BATTERY CLUSTER TOPOLOGY FOR LITHIUM-ION BATTERY ENERGY STORAGE SYSTEM AND METHOD FOR CONTROLLING BATTERY CLUSTER

Abstract

To provide battery cluster topology for a lithium ion battery energy storage system and a method for controlling a battery cluster.SOLUTION: Battery cluster parallel topology for a lithium ion battery energy storage system comprises at least two battery cluster units 1 connected in parallel. The battery cluster unit includes: N battery packs 11 (N is a natural number of 2 or more); N bidirectional DC / DC voltage conversion modules 12; N bypass switches 14; a BDCM cooperative controller unit 13; a circuit switch 15; and a connection primary bus 16.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the technical field of lithium ion battery energy storage systems, and in particular to a battery cluster topology for a lithium ion battery energy storage system and a method for controlling the battery cluster. [Background technology]

[0002] On September 22, 2020, at the 75th United Nations Congress, the Chinese government announced that "China will enhance its national independent contributions, adopt stronger policies and measures, and strive to peak its carbon dioxide emissions before 2030 and achieve carbon neutrality by 2060." Energy storage technology is one of the key technologies for achieving this goal, and lithium-ion battery energy storage technology is attracting attention as the most widely applied electrochemical energy storage technology. At the same time, China has become the world's largest new energy vehicle market, and since 2020, China has gradually retired a large number of lithium-ion power batteries. There are currently two main methods for dealing with these retired batteries: first, to cascade them into other applications (e.g., energy storage) without disposal, but simply reuse batteries that have lost capacity and can no longer be used in electric vehicles; and second, to disassemble discarded power batteries and recover valuable materials.

[0003] Both retired and new batteries have performance discrepancies due to factors such as their health state, internal resistance, self-discharge, etc. Large and medium-sized lithium-ion battery energy storage systems generally consist of multiple battery clusters connected in series, parallel, or mixed configurations, with battery clusters consisting of multiple battery packs connected in series, parallel, or mixed configurations, and battery packs consisting of multiple cells connected in series, parallel, or mixed configurations. Therefore, performance discrepancies among cells inevitably lead to mismatches in battery packs and battery clusters, which affect the performance of the battery packs and battery clusters and, in serious cases, may even lead to safety accidents.

[0004] In the case of maintenance replacement of old and new batteries, or the application of lithium-ion batteries to replace lead-acid batteries, due to inconsistencies in battery types and performance conditions, existing solutions require the replacement of the entire battery cluster or entire battery pack, which significantly wastes battery resources and increases costs.

[0005] In the parallel application of multiple battery clusters, if the types and performance states of the batteries in the battery clusters do not match, inrush current and reflux current will occur between the battery clusters, and in severe cases, this will lead to safety issues such as battery overcharging and over-discharging, which should be avoided as much as possible in the integration of energy storage systems.

[0006] Therefore, it is extremely necessary to consider how to reduce the installation cost or maintenance and replacement cost of the lithium-ion battery energy storage system, improve the system efficiency, and enhance the safety and reliability from a comprehensive perspective of the topology structure, control method and control measures of the lithium-ion battery energy storage system. Summary of the Invention

[0007] SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-mentioned drawbacks existing in the prior art and to provide a battery cluster topology and a battery cluster control method for a lithium-ion battery energy storage system. The present invention is achieved by the following aspects. [Means for solving the problem]

[0008] The present invention provides a battery cluster topology for a lithium-ion battery energy storage system, which includes P parallel-connected battery cluster units (P is a natural number equal to or greater than 2), each of which includes N battery packs (N is a natural number equal to or greater than 2), N bidirectional DC / DC voltage conversion modules, N bypass switches, a BDCM coordination controller unit, a circuit switch, and a connecting primary bus.

[0009] The output terminals of the N bidirectional DC / DC voltage conversion modules are sequentially connected in series, the negative output terminal of the first bidirectional DC / DC voltage conversion module is connected to the negative output terminal of the second bidirectional DC / DC voltage conversion module, the positive output terminal of the second bidirectional DC / DC voltage conversion module is connected to the negative output terminal of the third bidirectional DC / DC voltage conversion module, the positive output terminal of the (N-1)th bidirectional DC / DC voltage conversion module is connected to the negative output terminal of the Nth bidirectional DC / DC voltage conversion module, and the negative output terminal of the Nth bidirectional DC / DC voltage conversion module is connected to one terminal of a circuit switch, the other terminal of which is connected to the positive terminal of the primary bus.

[0010] The N battery packs are connected in parallel to the input terminals of the N bidirectional DC / DC voltage conversion modules, the positive terminal of a first battery pack is connected to the positive input terminal of the first bidirectional DC / DC voltage conversion module, the negative terminal of the first battery pack is connected to the negative input terminal of the first bidirectional DC / DC voltage conversion module, the positive terminal of an Nth battery pack is connected to the positive input terminal of the Nth bidirectional DC / DC voltage conversion module, and the negative terminal of the Nth battery pack is connected to the negative input terminal of the Nth bidirectional DC / DC voltage conversion module.

[0011] The N bypass switches are connected in parallel to the output terminals of the N bidirectional DC / DC voltage conversion modules, one end of a first bypass switch is connected to the negative output terminal of the first bidirectional DC / DC voltage conversion module, the other end of the first bypass switch is connected to the positive output terminal of the first bidirectional DC / DC voltage conversion module, one end of an Nth bypass switch is connected to the negative output terminal of the Nth bidirectional DC / DC voltage conversion module, and the other end of the Nth bypass switch is connected to the positive output terminal of the Nth bidirectional DC / DC voltage conversion module.

[0012] The bidirectional DC / DC voltage conversion module integrates the functions of the battery management unit (BMU), which calculates the battery pack's state of charge, estimates its health state, and manages the safety of the battery pack, and adjusts its output voltage according to commands from the BDCM cooperative controller unit. The bypass switch functions as a bidirectional DC / DC voltage conversion module.

[0013] The BDCM cooperative controller unit manages the battery cluster and has the functions of managing the charge and discharge of the battery cluster, calculating the state of charge of the battery cluster, managing the safety of the battery cluster, controlling the bypass switch OFF / ON, and controlling the circuit switch OFF / ON, as well as communicating with the outside and exchanging information. The battery pack consists of two or more lithium-ion battery cells connected in series.

[0014] The BDCM coordination controller unit is connected to the bidirectional DC / DC voltage conversion module, the bypass switch, and the circuit switch via a communication bus, and the battery management unit BMU of the bidirectional DC / DC voltage conversion module is communicatively connected to the basic management unit of the battery pack.

[0015] The method for controlling the battery cluster includes the steps of calculating a target battery cluster total voltage, starting a process control, and stopping the process control. The step of calculating the battery cluster target total voltage in the battery cluster control method is as follows:

[0016] Step 1: The nth BDCM cooperative controller unit reads the current voltage of each of the N batteries in the nth battery cluster unit, and adds up the voltages of the N battery packs to obtain the total voltage V_total_N of the nth battery cluster unit, where n is a natural number from 1 to P.

[0017] Step 2: Each BDCM cooperative controller unit broadcasts the total voltage of its corresponding battery cluster unit on its communication bus, and each BDCM cooperative controller unit compares the total voltage of its battery cluster unit with the total voltages of the other battery cluster units, and broadcasts the maximum value of the battery cluster unit total voltage in its own determined battery cluster unit on its communication bus.

[0018] Step 3: Each BDCM coordination controller unit receives the maximum battery cluster total voltage value broadcast on the communication bus, compares these results with its own determined maximum battery cluster total voltage value, and if the results are different, returns to step 1 and recalculates; if the results are the same, calculates the target battery cluster total voltage, and the nth battery cluster target total voltage V_target_cluster_n is V_target_cluster_n=V_max_cluster+V_con, where V_max_cluster is the maximum battery cluster total voltage value in all P battery cluster units, n is a natural number from 1 to P, V_con is a fixed limit value that satisfies V_con≦V_DC_sum−V_max_cluster, and V_DC_sum is the sum of the output voltage limit values of all bidirectional DC / DC voltage conversion modules in the battery cluster, which is the maximum battery cluster total voltage. The steps of initiating process control in the battery cluster control method are as follows:

[0019] Step 1: The nth BDCM coordination controller unit reads information from the battery pack and bidirectional DC / DC voltage conversion module of the nth battery cluster unit, including the charging state of the battery pack, the voltage of the battery pack, the temperature of the battery pack, and the fault information of the bidirectional DC / DC voltage conversion module. Step 2: The nth BDCM coordination controller unit determines the consistency of the states of all N battery packs in the nth battery cluster unit.

[0020] Step 3: If the battery pack status consistency of the nth battery cluster unit meets the requirement, the nth BDCM coordination controller unit broadcasts the output voltage V_out_n of all bidirectional DC / DC voltage conversion modules of the nth battery cluster via the communication bus, and V_out_n=V_target_cluster_n / m, where m is the number of all fault-free battery packs in the nth battery cluster. If the battery pack status consistency of the nth battery cluster unit does not meet the requirement, the discharge output voltage of the kth bidirectional DC / DC voltage conversion module of the nth battery cluster is calculated as follows:

number

number

number

[0021] Step 4: If the output voltages of the b bidirectional DC / DC voltage conversion modules in the nth battery cluster exceed the limit value (assuming the limit value is V_out_limit), the nth BDCM cooperative controller unit controls the output voltages of the bidirectional DC / DC voltage conversion modules to be V_out_limit, and the output voltages of all other bidirectional DC / DC voltage conversion modules in the nth battery cluster are V_out_n=(V_target_cluster_n-V_out_limit*b) / (mb), where m is the number of all fault-free battery packs in the nth battery cluster, and b is a natural number from 1 to m.

[0022] Step 5: The nth BDCM cooperative controller unit determines whether the total voltage of the nth battery cluster unit has reached the nth battery cluster target total voltage V_target_cluster_n. If not, return to step 1; if yes, proceed to the charging or discharging operation phase. In the above steps 1 to 5, n is a natural number from 1 to P, and P is the number of battery clusters. The step of stopping the process control in the battery cluster control method is as follows:

[0023] Step 1: The nth BDCM coordination controller unit detects a failure of the rth battery pack of the nth battery cluster unit, or a charge cut-off state of the rth battery pack, or a discharge cut-off state of the rth battery pack, or a failure of the rth bidirectional DC / DC voltage conversion module.

[0024] Step 2: The nth BDCM coordination controller units control the output voltages of the rth bidirectional DC / DC voltage conversion modules of the nth battery cluster unit to zero.

[0025] Step 3: The nth BDCM coordination controller units control the nth battery cluster units connected in parallel with the rth bidirectional DC / DC voltage conversion modules to close the bypass switches.

[0026] Step 4: The n-th BDCM coordination controller units control the outputs of the r-th bidirectional DC / DC voltage conversion modules of the n-th battery cluster unit to be turned off.

[0027] Step 5: Return to the step of calculating the battery cluster target total voltage, and execute the step of starting the process control, and if the total voltage of the battery cluster unit does not reach the battery cluster target total voltage or if the battery cluster unit enters an overcurrent protection state, stop the operation of the battery cluster unit. Compared with the prior art, the battery cluster topology for a lithium-ion battery energy storage system and the control method of the battery cluster of the present invention have the following advantages:

[0028] (1) It is advantageous for fully utilizing the performance of the battery packs. In each battery cluster of the present invention, the battery packs are connected in parallel to the input terminal of the bidirectional DC / DC voltage conversion module, and then connected in series via the output terminal of the bidirectional DC / DC voltage conversion module. A bypass switch is connected in parallel to the output terminal of each bidirectional DC / DC voltage conversion module. This topology structure allows the battery cluster control method of the present disclosure to realize dynamic management and control of each battery pack, actively adjusting the charging and discharging of the battery packs according to their performance, thereby fully utilizing the performance of the battery packs. This is particularly advantageous for cascaded battery packs with low compatibility.

[0029] (2) It is advantageous for improving the safety of the lithium-ion battery energy storage system. Before each battery cluster unit in the present invention performs parallel charging and discharging, it first calculates the target total voltage of the battery cluster and then initiates process control. This allows the total voltage of each battery cluster to achieve a state with small deviation, significantly reducing bias and free-circulating current phenomena during parallel charging and discharging of the battery clusters and improving safety. Furthermore, if a battery pack or bidirectional DC / DC voltage conversion module of any battery cluster fails or reaches a protection condition during operation of the energy storage system, the bypass switch connected in parallel to the output end of the bidirectional DC / DC voltage conversion module can be closed to immediately stop the operation of the bidirectional DC / DC voltage conversion module and battery pack, which is very advantageous for improving safety. [Brief explanation of the drawings]

[0030] [Figure 1] 2 is a schematic diagram of the circuit connections of a battery cluster unit according to one embodiment of the present invention; [Figure 2]FIG. 2 is a diagram of a parallel topology of a battery cluster according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0032] One embodiment of the present invention provides a battery cluster topology and a battery cluster control method for a lithium-ion battery energy storage system. As shown in Figures 1 and 2, the battery cluster topology for the lithium-ion battery energy storage system includes P (P is a natural number greater than or equal to 2) parallel-connected battery cluster units 1, each of which includes N (N is a natural number greater than or equal to 2) battery packs 11, N bidirectional DC / DC voltage conversion modules 12, one BDCM coordination controller unit 13, N bypass switches 14, a circuit switch 15, and a connecting primary bus 16.

[0033] As shown in FIG. 1 , the output terminals of the bidirectional DC / DC voltage conversion modules 12 are connected in series, with the negative output terminal of the first bidirectional DC / DC voltage conversion module connected to the negative electrode of the primary bus, the positive output terminal of the first bidirectional DC / DC voltage conversion module connected to the negative electrode of the second bidirectional DC / DC voltage conversion module, the positive output terminal of the second bidirectional DC / DC voltage conversion module connected to the negative electrode of the third bidirectional DC / DC voltage conversion module, the positive output terminal of the (N−1)th bidirectional DC / DC voltage conversion module connected to the negative output terminal of the Nth bidirectional DC / DC voltage conversion module, and the negative output terminal of the Nth bidirectional DC / DC voltage conversion module connected to one terminal of a circuit switch, the other terminal of which is connected to the positive electrode of the primary bus.

[0034] The N battery packs are connected in parallel to the input terminals of the N bidirectional DC / DC voltage conversion modules, with the positive terminal of a first battery pack connected to the positive input terminal of the first bidirectional DC / DC voltage conversion module, the negative terminal of the first battery pack connected to the negative input terminal of the first bidirectional DC / DC voltage conversion module, the positive terminal of an Nth battery pack connected to the positive input terminal of the Nth bidirectional DC / DC voltage conversion module, and the negative terminal of the Nth battery pack connected to the negative input terminal of the Nth bidirectional DC / DC voltage conversion module.

[0035] The N bypass switches are connected in parallel to the output terminals of the N bidirectional DC / DC voltage conversion modules, one end of a first bypass switch is connected to the negative output terminal of the first bidirectional DC / DC voltage conversion module, the other end of the first bypass switch is connected to the positive output terminal of the first bidirectional DC / DC voltage conversion module, one end of an Nth bypass switch is connected to the negative output terminal of the Nth bidirectional DC / DC voltage conversion module, and the other end of the Nth bypass switch is connected to the positive output terminal of the Nth bidirectional DC / DC voltage conversion module.

[0036] The bidirectional DC / DC voltage conversion module integrates the functions of a battery management unit (BMU), which can perform battery pack state of charge calculation, health estimation, and battery pack safety management, and adjusts its output voltage according to the instructions of the BDCM coordination controller unit. The bypass switch functions to bypass the bidirectional DC / DC voltage conversion module.

[0037] The BDCM cooperative controller unit manages the battery cluster and has the functions of managing the charge and discharge of the battery cluster, calculating the state of charge of the battery cluster, managing the safety of the battery cluster, controlling the ON / OFF of the bypass switch, and controlling the ON / OFF of the circuit switch, as well as communicating with the outside and exchanging information.

[0038] In an embodiment of the present disclosure, the battery pack is configured by two or more lithium-ion battery cells connected in series, and the battery pack integrates a basic management unit for voltage sampling, temperature sampling, and equalization purposes.

[0039] The BDCM coordination controller unit is connected to the bidirectional DC / DC voltage conversion module, the bypass switch, and the circuit switch via a communication bus, and the battery management unit BMU of the bidirectional DC / DC voltage conversion module is connected via communication with the basic management unit of the battery pack.

[0040] The method for controlling the battery cluster includes the steps of calculating a target total voltage of the battery cluster, starting a process control, and stopping the process control. In the battery cluster control method, the step of calculating the target total voltage of the battery cluster is as follows:

[0041] Step 1: The nth BDCM adjustment controller unit reads the current voltage of each of the N battery packs in the nth battery cluster unit, and adds up the voltages of these N battery packs to obtain the total voltage V_total_n of the nth battery pack unit, where n is a natural number from 1 to P.

[0042] Step 2: Each BDCM cooperative controller unit broadcasts the total voltage of its corresponding battery cluster unit on its communication bus, and each BDCM cooperative controller unit compares the total voltage of its battery cluster unit with the total voltages of the other battery cluster units and broadcasts the maximum value of the battery cluster total voltage of its own determined battery cluster unit on its communication bus.

[0043] Step 3: Each BDCM coordination controller unit receives the maximum value of the battery cluster total voltage broadcast on the communication bus, compares these results with the maximum value of the battery cluster total voltage determined by itself, and if the results are different, returns to step 1 and recalculates. If the results are the same, calculates the target battery cluster total voltage, and the target battery cluster total voltage of the nth battery cluster V_target_cluster_n is V_target_cluster_n = V_max_cluster + fixed limit value, where V_max_cluster is the maximum value of the battery cluster total voltages of all P battery cluster units, the fixed limit value is the allowable variation in the total voltages of the P battery clusters, and n is a natural number from 1 to P. The steps of initiating process control in the battery cluster control method are as follows:

[0044] Step 1: The nth BDCM coordination controller unit reads information from the battery pack and bidirectional DC / DC voltage conversion module of the nth battery cluster unit, including the charging state of the battery pack, the voltage of the battery pack, the temperature of the battery pack, and the fault information of the bidirectional DC / DC voltage conversion module. Step 2: The nth BDCM coordination controller unit determines the consistency of the states of all N battery packs in the nth battery cluster unit.

[0045] Step 3: If the consistency of the battery pack status of the nth battery cluster unit meets the requirement, the nth BDCM coordination controller unit broadcasts the output voltage V_out_n of all bidirectional DC / DC voltage conversion modules of the nth battery cluster on the communication bus, and V_out_n=V_target_cluster_n / number of all fault-free battery packs of the nth battery cluster. If the consistency of the battery pack status of the nth battery cluster unit does not meet the requirement, the discharge output voltage of the kth bidirectional DC / DC voltage conversion module of the nth battery cluster is calculated by the following formula 4:

number

number

number

[0046] Step 4: If the output voltage of a bidirectional DC / DC voltage conversion module in the nth battery cluster exceeds the limit value (assuming the limit value is V_out_limit), the nth BDCM cooperative controller unit controls the output voltage of the bidirectional DC / DC voltage conversion module to be V_out_limit, and the output voltages of all other bidirectional DC / DC voltage conversion modules in the nth battery cluster are V_out_n=(V_target_cluster_n-V_out_limit) / (the number of all non-faulty battery packs in the nth battery cluster-1).

[0047] Step 5: The nth BDCM cooperative controller unit determines whether the total voltage of the nth battery cluster unit has reached the nth battery cluster target total voltage V_target_cluster_n. If not, the process returns to step 1. If yes, the process moves to the charging or discharging operation stage. In the above steps 1 to 5, n is a natural number from 1 to P, and P is the number of battery clusters. The step of stopping the process control in the battery cluster control method is as follows:

[0048] Step 1: The nth BDCM coordination controller unit detects a failure of the rth battery pack of the nth battery cluster unit, or a charge cut-off state of the rth battery pack, or a discharge cut-off state of the rth battery pack, or a failure of the rth bidirectional DC / DC voltage conversion module.

[0049] Step 2: The nth BDCM coordination controller units control the output voltages of the rth bidirectional DC / DC voltage conversion modules of the nth battery cluster unit to zero.

[0050] Step 3: The nth BDCM coordination controller units control the nth battery cluster units connected in parallel with the rth bidirectional DC / DC voltage conversion modules to close the bypass switches.

[0051] Step 4: The n-th BDCM coordination controller units control the outputs of the r-th bidirectional DC / DC voltage conversion modules of the n-th battery cluster unit to be turned off.

[0052] Step 5: Return to the step of calculating the target total voltage of the battery cluster, and execute the step of starting the process control, and if the total voltage of the battery cluster unit does not reach the target total voltage of the battery cluster, or if the battery cluster unit enters an overcurrent protection state, stop the operation of the battery cluster unit.

[0053] The present invention is advantageous for fully utilizing the performance of battery packs. In each battery cluster of the present invention, the battery packs are connected in parallel to the input terminal of the bidirectional DC / DC voltage conversion module, and then connected in series via the output terminal of the bidirectional DC / DC voltage conversion module. A bypass switch is connected in parallel to the output terminal of each bidirectional DC / DC voltage conversion module. This topology structure allows the battery cluster control method of the present disclosure to realize dynamic management and control of each battery pack, actively adjusting the charging and discharging of the battery pack according to the performance of the battery pack, thereby fully utilizing the performance of the battery pack. This is particularly advantageous for battery packs using low-cost batteries.

[0054] In each battery cluster of the present invention, the battery packs are connected in parallel to the input terminal of the bidirectional DC / DC voltage conversion module, and then connected in series via the output terminal of the bidirectional DC / DC voltage conversion module. A bypass switch is connected in parallel to the output terminal of each bidirectional DC / DC voltage conversion module. This topology allows the battery cluster control method of the present disclosure to achieve dynamic management and control of each battery pack, actively adjusting the charging and discharging of the battery pack according to the battery pack's performance, thereby fully utilizing the battery pack's performance. This is particularly advantageous for consistent cascaded battery packs.

[0055] Before each battery cluster unit is charged and discharged in parallel, it first calculates the target total voltage of the battery cluster and then starts process control, resulting in a state where the total voltages of the battery clusters have little variation. This significantly reduces bias and free-circulating current during the parallel charging and discharging of the battery clusters, improving safety. Furthermore, if a battery pack or bidirectional DC / DC voltage conversion module in any battery cluster fails or reaches a protection condition during operation of the energy storage system, the bypass switch connected in parallel to the output end of the bidirectional DC / DC voltage conversion module can be closed to immediately stop the operation of the bidirectional DC / DC voltage conversion module and the battery pack, which is very advantageous in improving safety.

Claims

1. 1. A battery cluster topology for a lithium ion battery energy storage system, comprising: The battery cluster topology for the lithium-ion battery energy storage system includes P parallel-connected battery cluster units (P is a natural number equal to or greater than 2), each of the battery cluster units including N battery packs (N is a natural number equal to or greater than 2), N bidirectional DC / DC voltage conversion modules, N bypass switches, a BDCM coordination controller unit, a circuit switch, and a connecting primary bus; the output terminals of the N bidirectional DC / DC voltage conversion modules are sequentially connected in series, the negative output terminal of the first bidirectional DC / DC voltage conversion module is connected to the negative output terminal of the second bidirectional DC / DC voltage conversion module, the positive output terminal of the second bidirectional DC / DC voltage conversion module is connected to the negative output terminal of the third bidirectional DC / DC voltage conversion module, the positive output terminal of the (N-1)th bidirectional DC / DC voltage conversion module is connected to the negative output terminal of the Nth bidirectional DC / DC voltage conversion module, and the negative output terminal of the Nth bidirectional DC / DC voltage conversion module is connected to one end of a circuit switch, the other end of the circuit switch is connected to the positive terminal of the primary bus; The N battery packs are connected in parallel to the input terminals of the N bidirectional DC / DC voltage conversion modules, the positive terminal of a first battery pack is connected to the positive input terminal of the first bidirectional DC / DC voltage conversion module, the negative terminal of the first battery pack is connected to the negative input terminal of the first bidirectional DC / DC voltage conversion module, the positive terminal of an Nth battery pack is connected to the positive input terminal of the Nth bidirectional DC / DC voltage conversion module, and the negative terminal of the Nth battery pack is connected to the negative input terminal of the Nth bidirectional DC / DC voltage conversion module; the N bypass switches are connected in parallel to the output terminals of the N bidirectional DC / DC voltage conversion modules, one end of a first bypass switch is connected to the negative output terminal of the first bidirectional DC / DC voltage conversion module, the other end of the first bypass switch is connected to the positive output terminal of the first bidirectional DC / DC voltage conversion module, one end of an Nth bypass switch is connected to the negative output terminal of the Nth bidirectional DC / DC voltage conversion module, and the other end of the Nth bypass switch is connected to the positive output terminal of the Nth bidirectional DC / DC voltage conversion module; The bidirectional DC / DC voltage conversion module integrates the functions of a battery management unit (BMU) that performs battery pack state of charge calculation, health state estimation, and battery pack safety management, and adjusts its output voltage according to the command of the BDCM cooperative controller unit; The BDCM coordination controller unit manages the battery cluster, and has functions of managing the charge and discharge of the battery cluster, calculating the state of charge of the battery cluster, managing the safety of the battery cluster, controlling the bypass switch OFF / ON, and controlling the circuit switch OFF / ON, and also has a function of communicating with the outside and exchanging information; The method for controlling a battery cluster includes the steps of calculating a battery cluster target total voltage, starting a process control, and stopping the process control; The core algorithm of the step of calculating the target total voltage of the battery cluster is to determine the target total voltage of the nth battery cluster, V_target_cluster_n, where V_target_cluster_n=V_max_cluster+V_con, where V_max_cluster is the maximum value of the total voltage of the battery cluster in all P battery cluster units, n is a natural number from 1 to P, V_con is a fixed limit value, and the value of V_con satisfies V_con≦V_DC_sum−V_max_cluster, where V_DC_sum is the sum of the output voltage limit values of all bidirectional DC / DC voltage conversion modules in the battery cluster, which is the maximum value of the total voltage of the battery cluster; The core algorithm for initiating the process control is to determine the output voltage of the bidirectional DC / DC voltage conversion modules. When the consistency of the states of all the fault-free battery packs in the nth battery cluster is good, the output voltage of all the bidirectional DC / DC voltage conversion modules in the nth battery cluster is V_out_n=V_target_cluster_n / m, where m is the number of all the fault-free battery packs in the nth battery cluster. When the consistency of the states of all the fault-free battery packs in the nth battery cluster is poor, the discharge output voltage of the kth bidirectional DC / DC voltage conversion module in the nth battery cluster is expressed by the following equation 1: [Equation 1] The charging output voltage of the kth bidirectional DC / DC voltage conversion module of the nth battery cluster is expressed by the following formula 2: [Equation 2] where SOCnk is the charge ratio of the k-th battery pack in the n-th battery cluster, m is the number of all non-faulty batteries in the n-th battery cluster, and is expressed by the following formula 3: [Equation 3] is a battery cluster topology for a lithium-ion battery energy storage system, characterized in that: represents the sum of all m non-faulty battery charging ratios of the nth battery cluster; Adapting the battery pack topology used in lithium-ion battery storage systems to low cascade utilization battery packs; The BDCM coordination controller unit is connected to the bidirectional DC / DC voltage conversion module, the bypass switch, and the circuit switch via a communication bus, and the battery management unit BMU of the bidirectional DC / DC voltage conversion module is connected to and communicates with the basic management unit of the battery pack; The step of calculating a target total voltage of the battery cluster in the battery cluster control method includes: Step 1: The nth BDCM coordination controller unit reads the current voltage of each of the N batteries in the nth battery cluster unit, and adds up the voltages of the N battery packs to obtain a total voltage V_total_N of the nth battery cluster unit, where n is a natural number from 1 to P; Step 2: each BDCM coordination controller unit broadcasts the total voltage of its corresponding battery cluster unit on its communication bus, and each BDCM coordination controller unit compares the total voltage of its battery cluster unit with the total voltages of other battery cluster units, and broadcasts the maximum value of the battery cluster unit total voltages in its own battery cluster unit determined by itself on its communication bus; Each BDCM coordination controller unit receives the maximum battery cluster total voltage broadcasted on the communication bus, compares the results with its own determined maximum battery cluster total voltage, and if the results are different, returns to step 1 and performs recalculation. If the results are the same, calculates the target battery cluster total voltage. The target battery cluster total voltage V_target_cluster_n of the nth battery cluster is V_target_cluster_n=V_max_cluster+V_con, where V_max_cluster_n is the maximum battery cluster total voltage V_target_cluster_n. Step 3: a battery cluster topology for a lithium-ion battery energy storage system, wherein V_con is a fixed limit value and satisfies V_con≦V_DC_sum−V_max_cluster, where V_DC_sum is the sum of the output voltage limit values of all bidirectional DC / DC voltage conversion modules of the battery cluster, which is the maximum value of the battery cluster total voltage.

2. 2. The battery cluster topology for a lithium-ion battery energy storage system as claimed in claim 1, wherein the bypass switch functions to bypass a bidirectional DC / DC voltage conversion module, and the battery pack consists of two or more lithium-ion battery cells connected in series.

3. The step of initiating process control in the battery cluster control method includes: Step 1: the nth BDCM coordination controller unit reads information of the battery packs and the bidirectional DC / DC voltage conversion modules of the nth battery cluster unit, including the charging state of the battery packs, the voltage of the battery packs, the temperature of the battery packs, and the fault information of the bidirectional DC / DC voltage conversion modules; Step 2: the n-th BDCM coordination controller unit determines the consistency of the states of all N battery packs of the n-th battery cluster unit; If the battery pack status consistency of the nth battery cluster unit meets the requirement, the nth BDCM coordination controller unit will broadcast the output voltage V_out_n of all bidirectional DC / DC voltage conversion modules of the nth battery cluster via the communication bus, and V_out_n=V_target_cluster_n / m, where m is the number of all fault-free battery packs in the nth battery cluster. If the battery pack status consistency of the nth battery cluster unit does not meet the requirement, the discharge output voltage of the kth bidirectional DC / DC voltage conversion module of the nth battery cluster will be expressed as follows: [Equation 4] The charging output voltage of the k-th bidirectional DC / DC voltage conversion module of the n-th battery cluster is expressed by the following Equation 5: [Equation 5] where SOCnk is the charge ratio of the k-th battery pack in the n-th battery cluster, m is the number of all non-faulty batteries in the n-th battery cluster, and is expressed by the following formula 6: [Equation 6] represents the sum of the charging ratios of each of the m non-faulty batteries in the nth battery cluster, and obviously, m≦P; Step 4: if the output voltage of the b bidirectional DC / DC voltage conversion modules of the nth battery cluster exceeds a limit value (assuming the limit value is V_out_limit), the nth BDCM coordination controller unit controls the output voltage of the bidirectional DC / DC voltage conversion module to be V_out_limit, and the output voltages of all other bidirectional DC / DC voltage conversion modules of the nth battery cluster are V_out_n=(V_target_cluster_n-V_out_limit*b) / (m-b), where m is the number of all non-faulty battery packs of the nth battery cluster, and b is a natural number from 1 to m; Step 5 includes the n-th BDCM coordination controller unit determining whether the total voltage of the n-th battery cluster unit reaches the n-th battery cluster target total voltage V_target_cluster_n, and if not, returning to step 1, and if it has reached, transitioning to a charging or discharging operation stage; The battery cluster topology for a lithium-ion battery energy storage system as claimed in claim 1, characterized in that in the above steps 1 to 5, n is a natural number from 1 to P, and P is the number of battery clusters.

4. The step of stopping the process control in the battery cluster control method includes: Step 1: the nth BDCM coordination controller unit detects a failure of the rth battery pack of the nth battery cluster unit, or a charge cut-off state of the rth battery pack, or a discharge cut-off state of the rth battery pack, or a failure of the rth bidirectional DC / DC voltage conversion module; Step 2: the rth bidirectional DC / DC voltage conversion modules of the nth battery cluster unit adjust their output voltages to zero according to the command of the BDCM coordination controller unit; Step 3: the n-th BDCM coordination controller unit controls the n-th battery cluster unit connected in parallel with the r-th bidirectional DC / DC voltage conversion module to close the bypass switch; Step 4: the n-th BDCM coordination controller unit controls the output of the r-th bidirectional DC / DC voltage conversion module of the n-th battery cluster unit to be turned off; 2. The battery cluster topology for a lithium ion battery energy storage system as claimed in claim 1, further comprising: a step of returning to the step of calculating the battery cluster target total voltage, executing a step of starting process control, and stopping operation of the battery cluster unit if the total voltage of the battery cluster unit has not reached the battery cluster target total voltage or if the battery cluster unit enters an overcurrent protection state.

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