Battery state estimation system, battery state estimation method, and battery state estimation program

Abstract

The measurement value acquisition section acquires voltage data of the secondary battery measured at a fixed cycle during a period from a discharge end timing of the secondary battery to the first timing. The difference cumulative value calculation section calculates difference voltages between the voltage measured at the first timing and a plurality of voltages measured during an idle period at the first timing from the discharge end timing, and calculates cumulative values of the calculated plurality of difference voltages. The voltage variation amount estimation section refers to a pre-created table or a pre-created function which describes a relationship between (a) the cumulative value of the difference voltage and (b) a voltage variation amount from the first timing to a second timing at which the voltage of the secondary battery is regarded as converged, and estimates the voltage variation amount based on the calculated cumulative value of the difference voltage. The OCV estimation section adds the estimated voltage variation amount to the voltage measured at the first timing, and estimates the voltage at the second timing.

Description

Technical Field

[0001] This disclosure relates to a battery state estimation system, a battery state estimation method, and a battery state estimation procedure for estimating the voltage of a secondary battery after polarization relaxation. Background Technology

[0002] While maintenance charging allows for accurate determination of the full charge capacity (FCC) of a secondary battery, it is difficult to perform maintenance charging for batteries intended for standby or other applications where a fixed or higher remaining capacity must always be maintained. Therefore, the two-point OCV (Open Circuit Voltage) method is frequently used to determine the FCC. In the two-point OCV method, the FCC is estimated based on the difference ΔSOC between the SOC corresponding to the OCV at point 1 and the SOC corresponding to the OCV at point 2, and the cumulative current value during the period between the measurement timing of the OCV at point 1 and the measurement timing of the OCV at point 2. In other words, the two-point OCV method estimates the cumulative current value (FCC) corresponding to a 100% change in SOC based on the cumulative current value corresponding to the difference ΔSOC.

[0003] A secondary battery is an electrochemical device. When a charging current flows through it, the measured voltage rises non-linearly; when a discharging current flows through it, the measured voltage falls non-linearly. The voltage measured when current flows through the secondary battery is called the CCV (Closed Circuit Voltage) or operating voltage. After charging and discharging, the secondary battery spends time converging (relaxing) towards the OCV, which does not contain overvoltage components. The convergence time to the OCV depends on factors such as the type of cell, temperature, and SOH (State of Health).

[0004] Patent Document 1 discloses a method for estimating the OCV of a battery after polarization elimination following the completion of charging or discharging. In this method, the voltages at two points after two different given times following the end of charging or discharging are obtained. The ratio of these two voltages is set as a first parameter, and a coefficient determined using the two voltages and a table obtained from SOC-OCV lookup, along with SOC, temperature, and degree of degradation, is set as a second parameter. The product of the two parameters is used to correct either the first or second voltage, thereby estimating the voltage after polarization elimination.

[0005] Patent document 2 discloses the following method: using the voltage at 3 points in the middle of polarization relaxation, the future voltage after the 3rd point is estimated.

[0006] Prior art literature

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2019-45419

[0009] Patent Document 2: International Publication No. 14 / 050073 Summary of the Invention

[0010] The method described in Patent Document 1 uses the voltage, SOC, temperature, and degradation degree at two points midway through polarization relaxation to obtain correction values. However, the relationship between the data used and the correction values ​​is complex. To obtain high-precision correction values, numerous parameters need to be identified based on long-term investigations for each battery type. Furthermore, when the relationship between the data used and the correction values ​​is simplified and defined, the correction values ​​tend to deviate from the defined correspondence, leading to reduced accuracy. Additionally, the individual data used to derive the correction values ​​also require precision, making it difficult to achieve high accuracy.

[0011] In the method described in Patent Document 2, the estimation method after point 4 is based on the assumption that the time required for a fixed voltage change increases by a fixed multiple. It is difficult to select measurement points at point 3 so that the process after point 4 is consistent with the polarization relaxation process. This deviates from the battery characteristics and the estimation accuracy may be reduced.

[0012] A battery state estimation system according to one aspect of this disclosure includes: a measurement value acquisition unit that acquires voltage data of the secondary battery measured at fixed periods during a period from the end of discharge of the secondary battery to a first time interval; a difference accumulation value calculation unit that calculates the difference voltage between the voltage measured at the first time interval and a plurality of voltages measured during a rest period from the end of discharge of the secondary battery to the first time interval, and calculates the cumulative value of the calculated plurality of difference voltages; a voltage change estimation unit that, with reference to a pre-created table or a pre-created function describing the relationship between (a) the cumulative value of the difference voltages and (b) the voltage change from the first time interval to a second time interval where the voltage of the secondary battery is considered to have converged, estimates the voltage change from the first time interval to the second time interval based on the calculated cumulative value of the difference voltages; and an OCV estimation unit that adds the estimated voltage change to the voltage measured at the first time interval to estimate the voltage at the second time interval.

[0013] Furthermore, any combination of the above-mentioned constituent elements, or any manner in which the present disclosure is transformed between apparatus, system, method, computer program, etc., is also valid as a manner of the present disclosure.

[0014] According to this disclosure, the voltage of a secondary battery after polarization relaxation can be estimated simply and with high accuracy. Attached Figure Description

[0015] Figure 1 This is a diagram used to illustrate the battery pack involved in the implementation method.

[0016] Figure 2 This is a diagram showing an example of the measured voltage shift from the time when the discharge of a single cell in the battery pack according to the embodiment ends.

[0017] Figure 3 This is a diagram illustrating an example of a table describing the relationship between the cumulative value of the differential voltage and the voltage change in the battery pack according to the embodiment.

[0018] Figure 4 This is a schematic diagram illustrating a specific method for estimating the FCC (Full Charge Capacity) in a battery pack according to an embodiment.

[0019] Figure 5 This is a flowchart illustrating the process of FCC presumed processing performed by the battery management device involved in the implementation method. Detailed Implementation

[0020] Figure 1 This diagram illustrates the battery pack 1 according to the embodiment. The battery pack 1 according to the embodiment includes a battery pack 10 and a battery management device 20. The battery pack 1 is capable of supplying power to a load 2. In this embodiment, the load 2 is envisioned as a server or storage device in a data center. The battery pack 1 serves as a backup power source for the server or storage device.

[0021] Charger 4 is connected to commercial power system 3 and converts the AC power input from commercial power system 3 into DC power of a given voltage or current and supplies it to battery pack 1. Alternatively, charger 4 can be built into battery pack 1.

[0022] The battery pack 10 comprises multiple cells E1-En connected in series. The number of cells in series is determined by the specifications of the load 2. For the cells, lithium-ion battery cells, nickel-metal hydride battery cells, lead-acid battery cells, etc., can be used. Hereinafter, this specification presents an example using lithium-ion battery cells (nominal voltage: 3.6-3.7V). Furthermore, in order to increase the capacity, multiple cells can also be connected in parallel within the series connection of each cell.

[0023] Insert a switch SW1 into the power line connecting the battery pack 10 and the load 2 or charger 4 to switch the load 2 or charger 4 on / off. A semiconductor switch or relay can be used for switch SW1.

[0024] The battery management device 20 includes a measurement unit 21 and a control unit 22. The measurement unit 21 is composed of an AFE (Analog Front End) IC or an ASIC (Application Specific Integrated Circuit). The control unit 22 is composed of a microcontroller. The microcontroller includes a CPU, RAM, ROM, and I / O.

[0025] The measurement unit 21 is connected to each node of the multiple individual cells E1-En that are connected in series via multiple voltage measurement lines, and measures the voltage between two adjacent voltage measurement lines, thereby measuring the voltage of each individual cell E1-En.

[0026] The measurement unit 21 includes a multiplexer and an analog-to-digital (A / D) converter. The multiplexer outputs the voltages of multiple individual units E1-En in a given order to the A / D converter. The A / D converter converts the analog voltages input from the multiplexer into digital values. The measurement unit 21 then sends the converted digital voltage values ​​of each individual unit E1-En to the control unit 22 via a serial communication interface.

[0027] The measuring unit 21 measures the current flowing through the battery pack 10. A shunt resistor Rs is connected in the power line connecting the battery pack 10 to the load 2 or charger 4. A differential amplifier within the measuring unit 21 amplifies the voltage across the shunt resistor Rs and outputs it to an A / D converter within the measuring unit 21. The A / D converter converts the analog voltage representing the current flowing through the battery pack 10, which is input from the differential amplifier, into a digital value. The measuring unit 21 then transmits the converted digital current value to the control unit 22 via a serial communication interface.

[0028] A temperature sensor T1 (e.g., a thermistor) is disposed on the surface of the battery pack 10. An analog voltage representing the temperature value of the battery pack 10 measured by the temperature sensor T1, i.e., the voltage divided by the temperature sensor T1 and the voltage divider resistor, is input to the measuring unit 21. An A / D converter within the measuring unit 21 converts the input analog voltage representing the temperature value into a digital value. The measuring unit 21 then transmits the converted digital temperature value to the control unit 22 via a serial communication interface.

[0029] The control unit 22 manages the state of each cell E1-En based on the voltage value of each cell E1-En, the current value flowing through the battery pack 10, and the temperature value of the battery pack 10 received from the measurement unit 21. When the control unit 22 detects any of the following: overcharge, over-discharge, overcurrent, high temperature abnormality, or low temperature abnormality, it sends a cut-off signal to the measurement unit 21 to turn off the switch SW1.

[0030] The control unit 22 can estimate the battery state by executing firmware and other programs within the microcontroller. The control unit 22 combines the OCV method and the current accumulation method to estimate the SOC (State of Charge). The OCV method estimates the SOC based on the measured OCV (Open Circuit Voltage) and the SOC-OCV curve of each cell. The SOC-OCV curve of each cell is pre-created based on characteristic tests conducted by the battery manufacturer and is registered in the ROM of the control unit 22 at the time of shipment.

[0031] The current accumulation method estimates the state of charge (SOC) based on the initial charge-discharge velocity (OCV) of a single cell and the cumulative value of the measured current. However, in this method, the measurement error accumulates as the charging / discharging time increases. Therefore, it is preferable to use a weighted average of the SOC estimated using the current accumulation method and the SOC estimated using the OCV method.

[0032] The monomer deteriorates over time and with each charge-discharge cycle. This storage degradation occurs over time, based on the temperature and state of charge (SOC) at various points in time. It happens regardless of whether the cell is being charged or discharged. Storage degradation is primarily caused by the formation of a film (SEI - Solid Electrolyte Interphase) at the negative electrode. Generally, higher SOC and higher temperature at each time point accelerate the rate of storage degradation.

[0033] The degradation of a single cell through charge-discharge cycles occurs with an increase in the number of charge-discharge cycles. This degradation is primarily caused by cracks and peeling resulting from the expansion or contraction of the active material. The rate of charge-discharge degradation depends on the state of charge (SOC) range, temperature, and current rate used. Generally, a wider SOC range, higher temperature, and higher current rate lead to a faster rate of charge-discharge degradation.

[0034] As described above, in this embodiment, battery pack 1 is used for backup purposes for servers and storage devices within a data center. Therefore, the number of charge-discharge cycles is less, and charge-discharge degradation is less. The main factor contributing to degradation of the individual cells in battery pack 1 for backup purposes is storage degradation. As storage degradation occurs, the FCC (Full Charge Capacity) of the individual cells decreases.

[0035] In this embodiment, maintenance discharge is performed periodically to estimate the FCC of a single cell. While a complete discharge and full charge are sufficient for accurate measurement of the FCC, a low SOC state is undesirable for standby applications. Therefore, in this embodiment, partial discharge is performed with a fixed DOD (Depth of Discharge). For example, a partial discharge with DOD of 20% or 40% is performed. During maintenance discharge, a constant current (CC discharge) is used.

[0036] The control unit 22 has a measurement value acquisition unit 221, a difference accumulation value calculation unit 222, a voltage change estimation unit 223, an OCV estimation unit 224, and an FCC estimation unit 225 as functional blocks related to FCC estimation based on maintenance discharge.

[0037] The measurement acquisition unit 221 acquires the voltage data of each cell E1-En at the start timing of maintenance discharge of the battery pack 10 from the measurement unit 21 and stores it in RAM (Random Access Memory). Alternatively, the measurement acquisition unit 221 may store only the voltage data of the cell with the lowest voltage among the voltage data of each cell E1-En, i.e., the cell with the lowest voltage, in RAM. During maintenance discharge, the measurement acquisition unit 221 acquires current data from the measurement unit 21 at fixed intervals and stores it in RAM.

[0038] During the rest period from the end of discharge of the battery pack 10 to the first timeout, the measurement acquisition unit 221 acquires voltage data of each cell E1-En from the measurement unit 21 at a fixed period (e.g., a 10-second period, a 30-second period, or a 1-minute period). The first timeout may, for example, be set 15 minutes after the end of discharge. Alternatively, charging to restore the battery pack 10 to a full charge may begin from the first timeout. In this case, the first timeout becomes the end timeout of the rest period. The measurement acquisition unit 221 stores the voltage data of each cell E1-En acquired during the rest period in RAM. Furthermore, the measurement acquisition unit 221 may also store only the voltage data of the cell with the lowest voltage in RAM.

[0039] The difference accumulation calculation unit 222 calculates the voltage difference between the voltage measured at the first timing and the multiple voltages measured during the rest period at the first timing from the end of the discharge timing, and calculates the cumulative value of the multiple voltage differences as an evaluation value.

[0040] Based on experimental or simulated data, the designer pre-creates a correction table that records the relationship between (a) the cumulative value of the differential voltage (evaluation value) and (b) the voltage change (correction value) from the first timing point until the second timing point when the voltage of the individual cell is considered to have converged. The second timing point is a hypothetical timing point after polarization elimination; in reality, it is not necessary to pause until the second timing point. The second timing point depends on the type of individual cell. For example, the second timing point can also be set to one hour after the discharge end timing point. The correction table created is registered in the ROM (Read Only Memory) within the control unit 22 at the factory.

[0041] The voltage change estimation unit 223 refers to the above-mentioned table for correction and estimates the voltage change from the first timing to the second timing based on the cumulative value of the difference voltage calculated by the difference accumulation calculation unit 222.

[0042] Figure 2 This is a diagram showing an example of the measured voltage shift from the end of discharge timing of a single cell. The difference accumulation calculation unit 222 calculates the voltage difference between the voltage V(t1) measured at the first timing t1 and the multiple voltages measured during the period from the end of discharge timing at the first timing t1, and calculates the cumulative value of the calculated multiple difference voltages.

[0043] Figure 3 This is a diagram illustrating an example of the table described above, which shows the relationship between the cumulative value of the differential voltage and the voltage change. Referring to this table, the voltage change estimation unit 223 estimates the voltage change (voltage V(t2) - voltage V(t1)) from the first timing t1 to the second timing t2, corresponding to the cumulative value of the differential voltage calculated by the differential accumulation unit 222. The voltage V(t2) at the second timing t2 is considered to be the OCV without an overvoltage component.

[0044] Furthermore, the relationship between (a) the cumulative value of the differential voltage and (b) the voltage change can also be described by a function instead of the table above. The designer performs curve regression on a plot of the combination of the cumulative value of the differential voltage and the voltage change obtained through experiments or simulations, and pre-generates a function with the cumulative value of the differential voltage as the explanatory variable and the voltage change as the target variable. For curve regression, for example, the least squares method can be used. The voltage change estimation unit 223 uses the cumulative value of the differential voltage calculated by the cumulative value calculation unit 222 to estimate the voltage change as the explanatory variable of this function.

[0045] The OCV estimation unit 224 adds the voltage change estimated by the voltage change estimation unit 223 to the voltage measured at the first timing to estimate the voltage at the second timing. The voltage at the second timing becomes the estimated OCV for the discharge end timing.

[0046] The FCC estimation unit 225 uses the two-point OCV method to estimate the FCC of a single cell. Specifically, the FCC estimation unit 225 calculates the SOC difference (ΔSOC) between the SOC at the discharge start timing and the SOC at the discharge end timing based on the voltage at the discharge start timing (=OCV), the voltage at the second timing estimated by the OCV estimation unit 224 (=estimated OCV at the discharge end timing), and the SOC-OCV curve of the single cell. Since sufficient rest time is ensured before the start of maintenance discharge, the voltage measured at the discharge start timing is considered as the OCV. In maintenance discharge, the voltage at the discharge start timing is usually the full charge voltage.

[0047] The FCC estimation unit 225 calculates the cumulative current value Q during the discharge period between the discharge start timing and the discharge end timing. Based on the cumulative current value Q and the difference ΔSOC, the FCC estimation unit 225 calculates the current FCC of the individual cell.

[0048] Figure 4 This is a schematic diagram illustrating the FCC estimation method. The FCC estimation unit 225 uses the estimated OCV at the discharge start timing and the estimated OCV at the discharge end timing as the two-point OCV. Referring to the SOC-OCV curve, the FCC estimation unit 225 determines the SOC at the two points corresponding to the OCV at each of the two points. The FCC estimation unit 225 calculates the difference ΔSOC between the two points' SOCs. Figure 4 In the example shown, the SOCs at the two points are 100% and 80%, and the difference ΔSOC (=DOD) is 20%.

[0049] The FCC estimation unit 225 calculates the cumulative current Q during the discharge period. The FCC estimation unit 225 calculates the FCC of the cell using the following formula (Equation 1).

[0050] FCC=Q / ΔSOC …(Equation 1)

[0051] Charging of battery pack 10 needs to stop at the point when the minimum voltage cell reaches its FCC. The FCC of battery pack 10 is constrained by the FCC of the minimum voltage cell. Therefore, the FCC of battery pack 10 can be obtained by (FCC of the minimum voltage cell × number of cells in series).

[0052] In addition, the following formula (Equation 2) can be used to estimate the State of Health (SOH) of the monomer. SOH is defined as the ratio of the current FCC to the initial FCC. The lower the value (closer to 0%), the more severe the degradation.

[0053] SOH = Current FCC / Initial FCC × 100 … (Equation 2)

[0054] Figure 5This is a flowchart illustrating the FCC presumption processing performed by the battery management device 20 according to the embodiment. The measurement value acquisition unit 221 acquires voltage data of the minimum voltage cell at the start timing of maintenance discharge from the measurement unit 21 and stores it in RAM (S10). During maintenance discharge, the measurement value acquisition unit 221 acquires current data from the measurement unit 21 at fixed intervals and stores it in RAM (S11).

[0055] When the maintenance discharge ends (S12 "Yes"), the measurement value acquisition unit 221 acquires the voltage data of the smallest voltage cell from the measurement unit 21 at a fixed period and stores it in RAM (S13). When the first timing period, which is a fixed period, is reached from the end of the discharge timing (S14 "Yes"), the difference accumulation calculation unit 222 calculates the difference voltage between the voltage data at the first timing period and the multiple voltage data stored in RAM, and calculates the cumulative value of the calculated multiple difference voltages (S15).

[0056] The voltage change estimation unit 223, referring to a correction table, estimates the voltage change from the first timing point to the second timing point based on the calculated cumulative value of the difference voltage (S16). The OCV estimation unit 224 adds the estimated voltage change to the voltage at the first timing point and estimates the voltage at the second timing point, which corresponds to the OCV at the end of discharge (S17). The FCC estimation unit 225 estimates the FCC of the minimum voltage cell based on the voltage at the start of discharge (OCV), the estimated OCV at the end of discharge, and the cumulative value of the current during maintenance discharge (S18).

[0057] As explained above, according to this embodiment, the polarization-relaxed OCV of a secondary battery can be estimated simply and with high accuracy. In this embodiment, only voltage data during the polarization relaxation process is used to obtain the polarization-relaxed OCV. With fewer necessary parameters, the relationship between the evaluation value and the correction value based solely on voltage data can be easily correlated. Since only voltage data is used, the estimation is unaffected by the accuracy of other parameters, enabling high-accuracy estimation.

[0058] When estimating FCC based on voltage data defined by partial discharge, the difference between the measured voltage and OCV becomes significant if the measured voltage at the end of discharge is used directly. Therefore, a table or function that corrects for voltage changes based on diffusion resistance, etc., after maintenance discharge is used to estimate the OCV after polarization relaxation based on the shift of the measured voltage over a fixed period after the end of discharge.

[0059] In the maintenance discharge of battery pack 1 used for backup purposes in servers and storage within a data center, the discharge rate is constant, and the temperature inside the building is relatively stable. Therefore, the influence of current and temperature during maintenance discharge is minimal, allowing for high-precision OCV estimation based solely on voltage data. For example, according to the inventors' experiments, it has been confirmed that the voltage one hour after the end of discharge can be estimated with high precision based on voltage data acquired at one-minute intervals during the period from the end of discharge to 15 minutes later. If high-precision OCV estimation is possible, high-precision FCC estimation is also possible.

[0060] Furthermore, since only a small amount of voltage data needs to be temporarily stored, a large amount of RAM is unnecessary, thus reducing the increase in hardware costs. Also, since only one correction table is typically prepared, ROM capacity is not strained. Moreover, the correction table can be created according to each DOD mode during maintenance discharge. For example, a correction table for DOD 20% and a correction table for DOD 40% can be created. Alternatively, a correction table can be created according to each SOH division.

[0061] In this embodiment, since there is no need to set a long rest period after the maintenance discharge is completed, the period during which the backup capacity of battery pack 1 is reduced due to maintenance discharge can be shortened, and the reduction in the function of battery pack 1 as a backup power source can be minimized.

[0062] The present disclosure has been described above based on the embodiments. The embodiments are illustrative, and those skilled in the art should understand that various modifications are possible in the combination of these constituent elements and processing procedures, and such modifications are also within the scope of the present disclosure.

[0063] In the above embodiment, an example was described where the FCC estimation system was installed in the battery management device 20 within the battery pack 1. However, the FCC estimation system could also be installed in a cloud server. In this case, the battery management device 20 within the battery pack 1 is equipped with communication functionality. The battery management device 20 periodically sends voltage data to the cloud server. In this case, the limitations of RAM within the battery management device 20 are not considered, and high-sampling-rate voltage data can be sent to the cloud server. The cloud server can then estimate a more accurate polarization-relaxed OCV based on more voltage data.

[0064] In addition, the implementation method can also be determined by the following items.

[0065] [Project 1]

[0066] A battery state estimation system, comprising:

[0067] The measurement acquisition unit (221) acquires the voltage data of the secondary battery (E1) measured at fixed intervals during the period from the end of the discharge of the secondary battery (E1) to the first time interval.

[0068] The difference accumulation calculation unit (222) calculates the difference voltage between the voltage measured at the first timing and the multiple voltages measured during the rest period of the first timing from the end of the discharge timing, and calculates the cumulative value of the calculated multiple difference voltages.

[0069] The voltage change estimation unit (223) estimates the voltage change from the first timing point to the second timing point based on the calculated cumulative value of the difference voltage, referring to a pre-created table or a pre-created function that describes the relationship between (a) the cumulative value of the difference voltage and (b) the voltage change from the first timing point to the second timing point where the voltage of the secondary battery (E1) is considered to have converged; and

[0070] The OCV estimation unit (224) adds the estimated voltage change to the voltage measured at the first timing to estimate the voltage at the second timing.

[0071] Therefore, by timing the polarization relaxation process after the discharge ends, the OCV after polarization relaxation can be estimated simply and with high accuracy.

[0072] [Project 2]

[0073] In the battery state estimation system described in Project 1

[0074] It also includes a full charge capacity estimation unit (225) that estimates the full charge capacity of the secondary battery (E1) based on the voltage measured at the discharge start timing of the secondary battery (E1), the estimated voltage at the second timing, the SOC difference based on the SOC-OCV curve of the secondary battery (E1), and the cumulative current value during the period between the discharge start timing and the discharge end timing.

[0075] Therefore, even without setting a long pause period after the discharge ends, it is possible to estimate a high-precision FCC.

[0076] [Project 3]

[0077] In the battery state estimation system described in Project 2

[0078] The secondary battery (E1) is a backup secondary battery (E1) that is periodically subjected to maintenance discharge in order to estimate the full charge capacity.

[0079] Therefore, the reduction in the function as a backup power source can be minimized, and the FCC status of the secondary battery (E1) can be checked periodically.

[0080] [Project 4]

[0081] A method for estimating battery state includes the following steps:

[0082] The voltage data of the secondary battery (E1) is acquired at fixed intervals from the end of the discharge time of the secondary battery (E1) to the first time interval.

[0083] Calculate the voltage difference between the voltage measured at the first timing interval and the voltage difference between the voltage measured during the rest period at the first timing interval starting from the discharge end timing interval, and calculate the cumulative value of the calculated voltage difference.

[0084] Referring to a pre-created table or a pre-created function that describes the relationship between (a) the cumulative value of the differential voltage and (b) the voltage change from the first timing point to the second timing point where the voltage of the secondary battery (E1) is considered to have converged, the voltage change from the first timing point to the second timing point is estimated based on the calculated cumulative value of the differential voltage; and

[0085] The estimated voltage change is added to the voltage measured at the first timing, and the voltage at the second timing is estimated as the OCV.

[0086] Therefore, by timing the polarization relaxation process after the discharge ends, the OCV after polarization relaxation can be estimated simply and with high accuracy.

[0087] [Project 5]

[0088] A battery state estimation program causes a computer to perform the following processing:

[0089] The voltage data of the secondary battery (E1) is acquired at fixed intervals from the end of the discharge time of the secondary battery (E1) to the first time interval.

[0090] Calculate the voltage difference between the voltage measured at the first timing interval and the voltage difference between the voltage measured during the rest period at the first timing interval starting from the discharge end timing interval, and calculate the cumulative value of the calculated voltage difference.

[0091] Referring to a pre-created table or a pre-created function that describes the relationship between (a) the cumulative value of the differential voltage and (b) the voltage change from the first timing point to the second timing point where the voltage of the secondary battery (E1) is considered to have converged, the voltage change from the first timing point to the second timing point is estimated based on the calculated cumulative value of the differential voltage; and

[0092] The estimated voltage change is added to the voltage measured at the first timing, and the voltage at the second timing is estimated as the OCV.

[0093] Therefore, by timing the polarization relaxation process after the discharge ends, the OCV after polarization relaxation can be estimated simply and with high accuracy.

[0094] -Explanation of Figure Markers-

[0095] 1 Battery pack

[0096] 2. Load

[0097] 3. Commercial Power Systems

[0098] 4 Chargers

[0099] 10 battery packs

[0100] 20 Battery Management Device

[0101] 21 Measurement Department

[0102] 22 Control Department

[0103] 221 Measurement Acquisition Department

[0104] 222 Calculation of Cumulative Difference Value

[0105] 223 Voltage Change Estimation Section

[0106] 224 OCV Presumption Department

[0107] 225 FCC Presumption Section

[0108] E1-En monomer

[0109] Rs Shunt resistor

[0110] SW1 switch

[0111] T1 Temperature sensor.

Claims

1. A battery state estimation system, comprising: The measurement acquisition unit acquires voltage data of the secondary battery measured at fixed intervals during the period from the end of the discharge of the secondary battery to the first time interval. The differential cumulative value calculation unit calculates the voltage difference between the voltage measured at the first timing and the multiple voltages measured during the rest period of the first timing from the end of the discharge timing, and calculates the cumulative value of the calculated multiple voltage differences. The voltage change estimation unit refers to a pre-created table or a pre-created function that describes the relationship between (a) the cumulative value of the difference voltage and (b) the voltage change from the first timing point to the second timing point when the voltage of the secondary battery is considered to have converged. Based on the calculated cumulative value of the difference voltage, it estimates the voltage change from the first timing point to the second timing point. and OCV, or Open Circuit Voltage Estimation Unit, adds the estimated voltage change to the voltage measured at the first timing to estimate the voltage at the second timing.

2. The battery state estimation system according to claim 1, wherein, The battery state estimation system further includes a full charge capacity estimation unit, which estimates the full charge capacity of the secondary battery based on the voltage measured at the discharge start timing of the secondary battery, the estimated voltage at the second timing, the SOC difference of the SOC curve of the secondary battery (i.e., the state of charge-OCV curve), and the cumulative current value during the period between the discharge start timing and the discharge end timing.

3. The battery state estimation system according to claim 2, wherein, The secondary battery is a backup secondary battery, and maintenance discharge is performed periodically to estimate the full charge capacity.

4. A method for estimating the state of a battery, comprising the following steps: The voltage data of the secondary battery is acquired at fixed intervals during the period from the end of the discharge of the secondary battery to the first time interval. Calculate the voltage difference between the voltage measured at the first timing interval and the voltage difference between the voltage measured during the rest period at the first timing interval starting from the discharge end timing interval, and calculate the cumulative value of the calculated voltage difference. Referring to a pre-created table or a pre-created function that describes the relationship between (a) the cumulative value of the differential voltage and (b) the voltage change from the first timing point to the second timing point where the voltage of the secondary battery is considered to have converged, the voltage change from the first timing point to the second timing point is estimated based on the calculated cumulative value of the differential voltage; and The estimated voltage change is added to the voltage measured at the first timing, and the voltage at the second timing is estimated as the OCV, i.e., the open-circuit voltage.

5. A battery state estimation program that causes a computer to perform the following processing: Acquire voltage data of the secondary battery at fixed intervals during the period from the end of discharge of the secondary battery to the first time interval; Calculate the voltage difference between the voltage measured at the first timing interval and the voltage difference between the voltage measured during the rest period at the first timing interval starting from the discharge end timing interval, and calculate the cumulative value of the calculated voltage difference. Referring to a pre-created table or a pre-created function that describes the relationship between (a) the cumulative value of the differential voltage and (b) the voltage change from the first timing point to the second timing point where the voltage of the secondary battery is considered to have converged, the voltage change from the first timing point to the second timing point is estimated based on the calculated cumulative value of the differential voltage; and The estimated voltage change is added to the voltage measured at the first timing, and the voltage at the second timing is estimated as the OCV, i.e., the open-circuit voltage.

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