Power supply device and battery state estimation method

Abstract

To appropriately determine whether a battery in which an SOC-OCV curve has a flat area deteriorates.SOLUTION: A power unit includes: a battery in which an SOC-DCV curve includes a flat area; a current sensor for detecting current of the battery; a current integration part; a guaranteed capacity estimation part; and a determining part. The current integration part calculates an integrated current value when the battery is discharged from a first charged state to a second charged state. The guaranteed capacity estimation part estimates the guaranteed capacity of the battery by adding a correction value calculated based on a lower limit SOC for expressing the lower limit of a flat area and the integrated current value to the integrated current value. The determination part determines whether a guarantee SOH expressed by a ratio of the guaranteed capacity to the initial capacity or nominal capacity of the battery is larger than a predetermined threshold.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a technique for estimating the state of deterioration of a rechargeable battery. [Background technology]

[0002] Rechargeable batteries deteriorate through repeated charging and discharging, gradually reducing their capacity. As the battery capacity decreases, the operating time of devices that use the battery also decreases. For example, as the battery capacity of an electric vehicle decreases, the driving time or driving distance also decreases. Therefore, there is a demand for technology that can accurately estimate the state of battery deterioration.

[0003] The state of health (SOH) of a battery is expressed, for example, as the ratio of the current capacity to the initial capacity or the nominal capacity. That is, the SOH is expressed by equation (1a) or (1b).

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[0004] FIG. 1 is a diagram illustrating an example of a method for estimating battery capacity. In this example, the battery capacity is estimated using the SOC-OCV curve. Specifically, the current capacity of the battery is expressed by equation (2). The vertical and horizontal axes in FIG. 1 represent the open circuit voltage (OCV) and state of charge (SOC) of the battery, respectively.

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[0005] In this case, the integrated current amount during a certain measurement period is calculated. The OCV of the battery is measured at the start and end of this measurement period to obtain the corresponding SOC. For example, when OCV1 and OCV2 are obtained at the start and end of this measurement period, respectively, SOC1 and SOC2 are obtained, as shown in FIG. 1. The current capacity of the battery is calculated by inputting the integrated current amount, SOC1, and SOC2 into equation (2). Furthermore, the current SOH is obtained by inputting this value into equation (1a) or (1b). A method for estimating SOH using the SOC corresponding to the battery's OCV is described, for example, in Patent Document 1.

[0006] It is also possible to determine the battery capacity by measuring the cumulative current flow from a fully charged state to a fully discharged state. However, this method requires a dedicated device to discharge at a predetermined current and voltage. Therefore, this method cannot easily estimate the SOH of a battery installed in a vehicle, for example. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-071320 Summary of the Invention [Problem to be solved by the invention]

[0008] As mentioned above, a method for estimating battery capacity using the SOC-OCV curve has been proposed. However, this method is effective for batteries whose OCV changes with changes in SOH.

[0009] On the other hand, iron phosphate (LFP)-based lithium-ion batteries, which are inexpensive and relatively thermally stable, have been put into practical use. However, the SOC-OCV curve of a lithium-ion iron phosphate battery has a flat region (or plateau region), as shown in Figure 2. Therefore, using the SOC-OCV curve to estimate the battery capacity can result in low accuracy. For example, when acquiring the integrated current between SOC1 and SOC2 in Figure 2, the difference between the OCV corresponding to SOC1 and the OCV corresponding to SOC2 becomes small, resulting in a large measurement error. Therefore, when estimating the battery capacity using equation (2), the error in the denominator becomes large, resulting in low estimation accuracy. Note that this problem is not limited to lithium-ion iron phosphate batteries and can occur in any battery with a flat SOC-OCV curve.

[0010] An object according to one aspect of the present invention is to provide a method for appropriately determining whether a battery having a flat region in its SOC-OCV curve is degraded. [Means for solving the problem]

[0011] A power supply device according to one embodiment of the present invention comprises a battery having a flat region of its SOC-OCV curve, a current sensor for detecting the current of the battery, a current integration unit for calculating an accumulated current amount when the battery is discharged from a first state of charge to a second state of charge, a guaranteed capacity estimation unit for estimating the guaranteed capacity of the battery by adding a lower limit SOC representing the lower limit of the flat region and a correction value calculated based on the accumulated current amount to the accumulated current amount, and a determination unit for determining whether a guaranteed SOH, which is expressed as the ratio of the guaranteed capacity to the initial capacity or nominal capacity of the battery, is higher than a predetermined threshold.

[0012] In this configuration, the guaranteed capacity and guaranteed SOH of the battery are calculated based on the integrated current when discharging is started from a fully charged state. If the guaranteed SOH is higher than a predetermined threshold, it is determined that the battery capacity has not deteriorated. Therefore, for a battery whose SOC-OCV curve has a flat region, it is possible to determine whether the battery capacity has deteriorated even when the depth of discharge is shallow. In other words, it is possible to increase the frequency of determining whether the battery capacity has deteriorated.

[0013] The second state of charge may be a state where the state of charge is higher than the lower limit SOC. In other words, even if the depth of discharge is shallow, it is possible to determine whether the battery capacity has deteriorated. The correction value can be obtained, for example, by dividing the product of the lower limit SOC and the accumulated current by the result of subtracting the lower limit SOC from 100 percent. [Effects of the Invention]

[0014] According to the above-described embodiment, it is possible to appropriately determine whether a battery having a flat region of its SOC-OCV curve has deteriorated. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 10 is a diagram illustrating an example of a method for estimating the capacity of a battery. [Figure 2] FIG. 1 is a diagram showing an example of an SOC-OCV curve having a flat region. [Figure 3] FIG. 1 is a diagram showing an example of a method for estimating the capacity of a battery whose SOC-OCV curve has a flat region. [Figure 4] 1 is a diagram illustrating an example of a power supply device according to an embodiment of the present invention. [Figure 5] 10A and 10B are diagrams illustrating a method for estimating a battery state having a flat region. [Figure 6] FIG. 10 is a diagram illustrating a method for calculating the guaranteed capacity of a battery. [Figure 7] FIG. 10 is a diagram illustrating an example of a method for compensating for low accuracy in estimating SOH. [Figure 8]3 is a flowchart illustrating an example of a battery state estimation method according to an embodiment of the present invention. [Figure 9] 10A and 10B are diagrams illustrating variations of a method for estimating a battery state. DETAILED DESCRIPTION OF THE INVENTION

[0016] Figure 3 shows an example of a method for estimating the capacity of a battery whose SOC-OCV curve has a flat region. When the SOC-OCV curve has a flat region, measuring the OCV within that flat region and estimating the corresponding SOC can result in a large error. Therefore, it is preferable to estimate the battery capacity in a region where the OCV changes in response to changes in SOC.

[0017] In the case shown in Figure 3(a), the battery capacity is estimated based on the OCV measured when the SOC is higher than the flat region. In the case shown in Figure 3(b), the battery capacity is estimated based on the OCV measured when the SOC is lower than the flat region. However, in these cases, the change in SOC (i.e., the difference between SOC1 and SOC2) is small, so the accuracy of the battery capacity estimation is also low.

[0018] In the case shown in Figure 3(c), SOC1 is estimated from OCV1 measured in a region where the SOC is lower than the flat region, and SOC2 is estimated from OCV2 measured in a region where the SOC is higher than the flat region. These values ​​are then used to estimate the battery capacity. In this case, the difference in OCV is large and the change in SOC is also large, so the accuracy of the battery capacity estimation is high.

[0019] However, this method can only estimate battery capacity when the battery state changes from a fully charged or nearly fully charged state to a fully discharged or nearly fully discharged state. In other words, it cannot estimate battery capacity when the depth of discharge is shallow. For example, if the main battery of an electric vehicle is next charged when it is about 40 to 50 percent used from a fully charged state, it cannot estimate battery capacity. This may result in fewer opportunities to estimate battery capacity. As a result, there is a risk that the battery may continue to be used even when it has deteriorated and its capacity has decreased.

[0020] Therefore, the battery state estimation method according to an embodiment of the present invention provides a function that can determine whether the battery capacity has deteriorated to a predetermined threshold level even if the battery is not discharged until the SOC becomes lower than the flat region.

[0021] Fig. 4 shows an example of a power supply device according to an embodiment of the present invention. As shown in Fig. 4, the power supply device 100 according to the embodiment of the present invention includes a battery 10, a current sensor A, a voltage sensor V, and a control unit 20. Note that the power supply device 100 may include other circuits or functions not shown in Fig. 4.

[0022] The battery 10 is, for example, a battery pack composed of multiple battery modules connected in parallel. In this case, each battery module may be composed of multiple battery cells connected in series. The battery 10 is charged by a charger (not shown). In the following description, the battery pack, battery modules, or battery cells may be collectively referred to as a "battery."

[0023] In this embodiment, the battery 10 is a lithium-ion battery. Specifically, the battery 10 is an iron phosphate lithium-ion battery whose positive electrode contains lithium, iron, and phosphorus and whose negative electrode is made of graphite. Therefore, the SOC-OCV curve of the battery 10 has a flat region (or plateau region) in which the OCV is almost flat with respect to changes in SOC, as shown in FIG. 2 or FIG. 3 . Specifically, in the low SOC region where the SOC is lower than the flat region, the OCV also increases as the SOC increases. Also, in the high SOC region where the SOC is higher than the flat region, the OCV also increases as the SOC increases. In contrast, in the flat region, the slope of the OCV with respect to the SOC is close to zero.

[0024] The battery 10 can supply power to a load 200. The load 200 is not particularly limited, but in the case where the power supply device 100 is mounted on an electric vehicle, it is, for example, a traction motor. In addition, in the case where the power supply device 100 is mounted on an industrial vehicle such as a forklift, the load 200 may be a loading motor. Note that a relay RL is provided between the battery 10 and the load 200, which can cut off the supply of power from the battery 10 to the load 200.

[0025] The voltage sensor V detects the voltage of the battery 10. Here, the voltage sensor V may detect the voltage of the entire battery pack, the voltage of each battery module, or the voltage of each battery cell. The output signal of the voltage sensor V is acquired by the control unit 20.

[0026] Current sensor A detects the current of battery 10. That is, when battery 10 is being charged, current sensor A detects the charging current. When load 200 is driven by the power of battery 10, current sensor A detects the discharging current. The output signal of current sensor A is acquired by control unit 20. Current sensor A is, for example, a Hall-type current sensor. Hall-type current sensors include a Hall element, which is a magnetoelectric conversion element, and convert the magnetic field generated around the measured current into a voltage. Therefore, in this case, current sensor A outputs a voltage signal representing the current of battery 10. However, current sensor A3 may be realized with other configurations (for example, a shunt resistor).

[0027] The control unit 20 estimates the SOC and SOH of the battery 10. The control unit 20 also determines whether the deterioration of the battery 10 has progressed to a predetermined threshold level.

[0028] The control unit 20 includes a memory 21. The memory 21 stores SOC-OCV data, initial capacity data, and lower limit SOC data. The SOC-OCV data represents the SOC-OCV curve of the battery 10. Here, the SOC-OCV curve of the battery 10 is as shown in FIG. 5 and is assumed to be obtained in advance. The initial capacity data represents the initial capacity or nominal capacity of the battery 10. The initial capacity is measured when the battery 10 is first used. The nominal capacity is a known value and is provided by the vendor of the battery 10. In the following description, the initial capacity or nominal capacity may be collectively referred to as the "initial capacity." The lower limit SOC data represents the SOC at the lower end of the flat region of the SOC-OCV curve (i.e., the lower limit SOC). The lower limit SOC data is set in advance based on the SOC-OCV curve or the SOC-OCV data. In FIG. 5, the lower limit SOC is represented by an "X." However, the lower limit SOC represented by the lower limit SOC data does not have to be a fixed value. For example, since the SOC-OCV curve of the battery 10 may change over time, the lower limit SOC data may be updated in accordance with this change over time.

[0029] The control unit 20 includes a current integrator 22, an SOC estimator 23, an SOH estimator 24, a guaranteed capacity estimator 25, and a determiner 26. Note that the control unit 20 may include other functions not shown in FIG. 4.

[0030] The current integrator 22 monitors the current of the battery 10 based on the output signal of the current sensor A. The current integrator 22 then calculates the integrated current amount by integrating the current from the start to the end of measurement. The SOC estimator 23 detects the OCV of the battery 10 based on the output signal of the voltage sensor V. The SOC estimator 23 then estimates the corresponding SOC by referring to the SOC-OCV data using the detected OCV. For example, in the case shown in FIG. 3, if "OCV=OCV1", the state of charge of the battery 10 is estimated to be SOC1, and if "OCV=OCV2", the state of charge of the battery 10 is estimated to be SOC2.

[0031] The SOH estimation unit 24 estimates the SOH of the battery 10 using the above-described formulas (1a) and (2). At this time, the current integration unit 22 calculates the integrated current amount from the start to the end of the measurement period for measuring the SOH. The SOC estimation unit 23 detects the OCV at the start and end of the measurement period and estimates the SOC (SOC1, SOC2) corresponding to each OCV. The SOH estimation unit 24 then estimates the current capacity of the battery 10 by applying the integrated current amount obtained by the current integration unit 22 and the SOC estimated by the SOC estimation unit 23 to formula (2). The SOH estimation unit 24 then estimates the SOH of the battery 10 by applying the estimated current capacity to formula (1a). Note that the SOH estimation unit 24 uses initial capacity data stored in the memory 21 when estimating the current capacity.

[0032] The guaranteed capacity estimation unit 25 estimates the guaranteed capacity of the battery 10 based on the accumulated current of the battery 10 calculated by the current accumulation unit 22. The "guaranteed capacity" indicates that the current capacity of the battery 10 is equal to or greater than the corresponding value. For example, when the guaranteed capacity is 80 [Ah], the current capacity of the battery 10 is guaranteed to be equal to or greater than 80 [Ah].

[0033] When the guaranteed capacity estimation unit 25 estimates the guaranteed capacity of the battery 10, the current integration unit 22 calculates the integrated current amount when the battery 10 is discharged from the fully charged state to a second state of charge. The second state of charge is any state of charge other than the fully charged state, and may be within the flat region of the SOC-OCV curve. In the example shown in FIG. 5, the integrated current amount when the battery 10 is discharged from the fully charged state to the second state of charge is represented by "Y."

[0034] Furthermore, the guaranteed capacity estimation unit 25 calculates a correction value for correcting the accumulated current amount Y based on the accumulated current amount Y from the fully charged state to the second charged state and the lower limit SOC that represents the lower limit of the flat region of the SOC-OCV curve.The guaranteed capacity estimation unit 25 then calculates the guaranteed capacity of the battery 10 by adding this correction value to the accumulated current amount Y.

[0035] 5, the guaranteed capacity of the battery 10 is calculated by equation (3). Note that X is a lower limit SOC that indicates the lower limit of the flat region of the SOC-OCV curve, and is stored as lower limit SOC data in the memory 21. Furthermore, Y represents the integrated current amount when the battery 10 is discharged from the fully charged state to the second charged state, and is calculated by the current integrator 22.

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[0036] Here, the meaning of equation (3) will be explained. First, as shown in FIG. 6, it is assumed that the battery 10 is discharged from the fully charged state to the lower limit SOC (i.e., the second state of charge). In this case, the integrated current amount when discharging from the fully charged state to the second state of charge is "Y." Also, the integrated current amount when discharging from the second state of charge to the fully discharged state is "Z." Then, as is clear from FIG. 6, equation (4) is established.

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[0037] Therefore, the current integration amount Z when discharging from the second charged state to the fully discharged state is expressed by equation (5).

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[0038] The accumulated current amount Z expressed by equation (5) corresponds to the lower limit SOC of the battery 10 (i.e., the second state of charge) when converted to the state of charge of the battery 10. Here, the capacity of the battery 10 corresponds to the accumulated current amount when the battery 10 is discharged from the fully charged state to the fully discharged state. Therefore, in the case shown in FIG. 6, the capacity of the battery 10 corresponds to the sum of the accumulated current amount when the battery 10 is discharged from the fully charged state to the second state of charge and the accumulated current amount when the battery 10 is discharged from the second state of charge to the fully discharged state. Therefore, in the case shown in FIG. 6, the capacity of the battery 10 can be expressed as "Y+Z."

[0039] On the other hand, in the case shown in FIG. 5, the capacity of battery 10 corresponds to the sum of the integrated current Y when discharging from the fully charged state to the second state of charge, the integrated current Y when discharging from the second state of charge to the lower limit SOC, and the integrated current Z when discharging from the lower limit SOC to the fully discharged state. Therefore, if the second state of charge is higher than the lower limit SOC, the capacity of battery 10 is greater than the sum of the integrated current Y when discharging from the fully charged state to the second state of charge and the integrated current Z when discharging from the lower limit SOC to the fully discharged state. In other words, in the case shown in FIG. 5, the capacity of battery 10 will never be less than "Y + Z." Therefore, the value on the right side of equation (3) is the guaranteed capacity, which indicates the minimum capacity of battery 10.

[0040] In this way, guaranteed capacity estimation unit 25 calculates the guaranteed capacity of battery 10 by adding the accumulated current amount Z when discharging from the lower limit SOC to the fully discharged state to the accumulated current amount Y when discharging from the fully charged state to the second charged state. Note that accumulated current amount Z is an example of a correction value calculated based on the lower limit SOC that represents the lower limit of the flat region and the accumulated current amount when discharging from the fully charged state to the second charged state.

[0041] The determination unit 26 calculates the guaranteed SOH, which is expressed as the ratio of the guaranteed capacity to the initial capacity or nominal capacity of the battery 10. That is, the determination unit 26 calculates the guaranteed SOH using equation (6).

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[0042] "Guaranteed SOH" indicates that the current SOH of the battery 10 is equal to or greater than the specified value. For example, if the guaranteed SOH is 70 percent, the current SOH of the battery 10 is guaranteed to be equal to or greater than 70 percent. Note that in equation (6), the nominal capacity may be used instead of the initial capacity.

[0043] The determination unit 26 then compares the guaranteed SOH with a predetermined threshold. This threshold is not particularly limited, but may be, for example, an SOH corresponding to a state in which the capacity of the battery 10 has deteriorated to the point where it should be replaced. If the guaranteed SOH is higher than the threshold, the determination unit 26 determines that the capacity of the battery 10 has not deteriorated to the point where it should be replaced. On the other hand, if the guaranteed SOH is lower than the threshold, the determination unit 26 determines that there is a possibility that the capacity of the battery 10 has deteriorated to the point where it should be replaced.

[0044] For example, suppose the initial capacity or nominal capacity of battery 10 is 100 Ah, the lower limit SOC (i.e., X shown in FIG. 5) representing the lower end of the flat region of the SOC-OCV curve is 20 percent, and the threshold value used by determination unit 26 is 60 percent. Furthermore, suppose the integrated current Y when discharging from the fully charged state to the second state of charge is 50 Ah. In this case, the guaranteed SOH is 62.5 percent, which is greater than the threshold value. Therefore, determination unit 26 determines that the capacity of battery 10 has not deteriorated to the point where battery 10 should be replaced.

[0045] As described above, the battery state estimation method according to the embodiment of the present invention can determine whether the capacity of the battery 10 has deteriorated to the extent that replacement is required, even if the battery 10 is not discharged to an SOC below the flat region of the SOC-OCV curve. That is, even if the battery 10 is not discharged from an SOC state higher than the flat region to an SOC state lower than the flat region, it can determine whether the capacity of the battery 10 has deteriorated to the extent that replacement is required. Therefore, compared to a method of estimating the SOH based on the SOC (e.g., the method shown in FIG. 3(c)), it is possible to more frequently determine whether the capacity of the battery 10 has deteriorated to the extent that replacement is required.

[0046] FIG. 7 shows an example of a method for compensating for low accuracy in SOH estimation. In FIG. 7, circles represent SOH estimated for a single measurement. Each SOH value is obtained, for example, by the method described with reference to FIG. 3. That is, the SOH is obtained using an SOC estimated based on the OCV of the battery 10.

[0047] Here, when the SOC-OCV curve of the battery 10 has a flat region, as described above, calculating the SOH using the SOC estimated based on the OCV can result in a large error. Figure 7(a) shows a state in which the SOH estimation accuracy is poor and variability occurs.

[0048] In an embodiment of the present invention, the control unit 20 estimates the SOH of the battery 10 and calculates the guaranteed SOH. Here, the actual SOH of the battery 10 will never be lower than the guaranteed SOH. Therefore, as shown in FIG. 7(b), when the estimated SOH value is lower than the guaranteed SOH, the control unit 20 may correct the estimated value to the guaranteed SOH. By performing such correction, for example, when determining the state of the battery 10 based on the average of multiple SOH estimates obtained by multiple measurements, the influence of estimation errors can be mitigated.

[0049] 8 is a flowchart showing an example of a battery state estimation method according to an embodiment of the present invention. The processing of this flowchart may start, for example, when charging of the battery 10 is completed.

[0050] In S1, the control unit 20 determines whether the battery 10 is fully charged. Whether the battery 10 is fully charged is determined, for example, based on the voltage of the battery 10 detected by the voltage sensor V. When the battery 10 is fully charged, in S2 and S3, the current integrator 22 integrates the current discharged from the battery 10 to calculate the integrated current amount. When the discharge of the battery 10 is completed, the control unit 20 proceeds to S4. The "end of discharge" is not particularly limited, and may be, for example, when the next charging operation is started. Alternatively, when the power supply device 100 shown in FIG. 4 is mounted on an electric vehicle, it may be when the key switch of the electric vehicle is turned off.

[0051] In S4, the guaranteed capacity estimation unit 25 estimates the guaranteed capacity of the battery 10 based on the lower limit SOC, which represents the lower end of the flat region of the SOC-OCV curve, and the current integration amount calculated in S2 and S3. In the above-mentioned embodiment, this calculation is performed using equation (3). In S5, the determination unit 26 calculates the guaranteed SOH from the guaranteed capacity and initial capacity obtained in S4. In the above-mentioned embodiment, this calculation is performed using equation (6).

[0052] In S6, the determination unit 26 determines whether the guaranteed SOH is higher than a threshold value. This threshold value is, for example, an SOH corresponding to a state in which the battery 10 has deteriorated to the point where it should be replaced. If the guaranteed SOH is higher than the threshold value, the determination unit 26 determines in S7 that the battery 10 has not deteriorated to the point where it should be replaced. On the other hand, if the guaranteed SOH is lower than the threshold value, the determination unit 26 determines in S8 that there is a possibility that the battery 10 has deteriorated to the point where it should be replaced.

[0053] Note that if the accumulated current amount calculated in S2 and S3 is small, it may not be possible to accurately determine whether the capacity of the battery 10 has deteriorated. For example, when the next charge is performed after only a short period of use of the battery 10 from a fully charged state, the accumulated current amount calculated in S2 and S3 will be small, and the guaranteed SOH calculated by equation (6) will also be small. In this case, even if the capacity of the battery 10 has not deteriorated, the determination result in S6 may be "No." Therefore, the control unit 20 may repeatedly execute the procedure shown in FIG. 8, and determine that "the battery 10 has deteriorated" when the determination result in S6 is "No" a predetermined number of times in succession.

[0054] On the other hand, when the battery 10 is discharged from a fully charged state to a state equal to or lower than the lower limit SOC, the guaranteed SOH calculated by equation (6) may exceed 100%. Therefore, the procedure shown in FIG. 8 is effective when the battery 10 is discharged from a fully charged state to a second state of charge that is higher than the lower limit SOC. Even in this case, however, the determination result in S6 is "Yes," and it is determined that the battery 10 is not degraded. Furthermore, the control unit 20 can estimate the SOH of the battery 10 based on the SOC in parallel with the procedure shown in FIG. 8. When the battery 10 is discharged from a fully charged state to a state equal to or lower than the lower limit SOC, the SOH of the battery 10 can be accurately estimated based on the SOC, as described with reference to FIG. 3(c).

[0055] <Other embodiments> In the above-described embodiment, the guaranteed SOH is determined to be higher than the threshold value based on the accumulated current when discharging the battery 10 from the fully charged state to the second state of charge. However, the present invention is not limited to this method. Specifically, the control unit 20 may determine whether the guaranteed SOH is higher than the threshold value based on the accumulated current when discharging the battery 10 from an arbitrary first state of charge other than the fully charged state to the second state of charge. In this case, the first state of charge may be closer to the fully charged state than the upper limit of the flat region, as shown in FIG. 9(a). Alternatively, the first state of charge may be any state of charge within the flat region, as shown in FIG. 9(b). However, the closer the first state of charge is to the fully charged state, the more accurate the determination of whether the guaranteed SOH is higher than the threshold value.

[0056] In the above embodiment, the guaranteed SOH is determined to be higher than a threshold value based on the accumulated current when the battery 10 is discharged. However, the present invention is not limited to this method. For example, the control unit 20 may determine whether the guaranteed SOH is higher than a threshold value based on the accumulated current when the battery 10 is charged from the third state of charge to the fourth state of charge. In this case, the fourth state of charge (i.e., the state of charge at the end of the charging operation) is preferably a fully charged state, but does not have to be a fully charged state. The end of the charging operation is detected, for example, when the voltage of the battery 10 exceeds a predetermined threshold value or when the charging plug is unplugged. [Explanation of symbols]

[0057] 10 batteries 20 Control Unit 21 Memory 22 Current integration section 23 SOC Estimation Department 24 SOH Estimation Department 25 Guaranteed capacity estimation unit 26 Judgment section 100 Power supply

Claims

1. A battery having a flat region of a State of Charge (SOC)-Open Circuit Voltage (OCV) curve; a current sensor for detecting a current of the battery; a current integrator that calculates an integrated current amount when the battery is discharged from a first state of charge to a second state of charge; a guaranteed capacity estimation unit that estimates a guaranteed capacity of the battery by adding, to the integrated current amount, a correction value obtained by dividing the product of a lower limit SOC that indicates a lower limit of the flat region and the integrated current amount by a result of subtracting the lower limit SOC from 100 percent; a determination unit that determines whether a guaranteed SOH (State of Health) represented by a ratio of the guaranteed capacity to an initial capacity or a nominal capacity of the battery is higher than a predetermined threshold; A power supply device comprising:

2. The second state of charge is a state in which the charging rate is higher than the lower limit SOC.

2. The power supply device according to claim 1.

3. a voltage sensor for detecting the voltage of the battery; an SOC estimation unit that estimates an SOC corresponding to the voltage of the battery using the SOC-OCV curve; an SOH estimation unit that estimates an SOH of the battery based on the estimated SOC obtained by the SOC estimation unit, When the estimated SOH obtained by the SOH estimating unit is lower than the guaranteed SOH, the estimated SOH is corrected to the guaranteed SOH.

2. The power supply device according to claim 1.

4. the current integrator calculates an integrated amount of charging current when the battery is charged from a third state of charge to a fourth state of charge; The guaranteed capacity estimation unit estimates the guaranteed capacity by adding a lower limit SOC representing a lower limit of the flat region and a correction value calculated based on the integrated amount of charging current to the integrated amount of charging current.

2. The power supply device according to claim 1.

5. A method for estimating the state of a battery having a flat region of a State of Charge (SOC)-Open Circuit Voltage (OCV) curve, comprising: calculating an integrated current as the battery is discharged from a first state of charge to a second state of charge; a correction value obtained by dividing the product of a lower limit SOC representing a lower limit of the flat region and the current integrated amount by a result of subtracting the lower limit SOC from 100 percent, thereby estimating the guaranteed capacity of the battery, to the current integrated amount; Determining whether the ratio of the guaranteed capacity to the initial or nominal capacity of the battery is higher than a predetermined threshold. A battery state estimation method comprising:

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