Battery inspection device and battery inspection method

Abstract

A storage battery inspection device (10) is provided with: a storage control circuit (11) that applies an alternating current to a storage battery; a magnetic sensor (12) that senses a magnetic field component outside the storage battery and outputs a magnetic sensor signal representing the sensed magnetic field component; a cancellation coil (13) that generates a magnetic field component based on an input current, the generated magnetic field component being used to cancel a magnetic field component generated by magnetization of a magnetic body of the storage battery; a feedback circuit (14) that obtains a low-frequency signal showing a magnetic field component of a frequency lower than a frequency of the alternating current from the magnetic sensor signal and applies the input current to the cancellation coil (13) in accordance with the low-frequency signal; and a detection circuit (15) that obtains a detection signal showing a magnetic field component of a frequency identical to the frequency of the alternating current from the magnetic sensor signal.

Description

Technical Field

[0001] The present disclosure relates to a battery inspection device and the like for inspecting a battery. Background Art

[0002] Patent Document 1 describes a technology related to an evaluation device for inspecting secondary batteries. In the technology described in Patent Document 1, a controller calculates the magnitudes of multiple currents flowing through multiple parts of the secondary battery based on the magnetic field detected by a magnetic sensor, extracting the magnitudes of multiple currents within the electrolyte region between the electrodes. Furthermore, the controller creates a graph showing the distribution of the magnitudes of the multiple currents and displays it on a display device. Secondary batteries are also called storage batteries.

[0003] (Prior art literature)

[0004] (Patent Document)

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-32985 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] However, batteries may have magnetic electrode plates and other components. Consequently, magnetic sensors, affected by the magnetization of the battery's magnetic components, may not be able to properly sense the magnetic field generated by the current flowing between the electrodes. Consequently, using magnetic sensors to inspect batteries can sometimes be difficult.

[0008] Therefore, the present disclosure provides a battery inspection device or the like that can appropriately inspect the battery using a magnetic sensor even when the battery has a magnetic body.

[0009] Means used to solve problems

[0010] A battery inspection device according to one embodiment of the present disclosure is a device for inspecting a battery, comprising: a battery control circuit for applying an external voltage, in which an AC voltage is superimposed on a DC voltage, to the battery, thereby applying an AC current to the battery, wherein the DC voltage is a voltage for balancing the output voltage of the battery; a magnetic sensor for sensing a magnetic field component external to the battery and outputting a magnetic sensor signal representing the sensed magnetic field component; and a cancellation coil for generating a magnetic field component based on an input current, the generated magnetic field component being used to cancel a magnetic field component generated by magnetization of a magnetic body of the battery. a feedback circuit that obtains a low-frequency signal from the magnetic sensor signal output by the magnetic sensor when the alternating current is applied to the battery, applies the input current to the cancellation coil based on the low-frequency signal, and the low-frequency signal shows a magnetic field component with a frequency lower than the frequency of the alternating current; and a detection circuit that obtains a detection signal from the magnetic sensor signal output by the magnetic sensor when the alternating current is applied to the battery and the input current is applied to the cancellation coil, the detection signal showing a magnetic field component with a frequency the same as the frequency of the alternating current.

[0011] In addition, these general or specific solutions can be implemented by systems, devices, methods, integrated circuits, computer programs, or non-temporary recording media such as computer-readable CD-ROMs, or by any combination of systems, devices, methods, integrated circuits, computer programs, and recording media.

[0012] Effects of the Invention

[0013] According to one aspect of the present disclosure, even when a storage battery has a magnetic body, the storage battery can be appropriately inspected using a magnetic sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a block diagram showing the configuration of a battery inspection device according to an embodiment.

[0015] Figure 2 This is a flowchart showing the operation of the battery inspection device according to the embodiment.

[0016] Figure 3 It is a conceptual diagram showing a specific structure of the battery inspection device according to the embodiment.

[0017] Figure 4 It is a conceptual diagram showing a specific structure of the magnetic sensor according to the embodiment.

[0018] Figure 5 This is a conceptual diagram showing a state where a storage battery according to an embodiment is being inspected.

[0019] Figure 6 This is a graph showing changes in current applied to the battery according to the embodiment.

[0020] Figure 7 Graph showing changes in the storage rate of the storage battery according to the embodiment.

[0021] Figure 8 This is a conceptual diagram showing the overall structure of a battery inspection device according to an embodiment.

[0022] Figure 9 This is a block diagram showing the configuration of a feedback circuit according to an embodiment.

[0023] Figure 10 This is a block diagram showing the configuration of a signal processing circuit according to an embodiment.

[0024] Figure 11 This is a block diagram showing the configuration of a detection circuit according to an embodiment.

[0025] Figure 12 This is a conceptual diagram showing a coordinate system used for visualization in an embodiment.

[0026] Figure 13 This is a conceptual diagram showing the current flowing during battery inspection according to the embodiment.

[0027] Figure 14 This is a conceptual diagram showing an example in which a magnetic sensor for sensing a magnetic field component in a direction perpendicular to a planar electrode plate of a battery is located inside a cancel coil according to an embodiment.

[0028] Figure 15 This is a conceptual diagram showing an example in which a magnetic sensor for sensing a magnetic field component in a direction parallel to a planar electrode plate of a battery is located inside a cancel coil according to an embodiment.

[0029] Figure 16 This is a conceptual diagram showing an example in which a magnetic sensor for sensing a magnetic field component in a direction perpendicular to a planar electrode plate of a battery is located outside a cancel coil according to an embodiment.

[0030] Figure 17 This is a conceptual diagram showing an example in which a magnetic sensor for sensing a magnetic field component in a direction parallel to a planar electrode plate of a battery is located outside a cancel coil according to an embodiment.

[0031] Figure 18 This is a conceptual diagram showing an example in which a plurality of magnetic sensors sense magnetic field components in a direction perpendicular to a planar electrode plate of a battery according to an embodiment.

[0032] Figure 19 This is a conceptual diagram showing an example of a case where a plurality of magnetic sensors sense magnetic field components in a direction parallel to a planar electrode plate of a battery according to an embodiment.

[0033] Figure 20 This is a conceptual diagram showing an example in which a magnetic sensor for sensing a magnetic field component in a direction parallel to a planar electrode plate of a battery is located outside a cancel coil, and the central axis of the cancel coil is perpendicular to the electrode plate.

[0034] Figure 21 This is a conceptual diagram showing an example of surrounding using a magnetic field component according to an embodiment. DETAILED DESCRIPTION

[0035] A battery inspection device according to one embodiment of the present disclosure is a device for inspecting a battery, comprising: a battery control circuit for applying an external voltage, in which an AC voltage is superimposed on a DC voltage, to the battery, thereby applying an AC current to the battery, wherein the DC voltage is a voltage for balancing the output voltage of the battery; a magnetic sensor for sensing a magnetic field component external to the battery and outputting a magnetic sensor signal representing the sensed magnetic field component; and a cancellation coil for generating a magnetic field component based on an input current, the generated magnetic field component being used to cancel a magnetic field component generated by magnetization of a magnetic body of the battery. a feedback circuit that obtains a low-frequency signal from the magnetic sensor signal output by the magnetic sensor when the alternating current is applied to the battery, applies the input current to the cancellation coil based on the low-frequency signal, and the low-frequency signal shows a magnetic field component with a frequency lower than the frequency of the alternating current; and a detection circuit that obtains a detection signal from the magnetic sensor signal output by the magnetic sensor when the alternating current is applied to the battery and the input current is applied to the cancellation coil, the detection signal showing a magnetic field component with a frequency the same as the frequency of the alternating current.

[0036] Thus, the battery inspection device can appropriately eliminate magnetic field components with frequencies lower than the frequency of the alternating current flowing through the battery, as magnetic field components generated by the magnetization of the battery's magnetic body. Consequently, the battery inspection device can appropriately sense the magnetic field components generated by the alternating current flowing through the battery. Consequently, the battery inspection device can appropriately inspect batteries using a magnetic sensor, even when the battery contains magnetic bodies.

[0037] For example, the feedback circuit obtains the low-frequency signal from the magnetic sensor signal through a low-pass filter. The low-pass filter is a filter that cuts off frequency components higher than a cutoff frequency and passes frequency components lower than the cutoff frequency. The cutoff frequency is lower than the frequency of the AC current.

[0038] Therefore, the battery inspection device can appropriately obtain a low-frequency signal indicating a magnetic field component having a frequency lower than the frequency of the AC current flowing through the battery through the low-pass filter.

[0039] Furthermore, for example, the cutoff frequency is 1 / 10 or more of the frequency of the alternating current.

[0040] Therefore, the battery inspection device can appropriately obtain a low-frequency signal indicating a magnetic field component having a frequency lower than that of the AC current flowing through the battery while suppressing processing delay of the low-pass filter.

[0041] In addition, for example, the feedback circuit uses a PID control method to control the magnitude of the input current so that the intensity of the magnetic field component shown by the low-frequency signal is close to the target value, and applies the input current with the controlled magnitude to the elimination coil. The PID control method is a proportional integral differential control method.

[0042] Therefore, the battery inspection device can appropriately control the magnetic field component having a frequency lower than the frequency of the AC current flowing through the battery through feedback control based on the PID control method.

[0043] Furthermore, for example, the target value is zero.

[0044] Thus, the battery inspection device can reduce the intensity of the magnetic field component at a frequency lower than the frequency of the AC current flowing through the battery to near zero. In other words, the battery inspection device can appropriately eliminate the magnetic field component at a frequency lower than the frequency of the AC current flowing through the battery through feedback control using the PID control method.

[0045] In addition, for example, the feedback circuit includes: a signal processing circuit that obtains the low-frequency signal from the magnetic sensor signal output by the magnetic sensor when the alternating current is applied to the battery, and outputs a control signal indicating the magnitude of the input current based on the low-frequency signal; and a current amplification circuit that applies the input current having the magnitude indicated by the control signal to the cancellation coil.

[0046] Therefore, the battery inspection device can appropriately control the input current applied to the cancel coil.

[0047] In addition, for example, the signal processing circuit converts the magnetic sensor signal output from the magnetic sensor as an analog signal into a digital signal, obtains the low-frequency signal from the magnetic sensor signal converted into the digital signal, generates the control signal based on the low-frequency signal, converts the generated control signal into an analog signal, and outputs the control signal converted into the analog signal.

[0048] Therefore, the battery inspection device can control the input current with high accuracy through signal processing based on digital signals.

[0049] In addition, for example, the signal processing circuit does not convert the magnetic sensor signal output from the magnetic sensor as an analog signal into a digital signal, but instead obtains the low-frequency signal from the magnetic sensor signal output from the magnetic sensor as an analog signal, generates the control signal based on the low-frequency signal, and outputs the generated control signal.

[0050] Therefore, the battery inspection device can control the input current at high speed using the analog signal as it is.

[0051] Furthermore, for example, the magnetic sensor is located inside the cancel coil.

[0052] Therefore, the battery inspection device can appropriately generate a magnetic field component for canceling the magnetic field component generated by magnetization of the magnetic body of the battery at the position of the magnetic sensor.

[0053] Furthermore, for example, the magnetic sensor is located outside the cancellation coil.

[0054] Therefore, the battery inspection device can appropriately generate a magnetic field component for canceling the magnetic field component generated by magnetization of the magnetic body of the battery at a position spaced apart from the magnetic sensor. Therefore, the position of the cancel coil can be more flexibly determined.

[0055] Furthermore, for example, the magnetic sensor is located in a region on the central axis of the cancel coil.

[0056] Thus, the battery inspection device can generate a magnetic field component toward the magnetic sensor that cancels the magnetic field component generated by the magnetization of the battery's magnetic body. Thus, the battery inspection device can generate a magnetic field component near the magnetic sensor that cancels the magnetic field component generated by the magnetization of the battery's magnetic body.

[0057] Furthermore, for example, the magnetic sensor is located in a region different from a region on the central axis of the cancel coil.

[0058] Therefore, the battery inspection device can generate a magnetic field component with a flexibly specified direction at a position separated from the magnetic sensor as a magnetic field component for canceling the magnetic field component generated by magnetization of the magnetic body of the battery.

[0059] Furthermore, for example, the central axis of the cancel coil is perpendicular to the planar electrode plates in the battery.

[0060] Thus, the battery inspection device can generate a magnetic field component toward the battery for canceling the magnetic field component generated by the magnetization of the battery's magnetic body. Furthermore, the battery inspection device can generate a magnetic field component perpendicular to the planar electrode plates in the battery as the magnetic field component for canceling the magnetic field component generated by the magnetization of the battery's magnetic body.

[0061] Furthermore, for example, the central axis of the cancel coil is parallel to the planar electrode plates in the battery.

[0062] Therefore, the battery inspection device can generate a magnetic field component parallel to the planar electrode plates in the battery as a magnetic field component to cancel the magnetic field component generated by the magnetization of the battery's magnetic body. It can be assumed that a magnetic field component parallel to the planar electrode plates is generated outside the battery when AC current is applied. Therefore, the battery inspection device can cancel the magnetic field component generated by the magnetization of the battery's magnetic body and accurately sense the magnetic field component generated outside the battery when AC power is applied.

[0063] In addition, for example, the battery inspection device includes: a plurality of magnetic sensors serving as the magnetic sensors, and a plurality of cancellation coils serving as the cancellation coils, each of the plurality of cancellation coils corresponding to each of the plurality of magnetic sensors, and the feedback circuit obtains the low-frequency signal from the magnetic sensor signal output by each of the plurality of magnetic sensors, and applies the input current to the cancellation coil corresponding to the magnetic sensor among the plurality of cancellation coils based on the low-frequency signal.

[0064] Therefore, the battery inspection device can appropriately sense a wide range of magnetic field components in a short time.

[0065] For example, one aspect of the present disclosure relates to a battery inspection method for inspecting a battery. In the battery inspection method, an external voltage is applied to the battery, which is a voltage obtained by superimposing an AC voltage on a DC voltage, thereby applying an AC current to the battery. The DC voltage is a voltage for balancing the output voltage of the battery. While the AC current is being applied to the battery, a low-frequency signal is obtained from a magnetic sensor signal output by a magnetic sensor. The low-frequency signal indicates a magnetic field component having a frequency lower than that of the AC current. The magnetic sensor senses a magnetic field component external to the battery and outputs the magnetic sensor signal indicating the sensed magnetic field component. Based on the low-frequency signal, an input current is applied to a cancel coil that generates a magnetic field component based on the input current. The generated magnetic field component cancels a magnetic field component generated by magnetization of a magnetic body of the battery. A detection signal is obtained from the magnetic sensor signal output by the magnetic sensor while the AC current is being applied to the battery and the input current is being applied to the cancel coil. The detection signal indicates a magnetic field component having the same frequency as that of the AC current.

[0066] This allows for the accurate cancellation of magnetic field components with frequencies lower than the frequency of the alternating current flowing through the battery, as they are generated by the magnetization of the battery's magnetic material. This allows for accurate detection of the magnetic field components generated by the alternating current flowing through the battery. This allows for accurate battery inspection using magnetic sensors, even when the battery contains magnetic material.

[0067] The following embodiments are described using the accompanying drawings. The embodiments described below are general or specific examples. The values, shapes, materials, components, component configurations, connection configurations, steps, and step sequences shown in the following embodiments are examples and are not intended to limit the technical solutions.

[0068] A battery is a rechargeable and dischargeable battery, also known as a secondary battery. Furthermore, a magnetic field component is a component that constitutes a magnetic field. A magnetic field component can be a component corresponding to a spatial position, a component corresponding to a frequency, a component corresponding to a predetermined direction, or any combination of these. For convenience, a magnetic field component is sometimes referred to simply as the magnetic field.

[0069] The elimination of magnetic field components mentioned here is not limited to complete elimination of magnetic field components, but may also mean elimination of almost all magnetic field components, or elimination of part of magnetic field components, that is, suppression of magnetic field components.

[0070] (Implementation Method)

[0071] First, let's describe the battery inspection device of this embodiment. This embodiment performs non-destructive inspections on batteries. Such non-destructive inspections sometimes utilize X-rays, visible light, and microwaves. However, using any of these methods presents difficulties in inspecting the internal electrical state of a battery. Therefore, the battery inspection device of this embodiment utilizes information from magnetic fields.

[0072] Specifically, the current flowing inside the battery generates a magnetic field around the battery (outside the battery). The relationship between the current (J) and the magnetic field (H) in a steady state is expressed by Maxwell's equations as follows: Based on this relationship, the current flowing inside the battery can be estimated from the magnetic field outside the battery. The battery inspection device in this embodiment detects the electrical state of the battery by measuring the magnetic field.

[0073] Meanwhile, the state of electricity within a battery changes during its charge and discharge process. Observing these changing states during the charge and discharge process is useful for reliable battery inspection. However, measuring the magnetic field takes considerable time, so the state of electricity within the battery may change while the magnetic field is being measured. This change in the state of electricity within the battery also causes changes in the magnetic field, making accurate magnetic field measurement difficult.

[0074] In such situations, stopping the battery's charge and discharge can halt changes in the battery's electrical state. However, when charge and discharge are simply stopped, no current flows through the battery, and no magnetic field components corresponding to the battery's electrical state are generated. Therefore, measuring the magnetic field when charge and discharge are simply stopped is inappropriate.

[0075] Furthermore, batteries use magnetic materials in their electrodes and other components. The magnetization of these magnetic materials also generates a magnetic field component. Furthermore, the intensity of the magnetic field component generated by the magnetization of the battery's magnetic materials can sometimes be significantly greater than the intensity of the magnetic field component generated by the current flowing through the battery. For example, the intensity of the magnetic field component generated by the magnetization of the battery's magnetic materials can be estimated to be around several milliteslas, while the intensity of the magnetic field component generated by the current flowing through the battery can be estimated to be several microteslas or less.

[0076] In the above case, the magnetic sensor used to measure the magnetic field reacts strongly to the magnetic field component generated by the magnetization of the magnetic body of the battery. Therefore, it is difficult to accurately detect the subtle magnetic field component generated by the current flowing in the battery.

[0077] First, the battery inspection device of this embodiment applies an alternating current to the battery. This allows the device to halt (suppress) charging and discharging while allowing the alternating current to flow through the battery. The alternating current flowing through the battery also generates a magnetic field component outside the battery.

[0078] Furthermore, the battery inspection device of this embodiment uses a cancel coil to cancel magnetic field components with a frequency lower than that of the AC current. This allows the battery inspection device to maintain the magnetic field components generated by the AC current applied to the battery while canceling the magnetic field components generated by the magnetization of the battery's magnetic material.

[0079] Therefore, the battery inspection device of this embodiment can appropriately sense the magnetic field component generated by the AC current applied to the battery and appropriately inspect the electrical state of the battery.

[0080] Figure 1 This is a block diagram showing the configuration of the battery inspection device according to this embodiment. Figure 1 The battery inspection device 10 shown includes a power storage control circuit 11 , a magnetic sensor 12 , a preamplifier 18 , a cancel coil 13 , a feedback circuit 14 , a high-pass filter (HPF) 19 , a detection circuit 15 , an imaging circuit 16 , and a display 17 .

[0081] The power storage control circuit 11 is a circuit that applies voltage and current to the battery. Specifically, the power storage control circuit 11 applies an external voltage to the battery, which is a DC voltage superimposed with an AC voltage to balance the battery's output voltage, thereby applying AC current to the battery.

[0082] The magnetic sensor 12 is a sensor that detects magnetic field components. Specifically, the magnetic sensor 12 senses the magnetic field components outside the battery and outputs a magnetic sensor signal representing the sensed magnetic field components. For example, the intensity of the magnetic sensor signal output from the magnetic sensor 12 is proportional to the intensity of the magnetic field components sensed by the magnetic sensor 12.

[0083] The preamplifier 18 is a circuit that amplifies tiny signals, thereby generating a signal that can be used by subsequent circuits (such as the feedback circuit 14 and the high-pass filter 19). For example, the preamplifier 18 amplifies the magnetic sensor signal output from the magnetic sensor 12 and outputs the amplified magnetic sensor signal. In the present disclosure, the magnetic sensor signal output from the magnetic sensor 12 may also be a magnetic sensor signal output from the magnetic sensor 12 and amplified by the preamplifier 18.

[0084] The cancel coil 13 is a circuit that generates a magnetic field component based on an input current. Specifically, the cancel coil 13 generates a magnetic field component based on an input current to cancel a magnetic field component generated by magnetization of a magnetic body of the battery.

[0085] Feedback circuit 14 applies a current to cancel coil 13 based on the magnetic sensor signal output from magnetic sensor 12. This current serves as input current. Specifically, feedback circuit 14 obtains a low-frequency signal representing a magnetic field component having a frequency lower than that of the AC current from the magnetic sensor signal output from magnetic sensor 12 when AC current is applied to the battery.

[0086] For example, the strength of the low-frequency signal is proportional to the strength of the magnetic field components at frequencies lower than the frequency of the AC current. The low-frequency signal can indicate magnetic field components at all frequencies lower than the frequency of the AC current, or it can indicate magnetic field components at a portion of frequencies lower than the frequency of the AC current. Specifically, the low-frequency signal can indicate magnetic field components at frequencies lower than a reference frequency that is lower than the frequency of the AC current. Furthermore, the low-frequency signal can also indicate magnetic field components corresponding to DC components.

[0087] Feedback circuit 14 then applies a current to cancel coil 13 based on the low-frequency signal. This current serves as input current. More specifically, feedback circuit 14 applies a larger current to cancel coil 13 as the low-frequency signal obtained from the magnetic sensor signal increases—in other words, as the magnetic field component with a frequency lower than that of the alternating current increases.

[0088] High-pass filter 19 is a filter that cuts off frequency components lower than a cutoff frequency and passes frequency components higher than the cutoff frequency. The cutoff frequency of high-pass filter 19 is set to a frequency lower than the frequency of the AC current applied to battery 31. Thus, components with frequencies lower than the frequency of the AC current applied to battery 31 and lower than the cutoff frequency are removed from the magnetic sensor signal.

[0089] Here, "cutting off" frequency components lower than the cutoff frequency means suppressing the passage of frequency components lower than the cutoff frequency, and is not limited to completely cutting off frequency components lower than the cutoff frequency. Similarly, "allowing the passage of frequency components higher than the cutoff frequency" means suppressing the passage of frequency components higher than the cutoff frequency, and is not limited to completely allowing frequency components higher than the cutoff frequency to pass. The degree of cutoff and passage depends on the quality of high-pass filter 19.

[0090] Furthermore, the high-pass filter 19 may cut off or pass the component having the same cutoff frequency, or may cut off a part of the component having the same cutoff frequency and pass the other part.

[0091] In the present disclosure, the magnetic sensor signal output from the magnetic sensor 12 may be a magnetic sensor signal output from the magnetic sensor 12 and having its low-frequency component removed by the high-pass filter 19 . This magnetic sensor signal is input to the detection circuit 15 .

[0092] The detection circuit 15 performs detection, for example, phase detection. Specifically, the detection circuit 15 obtains, as a detection signal, a signal indicating a magnetic field component having the same frequency as the frequency of the AC current applied to the battery. More specifically, the detection circuit 15 obtains a detection signal indicating a magnetic field component having the same frequency as the AC current from the magnetic sensor signal output by the magnetic sensor 12 when the AC current is applied to the battery and the input current is applied to the cancel coil 13. This detection signal indicates a magnetic field component having the same frequency as the AC current.

[0093] For example, the intensity of the detection signal is proportional to the intensity of the magnetic field component having the same frequency as that of the AC current.

[0094] The imaging circuit 16 is a circuit for generating an image. Specifically, the imaging circuit 16 generates an image representing the state of the battery based on the detection signal obtained by the detection circuit 15. Here, the image may be expressed as a video.

[0095] The display 17 is a device (information display circuit) that displays images. Specifically, the display 17 has a screen and displays the image generated by the imaging circuit 16 on the screen.

[0096] The battery inspection device 10 may include only some of the power storage control circuit 11, magnetic sensor 12, cancel coil 13, feedback circuit 14, detection circuit 15, imaging circuit 16, and display 17. In other words, the battery inspection device 10 may not include all of these components. For example, the display 17 may be included in a device separate from the battery inspection device 10, or the imaging circuit 16 and display 17 may be included in a device separate from the battery inspection device 10.

[0097] Furthermore, the battery inspection device 10 may not include the preamplifier 18, the high-pass filter 19, or both. For example, the magnetic sensor signal output from the magnetic sensor 12 may be input to the feedback circuit 14 and the detection circuit 15 without passing through the preamplifier 18 or the high-pass filter 19.

[0098] Furthermore, two or more of the multiple components comprising the battery inspection device 10 may be implemented as a single circuit. Furthermore, these circuits are not limited to dedicated circuits and may also be general-purpose circuits. In particular, the circuit performing information processing may be a general-purpose circuit such as a processor that executes a program corresponding to the aforementioned processing.

[0099] Figure 2 Yes Figure 1 The flowchart of the operation of the battery inspection device 10 is shown. Figure 1 The multiple components of the battery inspection device 10 shown in FIG. Figure 2 The action shown.

[0100] First, the battery control circuit 11 applies an AC current of frequency f0 to the battery (S11). Specifically, the battery control circuit 11 applies an external voltage to the battery, which is a DC voltage superimposed with an AC voltage to balance the battery's output voltage.

[0101] The magnetic sensor 12 senses a magnetic field component when an alternating current is applied to the battery, and outputs a magnetic sensor signal indicating the sensed magnetic field component ( S12 ).

[0102] Feedback circuit 14 obtains a low-frequency signal lower than frequency f0 from the magnetic sensor signal (S13). Specifically, feedback circuit 14 obtains a low-frequency signal representing a magnetic field component having a frequency lower than frequency f0 of the AC current from the magnetic sensor signal output by magnetic sensor 12. Furthermore, feedback circuit 14 applies a current as input current to cancel coil 13 based on the low-frequency signal lower than frequency f0 (S14).

[0103] The cancellation coil 13 generates a magnetic field component based on the input current. Specifically, the cancellation coil 13 generates a low-frequency magnetic field component lower than the frequency f0, thereby canceling the low-frequency component lower than the frequency f0 from the magnetic field applied to the magnetic sensor 12 (S15). The detection circuit 15 obtains a detection signal having the frequency f0 from the magnetic sensor signal (S16). Specifically, the detection circuit 15 obtains a detection signal indicating a magnetic field component having the same frequency as the frequency f0 of the AC current from the magnetic sensor signal output by the magnetic sensor 12.

[0104] The battery control circuit 11, magnetic sensor 12, cancel coil 13, feedback circuit 14, and detection circuit 15 perform the above-described processing continuously and in parallel. Furthermore, when AC current is applied to the battery and input current is applied to the cancel coil 13, the magnetic sensor 12 senses magnetic field components at each of multiple locations around the battery and outputs a magnetic sensor signal representing the sensed magnetic field components.

[0105] When AC current is applied to the battery and input current is applied to the cancel coil 13 , the detection circuit 15 obtains magnetic sensor signals output by the magnetic sensor 12 at each of a plurality of positions around the battery and obtains a detection signal from the magnetic sensor signals.

[0106] After obtaining detection signals at all positions, for example, the imaging circuit 16 generates an image representing the battery state based on the detection signal of frequency f0 ( S17 ), and the display 17 displays the generated image ( S18 ).

[0107] Figure 3 Yes Figure 1 The schematic diagram of the specific structure of the battery inspection device 10 is shown. Figure 3 1 and 2 show a battery inspection device 10 and a battery 31. Figure 3 The battery inspection device 10 shown is Figure 1 The battery inspection device 10 shown corresponds to the specific example and includes a measuring unit 21 , a power supply unit 23 , a display 17 , and an information processing unit 24 .

[0108] For example, the power storage control circuit 11 is included in the power supply unit 23, and the imaging circuit 16 is included in the information processing unit 24. The feedback circuit 14 and the detection circuit 15 may each be included in the measurement unit 21, the information processing unit 24, or distributed in the measurement unit 21 and the information processing unit 24.

[0109] The measuring unit 21 includes a magnetic sensor 12 as a probe and a cancel coil 13 near the magnetic sensor 12. Furthermore, the measuring unit 21 measures the magnetic field using the magnetic sensor 12. Furthermore, the measuring unit 21 includes a sliding mechanism composed of an actuator, etc. Thus, the measuring unit 21 can scan the vicinity of the battery 31 using the magnetic sensor 12.

[0110] The measuring unit 21 also includes a rotating table 22. The rotating table 22 is a table for placing the battery 31, which is the inspection object, and has a rotatable mechanism composed of an actuator, etc. Thus, the measuring unit 21 can scan the vicinity of the battery 31 at various rotation angles using the magnetic sensor 12.

[0111] For example, the magnetic sensor 12 is located inside the cancel coil 13 , and as the magnetic sensor 12 moves, the cancel coil 13 also moves.

[0112] Here, the battery 31 is rotated by the rotating table 22, but the measuring unit 21 may be rotated around the battery 31 to scan the vicinity of the battery 31 at various rotation angles.

[0113] The power supply unit 23 is a device that applies voltage and current to the battery 31. Specifically, the power supply unit 32 applies an external voltage obtained by superimposing an AC voltage on a DC voltage to the battery 31, thereby applying an AC current to the battery 31. The DC voltage is a voltage used to balance the output voltage of the battery. The power supply unit 23 can also be a function generator. Figure 3 In the example of FIG, the power supply unit 23 applies voltage and current to the battery 31 via a lead wire.

[0114] The information processing unit 24 is a device that performs information processing. For example, the information processing unit 24 is a computer.

[0115] Specifically, the information processing unit 24 can apply current as input current to the cancel coil 13 based on the magnetic signal output from the magnetic sensor 12 via the measuring unit 21 or the like. In this case, the information processing unit 24 obtains a low-frequency signal representing a magnetic field component having a frequency lower than that of the AC current from the magnetic sensor signal output by the magnetic sensor 12 when AC current is applied to the battery 31. Furthermore, the information processing unit 24 can apply current as input current to the cancel coil 13 based on the low-frequency signal.

[0116] Furthermore, for example, the information processing unit 24 may also perform detection processing. Specifically, the information processing unit 24 obtains a detection signal indicating a magnetic field component having the same frequency as the frequency of the AC current from the magnetic sensor signal output by the magnetic sensor 12 when an AC current is applied to the battery 31 and an input current is applied to the cancel coil 13.

[0117] Furthermore, for example, the information processing unit 24 may generate an image representing the state of the battery 31 based on the detection signal. Furthermore, the information processing unit 24 may display the generated image on the display 17.

[0118] The battery 31 inspected by the battery inspection device 10 is a lithium battery or lithium-ion battery, for example. The battery 31 has a pair of electrode terminals 32 and 33. Each of the electrode terminals 32 and 33 is connected to the power supply unit 23 via a wire. While the power supply unit 23 applies alternating current to the battery 31, the measuring unit 21 measures the magnetic field using the magnetic sensor 12.

[0119] In addition, Figure 1 The specific example of the battery inspection device 10 shown is not limited to Figure 3 For example, some components may be omitted or other components may be added. Figure 3 Some or all of the illustrated measuring unit 21 , power supply unit 23 , display 17 , and information processing unit 24 may have an integrated structure.

[0120] Figure 4 Yes Figure 3 A conceptual diagram showing a specific structure of the magnetic sensor 12 is shown. The magnetic sensor 12 is composed of a TMR (Tunneling Magneto Resistive) element.

[0121] In a TMR element, an insulating film is sandwiched between magnetic films with a thickness of approximately 10 to 100 nm. More specifically, the TMR element is composed of multiple thin films: a soft layer 25, a tunnel layer 26, and a PIN layer (magnetization pinned layer) 27. The soft layer 25 is a magnetic film whose magnetization direction fluctuates according to the direction of external magnetization. The PIN layer 27 is a magnetic film whose magnetization direction remains fixed. Furthermore, the tunnel layer 26 is an insulating film.

[0122] The resistance is different when the direction of magnetization in the soft layer 25 is the same as that in the PIN layer 27 and when the directions are different. The magnetic field component can be sensed by utilizing this change in resistance.

[0123] For example, the magnetic sensor 12 utilizes these characteristics to sense and measure magnetic field components. Furthermore, the magnetic sensor 12 is not limited to the aforementioned example of a TMR element; it may also be composed of other elements such as a GMR (Giant Magneto Resistive) element or a SQUID (Superconducting Quantum Interference Device) element.

[0124] Figure 5 Yes Figure 3 The schematic diagram of the battery 31 being inspected is shown. Figure 5The illustrated battery 31 includes a pair of electrode terminals 32 and 33 , a pair of electrode plates 34 and 35 , an electrolyte 37 , and a metal package 38 . The pair of electrode plates 34 and 35 and the electrolyte 37 are covered by the metal package 38 .

[0125] For example, the magnetic sensor 12 senses magnetic field components at multiple locations on the scanning surface 41 above the battery 31 placed on the rotating stage 22. The scanning surface 41 is also referred to as the measurement surface. The magnetic sensor 12 can sequentially move to multiple locations on the scanning surface 41 to sense magnetic field components. This allows information on the magnetic field components of the scanning surface 41 to be obtained.

[0126] For example, the magnetic sensor 12 may also sense a magnetic field component at each of multiple locations on multiple scanning surfaces 41. Specifically, the magnetic sensor 12 may sense a magnetic field component at each of multiple locations on one scanning surface 41, and then sense a magnetic field component at each of multiple locations on another scanning surface 41. Thus, information on the magnetic field of each scanning surface 41 is obtained.

[0127] Furthermore, based on the magnetic field information of the multiple scan target surfaces 41, the magnetic field information of the reconstruction target surface 42, which is different from the scan target surfaces 41, can be calculated. For example, the reconstruction target surface 42 can be the surface corresponding to the upper surface of the electrode plate 34. Specifically, the magnetic field information of the multiple scan target surfaces 41 and Maxwell's equations can be used to calculate the magnetic field information of the reconstruction target surface 42. In addition, the conductivity distribution of the battery 31 can be calculated using the magnetic field information of the multiple scan target surfaces 41 or the reconstruction target surface 42 and Maxwell's equations.

[0128] The above calculation process can be performed by Figure 3 The information processing unit 24 can also be used Figure 1 The image generation processing circuit may perform the operation, or other components may perform the operation.

[0129] The current flowing inside battery 31 generates a magnetic field component outside battery 31. Magnetic sensor 12 senses the magnetic field component generated outside battery 31 by the current flowing inside battery 31. As the current flowing inside battery 31 changes, the magnetic field component outside battery 31 also changes.

[0130] For example, during the charge and discharge process of the battery 31 , metal may be precipitated from the electrode plate 34 or the electrode plate 35 , causing dendrites 36 to be generated and grow inside the battery 31 .

[0131] Dendrites 36 have a higher conductivity than the electrolyte 37. Therefore, when dendrites 36 form inside battery 31, the electrical state inside battery 31 changes. Consequently, the magnetic field components outside battery 31 also change. For example, battery inspection device 10 can detect the formation and growth of dendrites 36 by sensing the magnetic field components outside battery 31.

[0132] On the other hand, as dendrites 36 form and grow, the electrical state inside battery 31 changes, causing changes in the magnetic field components outside battery 31. Sensing magnetic field components at multiple locations outside battery 31 takes time, and it is not easy to sense magnetic field components that change over time over a wide range and with high resolution.

[0133] Furthermore, by stopping the charge and discharge of the battery 31 and suppressing the generation and growth of dendrites 36, changes in the internal electrical state of the battery 31 can also be suppressed. However, when the charge and discharge of the battery 31 is stopped, no magnetic field components based on the internal electrical state of the battery 31 are generated. Therefore, in this state, it is difficult to inspect the generation and growth of dendrites 36.

[0134] The battery control circuit 10 then applies an external voltage to the battery 31, which is a DC voltage superimposed with an AC voltage balanced with the output voltage of the battery 31. This allows the AC current to flow through the battery 31 while suppressing the formation and growth of dendrites 36. The AC current flowing through the battery 31 generates a magnetic field component based on the internal electrical state of the battery 31.

[0135] The battery inspection device 10 can detect the generation and growth of dendrites 36 by sensing the magnetic field components generated by the alternating current flowing through the battery 31. Furthermore, by extracting the magnetic field components corresponding to the frequency of the alternating current, the battery inspection device 10 can extract magnetic field components related to the internal electrical state of the battery 31. Therefore, the battery inspection device 10 can appropriately inspect the internal electrical state of the battery 31.

[0136] However, when the frequency of the AC current is high, the magnetic field component generated by the AC current is shielded by the shielding parts such as the electrode plates 34 and 35 and the metal package 38, and does not leak to the outside of the battery 31. Therefore, for example, the AC voltage and AC current use a frequency lower than the specified frequency. Here, the conductivity of the shielding part is σ s , the magnetic permeability of the shielding part is μ s , the thickness of the shielding part is ds In the case of s μ s d s 2 ). Thus, a magnetic field component is generated outside the battery 31.

[0137] Furthermore, to suppress the effects of charging and discharging and shorten the measurement time of the magnetic field component corresponding to the frequency of the AC current, a frequency lower than the specified frequency but higher than 1 / 2 of the specified frequency may be used. Alternatively, a frequency lower than the specified frequency but higher than 1 / 10 of the specified frequency may be used. Furthermore, to more reliably generate a magnetic field component outside of battery 31, a frequency lower than 1 / 2 of the specified frequency or lower than 1 / 10 of the specified frequency may be used.

[0138] Figure 6 It means to apply to Figure 3 Graph showing changes in the current of battery 31. In this example, battery inspection device 10 applies a DC voltage to battery 31 for charging battery 31 until time T1, thereby applying a DC current to battery 31. Furthermore, from time T1 to time T2, battery inspection device 10 applies a superimposed voltage, obtained by superimposing an AC voltage on the DC voltage to balance the output voltage of battery 31, thereby applying an AC current to battery 31.

[0139] Furthermore, from time T2 to time T3, the battery inspection device 10 applies a DC voltage for charging to the battery 31, thereby applying a DC current to the battery 31. Furthermore, from time t3 to time T4, the battery inspection device 10 applies a superimposed voltage, a voltage for achieving balance, to the battery 31 by superimposing an AC voltage on a DC voltage, thereby applying an AC current to the battery 31. Furthermore, from time T4, the battery inspection device 10 applies a DC voltage for charging to the battery 31, thereby applying a DC current to the battery 31.

[0140] Thus, the battery 31 is charged until time T1. Furthermore, the charging of the battery 31 is suppressed from time T1 to time T2. Furthermore, the battery 31 is charged from time T2 to time T3. Furthermore, the charging of the battery 31 is suppressed from time T3 to time T4. Furthermore, the battery 31 is charged from time T4.

[0141] Furthermore, while charging is in progress, dendrites 36 grow. Furthermore, while charging is suppressed, the growth of dendrites 36 stops. The battery inspection device 10 senses the magnetic field components surrounding the battery 31 during the period when dendrites 36 stop growing. Specifically, the battery inspection device 10 senses the magnetic field components surrounding the battery 31 while AC current is being applied to the battery 31.

[0142] Figure 7 Yes Figure 3 A graph showing changes in the charge rate of the battery 31 is shown. Figure 7 For example, with Figure 6 The example corresponds to. Figure 7 The vertical axis uses the storage rate instead of current. Figure 6 As described above, the charge rate increases during charging. Furthermore, the increase in charge rate is suppressed during charging. The battery inspection device 10 senses the magnetic field component during the period when the increase in charge rate is suppressed, thereby enabling inspection of dendrite 36 growth during the charging process.

[0143] Furthermore, the battery inspection device 10 can sense magnetic field components during each of multiple periods during the charging process when the increase in the charge rate is suppressed, and generate an image representing the state of the battery 31 based on the sensed magnetic field components. In other words, the battery inspection device 10 can generate multiple images corresponding to multiple moments during the charging process. Thus, the battery inspection device 10 can generate an image of the growth process of the dendrite 36.

[0144] In addition, Figure 6 as well as Figure 7 The figure shows the changes corresponding to the charging process. However, the battery inspection device 10 can perform the same operations during the discharge process as during the charging process. Furthermore, the battery 31 can be inspected regardless of whether the battery is charging or discharging. In other words, the battery inspection device 10 applies an AC current to the battery 31, senses the magnetic field components outside the battery 31, and generates an image representing the battery 31's condition based on the sensed magnetic field components, regardless of whether the battery is charging or discharging.

[0145] Figure 8 Yes Figure 1 A conceptual diagram of the overall structure of the battery inspection device 10 is shown. The battery control circuit 11 applies a superimposed voltage of AC and DC voltages to the battery 31. The DC voltage is a voltage used to balance the output voltage (also called the discharge voltage) of the battery 31 and is a compensation voltage used to maintain the state of charge of the battery 31. Specifically, the magnitude of the DC voltage is the same as the output voltage of the battery 31. This suppresses the charging and discharging of the battery 31.

[0146] A superimposed voltage of AC voltage and DC voltage is applied to battery 31, thereby applying AC current to battery 31. For example, an AC current of approximately 0.1 Hz to 10 Hz is applied to battery 31. Furthermore, the AC current applied to battery 31 generates a magnetic field component outside battery 31.

[0147] The magnetic sensor 12 senses a magnetic field component generated outside the battery 31 . The magnetic sensor 12 scans a two-dimensional plane perpendicular to the direction toward the battery 31 .

[0148] On the other hand, residual magnetization of the magnetic material in battery 31 can also generate a magnetic field component outside battery 31. When magnetic sensor 12 is affected by the magnetic field component generated by the residual magnetization of the magnetic material in battery 31, it becomes difficult to properly sense the magnetic field component generated by the AC current applied to battery 31.

[0149] The cancel coil 13 then generates a magnetic field component based on the input current. This generated magnetic field component cancels the magnetic field component generated by residual magnetization. The input current is the current applied to the cancel coil 13 by the feedback circuit 14. This input current is also called the feedback current.

[0150] The feedback circuit 14 includes a signal processing circuit 51 and a current amplifier circuit 52. The signal processing circuit 51 receives the magnetic sensor signal output by the magnetic sensor 12 and amplified by the preamplifier 18, and outputs a control signal to the current amplifier circuit 52. For example, the signal processing circuit 51 obtains a low-frequency signal from the magnetic sensor signal. This low-frequency signal indicates a magnetic field component with a frequency lower than that of the AC current. Based on the low-frequency signal, the signal processing circuit 51 outputs a control signal indicating the magnitude of the feedback current to be applied to the cancel coil 13.

[0151] Specifically, the signal processing circuit 51 outputs a control signal with a larger value as the magnetic field component of the low-frequency signal becomes larger. The magnetic field component of the low-frequency signal shows a magnetic field component with a frequency lower than the frequency of the alternating current, and the value of the control signal represents the magnitude of the feedback current.

[0152] The current amplifier circuit 52 applies a feedback current having a magnitude indicated by the control signal output from the signal processing circuit 51 to the cancel coil 13. This feedback current generates a magnetic field component based on a magnetic field component having a frequency lower than that of the alternating current. This generated magnetic field component cancels the magnetic field component generated by residual magnetization.

[0153] The magnetic field component generated by residual magnetization can be assumed to be composed of a magnetic field component with a frequency lower than that of the alternating current. Therefore, by generating a magnetic field component based on the magnetic field component with a frequency lower than that of the alternating current, the battery inspection device 10 can generate a magnetic field component of the same magnitude as the magnetic field component generated by residual magnetization. Consequently, the battery inspection device 10 can appropriately cancel the magnetic field component generated by residual magnetization.

[0154] The detection circuit 15 obtains a magnetic sensor signal from the magnetic sensor 12. For example, the detection circuit 15 obtains a magnetic sensor signal from the magnetic sensor 12 that has been amplified by the preamplifier 18 and the high-pass filter 19 and has had its low-frequency components removed. Furthermore, the detection circuit 15 obtains a reference signal from the power storage control circuit 11. Here, the reference signal represents the voltage or current applied to the battery 31.

[0155] Specifically, the reference signal can be an analog signal having the same frequency and phase as the AC voltage superimposed on the DC voltage in the power storage control circuit 11, or the AC current applied to the battery 31. Furthermore, the reference signal can be the same as the AC signal applied to the battery 31. In other words, the reference signal can be an analog signal having the same voltage and current as the voltage and current applied to the battery 31. Alternatively, the reference signal can be an analog signal or a digital signal representing information about the voltage or current applied to the battery 31.

[0156] The detection circuit 15 obtains, as a detection signal, a signal indicating a magnetic field component having the same frequency as the frequency of the AC current applied to the battery 31 based on the magnetic sensor signal and the reference signal.

[0157] The imaging circuit 16 generates an image representing the state of the battery 31 based on the detection signal obtained by the detection circuit 15. This image can represent the magnetic field components near the surface of the battery 31 or the conductivity distribution of the battery 31 as the state of the battery 31. The imaging circuit 16 then outputs an image signal representing the generated image to the display 17.

[0158] The display 17 displays an image showing the state of the battery 31 based on the image signal output from the imaging circuit 16 .

[0159] Figure 9 Yes Figure 8 FIG. 1 is a block diagram showing the structure of the feedback circuit 14. Figure 9As shown, the magnetic sensor 12 senses a magnetic field component and outputs a magnetic sensor signal representing the sensed magnetic field component. For example, the strength of the magnetic sensor signal is proportional to the strength of the magnetic field component. A stronger magnetic field component results in a stronger magnetic sensor signal. The frequency characteristics of the magnetic sensor signal are consistent with the frequency characteristics of the magnetic field component.

[0160] The signal processing circuit 51 in the feedback circuit 14 applies a low-pass filter (LPF) to the magnetic sensor signal output from the magnetic sensor 12 and amplified by the preamplifier 18. The cutoff frequency (f cut ), a frequency lower than the detection frequency (f0) is used. The cutoff frequency of a low-pass filter is also called the cutoff frequency. The detection frequency is the frequency of the AC current applied to the battery 31.

[0161] Therefore, the signal processing circuit 51 can obtain a low-frequency signal representing a magnetic field component having a frequency lower than the frequency of the AC current applied to the battery 31 .

[0162] Furthermore, if the low-pass filter's cutoff frequency is too low, it is assumed that low-pass filter processing will take time. For example, a processing delay corresponding to the period of the cutoff frequency (the inverse of the cutoff frequency) may occur. Therefore, the cutoff frequency can be set to be approximately the same as the detection frequency.

[0163] On the other hand, it is conceivable that errors may occur during processing related to the low-pass filter or the detection of magnetic field components. To this end, the cutoff frequency can be set to 1 / 10 of the detection frequency to ensure that even if errors occur, detection can be performed appropriately (obtaining a magnetic field component with the same frequency as the AC current). Alternatively, the cutoff frequency can be set to 1 / 10 or more of the detection frequency, depending on the balance between error and delay.

[0164] Therefore, the signal processing circuit 51 can appropriately obtain a low-frequency signal indicating a magnetic field component having a frequency lower than the frequency of the AC current flowing through the battery 31 while suppressing processing delay in the low-pass filter.

[0165] Furthermore, the signal processing circuit 51 generates a control signal for making the intensity of the low-frequency signal close to the target value through PID (Proportional-Integral-Differential) control. For example, the control signal represents a feedback current (I f ) size.

[0166] PID control is a feedback control method that uses the deviation between the measured value and the target value, the integral of the deviation, and the differential of the deviation to bring the continuously acquired measured value closer to the target value. For example, the target value can be the intensity of a low-frequency signal obtained when the magnetic field component is zero.

[0167] The operation of controlling the magnitude of the feedback current through PID control has been described with a focus on signal strength. If the focus is on the strength of the magnetic field component, the operation can be viewed as an operation to bring the strength of the magnetic field component indicated by the low-frequency signal closer to a target value. In this case, the target value can be zero. When battery 31 is not present or when battery 31 does not generate a magnetic field component, the strength of the magnetic field component sensed by magnetic sensor 12 can be set to zero.

[0168] For example, signal processing circuit 51 generates a control signal indicating the magnitude of a feedback current used to bring the intensity of the magnetic field component represented by the low-frequency signal close to zero. Furthermore, signal processing circuit 51 outputs a control signal to current amplifier circuit 52, which applies the feedback current to cancel coil 13 in accordance with the control signal.

[0169] Thus, battery inspection device 10 can reduce the intensity of magnetic field components at frequencies lower than the frequency of the alternating current applied to battery 31 and lower than the cutoff frequency of the low-pass filter to near zero. In other words, battery inspection device 10 can eliminate magnetic field components generated by the magnetization of the magnetic material in battery 31.

[0170] Figure 10 Yes Figure 9 FIG. 5 is a block diagram showing the structure of the signal processing circuit 51. Figure 10 In the example of , the signal processing circuit 51 includes an ADC (analog-to-digital converter) 61 , a low-pass filter 62 , a subtractor 63 , a PID operator 64 , an adder 65 , and a DAC (digital-to-analog converter) 66 .

[0171] The ADC 61 is a converter for converting analog signals into digital signals. A 16-bit AD converter or the like can be used as the ADC 61. The ADC 61 obtains the magnetic sensor signal output from the magnetic sensor 12 as an analog signal and converts the obtained magnetic sensor signal as an analog signal into a digital signal.

[0172] The low-pass filter 62 is a filter that cuts off frequency components higher than the cutoff frequency and passes frequency components lower than the cutoff frequency. The cutoff frequency of the low-pass filter 62 is suitable for a frequency lower than the frequency of the AC current applied to the battery 31. For example, the low-pass filter 62 averages the magnetic sensor signal over a period longer than the inverse of the detection frequency, in other words, longer than the period of the AC current applied to the battery 31, and outputs the averaged magnetic sensor signal.

[0173] Therefore, low-pass filter 62 allows components of the magnetic sensor signal with frequencies lower than the frequency of the AC current to pass through. In other words, a low-frequency signal representing a magnetic field component with a frequency lower than the frequency of the AC current applied to battery 31 is output from low-pass filter 62. The period used to average the magnetic sensor signal is also referred to as the accumulation time.

[0174] Here, "cutting off" frequency components higher than the cutoff frequency means suppressing the passage of frequency components higher than the cutoff frequency, and is not limited to completely cutting off frequency components higher than the cutoff frequency. Similarly, "allowing the passage of frequency components lower than the cutoff frequency" means suppressing the passage of frequency components lower than the cutoff frequency, and is not limited to completely passing frequency components lower than the cutoff frequency. The degree of cutoff and passing depends on the quality of low-pass filter 62.

[0175] Furthermore, the low-pass filter 62 may cut off or pass the component having the same cutoff frequency, or may cut off a portion of the component having the same cutoff frequency and pass the other portion.

[0176] Subtractor 63 is a computing unit that calculates the difference between the two signals. Specifically, subtractor 63 subtracts the low-frequency signal output by low-pass filter 62 from the input target value to calculate the difference as the deviation e(t). Here, t represents time. The input target value is the low-frequency signal when the intensity of the magnetic field component is zero.

[0177] The PID operator 64 is an operator that calculates the proportional term, integral term, and differential term of the deviation. Specifically, the PID operator 64 calculates the proportional term of the deviation e(t), the integral term of the deviation e(t) related to time t, and the differential term of the deviation e(t) related to time t. The proportional term is calculated by the deviation e(t) and the proportional gain K P The integral term is composed of the integral of the deviation e(t) related to time t and the integral gain K I The differential term is composed of the differential of the deviation e(t) related to time t and the differential gain K D Multiply to form.

[0178] The proportional term corresponds to the deviation e(t) itself and is associated with the current value of the deviation e(t). The integral term corresponds to the accumulation of the deviation e(t) and is associated with the actual value of the deviation e(t) in the past. The differential term corresponds to the change in the deviation e(t) and is associated with the predicted value of the deviation e(t) in the future.

[0179] The adder 65 is a computing unit that calculates the sum of multiple signals. Specifically, the adder 65 calculates the control signal as the sum of the proportional term of the deviation e(t), the integral term of the deviation e(t) with respect to time t, and the differential term of the deviation e(t) with respect to time t.

[0180] The DAC 66 is a converter for converting a digital signal into an analog signal. A 16-bit DA converter or the like can be used as the DAC 66. The DAC 66 obtains the control signal calculated by the adder 65 as a digital signal and converts the control signal obtained as a digital signal into an analog signal.

[0181] The control signal converted into an analog signal by the DAC 66 is input to the current amplifier circuit 52. The current amplifier circuit 52 then applies a feedback current having a magnitude corresponding to the sum of the proportional term, the integral term, and the differential term of the deviation to the cancel coil 13.

[0182] Thus, the battery inspection device 10 can reduce the deviation e(t) to zero using the proportional, integral, and differential terms corresponding to the current, actual, and predicted values ​​of the deviation e(t). Furthermore, the battery inspection device 10 can reduce the intensity of the magnetic field component at a frequency lower than the frequency of the AC current to near zero, thereby suppressing the effects of residual magnetization on the battery 31.

[0183] For example, regarding the proportional gain K in the above description P , integral gain K I and the differential gain K D Each of the differential gain K can use a value different from zero or zero. D Use zero so that PID control can be performed as PI control. In addition, the integral gain K I Zero is used so that PID control can be performed as PD control.

[0184] In the above description, a digital circuit system is used for the low-pass filter and PID control of the signal processing circuit 51. However, an analog circuit system may also be used for the low-pass filter and PID control of the signal processing circuit 51.

[0185] In other words, the low-pass filter 62, subtractor 63, PID calculator 64, and adder 65 can be constructed using analog circuits. Furthermore, the signal processing circuit 51 can apply the low-pass filter and PID control to the analog magnetic sensor signal without converting it to a digital signal. This allows the battery testing device 10 to quickly control the feedback current using the analog signal as is.

[0186] Figure 11 Yes Figure 8 FIG. 1 is a block diagram showing the structure of the detection circuit 15. Figure 11 In the example shown, detection circuit 15 includes a DI (direct injection box) 71, an ADC (analog-to-digital converter) 72, a mixer 73, and a low-pass filter 74 to perform phase detection. While this example illustrates phase detection, detection circuit 15 may also utilize other methods to obtain a detection signal.

[0187] DI71 is an impedance converter. Specifically, DI71 receives a reference signal output from the power storage control circuit 11, adjusts the voltage and current ratio of the reference signal, and generates a reference signal for phase detection. For example, the reference signal is generated as a digital signal.

[0188] The ADC 72 is a converter for converting analog signals into digital signals. A 16-bit AD converter or the like can be used as the ADC 72. The ADC 72 obtains the magnetic sensor signal output from the magnetic sensor 12 as an analog signal and converts the obtained magnetic sensor signal as an analog signal into a digital signal.

[0189] Mixer 73 is a circuit that mixes multiple signals. Specifically, mixer 73 multiplies the reference signal generated by DI 71 with the magnetic sensor signal converted to a digital signal by ADC 72, and outputs the result of the multiplication as a multiplication result signal. The DC component of the multiplication result signal corresponds to the magnetic field component with the same frequency as the AC current.

[0190] Low-pass filter 74 is a filter that blocks frequency components higher than the cutoff frequency and passes frequency components lower than the cutoff frequency. Low-pass filter 74 receives the multiplication result signal, blocks the AC component of the multiplication result signal, and passes the DC component of the multiplication result signal. Consequently, low-pass filter 74 outputs a detection signal corresponding to the magnetic field component at the same frequency as the AC current.

[0191] The detection circuit 15 stores the detection signal in the memory circuit 75. In the above example, a digital circuit method is used in the detection circuit 15, but an analog circuit method can also be used in the detection circuit 15. In other words, the detection circuit 15 can detect the magnetic sensor signal as an analog signal to obtain a detection signal indicating a magnetic field component with the same frequency as the alternating current.

[0192] The imaging circuit 16 generates an image showing the state of the battery 31 based on the detection signal stored in the memory circuit 75. The imaging circuit 16 can generate an image showing the conductivity distribution inside the battery 31 as the state of the battery 31. Figure 12 as well as Figure 13 An example in which the imaging circuit 16 derives the conductivity distribution inside the battery 31 will be described.

[0193] Figure 12 It means used for Figure 11 The diagram shows a conceptual diagram of a coordinate system for the imaging performed by the imaging circuit 16. Figure 12 The relationship between the battery 31 and the coordinate system is shown in FIG. The x-direction and the y-direction are two directions parallel to the planar electrode plates included in the battery 31 and are two directions perpendicular to each other. The z-direction is a direction perpendicular to the x-direction and the y-direction.

[0194] Figure 13 Yes Figure 12 A conceptual diagram showing the current flowing during battery 31 inspection is shown. Battery 31 has a pair of planar electrode plates 34 and 35, each corresponding to a single layer of lithium-ion battery cells. Electrode plate 34 is connected to electrode terminal 32, and electrode plate 35 is connected to electrode terminal 33. While AC current is flowing through battery 31, battery inspection device 10 uses magnetic sensor 12 to sense magnetic field components on scanning surface 41 above battery 31.

[0195] In addition, h represents the thickness of the electrode plate 34, h T represents the distance between a pair of electrode plates 34 and 35, j x represents the current in the x direction, j z represents the current in the z direction.

[0196] In this case, the following formula (1) holds true.

[0197] [Mathematical formula 1]

[0198]

[0199]

[0200]

[0201] Here, Δ represents an operator called Laplace operator or Laplace operator. In addition, H x represents the magnetic field component in the x direction, H y Indicates the magnetic field component in the y direction. represents the partial differential with respect to x, represents the partial differential with respect to y. Furthermore, σ(x, y) represents the conductivity distribution on the two-dimensional plane between the pair of electrode plates 34 and 35. Furthermore, σ0 represents the conductivity of electrode plate 34 and is a fixed value independent of the x- and y-coordinates. Furthermore, δ represents the δ function, and δ' represents the differential of the δ function. Furthermore, z0 represents the z coordinate of the center of electrode plate 34.

[0202] also,

[0203] [Mathematical formula 2]

[0204]

[0205] The potential distribution on a two-dimensional plane between the pair of electrode plates 34 and 35 is shown.

[0206] Based on formula (1), the following formula (2) is obtained.

[0207] [Mathematical formula 3]

[0208]

[0209]

[0210]

[0211] here,

[0212] [Formula 4]

[0213]

[0214] express

[0215] [Formula 5]

[0216]

[0217] The Fourier transformed function of the x-direction and y-direction, k x represents the wave number of the magnetic field component in the x direction, k y represents the wave number of the magnetic field component in the y direction. In addition, Q x Indicates H x The Fourier transformed function of the x-direction and the y-direction, Qy Indicates H y The Fourier transformed function of the x-direction and the y-direction.

[0218] Furthermore, Q x and Q y The following formula (3) is satisfied.

[0219] [Formula 6]

[0220]

[0221]

[0222] For example, the imaging circuit 16 derives the conductivity distribution σ(x, y) from the detection signal representing the magnetic field component generated by the AC current using equations (2) and (3), and generates an image representing the conductivity distribution σ(x, y).

[0223] The imaging circuit 16 may derive the conductivity distribution by a method different from the above. Alternatively, the imaging circuit 16 may generate an image representing the intensity distribution of the magnetic field component indicated by the detection signal instead of deriving the conductivity distribution.

[0224] Figure 14 It is used for sensing and Figure 8 The diagram shows a conceptual example of a case where the magnetic sensor 12 for detecting a magnetic field component perpendicular to a planar electrode plate in a battery 31 is located inside the cancel coil 13 .

[0225] exist Figure 14 In the example shown, magnetic sensor 12 is located inside cancel coil 13. Consequently, cancel coil 13 can generate a magnetic field component at the location of magnetic sensor 12 that cancels the magnetic field component generated by the magnetization of the magnetic body of battery 31. Therefore, battery inspection device 10 can cancel the magnetic field component generated by the magnetization of the magnetic body of battery 31 at the location of magnetic sensor 12, enabling accurate detection of the magnetic field component generated by AC power.

[0226] In addition, Figure 14 In the example, the central axis of the elimination coil 13 is perpendicular to the planar electrode plates in the battery 31 .

[0227] Thus, cancel coil 13 can generate a magnetic field component perpendicular to the planar electrode plates in battery 31 as a magnetic field component for canceling the magnetic field component generated by the magnetization of the magnetic body in battery 31. Consequently, battery inspection device 10 can cancel the magnetic field component generated by the magnetization of the magnetic body in battery 31 perpendicular to the planar electrode plates in battery 31, and can appropriately sense the magnetic field component generated by AC power.

[0228] Furthermore, the battery inspection device 10 can appropriately sense a magnetic field component that is affected when, for example, a hole is formed in a conductor of the battery 31 due to a crack.

[0229] Figure 15 It is used for sensing and Figure 8 The diagram shows a conceptual example of a case where the magnetic sensor 12 for the magnetic field component in the direction parallel to the planar electrode plates of the battery 31 is located inside the cancel coil 13 .

[0230] exist Figure 15 In the example, with Figure 14 Similar to the example, magnetic sensor 12 is located inside cancellation coil 13. Consequently, cancellation coil 13 can generate a magnetic field component at the location of magnetic sensor 12 that cancels the magnetic field component generated by the magnetization of the magnetic body of battery 31. Therefore, battery inspection device 10 can efficiently cancel the magnetic field component generated by the magnetization of the magnetic body of battery 31 at the location of magnetic sensor 12, and can appropriately sense the magnetic field component generated by AC power.

[0231] In addition, Figure 15 In the example, the central axis of the elimination coil 13 is parallel to the planar electrode plates in the battery 31 .

[0232] Therefore, the cancel coil 13 can generate a magnetic field component in a direction parallel to the planar electrode plates in the battery 31 as a magnetic field component for canceling the magnetic field component generated by the magnetization of the magnetic body of the battery 31. Therefore, the battery inspection device 10 can cancel the magnetic field component generated by the magnetization of the magnetic body of the battery 31 in a direction parallel to the planar electrode plates in the battery 31, and can appropriately sense the magnetic field component generated by the AC power.

[0233] In particular, it is conceivable that a magnetic field component parallel to the planar electrode plates of battery 31 is generated outside battery 31 to which an AC current is applied. Therefore, it is useful to cancel the magnetic field component generated by the magnetization of the magnetic body of battery 31 in a direction parallel to the planar electrode plates of battery 31 and to sense the magnetic field component generated by the AC power.

[0234] Figure 16 It is used for sensing and Figure 8 The diagram shows a conceptual example of a case where the magnetic sensor 12 is positioned outside the cancel coil 13 for detecting a magnetic field component perpendicular to the planar electrode plates of the battery 31 .

[0235] exist Figure 16 In this example, magnetic sensor 12 is located outside of cancel coil 13. Specifically, cancel coil 13 is positioned near magnetic sensor 12. In this case, cancel coil 13 can generate a magnetic field component that cancels the magnetic field component generated by the magnetization of the magnetic body of battery 31, even at a location separated from magnetic sensor 12. This allows for more flexible positioning of cancel coil 13.

[0236] In addition, Figure 16 In the example shown, the magnetic sensor 12 is located in a region on the central axis of the cancellation coil 13. Consequently, the cancellation coil 13 can generate a magnetic field component toward the magnetic sensor 12 that cancels the magnetic field component generated by the magnetization of the magnetic body of the battery 31. Consequently, the cancellation coil 13 can generate a magnetic field component near the magnetic sensor 12 that cancels the magnetic field component generated by the magnetization of the magnetic body of the battery 31.

[0237] In addition, Figure 16 In the example, with Figure 14 The same as the example, the central axis of the coil 13 is eliminated and is perpendicular to the planar electrode plates in the battery 31.

[0238] Therefore, the cancel coil 13 can generate a magnetic field component in a direction perpendicular to the planar electrode plates in the battery 31 as a magnetic field component for canceling the magnetic field component generated by the magnetization of the magnetic body of the battery 31. Therefore, the battery inspection device 10 can cancel the magnetic field component generated by the magnetization of the magnetic body of the battery 31 in a direction perpendicular to the planar electrode plates in the battery 31, and can appropriately sense the magnetic field component generated by the AC power.

[0239] Figure 17 It is used for sensing and Figure 8 The diagram shows a conceptual example of a case where the magnetic sensor 12 for the magnetic field component in the direction parallel to the planar electrode plates of the battery 31 is located outside the cancel coil 13 .

[0240] exist Figure 17 In the example, with Figure 16Similar to the example, magnetic sensor 12 is located outside of cancel coil 13. Specifically, cancel coil 13 is positioned near magnetic sensor 12. In this case, cancel coil 13 can also generate a magnetic field component that cancels the magnetic field component generated by the magnetization of the magnetic body of battery 31, even at a position separated from magnetic sensor 12. This allows for more flexible positioning of cancel coil 13.

[0241] In addition, Figure 17 In the example, magnetic sensor 12 is located in a region different from the region on the central axis of cancel coil 13. This allows the direction of the central axis of cancel coil 13 to be flexibly determined. Consequently, battery inspection device 10 can generate a flexibly directional magnetic field component at a location separated from magnetic sensor 12, serving as a magnetic field component for canceling the magnetic field component generated by the magnetization of the magnetic body of battery 31.

[0242] Moreover, in Figure 17 In the example, with Figure 15 The same as the example, the central axis of the coil 13 is eliminated and parallel to the planar electrode plates in the battery 31.

[0243] Therefore, the cancel coil 13 can generate a magnetic field component in a direction parallel to the planar electrode plates in the battery 31 as a magnetic field component for canceling the magnetic field component generated by the magnetization of the magnetic body of the battery 31. Therefore, the battery inspection device 10 can cancel the magnetic field component generated by the magnetization of the magnetic body of the battery 31 in a direction parallel to the planar electrode plates in the battery 31, and can appropriately sense the magnetic field component generated by the AC power.

[0244] Figure 18 It means that the plurality of magnetic sensors 12 sense the Figure 8 A conceptual diagram showing an example of a case where a magnetic field component is perpendicular to a planar electrode plate in a battery 31.

[0245] exist Figure 18 In the example shown, a battery inspection device 10 includes multiple magnetic sensors 12 and multiple cancel coils 13 corresponding to each of the multiple magnetic sensors 12. Specifically, the multiple cancel coils 13 correspond one-to-one to the multiple magnetic sensors 12. A feedback circuit 14 of the battery inspection device 10 obtains a low-frequency signal from the magnetic sensor signal output by each magnetic sensor 12 and applies a feedback current based on the low-frequency signal to the cancel coil 13 corresponding to the magnetic sensor 12.

[0246] Therefore, the battery inspection device 10 can appropriately sense a wide range of magnetic field components in a short period of time.

[0247] In addition, Figure 18 In the example, multiple magnetic sensors 12 are arranged in a matrix to cover the top surface of the battery 31. In other words, the multiple magnetic sensors 12 are arranged in a matrix on the measurement surface. Furthermore, multiple cancel coils 13, each corresponding to the multiple magnetic sensors 12, are positioned above the multiple magnetic sensors 12. Furthermore, the central axis of each cancel coil 13 is perpendicular to the planar electrode plates of the battery 31.

[0248] Thus, each cancel coil 13 can generate a magnetic field component in a direction perpendicular to the planar electrode plates in the battery 31 as a magnetic field component for canceling the magnetic field component generated by the magnetization of the magnetic body of the battery 31. Consequently, the battery inspection device 10 can cancel the magnetic field component generated by the magnetization of the magnetic body of the battery 31 in a direction perpendicular to the planar electrode plates in the battery 31, and can appropriately sense the magnetic field component generated by the AC power.

[0249] Figure 19 It means that the plurality of magnetic sensors 12 sense the Figure 8 A conceptual diagram showing an example of a case where the magnetic field component is in a direction parallel to the planar electrode plates in the battery 31 is shown.

[0250] Figure 19 Examples with Figure 18 The example is substantially the same as that of , but the central axis of each cancel coil 13 is parallel to the planar electrode plate in the battery 31 .

[0251] Thus, the cancel coil 13 can generate a magnetic field component in a direction parallel to the planar electrode plates in the battery 31 as a magnetic field component for canceling the magnetic field component generated by the magnetization of the magnetic body of the battery 31. Therefore, the battery inspection device 10 can cancel the magnetic field component generated by the magnetization of the magnetic body of the battery 31 in a direction parallel to the planar electrode plates in the battery 31, and can appropriately sense the magnetic field component generated by the AC power.

[0252] Figure 20 It is used for sensing and Figure 8 The schematic diagram shows an example in which the magnetic sensor 12 for the magnetic field component in the direction parallel to the planar electrode plates of the battery 31 is located outside the cancel coil 13 and the central axis of the cancel coil 13 is perpendicular to the electrode plates.

[0253] exist Figure 20 In the example, with Figure 16 as well as Figure 17Similar to the example, magnetic sensor 12 is located outside of cancel coil 13. Specifically, cancel coil 13 is positioned obliquely above magnetic sensor 12. In this case, cancel coil 13, at a distance from magnetic sensor 12, can generate a magnetic field component that cancels the magnetic field component generated by the magnetization of the magnetic body of battery 313. This allows for greater flexibility in determining the position of cancel coil 13.

[0254] Figure 21 This is a conceptual diagram showing an example of a surrounding using a magnetic field component in an embodiment, specifically showing Figure 20 The relationship between the magnetic sensor 12 and the cancellation coil 13 is shown. Figure 21 As shown, the cancel coil 13 generates a magnetic field component in a direction parallel to the electrode plate near the magnetic sensor 12 .

[0255] In other words, the cancel coil 13 can generate a magnetic field component in a direction parallel to the planar electrodes of the battery 31, as a magnetic field component for canceling the magnetic field component generated by the magnetization of the magnetic body of the battery 31. Thus, the battery inspection device 10 can cancel the magnetic field component generated by the magnetization of the magnetic body of the battery 31 in a direction parallel to the planar electrode plates of the battery 31, and can appropriately sense the magnetic field component generated by the AC power.

[0256] While the battery inspection device has been described above based on the embodiments, the battery inspection device is not limited to the embodiments. The embodiments may be modified as conceived by those skilled in the art, and various components of the embodiments may be combined in any manner. For example, a process performed by a specific component in the embodiments may be replaced by another component. Furthermore, the order of multiple processes may be altered, or multiple processes may be executed in parallel.

[0257] Furthermore, the battery inspection method, including the steps performed by the various components of the battery inspection device, can be executed by any device or system. For example, part or all of the battery inspection method can be executed by a computer equipped with a processor, memory, and input / output circuits. In this case, the battery inspection method can be executed by the computer executing a program that causes the computer to execute the battery inspection method.

[0258] Furthermore, the program may be recorded on a non-transitory computer-readable recording medium.

[0259] Furthermore, the various components of the battery inspection device may be comprised of dedicated hardware, general-purpose hardware that executes the aforementioned program, or a combination of these. Furthermore, the general-purpose hardware may be comprised of a memory storing the program and a general-purpose processor that reads and executes the program from the memory. The memory may be a semiconductor memory or a hard disk, and the general-purpose processor may be a CPU.

[0260] Furthermore, the dedicated hardware may be composed of a memory and a dedicated processor, etc. For example, the dedicated processor may refer to the memory for recording the measurement data to execute the above-mentioned battery inspection method.

[0261] Furthermore, each component of the battery inspection device may be a circuit. These circuits may constitute a single circuit as a whole, or they may be separate circuits. Furthermore, these circuits may correspond to dedicated hardware or general-purpose hardware that executes the program, etc.

[0262] Industrial Applicability

[0263] One aspect of the present disclosure provides a storage battery inspection device for inspecting storage batteries, which can be applied to storage battery manufacturing systems and the like.

[0264] Explanation of symbols

[0265] 10 Battery inspection device

[0266] 11. Power storage control circuit

[0267] 12 Magnetic Sensor

[0268] 13 Eliminate coil

[0269] 14 Feedback Circuit

[0270] 15 Detection Circuit

[0271] 16 Imaging Circuit

[0272] 17 Display

[0273] 18 Preamplifier

[0274] 19 High-pass filter (HPF)

[0275] 21 Measurement Department

[0276] 22 Rotary Table

[0277] 23 Power Supply

[0278] 24 Information Processing Department

[0279] 25 soft layers

[0280] 26 Tunnel Layer

[0281] 27 PIN layer (magnetization pinned layer)

[0282] 31 batteries

[0283] 32, 33 electrode terminals

[0284] 34, 35 electrode plates

[0285] 36 dendrites

[0286] 37 Electrolytes

[0287] 38 metal package

[0288] 41 Scan object surface

[0289] 42 Reconstructing the object surface

[0290] 51 signal processing circuit

[0291] 52 Current amplifier circuit

[0292] 61, 72 Analog-to-digital converter (ADC)

[0293] 62, 74 low-pass filter

[0294] 63 Subtractor

[0295] 64 PID calculator

[0296] 65 Adder

[0297] 66 Digital-to-Analog Converter (DAC)

[0298] 71 Direct Injection Tank (DI)

[0299] 73 Mixer

[0300] 75 Memory Circuit

Claims

1. A battery inspection device is a device for inspecting batteries, comprising: a power storage control circuit for applying an external voltage to the battery, which is a voltage obtained by superimposing an AC voltage on a DC voltage to balance the output voltage of the battery, thereby applying an AC current to the battery; a magnetic sensor configured to sense a magnetic field component external to the battery that is parallel to a planar electrode plate included in the battery and output a magnetic sensor signal representing the sensed magnetic field component; a cancellation coil for generating a magnetic field component based on an input current, the generated magnetic field component being used to cancel a magnetic field component generated by magnetization of a magnetic body of the battery; a feedback circuit for obtaining a low-frequency signal from the magnetic sensor signal output by the magnetic sensor in a state where the AC current is applied to the battery, and applying the input current to the cancellation coil based on the low-frequency signal, the low-frequency signal indicating a magnetic field component having a frequency lower than that of the AC current; as well as a detection circuit for obtaining a detection signal showing a magnetic field component having the same frequency as that of the AC current from the magnetic sensor signal output by the magnetic sensor in a state where the AC current is applied to the battery and the input current is applied to the cancel coil, the detection signal being a detection signal. The central axis of the cancel coil is parallel to the planar electrode plate included in the battery.

2. The battery inspection device according to claim 1, The feedback circuit obtains the low-frequency signal from the magnetic sensor signal through a low-pass filter, wherein the low-pass filter is a filter that cuts off frequency components higher than a cutoff frequency and passes frequency components lower than the cutoff frequency. The cut-off frequency is lower than the frequency of the alternating current.

3. The battery inspection device according to claim 2, The cutoff frequency is 1 / 10 or more of the frequency of the alternating current.

4. The battery inspection device according to any one of claims 1 to 3, The feedback circuit uses a PID control method to control the magnitude of the input current so that the intensity of the magnetic field component shown by the low-frequency signal is close to the target value, and applies the input current with the controlled magnitude to the elimination coil. The PID control method is a proportional integral differential control method.

5. The battery inspection device according to claim 4, The target value is zero.

6. The battery inspection device according to any one of claims 1 to 3, The feedback circuit comprises: a signal processing circuit that obtains the low-frequency signal from the magnetic sensor signal output by the magnetic sensor when the AC current is applied to the battery, and outputs a control signal indicating the magnitude of the input current based on the low-frequency signal; and The current amplifying circuit applies the input current having a magnitude indicated by the control signal to the cancel coil.

7. The battery inspection device according to claim 6, The signal processing circuit converts the magnetic sensor signal output from the magnetic sensor as an analog signal into a digital signal, obtains the low-frequency signal from the magnetic sensor signal converted into the digital signal, generates the control signal based on the low-frequency signal, converts the generated control signal into an analog signal, and outputs the control signal converted into the analog signal.

8. The battery inspection device according to claim 6, The signal processing circuit does not convert the magnetic sensor signal output from the magnetic sensor as an analog signal into a digital signal, but instead obtains the low-frequency signal from the magnetic sensor signal output from the magnetic sensor as an analog signal, generates the control signal based on the low-frequency signal, and outputs the generated control signal.

9. The battery inspection device according to any one of claims 1 to 3, The magnetic sensor is located inside the cancel coil.

10. The battery inspection device according to any one of claims 1 to 3, The magnetic sensor is located outside the cancellation coil.

11. The battery inspection device according to any one of claims 1 to 3, The magnetic sensor is located in a region on a central axis of the cancel coil.

12. The battery inspection device according to any one of claims 1 to 3, The magnetic sensor is located in a region different from a region on a central axis of the cancel coil.

13. The battery inspection device according to any one of claims 1 to 3, The battery inspection device comprises: a plurality of magnetic sensors as the magnetic sensors, and A plurality of cancel coils as the cancel coils, each of the plurality of cancel coils corresponding to each of the plurality of magnetic sensors, The feedback circuit obtains the low-frequency signal from the magnetic sensor signal output by each of the plurality of magnetic sensors, and applies the input current to the cancel coil corresponding to the magnetic sensor among the plurality of cancel coils according to the low-frequency signal.

14. A battery inspection method, comprising: By applying an external voltage obtained by superimposing an AC voltage on a DC voltage to the battery, an AC current is applied to the battery, wherein the DC voltage is a voltage for balancing the output voltage of the battery. In a state where the alternating current is applied to the battery, a low-frequency signal is obtained from a magnetic sensor signal output by a magnetic sensor, the low-frequency signal indicating a magnetic field component having a frequency lower than the frequency of the alternating current, the magnetic sensor being a sensor that senses a magnetic field component external to the battery and parallel to a planar electrode plate included in the battery, and outputs the magnetic sensor signal indicating the sensed magnetic field component. applying the input current to a cancellation coil that generates a magnetic field component based on the input current according to the low-frequency signal, the generated magnetic field component canceling a magnetic field component generated by magnetization of a magnetic body of the battery; obtaining a detection signal showing a magnetic field component having the same frequency as that of the AC current from the magnetic sensor signal output by the magnetic sensor in a state where the AC current is applied to the battery and the input current is applied to the cancel coil, The central axis of the cancel coil is parallel to the planar electrode plate included in the battery.

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