Power storage system, discharge control method, and discharge control program

Abstract

An acquisition unit (21) of a system management unit (20s) acquires voltages, currents, and temperatures from a plurality of power storage devices (5a-5c) connected in parallel. During discharge of the plurality of power storage devices (5a-5c), if the voltages acquired from the plurality of power storage devices (5a-5c) are less than a threshold voltage and at least one of the temperatures acquired from the plurality of power storage devices (5a-5c) exceeds a threshold temperature, a discharge current determination unit (22) generates a discharge current setting value for gradually reducing the discharge current. A notification unit (23) notifies a higher-order system (3) of the generated discharge current setting value.

Description

Energy storage system, discharge control method, and discharge control program

[0001] This disclosure relates to an energy storage system equipped with a temperature protection function, a discharge control method, and a discharge control program.

[0002] In typical lithium-ion batteries, chemical reactions caused by use in high-temperature environments (for example, the growth of the SEI (Solid Electrolyte Interphase) film formed on the negative electrode surface) can lead to capacity degradation and increased internal resistance.

[0003] In lithium-ion batteries, the temperature protection thresholds for charging and discharging are typically set to different values. Specifically, during charging, temperatures exceeding approximately 45°C increase the risk of degradation, while during discharging, temperatures up to approximately 60°C are acceptable. Thus, lithium-ion batteries generally require stricter temperature control during charging. In both charging and discharging, if the battery temperature exceeds the threshold temperature, the temperature protection function is activated, and the current path is cut off by a switch, stopping charging and discharging.

[0004] In large-capacity energy storage systems, multiple energy storage devices are sometimes connected in parallel. If a voltage difference occurs between parallel-connected energy storage devices, current will flow from the energy storage device with the higher voltage to the energy storage device with the lower voltage.

[0005] When multiple energy storage devices connected in parallel are discharging while the discharge threshold temperature is not exceeded but the charging threshold temperature is exceeded, a voltage difference will occur between the energy storage devices when the discharge stops. This can cause a lateral current to flow from the energy storage device with the higher voltage to the energy storage device with the lower voltage. When this lateral current occurs, a charging current will flow to the energy storage device with the lower voltage. However, if the temperature of the energy storage device with the lower voltage exceeds the charging threshold temperature, the temperature protection function will be activated and the device will stop.

[0006] Patent Document 1 discloses a method for comparing the voltage difference between energy storage devices, switching the devices on and off to perform charging and discharging, and equalizing the voltage to suppress crosscurrent. However, there is a possibility that the energy storage devices may repeatedly switch on and off due to voltage increases at the end of discharge, and introducing control to avoid this would make the control system complex. Also, depending on the voltage difference conditions, the load of the entire system may be concentrated on a single energy storage device, which may cause fuse blowing due to overcurrent or the system to shut down due to protection functions. A state in which discharge is not possible means that the purpose of the energy storage device, which is to supply power, is not being fulfilled, and this should be avoided as much as possible.

[0007] Japanese Patent Publication No. 2021-72676

[0008] This disclosure is made in light of these circumstances, and its purpose is to provide a technology for suppressing crosscurrent after discharge cessation between parallel-connected energy storage devices.

[0009] To solve the above problems, an energy storage system in one aspect of the present disclosure comprises a plurality of energy storage devices connected in parallel, and a management unit for managing the plurality of energy storage devices. The management unit includes an acquisition unit for acquiring voltage, current, and temperature from the plurality of energy storage devices, a discharge current determination unit for generating a discharge current setting value to gradually reduce the discharge current when the voltage acquired from the plurality of energy storage devices is below a threshold voltage and at least one of the temperatures acquired from the plurality of energy storage devices exceeds a threshold temperature during discharge, and a notification unit for notifying a higher-level system of the generated discharge current setting value.

[0010] Furthermore, any combination of the above components, as well as any conversion of the expressions of this disclosure between devices, systems, methods, computer programs, etc., are also valid forms of this disclosure.

[0011] According to this disclosure, it is possible to suppress lateral current flow between parallel-connected energy storage devices after discharge has stopped.

[0012] This is a diagram illustrating an example configuration of an energy storage system according to an embodiment. This diagram shows an example configuration of each battery module in Figure 1. Figures 3(a) and 3(b) show an example of the behavior of current and voltage before and after discharge cessation of two energy storage devices. This is a flowchart showing the flow of discharge current control by the energy storage system according to this embodiment.

[0013] Figure 1 is a diagram illustrating an example configuration of an energy storage system 1 according to an embodiment. The energy storage system 1 comprises a plurality of parallel-connected energy storage devices 5a-5c, a power converter 3, and a system management unit 20s. The first energy storage device 5a includes a plurality of series-connected battery modules 10aa-10ac, a first integrated management unit 20a, and a first switch SW1a. The first energy storage device 5a is constructed, for example, by stacking circuit boards on which the plurality of battery modules 10aa-10ac and the first integrated management unit 20a are mounted within a rectangular parallelepiped rack. The second energy storage device 5b and the third energy storage device 5c have the same configuration as the first energy storage device 5a. The number of parallel connections of the plurality of energy storage devices 5 and the number of series connections of the plurality of battery modules 10 within each energy storage device 5 can be designed arbitrarily.

[0014] The power paths for charging and discharging the multiple energy storage devices 5a-5c are merged into one and connected to the power converter 3. The power converter 3 is connected between the multiple energy storage devices 5a-5c and the commercial power grid 2. The power converter 3 can convert the DC power discharged from the multiple energy storage devices 5a-5c into AC power and output it to the commercial power grid 2. The power converter 3 can also convert the AC power input from the commercial power grid 2 into DC power and charge the multiple energy storage devices 5a-5c. Furthermore, the power converter 3 can convert the voltage of the DC power generated by the solar cell 4 into a predetermined voltage and charge the multiple energy storage devices 5a-5c.

[0015] The power converter 3 can be composed of a general power conditioner system (PCS), which includes a DC-DC converter and an inverter. The DC-DC converter performs control for constant current (CC) charging / discharging, constant voltage (CV) charging / discharging, or constant power (CP) charging / discharging, and the inverter performs conversion from DC power to AC power, or from AC power to DC power.

[0016] Furthermore, the power converter 3 may be connected to other renewable energy power generation devices (for example, wind power generators) or fuel cells in addition to the solar cells 4. The power converter 3 is positioned as a higher-level system from the perspective of the energy storage system 1.

[0017] The first switch SW1a of the first energy storage device 5a is inserted between the power converter 3 and the multiple battery modules 10aa-10ac. For example, a relay or a semiconductor switch can be used for the first switch SW1a. The first switch SW1a is controlled on / off by the first integrated management unit 20a. The second switch SW1b of the second energy storage device 5b and the third switch SW1c of the third energy storage device 5c are similar to the first switch SW1a of the first energy storage device 5a.

[0018] Figure 2 shows an example configuration of each battery module 10 in Figure 1. The battery module 10 includes a battery pack 11, a temperature sensor T1, a shunt resistor Rs, and a module management unit 12. The battery pack 11 includes a plurality of cells E1-En connected in series. Lithium-ion battery cells, nickel-metal hydride battery cells, lead-acid battery cells, etc., can be used as cells. Hereinafter, this specification assumes the use of lithium-ion battery cells (nominal voltage: 3.6-3.7V). In addition, multiple cells may be connected in parallel in the series stage of each cell in order to increase the capacity.

[0019] A shunt resistor Rs is connected in series with multiple cells E1-En. The shunt resistor Rs functions as a current sensing element. A Hall element may be used instead of the shunt resistor Rs. A temperature sensor T1 is installed near the multiple cells E1-En to detect the temperature of the multiple cells E1-En. For example, a thermistor can be used for the temperature sensor T1. Although only one temperature sensor T1 is shown in Figure 2, multiple temperature sensors T1 may be installed in a single battery module 10.

[0020] The module management unit 12 includes a voltage detection unit 12a, a temperature detection unit 12b, a current detection unit 12c, a control unit 12d, and a communication unit 12e. The voltage detection unit 12a is composed of an AFE (Analog Front End) IC or an ASIC (Application Specific Integrated Circuit). The control unit 12d is composed of a microcontroller. The microcontroller includes a CPU, RAM, ROM, and I / O.

[0021] The voltage detection unit 12a is connected to each node of a plurality of series-connected cells E1-En by a plurality of voltage measurement lines, and measures the voltage of each cell E1-En by measuring the voltage between two adjacent voltage measurement lines. The voltage detection unit 12a includes a multiplexer and an A / D converter. The multiplexer outputs the voltages of the plurality of cells E1-En to the A / D converter in a predetermined order. The A / D converter converts the analog voltage input from the multiplexer into a digital value. The voltage detection unit 12a transmits the digitally converted voltage values ​​of each cell E1-En to the control unit 12d via a serial communication interface.

[0022] The temperature detection unit 12b includes a voltage divider resistor and an A / D converter. The A / D converter converts the analog voltage indicating the temperature divided by the temperature sensor T1 and the voltage divider resistor into a digital value. The temperature detection unit 12b transmits the converted digital temperature value to the control unit 12d via a serial communication interface.

[0023] The current detection unit 12c includes a differential amplifier and an A / D converter. The differential amplifier amplifies the voltage across the shunt resistor Rs and outputs it to the A / D converter. The A / D converter converts the analog voltage indicating the current flowing through the battery pack 11, which is input from the differential amplifier, into a digital value. The current detection unit 12c transmits the digitally converted current value to the control unit 12d via a serial communication interface.

[0024] The control unit 12d manages the battery pack 11 based on the voltage, current, and temperature of multiple cells E1-En detected by the voltage detection unit 12a, current detection unit 12c, and temperature detection unit 12b. For example, it performs State of Charge (SOC) management and equalization control of multiple cells E1-En.

[0025] The control unit 12d estimates the State of Cost (SOC) by combining the Open Circuit Voltage (OCV) method and the current integration method. The OCV method estimates the SOC based on the measured OCV of the cell and the SOC-OCV curve of the cell. The SOC-OCV curve of the cell is created in advance based on characteristic tests conducted by the battery manufacturer and registered in the control unit 12d at the time of shipment.

[0026] The current integration method is a method for estimating the State of Charge (SOC) based on the OCV at the start of charging and discharging of the cell and the integrated value of the measured current. In the current integration method, measurement errors in the current accumulate as the charging and discharging time increases. Therefore, it is preferable to use a weighted average of the SOC estimated by the current integration method and the SOC estimated by the OCV method.

[0027] The communication unit 12e performs predetermined communication control (for example, communication control compliant with standards such as RS-485 or TCP / IP) and communicates with other battery modules 10 or the integrated management unit 20 via the communication line 30. The communication line 30 may be a metal cable or an optical fiber cable.

[0028] The first integrated management unit 20a acquires voltage, current, temperature, and SOC from each of the multiple battery modules 10aa-10ac. If the first integrated management unit 20a detects overcharging, over-discharging, overcurrent, or temperature abnormalities in any of the multiple battery modules 10aa-10ac, it turns off the first switch SW1a to protect the multiple battery modules 10aa-10ac.

[0029] The temperature protection thresholds for detecting temperature anomalies are set separately for charging and discharging. Specifically, the discharge threshold temperature is set to a higher value than the charging threshold temperature. Therefore, during discharge, if any of the temperatures obtained from the multiple battery modules 10aa-10ac exceed the charging threshold temperature but do not exceed the discharge threshold temperature, the first integrated management unit 20a will not turn off the first switch SW1a to perform a protection shutdown.

[0030] The first integrated management unit 20a integrates the voltage, current, temperature, and SOC acquired from each of the multiple battery modules 10aa-10ac to generate monitoring data for the first energy storage device 5a. The first integrated management unit 20a adds up the multiple voltages acquired from each of the multiple battery modules 10aa-10ac to generate voltage data for the first energy storage device 5a. The first integrated management unit 20a converts the multiple SOCs acquired from each of the multiple battery modules 10aa-10ac into capacities and calculates the total capacity of the first energy storage device 5a by summing up the converted capacities. The first integrated management unit 20a converts the calculated total capacity of the first energy storage device 5a into the SOC of the first energy storage device 5a. The first integrated management unit 20a selects the highest temperature among the multiple temperatures acquired from each of the multiple battery modules 10aa-10ac as the temperature of the first energy storage device 5a.

[0031] The first integrated management unit 20a transmits the generated monitoring data for the first energy storage device 5a to the system management unit 20s via the communication line 30. The second integrated management unit 20b and the third integrated management unit 20c process the data in the same manner as the first integrated management unit 20a.

[0032] Returning to Figure 1, the system management unit 20s is the controller for the entire energy storage system 1, managing multiple energy storage devices 5a-5c. The system management unit 20s includes an acquisition unit 21, a discharge current determination unit 22, and a notification unit 23. The system management unit 20s can be realized through the cooperation of hardware and software resources, or solely through hardware resources. Hardware resources that can be used include a CPU, ROM, RAM, I / O, ASIC, FPGA, and other LSIs. Software resources that can be used include programs such as firmware.

[0033] The acquisition unit 21 acquires monitoring data including the voltage, current, temperature, and SOC of the power storage device 5 from the integrated management units 20a - 20c of the plurality of power storage devices 5a - 5c, respectively. The discharge current determination unit 22 determines a discharge current set value for discharging from the power storage system 1. The notification unit 23 notifies the power conversion device 3, which is the upper system, of the discharge current set value determined by the discharge current determination unit 22. The power conversion device 3 sets the discharge current set value acquired from the system management unit 20s as the current command value of the DC / DC converter or the inverter, and controls the discharge current to the commercial power system 2.

[0034] During normal times, the discharge current determination unit 22 determines the discharge current set value to be notified to the upper system as a discharge current value preset according to the specifications of the power storage system 1. When the voltages of the plurality of power storage devices 5a - 5c reach the discharge termination voltage, the discharge current determination unit 22 sets the discharge current set value notified to the power conversion device 3 to 0 A.

[0035] In a high-temperature environment where at least one of the plurality of power storage devices 5a - 5c has not exceeded the discharge threshold temperature but has exceeded the charge threshold temperature, when discharging from the power storage system 1 stops while high-rate discharging is being performed, a cross current may occur between the plurality of power storage devices 5a - 5c.

[0036] FIGS. 3(a) - (b) are diagrams showing an example of the behavior of current and voltage before and after discharge stop of two power storage devices 5a - 5b. FIG. 3(a) shows an example of the behavior of current and voltage before and after discharge stop when the discharge control according to the present embodiment is not implemented, and FIG. 3(b) shows an example of the behavior of current and voltage before and after discharge stop when the discharge control according to the present embodiment is implemented. In FIGS. 3(a) - (b), the voltage (V) is shown as a value converted to the voltage per cell.

[0037] In the example shown in FIG. 3(a), the behavior of the OCV, the CCV1 of the first power storage device 5a, and the CCV2 of the second power storage device 5b when discharge stops while high-rate discharging (specifically, constant current discharge of 1 A) in a high-temperature environment is continued is shown. The CCV (Closed Circuit Voltage) corresponds to the terminal voltage of the cell measured by the voltage detection unit 12a during charge and discharge.

[0038] The cell voltage during charge and discharge is affected by the internal resistance R of the cell. The terminal voltage V of the cell during discharge ＣＣＶ and the open circuit voltage V ＯＣＶ are related as shown in the following (Equation 1). During discharge, as the internal resistance R of the cell increases, the voltage drop increases, and the terminal voltage V of the cell ＣＣＶ decreases.

[0039] V ＣＣＶ = V ＯＣＶ - I·R... (Equation 1)

[0040] When cells with different capacitances are charged and discharged in a parallel connection state, although the terminal voltages V ＣＣＶ are the same, the internal resistances R are different. Therefore, from the above (Equation 1), a current imbalance occurs. For example, when the terminal voltage V in terms of cells of the first power storage device 5a and the second power storage device 5b ＣＣＶ = 3.7V, the open circuit voltage V in terms of cells of the first power storage device 5a and the second power storage device 5b ＯＣＶ = 4.0V, the internal resistance R1 in terms of cells of the first power storage device 5a = 1.0Ω, and the internal resistance R2 in terms of cells of the second power storage device 5b = 2.0Ω, from the following (Equation 2), the current I1 flowing through the first power storage device 5a = 0.3A, and the current I2 flowing through the second power storage device 5b = 0.15A, resulting in a current imbalance.

[0041] V ＣＣＶ = V ＯＣＶ - I1·R1 = V ＯＣＶ - I2·R2... (Equation 2)

[0042] When discharge stops (I = 0), theoretically, from the above (Equation 1), the terminal voltage V ＣＣＶ = the open circuit voltage V ＯＣＶ However, the terminal voltage V ＣＣＶ does not reach the open circuit voltage V ＯＣＶ instantaneously and gradually converges. The reason why the terminal voltage V ＣＣＶ does not converge to the open circuit voltage V ＯＣＶ instantaneously is due to the influence of concentration overvoltage.

[0043] When discharge stops, the cell state can cause some energy storage devices 5 to experience large voltage increases while others experience small voltage increases, resulting in a voltage difference between the devices 5. However, since multiple parallel-connected energy storage devices 5 work to equalize the voltage, current flows from the energy storage device 5 with a large voltage increase to the energy storage device 5 with a small voltage increase, equalizing the voltage across the multiple energy storage devices 5, while maintaining the respective terminal voltages V ＣＣＶ Open circuit voltage V ＯＣＶ We are getting closer.

[0044] In the example shown in Figure 3(a), the terminal voltage V of the first energy storage device 5a is at the time of discharge cessation. ＣＣＶ１ However, the terminal voltage V of the second energy storage device 5b ＣＣＶ２ At a higher temperature, a crosscurrent flows from the first energy storage device 5a to the second energy storage device 5b. In this case, if the temperature of the second energy storage device 5b does not exceed the discharge threshold temperature but exceeds the charging threshold temperature, the inflow of charging current from the first energy storage device 5a will cause a protective shutdown. When the second energy storage device 5b is shut down for protection, the charging and discharging of the first energy storage device 5a and the second energy storage device 5b will stop with uneven voltages between them.

[0045] In contrast, in this embodiment, when discharge continues beyond the charging threshold temperature, the discharge current value requested from the higher-level system is gradually reduced, thereby suppressing crosscurrent flow between the energy storage devices 5 when the energy storage system 1 stops discharging.

[0046] Figure 4 is a flowchart showing the flow of discharge current control by the energy storage system 1 according to this embodiment. The acquisition unit 21 acquires monitoring data, including temperature, voltage, and current, from the integrated management units 20a-20c of the multiple energy storage devices 5a-5c, respectively (S10). The discharge current determination unit 22 compares the temperature of the multiple energy storage devices 5a-5c with the charging threshold temperature (S11). Note that a threshold temperature lower than the charging threshold temperature may be used instead of the charging threshold temperature. The lower the threshold temperature, the more likely the discharge current control according to this embodiment is to be activated.

[0047] If the temperatures of all energy storage devices 5a-5c are below the charging threshold temperature (N in S11), the process proceeds to step S16. If at least one of the temperatures obtained from the multiple energy storage devices 5a-5c exceeds the charging threshold temperature (Y in S11), the discharge current determination unit 22 compares the voltages of the multiple energy storage devices 5a-5c with the threshold voltage (S12). The threshold voltage is the trigger level voltage for starting the discharge current control according to this embodiment, and may be set to a voltage corresponding to, for example, a SOC of approximately 20% for the energy storage device 5.

[0048] If the voltages of the multiple energy storage devices 5a-5c are equal to or greater than the threshold voltage (N in S12), the process proceeds to step S16. If the voltages of the multiple energy storage devices 5a-5c are less than the threshold voltage (Y in S12), the discharge current determination unit 22 generates a discharge current setting value to gradually reduce the discharge current of the energy storage system 1. Specifically, the discharge current determination unit 22 calculates the difference between the threshold voltage and the voltages of the multiple energy storage devices 5a-5c, multiplies this difference by a predetermined coefficient K, and subtracts the result from the current discharge current setting value to generate a new discharge current setting value (S13).

[0049] If the new discharge current setting value becomes a negative value (Y in S14), the discharge current determination unit 22 sets the new discharge current setting value to 0 (S15). If the new discharge current setting value is not a negative value (N in S14), the process in step S15 is skipped. The notification unit 23 notifies the higher-level system of the new discharge current setting value (S16). Note that if the new discharge current setting value is the same as the current discharge current setting value, notification to the higher-level system may be skipped.

[0050] While the voltages of the multiple energy storage devices 5a-5c have not reached the discharge termination voltage (Y in S17), the process transitions to step S10, and steps S10-S16 are repeated. When the voltages of the multiple energy storage devices 5a-5c reach the discharge termination voltage (N in S17), the discharge is stopped.

[0051] As described above, according to this embodiment, when the charging threshold temperature is exceeded in at least one energy storage device 5, proportional control is performed using the difference between the threshold voltage determined from the cell characteristics and the voltages of the multiple energy storage devices 5a-5c as the manipulated variable and the discharge current value required by the higher-level system as the controlled variable. This makes it possible to keep the voltages of the multiple energy storage devices 5a-5c close to the OCV during discharge. That is, as shown in Figure 3(b), discharge can be stopped when the CCV and OCV of the energy storage device 5 are close together. This makes it possible to suppress the voltage difference between the multiple energy storage devices 5 when discharge is stopped with simple control. Therefore, crosscurrent can be suppressed without concentrating the load on a specific energy storage device 5. In addition, after discharge is stopped, a temperature exceeding the charging threshold temperature is detected in the energy storage device 5 into which the charging current flows, preventing protective shutdown.

[0052] The present disclosure has been described above based on embodiments. The embodiments are illustrative, and it will be understood by those skilled in the art that various modifications are possible in combinations of their components and processing processes, and that such modifications are also within the scope of the present disclosure.

[0053] In the embodiment described above, an example was shown in which the system management unit 20s is installed independently outside of the multiple energy storage devices 5a-5c. However, the functions of the system management unit 20s may also be implemented in any of the first integrated management unit 20a to the third integrated management unit 20c. The integrated management unit 20, on which the functions of the system management unit 20s are implemented, acts as a master unit and oversees the overall operation of the multiple energy storage devices 5a-5c.

[0054] The embodiments may be specified by the following items.

[0055] [Item 1] Energy storage system (1) comprising: a plurality of energy storage devices (5a-5c) connected in parallel; and a management unit (20s) for managing the plurality of energy storage devices (5a-5c), wherein the management unit (20s) includes: an acquisition unit (21) for acquiring voltage, current, and temperature from the plurality of energy storage devices (5a-5c); a discharge current determination unit (22) for generating a discharge current setting value to gradually reduce the discharge current when the voltage acquired from the plurality of energy storage devices (5a-5c) is below a threshold voltage and at least one of the temperatures acquired from the plurality of energy storage devices (5a-5c) exceeds a threshold temperature during discharge of the plurality of energy storage devices (5a-5c); and a notification unit (23) for notifying a higher-level system (3) of the generated discharge current setting value. According to this, crosscurrent between the plurality of energy storage devices (5a-5c) can be suppressed when the discharge of the energy storage system (1) is stopped. [Item 2] The discharge current determination unit (22) is characterized in that, during discharge of the plurality of energy storage devices (5a-5c), if the voltage obtained from the plurality of energy storage devices (5a-5c) is less than the threshold voltage and at least one of the temperatures obtained from the plurality of energy storage devices (5a-5c) exceeds the threshold temperature, it calculates the difference between the threshold voltage and the voltage of the plurality of energy storage devices (5a-5c), and subtracts the value obtained by multiplying the difference by a predetermined coefficient from the current discharge current setting value to generate a new discharge current setting value. This allows the discharge current to be reduced at an optimal pace. [Item 3] The discharge current determination unit (22) is characterized in that the threshold temperature is set to be below the charging threshold temperature. This prevents protective shutdown when a temperature exceeding the charging threshold temperature is detected in the energy storage device (5) into which the charging current flows after the discharge of the energy storage system (1) has stopped.[Item 4] A discharge control method for a plurality of parallel-connected energy storage devices (5a-5c), comprising: the steps of: acquiring voltage, current, and temperature from the plurality of energy storage devices (5a-5c); generating a discharge current setting value for gradually reducing the discharge current when, during discharge of the plurality of energy storage devices (5a-5c), the voltage acquired from the plurality of energy storage devices (5a-5c) is less than a threshold voltage and at least one of the temperatures acquired from the plurality of energy storage devices (5a-5c) exceeds a threshold temperature; and notifying a higher-level system (3) of the generated discharge current setting value. According to this method, crosscurrent between the plurality of energy storage devices (5a-5c) can be suppressed when the discharge of the energy storage system is stopped. [Item 5] A discharge control program for a plurality of parallel-connected energy storage devices (5a-5c), characterized in that it causes a computer to execute the following: a process of acquiring voltage, current, and temperature from the plurality of energy storage devices (5a-5c); a process of generating a discharge current setting value to gradually reduce the discharge current when the voltage acquired from the plurality of energy storage devices (5a-5c) is below a threshold voltage and at least one of the temperatures acquired from the plurality of energy storage devices (5a-5c) exceeds a threshold temperature during the discharge of the plurality of energy storage devices (5a-5c); and a process of notifying a higher-level system (3) of the generated discharge current setting value. According to this, crosscurrent between the plurality of energy storage devices (5a-5c) can be suppressed when the discharge of the energy storage system is stopped.

[0056] This disclosure can be used for temperature protection of energy storage systems in which multiple energy storage devices are connected in parallel.

[0057] 1 Energy storage system, 2 Commercial power grid, 3 Power converter, 4 Solar cell, 5 Energy storage device, 10 Battery module, 11 Battery pack, 12 Module management unit, 12a Voltage detection unit, 12b Temperature detection unit, 12c Current detection unit, 12d Control unit, 12e Communication unit, E1-En Cell, Rs Shunt resistor, T1 Temperature sensor, SW1 Switch, 20 Integrated management unit, 20s System management unit, 21 Acquisition unit, 22 Discharge current determination unit, 23 Notification unit, 30 Communication line.

Claims

1. An energy storage system comprising: a plurality of energy storage devices connected in parallel; and a management unit for managing the plurality of energy storage devices, wherein the management unit includes: an acquisition unit for acquiring voltage, current, and temperature from the plurality of energy storage devices; a discharge current determination unit for generating a discharge current setting value to gradually reduce the discharge current when, during discharge of the plurality of energy storage devices, the voltage acquired from the plurality of energy storage devices is below a threshold voltage and at least one of the temperatures acquired from the plurality of energy storage devices exceeds a threshold temperature; and a notification unit for notifying a higher-level system of the generated discharge current setting value.

2. The energy storage system according to claim 1, characterized in that, during the discharge of the plurality of energy storage devices, if the voltage obtained from the plurality of energy storage devices is less than the threshold voltage and at least one of the temperatures obtained from the plurality of energy storage devices exceeds the threshold temperature, the discharge current determination unit calculates the difference between the threshold voltage and the voltage of the plurality of energy storage devices, and subtracts the value obtained by multiplying the difference by a predetermined coefficient from the current discharge current setting value to generate a new discharge current setting value.

3. The energy storage system according to claim 1 or 2, characterized in that the threshold temperature is set to be below the charging threshold temperature.

4. A discharge control method for a plurality of parallel-connected energy storage devices, comprising: the steps of: acquiring voltage, current, and temperature from the plurality of energy storage devices; generating a discharge current setting value for gradually reducing the discharge current when, during the discharge of the plurality of energy storage devices, the voltage acquired from the plurality of energy storage devices is less than a threshold voltage and at least one of the temperatures acquired from the plurality of energy storage devices exceeds a threshold temperature; and notifying a higher-level system of the generated discharge current setting value.

5. A discharge control program for a plurality of parallel-connected energy storage devices, characterized in that it causes a computer to perform the following: a process of acquiring voltage, current, and temperature from the plurality of energy storage devices; a process of generating a discharge current setting value for gradually reducing the discharge current when the voltage acquired from the plurality of energy storage devices is below a threshold voltage and at least one of the temperatures acquired from the plurality of energy storage devices exceeds a threshold temperature during the discharge of the plurality of energy storage devices; and a process of notifying a higher-level system of the generated discharge current setting value.

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