Active balancing method and system for large-scale electrochemical energy storage system

Abstract

The present invention provides a method and system for active balancing of large-scale electrochemical energy storage systems, belonging to the field of electrical energy storage technology. The method utilizes a balancing switch method, utilizing balancing switches within a cluster of cells to control the transfer of power from cells with high power to cells with low power. This method can rapidly respond to imbalances within a cluster of cells, achieving power transfer through rapid switching. Compared to traditional cell management system balancing, this method eliminates one stage of conversion, resulting in higher efficiency, flexibility, and scalability.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric energy storage, and specifically relates to an active balancing method and system for a large-scale electrochemical energy storage system. Background Art

[0002] Electrochemical energy storage devices are devices that convert electrical energy into chemical energy through a chemical reaction for storage, and then release the chemical energy back into electrical energy through a reverse reaction when needed. In large-scale applications, these devices are often used to balance electricity supply and demand, improve grid stability, and facilitate the integration of renewable energy.

[0003] Electrochemical energy storage systems consist of hundreds or even thousands of battery cells connected in series or parallel. During the charge and discharge process, differences in the cells can lead to a decrease in the charge and discharge capacity of the entire cluster. Therefore, the battery management system employs a balancing strategy to balance the cells within the same cluster.

[0004] The balancing strategies of the battery cell management system are divided into active balancing and passive balancing. Passive balancing requires changing the status of other devices or components, which increases the complexity and cost of the circuit. In addition, since the difference between each single battery cell must be detected to achieve balancing, an additional data collection system is required. With the rapid development of renewable energy and the deep transformation of the power system, the market demand for large-scale electrochemical energy storage devices will continue to grow, and active balancing technology is gaining more and more attention. Active balancing is further divided into multiple technical routes, among which the current transfer method and power control method are the main ones. However, both methods have the problem of high system complexity and require high-quality electronic components and precise manufacturing processes, resulting in higher costs. In addition, complex algorithms and control systems will also increase costs.

[0005] Therefore, there is an urgent need for a method that is efficient, flexible and scalable, and can reduce the balancing cost and improve cost-effectiveness to a certain extent. Summary of the Invention

[0006] The present invention is achieved through the following technical solutions:

[0007] In a first aspect, the present invention provides a method for active balancing of a large-scale electrochemical energy storage system. The method uses a balancing switch method to control the transfer of power from cells with high power to cells with low power in the same cluster of cells.

[0008] The balancing switch uses a bidirectional DC / AC power converter to control bidirectional energy conversion between DC and AC;

[0009] The balanced switching method is achieved by implementing a balanced algorithm control strategy;

[0010] The balancing algorithm control strategy includes the following steps:

[0011] Step 1: Determine whether the energy storage system is in a charging state. If yes, proceed to step 2; if not, proceed to step 5.

[0012] Step 2: Calculate the average charge capacity of the same cluster of cells;

[0013] Step 3: Compare the chargeable capacity of a single cell with the average chargeable capacity. If the chargeable capacity of a single cell is greater than the sum of the average chargeable capacity and the threshold value, proceed to step 4. If the chargeable capacity of a single cell is less than the difference between the average chargeable capacity and the threshold value, proceed to step 8. If the chargeable capacity of a single cell is not less than the difference between the average chargeable capacity and the threshold value, and the chargeable capacity of a single cell is not greater than the sum of the average chargeable capacity and the threshold value, proceed to step 9.

[0014] Step 4: Charge and balance the battery cells, and then proceed to step 9;

[0015] Step 5: Determine whether the energy storage system is in a discharging state. If yes, proceed to step 6; if not, proceed to step 9.

[0016] Step 6: Calculate the average discharge capacity of the same cluster of cells;

[0017] Step 7: Compare the dischargeable capacity of a single cell with the average dischargeable capacity. If the dischargeable capacity of a single cell is greater than the sum of the average dischargeable capacity and the threshold value, proceed to step 8. If the dischargeable capacity of a single cell is less than the difference between the average dischargeable capacity and the threshold value, proceed to step 4. If the dischargeable capacity of a single cell is not less than the difference between the average dischargeable capacity and the threshold value, and the dischargeable capacity of a single cell is not greater than the sum of the average dischargeable capacity and the threshold value, proceed to step 9.

[0018] Step 8: Discharge and balance the battery cells;

[0019] Step 9: Terminate.

[0020] Furthermore, the step 2 is calculated by the following formula:

[0021] ge_ave = Formula (1)

[0022] Among them, ge_ave is the average chargeable capacity, is the percentage of remaining power, Is the health of the battery cell, i is the number of the battery cell in the cluster, n is the number of cells in the cluster.

[0023] Furthermore, step 6 is calculated by the following formula:

[0024] dge_ave = Formula (2)

[0025] Among them, dge_ave is the average discharge capacity, is the percentage of remaining power, Is the health of the battery cell, i Represents the number of the battery cell in the cluster, n is the number of cluster cells.

[0026] Furthermore, the step 4 is to adjust the charging rate by controlling the equalization switch to change the charging current to achieve equalization of the battery cells.

[0027] Furthermore, the step 8 is to adjust the discharge rate by controlling the balancing switch to change the discharge current to achieve balancing of the battery cells.

[0028] Preferably, performing charge and discharge balancing on the battery cells further includes adjusting the electric quantity of all the battery cells between clusters by using an external AC power supply.

[0029] A second aspect of the present invention further provides a battery cell management system based on the method of the present invention, the system comprising:

[0030] Energy storage converter PCS: adjusts the charging and discharging strategy of the battery cells and the output of AC power;

[0031] Cell cluster: consists of multiple cells connected in series;

[0032] Balancing switch: Each battery cell is connected to a balancing switch;

[0033] Cell management unit: formulates balancing strategies and controls the closing and opening of balancing switches;

[0034] Merging cabinet: All cells are connected to the merge cabinet after the AC power is converted by the balancing switch;

[0035] The combiner cabinet is also connected to an external AC power supply.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] High efficiency: The balancing switch method used in the present invention can quickly respond to the unbalanced state in the battery cell cluster and realize the transfer of electricity by quickly switching the switch. Compared with the traditional battery cell management system balancing, it has one less conversion level and is more efficient.

[0038] Flexibility: The balancing switch method can be flexibly configured according to the specific conditions and needs of the cell cluster. Instead of using a switch array, the station power is transferred to the cells for balancing by controlling the balancing switch to adapt to different balancing strategies.

[0039] Scalability: As the size of the battery cell cluster expands, the balanced switching method can maintain the balancing effect by increasing the number of switches and optimizing the control algorithm, and has good scalability.

[0040] Cost-effectiveness: Although the overall cost of active balancing technology is high, the balancing switch method can reduce the balancing cost and improve cost-effectiveness to a certain extent by optimizing circuit design and control strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is the algorithm flow chart of the present invention;

[0042] Figure 2 It is the battery cell management architecture of the present invention; DETAILED DESCRIPTION

[0043] The present invention is described in further detail below with reference to the accompanying drawings:

[0044] The present invention is an active balancing method for a large-scale electrochemical energy storage system. Specifically, a balancing switch method is used to control the transfer of electricity between single battery cells using a balancing switch, wherein the balancing switch selects a DC / AC power converter, and its connection relationship is that each battery cell will be connected to a balancing switch for balancing. The battery cells are connected in series to obtain a voltage range that can be accepted by the energy storage converter PCS, which is called a battery cell cluster. In the present invention, a battery cell cluster is composed of approximately 400 battery cells connected in series. When there is an inconsistency in the voltage of the single battery cells inside the battery cell cluster, the electricity is transferred from the battery cell with higher electricity to the battery cell with lower electricity by controlling the closing and opening of the balancing switch, thereby achieving balancing.

[0045] In the present invention, a switch is used to select cells within the same cluster that require balancing. The balancing switch is then controlled to balance cells with high and low charges. Furthermore, an external AC power source (typically the energy storage system's power system) can be used in conjunction with a bidirectionally controlled balancing switch to balance each cell. The present invention utilizes a bidirectionally controlled balancing switch because balancing involves both charging and discharging, necessitating a bidirectional controlled balancing switch. The bidirectional controlled balancing switch utilizes a bidirectional DC / AC power converter, a device capable of bidirectional energy conversion between direct current (DC) and alternating current (AC).

[0046] The balancing switching method of the present invention regulates the balancing switches by controlling them, eliminating the short circuits that can occur when a MOS (metal oxide semiconductor) failure occurs during typical switch array operation. The cell management system of the present invention formulates a balancing strategy based on monitoring results, controlling the closing and opening of the balancing switches of the switching elements to establish or disconnect power transfer paths.

[0047] The first embodiment of the present invention is an active balancing method for a large-scale electrochemical energy storage system, namely, a balancing switch method. The control strategy of this method is implemented by a balancing algorithm (i.e., formula (1), formula (2) and subsequent comparison of the difference between each battery cell and the average value). The process is as follows: Figure 1 shown.

[0048] The specific process is as follows:

[0049] The battery management system monitors each battery cell's voltage, temperature, remaining charge (SOC), and other parameters to determine the current charge and discharge status of the energy storage system. If the energy storage system is currently in a "discharge state" or "charge state," the control strategy's algorithm calculates the average chargeable / dischargeable capacity.

[0050] Step 1: Determine whether the energy storage system is in charging state

[0051] Determine whether the energy storage system is in a charging state. If it is in a charging state, proceed to step 2 to determine the balancing requirement.

[0052] Step 2: Calculate the average charge capacity of the same cluster of cells

[0053] The average chargeable capacity ge_ave is calculated using the following formula:

[0054] ge_ave = Formula (1)

[0055] in, is the percentage of remaining power, is the health of the battery cell, i represents the number of the battery cells in this cluster (for example, if there are 400 battery cells, i ranges from 1 to 400), and n is the number of battery cells in this cluster.

[0056] Step 3: Compare the difference between the charge capacity of each battery cell and the average charge capacity of the battery cell

[0057] Obtain the charge capacity of each cell in the cluster through the cell management system , the charge capacity of each battery cell Compare with the average charge capacity ge_ave of the same cluster of cells.

[0058] if ge_ave+ , then go to step 4, that is, perform charge balancing operation on the battery cell; wherein, The threshold value is set according to actual conditions. In the present invention, the threshold value is set to 2% of the average chargeable capacity.

[0059] if ge_ave- , then go to step 8, that is, perform discharge balancing operation on the battery cell.

[0060] if ge_ave+ , then go to step 9 and terminate.

[0061] Step 4: Charge and balance the cells

[0062] Adjust the charging rate and change the charging current by controlling the balancing switch to achieve energy transfer between cells or cell clusters. Specifically, pulse width modulation (PWM) technology is used to control the discharge of high-charge cells to low-charge cells through the balancing switch. This balancing switch control structure is a flyback circuit, a common switching power supply topology. Both it and PWM technology are well-known technologies and will not be discussed here. Furthermore, an external AC power supply can be used to adjust the charge level of all cells in the cluster to be consistent, that is, equal to the average value.

[0063] Step 5: Determine whether the energy storage system is in a discharging state

[0064] If the energy storage system is not in a charging state, it is determined whether the energy storage system is in a discharging state. If the energy storage system is in a discharging state, the operation of step 6 is performed, that is, the balancing demand is determined.

[0065] If the energy storage system is not in the discharging state, go to step 9, i.e. terminate.

[0066] Step 6: Calculate the average discharge capacity of the same cluster of cells

[0067] The average discharge amount dge_ave is calculated using the following formula:

[0068] dge_ave = Formula (2)

[0069] in, is the percentage of remaining power, is the health of the battery cell, i represents the number of the battery cells in this cluster (for example, if there are 400 battery cells, i ranges from 1 to 400), and n is the number of battery cells in this cluster.

[0070] Step 7: Compare the difference between the discharge capacity of each battery cell and the average discharge capacity of the battery cell.

[0071] The battery management system calculates the discharge capacity of each battery cell in the cluster After that, the discharge capacity Compare with the average discharge amount dge_ave of the same cluster.

[0072] if, dge_ave+ , then go to step 8, that is, perform discharge balancing operation on the battery cell, wherein, The threshold value is set to 2% of the average discharge capacity in the present invention.

[0073] if, dge_ave- , then go to step 4, that is, perform charge balancing operation on the battery cell;

[0074] if dge_ave+ , then go to step 9 and terminate.

[0075] Step 8: Discharge and balance the cells

[0076] Adjusting the discharge rate and varying the discharge current by controlling the balancing switch enables energy transfer between cells or cell clusters. Specifically, pulse width modulation (PWM) technology is used to control the discharge of cells with high charge to cells with low charge through the balancing switch. This balancing switch control structure is a flyback circuit, a common switching power supply topology. Both it and PWM technology are already known technologies and will not be discussed further here. Furthermore, an external AC power supply can be used to adjust the charge levels of all cells in the cluster to be consistent, that is, equal to the average value.

[0077] Step 9. Terminate

[0078] The balancing switch stops running, terminating the cell balancing operation.

[0079] In the present invention, the control strategy is executed cyclically until the battery cell management system feedbacks that all battery cells within the battery cluster and the battery cells between the battery clusters have achieved balance, and the operation is terminated.

[0080] The outstanding feature of the active balancing method for large-scale electrochemical energy storage systems of the present invention is that it uses the chargeable capacity / dischargeable capacity instead of the conventionally used SOC. The calculation of SOC has a large deviation, is complex, and has low calculation accuracy, but the chargeable capacity / dischargeable capacity not only takes into account the value of SOC but also the value of SOH, which is relatively more comprehensive. In addition, the time series artificial intelligence algorithm can also be used to accurately calculate the chargeable capacity and dischargeable capacity of the energy storage cell. The artificial intelligence algorithm here includes LSTM, RNN or transformer. The present invention takes a process of LSTM calculation as an example, and its steps include:

[0081] 1. Collect input historical data, including the voltage, temperature, and chargeable / dischargeable capacity of the battery cell during the charge / discharge process;

[0082] 2. Train the model;

[0083] 3. Using the trained model, input the real-time collected voltage and temperature of the battery cell into the model to calculate the real-time chargeable / dischargeable capacity of the battery cell.

[0084] Another embodiment of the present invention is a cell management system based on the balanced switching method of the present invention, such as Figure 2 As shown, the overall architecture usually includes the following key parts:

[0085] Energy storage converter PCS: Adjusts the charging and discharging strategy of the battery cells and the output of AC power according to actual needs.

[0086] Cell cluster: It is composed of multiple cells connected in series and is the direct object of power balancing.

[0087] Balancing switch: Each battery cell is connected to the combiner cabinet via a balancing switch. The balancing switch uses a bidirectional DC / AC power converter to achieve bidirectional energy conversion between direct current (DC) and alternating current (AC) for subsequent energy transmission or use.

[0088] Cell management unit: formulates balancing strategies based on monitoring results and controls the closing and opening of the balancing switches of switching elements.

[0089] Merging Cabinet: After all cells have converted AC power through balancing switches, the AC power is gathered into the Merging Cabinet. As a key node in the system, the Merging Cabinet is responsible for collecting, distributing, and possibly redistributing electrical energy.

[0090] The combiner cabinet is also connected to an external AC power supply, so that the system can obtain power from the external power supply for balanced operation.

[0091] Preferably, a plurality of balancing switches form a switch element for controlling the power transfer path between single cells. According to the monitoring results of the cell management unit and the balancing strategy, the balancing switch DC / AC is controlled to be closed or opened, thereby establishing or cutting off the power transfer path.

[0092] The above technical solution is only one embodiment of the present invention. For those skilled in the art, it is easy to make various types of improvements or modifications based on the principles disclosed in the present invention, and it is not limited to the technical solution described in the above specific embodiments of the present invention. Therefore, the above description is only preferred and does not have a restrictive meaning.

Claims

1. An active balancing method for a large-scale electrochemical energy storage system, characterized in that: The method is implemented using a battery cell management system, which includes: Energy storage converter PCS: adjusts the charging and discharging strategy of the battery cells and the output of AC power; Cell cluster: consists of multiple cells connected in series; Balancing switch: Each battery cell is connected to a balancing switch, which controls the power transfer path between the individual battery cells by controlling the closing and opening of the balancing switch; Cell management unit: formulates balancing strategies and controls the closing and opening of balancing switches; Merging cabinet: All cells are connected to the merge cabinet after the AC power is converted by the balancing switch; The junction cabinet is also connected to an external AC power supply; The method uses a balancing switch method, utilizing a bidirectional DC / AC power converter as a balancing switch in the same cluster of cells to control the transfer of power from cells with high power to cells with low power. The balancing switch controls the bidirectional energy conversion between DC and AC by implementing a balancing algorithm control strategy. The balancing algorithm control strategy includes the following steps: Step 1: Determine whether the energy storage system is in a charging state. If yes, proceed to step 2; if not, proceed to step 5. Step 2: Calculate the average charge capacity of the same cluster of cells; Step 3: Compare the chargeable capacity of a single cell with the average chargeable capacity. If the chargeable capacity of a single cell is greater than the sum of the average chargeable capacity and the threshold value, proceed to step 4. If the chargeable capacity of a single cell is less than the difference between the average chargeable capacity and the threshold value, proceed to step 8. If the chargeable capacity of a single cell is not less than the difference between the average chargeable capacity and the threshold value, and the chargeable capacity of a single cell is not greater than the sum of the average chargeable capacity and the threshold value, proceed to step 9. Step 4: Charge and balance the battery cells, and then proceed to step 9; Step 5: Determine whether the energy storage system is in a discharging state. If yes, proceed to step 6; if not, proceed to step 9. Step 6: Calculate the average discharge capacity of the same cluster of cells; Step 7: Compare the dischargeable capacity of a single cell with the average dischargeable capacity. If the dischargeable capacity of a single cell is greater than the sum of the average dischargeable capacity and the threshold value, proceed to step 8. If the dischargeable capacity of a single cell is less than the difference between the average dischargeable capacity and the threshold value, proceed to step 4. If the dischargeable capacity of a single cell is not less than the difference between the average dischargeable capacity and the threshold value, and the dischargeable capacity of a single cell is not greater than the sum of the average dischargeable capacity and the threshold value, proceed to step 9. Step 8: Discharge and balance the battery cells; Step 9: Terminate; The step 2 is calculated by the following formula: Formula (1) Among them, ge_ave is the average chargeable capacity, is the percentage of remaining power, Is the health of the battery cell, i is the number of the battery cell in the cluster, n is the number of cells in the cluster; The step 6 is calculated by the following formula: Formula (2) Among them, dge_ave is the average discharge capacity, is the percentage of remaining power, Is the health of the battery cell, i Represents the number of the battery cell in the cluster, n is the number of cluster cells; Steps 2 and 6 are also calculated using the LSTM method: Step 21, collecting historical data, including the voltage, temperature, chargeable capacity, and dischargeable capacity of the battery cell during the charging process; Step 22, training the model; Step 23: Input the real-time collected voltage and temperature of the battery cell into the model to calculate the average chargeable capacity and average dischargeable capacity in real time; Performing charge and discharge balancing on the battery cells also includes adjusting the electric quantity of all the battery cells between clusters through an external AC power supply.

2. The active balancing method for a large-scale electrochemical energy storage system according to claim 1, characterized in that: The step 4 is to adjust the charging rate by controlling the equalization switch to change the charging current to achieve equalization of the battery cells.

3. The active balancing method for a large-scale electrochemical energy storage system according to claim 1, characterized in that: The step 8 is to adjust the discharge rate by controlling the balancing switch to change the discharge current to achieve cell balancing.

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