Method and system for diagnosing abnormal single cell of battery pack

Abstract

The invention relates to a method and system for diagnosing an abnormal single cell of a battery pack in the technical field of batteries, the system comprises a diagnosis circuit and a BMS, the diagnosis method comprises the following steps: firstly, obtaining the impedance of each cell of the battery pack at a preset frequency through the BMS and the diagnosis circuit, secondly, carrying out outlier judgment on the impedance of each cell, and judging whether the cell is an aged cell; or repeatedly acquiring the impedance of the battery cell, and judging the battery cell with abnormal temperature rise according to whether the impedance of the battery cell resists continuous reduction or not. The method has the advantages that the aged battery cells in the battery pack are quickly and accurately diagnosed by acquiring the impedance data and performing outlier judgment, in addition, the battery cells with abnormal temperature rise can be timely found by detecting the impedance of the battery cells for multiple times and monitoring the impedance change rate, and potential safety hazards are effectively avoided.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a method and system for diagnosing abnormal single cells of a battery pack. Background Art

[0002] During the long-term use of lithium-ion batteries, some problems will inevitably occur, such as the increase of internal resistance and abnormal temperature rise. If these state changes are not captured in time, there will be major hidden dangers to the safe operation of electric vehicles. Impedance, as an important parameter for monitoring the internal state of the battery, can not only reflect the aging state of the battery, but is also closely related to its internal temperature.

[0003] However, the current full-frequency measurement of battery impedance usually relies on bulky electrochemical workstations, which is not only time-consuming but also difficult to apply in practice. Because this equipment is bulky, it is difficult to achieve portability and mobile detection. Secondly, the full-frequency measurement of impedance takes a long time and is not suitable for application scenarios that require fast response. In addition, there are technical difficulties in integrating the impedance detection system with the power battery electrical system, which may affect the performance and detection accuracy of the entire system.

[0004] Therefore, there is an urgent need for a battery pack abnormal single cell diagnosis method and system that can solve the above problems. Summary of the invention

[0005] In view of this, the present invention discloses a method and system for diagnosing abnormal single cells in a battery pack, which can quickly distinguish aging and abnormal temperature rise single cells in a battery pack, and is easy to integrate with a BMS, and has broad application prospects in vehicle-mounted 12V low-voltage systems. The technical solution of the present invention is implemented as follows:

[0006] The first aspect of the present invention discloses a method for diagnosing abnormal single cells of a battery pack, comprising the following steps:

[0007] S1: Obtain the impedance of each cell in the battery pack at a preset frequency;

[0008] S2: Perform outlier determination on the impedance of each battery cell to identify outlier aged batteries; and / or

[0009] Repeat step S1 to obtain the impedance of the battery cell multiple times, and diagnose the battery cell whose impedance continuously decreases as a battery cell with abnormal temperature rise.

[0010] In a possible implementation, in the step S1, the frequency range of the preset frequency is less than 100 KHz.

[0011] In a possible implementation, the step S1 specifically includes:

[0012] S1.1: Sending an excitation signal to the battery pack at the preset frequency to obtain a response current and a response voltage of each of the battery cells;

[0013] S1.2: Perform Fourier transform on the response current and response voltage of the response, and calculate the impedance of each of the battery cells.

[0014] In a possible implementation, the step of performing outlier determination on the impedance of the battery cell in step S2 to determine the outlier aged battery cell specifically includes:

[0015] S2.1: The impedances of the plurality of cells constitute a battery pack impedance set, outlier determination is performed on the battery pack impedance set, extreme values ​​in the battery pack impedance set are removed, and the expectation and standard deviation of the remaining cell impedances in the battery pack impedance set are calculated;

[0016] S2.2: Calculate the degree of deviation of each of the battery cells according to the expectation and the standard deviation. If the degree of deviation exceeds a first threshold value Q1, the battery cell is an aged battery cell.

[0017] In a possible implementation, in the step S2, the impedance of the battery cell is obtained multiple times, and the battery cell whose impedance continues to decrease is judged as a battery cell with abnormal temperature rise, which specifically includes: fitting the battery cell impedance change rate Q2 based on the impedance of the battery cell obtained multiple times, and if there is a battery cell impedance whose change rate exceeds a threshold value Q2, it is judged that the corresponding battery cell has abnormal temperature rise.

[0018] In a possible implementation, after the step S2, the method further includes: issuing an alarm after determining that the aged battery cell or the battery cell with abnormal temperature rise is detected.

[0019] The second aspect of the present invention discloses a battery pack abnormal single cell diagnosis system, including an impedance acquisition module, an aging diagnosis module and / or a temperature rise diagnosis module, wherein:

[0020] The impedance acquisition module is connected to the battery pack and is used to acquire the impedance of each battery cell in the battery pack at a preset frequency; the aging diagnosis module is connected to the impedance acquisition module and is used to perform outlier judgment on the impedance of each battery cell and identify outlier aged batteries; the temperature rise diagnosis module is connected to the impedance acquisition module and is used to acquire the impedance of the battery cell multiple times and diagnose the battery cell whose impedance continues to decrease as a battery cell with abnormal temperature rise.

[0021] In a possible implementation, the impedance acquisition module includes a detection unit and a calculation unit, wherein the detection unit is connected to the battery pack, and is used to send an excitation signal to the battery pack according to the preset frequency to obtain a response current and a response voltage of each of the battery cells; the calculation unit is communicatively connected to the detection unit, and is used to perform Fourier transform on the response current and the response voltage, and calculate the impedance of each of the battery cells.

[0022] In a possible implementation, the diagnostic system further includes an alarm module.

[0023] The aging diagnosis module and the temperature rise diagnosis module are both connected to the alarm module, and the alarm module is configured to generate an alarm after determining the aged battery cell or the battery cell with abnormal temperature rise.

[0024] The third aspect of the present invention is to disclose a computer-readable storage medium on which a computer program / instruction is stored. When the computer program / instruction is executed by a processor, the steps of the method described in the first aspect of the present application are implemented.

[0025] The advantages of the present invention are as follows:

[0026] (1) The present invention obtains the impedance data of all the cells in the battery pack and performs outlier judgment on the impedance data of all the cells, thereby quickly and accurately diagnosing the aged cells in the battery pack.

[0027] (2) The present invention can detect abnormal temperature rise of battery cells in a timely manner by stimulating the battery cells multiple times, obtaining the impedance of the battery cells multiple times, and monitoring the impedance change rate, thereby effectively avoiding safety hazards.

[0028] (3) The diagnostic method and system design of the present invention can be easily integrated into a battery management system, thereby improving detection efficiency and system compatibility.

[0029] (4) The present invention designs a diagnostic circuit and a BMS module with aging diagnosis, temperature rise diagnosis and alarm functions, providing comprehensive battery status monitoring and early warning. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only one embodiment of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 It is a flow chart of a method for diagnosing abnormal single cells of a battery pack according to the present invention;

[0032] Figure 2 A structural diagram of a battery pack abnormal single cell diagnosis system according to the present invention;

[0033] Figure 3 for Figure 2 The structure diagram of another battery pack abnormal single cell diagnosis system of the present invention is shown;

[0034] Figure 4 This is a diagram of impedance changes of the four battery cells used in the experiment in Example 1 of the present invention.

[0035] In the above drawings, the meanings of the reference numerals are as follows:

[0036] 1. Battery pack;

[0037] 2. BMS;

[0038] 21. Impedance acquisition module; 211. Detection unit; 212. Calculation unit; 22. Aging diagnosis module; 23. Temperature rise diagnosis module; 24. Alarm module; 25. Transmission module;

[0039] 3. Host computer. DETAILED DESCRIPTION

[0040] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by technicians in the technical field to which the present invention belongs; the terms used in the specific implementation methods are only for the purpose of describing specific embodiments and are not intended to limit the present invention; the terms "including" and "having" in the specification and claims of the present invention and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0042] In the description of the specific implementation methods of the present invention, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present invention, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0043] Reference to "embodiments" in the present invention means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the present invention may be combined with other embodiments.

[0044] In the description of the embodiments of the present invention, the term "and / or" is only a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in the present invention generally indicates that the associated objects before and after are in an "or" relationship.

[0045] It should be noted that, for the convenience of description, in the following embodiments, all identical technical features are marked with the same symbols.

[0046] During the long-term use of lithium-ion batteries, some problems will inevitably occur, such as the increase of internal resistance and abnormal temperature rise. If these state changes are not captured in time, there will be great hidden dangers for the safe operation of battery vehicles. Impedance, as a parameter for monitoring the internal state of the battery, can not only reflect the aging state of the battery, but also has a certain relationship with its internal temperature. However, the measurement of its full frequency often relies on a bulky electrochemical workstation, which is time-consuming and difficult to apply.

[0047] Therefore, the present invention proposes a diagnosis method and system for abnormal single cells in a battery pack, which can quickly distinguish aging and abnormal temperature rise single cells in the battery pack, and is easy to integrate into the BMS, and has broad application prospects in the vehicle-mounted 12V low-voltage system.

[0048] The embodiments of the present invention will be described in more detail below by way of examples. It should be noted that the embodiments of the present invention are not limited to these examples.

[0049] The present application discloses a method for diagnosing abnormal single cells of a battery pack, such as Figure 1 As shown, the following steps are included:

[0050] S1: Obtain the impedance of each battery cell in battery pack 1 at a preset frequency;

[0051] S2: Perform outlier determination on the impedance of each battery cell to identify outlier aged batteries; and / or

[0052] Repeat step S1 to obtain abnormal impedance of the battery cell multiple times, and diagnose the battery cell with continuously decreasing impedance as a battery cell with abnormal temperature rise.

[0053] Through the above method, the impedance of several cells is first obtained, and then the impedance of several cells is judged as outliers, so that the aged cells in the battery pack can be diagnosed. When the temperature rises, the diffusion rate of ions in the electrolyte will increase, and the diffusion impedance will be significantly reduced. Therefore, by obtaining the impedance of each cell multiple times in succession and observing the impedance of the cells obtained continuously, when the impedance of the cell continues to decrease, the cell is diagnosed as abnormal in temperature rise. The above process can realize the diagnosis of abnormal cells.

[0054] In some specific implementations, in step S1, the frequency range of the preset frequency is less than 100 KHz, and the impedance in this frequency range makes it easier to observe abnormal conditions of the battery cell. Furthermore, the staff can set a specific frequency based on characteristics such as temperature and battery cell related parameters.

[0055] In some specific implementations, step S1 specifically includes:

[0056] S1.1: Send an excitation signal to the battery pack 1 at a preset frequency to obtain a response current and a response voltage of each battery cell;

[0057] S1.2: Perform Fourier transform on the response current and voltage and calculate the impedance of each cell, which specifically includes the following steps:

[0058] Perform Fourier transform on the response voltage data and the response current data respectively to obtain their frequency domain representation:

[0059]

[0060] x(t) represents the voltage data V(t) or current data I(t), and X(f) represents its frequency domain representation V(f) and I(f). Dividing the two can get the impedance at the preset frequency:

[0061]

[0062] In some specific implementations, in step S2, outlier determination is performed on the impedance of the battery cell to determine the outlier aged battery cell, specifically including:

[0063] S2.1: The resistances of several cells constitute a battery pack impedance set. The extreme values ​​in the battery pack impedance set are removed, and the expected value and standard deviation of the remaining cell impedances in the battery pack impedance set are calculated. The calculation is performed using the following formula:

[0064] Z i ={Z1,Z2, .., Z n}-{Z max , Z min}

[0065]

[0066] Among them, {Z1, Z2, ..., Z n} represents the battery pack impedance set, Z max Indicates the maximum impedance, Z min Represents the minimum impedance, Z i represents the impedance set after removing extreme values; μ represents the expectation, and σ represents the standard deviation.

[0067] Specifically, when calculating the impedance expectation and standard deviation of all cells, since the maximum impedance and minimum impedance values ​​are usually considered to be outliers, they may be caused by measurement errors, calculation errors or other non-random factors. Removing these maximum impedance and minimum impedance can reduce the impact of these outliers on the overall expectation, make the expectation more accurately reflect the true distribution of the data, and improve the accuracy and reliability of the expectation and standard deviation.

[0068] S2.2: Based on the above expectation and standard deviation, calculate the deviation degree D of each battery cell. z , if the deviation degree D z If the first threshold Q1 is exceeded, the corresponding cell is an aged cell, which is calculated by the following formula:

[0069]

[0070] in, Indicates the deviation degree of the ith battery cell, specifically, the first threshold Q1 is 3. According to the normal distribution characteristics, the probability that the difference between the variable and the mean is within is 99.73%, and when it is outside, it can be considered as an aging abnormality.

[0071] In some specific implementations, in step S2, the impedance of the battery cell is obtained multiple times, and the battery cell with a continuously decreasing impedance is diagnosed as a battery cell with abnormal temperature rise, specifically including fitting the battery cell impedance change rate Q2 according to the impedance of the battery cell obtained multiple times, and if there is a battery cell impedance whose change rate exceeds the threshold value Q2, it is determined that the corresponding battery cell has abnormal temperature rise. .

[0072] In some preferred embodiments, the cell impedance change rate is calculated using the least squares method, which is a data fitting method that finds the best fitting curve by minimizing the sum of squares of errors between data points and fitting lines.

[0073] Specifically, each battery cell is stimulated several times, and the impedance value of the battery cell under each stimulation is recorded. The number of stimulations is used as the independent variable, and the impedance value of the battery cell is used as the dependent variable, and a straight line is fitted using the least squares method. Therefore, according to the impedance of each battery cell under several stimulations and the number of stimulations, a linear relationship characterizing the impedance of the battery cell and the number of stimulations is fitted, and then the slope parameter and intercept parameter of the change in the impedance of the battery cell are fitted, where the slope parameter is the rate of change. The linear relationship function is as follows:

[0074]

[0075] in, is the slope of the ith cell, b i is the intercept of the ith cell, k is the number of excitations of the ith cell, is the impedance of the ith cell at the kth excitation.

[0076] When the fitted slope is less than the threshold value Q2, it is determined that the temperature rise of the corresponding battery cell is abnormal.

[0077] It is understandable that when the cell is stimulated several times and the cell impedance is calculated multiple times, it is necessary to ensure that its response voltage and response current are the response signals (i.e., response voltage and response current) obtained for the same cell at the same stimulation. For example, when calculating the impedance of cell a under the i-th stimulation, it is necessary to calculate the resistance of cell a at the i-th measurement based on the response voltage of cell a obtained for the i-th time and the response current of cell a obtained for the i-th time.

[0078] In some specific implementations, an alarm is provided after an aged battery cell or a battery cell with abnormal temperature rise is determined. Specifically, a warning message may be displayed on a control panel or display screen to remind the operator to pay attention to abnormal battery status. The warning light may also be activated to flash or change color to warn the battery pack of problems in an intuitive manner, or an audible alarm, such as a buzzer, may be issued to further attract the operator's attention.

[0079] The present invention also discloses a diagnostic system for abnormal single cells of a battery pack, such as Figure 2 As shown, it mainly includes an impedance acquisition module 21, an aging diagnosis module 22 and / or a temperature rise diagnosis module 23, wherein:

[0080] The impedance acquisition module 21 is connected to the battery pack 1 and is used to obtain the impedance of each battery cell in the battery pack 1 at a preset frequency;

[0081] The aging diagnosis module 22 is connected to the impedance acquisition module 21 and is used to perform outlier determination on the impedance of each battery cell and identify outlier aged batteries;

[0082] The temperature rise diagnosis module 23 is connected to the impedance acquisition module 21 and is used to acquire the impedance of the battery cell multiple times and diagnose the battery cell with a continuously decreasing impedance as a battery cell with abnormal temperature rise.

[0083] When it is necessary to diagnose abnormal single cells in the battery pack, the impedance of each cell in the battery pack 1 is detected by the impedance acquisition module 21, and several cell impedances are sent to the aging diagnosis module 22, and the aging diagnosis module 22 makes outlier judgments on several cell impedances, thereby determining the aged cells. The temperature rise diagnosis module 23 can obtain the impedance of multiple cells, and observe the cell impedance obtained for each cell several times. If the cell impedance continues to decrease, the cell is judged to be a cell with abnormal temperature rise. Through the above device, the diagnosis of abnormal single cells in the battery pack can be realized.

[0084] In some specific embodiments, the impedance acquisition module 21 includes a detection unit 211 and a calculation unit 212, wherein the detection unit 211 is connected to the battery pack 1, and is used to send an excitation signal to the battery pack 1 according to the preset frequency to obtain a response current and a response voltage of each of the battery cells, and the calculation unit 212 is communicatively connected to the detection unit 211, and is used to perform Fourier transform on the response current and the response voltage, and calculate the impedance of each of the battery cells.

[0085] Specifically, the detection unit 211 includes an acquisition unit and a detection circuit, the acquisition unit and the detection circuit are communicatively connected, and the detection circuit is connected to the battery pack 1. The acquisition unit can be used to control the on and off of the detection circuit according to a certain preset frequency, and can send an excitation signal to the battery pack 1. After receiving the excitation signal, the battery cell of the battery pack 1 will generate a response signal (response voltage and response current) and send the corresponding signal to the acquisition unit.

[0086] Specifically, Figure 2 As shown, the acquisition unit is integrated on the BMS2 of the power battery. The detection circuit can be integrated on the BMS2 of the power battery, such as Figure 3 As shown, the detection circuit can also be integrated into the electrical system of the whole vehicle. Whether it is integrated on the BMS2 or in the electrical system of the whole vehicle, it is convenient to transmit the excitation signal to the battery pack 1.

[0087] Specifically, the above-mentioned BMS2 is a key component of the power battery, which is mainly responsible for monitoring and managing the status of the battery to ensure the safety, stability and long life of the battery. It can realize the information management of the power battery. The BMS2 detects the voltage, current and temperature of the battery in real time through sensors, and performs leakage detection, thermal management, battery balancing management, alarm reminders and other operations. It also controls the maximum output power and optimal charging current of the battery through algorithms to ensure the maximum mileage of electric vehicles.

[0088] Specifically, Figure 2 As shown, the calculation unit 212 can be set on the BMS2, and is connected to the acquisition unit for communication to receive the response voltage and response current sent by the acquisition unit, and calculate the impedance of each battery cell according to the response voltage and response current. Figure 3 As shown, the calculation unit 212 can also be set on a host computer other than the BMS2. The calculation unit 212 can be connected to the acquisition unit in a wired or wireless manner to achieve data transmission and calculation of the cell impedance.

[0089] In some specific implementations, the aging diagnosis module 22 is communicatively connected to the impedance acquisition module 21 , and is configured to receive the cell impedance sent by the impedance acquisition module 21 , and perform outlier determination based on the received cell impedances to diagnose aged cells.

[0090] It is understandable that when performing outlier judgment on several cells, it is necessary to ensure that the impedance of all cells is the impedance data detected under the same excitation. For example, a battery pack includes cells a, b, and c. When performing outlier judgment on these three cells, it is necessary to perform outlier judgment on the impedance obtained by calculating the response voltage and response current of cells a, b, and c under the i-th excitation.

[0091] The above outlier judgment is specifically to collect statistics on the impedance of all cells at the same preset frequency and the same test batch to form a data set, remove the maximum impedance and the minimum impedance in the data set, calculate the expectation and standard deviation of the impedance of the remaining cells in the data set, and calculate the deviation degree of each cell based on the standard deviation and expectation. If the deviation degree of a cell impedance exceeds the first threshold value Q1, the cell is judged as an aged cell.

[0092] In some specific embodiments, the temperature rise diagnosis module 23 is communicatively connected to the impedance acquisition module 21. The temperature rise diagnosis module 23 is configured to send a trigger signal to the impedance acquisition module 21 according to a certain preset time interval, and receive the cell impedance sent by the impedance acquisition module 21, and calculate the impedance change rate of each cell with the number of detections according to the cell impedance. The impedance acquisition module 21 is configured to obtain the impedance of each cell in the battery pack 1 at a preset frequency after receiving the trigger signal. If the impedance change rate of a cell exceeds the threshold value Q2, it means that the temperature rise of the cell is abnormal.

[0093] Specifically, when it is necessary to diagnose abnormality of the battery cell, the impedance acquisition module 21 first sends an excitation signal to the battery pack 1, calculates the impedance of each battery cell according to the response signal of the battery cell, and sends the battery cell impedance to the aging diagnosis module 22 and / or the temperature rise diagnosis module 23. In addition, the impedance acquisition module 21 will also send an excitation signal to the battery pack according to the trigger signal sent by the temperature rise diagnosis module 23, and send the calculated battery cell impedance to the temperature rise diagnosis module 23, so that the temperature rise diagnosis module 23 can diagnose the battery cell with abnormal temperature rise.

[0094] The impedance change rate of each battery cell with the number of detection times is calculated based on the battery cell impedance. Specifically, the battery cell impedance detected several times for each battery cell is fitted by the least squares method to obtain the change rate, and the change rate is compared with the second threshold to determine whether the battery cell has abnormal temperature rise.

[0095] In some optional embodiments, the temperature rise diagnosis module 23 is communicatively connected to the host computer 3, and is configured to send the cell impedance to the host computer 3 through the transmission module 25 after receiving the cell impedance sent by the impedance acquisition module 21. The host computer 3 is configured to fit the cell impedance of each cell after receiving the cell impedance, thereby generating a change rate, and send the change rate information to the temperature rise diagnosis module 23 through the transmission module 25. The temperature rise diagnosis module 23 is configured to receive the change rate information and diagnose the cell with abnormal temperature rise according to the change rate information.

[0096] Through the above settings, the host computer 3 uses the least squares method to perform linear fitting on the impedance data and the number of excitations of each battery cell. The host computer 3 calculates the battery cell impedance change rate, which can improve data processing efficiency and enhance the flexibility of the BMS2 system.

[0097] In some specific embodiments, the system also includes an alarm module 24, and the aging diagnosis module 22 and the temperature rise diagnosis module 23 are both communicatively connected to the alarm module 24, and are used to send an alarm signal to the alarm module 24 when aging batteries or batteries with abnormal temperature rise are diagnosed. The alarm module 24 is configured to generate an alarm after receiving the alarm signal.

[0098] Through the above settings, the alarm module 24 can display a warning message on the control panel or display screen to remind the operator to pay attention to the abnormal battery status. The alarm module 24 can also activate the warning light to flash or change color to warn the battery pack in an intuitive way, or issue a sound alarm, such as a buzzer sound, to further attract the attention of the operator. In addition, the alarm module 24 can send the alarm information to the host computer 3 or the mobile device of the relevant manager through the communication module to achieve remote monitoring and immediate response. In severe cases, the alarm module 24 can trigger the system to automatically shut down to prevent further damage and safety accidents.

[0099] The present application also provides a computer-readable storage medium, which may be a non-volatile computer-readable storage medium or a volatile computer-readable storage medium, wherein instructions are stored in the computer, and when the instructions are executed on a computer, the computer executes the steps of the above-mentioned method for diagnosing abnormal single cells of a battery pack.

[0100] Example 1

[0101] In this embodiment, if Figure 4 As shown, 4 battery cells are selected in series to simulate the on-board 12V low-voltage system as the experimental object, among which the internal resistance value of battery cell 1 is too large, indicating an aging battery cell. The other 3 battery cells have similar internal resistances, indicating normal batteries. Through the diagnostic method and system disclosed in the present application, a square wave excitation current is applied to the battery cells at room temperature to obtain the impedance of each battery cell under multiple excitations. The impedance model deviation degree and the impedance model change rate under multiple excitations are calculated. Then, a heating plate is used to heat battery cell 4 to simulate an abnormal internal temperature rise battery cell, and the impedance model deviation degree and the impedance model change rate under multiple current excitations are also calculated.

[0102] Specifically, in this embodiment, the threshold Q1 is set to 3, and the threshold Q2 is set to -0.025.

[0103] Through the above experiments, the calculation results under multiple current excitations at room temperature are as follows:

[0104] Table 1

[0105] <![CDATA[Degree of deviation D of impedance modulus z > <![CDATA[Impedance modulus change rate S z > Judgment result Battery 1 7.07 0.007 Aging battery Battery 2 0.71 0.019 No abnormality Battery 3 -1.35 -0.012 No abnormality Battery 4 -0.71 -0.002 No abnormality

[0106] The cell 4 is externally heated, and the calculation results under multiple current excitations are:

[0107] Table 2

[0108] <![CDATA[Degree of deviation D of impedance modulus z > <![CDATA[Impedance modulus change rate S z > Judgment result Battery 1 4.64 -0.0016 Aging battery Battery 2 0.71 0.004 No abnormality Battery 3 -0.71 -0.013 No abnormality Battery 4 -1.47 -0.030 Abnormal temperature rise battery

[0109] from Figure 4 As can be seen from the calculation results of Tables 1 and 2, the method proposed in the present invention can well distinguish between aging cells and cells with abnormal temperature rise in the battery pack. In practical applications, the thresholds and can be adjusted as needed. Since the present embodiment 1 uses external heating to simulate internal heat generation, affected by the heat conduction rate, etc., the heat is not completely and timely conducted to the inside, resulting in a small change in the impedance parameters. In actual situations, more often the battery generates heat from the inside to the outside, and the impedance parameter changes caused by the same temperature rise will be more obvious.

[0110] It should be pointed out that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for diagnosing abnormal single cells in a battery pack, characterized in that: The following steps are involved: S1: Obtain the impedance of each cell in the battery pack at a preset frequency; S2: performing outlier determination on the impedance of each of the battery cells to identify outlier aged battery cells; and / or Repeat step S1 to obtain the impedance of the battery cell multiple times, and diagnose the battery cell whose impedance continuously decreases as a battery cell with abnormal temperature rise.

2. A method for diagnosing abnormal single cells in a battery pack according to claim 1, characterized in that: In the step S1, the frequency range of the preset frequency is less than 100 KHz.

3. A method for diagnosing abnormal single cells in a battery pack according to claim 2, characterized in that: The S1 step specifically includes: S1.1: Sending an excitation signal to the battery pack at the preset frequency to obtain a response current and a response voltage of each of the battery cells; S1.2: Perform Fourier transform on the response current and the response voltage, and calculate the impedance of each of the battery cells.

4. A method for diagnosing abnormal single cells of a battery pack according to claim 3, characterized in that: The step S2 of performing outlier determination on the impedance of the battery cell to determine outlier aged battery cells specifically includes: S2.1: The impedances of the plurality of cells constitute a battery pack impedance set, extreme values ​​in the battery pack impedance set are removed, and the expectation and standard deviation of the remaining cell impedances in the battery pack impedance set are calculated; S2.2: Calculate the deviation degree D of each cell according to the expectation and the standard deviation. z , the degree of deviation D z The battery cells exceeding the first threshold Q1 are aged battery cells.

5. A method for diagnosing abnormal single cells of a battery pack according to claim 4, characterized in that: In the step S2, the impedance of the battery cell is obtained multiple times, and the battery cell whose impedance continuously decreases is judged to be a battery cell with abnormal temperature rise, which specifically includes: According to the impedance of the battery cell obtained multiple times, the battery cell impedance change rate Q2 is fitted, and if there is a battery cell impedance whose change rate exceeds the threshold value Q2, it is determined that the corresponding battery cell temperature rises abnormally.

6. The method for diagnosing abnormal single cells of a battery pack according to any one of claims 1 to 5, characterized in that: After the step S2, the method further includes: After the aged battery cell or the battery cell with abnormal temperature rise is determined, an alarm is issued.

7. A diagnostic system for abnormal single cells in a battery pack, characterized in that: It includes an impedance acquisition module, an aging diagnosis module and / or a temperature rise diagnosis module, wherein: The impedance acquisition module is connected to the battery pack and is used to acquire the impedance of each battery cell in the battery pack at a preset frequency; The aging diagnosis module is connected to the impedance acquisition module and is used to perform outlier judgment on the impedance of each battery cell to determine the outlier aged battery cell; The temperature rise diagnosis module is connected to the impedance acquisition module, and is used to obtain the impedance of the battery cell multiple times, and diagnose the battery cell whose impedance continuously decreases as a battery cell with abnormal temperature rise.

8. A battery pack abnormal single cell diagnosis system according to claim 7, characterized in that: The impedance acquisition module includes a detection unit and a calculation unit, wherein: The detection unit is connected to the battery pack and is used to send an excitation signal to the battery pack according to the preset frequency to obtain a response current and a response voltage of each of the battery cells; The calculation unit is communicatively connected to the detection unit, and is used to perform Fourier transform on the response current and the response voltage, and calculate the impedance of each of the battery cells.

9. A battery pack abnormal single cell diagnosis system according to claim 7, characterized in that: It also includes an alarm module. The aging diagnosis module and the temperature rise diagnosis module are both connected to the alarm module, and the alarm module is configured to generate an alarm after determining the aged battery cell or the battery cell with abnormal temperature rise.

10. A computer-readable storage medium having a computer program / instruction stored thereon, characterized in that: When the computer program / instructions are executed by a processor, the steps of the method according to claims 1 to 6 are implemented.

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