Capacity Estimation Device and Capacity Estimation Method

Abstract

A capacity estimation device (50) for estimating the capacity of a power storage unit (41) when charging the power storage unit comprises: a control unit (54) that reduces an average current indicative of the average value, per unit time period, of a charging current flowing in the power storage unit in a predetermined current restriction section after the start of charging of the power storage unit; and an estimation unit (55) that estimates the capacity on the basis of the voltage change rate of the power storage unit after the current restriction section or within the current restriction section.

Description

Cross - reference to related applications

[0001] This application is based on Japanese Application No. 2022 - 098233 filed on June 17, 2022, the contents of which are incorporated herein by reference.

Technical Field

[0002] The present disclosure relates to a capacity estimation device and a capacity estimation method.

Background Art

[0003] Conventionally, there has been a disclosure of estimating the capacity of a secondary battery constituting a battery pack. For example, the disclosure described in Patent Document 1 detects a singular point at which the voltage change rate of the secondary battery reaches a maximum value, and estimates the capacity corresponding to the detected singular point as the capacity of the secondary battery.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] When charging a secondary battery, there may be a portion with a high capacity and a portion with a low capacity. In a state where such non - uniform capacity (charging unevenness) occurs, the capacity at the time when the voltage change rate reaches the maximum value may deviate from the specific capacity, and the estimation accuracy of the capacity may decrease.

[0006] The present disclosure has been made in view of the above problems, and an object thereof is to provide a capacity estimation device and a capacity estimation method capable of accurately estimating the capacity of a power storage unit.

[0007] The present disclosure is a capacity estimation device that estimates the capacity of the power storage unit when charging the power storage unit, A control unit that reduces an average current indicating an average value per unit time of a charging current flowing through the power storage unit in a predetermined current limit section after charging of the power storage unit is started; And an estimation unit that estimates the capacity based on a voltage change rate of the power storage unit after or within the current limit section.

[0008] By reducing the average current in a current limit section where charging unevenness is likely to occur, the occurrence of charging unevenness is suppressed. Thereby, it is possible to suppress the deviation of the capacity when the voltage change rate reaches the maximum value from the specified capacity, and it becomes possible to accurately estimate the capacity of the power storage unit.

[0009] The present disclosure is A capacity estimation method for estimating the capacity of a power storage unit when charging the power storage unit, In a predetermined current limit section after charging of the power storage unit is started, the average current indicating the average value per unit time of the charging current flowing through the power storage unit is reduced, The capacity is estimated based on the voltage change rate of the power storage unit after or within the current limit section.

[0010] By reducing the average current in a current limit section where charging unevenness is likely to occur, the occurrence of charging unevenness is suppressed. Thereby, it is possible to suppress the deviation of the capacity when the voltage change rate reaches the maximum value from the specified capacity, and it becomes possible to accurately estimate the capacity of the power storage unit.

Brief Description of Drawings

[0011] The above objects, other objects, features, and advantages of the present disclosure will become clearer from the following detailed description with reference to the accompanying drawings. The drawings are

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Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the description of the drawings, the same parts are denoted by the same reference numerals and the description thereof is omitted.

[0013] <First Embodiment> Referring to FIG. 1, a configuration example of a battery control device 100 according to the first embodiment will be described. As shown in FIG. 1, the battery control device 100 includes a rotating electric machine 10, an inverter 20, a voltage sensor 30, a current sensor 31, first to fourth relay switches 32 to 35, a battery 40, and a BMU (Battery Management Unit) 50. The battery control device 100 monitors, as an example, the capacity and charge / discharge state of the battery 40. In the present embodiment, the capacity of the battery 40 is the amount of electricity [Ah] that the battery 40 can discharge, and may be expressed as the remaining amount.

[0014] An example of the battery 40 is an assembled battery configured by connecting a plurality of lithium-ion batteries 41 in series. The lithium-ion battery 41 is a secondary battery using lithium as a charge carrier, and a battery using lithium iron phosphate as a positive electrode active material and graphite (carbon) as a negative electrode active material is used. The use of the battery 40 is not particularly limited, but the battery 40 is mounted on, for example, an electric vehicle or a hybrid vehicle, and the electric power stored in the battery 40 is used for the running of these vehicles. The lithium-ion battery 41 constituting the battery 40 is sometimes called a battery cell.

[0015] The battery 40 is connected to the rotating electric machine 10 via the inverter 20. The rotating electric machine 10 inputs and outputs electric power to and from the battery 40, and during power running, applies a driving force to the vehicle by the electric power supplied from the battery 40. Further, during regeneration, the rotating electric machine 10 generates electricity using the deceleration energy of the vehicle and outputs electric power to the battery 40.

[0016] The voltage sensor 30 detects the voltage across each terminal of the lithium-ion battery 41 that constitutes the battery 40, and detects the battery voltage VB obtained by summing these terminal voltages. The current sensor 31 is provided on the connection line LC that connects the battery 40 and the inverter 20, and detects the magnitude and direction of the charge and discharge current IS, which is the current flowing into and out of the battery 40. Although not shown in the figure, the battery control device 100 also includes a temperature sensor. The temperature sensor detects the temperature of the lithium-ion battery 41. The detection values of each sensor are input to the BMU 50.

[0017] The battery 40 is configured to be connectable to an external charger 200 outside the vehicle via first and second external charging terminals TA and TB. The external charger 200 is, for example, a DC rapid charger. When the external charger 200 is connected to the first and second external charging terminals TA and TB of the battery 40, the battery 40 is charged at a constant current or at a constant voltage by the high-voltage DC power input from the external charger 200.

[0018] The first and second external charging terminals TA and TB are connected to the connection line LC via first and second charging paths LA and LB. Specifically, the first external charging terminal TA is connected via the first charging path LA to a first contact point PA between the positive terminal of the battery 40 and the inverter 20 on the connection line LC. The second external charging terminal TB is connected via the second charging path LB to a second contact point PB between the negative terminal of the battery 40 and the inverter 20 on the connection line LC.

[0019] The first relay switch 32 is provided between the first contact point PA and the inverter 20 on the connection line LC, and the second relay switch 33 is provided between the second contact point PB and the inverter 20 on the connection line LC. The first and second relay switches 32 and 33 switch the connection state between the battery 40 and the rotating electric machine 10. Also, the third relay switch 34 is provided in the first charging path LA, and the fourth relay switch 35 is provided in the second charging path LB. The third and fourth relay switches 34 and 35 switch the connection state between the battery 40 and the external charger 200.

[0020] The BMU50 is a microcomputer composed of a CPU, a ROM, a RAM, and an input / output interface for inputting and outputting various signals, etc., and has various functions. The BMU50 is connected to the first to fourth relay switches 32 to 35, and switches the connection states of the first to fourth relay switches 32 to 35 based on the capacity of the battery 40. The BMU50 is communicably connected to the travel control ECU61 via the in-vehicle network interface 60. The travel control ECU61 controls the inverter 20 to drive the rotating electric machine 10.

[0021] The functions provided by the BMU50 can be provided by software recorded in a physical memory device and a computer that executes it, software only, hardware only, or a combination thereof. For example, when the microcomputer is provided by an electronic circuit that is hardware, it can be provided by a digital circuit including a number of logic circuits or an analog circuit. For example, the microcomputer executes a program stored in a non-transitory tangible storage medium as a storage unit provided therein. When the program is executed, a method corresponding to the program is executed, and functions corresponding to the program are realized. The storage unit is, for example, a non-volatile memory. Note that the program stored in the storage unit can be updated via a network such as the Internet, for example.

[0022] In the present embodiment, the BMU50 also functions as a capacity estimation device that estimates the capacity of the lithium-ion battery 41. The BMU50 estimates the capacity of the lithium-ion battery 41 based on the detection values input from the respective sensors. The BMU50 includes an arithmetic unit 51, a determination unit 52, a setting unit 53, a control unit 54, and an estimation unit 55 as functions for processing the detection values input from the respective sensors. Details of these functions will be described later.

[0023] As a method for estimating the capacity of the lithium-ion battery 41, a method using the SOC-OCV characteristic indicating the correlation between the SOC (State Of Charge) indicating the state of charge of the lithium-ion battery 41 and the open circuit voltage OCV (Open Circuit Voltage) is known. The open circuit voltage OCV is the voltage between both terminals in a state where no load is applied to the lithium-ion battery 41 (a state where the circuit of the lithium-ion battery 41 is open). SOC [%] is represented by (current capacity / full capacity) × 100 of the lithium-ion battery 41, and represents the ratio of the capacity of the lithium-ion battery 41 to the full capacity.

[0024] In the lithium-ion battery 41 using active materials such as lithium iron phosphate and graphite, the open circuit voltage OCV is stable over a wide range of SOC. The region where the change in the open circuit voltage OCV is small is called the plateau region. In the plateau region, the voltage change rate of the open circuit voltage OCV with respect to the capacity of the lithium-ion battery 41 is equal to or less than a predetermined change rate. In the plateau region, it may be difficult to calculate the SOC of the lithium-ion battery 41 using the SOC-OCV characteristic.

[0025] FIG. 2 is a graph showing the relationship between the capacity Q and the OCV of the lithium-ion battery 41 before and after deterioration. Here, "initial" means when it is new. The vertical axis of FIG. 2 indicates the OCV, and the horizontal axis indicates the capacity Q [Ah] of the lithium-ion battery 41. The symbols PR1, PR21, and PR22 in FIG. 2 indicate the plateau regions. The plateau regions PR1 and PR22 indicate the plateau regions after the lithium-ion battery 41 has deteriorated, and the plateau region PR21 indicates the plateau region when it is new. The plateau region after deterioration and the plateau region when it is new partially overlap (plateau region PR22). As shown in FIG. 2, between the plateau region PR1 and the plateau region PR22, the voltage change rate of the open-circuit voltage OCV with respect to the capacity of the lithium-ion battery 41 is larger than the voltage change rate in the plateau regions PR1 and PR22. Between the plateau region PR1 and the plateau region PR22, when the capacity is a specific value (hereinafter referred to as the specific capacity A), the voltage change rate takes a maximum value. Further, the specific capacity A of the lithium-ion battery 41 when the voltage change rate takes a maximum value is almost the same and does not change between the initial lithium-ion battery 41 and the lithium-ion battery 41 after deterioration when charging over time. Therefore, when the voltage change rate takes a maximum value, it is possible to estimate the specific capacity A at that time as the capacity of the lithium-ion battery 41. The specific capacity A is the capacity determined by the structural change of the negative electrode of the lithium-ion battery 41. ΔQ in FIG. 2 indicates the capacity that decreases due to the deterioration of the lithium-ion battery 41.

[0026] Next, with reference to FIG. 3, the conditions for estimating the capacity of the lithium-ion battery 41 will be described. FIG. 3 is a graph showing voltage thresholds. The vertical axis of FIG. 3 indicates the voltage of the lithium-ion battery 41, and the horizontal axis indicates the integrated value of the charging current flowing through the lithium-ion battery 41. The integrated value of the charging current flowing through the lithium-ion battery 41 may be simply referred to as the current integrated value hereinafter. As shown in FIG. 3, when the charging of the lithium-ion battery 41 is started, the current integrated value increases, and accordingly, the voltage of the lithium-ion battery 41 rises. In the present embodiment, as a condition for estimating the capacity of the lithium-ion battery 41, it is a condition that the voltage of the lithium-ion battery 41 at the start of charging is higher than the voltage threshold V1. An example of the method for setting the voltage threshold V1 will be described with reference to FIG. 4.

[0027] FIG. 4 is a graph showing the relationship between the capacity of the lithium-ion battery 41 and the OCV, similar to FIG. 2. As shown in FIG. 4, the voltage change rate of the OCV of the lithium-ion battery 41 with respect to the capacity takes a maximum value due to the structural change of the negative electrode of the lithium-ion battery 41 between the two plateau regions PR1 and PR2 where the voltage change rate of the OCV is below a predetermined change rate. Therefore, when the voltage of the lithium-ion battery 41 is lower than that of the plateau region PR1 with a lower OCV, the maximum value of the voltage change rate of the OCV due to the structural change of the negative electrode of the lithium-ion battery 41 does not occur. Thus, as shown in FIG. 4, as an example, the voltage threshold V1 is set to the lowest voltage in the plateau region PR1 among the two plateau regions PR1 and PR2.

[0028] FIG. 5 is a graph showing a mode of detecting a specific capacity A based on the maximum value of the differential value of the voltage of the lithium-ion battery 41. The vertical axis in FIG. 5 indicates the differential value of the voltage of the lithium-ion battery 41, and the horizontal axis indicates the current integrated value. When the BMU 50 determines that the voltage of the lithium-ion battery 41 is higher than the voltage threshold V1, the BMU 50 calculates the differential value of the voltage of the lithium-ion battery 41. Specifically, the BMU 50 calculates the differential value of the voltage based on the current integrated value. The differential value of the voltage here indicates the voltage change rate with respect to the capacity of the lithium-ion battery 41. The BMU 50 determines whether or not the differential value of the voltage based on the current integrated value takes a maximum value. As shown in FIG. 5, when the differential value of the voltage based on the current integrated value takes a maximum value, the BMU 50 estimates that the capacity of the lithium-ion battery 41 at that time is the specific capacity A. Note that the capacity in FIG. 5 corresponds to the capacity between two minimum values.

[0029] Incidentally, when charging a secondary battery such as the lithium-ion battery 41, there may be a high-capacity portion and a low-capacity portion. In this embodiment, such non-uniformity of the capacity is referred to as "charging unevenness". Note that non-uniformity of the capacity may also occur during discharging, but here, the charging scenario will be described and the description of the discharging scenario will be omitted. The inventors have focused on the fact that in a state where charging unevenness occurs, the capacity at the time when the voltage change rate takes a maximum value during charging deviates from the specific capacity A. This point will be described with reference to FIG. 6. FIG. 6 is a graph showing a mode in which the maximum value of the voltage change rate corresponding to the specific capacity A deviates. As shown in FIG. 6, when rapid charging starts from a state where the capacity of the lithium-ion battery 41 is low (for example, 20%), the capacity at the time when the voltage change rate takes a maximum value shifts to the low-capacity side from the specific capacity A. In this case, if the capacity of the lithium-ion battery 41 at the time when the voltage change rate takes a maximum value is estimated as the specific capacity A, the estimated capacity will deviate from the correct capacity. The main causes of the deviation shown in FIG. 6 include that a large current such as rapid charging flows through the lithium-ion battery 41 and charging unevenness occurs, and the generated charging unevenness expands.

[0030] Next, with reference to FIG. 7, one cause of the expansion of charging unevenness will be described. FIG. 7 shows the lithium-ion battery 41 represented as a schematic equivalent circuit 70. The equivalent circuit 70 is composed of a part 71 and a part 72. Both parts have resistance and OCV. Consider a case where the OCV difference between these parts 71 and 72 is minute. The fact that the OCV difference is minute means that the current flowing between the parts is minute. When charging in this state, the charging current tends to be biased to the part with lower resistance, and only the capacity of the part with lower resistance becomes unidirectionally higher. As a result, the charging unevenness expands. To prevent this expansion of charging unevenness, when the current flowing between the parts is minute, a time for eliminating the charging unevenness is ensured. That is, in the present embodiment, during charging, in the capacity range where the OCV difference between the parts becomes minute, the average current flowing into the lithium-ion battery 41 is reduced. Hereinafter, the "capacity range where the OCV difference becomes minute" will be referred to as the intermediate SOC range. The intermediate SOC range is part or all of the plateau region PR1 in FIG. 4. For detailed control, it will be described with reference to FIG. 8.

[0031] The upper graph in FIG. 8 shows the relationship between the voltage change rate of the lithium-ion battery 41 and the capacity of the lithium-ion battery 41. The lower graph in FIG. 7 shows the relationship between the average current flowing into the lithium-ion battery 41 and the capacity of the lithium-ion battery 41. After the charging of the lithium-ion battery 41 is started, the BMU 50 determines whether the capacity of the lithium-ion battery 41 is the capacity in the intermediate SOC range. For this determination, the voltage change rate of the lithium-ion battery 41 is used. Specifically, as shown in FIG. 8, the BMU 50 determines whether the voltage change rate is equal to or less than a first predetermined value (β). If the voltage change rate is β or less, the BMU 50 determines that the capacity of the lithium-ion battery 41 is the capacity in the intermediate SOC range. As the value of β, the value of the voltage change rate between the plateau region PR1 and the plateau region PR2 shown in FIG. 9 may be adopted.

[0032] In the example shown in FIG. 8, after the start of charging, the voltage change rate gradually decreases. At the timing when the capacity reaches T1, the voltage change rate becomes β or less, and at the timing when the capacity reaches T2, the voltage change rate becomes greater than β. T1 < T2. For the sake of explanation here, T1 and T2 are referred to as timing T1 and timing T2, respectively. Timing T1 means the time when the capacity of the lithium-ion battery 41 reaches T1. The same applies to timing T2. As shown in FIG. 8, the BMU 50 reduces the average current flowing through the lithium-ion battery 41 at timing T1. The "average current" in the present embodiment is defined as the average value of the charging current per unit time. "Reducing the average current" means reducing it compared to the average current before timing T1.

[0033] The BMU 50 maintains the state of reducing the average current until the voltage change rate becomes greater than β. That is, the BMU 50 reduces the average current in the current limiting section 80 from timing T1 to timing T2. Then, the BMU 50 increases the average current that was reduced at the timing when the voltage change rate became greater than β, that is, at timing T2. "Increasing the average current" means increasing it compared to the average current in the current limiting section 80. In the example shown in FIG. 8, the average current after timing T2 is described as being the same magnitude as the average current before timing T1, but it is not limited to this. The average current after timing T2 may be greater than or less than the average current before timing T1 as long as it is greater than the average current in the current limiting section 80.

[0034] In this way, the BMU 50 reduces the average current flowing through the lithium-ion battery 41 in the current limiting section 80 where the voltage change rate is β or less, that is, in the intermediate SOC range where charging unevenness is likely to occur. As a result, even if charging unevenness occurs, it is possible to gain the time required for the charging unevenness to naturally disappear. As a result, the occurrence of charging unevenness is suppressed. Thereby, the deviation described in FIG. 6 is suppressed, and highly accurate capacity estimation becomes possible.

[0035] The BMU50 estimates the capacity of the lithium-ion battery 41 after the current limiting section 80. As described with reference to FIG. 5, the BMU50 determines whether or not the rate of change of the voltage of the lithium-ion battery 41 has reached a maximum value. When the rate of change of the voltage reaches a maximum value, the BMU50 estimates the capacity corresponding to the maximum value as the capacity of the lithium-ion battery 41. The BMU50 may be expressed as estimating the capacity corresponding to the interval between two minimum values as the capacity of the lithium-ion battery 41. Also, the BMU50 may be expressed as estimating the capacity corresponding to the maximum value between two minimum values as the capacity of the lithium-ion battery 41. As shown in FIG. 8, the BMU50 may be expressed as estimating the capacity of the lithium-ion battery 41 in the section from when the rate of change of the voltage turns from decreasing to increasing as indicated by reference numeral 81 until it turns from decreasing to increasing as indicated by reference numeral 82.

[0036] Next, with reference to the flowchart of FIG. 10, an operation example of the BMU50 will be described. The process shown in FIG. 10 is repeatedly executed at a predetermined time interval.

[0037] In step S101, the BMU50 determines whether or not charging of the lithium-ion battery 41 (battery 40) has started. The determination method is not limited. For example, the BMU50 may determine that charging has started when it receives a signal indicating that the off-vehicle charger 200 is connected to the vehicle. When the BMU50 determines that charging has started (YES in step S101), the process proceeds to step S102. On the other hand, when the BMU50 determines that charging has not started (NO in step S101), the process is repeatedly executed.

[0038] In step S102, the BMU50 determines whether or not the voltage of the lithium-ion battery 41 is higher than the voltage threshold V1 (see FIG. 3). When the BMU50 determines that the voltage of the lithium-ion battery 41 is higher than the voltage threshold V1 (YES in step S102), the process proceeds to step S103. On the other hand, when the BMU50 determines that the voltage of the lithium-ion battery 41 is less than or equal to the voltage threshold V1 (NO in step S102), the BMU50 ends the process.

[0039] In step S103, the BMU 50 calculates the voltage change rate of the lithium-ion battery 41. The process proceeds to step S104, and the BMU 50 determines whether the voltage change rate is less than or equal to β (see FIG. 8). When the BMU 50 determines that the voltage change rate is less than or equal to β, the process proceeds to step S105. The process in step S104 corresponds to the determination unit 52 of the BMU 50.

[0040] In step S105, the BMU 50 sets a current limit section 80 that reduces the average current flowing through the lithium-ion battery 41 at the timing T1 when the voltage change rate becomes less than or equal to β. The state where the average current is reduced is maintained until the voltage change rate becomes greater than β. The process in step S105 corresponds to the setting unit 53 and the control unit 54 of the BMU 50. As charging progresses, when the BMU 50 determines that the voltage change rate has become greater than β, the BMU 50 ends the current limit section 80, releases the current limit, and increases the reduced average current (step S106).

[0041] The process proceeds to step S107, and the BMU 50 determines whether the voltage change rate of the lithium-ion battery 41 has reached a maximum value (see FIG. 8). If the BMU 50 determines that the voltage change rate of the lithium-ion battery 41 has reached a maximum value (YES in step S107), the process proceeds to step S108. On the other hand, if the BMU 50 determines that the voltage change rate of the lithium-ion battery 41 has not reached a maximum value (NO in step S107), the process is repeatedly executed.

[0042] In step S108, the BMU 50 estimates the capacity corresponding to the maximum value as the capacity of the lithium-ion battery 41. The process in step S108 corresponds to the estimation unit 55 of the BMU 50.

[0043] In step S109, the BMU 50 calculates an integrated current value by integrating the current and time from when the voltage change rate reaches its maximum value. The process proceeds to step S110, where the BMU 50 determines whether the state of charge of the lithium-ion battery 41 is fully charged. If the BMU 50 determines that the state of charge of the lithium-ion battery 41 is fully charged (YES in step S110), the process proceeds to step S111. On the other hand, if the BMU 50 determines that the state of charge of the lithium-ion battery 41 is not fully charged (NO in step S110), the process is repeatedly executed.

[0044] In step S111, the BMU 50 calculates the SOH (State Of Health) indicating the degradation state of the lithium-ion battery 41. SOH [%] is represented by (current full capacity / full capacity of a new battery) × 100, and represents the ratio of the full capacity of the current lithium-ion battery 41 to the full capacity of a new lithium-ion battery 41. An example of the calculation method of SOH will be described. The BMU 50 adds the integrated current value calculated in step S109 to the capacity of the lithium-ion battery 41 estimated in step S108, and calculates the capacity at full charge as the current full capacity. Since the full capacity of a new battery is known, once the current full capacity is calculated, the SOH is calculated by the above formula. The process in step S111 corresponds to the calculation unit 51 of the BMU 50.

[0045] According to the first embodiment described in detail above, the following effects can be obtained.

[0046] After charging of the lithium ion battery 41 (power storage unit) starts, in a predetermined current limit section 80, the BMU 50 (control unit 54) reduces an average current indicating an average value per unit time of a charging current flowing through the lithium ion battery 41. The BMU 50 (estimation unit 55) estimates the capacity based on a voltage change rate of the lithium ion battery 41 after or within the current limit section. By reducing the average current in the current limit section 80 where charge unevenness is likely to occur, even if charge unevenness occurs, it becomes possible to gain time necessary for the charge unevenness to naturally disappear. As a result, generation of charge unevenness is suppressed. Thereby, the deviation described with reference to FIG. 6 is suppressed, and it becomes possible to accurately estimate the capacity of the lithium ion battery 41.

[0047] The BMU 50 sets the current limit section 80 based on a parameter that changes by charging the lithium ion battery 41. In FIG. 8, it was described that the BMU 50 sets the current limit section 80 using a voltage change rate (β) of the lithium ion battery 41. By using β, it becomes possible to set the current limit section 80 in an intermediate SOC range where charge unevenness is likely to occur. However, the parameter for limiting the average current is not limited to the voltage change rate. The parameter for limiting the average current only needs to be an index that can be grasped as being in the middle of charging. For example, the BMU 50 may reduce the average current when the voltage during charging is lower than a predetermined value, may reduce the average current when the integrated current amount during charging is lower than a predetermined value, or may reduce the average current when the charging time is shorter than a predetermined value. The voltage change rate, voltage, integrated current amount, and charging time during charging correspond to parameters that change by charging the lithium ion battery 41.

[0048] BMU50 sets the starting point of the current limit section 80 at the point where the voltage change rate becomes equal to or less than a first predetermined value, and sets the ending point of the current limit section 80 at the point where the voltage change rate becomes greater than the first predetermined value. An example of the first predetermined value is β. As described with reference to FIG. 8, BMU50 sets the timing T1 at which the voltage change rate becomes equal to or less than β as the starting point of the current limit section 80, and sets the timing T2 at which the voltage change rate becomes greater than β as the ending point of the current limit section 80. By using β in this way, it becomes possible to set the current limit section 80 in the intermediate SOC range where charge unevenness is likely to occur.

[0049] BMU50 estimates the capacity of the lithium-ion battery 41 corresponding to the interval between two minimum values of the voltage change rate after or within the current limit section. Since the deviation is suppressed by reducing the average current, it becomes possible to accurately estimate the capacity of the lithium-ion battery 41. In FIG. 8, BMU50 estimates the capacity of the lithium-ion battery 41 after the current limit section.

[0050] BMU50 calculates the degradation state of the lithium-ion battery 41 based on the estimated capacity of the lithium-ion battery 41, the current integration value obtained by integrating the charging current and time from when the capacity was estimated until the lithium-ion battery 41 satisfies the full charge condition, and the full capacity of the lithium-ion battery 41 when it is new. According to the present embodiment, by calculating the degradation state of the lithium-ion battery 41 using the accurately estimated capacity of the lithium-ion battery 41, a highly accurate degradation state can be obtained.

[0051] <Second Embodiment> Next, the second embodiment will be described with reference to FIGS. 11 to 13. In the flowchart of FIG. 13, the processes of steps S201 to S202, steps S204 to S207, and steps S209 to S213 are the same as the processes of steps S101 to S102, steps S103 to S106, and steps S107 to S111 shown in FIG. 10, so the description thereof will be omitted. Hereinafter, the description will focus on the differences.

[0052] When determining that the voltage change rate of the lithium-ion battery 41 with respect to the capacity reaches a maximum value, if the current for charging the lithium-ion battery 41 is greater than a predetermined current, it becomes difficult to discriminate the maximum value. In contrast, as shown in FIG. 11, during the charging of the lithium-ion battery 41, the disclosure focuses on the fact that the voltage change rate of the real part Zre of the impedance of the lithium-ion battery 41 with respect to the capacity changes significantly at a specific capacity A where the voltage change rate reaches a maximum value. Note that the impedance can be calculated based on the amplitude of the alternating voltage and the amplitude of the alternating current.

[0053] The reason for the change in the voltage change rate of the real part Zre of the impedance is that as the stage of the negative electrode changes, the reaction heat during charging decreases, and due to the decrease in the reaction heat, the temperature rise becomes moderate, and due to the moderate temperature rise, the decrease in the real part Zre of the impedance also becomes moderate. Therefore, the BMU 50 may determine that the voltage change rate has reached a maximum value when the voltage change rate of the impedance of the lithium-ion battery 41 with respect to the capacity changes beyond a predetermined degree.

[0054] An example of a specific method will be described. First, the BMU 50 calculates the real part Zre of the impedance of the lithium-ion battery 41. Subsequently, the BMU 50 calculates a differential value based on the current integrated value of the real part Zre of the impedance (the voltage change rate of the impedance of the lithium-ion battery 41 with respect to the capacity) (step S203 in FIG. 13). The BMU 50 determines whether the voltage change rate of the real part Zre of the impedance has changed significantly (step S208 in FIG. 13). Specifically, as shown in FIG. 12, the BMU 50 determines whether the differential value based on the current integrated value of the real part Zre of the impedance has changed by a predetermined value x or more. According to such a configuration, even when the current for charging the lithium-ion battery 41 is greater than a predetermined current, it is possible to determine that the voltage change rate of the lithium-ion battery 41 with respect to the capacity has reached a maximum value. The predetermined value x corresponds to a fifth predetermined value.

[0055] Note that instead of the real part Zre of the impedance of the lithium-ion battery 41, the imaginary part Zim of the impedance, the absolute value of the impedance, or the phase of the impedance can also be used. Further, instead of the voltage change rate of the real part Zre of the impedance, the change rate of the temperature of the lithium-ion battery 41 can also be used. That is, when the change rate of the temperature related to the lithium-ion battery 41 or the voltage change rate of the impedance of the lithium-ion battery 41 changes exceeding a predetermined value x, the BMU 50 may estimate that the voltage change rate has reached a maximum value.

[0056] <Modification Example> A part of the configuration of the above embodiment may be modified. Hereinafter, a modification example will be described.

[0057] · In the above embodiment, the power storage unit has been described as being configured by the lithium-ion battery 41, but it is not limited thereto and may be configured by a capacitor.

[0058] · The end point of the current limiting section 80, that is, the timing for increasing the average current is not limited to the timing T2. The timing for increasing the average current only needs to satisfy the condition that the voltage change rate is greater than β. For example, as shown in FIG. 14, the BMU 50 may increase the average current at the timing T3 immediately before the voltage change rate reaches the maximum value. In other words, the BMU 50 may set the point where the voltage change rate is greater than the first predetermined value and before the voltage change rate reaches the maximum value as the end point of the current limiting section 80. Although T3 shown in FIG. 14 indicates the capacity, for convenience of explanation, it is described as the timing. The timing T3 means the time when the capacity of the lithium-ion battery 41 reaches T3. At the timing T3, since the voltage change rate is greater than β, the condition is satisfied. By keeping the average current small until immediately before the voltage change rate reaches the maximum value, it becomes possible to gain more time necessary for naturally eliminating the charging unevenness. In FIG. 14, the BMU 50 estimates the capacity of the lithium-ion battery 41 after the current limiting section.

[0059] · The starting point of the current limit section 80, that is, the timing to reduce the average current, is not limited to timing T1. The timing to reduce the average current only needs to satisfy the condition that the voltage change rate is β or less. For example, as shown in FIG. 15, the BMU 50 may reduce the average current at timing T4. Although T4 shown in FIG. 15 indicates the capacity, for convenience of explanation, it is described as timing. Timing T4 means the time when the capacity of the lithium-ion battery 41 reaches T4. At timing T4, the voltage change rate is β or less, so the condition is satisfied. Also, as shown in FIG. 15, the BMU 50 may increase the average current at timing T5 from when the voltage change rate reaches the maximum value to when it reaches the minimum value. Although T5 shown in FIG. 15 indicates the capacity, for convenience of explanation, it is described as timing. Timing T5 means the time when the capacity of the lithium-ion battery 41 reaches T5. At timing T5, the voltage change rate is greater than β, so the condition is satisfied. By controlling the average current at such timings, it becomes possible to gain more time necessary for naturally eliminating the charging unevenness. In FIG. 15, the BMU 50 estimates the capacity of the lithium-ion battery 41 within the current limit section.

[0060] · In FIG. 8, the step method was taken as a method to reduce the average current, but it is not limited to this, and the slope method or the overshoot method may also be used. The "step method" mentioned here is a method of changing the average current having a certain magnitude to a smaller average current in a stepped manner. Also, the "slope method" is a method of gradually reducing the average current having a certain magnitude along a predetermined gradient. Also, the "overshoot method" is a method of reducing the average current having a certain magnitude to a smaller average current and making it smaller than the target value. Note that not only the average current is simply reduced, but also an intermittent form of flowing the average current such as repeating charging and pausing may be used. The average current during the pause does not have to be zero.

[0061] · When the BMU50 reduces the average current in the current limit section 80, the lower the temperature of the lithium-ion battery 41, the more the average current may be reduced. The reason is that charge unevenness is likely to expand at low temperatures, and to suppress the expansion of charge unevenness, the smaller the average current, the higher the effect. Also, although the temperature of the lithium-ion battery 41 is taken as a parameter, it is not limited to this, and a temperature correlated with the temperature of the lithium-ion battery 41 may be used. The "temperature correlated with the temperature of the lithium-ion battery 41" is, for example, the external temperature.

[0062] · When the BMU50 reduces the average current in the current limit section 80, the longer the time elapsed since the lithium-ion battery 41 was manufactured, the more the average current may be reduced. The reason is that the battery with a longer elapsed time since manufacture has advanced deterioration. The more deteriorated the battery, the more likely charge unevenness is to expand, and to suppress the expansion of charge unevenness, the smaller the average current, the higher the effect.

[0063] · When the BMU50 finishes the current limit section 80, releases the current limit, and increases the reduced average current, the higher the temperature of the lithium-ion battery 41, the more the average current may be increased. The reason is that charge unevenness is less likely to occur at high temperatures. Also, although the temperature of the lithium-ion battery 41 is taken as a parameter, it is not limited to this, and a temperature correlated with the temperature of the lithium-ion battery 41 may be used. The "temperature correlated with the temperature of the lithium-ion battery 41" is, for example, the external temperature.

[0064] · When the BMU50 finishes the current limit section 80, releases the current limit, and increases the reduced average current, the shorter the time elapsed since the lithium-ion battery 41 was manufactured, the more the average current may be increased. The reason is that the shorter the elapsed time since manufacture, the less the battery has advanced deterioration and the less likely charge unevenness is to occur.

[0065] · In FIGS. 8, 14, and 15, the horizontal axis of the graph was described as capacity, but it is not limited to this. The horizontal axis of the graph only needs to be a parameter correlated with the capacity. For example, the horizontal axis of the graph may be the charging time, SOC, etc.

[0066] · As shown in FIG. 16, after the charging of the lithium-ion battery 41 starts, when the voltage change rate becomes less than the fourth predetermined value C which is smaller than the third predetermined value B after exceeding the third predetermined value B which is larger than the second predetermined value K from the state where the voltage change rate is less than the second predetermined value K, it may be determined that the voltage change rate has reached the maximum value. The charging parameter on the horizontal axis of FIG. 16 is a parameter correlated with the charging time, and time, the capacity of the lithium-ion battery 41, the current integrated value, the temperature of the lithium-ion battery 41, the impedance of the lithium-ion battery 41, etc. can be adopted. The predetermined values K, B, and C are set corresponding to the section from when the voltage change rate turns from decreasing to increasing until it turns from decreasing to increasing again. According to such a configuration, based on the comparison of the voltage change rate with the three predetermined values K, B, and C, it is possible to easily determine that the voltage change rate has reached the maximum value.

[0067] · As described above, the battery 40 is provided with a plurality of lithium ion batteries 41. The BMU 50 may compare the rate of change in voltage of any one of the plurality of lithium ion batteries 41 with β. Further, the BMU 50 may compare the rate of change in voltage of two or more of the plurality of lithium ion batteries 41 with β. Further, the BMU 50 may compare the rate of change in voltage of all of the lithium ion batteries 41 with β. Here, the case where the BMU 50 compares the rate of change in voltage of all of the lithium ion batteries 41 with β will be described. In this case, when the BMU 50 ends the current limiting section 80, releases the current limit, and increases the average current, it is not necessary for the rate of change in voltage of all of the lithium ion batteries to be greater than β. This will be described with reference to FIG. 17. In FIG. 17, it is assumed that, as an example, ten lithium ion batteries 41 are provided. The battery cells in FIG. 17 indicate lithium ion batteries. The circles in FIG. 17 indicate that the rate of change in voltage is greater than β, and the crosses indicate that the rate of change in voltage is β or less.

[0068] In Case 1 of FIG. 17, the rate of change in voltage of one lithium ion battery 41 is greater than β, and the rates of change in voltage of the remaining nine lithium ion batteries 41 are β or less. When even one of them has a rate of change in voltage greater than β, the BMU 50 may end the current limiting section 80, release the current limit, and increase the reduced average current. As a result, the charging time is shortened as compared with the case where the average current is reduced until the rate of change in voltage of all of the lithium ion batteries 41 becomes greater than β.

[0069] In Case 2 of FIG. 17, the rates of change in voltage of four lithium ion batteries 41 are greater than β, and the rates of change in voltage of the remaining six lithium ion batteries 41 are β or less. When less than half of them have a rate of change in voltage greater than β, the BMU 50 may end the current limiting section 80, release the current limit, and increase the reduced average current. As a result, the charging time is shortened as compared with the case where the average current is reduced until the rate of change in voltage of all of the lithium ion batteries 41 becomes greater than β.

[0070] In Case 3 of FIG. 17, the voltage change rates of five lithium-ion batteries 41 are greater than β, and the voltage change rates of the remaining five lithium-ion batteries 41 are β or less. When more than half of the voltage change rates are greater than β, the BMU 50 may end the current limit section 80, release the current limit, and increase the reduced average current. As a result, the charging time is shortened as compared with the case where the average current is reduced until the voltage change rates of all the lithium-ion batteries 41 become greater than β.

[0071] In Case 4 of FIG. 17, the voltage change rates of all the lithium-ion batteries 41 are greater than β. When all the voltage change rates are greater than β, the BMU 50 may end the current limit section 80, release the current limit, and increase the reduced average current. As a result, it becomes possible to gain the time necessary for naturally eliminating the charge unevenness in all ten lithium-ion batteries 41. Consequently, the occurrence of charge unevenness is suppressed in all ten lithium-ion batteries 41. This Case 4 is effective in a state where there is a difference in the remaining amounts of the ten lithium-ion batteries 41.

[0072] The implementation frequencies of Cases 1 to 4 are not particularly limited. For example, Case 1 > Case 2 > Case 3 > Case 4. Suppose the battery 40 is charged ten times. In this case, as an example, Case 1 occurs four times, Case 2 occurs three times, Case 3 occurs two times, and Case 4 occurs once. Thus, by paying attention to the number of lithium-ion batteries 41 used for the comparison with β and increasing the average current, it becomes possible to shorten the charging time or gain the time necessary for naturally eliminating the charge unevenness.

[0073] The implementation frequencies of Cases 1 to 4 may be expressed as follows. (A) When BMU 50 determines that the voltage change rate of one or more but less than half of the lithium-ion batteries 41 is greater than β, without determining whether the voltage change rate of all the lithium-ion batteries 41 is greater than β, it releases the current limit and increases the reduced average current. (B) When BMU 50 determines that the voltage change rate of more than half of the lithium-ion batteries 41 is greater than β, without determining whether the voltage change rate of all the lithium-ion batteries 41 is greater than β, it releases the current limit and increases the reduced average current. When charging multiple times within a predetermined period, the frequency of the control according to (A) above with respect to the number of charging times is higher than the frequency of the control according to (B) above. The above (A) corresponds to Case 2, and the above (B) corresponds to Case 3. The frequency of the control according to (A) is 3 times out of 10, and the frequency of the control according to (B) is 2 times out of 10. That is, the frequency of (A) > the frequency of (B).

[0074] (C) When BMU 50 determines that the voltage change rate of one lithium-ion battery 41 is greater than β, without determining whether the voltage change rate of all the lithium-ion batteries 41 is greater than β, it releases the current limit and increases the reduced average current. (D) When BMU 50 determines that the voltage change rate of all the lithium-ion batteries 41 is greater than β, it releases the current limit and increases the reduced average current. When charging multiple times within a predetermined period, the frequency of the control according to (C) above with respect to the number of charging times is higher than the frequency of the control according to (D) above. The above (C) corresponds to Case 1, and the above (D) corresponds to Case 4. The frequency of the control according to (C) is 4 times out of 10, and the frequency of the control according to (D) is 1 time out of 10. That is, the frequency of (C) > the frequency of (D). Note that the frequency of (D) may be low, for example, about once every few days. This is because it takes a few days for a difference in the remaining amounts of the plurality of lithium-ion batteries 41 to occur.

[0075] In FIG. 17, an example of setting the end point of the current limiting section 80 according to the relationship between the number of lithium ion batteries 41 and β was described. The BMU 50 may also set the start point of the current limiting section 80 in the same manner as the setting method described in FIG. 17. That is, when a plurality of lithium ion batteries 41 are provided, the setting unit 53 may set the start point and the end point of the current limiting section 80 based on the voltage change rate of one or more of the plurality of lithium ion batteries 41.

[0076] Also, the method of setting the start point and the end point of the current limiting section 80 may be expressed as follows. (a) The setting unit 53 sets the start point and the end point of the current limiting section 80 based on the voltage change rate of one or more but less than half of the lithium ion batteries 41. (b) The setting unit 53 sets the start point and the end point of the current limiting section 80 based on the voltage change rate of half or more of the lithium ion batteries 41. When charging is performed a plurality of times within a predetermined period, the frequency of the setting according to (a) above with respect to the number of charging times is higher than the frequency of the setting according to (b) above. The above (a) corresponds to case 2, and the above (b) corresponds to case 3. The frequency of the setting according to (a) is 3 times out of 10 times, and the frequency of the setting according to (b) is 2 times out of 10 times. That is, the frequency of (a) > the frequency of (b).

[0077] (c) The setting unit 53 sets the start point and the end point of the current limiting section 80 based on the voltage change rate of one lithium ion battery 41. (d) The setting unit 53 sets the start point and the end point of the current limiting section 80 based on the voltage change rate of all the lithium ion batteries 41. When charging is performed a plurality of times within a predetermined period, the frequency of the setting according to (c) above with respect to the number of charging times is higher than the frequency of the setting according to (d) above. The above (c) corresponds to case 1, and the above (d) corresponds to case 4. The frequency of the setting according to (c) is 4 times out of 10 times, and the frequency of the setting according to (d) is 1 time out of 10 times. That is, the frequency of (c) > the frequency of (d).

[0078] The control unit and its method described in the present disclosure may be implemented by a dedicated computer provided by configuring a processor and a memory programmed to execute one or more functions embodied by a computer program. Alternatively, the control unit and its method described in the present disclosure may be implemented by a dedicated computer provided by configuring a processor with one or more dedicated hardware logic circuits. Or, the control unit and its method described in the present disclosure may be implemented by one or more dedicated computers configured by a combination of a processor programmed to execute one or more functions and a memory and a processor configured by one or more hardware logic circuits. Also, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions to be executed by a computer.

[0079] Hereinafter, the characteristic configurations extracted from each of the above-described embodiments will be described. [Configuration 1] A capacity estimation device that estimates the capacity of a power storage unit (41) when charging the power storage unit, a control unit (54) that reduces an average current indicating an average value per unit time of a charging current flowing through the power storage unit in a predetermined current limit section after the charging of the power storage unit is started; and an estimation unit (55) that estimates the capacity based on a voltage change rate of the power storage unit after or within the current limit section. A capacity estimation device comprising the same. [Configuration 2] The capacity estimation device according to Configuration 1, further comprising a setting unit that sets the current limit section based on a parameter that changes by charging the power storage unit. [Configuration 3] The parameter is a voltage change rate of the power storage unit, and the setting unit sets a point at which the voltage change rate becomes equal to or less than a first predetermined value as a start point of the current limit section. The capacity estimation device according to Configuration 1 or 2. [Configuration 4] The setting unit sets, as the end point of the current limiting section, a point at which the voltage change rate becomes greater than the first predetermined value. The control unit increases the average current after the current limiting section, and the capacitance estimation device according to any one of Configurations 1 to 3. [Configuration 5] The setting unit sets, as the end point of the current limiting section, a point at which the voltage change rate is greater than the first predetermined value and before the voltage change rate reaches a maximum value. The control unit increases the average current after the current limiting section, and the capacitance estimation device according to any one of Configurations 1 to 4. [Configuration 6] The estimation unit estimates, as the capacitance of the power storage unit, a capacitance corresponding to between two minimum values taken by the voltage change rate after or within the current limiting section, and the capacitance estimation device according to any one of Configurations 1 to 5. [Configuration 7] The control unit decreases the average current within the current limiting section as the temperature related to the power storage unit is lower, or decreases the average current as the time elapsed since the power storage unit was manufactured is longer, and the capacitance estimation device according to any one of Configurations 1 to 6. [Configuration 8] The control unit increases the average current after the current limiting section as the temperature related to the power storage unit is higher, or increases the average current as the time elapsed since the power storage unit was manufactured is shorter, and the capacitance estimation device according to any one of Configurations 1 to 7. [Configuration 9] When a plurality of power storage units are provided, the setting unit sets the start point and the end point of the current limiting section based on the voltage change rate of one or more of the plurality of power storage units, and the capacitance estimation device according to any one of Configurations 1 to 8. [Configuration 10] When a plurality of power storage units are provided, (a) The setting unit sets the start point and the end point of the current limiting section based on the voltage change rate of one or more but less than half of the power storage units, or (b) The setting unit sets the start point and the end point of the current limiting section based on the voltage change rates of more than half of the power storage units. In the case of charging a plurality of times within a predetermined period, the frequency at which the setting according to (a) above is performed with respect to the number of charging times is higher than the frequency at which the setting according to (b) above is performed. The capacity estimation device according to any one of Configurations 1 to 9. [Configuration 11] In the case where a plurality of the power storage units are provided, (c) The setting unit sets the start point and the end point of the current limiting section based on the voltage change rate of one power storage unit, or (d) The setting unit sets the start point and the end point of the current limiting section based on the voltage change rates of all the power storage units. In the case of charging a plurality of times within a predetermined period, the frequency at which the setting according to (c) above is performed with respect to the number of charging times is higher than the frequency at which the setting according to (d) above is performed. The capacity estimation device according to any one of Configurations 1 to 10. [Configuration 12] When the voltage change rate exceeds a third predetermined value (B) greater than the second predetermined value (K) from a state where the voltage change rate is less than the second predetermined value and then becomes less than a fourth predetermined value (C) smaller than the third predetermined value, the estimation unit estimates that the voltage change rate has reached a maximum value. The capacity estimation device according to any one of Configurations 1 to 11. [Configuration 13] When the change rate of the temperature related to the power storage unit or the voltage change rate of the impedance of the power storage unit changes exceeding a fifth predetermined value, the estimation unit estimates that the voltage change rate has reached a maximum value. The capacity estimation device according to any one of Configurations 1 to 12. [Configuration 14] The capacity estimation device according to any one of Configurations 1 to 13 further includes an arithmetic unit that calculates the deterioration state of the power storage unit based on the capacity estimated by the estimation unit, the current integration value obtained by integrating the charging current and time from when the capacity is estimated until the power storage unit satisfies the full charge condition, and the full capacity of the power storage unit when it is new. [Configuration 15] A capacity estimation method for estimating the capacity of the power storage unit (41) when charging the power storage unit, comprising: reducing an average current indicating an average value per unit time of a charging current flowing through the power storage unit in a predetermined current limiting section after the charging of the power storage unit is started; estimating the capacity based on a voltage change rate of the power storage unit after the current limiting section or within the current limiting section.

[0080] The present disclosure has been described based on embodiments, but it is understood that the present disclosure is not limited to such embodiments or structures. The present disclosure also includes various modifications and modifications within an equivalent range. In addition, various combinations and forms, and further, other combinations and forms including only one element, more than one element, or less than one element thereof, are also within the scope and spirit of the present disclosure.

Claims

1. A capacity estimation device for estimating the capacity of the power storage unit (41) when charging the power storage unit, comprising: A control unit (54) that reduces an average current indicating an average value per unit time of a charging current flowing through the power storage unit in a predetermined current limit section after the charging of the power storage unit is started; An estimation unit (55) that estimates the capacity based on a voltage change rate of the power storage unit after the current limit section or within the current limit section; A setting unit that sets the current limit section based on a parameter that changes by charging the power storage unit. The parameter is a voltage change rate of the power storage unit. The setting unit sets a point at which the voltage change rate becomes equal to or less than a first predetermined value as a start point of the current limit section, and sets a point at which the voltage change rate becomes greater than the first predetermined value as an end point of the current limit section. The control unit increases the average current after the current limit section. A capacity estimation device.

2. The setting unit sets a point before the voltage change rate becomes greater than the first predetermined value and before the voltage change rate reaches a maximum value as an end point of the current limit section. The control unit increases the average current after the current limit section. The capacity estimation device according to claim 1.

3. When a plurality of power storage units are provided, the setting unit sets a start point and an end point of the current limit section based on the voltage change rate of one or more of the plurality of power storage units. The capacity estimation device according to any one of claims 1 or 2.

4. When a plurality of power storage units are provided, (a) The setting unit sets a start point and an end point of the current limit section based on the voltage change rate of one or more and less than half of the power storage units, or (b) The setting unit sets a start point and an end point of the current limit section based on the voltage change rate of half or more of the power storage units. The capacity estimation device according to claim 3, wherein when charging is performed a plurality of times within a predetermined period, the frequency of performing the setting according to (a) with respect to the number of charging times is higher than the frequency of performing the setting according to (b).

5. When a plurality of the power storage units are provided, (c) The setting unit sets the start point and the end point of the current limit section based on the voltage change rate of one power storage unit, or (d) The setting unit sets the start point and the end point of the current limit section based on the voltage change rate of all the power storage units. The capacity estimation device according to claim 4, wherein when charging is performed a plurality of times within a predetermined period, the frequency of performing the setting according to (c) with respect to the number of charging times is higher than the frequency of performing the setting according to (d).

6. A capacity estimation device for estimating the capacity of a power storage unit (41) when charging the power storage unit, comprising: a control unit (54) that reduces an average current indicating an average value per unit time of a charging current flowing through the power storage unit in a predetermined current limit section after the charging of the power storage unit is started; an estimation unit (55) that estimates the capacity based on a voltage change rate of the power storage unit after the current limit section or within the current limit section, wherein the estimation unit estimates, as the capacity of the power storage unit, a capacity corresponding to between two minimum values taken by the voltage change rate after the current limit section or within the current limit section.

7. A capacity estimation device for estimating the capacity of a power storage unit (41) when charging the power storage unit, comprising: a control unit (54) that reduces an average current indicating an average value per unit time of a charging current flowing through the power storage unit in a predetermined current limit section after the charging of the power storage unit is started; an estimation unit (55) that estimates the capacity based on a voltage change rate of the power storage unit after the current limit section or within the current limit section, A capacity estimation device in which the control unit reduces the average current as the temperature of the power storage unit is lower or as the time elapsed since the power storage unit was manufactured is longer within the current limit section.

8. A capacity estimation device for estimating the capacity of a power storage unit (41) when charging the power storage unit, A control unit (54) that reduces an average current per unit time of a charging current flowing through the power storage unit in a predetermined current limit section after the charging of the power storage unit is started, An estimation unit (55) that estimates the capacity based on a voltage change rate of the power storage unit after the current limit section or within the current limit section, and A capacity estimation device in which the control unit increases the average current as the temperature of the power storage unit is higher or as the time elapsed since the power storage unit was manufactured is shorter after the current limit section.

9. The capacity estimation device according to any one of Claims 1, 2, 6, 7, and 8, further comprising an arithmetic unit that calculates a degradation state of the power storage unit based on the capacity estimated by the estimation unit, a current integration value obtained by integrating the charging current and time until the power storage unit satisfies a full charge condition after the capacity is estimated, and a full capacity of the power storage unit when new.

10. A capacity estimation device for estimating the capacity of a power storage unit (41) when charging the power storage unit, A control unit (54) that reduces an average current per unit time of a charging current flowing through the power storage unit in a predetermined current limit section after the charging of the power storage unit is started, An estimation unit (55) that estimates the capacity based on a voltage change rate of the power storage unit after the current limit section or within the current limit section, and When the voltage change rate exceeds a third predetermined value (B) greater than the second predetermined value (K) after being less than the second predetermined value (K), and then becomes less than a fourth predetermined value (C) smaller than the third predetermined value (B), the estimating unit estimates that the voltage change rate has reached a maximum value. A capacitance estimating device.

11. A capacitance estimating device for estimating the capacitance of a power storage unit (41) when charging the power storage unit, A control unit (54) that reduces an average current indicating an average value per unit time of a charging current flowing through the power storage unit in a predetermined current limiting section after the charging of the power storage unit is started; An estimating unit (55) that estimates the capacitance based on a voltage change rate of the power storage unit after or within the current limiting section, When the rate of change of the temperature related to the power storage unit or the rate of change of the voltage of the impedance of the power storage unit exceeds a fifth predetermined value, the estimating unit estimates that the voltage change rate has reached a maximum value. A capacitance estimating device.

12. A capacitance estimating method for estimating the capacitance of a power storage unit (41) when charging the power storage unit, A control step of reducing an average current indicating an average value per unit time of a charging current flowing through the power storage unit in a predetermined current limiting section after the charging of the power storage unit is started; An estimating step of estimating the capacitance based on a voltage change rate of the power storage unit after or within the current limiting section; A setting step of setting the current limiting section based on a parameter that changes by charging the power storage unit is performed, The parameter is a voltage change rate of the power storage unit, In the setting step, a point at which the voltage change rate becomes equal to or less than a first predetermined value is set as a start point of the current limiting section, and a point at which the voltage change rate becomes greater than the first predetermined value is set as an end point of the current limiting section, In the control step, after the current limiting section, the average current is increased. A capacitance estimating method.

13. A method for estimating the capacity of a power storage unit (41) when charging the power storage unit, comprising: a control step of reducing an average current indicating an average value per unit time of a charging current flowing through the power storage unit in a predetermined current limit section after the charging of the power storage unit is started; an estimation step of estimating the capacity based on a voltage change rate of the power storage unit after or within the current limit section; and In the estimation step, a capacity corresponding to between two minimum values taken by the voltage change rate after or within the current limit section is estimated as the capacity of the power storage unit. **Claim 14** A method for estimating the capacity of a power storage unit (41) when charging the power storage unit, comprising: a control step of reducing an average current indicating an average value per unit time of a charging current flowing through the power storage unit in a predetermined current limit section after the charging of the power storage unit is started; an estimation step of estimating the capacity based on a voltage change rate of the power storage unit after or within the current limit section; and In the control step, within the current limit section, the lower the temperature of the power storage unit, the smaller the average current, or the longer the time elapsed since the power storage unit was manufactured, the smaller the average current. **Claim 15** A method for estimating the capacity of a power storage unit (41) when charging the power storage unit, comprising: a control step of reducing an average current indicating an average value per unit time of a charging current flowing through the power storage unit in a predetermined current limit section after the charging of the power storage unit is started; an estimation step of estimating the capacity based on a voltage change rate of the power storage unit after or within the current limit section; and In the control step, after the current limiting section, the average current is increased as the temperature of the power storage unit is higher, or the average current is increased as the time elapsed since the power storage unit was manufactured is shorter. This is a method for estimating the capacity.

16. A method for estimating the capacity of a power storage unit (41) when charging the power storage unit, comprising: A control step of reducing an average current indicating an average value per unit time of a charging current flowing through the power storage unit in a predetermined current limiting section after the charging of the power storage unit is started; An estimating step of estimating the capacity based on a voltage change rate of the power storage unit after or within the current limiting section; and In the estimating step, when the voltage change rate changes from a state less than a second predetermined value (K) to exceed a third predetermined value (B) greater than the second predetermined value and then becomes less than a fourth predetermined value (C) smaller than the third predetermined value, it is estimated that the voltage change rate has reached a maximum value. This is a method for estimating the capacity.

17. A method for estimating the capacity of a power storage unit (41) when charging the power storage unit, comprising: A control step of reducing an average current indicating an average value per unit time of a charging current flowing through the power storage unit in a predetermined current limiting section after the charging of the power storage unit is started; An estimating step of estimating the capacity based on a voltage change rate of the power storage unit after or within the current limiting section; and In the estimating step, when a change rate of the temperature of the power storage unit or a voltage change rate of the impedance of the power storage unit changes exceeding a fifth predetermined value, it is estimated that the voltage change rate has reached a maximum value. This is a method for estimating the capacity.

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