Active equalization method and system of large-scale electrochemical energy storage system

Abstract

The invention provides an active equalization method and system for a large-scale electrochemical energy storage system, and belongs to the technical field of electric energy storage. According to the method, an equalization switch method is used, and an equalization switch is used for controlling the electric quantity to be transferred from an electric core with high electric quantity to an electric core with low electric quantity in the same cluster of electric cores. According to the invention, the unbalanced state in the battery cell cluster can be quickly responded, the transfer of the electric quantity is realized through the quick change-over switch, and compared with the equalization of the traditional battery cell management system, one-stage conversion is omitted, the efficiency is higher, and the flexibility and expandability are good.

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 for storage through chemical reactions and release the chemical energy into electrical energy through reverse reactions when needed. In large-scale applications, these devices are often used to balance electricity supply and demand, improve grid stability, and promote the consumption of renewable energy.

[0003] Electrochemical energy storage is composed of hundreds of battery cells connected in series and parallel. During the charging and discharging process, the differences in the battery cells will lead to a reduction in the charging and discharging capacity of the entire battery cluster. Therefore, the battery management system will use a balancing strategy to balance the same cluster of batteries.

[0004] The balancing strategies of the battery management system are divided into active balancing and passive balancing. Passive balancing requires changing the status of other devices or components, which will increase the complexity and cost of the circuit. In addition, since the difference between each single battery cell needs to be detected to achieve balancing, an additional 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 will receive 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, but both methods have the problem of high system complexity, and also 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: In a first aspect of the present invention, a method for active balancing of a large-scale electrochemical energy storage system is provided, wherein the method uses a balancing switch method to control the transfer of power from a high-power cell to a low-power cell in the same cluster of cells; The balancing switch uses a bidirectional DC / AC power converter to control bidirectional energy conversion between DC and AC; The balanced switching method is realized by implementing a balanced 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 no, proceed to step 5. Step 2, calculating the average charge capacity of the same cluster of cells; Step 3, compare the chargeable capacity of a single battery cell with the average chargeable capacity. If the chargeable capacity of a single battery 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 battery 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 battery cell is not less than the difference between the average chargeable capacity and the threshold value, and the chargeable capacity of a single battery cell is not greater than the sum of the average chargeable capacity and the threshold value, proceed to step 9. Step 4, performing charge equalization on the battery cell, and then proceeding to step 9; Step 5: determine whether the energy storage system is in a discharging state. If yes, proceed to step 6; if no, proceed to step 9; Step 6, calculating the average discharge capacity of the same cluster of cells; Step 7, compare the dischargeable capacity of a single battery cell with the average dischargeable capacity. If the dischargeable capacity of a single battery 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 battery 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 battery cell is not less than the difference between the average dischargeable capacity and the threshold value, and the dischargeable capacity of a single battery cell is not greater than the sum of the average dischargeable capacity and the threshold value, proceed to step 9. Step 8, discharging and balancing the battery cells; Step 9: Terminate.

[0007] Further, the step 2 is calculated by the following formula: ge_ave = Formula (1) Among them, ge_ave is the average chargeable capacity, is the remaining power percentage, Is the health of the battery cell. i is the number of the cell in the cluster, n is the number of cells in the cluster.

[0008] Further, the step 6 is calculated by the following formula: dge_ave = Formula (2) Among them, dge_ave is the average discharge capacity, is the remaining power percentage, Is the health of the battery cell. i Represents the number of cells in the cluster. n is the number of cluster cells.

[0009] 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.

[0010] 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.

[0011] Preferably, performing charge and discharge balancing on the battery cells further comprises adjusting the electric quantity of all the battery cells between clusters by an external AC power supply.

[0012] 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: Energy storage converter PCS: adjusts the charging and discharging strategy of the battery cells and the output of AC power; Cell cluster: It is composed of multiple cells connected in series; Balancing switch: Each battery cell is connected to a balancing switch; Cell management unit: formulate balancing strategies and control the closing and opening of balancing switches; Merger cabinet: The AC power of all cells converted by the balancing switch is gathered into the merge cabinet; The combiner cabinet is also connected to an external AC power source.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 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 level of conversion and is more efficient.

[0014] Flexibility: The balancing switch method can be flexibly configured according to the specific situation and needs of the battery cell cluster. Instead of using a switch array, the station electricity is used to control the balancing switch to transfer to the battery cells for balancing to adapt to different balancing strategies.

[0015] Scalability: As the size of the cell cluster increases, the balanced switching method can maintain the balancing effect by increasing the number of switches and optimizing the control algorithm, and has good scalability.

[0016] 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

[0017] Figure 1 It is the algorithm flow chart of the present invention; Figure 2 It is the battery cell management architecture of the present invention; DETAILED DESCRIPTION The present invention is further described in detail below in conjunction with the accompanying drawings: 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 cells, wherein the balancing switch selects a DC / AC power converter, and its connection relationship is that each cell will be connected to a balancing switch for balancing. The cells are connected in series to obtain a voltage range that the energy storage converter PCS can accept, which is called a cell cluster. In the present invention, a cell cluster is composed of approximately 400 cells connected in series. When there is an inconsistency in the voltage of the single cells inside the cell cluster, the electricity is transferred from the cell with higher electricity to the cell with lower electricity by controlling the closing and opening of the balancing switch, thereby achieving balancing.

[0018] In the present invention, a switch is used to select the battery cells that need to be balanced in the same cluster of battery cells, and then the battery cells with high power and low power are balanced by controlling the balancing switch; furthermore, an external AC power supply (generally the power system of the energy storage system station) can be used in combination with a bidirectional control balancing switch to balance each battery cell. The bidirectional control balancing switch is adopted in the present invention because there are two situations, charging and discharging, when balancing, so a bidirectional control balancing switch is required for control. The bidirectional control balancing switch adopts a bidirectional DC / AC power converter, which is a device that can realize bidirectional energy conversion between direct current (DC) and alternating current (AC).

[0019] The balancing switch method of the present invention adjusts by controlling the balancing switch, thereby preventing the short circuit of the system caused by the MOS failure switch array when the switch array is used under normal circumstances. The battery management system of the present invention formulates a balancing strategy based on the monitoring results, controls the closing and opening of the balancing switch of the switch element, and thus establishes or cuts off the power transfer path.

[0020] Embodiment 1 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., equation (1), equation (2) and subsequent comparison of the difference between each battery cell and the average value). The process is as follows: Figure 1 shown.

[0021] The specific process is as follows: The battery management system detects the voltage, temperature, remaining capacity (SOC) and other parameters of each battery cell to determine the current charge and discharge status of the energy storage system. If the current energy storage system is in the "discharge state" or "charge state", the average charge / discharge capacity is calculated through the algorithm in the control strategy.

[0022] Step 1: Determine whether the energy storage system is in charging state Determine whether the energy storage system is in a charging state. If it is in a charging state, perform the operation of step 2 to determine the balancing demand.

[0023] Step 2: Calculate the average charge capacity of the same cluster of cells The average chargeable capacity ge_ave is calculated by the following formula: ge_ave = Formula (1) in, is the remaining power percentage, 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 is from 1 to 400), and n is the number of battery cells in this cluster.

[0024] Step 3: Compare the difference between the charge capacity of each battery cell and the average charge capacity of the battery cell. 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 chargeable capacity ge_ave of the same cluster of cells.

[0025] if ge_ave+ , then go to step 4, that is, perform charge equalization operation on the battery cell; wherein, is a threshold value, and 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.

[0026] if ge_ave- , then go to step 8, that is, perform discharge balancing operation on the battery cell.

[0027] if ge_ave+ , then go to step 9 and terminate.

[0028] Step 4: Charge and balance the cells Adjust the charging rate and change the size of the charging current by controlling the balancing switch to achieve energy transfer between cells or cell clusters. Specifically, the pulse width modulation PWM technology is used to control the discharge of cells with high power to cells with low power through the balancing switch. This balancing switch control structure is a flyback circuit, which is a common switching power supply topology. It and PWM technology are both existing technologies and will not be described here. Furthermore, the power of all cells in the clusters can be adjusted to be consistent through an external AC power supply, that is, they are all equal to the average value.

[0029] Step 5: Determine whether the energy storage system is in a discharging state 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.

[0030] If the energy storage system is not in the discharging state, go to step 9, i.e. terminate.

[0031] Step 6: Calculate the average discharge capacity of the same cluster of cells The average discharge amount dge_ave is calculated by the following formula: dge_ave = Formula (2) in, is the remaining power percentage, 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 is from 1 to 400), and n is the number of battery cells in this cluster.

[0032] Step 7: Compare the difference between the discharge capacity of each battery cell and the average discharge capacity of the battery cell. 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 of the same cluster dge_ave.

[0033] if, dge_ave+ , then go to step 8, that is, perform discharge balancing operation on the battery cell, where: is the threshold value; in the present invention, the threshold value is set to 2% of the average dischargeable capacity.

[0034] if, dge_ave - , then go to step 4, that is, perform charge equalization operation on the battery cell; if dge_ave+ , then go to step 9 and terminate.

[0035] Step 8: Discharge and balance the cells Adjust the discharge rate and change the size of the discharge current by controlling the balancing switch to achieve energy transfer between cells or cell clusters. Specifically, the pulse width modulation PWM technology is used to control the high-power cell to discharge to the low-power cell through the balancing switch. This balancing switch control structure is a flyback circuit, which is a common switching power supply topology. It and PWM technology are both existing technologies and will not be described here. Furthermore, the power of all cells in the cluster can be adjusted to be consistent through an external AC power supply, that is, they are all equal to the average value.

[0036] Step 9. Termination The balancing switch stops running, terminating the cell balancing operation.

[0037] In the present invention, the control strategy is executed cyclically until the battery cell management system feeds back that all battery cells in the battery cluster and the battery cells between the battery clusters have achieved balance, and the operation is terminated.

[0038] The outstanding feature of the active balancing method of the large-scale electrochemical energy storage system of the present invention is that the chargeable capacity / dischargeable capacity is used instead of the conventional SOC. The calculation of SOC has a large deviation, complex calculation, and 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: 1. Collect input historical data, including the voltage, temperature, and chargeable / dischargeable capacity of the battery during the charging / discharging process; 2. Train the model; 3. Using the trained model, input the voltage and temperature of the battery cell collected in real time into the model to calculate the real-time chargeable / dischargeable capacity of the battery cell.

[0039] Another embodiment of the present invention is a battery 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: Energy storage converter PCS: adjusts the charging and discharging strategy of the battery cells and the output of AC power according to actual needs.

[0040] Cell cluster: It is composed of multiple cells connected in series and is the direct object of power balancing.

[0041] Balancing switch: Each battery cell is connected to the junction box through 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.

[0042] Battery cell management unit: formulates balancing strategies based on monitoring results and controls the closing and opening of the balancing switches of switching elements.

[0043] Merger cabinet: The AC power converted by all cells through the balancing switch is gathered in the merge cabinet. As an important node in the system, the merge cabinet is responsible for collecting, distributing and possibly redistributing electrical energy.

[0044] 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.

[0045] Preferably, a plurality of balancing switches form a switch element for controlling the power transfer path between single cells. According to the monitoring result and balancing strategy of the cell management unit, the closing and opening of the balancing switch DC / AC are controlled to establish or cut off the power transfer path.

[0046] The above technical solution is only one implementation mode 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 uses a balanced switch method, using a bidirectional DC / AC power converter as a balanced switch in the same cluster of cells to control the transfer of power from cells with high power to cells with low power; the balanced switch controls the bidirectional energy conversion between DC and AC by implementing a balanced 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 no, proceed to step 5. Step 2, calculating the average charge capacity of the same cluster of cells; Step 3, compare the chargeable capacity of a single battery cell with the average chargeable capacity. If the chargeable capacity of a single battery 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 battery 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 battery cell is not less than the difference between the average chargeable capacity and the threshold value, and the chargeable capacity of a single battery cell is not greater than the sum of the average chargeable capacity and the threshold value, proceed to step 9. Step 4, performing charge equalization on the battery cell, and then proceeding to step 9; Step 5: determine whether the energy storage system is in a discharging state. If yes, proceed to step 6; if no, proceed to step 9; Step 6, calculating the average discharge capacity of the same cluster of cells; Step 7, compare the dischargeable capacity of a single battery cell with the average dischargeable capacity. If the dischargeable capacity of a single battery 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 battery 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 battery cell is not less than the difference between the average dischargeable capacity and the threshold value, and the dischargeable capacity of a single battery cell is not greater than the sum of the average dischargeable capacity and the threshold value, proceed to step 9. Step 8, discharging and balancing the battery cells; Step 9: Terminate.

2. The active balancing method for a large-scale electrochemical energy storage system according to claim 1, characterized in that: The step 2 is calculated by the following formula: ge_ave = Formula (1) Among them, ge_ave is the average chargeable capacity, is the remaining power percentage, Is the health of the battery cell. i is the number of the cell in the cluster, n is the number of cells in the cluster.

3. The active balancing method for a large-scale electrochemical energy storage system according to claim 1, characterized in that: The step 6 is calculated by the following formula: dge_ave = Formula (2) Among them, dge_ave is the average discharge capacity, is the remaining power percentage, Is the health of the battery cell. i Represents the number of cells in the cluster. n is the number of cluster cells.

4. 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 the equalization of the battery cells.

5. 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 balancing of the battery cells.

6. The active balancing method for a large-scale electrochemical energy storage system according to claim 1, characterized in that: The charging and discharging equalization of the battery cells also includes adjusting the electric quantity of all the battery cells between clusters through an external AC power supply.

7. A battery cell management system, used to implement the method according to any one of claims 1 to 6, It is characterized in that The system comprises: Energy storage converter PCS: adjusts the charging and discharging strategy of the battery cells and the output of AC power; Cell cluster: It is composed of multiple cells connected in series; Balancing switch: Each battery cell is connected to a balancing switch; Cell management unit: formulate balancing strategies and control the closing and opening of balancing switches; Merger cabinet: The AC power of all cells converted by the balancing switch is gathered into the merge cabinet; The combiner cabinet is also connected to an external AC power source.

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