Battery storage system, deterioration determination device, and deterioration determination method

Abstract

To provide a storage battery system capable of accurately determining deterioration of a storage battery.SOLUTION: An approximate expression derivation unit (12) derives, on the basis of internal resistance values in time series calculated by an internal resistance value calculation unit (11), an approximate expression for approximating an internal resistance value of a storage battery (2). An approximate expression calculation unit (13) uses the approximate expression derived by the approximate expression derivation unit (12) to calculate the internal resistance value of the storage battery (2). A deterioration determination unit (17) determines deterioration of the storage battery (2) by comparing the internal resistance value of the storage battery (2) calculated by the approximate expression calculation unit (13) with a determination value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a technique for determining deterioration of a storage battery. [Background technology]

[0002] Techniques for determining deterioration of a storage battery include the inventions disclosed in the following Patent Documents 1 and 2. Patent Document 1 relates to a technique for estimating the lifespan of a lead-acid battery by estimating the initial internal resistance value of the storage battery, in which the internal resistance value of the lead-acid battery is measured multiple times over time, an Nth-order approximation equation is found from the relationship between the multiple internal resistance values ​​and the number of years since installation at the time of measurement, the initial internal resistance value of the lead-acid battery is calculated from the approximation equation, and the lifespan of the lead-acid battery is estimated from the calculated initial internal resistance value.

[0003] Patent Document 2 relates to a technology for measuring the secondary battery to be judged by an AC impedance method and judging the degree of deterioration of the secondary battery. In this conventional technology, the circuit characteristics of the secondary battery are fitted to an equivalent circuit model having a high-frequency side reaction resistor, a low-frequency side reaction resistor, a high-frequency side capacitor, and a low-frequency side capacitor. Then, the smaller the reciprocal of the product of the resistance value of the low-frequency side reaction resistor and the capacitance of the low-frequency side capacitor, the greater the degree of deterioration is judged to be. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-271438 A (Published October 18, 2007) [Patent Document 2] JP 2012-220199 A (Published on November 12, 2012) Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 can be applied to lead-acid batteries, but cannot be applied to storage batteries such as lithium-ion batteries. That is, the internal resistance value of a lead-acid battery is almost constant at the beginning of installation, and then increases gradually in a linear manner, and as it approaches the end of its life, the internal resistance value increases rapidly. Based on this general rule of thumb, deterioration is judged by using an N-th order equation. However, this method is only applicable to lead-acid batteries, and cannot be applied to lithium-ion batteries, etc., and is not very versatile.

[0006] Furthermore, the internal resistance of a secondary battery varies depending on the evaluation method, and the tendency toward deterioration varies for each internal resistance value, such as the DC internal resistance calculated from the VI characteristics, the AC internal resistance value evaluated by superimposing an AC voltage (current) of a constant frequency, and the internal resistance value as an equivalent circuit constant obtained by fitting analysis of current and voltage waveforms using an equivalent circuit, but Patent Document 1 is silent about the evaluation method.

[0007] In addition, Patent Document 2 uses an AC impedance method to fit the circuit characteristics of a secondary battery to an equivalent circuit model to determine the deterioration of the secondary battery. However, since there is a large variation in the measured values ​​from one measurement to the next, the calculated resistance value also varies, resulting in erroneous determination.

[0008] An object of one aspect of the present invention is to provide a storage battery system, a deterioration determination device, and a deterioration determination method that are capable of determining deterioration of a storage battery with high accuracy. [Means for solving the problem]

[0009] In order to solve the above problems, a storage battery system according to one embodiment of the present invention includes a storage battery, an ammeter that measures a current value of the storage battery, a voltmeter that measures a voltage value of the storage battery, an internal resistance value calculation unit that calculates an internal resistance value of the storage battery based on the current value measured by the ammeter and the voltage value measured by the voltmeter, an approximation equation derivation unit that derives an approximation equation for approximating the internal resistance value of the storage battery based on the time-series internal resistance values ​​calculated by the internal resistance value calculation unit, an approximation equation calculation unit that calculates the internal resistance value of the storage battery using the approximation equation derived by the approximation equation derivation unit, and a deterioration determination unit that compares the internal resistance value of the storage battery calculated by the approximation equation calculation unit with a determination value to determine deterioration of the storage battery. In addition, in order to solve the above-mentioned problems, a deterioration determination device according to one embodiment of the present invention includes an internal resistance value calculation unit that calculates an internal resistance value of a storage battery based on a current value measured by an ammeter and a voltage value measured by a voltmeter, an approximation equation derivation unit that derives an approximation equation for approximating the internal resistance value of the storage battery based on the time-series internal resistance values ​​calculated by the internal resistance value calculation unit, an approximation equation calculation unit that calculates the internal resistance value of the storage battery using the approximation equation derived by the approximation equation derivation unit, and a deterioration determination unit that compares the internal resistance value of the storage battery calculated by the approximation equation calculation unit with a determination value to determine deterioration of the storage battery. In addition, in order to solve the above-mentioned problems, a deterioration determination method according to one embodiment of the present invention includes the steps of measuring a current value of a storage battery, measuring a voltage value of the storage battery, calculating an internal resistance value of the storage battery based on the measured current value and the measured voltage value, deriving an approximation equation for approximating the internal resistance value of the storage battery based on the calculated time-series internal resistance value, calculating the internal resistance value of the storage battery using the derived approximation equation, and comparing the internal resistance value of the storage battery calculated using the approximation equation with a determination value to determine deterioration of the storage battery. Effect of the Invention

[0010] According to one aspect of the present invention, it is possible to determine the deterioration of a storage battery with high accuracy. [Brief description of the drawings]

[0011] [Figure 1] 1 is a block diagram showing a functional configuration of a storage battery system according to one embodiment of the present invention. [Diagram 2] 4 is a flowchart for explaining a processing procedure of a storage battery system according to one embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram showing an example of an equivalent circuit of a storage battery. [Figure 4] 1 is a graph showing an example of a relationship between elapsed time and an internal resistance value. [Diagram 5] 1 is a graph showing an example of the relationship between elapsed time+number of charge / discharge cycles and internal resistance value. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] (Embodiment 1) Hereinafter, an embodiment of the present invention will be described in detail. For the sake of convenience, the same members are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

[0013] <Configuration of storage battery system 100> 1 is a functional block diagram showing a schematic configuration of a storage battery system 100 according to one embodiment of the present invention. The storage battery system 100 includes a deterioration determination device 1, a storage battery 2, an ammeter 3, a voltmeter 4, and an RTC (Real Time Clock) 5.

[0014] In this embodiment, a lithium ion battery will be described as an example of the storage battery 2, but the present invention is not limited to this. The ammeter 3 measures the current of the storage battery 2 and outputs the current value to the deterioration determination device 1. The voltmeter 4 measures the voltage of the storage battery 2 and outputs the voltage value to the deterioration determination device 1. The RTC 5 outputs current time information to the deterioration determination device 1 in response to a request from the deterioration determination device 1.

[0015] The deterioration determination device 1 includes an internal resistance value calculation unit 11, an approximate formula derivation unit 12, an approximate formula calculation unit 13, an operation time measurement unit 14, a stoppage time measurement unit 15, a charge / discharge cycle number measurement unit 16, a deterioration determination unit 17, and a memory unit 18.

[0016] <Internal resistance calculation section> The internal resistance value calculation unit 11 periodically calculates the internal resistance value of the storage battery 2 from the current value output from the ammeter 3 and the voltage value output from the voltmeter 4, and stores the internal resistance value in the memory unit 18. At this time, in addition to the calculated internal resistance value, the internal resistance value calculation unit 11 obtains the operation time, stop time, and number of charge / discharge cycles at that time from the memory unit 18, and stores them as a set in the memory unit 18. The internal resistance value calculation unit 11 may also obtain the time at that time from the RTC 5 and add it to this information. Since this process is performed periodically, a large number of these data sets are stored in the memory unit 18.

[0017] The internal resistance value calculation unit 11 calculates the internal resistance value of the storage battery 2, for example, by performing a fitting analysis using an equivalent circuit of the storage battery 2. This fitting analysis using the equivalent circuit is well known, and therefore will not be described in detail here.

[0018] Furthermore, the internal resistance value calculation unit 11 may calculate a charging internal resistance value R21 and a discharging internal resistance value R22 from the current value output from the ammeter 3 and the voltage value output from the voltmeter 4, and set one of these values ​​as the internal resistance value of the storage battery 2. The charging internal resistance value R21 is the internal resistance value of the storage battery 2 when it is being charged, and the discharging internal resistance value R22 is the internal resistance value of the storage battery 2 when it is being discharged.

[0019] The internal resistance value calculation unit 11 acquires the current value I1, the current value I2, the voltage value U1, and the voltage value U2 from the storage unit 18, and calculates the charging internal resistance value R21 based on the following (Equation 1).

[0020] R21=(U2-U1) / (I2-I1) (Formula 1) Here, the voltage value U1 is the voltage value of the storage battery 2 measured when the storage battery 2 is charged for a first predetermined time with a constant current value I1 from a standby state in which no charging or discharging is occurring, and when the current value I1 is flowing immediately before the charging is completed. The voltage value U2 is the voltage value of the storage battery 2 measured when the storage battery 2 is charged for a first predetermined time with a constant current value I2 larger than the current value I1 from a standby state in which no charging or discharging is occurring, and when the current value I2 is flowing immediately before the charging is completed.

[0021] The internal resistance value calculation unit 11 periodically calculates the charging internal resistance value R21 while operating the storage battery 2. While operating the storage battery 2, the internal resistance value calculation unit 11 periodically checks that the storage battery 2 is within a predetermined SOC (State Of Charge) range, obtains the voltage value U1 and the voltage value U2 by charging the storage battery 2 with the current value I1 and the current value I2, and stores the current value I1, the current value I2, the voltage value U1, and the voltage value U2 in the storage unit 18. The SOC is, for example, when it is in the range of 45 to 55%. The internal resistance value calculation unit 11 calculates the charging internal resistance value R21 based on the current value I1, the current value I2, the voltage value U1, and the voltage value U2 stored in the storage unit 18.

[0022] Furthermore, the internal resistance value calculation unit 11 acquires the current value I3, the current value I4, the voltage value U3, and the voltage value U4 from the storage unit 18, and calculates the discharge internal resistance value R22 based on the following (Equation 2).

[0023] R22=(U3-U4) / (I4-I3) (Formula 2) Here, the voltage value U3 is the voltage value of the storage battery 2 measured when the storage battery 2 is discharged for a second predetermined time at a constant current value I3 from a standby state in which no charging or discharging is taking place, and when the current value I3 is flowing immediately before the discharge is completed. The voltage value U4 is the voltage value of the storage battery 2 measured when the storage battery 2 is discharged for a second predetermined time at a constant current value I4 larger than the current value I3 from a standby state in which no charging or discharging is taking place, and when the current value I4 is flowing immediately before the discharge is completed.

[0024] The internal resistance value calculation unit 11 periodically calculates the discharge internal resistance value R22 while operating the storage battery 2. While operating the storage battery 2, the internal resistance value calculation unit 11 periodically checks that the storage battery 2 is within a predetermined SOC range, acquires the voltage values ​​U3 and U4 by discharging the current values ​​I3 and I4 from the storage battery 2, and stores the current values ​​I3, I4, voltage values ​​U3, and U4 in the storage unit 18. The SOC is set to be, for example, when the SOC is in the range of 45 to 55%. The internal resistance value calculation unit 11 calculates the discharge internal resistance value R22 based on the current values ​​I3, I4, voltage values ​​U3, and voltage values ​​U4 stored in the storage unit 18.

[0025] The operation time measurement unit 14 monitors the operation status of the storage battery system 100, and refers to the RTC 5 to calculate the total operation time, which is then stored in the memory unit 18. Here, the operation time is the total time including the time during which the storage battery 2 is charging and the time during which the storage battery 2 is discharging. The operation time measurement unit 14 successively updates the operation time, and stores it in the memory unit 18.

[0026] The downtime measurement unit 15 monitors the stopped state of the storage battery system 100, and refers to the RTC 5 to calculate the total stopped time and store it in the memory unit 18. Here, the stopped time means a state in which the storage battery system 100 is neither charging nor discharging, and the stopped time may be calculated by subtracting the operation time from the total time. The downtime measurement unit 15 successively updates the stopped time and stores it in the memory unit 18.

[0027] The charge / discharge cycle number measuring unit 16 measures the number of charge / discharge cycles of the storage battery 2 and stores the number of charge / discharge cycles in the memory unit 18. For example, the charge / discharge cycle number measuring unit 16 starts charging when the SOC of the storage battery 2 is 10% or less, and counts one cycle when the SOC becomes 90% or more. Note that the method of measuring the number of charge / discharge cycles is not limited to this.

[0028] Here, the SOC of the storage battery 2 is calculated from the current capacity (Ah) charged and discharged to the storage battery 2 after the storage battery 2 is in a fully charged state (SOC 100%) or a fully discharged state (SOC 0%). Furthermore, the SOC of the storage battery 2 may be calculated from the current capacity charged and discharged to the storage battery 2 from the stopped state by putting the storage battery 2 in a stopped state in which no charging or discharging is being performed.

[0029] The approximate equation derivation unit 12 substitutes the internal resistance calculated by the internal resistance calculation unit 11 stored in the storage unit 18, the operation time measured by the operation time measurement unit 14, the stop time measured by the stop time measurement unit 15, and the number of charge / discharge cycles measured by the charge / discharge cycle number measurement unit 16 into the following (Equation 3), calculates coefficients a, b, c, and d by the least squares method, and derives an approximate equation. At this time, the most recent multiple data sets (internal resistance, operation time, stop time, number of charge / discharge cycles) stored in the storage unit 18 are used.

[0030] R1 = R0 + a × t1 α +b×t2 β +c×n γ +d...(Formula 3) Here, R1 is the internal resistance value of the storage battery 2 calculated using the approximation formula (Formula 3), and is a value used when performing the deterioration determination. When deriving the approximation formula, the internal resistance value calculated by the internal resistance value calculation unit 11 is substituted for R1.

[0031] R0 is an initial value of the internal resistance value of the storage battery 2 before or immediately after the start of operation. This initial value R0 is preferably calculated by the internal resistance value calculation unit 11 immediately after the start of operation. Alternatively, it may be calculated before the start of operation.

[0032] a is a coefficient determined by approximating the internal resistance value calculated multiple times over time for the storage battery 2 in operation. b is a coefficient determined by approximating the internal resistance value calculated multiple times over time for the storage battery 2 at rest. c is a coefficient determined by approximating the internal resistance value calculated multiple times according to the number of charge / discharge cycles for the storage battery 2 in operation. In addition, d is a constant determined by approximating the internal resistance value calculated multiple times regardless of whether the storage battery 2 is in operation or at rest.

[0033] t1 is the elapsed time during operation of the storage battery 2. Here, the operation time measured by the operation time measurement unit 14 and stored in the memory unit 18 is used.

[0034] t2 is the elapsed time during which the storage battery 2 is stopped. Here, the stopped time measured by the stopped time measuring unit 15 and stored in the memory unit 18 is used.

[0035] n is the number of charge / discharge cycles during operation of the storage battery 2. Here, the number of charge / discharge cycles measured by the charge / discharge cycle number measuring unit 16 and stored in the memory unit 18 is used.

[0036] It is desirable to set α, β, and γ to power constants that minimize error with respect to changes in the internal resistance value of the storage battery 2, but the so-called root rule is known, which states that the discharge capacity reduction of a lithium-ion battery is proportional to the 1 / 2 power of the operating time. Therefore, these power constants may be set to 1 / 2. In addition, it is said that the DC internal resistance of a lithium-ion battery is proportional to the operating time, so these power constants may be set to 1.

[0037] The storage battery 2 deteriorates even when it is stopped and no current is being applied. Therefore, by managing the elapsed time during operation, the elapsed time during stoppage, and the number of charge / discharge cycles, and calculating the internal resistance value of the storage battery 2 using (Equation 3), a more accurate approximation can be performed. Note that, if the elapsed time during stoppage or the number of charge / discharge cycles cannot be measured, the coefficients b and c may be set to 0, and the internal resistance value of the storage battery 2 may be approximated only by the elapsed time during operation.

[0038] The approximate equation calculation unit 13 substitutes the latest operation time t1, stop time t2, and number of charge / discharge cycles n into the approximate equation derived by the approximate equation derivation unit 12 to calculate the internal resistance value R1 of the storage battery 2.

[0039] The deterioration determination unit 17 determines deterioration of the storage battery 2 by comparing the internal resistance value of the storage battery 2 calculated by the approximation equation calculation unit 13 with the determination value. Since the determination value for determining deterioration varies depending on the characteristics of the storage battery 2 and the intended use, it is difficult to determine a determination value in general, but for example, the determination value may be set to 100 mΩ, and the deterioration determination unit 17 determines that the storage battery 2 is deteriorated when the internal resistance value calculated by the approximation equation calculation unit 13 exceeds 100 mΩ.

[0040] <Processing Procedure> 2 is a flowchart for explaining a processing procedure of the storage battery system 100 according to one embodiment of the present invention. First, the internal resistance value calculation unit 11 calculates the internal resistance value of the storage battery 2 as described above, and stores it in the memory unit 18 together with the operation time, the stop time, and the number of charge / discharge cycles (S1).

[0041] Next, the approximation equation derivation unit 12 obtains from the memory unit 18 the most recent internal resistance values ​​stored in the memory unit 18, along with the operation time, stop time, and number of charge / discharge cycles, and derives the approximation equation (Equation 3) by extracting the coefficients a, b, c, and d of the approximation equation (Equation 3) using the least squares method (S2).

[0042] Next, the approximation formula calculation unit 13 approximates the current internal resistance value R1 of the storage battery 2 by substituting the current operation time t1, stop time t2, and number of charge / discharge cycles n into the approximation formula derived by the approximation formula derivation unit 12 and performing calculations (S3).

[0043] Next, the deterioration determination unit 17 compares the internal resistance value R1 calculated by the approximate expression calculation unit 13 with the determination value and determines whether the internal resistance value R1 exceeds the determination value (S4). If the internal resistance value R1 exceeds the determination value (S4, Yes), the deterioration determination unit 17 determines that the storage battery 2 is deteriorated (S6) and ends the process.

[0044] If the internal resistance value R1 does not exceed the determination value (S4, No), the degradation determination unit 17 determines that the storage battery 2 is not degraded, waits for the calculation of the next internal resistance value (S5), and returns to step S2 to repeat the subsequent processes. Here, the calculation of the next internal resistance value may be performed periodically, for example, once a week, by the internal resistance value calculation unit 11.

[0045] Furthermore, as described above, when the internal resistance value is calculated periodically while the storage battery 2 is in operation, the process shown in FIG. 2 may be performed at that time.

[0046] As described above, in the storage battery system according to this embodiment, the internal resistance value calculation unit 11 periodically calculates the internal resistance value of the storage battery 2 based on the current value and voltage value of the storage battery 2. The approximate equation derivation unit 12 derives an approximate equation for approximating the internal resistance value of the storage battery 2 based on the internal resistance value calculated by the internal resistance value calculation unit 11, the operation time measured by the operation time measurement unit 14, and the like. Then, the approximate equation calculation unit 13 calculates the internal resistance value of the storage battery 2 by substituting the operation time, and the like, into the approximate equation derived by the approximate equation derivation unit 12. Therefore, it is possible to derive an approximate equation based on the most recent internal resistance value, operation time, and the like, and it is possible to perform a highly accurate deterioration determination.

[0047] In addition, since the approximate equation derivation unit 12 derives the approximate equation based on multiple internal resistance values ​​and their corresponding operating times, etc., it is possible to prevent a mistaken determination of deterioration even if an internal resistance value with a large error is included.

[0048] In addition, since an approximation formula is derived using the operation time t1, the stop time t2, and the number of charge / discharge cycles n, it is possible to perform deterioration determination with even higher accuracy.

[0049] (Embodiment 2) In this embodiment, multiple commercially available cylindrical lithium ion batteries of the same type were prepared, adjusted to SOC 50% at room temperature, and the initial value of the internal resistance was calculated using an AC impedance method. The batteries were then placed in a thermostatic chamber set at a temperature of 30°C, and a charge / discharge device was connected to the lithium ion batteries. An accelerated deterioration test was performed under any of the following four conditions: Condition 1: Save 50% of SOC Condition 2: Maintain SOC 90% Condition 3: Float charging at SOC 70% Condition 4: Charge / discharge cycle of SOC 10% to 90% The end.

[0050] The cells that underwent the accelerated aging test were periodically removed from the thermostatic chamber, adjusted to SOC 50% at room temperature, and the internal resistance was evaluated using the AC impedance method. In the AC impedance method, a voltage step of 5 mV was superimposed on the DC voltage of the battery cell at a frequency of 10 kHz to 10 mHz, and a fitting analysis was performed using an equivalent circuit to calculate the internal resistance as an equivalent circuit constant.

[0051] FIG. 3 is a diagram showing an example of an equivalent circuit of a storage battery. Here, R11 is an ohmic resistance, R12 and R13 are reactive resistances, CPE (Constant Phase Elements) 1 and CPE2 are capacitance components substituting for capacitors, and WZ is a diffusion resistance. L is a reactance component of the electrode terminal and cable, and R14 is a resistance component of the electrode terminal and cable. R11+R12+R13 is the internal resistance value of the storage battery 2.

[0052] Fig. 4 is a graph showing an example of the relationship between elapsed time and internal resistance value. The horizontal axis represents the 1 / 2 power of the elapsed time of the accelerated aging test, and the vertical axis represents the internal resistance value (R11+R12+R13 in the equivalent circuit shown in Fig. 3). As shown in Fig. 4, the internal resistance value increases as the elapsed time increases.

[0053] After 2594 hours, the internal resistance value of 50.9 on the horizontal axis of Figure 4, which is the power of 1 / 2, reaches a maximum of 107.8 mΩ. For example, if the judgment value is 100 mΩ, this battery cell is judged to be degraded. However, the internal resistance value after that does not show a continuous increase, but rather shows a downward trend. This is because, in the calculation of the periodic internal resistance value, the measurement is performed at room temperature using the AC impedance method, and it can be assumed that the internal resistance value temporarily increases when the temperature drops, for example, when the measurement is performed in winter. In this test, no sudden increase in the internal resistance value was observed even after more than 10,000 hours had passed, indicating that the storage battery can be used continuously.

[0054] Before the accelerated aging test, the internal resistance of the four battery cells was measured, and the average was R0 = 74.2 mΩ. Based on the approximation formula (Formula 3), the approximation formula derived for the internal resistance after 2594 hours is as follows: R1 = 74.2 + 0.3431 × t1 1 / 2 -2.0 (Formula 4) The approximate formula for this internal resistance is b=0, c=0, and α=1 / 2.

[0055] Using the approximate formula (Formula 4), the internal resistance value R1 after 2594 hours has elapsed is calculated to be 89.7 mΩ, and even if the deterioration judgment value is set to 100 mΩ, the four battery cells would not be judged as deteriorated. In this way, even if there is a temporary or specific increase in the internal resistance value, by judging the deterioration using the approximate formula, it is possible to prevent the storage battery from being erroneously judged as deteriorated, prevent unnecessary replacement of the storage battery, and enable more effective use of the storage battery.

[0056] In addition, using the approximation formula (Formula 3), the approximation formula derived for the internal resistance value after 18638 hours, that is, up to 136.5 on the horizontal axis of Figure 4 raised to the power of 1 / 2, is as follows: R1 = 74.2 + 0.0871 × t1 1 / 2 +4.86 (Formula 5) The approximate equation for this internal resistance value also assumes b=0, c=0, and α=1 / 2.

[0057] Using the approximation formula (Formula 5), ​​the internal resistance value R1 after 18,638 hours has elapsed is calculated to be 91.0 mΩ, and even if the deterioration judgment value is set to 100 mΩ, the four battery cells are not judged to be deteriorated. Using the approximation formula (Formula 5), ​​the time it takes to reach the deterioration judgment value of 100 mΩ is calculated to be t1 = 57,799 hours, and the lifespan of the storage battery can be estimated.

[0058] The time from the current time until the end of the battery life may be calculated and displayed as the estimated battery life on a display device (not shown). If the time until the end of the battery life falls below a certain period, for example, one year, a message urging the user to replace the battery may be displayed on a display device (not shown), or a warning signal may be generated and output.

[0059] In the above explanation, the approximate formula (Formula 4) is derived using the internal resistance value from the initial state of the storage battery until 2594 hours have elapsed, and the approximate formula (Formula 5) is derived using the internal resistance value until 18638 hours have elapsed. However, as explained in the first embodiment, the internal resistance value calculation unit 11 may periodically calculate the internal resistance value to derive the approximate formula in real time and determine the deterioration of the storage battery.

[0060] As described above, according to the storage battery system 100 of the present embodiment, the approximation formula is derived only based on the operation time of the storage battery 2, so that the approximation formula can be easily derived.

[0061] (Embodiment 3) In this embodiment, a plurality of commercially available cylindrical lithium ion batteries of the same type were prepared and adjusted to SOC 50% at room temperature. In a Nyquist diagram in which the real part of the impedance measured by an AC impedance method is plotted on the horizontal axis and the imaginary part is plotted on the vertical axis, the initial value was calculated as the internal resistance value, and the sum of the electron transfer resistance and the charge transfer resistance was then placed in a thermostatic chamber set at temperatures of 25°C, 40°C, and 60°C. A charge / discharge device was connected to the lithium ion batteries, and an accelerated deterioration test was performed by a cycle test at DOD (Depth Of Discharge) 100%.

[0062] The cells that underwent the accelerated aging test were periodically removed from the thermostatic chamber, adjusted to SOC 50% at room temperature, and the internal resistance was evaluated using the AC impedance method. In the AC impedance method, a voltage step of 5 mV was superimposed on the DC voltage of the battery cell at a frequency of 10 kHz to 10 mHz, and the total value of the electron transfer resistance and the charge transfer resistance was calculated as the internal resistance in a Nyquist diagram in which the real part of the impedance measured by the AC impedance method is on the horizontal axis and the imaginary part is on the vertical axis.

[0063] FIG. 5 is a graph showing an example of the relationship between the elapsed time + the number of charge / discharge cycles and the internal resistance value. The horizontal axis is the 1 / 2 power of the elapsed time + the 1 / 2 power of the number of charge / discharge cycles in the accelerated aging test, and the vertical axis is the internal resistance value. G1 shows a graph of the internal resistance value of a lithium-ion battery sample placed in a thermostatic chamber at 25°C. G2 shows a graph of the internal resistance value of another lithium-ion battery sample placed in a thermostatic chamber at 25°C. G3 and G4 show graphs of the internal resistance values ​​of lithium-ion battery samples placed in thermostatic chambers at 40°C and 60°C, respectively.

[0064] As shown in Figure 5, although there is some variation depending on the temperature and sample, the internal resistance value increases with an increase in the 1 / 2 power of the elapsed time in the accelerated aging test plus the 1 / 2 power of the number of charge / discharge cycles. By calculating the coefficient a of the operating time t1 and the coefficient b of the number of charge / discharge cycles t2 in the approximation formula (Formula 3), the internal resistance value can be approximated by the operating time t1 and the number of charge / discharge cycles t2.

[0065] As described above, according to the storage battery system 100 of this embodiment, an approximation formula is derived using the operating time and number of charge / discharge cycles of the storage battery 2, making it possible to derive an approximation formula that can calculate an internal resistance value with even higher accuracy.

[0066] [Software implementation example] The control blocks of the deterioration determination device 1 (particularly the internal resistance value calculation unit 11, the approximate formula derivation unit 12, the approximate formula calculation unit 13, the operation time measurement unit 14, the stop time measurement unit 15, the charge / discharge cycle number measurement unit 16 and the deterioration determination unit 17) may be realized by a logic circuit (hardware) formed in an integrated circuit (IC chip) or the like, or may be realized by software.

[0067] In the latter case, the deterioration determination device 1 includes a computer that executes instructions of a program, which is software that realizes each function. The computer includes, for example, one or more processors, and a computer-readable recording medium that stores the program. The object of the present invention is achieved by the processor reading the program from the recording medium and executing it in the computer. The processor may be, for example, a CPU (Central Processing Unit). The recording medium may be a "non-transient tangible medium", such as a ROM (Read Only Memory), a tape, a disk, a card, a semiconductor memory, a programmable logic circuit, or the like. The device may further include a RAM (Random Access Memory) that expands the program. The program may be supplied to the computer via any transmission medium (such as a communication network or a broadcast wave) that can transmit the program. Note that one aspect of the present invention may also be realized in the form of a data signal embedded in a carrier wave, in which the program is embodied by electronic transmission.

[0068] 〔summary〕 The storage battery system according to aspect 1 of the present invention includes a storage battery, an ammeter that measures a current value of the storage battery, a voltmeter that measures a voltage value of the storage battery, an internal resistance value calculation unit that calculates an internal resistance value of the storage battery based on the current value measured by the ammeter and the voltage value measured by the voltmeter, an approximation equation derivation unit that derives an approximation equation for approximating the internal resistance value of the storage battery based on the time-series internal resistance values ​​calculated by the internal resistance value calculation unit, an approximation equation calculation unit that calculates the internal resistance value of the storage battery using the approximation equation derived by the approximation equation derivation unit, and a deterioration determination unit that compares the internal resistance value of the storage battery calculated by the approximation equation calculation unit with a determination value to determine deterioration of the storage battery. In a storage battery system according to a second aspect of the present invention, in the above-mentioned first aspect, the internal resistance value calculation unit periodically calculates the internal resistance value of the storage battery based on the current value measured by the ammeter and the voltage value measured by the voltmeter. A storage battery system according to a third aspect of the present invention is a storage battery system according to the first or second aspect described above, further comprising an operation time measurement unit that measures the operation time of the storage battery, and an approximation equation derivation unit derives an approximation equation for approximating the internal resistance value of the storage battery based on the internal resistance value calculated by the internal resistance value calculation unit and the operation time measured by the operation time measurement unit, and an approximation equation calculation unit calculates the internal resistance value of the storage battery by substituting the operation time measured by the operation time measurement unit into the approximation equation derived by the approximation equation derivation unit. A storage battery system according to a fourth aspect of the present invention is the same as in the above-mentioned third aspect, except that the storage battery system further includes a charge / discharge cycle number measurement unit that measures the number of charge / discharge cycles of the storage battery, and the approximation equation derivation unit derives an approximation equation for approximating the internal resistance value of the storage battery based on the internal resistance value calculated by the internal resistance value calculation unit, the operation time measured by the operation time measurement unit, and the number of charge / discharge cycles measured by the charge / discharge cycle number measurement unit, and the approximation equation calculation unit calculates the internal resistance value of the storage battery by substituting the operation time measured by the operation time measurement unit and the number of charge / discharge cycles measured by the charge / discharge cycle number measurement unit into the approximation equation derived by the approximation equation derivation unit. A storage battery system according to a fifth aspect of the present invention is a storage battery system according to the above-mentioned fourth aspect, further comprising a stop time measurement unit that measures the stop time of the storage battery, and the approximation equation derivation unit derives an approximation equation for approximating the internal resistance value of the storage battery based on the internal resistance value calculated by the internal resistance value calculation unit, the operation time measured by the operation time measurement unit, the number of charge and discharge cycles measured by the charge and discharge cycle number measurement unit, and the stop time measured by the stop time measurement unit, and the approximation equation calculation unit calculates the internal resistance value of the storage battery by substituting the operation time measured by the operation time measurement unit, the number of charge and discharge cycles measured by the charge and discharge cycle number measurement unit, and the stop time measured by the stop time measurement unit into the approximation equation derived by the approximation equation derivation unit. A sixth aspect of the present invention relates to a storage battery system in any one of the first to fifth aspects, wherein the approximate equation derivation unit derives an approximate equation by applying a least squares method to the most recent internal resistance values ​​calculated by the internal resistance value calculation unit. A storage battery system according to a seventh aspect of the present invention is any one of the first to sixth aspects, in which the approximate equation deriving unit derives the approximate equation using the following equation (Equation 3).

[0069] R1 = R0 + a × t1 α +b×t2 β +c×n γ +d...(Formula 3) R1: Internal resistance of the battery R0: Initial value of the internal resistance of the battery a: Coefficient calculated by approximating the internal resistance value calculated multiple times over time for a storage battery in operation b: Coefficient calculated by approximating the internal resistance value calculated multiple times over time for a stopped storage battery c: Coefficient calculated by approximating the internal resistance value calculated multiple times according to the number of charge / discharge cycles for a storage battery in operation d: A constant calculated by approximating the internal resistance value calculated multiple times, regardless of whether the equipment is in operation or not. t1: Elapsed time during battery operation t2: Time elapsed while the storage battery is stopped n: Number of charge / discharge cycles during operation of the storage battery α: Power constant of t1 that minimizes error due to changes in the internal resistance of the battery β: Power constant of t2 that minimizes error due to changes in the internal resistance of the battery γ: Power constant of n that minimizes error due to changes in the internal resistance of the battery A deterioration determination device according to aspect 8 of the present invention includes an internal resistance value calculation unit that calculates an internal resistance value of a storage battery based on a current value measured by an ammeter and a voltage value measured by a voltmeter, an approximation equation derivation unit that derives an approximation equation for approximating the internal resistance value of the storage battery based on a time-series internal resistance value calculated by the internal resistance value calculation unit, an approximation equation calculation unit that calculates the internal resistance value of the storage battery using the approximation equation derived by the approximation equation derivation unit, and a deterioration determination unit that compares the internal resistance value of the storage battery calculated by the approximation equation calculation unit with a determination value to determine deterioration of the storage battery. A deterioration determination method according to a ninth aspect of the present invention includes the steps of measuring a current value of a storage battery, measuring a voltage value of the storage battery, calculating an internal resistance value of the storage battery based on the measured current value and the measured voltage value, deriving an approximation equation for approximating the internal resistance value of the storage battery based on the calculated time-series internal resistance value, calculating the internal resistance value of the storage battery using the derived approximation equation, and comparing the internal resistance value of the storage battery calculated using the approximation equation with a determination value to determine deterioration of the storage battery.

[0070] [Additional Notes] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0071] 1 Deterioration determination device 2. Storage battery 3 Ammeter 4. Voltmeter 5. RTC 11 Internal resistance calculation section 12 Approximate formula derivation part 13 Approximate formula calculation section 14 Operation Time Measurement Section 15 Stop time measurement section 16 Charge / discharge cycle count measurement unit 17 Deterioration determination section 18 Memory section 100 Battery Storage System

Claims

1. A storage battery, an ammeter that measures a current value of the storage battery; A voltmeter that measures a voltage value of the storage battery; an internal resistance value calculation unit that calculates an internal resistance value of the storage battery based on a current value measured by the ammeter and a voltage value measured by the voltmeter; an approximation equation derivation unit that derives an approximation equation for approximating the internal resistance value of the storage battery based on the time-series internal resistance value calculated by the internal resistance value calculation unit; an approximate equation calculation unit that calculates an internal resistance value of the storage battery by using the approximate equation derived by the approximate equation derivation unit; a deterioration determination unit that compares the internal resistance value of the storage battery calculated by the approximate expression calculation unit with a determination value to determine deterioration of the storage battery, Further, an operation time measurement unit that measures an operation time of the storage battery; a charge / discharge cycle number measurement unit that measures the number of charge / discharge cycles of the storage battery, the approximation formula derivation unit derives an approximation formula for approximating the internal resistance value of the storage battery based on the internal resistance value calculated by the internal resistance value calculation unit, the operation time measured by the operation time measurement unit, and the number of charge / discharge cycles measured by the charge / discharge cycle number measurement unit; and The approximate equation calculation unit calculates an internal resistance value of the storage battery by substituting the operation time measured by the operation time measurement unit and the number of charge / discharge cycles measured by the number of charge / discharge cycles measurement unit into the approximate equation derived by the approximate equation derivation unit.

2. The storage battery system further includes a stop time measurement unit that measures a stop time of the storage battery, the approximation formula derivation unit derives an approximation formula for approximating the internal resistance value of the storage battery based on the internal resistance value calculated by the internal resistance value calculation unit, the operation time measured by the operation time measurement unit, the number of charge / discharge cycles measured by the charge / discharge cycle number measurement unit, and the stop time measured by the stop time measurement unit; 2. The battery system according to claim 1, wherein the approximation formula calculation unit calculates an internal resistance value of the storage battery by substituting the operation time measured by the operation time measurement unit, the number of charge / discharge cycles measured by the charge / discharge cycle number measurement unit, and the stop time measured by the stop time measurement unit into the approximation formula derived by the approximation formula derivation unit.

3. A storage battery; an ammeter that measures a current value of the storage battery; A voltmeter that measures a voltage value of the storage battery; an internal resistance value calculation unit that calculates an internal resistance value of the storage battery based on a current value measured by the ammeter and a voltage value measured by the voltmeter; an approximation equation derivation unit that derives an approximation equation for approximating the internal resistance value of the storage battery based on the time-series internal resistance value calculated by the internal resistance value calculation unit; an approximate equation calculation unit that calculates an internal resistance value of the storage battery by using the approximate equation derived by the approximate equation derivation unit; a deterioration determination unit that compares the internal resistance value of the storage battery calculated by the approximate expression calculation unit with a determination value to determine deterioration of the storage battery, The approximate equation derivation unit derives the approximate equation using the following equation (Equation 3). R １ =R ０ + a×t １ α + b × t ２ β +c×n γ +d …………(Formula 3) R １ : Internal resistance of the battery R ０ :The initial value of the internal resistance of the storage battery a: Coefficient calculated by approximating the internal resistance value calculated multiple times over time for a storage battery in operation b: Coefficient calculated by approximating the internal resistance value calculated multiple times over time for a stopped storage battery c: Coefficient calculated by approximating the internal resistance value calculated multiple times according to the number of charge / discharge cycles for a storage battery in operation d: A constant calculated by approximating the internal resistance value calculated multiple times, regardless of whether the equipment is in operation or not. t １ : Elapsed time of battery operation t ２ : Elapsed time when the storage battery is stopped n: Number of charge / discharge cycles during operation of the storage battery α: t that minimizes error due to changes in the internal resistance of the battery １ Power constant β: The time that minimizes the error due to the change in the internal resistance of the battery ２ Power constant γ: Power constant of n that minimizes error due to changes in the internal resistance of the storage battery

4. The storage battery system according to any one of claims 1 to 3, wherein the internal resistance value calculation unit periodically calculates the internal resistance value of the storage battery based on the current value measured by the ammeter and the voltage value measured by the voltmeter.

5. The storage battery system according to any one of claims 1 to 4, wherein the approximate equation derivation unit derives an approximate equation by applying a least squares method to the most recent internal resistance values ​​calculated by the internal resistance value calculation unit.

6. an internal resistance value calculation unit that calculates an internal resistance value of the storage battery based on a current value measured by the ammeter and a voltage value measured by the voltmeter; an approximation equation derivation unit that derives an approximation equation for approximating the internal resistance value of the storage battery based on the time-series internal resistance value calculated by the internal resistance value calculation unit; an approximate equation calculation unit that calculates an internal resistance value of the storage battery by using the approximate equation derived by the approximate equation derivation unit; a deterioration determination unit that compares the internal resistance value of the storage battery calculated by the approximate expression calculation unit with a determination value to determine deterioration of the storage battery, Further, an operation time measurement unit that measures an operation time of the storage battery; a charge / discharge cycle number measurement unit that measures the number of charge / discharge cycles of the storage battery, the approximation formula derivation unit derives an approximation formula for approximating the internal resistance value of the storage battery based on the internal resistance value calculated by the internal resistance value calculation unit, the operation time measured by the operation time measurement unit, and the number of charge / discharge cycles measured by the charge / discharge cycle number measurement unit; and The approximation formula calculation unit calculates the internal resistance value of the storage battery by substituting the operation time measured by the operation time measurement unit and the number of charge / discharge cycles measured by the charge / discharge cycle number measurement unit into the approximation formula derived by the approximation formula derivation unit.

7. An internal resistance value calculation unit that calculates an internal resistance value of the storage battery based on a current value measured by an ammeter and a voltage value measured by a voltmeter; an approximation equation derivation unit that derives an approximation equation for approximating the internal resistance value of the storage battery based on the time-series internal resistance value calculated by the internal resistance value calculation unit; an approximate equation calculation unit that calculates an internal resistance value of the storage battery by using the approximate equation derived by the approximate equation derivation unit; a deterioration determination unit that compares the internal resistance value of the storage battery calculated by the approximate expression calculation unit with a determination value to determine deterioration of the storage battery, The deterioration determination device, wherein the approximation equation derivation unit derives the approximation equation using the following equation (Equation 3). R 1 =R 0 +a×t 1 α +b×t 2 β +c×n γ +d (Formula 3) R1: Internal resistance of the battery R 0 : Initial value of the internal resistance of the storage battery a: Coefficient calculated by approximating the internal resistance value calculated multiple times over time for a storage battery in operation b: Coefficient calculated by approximating the internal resistance value calculated multiple times over time for a stopped storage battery c: Coefficient calculated by approximating the internal resistance value calculated multiple times according to the number of charge / discharge cycles for a storage battery in operation d: A constant calculated by approximating the internal resistance value calculated multiple times, regardless of whether the equipment is in operation or not. t 1 : Elapsed time during operation of the storage battery t2: Elapsed time during which the storage battery is stopped n: Number of charge / discharge cycles during operation of the storage battery α: Power constant of t 1 that minimizes error due to changes in the internal resistance of the storage battery β: Power constant of t 2 that minimizes error due to changes in the internal resistance of the storage battery γ: Power constant of n that minimizes error due to changes in the internal resistance of the storage battery

8. Measuring a current value of a storage battery; Measuring a voltage value of the storage battery; calculating an internal resistance value of the storage battery based on the measured current value and the measured voltage value; Deriving an approximation equation for approximating an internal resistance value of the storage battery based on the calculated time-series internal resistance value; Calculating an internal resistance value of the storage battery using the derived approximation formula; a step of comparing an internal resistance value of the storage battery calculated using the approximation formula with a determination value to determine deterioration of the storage battery; Furthermore, measuring an operation time of the storage battery; measuring the number of charge / discharge cycles of the storage battery; In the step of deriving the approximation formula, an approximation formula for approximating the internal resistance value of the storage battery is derived based on the calculated internal resistance value, the measured operation time, and the measured number of charge / discharge cycles; A deterioration determination method, in which in the step of calculating the internal resistance value, the measured operating time and the measured number of charge / discharge cycles are substituted into the derived approximation formula to calculate the internal resistance value of the storage battery.

9. A step of measuring a current value of a storage battery; Measuring a voltage value of the storage battery; calculating an internal resistance value of the storage battery based on the measured current value and the measured voltage value; Deriving an approximation equation for approximating an internal resistance value of the storage battery based on the calculated time-series internal resistance value; Calculating an internal resistance value of the storage battery using the derived approximation formula; a step of comparing an internal resistance value of the storage battery calculated using the approximation formula with a determination value to determine deterioration of the storage battery; The degradation determination method, in the step of deriving the approximation equation, deriving the approximation equation using the following equation (Equation 3): R 1 =R 0 +a×t 1 α +b×t 2 β +c×n γ +d (Formula 3) R1: Internal resistance of the battery R 0 : Initial value of the internal resistance of the storage battery a: Coefficient calculated by approximating the internal resistance value calculated multiple times over time for a storage battery in operation b: Coefficient calculated by approximating the internal resistance value calculated multiple times over time for a stopped storage battery c: Coefficient calculated by approximating the internal resistance value calculated multiple times according to the number of charge / discharge cycles for a storage battery in operation d: A constant calculated by approximating the internal resistance value calculated multiple times, regardless of whether the equipment is in operation or not. t 1 : Elapsed time during operation of the storage battery t2: Elapsed time during which the storage battery is stopped n: Number of charge / discharge cycles during operation of the storage battery α: Power constant of t 1 that minimizes error due to changes in the internal resistance of the storage battery β: Power constant of t 2 that minimizes error due to changes in the internal resistance of the storage battery γ: Power constant of n that minimizes error due to changes in the internal resistance of the storage battery

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