Electricity storage device, information processing method, and computer program

Abstract

An electricity storage device comprises: an electricity storage unit having a plurality of electricity storage cells connected in series; and a control unit. The control unit acquires the remaining charge value of the electricity storage unit or the electricity storage cells and performs a full charging control on the electricity storage unit when the remaining charge value is within a predetermined range.

Description

Power storage device, information processing method, and computer program

[0001] The present invention relates to a power storage device, an information processing method, and a computer program.

[0002] In an energy storage device that uses multiple series-connected storage cells, the remaining charge can vary over time among the multiple storage cells. To reduce this variation in remaining charge among the storage cells, a balancer is known that equalizes the voltage among the storage cells.

[0003] Patent Document 1 proposes a capacity adjustment device that equalizes the capacity among a plurality of cells.

[0004] Japanese Patent Application Laid-Open No. 2007-244058

[0005] In the technique of Patent Document 1, there are cases where the accuracy of detecting the remaining capacity variation among the power storage cells is not sufficient.

[0006] An object of the present disclosure is to provide a technology that can improve the accuracy of detecting variations in remaining capacity between power storage cells.

[0007] According to one aspect of the present disclosure, there is provided a power storage device including a power storage unit having a plurality of power storage cells connected in series, and a control unit. The control unit acquires a remaining capacity value of the power storage unit or the power storage cells, and performs full charge control on the power storage unit when the remaining capacity value is within a predetermined range. The power storage device may further include a balancer electrically connected to each power storage cell, and the control unit may determine an imbalance amount of each power storage cell to be equalized by the balancer based on the voltage of each power storage cell after full charge control when the remaining capacity value is within the predetermined range.

[0008] According to the present disclosure, it is possible to improve the accuracy of detecting variations in remaining capacity among power storage cells. In particular, the technology of the present disclosure can be suitably applied to a power storage unit having a plateau region in its State of Charge (SOC)-Open Circuit Voltage (OCV) profile.

[0009] 1 is a diagram showing the relationship between the SOC of an LFP / Gr battery and the OCV of each cell and the voltage difference between the cells. FIG. 2 is a graph of voltage values ​​and current values ​​during charging when the charge start SOC is 0% and when the charge start SOC is 85%. FIG. 3 is a graph showing the relationship between the SOC of an LFP / Gr battery and the voltage difference between the cells for each remaining capacity variation. FIG. 4 is a perspective view showing an example of the configuration of a power storage device. FIG. 5 is an exploded perspective view of a power storage device. FIG. 6 is a block diagram showing an example of the configuration of a power storage device. FIG. 7 is a flowchart showing an example of an equalization processing procedure. FIG. 8 is a diagram explaining imbalance determination.

[0010] (1) According to one aspect of the present disclosure, there is provided a power storage device including a power storage unit having a plurality of power storage cells connected in series, and a control unit, wherein the control unit acquires a remaining capacity value of the power storage unit or the power storage cells, and performs full charge control on the power storage unit when the remaining capacity value is within a predetermined range.

[0011] Here, the remaining capacity may be the SOC or the amount of dischargeable electricity. The SOC may be the ratio of the remaining capacity to the fully charged capacity of the power storage unit or power storage cell at that time (so-called RSOC (Relative State Of Charge)), or the ratio of the remaining capacity to the fully charged capacity according to specifications (so-called ASOC (Absolute State Of Charge)). The remaining capacity may be a physical quantity expressed in units of Ah (ampere-hours).

[0012] In an energy storage device that uses multiple series-connected energy storage cells, a balancer is used to equalize the voltage (remaining capacity) variations that occur between the energy storage cells, thereby preventing overcharging or overdischarging of the energy storage device. The equalization process involves discharging other energy storage cells to match the voltage of a specific energy storage cell, thereby equalizing the voltage between the energy storage cells. To operate the balancer, it is necessary to accurately detect the voltage difference between the cells and determine the amount of imbalance corresponding to the voltage difference.

[0013] Some energy storage cells have a plateau region in their SOC-OCV profile. The plateau region refers to a region where there is almost no change in OCV relative to the change in SOC (almost horizontal). As an example of an energy storage cell having a plateau region, an iron-based energy storage cell containing iron in the positive electrode active material is known, and in particular, an LFP / Gr-based lithium-ion secondary battery is known. In the case of an energy storage cell having a plateau region, it is difficult to detect the voltage difference of the energy storage cell within the plateau region.

[0014] FIG. 1 is a diagram showing the relationship between the SOC of an LFP / Gr battery and the OCV of each cell and the voltage difference between the cells. The horizontal axis of FIG. 1 is SOC (unit: %), the left vertical axis is OCV (unit: volts (V)), and the right vertical axis is the voltage difference between the cells (unit: V). In FIG. 1, a solid line 101 represents the SOC-OCV profile of the first cell, a solid line 102 represents the SOC-OCV profile of the second cell, and a dashed line 103 represents the voltage difference between the cells. FIG. 1 shows an example in which the LFP / Gr battery has remaining capacity variations, and the remaining capacity of the second cell is 2% lower than that of the first cell.

[0015] As shown in Figure 1, when the SOC is in the plateau region, the OCV is almost constant, so even if an imbalance occurs between the cells, no voltage variation occurs and it is difficult to detect the voltage difference. When the SOC is not in the plateau region, the OCV changes, so voltage variation occurs due to the imbalance, making it possible to detect the voltage difference.

[0016] It is generally assumed that the charge and discharge of a power storage device is controlled so that the SOC is within a preset usable range. For example, if the power storage device is a low-voltage battery mounted on a vehicle, the charge and discharge are controlled so that the SOC is 50% to 90%. In the case of a power storage cell having a plateau region, full charge control may be performed in order to detect the voltage difference.

[0017] The inventors of the present application have found that current characteristics differ depending on the SOC at the start of charging. Figure 2 is a graph of voltage and current values ​​during charging when the starting SOC is 0% and when the starting SOC is 85%. The horizontal axis of Figure 2A represents SOC (%), and the vertical axis represents voltage (V). The horizontal axis of Figure 2B represents SOC (%), and the vertical axis represents current (A). Figure 2C is an enlarged view of a portion of the graph of Figure 2B.

[0018] In the example of full charge control shown in Figure 2, constant current charging (CC charging) is performed at a constant current value until the voltage value reaches a predetermined voltage value, and then constant voltage charging (CV charging) is performed at a constant voltage value once the voltage value reaches the predetermined voltage value. When switching to constant voltage charging, the current value of the charging current gradually decreases, and charging ends when the current value drops to a predetermined full charge end threshold. For convenience, in the following description, the state when the current value drops to the predetermined full charge end threshold is referred to as full charge, and the time when the current value drops to the predetermined full charge end threshold is referred to as the completion point of full charge control. Full charge does not necessarily mean that the SOC is 100%.

[0019] As shown in FIG. 2, the lower the SOC at the start of charging, the lower the SOC at the completion of full charge control.

[0020] FIG. 3 is a graph showing the relationship between the SOC and the inter-cell voltage difference for an LFP / Gr battery for each remaining capacity variation. The horizontal axis of FIG. 3 is SOC (%), and the vertical axis is the inter-cell voltage difference (V). In FIG. 3, solid line 104 represents the case where the remaining capacity variation between the first cell and the second cell is 0.4%, and solid line 105 represents the case where the remaining capacity variation between the first cell and the second cell is 0.2%. In the range of SOC below approximately 98.3%, almost no voltage difference occurs regardless of the amount of imbalance. In the range above approximately 98.3% SOC, the higher the SOC, the larger the voltage difference. The voltage difference increases as the remaining capacity variation increases.

[0021] As described above, in a storage cell having a plateau region, when the SOC value at which full charge control is completed becomes low, the voltage difference between the cells does not appear even if an imbalance occurs between the cells, making it difficult to detect the amount of imbalance from the voltage difference.

[0022] According to the energy storage device of (1), when the remaining capacity value of the energy storage unit or the energy storage cell is within a predetermined range, full charge control is performed on the energy storage unit. The predetermined range may be, for example, a usable range set for the energy storage unit or the energy storage cell. By starting charging when the remaining capacity value is relatively high, it is possible to suppress a decrease in SOC at the time of full charge completion, accurately detect voltage variations, and improve the accuracy of detecting remaining capacity variations.

[0023] (2) The power storage device according to (1) above may further include a balancer electrically connected to each of the power storage cells, and the control unit may determine the amount of imbalance of each of the power storage cells to be equalized by the balancer based on the voltage of each of the power storage cells after full charge control. The voltage after full charge control may be the voltage at the time when full charge control is completed.

[0024] According to the energy storage device of (2) above, by calculating the amount of imbalance between the cells based on the voltage of each storage cell after full charge control, when the voltage difference is well expressed, it becomes possible to calculate the capacity of the storage cells to within 0.1%, for example, and improve the accuracy of detecting the amount of imbalance. By limiting the conditions for executing full charge control, it is possible to accurately detect voltage variations and the amount of imbalance, eliminating the need for complex correction processing and simplifying the configuration of the energy storage device. It is possible to reduce the possibility that a voltage difference cannot be detected even when an imbalance occurs between the storage cells, and to prevent the energy storage device from becoming overcharged at an unintended time.

[0025] (3) In the energy storage device described in (1) or (2) above, the control unit may perform full charge control on the energy storage unit when the remaining capacity value is within a predetermined range and a specific time has elapsed since the remaining capacity value became within the predetermined range.

[0026] According to the above-described energy storage device (3), by taking into account the time elapsed since the remaining capacity value fell within a predetermined range as a determination requirement for full charge control, the charge start SOC can be further increased, and the accuracy of voltage variation detection can be improved.

[0027] (4) In the energy storage device described in any one of (1) to (3) above, the control unit may output a request for full charging of the energy storage unit when the remaining capacity value is within a predetermined range or when a specific time has elapsed since the remaining capacity value entered the predetermined range.

[0028] According to the power storage device described in (4) above, a full charge request can be output when predetermined requirements are met. The full charge request may be output to, for example, a vehicle ECU (Electronic Control Unit) that controls the charge or discharge amount of a vehicle in which the power storage device is installed. The vehicle ECU is an example of a higher-level device. By having the vehicle ECU fully charge the battery in response to the full charge request, the timing of full charge can be adjusted, and the accuracy of voltage variation detection can be improved.

[0029] (5) In the energy storage device described in any one of (1) to (4) above, the control unit may acquire the voltage of each storage cell after full charge control, and based on the acquired voltage of each storage cell, determine the discharge amount of each storage cell by a balancer electrically connected to each storage cell based on the voltage of the storage cell with the lowest voltage after full charge control among the storage cells and each of the other storage cells.

[0030] According to the power storage device described in (5) above, the discharge amount of each power storage cell can be determined with high accuracy by using the voltage of each power storage cell after full charge control in which the voltage difference is well expressed.

[0031] (6) In the energy storage device described in any one of (1) to (5) above, the control unit may correct the SOC value of the energy storage unit estimated by a current integration method that integrates a charging current and / or a discharging current flowing through the energy storage unit, using a voltage of each energy storage cell after full charge control.

[0032] The current integration method is a method of estimating the SOC by measuring the current value of the charge / discharge current of the storage cell at predetermined time intervals using a current sensor and adding or subtracting the measured current value from an initial value. The current integration method is prone to accumulating errors over time (such as measurement errors of the current sensor, errors due to individual differences in the current consumption of the management device that manages the storage cell, and errors due to individual differences in self-discharge of the storage cell).

[0033] According to the power storage device described in (6) above, it is possible to correct the SOC value of the power storage unit estimated by the current integration method based on the voltage of each power storage cell after full charge control is performed when predetermined requirements are satisfied, i.e., it is possible to execute a so-called "full charge reset." Since full charge is performed when predetermined requirements are satisfied, full charge is completed in a region where the slope of the SOC-OCV profile is steep, and it is possible to accurately estimate the SOC corresponding to the voltage of the power storage cell.

[0034] (7) In the power storage device according to any one of (1) to (6) above, the power storage cell may contain lithium iron phosphate as a positive electrode active material.

[0035] According to the energy storage device described in (7) above, voltage variations can be detected with high accuracy even in energy storage cells having a plateau region, and therefore, it is particularly useful in the case of energy storage cells containing lithium iron phosphate as the positive electrode active material.

[0036] (8) An information processing method according to one aspect of the present disclosure includes a computer that acquires a remaining capacity value of a storage unit having a plurality of storage cells connected in series or of the storage cells, and, if the remaining capacity value is within a predetermined range, executes a process of performing full charge control on the storage unit.

[0037] (9) A computer program according to one aspect of the present disclosure acquires a remaining capacity value of a storage unit having a plurality of storage cells connected in series or of the storage cells, and causes a computer to execute a process of performing full charge control on the storage unit when the remaining capacity value is within a predetermined range.

[0038] The present disclosure will be specifically described with reference to the drawings showing embodiments thereof.

[0039] (First embodiment) Fig. 4 is a perspective view showing a configuration example of the energy storage device 1, and Fig. 5 is an exploded perspective view of the energy storage device 1. Below, the configuration example of the energy storage device 1 will be described with reference to the "front-rear," "left-right," and "up-down" directions shown in the drawings.

[0040] The power storage device 1 is a battery that is suitable for installation in vehicles such as engine vehicles, electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and other mobile objects. The power storage device 1 may be a 12-volt (V) battery or a 48-V battery.

[0041] The energy storage device 1 includes a plurality of energy storage cells 2, a management device 3, a bus bar unit 4, and a circuit board 6. The energy storage cells 2, the management device 3, the bus bar unit 4, and the circuit board 6 are housed inside a housing case 10.

[0042] The storage case 10 is made of synthetic resin. The storage case 10 includes a case body 11 with an open top and a cover 12 that covers the opening of the case body 11. The dimensions of the case body 11 and the cover 12 are designed according to the dimensions and number of the energy storage cells 2 to be housed therein. The case body 11 and the cover 12 are fixed in a liquid-tight manner using connectors such as screws, adhesive, welding, or the like, with the energy storage cells 2, bus bar unit 4, and circuit board 6 housed inside.

[0043] The storage cell 2 is, for example, a lithium ion secondary battery cell. The storage cell 2 is, for example, an LFP battery containing LiFePO4 as a positive electrode active material, and has the plateau region described above.

[0044] The storage cell 2 includes a hollow rectangular parallelepiped case 21. A positive terminal 22 and a negative terminal 23 of the storage cell 2 are provided on the top surface of the case 21. An electrode assembly, an electrolyte, and the like are accommodated inside the case 21. A plurality of storage cells 2 are connected to form a single assembled battery 20. The assembled battery 20 is an example of a power storage unit. FIG. 5 shows the assembled battery 20 having four storage cells 2 connected in series. Some storage cells 2 may be connected in parallel.

[0045] Although not shown in detail, the electrode assembly is constructed by stacking a sheet-shaped positive electrode and a sheet-shaped negative electrode with two sheet-shaped separators in between and winding them (vertical or horizontal). The separators are formed from a porous resin film. Examples of the porous resin film include porous resin films made of resins such as polyethylene (PE) and polypropylene (PP).

[0046] The positive electrode is an electrode plate in which a positive electrode active material layer is formed on the surface of a long strip-shaped positive electrode substrate made of, for example, aluminum, an aluminum alloy, or the like. The positive electrode active material layer contains a positive electrode active material. The positive electrode active material used in the positive electrode active material layer can be a material capable of absorbing and releasing lithium ions. The positive electrode active material layer may further contain a conductive additive, a binder, etc.

[0047] The negative electrode is an electrode plate in which a negative electrode active material layer is formed on the surface of a long strip-shaped negative electrode substrate made of, for example, copper or a copper alloy. The negative electrode active material layer contains a negative electrode active material. The negative electrode active material can be a material capable of absorbing and releasing lithium ions. Examples of the negative electrode active material include graphite, hard carbon, and soft carbon. The negative electrode active material layer may further contain a binder, a thickener, and the like.

[0048] The electrolyte can be the same as that used in conventional lithium-ion secondary batteries. For example, an electrolyte containing a supporting salt in an organic solvent can be used. As the organic solvent, for example, an aprotic solvent such as carbonates, esters, or ethers can be used. As the supporting salt, for example, a lithium salt such as LiPF6, LiBF4, or LiClO4 can be suitably used. The electrolyte may contain various additives such as a gas generating agent, a film-forming agent, a dispersant, or a thickener.

[0049] 5 , the storage cells 2 are housed in the case body 11 such that the positive terminals 22 and negative terminals 23 of adjacent storage cells 2 face in opposite directions. In the following description, the storage cells 2 are also referred to as a first storage cell 2A, a second storage cell 2B, a third storage cell 2C, and a fourth storage cell 2D, in that order from the front side of the case body 11.

[0050] The energy storage device 1 is provided with charge / discharge paths that electrically connect the storage cells 2 housed in the case body 11 to the external terminals 13A and 13B. Part of the charge / discharge paths is formed by bus bars (not shown). For example, the negative terminal 23 of the first storage cell 2A is connected to the external terminal 13A via the bus bar. The positive terminal 22 of the first storage cell 2A and the negative terminal 23 of the second storage cell 2B are connected to each other via the bus bar. The positive terminal 22 of the second storage cell 2B and the negative terminal 23 of the third storage cell 2C are connected to each other via the bus bar. The positive terminal 22 of the third storage cell 2C and the negative terminal 23 of the fourth storage cell 2D are connected to each other via the bus bar. The positive terminal 22 of the fourth storage cell 2D is connected to the external terminal 13B via the bus bar. In this way, the storage cells 2A to 2D are connected in series by the bus bars.

[0051] A busbar unit 4 is disposed on the terminal surface of the energy storage cell 2. The busbar unit 4 includes the above-described busbars and a resin busbar frame 40 that holds the busbars. A circuit board 6 is disposed on the upper surface of the busbar frame 40. The circuit board 6 is fixed to the busbar frame 40 via spacers 41, for example, in a state spaced apart from the upper surface of the busbar frame 40.

[0052] In the embodiment, the storage cell 2 is a battery cell based on an LFP-based lithium ion secondary battery having a plateau region. Alternatively, the storage cell 2 may be another type of secondary battery having a plateau region. The storage cell 2 is not limited to a cell having a plateau region. The storage cell 2 may be an all-solid-state battery or a capacitor.

[0053] In the embodiment, the energy storage cell 2 is a rectangular battery cell with a wound electrode assembly. Alternatively, the energy storage cell 2 may be a cylindrical battery cell, a laminated (pouch) battery cell, or a battery cell with a stacked electrode assembly.

[0054] In the embodiment, the number of storage cells 2 housed in the case body 11 is four. Alternatively, the number of storage cells 2 housed in the case body 11 may be one or more and less than four, or may be more than four. The battery pack 20 may include, for example, twelve storage cells 2 connected in three parallel and four series.

[0055] 6 is a block diagram showing an example configuration of the energy storage device 1. The energy storage device 1 includes a battery pack 20, a management device 3, a balancer 61, a breaker circuit 62, a temperature sensor 63, a current sensor 64, and a voltage sensor 65. The management device 3, the balancer 61, the breaker circuit 62, the temperature sensor 63, the current sensor 64, and the voltage sensor 65 may be mounted on a circuit board 6 and configured as a circuit board unit.

[0056] The power storage device 1 is connected to a vehicle ECU 71, an electrical load 72 such as electrical equipment, and an alternator (not shown) via external terminals 13A and 13B. The vehicle ECU 71 is a vehicle control unit that controls the vehicle. The vehicle ECU 71 controls the electrical load 72 to control the amount of charge or discharge of the power storage device 1.

[0057] If the vehicle is an engine vehicle, while the engine is running, if the amount of power generated by the alternator is greater than the amount of power consumed by the electrical load 72, the electrical storage device 1 is charged by the alternator. If the amount of power generated by the alternator is less than the amount of power consumed by the electrical load 72, the electrical storage device 1 discharges to make up for the shortfall. When the vehicle is parked, the alternator stops generating power, so the electrical storage device 1 is not charged and only discharges to the vehicle ECU 71 and the electrical load 72.

[0058] When the vehicle can start traveling using a high-voltage system (driving power storage device) instead of an internal combustion engine, the power storage device 1 supplies power to start the high-voltage system. While the vehicle is parked, the power storage device 1 discharges power to the vehicle ECU 71 and the electrical load 72, and can also be charged by the high-voltage system.

[0059] The management device 3 is, for example, a Battery Management Unit (BMU) that manages the state of the energy storage cells 2. When the SOC of the energy storage cells 2 satisfies a predetermined condition, the management device 3 executes control to perform an equalization process that equalizes the voltages (capacities) between the energy storage cells 2. In one example, the management device 3 is mounted on the circuit board 6. Alternatively, the management device 3 may be mounted on a board separate from the circuit board 6, or may be a computer such as a terminal device or a server device that is connected to the outside of the energy storage device 1.

[0060] The balancer 61 is an equalization circuit for equalizing the voltages of the storage cells 2. A plurality of balancers 61 are provided according to the number of storage cells 2, and each balancer 61 is connected in parallel to a different storage cell 2. The balancer 61 includes, for example, a discharge load and a switch such as a field effect transistor (FET) or a relay, and consumes the amount of electricity in the storage cells 2 by passing a current through the discharge load. When the balancer 61 is activated and the switch is turned on, the storage cells 2 are discharged via the discharge load. By discharging the storage cell 2 with the larger capacity, the voltages (remaining capacities) of the storage cells 2A to 2D can be equalized.

[0061] The interruption circuit 62 is a circuit for connecting or disconnecting a charge / discharge path (current path) between the positive terminal 22 of the fourth storage cell 2D and the external terminal 13B. The interruption circuit 62 is configured by a semiconductor switch such as a metal oxide semiconductor field effect transistor (MOSFET). By switching the interruption circuit 62 from an on state to an off state, it is possible to block current from flowing out from the storage cell 2 to the outside and current from flowing in from the outside to the storage cell 2. Alternatively, the interruption circuit 62 may be configured by a relay switch.

[0062] The temperature sensor 63 is, for example, a thermistor, a thermocouple, etc. The temperature sensor 63 measures the temperature of the energy storage cell 2 or the energy storage device 1 in a time series manner. The temperature sensor 63 may be disposed at a position sufficiently separated from an electrically-heated element (for example, the interrupter circuit 62, a bus bar, a fastener, etc.) on the circuit board 6.

[0063] The current sensor 64 is, for example, a shunt resistor, and is connected in series to the storage cell 2. The current sensor 64 measures the current flowing through the storage cell 2 in a time series manner based on the voltage across the storage cell 2. Discharging and charging can be determined from the polarity (positive or negative) of the voltage across the cells. Alternatively, the current sensor 64 may be a magnetic sensor.

[0064] The voltage sensor 65 is connected in parallel to each storage cell 2. The voltage sensor 65 is connected to both ends of each storage cell 2, and measures the terminal voltage of each storage cell 2 and the total voltage of the battery pack 20 in time series.

[0065] The management device 3 is a computer and includes a control unit 31, a storage unit 32, and a communication unit 33. The management device 3 may be configured to perform distributed processing using multiple computers, may be realized by multiple virtual machines provided in a single server, or may be realized using a cloud server.

[0066] The control unit 31 is an arithmetic circuit including a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. The CPU or GPU included in the control unit 31 executes various computer programs stored in the ROM or the storage unit 32, and controls the operation of each of the above-mentioned hardware components. The control unit 31 may also include functions such as a timer that measures the elapsed time from when an instruction to start measurement is given until when an instruction to end measurement is given, a counter that counts numbers, and a clock that outputs date and time information.

[0067] The storage unit 32 includes a nonvolatile storage device such as a flash memory or a hard disk drive. The storage unit 32 stores various computer programs, data, and the like referenced by the control unit 31. The storage unit 32 may be an external storage device connected to the management device 3. The storage unit 32 of this embodiment stores a program 321 for causing a computer to execute equalization-related processing, and a characteristics table 322. The characteristics table 322 is data that indicates, in table format, the relative relationship between the closed circuit voltage (CCV) of the storage cell 2 and the remaining capacity (CCV-remaining capacity characteristics). The CCV-remaining capacity characteristics may be stored as a graph, a formula, or the like.

[0068] A computer program (computer program product) including the program 321 may be provided by a non-transitory recording medium 3A on which the computer program is readably recorded. The recording medium 3A is, for example, a portable memory such as a magnetic disk, an optical disk, or a semiconductor memory. The control unit 31 reads the desired computer program from the recording medium 3A using a reading device (not shown) and stores the read computer program in the memory unit 32. Alternatively, the computer program may be provided via communications. The program 321 may be a single computer program or may be composed of multiple computer programs, and may be executed on a single computer or on multiple computers interconnected by a communications network.

[0069] The communication unit 33 includes a communication interface for transmitting and receiving various signals and data. In response to instructions from the control unit 31, the communication unit 33 transmits to the circuit board 6 a control signal for opening and closing the balancer 61 switch and a control signal for opening and closing the breaker circuit 62 switch. The communication unit 33 receives temperature data output from the temperature sensor 63, current data output from the current sensor 64, and voltage data output from the voltage sensor 65. The communication unit 33 transmits and receives various data, including a full charge request, to and from the vehicle ECU 71 or other external devices.

[0070] 7 is a flowchart showing an example of an equalization processing procedure. The control unit 31 of the management device 3 executes the following processing in accordance with the program 321. The control unit 31 repeatedly executes the following processing, for example, at predetermined time intervals (e.g., every six months, every three months, etc.). The control unit 31 may start the following processing when a predetermined requirement is satisfied (e.g., when a predetermined period has elapsed since the previous SOC reset).

[0071] The control unit 31 of the management device 3 acquires the current SOC value of the battery pack 20 (step S11). The SOC of the battery pack 20 may be calculated using a current integration method. The current integration method is a method in which the current sensor 64 measures the charge / discharge current of the power storage device 1 at predetermined time intervals to measure the amount of power flowing in and out of the power storage device 1, and estimates the SOC by adding or subtracting this amount from the initial capacity. The control unit 31, for example, executes an SOC estimation process using the current integration method at predetermined intervals, and stores the obtained SOC in the storage unit 32 in association with the estimated date and time.

[0072] The control unit 31 determines whether the acquired current SOC value of the battery pack 20 is within a preset control range (step S12). The control range may be, for example, a usable range (e.g., SOC 50% to 90%) set for the battery pack 20, or an SOC range set for this determination process. Alternatively, the control unit 31 may acquire the current SOC values ​​of one or more storage cells 2 and determine whether the current SOC values ​​of one or more storage cells 2 are within the preset control range.

[0073] If it is determined that the current SOC value of the battery pack 20 is not within the preset control range (S12: NO), the control unit 31 ends the process. The control unit 31 may return the process to step S11 and wait until the SOC value falls within the preset control range.

[0074] If it is determined that the current SOC value is within the preset control range (S12: YES), the control unit 31 determines whether a preset specific time has elapsed since the SOC value of the battery pack 20 entered the preset control range (step S13). The elapsed time since the SOC value entered the control range can be calculated based on the SOC time-series data stored in the storage unit 32. The control unit 31 may proceed to step S14 without determining whether the specific time has elapsed.

[0075] If it is determined that the specific time has not elapsed since the SOC value of the battery pack 20 entered the control range (S13: NO), the control unit 31 returns the process to step S13 and waits until the specific time has elapsed.

[0076] If it is determined that a specific time has elapsed since the SOC value of the battery pack 20 entered the control range (YES in S13), the control unit 31 executes full charge control for the battery pack 20 (step S14). In step S14, the control unit 31 may output a full charge request to a higher-level device such as the vehicle ECU 71. In response to the full charge request received from the management device 3, the vehicle ECU 71 starts charging the battery pack 20.

[0077] After the full charge control is completed, the control unit 31 acquires the voltage of each storage cell 2 after the full charge control (step S15), and calculates the remaining capacity of each storage cell 2 based on the acquired voltage of each storage cell 2 (step S16). The control unit 31 determines the discharge amount of each storage cell 2 by the balancer 61 based on the calculated remaining capacity of each storage cell 2 (step S17). The processing of steps S15 to S17 corresponds to the imbalance determination.

[0078] 8 is a diagram for explaining the imbalance determination, and the processing of steps S15 to S17 will be described in detail with reference to FIG.

[0079] The graph on the left side of Figure 8 shows the change over time in the charging voltage (cell voltage) and charging current of each storage cell 2 during full charge control. During full charge control of the battery pack 20, charging is controlled so that the highest cell voltage does not exceed a preset maximum charging voltage. For example, consider an assembled battery 20 in which four storage cells 2A to 2D, each with a maximum cell charging voltage of 3.5 V, are connected in series. When charging at the maximum charging voltage of the assembled battery 20, assuming there is no variation in the remaining capacities of the storage cells 2A to 2D, the cell voltages of the storage cells 2A to 2D at the completion of full charge control will all be 3.5 V. In reality, because there is variation in the remaining capacities of the storage cells 2A to 2D, the cell voltages of the storage cells 2A to 2D at the completion of full charge control are not uniform, as shown in Figure 8. The storage cells 2 charged at the maximum cell charging voltage are fully charged, but the storage cells 2 whose charging voltage has dropped are insufficiently charged according to the amount of voltage variation and are not fully charged.

[0080] In step S15, the control unit 31 acquires the voltage of each of the storage cells 2A to 2D at the time when the full charge control is completed, i.e., at the time when the current value of the CV charging reaches a predetermined full charge end threshold, based on the current data and voltage data of the storage cells 2A to 2D. The voltages of the storage cells 2A to 2D may be CCV values ​​detected by the voltage sensor 65. The control unit 31 identifies the storage cell 2 with the smallest voltage after the full charge control as the minimum cell.

[0081] In step S16, the control unit 31 refers to the characteristics table 322 of CCV-remaining capacity characteristics stored in the storage unit 32, and obtains the remaining capacity corresponding to the CCV of each of the storage cells 2A to 2D after full charge control.

[0082] The CCV-remaining capacity characteristic may be generated by determining in advance, through experiments or the like, the correlation between the CCV and remaining capacity of the storage cell 2 at a predetermined full charge end threshold. When the OCV of the storage cell 2 can be detected, the SOC and remaining capacity can be calculated from the detected OCV of the storage cell 2 using an SOC-OCV profile. In the case of an in-vehicle storage cell 2, various electrical loads are connected to the storage cell 2, and there is almost no time when the amount of current flowing through the storage cell 2 becomes zero or nearly zero. Therefore, the remaining capacity is determined using the CCV instead of the OCV of the storage cell 2. By setting the full charge end threshold to a sufficiently small value, the influence of the internal resistance of the storage cell 2 can be reduced, thereby improving the accuracy of detecting the remaining capacity. To take into account the influence of actual capacity variations due to deterioration of the storage cell 2, the depth of discharge may be used instead of the remaining capacity.

[0083] In step S17, the control unit 31 uses the remaining capacity of the identified smallest cell as a reference and calculates the difference between the remaining capacity of the smallest cell and the remaining capacities of the other storage cells 2 for each storage cell 2. The obtained difference in remaining capacity is set as the discharge amount of the balancer 61.

[0084] 7, the control unit 31 operates the balancers 61 of the storage cells 2 to be equalized in accordance with the determined discharge amounts (step S18). The balancers 61 discharge the storage cells 2 other than the smallest cell, and the voltages (remaining capacities) of the storage cells 2A to 2D are equalized.

[0085] The control unit 31 corrects the SOC estimated by the current integration method by performing an SOC reset based on the voltages of the storage cells 2A to 2D after the full charge control (step S19). The control unit 31 calculates the SOC values ​​of the storage cells 2A to 2D based on the remaining capacities corresponding to the voltages of the storage cells 2A to 2D after the full charge control, which are determined by the imbalance determination, and the known actual capacities of the storage cells 2A to 2D. The control unit 31 corrects the SOC of the storage cells 2A to 2D calculated by the current integration method with the calculated SOC of the storage cells 2A to 2D. Alternatively, the control unit 31 may regard the voltages of the storage cells 2A to 2D after the full charge control as the OCV, estimate the SOC from the voltages of the storage cells 2A to 2D after the full charge control using an SOC-OCV profile, and correct the SOC calculated by the current integration method with the estimated SOC. The processing of step S19 may be omitted. The control unit 31 then ends the series of processing.

[0086] In the above process, the control unit 31 may execute the process from step S15 onwards even when full charge control is performed on the battery pack 20 independently of the full charge control in step S14. In this case, it is preferable that the control unit 31 executes steps S11 to S13 in parallel, and when it determines that the predetermined conditions are satisfied, executes the process from step S14 onwards again.

[0087] According to this embodiment, by controlling the timing of full charge execution for the equalization process in accordance with the SOC of the battery pack 20, it is possible to suppress a decrease in SOC after full charge control and improve the accuracy of detecting the voltage difference and the amount of imbalance.

[0088] The power storage device may be a high-voltage battery (a battery for driving a mobile object) mounted on a vehicle or other mobile object.

[0089] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The technical features described in each embodiment can be combined with each other, and the scope of the present invention is intended to include all modifications within the scope of the claims and equivalents thereto. The sequences shown in each embodiment are not limited, and within the scope of no contradiction, each processing step may be executed in a different order, or multiple processes may be executed in parallel. The entity that performs each process is not limited, and within the scope of no contradiction, the process of each device may be executed by another device.

[0090] The matters described in each embodiment can be combined with each other. Furthermore, the independent claims and dependent claims described in the claims can be combined with each other in any and all combinations, regardless of the reference format. Furthermore, the claims use a format in which a claim references two or more other claims (multiple claim format), but this is not limited to this. A multiple claim (multi-multi claim) that references at least one other multiple claim may also be used.

[0091] REFERENCE SIGNS LIST 1 Energy storage device 2 Energy storage cell 20 Battery pack 61 Balancer 3 Management device 31 Control unit 32 Storage unit 33 Communication unit 321 Program 322 Characteristics table 3A Recording medium

Claims

1. A power storage device comprising: a power storage unit having a plurality of power storage cells connected in series; and a control unit, wherein the control unit acquires a remaining capacity value of the power storage unit or the power storage cells; and, when the remaining capacity value is within a predetermined range, performs full charge control on the power storage unit.

2. The power storage device according to claim 1, wherein the remaining capacity value is an SOC.

3. The power storage device according to claim 1, wherein the remaining capacity value is a dischargeable amount of electricity.

4. The energy storage device according to claim 1, wherein the predetermined range is an available range set for the energy storage unit or the energy storage cell.

5. The power storage device according to claim 4, wherein the usable range is from 50% to 90% SOC.

6. The energy storage device according to claim 1, further comprising a balancer electrically connected to each of the energy storage cells, wherein the control unit determines the amount of imbalance of each of the energy storage cells to be equalized by the balancer based on the voltage of each of the energy storage cells after full charge control.

7. The power storage device according to claim 1, wherein, when the remaining capacity value is within a predetermined range and a specific time has elapsed since the remaining capacity value entered the predetermined range, the control unit performs full charge control on the power storage unit.

8. The energy storage device according to claim 1 or claim 6, wherein the control unit outputs a full charge request for the energy storage unit when the remaining capacity value is within a predetermined range or when a specific time has elapsed since the remaining capacity value entered the predetermined range.

9. The energy storage device according to claim 1 or claim 6, further comprising: acquiring a voltage of each storage cell after full-charge control; and determining an amount of discharge of each storage cell by a balancer electrically connected to each storage cell, based on the acquired voltage of each storage cell and the voltage of the storage cell having the lowest voltage after full-charge control among the storage cells and the voltage of each of the other storage cells.

10. The energy storage device according to claim 1 or 6, wherein the voltage of each energy storage cell after full charge control is used to correct an SOC value of the energy storage unit estimated by a current integration method that integrates a charging current and / or a discharging current flowing through the energy storage unit.

11. The power storage device according to claim 1 or claim 6, wherein the power storage cell contains lithium iron phosphate as a positive electrode active material.

12. The electricity storage device according to claim 1 or claim 6, wherein the electricity storage cell contains graphite as a negative electrode active material.

13. The power storage device according to claim 9, wherein the discharge amount is determined in a region where the SOC is 98.3% or more.

14. An information processing method in which a computer executes a process of acquiring a remaining capacity value of a storage unit having a plurality of storage cells connected in series or of the storage cells, and performing full-charge control on the storage unit when the remaining capacity value is within a predetermined range.

15. A computer program that causes a computer to execute a process of acquiring a remaining capacity value of a storage unit having a plurality of storage cells connected in series or of the storage cells, and performing full-charge control on the storage unit when the remaining capacity value is within a predetermined range.

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