Power storage device and method for controlling the power storage device

Abstract

To prevent a power storage device from being used in a state where a difference in electrical quantity between power storage cells is large.SOLUTION: A power storage device 1 connected with a vehicle 2 comprises a plurality of power storage cells 30A, a balancer circuit 38 for individually discharging each of the power storage cells 30A, a voltage sensor 35 for detecting a voltage of each of the power storage cells 30A, and a management part 37. the management part 37 executes a request process (S103) comprising a step of requiring charging of the power storage device 1 to the vehicle 2 when a predetermined condition under which a difference in electrical quantity between the power storage cells 30A is reduced; and a reduction process (S106) comprising a step of detecting the voltage of each of the power storage cells 30A with the voltage sensor 35 after charging the power storage device 1 by the vehicle 2, and a step of reducing the difference in electrical quantity between the power storage cells 30A by changing an operation time of the balancer circuit 38 according to a detected voltage difference.SELECTED DRAWING: Figure 8

Description

Technical Field

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

Background Art

[0002] When a power storage device including a plurality of power storage cells is left unattended for a long time, the difference in the amount of electricity [Ah] between the power storage cells increases due to the difference in the amount of self-discharge electricity [Ah] between the power storage cells. For this reason, conventionally, when the power storage device is charged, the voltage [V] of each power storage cell is detected, and the difference in the amount of electricity between the power storage cells is reduced by operating a balancer circuit according to the detected voltage (see, for example, Patent Document 1). Specifically, Patent Document 1 describes that cell balance during charging is achieved by a voltage equalization circuit that equalizes the voltages of a plurality of cells constituting a battery pack.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventionally, a power storage device mounted on a vehicle is charged by a vehicle generator (so-called alternator). When the power storage device is used at a high state of charge, the vehicle cannot receive regenerative charging, and the fuel consumption deteriorates. Therefore, in recent years, in order to leave room for accepting regenerative current, the state of charge (SOC) is often suppressed to around 70%. The vehicle periodically charges the power storage device to a high SOC, but the time interval tends to be long, such as one week. The vehicle may be parked for a long period of time, such as one to two months. Since the vehicle generator does not operate while the vehicle is parked, the time interval for charging the power storage device to a high SOC becomes longer when the vehicle is parked for a long time.

[0005] Conventionally, the problems caused by the long time interval for a charging device such as a vehicle generator to charge a power storage device to a high SOC have not been sufficiently studied. This specification discloses a technique capable of suppressing the use of a power storage device while the variation in the amount of electricity between power storage cells remains large.

Means for Solving the Problems

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

Effects of the Invention

[0007] With the above configuration, it is possible to suppress the use of the power storage device while the variation in the amount of electricity between the power storage cells remains large.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

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Figure 4A

Figure 4B

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12A

Figure 12B

Embodiments for Carrying Out the Invention

[0009] [Summary of Embodiments of the Present Disclosure] (1) According to one aspect of the present invention, a power storage device is a power storage device connected to a charging device, and includes a plurality of power storage cells, a balancer circuit that individually discharges each of the power storage cells, a voltage sensor that detects the voltage of each of the power storage cells, and a management unit. When a predetermined condition for reducing the difference in charge amount between the power storage cells is satisfied, the management unit performs a request process of requesting the charging device to charge the power storage device, and after the power storage device is charged by the charging device, the voltage sensor detects the voltage of each of the power storage cells, and by changing the operation time of the balancer circuit according to the detected voltage difference, a reduction process of reducing the difference in charge amount between the power storage cells is executed.

[0010] The above "charging device" can also be referred to as a "higher-level device". Alternatively, the "charging device" can also be referred to as a "charge control device". The above-mentioned "electric quantity" may be the remaining electric quantity of the storage cell. Alternatively, when the difference between the full charge capacity of the storage cell (in other words, the remaining electric quantity at full charge) and the current remaining electric quantity is defined as the remaining chargeable electric quantity of the storage cell, the above-mentioned "electric quantity" may be the remaining chargeable electric quantity of the storage cell. Reducing the difference in the remaining electric quantity is sometimes referred to as bottom balancing, and reducing the difference in the remaining chargeable electric quantity is sometimes referred to as top balancing. For example, when there is a difference in the full charge capacity between storage cells or when reducing the difference in electric quantity when the state of charge (SOC) is high, the difference in electric quantity may be reduced by top balancing, and when there is no difference in the full charge capacity between storage cells or when reducing the difference in electric quantity when the SOC is low, the difference in electric quantity may be reduced by bottom balancing.

[0011] There is a relatively accurate correlation between the voltage and the electric quantity of the storage cell. For this reason, conventionally, the electric quantity has been estimated from the voltage of the storage cell, and the difference in the electric quantity between the storage cells has been reduced by operating the balancer circuit according to the estimated electric quantity. However, there are some storage cells that cannot accurately estimate the electric quantity when the voltage is low. When the storage cell is charged, the voltage increases. For this reason, in a conventional power storage device including such a storage cell, when the power storage device is charged by a charging device, the voltage of each storage cell is detected, and the difference in the electric quantity between the storage cells is reduced by operating the balancer circuit according to the detected voltage.

[0012] As a result of intensive studies, the inventors of the present application have found that for a power storage device including a storage cell that cannot accurately estimate the electric quantity when the voltage is low, there are the following problems when the time interval at which the charging device charges the power storage device is long. When the time interval at which the charging device charges the power storage device is long, the difference in the self-discharge electric quantity of each storage cell causes the difference in the electric quantity between the storage cells to increase during that time. Therefore, there is a possibility that the power storage device is used with a large difference in the electric quantity between the storage cells. If the power storage device is used with a large difference in the electric quantity between the storage cells, the original performance cannot be exhibited at an early stage due to the influence of the storage cell with the least electric quantity.

[0013] According to the above-described power storage device, when a predetermined condition for reducing the difference in the amount of electricity between the power storage cells is satisfied, the charging device is requested to charge. Therefore, compared with the case where the charging device only charges periodically, the opportunity for the power storage device to be charged can be increased. For this reason, according to the above-described power storage device, for a power storage device including a power storage cell whose amount of electricity cannot be accurately estimated when the voltage is low, it is possible to suppress the power storage device from being used while the difference in the amount of electricity between the power storage cells remains large.

[0014] (2) When the management unit cannot estimate the difference in the amount of electricity between the power storage cells from the difference in voltage detected by the voltage sensor, the management unit may shorten the time until the next predetermined condition is satisfied as compared with the case where it can be estimated.

[0015] When the difference in the amount of electricity between the power storage cells cannot be estimated from the difference in voltage detected by the voltage sensor, even if the operation time of the balancer circuit is changed according to the detected voltage difference, there is a possibility that the difference in the amount of electricity between the power storage cells cannot be sufficiently reduced. If the difference in the amount of electricity between the power storage cells cannot be sufficiently reduced, the power storage device is used while the difference in the amount of electricity between the power storage cells remains large.

[0016] According to the above-described power storage device, when the difference in the amount of electricity between the power storage cells cannot be estimated from the difference in voltage detected by the voltage sensor, the time until the next predetermined condition is satisfied is shortened as compared with the case where it can be estimated. Therefore, it is possible to suppress the power storage device from being used while the difference in the amount of electricity between the power storage cells remains large.

[0017] (3) The power storage cell has a plateau region where the change in voltage with respect to the change in the state of charge of the power storage cell is small. When the voltage of any of the power storage cells after the power storage device is charged is equal to or lower than the upper limit voltage of the plateau region, the management unit may shorten the time until the next predetermined condition is satisfied as compared with the case where the voltage of any of the power storage cells is higher than the upper limit voltage of the plateau region.

[0018] As shown in FIG. 10, some of the power storage cells have a plateau region where the change in the open circuit voltage (OCV) of the power storage cell with respect to the change in the state of charge (SOC) is small. Specifically, the plateau region is, for example, a region where the change amount of the OCV with respect to the change amount of the 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 the power storage cell having the plateau region is in the plateau region, even if the SOC changes greatly, the change in voltage is small, so the amount of electricity cannot be accurately estimated from the voltage. For this reason, conventionally, a power storage device including a power storage cell having a plateau region has detected the voltage when charged to reduce the difference in the amount of electricity between the power storage cells.

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

[0020] Even if the difference in the amount of electricity between the power storage cells cannot be sufficiently reduced by only one operation of the balancer circuit, the difference in the amount of electricity will eventually be reduced if the operation of the balancer circuit is repeated. However, in recent years, the charging device has a tendency to charge the power storage device at longer time intervals, so the balancer circuit does not operate at short time intervals, and there is a possibility that the power storage device is used with a large difference in the amount of electricity between the power storage cells remaining.

[0021] According to the above-described power storage device, when the voltage of any of the power storage cells after the power 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 voltage of any of the power storage cells is greater than the upper limit voltage Vp. Therefore, the time until the next operation of the balancer circuit is shortened. For this reason, it is possible to suppress the use of the power storage device with a large difference in the amount of electricity between the power storage cells.

[0022] (4) The management unit executes an addition process of adding a first predetermined value to a correlation value correlated with the degree of variation in the amount of electricity between the power storage cells according to the passage of time, and a subtraction process of subtracting a second predetermined value from the correlation value after the reduction process. The predetermined condition is that the correlation value has reached a predetermined threshold value. In the subtraction process, when the voltage of any of the power storage cells after the power storage device is charged is equal to or lower than the upper limit voltage of the plateau region, the management unit may make the second predetermined value smaller than when the voltage of any of the power storage cells is higher than the upper limit voltage of the plateau region.

[0023] The above-mentioned "correlation value" may be a value representing the current degree of variation in % when the degree of variation in the amount of electricity between the power storage cells at a certain point in time is set to 100%, or an estimated value of an absolute value representing the degree of variation in the amount of electricity between the power storage cells (for example, standard deviation, variance, or the difference in the amount of electricity between the power storage cells). Alternatively, the correlation value may be the elapsed time since the previous operation of the balancer circuit.

[0024] The above-mentioned "first predetermined value" may be a positive value or a negative value. Adding a negative value can be regarded as 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 regarded as adding a positive value. According to the above-described power storage device, when the voltage of any of the power storage cells after the power 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 voltage of any of the power storage cells is higher than the upper limit voltage of the plateau region. Therefore, the time until the next predetermined condition is satisfied is shortened.

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

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

[0027] FIGS. 12A and 12B show an example of the temporal change in voltage when four power storage cells are charged. In FIGS. 12A and 12B, the solid line 103 is a graph of the charging current, and the others are graphs of the voltages of the respective power storage cells. FIG. 12A shows the case where the difference in the amount of electricity between the power storage cells is 50 mAh, and FIG. 12B shows the case where the difference in the amount of electricity between the power storage cells is 200 mAh.

[0028] For example, if the previous operation of the balancer circuit was an operation after the balancer circuit operated multiple times after the vehicle (charging device) had been parked for a long time, as shown in FIG. 12A, the voltage difference between the power storage cells after charging is relatively small. On the other hand, if the previous operation of the balancer circuit was the first operation of the balancer circuit after the vehicle had been parked for a long time, there is a possibility that the voltage difference between the power storage cells was not sufficiently reduced by the previous operation of the balancer circuit. In this case, as shown in FIG. 12B, the voltage difference between the power storage cells after charging becomes relatively large.

[0029] The inventors of the present application have found that when the voltage difference between power storage cells after the power storage device is charged is large, the estimation accuracy of the difference in the amount of electricity between the power 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 generally constant from the initial stage to the final stage of charging, so the difference in the amount of electricity can be detected with a certain degree of accuracy from the voltage after charging. On the other hand, as shown in FIG. 12B, when the voltage difference after charging is large, the voltage difference changes between the initial stage and the final stage of charging. Therefore, 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 has a certain 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 power storage cells.

[0030] According to 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 satisfied. Therefore, 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. For this reason, it is possible to suppress the power storage device from being used while the difference in the amount of electricity between the power storage cells remains large.

[0031] (6) The management unit executes an addition process of adding a first predetermined value to a correlation value correlated with the degree of variation in the amount of electricity between the power storage cells according to the passage of time, and after the reduction process, a subtraction process of subtracting a second predetermined value from the correlation value. The predetermined condition is that the correlation value has reached a predetermined threshold value. In the subtraction process, the management unit may make the second predetermined value smaller as the voltage difference between the power storage cells after the power storage device is charged is larger.

[0032] According to the above-described power storage device, the larger the voltage difference between the power storage cells after the power storage device is charged, the smaller the second predetermined value. Therefore, the larger the voltage difference, the shorter the time until the next predetermined condition is satisfied.

[0033] (7) In the addition process, the management unit may determine the first predetermined value according to at least one of the temperature of the storage battery cell and the state of charge of the storage device.

[0034] The change width per unit time of the degree of variation in the amount of electricity between the storage battery cells varies depending on the temperature of the storage battery cells and the state of charge (SOC) of the storage device. According to the above storage device, since the first predetermined value is determined according to at least one of the temperature of the storage battery cells and the SOC of the storage device, the actual degree of variation in the amount of electricity between the storage battery cells is accurately reflected by the correlation value. Therefore, it is possible to more appropriately determine whether or not the difference in the amount of electricity between the storage battery cells should be reduced.

[0035] [Details of Embodiments of the Present Disclosure] Embodiments of the present disclosure will be described below. The present disclosure is not limited to these examples, but is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. Embodiments of the present disclosure can be realized in various forms such as a device, a method, a computer program for realizing the functions of these devices or methods, and a recording medium on which the computer program is recorded.

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

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

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

[0039] The housing 71 houses a battery pack 30 composed of a plurality of power storage cells 30A and a circuit board unit 72. The power storage cell 30A is a secondary battery capable of repeated charge and discharge, and specifically, for example, a lithium ion secondary battery. The circuit board unit 72 is disposed above the battery pack 30. The lid 74 closes the upper opening 77 of the main body 73. An outer peripheral wall 78 is provided around the lid 74. The lid 74 has a protruding portion 79 that is substantially T-shaped in plan view. A positive electrode external terminal 80P is fixed to one corner portion of the front portion of the lid 74, and a negative electrode external terminal 80N is fixed to the other corner portion.

[0040] As shown in FIGS. 4A and 4B, the power storage cell 30A is obtained by housing an electrode body 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 has a separator made of a porous resin film disposed between a negative electrode element in which a negative electrode active material is applied to a base material made of copper foil and a positive electrode element in which a positive electrode active material is applied to a base material made of aluminum foil. All of these are in a strip shape, and are wound flatly so as to be accommodated in the case body 84 with the negative electrode element and the positive electrode element being shifted in position to opposite sides in the width direction with respect to the separator.

[0041] The positive electrode element has a positive electrode terminal 87 connected via a positive electrode current collector 86, and the negative electrode element has a negative electrode terminal 89 connected via a negative electrode current collector 88. The positive electrode current collector 86 and the negative electrode current collector 88 each consist of a flat pedestal portion 90 and a leg portion 91 extending from the pedestal portion 90. A through-hole is formed in the pedestal portion 90. The leg portion 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 consist of a terminal main body portion 92 and a shaft portion 93 protruding downward from the center portion of its lower surface. Among them, the terminal main body portion 92 and the shaft portion 93 of the positive electrode terminal 87 are integrally formed of aluminum (a single material). In the case of the negative electrode terminal 89, the terminal main body portion 92 is made of aluminum and the shaft portion 93 is made of copper, and they are assembled together. The terminal main body portions 92 of the positive electrode terminal 87 and the negative electrode terminal 89 are arranged at both ends of the lid 85 via gaskets 94 made of an insulating material, and are exposed outward from these gaskets 94.

[0042] As shown in FIG. 4A, the lid 85 has a pressure release valve 95. The pressure release valve 95 is located between the positive electrode terminal 87 and the negative electrode terminal 89. The pressure release valve 95 opens when the internal pressure of the case 82 exceeds a limit value to lower the internal pressure of the case 82.

[0043] (3) Electrical configuration of the power storage device As shown in FIG. 5, the power storage device 1 includes an assembled battery 30, a BMU 31 (an example of a management device), and a communication connector 32. The assembled battery 30 is connected to the positive electrode external terminal 80P by a power line 34P and to the negative electrode external terminal 80N by a power line 34N. The assembled battery 30 has 12 power storage cells 30A connected in 3 parallel and 4 series. For convenience, in FIG. 5, the 3 power storage cells 30A connected in parallel are represented by one battery symbol. Specifically, the power storage cell 30A contains, for example, LiFePO 4 (lithium iron phosphate) in the positive electrode active material and Gr (graphite) in the negative electrode active material, and is an LFP / Gr-based (so-called iron-based) lithium ion secondary battery. The LFP / Gr-based (so-called iron-based) lithium ion secondary battery is an example of a power storage cell 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 power line 34N of the negative electrode. The current sensor 33 detects the charge and 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 signal lines. 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 a contact type or a non-contact type, detects the temperature [°C] of the storage cell 30A, and outputs it to the management unit 37. Although omitted in FIG. 5, two or more temperature sensors 36 are provided. Each temperature sensor 36 detects the temperature of a different storage cell 30A. The management unit 37 sets, for example, the average value of the temperatures output from two or more temperature sensors 36 as the temperature of the power storage device 1.

[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 discharging each storage cell 30A individually. 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 are connected in parallel with the corresponding storage cell 30A. The switch element 38B is switched between an energized state and a cut-off state by the management unit 37. When the switch element 38B is in the energized 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, a 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 a management program executed by the management unit 37 and various types of data described later. The communication unit 37C is a circuit for the microcomputer 37A to communicate with the vehicle ECU 14. The communication connector 32 is a connector to which a communication cable for the BMU 31 to communicate with the vehicle ECU 14 is connected.

[0048] (4) Full charge of the power storage device Referring to FIG. 6, the full charge (an example of charging) of the power storage device 1 will be described. Here, CC (Constant Current)-CV (Constant Voltage) charging will be described as an example. In FIG. 6, the solid line 120 indicates the change in the charging current, and the dotted line 121 indicates the change in the voltage. In CC-CV charging, the power storage device 1 is charged at a constant current until the voltage of the power storage cell 30A reaches a predetermined value, and when the voltage reaches the predetermined value, it 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 Ith, it becomes a full charge. The predetermined threshold Ith can be determined as appropriate. For example, the current value when the SOC is 95% can be obtained in advance through experiments, and the obtained current value can be used as the threshold Ith. In this case, it becomes a full charge when the SOC reaches 95%.

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

[0050] Charging timing A: Regular full charge The vehicle ECU 14 periodically fully charges the power storage device 1, such as once a week (hereinafter referred to as periodic full charge). When fully charged at the charging timing B or charging timing C described hereinafter, it may be fully charged when a certain period of time has elapsed since being fully charged at the charging timing B or charging timing C, rather than when a certain period of time has elapsed since the previous periodic full charge.

[0051] Charging timing B: When resetting the estimated value of the SOC to full charge The management unit 37 estimates the SOC of the power storage device 1 by the current integration method. The current integration method is a method of estimating the SOC by detecting the current value at a predetermined time interval by the current sensor 33 and adding or subtracting the detected current value from the initial value. In the current integration method, the detection error of the current sensor 33 accumulates, and the estimated value of the SOC gradually becomes inaccurate. Therefore, the management unit 37 resets the estimated value of the SOC to full charge.

[0052] Specifically, there is a relatively accurate correlation between the open circuit voltage (OCV: Open Circuit Voltage) 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, for the power storage device 1 having a plateau region, the SOC cannot be accurately estimated from the OCV when the voltage is low. Therefore, when a predetermined condition for resetting the estimated value of the SOC is satisfied, 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, and may be the voltage when a current small enough to be regarded as the circuit being open is flowing.

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

[0054] (5) Operation of the Balancer Circuit With reference to FIG. 7, the operation of reducing the difference in the remaining charge amount between the power storage cells 30A by the balancer circuit 38 will be described. Here, the case of reducing by downward alignment will be described as an example. For convenience, here, the four power storage cells 30A are labeled 30A-1 to 30A-4.

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

[0056] The method of reducing the difference in the remaining charge amount according to the detected voltage difference is not limited to this. For example, the power storage cell 30A with the most remaining charge amount estimated from the detected voltage is 18 mAh, the second most is 12 mAh, the third most is 6 mAh, etc., and the amount of electricity to be discharged (or the discharge time) may be determined in advance according to the ranking.

[0057] The amount of electricity (or discharge time) determined in advance according to the ranking is also referred to as the balance amount. The management unit 37 may change the balance amount according to the detected voltage difference. For example, when the voltage difference is small, the balance amounts may be set to 18 mAh, 12 mAh, and 6 mAh, and when the voltage difference is large, the balance amounts may be changed to 24 mAh, 18 mAh, 6 mAh, etc.

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

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

[0060] The degree of variation in the remaining amount of electricity between the power storage cells 30A increases with the passage of time. Therefore, the management unit 37 adds a first predetermined value [%] to QF at regular intervals, and when QF reaches 100%, it requests a full charge from the vehicle ECU 14. The first predetermined value is a positive value. The fact that QF has reached 100% is an example of a predetermined condition for reducing the difference in the amount of electricity between the power storage cells.

[0061] The first predetermined value is determined based on, for example, the time from when the power storage device 1 with a variation degree of the remaining charge amount between the power storage cells 30A of 0% is left until the variation degree becomes 100%. This time is determined in advance by experiments. For example, assume that the time from when the variation degree is 0% to 100% is 1000 hours. In this case, if 0.1% is added to QF every hour, QF will become 100% after 1000 hours. Therefore, when adding the first predetermined value every hour, 0.1% is added as the first predetermined value, and when adding it every two hours, 0.2% is added as the first predetermined value. The time interval for adding the first predetermined value can be determined as appropriate.

[0062] With reference to FIG. 8, an example of the temporal change of QF will be described. In the following description, operating the balancer circuit 38 is referred to as the balancer operation. In FIG. 8, time point T0 is the time point when QF is 0%. Time point T1 is a charging timing other than the charging timing C (that is, the charging timing A or B). The power storage device 1 starts full charge at time point T1. Time point T2 is the time point when full charge is completed. When full charge is completed, the management unit 37 starts the balancer operation. Time point T3 is the time point when the balancer operation is completed. When the balancer circuit 38 is operated, the difference in the remaining charge amount between the power storage cells 30A (in other words, the variation degree of the remaining charge amount) becomes smaller. Therefore, when the balancer operation is completed, the management unit 37 subtracts the second predetermined value [%] from QF. The second predetermined value is also a positive value. The explanation of the second predetermined value will be described later.

[0063] Time point T4 is the timing when QF reaches 100% (that is, the charging timing C). When QF reaches 100%, the management unit 37 requests full charge from the vehicle ECU 14. Time point T5 is the time point when full charge is completed. When full charge is completed, the management unit 37 starts the balancer operation. Time point T6 is the time point when the balancer operation is completed. When the balancer operation is completed, the management unit 37 subtracts the 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 charge amount between the power storage cells 30A becomes smaller. Therefore, basically, the second predetermined value is determined to be the same as the current QF. For this reason, QF after subtracting the second predetermined value becomes 0%. However, in the cases of (a) and (b) described below, the difference in the remaining charge amount may not be sufficiently reduced even when the balancer circuit 38 is operated. For this reason, the management unit 37 makes the second predetermined value smaller than the current QF in order to shorten the time until the next predetermined condition is satisfied (in other words, to shorten the time until the next operation of the balancer circuit 38).

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

[0066] Reducing the second predetermined value shortens the time until the next QF reaches 100%. Therefore, the time until the next predetermined condition is satisfied becomes shorter compared to the case where the second predetermined value is not reduced (that is, 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 becomes shorter.

[0067] (b) When the voltage of any of the power storage cells is equal to or lower than the upper limit voltage of the plateau region after the power storage device is fully charged When the voltage of any of the power storage cells 30A after the power storage device 1 is fully charged (more specifically, before the balancer circuit 38 operates after the power storage device 1 is fully charged) is equal to or lower than the upper limit voltage Vp of the plateau region, the management unit 37 makes the second predetermined value smaller compared to the case where the voltage of any of the power storage cells 30A is higher than the upper limit voltage Vp of the plateau region. Specifically, for example, when the voltage of any one of the power 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 a value close to 0% (for example, 0% to 5%). For this reason, QF hardly decreases, and the time until the next predetermined condition is satisfied is shorter than when the voltage of any of the power storage cells 30A is higher than the upper limit voltage Vp of the plateau region.

[0068] (8) Process for reducing the difference in remaining charge amount between power storage cells based on QF With reference to FIG. 9, the flow of the process for reducing the difference in remaining charge amount between the power storage cells 30A based on QF will be described. This process is repeatedly executed at predetermined time intervals.

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

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

[0071] In S106, the management unit 37 starts the balancer operation (an example of a reduction process). In S107, the management unit 37 adds the first predetermined value to QF. In S108, the management unit 37 determines whether the balancer operation has been completed. If the balancer operation has been completed, the management unit 37 proceeds to S109, and if not, it returns to S107 to repeat 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 voltage difference between the power storage cells 30A after the power storage device 1 is fully charged. When the voltage of any of the power storage cells 30A after full charge is equal to or lower than the upper limit voltage Vp of the plateau region, the second predetermined value is determined to be a value close to 0%.

[0073] (9) Effects of the Embodiment According to the power storage device 1, when QF reaches 100%, a full charge is requested from the vehicle 2. Therefore, compared with the case where the power storage device 1 is fully charged only at the charging timing A (or only at the charging timings A and B), the opportunity for the power storage device 1 to be fully charged can be increased. For this reason, according to the power storage device 1, regarding the power storage device 1 including the power storage cells 30A whose remaining charge amount cannot be accurately estimated when the voltage is low, even if the time interval for the vehicle 2 to fully charge the power storage device 1 is long, it is possible to suppress the power storage device 1 from being used while the difference in the remaining charge amount between the power storage cells 30A remains large.

[0074] According to the power storage device 1, when it is impossible to estimate the difference in the charge amount between the power storage cells 30A from the voltage difference detected by the voltage sensor 35 (for example, when the voltage of any of the power storage cells 30A is equal to or lower than the upper limit voltage Vp of the plateau region, or when the voltage difference between the power storage cells 30A is large), compared with the case where it is possible to estimate (when the voltage of any of the power storage cells 30A is higher than the upper limit voltage Vp of the plateau region, or when the voltage difference between the power storage cells 30A is small), the time until the next predetermined condition is satisfied is shortened. Therefore, it is possible to suppress the power storage device 1 from being used while the difference in the charge amount between the power storage cells 30A remains large.

[0075] According to the power storage device 1, when the voltage of any one of the power storage cells 30A after the power 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 voltage of any of the power storage cells 30A is higher than the upper limit voltage Vp of the plateau region. Therefore, the time until the next operation of the balancer circuit 38 is shortened. For this reason, it is possible to suppress the power storage device 1 from being used while the difference in the remaining charge amount between the power storage cells 30A is large.

[0076] According to the power storage device 1, when the voltage of any one of the power storage cells 30A after the power 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 voltage of any of the power storage cells 30A is higher than the upper limit voltage Vp of the plateau region. Therefore, the time until the next QF reaches 100% is shortened. In other words, the time until the next predetermined condition is satisfied is shortened. For this reason, even if the time interval for the vehicle 2 to fully charge the power storage device 1 is long, it is possible to suppress the power storage device 1 from being used while the difference in the remaining charge amount between the power storage cells 30A is large.

[0077] According to the power storage device 1, the larger the voltage difference between the power storage cells 30A after being fully charged, the shorter the time until the next predetermined condition is satisfied. Therefore, it is possible to suppress the power storage device 1 from being used while the difference in the remaining charge amount between the power storage cells 30A is large.

[0078] According to the power storage device 1, the larger the voltage difference between the power storage cells 30A after being fully charged, the smaller the second predetermined value. Therefore, 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 satisfied is shortened. For this reason, it is possible to suppress the power storage device 1 from being used while the difference in the remaining charge amount between the power storage cells 30A is large.

[0079] <Embodiment 2> Embodiment 2 is a modification of Embodiment 1. The degree of variation in the remaining charge amount among the storage cells 30A also varies depending on the temperature of the storage cells 30A and the SOC of the power storage device 1. For this reason, when the management unit 37 according to Embodiment 2 adds the first predetermined value to the QF at regular intervals, it determines the first predetermined value according to the temperature of the storage cells 30A and the SOC of the power storage device 1. Specifically, when the temperature of the storage cells 30A is high, the management unit 37 increases the first predetermined value as compared with the case where the temperature is low. Alternatively, when the SOC of the power storage device 1 is high, the management unit 37 increases the first predetermined value as compared with the case where the SOC is low. How much to increase the first predetermined value according to the temperature of the storage cells 30A and the SOC of the power storage device 1 can be appropriately determined by experiments or the like.

[0080] According to the power storage device 1 according to Embodiment 2, since the first predetermined value is determined according to at least one of the temperature of the storage cells 30A and the SOC of the power storage device 1, the degree of variation in the remaining charge amount among the actual storage cells 30A is accurately reflected by the QF. For this reason, it is possible to more appropriately determine whether or not the difference in the remaining charge amount among the storage cells 30A should be reduced.

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

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

[0083] (2) In the above embodiment, an example was described in which the greater the voltage difference between the power storage cells 30A after full charge, the smaller the second predetermined value, and further, when the voltage of any one of the power 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 close to 0%. In contrast, it may be sufficient to simply make the second predetermined value smaller as the voltage difference between the power storage cells 30A after full charge becomes greater. Alternatively, it may be sufficient to simply make the second predetermined value a value close to 0% when the voltage of any one of the power 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 charge amount was described as an example of the charge amount of the power storage device 1, but the charge amount of the power storage device 1 may be the remaining chargeable charge amount. In the above embodiment, an example was described in which the difference in the remaining charge amount between the power storage cells 30A is reduced by under-matching, but when the charge amount of the power storage device 1 is the remaining chargeable charge amount, the difference in the charge amount may be reduced by over-matching.

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

[0086] (5) In the above embodiment, a passive type balancer circuit was described as an example of the balancer circuit 38. In contrast, the balancer circuit 38 may be an active type balancer circuit that reduces the difference by charging the power storage cell 30A with a low voltage using the power storage cell 30A with a high voltage.

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

[0088] (7) In the above-described embodiment, the case where the power storage device 1 is mounted on a vehicle (mobile body) has been described as an example. However, the power storage device 1 may be mounted on a mobile body such as an aircraft or a ship. In that case, the aircraft or the ship is an example of a charging device.

[0089] (8) In the above-described embodiment, the lithium-ion secondary battery has been described as an example of the power storage cell 30A. However, the power 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 power storage cells, a balancer circuit that discharges each of the power storage cells individually, a voltage sensor that detects the voltage of each of the power storage cells, a management unit, and includes, the management unit, when a predetermined condition for reducing the difference in the amount of electricity between the power storage cells is satisfied, a request process for requesting the charging device to charge the power storage device, after the power storage device is charged by the charging device, the voltage sensor detects the voltage of each of the power storage cells, and by operating the balancer circuit according to the detected voltage difference, a reduction process for reducing the difference in the amount of electricity between the power storage cells, and executes a power storage device.

Explanation of Reference Numerals

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

Claims

1. A power storage device connected to a charging device, comprising a plurality of power storage cells, a balancer circuit for individually discharging each of the power storage cells, a voltage sensor for detecting the voltage of each of the power storage cells, and a management unit, wherein the management unit performs a request process of requesting the charging device to charge the power storage device when a predetermined condition for reducing the difference in the amount of electricity between the power storage cells is satisfied, and after the power storage device is charged by the charging device, the management unit detects the voltage of each of the power storage cells by the voltage sensor, and changes the operation time of the balancer circuit according to the detected voltage difference, thereby reducing the difference in the amount of electricity between the power storage cells. A power storage device that executes the above.

2. The power storage device according to claim 1, wherein when the management unit cannot estimate the difference in the amount of electricity between the power storage cells from the voltage difference detected by the voltage sensor, the management unit shortens the time until the next predetermined condition is satisfied compared to when it can be estimated.

3. The power storage device according to claim 2, wherein the power storage cell has a plateau region where the change in voltage with respect to the change in the charge state of the power storage cell is small, and when the voltage of any one of the power storage cells after the power storage device is charged is equal to or lower than the upper limit voltage of the plateau region, the management unit shortens the time until the next predetermined condition is satisfied compared to when the voltage of any of the power storage cells is higher than the upper limit voltage of the plateau region.

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

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

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

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

8. A control method for a storage device connected to a charging device, The storage device includes a plurality of storage cells, a balancer circuit for individually discharging each of the storage cells, a voltage sensor for detecting the voltage of each of the storage cells, and is provided with The control method includes a request step of requesting the charging device to charge the storage device when a predetermined condition for reducing the difference in the amount of electricity between the storage cells is satisfied; After the storage device is charged by the charging device, the voltage of each storage cell is detected by the voltage sensor, and the operation time of the balancer circuit is changed according to the detected voltage difference, thereby reducing the difference in the amount of electricity between the storage cells. A reduction step; A control method for a storage device, including.

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