Design method of a metal foreign object detection circuit and a filter

Abstract

The present invention relates to the technical field of wireless power transmission systems, and particularly relates to a design method for a metal foreign object detection circuit and a filter, including: a foreign object detection coil and a detection module. The detection module is connected to the foreign object detection coil through a resonant capacitor and outputs a driving signal to the foreign object detection coil, and then collects a feedback signal from the foreign object detection coil; a first filter is provided at the connection point of the detection module and the resonant capacitor. The beneficial effect of the present invention is that by setting a filter in the metal foreign object detection circuit and filtering the induced signal generated during operation, the problem that the metal foreign object detection circuit in the prior art cannot work properly due to the influence of the induced voltage when the main power coil is working is avoided, and the overall safety of the wireless power transmission system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless power transmission systems, and particularly relates to a design method for a metal foreign object detection circuit and a filter. Background Art

[0002] A wireless power transmission system is a technology that realizes the transmission of electrical energy from a power generation device to a receiving end without using a cable based on the principle of electromagnetic induction. With the in-depth research on wireless power transmission technology and the development of the wireless power transmission industry, the application scenarios of wireless power transmission technology have become more diverse. For example, in the field of new energy vehicles, since the wireless power transmission system does not require a direct connection between the vehicle and the cable, it can achieve contactless charging in some scenarios, such as intersections, platforms, etc., thus avoiding the disadvantage of traditional electric vehicles that require long-term cable connection for charging. However, with the increase in the power of the wireless power transmission system, safety issues are gradually emerging.

[0003] In the prior art, when the wireless power transmission system is working, there may occasionally be metal foreign objects falling within the induction range of the coil. In this case, the metal foreign objects are prone to severe heating due to the eddy current effect, which may further cause a fire hazard. To address this problem, the prior art approach is to set up a foreign object sensing circuit in the wireless power transmission system, and determine whether there is a metal foreign object in the magnetic field by setting up a detection coil and based on the impedance change of the detection coil.

[0004] However, in the actual implementation process, the inventor found that in order to achieve a better detection effect, the detection coil is usually set in the main power coil. When the main power coil is working, the detection coil will generate a corresponding induced voltage, which causes the metal foreign object detection circuit to malfunction. Summary of the Invention

[0005] In view of the above problems existing in the prior art, a design method for a metal foreign object detection circuit and a filter is provided.

[0006] The specific technical solutions are as follows:

[0007] A metal foreign object detection circuit is applicable to a wireless power transmission system, and the wireless power transmission system has a main coil, and a foreign object detection coil of the metal foreign object detection circuit is provided in the main coil;

[0008] The metal foreign object detection circuit further includes a detection module, the detection module is connected to the foreign object detection coil through a resonant capacitor and outputs a driving signal to the foreign object detection coil, and then collects a feedback signal from the foreign object detection coil;

[0009] A first filter is provided at the connection point of the detection module and the resonant capacitor.

[0010] Preferably, the detection module includes:

[0011] A driving unit, the output end of the driving unit is connected to the resonant capacitor to output the driving signal to the foreign object detection coil;

[0012] A processing unit, the output end of the processing unit is connected to the input end of the driving unit;

[0013] A sampling unit, the input end of the sampling unit is connected to the resonant capacitor to obtain the feedback signal, and the output end of the sampling unit is connected to the input end of the processing unit.

[0014] Preferably, the driving unit includes:

[0015] A digital-to-analog converter, the input end of the digital-to-analog converter is connected to the output end of the processing unit;

[0016] A second filter, the input end of the second filter is connected to the output end of the digital-to-analog converter;

[0017] A first buffer, the input end of the first buffer is connected to the output end of the second filter;

[0018] A resistor, the first end of the resistor is connected to the output end of the first buffer, and the second end of the resistor is connected to the foreign object detection coil.

[0019] Preferably, the driving unit includes:

[0020] A digital-to-analog converter, the input end of the digital-to-analog converter is connected to the output end of the processing unit;

[0021] A second filter, the input end of the second filter is connected to the output end of the digital-to-analog converter;

[0022] A first buffer, the input end of the first buffer is connected to the output end of the second filter.

[0023] Preferably, the first end of the first filter is connected to the connection point between the resonant capacitor and the detection module, and the second end of the first filter is grounded;

[0024] A design method for determining the inductance parameter of the first filter according to the operating frequency of the wireless power transmission system is applicable to the above-mentioned metal foreign object detection circuit, including:

[0025] Step S1: For a wireless power transmission system, obtain the operating frequency of the wireless power transmission system;

[0026] Step S2: When the wireless power transmission system is working, obtain the induced voltage input by the foreign object detection coil at the operating frequency;

[0027] Step S3: Generate the inductance parameter of the first filter according to the induced voltage.

[0028] Preferably, the step S3 includes:

[0029] Step S31: Generate a desired attenuation according to the induced voltage and a preset normal working threshold.

[0030] Step S32: Obtain the device parameters of the wireless power transmission system, and generate the inductance parameter of the first filter according to the device parameters and the desired attenuation.

[0031] Preferably, in the step S32, the generation method of the first filter is:

[0032]

[0033] Wherein, L1 is the self-inductance value of the foreign object detection coil, ω is the working frequency, L2 is the inductance parameter, C1 is the capacitance value of the resonant capacitor, V1 is the induced voltage of the foreign object detection coil, V0 is the filtered voltage input to the detection module, Gain is the signal attenuation gain, and Atte is the desired attenuation.

[0034] The above technical solution has the following advantages or beneficial effects: By setting a filter in the metal foreign object detection circuit and filtering the induced signal generated during operation, the problem that the metal foreign object detection circuit in the prior art cannot work properly due to the influence of the induced voltage when the main power coil is working is avoided, and the overall safety of the wireless power transmission system is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Refer to the accompanying drawings to describe the embodiments of the present invention more fully. However, the accompanying drawings are only for illustration and explanation, and do not constitute a limitation on the scope of the present invention.

[0036] Figure 1 It is the overall schematic diagram of the embodiment of the present invention;

[0037] Figure 2 It is the schematic diagram of the filter design method in the embodiment of the present invention;

[0038] Figure 3 It is the schematic diagram of the sub-steps of step S3 in the embodiment of the present invention;

[0039] Figure 4 It is the equivalent circuit without setting the first filter in the embodiment of the present invention;

[0040] Figure 5 It is the equivalent circuit with the first filter set in the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0042] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other.

[0043] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but it is not limited to the present invention.

[0044] The present invention includes:

[0045] A metal foreign object detection circuit is applicable to a wireless power transmission system. The wireless power transmission system has a main coil, and a foreign object detection coil of the metal foreign object detection circuit is arranged in the main coil.

[0046] As Figure 1 shown, the metal foreign object detection circuit further includes a detection module A1. The detection module A1 is connected to the foreign object detection coil L1 through a resonant capacitor C1 and outputs a driving signal to the foreign object detection coil L1, and then collects a feedback signal from the foreign object detection coil.

[0047] A first filter L2 is arranged at the connection point of the detection module A1 and the foreign object detection coil L1.

[0048] Specifically, aiming at the problem that the metal foreign object detection circuit in the prior art cannot work normally when the main coil is working, in this embodiment, by arranging the first filter L2 behind the resonant capacitor C1 of the foreign object detection coil L1, the induced voltage generated when the foreign object detection coil L1 is working is attenuated, so that the metal foreign object detection circuit can work normally when the wireless power transmission system is transmitting power, and the safety of the wireless power transmission system during operation is improved.

[0049] In the actual implementation process, the above wireless power transmission system is configured as a transmitting end or a receiving end according to needs. According to the differences between the transmitting end and the receiving end, the main coil is a power transmission coil or a power receiving coil coupled to the power transmission coil. The foreign object detection coil L1 is a coil for detecting metal foreign objects in the induction range of the main coil, and it is usually arranged on the same plane as the main coil and concentrically arranged with the main coil.

[0050] In a preferred embodiment, the detection module A1 includes:

[0051] The driving unit A2, the output end of the driving unit A2 is connected to the resonant capacitor C1 to output a driving signal to the foreign object detection coil;

[0052] The processing unit DPU, the output end of the processing unit DPU is connected to the input end of the driving unit;

[0053] The sampling unit A3, the input end of the sampling unit A3 is connected to the resonant capacitor C1 to obtain a feedback signal, and the output end of the sampling unit is connected to the input end of the processing unit.

[0054] Specifically, to achieve a better metal foreign object detection effect, in this embodiment, the detection module A1 is set as an excitation & sampling circuit. The driving unit A2 is controlled by the processing unit DPU to generate a corresponding driving signal. Subsequently, the sampling unit A3 receives the feedback signal returned from the foreign object detection coil L1. Furthermore, the impedance change of the foreign object detection coil L1 can be obtained based on the feedback signal and the driving signal, thereby achieving a better metal foreign object detection effect.

[0055] During implementation, the above-mentioned processing unit DPU can be set as one or more application-specific integrated circuits (ASICs), DSPs, programmable logic devices (PLDs), complex programmable logic devices (CPLDs), field programmable gate arrays (FPGAs), general-purpose processors, controllers, microcontrollers (MCUs), microprocessors, or other electronic components according to actual needs, and is used to generate driving signals of specific frequencies and process and identify feedback signals.

[0056] In a preferred embodiment, the driving unit A2 includes:

[0057] The digital-to-analog converter U1, the input end of the digital-to-analog converter U1 is connected to the output end of the processing unit DPU;

[0058] The second filter U2, the input end of the second filter U2 is connected to the output end of the digital-to-analog converter U1;

[0059] The first buffer U3, the input end of the first buffer U3 is connected to the output end of the second filter U2;

[0060] The resistor R1, the first end of the resistor R1 is connected to the output end of the first buffer U3, and the second end of the resistor R1 is connected to the resonant capacitor C1.

[0061] Specifically, to achieve a better detection effect for metal foreign objects, in this embodiment, a digital-to-analog converter U1 for generating a specific frequency signal, a second filter U2 for band-pass filtering the output signal of the digital-to-analog converter U1, a first buffer U3 for calibrating the signal phase, and a resistor R1 are sequentially arranged in the driving unit A2. The driving unit A2 can generate an excitation signal under the control of the processing unit DPU and adjust the frequency and phase of the excitation signal as needed, so that after the feedback signal is obtained by the sampling unit A3 and input into the processing unit DPU, it can effectively determine whether there is a metal foreign object in the induction range of the coil according to the signal change of this frequency.

[0062] In a preferred embodiment, the sampling unit A3 includes:

[0063] A second buffer U4, the input end of the second buffer U4 is connected to the resonant capacitor C1;

[0064] A third filter U5, the input end of the third filter U5 is connected to the output end of the second buffer U4;

[0065] An analog-to-digital converter U6, the input end of the analog-to-digital converter U6 is connected to the output end of the third filter U5, and the output end of the analog-to-digital converter U6 is connected to the input end of the processing unit DPU.

[0066] Specifically, to achieve a better detection effect for metal foreign objects, in this embodiment, by sequentially arranging a second buffer U4 for phase matching, a third filter U5 for band-pass filtering the input signal, and an analog-to-digital converter U6 for sampling the input signal in the sampling unit A3, the sampling unit A3 can sequentially perform phase matching, filtering, and sampling on the feedback signal output by the foreign object detection coil L1 and then input it into the processing unit U2. Furthermore, the processing unit U2 can compare the input feedback signal of a specific frequency with the output driving signal to obtain the impedance change situation on the foreign object detection coil L1 and achieve a better metal foreign object detection effect.

[0067] In a preferred embodiment, the first end of the first filter L2 is connected to the connection point of the resonant capacitor C2 and the detection module A1, and the second end of the first filter L2 is grounded;

[0068] The inductance parameter of the first filter L2 is determined according to the operating frequency of the wireless power transmission system.

[0069] A design method of a filter is applicable to the above-mentioned metal foreign object detection circuit, as Figure 2 shown, including:

[0070] Step S1: For a wireless power transmission system, obtain the operating frequency of the wireless power transmission system;

[0071] Step S2: When the wireless power transmission system is operating, obtain the induced voltage input by the foreign object detection coil at the operating frequency;

[0072] Step S3: Generate the inductance parameter of the first filter according to the induced voltage and the operating frequency.

[0073] Specifically, for a wireless power transmission system, when the main coil is operating, it will generate an induced voltage on the metal foreign object detection coil, resulting in the problem that the metal foreign object detection circuit cannot operate normally. In this embodiment, by analyzing the operating frequency of the wireless power transmission system and the induced voltage that the wireless power transmission system will form on the foreign object detection coil, effective attenuation is performed on this voltage signal, avoiding the problem that a relatively large induced voltage is input into the sampling unit A3 together with the feedback signal, thereby affecting the normal comparison of the drive signal and the feedback signal by the processing unit DPU.

[0074] In a preferred embodiment, as Figure 3 shown, step S3 includes:

[0075] Step S31: Generate a desired attenuation according to the induced voltage and a preset normal operating threshold;

[0076] Step S32: Obtain the device parameters of the metal foreign object detection circuit, and generate the inductance parameter of the first filter according to the device parameters and the desired attenuation.

[0077] Specifically, to achieve a better detection effect of the processing unit DPU on the feedback signal of a specific frequency, in this embodiment, by comparing the induced voltage generated when the wireless power transmission system is operating with the normal operating threshold when the sampling unit A3 and the processing unit DPU are operating normally, a desired attenuation for the induced voltage is generated, so that a filter can be set according to the device parameters of the metal foreign object detection circuit to attenuate the induced voltage to the normal operating threshold of the processing unit DPU.

[0078] In a preferred embodiment, in step S32, the generation method of the first filter is:

[0079]

[0080] Among them, Z1 is the impedance of the foreign object detection coil, Z2 is the impedance of the first filter, Z3 is the impedance of the resonant capacitor, L1 is the self-inductance value of the foreign object detection coil, ω is the angular frequency of the operating frequency, L2 is the inductance parameter, C1 is the capacitance value of the resonant capacitor, V1 is the induced voltage of the foreign object detection coil, V0 is the filtered voltage input to the detection module, Gain is the signal attenuation gain, and Atte is the desired attenuation.

[0081] The following is further described in conjunction with a specific embodiment.

[0082] Taking Figure 1 the metal foreign object detection circuit shown as an example, the metal foreign object detection circuit includes a processing unit DPU, a driving unit A2, and a sampling unit A3. In this embodiment, the operating frequency of the wireless power transmission system is 85 Khz. For this operating frequency, a driving signal of 3 Mhz is output through the driving unit A2 to achieve a better detection effect for metal foreign objects. Among them, the self-inductance of the foreign object detection coil L1 is 5 uH, and the resonant capacitor is configured as 560 pF under the working condition of 3 Mhz.

[0083] When the first filter L2 is not set, its equivalent circuit is as shown in Figure 4 Figure [Figure number not provided in the original, assumed to be a specific figure number]. L4 is the main coil, and U7 is an AC source used to simulate the electromagnetic change situation when the main coil works. The frequency of this AC source is the same as the operating frequency of the wireless power transmission system, both being 85 Khz. Under this working condition, based on the transformer formula, the induced voltage V1 of the foreign object detection coil L1 is approximately 60 Vrms. Since there is no closed loop between the foreign object detection coil L1 and the resonant capacitor C1, the induced voltage V1 will directly act on the rear of the resonant capacitor C1, that is, the input end of the sampling unit A3, thereby making the input voltage V0≈60 Vrms affect the sampling of the 3 Mhz driving signal, and thus the metal foreign object detection circuit cannot work properly.

[0084] When the first filter L2 is set, its equivalent circuit is as shown in Figure 5 Figure [Figure number not provided in the original, assumed to be a specific figure number]. The first filter L2 forms a closed loop with the foreign object detection coil L1 and the resonant capacitor C1 through the grounding end. At this time, by adjusting the inductance value of the first filter L2, effective attenuation of the induced voltage can be achieved.

[0085] For this type of metal foreign object detection circuit, to achieve normal sampling of the 3 Mhz driving signal under the condition that the induced voltage V1 is approximately 60 Vrms, the expected attenuation should be -56 dB. Substituting the corresponding parameters into the above formula, it can be obtained that when the inductance value of the first filter L2 is 10 uH, it can meet the corresponding requirements.

[0086] After setting the first filter L2 to 10 uH, further verification of the equivalent circuit of Figure 5 Figure [Figure number not provided in the original, assumed to be a specific figure number] shows that:

[0087] It can be seen that when the first filter with an inductance value of 10 uH is set, the input voltage V0 attenuates to 0.095 V, and the gain is -56 dB. This input voltage will not affect the sampling of the 3 Mhz driving signal by the processing unit DPU.

[0088] The beneficial effects of the present invention are as follows: By setting a filter in the metal foreign object detection circuit and filtering the induced signals generated during operation, the problem that the metal foreign object detection circuit in the prior art cannot work properly due to the influence of the induced voltage when the main power coil is working is avoided, and the overall safety of the wireless power transmission system is improved.

[0089] The above are only the preferred embodiments of the present invention, and do not limit the implementation manners and protection scope of the present invention. For those skilled in the art, it should be realized that all the equivalent replacements and obvious changes made by using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A design method of a filter, characterized in that, Applicable to a metal foreign object detection circuit; The metal foreign object detection circuit is arranged in a wireless power transmission system, and the wireless power transmission system has a main coil, and a foreign object detection coil of the metal foreign object detection circuit is arranged in the main coil; The metal foreign object detection circuit further includes a detection module, the detection module is connected to the foreign object detection coil through a resonant capacitor and outputs a driving signal to the foreign object detection coil, and then collects a feedback signal from the foreign object detection coil; The detection module includes: A driving unit, the output end of the driving unit is connected to the resonant capacitor to output the driving signal to the foreign object detection coil; A processing unit, the output end of the processing unit is connected to the input end of the driving unit; A sampling unit, the input end of the sampling unit is connected to the resonant capacitor to obtain the feedback signal, and the output end of the sampling unit is connected to the input end of the processing unit; A first filter is arranged at the connection point of the detection module and the resonant capacitor; The design method includes: Step S1: For a wireless power transmission system, obtain the operating frequency of the wireless power transmission system; Step S2: When the wireless power transmission system is working, obtain the induced voltage input by the foreign object detection coil at the operating frequency; Step S3: Generate the inductance parameter of the first filter according to the induced voltage and the operating frequency; The step S3 includes: Step S31: Generate a desired attenuation according to the induced voltage and a preset normal operating threshold; Step S32: Obtain the device parameters of the metal foreign object detection circuit, and generate the inductance parameter of the first filter according to the device parameters and the desired attenuation.

2. The design method according to claim 1, wherein In the step S32, the method for generating the inductance parameter is: ； Among them, is the impedance of the foreign object detection coil, is the impedance of the first filter, is the impedance of the resonant capacitor, is the self-inductance value of the foreign object detection coil, is the angular frequency of the operating frequency, is the inductance parameter, is the capacitance value of the resonant capacitor, is the induced voltage of the foreign object detection coil, is the filtered voltage input to the detection module, is the signal attenuation gain, is the expected attenuation.

3. The design method according to claim 1, characterized in that, The driving unit includes: A digital-to-analog converter, the input end of the digital-to-analog converter is connected to the output end of the processing unit; A second filter, the input end of the second filter is connected to the output end of the digital-to-analog converter; A first buffer, the input end of the first buffer is connected to the output end of the second filter; A resistor, the first end of the resistor is connected to the output end of the first buffer, and the second end of the resistor is connected to the resonant capacitor.

4. The design method according to claim 1, characterized in that The sampling unit includes: A second buffer, the input end of the second buffer is connected to the resonant capacitor; A third filter, the input end of the third filter is connected to the output end of the second buffer; An analog-to-digital converter, the input end of the analog-to-digital converter is connected to the output end of the third filter, and the output end of the analog-to-digital converter is connected to the input end of the processing unit.

5. The design method according to claim 1, wherein The first end of the first filter is connected to the connection point of the resonant capacitor and the detection module, and the second end of the first filter is grounded; The inductance parameter of the first filter is determined according to the operating frequency of the wireless power transmission system.

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