Battery cluster grid-connected and off-grid switching method, energy storage system and storage medium

Abstract

The invention relates to the technical field of energy, particularly provides a battery cluster grid-connected and off-grid switching method, an energy storage system and a storage medium, and aims to solve the technical problem that the stability of the energy storage system is affected due to the fact that a circulating current risk possibly exists during grid-connected and off-grid switching in an existing method. In order to achieve the purpose, the battery cluster grid-connected and off-grid switching method comprises the steps that operation state information of each battery cluster is obtained, and the operation state information of each battery cluster at least comprises a cluster charge state; based on the operation state information of each battery cluster, determining whether the energy storage system is in a charge-discharge state; if yes, determining an on-grid and off-grid switching control strategy based on the cluster charge state; and controlling the battery cluster to perform grid-connected and off-grid switching based on the grid-connected and off-grid switching control strategy. The circulation risk caused by inconsistent energy levels among clusters can be avoided in advance, and the overall operation reliability of the energy storage system is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy, and particularly provides a battery cluster and off-grid switching method, an energy storage system and a storage medium. BACKGROUND

[0002] With the requirement of energy storage scale in new energy power station, grid frequency modulation and other scenarios jumping from kilowatt-hour level to megawatt-hour or even hundred megawatt-hour level, the capacity of a single battery cluster cannot meet the requirement. By connecting multiple standardized battery clusters in parallel on the DC side, a super large capacity energy storage system can be flexibly and economically combined like building blocks, and the system redundancy reliability is improved. However, this architecture also brings key technical challenges such as inter-cluster circulating current and consistency management. In view of the above problems, various battery cluster parallel switching schemes have emerged to meet the growing market demand.

[0003] In a parallel large energy storage system composed of multiple independent battery clusters, due to factors such as manufacturing process, operating temperature, aging degree, etc., there is inconsistency in voltage, capacity and internal resistance among the battery clusters. When directly connected in parallel, instantaneous large current circulating current is easy to occur, which endangers the safety of equipment, causes energy loss and accelerates battery aging. The existing parallel switching strategy either responds with lag and cannot prevent circulating current, or relies on the accuracy of state of charge algorithm, or there is still a large circulating current during switching, or the circulating current is limited by adding a damping resistor but a continuous power loss is generated, so it is difficult to balance system safety, operating efficiency and battery life. Therefore, a more optimal battery cluster and off-grid switching related technical solution is urgently needed. SUMMARY

[0004] In order to overcome the above defects, the present application is proposed to solve or at least partially solve the technical problem that the existing method may have circulating current risk during parallel and off-grid switching, thereby affecting the stability of the energy storage system. The present application provides a battery cluster and off-grid switching method, an energy storage system and a storage medium.

[0005] In a first aspect, the present application provides a battery cluster and off-grid switching method applied to an energy management system, the method comprising:

[0006] obtaining operating state information of each battery cluster, wherein the operating state information of each battery cluster at least includes cluster state of charge;

[0007] determining whether the energy storage system is in a charging and discharging state based on the operating state information of each battery cluster;

[0008] if yes, determining a parallel and off-grid switching control strategy based on the cluster state of charge;

[0009] controlling the battery cluster to perform parallel and off-grid switching based on the parallel and off-grid switching control strategy.

[0010] In an embodiment of the battery cluster and off-grid switching method of the application, the operation state information of the battery cluster further comprises a current of the battery cluster; and the determining whether the energy storage system is in a charging state or a discharging state based on the operation state information of the battery cluster comprises:

[0011] obtaining an operation instruction of the energy storage converter;

[0012] when it is detected that the current flows from the external load to the battery cluster and the operation instruction of the energy storage converter is a charging instruction, it is determined that the energy storage system is in a charging state;

[0013] when it is detected that the current flows from the battery cluster to the external load and the operation instruction of the energy storage converter is a discharging instruction, it is determined that the energy storage system is in a discharging state.

[0014] In an embodiment of the battery cluster and off-grid switching method of the application, the off-grid switching control strategy comprises a round-robin charging strategy, a round-robin discharging strategy and an intelligent switching strategy; and the determining the off-grid switching control strategy based on the cluster state of charge comprises:

[0015] when the energy storage system is in a charging state, it is determined whether the minimum cluster state of charge is greater than or equal to a first state of charge threshold and whether the difference between the maximum cluster state of charge and the minimum cluster state of charge is less than or equal to a second state of charge threshold; if yes, the round-robin charging strategy is executed, otherwise the intelligent switching strategy is executed;

[0016] when the energy storage system is in a discharging state, it is determined whether the maximum cluster state of charge is less than or equal to a third state of charge threshold and whether the difference between the maximum cluster state of charge and the minimum cluster state of charge is less than or equal to a second state of charge threshold; if yes, the round-robin discharging strategy is executed, otherwise the intelligent switching strategy is executed.

[0017] In an embodiment of the battery cluster and off-grid switching method of the application, the operation state information of the battery cluster further comprises a total voltage of each battery cluster;

[0018] the executing the round-robin charging strategy comprises:

[0019] determining a charging priority of each battery cluster based on the total voltage of the battery cluster, wherein the smaller the total voltage of the battery cluster is, the higher the charging priority is;

[0020] controlling the battery cluster with the highest charging priority to access the energy storage system for charging;

[0021] when the total voltage of the battery cluster with the highest charging priority is higher than the total voltage of the battery cluster with the second highest charging priority, and the difference between the total voltages exceeds a preset charging switching threshold, controlling the battery cluster with the second highest charging priority to access the energy storage system for charging and disconnecting the battery cluster with the highest charging priority;

[0022] Repeat the above steps until all battery clusters are fully charged.

[0023] In one embodiment of the battery cluster on-grid / off-grid switching method of this application, the operating status information of the battery cluster also includes the total voltage of each battery cluster;

[0024] The execution of the alternating discharge strategy includes:

[0025] The discharge priority of each battery cluster is determined based on the total voltage of each battery cluster, where the higher the total voltage of the battery cluster, the higher the discharge priority.

[0026] The battery cluster with the highest discharge priority is connected to the energy storage system for discharge.

[0027] When the total voltage of the battery cluster with the highest discharge priority is less than the total voltage of the battery cluster with the second highest discharge priority, and the difference between the two total voltages exceeds a preset discharge switching threshold, the battery cluster with the second highest discharge priority is controlled to connect to the energy storage system for discharge, and the battery cluster with the highest discharge priority is disconnected.

[0028] Repeat the above steps until all battery clusters have been discharged.

[0029] In one embodiment of the battery cluster on-grid and off-grid switching method of this application, the operating status information of the battery cluster also includes the total voltage and terminal temperature of each battery cluster;

[0030] The execution of the intelligent switching strategy includes:

[0031] The voltage difference, state of charge difference, and terminal temperature difference of each battery cluster are determined based on the total voltage, cluster state of charge, and terminal temperature of each battery cluster.

[0032] A cost function is constructed based on the voltage difference, the difference in state of charge of each battery cluster, and the temperature difference at the terminals.

[0033] The cost score for each battery cluster is calculated based on the cost function.

[0034] Determine whether the cost score of each battery cluster is greater than a preset risk threshold;

[0035] If so, the battery clusters with a cost score greater than a preset risk threshold will be removed from the energy storage system.

[0036] In one embodiment of the battery cluster grid-to-offline switching method of this application, the construction of the cost function based on the voltage difference, cluster state of charge difference, and terminal temperature difference of each battery cluster includes:

[0037] The voltage change rate and voltage acceleration of each battery cluster are determined based on the voltage difference of each battery cluster.

[0038] Based on the voltage difference, voltage change rate, voltage acceleration, cluster state of charge difference, and terminal temperature difference of each battery cluster, the voltage difference term, voltage change rate term, voltage acceleration term, cluster state of charge difference term, and terminal temperature difference term of each battery cluster are determined respectively.

[0039] The cost function is constructed based on the voltage difference term, voltage change rate term, voltage acceleration term, cluster state of charge difference term, and terminal temperature difference term for each battery cluster.

[0040] In one embodiment of the battery cluster grid-to-offline switching method of this application, the construction of the cost function based on the voltage difference term, voltage change rate term, voltage acceleration term, cluster state of charge difference term, and terminal temperature difference term of each battery cluster includes: constructing the cost function based on the weighted sum of the voltage difference term, voltage change rate term, voltage acceleration term, cluster state of charge difference term, and terminal temperature difference term of each battery cluster.

[0041] In a second aspect, an energy storage system is provided, the energy storage system comprising at least an energy management system, the energy management system comprising:

[0042] At least one processor;

[0043] And, a memory communicatively connected to the at least one processor;

[0044] The memory stores a computer program that, when executed by the at least one processor, implements the battery cluster and off-grid switching method as described in any one of claims 1 to 8.

[0045] In a third aspect, a computer-readable storage medium is provided, wherein a plurality of program codes are stored therein, the program codes being adapted to be loaded and executed by a processor to perform the battery cluster and off-grid switching method described in any of the preceding claims.

[0046] The above-described technical solutions of this application have at least one or more of the following beneficial effects:

[0047] The battery cluster grid-to-grid switching method in this application includes: acquiring the operating status information of each battery cluster, wherein the operating status information of each battery cluster includes at least the cluster state of charge; determining whether the energy storage system is in a charging / discharging state based on the operating status information of each battery cluster; if so, determining a grid-to-grid switching control strategy based on the cluster state of charge; and controlling the battery clusters to perform grid-to-grid switching based on the grid-to-grid switching control strategy. This method can proactively avoid the circulating current risk caused by inconsistent energy levels between clusters; simultaneously, through scientific switching control, it ensures the stability of the energy storage system's charging and discharging process, reduces energy loss, delays battery cluster aging, balances system operation safety, efficiency, and battery life, and improves the overall operational reliability of the energy storage system. Attached Figure Description

[0048] The disclosure of this application will become more readily understood with reference to the accompanying drawings. It will be readily understood by those skilled in the art that these drawings are for illustrative purposes only and are not intended to limit the scope of protection of this application. Furthermore, similar numbers in the drawings are used to denote similar components, wherein:

[0049] Figure 1 This is a schematic diagram of the energy storage system in one embodiment of this application;

[0050] Figure 2 This is a schematic diagram of the main process of the battery cluster on-grid and off-grid switching method in one embodiment of this application;

[0051] Figure 3 This is a schematic diagram of the main structure of the battery cluster on-grid / off-grid switching device in one embodiment of this application;

[0052] Figure 4 This is a schematic diagram of the energy management system in one embodiment of this application. Detailed Implementation

[0053] Some embodiments of this application are described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of this application and are not intended to limit the scope of protection of this application.

[0054] In the description of this application, "module" and "processor" can include hardware, software, or a combination of both. A module can include hardware circuitry, various suitable sensors, communication ports, memory, and can also include software components, such as program code, or a combination of software and hardware. A processor can be a central processing unit, microprocessor, image processor, digital signal processor, or any other suitable processor. The processor has data and / or signal processing capabilities. The processor can be implemented in software, in hardware, or a combination of both. Non-transitory computer-readable storage media includes any suitable medium capable of storing program code, such as magnetic disks, hard disks, optical disks, flash memory, read-only memory, random access memory, etc. The term "A and / or B" means all possible combinations of A and B, such as only A, only B, or A and B. The terms "at least one A or B" or "at least one of A and B" have a similar meaning to "A and / or B" and can include only A, only B, or A and B. The singular terms "a" or "this" can also include plural forms.

[0055] Current traditional parallel switching strategies either suffer from slow response times, fail to prevent circulating currents, rely on the accuracy of state-of-charge (POC) algorithms, or still exhibit significant circulating currents during switching, or limit circulating currents by adding damping resistors but incur continuous power losses. These strategies struggle to balance system safety, operational efficiency, and battery lifespan. Therefore, a superior technical solution for battery cluster parallel-to-off-grid switching is urgently needed. To address this, this application proposes a battery cluster parallel-to-off-grid switching method, an energy storage system, and a storage medium.

[0056] Next, we will first describe in detail the specific structure of the energy storage system in this application.

[0057] like Figure 1 As shown, the energy storage system includes multiple parallel battery clusters, an energy management system (EMS), an energy storage converter (PCS), and a DC bus. Multiple battery clusters are connected to the energy storage converter via the DC bus. Each battery cluster contains a battery management unit (BMU) and a cluster-level battery management unit (BCMU). Each battery cluster has a resistor R and a switch SW for balancing, as well as a Hall sensor (HALL) and a temperature monitoring component (Temp) for current monitoring. The energy management system interacts with the energy storage converter and the cluster-level battery management units of each battery cluster via a communication link, simultaneously sending control signals to the battery clusters to achieve functions such as monitoring the operating status of the entire energy storage system, grid-connected / off-grid switching control, and balancing management. It should be understood that, in addition to using Hall sensors (HALL) to monitor current, other sensors can also be used to monitor current; there are no specific limitations, as long as the monitoring of current in the circuit can be achieved.

[0058] See appendix Figure 2 , Figure 2 This is a schematic flowchart of the main steps of a battery cluster on-grid / off-grid switching method according to an embodiment of this application.

[0059] like Figure 2 As shown, the battery cluster on-grid / off-grid switching method in this application embodiment mainly includes the following steps S10-S40.

[0060] Step S10: Obtain the operating status information of each battery cluster, wherein the operating status information of each battery cluster includes at least the cluster state of charge.

[0061] A battery cluster is an independent energy storage unit formed by connecting multiple battery cells in series and in parallel. It is the core component of a large-scale parallel energy storage system and can realize the storage and release of electrical energy.

[0062] Operating status information refers to the dynamic parameters generated during the operation of the battery cluster, specifically including the state of charge (SOC) of the cluster, and may also include data such as the total voltage, current, and terminal temperature of the battery cluster.

[0063] The state of charge (SOC) of a battery cluster represents the proportion of its current remaining capacity to its rated capacity and is a core indicator reflecting the energy level of the battery cluster.

[0064] Step S20: Based on the operating status information of each battery cluster, determine whether the energy storage system is in a charging / discharging state. If so, proceed to step S30 below. Otherwise, when it is determined that the energy storage system is in a static state, passive equalization can be performed on the battery cluster.

[0065] The charging and discharging state is the working state of an energy storage system when it is receiving electrical energy (charging) or outputting electrical energy (discharging), which is different from the static state when there is no energy input or output.

[0066] Step S30: Determine and implement an off-grid switching control strategy based on the cluster charge state.

[0067] The grid-connected / off-grid switching control strategy is a set of rules formulated by the energy management system based on the operating status information of battery clusters. It is used to determine whether each battery cluster needs to be connected to or disconnected from the grid in order to achieve optimized system operation. The grid-connected / off-grid switching control strategy includes alternating charging strategy, alternating discharging strategy, and intelligent switching strategy.

[0068] Step S40: Control the battery cluster to perform grid-connected / off-grid switching based on the grid-connected / off-grid switching control strategy.

[0069] On-grid / off-grid switching is the operation of controlling the connection (grid-connected) or disconnect (off-grid) of the battery cluster to the DC bus of the energy storage system. It is a key means to adjust the connection status of the battery cluster and ensure the stable operation of the system.

[0070] Based on steps S10-S40 above, the operating status information of each battery cluster is first obtained, including at least the cluster state of charge. Based on this information, it is determined whether the energy storage system is in a charging / discharging state. If so, a grid-connected / off-grid switching control strategy is determined based on the cluster state of charge. The grid-connected / off-grid switching control strategy is then used to control the battery clusters to switch between grid and off-grid operation. This approach can proactively mitigate the circulating current risk caused by inconsistent energy levels between clusters. Simultaneously, through scientific switching control, the stability of the energy storage system's charging and discharging process is ensured, energy loss is reduced, battery cluster aging is delayed, and system operational safety, efficiency, and battery life are balanced, thereby improving the overall operational reliability of the energy storage system.

[0071] The following provides further explanation of steps S10 to S40.

[0072] Specifically, in step S10 above, the cluster-level battery management unit (BCMU) of each battery cluster acquires the total voltage of the battery cluster (determined by the total output voltage of the battery cells connected in series), the total current (monitored by the Hall sensor), and the temperature of the battery cluster (acquired by the temperature monitoring component Temp), and uploads this data to the energy management system (EMS) through a communication link, thereby obtaining operating status information such as the total voltage, total current, and terminal temperature of the battery cluster.

[0073] Each battery cluster's cluster-level battery management unit (BCMU) determines the cluster state of charge (SOC) based on the total voltage and current data of the battery cluster, combined with the capacity characteristic curve of the battery cluster, using the ampere-hour integration method or combining the open-circuit voltage-SOC correspondence, and then uploads the calculation results to the energy management system.

[0074] The above is a further explanation of step S10. Step S20 will be further explained below.

[0075] Specifically, step S20 can be implemented through steps S201 to S203.

[0076] Step S201: Obtain the operating instructions of the energy storage converter.

[0077] Specifically, the energy management system reads the current operating instructions of the energy storage converter in real time through the communication link with the energy storage converter. These instructions clarify whether the energy storage converter is in charging mode or discharging mode, which is one of the key bases for judging the charging and discharging status of the system.

[0078] Step S202: When it is detected that the current flows from the external load to the battery cluster and the working command of the energy storage converter is a charging command, it is determined that the energy storage system is in a charging state.

[0079] Specifically, when current is detected flowing from an external load to the battery cluster, and the energy storage converter's operating command is a charging command, it indicates that electrical energy is being stored in the battery cluster through the energy storage converter, thus determining that the energy storage system is in a charging state.

[0080] Step S203: When it is detected that the current flows from the battery cluster to the external load and the working command of the energy storage converter is a discharge command, it is determined that the energy storage system is in a discharge state.

[0081] Specifically, when current is detected flowing from the battery cluster to the external load, and the energy storage converter's operating command is a discharge command, it indicates that the electrical energy stored in the battery cluster is supplying power to the external load through the energy storage converter, thus determining that the energy storage system is in a discharge state.

[0082] By combining the operating commands of the energy storage converter with the current flow direction of the battery cluster, the charging and discharging status of the energy storage system can be accurately and reliably determined. This avoids the misjudgment problems that may occur when relying on a single current flow direction or a single command. It provides an accurate basis for formulating targeted grid-connected and off-grid switching control strategies based on the charging and discharging status, thereby ensuring the timeliness and rationality of the grid-connected and off-grid switching operation of the battery cluster.

[0083] The above is a further explanation of step S20. Step S30 will be further explained below.

[0084] Specifically, step S30 can be implemented through steps S301 to S302.

[0085] Step S301: When the energy storage system is in a charging state, determine whether the minimum cluster charge state is greater than or equal to the first charge state threshold, and whether the difference between the maximum cluster charge state and the minimum cluster charge state is less than or equal to the second charge state threshold; if so, execute the alternating charging strategy, otherwise execute the intelligent switching strategy.

[0086] The first state-of-charge threshold, the second state-of-charge threshold, and the third state-of-charge threshold are preset values, which can be adaptively adjusted according to the actual scenario, and are not specifically limited thereto. For example, 90% can be used as an example of the first state-of-charge threshold, 5% can be used as an example of the second state-of-charge threshold, and 10% can be used as an example of the third state-of-charge threshold.

[0087] For example, when the energy storage system is in the charging state, it is determined that cluster SOCmin≥90% and cluster SOCmax-cluster SOCmin≤5%. If the conditions are met, a voltage-based alternating charging strategy is executed; otherwise, a cost function-based intelligent switching strategy is executed.

[0088] Step S302: When the energy storage system is in a discharge state, determine whether the maximum cluster charge state is less than or equal to the third charge state threshold, and whether the difference between the maximum cluster charge state and the minimum cluster charge state is less than or equal to the second charge state threshold; if so, execute the alternating discharge strategy, otherwise execute the intelligent switching strategy.

[0089] For example, when the working state is the discharge state, it is determined that the cluster SOCmax ≤ 10% and the cluster SOCmax - cluster SOCmin ≤ 5%. If the conditions are met, a voltage-based alternating discharge strategy is executed; otherwise, a cost function-based intelligent switching strategy is executed.

[0090] The following details the specific methods for implementing the alternating charging strategy, the alternating discharging strategy, and the intelligent switching strategy.

[0091] In one specific embodiment of the battery cluster grid-connected / off-grid switching method of this application, the execution of the turn-by-turn charging strategy includes: determining the charging priority of each battery cluster based on the total voltage of each battery cluster, wherein the lower the total voltage of the battery cluster, the higher the charging priority; controlling the battery cluster with the highest charging priority to connect to the energy storage system for charging; when the total voltage of the battery cluster with the highest charging priority is higher than the total voltage of the battery cluster with the second highest charging priority, and the difference between the two total voltages exceeds a preset charging switching threshold, controlling the battery cluster with the second highest charging priority to connect to the energy storage system for charging, and disconnecting the battery cluster with the highest charging priority; repeating the above steps until all battery clusters have completed charging.

[0092] The preset charging switching threshold can be a pre-set value, which can be adaptively adjusted according to the actual scenario, and is not specifically limited thereto. In one embodiment, the preset charging switching threshold can also be determined by Vchg_switch = Ichg_max * Rchg_internal, where Vchg_switch is the maximum switching threshold allowed by the battery cluster during charging; Ichg_max is the maximum charging current value allowed by the battery cluster; and Rchg_internal is the internal resistance of the battery cluster during charging.

[0093] Specifically, when the energy storage system is charging, the lower the total voltage of the battery clusters, the higher the charging priority. The energy management system controls the contactor of the battery cluster with the highest charging priority to close, while the contactors of other battery clusters are open, allowing the highest-priority battery cluster to charge. When the total voltage of the highest-priority battery cluster rises to a level higher than that of the second-highest-priority battery cluster and exceeds the switching threshold, the contactor of the second-highest-priority battery cluster is closed first, followed by the contactor of the highest-priority battery cluster, thus switching the charging of the battery clusters. The energy management system will continue to perform cyclic charging control of the battery clusters in the above order to ensure that all battery clusters are fully charged.

[0094] By implementing a rotating charging strategy, each battery cluster can receive a balanced charging opportunity, effectively avoiding the problem of increased inconsistency in capacity and voltage between clusters caused by long-term undercharging or overcharging of some battery clusters, thus reducing the risk of circulating current in parallel operation from the source. At the same time, the charging priority can be dynamically adjusted according to the total voltage of each battery cluster to avoid uneven energy distribution under a single charging mode and slow down the aging rate of battery clusters. In addition, this strategy can flexibly adapt to the charging needs of the energy storage system, improving the overall consistency and lifespan of battery clusters while ensuring the charging efficiency of the system, and further enhancing the stability of the parallel energy storage system operation.

[0095] In one specific embodiment of the battery cluster grid-to-grid switching method of this application, the execution of the alternating discharge strategy includes: determining the discharge priority of each battery cluster based on the total voltage of each battery cluster, wherein the higher the total voltage of the battery cluster, the higher the discharge priority; controlling the battery cluster with the highest discharge priority to connect to the energy storage system for discharge; when the total voltage of the battery cluster with the highest discharge priority is less than the total voltage of the battery cluster with the second highest discharge priority, and the difference between the two total voltages exceeds a preset discharge switching threshold, controlling the battery cluster with the second highest discharge priority to connect to the energy storage system for discharge, and disconnecting the battery cluster with the highest discharge priority; repeating the above steps until all battery clusters have completed discharge.

[0096] The preset discharge switching threshold can be a pre-set value, which can be adaptively adjusted according to the actual scenario, and is not specifically limited thereto. In one embodiment, the preset discharge switching threshold can also be determined by Vdchg_switch = Idchg_max * Rdchg_internal, where Vdchg_switch is the maximum allowed switching threshold of the battery cluster during discharge; Idchg_max is the maximum allowed discharge current value of the battery cluster; and Rdchg_internal is the internal resistance of the battery cluster during discharge.

[0097] Specifically, when the energy storage system is discharging, the higher the total voltage of the battery cluster, the higher its discharge priority. The energy management system controls the contactor of the battery cluster with the highest discharge priority to close, while the contactors of other battery clusters are opened, allowing the highest-priority battery cluster to discharge. When the total voltage of the highest-priority battery cluster drops below that of the second-highest-priority battery cluster, and the voltage difference exceeds the switching threshold, the contactor of the second-highest-priority battery cluster is closed first, followed by the contactor of the highest-priority battery cluster, thus switching the battery cluster discharge. The energy management system continues to perform cyclic discharge control of the battery clusters in the above order to ensure that all battery clusters are fully discharged.

[0098] By implementing a staggered discharge strategy, each battery cluster can receive a balanced discharge opportunity, preventing the widening of voltage and capacity inconsistencies between clusters caused by prolonged over-discharge of some clusters and prolonged idleness of others. This reduces the risk of circulating current during parallel operation from the source. At the same time, the discharge priority can be dynamically adjusted based on the total voltage of each battery cluster to avoid uneven energy loss under a single discharge mode and slow down the aging rate of the battery clusters. In addition, this strategy can flexibly match the power demand of external loads, improving the overall consistency and lifespan of battery clusters while ensuring the system's discharge efficiency, and further enhancing the stability and reliability of the energy storage system.

[0099] In one specific embodiment of the battery cluster grid-to-grid switching method of this application, the execution of the intelligent switching strategy includes: determining the voltage difference, state of charge difference, and terminal temperature difference of each battery cluster based on the total voltage, cluster state of charge, and terminal temperature of each battery cluster; constructing a cost function based on the voltage difference, cluster state of charge difference, and terminal temperature difference of each battery cluster; calculating the cost score of each battery cluster based on the cost function; determining whether the cost score of each battery cluster is greater than a preset risk threshold; if so, switching off the battery clusters with cost scores greater than the preset risk threshold from the energy storage system.

[0100] The voltage difference is the difference between the total voltage of each battery cluster and the average total voltage of all battery clusters in the energy storage system.

[0101] The cluster state of charge difference is the difference between the cluster state of charge of each battery cluster and the average state of charge of all battery clusters in the energy storage system.

[0102] Terminal temperature difference is the difference between the terminal temperature of each battery cluster and the average terminal temperature of all battery clusters in the energy storage system.

[0103] The cost function is a mathematical model constructed by assigning preset weights to each parameter, with pressure difference, state of charge difference, and terminal temperature difference as the core parameters. It is used to quantify the risk level of each battery cluster to the stability of the energy storage system.

[0104] The cost score is a specific value calculated through a cost function. The higher the score, the more significant the voltage difference, state of charge difference, or temperature difference of the battery cluster, and the greater the possibility of generating risks such as circulating current and overheating in the energy storage system.

[0105] The preset risk threshold is a critical value set based on the energy storage system design standards, battery safety parameters, and operating experience. It is the core basis for determining whether a battery cluster needs to be cut out.

[0106] Specifically, when the energy storage system is in a charging and discharging state and the state of charge of the battery cluster is within a preset range, such as [10%, 90%], a smart switching strategy is executed on the battery cluster.

[0107] Specifically, the energy management system calculates the inter-cluster voltage difference, state-of-charge difference, and terminal temperature difference based on the total voltage of each battery cluster, the cluster state of charge, and the terminal temperature. For example, the energy management system obtains the average cluster voltage V_avg = ΣV_cluster_x / N based on the total cluster voltage V_cluster_x of each battery cluster, and calculates the voltage difference ΔV_cluster_x = V_cluster_x - V_avg between each parallel battery cluster and the average cluster voltage of the energy storage system, where N is the total number of battery clusters. Furthermore, to remove the influence of noise, ΔV_cluster_x is low-pass filtered to obtain a smoothed ΔV_cluster_x.

[0108] Specifically, the energy management system obtains the average cluster state of charge of all battery clusters in the entire energy storage system based on the cluster state of charge (SOC_cluster_x) of each battery cluster as: SOC_avg=ΣSOC_cluster_x / N. Then, the change in state of charge of each battery cluster is further determined as: ΔSOC_cluster_x=SOC_cluster_x-SOC_avg.

[0109] Specifically, the energy management system obtains the average terminal temperature of all battery clusters integrated into the entire energy storage system based on the measured terminal temperature value Temp_cluster_x of each battery cluster: Temp_avg=ΣTemp_cluster_x / N. Then, it further determines the terminal temperature change of each battery cluster as: ΔTemp_cluster_x=Temp_cluster_x-Temp_avg.

[0110] Next, a cost function can be constructed based on the pressure difference, state of charge difference, and terminal temperature difference. Then, the energy management system calculates the cost score for each battery cluster using this cost function; the score directly corresponds to the risk level of the battery cluster. Finally, the cost score of each battery cluster is compared with a preset risk threshold. If the cost score of a battery cluster exceeds the threshold, it indicates that its pressure difference, state of charge difference, or temperature difference has reached a level that may threaten system stability. In this case, the energy management system will issue a control command to disconnect the high-risk battery cluster from the DC bus of the energy storage system to prevent it from affecting the operational safety and stability of the entire system.

[0111] In one specific embodiment, constructing the cost function based on the voltage difference, cluster state of charge difference, and terminal temperature difference of each battery cluster includes: determining the voltage change rate and voltage acceleration of each battery cluster based on the voltage difference; determining the voltage difference term, voltage change rate term, voltage acceleration term, cluster state of charge difference term, and terminal temperature difference term for each battery cluster based on the voltage difference, voltage change rate term, voltage acceleration term, cluster state of charge difference term, and terminal temperature difference term for each battery cluster, respectively; and constructing the cost function based on the voltage difference term, voltage change rate term, voltage acceleration term, cluster state of charge difference term, and terminal temperature difference term for each battery cluster.

[0112] Specifically, the voltage change rate and voltage acceleration of each battery cluster can be determined based on the voltage difference between the clusters. The voltage change rate of the battery cluster can be determined by the following formula: v_cluster_x(t)=(ΔV_cluster_x(t)-ΔV_cluster_x(t-Δt)) / Δt. When v_cluster_x(t)>0, it indicates that the voltage difference between the battery clusters is widening, which easily generates or increases circulating current; when v_cluster_x(t)<0, it indicates that the voltage difference between the battery clusters is narrowing, and the circulating current situation is improving.

[0113] Furthermore, the voltage acceleration of the battery cluster can be determined by the following formula: α_cluster_x(t)=(v_cluster_x(t)-v_cluster_x(t-Δt)) / Δt. When α_cluster_x(t)>0, it indicates that the rate of change of the voltage difference of the battery cluster is increasing, that is, the voltage difference of the battery cluster is accelerating to expand or decelerating to shrink; when α_cluster_x(t)<0, it indicates that the rate of change of the voltage difference of the battery cluster is decreasing, that is, the voltage difference of the battery cluster is decelerating to expand or accelerating to shrink.

[0114] Specifically, after determining the voltage change rate and voltage acceleration of each battery cluster, the voltage difference term, voltage change rate term, voltage acceleration term, cluster state of charge difference term, and terminal temperature difference term of each battery cluster can be further determined separately.

[0115] Specifically, since voltage differences in the plateau region are more likely to lead to large SOC differences and generate large circulating currents, a nonlinear amplification strategy is adopted for the voltage difference term F(ΔV) as the core adjustment term. The voltage difference term can be expressed by the following formula:

[0116] in, For voltage difference, This is the voltage difference normalization coefficient. For alarm thresholds, This is a bias value used to ensure the continuity of the function at the threshold. The value can be any value within the range of (0.05V, 0.1V). The voltage normalization coefficient can be a value obtained in advance based on experiments, and there are no specific restrictions on it.

[0117] The voltage change rate term G(v) is mainly used to capture the dynamic trend of voltage change, and can be specifically expressed as:

[0118] in, The rate of change of voltage. This is the voltage change rate normalization parameter, which can be a pre-set parameter.

[0119] Specifically, in order to make more forward-looking predictions and determine whether the trend of voltage difference change is accelerating or slowing down, the voltage acceleration term is used. It can be represented as:

[0120] in, The rate of change of voltage. The normalized parameter for the rate of change of voltage. For voltage acceleration, This is the voltage change rate normalization parameter, which can be a pre-set normalization parameter. The acceleration term is only used when the voltage difference between battery clusters gradually increases and accelerates.

[0121] Specifically, the cluster charge state difference term can be expressed as:

[0122] in, Due to the poor charge state of the cluster, This is a normalization parameter for the state of charge. For example, 10% can be used as an example of a normalization parameter for the state of charge.

[0123] Furthermore, without circulating current, the temperatures of the parallel battery cluster terminals (Temp_cluster_x(t)) are basically the same. However, if circulating current exists, the terminal temperatures of the battery clusters with circulating current are significantly higher than the average temperature (Temp_cluster_x(t)). Therefore, it is also necessary to monitor the relative temperatures of the battery cluster terminals. The terminal temperature difference term for the battery cluster is:

[0124] in, For terminal temperature difference, This is a normalized parameter for terminal temperature. For example, 5°C can be used as an example of a normalized parameter for terminal temperature.

[0125] In one embodiment, constructing the cost function based on the voltage difference term, voltage change rate term, voltage acceleration term, cluster state of charge difference term, and terminal temperature difference term of each battery cluster includes: constructing the cost function based on the weighted sum of the voltage difference term, voltage change rate term, voltage acceleration term, cluster state of charge difference term, and terminal temperature difference term of each battery cluster.

[0126] Specifically, corresponding weights can be set for the differential voltage, rate of change of voltage, voltage acceleration, cluster state of charge difference, and terminal temperature difference of each battery cluster. For example, 0.8 can be used as an example of the weights for the differential voltage, rate of change of voltage, voltage acceleration, and cluster state of charge difference, and 1 can be used as an example of the weight for the terminal temperature difference.

[0127] The cost function is further determined by weighting the terms of voltage difference, voltage change rate, voltage acceleration, cluster state of charge difference, and terminal temperature difference for each battery cluster. :

[0128] in, , , , , These are the voltage difference term, voltage change rate term, voltage acceleration term, cluster state of charge difference term, and terminal temperature difference term for the battery cluster. , , , , These are the weights corresponding to the differential pressure term, voltage change rate term, voltage acceleration term, cluster charge state difference term, and terminal temperature difference term, respectively. Let be the cost function of battery cluster x at time t. The value determined by substituting the numerical values ​​is the cost score. The higher the cost score, the worse the current state of the battery cluster, and the higher the priority of disconnecting and merging the cluster.

[0129] Specifically, after constructing the cost function using the above formula, the multi-dimensional risks are transformed into a quantifiable mathematical model. Then, the cost score for each battery cluster is calculated using this function. Finally, the cost score of each cluster is compared with a preset risk threshold. If the score of a battery cluster exceeds the threshold, it indicates that its voltage drop, state of charge difference, or terminal temperature difference has reached a level that may cause safety hazards such as circulating current or overheating. At this point, the energy management system will issue an instruction to disconnect the high-risk battery cluster from the DC bus of the energy storage system to prevent it from affecting the stable operation of the entire system. Of course, the preset risk threshold can also be divided into multiple different intervals, such as a medium-risk threshold and a high-risk threshold, to further determine the risk level of each battery cluster, thereby achieving precise switching of each battery cluster.

[0130] By determining and implementing off-grid switching control strategies based on the cluster's state of charge, this approach can tailor charging and discharging strategies to specific charging and discharging scenarios, ensuring that each battery cluster receives a balanced charging and discharging opportunity and mitigating the circulating current risk caused by widening energy differences between clusters. Furthermore, by combining parameters such as total voltage and terminal temperature, it can further implement intelligent switching strategies, achieving precise disconnection of high-risk battery clusters through risk quantification. This effectively solves the problems of delayed response, large circulating current, or significant energy loss during switching in existing methods, while also taking into account the operational safety, energy utilization efficiency, and battery cluster lifespan of the energy storage system, significantly improving the overall stability and reliability of parallel large-scale energy storage systems.

[0131] The above is a further explanation of step S30. Step S40 will be further explained below.

[0132] Specifically, after determining the corresponding grid-connected / off-grid switching control strategy in step S30, the energy management system executes the corresponding grid-connected / off-grid switching operation. For example, if it is in a charging state, it can be adapted to a rotating charging strategy; if it is in a discharging state, it can be adapted to a rotating discharging strategy; and for executing the intelligent switching strategy, it drives the circuit switch action of the corresponding battery cluster by issuing control commands, so as to realize the off-grid disconnection of high-risk battery clusters or the grid connection of battery clusters that meet the operating requirements, ensuring that the energy storage system avoids safety hazards such as circulating current and overheating during charging and discharging, while maintaining stable energy output and operating efficiency.

[0133] It should be noted that although the steps in the above embodiments are described in a specific order, those skilled in the art will understand that in order to achieve the effect of this application, different steps do not necessarily have to be executed in such an order. They can be executed simultaneously (in parallel) or in other orders, and these variations are all within the scope of protection of this application.

[0134] Furthermore, this application also provides a battery cluster on-grid / off-grid switching device.

[0135] See appendix Figure 3 , Figure 3 This is a main structural block diagram of a battery cluster on-grid / off-grid switching device according to an embodiment of this application.

[0136] like Figure 3 As shown, the battery cluster grid-connected / off-grid switching device in this embodiment mainly includes an acquisition module 11, a first determination module 12, a second determination module 13, and a switching module 14. In some embodiments, one or more of the acquisition module 11, the first determination module 12, the second determination module 13, and the switching module 14 can be combined into a single module.

[0137] In some embodiments, the acquisition module 11 may be configured to acquire the operating status information of each battery cluster, wherein the operating status information of each battery cluster includes at least the cluster state of charge.

[0138] The first determining module 12 can be configured to determine whether the energy storage system is in a charging or discharging state based on the operating status information of each battery cluster.

[0139] The second determining module 12 is configured to determine and implement an off-grid switching control strategy based on the cluster charge state when the energy storage system is in a charging / discharging state.

[0140] The switching module 14 is configured to control the battery cluster to perform grid-to-grid switching based on the grid-to-offline switching control strategy.

[0141] In one implementation, a description of the specific function can be found in steps S10-S40.

[0142] The aforementioned battery cluster on-grid / off-grid switching device is used to perform Figure 2 The battery cluster parallel-to-offline switching method embodiments shown are similar in technical principle, the technical problems solved, and the technical effects produced. Those skilled in the art can clearly understand that, for the sake of convenience and brevity, the specific working process and related descriptions of the battery cluster parallel-to-offline switching device can be found in the embodiments of the battery cluster parallel-to-offline switching method, and will not be repeated here.

[0143] Furthermore, it should be understood that since the various modules are only provided to illustrate the functional units of the device described in this application, the physical devices corresponding to these modules may be the processor itself, or a part of the processor's software, hardware, or a combination of both. Therefore, the number of modules shown in the figures is merely illustrative.

[0144] Those skilled in the art will understand that the various modules in the device can be adaptively split or combined. Such splitting or combining of specific modules will not cause the technical solution to deviate from the principles of this application; therefore, the technical solutions after splitting or combining will fall within the protection scope of this application.

[0145] Those skilled in the art will understand that all or part of the processes in the method of the above-described embodiment can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable file, or some intermediate form. The computer-readable storage medium can include any entity or device capable of carrying the computer program code, a medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory, a random access memory, an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0146] Furthermore, this application also provides an energy storage system, which includes at least an energy management system, the energy management system comprising:

[0147] At least one processor;

[0148] And, a memory communicatively connected to the at least one processor;

[0149] The memory stores a computer program that, when executed by the at least one processor, implements the aforementioned battery cluster and off-grid switching method.

[0150] See Figure 4 As shown, Figure 4 The structure of an energy management system is illustrated by way of example, wherein the energy management system includes a processor 100 and a memory 200.

[0151] Furthermore, this application also provides a computer-readable storage medium. In one embodiment of the computer-readable storage medium according to this application, the computer-readable storage medium can be configured to store a program that performs the battery cluster and off-grid switching method of the above-described method embodiments. This program can be loaded and run by a processor to implement the above-described battery cluster and off-grid switching method. For ease of explanation, only the parts related to the embodiments of this application are shown; for specific technical details not disclosed, please refer to the method section of the embodiments of this application. The computer-readable storage medium can be a memory device formed by various electronic devices. Optionally, in the embodiments of this application, the computer-readable storage medium is a non-transitory computer-readable storage medium.

[0152] The technical solution of this application has been described in conjunction with the specific embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of this application is obviously not limited to these specific embodiments. Without departing from the principles of this application, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of this application.

Claims

1. A method for switching battery clusters between parallel and off-grid operation, applied to an energy management system, characterized in that, The method includes: Obtain the operating status information of each battery cluster, wherein the operating status information of each battery cluster includes at least the cluster state of charge; Based on the operating status information of each battery cluster, it is determined whether the energy storage system is in a charging or discharging state; If so, determine and implement an off-grid switching control strategy based on the cluster charge state; Based on the aforementioned grid-connected / off-grid switching control strategy, the battery clusters are controlled to perform grid-connected / off-grid switching.

2. The battery cluster parallel-to-offline switching method according to claim 1, characterized in that, The operating status information of the battery cluster also includes the current of the battery cluster; determining whether the energy storage system is in a charging / discharging state based on the operating status information of the battery cluster includes: Obtain the operating instructions from the energy storage converter; When the current is detected flowing from the external load to the battery cluster and the operating command of the energy storage converter is a charging command, it is determined that the energy storage system is in a charging state. When the current is detected flowing from the battery cluster to the external load and the operating command of the energy storage converter is a discharge command, it is determined that the energy storage system is in a discharge state.

3. The battery cluster parallel-to-offline switching method according to claim 1, characterized in that, The grid-connected / off-grid switching control strategy includes a rotating charging strategy, a rotating discharging strategy, and an intelligent switching strategy; the grid-connected / off-grid switching control strategy determined based on the cluster charge state includes: When the energy storage system is in a charging state, it is determined whether the minimum cluster charge state is greater than or equal to the first charge state threshold, and whether the difference between the maximum cluster charge state and the minimum cluster charge state is less than or equal to the second charge state threshold; if so, the alternating charging strategy is executed, otherwise the intelligent switching strategy is executed. When the energy storage system is in a discharge state, it is determined whether the maximum cluster charge state is less than or equal to the third charge state threshold, and whether the difference between the maximum cluster charge state and the minimum cluster charge state is less than or equal to the second charge state threshold; if so, the alternating discharge strategy is executed, otherwise the intelligent switching strategy is executed.

4. The battery cluster parallel-to-offline switching method according to claim 3, characterized in that, The operating status information of the battery clusters also includes the total voltage of each battery cluster; The execution of the alternating charging strategy includes: The charging priority of each battery cluster is determined based on the total voltage of each battery cluster, where the lower the total voltage of the battery cluster, the higher the charging priority. Control the battery clusters with the highest charging priority to connect to the energy storage system for charging; When the total voltage of the battery cluster with the highest charging priority is higher than the total voltage of the battery cluster with the second highest charging priority, and the difference between the two total voltages exceeds a preset charging switching threshold, the battery cluster with the second highest charging priority is controlled to connect to the energy storage system for charging, and the battery cluster with the highest charging priority is disconnected. Repeat the above steps until all battery clusters are fully charged.

5. The battery cluster parallel-to-offline switching method according to claim 3, characterized in that, The operating status information of the battery clusters also includes the total voltage of each battery cluster; The execution of the alternating discharge strategy includes: The discharge priority of each battery cluster is determined based on the total voltage of each battery cluster, where the higher the total voltage of the battery cluster, the higher the discharge priority. The battery cluster with the highest discharge priority is connected to the energy storage system for discharge. When the total voltage of the battery cluster with the highest discharge priority is less than the total voltage of the battery cluster with the second highest discharge priority, and the difference between the two total voltages exceeds a preset discharge switching threshold, the battery cluster with the second highest discharge priority is controlled to connect to the energy storage system for discharge, and the battery cluster with the highest discharge priority is disconnected. Repeat the above steps until all battery clusters have been discharged.

6. The battery cluster parallel-to-offline switching method according to claim 3, characterized in that, The operating status information of the battery clusters also includes the total voltage and terminal temperature of each battery cluster; The execution of the intelligent switching strategy includes: The voltage difference, state of charge difference, and terminal temperature difference of each battery cluster are determined based on the total voltage, cluster state of charge, and terminal temperature of each battery cluster. A cost function is constructed based on the voltage difference, the difference in state of charge of each battery cluster, and the temperature difference at the terminals. The cost score for each battery cluster is calculated based on the cost function. Determine whether the cost score of each battery cluster is greater than a preset risk threshold; If so, the battery clusters with a cost score greater than a preset risk threshold will be removed from the energy storage system.

7. The battery cluster parallel-to-offline switching method according to claim 6, characterized in that, The cost function constructed based on the voltage difference, cluster state of charge difference, and terminal temperature difference of each battery cluster includes: The voltage change rate and voltage acceleration of each battery cluster are determined based on the voltage difference of each battery cluster. Based on the voltage difference, voltage change rate, voltage acceleration, cluster state of charge difference, and terminal temperature difference of each battery cluster, the voltage difference term, voltage change rate term, voltage acceleration term, cluster state of charge difference term, and terminal temperature difference term of each battery cluster are determined respectively. The cost function is constructed based on the voltage difference term, voltage change rate term, voltage acceleration term, cluster state of charge difference term, and terminal temperature difference term for each battery cluster.

8. The battery cluster parallel-to-offline switching method according to claim 7, characterized in that, The construction of the cost function based on the voltage difference term, voltage change rate term, voltage acceleration term, cluster state of charge difference term, and terminal temperature difference term of each battery cluster includes: constructing the cost function based on the weighted sum of the voltage difference term, voltage change rate term, voltage acceleration term, cluster state of charge difference term, and terminal temperature difference term of each battery cluster.

9. An energy storage system, characterized in that, The energy storage system includes at least an energy management system, which includes: At least one processor; And, a memory communicatively connected to the at least one processor; The memory stores a computer program, which, when executed by the at least one processor, implements the battery cluster and off-grid switching method as described in any one of claims 1 to 8.

10. A computer-readable storage medium storing a plurality of program codes, characterized in that, The program code is adapted to be loaded and run by a processor to perform the battery cluster and off-grid switching method as described in any one of claims 1 to 8.

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