Battery monitoring device and program

Abstract

To provide a battery monitor and a program that can reduce the accuracy of calculating the state of a battery.SOLUTION: A BMU50 as a battery monitor is applied to a battery pack 10 with a plurality of serially connected battery cells 12. The BMU50 calculates the difference of the terminal voltage between a first battery cell and a second battery cell of battery cells 12 when the battery cells 12 are being charged. The BMU50 calculates the battery state of the battery cell 12 on the basis of the calculated difference. The battery state is SOC, for example.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a battery monitoring device and a program. [Background technology]

[0002] In batteries such as lithium-ion batteries, there is a region where the change in open circuit voltage (OCV) associated with the change in state of charge (SOC) is small. This region is called the plateau region. In the plateau region, it is difficult to calculate the SOC of a battery using the SOC-OCV characteristic, which shows the correlation between SOC and open circuit voltage (OCV).

[0003] Patent Document 1 describes that there is a battery characteristic in which the amount of voltage change accompanying the capacity change of the storage battery is relatively large in a part of the plateau region compared to other regions, and the amount of voltage change accompanying the capacity change is approximately constant in the other regions, and that there is a battery characteristic in which the phenomenon in which the amount of voltage change accompanying the capacity change becomes large occurs at a specific SOC. Patent Document 1 describes a state-of-charge estimation device that estimates the SOC of a storage battery by utilizing such characteristics. In detail, when the state of the storage battery during charging or discharging is in the plateau region, the estimation device calculates a time rate of change of the terminal voltage detection value of the storage battery. When the estimation device determines that the calculated time rate of change is an inflection point with an upward convex curve, it estimates that the current SOC of the storage battery is an SOC that is previously linked to the calculated time rate of change. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6351852 Summary of the Invention [Problem to be solved by the invention]

[0005] Although the amount of voltage change due to capacity change is relatively large in some areas of the plateau region, the absolute value of the amount of voltage change is small. Therefore, if noise is superimposed on the terminal voltage detection value of the storage battery, there is a concern that the accuracy of SOC calculation will be significantly reduced.

[0006] In addition, when calculating the battery state of a storage battery, such as the remaining capacity of the storage battery, as well as the SOC of the storage battery, there is a concern that the accuracy of the calculation of the battery state may be significantly reduced due to noise.

[0007] A primary object of the present invention is to provide an electrical monitoring device and a program that can suppress a decrease in the accuracy of calculating a battery state. [Means for solving the problem]

[0008] The present invention is applied to a battery pack including a plurality of battery cells connected in series, an acquisition unit that acquires a battery parameter, which is either a terminal voltage or an impedance of a first battery cell and a second battery cell among the battery cells, during charging or discharging of the battery cells; The battery state calculation unit calculates a difference between the acquired battery parameters of the first battery cell and the acquired battery parameters of the second battery cell, and calculates a battery state of the battery cell based on the calculated difference.

[0009] The multiple battery cells that make up the assembled battery are connected in series. Therefore, when either the terminal voltage or the impedance is used as the battery parameter, it is considered that the influence of noise on the battery parameters of each battery cell is about the same. Therefore, the difference between the battery parameters of two battery cells that make up the assembled battery is a value in which the influence of noise is reduced.

[0010] In view of this, the state calculation unit of the present invention calculates the difference between the acquired battery parameters of the first battery cell and the acquired battery parameters of the second battery cell, and calculates the battery states of the battery cells based on the calculated difference, thereby making it possible to suppress a decrease in the calculation accuracy of the battery state. [Brief description of the drawings]

[0011] [Figure 1] 1 is an overall configuration diagram of a system according to a first embodiment. [Diagram 2] FIG. 1 shows the configuration of a monitoring IC. [Diagram 3] FIG. 4 is a diagram showing the relationship between the voltage and capacity of a battery cell. [Figure 4] 1 is a flowchart showing the procedure of a SOC calculation process. [Diagram 5] 4 is a time chart showing changes in the terminal voltage, voltage difference, and SOC of a battery cell during charging. [Figure 6] FIG. 13 is a diagram showing a selection unit of a microcomputer according to a modified example of the first embodiment. [Figure 7] 4 is a timing chart showing the changes in terminal voltage of the battery cells with the highest and lowest terminal voltages. [Figure 8] 10 is a flowchart showing the procedure of an SOC calculation process according to a second embodiment. [Figure 9] 4 is a time chart showing changes in terminal voltage and voltage difference of a battery cell during charging. [Figure 10] 13 is a flowchart showing the procedure of an SOC calculation process according to a third embodiment. [Figure 11] 4 is a time chart showing changes in the terminal voltage, voltage difference, and voltage change over time of a battery cell during charging. [Figure 12] 13 is a flowchart showing the procedure of a capacitance difference calculation process according to a fourth embodiment. [Figure 13] 4 is a time chart showing changes in the terminal voltage, voltage difference, and current integrated value of a battery cell during charging. [Figure 14] 13 is a flowchart showing the procedure of an SOC calculation process according to the fifth embodiment. [Figure 15] 4 is a time chart showing changes in the SOC and terminal voltage of a battery cell. [Figure 16] FIG. 13 is a graph showing the relationship between the remaining capacity and the amount of voltage change of a battery cell according to the sixth embodiment. [Figure 17] 1 is a flowchart showing the procedure of a SOC calculation process. [Figure 18] 4 is a time chart showing changes in impedance and impedance difference of a battery cell; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] First Embodiment A first embodiment of a battery monitoring device according to the present invention will be described below with reference to the drawings. A system including the battery monitoring device of this embodiment is mounted on a vehicle such as a hybrid vehicle, an electric vehicle, or a fuel cell vehicle. The vehicle includes a passenger car, a bus, a construction vehicle, and an agricultural machine vehicle. However, the system is not limited to a system mounted on a vehicle, and may be, for example, a stationary system.

[0013] As shown in Fig. 1, the system 100 includes a battery pack 10. The battery pack 10 includes a series connection of a plurality of battery modules 11. Each battery module 11 includes a series connection of a plurality of battery cells 12. In this embodiment, each battery module 11 includes the same number of battery cells 12. However, each battery module 11 may include a different number of battery cells 12.

[0014] Each battery cell 12 is a chargeable and dischargeable storage battery (secondary battery), specifically, a lithium ion storage battery. The lithium ion storage battery of this embodiment is an LFP storage battery that uses lithium iron phosphate as the positive electrode active material and graphite as the negative electrode active material. The rated voltage of each battery cell 12 constituting the battery module 11 is the same, and the rated capacity [Ah] of each battery cell 12 is the same.

[0015] The system 100 includes a first charging path LA, a second charging path LB, a first external charging terminal TA, a second external charging terminal TB, a first switch SW1, and a second switch SW2. The first charging path LA connects the first external charging terminal TA and a positive electrode terminal of the battery cell having the highest potential among the battery cells 12 constituting the battery pack 10. The second charging path LB connects the second external charging terminal TB and a negative electrode terminal of the battery cell having the lowest potential among the battery cells 12 constituting the battery pack 10. The first charging path LA is provided with a first switch SW1, and the second charging path LB is provided with a second switch SW2.

[0016] When the first switch SW1 and the second switch SW2 are turned on, the battery pack 10 is connected to the off-vehicle charger 200 via the first and second external charging terminals TA and TB. The off-vehicle charger 200 is, for example, a DC quick charger. When the off-vehicle charger 200 is connected to the first and second external charging terminals TA and TB, the battery pack 10 is constant-current charged or constant-voltage charged by high-voltage DC power input from the off-vehicle charger 200. For example, the battery pack 10 is constant-current charged until just before it is fully charged, and then the charging is switched to constant-voltage charging. The off-vehicle charger 200 may be an AC charger instead of a DC charger.

[0017] The system 100 includes a rotating electric machine 20, an inverter 30, a first electric path L1, a second electric path L2, a third switch SW3, and a fourth switch SW4. The first electric path L1 connects a first connection point PA on the first charging path LA that is closer to the assembled battery 10 than the first switch SW1, to a high potential side terminal of the inverter 30. The second electric path L2 connects a second connection point PB on the second charging path LB that is closer to the assembled battery 10 than the second switch SW2, to a low potential side terminal of the inverter 30. The first electric path L1 is provided with a third switch SW3, and the second electric path L2 is provided with a fourth switch SW4.

[0018] When the third switch SW3 and the fourth switch SW4 are turned on, the rotating electric machine 20 inputs and outputs electric power to and from the battery pack 10 via the inverter 30. During power running, the rotating electric machine 20 provides propulsive force to the vehicle using electric power supplied from the battery pack 10, and during regeneration, the rotating electric machine 20 generates electric power using deceleration energy of the vehicle and supplies the electric power to the battery pack 10.

[0019] The system 100 includes a current sensor 40 and a BMU (Battery Management Unit) 50 as a battery monitoring device. The current sensor 40 detects a current flowing through the battery pack 10. In FIG. 1, the current sensor 40 detects a current flowing through a second charging path LB. The detection value of the current sensor 40 is input to the BMU 50.

[0020] The BMU 50 turns on or off the first to fourth switches SW1 to SW4. The BMU 50 is communicably connected to the cruise control ECU 42 via an in-vehicle network interface. The BMU 50 outputs a command to the cruise control ECU 42 to control the rotating electric machine 20 based on the remaining capacity [Ah] of the battery pack 10. Based on the command from the BMU 50, the cruise control ECU 42 performs switching control of the inverter 30 to control the control amount (e.g., torque) of the rotating electric machine 20 to a command value.

[0021] The BMU 50 includes a monitoring IC 60 and a microcomputer 70, which are provided individually for each battery module 11. The monitoring IC 60 detects the terminal voltage of each battery cell 12 that constitutes the battery module 11. Each monitoring IC 60 exchanges information with the microcomputer 70. The microcomputer 70 acquires the terminal voltage detected by each monitoring IC 60 via an insulating element (not shown).

[0022] The microcomputer 70 includes a CPU. The functions provided by the microcomputer 70 can be provided by software recorded in a physical memory device and a computer that executes the software, by software alone, by hardware alone, or by a combination of these. For example, when the microcomputer 70 is provided by an electronic circuit that is hardware, it can be provided by a digital circuit including a large number of logic circuits, or an analog circuit. For example, the microcomputer 70 executes a program stored in a non-transitory tangible storage medium as a storage unit provided in the microcomputer 70. The program includes, for example, a program for a process shown in FIG. 4. The program is executed to execute a method corresponding to the program. The storage unit is, for example, a non-volatile memory. The program stored in the storage unit can be updated, for example, via a network such as the Internet.

[0023] As shown in FIG. 2, the monitoring IC 60 includes a command unit 61, an A / D converter 62, a switch unit 63, and an equalization circuit unit 64. The command unit 61 has a function of interpreting commands from the microcomputer 70. The switch unit 63 has a function of arbitrarily selecting the voltage of each battery cell 12, and is, for example, a multiplexer. The A / D converter 62 converts the analog signal output from the switch unit 63 into a digital signal. The converted digital signal is transmitted to the microcomputer 70 via the command unit 61. As a result, the microcomputer 70 obtains the terminal voltage of the battery cell 12. The monitoring IC 60 performs processing according to the command from the microcomputer 70 by operating each of these units. For example, the monitoring IC 60 sequentially detects the terminal voltage of each battery cell 12 constituting the battery module 11 in a predetermined order.

[0024] The equalization circuit unit 64 performs an equalization process to reduce voltage variations in each battery cell 12 constituting the battery module 11 based on a command from the microcomputer 70. The equalization circuit unit 64 is connected to each battery cell 12. The equalization process is, for example, a process of discharging from the battery cell having the highest terminal voltage among the battery cells 12. Note that, for example, when the microcomputer 70 determines that the difference between the maximum voltage and the minimum voltage among the terminal voltage detection values ​​of each battery cell 12 is equal to or greater than a predetermined voltage, it may transmit a command to execute the equalization process to the monitoring IC 60.

[0025] Incidentally, a method of calculating the remaining capacity of the battery pack 10 using the SOC-OCV characteristic, which indicates the correlation between the SOC (State Of Charge) indicating the charge state of the battery pack 10 and the open circuit voltage (OCV), is known. However, in this embodiment, an LFP battery is used as the lithium ion battery. As shown in FIG. 3, the LFP battery has a plateau region SL in which the OCV is stable over a wide range of remaining capacity and the change in OCV associated with a change in capacity is small. At both ends of the plateau region SL, there are end regions SH in which the change in OCV associated with a change in capacity is larger than that in the plateau region SL. In the plateau region SL, it is difficult to calculate the SOC of the battery using the SOC-OCV characteristic and calculate the remaining capacity.

[0026] A part of the plateau region SL is a specific region SB where the change in OCV accompanying the capacity change is relatively large. The specific region SB is a region caused by the negative electrode configuration of the battery cell 12. When the SOC of the battery cell 12 becomes a specific SOC or remaining capacity, the state of the battery cell 12 transitions to the specific region SB. Therefore, when the state of the battery cell 12 transitions to the specific region SB, it can be understood that the current SOC or remaining capacity of the battery cell 12 is a specific SOC or remaining capacity. However, even though the change in OCV is relatively large, the amount of change in OCV is small. Therefore, if noise is superimposed on the terminal voltage detection value of the battery cell 12, there is a concern that the calculation accuracy of the SOC will be significantly reduced. In this embodiment, in order to address this problem, for example, the process shown in FIG. 4 is executed while the battery pack 10 is being charged by the off-vehicle charger 200.

[0027] 4 is a flowchart of the SOC calculation process of the battery cell 12 executed by the microcomputer 70. This process is repeatedly executed at a predetermined control period, for example, when it is determined that the state of the battery cell 12 is in the plateau region SL. Whether or not the state of the battery cell 12 is in the plateau region SL may be determined based on the terminal voltage of the battery cell acquired from the monitoring IC 60.

[0028] In step S10, the terminal voltage of the first battery cell detected by the monitoring IC 60 (hereinafter, first detected voltage V1d) and the terminal voltage of the second battery cell detected by the monitoring IC 60 (hereinafter, second detected voltage V2d) are acquired. The first battery cell and the second battery cell are two battery cells selected from the battery cells 12 that constitute the battery module 11. This selection method will be described in detail later. The process of step S10 corresponds to the "acquisition unit".

[0029] In step S11, the second detected voltage V2d is subtracted from the first detected voltage V1d to calculate a voltage difference ΔVd (corresponding to a "battery parameter").

[0030] In step S12, it is determined whether the calculated voltage difference ΔVd exceeds a determination value Vjde.

[0031] If the determination in step S12 is affirmative, the process proceeds to step S13, where the SOC of the first battery cell and the second battery cell are calculated as the specified value Sα. Note that the SOC of each battery cell 12 may be calculated as the specified value Sα, not limited to the first and second battery cells among the battery cells 12 constituting the battery module 11. Also, in step S13, the remaining capacity of the first and second battery cells may be calculated instead of the SOC. The processes in steps S11 to S13 correspond to a "state calculation unit."

[0032] The SOC calculation process will be described with reference to Fig. 5. Fig. 5(a) shows the transitions of the first and second detection voltages V1d, V2d, Fig. 5(b) shows the transitions of the voltage difference ΔVd, and Fig. 5(c) shows the transitions of the SOC of the first battery cell. In the example shown in Fig. 5, the battery pack 10 is being charged (constant current charging or constant voltage charging) by the external charger 200.

[0033] At time t1, the state of the first battery cell transitions from the end region SH to the plateau region SL, and the rate of increase in the terminal voltage associated with charging of the first battery cell slows down. At time t2, the state of the second battery cell transitions from the end region SH to the plateau region SL, and the rate of increase in the terminal voltage associated with charging of the second battery cell slows down. After time t2, the first and second detection voltages V1d, V2d become equivalent, and the voltage difference ΔVd becomes close to 0. Note that the SOC of the first and second battery cells after time t1 is a value calculated by the microcomputer 70 based on, for example, an initial SOC based on the open circuit voltage and a time-integrated value of the charging current flowing through the first and second battery cells.

[0034] After that, at time t3, the state of the first battery cell transitions to the specific region SB, and the rate of increase of the first detection voltage V1d temporarily increases from time t3 to t5. Meanwhile, the state of the second battery cell is still within the plateau region SL. Therefore, the voltage difference ΔVd increases after time t3, and the microcomputer 70 determines that the voltage difference ΔVd exceeds the determination value Vjde at time t4. Therefore, the microcomputer 70 calculates the SOC of the first and second battery cells as the specified value Sα. The determination value Vjde is set to a value that allows the determination that the current control period is an intermediate timing between time t3 and time t6. Note that the SOC of the first and second battery cells after time t4 may be calculated by the microcomputer 70 based on, for example, the specified value Sα and the time-integrated value of the charging current flowing through the first and second battery cells.

[0035] At time t6, the state of the second battery cell transitions to the specific region SB, and the rate of increase of the second detected voltage V2d temporarily increases from time t6 to t7. After time t7, the first and second detected voltages V1d, V2d become equivalent, and the voltage difference ΔVd approaches zero. As a result, the rate of decrease of the voltage difference ΔVd increases from time t6, and at time t7, the voltage difference ΔVd approaches zero. At time t8, the state of the first battery cell transitions to the edge region SH.

[0036] According to the present embodiment described above in detail, the following effects can be obtained.

[0037] Noise occurs due to instantaneous changes in the current flowing through the battery pack 10, and this noise may be superimposed on the terminal voltage detection value of each battery cell 12. Here, each battery cell 12 constituting the battery pack 10 is connected in series. For this reason, it is considered that the influence of noise on the terminal voltage detection value of each battery cell 12 is about the same. Therefore, the voltage difference ΔVd, which is the difference between the terminal voltage detection values ​​of the first and second battery cells, is a value in which the influence of noise is reduced. For this reason, by using the voltage difference ΔVd to estimate the SOC, it is possible to suppress a decrease in the calculation accuracy of the SOC even when noise occurs.

[0038] As the monitoring IC 60, an IC capable of setting the voltage detection range to either the entire voltage range that the battery cell 12 can take or a limited voltage range that is a part of the entire voltage range may be used. When the limited voltage range is selected as the voltage detection range, the resolution of the voltage detection is improved compared to when the entire voltage range is selected as the voltage detection range. For example, the limited voltage range is preferably set to the voltage range of the battery cell 12 included in the plateau region SL. In this case, the calculation accuracy of the SOC can be further improved. For example, when detecting the voltage of the battery cell 12 used in the process shown in FIG. 4, the microcomputer 70 sets the voltage detection range to the limited voltage range. On the other hand, when the limited voltage range is selected as the voltage detection range, the detected voltage is easily affected by noise. Here, according to the present embodiment that can reduce the influence of noise, it is not necessary to set a condition that there is no influence of noise as a condition for allowing the voltage detection of the battery cell 12 in the plateau region SL. This can relax the constraints on the voltage detection.

[0039] <Modification of the first embodiment> The microcomputer 70 may set the determination value Vjde to a larger value as the variation in SOC of each battery cell 12 increases at the start of charging the battery pack 10. This is based on the fact that the greater the variation in SOC, the greater the peak value of the voltage difference ΔVd.

[0040] Furthermore, the microcomputer 70 may set the determination value Vjde to be larger as the temperatures of the first and second battery cells are higher or the charging current detected by the current sensor 40 is smaller. This is based on the fact that the higher the temperature or the smaller the current, the larger the increase in the detected voltage in the specific region SB.

[0041] 6, the selection unit 71 of the microcomputer 70 may select the battery cell with the highest terminal voltage detection value as the first battery cell, and the battery cell with the lowest terminal voltage detection value as the second battery cell, among the battery cells 12. This is to increase the voltage difference ΔVd in the specific region SB and improve the accuracy of SOC calculation, as shown in FIG.

[0042] Furthermore, the selection unit 71 may select, from among the battery cells 12, the battery cell with the highest calculated SOC as the first battery cell, and select the battery cell with the lowest calculated SOC as the second battery cell.

[0043] Furthermore, the selection unit 71 may select two adjacent battery cells connected in series as the first battery cell and the second battery cell from among the battery cells 12. Since the temperatures of the two adjacent battery cells are close to each other, it is possible to improve the accuracy of calculating the SOC based on the voltage difference ΔVd.

[0044] Incidentally, the first and second battery cells may be selected from all the battery cells 12 that make up the battery pack 10, or may be selected from each battery cell 12 that makes up each battery module 11, or may be selected from each battery cell 12 that is to be monitored by the same monitoring IC 60.

[0045] The selection unit 71 may select the first and second battery cells from among the battery cells 12 that are the targets of AD conversion by the same A / D converter 62. In this case, the voltage detection errors of the battery cells 12 that are the targets of AD conversion have similar values, thereby improving the accuracy of SOC calculation.

[0046] Furthermore, the selection unit 71 may select two battery cells having close detection timings as the first and second battery cells from among the battery cells 12 constituting the battery pack 10. In this case, the noise superimposed on the terminal voltage detection values ​​of the first and second battery cells will be close to each other, thereby improving the accuracy of the SOC calculation.

[0047] Furthermore, the selection unit 71 may select the first and second battery cells from among the battery cells 12 constituting the assembled battery 10, which are provided with a temperature sensor (e.g., a thermistor). Furthermore, the selection unit 71 may select, from among the battery cells 12 constituting the assembled battery 10, battery cells whose temperatures are equal to or lower than a predetermined difference as the first and second battery cells.

[0048] · In step S11, a voltage difference ΔVd may be calculated by subtracting the first detection voltage V1d from the second detection voltage V2d. In this case, the process of step S12 may be “|ΔVd| > Vjde?”, or “ΔVd < Vjde? (where Vjde is a negative value)”.

[0049] · The SOC calculation process shown in FIG. 4 may be executed not only during charging of the battery pack 10 but also during discharging of the battery pack 10.

[0050] <Second Embodiment> Hereinafter, the second embodiment will be described with reference to the drawings, focusing on the differences from the first embodiment. FIG. 8 shows a flowchart of the SOC calculation process according to this embodiment. This process is repeatedly executed at a predetermined control cycle by the microcomputer 70, for example, when it is determined that the state of the battery cell 12 is the plateau region SL.

[0051] In step S20, the first detection voltage V1d and the second detection voltage V2d are acquired. In step S21, a voltage difference ΔVd is calculated by subtracting the second detection voltage V2d from the first detection voltage V1d.

[0052] In step S22, it is determined whether the determination flag Fjde is 0.

[0053] If it is determined in step S22 that the determination flag Fjde is 0, the process proceeds to step S23, and it is determined whether the calculated voltage difference ΔVd exceeds the first determination value Vjde1. If a negative determination is made in step S23, the process proceeds to step S26.

[0054] If an affirmative determination is made in step S23, the process proceeds to step S24, and the SOC of the first battery cell is calculated as the specified value Sα. Note that in step S24, instead of the SOC, the remaining capacity of the first battery cell may be calculated.

[0055] After completion of the process of step S24, the process proceeds to step S25, and the determination flag Fjde is set to 1. Then, the process proceeds to step S26.

[0056] In step S26, it is determined whether or not both of the conditions that the determination flag Fjde is 1 and that the calculated voltage difference ΔVd is less than the second determination value Vjde2 are satisfied. In this embodiment, the second determination value Vjde2 is set to a value smaller than the first determination value Vjde1. However, the present invention is not limited to this, and the second determination value Vjde2 may be set to a value larger than the first determination value Vjde1 or the same value as the first determination value Vjde1.

[0057] If the determination in step S26 is affirmative, the process proceeds to step S27, where the SOC of the second battery cell is calculated as a specified value Sα. Note that in step S27, the remaining capacity of the second battery cell may be calculated instead of the SOC.

[0058] The SOC calculation process will be described with reference to Fig. 9. Fig. 9(a) and (b) correspond to Fig. 5(a) and (b) above. In the example shown in Fig. 9, the battery pack 10 is being charged (constant current charging or constant voltage charging) by the external charger 200.

[0059] At time t1, the state of the first battery cell transitions from the edge region SH to the plateau region SL, and at time t2, the state of the second battery cell transitions from the edge region SH to the plateau region SL. After time t2, the first and second detection voltages V1d, V2d become equivalent, and the voltage difference ΔVd becomes close to zero.

[0060] After that, at time t3, the state of the first battery cell transitions to the specific region SB, and the rate of increase of the first detected voltage V1d temporarily increases from time t3 to t5. Meanwhile, the state of the second battery cell is still within the plateau region SL. Therefore, after time t3, the voltage difference ΔVd increases, and at time t4, the microcomputer 70 determines that the voltage difference ΔVd exceeds the first determination value Vjde1. Therefore, the microcomputer 70 calculates the SOC of the first battery cell as the specified value Sα.

[0061] At time t6, the state of the second battery cell transitions to the specific region SB, and the rate of increase of the second detection voltage V2d temporarily increases from time t6 to t8. As a result, at time t7, the microcomputer 70 determines that the voltage difference ΔVd falls below the second determination value Vjde2. Therefore, the microcomputer 70 calculates the SOC of the second battery cell as the specified value Sα. At time t9, the state of the first battery cell transitions to the edge region SH.

[0062] According to the present embodiment described above in detail, the SOC of the first and second battery cells can be calculated separately.

[0063] <Third embodiment> The third embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment. Fig. 10 shows a flowchart of the SOC calculation process according to this embodiment. This process is repeatedly executed at a predetermined control period when the microcomputer 70 determines that the state of the battery cell 12 is in the plateau region SL, for example.

[0064] In step S30, the first detected voltage V1d(t) and the second detected voltage V2d(t) are obtained.

[0065] In step S31, the voltage difference ΔVd(t) in the current control cycle is calculated by subtracting the second detected voltage V2d(t) obtained in the current control cycle from the first detected voltage V1d(t) obtained in the current control cycle.

[0066] In step S32, the voltage time change amount ΔAd is calculated by subtracting the voltage difference ΔVd(t−1) calculated in the previous control cycle from the voltage difference ΔVd(t) calculated in the current control cycle.

[0067] In step S33, it is determined whether the voltage time change amount ΔAd has crossed over zero.

[0068] If the determination in step S33 is affirmative, the process proceeds to step S34, where the SOC of the first battery cell and the second battery cell are calculated as a specified value Sα. Note that in step S34, the remaining capacities of the first and second battery cells may be calculated instead of the SOC.

[0069] The SOC calculation process will be described with reference to Fig. 11. Fig. 11(a) and (b) correspond to Fig. 5(a) and (b), and Fig. 11(c) shows the transition of the voltage time change amount ΔAd. In the example shown in Fig. 11, the battery pack 10 is being charged (constant current charging or constant voltage charging) by the off-vehicle charger 200.

[0070] At time t1, the state of the first battery cell transitions from the edge region SH to the plateau region SL, and at time t2, the state of the second battery cell transitions from the edge region SH to the plateau region SL. After time t2, the first and second detected voltages V1d, V2d become equivalent, so that the voltage difference ΔVd becomes close to 0, and the voltage time change ΔAd becomes 0 or a positive value close to 0.

[0071] After that, at time t3, the state of the first battery cell transitions to the specific region SB, and the rate of increase of the first detected voltage V1d temporarily increases from time t3 to t5, resulting in the voltage time change amount ΔAd becoming larger on the positive side.

[0072] After that, from time t4 to t5, the voltage change over time ΔAd becomes 0 or a positive value close to 0. At time t5, the state of the second battery cell transitions to the specific region SB, and the rate of increase of the second detected voltage V2d temporarily increases from time t5 to t6. As a result, the voltage change over time ΔAd changes significantly to the negative side. This causes the microcomputer 70 to determine that the voltage change over time ΔAd has crossed 0 at time t5. Therefore, the microcomputer 70 calculates the SOC of the first and second battery cells as the specified value Sα.

[0073] According to the present embodiment described above, it is possible to obtain the same effects as those of the first embodiment.

[0074] <Modification of the third embodiment> With reference to FIG. 11, the microcomputer 70 may calculate the SOC of the first and second battery cells as the specified value Sα at time t4 when the voltage time change amount ΔAd drops significantly to a value close to zero.

[0075] Instead of the voltage time change amount ΔAd, the following parameters (A) and (B) may be used. (A) (ΔVd(tm)-ΔVd(tm-1)) / ΔCa ΔCa indicates the capacity change amount [Ah] of the battery cell in a specified period from time tm-1 to time tm. The specified period is, for example, one control cycle of the microcomputer 70, or a period longer than one control cycle. The specified period can be set, for example, as the period required for the capacity change amount ΔCa to become a predetermined capacity change amount. ΔVd(tm-1) is a value obtained by subtracting the second detection voltage V2d obtained at time tm-1 from the first detection voltage V1d obtained at time tm. ΔVd(tm) is a value obtained by subtracting the second detection voltage V2d obtained at time tm from the first detection voltage V1d obtained at time tm. (B)(ΔVd(tm)-ΔVd(tm-1)) / ΔSOC ΔSOC indicates the SOC change amount of the battery cell in a specified period from time tm-1 to time tm. In this case, the specified period can be set as the period required for the SOC change amount ΔSOC to become a predetermined SOC change amount, for example, as described above.

[0076] <Fourth embodiment> The fourth embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment. In this embodiment, the difference between the remaining capacities of the first and second battery cells is calculated instead of the SOC. Fig. 12 shows a flowchart of the calculation process of the remaining capacity difference. This process is repeatedly executed at a predetermined control period when the microcomputer 70 determines that the state of the battery cell 12 is in the plateau region SL, for example.

[0077] In step S40, the first detected voltage V1d and the second detected voltage V2d are acquired. In step S41, the voltage difference ΔVd is calculated by subtracting the second detected voltage V2d from the first detected voltage V1d.

[0078] In step S42, it is determined whether or not the determination flag Fjde is 0. If it is determined in step S42 that the determination flag Fjde is 0, the process proceeds to step S43, where it is determined whether or not the calculated voltage difference ΔVd exceeds the first determination value Vjde1. If the determination in step S43 is positive, that is, if it is determined that the voltage difference ΔVd has changed in the positive direction and crossed the first determination value Vjde1, the process proceeds to step S44, where calculation of the time-integrated value of the charging current detected by the current sensor 40 is started. After completing the process of step S44, the process proceeds to step S45, where the determination flag Fjde is set to 1. Then, the process proceeds to step S46.

[0079] In step S46, it is determined whether or not both of the first condition that the determination flag Fjde is 1 and the second condition that the calculated voltage difference ΔVd is below the second determination value Vjde2 are satisfied. In other words, the second condition is a condition that the voltage difference ΔVd changes in the negative direction and crosses the second determination value Vjde2.

[0080] If the determination in step S46 is positive, the process proceeds to step S47, where the determination flag Fjde is set to 0, and the current integration process started in step S44 is terminated. In step S47, the time-integrated value of the charging current calculated by the current integration process is calculated as the remaining capacity difference between the first and second battery cells. Note that the SOC difference between the first and second battery cells may be calculated based on the remaining capacity difference.

[0081] The calculation process of the remaining capacity difference will be described with reference to Fig. 13. Figs. 13(a) and (b) correspond to Figs. 5(a) and (b). Fig. 13(c) shows the transition of the determination flag Fjde, Fig. 13(d) shows the transition of the time-integrated value of the charging current, and Fig. 13(e) shows the transition of the calculated value of the remaining capacity difference between the first and second battery cells. In the example shown in Fig. 13, the battery pack 10 is being charged (constant current charging or constant voltage charging) by the off-vehicle charger 200.

[0082] At time t1, the state of the first battery cell transitions from the edge region SH to the plateau region SL, and at time t2, the state of the second battery cell transitions from the edge region SH to the plateau region SL.

[0083] Then, at time t3, the state of the first battery cell transitions to the specific region SB, and the rate of increase of the first detected voltage V1d temporarily increases from time t3 to t5. As a result, at time t4, the microcomputer 70 determines that the voltage difference ΔVd has exceeded the first determination value Vjde1. As a result, the determination flag Fjde is set to 1, and the integration process of the charging current is started.

[0084] At time t6, the state of the second battery cell transitions to the specific region SB, and the rate of increase of the second detected voltage V2d temporarily increases from time t6 to t8. As a result, at time t7, the microcomputer 70 determines that the voltage difference ΔVd has fallen below the second determination value Vjde2. As a result, the determination flag Fjde is set to 0, and the integration process of the charging current ends. Then, the value of the charging current integrated from time t4 to t7 is calculated as the difference in remaining capacity between the first and second battery cells.

[0085] If the microcomputer 70 determines that the difference between the calculated remaining capacities is equal to or greater than a predetermined capacity, it may determine that at least one of the first and second battery cells is faulty. The microcomputer 70 may also determine the discharge amount of the battery cells in the equalization process based on the calculated difference between the remaining capacities.

[0086] <Fifth embodiment> The fifth embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment. In this embodiment, as shown in Fig. 14, if the difference in SOC between the first and second cells is small, a process to increase the difference is executed prior to the SOC calculation process. Note that in Fig. 14, the same processes as those shown in Fig. 4 are denoted by the same reference numerals for convenience.

[0087] In step S14, it is determined whether or not the charging start flag Fchr is 0. The charging start flag Fchr indicates that charging of the battery pack 10 has not yet started when it is 0, and indicates that charging has already started when it is 1. If it is determined in step S14 that the charging start flag Fchr is 1, the process proceeds to step S10.

[0088] On the other hand, if it is determined in step S14 that the charging start flag Fchr is 0, the process proceeds to step S15, where it is determined whether or not the absolute value of the difference between the SOC of the first battery cell (hereinafter, SOC1) and the SOC of the second battery cell (hereinafter, SOC2) is greater than the threshold value Sth. If the determination in step S15 is affirmative, the process proceeds to step S16, where the charging start flag Fchr is set to 1, and charging of the battery pack 10 by the off-vehicle charger 200 is started. In this embodiment, SOC1 and SOC2 correspond to the "electricity storage amount parameters." Note that the electricity storage amount parameters are not limited to SOC1 and SOC2, and may be, for example, the first and second detected voltages V1d and V2d, or the remaining capacities of the first and second battery cells.

[0089] On the other hand, if the determination in step S15 is negative, the process proceeds to step S17, where a discharge process is performed in which either the first or second battery cell is discharged. In this embodiment, the second battery cell is discharged first. The equalization circuit unit 64 may be used for this discharge. This discharge continues until the determination in step S15 is positive.

[0090] The above-described process will be further described with reference to Fig. 15. Fig. 15(a) shows the transition of SOC1 and SOC2, and Fig. 15(b) shows whether or not the discharge process of the second battery cell is performed. Fig. 15(c) and (d) correspond to Fig. 5(a) and (b) above.

[0091] At time t1, the microcomputer 70 determines that the absolute value of the difference between SOC1 and SOC2 is equal to or less than the threshold value Sth. Therefore, the microcomputer 70 executes a discharge process until time t2 when it is determined that the absolute value exceeds the threshold value Sth. After that, charging of the battery pack 10 is started, and an SOC estimation process is executed. At time t3, the microcomputer 70 determines that the voltage difference ΔVd exceeds the determination value Vjde, and calculates the SOC of the first battery cell as the specified value Sα.

[0092] When the difference between SOC1 and SOC2 is small, the voltage difference ΔVd calculated in the SOC calculation process becomes small, and there is a concern that the accuracy of the SOC calculation may decrease. Therefore, in this embodiment, a discharge process is performed prior to the SOC calculation process. This allows the SOC calculation process to be started with a large difference between SOC1 and SOC2, and prevents the accuracy of the SOC calculation from decreasing.

[0093] Incidentally, the timing of performing the discharge process to increase the difference between SOC1 and SOC2 is not limited to before charging the battery pack 10. For example, the microcomputer 70 may calculate the absolute value of the difference between SOC1 and SOC2 each time while the battery pack 10 is being charged, and when it is determined that the calculated absolute value is equal to or less than the threshold value Sth, perform the process of step S17 while charging the battery pack 10.

[0094] <Modification of the Fifth Embodiment> The threshold value Sth is a first threshold value Sth1, and the second threshold value Sth2 is a value greater than the first threshold value Sth1. In this case, the microcomputer 70 may execute the discharge process for a period from when it determines that the absolute value of the difference between SOC1 and SOC2 is equal to or less than the first threshold value Sth1 until it determines that the absolute value is equal to or greater than the second threshold value Sth2.

[0095] The process of step S17 in FIG. 14 may be changed to a charging process in which either the first or second battery cell is charged during the period from when a negative determination is made in step S15 to when a positive determination is made in step S15, instead of a discharging process.

[0096] Moreover, the difference in SOC between the first battery cell and the second battery cell may be increased by performing a discharging process on one of the first and second battery cells and a charging process on the other.

[0097] Sixth Embodiment The sixth embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment. In this embodiment, the impedance of the battery cell is used as the battery parameter instead of the terminal voltage of the battery cell. The reason for using the impedance will be described below.

[0098] In a storage battery, when the remaining capacity changes with the passage of current, the amount of reaction heat WR changes. As shown in the following formula (1), the amount of reaction heat WR is the amount of heat generated by the storage battery WB due to the passage of current minus the Joule heat WJ due to the impedance component of the storage battery. The amount of reaction heat WR is expressed as shown in the following formula (2) using the storage battery temperature TM, the charge / discharge current IS, and the voltage change ΔOCV, which is the amount of change in the open circuit voltage OCV per unit temperature. WB = WJ + WR (1) WR = TM × IS × ΔOCV (2) According to formula (2), the reaction heat WR is proportional to the voltage change ΔOCV. The voltage change ΔOCV has a value for each capacity of the storage battery, and some storage batteries have a voltage change ΔOCV that changes when the capacity changes. In such storage batteries, if the capacity changes, the reaction heat WR changes, and the temperature TM changes. In addition, in storage batteries, the temperature TM and impedance are correlated. Therefore, if the temperature TM of the storage battery changes, the impedance of the storage battery changes.

[0099] FIG. 16 shows the relationship between the remaining capacity and the voltage change amount ΔOCV in the battery cell 12 of this embodiment. As shown in FIG. 16, the battery cell 12 has a specific capacity range from the first capacity QA to the second capacity QB, and the specific capacity range is included in the plateau region SL. When the remaining capacity crosses the first capacity QA from the low capacity side, the voltage change amount ΔOCV increases rapidly, and when the remaining capacity crosses the second capacity QB from the low capacity side, the voltage change amount ΔOCV decreases rapidly. Since the change in the voltage change amount ΔOCV is steep at the first and second capacities QA and QB, the tendency of the impedance transition of the battery cell 12 during current flow changes when the first and second capacities QA and QB are crossed. FIG. 17 shows an SOC calculation process that focuses on this point. This process is repeatedly executed at a predetermined control period by the microcomputer 70, for example, when it is determined that the state of the battery cell 12 is in the plateau region SL.

[0100] In step S50, the impedance Z1 of the first battery cell and the impedance Z2 of the second battery cell are calculated. Taking the first battery cell as an example, the impedance Z1 of the first battery cell is calculated by dividing the amount of change ΔV1 in the first detected voltage V1d when the charging current flowing through the first battery cell changes while the battery pack 10 is being charged by the amount of change ΔIS in the charging current.

[0101] In step S51, the impedance difference ΔZ is calculated by subtracting the impedance Z1 of the first battery cell from the impedance Z2 of the second battery cell. The impedance difference ΔZ is a value in which the effects of noise are reduced. In step S52, it is determined whether the impedance difference ΔZ is below the determination value Zjde. If the determination in step S52 is positive, the process proceeds to step S53, where the SOC of the first battery cell and the second battery cell are calculated as a specified value Sα. Note that in step S53, the remaining capacity of the first and second battery cells may be calculated instead of the SOC.

[0102] The SOC calculation process will be described with reference to Fig. 18. Fig. 18(a) shows the transitions of the impedances Z1 and Z2 of the first and second battery cells, and Fig. 18(b) shows the transition of the impedance difference ΔZ. In the example shown in Fig. 18, the battery pack 10 is being charged by the off-vehicle charger 200.

[0103] When the state of the first and second battery cells is in the plateau region SL, the impedance difference ΔZ is substantially constant until time t1. At time t1, the impedance difference ΔZ starts to decrease, and at time t2, the microcomputer 70 determines that the impedance difference ΔZ falls below the determination value Zjde. Therefore, the microcomputer 70 calculates the SOC of the first and second battery cells as the specified value Sα. At time t3, the large decrease in the impedance of the second battery cell stops, and thereafter the impedance difference ΔZ becomes substantially constant.

[0104] According to the present embodiment described above, it is possible to obtain the same effects as those of the first embodiment.

[0105] <Other embodiments> Each of the above embodiments may be modified as follows.

[0106] With reference to FIG. 18, the microcomputer 70 may calculate the SOC of the first battery cell as the specified value Sα at time t1, and may calculate the SOC of the second battery cell as the specified value Sα at time t2.

[0107] In the second to fifth embodiments, an impedance difference ΔZ may be used instead of the voltage difference ΔVd.

[0108] The control unit and the method described in the present disclosure may be realized by a special-purpose computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. Alternatively, the control unit and the method described in the present disclosure may be realized by a special-purpose computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and the method described in the present disclosure may be realized by one or more special-purpose computers configured by a combination of a processor and a memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. In addition, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions executed by the computer. [Explanation of symbols]

[0109] 10...battery pack, 11...battery cell, 50...BMU.

Claims

1. A battery monitoring device applied to a battery pack (10) including a plurality of battery cells (12) connected in series, A computer (70), When each of the battery cells is being charged or discharged, and a state of a first battery cell among the battery cells and a state of a second battery cell among the battery cells other than the first battery cell are in a plateau region, the computer A process of acquiring terminal voltages of the first battery cell and the second battery cell; a process of calculating a difference (ΔVd) between the acquired terminal voltage of the first battery cell and the acquired terminal voltage of the second battery cell, and determining whether or not the calculated difference exceeds a determination value (Vjde); a process of calculating an SOC or remaining capacity of the battery cell as a specified value (Sα) when it is determined that the SOC or remaining capacity of the battery cell has exceeded the determination value; The battery monitoring device repeatedly executes the above at a predetermined control period.

2. A battery monitoring device applied to a battery pack (10) including a plurality of battery cells (12) connected in series, A computer (70), When each of the battery cells is being charged or discharged, and a state of a first battery cell among the battery cells and a state of a second battery cell among the battery cells other than the first battery cell are in a plateau region, the computer obtaining impedances of the first battery cell and the second battery cell; a process of calculating a difference (ΔZ) between the acquired impedance of the first battery cell and the acquired impedance of the second battery cell, and determining whether the calculated difference is below a determination value (Zjde); a process of calculating the SOC or remaining capacity of the battery cell as a specified value (Sα) when it is determined that the SOC or remaining capacity of the battery cell falls below the determination value; The battery monitoring device repeatedly executes the above at a predetermined control period.

3. The present invention is applied to a battery pack (10) including a plurality of battery cells (12) connected in series, an acquisition unit that acquires a battery parameter, which is either a terminal voltage or an impedance of a first battery cell and a second battery cell among the battery cells, during charging or discharging of the battery cells; a state calculation unit that calculates a difference (ΔVd, ΔZ) between the acquired battery parameters of the first battery cell and the acquired battery parameters of the second battery cell, and calculates a battery state of the battery cell based on the calculated difference; Equipped with The battery state of the battery cell is an SOC or a remaining capacity of the battery cell, The state calculation unit is Calculate the change in the calculated difference (ΔAd), A battery monitoring device that calculates the SOC or remaining capacity of the battery cell as a specified value (Sα) based on the calculated amount of change becoming close to a predetermined value when the states of the first battery cell and the second battery cell are in a plateau region.

4. The present invention is applied to a battery pack (10) including a plurality of battery cells (12) connected in series, an acquisition unit that acquires a battery parameter, which is either a terminal voltage or an impedance of a first battery cell and a second battery cell among the battery cells, during charging or discharging of the battery cells; a state calculation unit that calculates a difference (ΔVd, ΔZ) between the acquired battery parameters of the first battery cell and the acquired battery parameters of the second battery cell, and calculates a battery state of the battery cell based on the calculated difference; Equipped with the battery state of the battery cell is a difference in SOC or a difference in remaining capacity between the first battery cell and the second battery cell, The battery monitoring device, when the states of the first battery cell and the second battery cell are in a plateau region, the state calculation unit calculates a time-integrated value of the current flowing through the battery cells during a period from when the calculated difference changes in a first direction and crosses a first determination value (Vjde1) to when the calculated difference changes in a second direction opposite to the first direction and crosses a second determination value (Vjde2), and calculates a difference in SOC or a difference in remaining capacity between the first battery cell and the second battery cell based on the calculated time-integrated value.

5. The present invention is applied to a battery pack (10) including a plurality of battery cells (12) connected in series, an acquisition unit that acquires a battery parameter, which is either a terminal voltage or an impedance of a first battery cell and a second battery cell among the battery cells, during charging or discharging of the battery cells; a state calculation unit that calculates a difference (ΔVd, ΔZ) between the acquired battery parameters of the first battery cell and the acquired battery parameters of the second battery cell, and calculates a battery state of the battery cell based on the calculated difference; Equipped with The state calculation unit calculates the difference between a storage capacity parameter of the first battery cell, which is one of SOC, remaining capacity, or terminal voltage, and the storage capacity parameter of the second battery cell, and when the calculated difference is equal to or less than a threshold value (Sth), discharges or charges at least one of the first battery cell and the second battery cell until the calculated difference becomes greater than the threshold value.

6. The present invention is applied to a battery pack (10) including a plurality of battery cells (12) connected in series, an acquisition unit that acquires a battery parameter, which is either a terminal voltage or an impedance of a first battery cell and a second battery cell among the battery cells, during charging or discharging of the battery cells; a state calculation unit that calculates a difference (ΔVd, ΔZ) between the acquired battery parameters of the first battery cell and the acquired battery parameters of the second battery cell, and calculates a battery state of the battery cell based on the calculated difference; Equipped with The first battery cell and the second battery cell are Among the battery cells, a battery cell having a highest terminal voltage and a battery cell having a lowest terminal voltage; Among the battery cells, battery cells having the highest and lowest SOCs; Adjacent battery cells among the battery cells; Among the battery cells, a battery cell whose terminal voltage is detected at a timing close to the detection timing; or Among the battery cells, the battery cells having a temperature difference equal to or lower than a predetermined value A battery monitoring device,

7. The present invention is applied to a battery pack (10) having a plurality of battery cells (12) connected in series, an acquisition unit that acquires a battery parameter, which is either a terminal voltage or an impedance of a first battery cell and a second battery cell among the battery cells, during charging or discharging of the battery cells; a state calculation unit that calculates a difference (ΔVd, ΔZ) between the acquired battery parameters of the first battery cell and the acquired battery parameters of the second battery cell, and calculates a battery state of the battery cell based on the calculated difference; Equipped with The battery state of the battery cell is an SOC or a remaining capacity of the battery cell, when the state calculation unit determines that the calculated difference has crossed a determination value (Vjde, Vjde1, Vjde2, Zjde) in a case where the states of the first battery cell and the second battery cell are in a plateau region, the state calculation unit calculates an SOC or remaining capacity of the battery cell as a specified value (Sα); The state calculation unit calculates the difference between a storage capacity parameter of the first battery cell, which is one of SOC, remaining capacity, or terminal voltage, and the storage capacity parameter of the second battery cell, and when the calculated difference is equal to or less than a threshold value (Sth), discharges or charges at least one of the first battery cell and the second battery cell until the calculated difference becomes greater than the threshold value.

8. The present invention is applied to a battery pack (10) having a plurality of battery cells (12) connected in series, an acquisition unit that acquires a battery parameter, which is either a terminal voltage or an impedance of a first battery cell and a second battery cell among the battery cells, during charging or discharging of the battery cells; a state calculation unit that calculates a difference (ΔVd, ΔZ) between the acquired battery parameters of the first battery cell and the acquired battery parameters of the second battery cell, and calculates a battery state of the battery cell based on the calculated difference; Equipped with The battery state of the battery cell is an SOC or a remaining capacity of the battery cell, when the state calculation unit determines that the calculated difference has crossed a determination value (Vjde, Vjde1, Vjde2, Zjde) in a case where the states of the first battery cell and the second battery cell are in a plateau region, the state calculation unit calculates an SOC or remaining capacity of the battery cell as a specified value (Sα); The first battery cell and the second battery cell are Among the battery cells, a battery cell having a highest terminal voltage and a battery cell having a lowest terminal voltage; Among the battery cells, battery cells having the highest and lowest SOCs; Adjacent battery cells among the battery cells; Among the battery cells, a battery cell whose terminal voltage is detected at a timing close to the detection timing; or Among the battery cells, the battery cells having a temperature difference equal to or lower than a predetermined value A battery monitoring device,

9. The battery monitoring device according to any one of claims 1 to 8, wherein the negative electrode of each of the battery cells includes graphite.

10. The battery monitoring device according to any one of claims 1 to 9, wherein the positive electrode of each of the battery cells contains lithium iron phosphate.

11. A battery pack (10) including a plurality of battery cells (12) connected in series; A program applied to a system including a computer (70), When each of the battery cells is being charged or discharged, and a state of a first battery cell among the battery cells and a state of a second battery cell among the battery cells other than the first battery cell are in a plateau region, the computer A process of acquiring a terminal voltage of the first battery cell and a terminal voltage of the second battery cell; a process of calculating a difference (ΔVd) between the acquired terminal voltage of the first battery cell and the acquired terminal voltage of the second battery cell, and determining whether or not the calculated difference exceeds a determination value (Vjde); a process of calculating an SOC or remaining capacity of the battery cell as a specified value (Sα) when it is determined that the SOC or remaining capacity of the battery cell has exceeded the determination value; A program that repeatedly executes the above at a specified control period.

12. A battery pack (10) including a plurality of battery cells (12) connected in series; A program applied to a system including a computer (70), When each of the battery cells is being charged or discharged, and a state of a first battery cell among the battery cells and a state of a second battery cell among the battery cells other than the first battery cell are in a plateau region, the computer A process of acquiring an impedance of the first battery cell and an impedance of the second battery cell; a process of calculating a difference (ΔZ) between the acquired impedance of the first battery cell and the acquired impedance of the second battery cell, and determining whether the calculated difference is below a determination value (Zjde); a process of calculating the SOC or remaining capacity of the battery cell as a specified value (Sα) when it is determined that the SOC or remaining capacity of the battery cell falls below the determination value; A program that repeatedly executes the above at a specified control period.

13. A battery pack (10) including a plurality of battery cells (12) connected in series; A program applied to a system including a computer (70), The computer includes: a process of acquiring a battery parameter, which is either a terminal voltage or an impedance of a first battery cell among the battery cells, and the battery parameter of a second battery cell other than the first battery cell among the battery cells, during charging or discharging of the battery cells; a process of calculating a difference (ΔVd, ΔZ) between the acquired battery parameters of the first battery cell and the acquired battery parameters of the second battery cell, and calculating a battery state of the battery cell based on the calculated difference; The battery state of the battery cell is an SOC or a remaining capacity of the battery cell, The process of calculating the battery state includes: Calculate the change in the calculated difference (ΔAd), a program for calculating an SOC or remaining capacity of the battery cell as a specified value (Sα) based on the calculated amount of change becoming close to a predetermined value when the states of the first battery cell and the second battery cell are in a plateau region.

14. A battery pack (10) including a plurality of battery cells (12) connected in series; A program applied to a system including a computer (70), The computer includes: a process of acquiring a battery parameter, which is either a terminal voltage or an impedance of a first battery cell among the battery cells, and the battery parameter of a second battery cell other than the first battery cell among the battery cells, during charging or discharging of the battery cells; a process of calculating a difference (ΔVd, ΔZ) between the acquired battery parameters of the first battery cell and the acquired battery parameters of the second battery cell, and calculating a battery state of the battery cell based on the calculated difference; the battery state of the battery cell is a difference in SOC or a difference in remaining capacity between the first battery cell and the second battery cell, The process of calculating the battery state is a process of calculating, when the states of the first battery cell and the second battery cell are in a plateau region, a time-integrated value of current flowing through the battery cells during a period from when the calculated difference changes in a first direction and crosses a first determination value (Vjde1) to when the calculated difference changes in a second direction opposite to the first direction and crosses a second determination value (Vjde2), and calculating a difference in SOC or a difference in remaining capacity between the first battery cell and the second battery cell based on the calculated time-integrated value.

15. A battery pack (10) including a plurality of battery cells (12) connected in series; A program applied to a system including a computer (70), The computer includes: a process of acquiring a battery parameter, which is either a terminal voltage or an impedance of a first battery cell among the battery cells, and the battery parameter of a second battery cell other than the first battery cell among the battery cells, during charging or discharging of the battery cells; a process of calculating a difference (ΔVd, ΔZ) between the acquired battery parameters of the first battery cell and the acquired battery parameters of the second battery cell, and calculating a battery state of the battery cell based on the calculated difference; A program for calculating, in the process of calculating the battery state, a difference between a storage amount parameter, which is one of SOC, remaining capacity, or terminal voltage of the first battery cell, and the storage amount parameter of the second battery cell, and when the calculated difference is equal to or less than a threshold value (Sth), discharging or charging at least one of the first battery cell and the second battery cell until the calculated difference becomes greater than the threshold value.

16. A battery pack (10) including a plurality of battery cells (12) connected in series; A program applied to a system including a computer (70), The computer includes: a process of acquiring a battery parameter, which is either a terminal voltage or an impedance of a first battery cell among the battery cells, and the battery parameter of a second battery cell other than the first battery cell among the battery cells, during charging or discharging of the battery cells; a process of calculating a difference (ΔVd, ΔZ) between the acquired battery parameters of the first battery cell and the acquired battery parameters of the second battery cell, and calculating a battery state of the battery cell based on the calculated difference; The first battery cell and the second battery cell are Among the battery cells, a battery cell having a highest terminal voltage and a battery cell having a lowest terminal voltage; Among the battery cells, battery cells having the highest and lowest SOCs; Adjacent battery cells among the battery cells; Among the battery cells, a battery cell whose terminal voltage is detected at a timing close to the detection timing; or Among the battery cells, the battery cells having a temperature difference equal to or lower than a predetermined value A program that is either

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