Battery Fault Diagnosis Method for Energy Storage System

Abstract

The present invention provides a battery fault diagnosis method for an energy storage system. The battery fault diagnosis method for an energy storage system includes: S10: setting the discharge current of the energy storage system to a; S20: obtaining the voltage difference ΔVi of a single cell i, ΔVi = |Vi-V0|, Vi is the voltage of the single cell i, and V0 is the average voltage; S30: setting the discharge current of the energy storage system to b, where b≠a; S40: obtaining the voltage difference ΔUi of a single cell i, ΔUi = |Ui-U0|, Ui is the voltage of the single cell i, and U0 is the average voltage; S50: calculating the voltage difference change magnification Ei = ΔUi / ΔVi of the single cell i, and calculating the current change magnification e = b / a of the single cell i; S60: judging whether the single cell is faulty based on the voltage difference change magnification Ei and the current change magnification e of the single cell i. The battery fault diagnosis method for an energy storage system of the technical solution of the present invention can actively identify hidden faults of single cells, solving the problem that faults of the energy storage system are not easily exposed when the energy storage system is operating normally.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage batteries, and in particular to a battery fault diagnosis method for an energy storage system. Background Art

[0002] Battery safety has always been a major concern for users. Energy storage systems are typically composed of thousands of small batteries, the smallest of which are called "cells." Battery safety is often determined by these cells. Therefore, monitoring the status of each cell and taking immediate action when an abnormality is about to occur is essential.

[0003] The inventors are aware of a method for diagnosing battery faults in a battery pack. After the battery pack has undergone multiple charging, operating discharge operations, and a fault occurs, the battery pack fault is diagnosed based on remote monitoring data (stored data). Specifically, the battery pack is diagnosed as a whole based on the maximum voltage value Vmax and the minimum voltage value Vmin of the battery pack's series modules to screen out faulty battery packs.

[0004] The above method is to screen the faulty batteries according to the stored data after the battery pack fails. Regardless of whether it is a power battery or an energy storage battery, the danger of the charging and discharging state is much higher than that of the static state. The diagnostic method of this static state cannot play a role in fault prediction. The faulty battery can only be identified after the fault occurs during the charging and discharging process of the battery pack. If the battery fault does not appear, it is impossible to actively identify and judge the fault.

[0005] In the prior art, battery systems are composed of tens of thousands of single cells connected in series, with the positive and negative electrodes of each single cell connected by welding (resistance welding, laser welding, ultrasonic welding). Most batteries experience internal or external welding problems or poor battery manufacturing processes at the beginning of production or after a period of operation, such as external cold solder joints or internal failures of single cells. Under conventional charging and discharging conditions (constant current charging and discharging), the energy storage system can still operate normally despite these failures, meaning the failures are difficult to detect. Only after a period of vibration or operation, such as during transportation, will the failure of a single cell become apparent. However, the methods known to the inventors can only identify a faulty battery after it has occurred and manifested itself. If the battery failure does not manifest, it is impossible to proactively identify and determine the fault, and hidden faults are difficult to detect, which can easily cause failure of the entire battery system. Summary of the Invention

[0006] The main purpose of the present invention is to provide a battery fault diagnosis method for an energy storage system. The battery fault diagnosis method for the energy storage system can actively identify hidden faults of single cells, solving the problem that faults of the energy storage system are not easily exposed when the energy storage system is operating normally.

[0007] To achieve the above-mentioned object, the present invention provides a battery fault diagnosis method for an energy storage system. The energy storage system includes a plurality of single cells, each of which is numbered i, where i can be 1 to n and n is an integer greater than 1. The battery fault diagnosis method for the energy storage system includes: S10: adjusting the energy storage system to the end of discharge and setting the discharge current of the energy storage system to a; S20: obtaining the voltage difference ΔVi of the single cell i when the discharge current is a, where ΔVi = |Vi-V0|, Vi is the voltage of the single cell i when the discharge current is a, and V0 is the voltage of multiple single cells when the discharge current is a; S30: set the discharge current of the energy storage system to b, where b≠a; S40: obtain the voltage difference ΔUi of the single cell i, where ΔUi=|Ui-U0|, Ui is the voltage of the single cell i when the discharge current is b, and U0 is the average voltage of multiple single cells when the discharge current is b; S50: calculate the voltage difference change rate Ei=ΔUi / ΔVi of the single cell i, and calculate the current change rate e=b / a of the single cell; S60: determine whether the single cell is faulty based on the voltage difference change rate Ei and the current change rate e of the single cell i.

[0008] Furthermore, the step of determining whether a battery cell is faulty based on the voltage difference change rate Ei and the current change rate e of the single cell i includes: a step of determining whether Ei / e of the single cell i is greater than k; if so, determining that the single cell i is a faulty battery; if not, executing step S62 of determining that the single cell i is a normal battery, wherein k is the voltage difference rate threshold.

[0009] Furthermore, after step S10 and before step S20, the battery fault diagnosis method of the energy storage system further includes: a maintaining discharge step of maintaining discharge of the energy storage system; a judging step of determining whether the average temperature change of the plurality of single cells is less than 1° C. per minute; if so, executing the step of obtaining the voltage Vi of the single cell i; if not, executing the maintaining discharge step.

[0010] Furthermore, after step S10 and before step S20, the battery fault diagnosis method for the energy storage system further includes: S11: obtaining the voltage Vi of the single cell i; S12: calculating the average voltage V0 of the multiple single cells, V0 = (V1 + V2 + ... + Vn) / n; and / or, after step S30 and before step S40, the battery fault diagnosis method for the energy storage system further includes: obtaining the voltage Ui of the single cell i; calculating the average voltage U0 of the multiple single cells, U0 = (U1 + U2 + ... + Un) / n.

[0011] Furthermore, before S10, the battery fault diagnosis method of the energy storage system further includes: S6: entering an active diagnosis mode; determining whether the remaining battery capacity (SOC) of the energy storage system is less than 30% in step S7; if so, executing S10; if not, executing step S8 of discharging the energy storage system; and after step S8, repeating step S7.

[0012] Furthermore, before step S6, the battery fault diagnosis method of the energy storage system further includes: S1: starting the energy storage system; S2: setting a voltage difference ratio threshold value k; and a judgment step S3 of determining whether the remaining battery capacity SOC of the energy storage system is greater than the cutoff capacity of the energy storage system. If so, step S6 is executed; if not, step S5 of shutting down or recharging the energy storage system is executed.

[0013] Furthermore, when step S5 is to supplement the energy storage system with electricity, after step S5, the determination step S3 is repeatedly executed.

[0014] Furthermore, after determination step S62, the battery fault diagnosis method for the energy storage system further includes: determination step S70 of whether the difference between the current time and the time when the active diagnosis mode was last entered is greater than or equal to the period T; if so, determining step S71 of whether the remaining battery capacity (SOC) of the energy storage system is greater than the cutoff capacity of the energy storage system is executed; if not, delaying step S71 of waiting for one day is executed, and after step S71, determining step S70 is repeated.

[0015] Furthermore, the discharge current a is 0.5C; and / or the discharge current b is 2C, where C is the rate.

[0016] Furthermore, the discharge current b is less than or equal to the maximum discharge current of the energy storage system.

[0017] By applying the technical solution of the present invention, the energy storage system is discharged using different discharge currents a and b, and the corresponding voltage differences of each single cell at different discharge currents, i.e., ΔVi and ΔUi, are recorded. The voltage differences of each single cell at different discharge current rates are then compared to obtain the voltage difference change rate Ei of each single cell when the discharge current changes from a to b. The voltage difference change rate Ei of the single cell is then compared with the discharge current change rate e to determine whether the single cell has failed. In this way, the difference in the change in the internal resistance of the faulty cell at different currents at the end of discharge can be fully utilized to determine whether the single cell has failed and actively identify hidden faults in the single cell, i.e., actively find single cells that are about to fail. This allows the energy storage system to actively identify single cells that are about to fail or have already failed at the end of discharge, thereby solving the problem that faults of the energy storage system are difficult to expose during normal operation, thereby preventing failures of the entire energy storage system and preventing problems before they occur. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0019] Figure 1 A schematic flow chart showing an embodiment of a method for diagnosing battery faults in an energy storage system according to the present invention; and

[0020] Figure 2 Shown Figure 1 Another flowchart of a battery fault diagnosis method for an energy storage system. DETAILED DESCRIPTION

[0021] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0022] It should be noted that in the embodiments of the present invention, multiple single cells are connected in series. It should be noted that in the embodiments of the present invention, based on the internal resistance characteristics of the single cells, for a normal single cell, the DC internal resistance of the single cell changes linearly with the current. However, at the end of the discharge phase of a faulty single cell, the rate of change in its internal resistance is much higher than the rate of change in the current. That is, the greater the discharge current, the greater the internal resistance of the faulty single cell.

[0023] Therefore, if Figure 1As shown, an embodiment of the present invention provides a battery fault diagnosis method for an energy storage system. The energy storage system includes multiple single cells, each of which is numbered i, where i can be 1 to n, and n is an integer greater than 1. The battery fault diagnosis method for the energy storage system includes: S10: adjusting the energy storage system to the end of discharge, and setting the discharge current of the energy storage system to a; S20: obtaining the voltage difference ΔVi of the single cell i when the discharge current is a, where ΔVi = |Vi-V0|, Vi is the voltage of the single cell i when the discharge current is a, and V0 is the average voltage of multiple single cells when the discharge current is a; S30: setting the storage The discharge current of the energy system is b, where b≠a; S40: obtaining the voltage difference ΔUi of the single cell i, where ΔUi=|Ui-U0|, Ui is the voltage of the single cell i when the discharge current is b, and U0 is the average voltage of multiple single cells when the discharge current is b; S50: calculating the voltage difference change magnification Ei=ΔUi / ΔVi of the single cell i, and calculating the current change magnification e=b / a of the single cell; S60: judging whether the single cell is faulty based on the voltage difference change magnification Ei and the current change magnification e of the single cell i.

[0024] In the above technical solution, the energy storage system is discharged using different discharge currents a and b, and the corresponding voltage differences of each single cell at different discharge currents, i.e., ΔVi and ΔUi, are recorded. The voltage differences of each single cell at different discharge current rates are then compared to obtain the voltage difference change rate Ei of each single cell when the discharge current changes from a to b. The voltage difference change rate Ei of the single cell is then compared with the discharge current change rate e to determine whether the single cell has failed. In this way, the difference in the internal resistance of the faulty cell at different currents at the end of discharge can be fully utilized to determine whether the single cell has failed and actively identify hidden faults in the single cell, i.e., actively find single cells that are about to fail. This allows the energy storage system to actively identify single cells that are about to fail or have already failed at the end of discharge, thereby solving the problem that faults in the energy storage system are not easily exposed during normal operation, thereby avoiding failure of the entire energy storage system and preventing problems before they occur.

[0025] Furthermore, by adopting the battery fault diagnosis method of this embodiment, the energy storage system can be diagnosed before leaving the factory to identify hidden faults, thereby discovering in advance single cell problems such as cold solder joints and false solder joints in the energy storage system that are not easy to detect, thereby improving the product's factory qualification rate and product reliability in the field, and improving product quality.

[0026] It should be noted that, in the embodiment of the present invention, the end of discharge refers to when the remaining capacity SOC of the battery is less than 40%.

[0027] It should be noted that when the discharge current is adjusted from a to b, what changes is the discharge current rate.

[0028] like Figure 2 As shown, in an embodiment of the present invention, the step of determining whether a single cell is faulty based on the voltage difference change rate Ei and the current change rate e of the single cell i includes: a determination step of determining whether Ei / e of the single cell i is greater than k; if so, determining that the single cell i is a faulty battery; if not, executing determination step S62 of determining that the single cell i is a normal battery, wherein k is a voltage difference rate threshold.

[0029] Through the above settings, when Ei / e is greater than k, it can be determined that the voltage difference change rate Ei far exceeds the current change rate e, indicating that a hidden fault has occurred in the single cell. In this way, the characteristic that the internal resistance change rate (i.e., the voltage difference change rate) of the faulty battery at the end of discharge is much higher than the current change rate (i.e., the greater the discharge current, the greater the internal resistance of the faulty single cell will be than that of other normal single cells) can be fully utilized to proactively identify hidden faults in the single cell. In other words, when the entire energy storage system does not show any faults, the single cell that is about to have a problem or has already had a problem is proactively identified. This allows the energy storage system to proactively identify single cells that are about to have a problem or have already had a problem at the end of discharge, thereby solving the problem that faults in the energy storage system are not easily exposed during normal operation, thereby avoiding causing failures of the entire energy storage system and preventing problems before they occur.

[0030] like Figure 2 As shown, in an embodiment of the present invention, after step S10 and before step S20, the battery fault diagnosis method of the energy storage system further includes: a maintaining discharge step of maintaining discharge of the energy storage system; a judging step of judging whether the average temperature change of the plurality of single cells is less than 1° C. per minute; if so, executing the step of obtaining the voltage Vi of the single cell i; if not, executing the maintaining discharge step.

[0031] In the above technical solution, after the energy storage system has been discharging for a period of time, the change in the average temperature of multiple single cells is determined. This allows the temperature of the energy storage system to reach a stable state before obtaining the voltage Vi of single cell i. This improves the accuracy of the obtained voltage Vi, thereby improving the accuracy of fault identification, thereby resolving the problem of failures in the energy storage system being difficult to expose during normal operation, thereby avoiding failure of the entire energy storage system.

[0032] It should be noted that, in the embodiment of the present invention, the average temperature of the plurality of single cells refers to the sum of the temperatures of the plurality of single cells divided by the number of single cells, that is, the temperature of the energy storage system.

[0033] like Figure 2As shown, in the embodiment of the present invention, after step S10 and before step S20, the battery fault diagnosis method of the energy storage system further includes: S11: obtaining the voltage Vi of the single cell i; S12: calculating the average voltage V0 of the multiple single cells, V0 = (V1+V2+…+Vn) / n.

[0034] Through the above configuration, the voltage Vi of the single cell i and the average voltage value V0 of the multiple single cells can be obtained, so as to obtain the voltage difference ΔVi of the single cell i when the discharge current is a.

[0035] Specifically, in the embodiment of the present invention, sampling points are arranged at both ends of a single cell to measure the potential, and the potential difference between the two sampling points is calculated to obtain the voltage of the single cell.

[0036] like Figure 2 As shown, in the embodiment of the present invention, after step S30 and before step S40, the battery fault diagnosis method of the energy storage system further includes: obtaining the voltage Ui of the single cell i; and calculating the average voltage U0 of the multiple single cells, U0 = (U1+U2+…+Un) / n.

[0037] Through the above configuration, the voltage Ui of the single cell i and the average voltage U0 of multiple single cells can be obtained, so as to obtain the voltage difference ΔUi of the single cell i when the discharge current is b.

[0038] like Figure 2 As shown, in an embodiment of the present invention, before S10, the battery fault diagnosis method of the energy storage system further includes: S6: entering an active diagnosis mode; determining whether the remaining battery capacity (SOC) of the energy storage system is less than 30% in step S7, if so, executing S10; if not, executing step S8 of discharging the energy storage system, and after step S8, repeating step S7.

[0039] Through the above settings, it can be ensured that when the remaining battery capacity SOC is less than 30%, the discharge current is set and the voltage is collected to diagnose the energy storage system, thereby ensuring that the energy storage system is at the end of discharge and then the energy storage system is diagnosed. In this way, the accuracy of diagnosis can be improved, thereby solving the problem that the fault of the energy storage system is not easy to expose when it is operating normally, so as to avoid causing failure of the entire energy storage system.

[0040] like Figure 2As shown, in an embodiment of the present invention, before step S6, the battery fault diagnosis method of the energy storage system further includes: S1: starting the energy storage system; S2: setting the pressure difference ratio threshold value k; and step S3 of judging whether the remaining battery capacity SOC of the energy storage system is greater than the cutoff capacity of the energy storage system. If so, step S6 is executed; if not, step S5 of shutting down or recharging the energy storage system is executed.

[0041] The above arrangement can avoid the problem of power feeding due to over-discharge of the single cell of the energy storage system, that is, it can avoid the problem of internal electrolyte crystallization of the single cell due to over-discharge, thereby protecting the battery.

[0042] It should be noted that electrolyte crystallization will not only reduce the battery capacity, but excessive crystallization will also pierce the electrolyte diaphragm, causing short circuit damage or fire in the battery.

[0043] In the embodiment of the present invention, the cut-off capacity refers to the battery remaining capacity SOC being 5% to 20%.

[0044] Preferably, the cut-off capacity is set at 20% of the battery remaining capacity SOC.

[0045] It should be noted that k is the permissible range of the pressure difference change rate, which is obtained through a large number of experiments.

[0046] It should be noted that, in the embodiment of the present invention, the pressure difference ratio threshold is set after the energy storage system is started and the system can operate normally (that is, the system has no faults, such as communication failures, single cell leakage and other abnormal and obvious faults).

[0047] Specifically, in the embodiment of the present invention, when step S5 is to supplement the energy storage system, after step S5, the determination step S3 is repeated, so that the energy storage system can continue to be diagnosed.

[0048] like Figure 2 As shown, in an embodiment of the present invention, after determination step S62, the battery fault diagnosis method of the energy storage system further includes: determination step S70 of determining whether the difference between the current time and the time of last entering the active diagnosis mode is greater than or equal to the period T; if so, determining whether the remaining battery capacity SOC of the energy storage system is greater than the cutoff capacity of the energy storage system is executed; if not, executing step S71 of delaying and waiting for one day, and after step S71, repeating step S70.

[0049] In the above technical solution, a fixed period T can be set to regularly diagnose the energy storage system faults, so as to timely discover hidden faults of the energy storage system and avoid the problem of the entire system failing due to the failure of a single cell.

[0050] Furthermore, the time for fault diagnosis can be controlled manually, and there is sufficient time to take protective measures, thereby making the risk of fault diagnosis controllable.

[0051] It should be noted that, in the embodiment of the present invention, the period T is a manually set value, which may be one year, one month, or one week.

[0052] In one embodiment, the software operator may manually issue an active diagnosis instruction to enter the active diagnosis mode.

[0053] Specifically, in the embodiment of the present invention, the discharge current a is 0.5C, and the discharge current b is 2C, where C is the discharge rate. This prevents the discharge current from being too low, which could result in a low voltage in the battery cells and affect the accuracy of the differential pressure. It also prevents the discharge current from being too high, which could damage the battery cells.

[0054] Specifically, in the embodiment of the present invention, the discharge current b is less than or equal to the maximum discharge current of the energy storage system, so as to avoid the problem of single battery being damaged due to excessive discharge current.

[0055] It should be noted that the battery fault diagnosis method of the energy storage system of the present invention is simple in inspection method, has high inspection efficiency, does not require too many auxiliary equipment tools and personnel, and is simple and quick.

[0056] From the above description, it can be seen that the above-mentioned embodiments of the present invention achieve the following technical effects: by discharging the energy storage system using different discharge currents a and b, and recording the corresponding voltage differences of each single cell at different discharge currents, i.e., recording ΔVi and ΔUi, the voltage differences of each single cell at different discharge current rates are compared to obtain the voltage difference change magnification Ei of each single cell when the discharge current changes from a to b. The voltage difference change magnification Ei of the single cell is then compared with the discharge current change magnification e to determine whether the single cell has failed. In this way, the difference in the internal resistance of the faulty cell at different currents at the end of discharge can be fully utilized to determine whether the single cell has failed and proactively identify hidden faults in the single cell, i.e., proactively identify single cells that are about to fail. Thus, the energy storage system can proactively identify single cells that are about to fail or have already failed at the end of discharge, thereby resolving the problem that faults in the energy storage system are difficult to expose during normal operation, thereby preventing failures of the entire energy storage system and preventing them from occurring.

[0057] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A battery fault diagnosis method for an energy storage system, characterized in that: The energy storage system includes a plurality of single cells, each of which is numbered i, where i can be 1 to n, and n is an integer greater than 1. The battery fault diagnosis method of the energy storage system includes: S10: adjusting the energy storage system to the end of discharge, and setting the discharge current of the energy storage system to a; S20: Obtaining a voltage difference ΔVi of a single cell i when the discharge current is a, where ΔVi=|Vi-V0|, Vi is the voltage of the single cell i when the discharge current is a, and V0 is the average voltage of multiple single cells when the discharge current is a; S30: Setting the discharge current of the energy storage system to b, where b≠a; S40: Obtaining a voltage difference ΔUi of the single cell i, where ΔUi=|Ui-U0|, Ui is the voltage of the single cell i when the discharge current is b, and U0 is the average voltage of multiple single cells when the discharge current is b; S50: Calculate the voltage difference variation ratio Ei=ΔUi / ΔVi of the single cell i, and calculate the current variation ratio e=b / a of the single cell; S60: Determine whether the single cell i is faulty based on the voltage difference variation ratio Ei and the current variation ratio e of the single cell i.

2. The battery fault diagnosis method of the energy storage system according to claim 1, characterized in that: The step of judging whether a single cell is faulty according to the voltage difference change magnification Ei and the current change magnification e of the single cell i includes: A step of determining whether Ei / e of the single cell i is greater than k is performed. If yes, the single cell i is determined to be a faulty battery. If not, a step of determining whether the single cell i is a normal battery is performed S62, wherein k is a voltage difference ratio threshold.

3. The battery fault diagnosis method of the energy storage system according to claim 1, characterized in that: After step S10 and before step S20, the battery fault diagnosis method of the energy storage system further includes: A maintaining discharge step of maintaining discharge of the energy storage system; A step of determining whether the average temperature change of the plurality of single cells is less than 1° C. per minute is performed. If yes, a step of obtaining the voltage Vi of the single cell i is performed. If not, the maintaining discharge step is performed.

4. The battery fault diagnosis method of the energy storage system according to claim 1, characterized in that: After S10, in step Before S20, the battery fault diagnosis method of the energy storage system further includes: S11: Obtaining the voltage Vi of the single cell i; S12: Calculating an average voltage value V0 of the plurality of single cells, where V0 = (V1 + V2 + ... + Vn) / n; and / or, after step S30 and before step S40, the battery fault diagnosis method of the energy storage system further includes: Obtaining the voltage Ui of the single cell i; The voltage average value U0 of the plurality of single battery cells is calculated, where U0=(U1+U2+...+Un) / n.

5. The battery fault diagnosis method for an energy storage system according to any one of claims 1 to 4, characterized in that: In the Before S10, the battery fault diagnosis method of the energy storage system further includes: S6: Enter active diagnosis mode; Determine whether the remaining battery capacity SOC of the energy storage system is less than 30% in step S7. If yes, execute S10. If not, execute step S8 of discharging the energy storage system. After step S8, repeat the determination step S7.

6. The battery fault diagnosis method of the energy storage system according to claim 5, characterized in that: Before step S6, the battery fault diagnosis method of the energy storage system further includes: S1: Starting the energy storage system; S2: Set the pressure difference ratio threshold k; A determination step S3 is performed to determine whether the remaining battery capacity SOC of the energy storage system is greater than the cutoff capacity of the energy storage system. If yes, step S6 is executed; if not, step S5 is performed to shut down or recharge the energy storage system.

7. The battery fault diagnosis method for the energy storage system according to claim 6, characterized in that: When the step S5 is to supplement the energy storage system with electricity, the determination step S3 is repeated after the step S5.

8. The battery fault diagnosis method for an energy storage system according to claim 2, characterized in that: After the determination step S62, the battery fault diagnosis method of the energy storage system further includes: A judgment step S70 is performed to determine whether the difference between the current moment and the moment when the active diagnostic mode was last entered is greater than or equal to the period T. If so, a judgment step is performed to determine whether the remaining battery capacity SOC of the energy storage system is greater than the cutoff capacity of the energy storage system. If not, a step S71 of delaying and waiting for one day is performed, and after the step S71, the judgment step S70 is repeated.

9. The battery fault diagnosis method for an energy storage system according to any one of claims 1 to 4, characterized in that: The discharge current a is 0.5C; and / or the discharge current b is 2C, where C is the discharge rate.

10. The battery fault diagnosis method for an energy storage system according to any one of claims 1 to 4, characterized in that: The discharge current b is less than or equal to the maximum discharge current of the energy storage system.

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