Wireless power transmission foreign matter detection system and method based on average power change

Abstract

The invention relates to a wireless power transmission technology, and particularly discloses a wireless power transmission foreign matter detection system and method based on average power variation, a signal excitation unit in the system provides a foreign matter detection excitation signal for a detection coil unit through a high-pass filtering unit, and a signal conditioning unit comprises a multiplier, a low-pass filter and an amplifier. A sampling signal of the detection channel is multiplied by a reference signal homologous to the signal excitation unit by the multiplier, and then passes through the low-pass filter and the amplifier, and a direct-current bias signal representing power change is collected by the AD sampling unit; the controller unit and the feature extraction unit identify the average power change condition by identifying the direct current bias signal so as to determine whether foreign matter intervention exists in the wireless power transmission system. The circuit has the advantages that the circuit is simple in structure and convenient to implement, primary side interference can be effectively filtered out, reverse breakdown of a detection signal plate when primary side induced voltage is too large is avoided, and detection sensitivity is improved.

Description

Technical Field

[0001] This invention relates to the field of wireless power transmission technology, and in particular to a wireless power transmission foreign object detection system and method based on average power variation. Background Technology

[0002] Wireless power transfer (WPT) is a technology that integrates power electronics and automatic control theories and technologies to enable the loosely coupled, non-electrically contactless transmission of electrical energy between the power grid (or battery) and electrical devices via a medium (such as an electric field, magnetic field, microwave, or laser). Compared to traditional electrical contact-based power access technologies, wireless power transfer offers advantages such as higher reliability and security, smaller footprint, flexible usage, less susceptibility to external environmental interference, strong interaction with the power grid, and applicability in certain extreme environments and special conditions. Therefore, it is finding increasingly widespread development and application in consumer electronics, healthcare, electric vehicles, and other fields.

[0003] Magnetic coupled wireless power transfer (MC-WPT) uses a high-frequency alternating magnetic field generated by a high-frequency alternating current in the primary coil as the carrier for power transmission. However, due to the non-contact nature of the primary and secondary devices, foreign objects can easily enter the charging area. For foreign metals entering the high-frequency alternating magnetic field of the MC-WPT system, eddy current effects can cause heating and pose a safety hazard; for foreign organisms, prolonged exposure to the high-frequency alternating magnetic field can increase the probability of disease. Furthermore, these foreign objects can alter the original magnetic field distribution of the system, leading to a decrease in system transmission efficiency. Therefore, foreign object detection (FOD) technology is indispensable for MC-WPT systems.

[0004] Existing foreign object detection solutions mainly fall into three categories: those based on MC-WPT system parameters, those based on traditional sensors, and those based on detection coils. MC-WPT system parameter-based methods utilize the influence of foreign objects on relevant parameters of the MC-WPT system to detect them. These methods are low-cost and do not require additional detection mechanisms, but their detection accuracy is affected by the power level of the MC-WPT system, making them unsuitable for high-power applications. Traditional sensor-based methods detect foreign objects by placing sensors within the system, such as temperature sensors, vision cameras, and ultrasonic sensors. These methods offer large detection coverage and are unaffected by the power level of the MC-WPT system, but they are costly, have low integration, and require sophisticated sensors. In high-power and large-size applications, detection coil-based solutions are gradually becoming mainstream due to their low cost and high integration. Detection coils primarily use a magnetic field generated by a high-frequency excitation signal to couple with the metallic foreign object, thereby achieving detection.

[0005] For metallic foreign objects, the coupling mechanism with the detection coil is mainly achieved through the coupling between the eddy current field of the metallic foreign object and the inherent magnetic field of the detection coil. Therefore, the impedance of the detection coil can be detected. For biological foreign objects, due to their capacitive characteristics, they can be equivalent to a series and parallel capacitor-resistor model. When they come into contact with the detection coil, the stray capacitance of the detection coil changes, and the impedance of the coil can also be detected.

[0006] However, the existing technology has the following drawbacks: most of them use filtering out interference signals to extract the excitation signal and then extracting impedance features. Since the order of magnitude of the two signals is not much different, they are easily affected by interference signals that have not been filtered out, resulting in low detection sensitivity and easy to produce false alarms and missed alarms. Summary of the Invention

[0007] In view of this, the present invention first provides a wireless power transmission foreign object detection system based on average power variation. The system multiplies the sampled signal with a reference signal of the same frequency through signal conditioning, and uses a low-pass filter to extract the DC component in the output signal that is related to the phase of the detection signal to identify foreign objects. At the same time, in view of the large primary-side interference signal, the system configures an LC high-pass filter and designs a parallel resonant capacitor value for the detection coil to make the filter channel and the detection coil resonant as a whole, thereby improving the detection sensitivity.

[0008] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows:

[0009] A foreign object detection system for wireless power transmission based on average power variation is disclosed. The system comprises a signal excitation unit, a detection coil unit, a high-pass filter unit, a signal conditioning unit, an AD sampling unit, a controller unit, and a feature extraction unit. The signal excitation unit provides a foreign object detection excitation signal to the detection coil unit via the high-pass filter unit. The signal conditioning unit includes a multiplier, a low-pass filter, and an amplifier. The multiplier multiplies the sampled signal from the detection channel with a reference signal originating from the signal excitation unit. After passing through the low-pass filter and amplifier, the AD sampling unit acquires a DC bias signal characterizing power variation. The controller unit and the feature extraction unit identify the average power variation by recognizing the DC bias signal, thereby determining whether a foreign object has entered the wireless power transmission system.

[0010] Optionally, the detection coil unit samples the array coil, with each detection coil configured with a detection channel. Each detection channel is detected by cyclic scanning, thereby achieving full coverage of the area where the primary coil of the wireless power transmission system is located.

[0011] Optionally, the high-pass filter unit includes a filter inductor and two filter capacitors. The two ends of the filter inductor are connected in series with a filter capacitor and then connected to the two ends of a compensation capacitor. A detection coil is connected in parallel with the compensation capacitor. The overall impedance of the high-pass filter unit, the compensation capacitor and the detection coil is in a resonant state under normal conditions.

[0012] Optionally, the value of the compensation capacitor is C1 or C2, wherein:

[0013]

[0014] ω is the angular frequency of the foreign object detection excitation signal, L d To detect the self-inductance of the coil, L H C is the self-inductance value of the filter inductor. H This is the value of the filter capacitor.

[0015] Optionally, the detection coil in the detection coil unit is a reverse series detection coil, with the current flowing through the two sub-coils in opposite directions.

[0016] Optionally, the feature extraction unit detects foreign objects by detecting phase changes at a specific excitation frequency.

[0017] Optionally, whether to issue an alarm signal for foreign object intrusion can be determined by judging whether the difference between the DC bias signal and the preset reference value exceeds a preset threshold.

[0018] Optionally, there is inductive coupling between the detection coil unit and the primary-side transmitting coil.

[0019] Based on the above system, the present invention also provides a method for detecting foreign objects in wireless power transmission based on average power variation, used in the foreign object detection system described above, the key feature of which is that it includes the following steps:

[0020] S1: A foreign object detection excitation signal is applied to the detection coil unit through the signal excitation unit. The operating frequency of the foreign object detection excitation signal is higher than the operating frequency of the wireless power transmission system.

[0021] S2: Filter out primary-side interference in the wireless power transmission system through a high-pass filter unit;

[0022] S3: The current signal of the detection channel where the detection coil is located is obtained by using the sampling resistor, and the sampling signal is multiplied by the foreign object detection excitation signal by the multiplier in the signal conditioning unit;

[0023] S4: The AC signal is filtered out by a low-pass filter to obtain the DC bias signal characterizing the power change;

[0024] S5: The DC bias signal is amplified by an amplifier;

[0025] S6: The controller unit acquires the DC bias signal through the AD sampling unit and calculates the difference with the preset reference value to determine whether there is foreign object interference.

[0026] Optionally, when a foreign object is present in the system, an alarm signal is issued; when no foreign object is present, the DC bias signal corresponding to the current phase is updated to a reference signal.

[0027] The significant effects of this invention are:

[0028] The system has a simple circuit structure and is easy to implement. It can effectively filter out primary-side interference and avoid reverse breakdown of the detection signal board when the primary-side induced voltage is too large. After signal conditioning, the DC bias signal is used to characterize power changes, thereby improving the detection sensitivity. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the foreign object detection channel circuit according to an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the detection coil structure in an embodiment of the present invention;

[0031] Figure 3 This is a key signal waveform diagram of an embodiment of the present invention;

[0032] Figure 4 This is a system principle block diagram provided in the embodiments of the present invention;

[0033] Figure 5 This is a system workflow diagram provided in an embodiment of the present invention;

[0034] Figure 6 This is a system simulation model diagram provided in the embodiments of the present invention;

[0035] Figure 7 This is a waveform diagram of the voltage across the detection coil in the simulation experiment of this invention;

[0036] Figure 8 This is a waveform diagram of the voltage across the sampling resistor in the simulation experiment of this invention;

[0037] Figure 9 This is a waveform diagram of the simulated multiplier output signal in the simulation experiment of this invention;

[0038] Figure 10 This is a waveform diagram of the low-pass filter output signal in the simulation experiment of this invention;

[0039] Figure 11 This is a waveform diagram of the DC signal amplification output in the simulation experiment of this invention. Detailed Implementation

[0040] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The embodiments are given for illustrative purposes only and should not be construed as limiting the present invention. The accompanying drawings are for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0041] like Figures 1-4 As shown, this embodiment provides a foreign object detection system for wireless power transmission based on average power variation, including a signal excitation unit, a detection coil unit, a high-pass filter unit, a signal conditioning unit, an AD sampling unit, a controller unit, and a feature extraction unit. The signal excitation unit provides a foreign object detection excitation signal to the detection coil unit through the high-pass filter unit. The signal conditioning unit includes a multiplier, a low-pass filter, and an amplifier. The multiplier multiplies the sampled signal of the detection channel with a reference signal from the same source as the signal excitation unit. After passing through the low-pass filter and amplifier, the AD sampling unit acquires a DC bias signal characterizing power variation. The controller unit and the feature extraction unit identify the average power variation by recognizing the DC bias signal, thereby determining whether a foreign object has entered the wireless power transmission system.

[0042] pass Figure 1 It can be seen that L in each detection channel p M represents the primary coil, and L represents the mutual inductance between the detection coil and the primary coil. d L represents the detection coil. H With C HAn LC high-pass filter is constructed, where C is the capacitor to be designed. The LC high-pass filter can significantly reduce the primary-side induced signal across the AC source and sampling resistor, protecting the preceding excitation signal source circuit from reverse breakdown by the induced voltage on the detection coil under high-power fields, while also filtering out a large portion of the primary-side interference signal. In practical implementation, the physical structure of the detection coil is as follows... Figure 2 As shown, the detection coil in the detection coil unit adopts a reverse series detection coil, and the current flows in opposite directions in the two sub-coils. During the manufacturing process, the top and bottom PCB traces are separated by an FR-4 substrate and connected by vias to minimize the influence of the power magnetic field on the detection coil and reduce the induced voltage at both ends of the detection coil.

[0043] The current signal from the detection channel is converted into a voltage signal by flowing through the sampling resistor R. Due to the sampling signal u... d Since the impedance is derived from resistor R, to improve the sampling signal response to changes caused by foreign objects, the overall impedance Z of the sampling resistor is brought into a resonant state through the appropriate value of capacitor C. When a foreign object is introduced, it causes the detection coil L... d Changes occur, leading to Z becoming detuned, at which point Z exhibits a significant impedance change.

[0044]

[0045] When Z is in a resonant state, C has two possible values: C1 results in extremely low impedance, while C2 results in extremely high impedance.

[0046]

[0047] from Figure 3 It can be known that the sampled signal u d It consists of two parts, one part being the excitation signal u d1 The other part is the primary-side interference signal u d2 As shown in equation (3). Where ω1 represents the angular frequency of the excitation signal, ω2 represents the angular frequency of the primary-side induced voltage, α represents the phase of the excitation signal, β represents the phase of the primary-side induced voltage, and I1 and I2 represent the amplitudes of the excitation signal current component and the primary-side induced signal current component on the sampling resistor, respectively.

[0048] u d1 =RI1 cos(ω1t+α)

[0049] u d2 =RI2cos(ω2t+β) (3)

[0050] u d =u d1 +u d2

[0051] Sampled signal u dReference signal u, which originates from the same source as the excitation signal r Multiplication guarantees u d and u r The frequencies are exactly the same, both originating from the same passive crystal oscillator signal and amplified to obtain the output signal u. m And because u m This can be viewed as R times the voltage multiplied by the current, so u m This can be considered as R times the power. m The signal components are shown in Equation 4. Assume the reference signal u r Phase is 0, amplitude is A r At this time u m It contains four frequency signals: one DC component related to the phase of the excitation signal and three AC components. In specific implementation, the primary-side power transfer operating frequency is 85kHz, while the foreign object detection excitation signal is generally much higher than 85kHz, reaching the MHz level. Therefore, the DC signal frequency differs from the AC signal frequency by six orders of magnitude, while the excitation signal differs from the 85kHz signal by less than two orders of magnitude. Thus, the filtering frequency difference using the method proposed in this invention is very large, and the AC signal can be completely filtered out by a first-order low-pass filter.

[0052]

[0053] Based on equation (3), u d There are two signals, 4MHz and 85kHz, but their frequencies differ significantly. Within one or several cycles of the 4MHz signal, we can roughly determine the frequency difference between them. d The signal is considered as a 4MHz signal plus a DC bias corresponding to a certain point on an 85kHz signal, thus yielding the following result: Figure 3 The key signal waveform is shown.

[0054] Amplifying the extracted DC signal again can amplify the changes in the DC signal caused by the foreign object's interference, thereby improving the system's sensitivity. Assuming the foreign object's interference causes a phase shift in the sampling signal, with an shift amount of Δα, then the final DC signal u... L The synchronous change, after being amplified K times by the amplification stage, u o As shown in equation (5).

[0055]

[0056] The intrusion of foreign objects alters the impedance characteristic curve of the proposed detection coil. Therefore, foreign object detection can be achieved by detecting phase changes at a specific excitation frequency. The overall system design is as follows: Figure 4As shown. Due to the large surface area of ​​the primary edge to be detected, an array coil is usually designed to ensure detection accuracy. Each coil represents a channel, and a cyclic scanning method is used to detect each channel during detection. The flowchart is shown below. Figure 5 As shown; via Figure 4 and Figure 5 As can be seen, this embodiment also provides a method for detecting foreign objects in wireless power transmission based on average power variation, used in the aforementioned wireless power transmission foreign object detection system based on average power variation, characterized by including the following steps:

[0057] S1: A foreign object detection excitation signal is applied to the detection coil unit through the signal excitation unit. The operating frequency of the foreign object detection excitation signal is higher than the operating frequency of the wireless power transmission system.

[0058] S2: Filter out primary-side interference in the wireless power transmission system through a high-pass filter unit;

[0059] S3: The current signal of the detection channel where the detection coil is located is obtained by using the sampling resistor, and the sampling signal is multiplied by the foreign object detection excitation signal by the multiplier in the signal conditioning unit;

[0060] S4: The AC signal is filtered out by a low-pass filter to obtain the DC bias signal characterizing the power change;

[0061] S5: The DC bias signal is amplified by an amplifier;

[0062] S6: The controller unit acquires the DC bias signal through the AD sampling unit and calculates the difference with the preset reference value to determine whether there is foreign object interference.

[0063] During implementation, an alarm signal is issued when a foreign object is present; when no foreign object is present, the DC bias signal corresponding to the current phase is updated to the reference signal.

[0064] To further illustrate the significant effects of this invention, as described above, a system based on Simulink is constructed as follows: Figure 6 The simulation model is shown in Table 1. A voltage source is connected in series with the detection coil to simulate the induced voltage on the primary side. The equivalent model of the metallic foreign object is an LR series model. A switch is added to control the conduction of the foreign object circuit to simulate the intervention of the foreign object.

[0065] Table 1 Simulation Parameters

[0066]

[0067] Simulation results are as follows Figures 7-10 As shown, through Figure 7 and Figure 8It can be seen that when the induced voltage on the primary side is much greater than the amplitude of the detected signal, the induced voltage can be significantly filtered out after the front-end LC high-pass filter. At the same time, the induced voltage amplitude is also within a low, safe voltage range for subsequent components. The analog multiplier output is as follows... Figure 9 As shown, consistent with the theoretical derivation, multiple AC and DC components exist. The DC signal obtained after low-pass filtering is as follows: Figure 10 As shown, then after magnification, as shown in the image. Figure 11 The signal shown is compared with Figure 10 and Figure 11 It can be seen that the change in the DC component caused by the foreign object is significantly amplified, making it easier for the microcontroller to acquire this change. Simulation waveform analysis shows that even with an induced voltage on the detection coil much larger than the detection signal after the foreign object's intervention, a change will still occur at the final AD sampling port, and the magnitude of this change is much greater than the microcontroller's AD sampling resolution, allowing the microcontroller to detect the foreign object's intervention.

[0068] Finally, it should be noted that the above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention.

Claims

1. A wireless power transfer foreign object detection system based on average power variation, characterized in that, The system includes a signal excitation unit, a detection coil unit, a high-pass filter unit, a signal conditioning unit, an AD sampling unit, a controller unit, and a feature extraction unit. The signal excitation unit provides a foreign object detection excitation signal to the detection coil unit via the high-pass filter unit. The signal conditioning unit includes a multiplier, a low-pass filter, and an amplifier. The multiplier multiplies the sampled signal of the detection channel with a reference signal from the same source as the signal excitation unit. After passing through the low-pass filter and amplifier, the AD sampling unit acquires a DC bias signal characterizing power changes. The controller unit and the feature extraction unit identify the average power change by recognizing the DC bias signal, thereby determining whether a foreign object has entered the wireless power transmission system.

2. The wireless power transfer foreign object detection system based on average power variation according to claim 1, characterized in that, The detection coil unit samples the array coil, with each detection coil configured with a detection channel. Each detection channel is detected through a cyclic scanning method, thereby achieving full coverage of the area where the primary coil of the wireless power transmission system is located.

3. The wireless power transfer foreign object detection system based on average power variation according to claim 1 or 2, characterized in that, The high-pass filter unit includes a filter inductor and two filter capacitors. The two ends of the filter inductor are connected in series with a filter capacitor and then connected to the two ends of a compensation capacitor. A detection coil is connected in parallel with the compensation capacitor. The overall impedance of the high-pass filter unit, the compensation capacitor and the detection coil is in a resonant state under normal conditions.

4. The wireless power transfer foreign object detection system based on average power variation according to claim 3, characterized in that, The value of the compensation capacitor is either C1 or C2, where: ω is the angular frequency of the foreign object detection excitation signal, L d To detect the self-inductance of the coil, L H C is the self-inductance value of the filter inductor. H This is the value of the filter capacitor.

5. The wireless power transfer foreign object detection system based on average power variation according to claim 1 or 2, characterized in that, The detection coil in the detection coil unit is a reverse series detection coil, with the current flowing through the two sub-coils in opposite directions.

6. The wireless power transfer foreign object detection system based on average power variation according to claim 4, characterized in that, The feature extraction unit detects foreign objects by detecting phase changes at a specific excitation frequency.

7. The wireless power transfer foreign object detection system based on average power variation according to claim 4, characterized in that, The alarm signal for foreign object intrusion is determined by whether the difference between the DC bias signal and the preset reference value exceeds a preset threshold.

8. The wireless power transfer foreign object detection system based on average power variation according to claim 1, characterized in that, There is inductive coupling between the detection coil unit and the primary side transmitting coil.

9. A method for detecting foreign objects in wireless power transmission based on average power variation, used in the wireless power transmission foreign object detection system based on average power variation as described in any one of claims 1-8, characterized in that, Includes the following steps: S1: A foreign object detection excitation signal is applied to the detection coil unit through the signal excitation unit. The operating frequency of the foreign object detection excitation signal is higher than the operating frequency of the wireless power transmission system. S2: Filter out primary-side interference in the wireless power transmission system through a high-pass filter unit; S3: The current signal of the detection channel where the detection coil is located is obtained by using the sampling resistor, and the sampling signal is multiplied by the foreign object detection excitation signal by the multiplier in the signal conditioning unit; S4: The AC signal is filtered out by a low-pass filter to obtain the DC bias signal characterizing the power change; S5: The DC bias signal is amplified by an amplifier; S6: The controller unit acquires the DC bias signal through the AD sampling unit and calculates the difference with the preset reference value to determine whether there is foreign object interference.

10. The method for detecting foreign objects in wireless power transmission based on average power variation according to claim 9, characterized in that: When a foreign object is present, an alarm signal is issued; when no foreign object is present, the DC bias signal corresponding to the current phase is updated to the reference signal.

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