Abnormality detection method and abnormality detection device

Abstract

To provide an abnormality detection method of a battery that is effectively applied even to an LFP-based battery.SOLUTION: An abnormality detection method of a sub-battery (an LFP-based battery) that performs back-up of a main battery includes the steps of: charging the sub-battery up to a fully charged state; discharging a predetermined amount of current from the sub-battery in a fully charged state; maintaining the sub-battery in a state in which the current is equal to or less than a predetermined value until predetermined time elapses after the predetermined amount of current is discharged from the sub-battery; discharging a detection current for detecting abnormality of the sub-battery from the sub-battery after the predetermined time elapses; calculating the amount of a voltage drop that is difference between a cell voltage at the start of discharge of the detection current and a cell voltage at the end of discharge of the detection current for each of a plurality of battery cells constituting the sub-battery; and determining that the sub-battery is abnormal when difference between any two amounts of voltage drop among the plurality of calculated amounts of the voltage drop is equal to or greater than a predetermined threshold value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method and device for detecting an abnormality in a sub-battery that backs up a main battery. [Background technology]

[0002] Patent Document 1 discloses a vehicle battery control device that detects an abnormality in a sub-battery that backs up a main battery. This vehicle battery control device discharges a detection current for detecting an abnormality in the sub-battery, and for multiple battery cells that make up the sub-battery, calculates the amount of voltage drop in each battery cell by comparing the voltage of each battery cell before discharging the detection current with the voltage of each battery cell after discharging the detection current, and determines that the sub-battery is abnormal if the difference between the voltage drop amount of each battery cell and the voltage drop amount of other battery cells is equal to or greater than a threshold value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent application No. 2022-072365 Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned Patent Document 1 is a technology for determining the presence or absence of a battery abnormality based on the cell voltage that varies with the change in the battery's state of charge (SOC). This technology is effective for ternary lithium-ion batteries and the like, in which the change in open circuit voltage (OCV) according to the battery's state of charge (SOC) is easy to see, but there is a problem in that it is difficult to apply to iron phosphate lithium-ion batteries (LFP batteries) and the like, in which the change in open circuit voltage (OCV) according to the battery's state of charge (SOC) is difficult to see and the so-called SOC-OCV characteristic has a flat region.

[0005] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a method and device for detecting an abnormality in a battery that can be effectively applied to iron phosphate lithium-ion batteries and the like. [Means for solving the problem]

[0006] In order to solve the above problems, one aspect of the disclosed technology is a method for detecting an abnormality in a sub-battery, which is an iron phosphate lithium-ion battery that backs up a main battery, the abnormality detection method including the steps of charging the sub-battery to a fully charged state, discharging a predetermined amount of current from the fully charged sub-battery, maintaining the sub-battery in a state in which the current is equal to or less than a predetermined value until a predetermined time has elapsed after discharging the predetermined amount of current, discharging a detection current from the sub-battery for detecting an abnormality in the sub-battery after the predetermined time has elapsed, calculating a voltage drop amount, which is the difference between the cell voltage at the start of discharging the detection current and the cell voltage at the end of discharging, for each of multiple battery cells that constitute the sub-battery, and determining that the sub-battery is abnormal if the difference between any two of the multiple calculated voltage drop amounts is equal to or greater than a predetermined threshold. Effect of the Invention

[0007] According to the anomaly detection method of the present disclosure, anomaly detection can be effectively performed even when applied to an iron phosphate lithium ion battery or the like. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a functional block diagram of an anomaly detection device and its peripheral components according to an embodiment of the present disclosure. [Diagram 2] A diagram showing an example of the SOC-OCV characteristics of a sub-battery [Diagram 3] A flowchart for explaining the procedure for controlling abnormality determination of the sub-battery [Figure 4] Flowchart for explaining detailed procedures of anomaly detection processing DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The anomaly detection method disclosed herein charges the sub-battery to a fully charged state, then pre-discharges it to a state of charge SOC where the gradient of voltage change with respect to the state of charge SOC is gentle, and waits for the polarization caused by discharging to disappear before performing anomaly detection processing on the sub-battery. Therefore, even when applied to a lithium-ion iron phosphate battery with a flat region, anomaly detection can be effectively performed. Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0010] <Embodiment> [composition] 1 is a functional block diagram of an anomaly detection device 100 according to an embodiment of the present disclosure and its peripheral parts. The functional block illustrated in FIG. 1 includes a main battery 10, a sub-battery 20, a DC-DC converter 30, a sub-load 40, and the anomaly detection device 100.

[0011] The configuration of the control device 100 shown in FIG. 1 can be installed, for example, in vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs) that are equipped with functions that require a redundant power supply configuration, such as autonomous driving.

[0012] The main battery 10 is a chargeable and dischargeable secondary battery such as a lead-acid battery or a lithium-ion battery. The main battery 10 supplies its own stored power to a main load (primary system device) (not shown) and outputs it to the DCDC converter 30. The main battery 10 can also store power output by a generator such as an alternator (not shown). The main battery 10 may form a power supply circuit together with a generator that can serve as a power supply source.

[0013] The sub-battery 20 is a chargeable and dischargeable secondary battery configured by connecting multiple battery cells 211-21x (x is an integer of 2 or more) in series. The sub-battery 20 of this embodiment is an iron phosphate lithium ion battery having a flat region in the SOC-OCV characteristic. FIG. 2 shows an example of the SOC-OCV characteristic of the sub-battery 20. The sub-battery 20 stores the power output from the main battery 10 via the DCDC converter 30, and supplies the power stored in the sub-battery 20 to a sub-system load (secondary system device) 40. As an example, the sub-battery 20 has a backup function that maintains (continues) the power supply to the sub-system load 40 in place of the main battery 10 when a power failure occurs in the main battery 10.

[0014] The cell voltages of the multiple battery cells 211-21x that constitute the sub-battery 20 can be detected by multiple voltage sensors 221-22x, respectively, and the currents of the multiple battery cells 211-21x can be detected by a current sensor 230. The multiple voltage sensors 221-22x and the current sensor 230 may be provided inside the sub-battery 20 or outside the sub-battery 20. Values ​​detected by the multiple voltage sensors 221-22x and the current sensor 230 (the state of the sub-battery 20) are output to the abnormality detection device 100.

[0015] The DCDC converter 30 is a voltage converter provided between the main battery 10 and the sub-battery 20 and sub-load 40, and converts the input voltage of the main battery 10 into a voltage required for the sub-battery 20 and sub-load 40 and outputs it. For example, a step-down type DCDC converter that steps down the voltage of the main battery 10 and outputs it to the sub-battery 20 and sub-load 40 can be used for this DCDC converter 30. This DCDC converter 30 is configured to be controllable by the abnormality detection device 100.

[0016] The sub-load 40 is an in-vehicle device that uses the main battery 10 as a main power source and the sub-battery 20 as a redundant power source, and operates on power supplied from the main battery 10 or the sub-battery 20 via the DCDC converter 30. The sub-load 40 includes loads that require a redundant power supply configuration, such as important in-vehicle devices related to safe driving of the vehicle. Note that the sub-load 40 may also include loads that do not particularly require a redundant power supply configuration.

[0017] The abnormality detection device 100 is configured to detect an abnormality that occurs in the sub-battery 20 and determine whether the sub-battery 20 is normal or abnormal. An abnormality in the sub-battery 20 is, for example, a state in which the main battery 10 cannot be backed up in an emergency such as a failure of the main battery 10. This abnormality detection device 100 includes a charge / discharge processing unit 110, a calculation unit 120, and a determination unit 130.

[0018] The charge / discharge processing unit 110 controls the DCDC converter 30 to control the charge / discharge operation of the sub-battery 20. In this embodiment, the charge / discharge operation includes a first operation (pre-charge / discharge process) for making the state of the sub-battery 20 suitable for performing anomaly detection, and a second operation (main charge / discharge process) for performing anomaly detection. Details of the charge / discharge process performed by the charge / discharge processing unit 110 will be described later.

[0019] The calculation unit 120 acquires the state of the sub-battery 20 in the second operation, and calculates the change in cell voltage (amount of voltage drop) of each of the multiple battery cells 211-21x constituting the sub-battery 20 and the difference between the changes in the cell voltage (voltage drop amount difference). Details of the calculation process performed by the calculation unit 120 will be described later.

[0020] The determination unit 130 determines whether or not an abnormality has occurred in the sub-battery 20 based on the results (voltage drop amount, voltage drop amount difference) calculated by the calculation unit 120. The determination process performed by the determination unit 130 will be described in detail later.

[0021] A part or the whole of the anomaly detection device 100 may be configured by an electronic control unit (ECU) that typically includes a processor such as a microcomputer, a memory, an input / output interface, etc. This electronic control unit can realize a part or the whole of the functions performed by each of the components of the charge / discharge processing unit 110, the calculation unit 120, and the determination unit 130 described above by having the processor read and execute a program stored in the memory.

[0022] [control] Next, the control performed by the anomaly detection device 100 according to this embodiment will be described with further reference to Figures 3 and 4. Figure 3 is a flowchart illustrating the processing procedure of the anomaly determination control of the sub-battery 20 performed by the anomaly detection device 100.

[0023] The abnormality determination control for the sub-battery 20 illustrated in FIG. 3 is started at a predetermined timing (for example, when the ignition of the vehicle is turned on or off).

[0024] (Step S301) The charge / discharge processing unit 110 charges the sub-battery 20 until it reaches a fully charged state. The fully charged state can be determined by, for example, whether the cell voltage of any one of the multiple battery cells 211-21x constituting the sub-battery 20 has reached a voltage equivalent to a fully charged state (e.g., 3.5 V) or whether the current flowing through the multiple battery cells 211-21x has reached a predetermined current value (e.g., 0.8 A) or less. The voltage equivalent to a fully charged state and the predetermined current value can be set arbitrarily in accordance with the characteristics of the sub-battery 20. When the sub-battery 20 reaches a fully charged state, the process proceeds to step S302.

[0025] (Step S302) The charge / discharge processing unit 110 starts discharging the sub-battery 20, which is in a fully charged state, by flowing a constant current. This discharge is performed to change the charge rate SOC of the iron phosphate lithium ion battery from a region where the SOC-OCV characteristic has a steep gradient to a region where the gradient is gentle. The constant current value is set arbitrarily according to the characteristics of the sub-battery 20. When the charge / discharge processing unit 110 starts discharging the sub-battery 20, the process proceeds to step S303.

[0026] (Step S303) The charge / discharge processing unit 110 judges whether the total amount of current discharged by the sub-battery 20 (hereinafter referred to as the "discharge current amount") has reached a predetermined current amount. The predetermined current amount is a current amount that indicates that the charge rate SOC of the sub-battery 20 has fallen to a region with a gentle gradient in the SOC-OCV characteristic. By discharging the sub-battery 20 from a fully charged state by a predetermined current amount, it is possible to make the characteristics of the multiple battery cells 211-21x uniform if the sub-battery 20 is normal. If it is judged that the discharge current amount has reached the predetermined current amount (Yes in step S303), the process proceeds to step S304.

[0027] (Step S304) The charge / discharge processing unit 110 stops discharging the constant current value from the sub-battery 20 and maintains a state in which the current flowing from the sub-battery 20 is equal to or less than a predetermined current value. This state is maintained in order to eliminate polarization caused by discharging in the sub-battery 20. The predetermined current value is set arbitrarily in accordance with the characteristics of the sub-battery 20, but is preferably zero. When discharging from the sub-battery 20 is stopped and a state in which the current of the sub-battery 20 is maintained equal to or less than the predetermined current value is maintained, the process proceeds to step S305.

[0028] (Step S305) The charge / discharge processing unit 110 judges whether a predetermined time has passed since the discharge of the sub-battery 20 was stopped. This judgment is made to judge whether the polarization of the sub-battery 20 has been eliminated. Therefore, the predetermined time is set to a time (e.g., one minute) at which the polarization is estimated to be sufficiently eliminated, taking into consideration the balance between the characteristics of the sub-battery 20 and the required accuracy of abnormality detection. If it is judged that the predetermined time has passed since the discharge of the sub-battery 20 was stopped (Yes in step S305), the process proceeds to step S306.

[0029] The above-mentioned processes from step S301 to step S305 correspond to a first operation (pre-charge / discharge process) for putting the sub-battery 20 into a state suitable for performing anomaly detection.

[0030] (Step S306) The calculation unit 120 and the determination unit 130 perform an abnormality detection process to determine whether the sub-battery 20 is normal or abnormal. This abnormality detection process corresponds to the second operation (main charge / discharge process). Details of the abnormality detection process will be described later with reference to FIG. 4. After the abnormality detection process is performed by the calculation unit 120 and the determination unit 130, the process proceeds to step S307.

[0031] (Step S307) The charge / discharge processing unit 110 charges the sub-battery 20 toward the full charge state according to the result of the abnormality detection processing in step S306. More specifically, if the sub-battery 20 is determined to be normal, or if the detection and discharging of the sub-battery 20 is not successful (described later), or if the detection precondition is not met (described later), the sub-battery 20 is charged toward the full charge state. Note that even if the sub-battery 20 is determined to be abnormal, the sub-battery 20 may be charged toward the full charge state as long as the abnormality does not affect the safe running of the vehicle. When the charge / discharge processing unit 110 charges the sub-battery 20 toward the full charge state, the abnormality determination control for the sub-battery 20 ends.

[0032] [Anomaly detection process (Fig. 4)] FIG. 4 is a flowchart illustrating a detailed procedure of the abnormality detection process (step S306) in FIG.

[0033] (Step S401) The calculation unit 120 acquires the cell voltage of each of the multiple battery cells 211-21x constituting the sub-battery 20 when the charge / discharge processing unit 110 starts discharging the sub-battery 20. When the calculation unit 120 acquires the cell voltage of each of the multiple battery cells 211-21x (at the start of discharge), the process proceeds to step S402.

[0034] (Step S402) The charge / discharge processing unit 110 discharges a detection current from the sub-battery 20 to detect an abnormality in the sub-battery 20. The amount of the detection current and the discharge time are set arbitrarily according to the characteristics of the sub-battery 20. When discharge of the detection current from the sub-battery 20 starts, the process proceeds to step S403.

[0035] (Step S403) The charge / discharge processing unit 110 determines whether or not the discharge of the detection current from the sub-battery 20 has ended. The end of discharge can be determined by the passage of a predetermined discharge time. When the discharge of the detection current from the sub-battery 20 has ended, the process proceeds to step S404.

[0036] (Step S404) The calculation unit 120 acquires the cell voltage of each of the multiple battery cells 211-21x constituting the sub-battery 20 when discharging of the sub-battery 20 by the charge / discharge processing unit 110 is completed. When the calculation unit 120 acquires the cell voltage of each of the multiple battery cells 211-21x (at the end of discharging), the process proceeds to step S405.

[0037] (Step S405) The determination unit 130 judges whether the detection discharge of the sub-battery 20 was successful and the detection preconditions are met. This judgment can be made based on whether the detection current is equal to or greater than a predetermined threshold, whether the temperature and / or the charge rate SOC of the sub-battery 20 is within a predetermined detection range, whether there is no variation in the temperature difference in the battery pack (within a predetermined threshold), whether there is no variation in the charge rate SOC of each battery cell 211-21x (within a predetermined threshold), whether the multiple voltage sensors 221-22x and the current sensor 230 are normal, etc. If the determination unit 130 judges that the detection discharge of the sub-battery 20 was successful and the detection preconditions are met (Yes in step S405), the process proceeds to step S406. On the other hand, if the judgment unit 130 cannot determine that the detected discharge of the sub-battery 20 was successful and the detection prerequisites are met (step S405, No), the abnormality detection process for the sub-battery 20 ends (return to step S307 in Figure 3).

[0038] (Step S406) The calculation unit 120 calculates the voltage drop amount and the voltage drop amount difference based on the cell voltages acquired in steps S401 and S404. The voltage drop amount dVn indicates the amount of voltage drop caused by the detected discharge in the cell voltage of the battery cell 21n (n=1 to x), and is the voltage (Vcsn-Vcen) obtained by subtracting the cell voltage Vcen at the end of the discharge from the cell voltage Vcsn at the start of the discharge. The voltage drop amount difference ΔdVn indicates the difference in cell voltage between the multiple battery cells 211 to 21x, and is typically the absolute value difference (|dVn-dVm|) between the voltage drop amount dVn of two electrically adjacent battery cells 21n and the voltage drop amount dVm of the battery cell 21m (m=n-1). Note that the voltage drop amount difference ΔdVx (=|dVx-dV1|) between the rearmost battery cell 21x of the sub-battery 20 and the first battery cell 211 is calculated. It should be noted that the voltage drop difference ΔdVn can be obtained under any condition other than that between two adjacent battery cells. After the voltage drop amounts are calculated by the calculation unit 120 and the voltage drop differences are calculated from the voltage drop amounts, the process proceeds to step S407.

[0039] (Step S407) The determination unit 130 determines whether or not there are a predetermined number or more of voltage drop amount differences that are equal to or greater than a predetermined threshold among the voltage drop amount differences calculated in step S406. This determination is made to determine the degree of variation in cell voltage, and the predetermined threshold and the predetermined number can be set arbitrarily based on the performance required of the sub-battery 20, etc. If the determination unit 130 determines that there are a predetermined number or more voltage drop amount differences that are equal to or greater than the predetermined threshold (step S407, Yes), the process proceeds to step S408. On the other hand, if the determination unit 130 determines that there are not a predetermined number or more voltage drop amount differences that are equal to or greater than the predetermined threshold (step S407, No), the process proceeds to step S409.

[0040] (Step S408) The determination unit 130 determines that an abnormality has occurred in the sub-battery 20 (abnormality determination). When an abnormality has been determined in the sub-battery 20, the abnormality detection process for the sub-battery 20 ends (return to step S307 in FIG. 3).

[0041] (Step S409) The determination unit 130 determines that the sub-battery 20 is normal (normal determination). When the sub-battery 20 is determined to be normal, this abnormality detection process for the sub-battery 20 ends (return to step S307 in FIG. 3).

[0042] <Actions and Effects> According to the anomaly detection method and apparatus according to one embodiment of the present disclosure described above, the sub-battery is first charged to a fully charged state at which the battery state is determined, and then, in order to prevent erroneous detection due to a loss of cell balance, a pre-discharge is performed down to a storage rate SOC at which the voltage gradient of the SOC-OCV characteristic is gentle, and then an anomaly detection process is performed on the sub-battery after waiting for the elimination of polarization associated with this pre-discharge.

[0043] Therefore, the anomaly detection method according to an embodiment of the present disclosure can effectively detect anomalies even when applied to an iron phosphate lithium ion battery or the like having a flat region in the SOC-OCV characteristic where there is almost no change in voltage in response to fluctuations in the storage rate SOC.

[0044] One embodiment of the present disclosure has been described above, but the present disclosure can be understood as not only the above-mentioned anomaly detection method and anomaly detection device, but also as a program for causing a computer to execute the anomaly detection method, a computer-readable non-transitory recording medium storing the program, or a vehicle equipped with an anomaly detection device. [Industrial Applicability]

[0045] The abnormality detection method and abnormality detection device disclosed herein can be used in vehicles equipped with a sub-battery that backs up a main battery. [Explanation of symbols]

[0046] 10 Main battery 20 Sub Battery 30 DC-DC Converter 40 Subsystem Load 211~21x Battery Cells 221~22x Voltage Sensor 230 Current Sensor 100 Anomaly detection device 110 Charging and discharging processing unit 120 Calculation section 130 Judgment section

Claims

1. A method for detecting an abnormality in a sub-battery that is a lithium-ion iron phosphate battery that backs up a main battery, comprising: charging the sub-battery until it is fully charged; discharging a predetermined amount of current from the sub-battery in a fully charged state; maintaining the sub-battery in a state where the current is equal to or less than a predetermined value until a predetermined time has elapsed after discharging the predetermined amount of current; discharging a detection current from the sub-battery after the predetermined time has elapsed to detect an abnormality in the sub-battery; calculating a voltage drop amount, which is a difference between a cell voltage at the start of discharging the detected current and a cell voltage at the end of discharging, for each of a plurality of battery cells constituting the sub-battery; and determining that the sub-battery is abnormal if a difference between any two of the calculated voltage drop amounts is equal to or greater than a predetermined threshold.

2. An abnormality detection device that detects an abnormality in a sub-battery, which is a lithium-ion iron phosphate battery that backs up a main battery, a charging unit that charges the sub-battery until it is fully charged; a first discharge unit that discharges a predetermined amount of current from the sub-battery in a fully charged state; a processing unit that maintains the sub-battery in a state where the current is equal to or less than a predetermined value until a predetermined time has elapsed after discharging the predetermined amount of current from the sub-battery; a second discharge unit that discharges a detection current from the sub-battery after the predetermined time has elapsed, the detection current being used to detect an abnormality in the sub-battery; a calculation unit that calculates a voltage drop amount, which is a difference between a cell voltage at the start of discharging the detected current and a cell voltage at the end of discharging, for each of the plurality of battery cells that constitute the sub-battery; an abnormality detection device comprising: a judgment unit that judges an abnormality in the sub-battery based on whether a difference between any two of the calculated multiple voltage drop amounts is greater than or equal to a predetermined threshold value.

3. The abnormality detection device according to claim 2 , wherein the determination unit determines that the sub-battery is abnormal when the difference in the amount of voltage drop that is equal to or greater than the predetermined threshold value exceeds a predetermined number.

4. 4 . The abnormality detection device according to claim 2 , wherein the difference between any two of the voltage drop amounts is a difference between the voltage drop amounts of two of the battery cells that are electrically adjacent to each other.

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