A battery charging and discharging method at a battery pack level of an energy storage system

Abstract

This invention discloses a battery pack-level charging and discharging method for an energy storage system, belonging to the field of energy storage battery technology. It addresses the problems of existing charging and discharging methods failing to simultaneously achieve precise battery pack-level control, poor system efficiency and consistency, and insufficient safety protection. The method comprises a battery pack-level charging and discharging method for an energy storage system, which includes several parallel-connected battery packs, a battery management system, a power conversion system, and a monitoring terminal. Each battery pack is composed of several individual batteries connected in series and parallel. The method includes five major steps: charging / discharging preparation, charging control, discharging control, dynamic balancing adjustment, and safety protection. Based on the state parameters such as SOC, SOH, and temperature of each battery pack, the charging and discharging current and power are dynamically allocated to avoid overcharging or over-discharging of some battery packs due to uniform charging and discharging, effectively extending the battery pack's lifespan and reducing the battery degradation rate. Actual testing has verified that the battery pack's cycle life can be increased by more than 45%.

Description

Technical Field

[0001] A method for charging and discharging batteries at the battery pack level in an energy storage system is disclosed. This invention belongs to the field of energy storage battery technology, specifically relating to the technical field of charging and discharging methods for batteries at the battery pack level in energy storage systems. Background Technology

[0002] Existing energy storage systems primarily focus on system-level or individual battery-level charge and discharge control, which has several technical shortcomings: First, system-level charge and discharge control uses uniform charge and discharge parameters, failing to consider the consistency differences between different battery packs (such as deviations in parameters like capacity, internal resistance, and voltage). This leads to overcharging and over-discharging of some battery packs, accelerating battery aging and even posing safety hazards. Second, while individual battery-level control can achieve precise regulation, it suffers from high control complexity and hardware costs, and ignores the collaborative working characteristics of the battery pack as a whole, making it difficult to meet the high-efficiency operation requirements of large-scale energy storage systems. Third, existing charge and discharge methods lack dynamic balancing mechanisms. During long-term cyclic charge and discharge, the consistency deviation between battery packs gradually widens, leading to accelerated capacity decay and decreased charge and discharge efficiency of the entire energy storage system. Fourth, existing safety protection methods primarily target extreme faults (such as short circuits and overheating), lacking dynamic monitoring and prediction of the entire battery pack charge and discharge process. This results in delayed fault response and difficulty in effectively mitigating potential safety risks.

[0003] Furthermore, traditional charging and discharging methods often employ fixed strategies, failing to dynamically adjust based on the energy storage system's operating conditions (such as grid load demand, ambient temperature, and battery pack health), resulting in low energy utilization. Simultaneously, existing active balancing technologies suffer from low efficiency, fixed strategies, and poor reliability, while passive balancing technologies exhibit significant energy waste. Both fail to meet the high requirements of large-scale energy storage systems for battery pack consistency and energy efficiency. Therefore, developing a charging and discharging method that achieves precise battery pack-level control, dynamic balancing, safety, reliability, and high energy efficiency has become a pressing technical challenge in the field of energy storage. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the existing defects and provide a battery pack-level battery charging and discharging method for energy storage systems, thereby solving the problems of existing charging and discharging methods being unable to simultaneously achieve precise control at the battery pack level and system efficiency, poor consistency, insufficient safety protection, and low energy utilization.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A battery pack-level charging and discharging method for an energy storage system includes a battery pack-level charging and discharging method for an energy storage system. The energy storage system includes several battery packs connected in parallel, a battery management system (BMS), a power conversion system (PCS), and a monitoring terminal. The battery packs are composed of several individual batteries connected in series and parallel. The method includes five major steps: charging and discharging preparation, charging control, discharging control, dynamic balancing adjustment, and safety protection, as detailed below:

[0007] Step 1: Preparation for charging and discharging

[0008] 1.1 Battery Pack Status Monitoring: Real-time status parameters of each battery pack are collected through the Battery Management System (BMS), including battery pack voltage, total current, individual cell voltage, internal resistance, temperature, state of charge (SOC), and state of health (SOH), and the collected parameters are transmitted to the monitoring terminal. Among them, SOC is calculated using the ampere-hour integration method combined with the open-circuit voltage correction algorithm, and SOH is evaluated based on the number of battery pack cycles, capacity decay rate, and internal resistance change rate.

[0009] 1.2 Parameter Initialization: The monitoring terminal initializes the charging and discharging parameters of each battery pack according to the operating requirements of the energy storage system (such as charging and discharging power, target SOC, and operating mode), including charging cut-off voltage, discharging cut-off voltage, charging and discharging current threshold, equalization threshold, and safe temperature range; at the same time, it initializes the operating parameters of the power conversion system (PCS) to ensure that the operating state of the PCS matches that of the battery pack.

[0010] 1.3 Troubleshooting: The Battery Management System (BMS) analyzes the collected battery pack status parameters to determine whether there are faults such as overvoltage, undervoltage, overtemperature, abnormal internal resistance, or poor contact in a single cell. If a fault is found, an alarm signal is immediately issued and the charging and discharging circuit of the battery pack is cut off to prevent it from participating in charging and discharging. If there is no fault, the next charging and discharging control process is initiated.

[0011] Step 2: Charging Control

[0012] The charging control adopts a three-stage charging strategy of "constant current-constant voltage-trickle charge", and dynamically adjusts the charging parameters according to the battery pack status, as detailed below:

[0013] 2.1 Constant Current Charging Stage: The monitoring terminal allocates a corresponding constant current charging current to each battery pack based on its SOC and SOH, ensuring that the constant current charging current does not exceed the maximum allowable charging current of that battery pack. The power conversion system (PCS) converts the electrical energy from the grid or new energy power generation system into suitable DC power to provide constant current charging for each battery pack. During this stage, the battery management system (BMS) monitors the voltage and temperature of the battery packs in real time. If the battery pack temperature exceeds the lower limit of the safe temperature, the charging current is appropriately increased to improve charging efficiency; if the temperature approaches the upper limit of the safe temperature, the charging current is reduced to avoid overheating.

[0014] 2.2 Constant voltage charging stage: When the battery pack voltage reaches the preset charging cutoff voltage, it enters the constant voltage charging stage. At this time, the charging voltage remains constant and the charging current gradually decreases. The battery management system (BMS) monitors the current change of each battery pack in real time. When the charging current decreases to the preset trickle charging threshold, it enters the trickle charging stage.

[0015] 2.3 Trickle charging stage: A small trickle current is used to charge the battery pack, replenish the active material inside the battery pack, and repair some capacity decay until the battery pack's SOC reaches the target value. At this time, the battery management system (BMS) sends a charging completion signal, and the power conversion system (PCS) stops charging the battery pack. If there are any battery packs that are not fully charged, they continue to be charged until all battery packs reach the target SOC.

[0016] 2.4 Charging process adjustment: During the charging process, if the monitoring terminal detects an increase in grid load, insufficient power generation from new energy sources, or an abnormal state of the battery pack, it can dynamically adjust the charging power and charging speed to prioritize grid stability while protecting the safety of the battery pack.

[0017] Step 3: Discharge Control

[0018] The discharge control adopts a two-stage discharge strategy of "constant power-constant current", which dynamically allocates the discharge power based on the grid load demand and battery pack status, as detailed below:

[0019] 3.1 Constant Power Discharge Stage: The monitoring terminal determines the total discharge power of the energy storage system based on the grid load demand, and evenly distributes the total discharge power to each battery pack according to the SOC, SOH, and internal resistance of each battery pack, ensuring that the discharge power of each battery pack does not exceed its maximum allowable discharge power. The DC power released by the battery pack is converted into AC power by the power conversion system (PCS) and connected to the grid or supplied to the load. During this stage, the battery management system (BMS) monitors the voltage and temperature of the battery pack in real time. If the battery pack temperature exceeds the upper limit of the safe temperature, the discharge power is reduced to lower the temperature; if the temperature is lower than the lower limit of the safe temperature, the discharge power is adjusted appropriately to avoid damage to the battery pack due to low-temperature discharge.

[0020] 3.2 Constant Current Discharge Stage: When the battery pack voltage drops to the preset discharge cutoff voltage threshold, the constant current discharge stage begins, maintaining a constant discharge current until the battery pack's SOC drops to the target lower limit. At this point, the battery management system (BMS) issues a discharge stop signal, and the power conversion system (PCS) cuts off the discharge circuit of the battery pack. If there are still battery packs that can be discharged, the discharge continues until all battery packs reach the target lower SOC limit.

[0021] 3.3 Discharge process adjustment: During the discharge process, if the grid load decreases or a sudden load fluctuation occurs, the monitoring terminal dynamically adjusts the discharge power of each battery pack to avoid over-discharge of the battery pack and maximize the utilization of the battery pack's energy storage capacity; if an abnormality is detected in the battery pack, its discharge circuit is immediately cut off to ensure system safety.

[0022] Step 4: Dynamic Equalization Adjustment

[0023] Throughout the entire charging and discharging process, dynamic balancing adjustment at the battery pack level is performed synchronously. A bidirectional DC-DC module combined with an adaptive balancing scheduling algorithm is used to achieve lossless energy transfer between battery packs, as detailed below:

[0024] 4.1 Balance detection: The battery management system (BMS) collects the SOC and voltage of each battery pack in real time and calculates the SOC deviation and voltage deviation between each battery pack;

[0025] 4.2 Balance Judgment: When the SOC deviation between any two battery packs exceeds the preset balance threshold (0.2%~1%) or the voltage deviation exceeds the preset threshold (5mV~20mV), dynamic balance adjustment is initiated;

[0026] 4.3 Balancing Execution: Through the bidirectional DC-DC energy transfer module, a portion of the energy from battery packs with higher SOC and voltage is transferred to battery packs with lower SOC and voltage, achieving lossless energy transfer. During the balancing process, the SOC and voltage changes of each battery pack are monitored in real time, and the balancing current and balancing time are dynamically adjusted to ensure balancing efficiency. The bidirectional DC-DC module uses gallium nitride (GaN) power devices with a conversion efficiency of no less than 96% and an energy utilization rate of over 85%.

[0027] 4.4 Equalization Stop: When the SOC deviation of all battery packs is less than the equalization threshold and the voltage deviation is less than the preset threshold, the dynamic equalization adjustment stops and enters the normal charging and discharging state; through dynamic equalization adjustment, the battery pack SOC consistency deviation is ensured to be <0.2% under all operating conditions, and the voltage equalization accuracy reaches ±5mV.

[0028] Step 5: Safety Protection

[0029] Throughout the entire charging and discharging process, a multi-level safety protection mechanism is established to achieve real-time monitoring, early warning, and handling of faults, as detailed below:

[0030] 5.1 Real-time monitoring: The battery management system (BMS) monitors the voltage, current, temperature, SOC, SOH and insulation resistance of each battery pack in real time. The monitoring terminal receives the monitoring data in real time and performs real-time analysis.

[0031] 5.2 Fault warning: When the parameters of the battery pack are detected to be outside the safe range (such as single cell overvoltage, undervoltage, overtemperature, overcurrent, low insulation resistance), or when abnormal charging and discharging or equalization fault occurs, the monitoring terminal will immediately issue an audible and visual alarm signal and record the fault information (including fault type, fault location, and fault time), and transmit the fault information to the management personnel.

[0032] 5.3 Fault Handling: Based on the fault level, the corresponding handling measures will be automatically executed: for minor faults (such as temperature slightly higher than the safety limit), adjust the charging and discharging parameters (reduce charging and discharging current and power), start the heat dissipation or heating device, and eliminate the fault; for serious faults (such as short circuit, over-temperature runaway, insulation failure), immediately disconnect the charging and discharging circuit of the battery pack, stop its operation, and at the same time disconnect the energy storage system from the grid to prevent the fault from spreading.

[0033] 5.4 Redundancy Protection: Backup battery packs and backup PCS modules are set up. When a battery pack or PCS module fails, it automatically switches to the backup equipment to ensure the continuous operation of the energy storage system. At the same time, combined with cloud big data analysis, the battery degradation trend can be predicted 6 months in advance to optimize the maintenance plan and reduce downtime by more than 50%.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] This invention dynamically allocates charging and discharging current and power based on the state parameters such as SOC, SOH, and temperature of each battery pack, avoiding overcharging and over-discharging of some battery packs due to uniform charging and discharging, effectively extending the service life of the battery pack and reducing the rate of battery degradation. Actual tests have verified that the cycle life of the battery pack can be increased by more than 45%.

[0036] By employing a bidirectional DC-DC module combined with an adaptive equalization scheduling algorithm, dynamic equalization adjustment is achieved throughout the entire charging and discharging process. This keeps the SOC consistency deviation between battery packs within 0.2%, and the voltage equalization accuracy reaches ±5mV. This avoids the system efficiency decline caused by the expansion of consistency deviation, and improves the charging and discharging efficiency to over 90%, while increasing the energy utilization rate to over 85%. Compared with traditional passive equalization technology, this significantly reduces energy waste.

[0037] A multi-level safety protection mechanism is established to achieve real-time monitoring, fault early warning and rapid handling of the entire charging and discharging process. It can effectively avoid safety hazards such as overcharging, over-discharging, over-temperature and short circuit. At the same time, backup equipment is set up to ensure the continuous and stable operation of the energy storage system. The fault response speed is <200ms, which is a significant improvement compared with the existing technology.

[0038] It can dynamically adjust the charging and discharging strategy according to the grid load demand, ambient temperature, and battery pack status, adapting to various scenarios such as large-scale energy storage power stations and distributed energy storage systems. At the same time, it maximizes the use of new energy power generation, smooths grid load fluctuations, and improves energy allocation efficiency, which can reduce the cost per kilowatt-hour of energy storage systems by more than 0.08 yuan.

[0039] Employing battery pack-level control, it balances control accuracy and hardware cost. The bidirectional DC-DC module uses gallium nitride power devices, reducing the size by 40% compared to traditional solutions and lowering the cost per string by 30%. It eliminates the need for complex single-cell battery-level control hardware, making it easy to modify and directly replace existing BMS systems. This reduces modification costs by 60% and facilitates large-scale deployment and application. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the energy storage system of the present invention;

[0041] Figure 2 This is a flowchart of the charging and discharging method of the present invention;

[0042] Figure 3 This is a schematic diagram of the charging control process of the present invention;

[0043] Figure 4 This is a schematic diagram of the discharge control process of the present invention;

[0044] Figure 5 This is a schematic diagram illustrating the principle of dynamic equilibrium adjustment in this invention. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] Please see Figure 1-5 The present invention provides a technical solution:

[0047] like Figure 1As shown, the energy storage system to which this invention applies includes several parallel-connected battery packs, a battery management system (BMS), a power conversion system (PCS), and a monitoring terminal. Each battery pack is composed of several individual batteries connected in series and parallel. Each battery pack is equipped with an independent bidirectional DC-DC module for energy transfer between battery packs. The energy storage system also includes a heat dissipation / heating device, a backup battery pack, and a backup PCS module. The PCS is connected to the power grid and the load respectively to realize the conversion and transmission of electrical energy. The BMS is communicatively connected to each battery pack, PCS, monitoring terminal, heat dissipation / heating device, backup battery pack, and backup PCS module to realize data acquisition and command transmission.

[0048] like Figure 2 As shown, a battery pack-level charging and discharging method for an energy storage system includes five major steps: charging / discharging preparation, charging control, discharging control, dynamic balancing adjustment, and safety protection. Specific embodiments are as follows:

[0049] Example 1: Charging process, dynamic balancing, and safety protection

[0050] Step 1: Preparation for charging and discharging

[0051] 1.1 Battery Pack Status Detection: The BMS collected real-time status parameters of three parallel battery packs (numbered 1#, 2#, and 3#). Battery pack 1# had a SOC of 30%, SOH of 92%, temperature of 25℃, voltage of 32V, and internal resistance of 80mΩ; battery pack 2# had a SOC of 28%, SOH of 90%, temperature of 24℃, voltage of 31.5V, and internal resistance of 82mΩ; and battery pack 3# had a SOC of 32%, SOH of 93%, temperature of 26℃, voltage of 32.5V, and internal resistance of 78mΩ. All individual battery voltages were within the normal range (3.2V~3.6V), with no abnormalities.

[0052] 1.2 Parameter Initialization: The monitoring terminal is set with target SOC=95%, charging cut-off voltage=38.4V, discharging cut-off voltage=28.8V, charging / discharging current threshold=100A, equalization threshold (SOC deviation)=0.5%, and safe temperature range=0℃~55℃; the PCS is initialized with operating parameters: output voltage=38.4V, maximum output current=300A.

[0053] 1.3 Troubleshooting: The BMS analyzes the collected parameters and finds no faults such as overvoltage, undervoltage, overtemperature, or abnormal internal resistance, and then proceeds to the charging control process.

[0054] Step 2: Charging Control

[0055] 2.1 Constant Current Charging Stage: The monitoring terminal allocates constant current charging current based on the SOC and SOH of the three battery packs: Battery Pack #1 charging current = 100A, Battery Pack #2 charging current = 95A (current reduced appropriately due to slightly lower SOH), Battery Pack #3 charging current = 100A (current maintained at maximum due to slightly higher SOC); The PCS converts the AC power from the grid to 38.4V DC power for simultaneous constant current charging of the three battery packs; During charging, the BMS monitors the temperature in real time. When the temperature of Battery Pack #1 rises to 35℃, the current remains constant; when the temperature of Battery Pack #3 rises to 45℃, the charging current is reduced to 90A to prevent overheating;

[0056] 2.2 Constant voltage charging stage: After charging for 1.5 hours, the voltage of battery pack #1 reached 38.4V, entering the constant voltage charging stage, and the charging current gradually decreased; subsequently, battery packs #2 and #3 reached 38.4V in turn and entered the constant voltage charging stage.

[0057] 2.3 Trickle charging stage: When the charging current of all three battery packs decreases to 10A (trickle charging threshold), the trickle charging stage begins. A 10A trickle current is used for charging. After 30 minutes, the SOC of all three battery packs reaches 95%. The BMS sends a charging completion signal, and the PCS stops charging.

[0058] 2.4 Charging process adjustment: During the charging process, if the grid load suddenly increases, the monitoring terminal will reduce the total charging power from 30kW to 20kW and adjust the charging current of the three battery packs: 1#=65A, 2#=60A, 3#=65A. After the grid load is restored, the normal charging current will be restored.

[0059] Step 4: Dynamic Equilibrium Adjustment (Performed Simultaneously)

[0060] 4.1 Equalization Detection: During the charging process, the BMS collects the SOC and voltage of the three battery packs in real time. After charging for 30 minutes, it is detected that the SOC of battery pack #1 is 45%, the SOC of battery pack #2 is 42%, and the SOC of battery pack #3 is 48%. The SOC deviation between battery pack #1 and #3 is 3%, which exceeds the equalization threshold of 0.5%, and dynamic equalization adjustment is initiated.

[0061] 4.2 Balancing Execution: Through the bidirectional DC-DC module, some energy of battery pack #3 is transferred to battery pack #2. The balancing current is set to 20A. After 15 minutes, the SOC of battery pack #1 is detected to be 55%, SOC of battery pack #2 is 53%, and SOC of battery pack #3 is 54%. The SOC deviation is less than 0.5%, and the balancing adjustment is stopped.

[0062] 4.3 Subsequent equalization: During the constant voltage charging and trickle charging stages, the SOC deviation is continuously monitored. When the deviation exceeds 0.5%, equalization adjustment is restarted to ensure that after charging is completed, the SOC of all three battery packs is 95%, the voltage is 38.4V, and the deviation is less than 5mV.

[0063] Step 5: Security Measures (to be carried out simultaneously)

[0064] 5.1 Real-time monitoring: The BMS monitors the voltage, current, temperature, SOC, SOH and insulation resistance of the three battery packs in real time, and the monitoring terminal displays the monitoring data in real time;

[0065] 5.2 Fault Warning: During charging, if the voltage of a single cell in battery pack #2 suddenly rises to 3.7V (exceeding the single cell overvoltage threshold of 3.6V), the BMS will immediately issue an audible and visual alarm signal, record the fault information (single cell overvoltage, battery pack #2, time), and transmit it to the management personnel.

[0066] 5.3 Fault Handling: The fault was determined to be minor. The monitoring terminal reduced the charging current of battery pack #2 from 95A to 80A and activated the cooling device to lower the battery pack temperature. After 10 minutes, the individual battery voltage returned to 3.5V, the fault was eliminated, and the normal charging current was restored.

[0067] 5.4 Redundancy Protection: During charging, if the bidirectional DC-DC module of battery pack #1 fails, the BMS will immediately switch to the backup DC-DC module to ensure that battery pack #1 is charged normally without any downtime.

[0068] Example 2: Discharge process, dynamic equalization, and safety protection

[0069] Step 1: Charge / Discharge Preparation (Continuing from the state after charging is completed in Example 1)

[0070] 1.1 Battery Pack Status Detection: The BMS collected real-time status parameters of the three battery packs. The SOC of battery packs #1, #2, and #3 was 95%, the SOH was 92%, 90%, and 93% respectively, the temperature was 30℃, the voltage was 38.4V, and the internal resistance was normal.

[0071] 1.2 Parameter Initialization: The monitoring terminal is set with the target SOC lower limit = 20%, discharge cut-off voltage = 28.8V, discharge current threshold = 100A, equalization threshold (SOC deviation) = 0.5%, and safe temperature range = 0℃~55℃; the PCS is initialized with the following operating parameters: input voltage = 28.8V~38.4V, maximum input current = 300A;

[0072] 1.3 Troubleshooting: No fault found, proceed to discharge control procedure.

[0073] Step 3: Discharge Control

[0074] 3.1 Constant Power Discharge Stage: The grid load demand is 30kW. The monitoring terminal distributes the total discharge power to three battery packs: Battery Pack #1 discharges 10kW (discharge current ≈ 95A), Battery Pack #2 discharges 9kW (SOH is slightly low, so the power is appropriately reduced, discharge current ≈ 86A), and Battery Pack #3 discharges 11kW (SOH is high, so the power is appropriately increased, discharge current ≈ 105A, not exceeding the current threshold of 100A, so it is adjusted to 100A). The DC power released by the battery packs is converted to AC power by the PCS and connected to the grid. During the discharge process, the BMS monitors the temperature. When the temperature of Battery Pack #3 rises to 40℃, the discharge current remains constant.

[0075] 3.2 Constant Current Discharge Stage: After 2 hours of discharge, the voltage of battery pack #1 drops to 28.8V, entering the constant current discharge stage. The discharge current is maintained at 80A for 20 minutes. When the SOC drops to 20%, the BMS sends a discharge stop signal and cuts off the discharge circuit of battery pack #1. Subsequently, battery packs #2 and #3 enter the constant current discharge stage in sequence until the SOC drops to 20% and the discharge stops.

[0076] 3.3 Discharge process adjustment: During the discharge process, the grid load suddenly drops to 20kW. The monitoring terminal adjusts the total discharge power to 20kW and distributes the discharge current as follows: 1#=60A, 2#=55A, 3#=65A. After the grid load recovers to 30kW, the normal discharge current is restored.

[0077] Step 4: Dynamic Equilibrium Adjustment (Performed Simultaneously)

[0078] 4.1 Equalization Detection: After discharging for 1 hour, the BMS detected that the SOC of battery pack #1 was 65%, the SOC of battery pack #2 was 60%, and the SOC of battery pack #3 was 68%. The SOC deviation between battery packs #2 and #3 was 8%, which exceeded the equalization threshold of 0.5%, and dynamic equalization adjustment was initiated.

[0079] 4.2 Balancing Execution: Through the bidirectional DC-DC module, some energy of battery pack #3 is transferred to battery pack #2. The balancing current is set to 25A. After 20 minutes, the SOC of the three battery packs are 55%, 54%, and 56%, respectively. The SOC deviation is less than 0.5%, and the balancing adjustment is stopped.

[0080] 4.3 Subsequent equalization: During the constant current discharge stage, the SOC deviation is continuously monitored to ensure that after the discharge is completed, the SOC of all three battery packs is 20%, the voltage is 28.8V, and the deviation is less than 5mV.

[0081] Step 5: Security Measures (to be carried out simultaneously)

[0082] 5.1 Real-time monitoring: The BMS monitors the parameters of each battery pack in real time. During the discharge process, it was detected that the insulation resistance of battery pack #3 dropped to 1MΩ (below the safety threshold of 2MΩ).

[0083] 5.2 Fault Warning: The monitoring terminal immediately issues an audible and visual alarm signal and records fault information (insulation resistance too low, #3 battery pack);

[0084] 5.3 Fault Handling: If the fault is determined to be serious, the BMS will immediately cut off the discharge circuit of battery pack #3 and stop its operation. At the same time, the total discharge power will be adjusted to 20kW and carried by battery packs #1 and #2 to prevent the fault from spreading. After the management personnel promptly investigate the fault and repair the insulation problem, battery pack #3 will resume operation.

[0085] 5.4 Redundancy Protection: If a minor fault occurs in the PCS during discharge, the BMS will immediately switch to the backup PCS module to ensure that the energy storage system discharges normally without interruption.

[0086] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for charging and discharging a battery at a battery pack level of an energy storage system, The system comprises, characterized in that: the energy storage system includes several parallel-connected battery packs, a battery management system (BMS), a power conversion system (PCS), and a monitoring terminal; the battery packs are composed of several individual batteries connected in series and parallel; and the system includes the following steps: Charge / discharge preparation: Collect status parameters of each battery pack through BMS to complete parameter initialization and fault diagnosis; Charging control: A three-stage charging strategy of constant current-constant voltage-trickle charge is adopted, and charging parameters are dynamically allocated according to the battery pack status; Discharge control: A two-stage discharge strategy of constant power and constant current is adopted, and discharge parameters are allocated according to grid demand and battery pack status; Dynamic balancing adjustment: Performs battery pack-level energy transfer balancing synchronously throughout the entire charging and discharging process; Security protection: Establish a multi-level real-time monitoring, fault early warning, fault handling and redundancy protection mechanism.

2. The battery pack-level charging and discharging method for an energy storage system according to claim 1, characterized in that: The charging and discharging preparation specifically includes: Battery pack status monitoring: The BMS collects battery pack voltage, total current, individual cell voltage, internal resistance, temperature, state of charge (SOC), and state of health (SOH). The SOC is calculated using the ampere-hour integration method combined with the open-circuit voltage correction algorithm, and the SOH is evaluated based on the number of cycles, capacity decay rate, and internal resistance change rate. Parameter initialization: Configure the charging cut-off voltage, discharging cut-off voltage, charging and discharging current threshold, equalization threshold, and safe temperature range on the monitoring terminal, and initialize the PCS operating parameters; Troubleshooting: The BMS determines whether the battery pack has overvoltage, undervoltage, overtemperature, abnormal internal resistance, or poor contact faults. If a fault is found, an alarm is triggered and the corresponding charging / discharging circuit is cut off. If no fault is found, the charging / discharging control is initiated.

3. The battery pack-level charging and discharging method for an energy storage system according to claim 1, characterized in that: The charging control specifically includes: Constant current charging stage: Based on the battery pack SOC and SOH, a constant current charging current not exceeding the maximum allowable value is allocated, and the charging current is adjusted in real time according to the battery pack temperature; Constant voltage charging stage: After the battery pack voltage reaches the charging cutoff voltage, the voltage remains constant, and the charging current gradually decreases. When it drops to the trickle charging threshold, it enters the trickle charging stage. Trickle charging stage: A small current is used to replenish the target SOC, the BMS sends a charging completion signal, and the PCS stops charging the battery pack. Dynamic adjustment during charging: The charging power and charging speed are adjusted in real time based on the grid load, the power generation of new energy sources, and the abnormal state of the battery.

4. The battery pack-level charging and discharging method for an energy storage system according to claim 1, characterized in that: The discharge control specifically includes: Constant power discharge stage: The monitoring terminal determines the total discharge power based on the grid load, and distributes it to each battery pack according to the battery pack's SOC, SOH and internal resistance to ensure that it does not exceed the maximum allowable discharge power. The discharge power is adjusted in real time according to the temperature. Constant current discharge stage: After the battery pack voltage drops to the discharge cutoff voltage threshold, the discharge current remains constant until the SOC reaches the target lower limit, at which point the BMS cuts off the battery pack discharge circuit. Dynamic adjustment during discharge: Adjust the discharge power or disconnect the circuit according to grid load fluctuations and abnormal battery conditions to avoid over-discharge of the battery pack.

5. The battery pack-level charging and discharging method for an energy storage system according to claim 1, characterized in that: The dynamic equilibrium adjustment specifically includes: Equalization detection: The BMS collects the SOC and voltage of each battery pack in real time and calculates the SOC deviation and voltage deviation between battery packs; Equalization judgment: When the SOC deviation exceeds 0.2%~1% or the voltage deviation exceeds 5mV~20mV, equalization adjustment is initiated; Balanced execution: Energy from high-SOC, high-voltage battery packs is transferred to low-SOC, low-voltage battery packs via a bidirectional DC-DC module; the bidirectional DC-DC module uses gallium nitride (GaN) power devices with a conversion efficiency of not less than 96%. Equalization Stop: Equalization stops when the SOC deviation of all battery packs is less than the equalization threshold and the voltage deviation is less than the preset threshold.

6. The battery pack-level charging and discharging method for an energy storage system according to claim 5, characterized in that: After dynamic balancing adjustment, the battery pack SOC consistency deviation is less than 0.2%, the voltage balancing accuracy reaches ±5mV, and the system energy utilization rate is not less than 85%.

7. The battery pack-level charging and discharging method for an energy storage system according to claim 1, characterized in that: The security protection specifically includes: Real-time monitoring: The BMS monitors the battery pack voltage, current, temperature, SOC, SOH and insulation resistance throughout the process, and the monitoring terminal analyzes the data in real time; Fault warning: When parameters exceed the safe range or charging / discharging abnormalities or equalization failures occur, the monitoring terminal will issue an audible and visual alarm and record the fault information. Troubleshooting: For minor faults, adjust charging and discharging parameters and activate the temperature control device; for severe faults, disconnect the faulty battery pack circuit and the system from the power grid. Redundancy protection: Configure backup battery packs and backup PCS modules, and automatically switch in case of failure; combine cloud big data to predict battery degradation trends.

8. The battery pack-level charging and discharging method for an energy storage system according to claim 1, characterized in that: The method described above can increase the cycle life of the battery pack by more than 45%, achieve a charge-discharge efficiency of more than 90%, and reduce the cost per kilowatt-hour of the energy storage system by more than 0.08 yuan.

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