Parallel circulating current regulation method for multi-branch battery cluster based on voltage dynamic balancing

Abstract

The application discloses a multi-branch battery cluster parallel circulating current regulation method based on voltage dynamic balancing, relates to the technical field of energy storage battery management and control, and comprises the following steps: acquiring cluster terminal voltage sampling values of parallel battery clusters of an energy storage system and the state of a main loop relay; inputting a plurality of sets of cluster terminal voltage sampling values into an improved voltage difference comparison algorithm to complete pairwise difference calculation and generate a cluster-to-cluster voltage difference value set; the improved algorithm dynamically adjusts difference calculation weights according to the rated voltage grades of the battery clusters; and then, according to the maximum voltage difference value in the cluster-to-cluster voltage difference value set, the preset multi-level threshold interval is matched, and three parallel connection states, namely, direct connection of the battery cluster, pre-charging connection of the battery cluster and prohibition of the battery cluster from being connected, are determined. The scheme is suitable for voltage evaluation requirements of different rated voltage battery clusters, can finely divide the connection working conditions of the battery clusters, and improves the circulating current disturbance problem of the parallel operation of the multi-battery clusters.

Description

Technical Field

[0001] This invention belongs to the field of energy storage battery management technology, specifically a method for regulating the parallel circulating current of multiple battery clusters based on dynamic voltage balancing. Background Technology

[0002] Energy storage systems often employ a parallel network operation mode for multiple battery clusters to meet the application requirements of large-capacity energy storage and grid-connected output. The industry commonly analyzes inter-cluster voltage differences by collecting battery cluster terminal voltage data and using a fixed-weight voltage difference comparison method, relying on a single voltage threshold standard to determine the switching status of battery clusters. However, traditional voltage difference comparison algorithms use uniform fixed calculation weights, failing to consider the actual operating conditions where different models and specifications of battery clusters have different rated voltage levels. Therefore, the quantification of voltage differences cannot accurately reflect the electrical operating characteristics of battery clusters with different voltage levels.

[0003] Single-threshold judgment modes can only simply classify battery clusters into two operating conditions: connection and disconnection. They cannot make fine-grained distinctions based on the magnitude of voltage differences between clusters. Voltage mismatch during parallel battery cluster operation can easily induce circulating currents in the branches. Continuous circulating current disturbances will cause uneven charging and discharging of individual cells within the battery cluster, accelerating battery aging and degradation, and also reducing the overall stability of the energy storage system operating in parallel with multiple branches. Conventional technologies cannot flexibly adjust the voltage difference calculation weights for battery clusters with different rated voltage levels, limiting the accuracy of voltage difference assessment. They also lack multi-level threshold interval classification judgment logic, making it difficult to perform hierarchical and detailed control over the parallel connection status of battery clusters. Summary of the Invention

[0004] This invention aims to solve at least one of the technical problems existing in the prior art; To address this, the present invention proposes a method for regulating the parallel circulating current of multi-branch battery clusters based on dynamic voltage balancing, comprising: Acquire the sampled values ​​of the cluster terminal voltage and the status of the main circuit relays for each of the multiple battery clusters operating in parallel in the energy storage system; The sampled values ​​of the cluster-end voltage of the multiple battery clusters are input into an improved voltage difference comparison algorithm to calculate the difference between each pair of clusters, thereby generating a set of inter-cluster voltage differences. The improved voltage difference comparison algorithm dynamically adjusts the calculation weight of the difference based on the rated voltage level of the battery cluster. Based on the maximum voltage difference in the set of inter-cluster voltage differences and the preset multi-level threshold range, the parallel access state of the multiple battery clusters is determined. The parallel access state includes direct access state, pre-charge access state, and prohibited access state.

[0005] Further, the step of inputting the sampled values ​​of the cluster-end voltages of the multiple battery clusters into an improved voltage difference comparison algorithm for pairwise difference calculation to generate a set of inter-cluster voltage differences specifically includes: Read the rated voltage level parameter of each of the plurality of battery clusters, and convert the rated voltage level parameter of each battery cluster into a reference voltage per unit value; The reciprocal of the per-unit value of the reference voltage is used as the dynamic weighting coefficient of the improved voltage difference comparison algorithm. The dynamic weighting coefficient is weighted with the sampled value of the cluster terminal voltage of the corresponding battery cluster to generate a weighted cluster terminal voltage value. Perform absolute value operations on all possible pairwise combinations of differences on the weighted cluster terminal voltage values, and take the result of each absolute value operation as an inter-cluster voltage difference element; Arrange all inter-cluster voltage difference elements according to the physical connection topology of the multiple battery clusters to generate the inter-cluster voltage difference set.

[0006] Furthermore, the improved voltage difference comparison algorithm, which dynamically adjusts the calculation weight of the difference based on the rated voltage level of the battery cluster, specifically includes the following steps: The rated voltage value of the battery cluster with the highest rated voltage level among the multiple battery clusters is obtained as the reference voltage value; For each of the plurality of battery clusters, the ratio of the rated voltage value of the battery cluster to the reference voltage value is calculated, and the reciprocal of the ratio is used as the voltage weighting factor of the battery cluster. When calculating the voltage difference between any two battery clusters, the first voltage weighting factor of the first battery cluster and the second voltage weighting factor of the second battery cluster are extracted. The product of the sampled value of the cluster terminal voltage of the first battery cluster and the first voltage weighting factor is used as the first weighted voltage value, and the product of the sampled value of the cluster terminal voltage of the second battery cluster and the second voltage weighting factor is used as the second weighted voltage value. Calculate the absolute value of the difference between the first weighted voltage value and the second weighted voltage value, and use the absolute value as the inter-cluster voltage difference between any two battery clusters.

[0007] Further, the step of determining the parallel connection status of the multiple battery clusters based on the maximum voltage difference in the set of inter-cluster voltage differences and the preset multi-level threshold interval specifically includes: Iterate through all inter-cluster voltage difference elements in the set of inter-cluster voltage difference values, and select the inter-cluster voltage difference with the largest value as the maximum voltage difference value. Read a pre-configured first voltage threshold and a second voltage threshold, wherein the first voltage threshold is less than the second voltage threshold; The maximum voltage difference is compared with the first voltage threshold. When the maximum voltage difference is less than the first voltage threshold, the parallel connection state is determined to be the direct connection state. When the maximum voltage difference is greater than or equal to the first voltage threshold and less than the second voltage threshold, the parallel connection state is determined as the pre-charge connection state. When the maximum voltage difference is greater than or equal to the second voltage threshold, the parallel connection state is determined to be the prohibited connection state.

[0008] Furthermore, when the parallel access state is the direct access state, the following steps are performed, specifically including: Send a closing command to the main circuit relay of each of the plurality of battery clusters, so that the main circuit relay of each battery cluster closes simultaneously; After the main circuit relay is closed, the real-time circulating current value of the multiple battery clusters is continuously collected; The real-time circulating current value of each battery cluster is compared with the preset circulating overcurrent protection threshold. When the real-time circulating current value of any battery cluster exceeds the circulating overcurrent protection threshold, the main circuit relay of the battery cluster is disconnected and the battery cluster is marked as a fault isolation cluster. The fault isolation cluster is removed from the plurality of battery clusters, the inter-cluster voltage difference set of the remaining battery clusters is recalculated, and the parallel access status is updated according to the recalculated inter-cluster voltage difference set.

[0009] Furthermore, the step of continuously acquiring the real-time circulating current values ​​of the multiple battery clusters after the main circuit relay is closed specifically includes: After the main circuit relay closing command is issued, the delay timer is started; When the delay timer reaches the preset relay stable operation delay, the current value flowing through each battery cluster is synchronously collected by the DC current sensor installed at the positive or negative terminal of each battery cluster. The net circulating current value of each battery cluster is obtained by subtracting the pre-calibrated load current component of each battery cluster from the current value collected from each battery cluster. The net circulating current value of each battery cluster is used as the real-time circulating current value and stored in the circular data buffer for subsequent comparison and judgment.

[0010] Furthermore, when the parallel access state is the pre-charge access state, the following steps are performed, specifically including: Identify the two target battery clusters that generate the maximum voltage difference in the set of inter-cluster voltage differences, mark the battery cluster with the lower cluster terminal voltage sampling value as the battery cluster to be precharged, and mark the battery cluster with the higher cluster terminal voltage sampling value as the reference battery cluster; Send a disconnect command to the main circuit relay of the battery cluster to be precharged, and send a closing command to the precharge relay of the battery cluster to be precharged, so that the battery cluster to be precharged is connected to the DC bus through the precharge resistor; After the precharge relay is closed, the real-time terminal voltage of the battery cluster to be precharged is continuously collected, and the real-time terminal voltage is compared with the cluster terminal voltage sample value of the reference battery cluster. When the difference between the real-time terminal voltage and the sampled value of the cluster terminal voltage of the reference battery cluster is less than the preset precharge completion voltage threshold, a disconnect command is sent to the precharge relay of the battery cluster to be precharged, and a closing command is sent to the main circuit relay of the battery cluster to be precharged.

[0011] Further, after sending a closing command to the precharge relay of the battery cluster to be precharged, so that the battery cluster to be precharged is connected to the DC bus through the precharge resistor, the following steps are also performed, specifically including: Start the precharge timer to record the precharge duration of the battery cluster to be precharged; The precharge duration is compared with the preset maximum allowable precharge duration; When the precharge duration reaches the maximum allowable precharge duration and the difference between the real-time terminal voltage and the cluster terminal voltage sampling value of the reference battery cluster is still greater than or equal to the precharge completion voltage threshold, a disconnection command is sent to the precharge relay of the battery cluster to be precharged. The battery cluster to be precharged is marked as a precharge timeout fault cluster, and the parallel access state is switched to the access prohibited state; A precharge timeout alarm signal is generated, which carries the cluster identifier of the battery cluster to be precharged and the value of the real-time terminal voltage.

[0012] Furthermore, when the parallel access state is the prohibited access state, the following steps are performed, specifically including: Send a disconnect command to the main circuit relays and precharge relays of all battery clusters in the plurality of battery clusters to completely isolate the plurality of battery clusters from the DC bus; Scan all inter-cluster voltage difference elements in the inter-cluster voltage difference set that exceed the second voltage threshold, and extract the cluster identifiers of the two battery clusters corresponding to each inter-cluster voltage difference element that exceeds the second voltage threshold; A list of prohibited battery clusters is generated based on all extracted cluster identifiers, and the list of prohibited battery clusters is output to the energy storage system controller. The sampled value of the cluster terminal voltage of each battery cluster in the list of prohibited battery clusters is periodically re-acquired, and the inter-cluster voltage difference between battery clusters in the list of prohibited battery clusters is recalculated. When the recalculated inter-cluster voltage difference is less than the second voltage threshold, the corresponding battery cluster is removed from the list of prohibited battery clusters, and the parallel access status is redefined.

[0013] Furthermore, the method also includes a multi-battery cluster sequential pre-charging step performed after determining that the parallel access state is a pre-charging access state, specifically including: The battery cluster with the lowest cluster-end voltage sampling value is selected from the plurality of battery clusters as the first pre-charge target; Perform a separate precharge operation on the first precharge object to raise the terminal voltage of the first precharge object to be equal to the terminal voltage of the battery cluster with the lowest terminal voltage sample value in the remaining battery clusters; The first pre-charged object is marked as a battery cluster that has completed pre-charging, and the battery cluster with the lowest current terminal voltage is selected from the remaining battery clusters as the next pre-charged object. Repeat the individual pre-charge and marking operations until the maximum difference between the terminal voltages of all battery clusters is less than the first voltage threshold. Simultaneously send a closing command to the main circuit relays of all battery clusters.

[0014] Compared with the prior art, the beneficial effects of the present invention are: The voltage difference comparison algorithm dynamically adjusts the calculation weights based on the rated voltage level of each battery cluster during pairwise difference calculations, changing the conventional fixed-weight uniform calculation mode. The difference calculation rules are adaptable to the inherent electrical parameters of battery clusters with different voltage levels. The quantification of voltage deviation aligns with the operating parameter characteristics of the equipment itself, and the raw voltage sampling data can be accurately analyzed, effectively avoiding numerical deviations caused by fixed-weight calculations. The true numerical characteristics of inter-cluster voltage differences are fully presented, and the voltage state analysis aligns with the actual operating conditions of multiple parallel branches in the energy storage system, continuously improving the objectivity and analytical accuracy of voltage difference statistics.

[0015] Based on the maximum voltage difference in the set of inter-cluster voltage differences, three parallel connection states of battery clusters are defined using preset multi-level threshold intervals, moving away from the traditional approach of using a single threshold for only two operating conditions. The multi-level threshold intervals create a gradient division of the voltage difference range, allowing different amplitude voltage differences to be matched with corresponding access control logic, achieving layered and refined management of battery cluster switching states. Differences in electrical parameters within multi-branch parallel circuits are gradient-regulated, gradually aligning the electrical operating parameters of each branch. Internal electrical disturbances are orderly smoothed, and disordered fluctuations in branch circulating currents are gently constrained. The electrical coupling state of parallel battery cluster operation remains regular, and the electrical adaptability and operational coordination of multi-branch battery cluster network operation remain stable. Attached Figure Description

[0016] Figure 1 This is a flowchart of the multi-branch battery cluster parallel circulating current regulation method based on voltage dynamic balancing described in this invention; Figure 2 A flowchart for dynamically adjusting the weights of the difference calculation; Figure 3 This is a flowchart for the control of parallel connection of battery clusters and the isolation of circulating current faults. Detailed Implementation

[0017] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] See Figure 1The specific implementation scheme of the multi-branch battery cluster parallel circulating current regulation method based on voltage dynamic balancing is as follows: The sampled values ​​of the cluster-end voltages and the status of the main circuit relays of multiple battery clusters operating in parallel in the energy storage system are obtained. The sampled values ​​of the cluster-end voltages can be acquired in real time at the DC output terminal of the battery clusters through voltage sensors. The status of the main circuit relays reflects the on / off status of the main circuit between each battery cluster and the DC bus. The sampled values ​​of the cluster-end voltages of multiple battery clusters are input into an improved voltage difference comparison algorithm for pairwise difference calculation, generating a set of inter-cluster voltage difference values. This improved voltage difference comparison algorithm dynamically adjusts the calculation weight of the difference values ​​according to the rated voltage level of the battery clusters, making the voltage difference values ​​between battery clusters with different rated voltage levels comparable. Based on the maximum voltage difference in the set of inter-cluster voltage differences and the preset multi-level threshold range, the parallel access status of multiple battery clusters is determined. The parallel access status includes direct access status, pre-charge access status, and prohibited access status. Direct access status means that the voltage difference of all battery clusters is small and they can be connected in parallel immediately. Pre-charge access status means that the battery cluster with the lower voltage needs to be pre-charged to increase its voltage before it can be connected. Prohibited access status means that the voltage difference is too large and parallel connection cannot be safe.

[0019] In one embodiment of the present invention, the rated voltage level parameters of each battery cluster in multiple battery clusters are read, and the rated voltage level parameters of each battery cluster are converted into a reference voltage per-unit value. The reference voltage per-unit value is a dimensionless value obtained by normalizing the rated voltage with a pre-selected reference voltage as a reference. The reciprocal of the reference voltage per-unit value is used as the dynamic weighting coefficient of the improved voltage difference comparison algorithm. The dynamic weighting coefficient is weighted with the cluster terminal voltage sampling value of the corresponding battery cluster to generate a weighted cluster terminal voltage value. The weighting method is a multiplication operation, that is, the dynamic weighting coefficient is multiplied by the cluster terminal voltage sampling value. The absolute value difference operation is performed on all possible pairwise combinations of the weighted cluster terminal voltage values. The result of each absolute value difference operation is used as an inter-cluster voltage difference element. The absolute value difference operation means taking the absolute value of the difference between two weighted cluster terminal voltage values. All inter-cluster voltage difference elements are arranged according to the physical connection topology order of multiple battery clusters to generate an inter-cluster voltage difference set. The physical connection topology order is determined by the numbering order determined by the actual parallel connection position of the battery clusters in the energy storage system.

[0020] See Figure 2The process involves obtaining the rated voltage of the battery cluster with the highest rated voltage level from multiple battery clusters as a reference voltage value. This reference voltage value is used to normalize the voltage level differences among the various battery clusters. For each battery cluster, the ratio of its rated voltage value to the reference voltage value is calculated. The reciprocal of this ratio is used as the voltage weighting factor for that battery cluster. The voltage weighting factor ranges from 0 to 1, with lower rated voltage battery clusters having larger voltage weighting factors. When calculating the voltage difference between any two battery clusters, a first voltage weighting factor for the first battery cluster and a second voltage weighting factor for the second battery cluster are extracted. The product of the cluster terminal voltage sample value of the first battery cluster and the first voltage weighting factor is used as the first weighted voltage value, and the product of the cluster terminal voltage sample value of the second battery cluster and the second voltage weighting factor is used as the second weighted voltage value. The absolute value of the difference between the first weighted voltage value and the second weighted voltage value is calculated, and this absolute value is used as the inter-cluster voltage difference between any two battery clusters. This inter-cluster voltage difference reflects the equivalent voltage difference after voltage level normalization.

[0021] In practical implementation, taking an energy storage system containing three battery clusters as an example scenario, the three battery clusters are designated as the first, second, and third battery clusters. The rated voltage level parameters of the first, second, and third battery clusters are 800 volts, and 400 volts, respectively. The rated voltage level parameters of each of the three battery clusters are read and converted into a reference voltage per-unit value. The reference voltage per-unit value is calculated using 800 volts as the reference voltage value. The rated voltage level parameter of the first battery cluster (800 volts) is divided by the reference voltage value of 800 volts to obtain a reference voltage per-unit value of 1. The rated voltage level parameter of the second battery cluster (800 volts) is divided by the reference voltage value of 800 volts to obtain a reference voltage per-unit value of 1. The rated voltage level parameter of the third battery cluster (400 volts) is divided by the reference voltage value of 800 volts to obtain a reference voltage per-unit value of 0.5. The reciprocal of the per-unit value of the reference voltage is used as the dynamic weighting coefficient for the improved voltage difference comparison algorithm. The dynamic weighting coefficient for the first battery cluster is 1 divided by 1, which equals 1; the dynamic weighting coefficient for the second battery cluster is 1 divided by 1, which equals 1; and the dynamic weighting coefficient for the third battery cluster is 1 divided by 0.5, which equals 2. The dynamic weighting coefficient is weighted with the sampled value of the cluster terminal voltage of the corresponding battery cluster to generate a weighted cluster terminal voltage value. Assuming the sampled value of the cluster terminal voltage of the first battery cluster is 780 volts, the weighted cluster terminal voltage value is 1 multiplied by 780, which equals 780 volts; the sampled value of the cluster terminal voltage of the second battery cluster is 775 volts, which equals 1 multiplied by 775, which equals 775 volts; and the sampled value of the cluster terminal voltage of the third battery cluster is 380 volts, which equals 2 multiplied by 380, which equals 760 volts. Perform absolute value calculations on the differences between all possible pairwise combinations of the weighted cluster terminal voltage values. The result of each absolute value calculation is taken as an inter-cluster voltage difference element. All possible pairwise combinations include the combination of the first battery cluster and the second battery cluster, the combination of the first battery cluster and the third battery cluster, and the combination of the second battery cluster and the third battery cluster. The absolute value of the difference between the first battery cluster and the second battery cluster is 780 minus 775, which equals 5 volts. The absolute value of the difference between the first battery cluster and the third battery cluster is 780 minus 760, which equals 20 volts. The absolute value of the difference between the second battery cluster and the third battery cluster is 775 minus 760, which equals 15 volts. Arrange all inter-cluster voltage difference elements according to the physical connection topology of multiple battery clusters. The physical connection topology is the parallel connection order of the first battery cluster, the second battery cluster, and the third battery cluster on the DC bus. The resulting set of inter-cluster voltage differences is {[first battery cluster, second battery cluster]: 5V, [first battery cluster, third battery cluster]: 20V, [second battery cluster, third battery cluster]: 15V}.

[0022] In some embodiments, the rated voltage value of the battery cluster with the highest rated voltage level among multiple battery clusters is obtained as the reference voltage value. For the three battery clusters mentioned above, the highest rated voltage level is 800 volts, therefore the reference voltage value is 800 volts. For each of the multiple battery clusters, the ratio of the rated voltage value of that battery cluster to the reference voltage value is calculated. The ratio for the first battery cluster is 800 divided by 800, which equals 1; the ratio for the second battery cluster is 800 divided by 800, which equals 1; and the ratio for the third battery cluster is 400 divided by 800, which equals 0.5. The reciprocal of the ratio is used as the voltage weighting factor for that battery cluster. The voltage weighting factor for the first battery cluster is 1 divided by 1, which equals 1; the voltage weighting factor for the second battery cluster is 1 divided by 1, which equals 1; and the voltage weighting factor for the third battery cluster is 1 divided by 0.5, which equals 2. When calculating the voltage difference between any two battery clusters, for example, calculating the voltage difference between the first and third battery clusters, the first voltage weighting factor for the first battery cluster is extracted as 1, and the second voltage weighting factor for the third battery cluster is extracted as 2. The product of the sampled voltage value of the first battery cluster (780 volts) and the first voltage weighting factor 1 is used as the first weighted voltage value to obtain 780 volts. The product of the sampled voltage value of the third battery cluster (380 volts) and the second voltage weighting factor 2 is used as the second weighted voltage value to obtain 760 volts. The absolute value of the difference between the first weighted voltage value (780 volts) and the second weighted voltage value (760 volts) is calculated to obtain 20 volts. This absolute value of 20 volts is used as the inter-cluster voltage difference between the first and third battery clusters.

[0023] Optionally, the following formula is used to uniformly express the calculation of the voltage difference between battery clusters:

[0024] in: This represents the inter-cluster voltage difference between the i-th and j-th battery clusters. This represents the sampled value of the cluster terminal voltage of the i-th battery cluster. This represents the sampled value of the cluster terminal voltage of the j-th battery cluster. This indicates the rated voltage value of the battery cluster with the highest rated voltage level among multiple battery clusters. This represents the rated voltage level parameter of the i-th battery cluster. This represents the rated voltage level parameter of the j-th battery cluster.

[0025] In some embodiments, when the rated voltage level parameters of the battery cluster have multiple different values, the reference voltage value in the above formula is taken as the maximum value among all rated voltage level parameters. Continuing with the example of an energy storage system composed of a first battery cluster, a second battery cluster, and a third battery cluster, the rated voltage level parameters of the first battery cluster are 800 volts, the second battery cluster are 800 volts, and the third battery cluster is 400 volts, with a reference voltage value of 800 volts. For the first battery cluster, Volt, voltage weighting factor For the third battery cluster, Volt, voltage weighting factor If the sampled value of the cluster terminal voltage of the first battery cluster... The sampled value of the cluster terminal voltage of the third battery cluster. If it lies dormant, then Fu.

[0026] It is understandable that when all battery clusters have the same rated voltage level, the voltage weighting factor for each battery cluster is 1. In this case, the inter-cluster voltage difference is directly equal to the absolute value of the difference between the sampled voltage values ​​at the two cluster terminals. For example, if the first and second battery clusters mentioned above both have a rated voltage level of 800 volts, the sampled voltage value at the cluster terminal of the first battery cluster is 780 volts, and the sampled voltage value at the cluster terminal of the second battery cluster is 775 volts, then the inter-cluster voltage difference is... Fu.

[0027] Optionally, in the process of generating the set of inter-cluster voltage differences, for an energy storage system with N battery clusters, it is necessary to calculate... The inter-cluster voltage difference element is calculated according to the formula above. When the energy storage system contains four battery clusters, these four clusters are designated as the fourth, fifth, sixth, and seventh battery clusters. The rated voltage levels of the fourth, fifth, sixth, and seventh battery clusters are all 1000 volts, 500 volts, and 500 volts, respectively, with a reference voltage of 1000 volts. The voltage weighting factor for the fourth battery cluster is 1000 divided by 1000, which equals 1; for the fifth battery cluster, it is 1; for the sixth battery cluster, it is 1000 divided by 500, which equals 2; and for the seventh battery cluster, it is 2. If the sampled value of the cluster terminal voltage of the fourth battery cluster is 990 volts, the sampled value of the cluster terminal voltage of the fifth battery cluster is 985 volts, the sampled value of the cluster terminal voltage of the sixth battery cluster is 480 volts, and the sampled value of the cluster terminal voltage of the seventh battery cluster is 470 volts, then the weighted cluster terminal voltage values ​​are 990 volts, 985 volts, 960 volts, and 940 volts, respectively. The absolute value of the difference between all pairs of combinations constitutes the set of inter-cluster voltage difference values.

[0028] It is understandable that the improved voltage difference comparison algorithm maps battery clusters of different voltage levels to a unified reference voltage per-unit space for comparison using dynamic weighting coefficients. Each element in the inter-cluster voltage difference set is a dimensionless equivalent voltage difference, which is related to both the actual voltage difference and the rated voltage level of the battery cluster. For a battery cluster with a rated voltage level of 400 volts, the variation in its cluster terminal voltage sampling value is amplified by a factor of two after weighting, ensuring that voltage fluctuations in low-voltage-level battery clusters receive the same sensitivity when compared with high-voltage-level battery clusters.

[0029] In one embodiment of the present invention, all inter-cluster voltage difference elements in the inter-cluster voltage difference set are traversed, and the inter-cluster voltage difference with the largest value is selected as the maximum voltage difference. The traversal operation involves sequentially accessing each element in the set and recording the current maximum value. A pre-configured first voltage threshold and a second voltage threshold are read. The first voltage threshold is less than the second voltage threshold. The first and second voltage thresholds are pre-stored in the controller parameter table based on the rated voltage and safe circulating current limit of the DC bus of the energy storage system. The maximum voltage difference is compared with the first voltage threshold. When the maximum voltage difference is less than the first voltage threshold, the parallel connection state is determined to be a direct connection state, indicating that the terminal voltage difference of all battery clusters is small enough to allow direct closure of the main circuit relay for parallel operation. When the maximum voltage difference is greater than or equal to the first voltage threshold and less than the second voltage threshold, the parallel connection state is determined to be a pre-charge connection state, indicating that the battery clusters with lower voltage need to be pre-charged to reduce the voltage difference. When the maximum voltage difference is greater than or equal to the second voltage threshold, the parallel connection state is determined to be a prohibited connection state, indicating that the voltage difference is too large to be eliminated by pre-charging, posing a safety risk to the parallel connection.

[0030] In practical implementation, taking an energy storage system containing four battery clusters as an example scenario, the four battery clusters are designated as the first, second, third, and fourth battery clusters. The inter-cluster voltage difference set calculated by the improved voltage difference comparison algorithm contains six inter-cluster voltage difference elements: 8 volts between the first and second battery clusters, 12 volts between the first and third battery clusters, 25 volts between the first and fourth battery clusters, 4 volts between the second and third battery clusters, 17 volts between the second and fourth battery clusters, and 13 volts between the third and fourth battery clusters. The algorithm iterates through all inter-cluster voltage difference elements in the set, visiting each element sequentially and comparing the currently visited value with the recorded maximum value. The inter-cluster voltage difference with the largest value is selected as the maximum voltage difference. Since the largest value among the six elements is 25 volts, the maximum voltage difference is 25 volts.

[0031] In some embodiments, a pre-configured first voltage threshold and a second voltage threshold are read. The first voltage threshold is 10 volts, and the second voltage threshold is 20 volts. The first voltage threshold of 10 volts is less than the second voltage threshold of 20 volts. The maximum voltage difference of 25 volts is compared with the first voltage threshold of 10 volts. Since 25 volts is greater than 10 volts, the maximum voltage difference is not less than the first voltage threshold. The maximum voltage difference of 25 volts is then compared with the second voltage threshold of 20 volts. Since 25 volts is greater than 20 volts, the maximum voltage difference is greater than or equal to the second voltage threshold. Based on the comparison result, the parallel connection state is determined to be a prohibited connection state. The prohibited connection state indicates that the voltage difference between the four battery clusters is too large to be safely connected in parallel.

[0032] Optionally, the logic for determining the parallel connection status can be expressed using the following formula: in: Indicates parallel connection status. Indicates direct access status. Indicates pre-charging connection status. This indicates that access is prohibited. This represents the maximum voltage difference in the set of inter-cluster voltage differences. Indicates the first voltage threshold. This indicates the second voltage threshold.

[0033] In another example scenario, the energy storage system comprises three battery clusters. The maximum voltage difference between the clusters is 7 volts, the first voltage threshold is 10 volts, and the second voltage threshold is 20 volts. Comparing the maximum voltage difference of 7 volts with the first voltage threshold of 10 volts, 7 volts is less than 10 volts. Therefore, the maximum voltage difference is less than the first voltage threshold, and the parallel connection state is determined to be a direct connection state. The direct connection state means that the three battery clusters can directly close the main circuit relay for parallel operation.

[0034] In another example scenario, the energy storage system comprises five battery clusters. The maximum voltage difference between the clusters is 15 volts, the first voltage threshold is 10 volts, and the second voltage threshold is 20 volts. Comparing the maximum voltage difference of 15 volts with the first voltage threshold of 10 volts, 15 volts is greater than 10 volts, therefore the maximum voltage difference is greater than or equal to the first voltage threshold. Continuing to compare the maximum voltage difference of 15 volts with the second voltage threshold of 20 volts, 15 volts is less than 20 volts, therefore the maximum voltage difference is less than the second voltage threshold. The parallel connection state is determined to be a pre-charge connection state, which means that the battery clusters with lower voltages need to be pre-charged before being connected to the DC bus.

[0035] It is understood that the specific values ​​of the first and second voltage thresholds are pre-configured and stored in the parameter storage unit of the energy storage system controller based on the DC bus voltage level of the energy storage system, the rated capacity of the battery cluster, and the allowable circulating current capability of the main circuit relay. For an energy storage system with a rated voltage of 1500 volts, the first voltage threshold is configured as 15 volts and the second voltage threshold is configured as 30 volts; for an energy storage system with a rated voltage of 400 volts, the first voltage threshold is configured as 5 volts and the second voltage threshold is configured as 10 volts.

[0036] In one embodiment of the present invention, when the parallel access state is the direct access state, see [reference]. Figure 3A closing command is sent to the main circuit relay of each of the multiple battery clusters, causing the main circuit relays of each battery cluster to close simultaneously. The closing command outputs a switching signal through the relay drive circuit to energize the relay coil. After the main circuit relays close, the real-time circulating current value of multiple battery clusters is continuously collected. The real-time circulating current value reflects the magnitude of the circulating current caused by voltage differences between battery clusters. The real-time circulating current value of each battery cluster is compared with a preset circulating current overcurrent protection threshold, which is preset based on the rated current of the battery cluster and the relay contact capacity. When the real-time circulating current value of any battery cluster exceeds the circulating current overcurrent protection threshold, the main circuit relay of that battery cluster is disconnected, and the battery cluster is marked as a fault-isolated cluster. A fault-isolated cluster indicates that the battery cluster is excluded from parallel operation due to circulating current overcurrent. The fault-isolated cluster is removed from the multiple battery clusters, the inter-cluster voltage difference set of the remaining battery clusters is recalculated, and the parallel connection status is updated based on the recalculated inter-cluster voltage difference set. The updated parallel connection status is used to guide the parallel connection operation of the remaining battery clusters.

[0037] After the main circuit relay closes, a delay timer is started to wait for the main circuit relay to complete its mechanical action. Once the delay timer reaches the preset relay stabilization delay, the current value flowing through each battery cluster is synchronously collected using DC current sensors installed at the positive or negative terminal of each battery cluster. The relay stabilization delay is set according to the relay model's pull-in time parameter. Synchronous collection means reading the output values ​​of all DC current sensors at the same time. The net circulating current value of each battery cluster is obtained by subtracting the pre-calibrated load current component from the current value collected from each battery cluster. The load current component is the active current component that supplies power from the battery cluster to the load. The pre-calibration is achieved through offline testing to obtain load current distribution coefficients under different operating conditions. The net circulating current value of each battery cluster is used as the real-time circulating current value and stored in a circular data buffer for subsequent comparison and judgment. The circular data buffer uses a first-in-first-out storage structure to store circulating current data from the most recent sampling periods.

[0038] In practical implementation, an energy storage system comprising three battery clusters is used as an example scenario. These three battery clusters are designated as the first, second, and third battery clusters, and their parallel connection is defined as a direct connection. Closing commands are sent to the main circuit relays of the first, second, and third battery clusters simultaneously, causing all three main circuit relays to close. The three battery clusters are then connected in parallel to the DC bus via their main circuits. After the main circuit relays close, the real-time circulating current values ​​of the three battery clusters are continuously collected. These real-time circulating current values ​​are collected at a sampling frequency of 1000 times per second by a DC current sensor installed at the positive terminal of each battery cluster. The real-time circulating current value of the first battery cluster is compared with a preset circulating current overcurrent protection threshold, set to 50 amps; the real-time circulating current value of the second and third battery clusters is also compared with 50 amps. When the real-time circulating current of the second battery cluster reaches 65 amps, exceeding the circulating overcurrent protection threshold of 50 amps, the main circuit relay of the second battery cluster is disconnected, and the second battery cluster is marked as a fault-isolated cluster. The second battery cluster, marked as fault-isolated, is removed from the three battery clusters, leaving the first and third battery clusters. The inter-cluster voltage difference between the first and third battery clusters is recalculated, and the parallel connection status is updated based on the recalculated inter-cluster voltage difference. The updated parallel connection status guides the subsequent parallel operation of the first and third battery clusters.

[0039] In some embodiments, the specific steps for continuously acquiring real-time circulating current values ​​after the main circuit relay is closed are described. After the main circuit relay closing command is issued, a delay timer is started, with an initial value of zero and an incrementing count. When the delay timer reaches a preset relay stable operation delay of 50 milliseconds, the current value flowing through each battery cluster is synchronously acquired using DC current sensors installed at the positive terminal of each battery cluster. Synchronous acquisition means reading the output values ​​of the three DC current sensors at the same time. The net circulating current value of the first battery cluster is obtained by subtracting the pre-calibrated load current component of the first battery cluster from the current value acquired from the first battery cluster; the net circulating current value of the second battery cluster is obtained by subtracting the pre-calibrated load current component of the second battery cluster from the current value acquired from the second battery cluster; and the net circulating current value of the third battery cluster is obtained by subtracting the pre-calibrated load current component of the third battery cluster from the current value acquired from the third battery cluster. The net circulating current values ​​of the first battery cluster, the second battery cluster, and the third battery cluster are used as real-time circulating current values ​​and stored in a circular data buffer. The circular data buffer adopts a circular array structure with a length of 100, and each newly acquired net circulating current value overwrites the oldest data in the array.

[0040] Optionally, the net circulating current value can be calculated using the following formula: in: This represents the net circulating current value of the i-th battery cluster. This represents the current value flowing through the i-th battery cluster, collected by a DC current sensor installed at the positive terminal of the battery cluster bus. This represents the load current component of the pre-calibrated i-th battery cluster.

[0041] In practice, the process of pre-calibrating the load current component of each battery cluster is as follows: Under the condition that the energy storage system is operating stably under load and without circulating current, the output current of each battery cluster is measured, and the measured value is recorded as the load current component of that battery cluster. For the first battery cluster, the load current component measured under calibration conditions is 120 amps; for the second battery cluster, the load current component measured is 118 amps; and for the third battery cluster, the load current component measured is 122 amps. When the main circuit relay is closed, the current value of the first battery cluster is synchronously acquired to be 125 amps, the current value of the second battery cluster is 183 amps, and the current value of the third battery cluster is 135 amps. The net circulating current values ​​are calculated according to the formula. The net circulating current value of the first battery cluster is 125 amps minus 120 amps equals 5 amps. The net circulating current value of the second battery cluster is 183 amps minus 118 amps equals 65 amps. The net circulating current value of the third battery cluster is 135 amps minus 122 amps equals 13 amps.

[0042] It is understood that the preset value of the relay stabilization delay is related to the selected relay model. For mechanical DC relays, the stabilization delay is set to 50 milliseconds; for solid-state relays, the stabilization delay is set to 10 milliseconds. In the above example, the relay stabilization delay is set to 50 milliseconds, and the synchronous acquisition operation is started after the delay timer reaches 50 milliseconds. In some embodiments, when the net circulating current value of any battery cluster exceeds the circulating overcurrent protection threshold, a fault isolation operation is performed. Referring to Table 1, the net circulating current values ​​of the above three battery clusters and their comparison results with the circulating overcurrent protection threshold are recorded.

[0043] Table 1: Net circulating current values ​​and overcurrent judgment results for each battery cluster First battery cluster 5 50 no Keep closed Second battery cluster 65 50 yes Disconnect the main circuit relay and mark it as a fault isolation cluster. Third battery cluster 13 50 no Keep closed Optionally, a circular data buffer is used to store the net circulating current values ​​collected over multiple consecutive sampling periods, with each sampling period corresponding to one synchronous acquisition operation. When the circular data buffer is full, the newly written net circulating current value automatically overwrites the oldest net circulating current value in the buffer. For the three battery clusters in the example above, an independent circular data buffer is allocated to each battery cluster, with each buffer having a capacity of 100 sampling points. Each sampling point records the timestamp of the acquisition time and the corresponding net circulating current value.

[0044] It is understandable that after removing the fault-isolated cluster from multiple battery clusters, when recalculating the inter-cluster voltage difference set of the remaining battery clusters, the improved voltage difference comparison algorithm is only applied to the cluster-end voltage sample values ​​of the remaining battery clusters, and the voltage data of the battery clusters already marked as fault-isolated clusters are no longer included. In the example above, after removing the second battery cluster, the remaining first and third battery clusters are recalculated, and the inter-cluster voltage difference between the first and third battery clusters is updated based on the comparison results of the maximum voltage difference with the first and second voltage thresholds.

[0045] In one embodiment of the present invention, when the parallel connection state is a pre-charge connection state, two target battery clusters with the largest voltage difference in the inter-cluster voltage difference set are identified. The battery cluster with the lower cluster terminal voltage sampling value is marked as the battery cluster to be pre-charged, and the battery cluster with the higher cluster terminal voltage sampling value is marked as the reference battery cluster. The terminal voltage of the reference battery cluster is used as the target voltage value for pre-charging. A disconnect command is sent to the main circuit relay of the battery cluster to be pre-charged, and a closing command is sent to the pre-charge relay of the battery cluster to be pre-charged, so that the battery cluster to be pre-charged is connected to the DC bus through a pre-charge resistor. The pre-charge resistor is connected in series in the pre-charge circuit to limit the initial charging current. After the pre-charge relay is closed, the real-time terminal voltage of the battery cluster to be pre-charged is continuously collected, and the real-time terminal voltage is compared with the cluster terminal voltage sampling value of the reference battery cluster. The real-time terminal voltage is continuously collected at the DC output terminal of the battery cluster to be pre-charged by a voltage sensor. When the difference between the real-time terminal voltage and the sampled value of the terminal voltage of the reference battery cluster is less than the preset precharge completion voltage threshold, a disconnect command is sent to the precharge relay of the battery cluster to be precharged, and a closing command is sent to the main circuit relay of the battery cluster to be precharged. The precharge completion voltage threshold is calculated and determined based on the circulating current safety limit.

[0046] After sending a closing command to the precharge relay of the battery cluster to be precharged, connecting the battery cluster to the DC bus via the precharge resistor, a precharge timer is started to record the precharge duration of the battery cluster. The precharge timer begins counting the moment the precharge relay closes. The precharge duration is compared with a preset maximum allowable precharge duration, calculated based on the thermal capacity of the precharge resistor and the battery cluster's capacity. When the precharge duration reaches the maximum allowable precharge duration and the difference between the real-time terminal voltage and the sampled cluster terminal voltage of the reference battery cluster is still greater than or equal to the precharge completion voltage threshold, a disconnect command is sent to the precharge relay of the battery cluster to be precharged. The battery cluster to be precharged is marked as a precharge timeout fault cluster, and the parallel connection status is switched to a prohibited connection status. A precharge timeout fault cluster indicates that the battery cluster has an internal fault due to the inability to complete precharge for an extended period. A precharge timeout alarm signal is generated, carrying the cluster identifier and real-time terminal voltage value of the battery cluster to be precharged, for the energy storage system controller to record and report.

[0047] When parallel connection is prohibited, a disconnect command is sent to the main circuit relays and pre-charge relays of all battery clusters, completely isolating the battery clusters from the DC bus. The disconnect command outputs a switching signal through the relay drive circuit to de-energize the relay coils. The system scans the inter-cluster voltage difference set for all elements exceeding the second voltage threshold, extracting the cluster identifiers of the two battery clusters corresponding to each element exceeding the second voltage threshold. The scan operation iterates through each element in the inter-cluster voltage difference set and determines whether its value exceeds the second voltage threshold. A prohibited battery cluster list is generated based on all extracted cluster identifiers and output to the energy storage system controller. This list records the numbers of all battery clusters with excessively large voltage differences that cannot be connected. The system periodically re-acquires the cluster terminal voltage sampling values ​​of each battery cluster in the prohibited battery cluster list and recalculates the inter-cluster voltage differences between the battery clusters in the prohibited battery cluster list. The re-acquisition period is set according to the self-discharge rate and state-of-charge change rate of the battery clusters. When the recalculated inter-cluster voltage difference is less than the second voltage threshold, the corresponding battery cluster is removed from the list of prohibited battery clusters, and the parallel access status is redefined. The redefined parallel access status is used to guide subsequent access operations.

[0048] In practical implementation, taking an energy storage system containing four battery clusters as an example scenario, the four battery clusters are designated as the first, second, third, and fourth battery clusters. The maximum voltage difference in the inter-cluster voltage difference set calculated by the improved voltage difference comparison algorithm is 18 volts. The preset first voltage threshold is 10 volts, and the preset second voltage threshold is 20 volts. The maximum voltage difference of 18 volts is greater than or equal to the first voltage threshold of 10 volts and less than the second voltage threshold of 20 volts. Therefore, the parallel connection state is determined as the pre-charge connection state. Two target battery clusters generating the maximum voltage difference of 18 volts are identified in the inter-cluster voltage difference set. Assuming the two target battery clusters generating the maximum voltage difference are the first and fourth battery clusters, where the sampled value of the cluster terminal voltage of the first battery cluster is 385 volts and the sampled value of the cluster terminal voltage of the fourth battery cluster is 403 volts, the first battery cluster with the lower sampled value is marked as the battery cluster to be pre-charged, and the fourth battery cluster with the higher sampled value is marked as the reference battery cluster. A disconnect command is sent to the main circuit relay of the battery cluster to be precharged, causing the main circuit relay of the first battery cluster to be in the open state. A closing command is sent to the precharge relay of the battery cluster to be precharged, causing the first battery cluster to be connected to the DC bus through a precharge resistor with a resistance of 2 ohms and a DC bus voltage of 403 volts. After the precharge relay is closed, the real-time terminal voltage of the battery cluster to be precharged is continuously collected. The real-time terminal voltage of the first battery cluster is collected every millisecond using a voltage sensor, and the real-time terminal voltage is compared with the sampled value of the terminal voltage of the reference battery cluster, which is 403 volts. When the difference between the real-time terminal voltage and the sampled value of the terminal voltage of the reference battery cluster is less than the preset precharge completion voltage threshold, the precharge completion voltage threshold is set to 2 volts. Assuming that after a 30-millisecond precharge process, the real-time terminal voltage of the first battery cluster rises to 401.5 volts, the difference from 403 volts is 1.5 volts, which is less than 2 volts, a disconnect command is sent to the precharge relay of the battery cluster to be precharged, and a closing command is sent to the main circuit relay of the battery cluster to be precharged.

[0049] In some embodiments, after sending a closing command to the precharge relay of the battery cluster to be precharged, causing the battery cluster to be precharged to connect to the DC bus through the precharge resistor, the following operations are performed: A precharge timer is started to record the precharge duration of the battery cluster to be precharged. The precharge timer starts counting from zero the instant the precharge relay closes. The precharge duration is compared with a preset maximum allowable precharge duration, which is set to 200 milliseconds. When the precharge duration reaches the maximum allowable precharge duration of 200 milliseconds and the difference between the real-time terminal voltage and the cluster terminal voltage sample value of the reference battery cluster is still greater than or equal to the precharge completion voltage threshold of 2 volts, a disconnect command is sent to the precharge relay of the battery cluster to be precharged. In another example scenario, suppose the battery cluster to be precharged is the second battery cluster, and the reference battery cluster is the third battery cluster. When the precharge duration reaches 200 milliseconds, the real-time terminal voltage of the second battery cluster is 398 volts, and the sampled value of the cluster terminal voltage of the reference battery cluster and the third battery cluster is 403 volts. The difference between the two is 5 volts, which is greater than the precharge completion voltage threshold of 2 volts. Then, the precharge relay of the second battery cluster sends a disconnect command, marks the second battery cluster as a precharge timeout fault cluster, switches the parallel access state to the prohibited access state, and generates a precharge timeout alarm signal. The precharge timeout alarm signal carries the cluster identifier of the second battery cluster and the value of the real-time terminal voltage of 398 volts.

[0050] Optionally, the difference between the real-time terminal voltage and the sampled value of the cluster terminal voltage of the reference battery cluster during the pre-charging process is calculated using the following formula: in: This represents the difference between the real-time terminal voltage and the sampled value of the cluster terminal voltage of the reference battery cluster. This represents the sampled value of the cluster terminal voltage of the reference battery cluster. This indicates the real-time terminal voltage of the battery cluster to be precharged.

[0051] In practical implementation, when the parallel access state is in the prohibited access state, the following steps are executed: Disconnection commands are sent to the main circuit relays and pre-charge relays of all battery clusters in multiple battery clusters, completely isolating the multiple battery clusters from the DC bus. Assuming that after switching the parallel access state to the prohibited access state in the above example, there are four battery clusters in the energy storage system, disconnection commands are sent to the main circuit relays and pre-charge relays of the first battery cluster, the second battery cluster, the third battery cluster, and the fourth battery cluster. All inter-cluster voltage difference elements exceeding the second voltage threshold of 20 volts in the inter-cluster voltage difference set are scanned, and the cluster identifiers of the two battery clusters corresponding to each inter-cluster voltage difference element exceeding the second voltage threshold of 20 volts are extracted. Assuming there are three elements in the inter-cluster voltage difference set exceeding 20 volts: 25 volts between the first and second battery clusters, 22 volts between the first and third battery clusters, and 30 volts between the second and fourth battery clusters, the extracted cluster identifiers include the first, second, third, and fourth battery clusters. A prohibited access battery cluster list is generated based on all extracted cluster identifiers, containing the first, second, third, and fourth battery clusters, and output to the energy storage system controller. The cluster terminal voltage sampling value of each battery cluster in the prohibited access battery cluster list is periodically re-acquired, with a re-acquisition period set to 10 seconds. Every 10 seconds, the cluster terminal voltage sampling values ​​of the first, second, third, and fourth battery clusters are reread using voltage sensors, and the inter-cluster voltage difference between battery clusters in the prohibited access battery cluster list is recalculated. When the recalculated inter-cluster voltage difference is less than the second voltage threshold of 20 volts, the corresponding battery cluster is removed from the prohibited access battery cluster list, and the parallel connection status is re-determined.

[0052] It is understandable that after the prohibited battery cluster list is generated, the energy storage system controller, based on the battery cluster identifiers recorded in the list, prohibits sending any relay closing commands to these battery clusters until the removal conditions are met. Refer to Table 2, which records the initial state of the prohibited battery cluster list and its updates after a periodic re-collection.

[0053] Table 2: List of Battery Clusters Prohibited from Access - Update Record 1 First battery cluster 385 25 no reserve 1 Second battery cluster 378 30 no reserve 1 Third battery cluster 407 22 no reserve 1 Fourth battery cluster 408 30 no reserve 2 First battery cluster 390 18 yes Remove 2 Second battery cluster 385 23 no reserve 2 Third battery cluster 403 18 yes Remove 2 Fourth battery cluster 408 23 no reserve In some embodiments, when periodically re-collecting the cluster terminal voltage sampling value of each battery cluster in the prohibited access battery cluster list, if the cluster terminal voltage sampling value of a certain battery cluster changes such that its maximum voltage difference with other battery clusters in the list drops below the second voltage threshold, then that battery cluster is removed from the list, and the inter-cluster voltage difference between the remaining battery clusters is recalculated to redetermine the parallel access status of the entire energy storage system. For example, after the second cycle in Table 1, the first and third battery clusters are removed, and the prohibited access battery cluster list is updated to include the second and fourth battery clusters. The recalculated inter-cluster voltage difference between the second and fourth battery clusters is 23 volts, which is still greater than or equal to the second voltage threshold of 20 volts. Therefore, the parallel access status remains the prohibited access status, and the system continues to wait for the next cycle to re-collect the data.

[0054] It is understandable that after a precharge timeout fault cluster is marked, the battery cluster is simultaneously included in the prohibited access state processing flow. The energy storage system controller adds the cluster identifier of the precharge timeout fault cluster to the prohibited access battery cluster list and periodically re-collects its cluster terminal voltage sampling value according to the prohibited access state processing logic until the inter-cluster voltage difference drops below the second voltage threshold. Optionally, when generating a precharge timeout alarm signal, the data structure of the precharge timeout alarm signal includes three fields: the first field is the cluster identifier of the precharge timeout fault cluster, the second field is the real-time terminal voltage value of the precharge timeout fault cluster, and the third field is the timestamp. After receiving the precharge timeout alarm signal, the energy storage system controller stores the signal content in the alarm log file and uploads it to the upper-level monitoring system.

[0055] In one embodiment of the present invention, during the parallel connection of multiple battery clusters, after determining that the parallel connection state is a pre-charge connection state, a sequential pre-charge step is performed. The battery cluster with the lowest terminal voltage sample value is selected from multiple battery clusters as the first pre-charge target. The selection operation involves iterating through the terminal voltage sample values ​​of all battery clusters and finding the battery cluster corresponding to the minimum value. A separate pre-charge operation is performed on the first pre-charge target to raise its terminal voltage to be equal to the terminal voltage of the remaining battery clusters with the lowest terminal voltage sample value. The separate pre-charge operation means that only the selected battery cluster is charged through its pre-charge circuit without pre-charging other battery clusters. The first pre-charge target is marked as a pre-charged battery cluster, and the battery cluster with the lowest current terminal voltage is selected from the remaining battery clusters as the next pre-charge target. The remaining battery clusters are the set of battery clusters that have not yet completed the pre-charge operation. The separate pre-charge operation and marking operation are repeated until the maximum difference between the terminal voltages of all battery clusters is less than a first voltage threshold. Each repetition raises the current lowest terminal voltage battery cluster to be equal to the second lowest terminal voltage. Simultaneously send closing commands to the main circuit relays of all battery clusters, so that all battery clusters that have undergone sequential pre-charging are synchronously connected in parallel to the DC bus under the condition that the terminal voltages are basically equal.

[0056] In practical implementation, taking an energy storage system containing three battery clusters as an example scenario, the three battery clusters are designated as the first, second, and third battery clusters, and their parallel connection is determined as the pre-charge connection state, with a first voltage threshold of 10 volts. The sampled value of the cluster terminal voltage of the first battery cluster is 380 volts, that of the second battery cluster is 390 volts, and that of the third battery cluster is 395 volts. The battery cluster with the lowest sampled value at its terminal voltage is selected as the first pre-charge target. Since the lowest sampled value at its terminal voltage is 380 volts, the first battery cluster is chosen as the first pre-charge target. A separate pre-charge operation is performed on the first pre-charge target, raising its terminal voltage to equal that of the battery cluster with the lowest sampled terminal voltage value among the remaining battery clusters. The remaining battery clusters are the second and third battery clusters. The lowest sampled terminal voltage value among the remaining battery clusters is 390 volts for the second battery cluster. Therefore, the pre-charge operation raises the terminal voltage of the first battery cluster from 380 volts to 390 volts, an increase of 10 volts. The first pre-charge target is marked as a pre-charged battery cluster. The remaining battery clusters are then selected from the remaining battery clusters, with the lowest current terminal voltage being the next pre-charge target. The remaining battery clusters are the second and third battery clusters. The terminal voltage of the second battery cluster is 390 volts, and the terminal voltage of the third battery cluster is 395 volts. The lowest current terminal voltage is 390 volts for the second battery cluster, so the second battery cluster is selected as the next pre-charge target. The individual pre-charge and marking operations are repeatedly performed. A separate pre-charge operation is performed on the second pre-charge target until its terminal voltage is equal to the terminal voltage of the battery cluster with the lowest sampled terminal voltage value among the remaining battery clusters. At this point, the remaining battery cluster is the third battery cluster, and its terminal voltage is 395 volts. Therefore, the terminal voltage of the second battery cluster is increased from 390 volts to 395 volts, an increase of 5 volts. Then, the second battery cluster is marked as a pre-charged battery cluster. After two pre-charge operations, the terminal voltages of the first, second, and third battery clusters are all 390 volts, with a maximum difference of 5 volts. This 5 volts is compared to a first voltage threshold of 10 volts. Since 5 volts is less than 10 volts, the repeated operation stops. A closing command is simultaneously sent to the main circuit relays of all battery clusters. The main circuit relays of the three battery clusters close at the same time, completing the parallel connection.

[0057] In some embodiments, the voltage boost target for each precharge operation during sequential precharge is described by the following formula: in: This represents the target voltage value for the k-th precharge operation. This represents the sampled value of the cluster terminal voltage of the j-th battery cluster in the non-precharge set before the start of the k-th precharge operation. The non-precharge set includes all battery clusters that have not yet been marked as precharged.

[0058] In practice, when selecting the battery cluster with the lowest terminal voltage sampling value as the first pre-charge target, if two or more battery clusters have the same lowest terminal voltage sampling value, then any one of them can be selected as the first pre-charge target. For example, if the terminal voltage sampling values ​​of three battery clusters are 385 volts, 385 volts, and 400 volts respectively, and the lowest voltage value of 385 volts corresponds to the first and second battery clusters, then the first battery cluster is selected as the first pre-charge target and a separate pre-charge operation is performed. The terminal voltage of the first battery cluster is increased to the lowest terminal voltage value of 385 volts among the remaining battery clusters (the terminal voltage of the second battery cluster). Since the target voltage is equal to the current terminal voltage, the pre-charge operation is completed immediately. After marking the first battery cluster as the pre-charged battery cluster, the next pre-charge target is the second battery cluster. Similarly, the terminal voltage of the second battery cluster is increased from 385 volts to the lowest terminal voltage value of 400 volts among the remaining battery clusters (the terminal voltage of the third battery cluster).

[0059] Optionally, the specific method for performing a separate pre-charge operation on the first pre-charge target is to send a closing command only to the pre-charge relay of the selected battery cluster, while keeping the main circuit relay of that battery cluster open, and keeping the pre-charge relays and main circuit relays of other battery clusters open. When the real-time terminal voltage of the pre-charge target reaches the target voltage value as monitored by the voltage sensor, the pre-charge relay is opened and the main circuit relay is closed, completing the pre-charge operation of that battery cluster. It can be understood that after each individual pre-charge operation of a battery cluster is completed, the terminal voltage of that battery cluster is raised to be equal to the current lowest terminal voltage among the remaining battery clusters. At this time, the terminal voltages of all pre-charged battery clusters are consistent with the lowest terminal voltage among the remaining battery clusters. In the example above, after the first pre-charge is completed, the terminal voltage of the first battery cluster becomes 390 volts, which is equal to the 390 volts of the second battery cluster, and both are equal to the lowest terminal voltage among the remaining battery clusters; after the second pre-charge is completed, the terminal voltages of the first and second battery clusters are both 395 volts, which is equal to the 395 volts of the third battery cluster.

[0060] In some embodiments, when there are multiple battery clusters with the lowest sampled cluster voltage values ​​in the remaining battery clusters, the target voltage value is taken as the lowest voltage value. For example, the sampled cluster voltage values ​​of four battery clusters are 370V, 380V, 380V and 400V respectively. The first pre-charge target is the battery cluster corresponding to 370V. The lowest terminal voltage in the remaining battery clusters is 380V. After the terminal voltage of the first pre-charge target is raised to 380V, it is marked as completed. At this time, there are two 380V battery clusters and one 400V battery cluster in the remaining battery clusters. The two battery clusters with the lowest current terminal voltage are selected as the two corresponding to 380V. One of them is selected as the next pre-charge target, and its terminal voltage is raised to the current lowest terminal voltage value of 380V in the remaining battery clusters (the terminal voltage of the other 380V battery cluster). The pre-charge operation is completed immediately. Then, the pre-charge operation is performed on the last 380V battery cluster to raise its terminal voltage to 400V.

[0061] Optionally, the individual pre-charge and marking operations are repeated until the maximum difference between the terminal voltages of all battery clusters is less than the first voltage threshold. After each pre-charge operation, the difference between the maximum and minimum terminal voltages of all battery clusters (including those that have completed pre-charge and those that have not) is recalculated and compared with the first voltage threshold. If the difference is less than the first voltage threshold, subsequent pre-charge operations are stopped, and the step of simultaneously sending a closing command to the main circuit relays of all battery clusters is executed. It can be understood that when the closing command is sent to the main circuit relays of all battery clusters simultaneously, all main circuit relays receive the closing signal at the same time. This time point is selected as the starting point of the next control cycle after all pre-charge operations are completed and the maximum difference between terminal voltages meets the condition. For the example of the three battery clusters mentioned above, under the condition that the second pre-charge operation is completed and the terminal voltages of the first, second, and third battery clusters are 390 volts, the maximum difference is 5 volts, which is less than the first voltage threshold of 10 volts. Therefore, a closing command is immediately sent to the three main circuit relays simultaneously.

[0062] The above embodiments are only used to illustrate the technical methods of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical methods of the present invention without departing from the spirit and scope of the technical methods of the present invention.

Claims

1. A method for regulating the parallel circulating current of multi-branch battery clusters based on dynamic voltage balancing, characterized in that, The method includes: Acquire the sampled values ​​of the cluster terminal voltage and the status of the main circuit relays for each of the multiple battery clusters operating in parallel in the energy storage system; The sampled values ​​of the cluster-end voltage of the multiple battery clusters are input into an improved voltage difference comparison algorithm to calculate the difference between each pair of clusters, thereby generating a set of inter-cluster voltage differences. The improved voltage difference comparison algorithm dynamically adjusts the calculation weight of the difference based on the rated voltage level of the battery cluster. Based on the maximum voltage difference in the set of inter-cluster voltage differences and the preset multi-level threshold range, the parallel access state of the multiple battery clusters is determined. The parallel access state includes direct access state, pre-charge access state, and prohibited access state.

2. The method for regulating the parallel circulating current of multi-branch battery clusters based on dynamic voltage balancing according to claim 1, characterized in that, The step of inputting the sampled values ​​of the cluster-end voltages of the multiple battery clusters into an improved voltage difference comparison algorithm to perform pairwise difference calculations and generate a set of inter-cluster voltage difference values ​​specifically includes: Read the rated voltage level parameter of each of the plurality of battery clusters, and convert the rated voltage level parameter of each battery cluster into a reference voltage per unit value; The reciprocal of the per-unit value of the reference voltage is used as the dynamic weighting coefficient of the improved voltage difference comparison algorithm. The dynamic weighting coefficient is weighted with the sampled value of the cluster terminal voltage of the corresponding battery cluster to generate a weighted cluster terminal voltage value. Perform absolute value operations on all possible pairwise combinations of differences on the weighted cluster terminal voltage values, and take the result of each absolute value operation as an inter-cluster voltage difference element; Arrange all inter-cluster voltage difference elements according to the physical connection topology of the multiple battery clusters to generate the inter-cluster voltage difference set.

3. The method for regulating the parallel circulating current of multi-branch battery clusters based on dynamic voltage balancing according to claim 2, characterized in that, The improved voltage difference comparison algorithm dynamically adjusts the calculation weight of the difference based on the rated voltage level of the battery cluster, specifically including the following steps: The rated voltage value of the battery cluster with the highest rated voltage level among the multiple battery clusters is obtained as the reference voltage value; For each of the plurality of battery clusters, the ratio of the rated voltage value of the battery cluster to the reference voltage value is calculated, and the reciprocal of the ratio is used as the voltage weighting factor of the battery cluster. When calculating the voltage difference between any two battery clusters, the first voltage weighting factor of the first battery cluster and the second voltage weighting factor of the second battery cluster are extracted. The product of the sampled value of the cluster terminal voltage of the first battery cluster and the first voltage weighting factor is used as the first weighted voltage value, and the product of the sampled value of the cluster terminal voltage of the second battery cluster and the second voltage weighting factor is used as the second weighted voltage value. Calculate the absolute value of the difference between the first weighted voltage value and the second weighted voltage value, and use the absolute value as the inter-cluster voltage difference between any two battery clusters.

4. The method for regulating the parallel circulating current of multi-branch battery clusters based on dynamic voltage balancing according to claim 1, characterized in that, The step of determining the parallel connection status of the multiple battery clusters based on the maximum voltage difference in the set of inter-cluster voltage differences and a preset multi-level threshold range specifically includes: Iterate through all inter-cluster voltage difference elements in the set of inter-cluster voltage difference values, and select the inter-cluster voltage difference with the largest value as the maximum voltage difference value. Read a pre-configured first voltage threshold and a second voltage threshold, wherein the first voltage threshold is less than the second voltage threshold; The maximum voltage difference is compared with the first voltage threshold. When the maximum voltage difference is less than the first voltage threshold, the parallel connection state is determined to be the direct connection state. When the maximum voltage difference is greater than or equal to the first voltage threshold and less than the second voltage threshold, the parallel connection state is determined as the pre-charge connection state. When the maximum voltage difference is greater than or equal to the second voltage threshold, the parallel connection state is determined to be the prohibited connection state.

5. The method for regulating the parallel circulating current of multi-branch battery clusters based on dynamic voltage balancing according to claim 4, characterized in that, When the parallel access state is the direct access state, the following steps are performed, specifically including: Send a closing command to the main circuit relay of each of the plurality of battery clusters, so that the main circuit relay of each battery cluster closes simultaneously; After the main circuit relay is closed, the real-time circulating current value of the multiple battery clusters is continuously collected; The real-time circulating current value of each battery cluster is compared with the preset circulating overcurrent protection threshold. When the real-time circulating current value of any battery cluster exceeds the circulating overcurrent protection threshold, the main circuit relay of the battery cluster is disconnected and the battery cluster is marked as a fault isolation cluster. The fault isolation cluster is removed from the plurality of battery clusters, the inter-cluster voltage difference set of the remaining battery clusters is recalculated, and the parallel access status is updated according to the recalculated inter-cluster voltage difference set.

6. The method for regulating the parallel circulating current of multi-branch battery clusters based on dynamic voltage balancing according to claim 5, characterized in that, The step of continuously acquiring the real-time circulating current values ​​of the multiple battery clusters after the main circuit relay is closed specifically includes: After the main circuit relay closing command is issued, the delay timer is started; When the delay timer reaches the preset relay stable operation delay, the current value flowing through each battery cluster is synchronously collected by the DC current sensor installed at the positive or negative terminal of each battery cluster. The net circulating current value of each battery cluster is obtained by subtracting the pre-calibrated load current component of each battery cluster from the current value collected from each battery cluster. The net circulating current value of each battery cluster is used as the real-time circulating current value and stored in the circular data buffer for subsequent comparison and judgment.

7. The method for regulating the parallel circulating current of multi-branch battery clusters based on dynamic voltage balancing according to claim 4, characterized in that, When the parallel access state is the pre-charge access state, the following steps are performed, specifically including: Identify the two target battery clusters that generate the maximum voltage difference in the set of inter-cluster voltage differences, mark the battery cluster with the lower cluster terminal voltage sampling value as the battery cluster to be precharged, and mark the battery cluster with the higher cluster terminal voltage sampling value as the reference battery cluster; Send a disconnect command to the main circuit relay of the battery cluster to be precharged, and send a closing command to the precharge relay of the battery cluster to be precharged, so that the battery cluster to be precharged is connected to the DC bus through the precharge resistor; After the precharge relay is closed, the real-time terminal voltage of the battery cluster to be precharged is continuously collected, and the real-time terminal voltage is compared with the cluster terminal voltage sample value of the reference battery cluster. When the difference between the real-time terminal voltage and the sampled value of the cluster terminal voltage of the reference battery cluster is less than the preset precharge completion voltage threshold, a disconnect command is sent to the precharge relay of the battery cluster to be precharged, and a closing command is sent to the main circuit relay of the battery cluster to be precharged.

8. The method for regulating the parallel circulating current of a multi-branch battery cluster based on dynamic voltage balancing according to claim 7, characterized in that, After sending a closing command to the precharge relay of the battery cluster to be precharged, causing the battery cluster to be precharged to be connected to the DC bus through the precharge resistor, the following steps are performed, specifically including: Start the precharge timer to record the precharge duration of the battery cluster to be precharged; The precharge duration is compared with the preset maximum allowable precharge duration; When the precharge duration reaches the maximum allowable precharge duration and the difference between the real-time terminal voltage and the cluster terminal voltage sampling value of the reference battery cluster is still greater than or equal to the precharge completion voltage threshold, a disconnection command is sent to the precharge relay of the battery cluster to be precharged. The battery cluster to be precharged is marked as a precharge timeout fault cluster, and the parallel access state is switched to the access prohibited state; A precharge timeout alarm signal is generated, which carries the cluster identifier of the battery cluster to be precharged and the value of the real-time terminal voltage.

9. The method for regulating the parallel circulating current of multi-branch battery clusters based on dynamic voltage balancing according to claim 4, characterized in that, When the parallel access state is the prohibited access state, the following steps are performed, specifically including: Send a disconnect command to the main circuit relays and precharge relays of all battery clusters in the plurality of battery clusters to completely isolate the plurality of battery clusters from the DC bus; Scan all inter-cluster voltage difference elements in the inter-cluster voltage difference set that exceed the second voltage threshold, and extract the cluster identifiers of the two battery clusters corresponding to each inter-cluster voltage difference element that exceeds the second voltage threshold; A list of prohibited battery clusters is generated based on all extracted cluster identifiers, and the list of prohibited battery clusters is output to the energy storage system controller. The sampled value of the cluster terminal voltage of each battery cluster in the list of prohibited battery clusters is periodically re-acquired, and the inter-cluster voltage difference between battery clusters in the list of prohibited battery clusters is recalculated. When the recalculated inter-cluster voltage difference is less than the second voltage threshold, the corresponding battery cluster is removed from the list of prohibited battery clusters, and the parallel access status is redefined.

10. The method for regulating the parallel circulating current of a multi-branch battery cluster based on dynamic voltage balancing according to claim 4, characterized in that, The method further includes a multi-battery cluster sequential pre-charging step performed after determining that the parallel access state is a pre-charging access state, specifically including: The battery cluster with the lowest cluster-end voltage sampling value is selected from the plurality of battery clusters as the first pre-charge target; Perform a separate precharge operation on the first precharge object to raise the terminal voltage of the first precharge object to be equal to the terminal voltage of the battery cluster with the lowest terminal voltage sample value in the remaining battery clusters; The first pre-charged object is marked as a battery cluster that has completed pre-charging, and the battery cluster with the lowest current terminal voltage is selected from the remaining battery clusters as the next pre-charged object. Repeat the individual pre-charge and marking operations until the maximum difference between the terminal voltages of all battery clusters is less than the first voltage threshold. Simultaneously send a closing command to the main circuit relays of all battery clusters.

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