Deterioration diagnosis method and deterioration diagnosis device

Abstract

To accurately diagnose the deterioration state of a storage battery.SOLUTION: A deterioration diagnosis apparatus (1) is provided with: a measurement unit (10) for measuring terminal current, inter-terminal voltage and temperature at a plurality of positions in a battery module (90) during charging or discharging of the battery module (90); a temperature calculation unit (21) for calculating an analysis temperature (T) of the battery module (90); an analysis unit (22) for performing a transient response analysis based on the terminal current and the inter-terminal voltage and calculating a series resistance component; a correction unit (23) for correcting the series resistance component using the analysis temperature (T); and a diagnosis unit (24) for diagnosing a deterioration state of a storage battery based on the corrected series resistance component.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a technique for diagnosing the deterioration of a storage battery.

Background Art

[0002] Techniques for diagnosing the deterioration state of a storage battery are known. As such a conventional technique, a technique for determining the deterioration state from the circuit characteristics during charging and discharging of a storage battery has been studied (see Patent Document 1). Different from diagnostic techniques such as experimentally performing charging and discharging of a storage battery for diagnosing the deterioration state of the storage battery, according to this technique, it is not necessary to stop the operation of the storage battery. On the other hand, a technique for synthesizing an equivalent circuit in a short time from the circuit characteristics during charging and discharging of a storage battery has also been studied (see Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] It is desired to realize a technique that can determine the deterioration state from the circuit characteristics during charging and discharging of a storage battery and can accurately determine the deterioration state of a storage battery even in a battery module or a battery panel capable of storing a large amount of power. In one aspect of the disclosure of the present invention, it is made in view of such a situation, and an object is to realize a deterioration diagnosis method that can accurately determine the deterioration state of a storage battery from the circuit characteristics during charging and discharging of the storage battery even in a battery module or a battery panel.

Means for Solving the Problems

[0005] A degradation diagnosis method according to one aspect of the present invention includes: a measurement step of measuring terminal current, terminal voltage and temperature at multiple locations in the battery during charging or discharging of the battery; a temperature calculation step of calculating an analysis temperature representative of the temperatures at the multiple locations; an analysis step of performing transient response analysis of the battery based on the terminal current and terminal voltage and calculating the series resistance component; a correction step of correcting the series resistance component calculated in the analysis step to the series resistance component at a predetermined reference temperature using the analysis temperature; and a diagnosis step of calculating a capacity reduction rate, which is the rate of decrease of the battery's storage capacity relative to its initial storage capacity, based on the series resistance component at the reference temperature, and diagnosing the degradation state of the battery, wherein in the analysis step, the transient response analysis is performed by reducing the battery to an equivalent circuit including the series resistance component and a parallel connection circuit in which the parallel capacitance component and the parallel resistance component are connected in parallel, and a circuit in which these are connected in series.

[0006] A degradation diagnostic device according to one aspect of the present invention comprises: a measurement unit that measures terminal current, terminal voltage and temperature at multiple locations in a storage battery during charging or discharging; a temperature calculation unit that calculates an analysis temperature representative of the temperatures at the multiple locations; an analysis unit that performs transient response analysis of the storage battery based on the terminal current and terminal voltage and calculates a series resistance component; a correction unit that corrects the series resistance component calculated by the analysis unit to the series resistance component at a predetermined reference temperature using the analysis temperature; and a diagnostic unit that diagnoses the degradation state of the storage battery by calculating a capacity reduction rate, which is the rate of decrease of the storage capacity of the storage battery relative to the storage capacity in the initial state of the storage battery, based on the series resistance component at the reference temperature, wherein the analysis unit reduces the storage battery to an equivalent circuit including the series resistance component and a parallel connection circuit in which the parallel capacitance component and the parallel resistance component are connected in parallel, and then performs the transient response analysis.

[0007] Each aspect of the present invention may be implemented by a computer, in which case a control program for the degradation diagnosis device that implements the degradation diagnosis device by a computer by operating the computer as each part (software element) of the degradation diagnosis device, and a computer-readable recording medium on which the program is recorded also fall within the scope of the present invention. [Effects of the Invention]

[0008] According to one aspect of the present invention, a degradation diagnosis method or a degradation diagnosis device can accurately determine the degradation state of a battery, even if it is a battery module or battery panel, based on the circuit characteristics during charging and discharging of the battery. [Brief explanation of the drawing]

[0009] [Figure 1] A functional block diagram showing the schematic configuration of a deterioration diagnostic device according to Embodiment 1 of the present invention. [Figure 2] This figure shows an example of a battery module that the above-mentioned degradation diagnostic device performs degradation diagnosis on. [Figure 3] This is a flowchart illustrating the processing procedure of the deterioration diagnosis method performed by the above-mentioned deterioration diagnosis device. [Figure 4] This graph shows example waveforms of current Ib and voltage Vb measured by the measurement unit of the above-mentioned degradation diagnostic device. [Figure 5] This is a flowchart illustrating the procedure for calculating the analysis temperature performed by the above-mentioned degradation diagnostic device. [Figure 6] This is an example of an equivalent circuit for a battery, applied to the transient response analysis performed by the analysis unit of the above-mentioned degradation diagnostic device. [Figure 7] This is another example of a battery equivalent circuit that can be applied to the transient response analysis performed by the analysis unit of the above-mentioned degradation diagnostic device. [Figure 8] This graph summarizes the results of the series resistance component Ri calculated by transient response analysis at various temperatures. [Figure 9] This graph shows the dependence of the temperature correction coefficient A on the capacity degradation rate D. [Figure 10] This graph shows the dependence of the temperature correction coefficient B on the capacity degradation rate D. [Figure 11] This graph shows the dependence of the temperature correction coefficient C on the capacity degradation rate D. [Figure 12] This graph shows two plots: one (square) showing the relationship between the capacity degradation rate D and the series resistance component Ri under conditions where the battery module temperature is fixed, and another (circle) showing the relationship between the capacity degradation rate D and the corrected series resistance component Ri_st. [Figure 13] This graph shows a plot (triangle) illustrating the relationship between the capacity degradation rate D and the series resistance component Ri, and a plot (circle) illustrating the relationship between the capacity degradation rate D and the parallel resistance component R1, under conditions where the temperature of the battery module is fixed. [Figure 14] This is a flowchart illustrating the processing procedure of the deterioration diagnosis method performed by the deterioration diagnosis device according to Embodiment 2 of the present invention. [Figure 15] This table shows the error rate of the series resistance component, after temperature correction to the reference temperature, relative to the true value of the series resistance component at the reference temperature, under two conditions: when the temperature difference within the battery module is small and when it is large. [Modes for carrying out the invention]

[0010] [Embodiment 1] <Configuration of the deterioration diagnostic device> The following describes in detail one embodiment of the present invention. Figure 1 is a functional block diagram showing the schematic configuration of a degradation diagnosis device 1 according to one embodiment of the present invention. Figure 2 is a schematic diagram showing an example of a battery module 90 that the degradation diagnosis device 1 performs degradation diagnosis on. The degradation diagnosis device 1 is a device that performs a degradation diagnosis method according to one embodiment of the present invention.

[0011] As shown in Figure 1, the degradation diagnosis device 1 monitors the battery module 90, which is a storage battery, or secondary battery, and performs a degradation diagnosis of the battery module 90. The degradation diagnosis device 1 does not need to be a device that is physically housed in a single enclosure, as long as each functional block shown in Figure 1 and the following description is realized.

[0012] As shown in FIG. 2, the battery module 90 (storage battery) is, for example, a storage battery module configured by connecting a number of cells 91, which are, for example, lithium ion batteries, in series.

[0013] The deterioration diagnosis device 1 includes a measurement unit 10, an arithmetic processing unit 20, and a storage unit 30. The storage unit 30 is a memory for storing information, and may be configured by a single or a combination of a magnetic disk, a semiconductor memory, and any other known memory device.

[0014] The measurement unit 10 includes an ammeter 11, a voltmeter 12, and a thermometer 13. The ammeter 11 monitors a terminal current Ib that flows through the terminals of the battery module 90. Specifically, the ammeter 11 measures the current Ib that flows through the terminal P1 or the terminal P2 in FIG. 2. In this specification, the current Ib when charging is being performed is represented as a positive value, and the current Ib when discharging is being performed is represented as a negative value.

[0015] The voltmeter 12 monitors a terminal voltage Vb that is applied between the terminals of the battery module 90. Specifically, the voltmeter 12 measures the voltage Vb that is applied between the terminals P1 and P2 in FIG. 2.

[0016] The thermometer 13 monitors the temperatures T1 to Tk (k is a natural number) at a plurality of positions within the battery module 90. Specifically, the thermometer 13 measures the temperatures of a plurality of cells 91 in the battery module 90 shown in FIG. 2. The position for measuring the temperature may be one location for each cell 91. The cells 91 for measuring the temperature can be arbitrarily set.

[0017] In the present embodiment, among the 14 cells 91 connected in series in the battery module 90, the temperatures T1 to T4 are measured at any four temperature measurement cells (911). The thermometer 13 measures, for example, the temperature on the surface of the temperature measurement cell 911.

[0018] The current Ib measured by the ammeter 11 is converted from analog to digital by the AD converter 14 and transmitted as a digital signal to the arithmetic processing unit 20. The voltage Vb measured by the voltmeter 12 is converted from analog to digital by the AD converter 15 and transmitted as a digital signal to the arithmetic processing unit 20. The temperature T1 to Tk measured by the thermometer 13 are converted from analog to digital by the AD converter 16 and transmitted as a digital signal to the arithmetic processing unit 20.

[0019] With the above configuration, the measurement unit 10 enables the degradation diagnostic device 1 to measure the current Ib (terminal current), voltage Vb (voltage between terminals), and temperatures T1 to Tk at multiple locations on the battery module 90 during charging or discharging.

[0020] The calculation processing unit 20 has the following functional blocks: a temperature calculation unit 21, an analysis unit 22, a correction unit 23, a diagnostic unit 24, and a control unit 25.

[0021] The temperature calculation unit 21 is a functional block that calculates the analyzed temperature T of the battery module 90. Here, the analyzed temperature T is a temperature that can be considered to be the temperature of the battery module 90 when the current Ib and voltage Vb are measured by the measurement unit 10, and is a temperature that represents the temperature of multiple locations on the battery module 90 measured by the measurement unit 10.

[0022] The analysis unit 22 is a functional block that performs transient response analysis of the battery module 90 based on the current Ib and voltage Vb, and calculates the series resistance component Ri.

[0023] The correction unit 23 is a functional block that corrects the series resistance component Ri calculated by the analysis unit 22 to the series resistance component Ri_st at a predetermined reference temperature Tst, using the analysis temperature T.

[0024] The diagnostic unit 24 is a functional block that diagnoses the degradation state of the battery module 90 by calculating the capacity degradation rate D of the battery module 90's energy storage capacity based on the series resistance component Ri_st at the reference temperature Tst calculated by the correction unit 23. The capacity degradation rate D is the percentage decrease in the battery module 90's energy storage capacity relative to its initial state.

[0025] The control unit 25 is a functional block that oversees the arithmetic processing unit 20 and controls each part of the degradation diagnosis device 1. In one example, the control unit 25 may be a CPU (Central Processing Unit). The control unit 25 reads the control program, which is software stored in the memory unit 30, loads it into memory such as RAM (Random Access Memory), and executes various functions.

[0026] The operations performed by each functional block of the arithmetic processing unit 20 will be described in detail later.

[0027] <Operation of the deterioration diagnostic device> Referring to Figures 3 to 13, the details of the degradation diagnosis method, which is a characteristic operation performed by the degradation diagnosis device 1, will be explained. Figure 3 is a flowchart showing the degradation diagnosis method performed by the degradation diagnosis device 1 step by step. Note that if the units are not indicated on the axes of the graphs in each figure, the axes are in arbitrary units.

[0028] At the start of the degradation diagnosis method, the control unit 25 acquires the current Ib, voltage Vb, and temperatures T1 to T4 at multiple locations in the battery module 90, which are measured by the measurement unit 10 (step S1, measurement step).

[0029] Figure 4 is a graph showing an example of the waveform of the current Ib detected by the ammeter 11 of the measurement unit 10 and the waveform of the voltage Vb detected by the voltmeter 12. Figure 4 shows a situation in which a discharge with a temporarily large current value occurs. As shown in the figure, the voltage Vb gradually decreases while the discharge is occurring.

[0030] Next, the control unit 25 controls the temperature calculation unit 21 to calculate the analysis temperature T of the battery module 90 (step S2, temperature calculation step). The temperature calculation unit 21 determines the analysis temperature T based on the temperature difference between T1 to T4 at multiple locations in the battery module 90 measured in step S1.

[0031] When the degradation diagnosis is performed on a battery consisting of individual cells 91, there is no temperature variation within the battery. Therefore, in a battery consisting of individual cells 91, it is acceptable to measure the temperature at only one point within the battery and use that temperature as the representative temperature for that battery.

[0032] However, in this embodiment, when the target of degradation diagnosis is a battery module 90 composed of numerous cells 91, the temperature differs for each cell 91, and temperature variations may occur within the battery module 90. Therefore, if the temperature is measured at only one point in the battery module 90 and this temperature is used as the representative temperature of the battery module 90, the temperature variations within the battery module 90 cannot be taken into account, and accurate temperature correction in subsequent processing cannot be performed. As a result, accurate degradation diagnosis becomes impossible.

[0033] Therefore, the temperature calculation unit 21 calculates the analysis temperature T as a representative temperature of the battery module 90, taking into consideration that temperature variations may occur within the battery module 90.

[0034] Figure 5 is a flowchart illustrating the procedure for the temperature calculation step performed by the degradation diagnostic device 1. Based on Figure 5, the analysis temperature calculation process performed by the temperature calculation unit 21 will be explained.

[0035] First, the temperature calculation unit 21 extracts the maximum temperature Tmax and minimum temperature Tmin from the multiple temperatures T1 to T4 measured by the measurement unit 10 in step S1 of Figure 3 (step S201). Then, the temperature calculation unit 21 calculates the difference between the maximum temperature Tmax and the minimum temperature Tmin (step S202) and determines whether the difference between the maximum temperature Tmax and the minimum temperature Tmin is below a predetermined threshold (step S203). This predetermined threshold is set as appropriate, and one example is that it is about 10°C.

[0036] If the difference between the maximum temperature Tmax and the minimum temperature Tmin is less than or equal to a predetermined threshold (YES in step S203), the temperature calculation unit 21 sets the median value between the maximum temperature Tmax and the minimum temperature Tmin as the analysis temperature T (step S204). In other words, the temperature calculation unit 21 calculates the analysis temperature T as (Tmax + Tmin) / 2.

[0037] Since the analysis temperature T is determined based on the temperatures T1 to T4 at multiple locations in the battery module 90, which are acquired in the same step as the current Ib and voltage Vb used in the transient response analysis described later, it can be considered as the temperature of the battery module 90 corresponding to the initial values ​​(current Ib, voltage Vb) of the transient response analysis interval.

[0038] The temperature calculation unit 21 terminates the degradation diagnosis process for the battery module 90 if the difference between the maximum temperature Tmax and the minimum temperature Tmin is not below a predetermined threshold (NO in step S203). In other words, the degradation diagnosis device 1 executes the degradation diagnosis process from S3 onwards if the difference between the maximum temperature Tmax and the minimum temperature Tmin is below a predetermined threshold.

[0039] The temperature calculation unit 21 may, in addition to the above, measure the temperature at multiple locations within the battery module 90 and use the average temperature as the analysis temperature T. In that case, the analysis temperature T is calculated as (T1 + T2 + T3... + Tk) / k, where T1, T2, T3, ..., Tk are the k temperature measurements taken in the battery module 90.

[0040] In the temperature calculation unit 21, the degradation diagnosis process is executed when the temperature difference between the maximum temperature Tmax and the minimum temperature Tmin is below a predetermined threshold, that is, when the temperature difference is small. Furthermore, considering the accuracy of temperature measurement, it is desirable to use the median value of the maximum temperature Tmax as the analysis temperature T.

[0041] Note that steps S2 and S3 may be performed in any order.

[0042] Next, the control unit 25 instructs the analysis unit 22 to perform a transient response analysis of the battery module 90 during charging or discharging, based on the acquired waveform data of current Ib and voltage Vb. At this time, the analysis unit 22 performs a transient response analysis of the battery module 90 based on the waveforms of current Ib and voltage Vb and calculates the series resistance component Ri of the battery module 90 (step S3, analysis step).

[0043] Figure 6 shows an example of an equivalent circuit of the battery module 90 applied to the transient response analysis performed by the analysis unit 22 of the degradation diagnostic device 1. In the transient response analysis of the battery module 90, the analysis unit 22 treats the battery module 90 as the equivalent circuit shown in Figure 6.

[0044] The internal equivalent circuit between the terminals of the battery module 90 is represented by a circuit in which a series resistance component Ri, a parallel RC parallel circuit (parallel connection circuit) consisting of a parallel capacitance component Cn and a parallel resistance component Rn, a series capacitance component Co, and an electromotive force Eo are connected in series. In other words, the analysis unit 22 reduces the battery module 90 to an equivalent circuit that includes a series resistance component Ri, a parallel connection circuit in which a parallel capacitance component Cn and a parallel resistance component Rn are connected in parallel, and a circuit in which these parallel connection circuits are connected in series, and then performs transient response analysis.

[0045] Here, the electromotive force Eo is the open-circuit voltage between the terminals of the battery module 90. The sign n in the parallel capacitive component Cn and the parallel resistive component Rn represents the index of the RC parallel circuit. When the number of stages in the RC parallel circuit is M, the index n is a natural number between 1 and M.

[0046] In other words, the internal impedance between the terminals of the battery module 90 is expressed by the series connection of the impedances of each stage of the RC parallel circuit (parallel connection circuit) consisting of the parallel capacitive component Cn and the parallel resistive component Rn, the series resistive component Ri, and the series capacitive component Co.

[0047] In step S3, the waveform data of current Ib and voltage Vb shown in Figure 4 are fitted to this equivalent circuit to calculate the series resistance component Ri of the battery module 90.

[0048] Figure 7 shows another example of the equivalent circuit of the battery module 90, which is applied to the transient response analysis performed by the analysis unit 22 of the degradation diagnostic device 1. In Figure 6, the number of stages M of the RC parallel circuit may be one, in which case the equivalent circuit is represented as in Figure 7.

[0049] The parallel resistance component Rn is also the resistance component corresponding to the reaction resistance component of the battery module 90. The series capacitance component Co and the electromotive force Eo, which is the open-circuit voltage, are intrinsic values ​​of the battery module 90 that do not change depending on the degradation state of the battery module 90, and are stored in the storage unit 30 in advance. The correction unit 23 performs the fitting by referring to the values ​​of the series capacitance component Co and electromotive force Eo stored in the storage unit 30.

[0050] The principle of temperature correction will be explained using Figures 8 to 11. Figures 8 to 11 show the results of an experimental battery used to investigate the temperature correction method. In the graphs shown in Figures 8 to 11, temperature T represents the measured temperature of the battery.

[0051] Figure 8 is a graph summarizing the results of the series resistance component Ri calculated for various battery temperatures T. Plots with different symbols represent results for different states of battery degradation. In Figure 8, the series resistance component Ri increases as battery degradation progresses. That is, the result represented by a triangle represents the most severely degraded state of the battery among the three results in Figure 8.

[0052] As shown in Figure 8, the series resistance component Ri is highly dependent on the battery temperature T.

[0053] In this specification, the state of battery degradation will be represented by the capacity degradation rate D, which is the percentage decrease in the battery's storage capacity Q relative to its initial storage capacity Qo:

[0054]

number

[0055] Here, the unit of the volume reduction rate D is percent (%).

[0056] In each plot in Figure 8, where the degradation state differs from one another, the relationship between temperature T and the series resistance component Ri can be well approximated by equation (2):

[0057]

number

[0058] The coefficients A, B, and C used here will be referred to as temperature correction coefficients.

[0059] Figures 9, 10, and 11 are graphs showing the dependence of the temperature correction coefficients A, B, and C on the capacity degradation rate D, respectively. As is clear from Figures 9 to 11, the temperature correction coefficient A is a parameter that depends greatly on the capacity degradation rate D. On the other hand, the temperature correction coefficient B is a parameter that does not depend on the capacity degradation rate D, and the dependence of the temperature correction coefficient C on the capacity degradation rate D is small. Therefore, in equation (2), the temperature correction coefficient A is a function of the capacity degradation rate D, but the temperature correction coefficients B and C are considered to be constants that do not depend on the capacity degradation rate D.

[0060] Therefore, considering the series resistance component Ri_st at a reference temperature Tst of the battery, the temperature correction coefficient A can be eliminated from equation (2), and the series resistance component Ri_st at the reference temperature Tst is expressed by equation (3):

[0061]

number

[0062] In each equation, temperature T and reference temperature Tst shall be expressed in absolute temperatures.

[0063] Based on the temperature correction principle described above, the series resistance component Ri_st at the reference temperature Tst can be calculated from the calculated series resistance component Ri, regardless of the battery's degradation state, that is, even if the capacity degradation rate D is unknown.

[0064] In this invention, based on the principle of temperature correction, the above temperature correction is performed using the analysis temperature T as the temperature T in order to diagnose the degradation of the battery module 90.

[0065] Returning to the explanation of the degradation diagnosis procedure, the control unit 25 then controls the correction unit 23 to calculate the series resistance component Ri_st at a reference temperature Tst from the series resistance component Ri calculated by the analysis unit 22 based on the acquired analysis temperature T. In other words, the correction unit 23 corrects the series resistance component Ri to the predetermined series resistance component Ri_st at a reference temperature Tst using the analysis temperature T.

[0066] The temperature correction coefficients B and C are predetermined values ​​for each battery module 90 and are stored in the storage unit 30 beforehand. The correction unit 23 refers to the values ​​of the temperature correction coefficients B and C stored in the storage unit 30 and performs the correction according to equation (3) (step S4, correction step).

[0067] Next, the control unit 25 controls the diagnostic unit 24 to calculate the capacity degradation rate D of the battery module 90 based on the series resistance component Ri_st at the reference temperature Tst. As described above, the capacity degradation rate D is an indicator of the state of degradation of the battery module 90, and in this way, the degradation diagnostic device 1 realizes the degradation diagnosis of the battery module 90 (step S5, diagnostic step).

[0068] The principle of calculating the capacity degradation rate will be explained using Figure 12. Figure 12 is a graph showing the relationship between the capacity degradation rate D and the series resistance component Ri under the condition that the battery temperature T is fixed (square), and the relationship between the capacity degradation rate D and the corrected series resistance component Ri_st (circle). Figure 12 shows the results when using an experimental battery for investigating the capacity degradation rate calculation method similar to that in Figures 8 to 11, and temperature T represents the measurement temperature of the battery.

[0069] The plots represented by squares in Figure 12 show the relationship between the capacity degradation rate D and the series resistance component Ri under the condition that the battery temperature T is fixed at 25°C. As shown in the figure, the capacity degradation rate D has a strong dependence on the series resistance component Ri and can be well expressed by a linear equation. In other words, if the series resistance component Ri can be calculated under the condition that the temperature T is constant, the capacity degradation rate D can be accurately determined. However, in reality, it is difficult to expect that the current Ib and voltage Vb can be measured under the condition that the temperature T is constant when a battery is actually in operation.

[0070] Furthermore, in Figure 12, although the battery temperature T during measurement is different from 25°C, the series resistance component Ri_st at the reference temperature Tst is plotted as a circle, obtained by correcting the series resistance component Ri according to the procedure described above, with the reference temperature Tst set to 25°C. Even in this case, it can be seen that the capacity degradation rate D has a strong dependence on the corrected series resistance component Ri_st and can be well expressed by a linear equation. In other words, it is clear that the series resistance component Ri is properly corrected to the series resistance component Ri_st at the reference temperature Tst by the procedure described above.

[0071] Therefore, the capacitance degradation rate D can be accurately estimated using the series resistance component Ri_st at the reference temperature Tst, by the linear equation (4).

[0072]

number

[0073] Here, the constant Rio is the series resistance component at the reference temperature Tst in the initial state, and the coefficient d is referred to as the degradation correction coefficient.

[0074] The constant Rio and the degradation correction coefficient d are predetermined values ​​for each battery and are stored in the storage unit 30 beforehand. In step S4, the diagnostic unit 24 refers to the values ​​of the constant Rio and the degradation correction coefficient d stored in the storage unit 30 and calculates the battery capacity degradation rate D from the series resistance component Ri_st at the reference temperature Tst according to equation (4).

[0075] In this invention, the above-mentioned capacity degradation rate D is used for the degradation diagnosis of the battery module 90, based on the principle of calculating the capacity degradation rate.

[0076] Furthermore, according to equations (1) to (4), the storage capacity Q of the battery module 90 is:

[0077]

number

[0078] It can be expressed as follows.

[0079] <Mechanism of action, effect> According to Embodiment 1, the degradation diagnostic device 1 monitors the terminal current (current Ib) and terminal voltage (voltage Vb) of the battery module 90 during charging or discharging, and calculates the analysis temperature T of the battery module 90. From the circuit characteristics of the battery, it is possible to calculate the capacity reduction rate D, which is an indicator of degradation of the battery module 90.

[0080] Therefore, the degradation state of the battery module 90 can be diagnosed without performing tests that determine the charging capacity by discharging and fully charging the battery module 90. Alternatively, the degradation state of the battery module 90 can be diagnosed without performing tests that introduce a specific current or apply a specific voltage to the battery module 90. Thus, according to Embodiment 1, the degradation state of the battery module 90 can be diagnosed while maintaining the operation of the battery module 90.

[0081] Furthermore, according to the degradation diagnosis method of Embodiment 1, the temperature is measured at multiple locations on the battery module 90, and the circuit characteristics (series resistance component Ri) of the battery module 90 are corrected using the analysis temperature T that represents the temperatures at the multiple locations. Therefore, even in battery modules where there are temperature variations, the strong influence of temperature on the battery module can be accurately canceled, and the degradation state of the storage battery can be correctly diagnosed.

[0082] In particular, Embodiment 1 employs a clever method, as shown in equation (3), that cancels out the effect of the analysis temperature T without being affected by the degradation state (capacity reduction rate D) of the battery module 90, thereby enabling accurate diagnosis of the degradation state of the battery module 90.

[0083] Furthermore, the degradation diagnosis method of Embodiment 1 is based on the use of a circuit parameter called the series resistance component Ri, which can accurately predict the capacity reduction rate D, an indicator of the degradation state of the battery module 90, as shown in equation (4) and Figure 12. Therefore, the degradation diagnosis method of Embodiment 1 makes it possible to accurately diagnose the degradation state of the battery module 90.

[0084] Figure 13 is a graph showing the relationship between the capacity degradation rate D and the series resistance component Ri or the parallel resistance component R1 (reaction resistance component) under the condition that the analysis temperature T of the battery module 90 is kept constant in order to eliminate the effect of the analysis temperature T. Here, the equivalent circuit used for the transient response analysis was the equivalent circuit shown in Figure 7, which consists of one stage M of an RC parallel circuit.

[0085] As shown in Figure 13, the capacitance degradation rate D changes uniformly with respect to the series resistance component Ri, whereas its dependence on the parallel resistance component R1 is unclear in some regions. Furthermore, the capacitance degradation rate D can be expressed as a linear equation with respect to the series resistance component Ri, and it is possible to predict the capacitance degradation rate D with good accuracy over a wide range of values.

[0086] Therefore, in Embodiment 1, the battery module 90 is represented by the equivalent circuit shown in Figure 6 or Figure 7, and by extracting a specific component called the series resistance component Ri with respect to the resistance, it is possible to accurately diagnose the degradation state of the battery module 90.

[0087] [Embodiment 2] Other embodiments of the present invention will be described below. For the sake of clarity, components having the same function as those described in the above embodiments will be denoted by the same reference numerals, and their descriptions will not be repeated.

[0088] Figure 14 is a flowchart showing the degradation diagnosis method performed by the degradation diagnosis device 1 according to Embodiment 2. The degradation diagnosis method according to Embodiment 2 is the same as that according to Embodiment 1 shown in Figure 3, except that a decision step SJ is added between steps S2 and S3, causing a branch in the flow.

[0089] In step SJ, following step S2, the control unit 25 determines whether the acquired analysis temperature T is within the required range, that is, whether the acquired analysis temperature T is greater than or equal to the lower limit temperature Tr1 and less than or equal to the upper limit temperature Tr2 (step SJ, temperature determination step). If it is determined that the analysis temperature T is within the required range (YES in step SJ), the flow proceeds to step S3. Otherwise (NO in step SJ), the degradation diagnosis process is terminated.

[0090] In the degradation diagnosis method according to Embodiment 2, the degradation state of the battery module 90 is diagnosed only when the acquired analysis temperature T is within the required range, thereby enabling more accurate degradation diagnosis. The condition that the acquired analysis temperature T is within the required range is not limited to the example described above; the condition may also be that the analysis temperature T is above the lower limit temperature Tr1, or that the temperature T is below the upper limit temperature Tr2.

[0091] [Experimental Example] An experimental example of the present invention is described below. In this experimental example, a simulated experiment was conducted on temperature correction in degradation diagnosis according to the present invention, and the results were verified.

[0092] (Experimental method) In this experiment, first, the current Ib, voltage Vb, and temperature T1 to T14 of the battery module 90 were measured during charging and discharging. Furthermore, the series resistance component Ri was calculated using transient response analysis based on the measured current Ib and voltage Vb. Finally, the average temperature Tm from T1 to T14 was determined.

[0093] Next, the temperatures T1 to T14 at each measurement point and the average temperature Tm were applied to equations (2) and (3) of Embodiment 1, and the series resistance component Ri calculated by transient response analysis was temperature-corrected to calculate the series resistance component Ri_st at a predetermined reference temperature Tst. In this experiment, the reference temperature Tst was set to 25°C.

[0094] Next, the true value of the series resistance component at the reference temperature Tst was defined as Rs, and the error rate of the series resistance component Ri_st relative to the true value Rs was calculated using |Ri_st-Rs| / Rs(%) when temperatures T1 to T14 and the average temperature Tm were applied.

[0095] Here, the true value Rs was determined by performing multiple tests in which a test waveform (short pulse waveform) was applied while each part of the battery module 90 was kept at approximately the same temperature as the reference temperature Tst, and the average value of the series resistance component Ri from these tests was adopted.

[0096] Furthermore, the battery module 90 was charged and discharged under various conditions, and the series of procedures described above were performed. In this process, the results of nine experiments were extracted for each of two cases: one where the temperature difference within the battery module 90 was small, and another where the temperature difference within the battery module 90 was large. Here, the case where the temperature difference within the battery module 90 is small is when the difference between the maximum temperature Tmax and the minimum temperature Tmin within the temperature range T1 to T14 is below a predetermined threshold. The case where the temperature difference within the battery module 90 is large is when the difference between the maximum temperature Tmax and the minimum temperature Tmin within the temperature range T1 to T14 is greater than a predetermined threshold.

[0097] Furthermore, for both the case where the temperature difference within the battery module 90 is small and the case where the temperature difference within the battery module 90 is large, the average error rate was calculated for each of the nine extracted experiments, for the temperatures T1 to T14 at each measurement point and the average temperature Tm.

[0098] (Experimental results) Figure 15 is a table showing the results of the above experiment when the temperature difference within the battery module 90 is small (when the temperature difference is below a predetermined threshold) and when the temperature difference is large (when the temperature difference exceeds a predetermined threshold). Specifically, Figure 15 shows the average error rate of nine experiments extracted for both the small and large temperature difference cases within the battery module 90.

[0099] As shown in Figure 15, when the temperature difference within the battery module 90 is small, the error rate was found to be in the 1% range, indicating low variability, regardless of which of the temperatures T1 to T14 was used for single-point temperature correction. Furthermore, the error rate of the average temperature Tm when the temperature difference within the battery module 90 is small was 1.1%, the smallest error rate in this case, confirming that proper temperature correction was achieved. Therefore, it was confirmed that proper temperature correction can be achieved by adopting the average temperature Tm as the analysis temperature T within the battery module 90 when the difference between the maximum temperature Tmax and the minimum temperature Tmin is below a predetermined threshold.

[0100] On the other hand, when the temperature difference within the battery module 90 is large, the error rate due to temperature correction at the average temperature Tm exceeds 10%, confirming that proper temperature correction is not being performed. As a result, it was confirmed that if the difference between the maximum temperature Tmax and the minimum temperature Tmin is greater than a predetermined threshold, an incorrect capacity degradation rate D is calculated, and a correct degradation diagnosis cannot be performed.

[0101] Furthermore, it was confirmed that when there is a large temperature difference within the battery module 90, the error rate due to temperature correction differs significantly depending on whether temperature T1 to T14 is used for single-point temperature correction. This is presumed to be because when transient response analysis is performed on a battery module 90 containing multiple cells 91, the transient phenomena of the series-connected cells 91 within the battery module 90 are averaged out, resulting in a larger error rate.

[0102] [Examples of implementation using software] The function of the deterioration diagnosis device 1 (hereinafter referred to as "the device") is a program that causes the device to function as a computer, and can be realized by a program that causes the computer to function as each control block of the device (in particular, each part included in the arithmetic processing unit 20).

[0103] In this case, the device includes a computer having at least one control device (e.g., a processor) and at least one storage device (e.g., memory) as hardware for executing the program. By executing the program using this control device and storage device, the functions described in each of the embodiments are realized.

[0104] The above program may be recorded on one or more computer-readable recording media, not temporary ones. These recording media may or may not be provided by the above device. In the latter case, the program may be supplied to the above device via any wired or wireless transmission medium.

[0105] Furthermore, some or all of the functions of each of the above control blocks can also be realized by logic circuits. For example, an integrated circuit in which logic circuits functioning as each of the above control blocks are formed is also included in the scope of the present invention. In addition, it is also possible to realize the functions of each of the above control blocks by, for example, a quantum computer.

[0106] Furthermore, each process described in the above embodiments may be performed by AI (Artificial Intelligence). In this case, the AI ​​may operate on the control device described above, or it may operate on other devices (for example, an edge computer or a cloud server).

[0107] The present invention is not limited to the embodiments described above, 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.

[0108] 〔summary〕 A degradation diagnosis method according to Embodiment 1 of the present invention includes: a measurement step of measuring the terminal current (current Ib), terminal voltage (voltage Vb), and temperature at multiple locations in the battery (battery module 90) during charging or discharging of the battery; a temperature calculation step of calculating an analysis temperature (T) that represents the temperatures at the multiple locations; an analysis step of performing a transient response analysis of the battery based on the terminal current and terminal voltage and calculating the series resistance component (Ri); and using the analysis temperature, the series resistance component (Ri) calculated in the analysis step is used to determine the series resistance at a predetermined reference temperature (Tst). The analysis step includes a correction step of correcting for the resistance component (Ri_st), and a diagnostic step of calculating the capacity degradation rate (D), which is the rate of decrease of the storage capacity of the battery relative to the storage capacity in the initial state of the battery, based on the series resistance component (Ri_st) at the reference temperature (Tst), and diagnosing the degradation state of the battery, wherein in the analysis step, the transient response analysis is performed by reducing the battery to an equivalent circuit that includes the series resistance component (Ri), and a parallel connection circuit in which the parallel capacitance component (Cn) and the parallel resistance component (Rn) are connected in parallel, and a circuit in which these parallel connection circuits are connected in series.

[0109] With the above configuration, by monitoring the terminal current and terminal voltage of the battery during charging or discharging, and calculating an analytical temperature that represents the temperature at multiple locations in the battery, it is possible to calculate the capacity degradation rate, which is an indicator of battery degradation, from the circuit characteristics of the battery.

[0110] Therefore, the degradation state of the battery can be diagnosed without performing tests that determine the charging capacity by discharging and fully charging the battery. Alternatively, the degradation state of the battery can be diagnosed without performing tests that introduce a specific current or apply a specific voltage to the battery. Thus, the degradation state of the battery can be diagnosed while maintaining battery operation.

[0111] Furthermore, the temperature is measured at multiple locations within the battery, and the circuit characteristics of the battery are corrected using the analysis temperature that represents the temperatures at these multiple locations. Therefore, even in battery modules or battery panels where there are temperature variations within the battery, the strong influence of temperature in the battery can be accurately canceled out, and the state of battery degradation can be correctly diagnosed.

[0112] As a result, even with battery modules or battery panels, it is possible to realize a degradation diagnosis method that can accurately determine the degradation state of a storage battery from the circuit characteristics during charging and discharging.

[0113] In the degradation diagnosis method according to embodiment 2 of the present invention, in embodiment 1, the diagnosis step may be performed when the difference between the maximum temperature (Tmax) and the minimum temperature (Tmin) among the temperatures at multiple locations in the storage battery (battery module 90) is less than or equal to a predetermined threshold.

[0114] In a storage battery, if the difference between the maximum and minimum temperatures measured at multiple locations is large, accurate degradation diagnosis cannot be performed. Therefore, as in the above configuration, if the difference between the maximum and minimum temperatures at multiple locations in the storage battery is below a predetermined threshold, the diagnostic step is executed. If the difference between the maximum and minimum temperatures is large, the diagnostic step is not executed, thereby preventing inaccurate degradation diagnosis.

[0115] In the degradation diagnosis method according to embodiment 3 of the present invention, in embodiment 1 or 2 above, when the analysis temperature is expressed as T[K], the reference temperature as Tst[K], and the series resistance component at the analysis temperature T as Ri in the correction step, the series resistance component Ri_st at the reference temperature Tst may be calculated from the above formula (3) using temperature correction coefficients B and C.

[0116] With the above configuration, the effects of temperature are canceled out, and the series resistance component can be calculated appropriately.

[0117] In the degradation diagnosis method according to aspect 4 of the present invention, in any of aspects 1 to 3 above, the capacitance reduction rate (D) may be calculated in the diagnosis step from a linear equation for the series resistance component (Ri_st) at the reference temperature (Tst).

[0118] According to the above configuration, in calculating the capacity degradation rate, which is an indicator of the battery's degradation state, a series resistance component that can accurately predict the capacity degradation rate is used as a parameter. Therefore, the capacity degradation rate is calculated accurately, and the battery's degradation state can be accurately diagnosed.

[0119] In the degradation diagnosis method according to embodiment 5 of the present invention, any of embodiments 1 to 4 further includes a temperature determination step of determining whether the analysis temperature (T) is within a predetermined range, and in the temperature determination step, if it is determined that the analysis temperature is not within the predetermined range, the degradation diagnosis process of the storage battery (battery module 90) may be terminated.

[0120] With the above configuration, the battery degradation diagnosis process is performed only when the analysis temperature is within the required range, resulting in a more accurate degradation diagnosis.

[0121] A degradation diagnostic device according to embodiment 6 of the present invention comprises: a measurement unit that measures terminal current, terminal voltage and temperature at multiple locations in the battery during charging or discharging of the battery; a temperature calculation unit that calculates an analysis temperature representative of the temperatures at the multiple locations; an analysis unit that performs transient response analysis of the battery based on the terminal current and terminal voltage and calculates a series resistance component; a correction unit that corrects the series resistance component calculated by the analysis unit to the series resistance component at a predetermined reference temperature using the analysis temperature; and a diagnostic unit that diagnoses the degradation state of the battery by calculating a capacity reduction rate, which is the rate of decrease of the battery's storage capacity relative to its initial storage capacity, based on the series resistance component at the reference temperature, wherein the analysis unit reduces the battery to an equivalent circuit including the series resistance component and a parallel connection circuit in which the parallel capacitance component and the parallel resistance component are connected in parallel, and then performs the transient response analysis.

[0122] According to the above configuration, a deterioration diagnostic device that achieves the same effects as in Embodiment 1 can be realized.

[0123] The present invention is not limited to the embodiments described above, 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]

[0124] 1. Deterioration diagnostic device 10 Measuring part 11 Ammeter 12 Voltmeter 13 Thermometer 14, 15, 16 AD converters 20 Arithmetic Processing Unit 21 Temperature calculation section 22 Analysis Department 23 Correction section 24 Diagnostic Department 25 Control Unit 30 Storage section 90 Battery Modules (Rechargeable Batteries) 911 cells C1~CM, Cn parallel capacitance component Co series capacitance component Ri series resistance component R1~RM, Rn parallel resistance component Eo Electromotive force (open circuit voltage) Ib current (terminal current) Vb Voltage (Voltage between terminals) T analysis temperature Tst reference temperature Ri_st Series resistance component at reference temperature D Capacity reduction rate

Claims

1. A measurement step of measuring the terminal current, terminal voltage and temperature of multiple cells in a battery including multiple cells during charging or discharging, A temperature calculation step for calculating an analysis temperature that represents the temperatures of the multiple cells, An analysis step to perform transient response analysis of the battery based on the terminal current and the terminal voltage and calculate the series resistance component, A correction step in which the series resistance component calculated in the analysis step is corrected to the series resistance component at a predetermined reference temperature using the analysis temperature, A diagnostic step includes calculating a capacity degradation rate, which is the percentage decrease in the storage capacity of the battery relative to its initial storage capacity, based on the series resistance component at the reference temperature, to diagnose the degradation state of the battery. In the analysis step, the transient response analysis is performed by reducing the battery to an equivalent circuit that includes the series resistance component, and a parallel connection circuit in which the parallel capacitance component and the parallel resistance component are connected in parallel, and a circuit connected in series. The diagnostic step is executed when the difference between the maximum and minimum temperatures among the multiple cells in the aforementioned storage battery is less than or equal to a predetermined threshold. In the correction step, A degradation diagnosis method characterized in that, when the analysis temperature is represented as T [K], the reference temperature as Tst [K], and the series resistance component at the analysis temperature T as Ri, the series resistance component Ri_st at the reference temperature Tst is calculated from the following formula (E1) using temperature correction coefficients B and C. [Math 1]

2. In the diagnostic step, The degradation diagnosis method according to claim 1, characterized in that the capacitance reduction rate is calculated from a linear equation for the series resistance component at the reference temperature.

3. The method further includes a temperature determination step of determining whether the analysis temperature is within a predetermined range, The degradation diagnosis method according to claim 1, characterized in that, in the temperature determination step, if it is determined that the analyzed temperature is not within the predetermined range, the degradation diagnosis process of the storage battery is terminated.

4. A measuring unit for measuring terminal current, terminal voltage and temperature of multiple cells in a battery, which includes multiple cells, during charging or discharging of the battery, A temperature calculation unit that calculates an analysis temperature that represents the temperatures of the multiple cells, An analysis unit that performs transient response analysis of the battery based on the terminal current and the terminal voltage and calculates the series resistance component, A correction unit that corrects the series resistance component calculated by the analysis unit to the series resistance component at a predetermined reference temperature using the analysis temperature, The system includes a diagnostic unit that diagnoses the deterioration state of the battery by calculating a capacity degradation rate, which is the percentage decrease in the battery's storage capacity relative to its initial storage capacity, based on the series resistance component at the aforementioned reference temperature. The analysis unit reduces the storage battery to an equivalent circuit that includes the series resistance component, and a parallel connection circuit in which the parallel capacitance component and the parallel resistance component are connected in parallel, and a circuit in which these parallel connection circuits are connected in series, and then performs the transient response analysis. The diagnostic unit performs the diagnosis when the difference between the maximum temperature and the minimum temperature among the multiple cells in the storage battery is less than or equal to a predetermined threshold. The correction unit, A deterioration diagnostic device characterized in that, when the analysis temperature is represented as T [K], the reference temperature as Tst [K], and the series resistance component at the analysis temperature T as Ri, the series resistance component Ri_st at the reference temperature Tst is calculated from the following formula (E1) using temperature correction coefficients B and C. [Math 1]

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