Secondary battery state diagnosis system and state diagnosis method

Abstract

Provided are a state diagnosis system and a state diagnosis method for a secondary battery, with which it is possible to estimate more accurate full charge capacity for a secondary battery of an electric vehicle even if there is a period in which data is not acquired. A calculation unit of a secondary battery state diagnosis system performs: (a) a process for calculating a first SOC on the basis of a first voltage at a first timing at which charging-related voltage application is started; (b) calculating a relaxation time on the basis of a second voltage and the temperature at a second time when the voltage application related to the charging ends at the second time; (c) calculating a second SOC based on a third voltage at a third time after the second time; and (d) when the time from the second time to the third time is equal to or greater than the relaxation time, estimating the full charge capacity of the battery cell or the assembled battery on the basis of the charging-related current, the first SOC, and the second SOC.

Description

Technical Field

[0001] The present invention relates to a secondary battery status diagnosis system and a secondary battery status diagnosis method. Background Art

[0002] When externally charging a secondary battery in an electric vehicle, calculating the SOC (State of Charge) and full charge capacity becomes important. These values can be calculated based on the battery temperature, voltage and current associated with charging, and other factors. An example of such technology is described in Patent Document 1.

[0003] Furthermore, when measuring the voltage of a battery during or immediately after charging, it is important to evaluate the polarization voltage. Paragraph

[0050] of Patent Document 2 describes an example of a mathematical formula for calculating the polarization voltage.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-202010

[0007] Patent Document 2: Japanese Patent Application Laid-Open No. 2017-107763 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] However, in electric vehicles and the like, there are periods during which battery data is not acquired. Therefore, conventional technologies sometimes have a problem in that it is difficult to accurately estimate the full charge capacity.

[0010] The telematics device acquires measurement data from the secondary battery mounted in an electric vehicle via the battery management system (BMS). In this configuration, the telematics device stops acquiring data when the electric vehicle is powered off, resulting in a period of time when no measurement data is available.

[0011] Due to this period of time, the OCV of the battery after polarization relaxation may not be obtained, making it difficult to accurately calculate the SOC and accurately estimate the full charge capacity.

[0012] The present invention has been made to solve such a problem, and an object of the present invention is to provide a secondary battery state diagnosis system and state diagnosis method capable of estimating a more accurate full charge capacity even when there is a period when battery data is not acquired.

[0013] Means for solving problems

[0014] An example of a secondary battery state diagnosis system according to the present invention is a secondary battery state diagnosis system including a data acquisition unit and a calculation unit, wherein:

[0015] The data acquisition unit acquires current, voltage, and temperature related to a battery cell, or current, voltage, and temperature related to a battery pack in which a plurality of battery cells are combined.

[0016] (a) when the battery cell or the battery pack is externally charged, the calculation unit calculates a first SOC using an SOC-OCV relationship table based on a first voltage at a first time when voltage application related to charging is started, wherein the SOC-OCV relationship table is a table indicating a relationship between voltage and SOC;

[0017] (b) when the voltage application related to the charging ends at a second time, the calculation unit calculates a relaxation time of the battery cell or the battery pack based on the second voltage at the second time and the temperature;

[0018] (c) when the data acquisition unit acquires a third voltage at a third time after the second time, the calculation unit calculates a second SOC based on the third voltage using the SOC-OCV relationship table;

[0019] (d) When the time from the second time to the third time is equal to or longer than the relaxation time, the calculation unit estimates the full charge capacity of the battery cell or the battery pack based on the current related to the charge, the first SOC, and the second SOC.

[0020] This description incorporates the disclosure of Japanese Patent Application No. 2023-039533 upon which the present application claims priority.

[0021] Effects of the Invention

[0022] According to the secondary battery state diagnosis system and state diagnosis method of the present invention, even when there is a period when battery data is not acquired, it is possible to estimate the full charge capacity more accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a configuration example of a secondary battery status diagnosis system including the first embodiment of the present invention.

[0024] Figure 2 yes Figure 1 An example of a battery SOC-OCV relationship table.

[0025] Figure 3 Yes Figure 1 Graph showing changes in the battery's condition during and before and after external charging.

[0026] Figure 4 This is a flowchart showing the processing executed by the secondary battery status diagnosis system according to the first embodiment.

[0027] Figure 5 This is a flowchart showing the processing executed by the secondary battery status diagnosis system according to the second embodiment. DETAILED DESCRIPTION

[0028] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0029] [Implementation Method 1]

[0030] Figure 1 A configuration example of a secondary battery status diagnosis system (hereinafter sometimes referred to simply as a "battery diagnosis system") according to this embodiment is shown. The secondary battery status diagnosis system is provided in association with an electric vehicle 10 (which may also be referred to as an EV).

[0031] The electric vehicle 10 includes the following components.

[0032] An electric motor 11 that drives the electric vehicle 10 .

[0033] - A battery 13 that supplies power to the motor 11. The battery 13 is a secondary battery and may be, for example, a single secondary battery cell or a battery pack composed of a plurality of secondary battery cells. Hereinafter, the secondary battery may be simply referred to as a "battery."

[0034] The inverter 12 converts the electric power supplied from the battery 13 and supplies the converted electric power to the electric motor 11 .

[0035] A battery management device 14 controls and manages the battery 13 .

[0036] An ignition switch 15 for performing operations related to the power supply of the electric vehicle 10 (particularly the battery management device 14 ).

[0037] A telematics terminal 20 is mounted on the electric vehicle 10. The telematics terminal 20 acquires data related to the electric vehicle 10. The telematics terminal 20 may also have functions such as a car navigation system and a drive recorder.

[0038] The telematics terminal 20 includes a data acquisition unit 21 and a wireless communication unit 22 .

[0039] The data acquisition unit 21 is communicatively connected to the battery management device 14 of the electric vehicle 10 via a wired or wireless connection, and is capable of acquiring data related to the battery 13. Specifically, the data acquisition unit 21 acquires a timestamp, the current related to the battery 13, the voltage related to the battery 13, and the temperature related to the battery 13 (or the temperature of the battery's surrounding environment). The timestamp indicates the date and time when the measurement data was acquired (or the date and time when the measurement was performed). Therefore, a temperature sensor, current sensor, voltage sensor, etc. may also be provided in association with the battery 13.

[0040] The wireless communication unit 22 can communicate with an external computer (for example, a telematics server 30 described later) via wireless communication.

[0041] The telematics server 30 is disposed outside the electric vehicle 10 (eg, remotely), and acquires data related to the electric vehicle 10. The telematics server 30 includes a wireless communication unit 31 and a calculation unit 32.

[0042] The wireless communication unit 31 can communicate wirelessly with an external computer (eg, the telematics terminal 20 ). In particular, the wireless communication unit 22 of the telematics terminal 20 and the wireless communication unit 31 of the telematics server 30 can communicate wirelessly.

[0043] The calculation unit 32 can perform calculations based on the data acquired via the wireless communication unit 31 and output the results.

[0044] The battery diagnosis system of the present embodiment is configured to include a telematics terminal 20 and a telematics server 30 . In particular, the battery diagnosis system includes a data acquisition unit 21 and a calculation unit 32 .

[0045] The battery management device 14, telematics terminal 20, and telematics server 30 each have a known computer structure, for example, including a computing unit and a storage unit. The computing unit includes, for example, a processor, and the storage unit includes, for example, a storage medium such as a semiconductor memory device and a magnetic disk drive. Some or all of the storage medium may be non-transitory.

[0046] The storage unit may store a program, and the processor may execute the program to cause each computer to perform the functions described in this embodiment, thereby realizing a battery diagnosis system.

[0047] In addition, Figure 1 In the example, the battery management device 14, the telematics terminal 20, and the telematics server 30 are each composed of an independent computer, but the hardware structure is not limited to Figure 1The structure can be variously designed as described in [other embodiments] below.

[0048] Figure 2 This shows an example of a SOC-OCV relationship table for battery 13. The SOC-OCV relationship table is a table showing the relationship between OCV (voltage, specifically open-circuit voltage) and SOC (charge rate or state of charge), and is stored, for example, in the storage unit of calculation unit 32. The SOC-OCV relationship table can be used to calculate the SOC of battery 13 based on the OCV of battery 13. The storage unit may also store information such as an SOC-charge resistance curve, an SOC-discharge resistance curve, the number of battery cells, and rated capacity.

[0049] Below, use Figure 3 and Figure 4 An example of the operation of the secondary battery state diagnosis system according to this embodiment will be described.

[0050] Figure 3 The diagram shows changes in the state of the battery 13 during and before and after external charging. External charging refers to charging by supplying electric power from a charging facility installed outside the electric vehicle 10, for example. Figure 3 The horizontal axis represents time, the left vertical axis represents voltage (the graph of the thick solid line and the graph of the thick dashed line), and the right vertical axis represents current (the graph of the thin dashed line).

[0051] Figure 4 FIG. 1 is a flowchart showing the processing performed by the secondary battery status diagnosis system. Figure 3 If the condition changes, the battery diagnostic system will execute Figure 4 processing.

[0052] exist Figure 3 Charging begins at time T1 (the first moment). That is, the application of voltage related to charging begins. Furthermore, there are cases where normal charging cannot occur due to a malfunction of the battery 13, but even in such cases, the application of voltage related to charging begins. At this point in time, the power supply of the electric vehicle 10 is turned on, and the power supply of the data acquisition unit 21 of the telematics terminal 20 (or the data acquisition operation, the same applies hereinafter) is also turned on.

[0053] Before time T1 (it can be considered that time T1 is substantially included), the OCV can be measured, and the OCV is acquired by the data acquisition unit 21 .

[0054] When charging starts, the calculation unit 32 extracts and obtains the charging data ( Figure 4 The charging data particularly includes the voltage at time T1 (first voltage). The first voltage is measured as, for example, OCV, but measurement as CCV (closed circuit voltage) is not particularly excluded.

[0055] Next, the calculation unit 32 calculates the first SOC based on the voltage immediately before charging begins (step S2). Specifically, the SOC at time T1 (the first SOC) is calculated using the SOC-OCV relationship table based on the voltage at time T1 (the first voltage). Furthermore, depending on the measured current value, the first voltage may not match the OCV. In this case, the voltage obtained by subtracting the overvoltage from the first voltage can be estimated as the OCV to calculate the first SOC. In other words, the calculation unit 32 can calculate the first SOC based on the value obtained by subtracting the overvoltage from the first voltage. This improves estimation accuracy.

[0056] After time T1, the voltage of battery 13 increases as charging progresses. During charging, the polarization of battery 13 prevents accurate OCV measurement. As shown in the figure, the measured voltage (thick solid line) differs from the actual OCV (thick dashed line, assuming no polarization).

[0057] At time T2 (the second time), charging is complete. That is, the application of voltage associated with charging is complete. Furthermore, there are cases where normal charging cannot occur due to a malfunction of battery 13, for example. Even in such cases, the application of voltage associated with charging is complete. The time from time T1 to time T2 is the charging time. At time T2, the polarization of battery 13 also prevents accurate OCV measurement. After time T2, polarization begins to ease, and the measured voltage gradually approaches the actual OCV.

[0058] When charging is completed, the calculation unit 32 calculates the cumulative value of the charging current (step S3). In addition, the relaxation time relative to the polarization of the charged battery is calculated (step S4). In a secondary battery, the active material in the electrode is used to perform an ion storage and release reaction during charging and discharging. The storage and release reaction does not occur instantaneously, and the storage and release reaction requires a certain amount of time. The relaxation time can be calculated based on the temperature of the battery 13, the voltage at time T2 (the second voltage), etc. (other data can also be used). Regarding the specific calculation method of the relaxation time, it can be appropriately designed by those skilled in the art based on known technologies, for example, Formula 5 described in paragraph

[005] of Patent Document 2 can be used.

[0059] In this way, the calculation unit 32 calculates the relaxation time of the battery 13 based on the temperature of the battery 13 and the voltage at time T2. The temperature used here is, for example, the temperature at time T2, but the temperature at another time may be used.

[0060] At time T3, the power supply to electric vehicle 10 is turned off. Accordingly, the power supply to data acquisition unit 21 is also turned off (step S5). Therefore, after time T3, it is impossible to measure or acquire data related to battery 13 (including voltage). Time T3 is assumed to be before the polarization of battery 13 is eliminated. In other words, accurate OCV measurement is impossible even at time T3.

[0061] At time T4, the polarization of battery 13 has been fully eliminated, and the polarization voltage has decayed to a level that barely affects the SOH estimation error. In other words, the period from time T2 to time T4 can be considered the time for the polarization of battery 13 to relax. At time T4, the power supply to the data acquisition unit 21 is turned off, making it impossible to measure OCV. While time T4 is the time when the voltage associated with polarization reaches zero, it can also be the time when the voltage associated with polarization falls below a predetermined threshold.

[0062] At time T5 (third time), the electric vehicle 10 is powered on. Accordingly, the data acquisition unit 21 is also powered on (step S6). Consequently, at and after time T5, the data acquisition unit 21 acquires data (including voltage) from the battery 13.

[0063] The calculation unit 32 determines whether the time from the time when charging is completed (time T2) to the time when the power of the data acquisition unit is turned on (time T5) is longer than the relaxation time (step S7). If the time from time T2 to time T5 is shorter than the relaxation time, the battery diagnosis system ends. Figure 4 In this case, the calculation of the full charge capacity (step S10 described later) is not performed, thereby avoiding the calculation of the full charge capacity with low accuracy due to the influence of polarization.

[0064] If the time from time T2 to time T5 is longer than the relaxation time, the calculation unit 32 determines whether the time from time T2 to time T5 is within a predetermined natural discharge time threshold (step S8). The natural discharge time threshold can be appropriately determined by a person skilled in the art to be a time threshold that is long enough to prevent the natural discharge of the battery 13 from being ignored. Specific examples include 5 days, 7 days, and the like.

[0065] If the time from time T2 to time T5 exceeds the natural discharge time threshold, the battery diagnosis system ends. Figure 4 In this case, the calculation of the full charge capacity (step S10 described later) is not performed, thereby avoiding the calculation of a low-precision full charge capacity that includes the influence of natural discharge.

[0066] If the time from time T2 to time T5 is within the natural discharge time threshold, the calculation unit 32 calculates the SOC at time T5 (the second SOC) based on the voltage at time T5 (more strictly speaking, the voltage immediately after power is applied to the data acquisition unit 21) (the third voltage) using the SOC-OCV relationship table (step S9). Furthermore, depending on the measured current value, there is a possibility that the third voltage and the OCV may not match. In this case, the voltage obtained by subtracting the overvoltage from the third voltage can be estimated as the OCV to calculate the second SOC. In other words, the calculation unit 32 can calculate the second SOC based on the value obtained by subtracting the overvoltage from the third voltage. This improves estimation accuracy.

[0067] Next, the calculation unit 32 estimates the full charge capacity of the battery 13 based on the current related to charging (current measured during the charging time), the SOC at time T1 (first SOC), and the SOC at time T5 (second SOC) (step S10 ).

[0068] The full charge capacity can be estimated using the following formula, for example.

[0069] Qmax={∫Adt / (second SOC-first SOC)}×100

[0070] Where Qmax is the full charge capacity, and A is the current value measured during the charge time, integrated over the charge time (from time T1 to time T2). This formula calculates the full charge capacity based on the ratio of the increase in SOC due to charging to the amount of electricity corresponding to that increase. The full charge capacity is not limited to the above formula; other methods can also be used to estimate it.

[0071] After step S10, the battery diagnosis system ends Figure 4 In addition, although not specifically shown in the figure, the battery diagnosis system can store the estimated full charge capacity and can also output it.

[0072] As described above, according to the battery diagnosis system of the first embodiment, even when there is a period in which the data of the battery 13 is not acquired, it is possible to estimate the full charge capacity more accurately based on the first SOC and the second SOC.

[0073] [Implementation Method 2]

[0074] Hereinafter, a secondary battery state diagnosis system according to Embodiment 2 will be described. Embodiment 2 partially changes the operation of calculation unit 32 in Embodiment 1. Hereinafter, descriptions of parts common to Embodiment 1 may be omitted.

[0075] Figure 5This is a flowchart showing the processing executed by the secondary battery status diagnosis system according to Embodiment 2. Steps S1 to S9 may be the same as those in Embodiment 1.

[0076] After step S9, the calculation unit 32 determines whether the difference between the second SOC and the first SOC is greater than or equal to a predetermined difference threshold (step S9a). As a specific example, the predetermined difference threshold is 5%. In this specific example, when the first SOC is 50% and the second SOC is 53%, the difference is 3%, and therefore the difference is determined to be less than the threshold. However, when the first SOC is 50% and the second SOC is 56%, the difference is 6%, and therefore the difference is determined to be greater than or equal to the threshold.

[0077] When the difference between the second SOC and the first SOC is less than the threshold, the battery diagnosis system ends. Figure 4 That is, the calculation unit 32 does not calculate the full charge capacity.

[0078] When the difference between the second SOC and the first SOC is equal to or greater than the threshold, the calculation unit 32 determines whether the magnitude of the current at the data acquisition unit ON time (time T5) acquired by the data acquisition unit 21 is equal to or less than a predetermined current threshold (step S9b).

[0079] If the current exceeds the predetermined current threshold, the battery diagnosis system ends. Figure 4 That is, the calculation unit 32 does not calculate the full charge capacity.

[0080] When the magnitude of the current is equal to or smaller than the predetermined current threshold, the calculation unit 32 calculates the full charge capacity of the battery 13 in the same manner as in the first embodiment (step S10 ).

[0081] The calculation unit 32 then estimates the SOH (State of Health) of the battery 13 based on the full charge capacity of the battery 13 (step S11). For example, the SOH is estimated as a value obtained by dividing a predetermined capacity (specifically, the initial full charge capacity) by the full charge capacity.

[0082] As described above, according to the battery diagnosis system of the second embodiment, similarly to the first embodiment, even when there is a period in which the data of the battery 13 is not acquired, it is possible to estimate a more accurate full charge capacity based on the first SOC and the second SOC.

[0083] Furthermore, in Embodiment 2, the full charge capacity is estimated only when the difference between the second SOC and the first SOC is 5% or greater, as determined in step S9a; otherwise, no estimation is made. Therefore, the full charge capacity is estimated only when a significant change in the SOC requires a new estimation, improving processing efficiency. Setting the threshold to 5% or greater allows for appropriate determination of whether a new full charge capacity estimation should be made. Furthermore, setting the threshold to 10% or greater is more preferable.

[0084] Furthermore, in the second embodiment, the full charge capacity is estimated only when a large current is not flowing (i.e., when a large charge or discharge is not occurring) at time T5, as determined in step S9b. Otherwise, no estimation is performed. When a large current is flowing, the accuracy of the full charge capacity estimation may decrease due to, for example, polarization of the battery 13. However, the determination in step S9b omits the full charge capacity estimation in such cases, thereby preventing the calculation of a low-accuracy full charge capacity.

[0085] Furthermore, in the second embodiment, SOH is estimated based on the full charge capacity, thereby being able to know the health or degradation state of the battery 13. For example, SOH can be estimated based on the relationship SOH = 100 × full charge capacity of battery / rated capacity of battery.

[0086] [Other embodiments]

[0087] In Embodiments 1 and 2, the determination processes of steps S8, S9a, and S9b can be implemented in any combination. For example, in Embodiment 1, step S8 can be omitted, and the full charge capacity can be estimated regardless of the natural discharge condition.

[0088] The hardware structure of the secondary battery status diagnosis system is not limited to Figure 1 The structure can be modified in various ways. For example, the calculation unit 32 can be provided in the telematics terminal 20 (in which case the telematics server 30 can be omitted). Alternatively, the data acquisition unit 21 and the calculation unit 32 can be provided in the battery management device 14 (in which case the telematics terminal 20 and the telematics server 30 can be omitted). Alternatively, the data acquisition unit 21 can be provided in the telematics server 30 (in which case the telematics terminal 20 can only have a relay function for data transmission and reception).

[0089] Description of Reference Signs

[0090] 10…Electric vehicles

[0091] 11…Electric motor

[0092] 11…Electric vehicles

[0093] 12…Inverter

[0094] 13…Battery

[0095] 14…Battery management device

[0096] 15…Ignition switch

[0097] 20…Telematics terminal (battery diagnostic system)

[0098] 21…Data Acquisition Department

[0099] 22…Wireless Communications Department

[0100] 30…Telematics server (battery diagnostic system)

[0101] 31…Wireless Communications Department

[0102] 32…Computing Department

[0103] T1…First Moment

[0104] T2…Second Moment

[0105] T5…the third moment

[0106] All publications, patents and patent applications cited in this specification are incorporated herein by reference.

Claims

1. A secondary battery status diagnosis system comprising a data acquisition unit and a calculation unit, It is characterized by: The data acquisition unit acquires current, voltage, and temperature related to a battery cell, or current, voltage, and temperature related to a battery pack in which a plurality of battery cells are combined. (a) when the battery cell or the battery pack is externally charged, the calculation unit calculates a first SOC using an SOC-OCV relationship table based on a first voltage at a first time when voltage application related to charging is started, wherein the SOC-OCV relationship table is a table indicating a relationship between voltage and SOC; (b) when the voltage application related to the charging ends at a second time, the calculation unit calculates a relaxation time of the battery cell or the battery pack based on the second voltage at the second time and the temperature; (c) when the data acquisition unit acquires a third voltage at a third time after the second time, the calculation unit calculates a second SOC based on the third voltage using the SOC-OCV relationship table; (d) When the time from the second time to the third time is equal to or longer than the relaxation time, the calculation unit estimates the full charge capacity of the battery cell or the battery pack based on the current related to the charge, the first SOC, and the second SOC.

2. The secondary battery status diagnosis system according to claim 1, wherein: The calculation unit estimates the full charge capacity when the difference between the second SOC and the first SOC is equal to or greater than a predetermined difference threshold.

3. The secondary battery status diagnosis system according to claim 1, wherein: The calculation unit calculates a first SOC based on a value obtained by subtracting an overvoltage from the first voltage, and / or calculates a second SOC based on a value obtained by subtracting an overvoltage from the third voltage.

4. The secondary battery status diagnosis system according to claim 1, wherein: The calculation unit estimates the full charge capacity when the magnitude of the current at the third time point acquired by the data acquisition unit is equal to or smaller than a predetermined current threshold.

5. The secondary battery status diagnosis system according to claim 1, wherein: The calculation unit further estimates the SOH of the battery cell or the battery pack based on the full charge capacity.

6. A method for diagnosing the status of a secondary battery, characterized in that: The data acquisition unit acquires the current, voltage, and temperature related to a battery cell, or the current, voltage, and temperature related to a battery pack in which a plurality of battery cells are combined. (a) when the battery cell or the battery pack is externally charged, the calculation unit calculates a first SOC using an SOC-OCV relationship table indicating a relationship between voltage and SOC based on a first voltage at a first time when voltage application related to charging is started; (b) when the voltage application related to the charging ends at a second time, the calculation unit calculates a relaxation time of the battery cell or the battery pack based on the second voltage at the second time and the temperature; (c) when the data acquisition unit acquires a third voltage at a third time after the second time, the calculation unit calculates a second SOC based on the third voltage using the SOC-OCV relationship table; (d) When the time from the second time to the third time is equal to or longer than the relaxation time, the calculation unit estimates the full charge capacity of the battery cell or the battery pack based on the current related to the charge, the first SOC, and the second SOC.

7. The secondary battery status diagnosis method according to claim 6, characterized in that: The calculation unit estimates the full charge capacity when the difference between the second SOC and the first SOC is equal to or greater than a predetermined difference threshold.

8. The secondary battery status diagnosis method according to claim 6, characterized in that: The calculation unit calculates a first SOC based on a value obtained by subtracting an overvoltage from the first voltage, and / or calculates a second SOC based on a value obtained by subtracting an overvoltage from the third voltage.

9. The secondary battery status diagnosis method according to claim 6, characterized in that: The calculation unit estimates the full charge capacity when the magnitude of the current at the third time point acquired by the data acquisition unit is equal to or smaller than a predetermined current threshold.

10. The secondary battery status diagnosis method according to claim 6, characterized in that: The calculation unit further estimates the SOH of the battery cell or the battery pack based on the full charge capacity.

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