Deterioration diagnosis method and deterioration diagnosis device

Abstract

To realize a deterioration diagnosis method that can determine a deterioration state of a storage battery with high accuracy from circuit characteristics of the storage battery during charging and discharging.SOLUTION: A deterioration diagnosis method measures temperature (T) of a battery (90) in operation and current (Ib) and voltage (Vb) at predetermined intervals, extracts a single pulse waveform or a single step waveform from the current (Ib), and if the current (Ib) and voltage (Vb) are determined to be suitable for transient response analysis based on the current (Ib) during a current rapid change period in the extracted waveform, performs transient response analysis based on the current (Ib) and voltage (Vb), and further performs diagnoses of the deterioration state of the battery (90) based on a series resistance component (Ri_st) at a reference temperature (Tst) which is corrected.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] There are known techniques for diagnosing the degradation state of a storage battery. As one such conventional technique, Patent Document 1 discloses a technique for determining the degradation state of a storage battery from the circuit characteristics during charging and discharging of the storage battery. The technique of Patent Document 1 performs degradation diagnosis by performing transient response analysis of the storage battery based on the terminal current and inter-terminal voltage measured from the storage battery in operation. According to the technique of Patent Document 1, it is not necessary to stop the operation of the storage battery in order to diagnose the degradation state of the storage battery, and it is possible to determine the degradation state while the storage battery is operating. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-175876 A Summary of the Invention [Problem to be solved by the invention]

[0004] When the waveforms of the current and voltage that fluctuate during charging and discharging of a storage battery are pulse waveforms or step waveforms, the accuracy of the transient response analysis depends heavily on the points where the current fluctuation is large. For example, if a deterioration diagnosis is performed based on the current value measured immediately after the current fluctuation begins and before the current fluctuation ends, there is a problem that the accuracy of the deterioration diagnosis may be reduced.

[0005] An object of one embodiment of the present invention is to provide a degradation diagnosis method that can determine the degradation state of a storage battery with high accuracy from circuit characteristics during charging and discharging of the storage battery. [Means for solving the problem]

[0006] In order to solve the above problems, a deterioration diagnosis method according to one aspect of the present invention includes a measurement step of measuring a battery temperature and a terminal current and an inter-terminal voltage at predetermined intervals of a storage battery in operation; an extraction step of extracting a single pulse waveform or a single step waveform from the terminal current measured in the measurement step; a suitability determination step of determining whether or not the terminal current and the inter-terminal voltage are suitable for a transient response analysis for calculating a series resistance component of the storage battery at the battery temperature, based on the terminal current during a period of sudden current change in which the current suddenly changes in the single pulse waveform or the single step waveform; and if it is determined that the terminal current and the inter-terminal voltage are suitable for the transient response analysis, The method includes an analysis step of performing the transient response analysis of the storage battery based on the terminal current and the terminal voltage, in which the series resistance component and a parallel connection circuit in which a parallel capacitance component and a parallel resistance component are connected in parallel are reduced to an equivalent circuit including a series-connected circuit, and calculating the series resistance component of the storage battery at the storage battery temperature; a first correction step of correcting the series resistance component at the storage battery temperature to the series resistance component at a predetermined reference temperature; and a diagnosis step of calculating a capacity decline rate, which is the rate of decline 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, to diagnose the deterioration state of the storage battery.

[0007] In order to solve the above problems, a deterioration diagnosis device according to one aspect of the present invention includes a measurement unit that measures a battery temperature of a storage battery in operation and a terminal current and an inter-terminal voltage at predetermined intervals; an extraction unit that extracts a single pulse waveform or a single step waveform from the terminal current measured by the measurement unit; a suitability determination unit that determines whether or not the terminal current and the inter-terminal voltage are suitable for a transient response analysis for calculating a series resistance component of the storage battery at the battery temperature, based on the terminal current during a period of sudden current change in which current suddenly changes in the single pulse waveform or the single step waveform; and a suitability determination unit that, when it is determined that the terminal current and the inter-terminal voltage are suitable for the transient response analysis, determines whether or not the terminal current and the inter-terminal voltage are suitable for the transient response analysis. The system includes an analysis unit that performs the transient response analysis of the storage battery based on the current and the inter-terminal voltage, in which the series resistance component and a parallel connection circuit in which a parallel capacitance component and a parallel resistance component are connected in parallel are reduced to an equivalent circuit including a series-connected circuit, and calculates the series resistance component of the storage battery at the storage battery temperature, a first correction unit that corrects the series resistance component at the storage battery temperature to the series resistance component at a predetermined reference temperature, and a diagnosis unit that calculates a capacity decline rate, which is the rate of decline 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, and diagnoses the deterioration state of the storage battery.

[0008] The deterioration diagnosis device according to each aspect of the present invention may be realized by a computer. In this case, the control programs of each device that realizes the storage device and the power generation device by having the computer operate as each part (software element) of the storage device and the power generation device, and the computer-readable recording medium on which they are recorded, also fall within the scope of the present invention. Effect of the Invention

[0009] According to one aspect of the present invention, it is possible to realize a degradation diagnosis method that can determine the degradation state of a storage battery with high accuracy from the circuit characteristics during charging and discharging of the storage battery. [Brief description of the drawings]

[0010] [Figure 1] 1 is a functional block diagram showing a schematic configuration of a degradation diagnosis device according to an embodiment of the present invention. [Diagram 2] 1 is a graph illustrating extraction of a terminal current waveform. [Diagram 3] 4 is a graph illustrating a correction standard for a terminal current and a terminal voltage. [Figure 4] 11 is a graph illustrating an example of a correction procedure. [Diagram 5] 1 is a graph showing measured values ​​of terminal current and terminal voltage in an experimental example. [Figure 6] 13 is a graph showing a corrected inter-terminal voltage in the above experimental example. [Figure 7] 11 is a table showing correction results in the above experimental example. [Figure 8] 2 is an equivalent circuit of a battery applied to a transient response analysis performed by an analysis unit of the degradation diagnosis device. [Figure 9] 1 is a graph showing the results of series resistance component Ri calculated by transient response analysis at various temperatures T. Plots with different symbols represent results when the battery degradation state is different. [Figure 10] 1 is a graph showing the dependency of a temperature correction coefficient A on a capacity decrease rate D. [Figure 11] 1 is a graph showing the dependency of a temperature correction coefficient B on a capacity decrease rate D. [Figure 12] 1 is a graph showing the dependency of a temperature correction coefficient C on a capacity decrease rate D. [Figure 13] This is a graph showing plots (squares) showing the relationship between the capacity decay rate D and the series resistance component Ri under conditions where the battery temperature T is fixed, and plots (circles) showing the relationship between the capacity decay rate D and the corrected series resistance component Ri_st. [Figure 14] 4 is a flowchart for illustrating a processing procedure of a degradation diagnosis method executed by the degradation diagnosis device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [Embodiment] A detailed description of the first embodiment of the present invention will be given below. However, the following description is an example of a degradation diagnosis device and a degradation diagnosis method according to the present invention, and the technical scope of the present invention is not limited to the illustrated example. Note that when no unit is indicated on the axis of a graph in each figure, the axis is in an arbitrary unit.

[0012] (Configuration of Deterioration Diagnosis Device) An embodiment of the present invention will be described in detail below. Fig. 1 is a functional block diagram showing a schematic configuration of a degradation diagnosis device 1 according to an embodiment of the present invention. The degradation diagnosis device 1 is a device that executes a degradation diagnosis method according to an embodiment of the present invention.

[0013] Deterioration diagnosis device 1 monitors battery 90, which is a storage battery, i.e., a secondary battery, and performs deterioration diagnosis of battery 90. Battery 90 is, for example, a lithium ion secondary battery. Deterioration diagnosis device 1 does not need to be a device physically housed in a single housing, so long as each of the functional blocks shown in FIG. 1 and in the following description is realized.

[0014] The degradation diagnosis device 1 includes a measurement unit 10, a control unit 20, and a storage unit 30. The storage unit 30 is a memory that stores information, and may be configured using a magnetic disk, a semiconductor memory, or any other known memory device, either alone or in combination. The storage unit 30 stores various programs executed by the control unit 20 and data used by the programs.

[0015] The measurement unit 10 measures the battery temperature (temperature T) of the battery 90 (storage battery) during operation at predetermined intervals, as well as the terminal current (current Ib) and inter-terminal voltage (voltage Vb) at predetermined intervals. The temperature T is measured at the same time as the current Ib and voltage Vb.

[0016] The measurement unit 10 has an ammeter 11 that monitors the current Ib, which is a terminal current flowing through the terminals of the battery 90. The ammeter 11 measures the current Ib at a predetermined interval. In this specification, the current Ib is expressed as a positive value when charging is performed, and the current Ib is expressed as a negative value when discharging is performed.

[0017] The measuring unit 10 has a voltmeter 12 that monitors a voltage Vb, which is a terminal voltage applied between the terminals of the battery 90. The voltmeter 12 measures the voltage Vb at the same predetermined intervals as the current Ib.

[0018] The measurement unit 10 also has a thermometer 13 that monitors the temperature T of the battery 90. More specifically, the thermometer 13 may be configured to measure the temperature of the surface of a cell of the battery 90. Alternatively, the thermometer 13 may be configured to measure the temperature of the terminals of the battery 90. The temperature T is measured at the same predetermined intervals and at the same timing as the current Ib and the voltage Vb.

[0019] The value of current Ib measured by ammeter 11 is analog-to-digital converted by AD converter 14 and transmitted as a digital signal to control unit 20. The value of voltage Vb measured by voltmeter 12 is analog-to-digital converted by AD converter 15 and transmitted as a digital signal to control unit 20. The value of temperature T measured by thermometer 13 is analog-to-digital converted by AD converter 16 and transmitted as a digital signal to control unit 20.

[0020] By using measuring section 10 having the above configuration, degradation diagnosis device 1 can measure temperature T, current Ib, and voltage Vb of battery 90 while battery 90 is being charged or discharged.

[0021] The control unit 20 comprehensively controls each unit of the degradation diagnosis device 1. The functions of the control unit 20 may be realized by a CPU executing a program stored in the storage unit 30. The control unit 20 has an extraction unit 21, a suitability determination unit 22, a pre-analysis correction unit 23, an analysis unit 24, a post-analysis correction unit 25, and a diagnosis unit 26.

[0022] The degradation diagnosis device 1 diagnoses the degradation state using transient response analysis. In the control unit 20, the extraction unit 21, the suitability determination unit 22, and the pre-analysis correction unit 23 perform pre-processing of the transient response analysis on the measured values ​​measured by the measurement unit 10 so that data suitable for the transient response analysis is obtained. In addition, in the control unit 20, the analysis unit 24, the post-analysis correction unit 25, and the diagnosis unit 26 use the pre-processed data to diagnose the degradation state of the battery 90 using transient response analysis. The operations performed by each functional block of the control unit 20 will be described later.

[0023] (Extraction part) The extraction unit 21 extracts a single pulse waveform or a single step waveform from the measured current Ib. Specifically, when the extraction unit 21 detects that the current Ib fluctuates from a first steady-state current Ib1 to a second steady-state current Ib2 different from the first steady-state current Ib1 within a first predetermined fluctuation period tr1, the extraction unit 21 extracts a single step waveform from the current Ib during an extraction period te including the period during which the current Ib fluctuates from the first steady-state current Ib1 to the second steady-state current Ib2.

[0024] 2001 in Fig. 2 is a diagram for explaining extraction of a single step waveform of the current Ib, which is the terminal current. Note that 2001 in Fig. 2 and 2002 in Fig. 2 show a state in which the battery 90 is being charged, and when the battery 90 is being discharged, the positive and negative polarities of the current are reversed.

[0025] 2, when the battery 90 is charged, the current Ib suddenly changes from a first steady-state current Ib1 to a second steady-state current Ib2 during a sudden current change period. Here, the first steady-state current Ib1 indicates, for example, the current value of the current Ib when the battery 90 is in a resting state. The second steady-state current Ib2 indicates the current value of the current Ib that continues for a certain period of time in a state that is considered to be the same current value after changing from the first steady-state current Ib1, and indicates, for example, the current value of the current Ib when the battery 90 is in a charging state.

[0026] The current rapid change period refers to the period from immediately after the current change starts to before the current change ends. The current change starts when it can be considered that the current Ib starts to change from the first steady-state current Ib1 to the second steady-state current Ib2, and for example, when the slope of the current change over a short period of time becomes equal to or greater than a predetermined value. The current change ends when it can be considered that the current Ib changes from the first steady-state current Ib1 to the second steady-state current Ib2, and for example, when the slope of the current change over a short period of time becomes equal to or smaller than a predetermined value.

[0027] The extraction unit 21 determines that the current Ib has a single step waveform when it detects, for example, that (1) the first steady-state current Ib1 continues for at least the first predetermined steady-state time X1, (2) thereafter, in the current sudden change period, the current Ib changes from the first steady-state current Ib1 to the second steady-state current Ib2 within the first predetermined fluctuation period tr1, and (3) the state in which the current Ib is the second steady-state current Ib2 continues for the second predetermined steady-state time X2.Then, the extraction unit 21 extracts the current Ib during the extraction period te including the period in which the current Ib changes from the first steady-state current Ib1 to the second steady-state current Ib2 as a single step waveform.

[0028] The first predetermined steady-state time X1 and the second predetermined steady-state time X2 can be set arbitrarily depending on the usage status of the battery 90. The first predetermined fluctuation period tr1 can also be set appropriately. For example, the first predetermined fluctuation period tr1 can be set to within twice the predetermined interval at which the measurement unit 10 measures the current Ib and the voltage Vb.

[0029] Furthermore, when the extraction unit 21 detects that the measured current Ib changes from the first steady-state current Ib1 to the second steady-state current Ib2 within the first predetermined change period tr1, and then changes from the second steady-state current Ib2 to the first steady-state current Ib1 within the second predetermined change period tr2 before the second predetermined steady-state time X2 has elapsed, the extraction unit 21 extracts the current Ib as a single pulse waveform during the extraction period te including the period during which the current Ib changes from the first steady-state current Ib1 through the second steady-state current Ib2 to the first steady-state current Ib1.

[0030] 2002 in Fig. 2 is a diagram for explaining extraction of a single pulse waveform of current Ib, which is a terminal current. As shown in 2002 in Fig. 2, when the battery 90 is charged, the current Ib suddenly changes from the first steady-state current Ib1 to the second steady-state current Ib2 during a period of sudden current change. Also, when charging of the battery 90 is completed, the current Ib suddenly changes from the second steady-state current Ib2 to the first steady-state current Ib1 during a period of sudden current change.

[0031] The extraction unit 21 determines that the current Ib has a single pulse waveform when it detects, for example, that (1) the first steady-state current Ib1 continues for at least the first predetermined steady-state time X1, (2) thereafter, in the current sudden change period, the current Ib changes from the first steady-state current Ib1 to the second steady-state current Ib2 within the first predetermined change period tr1, (3) the state in which the current Ib is the second steady-state current Ib2 continues, and after the current Ib becomes the second steady-state current Ib2, the current Ib changes again from the second steady-state current Ib2 to the first steady-state current Ib1 within less than the second predetermined steady-state time X2, and (4) the state in which the current Ib is the first steady-state current Ib1 continues for a third predetermined steady-state time X3.Then, the extraction unit 21 extracts the current Ib as a single pulse waveform during the extraction period te including the period in which the current Ib changes from the first steady-state current Ib1 through the second steady-state current Ib2 to the first steady-state current Ib1.

[0032] The third predetermined steady-state time X3 can be set arbitrarily depending on the usage status of the battery 90. The second predetermined fluctuation period tr2 can also be set appropriately. For example, the second predetermined fluctuation period tr2 can be set to within twice the predetermined interval at which the measurement unit 10 measures the current Ib and the voltage Vb.

[0033] (Compliance Judgment Section) The suitability judgment unit 22 judges, based on the current Ib during a period of sudden current change in which the current suddenly changes in a single pulse waveform or a single step waveform, whether the current Ib and voltage Vb are suitable for transient response analysis for calculating the series resistance component Ri of the battery 90 at temperature T.

[0034] When the current fluctuation of a single pulse waveform or a single step waveform is large, for example, performing a deterioration diagnosis of battery 90 based on the current Ib and voltage Vb measured during the sudden current change period until the current Ib changes from the first steady-state current Ib1 to the second steady-state current Ib2 may result in a decrease in the accuracy of the deterioration diagnosis. Therefore, when a single pulse waveform or a single step waveform is extracted from current Ib by extraction unit 21, suitability determination unit 22 determines whether or not the current Ib and voltage Vb measured during the sudden current change period are suitable for transient response analysis based on the current Ib during the sudden current change period.

[0035] If the absolute value of the value obtained by subtracting the ratio of the current Ib measured during the current sudden change period to the second steady-state current Ib2 from 1 for each current Ib measured during the current sudden change period, i.e., |1-Ib / Ib2|, is within a threshold value σ, the suitability judgment unit 22 judges that the current Ib and the voltage Vb measured at the same timing as the current Ib are suitable for transient response analysis. Also, if |1-Ib / Ib2| is greater than the threshold value σ, the suitability judgment unit 22 judges that the current Ib and the voltage Vb measured at the same timing as the current Ib are unsuitable for transient response analysis.

[0036] The smaller the ratio of the current Ib measured during the sudden current change period to the second steady-state current Ib2, i.e., the greater the difference between the second steady-state current Ib2 and the current Ib measured during the sudden current change period, the lower the accuracy of the transient response analysis. Therefore, by appropriately setting the threshold value σ, the suitability determination unit 22 determines that the current Ib for which the difference between the second steady-state current Ib2 and the current Ib measured during the sudden current change period is large, which reduces the accuracy of the transient response analysis, is unsuitable for the transient response analysis.

[0037] In addition, although the above describes the sudden current change period during which the current Ib changes from the first steady-state current Ib1 to the second steady-state current Ib2 (hereinafter referred to as the first sudden current change period), the suitability determination unit 22 also performs similar processing for the sudden current change period during which the current Ib changes from the second steady-state current Ib2 to the first steady-state current Ib1 (hereinafter referred to as the second sudden current change period) when the current Ib has a single pulse waveform.

[0038] In the above case, the suitability judgment unit 22 judges that the current Ib and the voltage Vb measured at the same time as the current Ib are suitable for transient response analysis if the absolute value of the value obtained by subtracting from 1 the ratio of the difference between the second steady-state current Ib2 and the current Ib measured at the second current sudden change period to the difference between the second steady-state current Ib2 and the first steady-state current Ib1, that is, |1-{(Ib2-Ib) / (Ib2-Ib1)}|, for each current Ib measured during the current sudden change period, is within a threshold value σ. Also, the suitability judgment unit 22 judges that the current Ib and the voltage Vb measured at the same time as the current Ib are unsuitable for transient response analysis if |1-{(Ib2-Ib) / (Ib2-Ib1)}| is greater than the threshold value σ.

[0039] (Pre-analysis correction section) When the suitability determination unit 22 determines that the current Ib and the voltage Vb are unsuitable for the transient response analysis, the pre-analysis correction unit 23 corrects the current Ib and the voltage Vb based on the current response time tα, which is the time required to vary the current in the battery 90. The corrected current Ib and voltage Vb are stored in the storage unit 30 as reference values. The storage unit 30 may further store measurements taken by the measurement unit 10.

[0040] 3 is a graph for explaining the correction standard of the terminal current (current Ib) and the inter-terminal voltage (voltage Vb). In FIG. 3, Current Data shows the waveform of the current Ib.

[0041] As shown in Figure 3, patterns 1 to 3 are possible patterns in which the current Ib and voltage Vb are measured after the current fluctuation ends in a waveform in which the current changes suddenly. Pattern 1 is a pattern in which the current Ib is measured most recently after the current fluctuation ends, since the measurement is made just before the current fluctuation begins. Pattern 2 is a pattern in which the current Ib is measured just after the voltage fluctuation ends. Pattern 3 is a pattern in which the current Ib is measured at a time intermediate between patterns 1 and 2.

[0042] Correction before the transient response analysis is performed based on the measurement time of Pattern 3. By using the measurement time of Pattern 3 as the reference, the accuracy of the transient response analysis can be stably maintained even when the measurement of the current Ib is Pattern 1 or Pattern 2.

[0043] In addition, in the case of pattern 1, the internal resistance value of the equivalent circuit used in the transient response analysis is calculated to be larger than in patterns 2 and 3, and in the case of pattern 2, the internal resistance value is calculated to be smaller than in patterns 1 and 3. The difference in the internal resistance values ​​calculated in patterns 1 and 2 is within the allowable range, and correction of the current Ib and voltage Vb before the transient response analysis is not required. As with patterns 1 and 2, correction of the current Ib and voltage Vb before the transient response analysis is also not required for pattern 3. As described above, correction before the transient response analysis is required when the current Ib is measured between the first steady-state current Ib1 and the second steady-state current Ib2 during the period of sudden current change.

[0044] When pattern 3 is used as the standard for correction, the difference in measurement time with pattern 1 or pattern 2 is a maximum of half the sampling period tβ (predetermined interval), and therefore correction is performed taking this into consideration.

[0045] Specifically, the pre-analysis correction section 23 corrects the voltage Vb using the following formula (A). Vh=Vc-th×ΔV Formula (A) Here, Vh is the corrected voltage, and Vc is the voltage immediately after the current fluctuation ends. The voltage immediately after the current fluctuation ends refers to the voltage at the time when it can be considered that the current Ib has changed from the first steady-state current Ib1 to the second steady-state current Ib2. The time when it can be considered that the current Ib has changed from the first steady-state current Ib1 to the second steady-state current Ib2 refers to, for example, the time when the slope of the current fluctuation over a short period of time becomes equal to or smaller than a predetermined value.

[0046] ΔV is the average value of the slope of the voltage fluctuation for a short time immediately after the end of the current fluctuation in the past measured values. Note that ΔV may be the slope for a short time from the voltage Vb immediately after the current fluctuation measured by the measurement unit 10, instead of the past measured values.

[0047] Furthermore, th indicates the correction time. When the current response time tα of the degradation diagnosis device 1 is extremely shorter than the sampling period tβ (predetermined interval) of the measurement unit 10, for example when the sampling period tβ is 1 second and the current response time tα is 1 millisecond, the pre-analysis correction unit 23 sets half of the sampling period tβ as the correction time th. In other cases, the pre-analysis correction unit 23 sets half of tβ-tα{1-(Ib / Ib2)} as the correction time th.

[0048] Moreover, the pre-analysis correction unit 23 corrects the current Ib using the following formula (A). Ih=Ib2 Equation (a) Here, Ih denotes the corrected current, and Ib2 denotes the second steady-state current Ib2.

[0049] In addition, while the above describes the correction of the current Ib and voltage Vb measured during the first current sudden change period, the pre-analysis correction unit 23 also performs similar processing for correcting the current Ib and voltage Vb measured during the second current sudden change period when the current Ib has a single pulse waveform.

[0050] In this case, the correction by pre-analysis correction unit 23 differs in the following respects. That is, regarding the correction of voltage Vb measured during the second current sudden change period, unless the current response time tα of degradation diagnosis device 1 is extremely shorter than the sampling period tβ, pre-analysis correction unit 23 sets the correction time th to half of tβ-tα[1-{(Ib2-Ib) / (Ib2-Ib1)}]. Moreover, the correction of current Ib is made by the following formula (iii). Ih=Ib1 Formula (c) Here, Ih indicates the corrected voltage, and Ib1 indicates the first steady-state current Ib1.

[0051] (Correction procedure before transient response analysis) 4 is a graph illustrating an example of a correction procedure. First, the pre-analysis correction unit 23 detects the current Ib and the voltage Vb that are determined by the suitability determination unit 22 to be unsuitable for the transient response analysis as correction targets (see 4001 in FIG. 4).

[0052] Next, the pre-analysis correction unit 23 sets the current Ib determined to be unsuitable for the transient response analysis as the second steady-state current Ib2, which is then set as the corrected current Ih. In other words, the pre-analysis correction unit 23 copies the second steady-state current Ib2 to the current Ib determined to be unsuitable for the transient response analysis (see formula (A)).

[0053] Furthermore, for the voltage Vb determined to be unsuitable for the transient response analysis, the pre-analysis correction unit 23 uses the voltage immediately after the end of the voltage fluctuation to obtain a corrected voltage Vh from the above formula (A). In other words, the pre-analysis correction unit 23 copies the voltage Vc immediately after the start of the voltage fluctuation to the voltage Vb determined to be unsuitable for the transient response analysis (see 4002 in FIG. 4), and obtains the corrected voltage Vh from the above formula (A) (see 4003 in FIG. 4).

[0054] In this way, if the suitability judgment unit 22 judges that the current Ib and voltage Vb measured during the period of sudden current change are unsuitable for transient response analysis, the pre-analysis correction unit 23 corrects the current Ib and voltage Vb based on the current response time tα.

[0055] Furthermore, in the analysis unit 24 described later, a transient response analysis is performed based on the corrected current Ih and voltage Vh, and then the degradation state is diagnosed. Therefore, the current Ib and voltage Vb determined to be unsuitable for the transient response analysis are corrected so that a proper degradation state can be diagnosed even if they are used in the transient response analysis, and then the transient response analysis is performed, so that the degradation state of the battery 90 can be determined with high accuracy.

[0056] [Verification of corrections] The above-mentioned correction by the pre-analysis correction unit 23 will be verified below with reference to Fig. 5 to Fig. 7. Fig. 5 is a graph showing measured values ​​of the terminal current (current Ib) and the inter-terminal voltage (voltage Vb) in an experimental example. In the graph shown in Fig. 5, the current Case1_I and the voltage Case1_V include the current Ib and the voltage Vb, which are not suitable for the transient response analysis, as indicated by the arrows.

[0057] Fig. 6 is a graph showing the corrected voltage Case1_V. The circles indicate the corrected voltage Case1_V, the triangles indicate the uncorrected voltage Case1_V, and the squares indicate the voltage Vb when good transient response analysis could be performed for measurement data other than Case 1. Fig. 6 shows that the correction by the pre-analysis correction unit 23 has corrected the voltage Vb, which is not suitable for transient response analysis as indicated by the arrow in Fig. 5, so that good transient response analysis can be performed.

[0058] Fig. 7 is a table showing the verification results in the experimental example. Fig. 7 shows the error rates of the transient response analysis results of the current Case1_I and the voltage Case1_V before and after correction by the pre-analysis correction unit 23, relative to the transient response analysis results of the measurement data in which the accuracy of the transient response analysis was good. As shown in Fig. 7, it can be seen that the error rate after correction (1.7%) has been improved from the error rate before correction (5.1%).

[0059] (Analysis Department) The analysis unit 24 analyzes the current Ib and voltage Vb measured by the measurement unit 10 while the battery 90 is being charged or discharged, and calculates the series resistance component Ri at temperature T.

[0060] If the suitability judgment unit 22 judges that the current Ib and voltage Vb measured during the period of sudden current change are suitable for transient response analysis, the analysis unit 24 performs a transient response analysis of the battery 90 based on the current Ib and voltage Vb, and calculates the series resistance component Ri at temperature T.

[0061] In addition, if the suitability judgment unit 22 judges that the current Ib and voltage Vb measured during the period of sudden current change are unsuitable for transient response analysis, the analysis unit 24 performs a transient response analysis on the battery 90 based on the current Ib and voltage Vb corrected by the pre-analysis correction unit 23, and calculates the series resistance component Ri at temperature T of the battery 90.

[0062] Fig. 8 shows an equivalent circuit of a battery 90 applied to the transient response analysis performed by the analysis unit 24 of the deterioration diagnosis device 1. In the transient response analysis of the battery 90, the analysis unit 24 treats the battery 90 as the equivalent circuit shown in Fig. 8. In other words, the analysis unit 24 performs the transient response analysis of the battery 90 by reducing 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 to an equivalent circuit including a circuit connected in series.

[0063] The internal equivalent circuit between the terminals of the battery 90 is represented by a circuit in which one or more stages of an RC parallel circuit (parallel connection circuit) of a series resistance component Ri, a parallel capacitance component Cn, and a parallel resistance component Rn are connected in series, a series capacitance component C0, and an electromotive force E. Here, the electromotive force E is the open circuit voltage between the terminals of the battery 90. The symbol n in the parallel capacitance component Cn and the parallel resistance component Rn represents the index of the RC parallel circuit. When the number of stages of the RC parallel circuit is M, the index n is any natural number from 1 to M.

[0064] That is, the internal impedance between the terminals of the battery 90 is represented by a series connection of the impedance of each stage of an RC parallel circuit (parallel connection circuit) of a parallel capacitance component Cn and a parallel resistance component Rn, a series resistance component Ri, and a series capacitance component C0.

[0065] The analysis unit 24 fits the waveform data of the current Ib and the voltage Vb to such an equivalent circuit to calculate the series resistance component Ri at the temperature T of the battery 90. Note that the number of stages M of the RC parallel circuit may be one, and in that case, the equivalent circuit is expressed as a parallel capacitance component C1 and a parallel resistance component R1 as shown in FIG.

[0066] The parallel resistance component Rn is also a resistance component equivalent to the reaction resistance component of the battery 90. The series capacitance component C0 and the electromotive force E, which is the open circuit voltage, are values ​​specific to the battery 90 that do not vary depending on the deterioration state of the battery 90, and are stored in advance in the storage unit 30. The analysis unit 24 performs the fitting by referring to the values ​​of the series capacitance component C0 and the electromotive force E stored in the storage unit 30.

[0067] (Relationship between series resistance and temperature) FIG. 9 is a graph showing the results of the calculated series resistance component Ri at various temperatures T of the battery 90. As shown in FIG. 9, it can be seen that the series resistance component Ri is highly dependent on the temperature T of the battery 90. In addition, in FIG. 9, each plot with a different symbol indicates the results obtained in cases where the deterioration state of the battery 90 is different. The more the deterioration of the battery 90 progresses, the larger the series resistance component Ri becomes. In other words, the result represented by a triangle represents the most deteriorated state of the battery 90 among the three results in FIG. 9.

[0068] In this specification, the deterioration state of the battery 90 is represented by a capacity decrease rate D, which is the rate of decrease of the storage capacity Q of the battery 90 relative to the storage capacity Q0 of the battery 90 in the initial state:

number

[0069] In each plot of FIG. 9, which shows different degradation states, the relationship between temperature T and series resistance Ri can be well approximated by equation (2):

number

[0070] 10, 11, and 12 are graphs showing the dependence of temperature correction coefficients A, B, and C on capacity decline rate D. As is clear from the figures, temperature correction coefficient A is a parameter that depends heavily on capacity decline rate D. On the other hand, temperature correction coefficient B is a parameter that does not depend on capacity decline rate D, and temperature correction coefficient C has little dependence on capacity decline rate D. Therefore, in equation (2), while temperature correction coefficient A is a function of capacity decline rate D, temperature correction coefficients B and C are considered to be constants that do not depend on capacity decline rate D.

[0071] Thus, when considering the series resistance component Ri_st at a certain reference temperature Tst of the battery 90, the temperature correction coefficient A is eliminated from the equation (2) and the series resistance component Ri_st at the reference temperature Tst is expressed by the equation (3):

number

[0072] In this way, the series resistance component Ri_st at the reference temperature Tst can be calculated from the measured series resistance component Ri at a certain temperature T, regardless of the state of deterioration of the battery 90, i.e., even if the capacity degradation rate D is unknown.

[0073] (Post-analysis correction section) The post-analysis correction unit 25 (first correction unit) calculates the series resistance component Ri_st at the reference temperature Tst from the series resistance component Ri calculated by the analysis unit 24, based on the acquired temperature T. In other words, the post-analysis correction unit 25 corrects the series resistance component Ri at the temperature T to the series resistance component Ri_st at a predetermined reference temperature Tst.

[0074] Specifically, post-analysis correction unit 25 performs the correction according to formula (3) by referring to the values ​​of temperature correction coefficients B and C stored in storage unit 30. Temperature correction coefficients B and C are values ​​determined for each battery 90 and are stored in advance in storage unit 30.

[0075] (Diagnostics Department) Diagnosis unit 26 calculates capacity decline rate D, which is the rate of decline of the charge storage capacity of battery 90 relative to the charge storage capacity in the initial state of battery 90, based on series resistance component Ri_st at the reference temperature, and diagnoses the degradation state of battery 90. As described above, capacity decline rate D is an index that indicates the degradation state of battery 90. In this way, degradation diagnosis device 1 realizes degradation diagnosis of battery 90.

[0076] 13 is a graph showing plots (squares) showing the relationship between the capacity decay rate D and the series resistance component Ri when the battery temperature T is fixed, and plots (circles) showing the relationship between the capacity decay rate D and the corrected series resistance component Ri_st. The plots represented by squares in FIG. 13 show the relationship between the capacity decay rate D and the series resistance component Ri when the temperature T of the battery 90 is fixed at 25° C.

[0077] 13, it is understood that the capacity degradation rate D is robust to 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 a condition of constant temperature T, the capacity degradation rate D can be accurately determined. However, in reality, it is difficult to expect that the current Ib and voltage Vb will be measured under a condition of constant temperature T when the battery 90 is actually operated.

[0078] 13, the temperature T of the battery 90 during measurement is different from 25° C., but the series resistance component Ri_st at the reference temperature Tst obtained by correcting the series resistance component Ri according to the above procedure with the reference temperature Tst set to 25° C. is plotted as a circle. Even in this case, it is understood that the capacity decrease rate D is highly dependent 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 according to the above procedure.

[0079] Therefore, the capacity decay rate D can be accurately estimated by the linear equation (4) using the series resistance component Ri_st at the reference temperature Tst:

number

[0080] The constant Ri0 and the deterioration correction coefficient d are values ​​determined for each battery 90 and are stored in advance in the storage unit 30. The diagnosis unit 26 refers to the values ​​of the constant Ri0 and the deterioration correction coefficient d stored in the storage unit 30, and calculates the capacity decrease rate D of the battery 90 from the series resistance component Ri_st at the reference temperature Tst according to equation (4).

[0081] According to the formulas (1) to (4), the storage capacity Q of the battery 90 is given by

number

[0082] (Processing flow of the deterioration diagnosis device) Fig. 14 is a flowchart for explaining the processing steps of the degradation diagnosis method executed by degradation diagnosis device 1. As shown in Fig. 14, first, measurement unit 10 measures temperature T, and current Ib and voltage Vb at predetermined intervals of battery 90 in operation (step S1, measurement step).

[0083] Next, the extraction unit 21 extracts a single pulse waveform or a single step waveform from the current Ib measured in step S1 (step S2, extraction step).

[0084] The suitability determination unit 22 determines, based on the current Ib during a period of sudden current change in which the current suddenly changes in a single pulse waveform or a single step waveform, whether or not the current Ib and voltage Vb are suitable for transient response analysis for calculating the series resistance component Ri of the battery 90 at temperature T (step S3, suitability determination step).

[0085] In step S3, if it is determined that the current Ib and the voltage Vb are not suitable for the transient response analysis (NO in step S3), the pre-analysis correction unit 23 corrects the current Ib and the voltage Vb based on the current response time tα, which is the time required for the current to vary in the battery 90 (step S4, second correction step). The analysis unit 24 executes a transient response analysis based on the current Ib and voltage Vb corrected in step S4, and calculates the series resistance component Ri of the battery 90 at temperature T (step S5, analysis step).

[0086] In step S3, if it is determined that the current Ib and the voltage Vb are suitable for transient response analysis (YES in step S3), the analysis unit 24 performs a transient response analysis based on the current Ib and voltage Vb, and calculates the series resistance component Ri of the battery 90 at temperature T (step S5, analysis step).

[0087] Thereafter, the post-analysis correction unit 25 corrects the series resistance component Ri at temperature T calculated in step S5 to the series resistance component Ri_st at a predetermined reference temperature Tst (step S6, first correction step).Then, the diagnosis unit 26 calculates a capacity decrease rate D, which is a decrease rate of the storage capacity Q of the battery 90 relative to the storage capacity Q0 in the initial state of the battery 90, based on the series resistance component Ri_st at the reference temperature Tst corrected in step S6, and diagnoses the degradation state of the battery 90 (step S7, diagnosis step).

[0088] Thus, in this embodiment, when a single pulse waveform or a single step waveform is extracted from the current Ib measured at a predetermined interval, in the suitability determination step, it is determined whether or not the current Ib and voltage Vb measured during the period of sudden current change are suitable for transient response analysis based on the current Ib during the period of sudden current change. If it is determined that they are suitable for transient response analysis, the transient response analysis is performed based on the current Ib and voltage Vb, and if it is determined that they are not suitable for transient response analysis, the transient response analysis is performed based on the current Ib and voltage Vb corrected to be suitable for the transient response analysis.

[0089] Therefore, since the degradation state is diagnosed by performing a transient response analysis on the current Ib and voltage Vb suitable for the transient response analysis, the degradation state of the battery 90 can be determined with high accuracy from the circuit characteristics when the battery 90 is charged and discharged.

[0090] In addition, the deterioration diagnosis device 1 can calculate the capacity degradation rate D, which is an index of deterioration of the battery 90, from the battery circuit characteristics by monitoring the current Ib and voltage Vb of the battery 90 during charging or discharging, and the temperature T of the battery 90.

[0091] Therefore, the deterioration state of the battery 90 can be diagnosed without performing a test such as discharging and fully charging the battery 90 to determine the charge capacity.

[0092] Moreover, according to the degradation diagnosis method of the embodiment, the temperature T of the battery 90 is measured and the circuit characteristics (series resistance component Ri) of the battery 90 are corrected, so that it is possible to cancel the strong influence of the temperature T as shown in Fig. 9 and correctly diagnose the degradation state of the battery 90. In particular, in the first embodiment, as shown in formula (3), a clever technique is used that can cancel the influence of the temperature T without being influenced by the degradation state of the battery 90 (capacity decrease rate D), and it is possible to accurately diagnose the degradation state of the battery 90.

[0093] 13, the degradation diagnosis method of the first embodiment is based on the use of a circuit parameter called a series resistance component Ri that can accurately predict the capacity decrease rate D, which is an index showing the degradation state of the battery 90. Therefore, according to the degradation diagnosis method of the first embodiment, it becomes possible to accurately diagnose the degradation state of the battery 90.

[0094] 〔summary〕 The degradation diagnosis method according to the first aspect of the present invention includes a measurement step of measuring a battery temperature (temperature T) and a terminal current (current Ib) and an inter-terminal voltage (voltage Vb) at predetermined intervals of a storage battery (battery 90) in operation; an extraction step of extracting a single pulse waveform or a single step waveform from the terminal current (current Ib) measured in the measurement step; a suitability determination step of determining whether or not the terminal current (current Ib) and the inter-terminal voltage (voltage Vb) are suitable for a transient response analysis for calculating a series resistance component (Ri) of the storage battery (battery 90) at the battery temperature (temperature T) based on the terminal current (current Ib) during a current abrupt change period in which the current abruptly changes in the single pulse waveform or the single step waveform; and a suitability determination step of determining whether or not the terminal current (current Ib) and the inter-terminal voltage (voltage Vb) are suitable for a transient response analysis for calculating a series resistance component (Ri) of the storage battery (battery 90) at the battery temperature (temperature T) when it is determined that the terminal current (current Ib) and the inter-terminal voltage (voltage Vb) are suitable for the transient response analysis. the series resistance component (Ri) at the battery temperature (temperature T) of the storage battery (battery 90) is calculated based on a voltage (Vb) of the storage battery (battery 90) at a predetermined reference temperature (Tst), and a capacity decrease rate (D) is calculated based on the series resistance component (Ri_st) at the reference temperature (Tst) to calculate a capacity decrease rate (D), which is a decrease rate of a storage capacity (Q) of the storage battery (battery 90) relative to a storage capacity (Q0) in an initial state of the storage battery (battery 90), to diagnose a deterioration state of the storage battery (battery 90).

[0095] When the current fluctuation of a single pulse waveform or a single step waveform is large, for example, when a deterioration diagnosis of a storage battery is performed based on the terminal current and terminal voltage measured immediately after the current fluctuation starts and before the current fluctuation ends, the accuracy of the deterioration diagnosis may be reduced.

[0096] Therefore, according to the above configuration, when a single pulse waveform or a single step waveform is extracted from the terminal current measured at a predetermined interval, in the suitability determination step, it is determined whether or not the terminal current and the terminal voltage are suitable for a transient response analysis based on the terminal current during the period of sudden current change. Also, when it is determined that the terminal current and the terminal voltage are suitable for a transient response analysis, a transient response analysis is performed based on the terminal current and the terminal voltage to diagnose the deterioration state.

[0097] Therefore, transient response analysis is performed and the deterioration state is diagnosed only for the terminal current and terminal voltage suitable for transient response analysis, so the deterioration state of the storage battery can be determined with high accuracy from the circuit characteristics when the storage battery is charged and discharged.

[0098] The deterioration diagnosis method according to aspect 2 of the present invention, in the above-mentioned aspect 1, further includes a second correction step of correcting the terminal current (current Ib) and the terminal voltage (voltage Vb) based on a current response time, which is the time required to change the current in the storage battery, if the terminal current (current Ib) and the terminal voltage (voltage Vb) are determined to be unsuitable for the transient response analysis in the suitability determination step, and in the analysis step, the transient response analysis may be performed on the storage battery (battery 90) based on the terminal current (current Ib) and the terminal voltage (voltage Vb) corrected in the second correction step, and the series resistance component (Ri) of the storage battery (battery 90) at the storage battery temperature (temperature T) may be calculated.

[0099] According to the above configuration, if the terminal current and the terminal voltage are determined to be unsuitable for the transient response analysis in the suitability determination step, the terminal current and the terminal voltage are corrected based on the current response time in the second correction step. In addition, in the analysis step, a transient response analysis is performed based on the corrected terminal current and the terminal voltage, and then the degradation state is diagnosed. Therefore, the terminal current and the terminal voltage determined to be unsuitable for the transient response analysis are corrected so that a proper degradation state can be diagnosed even if they are used in the transient response analysis, and then the transient response analysis is performed, so that the degradation state of the storage battery can be determined with high accuracy.

[0100] A degradation diagnosis method according to a third aspect of the present invention is, in the first or second aspect, characterized in that, in the extraction step, when it is detected that the terminal current (current Ib) fluctuates from a first steady-state current (Ib1) to a second steady-state current (Ib2) different from the first steady-state current (Ib1) within a first predetermined fluctuation period (tr1), the terminal current (current Ib) during an extraction period (te) including a period during which the terminal current (current Ib) fluctuates from the first steady-state current (Ib1) to the second steady-state current (Ib2) is extracted as the single step waveform, and When it is detected that the terminal current (current Ib) fluctuates from the steady-state current (Ib1) to the second steady-state current (Ib2) within a first predetermined fluctuation period (tr1) and then fluctuates from the second steady-state current (Ib2) to the first steady-state current (Ib1) within a second predetermined fluctuation period (tr2) before a predetermined steady-state time (X2) has elapsed, the terminal current (current Ib) during an extraction period (te) including a period during which the terminal current (current Ib) fluctuates from the first steady-state current (Ib1) via the second steady-state current (Ib2) to the first steady-state current (Ib1) may be extracted as the single pulse waveform.

[0101] According to the above configuration, a single pulse wave or a single step waveform of the terminal current can be suitably extracted.

[0102] In the deterioration diagnosis method according to aspect 4 of the present invention, in the above-mentioned aspect 3, in the suitability determination step, if the absolute value of the value obtained by subtracting the ratio of the terminal current (current Ib) measured during the sudden current change period to the second steady-state current (Ib2) from 1 for each of the terminal currents (current Ib) measured during the sudden current change period is within a threshold value (σ), the terminal current (current Ib) is determined to be suitable for the transient response analysis, and if the absolute value is greater than the threshold value (σ), the terminal current (current Ib) is determined to be unsuitable for the transient response analysis.

[0103] The smaller the ratio of the terminal current measured during the sudden current change period to the second steady-state current, i.e., the greater the difference between the second steady-state current and the terminal current measured during the sudden current change period, the lower the accuracy of the transient response analysis. According to the above configuration, by appropriately setting the threshold value, when the terminal current measured during the sudden current change period includes a terminal current whose difference from the second steady-state current is large, which reduces the accuracy of the transient response analysis, it can be appropriately determined in the suitability determination step that the terminal current is unsuitable for the transient response analysis.

[0104] A deterioration diagnosis device according to a fifth aspect of the present invention includes a measurement unit (10) that measures a battery temperature (temperature T) of a storage battery (battery 90) in operation, and a terminal current (current Ib) and an inter-terminal voltage (voltage Vb) at predetermined intervals, an extraction unit (21) that extracts a single pulse waveform or a single step waveform from the terminal current (current Ib) measured by the measurement unit (10), a suitability determination unit (22) that determines whether or not the terminal current (current Ib) and the inter-terminal voltage (voltage Vb) are suitable for a transient response analysis for calculating a series resistance component (Ri) of the storage battery (battery 90) at the battery temperature (temperature T) based on the terminal current (current Ib) during a current abrupt change period in which the current changes abruptly in the single pulse waveform or the single step waveform, and a suitability determination unit (22) that determines whether or not the terminal current (current Ib) and the inter-terminal voltage (voltage Vb) are suitable for the transient response analysis, when it is determined that the terminal current (current Ib) and the inter-terminal voltage (voltage Vb) are suitable for the transient response analysis. The analysis unit (24) performs the transient response analysis of the storage battery (battery 90) by reducing the series resistance component (Ri) and a parallel connection circuit in which a parallel capacitance component (Cn) and a parallel resistance component (Rn) are connected in parallel to an equivalent circuit including a series-connected circuit based on the series resistance component (Ri) and calculates the series resistance component (Ri) of the storage battery (battery 90) at the storage battery temperature (temperature T). and a diagnosis unit (26) that calculates a capacity decrease rate (D), which is a rate of decrease of a storage capacity (Q) of the storage battery (battery 90) relative to a storage capacity (Q0) in an initial state of the storage battery (battery 90), based on the series resistance component (Ri_st) at the reference temperature (Tst), and diagnoses a degradation state of the storage battery (battery 90).

[0105] According to the above configuration, the same effects as those of the first aspect are achieved.

[0106] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. The technical scope of the present invention also includes embodiments obtained by appropriately combining the technical means disclosed in the embodiments. Furthermore, new technical features can be formed by combining the technical means disclosed in the embodiments. [Explanation of symbols]

[0107] 1. Deterioration diagnosis device 10 Measuring part 21 Extraction part 22 Compliance Judgment Section 23 Pre-analysis correction section 24 Analysis Department 25 Post-analysis correction section (first correction section) 26 Diagnostic Department 90 batteries C1, Cn parallel capacitance component C0 Series capacitance component Ri series resistance component R1, Rn parallel resistance component Ib current (terminal current) Ib1 First steady-state current Ib2 Second steady-state current Vb Voltage (Terminal voltage) T temperature (storage battery temperature) Tst reference temperature tr1 First specified variable period tr2 Second specified variable period te Extraction period Ri_st Series resistance component at reference temperature D Capacity reduction rate

Claims

1. a measuring step of measuring a battery temperature, and a terminal current and an inter-terminal voltage at predetermined intervals of the battery in operation; an extraction step of extracting a single pulse waveform or a single step waveform from the terminal current measured in the measurement step; a suitability determination step of determining whether or not the terminal current and the terminal voltage are suitable for a transient response analysis for calculating a series resistance component of the storage battery at the storage battery temperature, based on the terminal current during a current sudden change period in which the current suddenly changes in the single pulse waveform or the single step waveform; an analysis step of performing the transient response analysis of the storage battery based on the terminal current and the terminal voltage when it is determined that the terminal current and the terminal voltage are suitable for the transient response analysis, by reducing the series resistance component and a parallel connection circuit in which a parallel capacitance component and a parallel resistance component are connected in parallel to an equivalent circuit including a series-connected circuit, and calculating the series resistance component of the storage battery at the battery temperature; a first correction step of correcting the series resistance component at the storage battery temperature to the series resistance component at a predetermined reference temperature; and a diagnosis step of calculating a capacity decline rate, which is the rate of decline of the storage capacity of the storage battery relative to the storage capacity in an initial state of the storage battery, based on the series resistance component at the reference temperature, to diagnose a deterioration state of the storage battery.

2. When it is determined in the suitability determination step that the terminal current and the terminal voltage are not suitable for the transient response analysis, the method further includes a second correction step of correcting the terminal current and the terminal voltage based on a current response time that is a time required to vary a current in the storage battery, 2. The degradation diagnosis method according to claim 1, wherein in the analysis step, a transient response analysis is performed on the storage battery based on the terminal current and the inter-terminal voltage corrected in the second correction step, and the series resistance component of the storage battery at the battery temperature is calculated.

3. In the extraction step, When it is detected that the terminal current varies from a first steady-state current to a second steady-state current different from the first steady-state current within a first predetermined variation period, the terminal current during an extraction period including a period during which the terminal current varies from the first steady-state current to the second steady-state current is extracted as the single step waveform; 2. The degradation diagnosis method according to claim 1, wherein, when it is detected that the terminal current fluctuates from a first steady-state current to the second steady-state current within a first predetermined fluctuation period, and then fluctuates from the second steady-state current to the first steady-state current within a second predetermined fluctuation period before a predetermined steady-state time has elapsed, the terminal current during an extraction period including a period during which the terminal current fluctuates from the first steady-state current via the second steady-state current to the first steady-state current is extracted as the single pulse waveform.

4. In the suitability determination step, 4. The degradation diagnosis method according to claim 3, further comprising the steps of: determining, for each of the terminal currents measured during the sudden current change period, if an absolute value of a value obtained by subtracting a ratio of the terminal current measured during the sudden current change period to the second steady-state current from 1 is within a threshold value, the terminal current is determined to be suitable for the transient response analysis; and determining, if the absolute value is greater than the threshold value, the terminal current is determined to be unsuitable for the transient response analysis.

5. a measurement unit that measures a battery temperature of the battery in operation and a terminal current and an inter-terminal voltage at predetermined intervals; an extraction unit that extracts a single pulse waveform or a single step waveform from the terminal current measured by the measurement unit; a suitability determination unit that determines whether or not the terminal current and the terminal voltage are suitable for a transient response analysis for calculating a series resistance component of the storage battery at the storage battery temperature, based on the terminal current during a current sudden change period in which a current suddenly changes in the single pulse waveform or the single step waveform; an analysis unit that, when it is determined that the terminal current and the terminal voltage are suitable for the transient response analysis, performs the transient response analysis of the storage battery by reducing the series resistance component and a parallel connection circuit in which a parallel capacitance component and a parallel resistance component are connected in parallel to an equivalent circuit including a series connected circuit based on the terminal current and the terminal voltage, and calculates the series resistance component of the storage battery at the storage battery temperature; a first correction unit that corrects the series resistance component at the storage battery temperature to the series resistance component at a predetermined reference temperature; and a diagnosis unit that calculates a capacity decline rate, which is a rate of decline in the storage capacity of the storage battery relative to the storage capacity in an initial state of the storage battery, based on the series resistance component at the reference temperature, and diagnoses a deterioration state of the storage battery.

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