A current equalization control method and device for a battery energy storage system

Abstract

The present application relates to the technical field of battery management, and particularly relates to a current equalization control method and device for a battery energy storage system, which comprises the following steps: generating a target adjustment resistance value of an adjustable impedance unit based on operation data of each battery cluster in a charging and discharging process, so as to determine an optimal on-off combination scheme of each resistance branch in the adjustable impedance unit; performing steady-state current equalization on the battery cluster based on the optimal on-off combination scheme, and triggering a transient circulating current protection mechanism to establish a high-resistance parallel path composed of pre-charging resistors between different battery clusters when it is detected that the battery energy storage system reaches a charging and discharging cutoff condition; gradually equalizing voltage deviations between all battery clusters through the high-resistance parallel path, and performing a shutdown operation of the battery energy storage system after all voltage deviations are less than a preset safety threshold. The present application equalizes inter-cluster current through the adjustable impedance unit during steady-state operation, and realizes transient circulating current suppression by establishing a high-resistance parallel path at the moment of cutoff, thereby improving the safety of the system.

Description

Technical Field

[0001] This invention relates to the field of battery management technology, and in particular to a current balancing control method and apparatus for a battery energy storage system. Background Technology

[0002] In large-scale energy storage systems, to improve capacity and voltage levels, traditional methods typically involve connecting multiple battery clusters in parallel to the DC bus. Ideally, the voltage, internal resistance, and capacity of each battery cluster should be identical to achieve even current distribution. However, in actual production and use, cells from the same batch may exhibit capacity differences (e.g., mixing cells of different capacity levels within the same batch) and internal resistance differences. Furthermore, as usage time increases, the aging of each cell varies, leading to inconsistent DC impedances among the parallel battery clusters. This inconsistency can cause uneven current distribution among the battery clusters during charging and discharging, as well as inter-cluster circulating current problems at the moment of charge / discharge cutoff. (1) Uneven current during charging and discharging: During charging and discharging, the battery cluster with smaller internal resistance will bear a larger current. This makes the actual charge and discharge rate of the cell with the smallest capacity in the cluster higher than the rated operating rate of the system. On the one hand, this will cause the small capacity cell to be fully charged or discharged in advance, forcing the entire system to stop charging and discharging, while the capacity of the cells in other clusters has not been fully released, resulting in a reduction in the actual usable capacity of the system. On the other hand, the cell is in an overcurrent state for a long time, which will accelerate aging and decay, and even cause a sudden drop in capacity, significantly shortening the service life of the entire energy storage system.

[0003] (2) Inter-cluster circulating current at the moment of charge / discharge cutoff: At the moment of system charge / discharge start-up or cutoff, due to the polarization effect of the cells, internal resistance differences and inconsistent state of charge (SOC), the voltage of each battery cluster will generate a short-term large voltage difference. This transient voltage difference will directly cause the high-voltage cluster to discharge to the low-voltage cluster, forming a violent inter-cluster circulating current. The initial circulating current of a new system may be several amperes to tens of amperes, but as the system ages and the consistency deteriorates, the circulating current is very likely to exceed the rated current designed for each battery cluster, causing irreversible damage to the cells, relays and connectors in the circuit.

[0004] In summary, existing technologies are unable to effectively solve the current imbalance problem during steady-state operation and transient switching, which seriously affects the capacity utilization, cycle life and operational safety of multi-cluster parallel battery systems. Summary of the Invention

[0005] To address the above technical problems, this invention provides a current balancing control method and apparatus for a battery energy storage system.

[0006] In a first aspect, the present invention provides a current balancing control method for a battery energy storage system, the battery energy storage system comprising at least two parallel battery clusters, wherein an adjustable impedance unit is connected in series between the negative terminal of each battery cluster and the negative terminal of a common DC bus, the adjustable impedance unit being composed of multiple resistor branches with different resistance values ​​connected in parallel, the method comprising the following steps: Real-time data collection of each battery cluster during charging and discharging, and determination of the target total resistance required for each battery cluster to become consistent based on the data. The target adjustment resistance value of the adjustable impedance unit is generated based on the target total resistance value of each battery cluster, and the optimal on / off combination scheme of each resistor branch in the adjustable impedance unit is determined based on the target adjustment resistance value. Based on the optimal on / off combination scheme, the steady-state current balance of the battery cluster is achieved by regulating the on / off state of the resistor branch. When the battery energy storage system is detected to have reached the charging / discharging cutoff condition, a transient circulating current protection mechanism is triggered to establish a high-resistance parallel path composed of pre-charge resistors between different battery clusters. The voltage deviation between all battery clusters is gradually balanced through the high-resistance parallel path, and the battery energy storage system is shut down after all the voltage deviations are less than a preset safety threshold.

[0007] In a further embodiment, the operating data includes at least the open-circuit voltage of the battery cluster, the internal resistance of the battery cluster, and the common DC bus voltage. The step of determining the target total resistance value required for each battery cluster to converge based on the operating data includes: The target average current is obtained based on the total current of the battery energy storage system measured on the common DC bus and the total number of parallel battery clusters. Calculate the voltage difference between the open-circuit voltage of the battery cluster and the voltage of the common DC bus, and based on the voltage difference, obtain the target total resistance value required for the current of each battery cluster to approach the target average current.

[0008] In a further implementation, the target adjusted resistance is the difference between the target total resistance and the internal resistance of the battery cluster.

[0009] In a further embodiment, the resistor branch includes at least a switching device and a resistor connected in series, and the step of determining the optimal on / off combination scheme of each resistor branch in the adjustable impedance unit based on the target resistance value includes: Based on the resistance value of each resistor branch, calculate the equivalent total resistance value under the on / off combination of all resistor branches in the adjustable impedance unit that are in the conducting state. Based on the resistance deviation between the equivalent total resistance of each resistor branch switching combination and the target adjustment resistance, candidate switching combination schemes are selected. The optimal on / off combination scheme is selected from the candidate on / off combination schemes according to the preset priority rules.

[0010] In a further embodiment, the adjustable impedance unit further includes at least a resistance-free through branch; When the target adjustment resistance is zero, the optimal on / off combination scheme is to only conduct the straight-through branch.

[0011] In a further embodiment, each battery cluster includes multiple individual cells, and a main positive relay and a pre-charge circuit are connected in parallel between the positive terminal of each battery cluster and the positive terminal of the common DC bus. The pre-charge circuit is composed of a pre-charge relay and a pre-charge resistor connected in series. The step of triggering the transient circulating current protection mechanism to establish a high-resistance parallel path composed of the pre-charge resistor between different battery clusters when the battery energy storage system is detected to have reached the charge / discharge cutoff condition includes: During the charging and discharging process of the battery energy storage system, the voltage value of each individual cell in each battery cluster is monitored in real time. When the voltage value of any individual cell reaches the preset cutoff warning threshold, it is determined that the battery energy storage system is about to reach the charging and discharging cutoff condition, and the transient circulating current protection mechanism is triggered to generate a pre-charge relay closing drive signal. In response to the precharge relay closing drive signal, the precharge relays of all battery clusters are closed, and the main positive relays of each battery cluster are controlled to be in the closed state; After confirming that all pre-charge relays are closed, the main positive relays of all battery clusters are opened, so that the connection path between each battery cluster and the common DC bus is switched from low-resistance parallel connection of the main circuit to high-resistance parallel connection of the pre-charge circuit, forming a high-resistance parallel path; wherein, the low-resistance parallel connection of the main circuit is the low-impedance parallel connection of each battery cluster through the main positive relays; the high-resistance parallel connection of the pre-charge circuit is that the positive terminal of each battery cluster is connected to the positive terminal of the common DC bus through the pre-charge relays and the pre-charge resistors in series.

[0012] In a further embodiment, the resistance value of the pre-charge resistor is greater than the on-resistance when the main positive relay is closed.

[0013] In a further embodiment, the step of performing a shutdown operation on the battery energy storage system after all the voltage deviations are less than a preset safety threshold includes: Once all the voltage deviations are less than a preset safety threshold, the pre-charge relays of each battery cluster are disconnected, thus cutting off the electrical connection between each battery cluster and the common DC bus.

[0014] Secondly, the present invention provides a current balancing control device for a battery energy storage system, the battery energy storage system comprising at least two parallel battery clusters, wherein an adjustable impedance unit is connected in series between the negative terminal of each battery cluster and the negative terminal of a common DC bus, the adjustable impedance unit being composed of multiple resistor branches of different resistance values ​​connected in parallel, the device comprising: The data acquisition module is used to collect the operating data of each battery cluster in real time during the charging and discharging process, and based on the operating data, determine the target total resistance value required for each battery cluster to become consistent. The resistor combination module is used to generate the target adjustment resistance value of the adjustable impedance unit based on the target total resistance value of each battery cluster, and to determine the optimal on / off combination scheme of each resistor branch in the adjustable impedance unit based on the target adjustment resistance value. The equalization control module is used to perform steady-state current equalization of the battery clusters by adjusting the on / off state of the resistor branch based on the optimal on / off combination scheme, and to trigger a transient circulating current protection mechanism to establish a high-resistance parallel path composed of pre-charge resistors between different battery clusters when the battery energy storage system is detected to have reached the charge / discharge cutoff condition. The safety control module is used to gradually equalize the voltage deviation between all battery clusters through the high-resistance parallel path, and to perform a shutdown operation of the battery energy storage system after all the voltage deviations are less than a preset safety threshold.

[0015] In a further embodiment, the adjustable impedance unit further includes at least a resistance-free through branch; When the target adjustment resistance is zero, the optimal on / off combination scheme is to only conduct the straight-through branch.

[0016] This invention provides a current balancing control method and apparatus for a battery energy storage system. The battery energy storage system includes at least two parallel battery clusters. An adjustable impedance unit is connected in series between the negative terminal of each battery cluster and the negative terminal of a common DC bus. The adjustable impedance unit is composed of multiple parallel resistor branches with different resistance values. The method includes: real-time acquisition of operating data of each battery cluster during charging and discharging; determining the target total resistance value required for each battery cluster to become consistent based on the operating data; generating a target adjustment resistance value for the adjustable impedance unit based on the target total resistance value of each battery cluster; determining the optimal on / off combination scheme of each resistor branch in the adjustable impedance unit based on the target adjustment resistance value; performing steady-state current balancing of the battery clusters by adjusting the on / off state of the resistor branches based on the optimal on / off combination scheme; triggering a transient circulating current protection mechanism to establish a high-resistance parallel path composed of pre-charge resistors between different battery clusters when the battery energy storage system is detected to have reached the charging / discharging cutoff condition; gradually balancing the voltage deviation between all battery clusters through the high-resistance parallel path; and performing a shutdown operation of the battery energy storage system after all voltage deviations are less than a preset safety threshold. Compared with existing technologies, this method dynamically adjusts the adjustable impedance units connected in series in each battery cluster during steady-state operation to achieve balanced current distribution between clusters. At the moment of cutoff, a high-resistance parallel topology is established using a pre-charge circuit to avoid severe circulating current damage to devices caused by large voltage differences between clusters at the moment of charge and discharge cutoff. This achieves balanced current distribution between clusters and suppression of circulating current under all operating conditions, thereby improving the overall safety and reliability of the battery energy storage system. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the current balancing control method for a battery energy storage system provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the battery energy storage system structure provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the adjustable impedance unit topology provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the pre-charge circuit structure provided in an embodiment of the present invention; Figure 5 This is a block diagram of the current balancing control device for a battery energy storage system provided in an embodiment of the present invention.

[0018] Explanation of reference numerals in the attached diagram: 101, Data acquisition module; 102, Resistor combination module; 103, Equalization control module; 104, Safety control module. Detailed Implementation

[0019] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The embodiments are given for illustrative purposes only and should not be construed as limiting the present invention. The accompanying drawings are for reference and illustration only and do not constitute a limitation on the scope of patent protection of the present invention, because many changes can be made to the present invention without departing from the spirit and scope of the present invention.

[0020] Figure 1 This is a schematic flowchart of a current balancing control method for a battery energy storage system provided in an embodiment of the present invention. The present invention provides a current balancing control method for a battery energy storage system, which includes at least two parallel battery clusters. An adjustable impedance unit is connected in series between the negative terminal of each battery cluster and the negative terminal of a common DC bus. The adjustable impedance unit is composed of multiple resistor branches with different resistance values ​​connected in parallel. Figure 2 This is a schematic diagram of a battery energy storage system provided in an embodiment of the present invention. In this embodiment, the battery energy storage system includes a common DC bus, a combiner cabinet, N parallel battery clusters, N high-voltage boxes, and a battery management system main control unit. Each battery cluster includes multiple battery packs connected in series, such as... Figure 2 The first battery pack, PACK1, to the sixth battery pack, PACK6, are shown in diagrams. The positive and negative terminals of each battery pack are connected in series. The positive terminal of PACK1 is connected to BAT+, and the negative terminal of PACK1 is connected to the positive terminal of PACK2, and so on. The negative terminal of PACK6 is connected to BAT-. The specific number of battery packs can vary depending on the actual configuration. Each battery pack consists of several individual battery cells connected in series and parallel. The common DC bus consists of the positive terminal L+ and the negative terminal L- of the DC bus. The common DC bus serves as the connection point for all battery cells. The common power combiner point of the battery clusters collects the electrical energy of each battery cluster and supplies it to the external energy storage converter, or distributes the electrical energy of the energy storage converter to each battery cluster; the combiner cabinet is used to centrally connect the power cables of each battery cluster and connect to the external energy storage converter; the N parallel battery clusters include battery cluster 1, battery cluster 2, ..., battery cluster N, where N≥2; the main control unit of the battery management system is used to collect voltage and other signals of each battery cluster and control the relays and adjustable resistor units of all clusters to achieve coordinated and balanced control.

[0021] In this embodiment, each high-voltage box has the same internal structure. The output terminal (bus side) of the main positive relay KM1 in all high-voltage boxes is connected to the same DC bus positive terminal L+. The output terminal of the precharge circuit in all high-voltage boxes is also connected to the same DC bus positive terminal L+. The output terminal OUT of the adjustable resistor unit in all high-voltage boxes is connected to the same DC bus negative terminal L-. Each battery cluster is connected to the common DC bus L+ and L- in parallel through the high-voltage box. This embodiment takes high-voltage box #1 as an example to illustrate the internal structure of the high-voltage box. The high-voltage box includes at least positive side circuit elements, negative side circuit elements, and auxiliary elements. The positive side circuit elements include the main positive relay KM1, the precharge circuit, and the fuse FU1. One end of the main positive relay KM1 is connected to the positive terminal of the battery pack PACK1 in the battery cluster through the positive terminal BAT+ of the battery cluster. The other end of the main positive relay KM1 is connected to the DC bus positive terminal L+ in the combiner cabinet. The precharge circuit consists of the precharge relay K and the precharge circuit. The precharge circuit is constructed by series connection of resistors R. The entire precharge circuit is connected in parallel across the two ends of the main positive relay KM1. That is, after the precharge relay and the precharge resistor are connected in series, one end of the precharge relay is connected to the positive terminal BAT+ of the battery cluster, and the other end is connected to the positive terminal L+ of the DC bus. The fuse FU1 is connected in series between the positive terminal BAT+ of the battery cluster and the main positive relay KM1, or between the main positive relay and the bus. In this embodiment, the main positive relay KM1 is closed during normal charging and discharging to form the main circuit (low-resistance path) of the positive terminal of the battery cluster, and is opened during shutdown or protection to cut off the main circuit. When the system starts, the precharge relay KM1 and the precharge resistor R close first to precharge the DC bus capacitor to prevent inrush current. During the transient suppression stage of this embodiment, the precharge relay is closed first and then the main positive relay is opened, so that each battery cluster forms a high-resistance parallel path through the precharge resistor to limit the circulating current between clusters. The main negative relay KM2 is closed during normal operation and works with the main positive relay to complete the on / off control of the main circuit.

[0022] The negative side circuit components include a main negative relay KM2, an adjustable resistor unit, and a fuse FU2. One end of the main negative relay KM2 is connected to the negative terminal of battery pack PACK6 within the battery cluster via the negative terminal BAT- of the battery cluster. The other end of the main negative relay KM2 is connected to the input terminal IN of the adjustable resistor unit. The input terminal IN of the adjustable resistor unit is connected to the other end of the main negative relay KM2, and the output terminal OUT of the adjustable resistor unit is connected to the negative terminal L- of the DC bus in the combiner cabinet. The adjustable resistor unit consists of multiple parallel resistor branches, each with a switching device and a precision resistor connected in series. The switching on and off is controlled by the main control unit of the battery management system to change the circuit. The equivalent resistance value of the adjustable resistor unit connected to the circuit is specified. The switching device can be a relay or a semiconductor switch, such as a metal-oxide-semiconductor field-effect transistor. In this embodiment, the adjustable resistor unit is connected in series between the negative terminal of the battery cluster and the negative terminal of the DC bus. The main control unit of the battery management system selects the on / off combination of the internal resistor branch to dynamically change the total resistance value of the main circuit of the battery cluster, thereby balancing the inter-cluster current during steady-state operation. The through branch can achieve zero-loss operation when no adjustment is required. The fuse FU2 is connected in series between the negative terminal BAT- of the battery cluster and the main negative relay KM2. It is used for negative overcurrent protection. When the current increases abnormally, it blows to cut off the fault circuit.

[0023] Auxiliary components include a disconnect switch QS, a circuit breaker QF1, a surge protector SPD1, a fuse Fub, and a control signal interface (CTRL control terminal). The disconnect switch QS is located on the input side of the high-voltage box and is used to manually disconnect the battery pack from the high-voltage box for easy maintenance. The circuit breaker QF1 is located inside the high-voltage box or on the combiner cabinet side and is used for short-circuit and overload protection. The surge protector SPD1 is connected between the positive and negative terminals of the DC bus or inside the high-voltage box and is used to suppress lightning surges and operational overvoltages. The fuse Fub is used for secondary protection at the battery pack or cluster level. The control signal interface is used to receive control signals from the main control unit of the battery management system to control the on / off state of the switches inside the adjustable resistor unit.

[0024] The current balancing control method for the battery energy storage system provided in this embodiment is applied to the aforementioned battery energy storage system consisting of multiple battery clusters connected in parallel to a DC bus. The current balancing control method includes a steady-state charging / discharging stage and a charging / discharging cutoff switching stage. During the steady-state charging / discharging stage, the system dynamically adjusts the total circuit resistance of each cluster through an adjustable impedance unit to suppress inter-cluster current differences caused by differences in cell internal resistance and aging differentiation. When the voltage of any single cell reaches a preset cutoff warning threshold, the system enters the charging / discharging cutoff switching stage. By changing the relay action sequence, the pre-charge circuit is used to suppress inter-cluster circulating current at the moment of shutdown. Figure 1 As shown, the current balancing control method for the battery energy storage system provided in this embodiment includes the following steps: S1. Real-time acquisition of operating data of each battery cluster during the charging and discharging process, and determination of the target total resistance value required for each battery cluster to become consistent based on the operating data.

[0025] In some implementations, the operating data includes at least the open-circuit voltage of the battery cluster, the internal resistance of the battery cluster, and the common DC bus voltage. The step of determining the target total resistance value required for the battery clusters to converge based on the operating data includes: The target average current is obtained based on the total current of the battery energy storage system measured on the common DC bus and the total number of parallel battery clusters. Calculate the voltage difference between the open-circuit voltage of the battery cluster and the voltage of the common DC bus, and based on the voltage difference, obtain the target total resistance value required for the current of each battery cluster to approach the target average current.

[0026] In a specific embodiment, after the battery energy storage system begins charging and discharging, the main control unit of the battery management system collects real-time operating data of each battery cluster during the charging and discharging process. This operating data includes at least the open-circuit voltage of the battery cluster, the voltage of the common DC bus, and the internal resistance of the battery cluster. The open-circuit voltage of the battery cluster can be obtained through the voltage acquisition module of the battery management system (BMS); the common DC bus voltage is measured by a voltage sensor installed between the positive and negative terminals of the DC bus; the internal resistance of the battery cluster can be estimated in real-time by the battery management system based on historical charging and discharging data, temperature, and aging status, or obtained by combining the factory nominal value with a correction factor. Then, this embodiment... Based on Kirchhoff's voltage law, the total current value of the battery energy storage system measured on the common DC bus is divided by the total number of parallel battery clusters in the battery energy storage system to obtain the current value that each battery cluster should bear under ideal equilibrium conditions. The current value that each battery cluster should bear under ideal equilibrium conditions is used as the target average current. The total current value of the battery energy storage system measured on the common DC bus can be measured by a current sensor installed on the DC bus. The total current value of the battery energy storage system refers to the total current flowing through the common DC bus. The measurement point can be located at the common junction of the positive or negative terminals of the DC bus (e.g., before the connection point between the bus copper bus and the energy storage converter). This current is the sum of the currents of all parallel battery clusters.

[0027] For the i-th battery cluster, this embodiment subtracts the current common DC bus voltage from the open-circuit voltage of the battery cluster to obtain the driving voltage difference of the battery cluster. If the driving voltage difference is positive, it means that the current flows from the battery to the bus during discharge. If the driving voltage difference is negative, it means that the current flows from the bus to the battery during charging. Then, this embodiment divides the driving voltage difference by the target average current to obtain the target total resistance value that the main circuit of the battery cluster should have from the positive terminal to the negative terminal. This target total resistance value makes the current flowing through the battery cluster under the driving voltage exactly equal to the target average current, thereby achieving the same current as other clusters. For a certain battery cluster, the target total resistance value of its main circuit refers to the sum of all series resistances from the positive terminal of the battery cluster through the internal resistance and the adjustable impedance unit to the negative terminal (i.e., the internal resistance plus the resistance value currently connected to the adjustable impedance unit). When the total resistance value of each cluster is adjusted to a certain specific value, the actual current of all clusters is equal to the target average current, ensuring that the current distribution of each cluster tends to be consistent, fundamentally avoiding the problem of reduced capacity utilization caused by uneven current.

[0028] S2. Generate the target adjustment resistance value of the adjustable impedance unit based on the target total resistance value of each battery cluster, and determine the optimal on / off combination scheme of each resistor branch in the adjustable impedance unit based on the target adjustment resistance value.

[0029] In some embodiments, the resistor branch includes at least a switching device and a resistor connected in series, and the step of determining the optimal on / off combination scheme of each resistor branch in the adjustable impedance unit based on the target resistance value includes: Based on the resistance value of each resistor branch, calculate the equivalent total resistance value under the on / off combination of all resistor branches in the adjustable impedance unit that are in the conducting state. Based on the resistance deviation between the equivalent total resistance of each resistor branch switching combination and the target adjustment resistance, candidate switching combination schemes are selected. The optimal on / off combination scheme is selected from the candidate on / off combination schemes according to the preset priority rules.

[0030] In this embodiment, the adjustable impedance unit is connected in series between the negative terminal of the battery cluster and the negative terminal of the common DC bus. Its resistance is dynamically adjustable. The total resistance of the main circuit of the battery cluster is equal to the internal resistance of the battery cluster plus the resistance currently connected to the adjustable impedance unit. Therefore, given the internal resistance and the target total resistance, this embodiment can deduce the target resistance value that the adjustable impedance unit should be adjusted to. This embodiment calculates the difference between the target total resistance and the internal resistance of a battery cluster to obtain the target adjustment resistance value that the adjustable impedance unit needs to achieve. At the same time, this embodiment subtracts the current connected resistance value of the adjustable impedance unit from the target adjustment resistance value to obtain the resistance adjustment change of the adjustable impedance unit. If the resistance adjustment change is positive, it indicates that the resistance needs to be increased; if the resistance adjustment change is negative, it indicates that the resistance needs to be increased. A negative value indicates that the resistance needs to be reduced; if the resistance adjustment change is zero, it indicates that the current resistance already meets the requirements and no adjustment is needed. In some embodiments, the adjustable impedance unit also includes a through branch with no resistance but a switching device. When the target adjustable resistance is zero, the optimal on / off combination scheme is to only conduct the through branch, keeping the battery cluster circuit in a low-resistance state. The through branch is used to conduct directly when no resistance adjustment is needed, achieving zero-loss conduction of the main circuit, thereby ensuring the efficiency of the system under normal operating conditions. In this embodiment, the resistance values ​​of each branch with resistance are configured according to binary weights, so that each branch can cover multiple equivalent resistance levels from zero ohms to the maximum resistance value through different on / off combinations. For example, Figure 3 As shown, the adjustable impedance unit includes four resistive branches and one direct-through branch. The resistance R1 of the first resistive branch is set to 1 ohm, the resistance R2 of the second resistive branch is set to 2 ohms, the resistance R3 of the third resistive branch is set to 4 ohms, the resistance R4 of the fourth resistive branch is set to 8 ohms, and the resistance R5 of the direct-through branch is set to 0 ohms. The direct-through branch consists only of switching devices and has no series resistors. In practical applications, the resistance values ​​and the number of branches can be adjusted according to the required adjustment range and accuracy of the system. With adjustments, the above four binary configurations (1, 2, 4, and 8 ohms) combined with direct-through branches can achieve all equivalent resistance values ​​from 0 ohms to 15 ohms in 1-ohm steps, resulting in 16 combinations. If higher precision or a wider range is required, branches can be added or weights can be changed (e.g., using 0.5, 1, 2, and 4 ohms). It should be noted that this embodiment uses binary weight configuration for the resistance values ​​of each resistor branch, allowing a small number of branches to combine multiple equivalent resistance values, achieving a balance between adjustment accuracy and cost.

[0031] For an adjustable impedance unit composed of multiple parallel resistor branches, when several resistor branches are closed, the equivalent total resistance of the adjustable impedance unit is equal to the parallel result of the resistance values ​​of all closed resistor branches. In this embodiment, the equivalent total resistance of the adjustable impedance unit under the combination of on and off states of all resistor branches in the conducting state is equal to the sum of the numerical value divided by the reciprocals of the resistance values ​​of each closed resistor branch. For example, for Figure 3 The adjustable impedance unit shown in this embodiment has an equivalent total resistance of 1 ohm if only the first resistor branch (1 ohm) is closed; an equivalent total resistance of 2 ohms if only the second resistor branch (2 ohms) is closed; and an equivalent total resistance of 2 ohms if both the first and second resistor branches (1 ohm and 2 ohms in parallel) are closed simultaneously. The calculation is as follows: 1 ÷ 1 = 1, 1 ÷ 2 =0.5, the sum of the resistance values ​​of the two closed resistor branches is 1.5, and taking the reciprocal of the sum of the resistance values ​​of the two closed resistor branches gives about 0.6667 ohms; if the first resistor branch, the second resistor branch, and the third resistor branch (1 ohm, 2 ohms, 4 ohms in parallel) are closed at the same time, the reciprocals of the resistance values ​​of each closed branch are 1, 0.5, and 0.25 respectively, and the sum of the reciprocals of the resistance values ​​of each closed branch is 1.75, so the equivalent total resistance is about 0.5714 ohms; if only the through branch 5 (0 ohms) is closed, then theoretically the equivalent total resistance is 0 ohms (actually the switching resistance, which can be ignored).

[0032] Next, this embodiment calculates the absolute value of the difference between the equivalent total resistance of each resistor branch switching combination and the target adjustment resistance value to obtain the resistance deviation. It then compares the resistance deviations of all resistor branch switching combinations and selects one or more resistor branch switching combinations with the smallest resistance deviation as candidate switching combination schemes. In practical applications, due to the discrete characteristics of parallel resistor networks, there may be situations where the deviations of the calculated equivalent total resistance value from the target value are equal for two or more different branch switching combinations. For example, when the target adjustment resistance value is 1.5 ohms, the deviations between conducting a 1-ohm resistor branch alone and conducting a 2-ohm resistor branch alone are... The difference is 0.5 ohms. Therefore, when there is only one resistance branch on / off combination with the smallest resistance deviation among the candidate on / off combinations, that resistance branch on / off combination is the optimal on / off combination. When there are two or more different resistance branch on / off combinations among the candidate on / off combinations, and their equivalent resistance values ​​have the same absolute error as the target resistance value, this embodiment needs to preset priority rules to determine the unique optimal on / off combination. Priority rules may include prioritizing the selection of smaller resistance branches, prioritizing the selection of combinations with fewer branches, and prioritizing the selection of direct-through branches. Specifically, prioritizing the selection of smaller resistance branches involves selecting each... The branch numbers of the combinations are arranged in ascending order. The smallest branch number of two combinations is compared, with the smaller number taking precedence. If the smallest branch numbers are the same, the next smallest number is compared, and so on. Branches with smaller resistance values ​​are prioritized to reduce the number of switching operations or lower module power consumption. For example, assuming the target adjustment resistance is 1.5 ohms, there are two on / off combination schemes with an equivalent resistance of 1.5 ohms: one is a single branch with a resistance of 1.5 ohms that only conducts (let's say branch six), and the other is branches one (with a resistance of 1 ohm) and two (with a resistance of 2 ohms) that simultaneously conduct. According to the priority rule, the branch with the smaller resistance value is selected first. Given the minimum branch number in the conducting state, the branch number of branch one is less than the branch number of branch six. Therefore, this embodiment prioritizes the combination scheme of simultaneously conducting branch one and branch two. If multiple combinations have the same deviation, the combination with the fewest conducting branches is preferred to reduce the operating frequency and energy loss of the switching devices. When the target adjustment resistance is 0 ohms or close to 0 ohms, the direct-through branch with no resistance is directly conducted, while all resistive branches are disconnected to achieve zero-loss operation. This embodiment can select one or a combination of the above rules to execute according to the actual needs of the system.

[0033] S3. Based on the optimal on / off combination scheme, the steady-state current balance of the battery cluster is achieved by adjusting the on / off state of the resistor branch, and when the battery energy storage system is detected to have reached the charging / discharging cutoff condition, a transient circulating current protection mechanism is triggered to establish a high-resistance parallel path composed of pre-charge resistors between different battery clusters.

[0034] In some implementations, a main positive relay and a pre-charge circuit are connected in parallel between the positive terminal of each battery cluster and the positive terminal of the common DC bus. The pre-charge circuit is composed of a pre-charge relay and a pre-charge resistor connected in series. The step of triggering the transient circulating current protection mechanism to establish a high-resistance parallel path composed of the pre-charge resistor between different battery clusters when the battery energy storage system is detected to have reached the charge / discharge cutoff condition includes: During the charging and discharging process of the battery energy storage system, the voltage value of each individual cell in each battery cluster is monitored in real time. When the voltage value of any individual cell reaches the preset cutoff warning threshold, it is determined that the battery energy storage system is about to reach the charging and discharging cutoff condition, and the transient circulating current protection mechanism is triggered to generate a pre-charge relay closing drive signal. In response to the precharge relay closing drive signal, the precharge relays of all battery clusters are closed, and the main positive relays of each battery cluster are controlled to be in the closed state; After confirming that all pre-charge relays are closed, the main positive relays of all battery clusters are opened, so that the connection path between each battery cluster and the common DC bus is switched from low-resistance parallel connection of the main circuit to high-resistance parallel connection of the pre-charge circuit, forming a high-resistance parallel path; wherein, the low-resistance parallel connection of the main circuit is the low-impedance parallel connection of each battery cluster through the main positive relays; the high-resistance parallel connection of the pre-charge circuit is that the positive terminal of each battery cluster is connected to the positive terminal of the common DC bus through the pre-charge relays and the pre-charge resistors in series.

[0035] In a specific embodiment, after selecting the optimal on / off combination scheme, the controller needs to perform a switching operation to switch the adjustable impedance unit from the current combination to the target combination. To avoid the battery cluster circuit being interrupted due to an open circuit in the adjustable impedance unit (all branches being disconnected) during the switching process, this embodiment preferentially adopts a "close first, then disconnect" switching strategy to avoid the generation of instantaneous low-resistance paths or additional circulating currents during the switching process. The "close first, then disconnect" switching strategy first disconnects all currently conducting resistor branch switches or, as needed, disconnects unnecessary branches first, and then closes the required branches in the target combination. This switching strategy of breaking first and then closing avoids additional parallel circulating currents or instantaneous low-resistance paths caused by simultaneous conduction of different resistance branches during switching. This embodiment uses switching from the current combination A to the target combination B as an example to illustrate the specific switching operation steps. First, it identifies the branches in the target combination B that need to be closed but are not yet closed in the current combination A (new branches), and identifies the branches in the current combination A that need to be opened but do not need to be closed in the target combination B (branches to be opened). Then, the controller closes the switching devices of all newly added branches, and after confirming that the newly added branches have been reliably closed, it then... Disconnect all switching devices in the branches to be disconnected. If the newly added branch overlaps with the branch to be disconnected (i.e., a branch has the same state in the current combination and the target combination), no operation is required. If the target combination contains a through branch (zero resistance) and the current combination does not contain a through branch, close the through branch first, then disconnect the other branches to ensure that the loop is always conducting. This closing-then-disconnecting sequence ensures that the adjustable impedance unit always has at least one conducting path during the switching process, thereby avoiding voltage spikes or current interruptions caused by momentary open circuits. It should be noted that when the target adjustable resistance is zero or less than that in the system... When the minimum non-zero parallel equivalent resistance is reached, this embodiment should select a straight-through branch (i.e., only close the branch without resistance). When the straight-through branch is conducting, the equivalent resistance of the adjustable impedance unit is approximately zero, the system has no additional power loss, and the main circuit achieves zero-loss conduction, operating in a high-efficiency state. Through the above operations, this embodiment dynamically adjusts the total resistance of the main circuit of each battery cluster to be consistent, thereby making the actual current flowing through each battery cluster consistent, effectively suppressing the problem of uneven current distribution during charging and discharging. This steady-state balancing process continues to run until the system detects the charging and discharging cutoff condition.

[0036] Next, based on the detected individual cell voltage warning information, this embodiment modifies the relay switching sequence and utilizes the pre-charge circuit to establish a high-resistance parallel path composed of pre-charge resistors between different battery clusters, thereby suppressing inter-cluster circulating current during shutdown. Specifically, Figure 4This is a schematic diagram of the pre-charge circuit structure provided in this embodiment of the invention. In this embodiment, a cutoff warning threshold is preset. This cutoff warning threshold can be flexibly set according to the characteristics of the battery cell and the system response time. However, it should be ensured that the cutoff warning threshold is higher than the discharge cutoff protection voltage or lower than the charging cutoff protection voltage, so that when the voltage of any single battery cell reaches the cutoff warning threshold, the transient suppression mechanism is triggered in advance, thereby gaining enough time to complete a series of operations such as closing the pre-charge relay, opening the main positive relay, and waiting for voltage equalization. This avoids being unable to handle the situation due to the rapid voltage change. In this embodiment, during the charging and discharging process of the battery energy storage system, the battery management system continuously monitors the voltage value of each single battery cell. During discharge, the voltage gradually decreases; during charging, the voltage gradually increases. This embodiment uses the discharge process as an example for explanation. The same applies to the charging cutoff, only the voltage direction is reversed. During the discharge process, this embodiment compares the voltage value of each single battery cell with the preset cutoff warning threshold in real time. If no warning is triggered, the system continues to perform steady-state current equalization (adjusted by the adjustable impedance unit). Steady-state adjustment and transient suppression do not affect each other and work under different operating conditions.

[0037] When the voltage of any single cell is detected to be less than or equal to the cutoff warning threshold (during discharge), the system is determined to be about to reach the charge / discharge cutoff condition, triggering the transient circulating current protection mechanism. At this time, the main control unit of the battery management system generates a pre-charge relay closing drive signal and controls the mechanical contacts of the pre-charge relay to close through the pre-charge relay closing drive signal, thus opening the pre-charge circuit. The pre-charge relay is reliably closed through the auxiliary contacts of the pre-charge relay or the voltage detection circuit, for example, by detecting that the voltage difference across the pre-charge relay changes from a high resistance state to a low resistance state, or through a switch feedback signal. Since the main positive relays of each battery cluster remain closed at this stage, the pre-charge relay and the main positive relay are simultaneously turned on, but the current path still mainly flows through the main positive relay (because its on-resistance is much lower than the pre-charge resistance), allowing the system to continue normal charging and discharging. The connection of the pre-charge circuit has not yet affected the main circuit current, thus completing the mechanical action preparation of the pre-charge circuit in advance without stopping the system, avoiding the impact caused by simultaneous action.

[0038] In this embodiment, after confirming that all pre-charge relays are closed, the main positive relay is disconnected. Specifically, a main positive relay disconnection drive signal is sent to the main positive relay of each battery cluster to separate the mechanical contacts of the main positive relay, cutting off the main circuit. The reliable disconnection of the main positive relay is confirmed through the auxiliary contacts of the main positive relay. After the main positive relay is disconnected, the path from the positive terminal of each battery cluster to the positive terminal of the DC bus switches from the main positive relay to the pre-charge circuit. Since a pre-charge resistor with a high resistance (e.g., 100 ohms) is connected in series in the pre-charge circuit, the parallel connection between the battery clusters changes from the original low-resistance parallel connection (the main circuit resistance includes the battery internal resistance and the adjustable impedance unit) to a high-resistance parallel connection (the main circuit has a pre-charge resistor of several hundred ohms connected in series). At this time, the system is not charging or discharging (because the energy storage converter...). (The device has reduced its power to 0 or is about to stop), but the clusters are still connected through the pre-charge resistor. The entire system switches from a low-resistance parallel topology in the main circuit to a high-resistance parallel topology in the pre-charge circuit. In this embodiment, taking the moment when the voltage of the first battery cluster is higher than that of the second battery cluster at the moment of discharge cutoff as an example, the current flows out from the positive terminal of the first battery cluster with higher voltage, flows through the pre-charge relay of the first battery cluster, then flows through the pre-charge resistor of the first battery cluster, and reaches the positive terminal of the common DC bus; then through the positive conductor of the common DC bus, it flows to the pre-charge resistor and pre-charge relay of the second battery cluster with lower voltage, and finally flows into the positive terminal of the second battery cluster. The current then flows from the negative terminal of the second battery cluster through the adjustable impedance unit and the negative terminal of the common DC bus back to the negative terminal of the first battery cluster, forming a closed loop. This circulating current is limited by the high resistance of the pre-charge resistor, and the amplitude is suppressed within a safe range.

[0039] It should be noted that, in this embodiment, the main circuit refers to the complete current path from the positive terminal of the battery cluster through the main positive relay (closed state), the series connection within the battery cluster, and the negative terminal of the battery cluster through the adjustable impedance unit, finally reaching the positive and negative terminals of the common DC bus. During normal charging and discharging, the main circuit bears all the charging and discharging current. All the main positive relays of the battery clusters are closed, and the pre-charge relays are open. At this time, each battery cluster is connected to the common DC bus in parallel through its own main circuit. Since the resistance of each main circuit is in the milliohm range, the parallel connection between the battery clusters is a low-resistance parallel connection. The pre-charge circuit is a branch composed of a pre-charge relay and a pre-charge resistor connected in series. The branch circuit is connected in parallel across the two ends of the main positive relay (i.e., between the positive terminal of the battery cluster and the positive terminal of the common DC bus). The high-resistance parallel connection of the precharge circuit means that the positive terminal of each battery cluster is connected to the positive terminal of the common DC bus through the precharge relay and the precharge resistor in series. The resistance of the precharge resistor is much greater than the on-resistance when the main positive relay is closed. During the transient protection phase, the precharge relays of all battery clusters are closed and the main positive relay is open. At this time, each battery cluster is connected to the common DC bus in parallel through its own precharge circuit. Since each precharge circuit has a high-resistance precharge resistor in series, the parallel connection between the battery clusters is a high-resistance parallel connection, and the precharge circuit exhibits high-resistance characteristics.

[0040] S4. Gradually equalize the voltage deviation between all battery clusters through the high-resistance parallel path, and perform a shutdown operation on the battery energy storage system after all the voltage deviations are less than a preset safety threshold.

[0041] In some embodiments, the step of performing a shutdown operation on the battery storage system after all the voltage deviations are less than a preset safety threshold includes: Once all the voltage deviations are less than a preset safety threshold, the pre-charge relays of each battery cluster are disconnected, thus cutting off the electrical connection between each battery cluster and the common DC bus.

[0042] In a specific embodiment, under a high-resistance parallel path, the main control unit of the battery management system continuously monitors the voltage value of each battery cluster (i.e., the open-circuit voltage between the positive and negative terminals of each battery cluster). Since all battery clusters are connected in parallel through a pre-charge resistor, the high-resistance path allows a small equalization current to flow between the battery clusters, causing the higher-voltage battery cluster to discharge to the lower-voltage battery cluster, gradually leveling out the voltage difference between the clusters. In this embodiment, the voltage values ​​of any two battery clusters are subtracted, and the absolute value of the subtraction result is taken to obtain the voltage deviation between the two battery clusters. It should be noted that the voltage deviation here can be one or more of the difference between the DC bus side voltage and the voltage of each battery cluster side (i.e., the voltage difference across the pre-charge resistor) and the difference between the open-circuit voltages of different battery clusters. Then, in this embodiment, all battery cluster pairs are traversed to find the maximum voltage deviation. This embodiment continuously compares the maximum voltage deviation with the maximum voltage deviation. If the maximum voltage deviation exceeds the preset safety threshold, the pre-charge relay remains closed and the main positive relay remains open, waiting for the equalization process to continue. The controller waits for a preset period of time to continue monitoring and comparing the maximum voltage deviation with the preset safety threshold until the voltage deviation between all battery clusters is detected to be less than the preset safety threshold. At this point, a disconnect command is sent to the pre-charge relay of each battery cluster. The disconnect command controls all pre-charge relays to disconnect simultaneously or sequentially. After confirming that all pre-charge relays have disconnected, all high-voltage circuits in the system are completely cut off, and the shutdown process ends. Thus, the entire charging and discharging cutoff process is completed. This embodiment utilizes the current-limiting characteristics of the pre-charge resistor and uses a high-resistance path as a buffer to achieve spontaneous voltage equalization between clusters at a safe current level, avoiding the instantaneous impact current caused by excessive voltage difference when directly connected in parallel.

[0043] In summary, this embodiment continuously reduces the current difference between battery clusters during normal operation through the adjustable impedance unit, thereby indirectly reducing the polarization voltage difference between battery clusters. This ensures that the voltages of each battery cluster are already relatively close when entering the cutoff moment, thus reducing the initial voltage difference at the cutoff moment and shortening the time required to equalize the voltage through the high-resistance path. At the same time, in the transient circulating current suppression stage, the high-resistance parallel connection of the pre-charge circuit solves the problem of sudden change in impact voltage difference caused by inductive characteristics and polarization effect when the main positive relay is momentarily disconnected, which cannot be handled in the steady-state adjustment stage. Thus, it achieves comprehensive suppression of current difference and circulating current problems in multi-cluster parallel battery systems.

[0044] This invention provides a current balancing control method for a battery energy storage system. The method includes real-time acquisition of operating data of each battery cluster during the charging and discharging process, and determining the target total resistance value required for each battery cluster to become consistent based on the operating data; generating a target adjustment resistance value for an adjustable impedance unit based on the target total resistance value of each battery cluster, and determining the optimal on / off combination scheme for each resistor branch in the adjustable impedance unit based on the target adjustment resistance value; performing steady-state current balancing of the battery cluster by adjusting the on / off state of the resistor branches based on the optimal on / off combination scheme, and triggering a transient circulating current protection mechanism to establish a high-resistance parallel path composed of pre-charged resistors between different battery clusters when the battery energy storage system is detected to have reached the charging and discharging cutoff condition; gradually balancing the voltage deviation between all battery clusters through the high-resistance parallel path, and performing a shutdown operation of the battery energy storage system after all voltage deviations are less than a preset safety threshold. Compared with existing technologies, this method dynamically adjusts the adjustable impedance units connected in series in each battery cluster during steady-state operation to achieve balanced current distribution between clusters. At the moment of cutoff, a high-resistance parallel topology is established using a pre-charge circuit to avoid severe circulating current damage to devices caused by large voltage differences between clusters at the moment of charge and discharge cutoff. This achieves balanced current distribution between clusters and suppression of circulating current under all operating conditions, thereby improving the overall safety and reliability of the battery energy storage system.

[0045] It should be noted that the sequence number of each process does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0046] In one embodiment, such as Figure 5 As shown, this embodiment of the invention provides a current balancing control device for a battery energy storage system. The battery energy storage system includes at least two parallel battery clusters. An adjustable impedance unit is connected in series between the negative terminal of each battery cluster and the negative terminal of a common DC bus. The adjustable impedance unit is composed of multiple resistor branches with different resistance values ​​connected in parallel. The device includes: The data acquisition module 101 is used to collect the operating data of each battery cluster in real time during the charging and discharging process, and determine the target total resistance value required for each battery cluster to become consistent based on the operating data. The resistor combination module 102 is used to generate a target adjustment resistance value for the adjustable impedance unit based on the target total resistance value of each battery cluster, and to determine the optimal on / off combination scheme for each resistor branch in the adjustable impedance unit based on the target adjustment resistance value. The equalization control module 103 is used to perform steady-state current equalization of the battery cluster by adjusting the on / off state of the resistor branch based on the optimal on / off combination scheme, and to trigger a transient circulating current protection mechanism to establish a high-resistance parallel path composed of pre-charge resistors between different battery clusters when the battery energy storage system is detected to have reached the charge / discharge cutoff condition. The safety control module 104 is used to gradually equalize the voltage deviation between all battery clusters through the high-resistance parallel path, and to perform a shutdown operation of the battery energy storage system after all the voltage deviations are less than a preset safety threshold.

[0047] In some embodiments, the adjustable impedance unit further includes at least a resistorless through branch; When the target adjustment resistance is zero, the optimal on / off combination scheme is to only conduct the straight-through branch.

[0048] Specific limitations regarding the current balancing control device for a battery energy storage system can be found in the above-described limitations regarding the current balancing control method for a battery energy storage system, and will not be repeated here. Those skilled in the art will recognize that the various modules and steps described in conjunction with the embodiments disclosed in this application can be implemented in hardware, software, or a combination of both. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0049] This invention provides a current balancing control device for a battery energy storage system. The device uses a data acquisition module to collect real-time operating data of each battery cluster during charging and discharging, and based on this data, determines the target total resistance value required for each battery cluster to reach uniformity. A resistor combination module generates a target adjustment resistance value for an adjustable impedance unit based on the target total resistance value of each battery cluster, and determines the optimal on / off combination scheme for each resistor branch in the adjustable impedance unit based on the target adjustment resistance value. The balancing control module, based on the optimal on / off combination scheme, performs steady-state current balancing of the battery clusters by adjusting the on / off state of the resistor branches. When the battery energy storage system detects that it has reached the charging / discharging cutoff condition, a transient circulating current protection mechanism is triggered to establish a high-resistance parallel path composed of pre-charged resistors between different battery clusters. The safety control module gradually balances the voltage deviation between all battery clusters through the high-resistance parallel path, and executes a shutdown operation of the battery energy storage system after all voltage deviations are less than a preset safety threshold. Compared with existing technologies, this device dynamically adjusts the adjustable impedance units connected in series in each battery cluster during steady-state operation to achieve balanced current distribution between clusters. At the moment of cutoff, it uses a pre-charge circuit to establish a high-resistance parallel topology, avoiding severe circulating current damage to devices caused by large voltage differences between clusters at the moment of charge and discharge cutoff. This achieves balanced current distribution between clusters and suppression of circulating current under all operating conditions, improving the overall safety and reliability of the battery energy storage system.

[0050] The embodiments described above are merely preferred embodiments of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various improvements and substitutions without departing from the technical principles of this invention, and these improvements and substitutions should also be considered within the scope of protection of this application. Therefore, the scope of protection of this patent application should be determined by the scope of the claims.

Claims

1. A current equalization control method of a battery energy storage system, characterized by, The battery energy storage system includes at least two battery clusters connected in parallel. An adjustable impedance unit is connected in series between the negative terminal of each battery cluster and the negative terminal of a common DC bus. The adjustable impedance unit is composed of multiple parallel resistor branches with different resistance values. The method includes the following steps: Real-time data collection of each battery cluster during charging and discharging, and determination of the target total resistance required for each battery cluster to become consistent based on the data. The target adjustment resistance value of the adjustable impedance unit is generated based on the target total resistance value of each battery cluster, and the optimal on / off combination scheme of each resistor branch in the adjustable impedance unit is determined based on the target adjustment resistance value. Based on the optimal on / off combination scheme, the steady-state current balance of the battery cluster is achieved by regulating the on / off state of the resistor branch. When the battery energy storage system is detected to have reached the charging / discharging cutoff condition, a transient circulating current protection mechanism is triggered to establish a high-resistance parallel path composed of pre-charge resistors between different battery clusters. The voltage deviation between all battery clusters is gradually balanced through the high-resistance parallel path, and the battery energy storage system is shut down after all the voltage deviations are less than a preset safety threshold.

2. The current balancing control method for a battery energy storage system as described in claim 1, characterized in that, The operating data includes at least the open-circuit voltage of the battery cluster, the internal resistance of the battery cluster, and the common DC bus voltage. The step of determining the target total resistance value required for each battery cluster to become consistent based on the operating data includes: The target average current is obtained based on the total current of the battery energy storage system measured on the common DC bus and the total number of parallel battery clusters. Calculate the voltage difference between the open-circuit voltage of the battery cluster and the voltage of the common DC bus, and based on the voltage difference, obtain the target total resistance value required for the current of each battery cluster to approach the target average current.

3. The current balancing control method for a battery energy storage system as described in claim 2, characterized in that: The target adjustment resistance value is the difference between the target total resistance value and the internal resistance of the battery cluster.

4. The current balancing control method for a battery energy storage system as described in claim 1, characterized in that, The resistor branch includes at least a switching device and a resistor connected in series. The step of determining the optimal on / off combination scheme of each resistor branch in the adjustable impedance unit based on the target resistance value includes: Based on the resistance value of each resistor branch, calculate the equivalent total resistance value under the on / off combination of all resistor branches in the adjustable impedance unit that are in the conducting state. Based on the resistance deviation between the equivalent total resistance of each resistor branch switching combination and the target adjustment resistance, candidate switching combination schemes are selected. The optimal on / off combination scheme is selected from the candidate on / off combination schemes according to the preset priority rules.

5. The current balancing control method for a battery energy storage system as described in claim 4, characterized in that: The adjustable impedance unit also includes at least a resistance-free through branch; When the target adjustment resistance is zero, the optimal on / off combination scheme is to only conduct the straight-through branch.

6. The current balancing control method for a battery energy storage system as described in claim 1, characterized in that, Each battery cluster includes multiple individual cells. A main positive relay and a pre-charge circuit are connected in parallel between the positive terminal of each battery cluster and the positive terminal of the common DC bus. The pre-charge circuit is composed of a pre-charge relay and a pre-charge resistor connected in series. The step of triggering the transient circulating current protection mechanism to establish a high-resistance parallel path composed of the pre-charge resistor between different battery clusters when the battery energy storage system is detected to have reached the charge / discharge cutoff condition includes: During the charging and discharging process of the battery energy storage system, the voltage value of each individual cell in each battery cluster is monitored in real time. When the voltage value of any individual cell reaches the preset cutoff warning threshold, it is determined that the battery energy storage system is about to reach the charging and discharging cutoff condition, and the transient circulating current protection mechanism is triggered to generate a pre-charge relay closing drive signal. In response to the precharge relay closing drive signal, the precharge relays of all battery clusters are closed, and the main positive relays of each battery cluster are controlled to be in the closed state; After confirming that all pre-charge relays are closed, the main positive relays of all battery clusters are opened, so that the connection path between each battery cluster and the common DC bus is switched from low-resistance parallel connection of the main circuit to high-resistance parallel connection of the pre-charge circuit, forming a high-resistance parallel path; wherein, the low-resistance parallel connection of the main circuit is the low-impedance parallel connection of each battery cluster through the main positive relays; the high-resistance parallel connection of the pre-charge circuit is that the positive terminal of each battery cluster is connected to the positive terminal of the common DC bus through the pre-charge relays and the pre-charge resistors in series.

7. The current balancing control method for a battery energy storage system as described in claim 6, characterized in that: The resistance value of the pre-charge resistor is greater than the on-resistance when the main positive relay is closed.

8. The current balancing control method for a battery energy storage system as described in claim 6, characterized in that, The step of performing a shutdown operation on the battery energy storage system after all voltage deviations are less than a preset safety threshold includes: Once all the voltage deviations are less than a preset safety threshold, the pre-charge relays of each battery cluster are disconnected, thus cutting off the electrical connection between each battery cluster and the common DC bus.

9. A current balancing control device for a battery energy storage system, characterized in that, The battery energy storage system includes at least two battery clusters connected in parallel. An adjustable impedance unit is connected in series between the negative terminal of each battery cluster and the negative terminal of a common DC bus. The adjustable impedance unit is composed of multiple parallel resistor branches with different resistance values. The device includes: The data acquisition module is used to collect the operating data of each battery cluster in real time during the charging and discharging process, and based on the operating data, determine the target total resistance value required for each battery cluster to become consistent. The resistor combination module is used to generate the target adjustment resistance value of the adjustable impedance unit based on the target total resistance value of each battery cluster, and to determine the optimal on / off combination scheme of each resistor branch in the adjustable impedance unit based on the target adjustment resistance value. The equalization control module is used to perform steady-state current equalization of the battery clusters by adjusting the on / off state of the resistor branch based on the optimal on / off combination scheme, and to trigger a transient circulating current protection mechanism to establish a high-resistance parallel path composed of pre-charge resistors between different battery clusters when the battery energy storage system is detected to have reached the charge / discharge cutoff condition. The safety control module is used to gradually equalize the voltage deviation between all battery clusters through the high-resistance parallel path, and to perform a shutdown operation of the battery energy storage system after all the voltage deviations are less than a preset safety threshold.

10. The current balancing control device for a battery energy storage system as described in claim 9, characterized in that: The adjustable impedance unit also includes at least a resistance-free through branch; When the target adjustment resistance is zero, the optimal on / off combination scheme is to only conduct the straight-through branch.

Images