Energy storage system and voltage balance control method thereof

Abstract

The invention discloses an energy storage system and a voltage balance control method thereof, and belongs to the technical field of energy storage. The energy storage system comprises at least two battery clusters, each battery cluster comprises at least two battery packs and DCDC converters thereof, the battery packs and the DCDC converters are in one-to-one correspondence, the input end of each DCDC converter in each battery cluster is connected with one battery pack, and the output end of each DCDC converter in each battery cluster is connected with the DCDC converters of the same battery cluster and other battery clusters in parallel. The system can solve the problems that in the prior art, when battery clusters are combined, circulation is likely to be generated due to voltage imbalance, and the capacity of the battery clusters is affected.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage, and in particular relates to an energy storage system and a voltage balancing control method thereof. Background Art

[0002] Currently, there are centralized energy storage systems and string energy storage systems, both of which have battery clusters in parallel. During the operation of the energy storage system, as the use time increases, the voltage difference between the parallel battery clusters will increase, and there will be voltage imbalance between the battery clusters, resulting in circulating current when the clusters are connected, affecting battery safety. In addition, the increase in the voltage difference between the battery packs in the battery cluster will also affect the capacity of the battery cluster, resulting in a reduction in the input and output power of the battery cluster.

[0003] In addition, with the advancement of power battery technology, many power batteries with reduced capacity are used for cascade utilization, but the state of charge, health status, internal resistance and other performance of these power batteries are inconsistent. In energy storage applications, inconsistent performance of each battery will affect the overall charging and discharging energy of the energy storage system. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an energy storage system and a voltage balancing control method thereof in view of the above-mentioned deficiencies in the prior art, which can simultaneously achieve voltage balancing between battery clusters and between battery packs within a battery cluster, avoid circulating current when battery clusters are connected in parallel, ensure the capacity and safety of the battery cluster, and can be widely used in scenarios of cascade utilization of power batteries.

[0005] In a first aspect, the present invention provides an energy storage system, comprising at least two battery clusters, each battery cluster comprising at least two battery packs and their DC / DC converters, the battery packs corresponding to the DCDC converters one by one. For each DCDC converter in each battery cluster, its input end is connected to a battery pack, and its output end is connected in parallel to the DCDC converters of the same battery cluster and other battery clusters.

[0006] Preferably, each battery cluster further comprises at least two first relays, and the DCDC converters correspond to the first relays one by one. The output end of the DCDC converter is connected in parallel with the DCDC converters of the same battery cluster and other battery clusters through the first relays.

[0007] Preferably, each battery cluster further includes a main control unit. The main control unit is connected to each battery pack and each first relay in the battery cluster, and is used to obtain a first voltage difference and control the first relay to open / close according to the first voltage difference, wherein the first voltage difference is used to characterize the voltage difference between each battery pack in the battery cluster.

[0008] Preferably, the energy storage system further comprises a master control unit. The master control unit is connected to the main control unit of each battery cluster, and is used to obtain a second voltage difference, and send a voltage balancing control instruction or a stop voltage balancing control instruction to the main control unit according to the second voltage difference, wherein the second voltage difference is used to characterize the voltage difference between each battery cluster.

[0009] Preferably, the main control unit is further configured to control all first relays in the battery cluster to close after receiving the voltage balancing control instruction.

[0010] Preferably, each battery cluster further comprises a main positive relay connected to the main control unit, and the main control unit is further configured to control the main positive relay to close after receiving a stop voltage balancing control instruction, so as to power on the battery clusters in parallel.

[0011] Preferably, the main control unit is further configured to control all first relays in the battery cluster to be disconnected after receiving the instruction to stop voltage balancing control.

[0012] Preferably, the energy storage system further comprises an energy storage converter PCS. Each battery cluster is connected to the DC side of the PCS via its own main positive relay.

[0013] In a second aspect, the present invention further provides a voltage balancing control method for an energy storage system, which is applied to the energy storage system described in the first aspect, and the control method includes: obtaining a first voltage difference and a second voltage difference, wherein the first voltage difference is used to characterize the voltage difference between each battery pack in the battery cluster, and the second voltage difference is used to characterize the voltage difference between each battery cluster; and controlling whether the DCDC converter corresponding to each battery pack is working according to the first voltage difference and the second voltage difference.

[0014] The energy storage system and voltage balancing control method provided by the present invention, because each battery pack is provided with a corresponding DCDC converter, and each DCDC converter is connected in parallel with the DCDC converters of the same battery cluster and other battery clusters, so that when there is a voltage difference between battery clusters and / or within a battery cluster, the DCDC converters corresponding to each battery pack can realize charging and discharging between the high-voltage battery pack and the low-voltage battery pack, and at the same time realize voltage balancing between battery clusters and between battery packs in a battery cluster, avoid circulating current when battery clusters are connected in parallel, and ensure the capacity and safety of the battery cluster. And it can be widely used in the scene of cascade utilization of power batteries, to realize the energy transfer between inconsistent cascade power batteries in the process of charging and discharging of energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of the structure of an energy storage system according to Embodiment 1 of the present invention;

[0016] Figure 2 A schematic flow chart of a voltage balancing control method for an energy storage system according to Embodiment 2 of the present invention;

[0017] Figure 3 A schematic diagram of another voltage balancing control method for an energy storage system according to Embodiment 2 of the present invention;

[0018] Figure 4 Schematic diagram of another voltage balancing control method for an energy storage system according to Embodiment 2 of the present invention. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the technical solution of the present invention, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0020] It should be understood that the specific embodiments and drawings described herein are only used to explain the present invention rather than to limit the present invention.

[0021] It can be understood that, in the absence of conflict, the various embodiments of the present invention and the various features in the embodiments can be combined with each other.

[0022] It can be understood that, for the convenience of description, the drawings of the present invention only show the parts related to the present invention, while the parts irrelevant to the present invention are not shown in the drawings.

[0023] It can be understood that each unit and module involved in the embodiments of the present invention may correspond to only one physical structure, or may be composed of multiple physical structures, or multiple units and modules may be integrated into one physical structure.

[0024] It can be understood that, without conflict, the functions and steps marked in the flowcharts and block diagrams of the present invention may occur in an order different from that marked in the drawings.

[0025] It is understood that the flowcharts and block diagrams of the present invention illustrate the possible architectures, functions, and operations of the systems, devices, equipment, and methods according to the various embodiments of the present invention. Each box in the flowchart or block diagram may represent a unit, module, program segment, or code, which contains executable instructions for implementing the specified functions. Moreover, each box or combination of boxes in the block diagram and flowchart may be implemented by a hardware-based system that implements the specified functions, or may be implemented by a combination of hardware and computer instructions.

[0026] It can be understood that the units and modules involved in the embodiments of the present invention can be implemented by software or hardware. For example, the units and modules can be located in a processor.

[0027] Embodiment 1:

[0028] like Figure 1As shown, this embodiment provides an energy storage system, including at least two battery clusters. Each battery cluster includes at least two battery packs and DC-DC converters thereof, and the battery packs correspond to the DC-DC converters one by one.

[0029] For each DCDC converter in each battery cluster, its input end is connected to a battery pack, and its output end is connected in parallel to the DCDC converters of the same battery cluster and other battery clusters.

[0030] In this embodiment, the battery pack corresponds to the DCDC converter one by one, that is, one battery pack corresponds to one DCDC converter, the DCDC converter and the battery pack are independent devices, or the DCDC converter is arranged in the battery pack. This embodiment does not limit the installation form of the two.

[0031] Since each battery pack is provided with a corresponding DCDC converter, and each DCDC converter is connected in parallel with the DCDC converters of the same battery cluster and other battery clusters, when there is a voltage difference between battery clusters and / or within a battery cluster, the DCDC converters corresponding to each battery pack are controlled (such as the operation of the DCDC converter is controlled by the master control of the energy storage system and the master control in the battery cluster), or based on the control function of each DCDC converter itself, the high-voltage battery pack and the low-voltage battery pack are charged and discharged, thereby achieving not only voltage balance between battery clusters, but also voltage balance between different battery packs in the same battery cluster, avoiding the generation of circulating current when the battery clusters are clustered, and ensuring the capacity and safety of the battery cluster, that is, ensuring the long life and high-efficiency use of the battery system in the energy storage system. And it can be widely used in the scenario of cascade utilization of power batteries to achieve the energy transfer between inconsistent cascade power batteries in the charging and discharging process of the energy storage system.

[0032] In some embodiments, each battery cluster further includes at least two first relays, and the DCDC converters correspond to the first relays one by one. The output end of the DCDC converter is connected in parallel with the DCDC converters of the same battery cluster and other battery clusters through the first relays.

[0033] In this embodiment, in order to simplify the control, a corresponding first relay is provided for each DCDC converter in the battery cluster, that is, one DCDC converter corresponds to one first relay. By controlling the opening / closing of the first relay corresponding to the DCDC converter, the charge and discharge control between the battery clusters and between the battery packs in the battery cluster is realized, and the control process is simple.

[0034] In some embodiments, each battery cluster further includes a main control unit. The main control unit is connected to each battery pack and each first relay in the battery cluster, and is used to obtain a first voltage difference and control the first relay to open / close according to the first voltage difference, wherein the first voltage difference is used to characterize the voltage difference between each battery pack in the battery cluster.

[0035] In this embodiment, the main control unit is used to control the opening / closing of the first relay according to the first voltage difference, including two ways. The first way: the main control unit is used to determine whether the first voltage difference exceeds the first threshold value. In response to the first voltage difference exceeding the first threshold value, the main control unit controls all the first relays in the battery cluster to close, so as to achieve voltage balance between the battery clusters and between the battery packs in the battery cluster. In response to the first voltage difference being less than or equal to the first threshold value, all the first relays in the battery cluster are controlled to be disconnected to exit the voltage balance mode. The second way: the main control unit is used to determine whether the first voltage difference exceeds the first threshold value. In response to the first voltage difference exceeding the first threshold value, the main control unit controls the first relays corresponding to the two battery packs related to the first voltage difference in the battery cluster to close, so as to achieve voltage balance between the two battery packs. In response to the first voltage difference being less than or equal to the first threshold value, the main control unit controls the first relays corresponding to the two battery packs related to the first voltage difference in the battery cluster to be disconnected to exit the voltage balance mode. It should be noted that in the first way, if all the first relays in all the battery clusters in the energy storage system are closed, the energy storage system simultaneously achieves voltage balance between the battery clusters and voltage balance between the battery packs in the battery cluster. For the second way, for example, Figure 1 When the first voltage difference between battery pack 1 and battery pack 3 exceeds the first threshold, the main control unit is used to control the first relays corresponding to DCDC converter 11 and DCDC converter 31 to close, so as to realize the charging and discharging between battery pack 1 and battery pack 3. This method can avoid controlling all the first relays in the battery cluster, thereby simplifying the control.

[0036] In some embodiments, the energy storage system further includes a master control unit. The master control unit is connected to the main control unit of each battery cluster, and is used to obtain a second voltage difference, and send a voltage balancing control instruction or a stop voltage balancing control instruction to the main control unit according to the second voltage difference, wherein the second voltage difference is used to characterize the voltage difference between each battery cluster.

[0037] In this embodiment, the main control unit is used to collect the voltage of each battery pack and the voltage of the battery cluster in which it is located, and feed the collected voltage back to the main control unit. The main control unit is used to calculate the second voltage difference based on the voltage fed back by the main control units of different battery clusters. The main control unit is used to determine whether the second voltage difference exceeds the second threshold value. In response to the second voltage difference exceeding the second threshold value, the main control unit is used to send a voltage balancing control instruction to the main control unit, so that the main control unit controls all the first relays of the battery cluster to close. In response to the second voltage difference being less than or equal to the second threshold value, the main control unit is used to send a stop voltage balancing control instruction to the main control unit (i.e., exit the voltage balancing mode), so that the main control unit controls all the first relays of the battery cluster to disconnect. Example Figure 1When the voltage difference between the first battery cluster 101 and the second battery cluster 102 exceeds the second threshold, the master control unit is used to send a voltage balancing control instruction to the main control units of the two battery clusters, so that the main control units control all the first relays in the battery clusters to close, that is, all the first relays in the battery cluster 101 and the battery cluster 102 to close. It can be understood that if all the first relays in all the battery clusters are closed, the energy storage system simultaneously realizes voltage balancing between the battery clusters and voltage balancing between the battery packs in the battery clusters.

[0038] In some embodiments, the voltage balancing control instruction and the stop voltage balancing control instruction include a first relay identifier, and the second voltage difference also includes a voltage difference between each battery pack between the battery clusters. The general control unit is also used to determine whether the second voltage difference exceeds the second threshold value. In response to the second voltage difference exceeding the second threshold value, the general control unit is used to send a voltage balancing control instruction to the main control unit, so that the main control unit controls the closure of part of the first relays in the battery cluster. For example, since the control instruction includes the first relay identifier to be controlled, the main control unit can be used to control the closure of the first relay corresponding to the battery pack with the largest voltage in the battery cluster (such as the first battery cluster 101), and the main control unit of another battery cluster can be used to control the closure of the first relay corresponding to the battery pack with the smallest voltage in the battery cluster (such as the second battery cluster 102), so as to achieve the discharge of the high-voltage battery pack in the first battery cluster to the low-voltage battery pack in the second battery cluster, and complete the voltage balancing between the battery packs between the battery clusters. In this embodiment, the voltage balancing of the high and low battery packs between the battery clusters is achieved by controlling part of the first relays, which can simplify the control and improve the control efficiency.

[0039] In some embodiments, the main control unit is further configured to control all first relays in the battery cluster to close after receiving the voltage balancing control instruction.

[0040] In some embodiments, each battery cluster further comprises a main positive relay. The main positive relay is connected to the main control unit. The main control unit is further configured to control the main positive relay to close after receiving a stop voltage balancing control instruction, so that the battery clusters are powered on in parallel.

[0041] In some embodiments, the main control unit is further configured to control all first relays in the battery cluster to be disconnected after receiving the instruction to stop voltage balancing control.

[0042] In some embodiments, the energy storage system further includes an energy storage converter PCS. Each battery cluster is connected to the DC side of the PCS through its own main positive relay.

[0043] The energy storage system provided in this embodiment is provided with a DCDC converter corresponding to each battery pack, and each DCDC converter is connected in parallel with the DCDC converters of the same battery cluster and other battery clusters, so that when there is a voltage difference between battery clusters and / or within a battery cluster, the DCDC converter corresponding to each battery pack is controlled (such as the operation of the DCDC converter is controlled by the master control of the energy storage system and the master control in the battery cluster), or based on the control function of each DCDC converter itself, the high-voltage battery pack and the low-voltage battery pack are charged and discharged, thereby not only achieving voltage balance between battery clusters, but also achieving voltage balance between different battery packs in the same battery cluster, avoiding the generation of circulating current when the battery clusters are clustered, and ensuring the capacity and safety of the battery cluster, that is, ensuring the long life and high-efficiency use of the battery system in the energy storage system. In addition, in the scenario of cascade utilization of power batteries, the energy storage system structure of this embodiment can realize the energy transfer between cascade batteries and between battery packs in the battery cluster, thereby improving the utilization rate of cascade batteries. Furthermore, a corresponding first relay is set for each DCDC converter, and the charging and discharging of the DCDC converter is realized by controlling the opening / closing of the first relay, and the control method is simpler. In addition, the main control unit is used to control the opening / closing of some first relays, which can achieve voltage balance between battery clusters and between battery packs in the battery cluster, and the control method is simple and improves control efficiency.

[0044] Embodiment 2:

[0045] This embodiment provides a voltage balancing control method for an energy storage system, which is applied to the energy storage system described in Embodiment 1, and particularly to the main control unit or the master control unit in Embodiment 1. This embodiment is described by taking the main control unit as an example.

[0046] like Figure 2 As shown, the voltage balancing control method includes:

[0047] Step S101 , obtaining a first voltage difference and a second voltage difference, wherein the first voltage difference is used to characterize the voltage difference between battery packs in a battery cluster, and the second voltage difference is used to characterize the voltage difference between battery clusters.

[0048] Step S102 , controlling whether the DCDC converter corresponding to each battery pack is working according to the first voltage difference and the second voltage difference.

[0049] In this embodiment, the main control unit obtains the first voltage difference between the battery packs in the battery cluster, and controls whether the DCDC converter corresponding to the battery pack in the battery cluster works according to the first voltage difference. Figure 1As shown, the first voltage difference between battery pack 2 and battery pack 3 exceeds the first threshold, and the main control unit 110 controls the DCDC converter 21 and the DCDC converter 31 to work, so as to achieve voltage balance between battery pack 2 and battery pack 3. The main control unit obtains the second voltage difference, which may be sent to the main control unit by the master control unit, or obtained by the main control unit from the master control unit. Figure 1 As shown, the second voltage difference between the voltage of the first battery cluster 101 and the voltage of the second battery cluster 102 exceeds the second threshold value. Specifically, the total voltage of battery pack 2 and battery pack 3 is higher than the voltage of battery pack 7. Then, the DCDC converter 71 is controlled to operate, and the voltage balance among battery pack 2, battery pack 3 and battery pack 7 is achieved at the same time, that is, the voltage balance between battery clusters and the battery packs within the battery cluster is achieved at the same time.

[0050] In some embodiments, the main control unit can control the operation of all DCDC converters in the battery cluster, and simultaneously achieve voltage balancing between battery clusters and battery packs within the battery cluster.

[0051] In some embodiments, whether the DCDC converter corresponding to each battery pack is working is controlled according to the first voltage difference and the second voltage difference, including: controlling the opening / closing of the first relay corresponding to the DCDC converter according to the first voltage difference and the second voltage difference to achieve control of the working state of the DCDC converter.

[0052] In some embodiments, after acquiring the first voltage difference and the second voltage difference, and before controlling whether the DCDC converter corresponding to each battery pack is working according to the first voltage difference and the second voltage difference, the voltage balancing control method also includes: receiving a voltage balancing control instruction sent by the main control unit or stopping the voltage balancing control instruction.

[0053] In some embodiments, the opening / closing of the first relay corresponding to the DCDC converter is controlled according to the first voltage difference and the second voltage difference, including: after receiving a voltage balancing control instruction, controlling all the first relays in the battery cluster to close, so as to achieve voltage balancing between battery clusters and between battery packs in the battery cluster, wherein the voltage balancing control instruction is used to be determined according to the second voltage difference.

[0054] In some embodiments, the voltage balancing control method further includes: after receiving the instruction to stop the voltage balancing control, controlling the main positive relay to close so that the battery clusters are powered on in parallel.

[0055] In some embodiments, the voltage balancing control method further includes: after receiving a stop voltage balancing control instruction, controlling all first relays in the battery cluster to be disconnected, wherein the stop voltage average control instruction is used to be determined according to the second voltage difference.

[0056] The energy storage system and voltage balancing control method of this embodiment are described below with a specific embodiment.

[0057] like Figure 1 As shown, the energy storage system includes a first battery cluster 101, wherein the first battery cluster 101 includes a main control unit 110, battery packs 1 to 4, DCDC converters 11 to 41, and a main positive relay 201. The main control unit 110 is used to collect the voltage of the battery pack in the battery cluster. One end of the DCDC converter is connected to the battery pack, and the other end is connected to one end of the DCDC converter in the second battery cluster 102 through the first relay. The first battery cluster 101 is connected in parallel with the DCDC converter in the second battery cluster 102. The main positive relay 201 is the main positive relay of the first battery cluster 101, and the main positive relay is used to realize the convergence between battery clusters. The second battery cluster 102 includes a main control unit 111, battery packs 5 to 8, DCDC converters 51 to 81, and a main positive relay 202, and its functions are consistent with those of the first battery cluster 101.

[0058] PCS103 is a DC to AC converter for energy storage system.

[0059] The main control unit 130 is connected to the main control units 110 and 111 for communication and is used to obtain voltage information in the battery cluster. Figure 1 The energy storage system shown can achieve the following three functions:

[0060] ① The function of suppressing circulating current when the battery clusters are powered on.

[0061] In the energy storage system, when there are multiple clusters in parallel, when the voltage between the battery clusters is unbalanced, a circulating current will be generated when the clusters are closed. Therefore, the total voltage between the clusters is determined before the energy storage system is connected in parallel.

[0062] like Figure 3 As shown, the voltage balancing control method of the energy storage system includes:

[0063] Step S11: the main control unit 110 and the main control unit 111 send the voltage information in the battery cluster to the main control unit 130. The main control unit 130 makes a judgment based on the voltage difference information (i.e., the second voltage difference) between the battery clusters. When the voltage difference (i.e., the second voltage difference) between the two battery clusters is large, it is necessary to balance the voltage between the battery clusters. The first relays connected to one end of the DCDC converters in the two battery clusters are all closed. The two main control units in the battery cluster respectively control the DCDC converters to perform charge and discharge control, so that the high-voltage battery cluster discharges the low-voltage battery cluster through the DCDC converter, thereby achieving voltage difference balance between the two battery clusters.

[0064] Step S12: The main control unit 130 sends a stop voltage balancing mode (i.e., stop voltage balancing control instruction) based on the voltage information of the main control unit 110 and the main control unit 111 when the voltage difference drops to within the required range. The main control unit controls the first relay at one end of the DCDC converter corresponding to the battery pack to disconnect and stop the operation of the DCDC converter.

[0065] Step S13: the main control unit 130 determines that the voltage difference between the battery clusters reaches the required range, the main control unit 110 closes the main positive relay 201, and the main control unit 111 closes the main positive relay 202 to perform cluster electrical convergence.

[0066] ② Voltage balancing function between battery packs within a battery cluster.

[0067] like Figure 4 As shown, the voltage balancing control method of the energy storage system includes:

[0068] Step S21: the main control unit 110 of the first battery cluster 101 collects voltage information of battery packs in the battery cluster and determines the voltage difference between the battery packs (ie, the first voltage difference).

[0069] Step S22: When the voltage difference is large (i.e., the first voltage difference is greater than the first threshold), the charging and discharging of the battery packs within the cluster can be achieved by controlling the closing of the first relay connected to one end of the DCDC converter corresponding to the high-voltage and low-voltage battery packs, that is, the voltage balancing of the battery packs within the cluster can be achieved. Alternatively, the discharge of the high-voltage battery pack in the first cluster to the low-voltage battery pack in the second cluster can be achieved by closing the first relay at the connecting end of the DCDC converters between clusters, thereby achieving voltage balancing of the battery packs between battery clusters.

[0070] ③Energy balance control between battery packs during cascade utilization.

[0071] The energy balancing control method of the energy storage system using the second-life battery pack includes:

[0072] Step S31: The main control unit calculates the SOH (State of Health) and capacity of each battery pack and sends them to the main control unit.

[0073] Step S32: The master control unit performs energy balancing calculation of the battery packs in the energy storage system according to the SOH and capacity of the battery packs.

[0074] Step S33: During the constant power charging and discharging process, the master control unit sends a control instruction to the main control unit according to the charging and discharging energy of the battery pack, so that the main control unit enables the DCDC energy transfer from the high-energy battery pack to the low-energy battery pack. This prevents the charging and discharging energy of the entire energy storage system from being affected by the low capacity of a certain battery pack, and does not affect the charging and discharging energy of the system due to the difference in SOH of the tiered battery packs.

[0075] The energy storage system and voltage balancing control method of this embodiment can avoid the generation of circulating current in the process of multi-cluster parallel connection in centralized or string systems, reduce the increase of other pre-charging circuits, and reduce the need to increase the cost of balancing resistors and relays. In addition, the voltage balance of the battery pack in the battery cluster can be achieved through the DCDC converter, and the voltage balance of the two cluster-level battery packs can be achieved by connecting the battery pack of another battery cluster through the DCDC converter, so that the voltage balance between clusters and between cluster battery packs can be achieved within the cluster, so that the voltage difference of the batteries within the cluster can be minimized, thereby reducing the impact of high-voltage and low-voltage batteries within the cluster on the capacity of the energy storage system. In addition, the utilization rate of the cascade battery pack in the battery cluster is improved, and the difficulty of applying the cascade battery pack is reduced.

[0076] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, but the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. An energy storage system, characterized in that: comprising at least two battery clusters, Each battery cluster includes at least two battery packs and their DC-DC converters, and the battery packs correspond to the DC-DC converters one by one. For each DCDC converter in each battery cluster, its input end is connected to a battery pack, and its output end is connected in parallel to the DCDC converters of the same battery cluster and other battery clusters.

2. The energy storage system according to claim 1, characterized in that: Each battery cluster further includes at least two first relays, and the DCDC converters correspond to the first relays one by one. The output end of the DCDC converter is connected in parallel with the DCDC converters of the same battery cluster and other battery clusters through the first relay.

3. The energy storage system according to claim 2, characterized in that: Each battery cluster also includes a main control unit, The main control unit is connected to each battery pack and each first relay in the battery cluster for acquiring a first voltage difference and controlling the first relay to open / close according to the first voltage difference, wherein the first voltage difference is used to characterize the voltage difference between each battery pack in the battery cluster.

4. The energy storage system according to claim 3, characterized in that: The energy storage system further includes a master control unit. The main control unit is connected to the main control unit of each battery cluster, and is used to obtain a second voltage difference, and send a voltage balancing control instruction or a stop voltage balancing control instruction to the main control unit according to the second voltage difference, wherein the second voltage difference is used to characterize the voltage difference between each battery cluster.

5. The energy storage system according to claim 4, characterized in that: The main control unit is further used to control all first relays in the battery cluster to close after receiving a voltage balancing control instruction.

6. The energy storage system according to claim 4, characterized in that: Each battery cluster also includes a main positive relay, The main positive relay is connected to the main control unit. The main control unit is also used to control the main positive relay to close after receiving the stop voltage balancing control instruction, so as to power on the battery clusters in parallel.

7. The energy storage system according to claim 6, characterized in that: The main control unit is further used to control all first relays in the battery cluster to be disconnected after receiving the instruction to stop voltage balancing control.

8. The energy storage system according to claim 1, characterized in that: The energy storage system also includes an energy storage converter PCS, Each battery cluster is connected to the DC side of the PCS via its own main positive relay.

9. A voltage balancing control method for an energy storage system, characterized in that: Applied to the energy storage system according to any one of claims 1 to 8, the control method comprises: Obtaining a first voltage difference and a second voltage difference, wherein the first voltage difference is used to characterize the voltage difference between battery packs in the battery cluster, and the second voltage difference is used to characterize the voltage difference between the battery clusters; Whether the DCDC converter corresponding to each battery pack is operating is controlled according to the first voltage difference and the second voltage difference.

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