Parallel control method and parallel control system for multi-cluster battery

Abstract

The application provides a parallel control method and system of multi-cluster batteries, and relates to the field of energy storage. The method comprises the following steps: online identification and update of the action delay and equivalent impedance of the main contactor, instead of the static factory calibration value; stripping of the polarization voltage component of the battery cluster after being separated from the charging and discharging to obtain the open circuit voltage; in the case of polarization stripping failure, the open circuit voltage is obtained by applying a micro-power disturbance through the energy storage converter; based on the parameter reference and the voltage difference between the open circuit voltage and the bus voltage, the multi-level parallel operation decision of the single battery cluster is executed; in the case of receiving the emergency instruction of the power grid, the multi-level parallel operation decision is stopped and the main contactor in all operations is disconnected; after the execution of the multi-level parallel operation decision, the charging power and the discharging power are independently limited. The application aims to improve the problems of inaccurate parallel operation reference, lack of safety protection and conflict of power grid response of the existing control strategy in the direct parallel system of multi-cluster batteries without converter.

Description

Technical Field

[0001] This application relates to the field of energy storage, specifically to a parallel control method and a parallel control system for multiple battery clusters. Background Technology

[0002] Currently, in multi-cluster battery direct parallel systems without independent DC / DC converters, most existing solutions adopt an open-loop control architecture with static factory parameters and independent decentralized decision-making for each cluster. This leads to problems such as inaccurate parallel operation reference, lack of safety protection, and grid conflicts throughout the product lifecycle. Summary of the Invention

[0003] The main purpose of this application is to propose a parallel control method and a parallel control system for multiple battery clusters, aiming to improve the problems of inaccurate parallel reference, lack of safety protection and grid response conflict in existing control strategies for direct parallel systems of multiple clusters without converters.

[0004] This application proposes a parallel control method for multiple battery clusters, applied to a direct parallel system of multiple battery clusters without independent converters. The system includes multiple battery clusters, a DC bus, an energy storage converter, and a control module. The multiple battery clusters are connected to the DC bus via a main contactor and a pre-charge circuit. The parallel control method for the multiple battery clusters includes: The action delay and equivalent impedance of the main contactor are identified and updated online in an event-driven manner, replacing the static factory calibration values ​​and providing a parameter benchmark for subsequent parallel connection decisions. The polarization voltage component of the battery cluster after it has been disconnected from charging and discharging is stripped to obtain the open circuit voltage; in the case of failure of polarization stripping, a micro-power perturbation is applied through the energy storage converter to obtain the open circuit voltage through online calibration. Only one cluster of batteries is allowed to perform parallel operation at any given time. Based on the parameter reference and the voltage difference between the open circuit voltage and the bus voltage, a multi-level parallel operation decision is made for the single cluster of batteries. During the grid dispatching process of the energy storage converter, the timing for executing multi-level parallel operation decisions is determined based on the trajectory of the bus voltage. Upon receiving an emergency command from the power grid, the multi-level parallel operation decision-making process is suspended and all main contactors in operation are disconnected. After the multi-level parallel operation decision is executed, the charging power and discharging power are independently limited, and the power reduction and recovery are carried out in a way that the limiting rate is greater than the recovery rate.

[0005] Optionally, the operating delay of the main contactor is updated in the following manner: The time difference between the moment the closing command of the main contactor is issued and the moment when the main circuit current is first established is recorded as the measured value of the delay of this action. Obtain the temperature of the coil of the main contactor, and normalize the measured value to a preset reference temperature according to the temperature; The normalized measurement value is filtered to obtain the updated operating delay of the main contactor.

[0006] Optionally, the equivalent impedance of the main circuit is updated in the following way: The system detects current changes in the battery cluster branch and determines that a current step event has occurred if the current change exceeds a preset amount within a preset time window. The difference between the current values ​​in one frame before and after the current step event is obtained, as well as the voltage difference between the battery cluster terminal voltage and the bus voltage in one frame before and after the current step event. The ratio of the voltage difference to the difference of the current value is used as the measured value; The measured values ​​are validated, and those that fail the validation are discarded. The validated measured values ​​are then filtered to obtain the updated equivalent impedance of the main circuit. The update formula for the equivalent impedance of the main circuit is as follows:

[0007] The voltage difference between the battery cluster terminal voltage and the bus voltage in the frame following the current step event. The voltage difference between the battery cluster terminal voltage and the bus voltage in the frame preceding the current step event. It is the difference between the current values ​​in one frame before and after the current step event. The equivalent impedance of the main circuit is given.

[0008] Optionally, the step of stripping the polarization voltage component from the battery cluster after it has been disconnected from charging and discharging to obtain the open-circuit voltage includes: After the battery cluster is removed from the charging and discharging state, the sequence of the terminal voltage of the battery cluster changes over time within a preset period of time is obtained. Using the exponential decay relationship of voltage value over time as a model, the terminal voltage is fitted to solve for the undetermined parameters of the model, which include at least the open-circuit voltage of the battery cluster.

[0009] Optionally, in the event of polarization stripping failure, applying a micro-power perturbation to the energy storage converter to obtain the open-circuit voltage through online calibration includes: Connect the battery cluster to be calibrated to the energy storage converter; At least two power pulses of different amplitudes are applied to the battery cluster to be calibrated by an energy storage converter, and the duration of the power pulses is less than a preset time threshold. Obtain the voltage and current response values ​​during the application of the power pulse; Based on the linear relationship between the voltage response value and the current response value, the open-circuit voltage is obtained by solving the simultaneous equations.

[0010] Optionally, the provision that only one battery cluster is allowed to perform parallel operation at any given time, based on the parameter reference and the voltage difference between the open-circuit voltage and the bus voltage, includes performing multi-level parallel operation decisions for this single battery cluster: When the bus voltage is not zero, the paralleling priority of the battery clusters is determined based on the voltage difference from smallest to largest. Based on the priority, parallel operation rights are sequentially assigned to the plurality of battery clusters, and only the battery cluster holding the execution right is allowed to enter the parallel operation; After the battery clusters have completed parallel operation, the bus voltage is remeasured and the voltage difference of all battery clusters that have not yet been paralleled is recalculated, and the remaining parallel operation priority order is updated accordingly.

[0011] Optionally, when the bus voltage is zero, one of the plurality of battery clusters is selected as the pioneer cluster; The DC bus is current-limited charged through the pre-charge circuit of the pioneer cluster to establish the bus voltage; After the bus voltage is successfully established, the remaining battery clusters are sequentially connected to the bus. If the lead cluster fails to establish voltage, the next battery cluster is selected as the lead cluster to try to establish bus voltage again.

[0012] Optionally, the multi-level parallel decision-making includes the following three levels of determination: When the voltage difference is less than or equal to a preset first threshold, the main contactor is directly closed after the main contactor action delay compensation to complete the parallel operation; When the voltage difference is greater than the preset first threshold and less than or equal to the preset second threshold, the pre-charge contactor is closed first, and the voltage difference is limited by the pre-charge resistor. After the voltage difference decays to the first threshold, the main contactor is closed and the pre-charge contactor is opened to complete the switching. If the voltage difference is greater than the preset second threshold, the battery cluster will be placed in a waiting queue and temporarily not connected to the grid.

[0013] Optionally, determining the timing for executing multi-level parallel operation decisions based on the bus voltage trajectory during grid dispatching by the energy storage converter includes: The bus voltage is acquired during the execution of grid dispatch instructions by the energy storage converter; The rate of change of the bus voltage is determined based on the trend of the bus voltage change within the sliding time window. Based on the bus voltage and the rate of change, the predicted trajectory of the bus voltage within a preset time period is determined; The moment when the predicted trajectory equals the open-circuit voltage is taken as the zero-voltage-difference crossover moment; Before the zero differential pressure crossover moment, the main contactor closing command is issued one action delay in advance.

[0014] This application also proposes a multi-cluster battery parallel control system, which includes a control module and an energy storage converter, wherein the control module is configured to execute the multi-cluster battery parallel control method as described in any of the above claims.

[0015] This application proposes a parallel control method for multiple battery clusters, applied to a direct parallel system of multiple battery clusters without independent converters. The system includes multiple battery clusters, a DC bus, an energy storage converter, and a control module. The multiple battery clusters are connected to the DC bus via a main contactor and a pre-charge circuit. The parallel control method includes: online identification and updating of the main contactor's operating delay and the main circuit's equivalent impedance in an event-driven manner, replacing the static factory calibration values ​​and providing a parameter reference for subsequent parallel connection decisions; stripping the polarization voltage component of the battery clusters after they have been disconnected from charging and discharging to obtain the open-circuit voltage; and, in the event of polarization stripping failure, using the energy storage converter... The device applies a micro-power disturbance to obtain the open-circuit voltage for online calibration; only a single cluster of batteries is allowed to perform parallel operation at any given time, and multi-level parallel operation decisions are made for the single cluster of batteries based on the parameter reference and the voltage difference between the open-circuit voltage and the bus voltage; wherein, during the grid dispatching of the energy storage converter, the timing of the multi-level parallel operation decision is determined based on the trajectory of the bus voltage; in the event of receiving an emergency grid command, the execution of the multi-level parallel operation decision is suspended and all main contactors in operation are disconnected; after the execution of the multi-level parallel operation decision is completed, the charging power and discharging power are independently limited, and power reduction and recovery are performed in a manner where the limiting rate is greater than the recovery rate.

[0016] By implementing the above settings, and replacing static factory parameters with online updates of contactor action delay and main circuit equivalent impedance, stripping polarization voltage or obtaining true open-circuit voltage through online micro-power disturbances, allowing only one cluster to perform parallel operation at a time and determining the parallel operation timing based on the bus voltage trajectory during grid dispatch, and performing power reduction and recovery in an asymmetric manner with a limiting rate greater than the recovery rate, reliable calibration of the voltage reference, serialized and safe execution of parallel operation, parallel coordination between parallel operation and grid dispatch, and stable control of boundary power during steady-state operation are achieved throughout the parallel operation process. This improves the problems of inaccurate parallel operation reference, lack of safety protection, and grid response conflicts that exist in existing schemes in converter-less multi-cluster direct parallel systems. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0018] Figure 1 This is a schematic flowchart illustrating an embodiment of the parallel control method and parallel control system for multiple battery clusters according to this application. Figure 2 This is a schematic diagram of the parallel control method for multiple battery clusters and the method for updating action delay in the parallel control system for multiple battery clusters in this application; Figure 3 This is a schematic diagram of the parallel control method for multiple battery clusters and the method for updating the equivalent impedance of the main circuit in the parallel control system for multiple battery clusters in this application. Figure 4 This is a schematic diagram of the parallel control method for multiple battery clusters and the method for obtaining open-circuit voltage in the parallel control system for multiple battery clusters of this application. Figure 5 This is a schematic diagram of the parallel control method for multiple battery clusters and the method for obtaining open-circuit voltage through online calibration in the parallel control system for multiple battery clusters of this application. Figure 6 A schematic diagram illustrating the parallel control method for multiple battery clusters and the method for determining parallel operation priority in the parallel control system for multiple battery clusters of this application; Figure 7 This is a schematic diagram of the parallel control method for multiple cluster batteries and the method for selecting the pioneer cluster in the parallel control system for multiple cluster batteries of this application. Figure 8 This is a schematic diagram illustrating the parallel control method for multiple battery clusters and the multi-level parallel decision-making method in the parallel control system for multiple battery clusters of this application. Figure 9 This is a schematic diagram illustrating the parallel control method for multiple battery clusters and the method for determining the timing of parallel operation decisions in the parallel control system for multiple battery clusters as described in this application. Figure 10 This is a schematic diagram of the structural topology of an embodiment of the parallel control method and parallel control system for multiple battery clusters of this application.

[0019] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0021] It should be noted that if the embodiments of this application involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0022] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution that simultaneously satisfies A and B. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0023] Currently, in multi-cluster battery direct parallel systems without independent DC / DC converters, most existing solutions adopt an open-loop control architecture with static factory parameters and independent decentralized decision-making for each cluster, which leads to problems such as inaccurate parallel operation reference and lack of safety protection during the life cycle.

[0024] Therefore, this application proposes a parallel control method for multiple battery clusters, applicable to a direct parallel system of multiple battery clusters without independent converters, referencing... Figure 10 The system includes multiple battery clusters, a DC bus, an energy storage converter, and a control module. The multiple battery clusters are connected to the DC bus through a main contactor and a pre-charge circuit.

[0025] Optionally, the control module can be implemented using a main controller, such as an MCU, PLC, DSP (Digital Signal Processor), SOC (System-on-Chip), or FPGA (Field-Programmable Gate Array). The control module is used to execute the parallel control method for the multi-cluster batteries.

[0026] Optionally, in the hardware architecture that eliminates the independent DC / DC converter, the main circuit retains the following components: fuse, passive miniature circuit breaker, main contactor KM1, and a pre-charge circuit consisting of pre-charge contactor KM2 connected in series with pre-charge resistor Rpre. The sensing layer is configured with cluster-end voltage sampling Vbat, bus voltage sampling Vbus, and main circuit current sensor CT.

[0027] In one embodiment of this application, reference is made to Figure 1 Parallel control methods for multiple battery clusters include: S100 uses an event-driven approach to identify and update the operating delay of the main contactor and the equivalent impedance of the main circuit online, replacing the static factory calibration values ​​and providing a parameter benchmark for subsequent parallel connection decisions.

[0028] In this embodiment, optionally, in the event-driven mode, the system does not update parameters at a fixed time period, but triggers the corresponding parameter measurement and update process when a specific event occurs during actual operation, such as the main contactor performing a closing action or a large current step in the battery cluster branch.

[0029] In one example, the update process for the main contactor's action delay is as follows: Each time the main contactor performs a closing action, the control module records the moment the closing command is issued and monitors the establishment moment of the main circuit current. The difference between the two is used as the measured value of the action delay for that action. Considering that the contactor coil resistance changes with temperature, which will affect the action delay, the control module synchronously collects the coil temperature, normalizes the measured value to a unified reference temperature, and then performs filtering to obtain the updated action delay value, which is used for feedforward compensation in subsequent closing operations.

[0030] S200: Strip the polarization voltage component of the battery cluster after it has been disconnected from charging and discharging to obtain the open circuit voltage; if polarization stripping fails, apply a micro-power perturbation through the energy storage converter to obtain the open circuit voltage through online calibration.

[0031] In this embodiment, optionally, open-circuit voltage calibration is performed on the battery cluster after it has been removed from the charge / discharge state, either on the basis of or in parallel with the completion of parameter self-learning. Specifically, when a battery cluster is removed from the charge / discharge state, for example, after being shut down for paralleling or restarted after maintenance, the control module continuously collects the terminal voltage of the battery cluster to obtain a decay sequence of the terminal voltage over a preset time period. The control module fits the terminal voltage sequence using the exponential decay relationship of the voltage value over time as a model, and extracts the open-circuit voltage value after removing the polarization voltage component from the fitting result.

[0032] Optionally, if the above fitting process fails to converge to a reliable open-circuit voltage value due to insufficient voltage signal characteristics, such as when the battery is in the flat voltage region of lithium iron phosphate, the control module switches to online calibration mode. In this mode, an electrical connection is established between the battery cluster to be calibrated and the energy storage converter. The energy storage converter applies at least two power pulses of different amplitudes to the battery cluster. The control module collects the voltage and current responses during each pulse, and solves the equations using the linear relationship between voltage and current to obtain the true open-circuit voltage of the battery cluster.

[0033] S300: Only one cluster of batteries is allowed to perform parallel operation at the same time. Based on the parameter reference and the voltage difference between the open circuit voltage and the bus voltage, multi-level parallel operation decision is performed on the single cluster of batteries. Among them, during the grid dispatching of the energy storage converter, the timing of multi-level parallel operation decision is determined based on the bus voltage trajectory.

[0034] Optionally, after obtaining the open-circuit voltage, the control module calculates the difference between the open-circuit voltage and the DC bus voltage, and performs parallel decision-making based on the parameter reference in S100.

[0035] Optionally, to prevent the superposition of current surges caused by multiple battery clusters simultaneously closing the main contactor, the control module allows only one battery cluster to perform parallel operation at a time. Specific implementation methods include, but are not limited to: the control module sorts the battery clusters to be paralleled from smallest to largest according to their differential voltage values, granting parallel operation rights sequentially; only the battery cluster that obtains the right to execute can enter the subsequent parallel operation process.

[0036] Optionally, for each individual battery cluster that gains execution rights, the control module performs multi-level parallel operation decisions based on parameter benchmarks, such as the updated main circuit equivalent impedance and main contactor operating delay, as well as the voltage difference of the battery cluster. In one example, this multi-level decision could be to directly close the main contactor to complete the parallel operation when the voltage difference is minimal; when the voltage difference is moderate, the current is first limited by the pre-charge resistor, and the main contactor is switched on after the voltage difference decays; when the voltage difference is too large, parallel operation is temporarily suspended and the battery is placed in a waiting queue.

[0037] Optionally, while the energy storage converter is executing grid dispatch commands, such as power regulation commands, the DC bus voltage may be dynamically changing. Under this condition, the control module predicts the short-term trajectory of the bus voltage based on its current value and trend, determines the future moment when the open-circuit voltage of the cluster to be paralleled equals the bus voltage based on the predicted trajectory, and issues a paralleling command in advance before this moment arrives.

[0038] S400: Upon receiving an emergency command from the power grid, suspend the execution of multi-level parallel operation decisions and disconnect all main contactors in operation.

[0039] Optionally, at any stage of the parallel operation decision execution, if the control module receives an emergency grid command, such as a primary frequency regulation command, a high / low voltage ride-through command, or an emergency power cut-off command, it immediately suspends the currently executing parallel operation process, disconnects all closed or in the process of closing main contactors, and transfers system control to the energy storage converter to execute the grid emergency response. The execution time of the above operations is configured to be shorter than the response time limit required by the grid emergency command.

[0040] S500: After the multi-level parallel operation decision is executed, the charging power and discharging power are independently limited, and the power is reduced and restored in such a way that the limiting rate is greater than the recovery rate.

[0041] Optionally, after all multi-cluster batteries have been connected in parallel and the system has entered the multi-cluster parallel operation state, the control module independently limits the allowable charging power and discharging power of the entire station.

[0042] Optionally, when the operating parameters of any battery cluster, such as cell voltage, temperature, or state of charge, reach the power limit trigger condition, the control module rapidly reduces the allowable power in the corresponding direction in a step manner, so that the operating parameter quickly moves away from the danger boundary; when the operating parameter falls back to the safe recovery threshold and stabilizes, the control module gradually restores the allowable power at a gentle slope that is significantly slower than the reduction rate.

[0043] By implementing the above settings, and replacing static factory parameters with online updates of contactor action delay and main circuit equivalent impedance, stripping polarization voltage or obtaining true open-circuit voltage through online micro-power disturbances, allowing only one cluster to perform parallel operation at a time and determining the parallel operation timing based on the bus voltage trajectory during grid dispatch, and performing power reduction and recovery in an asymmetric manner with a limiting rate greater than the recovery rate, reliable calibration of the voltage reference, serialized and safe execution of parallel operation, parallel coordination between parallel operation and grid dispatch, and stable control of boundary power during steady-state operation are achieved throughout the parallel operation process. This improves the problems of inaccurate parallel operation reference, lack of safety protection, and grid response conflicts that exist in existing schemes in converter-less multi-cluster direct parallel systems.

[0044] According to some embodiments of this application, optionally, in one embodiment of this application, reference is made to... Figure 2 The main contactor's action delay is updated in the following way: S110. Record the time difference between the moment the main contactor closes and the moment the main circuit current is first established as the measured value of the delay of this action. S111. Obtain the temperature of the main contactor coil and normalize the measured value to a preset reference temperature. S112. The normalized measured values ​​are filtered to obtain the updated operating delay of the main contactor.

[0045] In this embodiment, optionally, the control module records the absolute time stamp t at each moment when it sends a closing trigger level to the drive coil of the main contactor KM1. cmd Simultaneously, the control module continuously monitors the output of the main circuit current sensor CT, using the moment when the current first exceeds a preset conduction threshold (e.g., 0.5A) and remains above that threshold for a preset duration during subsequent sampling periods as the starting point for the time t. on This is to reduce the interference of contactor contact bounce on the delay measurement. Single action delay amount. .

[0046] Optionally, the total engagement delay of the contactor is composed of the coil current rise time and the armature starting and movement time. The coil current rise time is dominated by the temperature coefficient of the copper winding resistance, while the armature starting and movement time are less sensitive to temperature. To eliminate the main interference of temperature on the delay measurement, this scheme approximates the temperature dependence of the total delay as the temperature effect of the coil winding resistance, and performs calculations accordingly. Simultaneously record the temperature sensor readings near the coil of the main contactor KM1. The original delay is normalized to the reference temperature T. ref For example, the sample is fed into the filter after reaching 25°C: Among them, α cu ≈0.004K 1 The temperature coefficient of resistance of the copper winding. The measured values ​​are normalized. The above temperature normalization process is used to eliminate systematic deviations between measured values ​​under different ambient temperatures, making the results comparable. For wide temperature range applications, such as those exceeding the typical temperature range of -10℃ to +50℃ for prefabricated energy storage modules, a piecewise linear lookup table method can be used instead of the normalization formula, which falls within the scope of this invention.

[0047] Optionally, the normalized delay sequence obtained from each valid closure event, excluding scenarios such as pre-charge circuit conduction, is smoothly updated using a first-order low-pass digital filter: , where α is the filter coefficient, typically 0.05–0.15, and k is the update sequence number.

[0048] It is necessary to understand that The update event is triggered by the contactor closing action, and the event interval depends on the system parallel operation frequency, which is a naturally non-uniform sampling sequence. The first-order low-pass filter, recursively, only needs to store the filter value of the previous frame, naturally adapting to the non-uniform sampling interval; fixed-window methods such as moving averages have difficulty managing the weights of old samples in this scenario. The smaller value of α is chosen as an engineering consideration to suppress random noise in a single measurement while maintaining the ability to track the actual aging drift. This filter improves the problem of original measurement noise coupling to feedforward compensation, causing closure point deviation.

[0049] Optionally, the normalized value can be used to calculate the action delay at the current temperature: ,in, Delay the operation of the updated main contactor.

[0050] By normalizing the action delay to the reference temperature instead of filtering directly at the real-time temperature, the spurious drift of the filter output under seasonal / diurnal temperature variations is reduced, improving the fixed compensation failure problem caused by the contactor engagement delay drifting with temperature. Simultaneously, the first-order filter reduces random noise in single measurements while maintaining the ability to track true aging drift, providing a reliable parameter benchmark for subsequent parallel operation decisions.

[0051] According to some embodiments of this application, optionally, in one embodiment of this application, reference is made to... Figure 3 The equivalent impedance of the main circuit is updated in the following way: S120. Detect the current change in the battery cluster branch, and determine that a current step event has occurred if the current change exceeds a preset amount within a preset time window. S121. Obtain the difference in current value in one frame before and after the current step event, and the voltage difference between the battery cluster terminal voltage and the bus voltage in one frame before and after the current step event. S122. Use the ratio of the voltage difference to the current difference as an estimate. S123. Verify the validity of the measured values, discard the estimated values ​​that fail the verification, and filter the estimated values ​​that pass the verification to obtain the updated equivalent impedance of the main circuit. The formula for calculating the estimated value is as follows:

[0052] The voltage difference between the battery cluster terminal voltage and the bus voltage in the frame following the current step event. The voltage difference between the battery cluster terminal voltage and the bus voltage in the frame preceding the current step event. It is the difference between the current values ​​in one frame before and after the current step event. The equivalent impedance of the main circuit is given.

[0053] In this embodiment, optionally, the system does not rely on micro-ripple signals below the noise floor of the high-voltage sensor for impedance identification. Instead, it utilizes a large current step event with a sufficient signal-to-noise ratio that naturally occurs in the main circuit. The triggering condition is that the change in current of this cluster branch exceeds a preset change amount, such as 5A, within a preset time window, such as 100ms. When the triggering condition is met, the control module extracts one frame before and after the step event. and Calculate the estimated value .

[0054] Optionally, a validity check is applied to the estimated value: if the estimated value is less than zero or exceeds a preset range, such as between 0.5 times and 3 times the rated impedance, or if the current direction reverses before and after the step, the estimated value is discarded. The value that passes the check is then updated using a first-order low-pass filter. , This is the updated equivalent impedance of the main circuit.

[0055] It is important to understand that β is the filter coefficient, typically 0.02–0.10, which is smaller than the filter coefficient α. The aging rate of the equivalent impedance of the main circuit is much slower than the drift rate of the contactor mechanical delay, thus allowing for a longer filter time constant to adequately suppress random errors in single identification. At the same time, when the current step amplitude is small, the relative error of the main circuit current sensor increases, and a smaller β reduces the disturbance weight of such low signal-to-noise ratio samples on the filter output.

[0056] Optionally, the last valid online identification update time is recorded as t. last If the time period [t] last ,t las t+T stall ](T stall If no current step event meeting the trigger condition occurs within 24 hours, the control module starts the impedance confidence timer. last +T stall If there is no trigger for a continuous duration of T, degrade (e.g., 168h) — i.e., from tl ast Total cumulative non-triggered duration T stall +T degrade(e.g., 192h) If the control module determines that the online identification path for the equivalent impedance of the main circuit has been stagnant for an extended period, it will continue to use the last valid online identification value. Simultaneously, the control module will report an alarm to the maintenance system, prompting that a large current step calibration or manual impedance test needs to be scheduled during maintenance. If another large current step event occurs, the system will immediately switch back to the online identification path and overwrite with the new value, while simultaneously clearing the confidence timer.

[0057] With the above settings, the equivalent impedance of the main circuit is calculated using the differential modulus before and after the step, which reduces the interference of the sensor's DC bias. This differential modulus directly corresponds to the complete voltage drop across the main circuit of this cluster, including all impedance components from the cell internal resistance to the bus junction point. No additional test signal is required, which improves the problem that the factory calibration value is inaccurate due to aging and cannot be updated due to lack of effective excitation.

[0058] According to some embodiments of this application, optionally, in one embodiment of this application, reference is made to... Figure 4 To obtain the open-circuit voltage by stripping the polarization voltage component from a battery cluster after it has been removed from charge / discharge cycles, the following steps are included: S210. After the battery cluster leaves the charging / discharging state, obtain the sequence of the battery cluster's terminal voltage changing with time within a preset time period. S220. Using the exponential decay relationship of voltage value over time as a model, fit the terminal voltage and solve for the undetermined parameters of the model. The undetermined parameters include at least the open-circuit voltage of the battery cluster.

[0059] In this embodiment, optionally, after the battery cluster leaves the charging / discharging state, a discrete sequence of terminal voltages is collected within the subsequent time period t∈[t0,t0+Δt]. The preset duration Δt is typically 5–10 minutes, the sampling interval is 1–10 seconds, and a first-order RC exponential decay model is used for fitting. ,in, Let τ be the initial amplitude of the polarization voltage, τ be the polarization time constant, OCV be the open-circuit voltage of the target battery cluster, and V(t) be the sequence of the terminal voltage of the battery cluster changing with time.

[0060] Optionally, the solution method in this embodiment is the three-point method. Three equally spaced sampling times t0, t1, and t2 are selected in the voltage sequence, corresponding to voltage values ​​V0, V1, and V2. The time constant τ is directly solved using the following formula: Then, substituting these values ​​into the model equations, we can obtain the OCV and... .

[0061] Optionally, to suppress the interference of sensor background noise on the three-point method, a moving average filter with a window width of M points is applied to the original voltage sequence before performing the three-point solution. A typical value for M is 5–10. The three sampled values ​​V0, V1, and V2 are taken from the filtered sequence. A triple validity check is performed before calculation; if any condition is triggered, it automatically downgrades to least squares fitting. For example, |V1 V0∣ <V noise_floor The voltage sequence may be either non-monotonic decreasing or non-exponentially decaying.

[0062] In one example, V noise_floor If the peak-to-peak value of the sensor's noise floor is taken as three times, such as 150mV, then the polarization attenuation is determined to be submerged in the noise; if (V2) V1) / (V1 V0)≤0 indicates that the voltage sequence is not monotonically decreasing, and τ has no real solution; if (V2)≤0, it means that the voltage sequence is not monotonically decreasing, and τ has no real solution. V 1） ≥ (V1 V 0) That is, the voltage difference ratio is not less than 1, corresponding to (e If Δt / τ) ≥ 1 and τ ≤ 0, it indicates that the voltage sequence is not in an exponential decay pattern, which also triggers degradation. In the above cases, the least squares fitting is automatically performed on all sampling points within the Δt window.

[0063] With the above settings, the single RC model only needs to determine three parameters, and the three-point method can be used for closed-loop solution, satisfying the computing power constraints of the embedded MCU. If the triple validity check of the three-point method triggers degradation, it automatically switches to full-window least squares fitting. The above model separates the polarization voltage component from the terminal voltage, extracting a more accurate open-circuit voltage, so that subsequent parallel operation decisions are based on a reliable voltage reference.

[0064] According to some embodiments of this application, optionally, in one embodiment of this application, reference is made to... Figure 5 In the event of polarization stripping failure, obtaining the open-circuit voltage through online calibration by applying a micro-power perturbation to the energy storage converter includes: S230. Connect the battery cluster to be calibrated to the energy storage converter; S240. Apply at least two power pulses of different amplitudes to the battery cluster to be calibrated through the energy storage converter, and the duration of the power pulses is less than a preset time threshold. S250: Obtain the voltage response and current response values ​​during the power pulse application period; S260. Based on the linear relationship between the voltage response value and the current response value, the open-circuit voltage is obtained by solving the equations simultaneously.

[0065] In this embodiment, optionally, when the battery cluster operates in the LFP voltage flat region for a long time, causing the above polarization stripping process to be affected by |V1 V0∣ <V noise_floor If a reliable open-circuit voltage cannot be obtained even after repeated downgrading to least squares fitting, the system can execute the following preemptive online calibration process during planned maintenance windows or low-load periods permitted by grid dispatch: the control module instructs the energy storage converter to disconnect the main contactors of all other healthy battery clusters except the one to be calibrated, thus disconnecting them from the DC bus.

[0066] Optionally, after the battery cluster to be calibrated is independently connected to the bus, the energy storage converter applies at least two charge / discharge power pulses of different amplitudes to it, for example, charge / discharge at a current rate of 0.05C–0.1C, corresponding to approximately 5%–10% of the rated power, with each pulse lasting 1–5 seconds. The voltage response V is simultaneously acquired. measured The true open-circuit voltage OCV can be directly solved by combining the current response I with the two-point difference method or multi-point linear regression. true and R bat_internal : The physical basis of this formula is that the SOC change is extremely small under micro-power short-pulse excitation, and the OCV is... true This can be considered constant within this timescale. Two pulses of different amplitudes provide two independent sets of voltage-current measurements, each satisfying a linear relationship: , jointly eliminate R bat_internal OCV is obtained true The closed solution.

[0067] With the above settings, this method does not rely on lookup tables or polarization model parameters and is equally effective in the flat region of LFP. It improves the defect of the polarization voltage stripping method in the flat region where the polarization attenuation signal is submerged in the sensor's background noise.

[0068] According to some embodiments of this application, optionally, in one embodiment of this application, reference is made to... Figure 6 Only one battery cluster is allowed to perform parallel operation at any given time. Based on the parameter reference and the voltage difference between the open-circuit voltage and the bus voltage, the multi-level parallel operation decision for this single battery cluster includes: S310. When the bus voltage is not zero, determine the paralleling priority of the battery clusters based on the order of voltage difference from small to large. S320: Parallel operation execution rights are assigned to multiple battery clusters based on priority, and only the battery cluster holding the execution rights is allowed to enter the parallel operation; S330: After the battery clusters have completed parallel operation, remeasure the bus voltage and recalculate the voltage difference of all battery clusters that have not yet been paralleled, and update the remaining parallel operation priority order accordingly.

[0069] In this embodiment, optionally, when the entire station loses power, i.e., the bus voltage equals zero and enters a black-start state, the control module scans all battery clusters and selects a pioneer cluster based on priority. When the bus voltage is not zero and the voltage difference between the clusters to be connected meets a preset threshold condition, the control module does not allow multiple clusters to close simultaneously. The system maintains a global mutex: only one cluster holds the execution token at any given time. The token allocation principle is minimum voltage difference priority—that is, the cluster with the smallest ΔV to be connected has priority in obtaining the execution right. Unlike probabilistic concurrent control based on random backoff or timeout retries, the global mutex mechanism of this scheme provides a deterministic timing isolation guarantee—at any given time, at most one battery cluster is in the contactor closed execution state.

[0070] Optionally, after the cluster that obtained the token completes the contactor closure, the system enforces a 500ms stabilization wait period or when |dV bus / dt|If the sampling period is below the preset convergence threshold for N consecutive sampling periods... End the waiting period in advance. The typical value is 0.5V / s–2.0V / s. This step ensures that the surge energy is evenly distributed in the parallel circuit and the bus voltage reaches a new steady-state equilibrium. After the waiting period expires, the token is released, and the control module recalculates the voltage difference of all remaining clusters to be paralleled with the updated bus voltage and dynamically reorders the waiting queue.

[0071] With the above settings, the mechanism ensures that each round of parallel decision-making is based on the latest system state, reducing the impact of multiple clusters being judged as qualified under the old benchmark due to outdated evaluation benchmarks.

[0072] According to some embodiments of this application, optionally, in one embodiment of this application, reference is made to... Figure 7 S340. When the bus voltage is zero, select one of the multiple battery clusters as the pioneer cluster. S341. Current-limited charging of the DC bus is performed through the pre-charge circuit of the pioneer cluster to establish the bus voltage; S342. After the bus voltage is successfully established, the remaining battery clusters are connected to the bus in sequence. S343. If the lead cell cluster fails to establish voltage, the next cell cluster is selected as the lead cell cluster to try to establish bus voltage again.

[0073] In this embodiment, optionally, when the entire station loses power (i.e., the bus voltage equals zero and enters a black-start state), the control module scans all battery clusters and selects a pioneer cluster based on priority ranking. The priority ranking is as follows: first, the most thorough polarization elimination and the longest resting time; second, the optimal battery health state; and third, the terminal voltage closest to the system nominal voltage. The pioneer cluster performs current-limited pre-charge and voltage build-up on the DC bus capacitor by closing the pre-charge contactor KM2. If the Joule integral exceeds the limit or the pre-charge timeout is detected during the pre-charge process, the voltage build-up is determined to have failed, and the cluster enters the cooling retreat queue. That is, clusters that fail to build up voltage enter the retreat waiting queue. After the cooling time exceeds a preset time, it can re-participate in the pioneer cluster election, determined according to the pre-charge thermal resistance time constant. In one example, the preset time is 30s-60s.

[0074] Optionally, if a reliable open-circuit voltage cannot be obtained for a suboptimal candidate cluster due to its location in the LFP voltage flat region, the open-circuit voltage evaluation step is skipped, and the current terminal voltage of the cluster is directly used as an approximation of the open-circuit voltage for black-start voltage build-up determination. In this case, the pre-charge resistor limits the closing circulating current to below a preset current value, which is far below the safety threshold of the contactor and fuse. In one example, the preset current value is 50A.

[0075] Optionally, if all candidate clusters fail to establish voltage in succession, the control module determines that there is an irreversible short circuit or insulation fault on the DC bus, disconnects all contactors, reports an alarm, and locks the black-start state machine. This locked state can only be manually cleared by maintenance personnel after completing on-site troubleshooting. After successful voltage establishment, the bus enters the energized state, and the remaining battery clusters switch to the serialized parallel operation process.

[0076] Through the above settings, the pre-charge voltage building and successor rotation mechanism after failure of the pioneer cluster enable the system to establish bus voltage autonomously without external power supply after a complete power outage, achieving black start. Furthermore, the current limiting protection of the pre-charge circuit and the candidate cluster rotation attempt ensure the safety and success rate of the voltage building process.

[0077] According to some embodiments of this application, optionally, in one embodiment of this application, reference is made to... Figure 8 Multi-level parallel decision-making includes the following three levels of judgment: S350: When the voltage difference is less than or equal to the preset first threshold, the main contactor is directly closed after the main contactor action delay compensation to complete the parallel operation. S351. When the voltage difference is greater than the preset first threshold and less than or equal to the preset second threshold, the pre-charge contactor is closed first, and the voltage difference is limited by the pre-charge resistor. After the voltage difference decays to the first threshold, the main contactor is closed and the pre-charge contactor is opened to complete the switching. S352. If the voltage difference is greater than the preset second threshold, the battery cluster is placed in the waiting queue and temporarily not connected to the grid.

[0078] In this embodiment, optionally, the preset first threshold is: , The upper limit of the safe surge current of the contactor is selected based on the rated making capacity in the contactor's datasheet, with typical values ​​of 2kA–5kA. The equivalent impedance of the current loop is identified online; To prevent noise lockout, the full-scale deviation of the high-voltage sensor is used as the additive bias term to ensure that ΔV is consistent with... The algebraic difference does not fall into the undeterminable range due to sampling noise. When the voltage difference of the battery clusters is less than or equal to the preset first threshold, the control module directly closes the main contactor KM1 to achieve direct-parallel operation without pre-charging.

[0079] Optionally, the preset second threshold is , The single-pulse energy tolerance value for the pre-charge resistor is provided in the manufacturer's datasheet; The total capacity of the DC bus supporting capacitor for the energy storage converter is obtained from the nameplate parameters or factory test report of the energy storage converter. When the voltage difference is less than or equal to the preset second threshold, the control module closes the pre-charge contactor KM2, and the pre-charge resistor performs resistive current limiting and current sharing on the voltage difference. Since the pre-charge resistor in the actual system is much larger than the equivalent impedance of the main circuit, the voltage drop component on the equivalent impedance of the main circuit during pre-charging can be ignored. Therefore, the voltage difference is directly compared with the preset first threshold as the criterion for closing the main contactor KM1.

[0080] If the voltage difference is less than or equal to a preset first threshold, first close the main contactor KM1, and after confirming that the auxiliary contact of the main contactor KM1 has engaged, then open the pre-charge contactor KM2. At this time, it is necessary to ensure that the busbar always has a low-impedance path. This reduces the secondary voltage difference caused by busbar capacitor voltage drift during the gap when the pre-charge contactor KM2 is open first and the main contactor KM1 is not closed. If the main contactor KM1 does not engage within the timeout window, for example, 500ms, it is determined that the main contactor KM1 engagement timeout has occurred, an alarm is reported, and the cluster is marked as non-parallel operation, requiring on-site troubleshooting by maintenance personnel.

[0081] Optionally, if the voltage difference exceeds a preset second threshold, the battery cluster is placed in a suspension queue. The system determines the timing for executing multi-level parallel operation decisions based on the bus voltage trajectory. If there is no natural convergence trend for an extended period, an alarm is reported to prompt manual intervention.

[0082] It is important to understand that, in one embodiment, to prevent a single fault such as controller crash or communication interruption from causing the pre-charge circuit to remain energized for an extended period, the following independent shutdown paths are established: First, software protection: the control module internally sets up a heat accumulation model based on Joule integral. During the conduction of the pre-charge circuit, heat is continuously accumulated. When the heat reaches a preset proportion of the tolerance limit provided by the pre-charge resistor manufacturer, the control module immediately issues a disconnect command to the pre-charge contactor KM2. The DC breaking capacity of KM2 should cover the maximum possible current of the pre-charge circuit under the worst operating conditions. Taking a 1500V system as an example, the typical value range of the pre-charge resistor is 20Ω–100Ω, corresponding to a maximum possible current range of 15A–75A. The DC breaking capacity of the pre-charge contactor should not be lower than this value, ensuring that the arc energy is within the rated breaking range of the contactor when disconnecting under load.

[0083] Second, an over-temperature protection device independent of the control module and any control software is set up. For example, a temperature fuse is installed in series with the pre-charge resistor to form a strong thermal coupling. When the temperature of the pre-charge resistor reaches the device's activation threshold, this protection device irreversibly cuts off the pre-charge circuit in a purely physical manner. This hardware path is unaffected by any software state, MCU reset, or communication interruption. Third, the judgment criterion for extreme contactor contact welding failure scenarios is as follows: after the control module issues a disconnect command, within a preset timeout window, such as 500ms, the auxiliary contact feedback of KM1 / KM2 still has not switched to the open state, while the main circuit current sensor still detects continuous current. This state indicates that the armature cannot be released due to the welding of the main contact, causing the auxiliary contact to remain in the closed position synchronously with the main contact. After confirming the welding, the control module instructs the protection device of the main circuit of this cluster to irreversibly cut off the electrical connection between the cluster and the bus, such as an active detonating fuse or a conventional high breaking capacity fuse.

[0084] Through the above settings, the three-level parallel decision-making model enables precise matching between the parallel operation mode and the actual pressure difference; the pre-charge multi-redundancy protection reduces the risk of pre-charge runaway caused by a single fault mode through three independent paths: software Joule integral, hardware over-temperature cutoff, and fusion welding physical isolation. Both of these measures jointly ensure the safety and reliability of the parallel execution process from the two dimensions of correct parallel operation and safety protection.

[0085] According to some embodiments of this application, optionally, in one embodiment of this application, reference is made to... Figure 9 During grid dispatching by the energy storage converter, the timing for executing multi-level parallel operation decisions based on the bus voltage trajectory includes: S360. Obtain bus voltage during the execution of grid dispatch instructions by the energy storage converter; S361. Determine the rate of change of the bus voltage based on the trend of the bus voltage change within the sliding time window; S362. Based on the bus voltage and the rate of change, determine the predicted trajectory of the bus voltage within a preset time period; S363. The moment when the predicted trajectory equals the open-circuit voltage is taken as the zero-difference voltage crossover moment; S364. Before the zero differential pressure crossover moment, issue the main contactor closing command one action delay in advance.

[0086] In this embodiment, optionally, to resolve the timing conflict between parallel operation and grid dispatch commands, this scheme employs a non-intrusive trajectory prediction mechanism. When the energy storage converter is executing power commands issued by the grid dispatch and the bus voltage exhibits dynamic fluctuations, the control module does not require the energy storage converter to suspend power output to cooperate with the parallel operation. Instead, the control module performs a first-order IIR low-pass filter on the bus voltage sampling sequence to obtain a smoothed bus voltage. Based on the smoothed bus voltage, an estimate of the bus voltage change rate is calculated using a sliding window backward differential method. ,in, The smoothed bus voltage. The value is the estimated rate of change of the bus voltage, N is the number of sampling points in the differential window, typically ranging from 20 to 50, and Ts is the sampling period.

[0087] Optionally, based on the current smoothed voltage and rate of change estimation, the control module extrapolates the short-term predicted trajectory of the bus voltage online: The control module takes the moment when the short-term predicted trajectory equals the open-circuit voltage of the battery cluster to be connected as the zero-differential voltage crossover moment. Before the zero-differential voltage crossover moment arrives, it issues the main contactor closing command with an advance action delay, so that the contacts achieve physical zero-differential voltage impact on the dynamic bus.

[0088] In one example, when the rate of change of the bus voltage is less than the preset rate of change, such as less than 0.6, the control module determines that the short-term predicted trajectory is unreliable, terminates the trajectory prediction process, and performs the above three-level judgment based on the latest sampled bus voltage.

[0089] In another embodiment, the system defines the following grid safety protocol instructions as the highest priority interruption sources: primary frequency regulation, AGC emergency regulation, high voltage ride-through, low voltage ride-through, and emergency power cut-off. Once the control module receives the above interruption signal, the currently executing paralleling process will be immediately stopped, and the system execution state will be rolled back: First, immediately stop the contactor operation currently performing the closing action; if it is already closed, immediately disconnect it; if it is executing the closing sequence, cancel it, and clear all paralleling requests in the waiting queue that have not yet obtained the execution token; Second, confirm that all contactors on the waiting cluster side have been disconnected, and the system topology is restored to the state before the paralleling process started—only the main contactor KM1 of the stable operating cluster remains closed; Third, the control module releases the global mutex lock, and the energy storage converter unconditionally executes the grid dispatching instructions.

[0090] With the above settings, bus voltage trajectory prediction enables parallel operation and grid dispatch to be executed in parallel without interruption, reducing timing conflicts between parallel operation and grid-related commands, and allowing the system to complete its rapid response to the grid while performing parallel operation.

[0091] This application also proposes a parallel control system for multiple battery clusters, including a control module and an energy storage converter, wherein the control module is configured to execute the parallel control method for multiple battery clusters as described in any of the above claims.

[0092] In this embodiment, since the technical solution and its effects of the multi-cluster battery parallel control system have been described in detail in the description of the above method, those skilled in the art can understand the specific structure and working principle of the system, so they will not be repeated here.

[0093] The above description is merely an exemplary embodiment of this application and does not limit the patent scope of this application. Any equivalent structural transformations made based on the technical concept of this application and the contents of the specification and drawings of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A parallel control method for multiple battery clusters, applied to a direct parallel system of multiple battery clusters without independent converters, the system comprising multiple battery clusters, a DC bus, an energy storage converter, and a control module, wherein the multiple battery clusters are connected to the DC bus via a main contactor and a pre-charge circuit, characterized in that... The parallel control method for the multiple battery clusters includes: The action delay and equivalent impedance of the main contactor are identified and updated online in an event-driven manner, replacing the static factory calibration values ​​and providing a parameter benchmark for subsequent parallel connection decisions. The polarization voltage component of the battery cluster after it has been disconnected from charging and discharging is stripped to obtain the open circuit voltage; in the case of failure of polarization stripping, a micro-power perturbation is applied through the energy storage converter to obtain the open circuit voltage through online calibration. Only one cluster of batteries is allowed to perform parallel operation at any given time. Based on the parameter reference and the voltage difference between the open circuit voltage and the bus voltage, a multi-level parallel operation decision is made for the single cluster of batteries. During the grid dispatching process of the energy storage converter, the timing for executing multi-level parallel operation decisions is determined based on the trajectory of the bus voltage. Upon receiving an emergency command from the power grid, the multi-level parallel operation decision-making process is suspended and all main contactors in operation are disconnected. After the multi-level parallel operation decision is executed, the charging power and discharging power are independently limited, and the power reduction and recovery are carried out in a way that the limiting rate is greater than the recovery rate.

2. The parallel control method for multiple battery clusters as described in claim 1, characterized in that, The operating delay of the main contactor is updated in the following way: The time difference between the moment the closing command of the main contactor is issued and the moment when the main circuit current is first established is recorded as the measured value of the delay of this action. Obtain the temperature of the coil of the main contactor, and normalize the measured value to a preset reference temperature according to the temperature; The normalized measurement value is filtered to obtain the updated operating delay of the main contactor.

3. The parallel control method for multiple battery clusters as described in claim 1, characterized in that, The equivalent impedance of the main circuit is updated in the following way: The system detects current changes in the battery cluster branch and determines that a current step event has occurred if the current change exceeds a preset amount within a preset time window. The difference between the current values ​​in one frame before and after the current step event is obtained, as well as the voltage difference between the battery cluster terminal voltage and the bus voltage in one frame before and after the current step event. The ratio of the voltage difference to the difference of the current value is used as the measured value; The measured values ​​are validated, and those that fail the validation are discarded. The validated measured values ​​are then filtered to obtain the updated equivalent impedance of the main circuit. The update formula for the equivalent impedance of the main circuit is as follows: The voltage difference between the battery cluster terminal voltage and the bus voltage in the frame following the current step event. The voltage difference between the battery cluster terminal voltage and the bus voltage in the frame preceding the current step event. It is the difference between the current values ​​in one frame before and after the current step event. The equivalent impedance of the main circuit is given.

4. The parallel control method for multiple battery clusters as described in claim 1, characterized in that, The step of stripping the polarization voltage component from the battery cluster after it has been removed from charging and discharging to obtain the open-circuit voltage includes: After the battery cluster is removed from the charging and discharging state, the sequence of the terminal voltage of the battery cluster changes over time within a preset period of time is obtained. Using the exponential decay relationship of voltage value over time as a model, the terminal voltage is fitted to solve for the undetermined parameters of the model. The undetermined parameters include at least the open-circuit voltage of the battery cluster.

5. The parallel control method for multiple battery clusters as described in claim 1, characterized in that, In the event of polarization stripping failure, applying a micro-power disturbance to the energy storage converter to obtain the open-circuit voltage through online calibration includes: Connect the battery cluster to be calibrated to the energy storage converter; At least two power pulses of different amplitudes are applied to the battery cluster to be calibrated by an energy storage converter, and the duration of the power pulses is less than a preset time threshold. Obtain the voltage response and current response values ​​during the application of the power pulse; Based on the linear relationship between the voltage response value and the current response value, the open-circuit voltage is obtained by solving the simultaneous equations.

6. The parallel control method for multiple battery clusters as described in claim 1, characterized in that, The provision that only one battery cluster is allowed to perform parallel operation at any given time, based on the parameter reference and the voltage difference between the open-circuit voltage and the bus voltage, includes the following multi-level parallel operation decision-making for this single battery cluster: When the bus voltage is not zero, the paralleling priority of the battery clusters is determined based on the voltage difference from smallest to largest. Based on the priority, parallel operation rights are sequentially assigned to the plurality of battery clusters, and only the battery cluster holding the execution right is allowed to enter the parallel operation; After the battery clusters have completed parallel operation, the bus voltage is remeasured and the voltage difference of all battery clusters that have not yet been paralleled is recalculated, and the remaining parallel operation priority order is updated accordingly.

7. The parallel control method for multiple battery clusters as described in claim 6, characterized in that, When the bus voltage is zero, one of the plurality of battery clusters is selected as the pioneer cluster; The DC bus is current-limited charged through the pre-charge circuit of the pioneer cluster to establish the bus voltage; After the bus voltage is successfully established, the remaining battery clusters are sequentially connected to the bus. If the lead cluster fails to establish voltage, the next battery cluster is selected as the lead cluster to try to establish bus voltage again.

8. The parallel control method for multiple battery clusters as described in claim 1, characterized in that, The multi-level parallel decision-making includes the following three levels of judgment: When the voltage difference is less than or equal to a preset first threshold, the main contactor is directly closed after the main contactor action delay compensation to complete the parallel operation; When the voltage difference is greater than the preset first threshold and less than or equal to the preset second threshold, the pre-charge contactor is closed first, and the voltage difference is limited by the pre-charge resistor. After the voltage difference decays to the first threshold, the main contactor is closed and the pre-charge contactor is opened to complete the switching. If the voltage difference is greater than the preset second threshold, the battery cluster will be placed in a waiting queue and temporarily not connected to the grid.

9. The parallel control method for multiple battery clusters as described in claim 1, characterized in that, The determination of the timing for executing multi-level parallel operation decisions based on the bus voltage trajectory during grid dispatching by the energy storage converter includes: The bus voltage is acquired during the execution of grid dispatch instructions by the energy storage converter; The rate of change of the bus voltage is determined based on the trend of the bus voltage change within the sliding time window. Based on the bus voltage and the rate of change, the predicted trajectory of the bus voltage within a preset time period is determined; The moment when the predicted trajectory equals the open-circuit voltage is taken as the zero-voltage-difference crossover moment; Before the zero differential pressure crossover moment, the main contactor closing command is issued one action delay in advance.

10. A multi-cluster battery parallel control system, characterized in that, The multi-cluster battery parallel control system includes a control module and an energy storage converter, wherein the control module is configured to perform the multi-cluster battery parallel control method as described in any one of claims 1 to 9.

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