Open-circuit voltage measurement method and open-circuit voltage measurement device

Abstract

Provided is a method and apparatus for measuring open circuit voltage capable of accurately grasping the deterioration state of a secondary battery even when the secondary battery mounted on a vehicle is in a low SOC state. The method includes the steps of: charging a secondary battery for a certain period of time until polarization characteristics are eliminated (ST2) in the case where the secondary battery is discharged and is in a low charge rate state; determining whether or not measurement of open circuit voltage (OCV) of the secondary battery is possible (ST6); and performing measurement of OCV of the secondary battery (ST7) in the case where it is determined that measurement of OCV is possible.

Description

Technical Field

[0001] The embodiments of the present invention relate to an open-circuit voltage measurement method and an open-circuit voltage measurement device. Background Technology

[0002] Patent Document 1 discloses a technique for measuring the open-circuit voltage (hereinafter appropriately referred to as "OCV") when the charge rate (hereinafter appropriately referred to as "SOC: State of Charge") of the chemical battery installed in a vehicle is high.

[0003] The technology disclosed in Patent Document 1 shows that a stable OCV is determined by allowing a chemical cell in a high SOC state to wait for a predetermined time. By measuring the stable OCV, the health state (or, manifested as a "deterioration state", hereinafter appropriately referred to as "SOH: State of Health") can be determined with high precision.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2013-061337 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] In estimating SOH, high-precision estimation requires not only accurate measurement of the OCV value under high charge rate (high SOC) conditions but also accurate measurement of the OCV value under low charge rate (low SOC) conditions. In the technology disclosed in Patent Document 1, as described above, to ensure the accuracy of the measurement under high SOC conditions, a stable OCV measurement is performed by waiting for a predetermined time.

[0009] On the other hand, the measurement of OCV under low SOC conditions is not mentioned. Furthermore, in the case of secondary batteries installed in vehicles, for example, they may discharge while driving and reach a low SOC state after driving, but the voltage of a secondary battery in a low SOC state is usually unstable. Under such unstable voltage conditions, it is impossible to reliably measure OCV.

[0010] Furthermore, by allowing the secondary battery to stand for a period of time after discharge, such as waiting for a predetermined time as shown in Patent Document 1, voltage stabilization can be achieved. However, in many cases, vehicle users start charging immediately after driving, and the voltage of the secondary battery is unstable during charging, making it difficult to measure stable OCV even at low SOC.

[0011] This invention was made to solve the above-mentioned problems. The purpose of this invention is to provide an open-circuit voltage measurement method and device that can perform high-precision OCV measurement even when the secondary battery installed in the vehicle is in a low SOC state, thereby enabling high-precision understanding of the degradation state of the secondary battery.

[0012] Solution for solving the problem

[0013] The open-circuit voltage measuring device in the embodiment includes: a measurement condition determination unit that determines whether the open-circuit voltage (OCV) of the secondary battery can be measured; a charging current control unit that, when the secondary battery is discharged and in a low charge rate state, performs a charging process to charge the secondary battery for a certain period of time until the polarization characteristics are eliminated; and an OCV measuring unit that, when the measurement condition determination unit determines that the OCV can be measured, performs the OCV measurement of the secondary battery in a low charge rate state.

[0014] In addition, the open-circuit voltage measurement method in the embodiment includes the following steps: when the secondary battery is discharged and in a low charge rate state, charging the secondary battery for a certain period of time until the polarization characteristics are eliminated; determining whether the open-circuit voltage (OCV) of the secondary battery can be measured; and if it is determined that the OCV can be measured, performing the OCV measurement of the secondary battery.

[0015] The effects of the invention

[0016] This invention employs such a structure and measurement method that it is possible to perform high-precision OCV measurement even when the secondary battery installed in the vehicle is in a low SOC state, thereby enabling a high-precision understanding of the degradation state of the secondary battery. Attached Figure Description

[0017] Figure 1 This is a block diagram illustrating the internal structure of the open-circuit voltage measuring device according to an embodiment of the present invention.

[0018] Figure 2 This is a schematic diagram showing the voltage change of a secondary battery installed in a vehicle over time.

[0019] Figure 3 Is Figure 2 The timeline shown in the diagram is circled.

[0020] Figure 4 This is a flowchart illustrating the process of measuring the OCV (Open Circuit Voltage) to understand the degradation state of a secondary battery using the open circuit voltage measuring device in an embodiment of the present invention.

[0021] Figure 5 This is a flowchart illustrating the process of measuring the OCV (Open Circuit Voltage) to understand the degradation state of a secondary battery using the open circuit voltage measuring device in an embodiment of the present invention. Detailed Implementation

[0022] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Please note that the drawings are schematic and may differ from actual embodiments. Furthermore, the embodiments of the present invention shown below illustrate apparatus and methods for implementing the technical concept of the present invention; the technical concept of the present invention is not limited to the structure and arrangement of the constituent components as described below. Various modifications can be made to the technical concept of the present invention within the technical scope defined by the claims.

[0023] Figure 1 This is a block diagram showing the internal structure of the open-circuit voltage measuring device 1 according to an embodiment of the present invention. This open-circuit voltage measuring device 1 is particularly used for high-precision measurement of the OCV (open-circuit voltage value) of a vehicle-mounted battery (secondary battery) in a low SOC (state of charge) state. Furthermore, the OCV value measured by the open-circuit voltage measuring device 1 is used to estimate the degradation state of the measured secondary battery.

[0024] Regarding this, use Figure 2 Let me explain. Figure 2 This is a schematic diagram illustrating the voltage change of a secondary battery installed in a vehicle over time. Figure 2 In the diagram, the vertical axis represents the value of "voltage," and the horizontal axis represents "time." Furthermore, a solid line is used to represent the change of voltage over time.

[0025] "IGNOFF" indicates that the ignition system has switched from on to off, while "IGNON" indicates that the ignition system has switched from off to on. During the initial "IGNOFF1" to "IGNON" period, the vehicle is in a state where the power supply is not connected, i.e., the vehicle is parked, and therefore the voltage of the secondary battery gradually decreases.

[0026] Furthermore, when the vehicle transitions from this state to "IGNON" and is in motion, the battery discharges due to power consumption during driving, thus reducing the voltage of the secondary battery. Then, when driving ends and the vehicle stops, the ignition system is deactivated again (represented by the time point "IGNOFF2"). In this state, as... Figure 2 As shown, the voltage of the secondary battery is at its lowest value due to discharge. When the vehicle's journey ends, the user, for example, connects the charger to the vehicle to perform a charging process in preparation for the next trip. Through this charging process, the voltage of the secondary battery rises again. This is represented by the voltage value gradually increasing as it moves from "IGNOFF2" to the right of the horizontal axis indicating time.

[0027] exist Figure 2 In the figure, two downward arrows are shown parallel to the vertical axis representing voltage. These two arrows indicate the timing for measuring OCV. The arrow on the left of the figure indicates the timing for measuring OCV under low SOC conditions, and the arrow on the right of the figure indicates the timing for measuring OCV under high SOC conditions. Moreover, SOH (deterioration state) is calculated using the following equation (1).

[0028]

[0029] That is, ΔSOC is calculated using the OCV values ​​under low SOC and high SOC conditions. Furthermore, the displacement (ΔAh) between the time intervals in which OCV is measured is divided by this ΔSOH, and this result is further divided by the capacity of the secondary battery when it is brand new (new capacity), thereby calculating SOH (deterioration state).

[0030] The open-circuit voltage measuring device 1 in the embodiments of the present invention is mainly used when measuring the OCV under a low SOC state. On the other hand, as mentioned above, the calculation of SOH also requires measuring the OCV under a high SOC state.

[0031] Therefore, the OCV under this high SOC state is determined using existing OCV measurement methods and devices. Alternatively, the open-circuit voltage measuring device 1 in this embodiment of the invention can also be used to measure the OCV under the high SOC state.

[0032] Back Figure 1 The open-circuit voltage measuring device 1 includes an information acquisition unit 11, a measurement condition determination unit 12, a charging current control unit 13, an OCV measuring unit 14, and a degradation state determination unit 15. However, regarding these components constituting the open-circuit voltage measuring device 1, Figure 1 Only the structures necessary to illustrate embodiments of the present invention are shown.

[0033] Therefore, it may also include a display device for indicating the final determined state of degradation of the secondary battery, an input device for inputting parameters and conditions required for measuring OCV, or a communication control device for connecting the open-circuit voltage measuring device 1 to an external device. Alternatively, it may be provided with a storage unit that stores various information such as conditions set for performing the OCV measurement and the program for measuring OCV.

[0034] Furthermore, the following description assumes that the open-circuit voltage measuring device 1 is configured as a single device. However, the open-circuit voltage measuring device may also be installed inside, for example, a battery management system (BMS), a control device that controls the entire vehicle, or connected to such devices.

[0035] Furthermore, in embodiments of the present invention, the secondary battery to which the assessment of deterioration is made is a battery capable of multiple charge-discharge cycles, such as a storage battery installed in a vehicle or a storage battery installed in an electric vehicle to provide driving force. Additionally, various types exist as "secondary batteries," and lithium-ion batteries can be cited as an example.

[0036] The information acquisition unit 11 receives information such as "on" or "off" from the battery controller, or information about the charger being connected to the secondary battery, which is necessary for measuring OCV and estimating the degradation state of the secondary battery.

[0037] The measurement condition determination unit 12 determines whether the open-circuit voltage measuring device 1 can measure the OCV of the secondary battery being measured. For example, it determines whether the voltage of the secondary battery is stable. That is, when the secondary battery has polarization characteristics, there is a possibility of voltage instability, such as a sharp drop in voltage. Moreover, when the voltage changes and is unstable, it is impossible to measure the OCV, or it is impossible to measure the OCV with high accuracy. Therefore, it is necessary to determine whether the voltage of the secondary battery is stable enough to allow the open-circuit voltage measuring device 1 to measure the OCV.

[0038] When determining whether the voltage of the secondary battery is stable, the following methods can be used, for example: measuring the voltage of the secondary battery, obtaining the voltage change (ΔV) at multiple different times, and determining whether the voltage change is within a predetermined threshold range.

[0039] Alternatively, the following method can be used: pre-determine the time until the voltage of the secondary battery recovers and stabilizes after the vehicle has finished driving and is in a discharged state, and determine that the voltage of the secondary battery is stable based on the elapsed time.

[0040] In order to accurately measure the OCV of the secondary battery in a low SOC state, the charging current control unit 13 controls the charging process when performing charging processing on the secondary battery. The charging current control unit 13 detects that a charger is connected to the vehicle and starts charging.

[0041] In other words, in order to accurately measure OCV when the secondary battery is at a low SOC state, the voltage in the secondary battery must be stable. Voltage stabilization takes time during the recovery process of a secondary battery that has been discharged while driving. Furthermore, as mentioned above, the user may have already started charging before the voltage stabilizes.

[0042] Therefore, in embodiments of the present invention, for example, a short-term charging process is performed on the secondary battery when the user has already started charging, thereby actively eliminating polarization characteristics. That is, a pre-set charging process for a certain period of time is performed in order to eliminate polarization characteristics and stabilize the voltage.

[0043] On the other hand, if charging continues for an extended period, the charging process will proceed from a low SOC state to a high SOC state, which is no different from normal charging. However, the voltage becomes unstable during charging. Therefore, when it is determined that a charging time corresponding to the charging current has elapsed and preset conditions are met, the charging current control unit 13 controls the charging current to decrease compared to the charging current during the charging process.

[0044] If the measurement condition determination unit 12 determines that OCV measurement can be performed under a low SOC condition, the OCV measurement unit 14 performs the OCV measurement. The OCV measurement method performed by the OCV measurement unit 14 can be any known method. The measured OCV value is sent to the degradation condition determination unit 15.

[0045] The degradation state determination unit 15 uses the OCV value measured in the OCV measurement unit 14 under a low SOC state to determine the degradation state of the secondary battery. Specifically, based on the OCV information under the low SOC state and the OCV information under the high SOC state, the SOH is calculated using the above formula (1) to determine the degradation state. In addition, for example, a display device is used to notify the user of the degradation state of the secondary battery determined by the degradation state determination unit 15.

[0046] The functions of each part of the open-circuit voltage measuring device 1 are as described above. Therefore, a time diagram is used to further explain the operation of each part. Figure 3 Is Figure 2 The timeline shown in the diagram is circled.

[0047] exist Figure 3The timeline diagram shows the operation of various components in the vehicle, including the battery controller and charger, under low SOC conditions, using "on" and "off" indicators. Changes in current and voltage are also shown. On the left side of the timeline, from top to bottom, the following devices are displayed: Battery Management System (BMS), Ignition System, Charger, Vehicle Controller (HEVC), Current, and Voltage. Furthermore, the timeline is shown as it progresses from left to right.

[0048] The leftmost part of the timeline shows the ignition system changing from "on" to "off". Because the ignition system is now off, the battery controller is also off. Furthermore, the secondary battery is at its lowest discharge point at this time, indicated by the solid line representing the lowest voltage. This position is... Figure 2 The location of “IGNOFF2” in the text.

[0049] Regarding the "ignition system," it will remain in the "off" state for the time being and will not change to the "on" state. On the other hand, the "battery controller" will also become "off" at the same time as the "ignition system" becomes "off," but will immediately change back to "on." The trigger for the "battery controller" to become "on" is, for example, when the user performs certain actions on the vehicle.

[0050] When the "battery controller" is switched to "on", the open-circuit voltage measuring device 1 immediately measures the change in voltage. That is, the information acquisition unit 11 acquires the information that the "battery controller" has been switched to "on" and sends this information to the measurement condition determination unit 12. In the measurement condition determination unit 12, based on the "battery controller" being switched to "on", the information acquisition unit 11 acquires voltage values ​​at multiple times from the voltmeter and calculates the voltage change ΔV between these voltage values.

[0051] Furthermore, this explanation assumes that the measurement condition determination unit 12 obtains the voltage value from the voltmeter, but for example, it may also be set that the measurement condition determination unit 12 obtains the voltage value itself.

[0052] On the other hand, as mentioned above, after driving, the user charges the vehicle for the next trip. Specifically, the user plugs the charger into the vehicle's charging port to connect the charger to the vehicle. At this point, the charger switches from "disconnected" to "connected".

[0053] Furthermore, charging begins at the exact time when preparations for the actual charging process are complete. Additionally, when charging begins, the Vehicle Controller (HEVC) changes from an "off" to an "on" state. Moreover, the current value increases upon initiation of the charging process.

[0054] However, the charging process here is merely a process performed to enable the open-circuit voltage measuring device 1 to measure the OCV when the secondary battery is in a low SOC state. Therefore, as described above, the charging current control unit 13 performs a charging process that charges the secondary battery for a certain period of time until the polarization characteristics are eliminated.

[0055] Furthermore, the charging current control unit 13 determines whether preset conditions are met before a certain period of time has elapsed. The current control unit 13 performs this determination to confirm whether the open-circuit voltage measuring device 1 can measure the open-circuit voltage (OCV) after a certain period of time has elapsed.

[0056] Here, pre-set conditions include, for example, the temperature of the secondary battery and whether the state of charge (SOC) condition is met. The former is used to confirm whether the secondary battery is in a high temperature state, such as above 60°C, or a low temperature state, such as below 0°C. This is because if the secondary battery is in an excessively high or low temperature state, it is difficult to accurately measure the open-circuit voltmeter (OCV).

[0057] Furthermore, the purpose of the open-circuit voltage measuring device 1 in the embodiments of the present invention is particularly to measure the OCV in a low SOC state. However, if the SOC state is already high at that point, the open-circuit voltage measuring device 1 does not need to perform the OCV measurement process thereafter. Therefore, the charging current control unit 13 determines whether the open-circuit voltage measuring device 1 can perform the OCV measurement process thereafter based on the preset SOC conditions.

[0058] Furthermore, these conditions can be stored by the charging current control unit 13, or they can also be stored in... Figure 1 For example, in the storage section (not shown) of the open-circuit voltage measuring device 1.

[0059] If the charging current control unit 13 determines that the preset conditions are met, it controls the charging current to decrease compared to the charging current during the charging process. In other words, it limits the amount of charge applied to the secondary battery.

[0060] This is because if such charging continues, it will be a so-called secondary battery charging process from low SOC to high SOC. Since the voltage is unstable during the charging process, the result will be that the OCV can no longer be measured.

[0061] On the other hand, the reason why the charging current control unit 13 performs the control of limiting the charging amount as described above and does not perform the process of interrupting (stopping) the charging process is as follows. That is, if the charging is interrupted after the charging has started, for example, the vehicle controller determines that the charger has stopped charging and starts the process after the charging has stopped if it does not resume charging for a certain period of time.

[0062] Therefore, the charging current control unit 13 performs a process of limiting the charging current to a level lower than the charging current during the charging process. Furthermore, in this case, the charging current is limited to a level that will not be considered a charging interruption. Thus, the preset conditions here can be considered as conditions for determining whether the charging current control unit 13 should limit the charging amount of the secondary battery.

[0063] exist Figure 3 This is shown in the text. That is, observation. Figure 3 The "Current" column in the time graph shows the state where there is no current flow before charging begins (zero charge), but the charging current increases as charging begins. Furthermore, a constant charging current is supplied to the secondary battery before the charging current control unit 13 limits the charging current.

[0064] In parallel with the charging process, the charging current control unit 13 determines whether the above conditions are met. If the conditions are met, the charging current is limited. However, the charging current limited by the charging current control unit 13 is different from the current before charging started. This is to avoid interrupting the charging process. Furthermore, after the open-circuit voltage measuring device 1 measures the OCV (Open Circuit Voltage), which will be described later, the charging current control unit 13 restarts the charging process.

[0065] When the charging current is limited by the charging current control unit 13, the condition determination unit 12 determines whether the polarization characteristics of the secondary battery have been eliminated, i.e., whether the voltage is stable. Therefore, as Figure 3 As shown, the measurement condition determination unit 12 calculates the value of ΔV and determines whether it is within a preset threshold range. If the result indicates that the voltage of the secondary battery is stable, the OCV measurement unit 14 measures the OCV of the secondary battery. Figure 3 (OCV Measurement 1 in the timeline).

[0066] Furthermore, the determination unit 12 does not immediately perform the aforementioned determination after the charging current is limited by the charging current control unit 13 because it considers that the voltage is unstable immediately after the charging current is limited. Therefore, the determination is performed after a short interval.

[0067] The OCV information measured by the OCV measuring unit 14 under the low SOC state is sent to the degradation state determination unit 15. In the degradation state determination unit 15, based on the obtained OCV information under the low SOC state and the additionally obtained OCV information under the high SOC state, the SOH is calculated using the above formula (1), and the degradation state of the secondary battery is determined.

[0068] Furthermore, the degradation state determination unit 15 can obtain information about the OCV under high SOC conditions from other measuring devices, or it can obtain the results measured by the open-circuit voltage measuring device 1 in the embodiment of the present invention. Additionally, the value of "ΔAh" can also be calculated in the degradation state determination unit 15, for example.

[0069] Furthermore, regarding the "new capacity," it is measured before shipment from the factory, and the measured value is used as the new capacity for each secondary battery (rechargeable battery). Therefore, it is stored in the storage unit as a constant parameter. Thus, the degradation condition determination unit 15 can also obtain this new capacity information from the storage unit.

[0070] The process for measuring OCV under low SOC conditions by the open-circuit voltage measuring device 1 is basically as described above. However, for example, consider the case where the OCV under low SOC conditions can be measured before the charging current control unit 13 performs the process of limiting the amount of charging current.

[0071] Specifically, the following situations: the ignition system is "disconnected" after the vehicle has been driven. Figure 2 After “IGNOFF2” and before the charger is connected to the vehicle to start charging, for example, when the determination condition unit 12 determines whether the voltage of the secondary battery is stable, it determines that the voltage is stable.

[0072] Alternatively, the following condition may also apply: the measurement condition determination unit 12 determines that a predetermined time has elapsed since the ignition device was "disconnected" in the vehicle. As mentioned above, even a secondary battery that is in a discharged state due to driving will have its polarization characteristics eliminated and its voltage stabilized after a period of time, such as 6 hours. That is, the following condition applies: time has elapsed without the user performing charging.

[0073] In these cases, it is believed that the OCV under low SOC conditions can be measured immediately without charging the secondary battery through the charging current control unit 13 to stabilize the voltage of the secondary battery.

[0074] Therefore, when the measurement condition determination unit 12 determines that the conditions described above are met, the open-circuit voltage measuring device 1 performs an OCV measurement before connecting the charger. Figure 3 In the timeline, “OCV Measurement 2” indicates an OCV measurement performed at such a time interval.

[0075] Furthermore, if the determination of whether the voltage of the secondary battery is stable by the measurement condition determination unit 12 is determined to be unstable, or if the determination of whether to limit the charging current by the charging current control unit 13 is determined to be unlimited, the open-circuit voltage measuring device 1 will not measure the OCV. Therefore, SOH will not be calculated, and the determination of the degradation state of the secondary battery will not be performed.

[0076] [action]

[0077] Next, the process for measuring OCV under low SOC conditions by the open-circuit voltage measuring device 1 will be explained. Figure 4 and Figure 5 This is a flowchart illustrating the process of determining the deterioration state of a secondary battery by measuring the open-circuit voltage (OCV) using the open-circuit voltage measuring device 1 in an embodiment of the present invention.

[0078] In addition, Figure 4 In the flowchart shown, the process begins after the vehicle has started moving and the voltage has decreased due to the discharge of the secondary battery during driving. Figure 2 The state of “IGNOFF2” is shown.

[0079] Moreover, Figure 3 In terms of the timeline, after the battery controller transitions from the "off" state to the "on" state, the following is... Figure 4 The flowchart begins. Additionally, in Figure 4 or Figure 5 In the flowchart, secondary batteries are referred to as "storage batteries".

[0080] First, the measurement condition determination unit 12 determines whether the OCV (ST1) under a low SOC state can be measured by the open circuit voltage measuring device 1. The measurement conditions here are, for example, whether the change in voltage converges to a certain range relative to a threshold, or whether a preset time has elapsed after the secondary battery being measured has been "disconnected" from the ignition device.

[0081] The measurement condition determination unit 12 determines the measurement condition. If the measurement condition of OCV is not met (ST1 "No"), it further determines whether the charger has been connected to the battery (secondary battery), that is, whether the charging process has started (ST2).

[0082] If it is determined that charging has started ("Yes" in ST2), the charging current control unit 13 controls the charging current for a certain period of time. Then, before the certain period of time has elapsed, the charging current control unit 13 determines whether the condition for limiting the charging current is met (ST3).

[0083] As described above, the conditions for limiting the charging current here refer to conditions such as the temperature of the secondary battery and whether the SOC condition is met. If the charging current control unit 13 determines that the charging current limiting condition is met (ST3 "Yes"), the charging current control unit 13 limits the charging current (ST4).

[0084] In the measurement condition determination unit 12, a determination is made as to whether the charging current is limited by the charging current control unit 13 (ST5). If it is determined that the charging current is limited (ST5 is "Yes"), then it is determined whether the measurement condition of OCV is met (ST6). Here, as described above, the measurement condition determination unit 12 determines whether the voltage is stable, for example, by comparing the amount of voltage change with a threshold.

[0085] As a result, if the measurement condition determination unit 12 determines that the voltage is stable (ST6 "Yes"), this result is sent to the OCV measurement unit 14, where the OCV measurement is performed (ST7). This state is... Figure 3 The timing in the time graph is indicated as "OCV Measurement 1".

[0086] In the OCV measurement unit 14, the measured OCV information is sent to the degradation state determination unit 15. In the degradation state determination unit 15, a low SOC (State of Occurrence) is calculated based on the measured OCV information. Figure 5 (ST8). Furthermore, the SOH (ST9) is calculated using an additional calculated high SOC, for example, based on equation (1) above. Then, the degradation state of the secondary battery is determined based on the calculated SOH (ST10).

[0087] On the other hand, OCV measurement is not performed when the battery is not charged (ST2 "No"), when the condition for limiting the charging current by the charging current control unit 13 is not met (ST3 "No"), when the measurement condition determination unit 12 determines that the charging current is not limited (ST5 "No"), or when the OCV measurement condition is not met (ST6 "No"). Figure 5 (ST11). Moreover, in these cases, SOH is not calculated, nor is the degradation state of the secondary battery determined.

[0088] Furthermore, if the measurement condition determination unit 12 determines the OCV measurement condition (ST1) before charging of the secondary battery begins (ST2), and the measurement condition is determined to be met (ST1 indicates "Yes"), the OCV is measured by the open-circuit voltage measuring device 1 at that time point (ST12). This measurement is equivalent to... Figure 3 "OCV Measurement 2" is shown in the time graph.

[0089] Then, the low SOC is calculated based on the measurement of OCV, and the SOH is calculated using other available information such as the high SOC. As a result, the degradation state of the secondary battery is determined in the degradation state determination unit 15. Figure 5 (ST8~ST10).

[0090] As explained above, by using the open-circuit voltage measurement method and open-circuit voltage measurement device in the embodiments of the present invention, even if the secondary battery installed in the vehicle is in a low SOC state, high-precision OCV measurement can be performed, and the degradation state of the secondary battery can be accurately grasped.

[0091] Furthermore, during the voltage recovery process after discharge in the secondary battery, the OCV under low SOC conditions can be measured as early as possible. Therefore, the difference between the SOH (severity of decay) and the OCV under high SOC conditions can be obtained more significantly. Consequently, the value of ΔSOC relative to ΔAh can be increased, allowing for more accurate estimation of the secondary battery's degradation state.

[0092] Furthermore, the explanation up to this point has been based on the premise that when the open-circuit voltage measuring device 1 charges the secondary battery to measure the OCV in a low SOC state, a charging process is performed for a certain period of time until the polarization characteristics of the secondary battery are eliminated. However, although the polarization characteristics of the secondary battery vary depending on the load current, the types of chargers connected to the vehicle are diverse, and the load current flowing during the charging process also varies.

[0093] Therefore, the charging current control unit 13 can also control the charging process according to each type of connected charger after the secondary battery charging begins, so as to charge according to the charging time corresponding to the charging current. That is, when the charging current control unit 13 performs such control, the charging time is shorter when the charging current for the secondary battery is large. On the other hand, the charging time is longer when the charging current is small.

[0094] Furthermore, so far, the determination of whether the polarization characteristics of the secondary battery have been eliminated, i.e. whether the measurement conditions have been met, has been explained based on the premise of comparing the change in voltage with a threshold.

[0095] However, alternative methods are also possible, such as the following: A timeframe is pre-set for the period from when the vehicle stops and the secondary battery's charging rate gradually recovers until the voltage stabilizes; the measurement conditions are determined to be met based on the elapsed time. Alternatively, both the method using the voltage change and the method using the time can be combined.

[0096] [Effects of the Example]

[0097] (1) Includes the following steps: when the secondary battery is discharged and in a low charge rate state, charge the secondary battery for a certain period of time until the polarization characteristics are eliminated; determine whether the open circuit voltage (OCV) of the secondary battery can be measured; and if it is determined that the OCV can be measured, perform the OCV measurement of the secondary battery.

[0098] By using this OCV measurement method, the OCV in a low SOC state can be measured, thereby enabling high-precision measurement of OCV even in a low SOC state. In particular, by performing a charging process on a secondary battery that has been discharged and is in a low charge rate (low SOC) state for a certain period of time, the polarization characteristics in the secondary battery can be eliminated.

[0099] (2) Includes the following steps: After starting to charge the secondary battery, determine whether the charging time corresponding to the charging current has elapsed and whether the preset conditions are met, including the following steps: If these conditions are met, control the charging current to be reduced compared to the charging current during the charging process.

[0100] By controlling the charging current, the polarization characteristics of the secondary battery can be eliminated during the charging process, and further charging can be avoided, thus enabling the measurement of OCV under stable voltage conditions. Furthermore, by controlling the charging current to reduce the amount of charging current during the charging process to a level that does not interrupt the charging process, the OCV measurement process can be performed while avoiding situations deemed as charging interruptions.

[0101] (3) The determination of whether OCV can be measured is made by the following steps: comparing the change in voltage of the secondary battery with a preset threshold. If the change in voltage is determined to be stable, it is determined that OCV can be measured.

[0102] By limiting the charging current in the charging current control unit and then determining whether the voltage of the secondary battery is stable, a higher precision OCV measurement can be performed.

[0103] (4) Before charging the secondary battery, the following steps are included: determining whether OCV measurement can be performed.

[0104] In the open-circuit voltage measurement method of the embodiments of the present invention, the secondary battery to be measured is charged before performing the OCV measurement, and it is determined whether the voltage is stable. Therefore, higher accuracy OCV measurement is possible.

[0105] (5) Includes the following steps: after starting to charge the secondary battery, determine whether the charging time corresponding to the charging current has elapsed and whether the preset conditions are met; if the preset conditions are not met, control the amount of charging current to maintain the charging current.

[0106] Generally, OCV is measured after the secondary battery has been charged following discharge. However, depending on the conditions, it is sometimes possible to measure OCV without charging. Therefore, in order to enable OCV measurement in such cases, the measurement condition determination unit determines the feasibility of OCV measurement before charging the secondary battery.

[0107] (6) After performing the OCV measurement step, the following steps are included: using the measured OCV information to determine the degradation state of the secondary battery.

[0108] By performing OCV measurements in this way, not only can we obtain OCV information, but we can also use this OCV information to calculate SOC and SOH, thereby determining the degradation state of the secondary battery.

[0109] (7) In the step of determining the degradation state of the secondary battery, the OCV information of the secondary battery when it is in a low charge rate state and the OCV information of the secondary battery when it is charged and in a high charge rate state are used to determine the degradation state of the secondary battery.

[0110] By performing such a degradation state determination process, the degradation state of the secondary battery can be determined with high precision using information from the highly accurate measured OCV.

[0111] (8) An open-circuit voltage measuring device for measuring the open-circuit voltage (OCV) of a secondary battery, the open-circuit voltage measuring device comprising: a measurement condition determination unit that determines whether OCV measurement can be performed; a charging current control unit that performs a charging process for charging the secondary battery for a certain period of time until the polarization characteristics are eliminated when the secondary battery is discharged and in a low charge rate state; and an OCV measuring unit that performs OCV measurement when the measurement condition determination unit determines that OCV measurement can be performed when the secondary battery is in a low charge rate state.

[0112] By using such an open-circuit voltage measuring device to measure the OCV in a low SOC state, the OCV can be measured with high accuracy even in a low SOC state. In particular, by performing a charging process on a secondary battery that has been discharged and is in a low charge rate (low SOC) state for a certain period of time, the polarization characteristics in the secondary battery can be eliminated.

[0113] Explanation of reference numerals in the attached figures

[0114] 1: Open circuit voltage measuring device; 11: Information acquisition unit; 12: Measurement condition determination unit; 13: Charging current control unit; 14: OCV measuring unit; 15: Deterioration state determination unit.

Claims

1. A method for measuring open-circuit voltage, characterized in that, Includes the following steps: When the secondary battery is discharged and in a low charge rate state, the secondary battery is charged for a certain period of time until the polarization characteristics are eliminated. Determine whether the open-circuit voltage (OCV) of the secondary battery can be measured. as well as If it is determined that the OCV measurement can be performed, the OCV measurement of the secondary battery is performed.

2. The method for measuring open-circuit voltage according to claim 1, characterized in that, The open-circuit voltage measurement method includes the following steps: after starting to charge the secondary battery, determining whether a charging time corresponding to the charging current has elapsed and whether a preset condition has been met. The open-circuit voltage measurement method includes the following steps: under these conditions, control is performed to reduce the charging current compared to the charging current during the charging process.

3. The method for measuring open-circuit voltage according to claim 1, characterized in that, The determination of whether the OCV can be measured is made by the following steps: comparing the change in voltage of the secondary battery with a preset threshold, and if the change in voltage is determined to be stable, it is determined that the OCV can be measured.

4. The method for measuring open-circuit voltage according to claim 2, characterized in that, The determination of whether the OCV can be measured is made by the following steps: comparing the change in voltage of the secondary battery with a preset threshold, and if the change in voltage is determined to be stable, it is determined that the OCV can be measured.

5. The method for measuring open-circuit voltage according to claim 1, characterized in that, Before charging the secondary battery, the following steps are included: determining whether the OCV measurement can be performed.

6. The open-circuit voltage measuring device according to claim 1, characterized in that, The open-circuit voltage measurement method includes the following steps: after starting to charge the secondary battery, determining whether a charging time corresponding to the charging current has elapsed and whether a preset condition has been met. If it is determined that the preset conditions are not met, control is performed to maintain the charging current.

7. The method for determining open-circuit voltage according to any one of claims 1 to 6, characterized in that, After performing the OCV measurement step, the following steps are included: using the measured OCV information to determine the degradation state of the secondary battery.

8. The method for measuring open-circuit voltage according to claim 7, characterized in that, In the step of determining the degradation state of the secondary battery, the OCV information of the secondary battery when it is in a low charge rate state and the OCV information of the secondary battery when it is charged and in a high charge rate state are used to determine the degradation state of the secondary battery.

9. An open-circuit voltage measuring device, characterized in that, have: The measurement condition determination unit determines whether the open-circuit voltage (OCV) of the secondary battery can be measured. The charging current control unit performs a charging process that charges the secondary battery for a certain period of time until the polarization characteristics are eliminated when the secondary battery is discharged and in a low charging rate state. as well as When the measurement condition determination unit determines that the OCV measurement can be performed, the OCV measurement unit performs the measurement of the OCV when the secondary battery is in a low charge rate state.

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