A battery cluster parallel control method in an energy storage system

Abstract

The present invention discloses a battery cluster parallel control method in an energy storage system. By calculating the maximum allowable parallel pressure difference as the dynamic pressure difference threshold for parallel connection, and taking it as one of the control logics for whether parallel connection can be performed, the defect of the prior art of taking a fixed pressure difference for parallel connection can be overcome. In addition, the battery cluster parallel control method in the energy storage system of the present invention can enable the cluster to be connected to perform insulation detection in advance by setting the insulation detection pressure difference threshold to be greater than the maximum allowable parallel pressure difference. The system can prepare the insulation detection environment in advance to avoid missing the pressure difference condition for system parallel connection due to insulation detection, thereby affecting the normal parallel connection of the system.

Description

Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to a battery cluster parallel control method in an energy storage system. Background Art

[0002] With the development of new energy technologies, the demand for capacity expansion of existing energy storage systems is increasing. Therefore, how to ensure the smooth parallel connection of each battery cluster in the system has become a hot topic of research.

[0003] In the prior art, each battery cluster in the energy storage system must meet the insulation requirements before parallel connection, and a fixed value is used as the voltage difference condition for system parallel connection. If the value is too large, the risk of system overcurrent will increase, and if the value is too small, some clusters will be difficult to connect. In addition, the use of a fixed value as the voltage difference for system parallel connection and the use of a fixed cycle and timed polling for insulation detection will result in missing the voltage difference condition for system parallel connection due to insulation detection, affecting the normal parallel connection of the system.

[0004] Therefore, it is necessary to design a battery cluster parallel control method in an energy storage system to solve the problems existing in the above-mentioned prior art. Summary of the invention

[0005] The purpose of the present invention is to solve the shortcomings of the prior art and propose a parallel control method for battery clusters in an energy storage system. The energy storage system includes battery clusters 1 to N, and each of the battery clusters is selectively connected to a bus through a parallel pre-charging circuit or switch.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for controlling battery clusters in parallel in an energy storage system, wherein the energy storage system comprises battery clusters 1 to N, each of which is selectively connected to a bus via a parallel pre-charging circuit or switch, and the method specifically comprises the following steps:

[0008] Step 1: At different average temperatures and SOCs, calculate the maximum allowable pressure difference that each battery cluster branch can tolerate instantaneously and the maximum allowable pressure difference that can be tolerated continuously, and compare the two to take the smaller value as the maximum allowable pressure difference in parallel;

[0009] Step 2: According to step 1, the maximum allowable parallel pressure difference under different average temperatures and SOCs is obtained and made into a table;

[0010] Step 3: Performing a first round of insulation detection on the N battery clusters, the battery clusters that pass the detection are qualified battery clusters, closing the pre-charging circuits corresponding to the qualified battery clusters, pre-charging the bus, and the energy storage system enters soft start, detecting the real-time voltage difference between each qualified battery cluster and the bus;

[0011] Step 4: When the real-time voltage difference between any of the qualified battery clusters and the bus reaches the pre-charge voltage difference threshold, it indicates that the pre-charge is successful, the switch corresponding to any of the qualified battery clusters is closed, and the pre-charge circuits corresponding to all the qualified battery clusters are disconnected, and the soft start is completed;

[0012] Step 5: Determine whether the real-time voltage difference between the remaining qualified battery clusters and the bus is less than or equal to the insulation detection voltage difference threshold. If so, treat the remaining qualified battery clusters as qualified battery clusters and proceed to step 6. If not, repeat step 5.

[0013] Step 6: Determine whether the qualified battery cluster is within the validity period of the first round of insulation test. If so, proceed to step 7. If not, mark it as a cluster to be tested and proceed to step 8.

[0014] Step 7: Determine whether the real-time voltage difference between the qualified battery cluster and the bus is less than or equal to the maximum allowable parallel voltage difference. If so, proceed to step 10; if not, repeat step 7;

[0015] Step 8: For the clusters to be tested, a cluster with the smallest voltage difference with the bus is selected to enable it to perform a second insulation test. If it passes the test, return to step 7;

[0016] Step 9: Repeat step 8 for the cluster to be tested that has not undergone the second insulation test;

[0017] Step 10: Selectively merge the qualified battery clusters that meet the conditions into the bus according to the power demand;

[0018] Wherein, N is a positive integer greater than or equal to 2, the battery cluster branch refers to a branch formed by a battery cluster and a corresponding switch connected in series; the insulation detection pressure difference threshold > the parallel maximum allowable pressure difference > the pre-charge pressure difference threshold.

[0019] Furthermore, the calculation of the maximum allowable pressure difference that each battery cluster branch can withstand instantaneously includes:

[0020] Step 1.1: Compare the pulse SOP of the battery cell at the current battery cluster duration and the instantaneous withstand current of the corresponding switch in its branch, and take the minimum value as the maximum current allowed at the initial moment;

[0021] Step 1.2: The internal resistance of the current battery cluster at the initial moment is multiplied by the maximum current allowed at the initial moment to obtain the maximum allowable voltage difference that can be tolerated instantaneously.

[0022] Furthermore, the calculation of the maximum allowable pressure difference that each battery cluster branch can sustain continuously includes:

[0023] Step 1.3: Compare the current battery cluster continuous SOP and the rated current of the corresponding switch in its branch, take the minimum value, and obtain the maximum allowable continuous current;

[0024] Step 1.4: multiply the internal resistance of the current battery cluster by the maximum allowable continuous current to obtain the maximum allowable voltage difference for continuous tolerance;

[0025] Step 1.5: Compare the maximum allowable pressure difference of the instantaneous tolerance and the maximum allowable pressure difference of the continuous tolerance, and take the smaller value as the maximum allowable pressure difference of the parallel connection.

[0026] Furthermore, the switch is a relay, or an IGBT, or a MOSFET.

[0027] Furthermore, the internal resistance includes the internal resistance of the battery cells and the wire group of the battery cluster.

[0028] Furthermore, the instantaneous withstand current of the switch is obtained by checking the switch model.

[0029] Furthermore, the first round of insulation detection includes:

[0030] The battery clusters are tested for insulation one by one, and the battery clusters that pass the test are marked as qualified battery clusters.

[0031] Furthermore, the qualified battery cluster that meets the conditions is a qualified battery cluster that is still within the validity period of the first insulation test and the pressure difference between it and the bus is less than or equal to the maximum allowable parallel pressure difference, or a qualified battery cluster that is outside the validity period of the first insulation test but passes the second insulation test and the pressure difference between it and the bus is less than or equal to the maximum allowable parallel pressure difference.

[0032] Furthermore, multiple qualified battery clusters meeting the conditions are incorporated into the bus by incorporating them one by one or simultaneously.

[0033] Furthermore, the qualified battery cluster that meets the conditions is incorporated into the bus, which means that the qualified battery cluster that meets the conditions is incorporated into the bus by closing a corresponding switch.

[0034] Compared with the prior art, the present invention provides a battery cluster parallel control method in an energy storage system:

[0035] The control method for parallel insulation detection of batteries calculates the dynamic voltage difference threshold for parallel connection (maximum allowable voltage difference for parallel connection) as one of the control logics for whether parallel connection can be established, thereby overcoming the defect of the prior art that a fixed voltage difference is used as a parallel connection condition. In addition, the method of the present invention sets the insulation detection voltage difference threshold to be greater than the maximum allowable voltage difference for parallel connection, and performs insulation detection in advance based on the real-time voltage difference between the battery cluster and the bus, thereby avoiding missing the system parallel voltage difference condition due to insulation detection, and ensuring smooth parallel connection of the energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The figure is a schematic diagram of an energy storage system in the prior art.

[0037] Figure 2 The present invention is a flow chart of a method for controlling parallel connection of battery clusters in an energy storage system.

[0038] Figure 3 Schematic diagram of the internal resistance of a battery cell in one embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Example

[0040] Figure 1 An energy storage system is shown, including N battery clusters (battery cluster 1, battery cluster 2, ... battery cluster N) and a bus. Battery cluster n is selectively connected to the bus through a parallel pre-charging circuit n or a switch n. Specifically, the positive (+) and negative (-) ends of battery cluster n are connected to the positive (+) and negative (-) ends of the bus through the pre-charging circuit n, or the positive (+) and negative (-) ends of battery cluster n are connected to the positive (+) and negative (-) ends of the bus through the switch n. When the positive (+) and negative (-) ends of battery cluster n are connected to the positive (+) and negative (-) ends of the bus through the closing of switch n, battery cluster n is incorporated into the bus.

[0041] Wherein, N is a positive integer greater than or equal to 2, and n is an integer between 1 and N.

[0042] Battery cluster branch 1 refers to a branch formed by battery cluster 1 and corresponding switch 1 in series; battery cluster branch 2 refers to a branch formed by battery cluster 2 and corresponding switch 2 in series, ..., battery cluster branch N refers to a branch formed by battery cluster N and corresponding switch N in series.

[0043] In one embodiment, the switch n is a relay. In other embodiments, the switch n may be an IGBT or a MOSFET.

[0044] In one embodiment, switches 1 to N are switches of the same type and model.

[0045] In one embodiment, the pre-charging circuits 1 to N are the same, and each includes a resistor and a relay or other controllable switch connected in series therewith.

[0046] The present invention provides a battery cluster parallel control method in an energy storage system, which is applied to the above energy storage system.

[0047] The method comprises the following steps:

[0048] Step 1: At different average temperatures and SOCs, calculate the maximum allowable pressure difference that each battery cluster branch can tolerate instantaneously and the maximum allowable pressure difference that it can tolerate continuously, and compare the two to take the smaller value as the maximum allowable pressure difference in parallel.

[0049] The calculation principle of step 1: adopt the Thevenin second-order equivalent battery model, take the parameter identification results under different temperatures and SOCs as input, take the battery cluster cell and switch tolerance as conditions, and reversely derive the maximum allowable pressure difference when the battery cluster is connected to the bus under different temperatures and SOCs (maximum allowable pressure difference in parallel); wherein, the battery cluster is connected to the bus means that the battery cluster is connected to the bus by closing its corresponding switch; the battery cluster cell and switch tolerance are divided into the current tolerance at the moment of input (when the switch is closed) and the continuous current tolerance after the switch is closed; the current tolerance at the moment of input (when the switch is closed) is characterized by the instantaneous tolerance current, and the instantaneous tolerance current involves the instantaneous tolerance current of the cell and the instantaneous tolerance current of the switch; the continuous current tolerance after the switch is closed is characterized by the maximum allowable continuous current, and the continuous current tolerance involves the continuous current tolerance of the switch and the continuous current tolerance of the cell. Specifically,

[0050] (1) Calculate the maximum allowable voltage difference that each battery cluster branch can withstand instantaneously:

[0051] Obtain the instantaneous withstand current of the switch: it is related to the switch model and can be obtained / checked from the switch specification sheet, etc.;

[0052] Obtain the instantaneous withstand current of the battery cell. Since the instantaneous withstand data of the battery cluster battery cell (referred to as the battery cell) cannot be provided, the battery cell continuous pulse SOP data is defined here as the upper limit of the withstand current. The corresponding continuous pulse SOP table can be selected according to the average temperature range of the current battery cluster (referred to as the current cluster), and then the corresponding continuous pulse SOP can be obtained according to the current cluster SOC as the instantaneous withstand current of the battery cell.

[0053] Step 1.1: Compare the pulse SOP of the current battery cluster cell duration and the instantaneous withstand current of the corresponding switches in its branches, and take the minimum value as the maximum current allowed at the initial moment.

[0054] Compare the instantaneous withstand current of the current battery cell (cell duration pulse SOP) and the instantaneous withstand current of the corresponding switch in its branch, and take the minimum value as the maximum current allowed at the initial moment;

[0055] Step 1.2: The internal resistance of the current battery cluster at the initial moment is multiplied by the maximum current allowed at the initial moment to obtain the maximum allowable voltage difference that can be tolerated instantaneously.

[0056] Specifically, the internal resistance of the single battery cluster is calculated according to the internal resistance of the cells and the line resistance of the current battery cluster at the initial moment, and multiplied by the maximum current allowed at the initial moment to obtain the maximum allowable voltage difference that can be tolerated instantaneously.

[0057] Among them, the internal resistance of the battery cell at the initial moment can be obtained in the following way: select the corresponding RC table according to the interval of the average temperature of the current cluster at the initial moment, and then obtain the corresponding RC identification parameters according to the current cluster SOC; calculate the internal resistance of the battery cell at the initial moment according to the Thevenin second-order equivalent battery model and RC identification parameters.

[0058] (2) Calculate the maximum allowable voltage difference that each battery cluster branch can sustain continuously:

[0059] The continuous current tolerance of the switch is the rated current of the switch in the current battery cluster branch. The rated current value of the switch can be obtained from the switch specification, etc.

[0060] The continuous current tolerance of the battery cell is the SOP under the current temperature and SOC, that is, the corresponding continuous current SOP table is selected according to the interval of the average temperature of the current cluster, and the corresponding continuous SOP is obtained according to the current cluster SOC;

[0061] Step 1.3: Compare the current battery cluster continuous SOP and the rated current of the corresponding switch in its branch, take the minimum value between the two, and obtain the maximum allowable continuous current.

[0062] The continuous SOP of a battery cluster refers to the current allowed for the battery cluster to operate for a long time or in a steady state.

[0063] Step 1.4: The current internal resistance of the battery cluster at the time of continuous operation is multiplied by the maximum allowable continuous current to obtain the maximum allowable voltage difference of continuous tolerance.

[0064] Specifically, the internal resistance of the battery cluster is calculated according to the internal resistance of the battery cell and the line resistance at the current battery cluster duration, and multiplied by the maximum allowed continuous current to obtain the maximum allowable voltage difference that can be continuously tolerated;

[0065] Among them, the internal resistance of the battery cell at the duration moment can be obtained in the following manner: select the corresponding RC table according to the interval of the average temperature of the current cluster at the duration moment, and then obtain the corresponding RC identification parameters according to the current cluster SOC; calculate the internal resistance of the battery cell at the duration moment according to the Thevenin second-order equivalent battery model and the RC identification parameters.

[0066] Step 1.5: Compare the maximum allowable pressure difference that can be tolerated instantaneously and the maximum allowable pressure difference that can be tolerated continuously, and take the smaller value as the maximum allowable pressure difference in parallel.

[0067] In one embodiment, the schematic diagram of the internal resistance of the battery cell can be found in Figure 3, the horizontal axis t represents time, and the vertical axis R represents the resistance of the battery cell. It can be seen that the battery cell internal resistance is smaller at the initial moment (left side), and the battery cell internal resistance is larger during the continuous moment (right side).

[0068] Specifically, if the maximum allowable pressure difference that can be tolerated instantaneously is greater than the maximum allowable pressure difference that can be tolerated continuously, the maximum allowable pressure difference that can be tolerated continuously is taken as the maximum allowable pressure difference when the battery cluster is incorporated (maximum allowable pressure difference in parallel); if the maximum allowable pressure difference that can be tolerated instantaneously is less than the maximum allowable pressure difference that can be tolerated continuously, the maximum allowable pressure difference that can be tolerated instantaneously is taken as the maximum allowable pressure difference when the battery cluster is incorporated (maximum allowable pressure difference in parallel).

[0069] Step 2: According to step 1, the maximum allowable parallel pressure difference under different average temperatures and SOCs is obtained and made into a table.

[0070] Under different average temperatures and SOCs, the corresponding data of the maximum allowable parallel pressure difference is obtained, and the data is output into a table. The maximum allowable parallel pressure difference can be obtained by looking up the table according to the average temperature and SOC of the battery cluster.

[0071] Step 3: Perform the first round of insulation detection on N battery clusters. The battery clusters that pass the detection are qualified battery clusters. The pre-charging circuits corresponding to the qualified battery clusters are closed to pre-charge the bus. The energy storage system enters soft start and detects the real-time voltage difference between each qualified battery cluster and the bus.

[0072] In one embodiment, the number of qualified battery clusters is M (M is a positive integer less than or equal to N), then in step 3, these M qualified battery clusters are connected to the bus by closing their respective corresponding pre-charging circuits, that is, these M qualified battery clusters participate in pre-charging, and the remaining (NM) battery clusters are unqualified battery clusters and do not participate in pre-charging.

[0073] It can be understood that after the energy storage system enters soft start, the bus voltage starts to rise from 0. Since the voltage of the qualified battery cluster is relatively stable, the difference between the real-time voltage of the qualified battery cluster and the real-time voltage of the bus (i.e., the real-time voltage difference between the qualified battery cluster and the bus) will become smaller and smaller.

[0074] The first round of insulation testing in step 3 includes:

[0075] The battery clusters are tested for insulation one by one, and the battery clusters that pass the test are marked as qualified battery clusters.

[0076] Step 4: When the real-time voltage difference between any qualified battery cluster and the bus reaches the pre-charge voltage difference threshold, it indicates that the pre-charge is successful, and the corresponding switch of any qualified battery cluster is closed, and the corresponding pre-charge circuits of all qualified battery clusters are disconnected, and the soft start is completed.

[0077] In one embodiment, when the real-time voltage difference between one qualified battery cluster among M qualified battery clusters and the bus reaches the pre-charge voltage difference threshold first, it indicates that the pre-charge is successful, and the corresponding switch of the (one) qualified battery cluster is closed so that the qualified battery cluster is merged into the bus, and the corresponding pre-charge circuits of the M battery clusters are disconnected, and the soft start of the energy storage system is completed; the corresponding switch of the one qualified battery cluster is closed first and then the M pre-charge circuits are disconnected, so as to avoid power failure between the battery cluster and the bus, or to maintain the electrical connection between the battery cluster and the bus.

[0078] Among them, the maximum allowable parallel pressure difference is greater than the pre-charge pressure difference threshold.

[0079] Step 5: Determine whether the real-time voltage difference between the remaining qualified battery clusters and the bus is less than or equal to the insulation detection voltage difference threshold. If so, treat it as a qualified battery cluster and proceed to step 6. If not, repeat step 5.

[0080] In one embodiment, for the remaining (M-1) qualified battery clusters that are not connected to the bus except the qualified battery cluster that has been connected to the bus, if the real-time voltage difference between the qualified battery cluster and the bus is less than or equal to the insulation detection voltage difference threshold, then proceed to step 6; if the real-time voltage difference between the qualified battery cluster and the bus is greater than the insulation detection voltage difference threshold, then continue to detect the real-time voltage difference between it and the bus and compare it with the insulation detection voltage difference threshold (because the real-time voltage difference between the qualified battery cluster and the bus is variable) to determine whether to proceed to step 6.

[0081] Among them, the insulation detection voltage difference threshold is greater than the maximum allowable parallel voltage difference.

[0082] Among them, the insulation detection voltage difference threshold is greater than the maximum allowable parallel voltage difference, so that the battery cluster can be tested for insulation in advance to ensure the smooth parallel connection of the energy storage system.

[0083] Step 6: Determine whether the qualified battery cluster is within the validity period of the first round of insulation test. If so, proceed to step 7. If not, mark it as a cluster to be tested and proceed to step 8.

[0084] Among them, being within the validity period of the first round of insulation test indicates that the qualified battery cluster has passed the first round of insulation test, that is, its first round of insulation test is qualified, and when judging in step 6, it is still within the validity period of the first round of insulation test, for example, the validity period of the first round of insulation test is 10 minutes, and the time from step 6 to the end of the first round of insulation test is 6 minutes; for another example, the validity period of the first round of insulation test is 30 seconds, and the time from step 6 to the end of the first round of insulation test is 5 seconds; and so on; wherein the cluster to be tested is a qualified battery cluster outside the validity period of the first round of insulation test, that is, it has passed the first round of insulation test but the validity period of the first round of insulation test has expired, for example, the validity period of the first round of insulation test is 10 minutes, and the time from step 6 to the end of the first round of insulation test is 12 minutes; for another example, the validity period of the first round of insulation test is 30 seconds, and the time from step 6 to the end of the first round of insulation test is 50 seconds. It can be understood that the validity period of the first round of insulation test is for each battery cluster to be tested.

[0085] Step 7: Determine whether the real-time voltage difference between the qualified battery cluster and the bus is less than or equal to the maximum allowable parallel voltage difference. If so, proceed to step 10; if not, repeat step 7.

[0086] In one embodiment, the real-time pressure difference between the qualified battery cluster and the bus is judged. If the real-time pressure difference is less than or equal to the maximum allowable parallel pressure difference, step 10 is entered; if the real-time pressure difference is greater than the maximum allowable parallel pressure difference, step 7 is repeated, that is, the real-time pressure difference is continuously detected and compared with the maximum allowable parallel pressure difference (because the real-time pressure difference between the qualified battery cluster and the bus is variable) to determine whether to enter step 10.

[0087] Step 8: For the cluster to be tested, select the cluster with the smallest voltage difference with the bus, and enable it to perform a second insulation test. If it passes the test, return to step 10.

[0088] In step 8, a cluster with the smallest voltage difference with the bus is selected to enable it to perform a second insulation test, so that the cluster to be tested with the smallest voltage difference with the bus is preferentially selectively incorporated into the bus (step 10).

[0089] Step 9: Repeat step 8 for the cluster to be inspected that has not undergone the second insulation inspection.

[0090] Since the insulation test is performed on battery clusters one by one, in order to avoid omissions and to ensure that the clusters to be tested with a small voltage difference with the bus are selectively incorporated into the bus preferentially, step 8 is repeated for the clusters to be tested that have not undergone the second insulation test, so that after searching through step 8, all clusters to be tested that meet the conditions (pass the second insulation test) can return to step 7.

[0091] Step 10: Selectively integrate qualified battery clusters that meet the conditions into the bus according to power requirements.

[0092] It can be understood that if the power requirement of the energy storage system is large, more qualified battery clusters will be connected to the bus; if the power requirement of the energy storage system is small, fewer qualified battery clusters will be connected to the bus. There are two types of qualified battery clusters that meet the conditions in step 10. One is a qualified battery cluster that is still within the validity period of the first insulation test and the pressure difference between it and the bus is less than or equal to the maximum allowable parallel pressure difference; the other is a qualified battery cluster that is outside the validity period of the first insulation test but passes the second insulation test, and the pressure difference between it and the bus is less than or equal to the maximum allowable parallel pressure difference.

[0093] The integration into the bus is achieved by closing the corresponding switches of the aforementioned battery cluster.

[0094] In one embodiment, if there are two or more qualified battery clusters that meet the conditions and need to be connected to the bus, the connection method is to close the corresponding switches of the qualified battery clusters one by one to connect to the bus. This can avoid excessive impact (pulse) current when connecting, and improve safety.

[0095] In another embodiment, if there are two or more qualified battery clusters that meet the conditions and need to be connected to the bus, the connection method is to close the corresponding switches of all qualified battery clusters that meet the conditions at the same time to connect to the bus. This can save the time of connecting the battery clusters to the bus and is more efficient when the impact (pulse) current condition is met.

[0096] The battery cluster parallel control method in the energy storage system of the present invention can overcome the defect of the prior art that a fixed pressure difference is used as a parallel condition by calculating the dynamic pressure difference threshold of the parallel connection (the maximum allowable pressure difference of the parallel connection) as one of the control logics for whether the parallel connection can be performed. In addition, the battery cluster parallel control method in the energy storage system of the present invention can enable the cluster to be connected to perform insulation detection in advance by setting the insulation detection pressure difference threshold to be greater than the maximum allowable pressure difference of the parallel connection. The system can prepare the insulation detection environment in advance to avoid missing the pressure difference condition of the system parallel connection due to the insulation detection, thereby affecting the normal parallel connection of the system.

[0097] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for controlling battery clusters in parallel in an energy storage system, wherein the energy storage system comprises battery clusters 1 to N, each of which is selectively connected to a bus via a parallel pre-charging circuit or switch, characterized in that: The method specifically comprises the following steps: Step 1: At different average temperatures and SOCs, calculate the maximum allowable pressure difference that each battery cluster branch can tolerate instantaneously and the maximum allowable pressure difference that can be tolerated continuously, and compare the two to take the smaller value as the maximum allowable pressure difference in parallel; Step 2: According to step 1, the maximum allowable parallel pressure difference under different average temperatures and SOCs is obtained and made into a table; Step 3: Performing a first round of insulation detection on the N battery clusters, the battery clusters that pass the detection are qualified battery clusters, closing the pre-charging circuits corresponding to the qualified battery clusters, pre-charging the bus, and the energy storage system enters soft start, detecting the real-time voltage difference between each qualified battery cluster and the bus; Step 4: When the real-time voltage difference between any of the qualified battery clusters and the bus reaches the pre-charge voltage difference threshold, it indicates that the pre-charge is successful, the switch corresponding to any of the qualified battery clusters is closed, and the pre-charge circuits corresponding to all the qualified battery clusters are disconnected, and the soft start is completed; Step 5: Determine whether the real-time voltage difference between the remaining qualified battery clusters and the bus is less than or equal to the insulation detection voltage difference threshold. If so, treat the remaining qualified battery clusters as qualified battery clusters and proceed to step 6. If not, repeat step 5. Step 6: Determine whether the qualified battery cluster is within the validity period of the first round of insulation test. If so, proceed to step 7. If not, mark it as a cluster to be tested and proceed to step 8. Step 7: Determine whether the real-time voltage difference between the qualified battery cluster and the bus is less than or equal to the maximum allowable parallel voltage difference. If so, proceed to step 10; if not, repeat step 7; Step 8: For the clusters to be tested, a cluster with the smallest voltage difference with the bus is selected to enable it to perform a second insulation test. If it passes the test, return to step 7; Step 9: Repeat step 8 for the cluster to be tested that has not undergone the second insulation test; Step 10: Selectively merge the qualified battery clusters that meet the conditions into the bus according to the power demand; Wherein, N is a positive integer greater than or equal to 2, the battery cluster branch refers to a branch formed by a battery cluster and a corresponding switch connected in series; the insulation detection pressure difference threshold > the parallel maximum allowable pressure difference > the pre-charge pressure difference threshold.

2. A method for controlling battery clusters in parallel in an energy storage system according to claim 1, characterized in that: The calculation of the maximum allowable voltage difference that each battery cluster branch can withstand instantaneously includes: Step 1.1: Compare the pulse SOP of the battery cell at the current battery cluster duration and the instantaneous withstand current of the corresponding switch in its branch, and take the minimum value as the maximum current allowed at the initial moment; Step 1.2: The internal resistance of the current battery cluster at the initial moment is multiplied by the maximum current allowed at the initial moment to obtain the maximum allowable voltage difference that can be tolerated instantaneously.

3. A method for controlling battery clusters in parallel in an energy storage system according to claim 2, characterized in that: The calculation of the maximum allowable voltage difference that each battery cluster branch can sustain continuously includes: Step 1.3: Compare the current battery cluster continuous SOP and the rated current of the corresponding switch in its branch, take the minimum value, and obtain the maximum allowable continuous current; Step 1.4: multiply the internal resistance of the current battery cluster by the maximum allowable continuous current to obtain the maximum allowable voltage difference for continuous tolerance; Step 1.5: Compare the maximum allowable pressure difference of the instantaneous tolerance and the maximum allowable pressure difference of the continuous tolerance, and take the smaller value as the maximum allowable pressure difference of the parallel connection.

4. A method for controlling battery clusters in parallel in an energy storage system according to claim 1, characterized in that: The switch is a relay, or an IGBT, or a MOSFET.

5. A method for controlling battery clusters in parallel in an energy storage system according to claim 2 or 3, characterized in that: The internal resistance includes the internal resistance of the cells and the wire group of the battery cluster.

6. A method for controlling battery clusters in parallel in an energy storage system according to claim 5, characterized in that: The instantaneous withstand current of the switch can be obtained by checking the switch model.

7. A method for controlling battery clusters in parallel in an energy storage system according to claim 1, characterized in that: The first round of insulation testing includes: The battery clusters are tested for insulation one by one, and the battery clusters that pass the test are marked as qualified battery clusters.

8. A method for controlling battery clusters in parallel in an energy storage system according to claim 1, characterized in that: The qualified battery cluster that meets the conditions is a qualified battery cluster that is still within the validity period of the first insulation test and the pressure difference between it and the bus is less than or equal to the maximum allowable parallel pressure difference, or a qualified battery cluster that is outside the validity period of the first insulation test but has passed the second insulation test and the pressure difference between it and the bus is less than or equal to the maximum allowable parallel pressure difference.

9. A method for controlling battery clusters in parallel in an energy storage system according to claim 8, characterized in that: By incorporating the plurality of qualified battery clusters that meet the conditions into the bus one by one or simultaneously.

10. A method for controlling battery clusters in parallel in an energy storage system according to claim 9, characterized in that: The qualified battery cluster that meets the conditions is incorporated into the bus, which means that the qualified battery cluster that meets the conditions is incorporated into the bus by closing the corresponding switch.

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