Anomaly detection method and anomaly 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 apparatus for detecting an abnormality in a sub-battery that backs up a main battery.

Background Art

[0002] Patent Document 1 discloses a vehicle battery control device that detects an abnormality in a sub-battery that backs up a main battery. In this vehicle battery control device, a detection current for detecting an abnormality in the sub-battery is discharged, and for a plurality of battery cells constituting the sub-battery, the voltage of each battery cell before discharging the detection current and the voltage of each battery cell after discharging the detection current are compared respectively to calculate the voltage drop amount of each battery cell. When the difference between the voltage drop amount of one battery cell and the voltage drop amount of other battery cells is equal to or greater than a threshold value, it is determined that the sub-battery is abnormal.

Prior Art Literature

Patent Literature

[0003]

Patent Literature 1

Summary of the Invention

Problem to be Solved by the Invention

[0004] The above-mentioned Patent Document 1 discloses a technology for determining whether a battery is abnormal based on a cell voltage that fluctuates in accordance with a change in the state of charge (SOC) of the battery. This technology is effective for ternary lithium-ion batteries and the like, in which the change in open circuit voltage (OCV) corresponding to the SOC of the battery is easy to identify. However, there is a problem that it is difficult to apply this technology to lithium iron phosphate lithium-ion batteries (LFP batteries) and the like, which have a flat region in the so-called SOC-OCV characteristic where the change in OCV corresponding to the SOC of the battery is difficult to identify.

[0005] This disclosure has been made in view of the above-mentioned problems, and aims to provide a battery abnormality detection method and apparatus that is also effective for lithium iron phosphate batteries and the like. [Means for solving the problem]

[0006] To solve the above problems, one aspect of the disclosed technology is a method for detecting abnormalities in a sub-battery, which is a lithium iron phosphate battery that backs up a main battery, and the method includes 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 where the current is below a predetermined value for a predetermined time after discharging the predetermined amount of current; discharging a detection current from the sub-battery for detecting abnormalities in the sub-battery after the predetermined time has elapsed; calculating the voltage drop amount for each of the multiple battery cells constituting the sub-battery, which is the difference between the cell voltage at the start of discharge of the detection current and the cell voltage at the end of discharge; and determining that the sub-battery is abnormal if the difference between any two of the calculated voltage drop amounts is greater than or equal to a predetermined threshold. [Effects of the Invention]

[0007] According to the anomaly detection method described in this disclosure, anomalies can be effectively detected even when applied to lithium iron phosphate batteries and the like. [Brief explanation of the drawing]

[0008] [Figure 1] Functional block diagram of an anomaly detection device and its peripheral parts according to one embodiment of this disclosure. [Figure 2] A diagram showing an example of the SOC-OCV characteristics of a sub-battery. [Figure 3] Flowchart illustrating the processing procedure for detecting and controlling abnormalities in the auxiliary battery. [Figure 4] A flowchart illustrating the detailed procedure for anomaly detection processing. [Modes for carrying out the invention]

[0009] The anomaly detection method of this disclosure involves charging the sub-battery to a fully charged state, then pre-discharging it to a state of charge (SOC) where the voltage change gradient relative to the SOC is gradual, waiting for the polarization to be resolved by the discharge, and then performing an anomaly detection process on the sub-battery. Therefore, anomaly detection can be effectively performed even when applied to lithium iron phosphate batteries having a flat region. The embodiments of this disclosure will be described in detail below with reference to the drawings.

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

[0011] The configuration of the control device 100 shown in Figure 1 can, as an example, be installed in vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs) that implement functions requiring redundant power supply configurations, such as autonomous driving.

[0012] The main battery 10 is a rechargeable secondary battery, such as a lead-acid battery or a lithium-ion battery. The main battery 10 supplies the power it stores to a main load (primary system equipment) (not shown) or outputs it to a DC-DC converter 30. The main battery 10 can also store power output by a generator, such as an alternator (not shown). This main battery 10 may also form a power supply circuit together with a generator or other power source.

[0013] The sub-battery 20 is a rechargeable secondary battery configured by connecting multiple battery cells 211 to 21x (where x is an integer of 2 or more) in series. The sub-battery 20 in this embodiment is a lithium iron phosphate battery having a flat region in its SOC-OCV characteristics. Figure 2 shows an example of the SOC-OCV characteristics of the sub-battery 20. The sub-battery 20 stores power output from the main battery 10 via the DC-DC converter 30 and supplies the power it has stored to the sub-system load (secondary system equipment) 40. As an example, this 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 in the event of a power loss in the main battery 10.

[0014] The voltage of each of the multiple battery cells 211 to 21x constituting the sub-battery 20 can be detected by multiple voltage sensors 221 to 22x, and the current of the multiple battery cells 211 to 21x can be detected by a current sensor 230. These multiple voltage sensors 221 to 22x and current sensor 230 may be installed inside the sub-battery 20 or outside the sub-battery 20. The values ​​detected by the multiple voltage sensors 221 to 22x and current sensor 230 (the state of the sub-battery 20) are output to the abnormality detection device 100.

[0015] The DC-DC converter 30 is installed between the main battery 10 and the sub-battery 20 and sub-system load 40, and is a voltage converter that converts the voltage of the input main battery 10 into the voltage required by the sub-battery 20 and sub-system load 40 and outputs it. For example, a step-down type DC-DC converter that steps down the voltage of the main battery 10 and outputs it to the sub-battery 20 and sub-system load 40 can be used for this DC-DC converter 30. This DC-DC 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 its main power source and the sub battery 20 as a redundant power source, and operates with power supplied from the main battery 10 or power supplied from the sub battery 20 via the DCDC converter 30. This 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 loads that do not particularly require a redundant power supply configuration may be included in the sub load 40.

[0017] The abnormality detection device 100 is configured to detect an abnormality that has occurred in the sub battery 20 and determine whether the sub battery 20 is normal or abnormal. An abnormality of the sub battery 20 refers to, for example, a case where 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 the present embodiment, as the charge / discharge operation, a first operation (preliminary charge / discharge processing) for bringing the state of the sub battery 20 into a state suitable for performing abnormality detection, and a second operation (main charge / discharge processing) for performing abnormality detection are performed. Details of the charge / discharge processing performed by this 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 each cell voltage (voltage drop amount) of the plurality of battery cells 211 to 21x constituting the sub battery 20, and the difference between the changes in the cell voltages (voltage drop difference). Details of the calculation processing performed by this 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 difference) calculated by the calculation unit 120. Details of the determination processing performed by this determination unit 130 will be described later.

[0021] Part or all of this abnormality detection device 100 can typically be configured by an electronic control unit (ECU: Electronic Control Unit) including a processor such as a microcontroller, a memory, and an input / output interface. This electronic control unit can realize part or all of the functions performed by each configuration of the charge / discharge processing unit 110, calculation unit 120, and determination unit 130 described above by causing the processor to read and execute a program stored in the memory.

[0022] Control Next, with further reference to FIG. 3 and FIG. 4, the control performed by the abnormality detection device 100 according to the present embodiment will be described. FIG. 3 is a flowchart explaining the processing procedure of abnormality determination control for the sub-battery 20 executed by the abnormality detection device 100.

[0023] The abnormality determination control for the sub-battery 20 illustrated in FIG. 3 is started when a predetermined timing comes (for example, when the ignition of the vehicle is turned on or turned 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 based on the fact that the voltage of any cell among the plurality of battery cells 211 to 21x constituting the sub-battery 20 has reached a voltage equivalent to full charge (for example, 3.5V), or that the current flowing through the plurality of battery cells 211 to 21x has become equal to or lower than a predetermined current value (for example, 0.8A). Note that the voltage equivalent to full charge and the predetermined current value can be arbitrarily set according to the characteristics of the sub-battery 20. When the sub-battery 20 reaches the fully charged state, the process proceeds to step S302.

[0025] (Step S302) The charge / discharge processing unit 110 starts discharging the fully charged sub-battery 20 by supplying a constant current. This discharge is performed to change the state of charge (SOC) of the lithium iron phosphate battery from a region where the SOC-OCV characteristic has a steep slope to a region where it has a gentle slope. The constant current value is arbitrarily set according to the characteristics of the sub-battery 20. Once 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 determines whether the total amount of current discharged by the sub-battery 20 (hereinafter referred to as "discharge current") has reached a predetermined current. The predetermined current is the amount of current that indicates the storage rate (SOC) of the sub-battery 20 has decreased to the region of the gentle slope of the SOC-OCV characteristics. By discharging the sub-battery 20 by a predetermined current from a fully charged state, the characteristics of multiple battery cells 211~21x can be made uniform if the sub-battery 20 is functioning correctly. If it is determined that the discharge current has reached a predetermined current (step S303, yes), the process proceeds to step S304.

[0027] (Step S304) The charge / discharge processing unit 110 stops discharging the sub-battery 20 to a constant current value and maintains a state in which the current flowing from the sub-battery 20 is below a predetermined current value. This state maintenance is performed to eliminate the polarization caused by the discharge that has occurred in the sub-battery 20. The predetermined current value is arbitrarily set according to the characteristics of the sub-battery 20, but it is desirable that it be zero. Once the discharge from the sub-battery 20 is stopped and the state in which the current of the sub-battery 20 is below the predetermined current value is maintained, the process proceeds to step S305.

[0028] (Step S305) The charge / discharge processing unit 110 determines whether a predetermined time has elapsed since the discharge of the sub-battery 20 was stopped. This determination is made to determine whether the polarization of the sub-battery 20 has been resolved. Therefore, the predetermined time is set to a time (for example, 1 minute) in which it is estimated that the polarization has been sufficiently resolved, taking into consideration the characteristics of the sub-battery 20 and the balance with the required accuracy of anomaly detection. If it is determined that a predetermined time has elapsed since the discharge of the sub-battery 20 was stopped (step S305, yes), the process proceeds to step S306.

[0029] The processes described above from step S301 to step S305 constitute the first operation (pre-charge / discharge process) to bring the state of the sub-battery 20 into a state suitable for abnormality 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 Figure 4. Once the calculation unit 120 and the determination unit 130 have performed the abnormality detection process, the process proceeds to step S307.

[0031] (Step S307) The charge / discharge processing unit 110 charges the sub-battery 20 toward a fully charged state according to the result of the abnormality detection process in step S306 above. More specifically, if the sub-battery 20 is determined to be normal, or if the detection discharge of the sub-battery 20 is unsuccessful (described later), or if the detection preconditions are not met (described later), the sub-battery 20 is charged toward a fully charged state. Even if the sub-battery 20 is determined to be abnormal, if the abnormality does not affect the safe operation of the vehicle, the sub-battery 20 may be charged toward a fully charged state. Once the charge / discharge processing unit 110 has charged the sub-battery 20 toward a fully charged state, the abnormality detection control of the sub-battery 20 is terminated.

[0032] [Anomaly detection process (Figure 4)] Figure 4 is a flowchart illustrating the detailed procedure of the anomaly detection process (step S306) in Figure 3.

[0033] (Step S401) The calculation unit 120 acquires the cell voltage of each of the multiple battery cells 211 to 21x that make up the sub-battery 20 when the charge / discharge processing unit 110 starts discharging the sub-battery 20. Once the calculation unit 120 has acquired the cell voltages of each of the multiple battery cells 211 to 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 arbitrarily set according to the characteristics of the sub-battery 20. When the discharge of the detection current from the sub-battery 20 begins, the process proceeds to step S403.

[0035] (Step S403) The charge / discharge processing unit 110 determines whether the discharge of the detected current from the sub-battery 20 has finished. The end of discharge can be determined by the elapsed time of a predetermined discharge period. When the discharge of the detected current from the sub-battery 20 has finished, 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 to 21x that make up the sub-battery 20 when the charge / discharge processing unit 110 has finished discharging the sub-battery 20. Once the calculation unit 120 has acquired the cell voltages of each of the multiple battery cells 211 to 21x (at the end of discharge), the process proceeds to step S405.

[0037] (Step S405) The determination unit 130 determines whether the detection discharge of the sub-battery 20 was successful and whether the detection preconditions were met. This determination can be made based on whether the detection current is flowing above a predetermined threshold, whether the temperature and / or state of charge (SOC) of the sub-battery 20 is within a predetermined detection range, whether there is no variation in the temperature difference within the battery pack (within a predetermined threshold), whether there is no variation in the difference in the SOC of each battery cell 211 to 21x (within a predetermined threshold), and whether the multiple voltage sensors 221 to 22x and current sensor 230 are functioning correctly. If the determination unit 130 determines that the detection discharge of the sub-battery 20 was successful and the detection preconditions were met (step S405, yes), the process proceeds to step S406. On the other hand, if the determination unit 130 cannot determine that the detection discharge of the sub-battery 20 was successful and that the detection preconditions were met (step S405, no), the abnormality detection process for the main sub-battery 20 is terminated (returning to step S307 in Figure 3).

[0038] (Step S406) The calculation unit 120 calculates the voltage drop and the voltage drop difference based on the cell voltages acquired in steps S401 and S404, respectively. The voltage drop dVn indicates the amount of voltage reduction due to detection discharge for the cell voltage of battery cells 21n (n=1 to x), and is the voltage obtained by subtracting the cell voltage Vcen at the end of discharge from the cell voltage Vcsn at the start of discharge (Vcsn-Vcen). The voltage drop difference △dVn indicates the difference in cell voltage between multiple battery cells 211 to 21x, and is typically the absolute difference (|dVn-dVm|) between the voltage drop dVn of two electrically adjacent battery cells 21n and the voltage drop dVm of battery cell 21m (m=n-1). Note that for the last battery cell 21x of the sub-battery 20, the voltage drop difference △dVx (=|dVx-dV1|) is calculated between it and the first battery cell 211. Furthermore, the voltage drop difference △dVn can be determined under arbitrary conditions other than those for two adjacent battery cells. Once the calculation unit 120 calculates the voltage drop for each cell and the voltage drop difference is calculated from these voltage drop amounts, the process proceeds to step S407.

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

[0040] (Step S408) The determination unit 130 determines that there is an abnormality in the sub-battery 20 (abnormality determination). When the sub-battery 20 is determined to be abnormal, the abnormality detection process for the main sub-battery 20 ends (return to step S307 in Figure 3).

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

[0042] <Effects and Actions> According to the abnormality 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 in which the battery state is determined, then pre-discharge is performed to a storage rate (SOC) where the voltage gradient of the SOC-OCV characteristics is gentle, in order to prevent false detection due to cell imbalance, and then abnormality detection processing is performed on the sub-battery after waiting for the polarization associated with this pre-discharge to be resolved.

[0043] Therefore, the abnormality detection method according to one embodiment of this disclosure can effectively detect abnormalities even when applied to lithium iron phosphate batteries and the like, which have a flat region in the SOC-OCV characteristics where there is almost no change in voltage in response to fluctuations in the storage rate (SOC).

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

[0045] The anomaly detection method and anomaly detection device described herein can be used in vehicles equipped with a sub-battery that backs up the main battery, etc. [Explanation of Symbols]

[0046] 10 Main battery 20 auxiliary batteries 30 DC-DC converters 40 Subsystem load 211~21x battery cells 221~22x Voltage Sensor 230 Current Sensor 100 Anomaly detection device 110 Charge / Discharge Processing Unit 120 Calculation Unit 130 Judgment section

Claims

1. A method for detecting abnormalities in a sub-battery, which is a lithium iron phosphate battery that backs up the main battery, The steps include: charging the aforementioned auxiliary battery until it is fully charged; The steps include: discharging a predetermined amount of current from the fully charged sub-battery to indicate that the storage rate of the sub-battery has decreased to a predetermined flat region where the voltage change gradient in the SOC-OCV characteristics is gentler; The steps include: discharging the predetermined current amount and then maintaining the sub-battery in a state where the current is below a predetermined value until a predetermined time has elapsed; After the predetermined time has elapsed, the step of discharging a detection current from the sub-battery to detect an abnormality in the sub-battery, The steps include: calculating the voltage drop, which is the difference between the cell voltage at the start of discharge and the cell voltage at the end of discharge, for each of the multiple battery cells constituting the sub-battery; An abnormality detection method comprising the step of determining that the sub-battery is abnormal if the difference between any two of the multiple voltage drop amounts calculated is greater than or equal to a predetermined threshold.

2. An anomaly detection device that detects abnormalities in a sub-battery, which is a lithium iron phosphate battery that backs up the main battery, A charging unit for charging the aforementioned sub-battery to a fully charged state, A first discharge unit discharges a predetermined amount of current from the fully charged sub-battery, which indicates that the storage rate of the sub-battery has decreased to a predetermined flat region where the voltage change gradient in the SOC-OCV characteristics is gentle, A processing unit that, after discharging a predetermined amount of current from the sub-battery, maintains the sub-battery in a state where the current is below a predetermined value until a predetermined time has elapsed, After the predetermined time has elapsed, a second discharge unit discharges a detection current from the sub-battery to detect an abnormality in the sub-battery, A calculation unit calculates the voltage drop amount, which is the difference between the cell voltage at the start of discharge and the cell voltage at the end of discharge, for each of the multiple battery cells constituting the sub-battery, An abnormality detection device comprising: a determination unit that determines an abnormality in the sub-battery based on whether the difference between any two of the calculated voltage drop amounts is greater than or equal to a predetermined threshold.

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

4. The abnormality detection device according to claim 2 or 3, wherein the difference between any two of the aforementioned voltage drop amounts is the difference between the voltage drop amounts of two electrically adjacent battery cells.

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