Power storage device and control method for the same

Abstract

To provide a power storage device and a control method for the same that suppress use of power storage cells while a large difference in amounts of electricity between the power storage cells remains.SOLUTION: A power storage device 1 connected to a vehicle 2 comprises: a plurality of power storage cells 30A; a balancer circuit 38 which individually discharges each power storage cell 30A; a voltage sensor 35 which detects voltage of each power storage cell 30A; and a management section 37. The management section 37 executes: a request process (S103) to request the vehicle 2 to charge the power storage device 1 when a predetermined condition for reducing a difference in amounts of electricity between the power storage cells 30A is met; and a reduction process (S106), after the vehicle 2 has charged the power storage device 1, to detect the voltage of each power storage device 30A with the voltage sensor 35 and to reduce the difference in the amounts of electricity between the power storage cells 30A by adjusting operation time of the balancer circuit 38 in accordance with a difference in the detected voltage.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a power storage device and a control method for the power storage device. [Background technology]

[0002] When a power storage device including multiple storage cells is left unused for a long period of time, the difference in the amount of electricity [Ah] between the storage cells increases due to the difference in the amount of electricity [Ah] that the storage cells self-discharge. For this reason, conventionally, when the power storage device is charged, the voltage [V] of each storage cell is detected and a balancer circuit is operated according to the detected voltage to reduce the difference in the amount of electricity between the storage cells (see, for example, Patent Document 1). Specifically, Patent Document 1 describes that cell balance is achieved during charging using a voltage equalization circuit that equalizes the voltages of multiple cells that make up a battery pack. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-71936 A (paragraph 0026) Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, electric storage devices mounted on vehicles are charged by a vehicle generator (also known as an alternator). When an electric storage device is used at a high state of charge, it cannot accept the vehicle's regenerative charging, resulting in a deterioration in fuel efficiency. Therefore, in recent years, the state of charge (SOC) is often limited to around 70% to leave room for accepting regenerative current. Vehicles periodically charge their electric storage devices to a high SOC, but the time intervals tend to be long, such as one week. Vehicles may be parked for long periods of time, such as one to two months. Because the vehicle generator does not operate while the vehicle is parked, the time interval between charging the power storage device to a high SOC increases when the vehicle is parked for a long period of time.

[0005] In the past, sufficient consideration had not been given to the problems that arise when the time intervals at which a charging device such as a vehicle generator charges an electricity storage device to a high SOC become longer. This specification discloses a technique that can prevent a power storage device from being used while large variations in the amount of electricity between power storage cells remain. [Means for solving the problem]

[0006] The storage device connected to the charging device includes a plurality of storage cells, a balancer circuit that individually discharges each of the storage cells, a voltage sensor that detects the voltage of each of the storage cells, and a management unit. When a predetermined condition for reducing the difference in the amount of electricity between the storage cells is met, the management unit executes a request process that requests the charging device to charge the storage device, and a reduction process that, after the storage device is charged by the charging device, detects the voltage of each of the storage cells using the voltage sensor and reduces the difference in the amount of electricity between the storage cells by changing the operating time of the balancer circuit according to the detected voltage difference. [Effects of the Invention]

[0007] With the above configuration, it is possible to prevent the power storage device from being used with large variations in the amount of electricity between the power storage cells. [Brief explanation of the drawings]

[0008] [Figure 1] Schematic diagram of a vehicle and a power storage device according to a first embodiment. [Figure 2] Schematic diagram of a vehicle's power supply system [Figure 3] Exploded perspective view of the power storage device [Figure 4A] Plan view of the storage cell [Figure 4B] Cross-sectional view of line AA shown in FIG. 4A [Figure 5] A block diagram showing the electrical configuration of the power storage device. [Figure 6]Graph showing changes in current and voltage when a storage device is fully charged using CC-CV charging [Figure 7] Graph for explaining reduction of difference in remaining electric charge between storage cells [Figure 8] Graph showing changes in QF over time [Figure 9] Flowchart of a process for reducing the difference in remaining charge between storage cells based on QF [Figure 10] Graph showing an example of a plateau region [Figure 11] A graph showing the voltage change over time when two storage cells with plateau regions are charged. [Figure 12A] A graph showing the change in voltage when the storage device is fully charged (when the difference in the amount of electricity between the storage cells is 50mAh) [Figure 12B] A graph showing the change in voltage when the storage device is fully charged (when the difference in the amount of electricity between the storage cells is 200mAh) DETAILED DESCRIPTION OF THE INVENTION

[0009] [Summary of the embodiments of the present disclosure] (1) According to one aspect of the present invention, a storage device is connected to a charging device and includes a plurality of storage cells, a balancer circuit that individually discharges each of the storage cells, a voltage sensor that detects the voltage of each of the storage cells, and a management unit, wherein the management unit executes a request process that requests the charging device to charge the storage device when a predetermined condition for reducing a difference in the amount of electricity between the storage cells is met, and a reduction process that, after the storage device is charged by the charging device, detects the voltage of each of the storage cells using the voltage sensor and reduces the difference in the amount of electricity between the storage cells by changing the operating time of the balancer circuit according to the detected voltage difference.

[0010] The above-mentioned "charging device" can be rephrased as "host device." Alternatively, the "charging device" can be rephrased as "charging control device." The "amount of electricity" may be the remaining amount of electricity in the storage cell. Alternatively, if the difference between the full charge capacity of the storage cell (in other words, the remaining amount of electricity when fully charged) and the current remaining amount of electricity is defined as the remaining amount of electricity that can be charged in the storage cell, the "amount of electricity" may be the remaining amount of electricity that can be charged in the storage cell. Reducing the difference in the remaining amount of electricity is sometimes called lower matching, and reducing the difference in the remaining chargeable amount of electricity is sometimes called upper matching. For example, when there is a difference in full charge capacity between the storage cells or when the SOC is high, the difference in the amount of electricity can be reduced by upper matching, and when there is no difference in full charge capacity between the storage cells or when the SOC is low, the difference in the amount of electricity can be reduced by lower matching.

[0011] There is a relatively accurate correlation between the voltage and the amount of electricity of a storage cell. For this reason, in the past, the amount of electricity was estimated from the voltage of the storage cell, and a balancer circuit was operated according to the estimated amount of electricity to reduce the difference in the amount of electricity between the storage cells. However, some storage cells cannot accurately estimate the amount of electricity when their voltage is low. The voltage of a storage cell increases when it is charged. For this reason, conventional storage devices equipped with such storage cells detect the voltage of each storage cell when the storage device is charged by a charging device, and reduce the difference in the amount of electricity between the storage cells by operating a balancer circuit according to the detected voltage.

[0012] As a result of extensive research, the inventors of the present application have discovered that a storage device having a storage cell that cannot accurately estimate the amount of electricity when the voltage is low has the following problem when the time interval between charging of the storage device by the charging device is long. If the time interval between charging the power storage device by the charging device is long, the difference in the amount of electricity between the power storage cells will increase due to differences in the amount of electricity self-discharged by each power storage cell, and so the power storage device may be used with a large difference in the amount of electricity between the power storage cells.If the power storage device is used with a large difference in the amount of electricity between the power storage cells, it will soon be unable to demonstrate its original performance due to the influence of the power storage cell with the least amount of electricity.

[0013] According to the above-described power storage device, when a predetermined condition for reducing the difference in the amount of electricity between the storage cells is met, a request is made to the charging device to charge the power storage device, thereby increasing the opportunities for charging the power storage device compared to when the charging device only periodically charges the power storage device. Therefore, with the above-described power storage device, for a power storage device including storage cells whose amount of electricity cannot be accurately estimated when the voltage is low, it is possible to prevent the power storage device from being used while the difference in the amount of electricity between the storage cells remains large.

[0014] (2) When the management unit cannot estimate the difference in the amount of electricity between the storage cells from the difference in voltage detected by the voltage sensor, the management unit may shorten the time until the next time the specified condition is met compared to when the difference in the amount of electricity can be estimated.

[0015] If the difference in the amount of electricity between the storage cells cannot be estimated from the difference in voltage detected by the voltage sensor, the difference in the amount of electricity between the storage cells may not be sufficiently reduced even if the operation time of the balancer circuit is changed according to the difference in the detected voltage. If the difference in the amount of electricity between the storage cells cannot be sufficiently reduced, the storage device will be used with a large difference in the amount of electricity between the storage cells.

[0016] According to the above-described energy storage device, when the difference in the amount of electricity between the storage cells cannot be estimated from the difference in voltage detected by the voltage sensor, the time until the next specified condition is met is shortened compared to when the difference can be estimated, thereby preventing the energy storage device from being used while the difference in the amount of electricity between the storage cells remains large.

[0017] (3) The storage cells may have a plateau region in which voltage change in response to a change in the state of charge of the storage cells is small, and the management unit may shorten the time until the next time the specified condition is met when the voltage of any of the storage cells after the storage device is charged is equal to or lower than an upper limit voltage of the plateau region, compared to when the voltage of any of the storage cells is higher than the upper limit voltage of the plateau region.

[0018] As shown in FIG. 10, some storage cells have a plateau region in which the change in the open circuit voltage (OCV) of the storage cell relative to the change in state of charge (SOC) is small. Specifically, the plateau region is, for example, a region in which the change in OCV relative to the change in SOC is 2 mV / % or less. In FIG. 10, the voltage Vp is the upper limit voltage of the plateau region. When the voltage of a storage cell having a plateau region is in the plateau region, the change in voltage is small even if the SOC changes significantly, so the amount of electricity cannot be accurately estimated from the voltage. For this reason, in the past, a storage device including storage cells having a plateau region detected the voltage when the cell was charged to reduce the difference in the amount of electricity between the storage cells.

[0019] The present inventors have found that a power storage device including a power storage cell having a plateau region has the following problems when the time interval between charges is long. FIG. 11 shows an example of the change over time in voltage when two storage cells having a plateau region are charged. In FIG. 11, solid line 101 shows the change in voltage of a storage cell having a relatively high voltage, and solid line 102 shows the change in voltage of a storage cell having a relatively low voltage. As shown in FIG. 11, if the difference in voltage between the storage cells (in other words, the difference in the amount of electricity) is large, the voltage of any of the storage cells may not exceed the upper limit voltage Vp of the plateau region even when the energy storage device is charged. In other words, the voltage of any of the storage cells may be equal to or lower than the upper limit voltage Vp of the plateau region. When the voltage is equal to or lower than the upper limit voltage Vp of the plateau region, the amount of electricity in the storage cell cannot be accurately estimated from the voltage, and therefore, the difference in the amount of electricity between the storage cells cannot be sufficiently reduced even when the balancer circuit is operated.

[0020] Even if a single operation of the balancer circuit is not enough to sufficiently reduce the difference in the amount of electricity between the storage cells, repeated operation of the balancer circuit will eventually reduce the difference in the amount of electricity. However, in recent years, there has been a trend toward longer time intervals at which charging devices charge storage devices, so there is a possibility that the balancer circuit will not operate at short time intervals, and the storage device may be used with a large difference in the amount of electricity between the storage cells.

[0021] According to the above-described energy storage device, when the voltage of any of the energy storage cells after the energy storage device is charged is equal to or lower than the upper limit voltage Vp of the plateau region, the time until the next predetermined condition is satisfied is shorter than when the voltages of all the energy storage cells are higher than the upper limit voltage Vp, thereby shortening the time until the next operation of the balancer circuit. This makes it possible to prevent the energy storage device from being used while the difference in the amount of electricity between the energy storage cells remains large.

[0022] (4) The management unit may perform an addition process that adds a first predetermined value to a correlation value that correlates with the degree of variation in the amount of electricity between the storage cells as time passes, and a subtraction process that subtracts a second predetermined value from the correlation value after the reduction process, wherein the predetermined condition is that the correlation value has reached a predetermined threshold value, and in the subtraction process, the management unit may make the second predetermined value smaller when the voltage of any of the storage cells after the storage device is charged is equal to or lower than an upper limit voltage of a plateau region compared to when the voltages of all the storage cells are higher than the upper limit voltage of the plateau region.

[0023] The above-mentioned "correlation value" may be, for example, a value that expresses the current degree of variation in the amount of electricity between the storage cells in percentage, assuming that the degree of variation in the amount of electricity between the storage cells at a certain point in time is 100%, or may be an estimated value of an absolute value that expresses the degree of variation in the amount of electricity between the storage cells (for example, standard deviation or variance, or difference in the amount of electricity between the storage cells). Alternatively, the correlation value may be the elapsed time since the balancer circuit was last operated.

[0024] The above-mentioned "first predetermined value" may be a positive value or a negative value. Adding a negative value can be said to be subtracting a positive value. That is, the correlation value may have a positive correlation or a negative correlation with the degree of variation in the amount of electricity. In other words, the correlation value may be a so-called up-counter or a down-counter. When the first predetermined value is a positive value, the second predetermined value is also a positive value, and when the first predetermined value is a negative value, the second predetermined value is also a negative value. Subtracting a negative value can be said to be adding a positive value. According to the above-described energy storage device, when the voltage of any of the storage cells after the energy storage device is charged is equal to or lower than the upper limit voltage of the plateau region, the second predetermined value is made smaller than when the voltages of all the storage cells are higher than the upper limit voltage of the plateau region, thereby shortening the time until the next predetermined condition is met.

[0025] (5) The management unit may shorten the time until the predetermined condition is satisfied next time as the difference in voltage between the power storage cells after the power storage device is charged increases.

[0026] The above "difference in voltage between the storage cells" refers to the difference between the voltage of the storage cell with the highest voltage and the voltage of the storage cell with the lowest voltage.

[0027] Figures 12A and 12B show an example of the change in voltage over time when four storage cells are charged. In Figures 12A and 12B, solid line 103 is a graph of the charging current, and the rest are graphs of the voltage of each storage cell. Figure 12A shows a case where the difference in the amount of electricity between the storage cells is 50 mAh, and Figure 12B shows a case where the difference in the amount of electricity between the storage cells is 200 mAh.

[0028] For example, if the previous balancer circuit operation was an operation after the vehicle (charging device) had been parked for a long period of time and the balancer circuit had operated multiple times, the voltage difference between the storage cells after charging will be relatively small, as shown in Fig. 12A. In contrast, if the previous balancer circuit operation was the first balancer circuit operation after the vehicle had been parked for a long period of time, the voltage difference between the storage cells may not have been sufficiently reduced by the previous balancer circuit operation. In this case, the voltage difference between the storage cells after charging will be relatively large, as shown in Fig. 12B.

[0029] The present inventors have found that when the voltage difference between the storage cells after charging the energy storage device is large, the accuracy of estimating the difference in the amount of electricity between the storage cells decreases compared to when the voltage difference is small. Specifically, as shown in FIG. 12A , when the voltage difference after charging is small, the voltage difference is roughly constant from the beginning to the end of charging, so the difference in the amount of electricity can be detected with a certain degree of accuracy from the voltage after charging. In contrast, as shown in FIG. 12B , when the voltage difference after charging is large, the voltage difference changes between the beginning and end of charging, so even if an attempt is made to estimate the difference in the amount of electricity from the voltage difference, it cannot be uniquely determined, and the estimated difference in the amount of electricity will have a certain degree of error. For this reason, even if the balancer circuit is operated, it may not be possible to sufficiently reduce the difference in the amount of electricity between the storage cells.

[0030] In the above-described power storage device, the larger the voltage difference between the power storage cells after charging, the shorter the time until the next predetermined condition is met, so when the voltage difference is large, the time until the next operation of the balancer circuit is shorter than when the voltage difference is small, which makes it possible to prevent the power storage device from being used with a large difference in the amount of electricity between the power storage cells.

[0031] (6) The management unit may perform an addition process that adds a first predetermined value to a correlation value that correlates with the degree of variation in the amount of electricity between the storage cells over time, and a subtraction process that subtracts a second predetermined value from the correlation value after the reduction process, wherein the predetermined condition is that the correlation value has reached a predetermined threshold, and the management unit may reduce the second predetermined value in the subtraction process as the difference in voltage between the storage cells after the storage device is charged increases.

[0032] According to the above-described power storage device, the second predetermined value is made smaller as the voltage difference between the power storage cells after the power storage device is charged increases, and therefore the larger the voltage difference, the shorter the time until the next predetermined condition is met.

[0033] (7) In the addition process, the management unit may determine the first predetermined value in accordance with at least one of a temperature of the power storage cell and a state of charge of the power storage device.

[0034] The range of change per unit time in the degree of variation in the amount of electricity between the storage cells varies depending on the temperature of the storage cells and the state of charge (SOC) of the storage device. According to the above storage device, the first predetermined value is determined based on at least one of the temperature of the storage cells and the SOC of the storage device, so that the actual degree of variation in the amount of electricity between the storage cells is accurately reflected in the correlation value. This makes it possible to more appropriately determine whether the difference in the amount of electricity between the storage cells should be reduced.

[0035] [Details of the embodiments of the present disclosure] The present disclosure will be described below with reference to exemplary embodiments. The present disclosure is not limited to these examples, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope of the claims. The embodiments of the present disclosure can be realized in various forms, such as an apparatus, a method, a computer program for realizing the functions of these apparatuses or methods, and a recording medium on which the computer program is recorded.

[0036] <Embodiment 1> The first embodiment will be described with reference to Figures 1 to 9. In the following description, the reference numerals of the drawings may be omitted for the same components, with some exceptions.

[0037] (1) Energy storage device As shown in FIG. 1, a power storage device 1 according to the first embodiment is mounted on a vehicle 2 (an example of a charging device) such as an automobile. As shown in Fig. 2, the power storage device 1 supplies power to an engine starting device 10 (starter motor) and various auxiliary devices 12 (electric power steering, electric brakes, headlights, air conditioner, etc.) equipped in the vehicle 2. The power storage device 1 is charged by a vehicle generator 13 (alternator). The power storage device 1 may be charged by regenerative charging during braking. The engine starting device 10, the auxiliary machinery 12, the vehicle generator 13, and the power storage device 1 are communicably connected to a vehicle ECU (Engine Control Unit) 14 via communication cables.

[0038] (2) Configuration of the power storage device As shown in Fig. 3, the energy storage device 1 includes a housing 71. The housing 71 includes a main body 73 and a lid 74 made of a synthetic resin material. The main body 73 is cylindrical and has a bottom. The main body 73 includes a bottom portion 75 and four side portions 76. The four side portions 76 form an upper opening 77 at the upper end portion.

[0039] The housing 71 houses the battery pack 30, which is made up of a plurality of storage cells 30A, and a circuit board unit 72. The storage cells 30A are secondary batteries that can be repeatedly charged and discharged, and specifically, lithium-ion secondary batteries, for example. The circuit board unit 72 is disposed on top of the battery pack 30. The lid 74 closes an upper opening 77 of the main body 73. An outer peripheral wall 78 is provided around the periphery of the lid 74. The lid 74 has a protruding portion 79 that is generally T-shaped in plan view. A positive external terminal 80P is fixed to one corner of the front of the lid 74, and a negative external terminal 80N is fixed to the other corner.

[0040] 4A and 4B, the energy storage cell 30A contains an electrode assembly 83 together with a non-aqueous electrolyte in a rectangular parallelepiped case 82. The case 82 has a case body 84 and a lid 85 that closes the upper opening thereof. Although not shown in detail, the electrode body 83 comprises a negative electrode element made of a copper foil substrate coated with a negative electrode active material, a positive electrode element made of an aluminum foil substrate coated with a positive electrode active material, and a separator made of a porous resin film disposed between them. Both of these are strip-shaped, and are wound flat so that they can be housed in the case body 84, with the negative electrode element and the positive electrode element offset from each other on opposite sides in the width direction relative to the separator.

[0041] A positive electrode terminal 87 is connected to the positive electrode element via a positive electrode current collector 86, and a negative electrode terminal 89 is connected to the negative electrode element via a negative electrode current collector 88. The positive electrode current collector 86 and the negative electrode current collector 88 each comprise a flat base 90 and a leg 91 extending from the base 90. A through hole is formed in the base 90. The leg 91 is connected to the positive electrode element or the negative electrode element. The positive electrode terminal 87 and the negative electrode terminal 89 each comprise a terminal body 92 and a shaft 93 protruding downward from the center of the underside of the terminal body 92. Of these, the terminal body 92 and shaft 93 of the positive electrode terminal 87 are integrally molded from aluminum (a single material). In the negative electrode terminal 89, the terminal body 92 is made of aluminum, and the shaft 93 is made of copper, and these are assembled together. The terminal bodies 92 of the positive electrode terminal 87 and the negative electrode terminal 89 are disposed on both ends of the lid 85 via gaskets 94 made of an insulating material, and are exposed to the outside from the gaskets 94 .

[0042] 4A, the lid 85 has a pressure relief valve 95. The pressure relief valve 95 is located between the positive terminal 87 and the negative terminal 89. The pressure relief valve 95 opens to reduce the internal pressure of the case 82 when the internal pressure of the case 82 exceeds a limit value.

[0043] (3) Electrical configuration of the power storage device As shown in FIG. 5, the power storage device 1 includes a battery pack 30, a BMU 31 (an example of a management device), and a communication connector 32. The battery pack 30 is connected to a positive electrode external terminal 80P by a power line 34P and to a negative electrode external terminal 80N by a power line 34N. The battery pack 30 has 12 storage cells 30A connected in three parallel connections and four in series. For convenience, three storage cells 30A connected in parallel are represented by a single battery symbol in FIG. 5. Specifically, the storage cells 30A are LFP / Gr-based (so-called iron-based) lithium-ion secondary batteries containing, for example, LiFePO4 (lithium iron phosphate) as the positive electrode active material and Gr (graphite) as the negative electrode active material. LFP / Gr-based (so-called iron-based) lithium-ion secondary batteries are an example of storage cells having a plateau region.

[0044] The BMU 31 includes a current sensor 33 , a voltage sensor 35 , a temperature sensor 36 , a balancer circuit 38 and a management unit 37 . The current sensor 33 is located on the negative electrode side of the battery pack 30 and is provided on the negative electrode power line 34N. The current sensor 33 detects the charge / discharge current [A] of the battery pack 30 and outputs it to the management unit 37.

[0045] The voltage sensor 35 is connected to both ends of each storage cell 30A by a signal line. The voltage sensor 35 detects the battery voltage [V] of each storage cell 30A and outputs it to the management unit 37. The total voltage [V] of the battery pack 30 is the sum of the voltages of the four storage cells 30A connected in series. The temperature sensor 36 is of a contact type or a non-contact type, and detects the temperature [°C] of the energy storage cell 30A and outputs the detected temperature to the management unit 37. Although omitted from FIG. 5 , two or more temperature sensors 36 are provided. Each temperature sensor 36 detects a different temperature of the energy storage cell 30A. The management unit 37 determines the temperature of the energy storage device 1 as the average value of the temperatures output from, for example, two or more temperature sensors 36.

[0046] The balancer circuit 38 is a passive balancer circuit that reduces the difference in the amount of electricity between the storage cells 30A by individually discharging each storage cell 30A. The balancer circuit 38 has a discharge resistor 38A and a switch element 38B for each storage cell 30A. The discharge resistor 38A and the switch element 38B are connected in series and connected in parallel to the corresponding storage cell 30A. The switch element 38B is switched between a conducting state and a cut-off state by the management unit 37. When the switch element 38B is in the conducting state, the corresponding storage cell 30A is discharged by the discharge resistor 38A.

[0047] The management unit 37 includes a microcomputer 37A in which a CPU, RAM, etc. are integrated into one chip, a storage unit 37B, and a communication unit 37C. The microcomputer 37A manages the power storage device 1 by executing a management program stored in the storage unit 37B. The storage unit 37B is a rewritable storage medium, and stores the management program executed by the management unit 37 and various data described later. The communication unit 37C is a circuit that enables the microcomputer 37A to communicate with the vehicle ECU 14. The communication connector 32 is a connector to which a communication cable is connected for communication between the BMU 31 and the vehicle ECU 14 .

[0048] (4) Fully charge the storage device Full charging (one example of charging) of the energy storage device 1 will be described with reference to Fig. 6. Here, CC (Constant Current)-CV (Constant Voltage) charging will be described as an example. In Fig. 6, a solid line 120 indicates changes in charging current, and a dotted line 121 indicates changes in voltage. In CC-CV charging, the energy storage device 1 is charged with a constant current until the voltage of the energy storage cell 30A reaches a predetermined value, and once the voltage reaches the predetermined value, charging is switched to constant voltage charging. In constant voltage charging, the current value gradually decreases, and when the current value decreases to a predetermined threshold value Ith, the energy storage device 1 is fully charged. The predetermined threshold value Ith can be determined appropriately. For example, the current value when the SOC is 95% may be determined in advance by experiment, and the determined current value may be used as the threshold value Ith. In this case, the battery is fully charged when the SOC reaches 95%.

[0049] In the first embodiment, the power storage device 1 is fully charged at the following three charging timings (charging timings A, B, and C). The following three are examples of the timings at which the power storage device 1 is fully charged, and the timings at which the power storage device 1 is fully charged are not limited to the following three.

[0050] Charging timing A: Regular full charge Vehicle ECU 14 fully charges power storage device 1 periodically, such as once a week (hereinafter referred to as periodic full charging). When power storage device 1 is fully charged at charging timing B or charging timing C described below, full charging may be performed not when a certain time has elapsed since the previous periodic full charging, but when a certain time has elapsed since full charging at charging timing B or charging timing C.

[0051] Charging timing B: When the estimated SOC value is reset to full charge The management unit 37 estimates the SOC of the power storage device 1 using the current integration method. The current integration method estimates the SOC by detecting a current value at predetermined time intervals using the current sensor 33 and adding or subtracting the detected current value from an initial value. With the current integration method, the estimated SOC value becomes increasingly inaccurate due to the accumulation of detection errors from the current sensor 33. For this reason, the management unit 37 resets the estimated SOC value to full charge.

[0052] Specifically, there is a relatively accurate correlation between the open circuit voltage (OCV) of the power storage device 1 and the SOC. Therefore, the management unit 37 updates the SOC estimated by the current integration method with the SOC estimated from the OCV. However, if the voltage of the power storage device 1 having a plateau region is low, the SOC cannot be accurately estimated from the OCV. Therefore, when a predetermined condition for resetting the estimated value of the SOC is met, the management unit 37 requests the vehicle ECU 14 to fully charge the power storage device 1, and after the power storage device 1 is fully charged, the voltage sensor 35 detects the OCV. The OCV is not limited to the voltage when the circuit is completely open, but may be the voltage when a small current flows that can be considered to be open.

[0053] Charging timing C: When the index value (QF: Quality Factor) described below reaches 100% (an example of a predetermined threshold value) Although details will be described later, the management unit 37 determines whether or not the difference in the remaining amount of electricity between the storage cells 30A should be reduced based on an index value (hereinafter referred to as QF) that correlates with the degree of variation in the remaining amount of electricity between the storage cells 30A. QF is an example of a correlation value. When the management unit 37 determines that the difference in the remaining amount of electricity should be reduced, it requests the vehicle ECU 14 to fully charge the storage device 1, and after the storage device 1 is fully charged, it operates the balancer circuit 38 to reduce the difference in the remaining amount of electricity between the storage cells 30A.

[0054] (5) Operation of the balancer circuit 7, the operation of reducing the difference in remaining electric charge between the power storage cells 30A by the balancer circuit 38 will be described. Here, the case of reduction by bottom balancing will be described as an example. For convenience, the four power storage cells 30A are denoted by the reference numerals 30A-1 to 30A-4.

[0055] When the energy storage device 1 is fully charged, the management unit 37 detects the voltage of each storage cell 30A using the voltage sensor 35 and estimates the remaining amount of electricity from the detected voltage. The management unit 37 uses the storage cell 30A with the lowest voltage (here, storage cell 30A-4) as a reference, and determines a discharge time (an example of an operating time) for each of the other three storage cells 30A (here, storage cells 30A-1, 30A-2, and 30A-3) from the difference between the remaining amount of electricity in the reference storage cell 30A-4 and the remaining amount of electricity in the other storage cells 30A. The management unit 37 reduces the difference in the remaining amount of electricity among the storage cells 30A by operating the balancer circuit 38 for the discharge time determined for each of the other storage cells 30A.

[0056] The method of reducing the difference in remaining amount of electricity according to the difference in detected voltage is not limited to this. For example, the amount of electricity to be discharged (or the discharge time) may be predetermined according to the order, such as 18 mAh for the storage cell 30A with the largest remaining amount of electricity estimated from the detected voltage, 12 mAh for the storage cell 30A with the second largest remaining amount of electricity, and 6 mAh for the storage cell 30A with the third largest remaining amount of electricity.

[0057] The amount of electricity (or discharge time) predetermined according to the order is also called a balance amount. The management unit 37 may change the balance amount according to the detected voltage difference. For example, if the voltage difference is small, the balance amount may be set to 18 mAh, 12 mAh, or 6 mAh, and if the voltage difference is large, the balance amount may be set to 24 mAh, 18 mAh, or 6 mAh.

[0058] (6) Charging timing C The charging timing C will be specifically described with reference to Fig. 8. As described above, the management unit 37 determines the charging timing C based on QF [%]. QF is defined as follows.

[0059] 0%: A state in which the degree of variation in the remaining amount of electricity between the storage cells 30A is small and there is no need to reduce the difference in the remaining amount of electricity. Specifically, for example, a state in which the difference between the remaining amount of electricity in the storage cell 30A with the highest voltage and the remaining amount of electricity in the storage cell 30A with the lowest voltage is 35 mAh or less. 100%: A state in which the degree of variation in the remaining amount of electricity between the storage cells 30A is large and the difference in the remaining amount of electricity should be reduced. Specifically, for example, a state in which the difference in the remaining amount of electricity between the storage cell 30A with the highest voltage and the storage cell 30A with the lowest voltage is 300 mAh or more.

[0060] The degree of variation in the remaining amount of electricity among the storage cells 30A increases over time. For this reason, the management unit 37 adds a first predetermined value [%] to QF at regular time intervals, and requests the vehicle ECU 14 to fully charge when QF reaches 100%. The first predetermined value is a positive value. When QF reaches 100%, this is an example of a predetermined condition for reducing the difference in the amount of electricity among the storage cells.

[0061] The first predetermined value is determined based on, for example, the time it takes for the degree of variation in the remaining amount of electricity among the storage cells 30A to reach 100% after the energy storage device 1 is left unused when the degree of variation is 0%. This time is determined in advance through experiments. For example, assume that the time it takes for the degree of variation to reach 100% from 0% is 1000 hours. In this case, if 0.1% is added to QF every hour, QF will reach 100% after 1000 hours. Therefore, for example, if the first predetermined value is added every hour, 0.1% is added as the first predetermined value, and if it is added every two hours, 0.2% is added as the first predetermined value. The number of hours at which the first predetermined value is added can be determined as appropriate.

[0062] An example of the change in QF over time will be described with reference to Figure 8. In the following description, operating the balancer circuit 38 is referred to as balancer operation. In Figure 8, time T0 is the time when QF is 0%. Time T1 is a charging timing other than charging timing C (i.e., charging timing A or B). Full charging of the storage device 1 begins at time T1. Time T2 is the time when full charging is completed. The management unit 37 starts the balancing operation when full charging is completed. Time T3 is the time when the balancing operation is completed. When the balancer circuit 38 is operated, the difference in the remaining amount of electricity between the storage cells 30A (in other words, the degree of variation in the remaining amount of electricity) becomes smaller, so when the balancing operation is completed, the management unit 37 subtracts a second predetermined value [%] from QF. The second predetermined value is also a positive value. The second predetermined value will be explained later.

[0063] Time T4 is the timing when QF reaches 100% (i.e., charging time C). When QF reaches 100%, the management unit 37 requests full charging from the vehicle ECU 14. Time T5 is the time when full charging is completed. When full charging is completed, the management unit 37 starts balancing operation. Time T6 is the time when balancing operation is completed. When balancing operation is completed, the management unit 37 subtracts a second predetermined value from QF.

[0064] (7) Determination of the second predetermined value When the balancer circuit 38 is operated, the difference in the remaining amount of electricity between the storage cells 30A becomes smaller, so the second predetermined value is basically determined to be the same value as the current QF. Therefore, the QF after subtracting the second predetermined value becomes 0%. However, in cases (a) and (b) described below, operating the balancer circuit 38 may not sufficiently reduce the difference in the remaining amount of electricity. For this reason, in these cases, the management unit 37 sets the second predetermined value to be smaller than the current QF in order to shorten the time until the next predetermined condition is met (in other words, to shorten the time until the next operation of the balancer circuit 38).

[0065] (a) When the voltage difference between the storage cells is large after the storage device is fully charged The management unit 37 decreases the second predetermined value as the voltage difference between the storage cells 30A increases after the storage device 1 is fully charged (more specifically, after the storage device 1 is fully charged and before the balancer circuit 38 operates). The second predetermined value corresponding to the voltage difference is determined in advance by experiment and stored in the memory unit 37B. The management unit 37 determines the second predetermined value by reading the second predetermined value corresponding to the voltage difference from the memory unit 37B.

[0066] If the second predetermined value is reduced, the time until the next QF reaches 100% is shortened, and the time until the next predetermined condition is met is therefore shorter than when the second predetermined value is not reduced (i.e., when the voltage difference between the power storage cells 30A is small). In other words, the time until the next operation of the balancer circuit 38 is shortened.

[0067] (b) When the voltage of any of the storage cells after the storage device is fully charged is equal to or lower than the upper limit voltage of the plateau region. If the voltage of any of the storage cells 30A is equal to or lower than the upper limit voltage Vp of the plateau region after the storage device 1 is fully charged (more specifically, after the storage device 1 is fully charged and before the balancer circuit 38 operates), the management unit 37 reduces the second predetermined value compared to when the voltages of all of the storage cells 30A are higher than the upper limit voltage Vp of the plateau region. Specifically, for example, when the voltage of any of the storage cells 30A is equal to or lower than the upper limit voltage Vp of the plateau region, the management unit 37 determines the second predetermined value to be close to 0% (for example, 0% to 5%). As a result, the QF hardly decreases, and the time until the next predetermined condition is met becomes shorter than when the voltage of any of the storage cells 30A is higher than the upper limit voltage Vp of the plateau region.

[0068] (8) Processing to reduce the difference in the remaining charge between storage cells based on QF The flow of processing for reducing the difference in remaining amount of electricity between the power storage cells 30A based on QF will be described with reference to Fig. 9. This processing is repeatedly executed at predetermined time intervals.

[0069] In S101, the management unit 37 adds a first predetermined value to the QF (an example of an addition process). It is assumed that the QF is 0% when the use of the power storage device 1 starts. In S102, the management unit 37 determines whether QF is 100% or more (i.e., whether a predetermined condition for reducing the difference in the remaining amount of electricity between the power storage cells 30A is met). If QF is 100% or more, the management unit 37 proceeds to S103, and if QF is less than 100%, the management unit 37 ends this process.

[0070] In S103, management unit 37 requests vehicle ECU 14 to fully charge power storage device 1 (an example of request processing). In S104, the management unit 37 adds a first predetermined value to QF. In S105, the management unit 37 determines whether or not full charging has been completed. If full charging has been completed, the management unit 37 proceeds to S106, and if not, returns to S104 and repeats the process.

[0071] In S106, the management unit 37 starts a balancer operation (an example of a reduction process). In S107, the management unit 37 adds a first predetermined value to QF. In S108, the management unit 37 determines whether the balancer operation is complete. If the balancer operation is complete, the management unit 37 proceeds to S109, and if not, the management unit 37 returns to S107 and repeats the process.

[0072] In S109, the management unit 37 subtracts a second predetermined value from QF (an example of subtraction processing). As described above, the second predetermined value is determined according to the difference in voltage between the storage cells 30A after the energy storage device 1 is fully charged. If the voltage of any of the storage cells 30A after being fully charged is equal to or lower than the upper limit voltage Vp of the plateau region, the second predetermined value is determined to be close to 0%.

[0073] (9) Effects of the embodiment According to the power storage device 1, when QF reaches 100%, a request is made to the vehicle 2 for full charging, and therefore the opportunities for the power storage device 1 to be fully charged can be increased compared to when the power storage device 1 is fully charged only at charging timing A (or when the power storage device 1 is fully charged only at charging timing A or B). Therefore, with respect to the power storage device 1 including the power storage cells 30A for which the remaining amount of electricity cannot be accurately estimated when the voltage is low, the power storage device 1 can be prevented from being used while the difference in the remaining amount of electricity between the power storage cells 30A remains large, even if the time interval between when the vehicle 2 fully charges the power storage device 1 is long.

[0074] According to the energy storage device 1, when the difference in the amount of electricity between the storage cells 30A cannot be estimated from the difference in voltage detected by the voltage sensor 35 (for example, when the voltage of any of the storage cells 30A is equal to or lower than the upper limit voltage Vp of the plateau region or when the difference in voltage between the storage cells 30A is large), the time until the next time the specified condition is met is shorter than when the difference can be estimated (when the voltage of all of the storage cells 30A is higher than the upper limit voltage Vp of the plateau region or when the difference in voltage between the storage cells 30A is small), so it is possible to prevent the energy storage device 1 from being used while the difference in the amount of electricity between the storage cells 30A remains large.

[0075] According to the energy storage device 1, when the voltage of any of the storage cells 30A after the energy storage device 1 is fully charged is equal to or lower than the upper limit voltage Vp of the plateau region, the time until the next predetermined condition is satisfied is shorter than when the voltages of all the storage cells 30A are higher than the upper limit voltage Vp, thereby shortening the time until the next operation of the balancer circuit 38. This makes it possible to prevent the energy storage device 1 from being used while the difference in the remaining amount of electricity between the storage cells 30A remains large.

[0076] According to the energy storage device 1, when the voltage of any of the storage cells 30A after the energy storage device 1 is fully charged is equal to or lower than the upper limit voltage Vp of the plateau region, the second predetermined value is made smaller than when the voltages of all the storage cells 30A are higher than the upper limit voltage Vp of the plateau region, thereby shortening the time until the next QF reaches 100%. In other words, the time until the next predetermined condition is met is shortened. Therefore, even if the time interval between full charges of the vehicle 2 to the energy storage device 1 is long, it is possible to prevent the energy storage device 1 from being used while the difference in the remaining amount of electricity between the storage cells 30A remains large.

[0077] According to the energy storage device 1, the larger the voltage difference between the storage cells 30A after being fully charged, the shorter the time until the next specified condition is met, so that the energy storage device 1 can be prevented from being used while the difference in the remaining amount of electricity between the storage cells 30A remains large.

[0078] According to the energy storage device 1, the larger the voltage difference between the storage cells 30A after full charge, the smaller the second predetermined value is set, so the time until the next QF reaches 100% is shorter than when the voltage difference is small. In other words, the time until the next predetermined condition is met is shorter. This makes it possible to prevent the energy storage device 1 from being used while the remaining amount of electricity between the storage cells 30A remains large.

[0079] <Embodiment 2> The second embodiment is a modification of the first embodiment. The degree of variation in the remaining amount of electricity among the energy storage cells 30A also varies depending on the temperature of the energy storage cells 30A and the SOC of the energy storage device 1. Therefore, when adding a first predetermined value to QF at regular intervals, the management unit 37 according to the second embodiment determines the first predetermined value depending on the temperature of the energy storage cells 30A and the SOC of the energy storage device 1. Specifically, the management unit 37 increases the first predetermined value when the temperature of the energy storage cells 30A is high compared to when the temperature is low. Alternatively, the management unit 37 increases the first predetermined value when the SOC of the energy storage device 1 is high compared to when the SOC is low. How much to increase the first predetermined value depending on the temperature of the energy storage cells 30A and the SOC of the energy storage device 1 can be determined appropriately through experiments, etc.

[0080] According to the energy storage device 1 of the second embodiment, the first predetermined value is determined according to at least one of the temperature of the energy storage cells 30A and the SOC of the energy storage device 1, so that the QF accurately reflects the degree of variation in the actual remaining amounts of electricity among the energy storage cells 30A, thereby making it possible to more appropriately determine whether or not the difference in the remaining amounts of electricity among the energy storage cells 30A should be reduced.

[0081] <Other embodiments> The present invention is not limited to the embodiments described above and illustrated in the drawings, and the following embodiments, for example, are also included within the technical scope of the present invention.

[0082] (1) In the above embodiment, charging is described using a full charge as an example, but charging is not limited to a full charge. For example, charging may be performed up to a range in which the difference in the amount of electricity between the storage cells 30A can be detected. However, even if charging is performed up to that range, the difference in the amount of electricity may not be accurately detected if the voltage of any of the storage cells 30A is equal to or lower than the upper limit voltage Vp of the plateau region or if the difference in voltage between the storage cells 30A is large.

[0083] (2) In the above embodiment, the second predetermined value is decreased as the difference in voltage between the storage cells 30A after full charge increases, and further, when the voltage of any of the storage cells 30A is equal to or lower than the upper limit voltage Vp of the plateau region, the second predetermined value is set to a value closer to 0%. In contrast, the second predetermined value may simply be decreased as the difference in voltage between the storage cells 30A after full charge increases. Alternatively, the second predetermined value may simply be set to a value closer to 0% when the voltage of any of the storage cells 30A is equal to or lower than the upper limit voltage Vp of the plateau region.

[0084] (3) In the above embodiment, the remaining amount of electricity is used as an example of the amount of electricity in the energy storage device 1, but the amount of electricity in the energy storage device 1 may be the remaining amount of chargeable electricity. In the above embodiment, the case where the difference in the remaining amount of electricity between the energy storage cells 30A is reduced by bottom matching is used as an example, but if the amount of electricity in the energy storage device 1 is the remaining amount of chargeable electricity, the difference in the amount of electricity may be reduced by top matching.

[0085] (4) In the above embodiment, the correlation value is described as QF, but the correlation value is not limited to QF. For example, the correlation value may be an estimate of an absolute value (e.g., standard deviation or variance) that represents the degree of variation in the amount of electricity among the storage cells 30A. Alternatively, the correlation value may be the elapsed time since the last time the energy storage device 1 was fully charged.

[0086] (5) In the above embodiment, a passive balancer circuit has been described as an example of the balancer circuit 38. However, the balancer circuit 38 may be an active balancer circuit that reduces the difference by charging the lower-voltage storage cell 30A with the higher-voltage storage cell 30A.

[0087] (6) In the above embodiment, an LFP / Gr-based (so-called iron-based) lithium ion secondary battery was used as an example of the storage cell 30A having a plateau region, but the storage cell 30A having a plateau region is not limited to this.

[0088] (7) In the above embodiment, the power storage device 1 is mounted on a vehicle (mobile body), but the power storage device 1 may be mounted on a mobile body such as an aircraft or a ship. In this case, the aircraft or the ship is an example of a charging device.

[0089] (8) In the above embodiment, the storage cell 30A is described as a lithium ion secondary battery, but the storage cell 30A may be a capacitor that involves an electrochemical reaction.

[0090] (9) The power storage device may be configured as follows. A power storage device connected to a charging device, A plurality of storage cells; a balancer circuit that individually discharges each of the storage cells; a voltage sensor for detecting a voltage of each of the storage cells; The management department and Equipped with The management unit a request process for requesting the charging device to charge the power storage device when a predetermined condition for reducing a difference in the amount of electricity between the power storage cells is met; a reduction process for reducing a difference in the amount of electricity between the storage cells by detecting a voltage of each of the storage cells using the voltage sensor after the storage device is charged by the charging device and operating the balancer circuit according to a difference in the detected voltage; A power storage device that performs the above. [Explanation of symbols]

[0091] 1: Energy storage device 2: Vehicle (an example of a charging device) 30A: Energy storage cell 35: Voltage sensor 37: Management Department 38: Balancer circuit Vp: Upper limit voltage

Claims

1. A power storage device connected to a charging device, A plurality of storage cells; a balancer circuit that individually discharges each of the storage cells; a voltage sensor for detecting a voltage of each of the storage cells; The management department and Equipped with The management unit a request process for requesting the charging device to charge the power storage device when a predetermined condition for reducing a difference in the amount of electricity between the power storage cells is met; a reduction process for reducing a difference in the amount of electricity between the storage cells by detecting a voltage of each of the storage cells using the voltage sensor after the storage device is charged by the charging device and changing an operation time of the balancer circuit according to a difference in the detected voltage; A power storage device that performs the above.

2. The power storage device according to claim 1, When the management unit cannot estimate the difference in electrical quantity between the storage cells from the difference in voltage detected by the voltage sensor, the management unit shortens the time until the next time the specified condition is met compared to when the difference can be estimated.

3. The power storage device according to claim 2, the storage cell has a plateau region in which a change in voltage relative to a change in the state of charge of the storage cell is small, When the voltage of any of the storage cells after the storage device is charged is equal to or lower than the upper limit voltage of a plateau region, the management unit shortens the time until the next time the specified condition is met compared to when the voltages of all of the storage cells are higher than the upper limit voltage of the plateau region.

4. The power storage device according to claim 3, The management unit an addition process of adding a first predetermined value to a correlation value correlated with a degree of variation in the amount of electricity between the power storage cells over time; a subtraction process of subtracting a second predetermined value from the correlation value after the reduction process; Run the predetermined condition is that the correlation value reaches a predetermined threshold value; In the subtraction process, if the voltage of any of the storage cells after the storage device is charged is equal to or lower than an upper limit voltage of a plateau region, the management unit reduces the second predetermined value compared to when the voltages of all of the storage cells are higher than the upper limit voltage of the plateau region.

5. The power storage device according to any one of claims 2 to 4, The management unit shortens the time until the predetermined condition is satisfied next time as the difference in voltage between the power storage cells after the power storage device is charged increases.

6. The power storage device according to claim 5, The management unit an addition process of adding a first predetermined value to a correlation value correlated with a degree of variation in the amount of electricity between the power storage cells over time; a subtraction process of subtracting a second predetermined value from the correlation value after the reduction process; Run the predetermined condition is that the correlation value reaches a predetermined threshold value; In the subtraction process, the management unit reduces the second predetermined value as the difference in voltage between the power storage cells after the power storage device is charged increases.

7. The power storage device according to claim 4 or 6, In the addition process, the management unit determines the first predetermined value according to at least one of a temperature of the power storage cell and a state of charge of the power storage device.

8. A control method for a power storage device connected to a charging device, comprising: The power storage device is A plurality of storage cells; a balancer circuit that individually discharges each of the storage cells; a voltage sensor for detecting a voltage of each of the storage cells; Equipped with The control method includes: a request step of requesting the charging device to charge the power storage device when a predetermined condition for reducing a difference in the amount of electricity between the power storage cells is met; a reduction step of detecting a voltage of each of the storage cells by the voltage sensor after the storage device is charged by the charging device, and reducing a difference in the amount of electricity between the storage cells by changing an operation time of the balancer circuit in accordance with a difference in the detected voltage; A method for controlling an electricity storage device, comprising:

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