OCV measurement method and OCV measurement device

Abstract

Provided are an OCV measurement method and an OCV measurement device that enable highly accurate OCV measurement even when a secondary battery installed in a vehicle is in a low SOC state, thereby allowing the deterioration state of the secondary battery to be ascertained with high accuracy. The present invention comprises: a step (ST2) in which, when a secondary battery has been discharged and is in a low charge state, the secondary battery is charged for a set time until a polarization characteristic is eliminated; a step (ST6) in which it is determined whether the open circuit voltage (OCV) of the secondary battery can be measured; and a step (ST7) in which, when it has been determined that the OCV can be measured, the OCV of the secondary battery is measured.

Description

OCV measurement method and OCV measurement device

[0001] An embodiment of the present invention relates to an OCV measurement method and an OCV measurement device.

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

[0003] The technology disclosed in Patent Document 1 shows that a stable OCV is measured for a chemical battery in a high SOC state by waiting for a specified time. By measuring the stable OCV, it is possible to determine the state of health (also referred to as a "degraded state"; hereinafter, referred to as "SOH: State of Health") with high accuracy.

[0004] JP 2013-061337 A

[0005] In order to estimate the SOH with high accuracy, it is necessary to measure with high accuracy not only the OCV value at a high state of charge (high SOC) but also the OCV value at a low state of charge (low SOC). In the technology disclosed in Patent Document 1, as described above, in order to ensure the accuracy of measurement at a high SOC, stable OCV measurement is performed by waiting for a specified time.

[0006] On the other hand, there is no mention of measuring the OCV in a low SOC state. Furthermore, in the case of a secondary battery mounted on a vehicle, for example, it is discharged while driving and reaches a low SOC state after driving, but the voltage of the secondary battery in a low SOC state is often unstable. In such an unstable voltage state, the OCV cannot be measured stably.

[0007] Furthermore, the voltage of the secondary battery can be stabilized by waiting a certain period of time even after discharge, such as waiting for a specified period of time as shown in Patent Document 1. However, after driving, the vehicle user often starts charging immediately, and the voltage of the secondary battery is not stable during charging, making it difficult to measure the OCV stably in a low SOC state.

[0008] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an OCV measurement method and an OCV measurement device that enable highly accurate measurement of the OCV of a secondary battery mounted on a vehicle even when the secondary battery is in a low SOC state, thereby making it possible to grasp the deterioration state of the secondary battery with high accuracy.

[0009] The OCV measuring device in the embodiment includes a measurement condition determination unit that determines whether or not it is possible to measure the open circuit voltage (OCV) of the secondary battery, a charging current control unit that executes a charging process to charge 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 state of charge, and an OCV measuring unit that executes measurement of the OCV of the secondary battery when it is in a low state of charge when it is determined by the measurement condition determination unit that it is possible to measure the OCV.

[0010] Moreover, the OCV measurement method in the embodiment includes the steps of: 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 charging rate state; determining whether or not it is possible to measure the open circuit voltage (OCV) of the secondary battery; and measuring the OCV of the secondary battery when it is determined that it is possible to measure the OCV.

[0011] Because the present invention employs such a configuration and measurement method, it is possible to measure the OCV with high accuracy even when the secondary battery mounted on a vehicle is in a low SOC state, thereby making it possible to grasp the deterioration state of the secondary battery with high accuracy.

[0012] Fig. 3 is a block diagram showing the internal configuration of an OCV measurement device according to an embodiment of the present invention. Fig. 4 is a schematic diagram showing changes in voltage over time of a secondary battery mounted on a vehicle. Fig. 5 is a time chart of the portion surrounded by a circle in the schematic diagram shown in Fig. 2. Fig. 6 is a flowchart showing a flow of measuring OCV by an OCV measurement device according to an embodiment of the present invention and understanding the deterioration state of a secondary battery. Fig. 7 is a flowchart showing a flow of measuring OCV by an OCV measurement device according to an embodiment of the present invention and understanding the deterioration state of a secondary battery.

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the drawings are schematic and may differ from the actual product. Furthermore, the embodiments of the present invention shown below are merely examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not limit the structure, arrangement, etc. of the components to those described below. The technical concept of the present invention can be modified in various ways within the technical scope defined by the claims.

[0014] 1 is a block diagram showing the internal configuration of an OCV measurement device 1 according to an embodiment of the present invention. The OCV measurement device 1 is used to measure with high accuracy the OCV of a battery (secondary battery) mounted on a vehicle, particularly when the battery is in a low SOC state. The OCV value measured by the OCV measurement device 1 is used to estimate the degradation state of the measured secondary battery.

[0015] This point will be explained using Figure 2. Figure 2 is a schematic diagram showing the change in voltage over time of a secondary battery mounted on a vehicle. In Figure 2, the vertical axis represents the "voltage" value, and the horizontal axis represents "time." The solid line shows the change in voltage over time.

[0016] "IGNOFF" indicates when the ignition is switched from on to off, and conversely, "IGNON" indicates when the ignition is switched from off to on. Between the initial "IGNOFF1" and "IGNON", the vehicle is not powered on, i.e., the vehicle is stopped, so the voltage of the secondary battery gradually drops.

[0017] Then, when the power switch switches from this state to "IGNON" and the vehicle starts to drive, the secondary battery voltage drops as power is consumed and discharged during driving. Then, when driving ends and the vehicle is stopped, the ignition is turned off again (the point indicated as "IGNOFF2"). In this state, as shown in FIG. 2, the secondary battery voltage is at its lowest due to discharge. When the user finishes driving the vehicle, for example, the user connects a charger to the vehicle and performs a charging process in preparation for the next drive. This charging process causes the secondary battery voltage to rise again. This is indicated by the voltage value gradually increasing from "IGNOFF2" toward the right side of the horizontal axis indicating time.

[0018] In Figure 2, two downward arrows are shown parallel to the vertical axis indicating voltage. These two arrows indicate the timing for measuring the OCV. The arrow on the left side of the drawing indicates the timing for measuring the OCV in a low SOC state, and the arrow on the right side of the drawing indicates the timing for measuring the OCV in a high SOC state. Then, the SOH (state of health) is calculated using the following equation (1):

[0019] SOH = (ΔAh / ΔSOC) / new capacity (1)

[0020] That is, ΔSOC is calculated using the OCV value in a low SOC state and the OCV value in a high SOC state. The SOH (state of health) is calculated by dividing the change (ΔAh) between the timings of OCV measurements by ΔSOH, and then dividing this result by the capacity of the secondary battery when it was new (new capacity).

[0021] The OCV measuring device 1 according to the embodiment of the present invention is mainly used to measure the OCV in a low SOC state. However, as described above, it is also necessary to measure the OCV in a high SOC state in order to calculate the SOH.

[0022] Therefore, for the OCV in the high SOC state, a value measured using an existing OCV measurement method or measurement device is used. Of course, the OCV in the high SOC state may also be measured using the OCV measurement device 1 according to the embodiment of the present invention.

[0023] 1 , the OCV measuring device 1 includes an information acquiring unit 11, a measurement condition determining unit 12, a charging current control unit 13, an OCV measuring unit 14, and a degradation state determining unit 15. However, with regard to the components constituting the OCV measuring device 1, only the components necessary for explaining the embodiment of the present invention are shown in FIG.

[0024] Therefore, the OCV measuring device 1 may be provided with a display device that shows the final result of the determined deterioration state of the secondary battery, an input device for inputting parameters and conditions required for measuring the OCV, or a communication control device for connecting an external device to the OCV measuring device 1. Alternatively, the OCV measuring device 1 may be provided with a storage unit that stores various information such as conditions set for measuring the OCV and a program for measuring the OCV.

[0025] The following description will be given on the assumption that the OCV measuring device 1 is configured as a single device. However, the OCV measuring device may be provided inside a battery controller (Battery Management System: BMS) or a control device that controls the entire vehicle, for example. Alternatively, the OCV measuring device may be connected to these devices and used.

[0026] In the present embodiment, the secondary battery whose degradation state is to be estimated is a battery that can be charged and discharged multiple times, such as a battery mounted on a vehicle or a storage battery mounted on an electric vehicle to provide driving force. There are various types of "secondary battery," but here, for example, a lithium-ion battery can be mentioned.

[0027] The information acquisition unit 11 acquires information necessary to measure the OCV and estimate the deterioration state of the secondary battery, for example, by receiving information on whether the battery controller is ON or OFF, or by receiving information that a charger is connected to the secondary battery.

[0028] The measurement condition determination unit 12 determines whether the OCV measurement device 1 can measure the OCV of the secondary battery to be measured. For example, it determines whether the voltage of the secondary battery has stabilized. That is, when the secondary battery has polarization characteristics, the voltage value may become unstable, for example, due to a sudden drop in voltage. When the voltage is unstable due to fluctuations, the OCV cannot be measured, or cannot be measured with high accuracy. Therefore, it is necessary to determine whether the voltage of the secondary battery has stabilized to the extent that the OCV can be measured by the OCV measurement device 1.

[0029] The following method can be used to determine whether the voltage of the secondary battery has stabilized: For example, the voltage of the secondary battery is measured, and the amount of change in voltage (ΔV) at multiple different times is obtained, and then it is determined whether the amount of change in voltage is within a preset threshold range.

[0030] Another method is to determine in advance the time it takes for the voltage of a secondary battery that has been in a discharged state after the vehicle has stopped running to recover and stabilize, and then determine that the voltage of the secondary battery has stabilized when that time has passed.

[0031] The charging current control unit 13 controls the charging process when the charging process is executed on the secondary battery in order to measure the OCV of the secondary battery with high accuracy in a low SOC state. The charging current control unit 13 detects that a charger is connected to the vehicle and starts charging.

[0032] That is, in order to measure the OCV of a secondary battery with high accuracy when the battery is in a low SOC state, the voltage of the secondary battery must be stable. During the recovery process of a secondary battery discharged by running a vehicle, it takes time for the voltage to stabilize. Also, as mentioned above, the user may start charging the battery before the voltage stabilizes.

[0033] Therefore, in the embodiment of the present invention, for example, when a user starts charging, the secondary battery is charged for a short period of time to actively eliminate the polarization characteristics. That is, the charging process is performed for a predetermined fixed period of time to eliminate the polarization characteristics and stabilize the voltage.

[0034] On the other hand, if the charging process is continued for a long time, this is no different from a normal charging process in that the charging process is carried out from a low SOC state to a high SOC state, and the voltage will actually become unstable during charging. Therefore, when the charging current control unit 13 determines that the charging time corresponding to the charging current has elapsed and that the preset condition has been satisfied, it controls the amount of charging current to be reduced compared to the amount of charging current during charging.

[0035] The OCV measurement unit 14 measures the OCV when the measurement condition determination unit 12 determines that the OCV can be measured in a low SOC state. A known method can be used as the OCV measurement method performed by the OCV measurement unit 14. The measured OCV value is transmitted to the degradation state determination unit 15.

[0036] The degradation state determination unit 15 determines the degradation state of the secondary battery using the OCV value in a low SOC state measured by the OCV measurement unit 14. Specifically, the degradation state is determined by calculating the SOH using the above-mentioned formula (1) based on the OCV information in a low SOC state and the OCV information in a high SOC state. The degradation state of the secondary battery determined by the degradation state determination unit 15 is notified to the user using, for example, a display device.

[0037] The functions of each part of the OCV measuring device 1 have been described above. The function of each part will now be further described using a time chart. Figure 3 is a time chart for the part surrounded by a circle in the schematic diagram shown in Figure 2.

[0038] The time chart shown in Figure 3 indicates the operation of each component provided in the vehicle, such as the battery controller, and the charger in a low SOC state as ON or OFF, and also shows changes in current and voltage. The left side of the time chart shows, from top to bottom, the "battery controller (BMS)," "ignition," "charger," and "vehicle controller (HEVC)," as well as "current" and "voltage." Time is shown elapsed from left to right on the time chart.

[0039] The leftmost part of the time chart shows the state when the "ignition" is turned from ON to OFF. When the "ignition" is turned OFF, the "battery controller" is also turned OFF. At this point, the secondary battery is in the most discharged state, and the solid line indicating the voltage is at its lowest point. This position is the "IGNOFF2" position in Figure 2.

[0040] The "ignition" remains in the OFF state and does not turn ON. On the other hand, the "battery controller" turns OFF when the "ignition" is turned OFF, but immediately turns ON again. A possible trigger for the "battery controller" to turn ON is, for example, when the user performs some action on the vehicle.

[0041] As soon as the "battery controller" is turned on, the OCV measuring device 1 measures the amount of change in voltage. That is, the information acquiring unit 11 acquires information that the "battery controller" has been turned on and transmits the information to the measurement condition determining unit 12. When the "battery controller" is turned on, the measurement condition determining unit 12 separately acquires voltage values ​​at multiple times from the voltmeter via the information acquiring unit 11, and calculates the amount of change in voltage ΔV between those values.

[0042] Although the description here is based on the assumption that the measurement condition determining unit 12 obtains the voltage value from a voltmeter, the measurement condition determining unit 12 may obtain the voltage value by itself, for example.

[0043] As described above, after a trip, the user charges the vehicle for the next trip. Specifically, the user plugs the charger into a charging port on the vehicle to connect the charger to the vehicle. At this point, the charger switches from OFF to ON.

[0044] Then, when the preparations required for the actual charging process are complete, charging begins. When charging starts, the vehicle controller (HEVC) changes from OFF to ON. When the charging process starts, the current value increases.

[0045] However, the charging process here is executed solely to enable the OCV 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 executes the charging process to charge the secondary battery for a certain period of time until the polarization characteristic is eliminated.

[0046] Furthermore, immediately before the lapse of a certain period of time, the charging current control unit 13 determines whether a preset condition is satisfied in order to confirm whether the OCV measurement device 1 can measure the OCV after the lapse of the certain period of time.

[0047] The preset conditions here refer to, for example, whether the temperature and SOC conditions of the secondary battery are met. The former is a condition for checking whether the secondary battery is in a high temperature state (60°C or higher) or a low temperature state (0°C or lower). This is because if the secondary battery is in an excessively high or low temperature state, it becomes difficult to accurately measure the OCV.

[0048] Furthermore, although the OCV measuring device 1 in the embodiment of the present invention is intended to measure the OCV particularly in a state of low SOC, if the SOC is already high at this point, for example, there is no need for the OCV measuring device 1 to subsequently execute the process of measuring the OCV. Therefore, the charging current control unit 13 determines, based on preset SOC conditions, whether or not the OCV measuring device 1 can subsequently execute the process of measuring the OCV.

[0049] These conditions may be stored in the charging current control unit 13, or may be stored in, for example, a storage unit not shown in the OCV measuring device 1 of FIG.

[0050] If the charging current control unit 13 determines that the predetermined condition is satisfied, the charging current control unit 13 performs control to reduce the amount of charging current compared to the amount of charging current during charging, i.e., controls to reduce the amount of charging to the secondary battery.

[0051] This is because if the charging process continues as is, the so-called secondary battery charging process will be carried out from a low SOC to a high SOC, and since the voltage will not stabilize during charging, it will ultimately become impossible to measure the OCV.

[0052] On the other hand, the reason why the charging current control unit 13 does not interrupt (stop) the charging process but instead controls to reduce the amount of charge as described above is as follows: If charging is interrupted after it has started, for example, the vehicle controller will determine that the charger has stopped charging, and if the charger is not restored within a certain time, the processing that would be performed when charging was stopped will be initiated.

[0053] Therefore, the charging current control unit 13 performs a process of reducing the charging current so that the amount of charging current is lower than the amount of charging current during charging. In this case, the charging current is reduced to an amount that does not result in a determination that charging has been interrupted. Therefore, the preset conditions here can be said to be conditions for the charging current control unit 13 to determine whether or not to reduce the amount of charging of the secondary battery.

[0054] This is illustrated in Figure 3. In other words, the "Current" column in the time chart in Figure 3 shows that no current flows (the amount of charge is zero) until charging starts, but as charging starts, the amount of charging current increases. A constant amount of charging current is supplied to the secondary battery until the amount of charging current is reduced by charging current control unit 13.

[0055] In parallel with the charging process, the charging current control unit 13 determines whether the above-mentioned conditions are met, and if it determines that the conditions are met, the amount of charging current is reduced. However, the amount of charging current reduced by the charging current control unit 13 is not the same as the amount of current before the start of charging. This is to avoid the charging process being judged as being interrupted. Then, after the OCV is measured by the OCV measurement device 1, which will be described later, charging is resumed by the charging current control unit 13.

[0056] When the charging current control unit 13 reduces the amount of charging current, the measurement condition determination unit 12 determines whether the polarization characteristics of the secondary battery have been resolved, i.e., whether the voltage has stabilized. To this end, as shown in FIG. 3 , the measurement condition determination unit 12 calculates the value of ΔV and determines whether it is within a preset threshold range. If it is determined that the voltage of the secondary battery is stable, the OCV measurement unit 14 measures the OCV of the secondary battery ("OCV measurement 1" in the time chart of FIG. 3 ).

[0057] The reason why the measurement condition determination unit 12 does not make the above determination immediately after the charging current control unit 13 reduces the amount of charging current is because it is considered that the voltage is not stable immediately after the charging current is reduced. Therefore, the determination is made after a short time has elapsed.

[0058] The OCV information in the low SOC state measured by the OCV measurement unit 14 is transmitted to the degradation state determination unit 15. The degradation state determination unit 15 calculates the SOH using the above-described formula (1) based on the acquired OCV information in the low SOC state and separately acquired OCV information in the high SOC state, and determines the degradation state of the secondary battery.

[0059] The deterioration state determination unit 15 may obtain the OCV information in the high SOC state from another measurement device, or may obtain the result of measurement by the OCV measurement device 1 according to the embodiment of the present invention. The value of "ΔAh" may be calculated by the deterioration state determination unit 15, for example.

[0060] The "new battery capacity" is measured before shipping from the factory, and the measured value is recognized as the new battery capacity for each secondary battery. Therefore, it is stored in advance in a storage unit, for example, as an unchanging parameter. Therefore, the degradation state determination unit 15 may acquire information about the new battery capacity from the storage unit.

[0061] The above-described process is the basic flow of the OCV measurement process in a low SOC state by the OCV measurement device 1. However, for example, there may be a case where the OCV in a low SOC state can be measured before the process of reducing the amount of charging current by the charging current control unit 13 is executed.

[0062] That is, after the vehicle is running and the ignition is turned off ("IGNOFF2" in Figure 2) but before the charger is connected to the vehicle and charging begins, when the measurement condition determination unit 12 determines whether the voltage of the secondary battery is stable, it determines that the voltage is stable.

[0063] Alternatively, this also applies when the measurement condition determination unit 12 determines that a predetermined time has elapsed since the ignition of the vehicle was turned off. As described above, even if a secondary battery has been in a discharged state due to driving, after the passage of, for example, six hours, the polarization characteristic is eliminated and the voltage stabilizes. In other words, this is the case when time has passed without the user performing a charging process.

[0064] In these cases, it is not necessary to stabilize the voltage of the secondary battery by charging the secondary battery using the charging current control unit 13, and it is thought that the OCV in a low SOC state can be measured immediately.

[0065] Therefore, when the measurement condition determination unit 12 determines that the above-described conditions are satisfied, the OCV measurement device 1 measures the OCV before the charger is connected. In the time chart of Fig. 3, "OCV measurement 2" indicates the OCV measurement that is performed at this timing.

[0066] If the measurement condition determination unit 12 determines that the voltage of the secondary battery is not stable as a result of determining whether it is stable, or if the charging current control unit 13 determines that the charging current should not be reduced as a result of determining whether it should be reduced, the OCV measurement device 1 does not measure the OCV. Therefore, the SOH is not calculated, and the deterioration state of the secondary battery is not determined.

[0067] [Operation] Next, a description will be given of the flow of processing for measuring the OCV in a low SOC state by the OCV measuring device 1. Figures 4 and 5 are flowcharts showing the flow for measuring the OCV by the OCV measuring device 1 according to an embodiment of the present invention and understanding the deterioration state of the secondary battery.

[0068] In the flowchart shown in FIG. 4, the process starts when the voltage has dropped due to discharge of the secondary battery while the vehicle is running, that is, when the vehicle is in the "IGNOFF2" state shown in FIG.

[0069] In terms of the time chart of Fig. 3, the transition of the battery controller from the OFF state to the ON state is the start of the flowchart of Fig. 4. In addition, in the flowcharts of Fig. 4 and Fig. 5, the secondary battery is referred to as a "battery."

[0070] First, the measurement condition determination unit 12 determines whether or not the OCV in a low SOC state can be measured by the OCV measurement device 1 (ST1). The measurement conditions here include, for example, whether the amount of change in voltage is within a certain range as compared with a threshold value, or whether a preset time has elapsed since the ignition of the secondary battery to be measured was turned off.

[0071] The measurement condition determination unit 12 determines whether the measurement conditions are met, and if the OCV measurement conditions are not met (NO in ST1), it further determines whether a charger is connected to the battery (secondary battery), i.e., whether the charging process has started (ST2).

[0072] If it is determined that the charging process 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 or not the condition for restricting the charging current is met (ST3).

[0073] The condition for reducing the charging current here is, as described above, whether the temperature and SOC conditions of the secondary battery are met, for example. If the charging current control unit 13 determines that the condition for reducing the charging current is met (YES in ST3), the charging current control unit 13 reduces the charging current (ST4).

[0074] The measurement condition determination unit 12 determines whether the charging current has been reduced by the charging current control unit 13 (ST5), and if it determines that the charging current has been reduced (YES in ST5), it then determines whether the OCV measurement conditions are met (ST6). Here, as described above, the measurement condition determination unit 12 determines whether the voltage has stabilized by, for example, comparing the amount of change in voltage with a threshold value.

[0075] As a result, if the measurement condition determination unit 12 determines that the voltage is stable (YES in ST6), the result is sent to the OCV measurement unit 14, and the OCV measurement unit 14 measures the OCV (ST7). This state corresponds to the timing indicated as "OCV measurement 1" in the time chart of FIG. 3.

[0076] The OCV measurement unit 14 transmits information about the measured OCV to the degradation state determination unit 15. The degradation state determination unit 15 calculates a low SOC based on the measured OCV information (ST8 in FIG. 5). Furthermore, the degradation state determination unit 15 calculates the SOH based on, for example, the above-mentioned formula (1) using a separately calculated high SOC (ST9). Then, the degradation state of the secondary battery is determined based on the calculated SOH (ST10).

[0077] On the other hand, if the battery is not being charged (NO in ST2), if the charging current control unit 13 determines that the condition for throttling the charging current is not met (NO in ST3), if the measurement condition determination unit 12 determines that the charging current is not being throttled (NO in ST5), or if the condition for measuring the OCV is not met (NO in ST6), then the OCV is not measured (ST11 in FIG. 5). In these cases, the SOH is not calculated, and the state of deterioration of the secondary battery is not determined.

[0078] Furthermore, before charging of the secondary battery is started (ST2), if the measurement condition determination unit 12 determines whether the OCV measurement condition is met (ST1), and if it determines that the measurement condition is met (YES in ST1), the OCV is measured by the OCV measuring device 1 at this point (ST12). This measurement corresponds to "OCV measurement 2" in the time chart shown in FIG. 3.

[0079] Then, the low SOC is calculated by measuring the OCV, and the SOH is calculated using separately obtained information such as the high SOC, etc. As a result, the deterioration state of the secondary battery is determined in the deterioration state determination unit 15 (ST8 to ST10 in FIG. 5).

[0080] As described above, by using the OCV measurement method and OCV measurement device according to the embodiment of the present invention, it is possible to measure the OCV with high accuracy even when the secondary battery mounted on a vehicle is in a low SOC state, and to grasp the deterioration state of the secondary battery with high accuracy.

[0081] Furthermore, in the process of voltage recovery after discharge of the secondary battery is completed, it is possible to measure the OCV in a low SOC state as early as possible. Therefore, it is possible to take a large difference from the OCV in a high SOC state used to measure the SOH (state of health) of the secondary battery. Therefore, the value of ΔSOC can be made large relative to ΔAh, and the state of health of the secondary battery can be estimated more accurately.

[0082] In the above description, it has been assumed that the OCV measuring device 1 performs a charging process in which the secondary battery is charged for a certain period of time until the polarization characteristics of the secondary battery are eliminated when charging the secondary battery to measure the OCV in a low SOC state. However, the polarization characteristics of the secondary battery differ depending on the load current, and there are various types of chargers connected to a vehicle, and the load current that flows during the charging process also differs.

[0083] Therefore, after starting charging of the secondary battery, the charging current control unit 13 may control the charging process so that charging is performed according to the charging time corresponding to the charging current for each type of connected charger. In other words, when the charging current control unit 13 performs such control, the charging time becomes shorter when the charging current for the secondary battery is large. On the other hand, the charging time becomes longer when the charging current is small.

[0084] Furthermore, the above explanation has been given on the assumption that the determination of whether the polarization characteristics of the secondary battery have been resolved, i.e., whether the measurement conditions have been met, is made by comparing the amount of change in voltage with a threshold value.

[0085] However, instead of this method, for example, it is also possible to set a time in advance for the voltage to stabilize as the charging rate of the secondary battery gradually recovers after the vehicle is stopped, and to determine that the measurement condition is met when the set time has elapsed.Furthermore, it is also possible to use a combination of the method using the amount of change in voltage and the method using time.

[0086] [Effects of the embodiment] (1) The method includes the steps of 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 charging rate state, determining whether or not the open circuit voltage (OCV) of the secondary battery can be measured, and measuring the OCV of the secondary battery when it is determined that the OCV can be measured.

[0087] By measuring the OCV in a low SOC state using such an OCV measurement method, it is possible to measure the OCV with high accuracy even in a low SOC state. In particular, by performing a charging process in which a secondary battery that has been discharged and is in a low state of charge (low SOC) is charged for a certain period of time, it is possible to eliminate polarization characteristics in the secondary battery.

[0088] (2) After starting charging of the secondary battery, a charging time corresponding to the charging current elapses, and a step is included in which it is determined whether or not predetermined conditions are met, and if these conditions are met, a step is included in which control is performed to reduce the amount of charging current compared to the amount of charging current during charging.

[0089] By performing such control by the charging current control unit, the polarization characteristics of the secondary battery are eliminated by the charging process, and it is possible to prevent the charging process from continuing, so that the OCV can be measured in a stable voltage state. Furthermore, by performing control to reduce the charging current below the amount of charging current during charging to an extent that does not interrupt the charging process, it is possible to perform the OCV measurement process while avoiding a situation in which it is determined that the charging process has been interrupted.

[0090] (3) The determination of whether or not the OCV can be measured is a step of comparing the amount of change in the voltage of the secondary battery with a preset threshold, and determining that the OCV can be measured if it is determined that the amount of change in voltage is stable.

[0091] By determining whether the voltage of the secondary battery has stabilized after the charging current control unit has reduced the amount of charging current, it is possible to measure the OCV with higher accuracy.

[0092] (4) The method includes a step of determining whether or not OCV measurement is possible before the step of charging the secondary battery.

[0093] In the OCV measurement method according to the embodiment of the present invention, the secondary battery to be measured is charged before the OCV measurement and then it is determined whether the voltage has stabilized, which enables more accurate OCV measurement.

[0094] (5) After charging of the secondary battery is started, a charging time corresponding to the charging current elapses, and a step is provided in which a determination is made as to whether or not a predetermined condition is met. If it is determined that the predetermined condition is not met, control is performed to maintain the amount of charging current.

[0095] Although it is basic to measure the OCV after charging a discharged secondary battery, there are cases where it is possible to measure the OCV without charging, so in order to make it possible to measure the OCV even in such cases, the measurement condition determination unit determines whether it is possible to measure the OCV before charging the secondary battery.

[0096] (6) After the step of measuring the OCV, a step of determining the deterioration state of the secondary battery using information on the measured OCV is included.

[0097] By measuring the OCV in this manner, not only can OCV information be obtained, but the state of deterioration of the secondary battery can also be determined by calculating the SOC and SOH using this OCV information.

[0098] (7) The step of determining the deterioration state of the secondary battery determines the deterioration state of the secondary battery using OCV information when the secondary battery is in a low charging state and OCV information when the secondary battery is charged and in a high charging state.

[0099] By executing such a process for determining the deterioration state, it is possible to determine the deterioration state of the secondary battery with high accuracy using information on the OCV measured with high accuracy.

[0100] (8) An OCV measurement device that measures the open circuit voltage (OCV) of a secondary battery, the OCV measurement device comprising: a measurement condition determination unit that determines whether or not OCV measurement is possible; a charging current control unit that executes a charging process to charge the secondary battery for a certain period of time until the polarization characteristics are eliminated when the secondary battery is discharged and in a state of low charge; and an OCV measurement unit that executes OCV measurement when the secondary battery is in a state of low charge as a result of the measurement condition determination unit determining that OCV measurement is possible.

[0101] By measuring the OCV in a low SOC state using such an OCV measuring device, it is possible to measure the OCV with high accuracy even in a low SOC state. In particular, by performing a charging process in which a secondary battery that has been discharged and is in a low state of charge (low SOC) is charged for a certain period of time, it is possible to eliminate polarization characteristics in the secondary battery.

[0102] 1... OCV 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. When the secondary battery is discharged and in a low state of charge, a step of charging the secondary battery for a certain period of time until the polarization characteristics are eliminated; a step of determining whether the open circuit voltage (OCV) of the secondary battery can be measured; and a step of executing the measurement of the OCV of the secondary battery when it is determined that the measurement of the OCV is possible. An OCV measurement method characterized by comprising the above steps.

2. After starting charging of the secondary battery, a step of determining whether a charging time corresponding to the charging current has elapsed and whether preset conditions are satisfied is provided. When these conditions are satisfied, a step of controlling to reduce the charging current amount compared to the charging current amount during charging is provided. The OCV measurement method according to claim 1, characterized by comprising the above steps.

3. The determination of whether the OCV can be measured is a step of comparing the change amount of the voltage of the secondary battery with a preset threshold value, and determining that the measurement of the OCV is possible when it is determined that the change amount of the voltage is stable. The OCV measurement method according to claim 1, characterized by comprising the above steps.

4. The determination of whether the OCV can be measured is a step of comparing the change amount of the voltage of the secondary battery with a preset threshold value, and determining that the measurement of the OCV is possible when it is determined that the change amount of the voltage is stable. The OCV measurement method according to claim 2, characterized by comprising the above steps.

5. Before the step of charging the secondary battery, a step of determining whether the OCV can be measured is included. The OCV measurement method according to claim 1, characterized by comprising the above steps.

6. After starting charging of the secondary battery, a step of determining whether a charging time corresponding to the charging current has elapsed and whether preset conditions are satisfied is provided. When it is determined that the preset conditions are not satisfied, control is performed to maintain the charging current amount. The OCV measurement device according to claim 1, characterized by comprising the above steps.

7. After the step in which the measurement of the OCV is executed, a step of determining the deterioration state of the secondary battery using the measured OCV information is provided. The OCV measurement method according to any one of claims 1 to 6, characterized by comprising the above steps.

8. The step of determining the degradation state of the secondary battery is to determine the degradation state of the secondary battery by using the OCV information when the secondary battery is in a low state of charge and the OCV information when the secondary battery is charged to a high state of charge. The OCV measurement method according to claim 7, characterized in that.

9. A measurement condition determination unit that determines whether it is possible to measure the open circuit voltage (OCV) of a secondary battery; a charging current control unit that, when the secondary battery is discharged and in a low state of charge, performs a charging process of charging the secondary battery for a certain period of time until the polarization characteristics are eliminated; and an OCV measurement unit that, when it is determined by the measurement condition determination unit that the OCV can be measured, measures the OCV when the secondary battery is in a low state of charge. An OCV measurement device, characterized in that it comprises.

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