a full-area foreign object detection circuit and a blind-area foreign object detection circuit. The full-area foreign object detection circuit includes a full-area foreign object detection coil module corresponding to the wireless charging transmitting coil. The blind-area foreign object detection circuit adopts the metal foreign object detection circuit described above, wherein the four blind-area detection coils are arranged in the detection blind spot of the full-area foreign object detection circuit and are located above the full-area foreign object detection coil module.

[0012] Optionally, the area covered by the four blind area detection coils in the metal foreign object detection circuit is larger than the blind area of ​​the full-area foreign object detection circuit.

[0013] Optionally, the full-area foreign object detection coil module is provided with a plurality of full-area foreign object detection sub-coils distributed in a centrally symmetrical manner and laid on the upper surface of the wireless charging transmitting coil; the four blind spot detection coils in the metal foreign object detection circuit are located above the center of the full-area foreign object detection coil module.

[0014] Optionally, the full-area foreign object detection sub-coil and the four blind-area detection coils in the metal foreign object detection circuit are all rectangular coils and have the same width.

[0015] Optionally, the full-area foreign object detection sub-coils in the full-area foreign object detection coil module are distributed in a 2×8 array.

[0016] Optionally, during parameter design, the compensation capacitor and sampling resistor in the over-compensation signal acquisition channel and the under-compensation signal acquisition channel are calculated based on the sampling voltage equation U D Select and match parameters according to the design principle of first determining the sampling resistor and then determining the compensation capacitor;

[0017]

[0018] Where: M is the mutual inductance between the wireless charging transmitter coil and the blind area foreign object detection coil, U OC is the open circuit voltage on the wireless charging transmitting coil, R D R is the sampling resistor connected in series with the blind area foreign object detection coil. P It is the sum of the internal resistance of the wireless charging transmitting coil and the impedance introduced by the receiving coil circuit to the transmitting coil side. S It represents the internal resistance of the blind spot foreign object detection coil, and ω is the system operating frequency.

[0019] The remarkable effects of the present invention are:

[0020] (1) Based on the full-area differential foreign object detection coil solution, the present invention proposes adding a blind-area differential foreign object detection coil, so that the foreign object detection system can sensitively detect the entire area above the transmitting coil of the wireless charging system without any detection blind area.

[0021] (2) The design of the detection coil series resonant circuit of the present invention improves the system's detection sensitivity to metal foreign objects, and the design of the blind spot foreign object detection coil ensures the system's detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the blind spot location of the existing foreign object detection solution;

[0023] Figure 2 It is a schematic diagram of the coil installation structure of the present invention;

[0024] Figure 3 Schematic diagram of the installation position of the blind spot detection coil proposed by the present invention;

[0025] Figure 4 is a circuit schematic diagram of a first differential foreign object detection circuit proposed in the present invention;

[0026] Figure 5 is a circuit schematic diagram of a second differential foreign object detection circuit proposed by the present invention;

[0027] Figure 6 This is the impedance vector analysis diagram of the blind zone foreign object detection circuit when there is no foreign object;

[0028] Figure 7 Impedance vector analysis diagram of the blind zone foreign object detection circuit when a foreign object is present;

[0029] Figure 8 It is the relationship diagram between the voltage across the sampling resistor and the series compensation capacitor and sampling resistor;

[0030] Figure 9 : is the output voltage waveform of the blind zone differential foreign object detection circuit when there is no metal foreign object in a specific embodiment;

[0031] Figure 10 The sampling voltage waveform of the blind zone differential foreign object detection circuit in a specific embodiment;

[0032] Figure 11 In a specific embodiment, the output voltage waveform of the blind zone differential foreign object detection circuit when there is a metal foreign object;

[0033] Markings in the figure: 1-wireless charging transmitting coil, 2-full-area foreign object detection circuit, 3-blind-area foreign object detection circuit 3, 31-overcompensation circuit and undercompensation circuit, 32-bandpass filter circuit, 33-rectifier filter circuit, 34-differential amplifier circuit. DETAILED DESCRIPTION

[0034] 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.

[0035] like Figure 1 As shown in the figure, traditional full-area metal foreign body detection coils often adopt a centrally symmetrical differential structure. When the metal foreign body is located at the center of the transmitting coil, it has the same impact on the magnetic fields of the two detection coils in the same group. At this time, the differential voltage output is zero, and the metal foreign body detection at the center of the transmitting coil cannot be achieved. Therefore, there is a detection blind spot in the central area.

[0036] In order to realize the detection of metal foreign bodies without blind spots, the present invention first proposes a metal foreign body detection circuit. Figure 2 、 Figure 3 、 Figure 4 and Figure 5It can be seen that it includes four blind spot detection coils distributed in four quadrant planes, among which the first quadrant blind spot detection coil and the third quadrant blind spot detection coil are connected to the first differential foreign object detection circuit; the second quadrant blind spot detection coil and the fourth quadrant blind spot detection coil are connected to the second differential foreign object detection circuit, and the first differential foreign object detection circuit and the second differential foreign object detection circuit are both provided with differential amplifier circuits, among which one blind spot detection coil is connected to one input end of the differential amplifier circuit through the over-compensation signal acquisition channel, and the other blind spot detection coil is connected to the other input end of the differential amplifier circuit through the under-compensation signal acquisition channel. When the absolute value of the output voltage of the first differential foreign object detection circuit or / and the second differential foreign object detection circuit is higher than the preset threshold, it is judged that a metal foreign object is present.

[0037] In specific implementation, the four blind spot detection coils have the same structure. The over-compensation signal acquisition channel includes an over-compensation circuit, a band-pass filter circuit, and a rectifier filter circuit connected in sequence. The under-compensation signal acquisition channel includes an under-compensation circuit, a band-pass filter circuit, and a rectifier filter circuit connected in sequence.

[0038] from Figure 4 and Figure 5 It can be seen that both the over-compensation circuit and the under-compensation circuit 31 adopt the series capacitor compensation method, including the compensation capacitor and the sampling resistor. Through parameter design, the total impedance of the circuit after the series capacitor compensation is jωX D >0 is under-compensation, the total circuit impedance jωX D When <0, it is overcompensated. The band-pass filter circuit 32 samples the Butterworth second-order active band-pass filter circuit. The center frequency is designed to be the operating frequency of the electric vehicle wireless charging, which is 85kHz in this embodiment. The input voltage of the band-pass filter circuit is the sampling voltage of the over-compensation circuit or the under-compensation circuit. The rectifier filter circuit 33 uses a diode and a capacitor for rectification and filtering. The output voltage of the band-pass filter circuit 32 is converted into a DC output after passing through the rectifier filter circuit 33. Finally, the differential amplifier circuit 34 performs differential amplification processing to output a differential voltage U OA 、U OB In this example, the four blind spot detection coils are C1, C2, C3, and C4, where C2 and C3 are connected to the under-compensation signal acquisition channel, and C1 and C4 are connected to the over-compensation signal acquisition channel. The output differential voltage of the first differential foreign object detection circuit is recorded as U OA The output differential voltage of the second differential foreign body detection circuit is recorded as U OB, the series capacitors over-compensate and under-compensate the blind spot detection coils respectively. By designing a reasonable series capacitor value, the voltage amplitudes at both ends of the sampling resistor are the same when there is no metal foreign object near the blind spot foreign object detection coil. The sampling voltage is filtered by the bandpass filter circuit and rectified, and finally connected to the differential amplifier circuit to achieve zero differential voltage output of the blind spot differential foreign object detection circuit when there is no metal foreign object; when a metal foreign object is present, due to the different compensation methods of the blind spot foreign object detection coil group resulting in different output rectified voltages, the blind spot detection circuit outputs a voltage signal to achieve metal foreign object detection near the blind spot. The specific principle is as follows:

[0039] When there is no metal foreign body, the impedance vectors of the two blind spot detection circuits are as follows: Figure 6 shown.

[0040] The C1 blind zone detection circuit is under-compensated for capacitance. At this time, jωL D >1 / jωC D1 ,jωX D1 >0; C3 blind zone detection circuit is capacitor overcompensation, at this time jωL D <1 / jωC D3 ,jωX D3 <0. Set a reasonable capacitance to make the sampling voltage amplitude of the detection circuit the same, thereby eliminating the amplitude difference caused by incomplete compensation;

[0041] When a metal foreign body exists, the impedance vectors of the two blind zone foreign body detection circuits are as follows: Figure 7 shown.

[0042] Depend on Figure 7 It can be seen that the blind spot foreign body detection coil will be affected by the equivalent impedance of the metal foreign body, resulting in a change in the resonant state. The existence of the equivalent impedance of the metal foreign body will cause the sampling voltage amplitude of the capacitor under-compensation and capacitor over-compensation blind spot detection circuits to have different changes. The same size of the metal foreign body equivalent impedance will act on the two blind spot foreign body detection coils to produce different voltage amplitude changes. The phase deviation caused by the different compensation methods is eliminated through rectification and filtering, and finally the blind spot metal foreign body detection signal is output by differential amplification. The threshold voltage U can be set based on empirical data. MTH When the output voltage of the differential foreign object detection circuit exceeds its safety threshold U MTH When the system is running, it will give an alarm and stop working.

[0043] When implemented, we can get Figure 2A wireless charging metal foreign object detection system without blind spots is shown in the figure, which includes a wireless charging transmitting coil 1, a full-area foreign object detection circuit 2, and a blind-area foreign object detection circuit 3. The full-area foreign object detection circuit 2 includes a full-area foreign object detection coil module corresponding to the wireless charging transmitting coil 1. As can be seen from the figure, the full-area foreign object detection coil module is provided with multiple full-area foreign object detection sub-coils distributed in a centrally symmetrical manner and laid on the upper surface of the wireless charging transmitting coil. In this example, the full-area foreign object detection sub-coils are arranged in a rectangular shape and distributed in a 2×8 array; A1, A2, …, A 16 、B 16 ,…,B2,B1 and other 16 groups of full-area foreign object detection sub-coils are sequentially covered on the surface of the wireless charging transmitting coil 1; the blind-area foreign object detection circuit 3 adopts the metal foreign object detection circuit described above, and the four blind-area detection coils are set in the center of the full-area foreign object detection coil module and are located above the full-area foreign object detection sub-coil. In this example, the four blind-area detection coils are all rectangular coils, and the width is the same as that of the full-area foreign object detection sub-coil.

[0044] In order to achieve full coverage of the detection blind area, the area covered by the four blind area detection coils in the metal foreign object detection circuit is larger than the blind area of ​​the full-area foreign object detection circuit.

[0045] During parameter design, the compensation capacitor and sampling resistor in the over-compensation signal acquisition channel and the under-compensation signal acquisition channel are calculated based on the sampling voltage equation U D Select and match parameters according to the design principle of first determining the sampling resistor and then determining the compensation capacitor;

[0046]

[0047] Where: M is the mutual inductance between the wireless charging transmitter coil and the blind area foreign object detection coil, U OC is the open circuit voltage on the wireless charging transmitting coil, R D R is the sampling resistor connected in series with the blind area foreign object detection coil. P It is the sum of the internal resistance of the wireless charging transmitting coil and the impedance introduced by the receiving coil circuit to the transmitting coil side. S It represents the internal resistance of the blind spot foreign object detection coil, and ω is the system operating frequency.

[0048] Depend on Figure 8 It can be seen that when the series sampling resistor of the blind zone differential foreign object detection circuit is 0.1Ω, the series incomplete compensation capacitor value has a wider selection range. Therefore, compensation capacitors of 3.2uF and 12uF are selected respectively to realize under-compensation and over-compensation of the detection coil to achieve the same sampling voltage amplitude when there is no metal foreign object.

[0049] In order to further understand the technical effects of the above invention, this embodiment is further applied to an electric vehicle wireless power transmission platform for verification. The system-related dimensional parameters are shown in Table 1, and the related electrical parameters are shown in Table 2.

[0050] Table 1 System experimental parameters

[0051]

[0052] Table 2 System electrical parameters

[0053]

[0054] In order to verify the performance of the blind-spot differential foreign object detection circuit and determine its voltage threshold, a functional verification experiment of the blind-spot differential foreign object detection circuit is carried out, and the size of its judgment voltage threshold is determined based on the experimental verification results.

[0055] When there is no metal foreign body, the output voltage of the blind zone metal foreign body detection circuit is as follows: Figure 9 As shown, the output voltage of the blind zone differential foreign object detection circuit is 17.8mV. At this time, the voltage amplitude across the sampling resistor connected to the blind zone foreign object detection coil is as follows: Figure 10 As shown, it can be seen that the output voltage amplitudes of the two detection coil capacitance compensation methods are basically the same, which is 3.55V.

[0056] When the metal foreign body is located in the detection blind area, the blind area differential foreign body detection circuit outputs a voltage as follows: Figure 11 shown.

[0057] from Figure 11 It can be seen that the output detection voltage of the blind zone differential foreign object detection circuit is -224mV. Considering that there may be smaller metal foreign objects in the blind zone, the blind zone foreign object detection voltage threshold U is set. MTH =0.1V. When the absolute value of the output voltage of a blind area differential foreign object detection circuit is higher than 0.1V, the system will stop working, thereby ensuring the safety of the electric vehicle wireless charging system.

[0058] It is not difficult to see that the metal foreign object detection circuit and the wireless charging metal foreign object detection system without blind spots proposed in the present invention can eliminate the blind spots of the foreign object detection coil and ensure the safe operation of the electric vehicle wireless charging system.

[0059] Finally, it should be noted that the above embodiments are preferred implementations of the present invention, but the implementations 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 equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A metal foreign body detection circuit, characterized in that: It includes four blind spot detection coils distributed in four quadrant planes, wherein the first quadrant blind spot detection coil and the third quadrant blind spot detection coil are connected to the first differential foreign object detection circuit; the second quadrant blind spot detection coil and the fourth quadrant blind spot detection coil are connected to the second differential foreign object detection circuit, and the first differential foreign object detection circuit and the second differential foreign object detection circuit are both provided with a differential amplifier circuit, wherein one blind spot detection coil is connected to one input end of the differential amplifier circuit through an over-compensation signal acquisition channel, and the other blind spot detection coil is connected to the other input end of the differential amplifier circuit through an under-compensation signal acquisition channel. When the absolute value of the output voltage of the first differential foreign object detection circuit or / and the second differential foreign object detection circuit is higher than a preset threshold, it is judged that a metal foreign object is present.

2. The metal foreign body detection circuit according to claim 1, characterized in that: The over-compensation signal acquisition channel includes an over-compensation circuit, a band-pass filter circuit, and a rectifier filter circuit connected in sequence; the under-compensation signal acquisition channel includes an under-compensation circuit, a band-pass filter circuit, and a rectifier filter circuit connected in sequence.

3. The metal foreign body detection circuit according to claim 2, characterized in that: The over-compensation circuit and the under-compensation circuit both adopt a series capacitor compensation method.

4. The metal foreign body detection circuit according to any one of claims 1 to 3, characterized in that: The four blind spot detection coils have the same structure.

5. A wireless charging metal foreign body detection system without blind spots, characterized in that: It includes a full-area foreign object detection circuit and a blind-area foreign object detection circuit. The full-area foreign object detection circuit includes a full-area foreign object detection coil module corresponding to the wireless charging transmitting coil. The blind-area foreign object detection circuit adopts the metal foreign object detection circuit described in any one of claims 1 to 4, wherein the four blind-area detection coils are arranged in the detection blind area of ​​the full-area foreign object detection circuit and are located above the full-area foreign object detection coil module.

6. The wireless charging metal foreign body detection system without blind spots according to claim 5, characterized in that: The area covered by the four blind area detection coils in the metal foreign object detection circuit is larger than the blind area of ​​the full-area foreign object detection circuit.

7. The wireless charging metal foreign body detection system without blind spots according to claim 6, characterized in that: The full-area foreign object detection coil module is provided with a plurality of full-area foreign object detection sub-coils distributed in a centrally symmetrical manner and laid on the upper surface of the wireless charging transmitting coil; the four blind spot detection coils in the metal foreign object detection circuit are located above the center of the full-area foreign object detection coil module.

8. The wireless charging metal foreign body detection system without blind spots according to claim 7, characterized in that: The full-area foreign object detection sub-coil and the four blind-area detection coils in the metal foreign object detection circuit are all rectangular coils with the same width.

9. The wireless charging metal foreign body detection system without blind spots according to claim 8, characterized in that: The full-area foreign object detection sub-coils in the full-area foreign object detection coil module are distributed in a 2×8 array.

10. The wireless charging metal foreign body detection system without blind spots according to any one of claims 5 to 9, characterized in that: During parameter design, the compensation capacitor and sampling resistor in the over-compensation signal acquisition channel and the under-compensation signal acquisition channel are calculated based on the sampling voltage equation U D Select and match parameters according to the design principle of first determining the sampling resistor and then determining the compensation capacitor; Where: M is the mutual inductance between the wireless charging transmitting coil and the blind area foreign object detection coil, U OC is the open circuit voltage on the wireless charging transmitting coil, R D R is the sampling resistor connected in series with the blind area foreign object detection coil. P It is the sum of the internal resistance of the wireless charging transmitting coil and the impedance introduced by the receiving coil circuit to the transmitting coil side. S It represents the internal resistance of the blind spot foreign object detection coil, and ω is the system operating frequency.

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