Energy storage device

Abstract

To provide an energy storage device that can perform equalization processing at appropriate intervals while the device is left unused. [Solution] The energy storage device 100 includes an energy storage module 30 containing a plurality of energy storage cells 31, and a battery ECU 10 that performs an equalization process to equalize the State of Charge (SOC) of the plurality of energy storage cells 31. If the amount of self-discharge per unit time of the energy storage module 30 is defined as the unit discharge amount, and the time until the next equalization process is performed is defined as the waiting time, the battery ECU 10 makes the waiting time when the unit discharge amount is large shorter than the waiting time when the unit discharge amount is small.

Description

Technical Field

[0006] , , , ,

[0001] The present disclosure relates to a power storage device.

Background Art

[0002] Japanese Patent Application Publication No. 2024-507529 (Patent Document 1) discloses a system that performs a balancing process for equalizing the SOC (State Of Charge) of a plurality of batteries connected in series.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

[0007] In an energy storage device according to one aspect of this disclosure, as described above, the standby time when the unit discharge amount is large is shorter than the standby time when the unit discharge amount is small. Here, the larger the unit discharge amount, the more likely variations in the State of Charge (SOC) are to occur. Therefore, by configuring the device as described above, the frequency of the equalization process when the SOC variation is large can be made higher than the frequency of the equalization process when the SOC variation is small. This effectively suppresses the occurrence of SOC variations. Furthermore, it is possible to suppress excessive execution of the equalization process when the SOC variation is small. As a result, it is possible to suppress the increase in power consumption of the energy storage device due to the equalization process. In this way, by making the standby time when the unit discharge amount is large shorter than the standby time when the unit discharge amount is small, the equalization process can be performed at an appropriate frequency while the energy storage device is idle.

[0008] The first multiplicative value, which is the product of an integer greater than or equal to 1 and the unit discharge rate, is converted to a State of Charge (SOC) value and is defined as the converted value. If the minimum integer that satisfies the condition that the converted value is greater than or equal to the first threshold is defined as the minimum integer, the control unit may use the second multiplicative value, which is the product of the unit time and the minimum integer, as the waiting time. With this configuration, the minimum integer can be reduced when the unit discharge rate is large. As a result, the waiting time can be easily shortened when the unit discharge rate is large.

[0009] When the SOC of multiple equalized energy storage cells is defined as the equalized SOC, the control unit may, if the converted value is greater than or equal to the first threshold and the difference obtained by subtracting the converted value from the equalized SOC is less than the second threshold, prohibit the next equalization process. If the converted value is greater than or equal to the first threshold and the difference is greater than or equal to the second threshold, the control unit may perform the next equalization process after a waiting period. This configuration makes it possible to suppress the SOC of the energy storage module from becoming excessively low due to the equalization process. In other words, it is possible to reduce the risk of over-discharge of the energy storage module.

[0010] The control unit determines whether the difference falls within a predetermined range when the converted value is equal to or greater than the first threshold and the difference is equal to or greater than the second threshold. If it determines that the difference falls within the predetermined range, it may perform the next equalization process after a waiting period. This configuration makes it possible to suppress the execution of the equalization process in the SOC band where the difference is higher than the predetermined range.

[0011] If the control unit determines that the difference is not within a predetermined range, it may increment the minimum integer and then use the incremented minimum integer to re-determine whether the difference is within the predetermined range. With this configuration, the waiting time can be increased by incrementing the minimum integer. As a result, the equalization process can be executed only after the difference is within the predetermined range. [Effects of the Invention]

[0012] According to this disclosure, an equalization process can be performed at appropriate intervals while the energy storage device is left idle. [Brief explanation of the drawing]

[0013] [Figure 1] This diagram shows the configuration of a vehicle equipped with an energy storage device according to this embodiment. [Figure 2] This diagram shows the configuration of the energy storage device according to this embodiment. [Figure 3] This diagram shows the configuration of the energy storage module of the energy storage device according to this embodiment. [Figure 4] This figure shows the SOC-OCV curve for an energy storage module (energy storage cell). [Figure 5] This is a flowchart illustrating the control of the energy storage device by the battery ECU according to this embodiment. [Modes for carrying out the invention]

[0014] Embodiments of this disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0015] Figure 1 shows a vehicle 110 equipped with a power storage device 100 according to an embodiment of the present disclosure, and a power stand 200 that exchanges power between the vehicle 110 and the vehicle 110. The power storage device 100 is configured to be detachably attached to the vehicle 110. The vehicle 110 is an example of the "electrical equipment" in the present disclosure.

[0016] The vehicle 110 includes a body 110a, an ECU (Electronic Control Unit) 111, a charger / discharger 112, and an inlet 113.

[0017] Vehicle 110 is electrically connected to power stand 200 via cable 201, enabling power exchange (charging and discharging) between it and power stand 200. This power exchange takes place with a plug 202 at the end of cable 201 connected to the inlet 113 of vehicle 110.

[0018] The vehicle 110 may be, for example, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a battery electric vehicle. The energy storage device 100 may also be installed in electrical equipment other than the vehicle (for example, a stationary energy storage device).

[0019] In the vehicle 110 in the plugin state, external charging (charging the power storage device 100 with power from outside the vehicle) and external discharging (discharging the power of the power storage device 100 to the outside of the vehicle) are possible. Note that the vehicle 110 may be capable of performing only external charging. The charger / discharger 112 performs power conversion and the like between the power stand 200 and the power storage device 100 in external charging and external discharging. This power conversion is controlled by the ECU 111.

[0020] FIG. 2 is a diagram showing a detailed configuration of the power storage device 100. The power storage device 100 includes a battery ECU 10, a positive electrode terminal 20, a negative electrode terminal 21, a cutoff circuit 22, a current sensor 23, a cutoff circuit 24, and a fuse 25. The power storage device 100 further includes a power storage module 30 including a plurality (seven in FIG. 2) of power storage cells 31, a voltage sensor 40, and an ECU power supply 50. Note that the battery ECU 10 is an example of the "control unit" of the present disclosure.

[0021] The battery ECU 10 includes a processor 11, a memory 12, and a communication unit 13. The memory 12 is configured to be able to store stored information. In addition to programs, information used in the programs (for example, maps, mathematical formulas, and various parameters) are stored in the memory 12. In the present embodiment, by the processor 11 executing the programs stored in the memory 12, various processes (for example, equalization processing described later) by the battery ECU 10 are executed. However, these processes may be executed only by hardware (electronic circuits) without using software.

[0022] The communication unit 13 acquires information from various devices by CAN (Controller Area Network) communication or the like. For example, the communication unit 13 acquires the respective detection values from the voltage sensor 40, the current sensor 23, and the like. Further, based on the detection values acquired by the communication unit 13, the processor 11 transmits control signals to the cutoff circuit 22, the cutoff circuit 24, and the like.

[0023] In the energy storage device 100, a series circuit is formed in which the positive terminal 20, the circuit breaker 22, the energy storage module 30, the circuit breaker 24, the fuse 25, and the negative terminal 21 are electrically arranged in that order. The current sensor 23 detects the current value flowing between the circuit breaker 22 and the energy storage module 30 in the above series circuit.

[0024] The ECU power supply 50 supplies power to the battery ECU 10. The ECU power supply 50 is electrically connected to point 26 between the current sensor 23 and the energy storage module 30 in the series circuit, and to point 27 between the energy storage module 30 and the circuit breaker 24 in the series circuit.

[0025] Multiple energy storage cells 31 are electrically connected in series. The voltage sensor 40 detects the voltage value of each of the multiple energy storage cells 31.

[0026] Figure 3 schematically shows multiple energy storage cells 31 of the energy storage module 30. The energy storage module 30 has multiple switches 32 and multiple resistors 33. Specifically, a series circuit in which one switch 32 and one resistor 33 are connected in series is connected in parallel to each energy storage cell 31.

[0027] The open / closed state of each switch 32 is controlled by the processor 11 (Figure 2). When a switch 32 is closed, the energy storage cell 31 connected in parallel to the closed switch 32 is discharged. This causes the State of Charge (SOC) of the energy storage cell 31 to decrease. The processor 11 performs an equalization process (balancing process) to equalize the SOC of multiple energy storage cells 31 by switching which energy storage cell 31 is discharged based on the SOC of each energy storage cell 31. Note that the method of equalization is not limited to the example above.

[0028] Figure 4 is a diagram showing the relationship between the voltage (OCV: Open Circuit Voltage) of the energy storage module 30 (energy storage cell 31) and the State of Charge (SOC). In Figure 4, the vertical axis represents voltage and the horizontal axis represents SOC. In this embodiment, the energy storage cell 31 is, for example, an iron phosphate battery (lithium iron phosphate battery). The SOC-OCV curve data shown in Figure 4 may be stored in the memory 12 of the battery ECU 10. The processor 11 of the battery ECU 10 may calculate the SOC of each energy storage cell 31 from the voltage value of each energy storage cell 31 detected by the voltage sensor 40, based on the SOC-OCV curve data stored in the memory 12. Note that the method for calculating SOC is not limited to the above example.

[0029] As shown in Figure 4, the SOC-OCV curve of the lithium-ion battery has a steep slope in the high SOC range (e.g., 90% or more) and the low SOC range (e.g., 30% or less), and a shallow slope in the intermediate SOC range (e.g., 30% to 90%). Note that the energy storage cell 31 may be a battery other than iron phosphate-based (e.g., ternary-based).

[0030] The energy storage cell 31 gradually discharges (self-discharges) when left unattended without external charging or discharging. The amount of self-discharge of the energy storage cell 31 increases as the remaining charge (SOC) of the energy storage cell 31 increases. Therefore, in the range of high SOC, the amount of self-discharge of the energy storage cell 31 is large, so the SOCs of the energy storage cells 31 tend to vary. Conversely, in the range of low SOC, the amount of self-discharge of the energy storage cell 31 is small, so the SOCs of the energy storage cells 31 tend to vary less. The amount of self-discharge of the energy storage cell 31 increases as the temperature of the environment in which the energy storage cell 31 is left unattended increases.

[0031] Furthermore, in the range where SOC is high, the change in SOC in response to voltage changes is relatively small. This means that even if there are errors in voltage sensing between the energy storage cells 31, the SOC is less likely to shift. Therefore, the accuracy of the equalization process is higher in the range where SOC is high.

[0032] If the equalization process is performed too frequently, the power consumption required to perform the equalization process increases, and the power stored in the energy storage cell 31 is released during the equalization process, which is a disadvantage. Conversely, if the equalization process is performed too infrequently, the difference in State of Charge (SOC) cannot be eliminated. Therefore, it is desirable to perform the equalization process at an appropriate frequency while the energy storage device is idle.

[0033] Therefore, in this embodiment, the battery ECU 10 shortens the waiting time when the unit discharge amount is large compared to the waiting time when the unit discharge amount is small. In this embodiment, the unit discharge amount refers to the amount of self-discharge of the energy storage module 30 per day. In this embodiment, the waiting time refers to the time until the next equalization process is performed. One day is an example of "unit time" in this disclosure.

[0034] This allows for a higher frequency of equalization processing in the high SOC range, where variations in SOC between energy storage cells 31 are more likely and the accuracy of equalization processing is high, and a lower frequency of equalization processing in the low SOC range, where variations in SOC between energy storage cells 31 are less likely and the accuracy of equalization processing is low. As a result, equalization processing can be performed at an appropriate frequency while the energy storage device 100 is idle.

[0035] (Control flow) Figure 5 is a flowchart showing the processing in the energy storage device 100 according to this embodiment. This control flow is executed by the battery ECU 10 (processor 11). Note that the control flow shown in Figure 5 is executed while the energy storage device 100 is removed from the vehicle 110 and left alone.

[0036] In step S1, the battery ECU 10 determines whether the SOC of the energy storage module 30 is equal to or greater than the threshold Th1 (for example, 30%). If the SOC of the energy storage module is equal to or greater than the threshold Th1 (Yes in S1), the process proceeds to step S2. If the SOC of the energy storage module is less than the threshold Th1 (No in S1), the process proceeds to step S16. In the following, the SOC of the energy storage module 30 refers to the average value of the SOCs of each of the multiple energy storage cells 31.

[0037] In step S2, the battery ECU 10 determines whether the initial equalization process after charging (external charging) or discharging (external discharging) has been performed. The battery ECU 10 (processor 11) may make this determination based on the execution history of the equalization process and the execution history of charging (discharging) stored in memory 12. If the initial equalization process has been performed (Yes in S2), the process proceeds to step S3. If the initial equalization process has not been performed (No in S2), the process proceeds to step S4.

[0038] In step S3, the battery ECU 10 determines whether a certain time Ta has elapsed since the initial equalization process (or the previous S15 process if the process in step S15 described below has already been performed). If the process in step S15 has not yet been performed, the certain time Ta may be, for example, 3 days since the initial equalization process. If the process in step S15 has been performed, the certain time Ta may be N days since the previous S15 process. If a certain time Ta has elapsed (Yes in S3), the process proceeds to step S6. If a certain time Ta has not elapsed (No in S3), the process returns to step S1.

[0039] In step S4, the battery ECU 10 determines whether the polarization of the energy storage module 30 (energy storage cell 31) has been resolved. For example, the battery ECU 10 may determine that the polarization has been resolved if a certain amount of time (the time required for the polarization to be resolved) has elapsed since the completion of charging (external charging) or discharging (external discharging). If it is determined that the polarization has been resolved (Yes in S4), the process proceeds to step S5. If it is determined that the polarization has not been resolved (No in S4), the process returns to step S1.

[0040] In step S5, the battery ECU 10 performs the initial equalization process. After that, the process returns to step S1.

[0041] In step S6, the battery ECU 10 calculates the daily self-discharge rate (hereinafter referred to as the unit discharge rate). Specifically, if the process in step S15 has not yet been executed, the battery ECU 10 calculates the unit discharge rate by dividing the difference between the state of charge (SOC) of the energy storage module 30 at the time of step S6 and the state of charge (SOC) of the energy storage module 30 at the time of the previous equalization process by a certain time period Ta (i.e., 3) in step S3. If the process in step S15 has been executed, the battery ECU 10 calculates the unit discharge rate by dividing the difference between the state of charge (SOC) of the energy storage module 30 at the time of step S6 and the state of charge (SOC) of the energy storage module 30 at the time of step S6 by a certain time period Ta (i.e., N) in step S3.

[0042] In step S7, the battery ECU 10 determines whether the variation in SOC among the energy storage cells 31 is greater than or equal to a threshold Th2 (for example, 5%). For example, the battery ECU 10 may determine whether the difference between the average value of the SOC of all energy storage cells 31 and the SOC furthest from the average value is greater than or equal to a threshold Th2. If the variation in SOC among the energy storage cells 31 is greater than or equal to a threshold Th2 (Yes in S7), the process proceeds to step S8. If the variation in SOC among the energy storage cells 31 is less than a threshold Th2 (No in S7), it is determined that the SOC has already been equalized, and the process proceeds to step S9.

[0043] In step S8, the battery ECU 10 performs an equalization process. After that, the process proceeds to step S9. During the equalization process in step S8 (discharge), the battery ECU 10 may be put into sleep mode (off state) to reduce power consumption. The battery ECU 10 may be restarted after the equalization process is completed (discharge). In this case, the process may resume from step S9.

[0044] In step S9, the battery ECU 10 calculates the State of Charge (SOC) of the energy storage module 30 and assigns the calculated SOC to a variable called SOC1. The SOC calculated in step S9 is an example of the "equalized SOC" as defined in this disclosure.

[0045] In step S10, the battery ECU 10 calculates the product of the unit discharge amount calculated in step S6 and N, which is an integer greater than or equal to 1, and then calculates a converted value by converting the above multiplied value to the State of Charge (SOC) of the energy storage cell 31. The battery ECU 10 then assigns the above converted value to the variable SOC2. The initial value of N is 1.

[0046] In step S11, the battery ECU 10 determines whether SOC2 is greater than or equal to the threshold Th3. If SOC2 is greater than or equal to the threshold Th3 (Yes in S11), the process proceeds to step S12. If SOC2 is less than the threshold Th3 (No in S11), the process proceeds to step S14. Note that the threshold Th2 is an example of the "first threshold" in this disclosure.

[0047] For example, the threshold Th3 may be set to a value that is smaller than the unit discharge amount in the high SOC range (e.g., 90% or more) and larger than the unit discharge amount in the intermediate SOC range (e.g., 30% to 90%). This makes it easier to determine "Yes" in step S11 even if N is small in the high SOC range. On the other hand, in the intermediate SOC range, it is easier to determine "No" in step S11 if N is small. The threshold Th3 may be a fixed value set in advance based on the design data of the energy storage cell 31, etc. The battery ECU 10 may also periodically calculate (update) the threshold Th3 based on historical information of the unit discharge amount during past self-discharge.

[0048] In step S12, the battery ECU 10 determines whether the difference obtained by subtracting SOC2 from SOC1 is greater than or equal to the threshold Th4. If the above difference is greater than or equal to the threshold Th4 (Yes in S12), the process proceeds to step S12. If the above difference is less than the threshold Th4 (No in S12), the process proceeds to step S16. The threshold Th4 may be equal to the threshold Th1, or it may be slightly lower than the threshold Th1 (for example, threshold Th1 - 5%). The threshold Th4 is an example of the "second threshold" in this disclosure.

[0049] In step S13, the battery ECU 10 determines whether the difference in step S12 falls within a predetermined range. The upper limit of the predetermined range may be a value within the higher range of the State of Optimum (for example, 95%). The lower limit of the predetermined range may be the threshold Th4, or a value slightly higher than the threshold Th4 (for example, the threshold Th4 + 5%). In step S13, it is also possible to determine only whether the difference is less than or equal to the upper limit. If the difference falls within the predetermined range (Yes in S13), the process proceeds to step S15. If the difference does not fall within the predetermined range (No in S13), the process proceeds to step S14.

[0050] In step S14, the battery ECU 10 increments N. That is, the battery ECU 10 increases the value of N by 1. Then the process returns to step S10.

[0051] In step S15, the battery ECU 10 schedules the next equalization process to be performed after N days. After that, the process ends. Note that N days is an example of the "waiting time" in this disclosure.

[0052] In step S16, the battery ECU 10 prohibits the next equalization process. That is, the battery ECU 10 does not reserve the next equalization process. After that, the process ends.

[0053] After the execution of each of the processes in step S15 and step S16, the control flow shown in Figure 5 may be executed again after a predetermined period of time. The predetermined period may be a pre-set period (for example, 1 day), or it may be N days if step S15 was executed in the previous control flow. The battery ECU 10 may be in a sleep state until the control flow shown in Figure 5 is executed again. Alternatively, after the execution of step S15, the control flow shown in Figure 5 may not be executed again, and the equalization process may be executed N days after the time of step S15.

[0054] As can be seen from steps S11 and S13 above, when the unit discharge amount (SOC2) is small, the process moves to step S14 and N is incremented. Therefore, the battery ECU 10 makes the waiting time until the next equalization process (N days) when the unit discharge amount is large shorter than the waiting time until the next equalization process (N days) when the unit discharge amount is small.

[0055] As described above, in this embodiment, the battery ECU 10 shortens the waiting time (N days) when the unit discharge amount is large compared to the waiting time (N days) when the unit discharge amount is small. This allows the equalization process to be performed at a high frequency when the variation in SOC is large and the accuracy of the equalization process is high. As a result, the variation in SOC between energy storage cells 31 can be further suppressed. Also, when the variation in SOC is small and the accuracy of the equalization process is low, the equalization process can be performed at a low frequency. As a result, it is possible to suppress the high frequency of the equalization process when the need for it is low. This reduces the power consumption of the energy storage device 100 and suppresses the unnecessary loss of power stored in the energy storage cells 31 due to the equalization process.

[0056] (modified version) The above embodiment shows an example of determining the time until the next equalization treatment based on the amount of self-discharge per day, but the disclosure is not limited thereto. The time until the next equalization treatment may also be determined based on the amount of self-discharge per period other than one day (for example, one hour).

[0057] In the above embodiment, the control flow shown in Figure 5 is an example of a control flow that is executed while the energy storage device 100 is removed from the vehicle 110 and left standing on its own, but the disclosure is not limited thereto. This control flow may also be executed while the energy storage device 100 is attached to the vehicle 110 when charging, discharging, or driving is not taking place.

[0058] In the above embodiment, an example was shown in which the unit discharge amount is calculated in step S6 by dividing the change in SOC by a certain time Ta in step S3, but the disclosure is not limited thereto. The unit discharge amount may also be calculated by dividing a value obtained by correcting the change in SOC with a coefficient based on the ambient temperature of the energy storage device 100 by a certain time Ta. For example, if the ambient temperature is higher than the reference temperature (e.g., 20°C), a correction may be made to increase the change in SOC using a coefficient based on the ambient temperature and the reference temperature. If the ambient temperature is lower than the reference temperature, a correction may be made to decrease the change in SOC using a coefficient based on the ambient temperature and the reference temperature. This makes it possible to shorten the waiting time until the next equalization process when the ambient temperature is high compared to when the ambient temperature is low. As a result, the frequency of performing the equalization process can be increased when variations in SOC between energy storage cells 31 are likely to occur due to the high ambient temperature.

[0059] In the above embodiment, an example was shown in which the timing of the next equalization process is determined using the control flow shown in Figure 5, but the disclosure is not limited thereto. The timing of the next equalization process may be determined without using the control flow shown in Figure 5. For example, the waiting time may be determined from the self-discharge rate per unit time (e.g., one day) using a map that shows the relationship between the self-discharge rate per unit time and the waiting time until the next equalization process. This map is designed so that the waiting time decreases as the self-discharge rate per unit time increases.

[0060] The configurations of each of the above embodiments and each of the modified examples may be combined with each other.

[0061] It should be noted that the embodiments disclosed herein are illustrative in all respects and not restrictive. The scope of this disclosure is defined by the claims rather than the description of the embodiments above, and includes all modifications within the meaning and scope equivalent to the claims. [Explanation of Symbols]

[0062] 10 Battery ECU (control unit), 11 Processor, 12 Memory, 13 Communication unit, 30 Energy storage module, 31 Energy storage cell, 100 Energy storage device, 110 Vehicle (electrical equipment).

Claims

1. A power storage device that can be attached to and detached from electrical equipment, A storage module containing multiple energy storage cells, The system includes a control unit that performs an equalization process to equalize the state of charge (SOC) of the plurality of energy storage cells, The self-discharge amount per unit time of the aforementioned energy storage module is defined as the unit discharge amount. If the waiting time is defined as the time until the next equalization process is performed, The control unit makes the waiting time when the unit discharge amount is large shorter than the waiting time when the unit discharge amount is small.

2. The first multiplication value, which is the product of an integer of 1 or more and the unit discharge amount, is converted to a SOC value and the result is used as the converted value. If we define the minimum integer among the integers that satisfy the condition that the conversion value is equal to or greater than the first threshold, then the minimum integer is defined as the minimum integer. The energy storage device according to claim 1, wherein the control unit sets the waiting time to a second multiplicative value which is the product of the unit time and the minimum integer.

3. If the SOC of the aforementioned multiple energy storage cells that have been equalized is called the equalized SOC, The control unit, If the conversion value is equal to or greater than the first threshold, and the difference obtained by subtracting the conversion value from the equalized SOC is less than the second threshold, the next equalization process is prohibited. The energy storage device according to claim 2, wherein if the converted value is equal to or greater than the first threshold and the difference is equal to or greater than the second threshold, the next equalization process is performed after the waiting time.

4. The control unit, If the converted value is equal to or greater than the first threshold, and the difference is equal to or greater than the second threshold, it is determined whether the difference falls within a predetermined range. The energy storage device according to claim 3, wherein if it is determined that the difference falls within the predetermined range, the next equalization process is performed after the waiting time.

5. The energy storage device according to claim 4, wherein the control unit determines that the difference is not within the predetermined range, increments the minimum integer, and uses the incremented minimum integer to determine again whether or not the difference is within the predetermined range.

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