A dual-layer power distribution method for dual-battery energy storage system based on balanced control

Abstract

The present invention discloses a double-layer power distribution method for a dual-battery energy storage system based on balanced control. It includes the following steps: initially grouping the battery cells according to their health status and state of charge, switching the battery pack charge / discharge state during operation when the state of charge exceeds the limit; completing the upper-layer power distribution of the battery energy storage system based on the principle that the charging group responds to the charging power first and the discharging group responds to the discharging power first; calculating the imbalance degree of the health status of the battery group, and then determining the power distribution mode within the two battery groups respectively; calculating the imbalance index of the battery cells of the battery group, and distributing the power adjustment instructions of the battery group to the battery cells in the group according to the determined power distribution mode and imbalance index. The present invention groups the battery cells to reduce their life loss, uses the health status and state of charge balanced control method to perform power distribution, realizes the balance of the health status and the state of charge of the battery cells, and further extends the service life.

Description

Technical Field

[0001] The present invention relates to the technical field of electric energy storage, and in particular to a power distribution method for a battery energy storage system for balanced control. Technical Background

[0002] The achievement of the "dual carbon" goals requires the integration of renewable energy into the power grid on a larger scale. However, the inherent intermittency and volatility of renewable energy pose significant challenges to the safe operation of the power grid. Battery energy storage systems (BESS) have gradually become more widely used to smooth out renewable energy fluctuations due to their advantages such as fast response speed and the ability to shift energy in time and space. As the installed scale of BESS increases, its high investment cost and limited service life have gradually attracted the attention of many scholars. Currently, how to control the efficient and long-term operation of BESS has become a key issue that needs to be addressed.

[0003] Maintaining a balanced state of battery cells within a BESS during operation is crucial for improving its sustainable control capabilities and extending its service life. Due to the large footprint and advanced cooling systems of a BESS, battery cell balance primarily involves balancing the state of health (SOH) and state of charge (SOC). In this context, studying how to simultaneously maintain balanced SOH and SOC within battery cells plays a crucial role in improving the dispatchability potential of the BESS and extending its service life. Summary of the Invention

[0004] The purpose of the present invention is to design a dual-layer power distribution method for a dual-battery energy storage system that simultaneously controls SOH balance and SOC balance, so as to gradually balance the originally unbalanced battery cells during operation, thereby improving the sustainable regulation capability of the BESS and extending the service life of the BESS. The present invention provides a dual-layer power distribution method for a dual-battery energy storage system based on balanced control. It not only provides a judgment standard for the imbalance of the health status of the battery pack and provides a method for calculating the imbalance index of the battery cell, but also designs two power distribution modes based on this, which are respectively suitable for the lower-layer power distribution methods that the battery pack should adopt when the SOH is unbalanced and the SOH is balanced, thereby achieving the SOH and SOC of the battery cells in the two battery packs gradually tending to balance during operation. Finally, the effectiveness of the detection method was verified by simulation.

[0005] The present invention adopts a technical solution: a double-layer power distribution method for a dual-battery energy storage system based on balanced control, which includes the following steps:

[0006] (1) Determine the charging group and the discharging group, assign the battery energy storage system power adjustment instructions to the charging group and the discharging group, realize the upper power distribution of the battery energy storage system, calculate the health status imbalance of the two battery groups, and determine the power distribution mode of the two battery groups respectively;

[0007] (2) Calculate the imbalance index of the battery pack cells and distribute the power adjustment instructions of the battery pack to the battery cells in the group according to the power distribution mode and the imbalance index.

[0008] In step (1), the method for determining the charging group and the discharging group is as follows: at the initial moment, the group with the higher average SOC of the two battery groups is used as the discharging group, and the group with the lower average SOC is used as the charging group; during operation, when the SOC of the battery cell exceeds the limit, the charging and discharging state of the battery group is switched, and the original charging group is used as the discharging group, and the discharging group is used as the charging group.

[0009] In step (1), the method of allocating the power adjustment instructions of the BESS to the charging group and the discharging group is as follows: if the BESS needs to be charged, the charging group responds first, and if there is a power difference, it is supplemented by the discharging group; if the BESS needs to be discharged, the discharging group responds first, and if there is a power difference, it is supplemented by the charging group, thereby completing the upper-level power allocation of the BESS.

[0010] In step (1), the health status imbalance degree of the two battery packs is calculated as follows:

[0011]

[0012] Among them, f USOH SOH is the imbalance degree of the battery pack health status. F1 is the extremely poor health status of all battery cells in the battery pack. F2 is the imbalance degree of the health status of all battery cells. max and SOH min Represents the maximum and minimum health status of all battery cells, SOH i and SOH j Represent the health status of the i-th and j-th battery cells respectively, and N is the number of battery cells in the battery pack;

[0013] In step (1), the method for determining the power distribution mode of the two battery packs is: when f USOH When it is 1, the battery pack adopts mode 1 to distribute the power of the battery cells in the battery pack. USOH When it is 0, the battery pack adopts mode 2 to distribute the power of the battery cells in the battery pack.

[0014] In step (2), the imbalance index calculation formula of the battery cell is as follows:

[0015]

[0016] Among them, f UHC,i and represents the imbalance index of battery cell i, f 1,i and f 2,i They represent the health status index and charge status index of the current battery cell i, respectively. λ1 and λ2 represent weight coefficients, whose values ​​are related to the power allocation mode. S cd It is the charge and discharge status flag, which takes 1 when discharging and -1 when charging. i Indicates the state of charge of the i-th battery cell.

[0017] In step (2), the method for allocating the battery pack power adjustment instructions to the battery cells therein under different power allocation modes is as follows:

[0018] Power allocation mode 1: In mode 1, the health status of the battery cells in the battery pack varies greatly. Therefore, the values ​​of λ1 and λ2 are set to 50% and 50%, respectively. This allows the calculation of the imbalance index of all battery cells in the battery pack. In this case, the power adjustment command for battery cell i is as follows:

[0019]

[0020] Power distribution mode 2: In mode 2, the health status of the battery cells in the battery pack is almost the same. Therefore, the main consideration is to balance the state of charge. Therefore, the values ​​of λ1 and λ2 are 0 and 100%, respectively. This can be used to calculate the imbalance index of all battery cells in the battery pack. In this case, the power adjustment command for battery cell i is as follows:

[0021]

[0022] The technical solution provided by the present invention has the following beneficial effects:

[0023] A criterion for judging the imbalance degree of the health status of a battery pack is given; a method for calculating the imbalance index of a battery cell is provided; and two power distribution modes are designed. When the SOH imbalance degree of the battery pack is 1, mode 1 can quickly balance the SOH of all battery cells in the battery pack while maintaining the battery pack's relatively accurate tracking of power regulation instructions. When the SOH imbalance degree of the battery pack is 0, mode 2 can quickly balance the SOC of all battery cells in the battery pack while maintaining the SOH balance. The coordinated cooperation of the two power distribution modes can achieve a gradual balance in the SOH and SOC of the battery cells in the two battery packs during operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below in conjunction with the accompanying drawings:

[0025] Figure 1is a flow chart of the present invention;

[0026] Figure 2 It is the SOH change curve during the operation of the battery unit;

[0027] Figure 3 is the SOC change curve during the operation of the battery unit;

[0028] Figure 4 is the response result of BESS to the power adjustment command. Specific implementation plan

[0029] In order to better understand the purpose, technical solutions and technical effects of the present invention, the present invention is further explained below with reference to the accompanying drawings.

[0030] The present invention proposes a double-layer power distribution method for a dual-battery energy storage system based on balanced control. Figure 1 Flowchart of the present invention, its implementation process includes the following detailed steps.

[0031] Step 1: Determine the charging and discharging groups, assign the battery energy storage system power adjustment instructions to the charging and discharging groups, implement the upper-level power distribution of the battery energy storage system, calculate the health status imbalance of the two battery groups, and determine the power distribution mode for the two battery groups:

[0032] 1) The method for determining the charging group and the discharging group is as follows: at the initial moment of operation, the group with the higher average SOC of the two battery groups is used as the discharging group, and the group with the lower average SOC is used as the charging group; during operation, when the SOC of a battery cell exceeds the limit, it is necessary to switch the charge and discharge states of the battery groups, so that the original charging group becomes the discharging group and the discharging group becomes the charging group.

[0033] 2) The method for allocating BESS power adjustment commands to the charging group and the discharging group is as follows: if the BESS needs to be charged, the charging group responds first, and if there is a power difference, the discharging group supplements it; if the BESS needs to be discharged, the discharging group responds first, and if there is a power difference, the charging group supplements it, thus completing the upper-level power allocation of the BESS. This process can be summarized in Table 1 below:

[0034] Table 1 Power regulation instructions allocated to two battery packs in different states

[0035]

[0036] 3) The health status imbalance calculation method of two battery groups is as follows:

[0037]

[0038] Among them, f USOHSOH is the imbalance degree of the battery pack health status. F1 is the extremely poor health status of all battery cells in the battery pack. F2 is the imbalance degree of the health status of all battery cells. max and SOH min Represents the maximum and minimum health status of all battery cells, SOH i and SOH j They represent the health status of the i-th and j-th battery cells respectively, and N is the number of battery cells in the battery pack.

[0039] 4) The method for determining the power distribution mode of the two battery packs is: when f USOH When it is 1, the battery pack adopts mode 1 to distribute the power of the battery cells in the battery pack. USOH When it is 0, the battery pack adopts mode 2 to distribute the power of the battery cells in the battery pack.

[0040] Step 2 calculates the imbalance index of the battery pack cells and distributes the power adjustment instructions of the battery pack to the battery cells in the group according to the power distribution mode and the imbalance index:

[0041] 1) The calculation formula of the battery cell imbalance index is as follows:

[0042]

[0043] Among them, f UHC,i and represents the imbalance index of battery cell i, f 1,i and f 2,i They represent the health status index and charge status index of the current battery cell i, respectively. λ1 and λ2 represent weight coefficients, whose values ​​are related to the power allocation mode. S cd It is the charge and discharge status flag, which takes 1 when discharging and -1 when charging. i Indicates the state of charge of the i-th battery cell.

[0044] 2) The method for allocating battery pack power regulation instructions to the battery cells in different power allocation modes is as follows:

[0045] Power allocation mode 1: In mode 1, the health status of the battery cells in the battery pack varies greatly. Therefore, the values ​​of λ1 and λ2 are set to 50% and 50%, respectively. This allows the calculation of the imbalance index of all battery cells in the battery pack. In this case, the power adjustment command for battery cell i is as follows:

[0046]

[0047] Power distribution mode 2: In mode 2, the health status of the battery cells in the battery pack is almost the same. Therefore, the main consideration is to balance the state of charge. Therefore, the values ​​of λ1 and λ2 are 0 and 100%, respectively. This can be used to calculate the imbalance index of all battery cells in the battery pack. In this case, the power adjustment command for battery cell i is as follows:

[0048]

[0049] To further understand the present invention and verify the effectiveness of the proposed two-tier power allocation method for a dual-battery energy storage system based on balanced control, a simulation was performed using the power regulation instructions of a battery energy storage system. The battery energy storage system has a capacity of 10MW / 10MWh, and the capacity of both battery packs is 5MW / 5MWh. Other relevant parameters are shown in Table 2 below.

[0050] Table 2 Battery energy storage system related parameters

[0051]

[0052] At the initial moment, the charging and discharging groups are determined based on the average SOC of the two battery groups. Then, based on the principle that the charging group prioritizes charging power and the discharging group prioritizes discharging power, the BESS power adjustment commands are distributed to the two battery groups, completing the upper-level power allocation. The SOH imbalance of the two battery groups is then calculated, and the appropriate lower-level power allocation mode is determined. Based on this, the imbalance index of the battery cells within the group is calculated, and the power adjustment commands of the battery group are then distributed to the battery cells within it, completing the lower-level power allocation. During operation, if the SOC of a battery cell exceeds the limit, the charging and discharging state of the two battery groups is switched.

[0053] The SOH change curves of all battery cells during operation are shown in the attached figure. Figure 2 As shown in the figure, the SOH deviation of the battery cells in the two battery groups is large at the beginning of operation. Therefore, the main goal in the early stage of operation is to balance the SOH. When t = 567 minutes, the SOH of battery group 1 is balanced, and when t = 638 minutes, the SOH of battery group 2 is balanced. This shows the effectiveness of the proposed power allocation method in balancing the SOH of battery cells.

[0054] The SOC change curves of all battery cells during operation are shown in the attached figure. Figure 3As shown in the figure, at the beginning of operation, due to the large deviation in the SOH of the battery cells in the two battery packs, the main goal is to balance the SOH, so the SOC of the battery cells in the battery packs will have a large deviation. After the SOH of the two battery packs is balanced, the main goal is to balance the SOC. When t = 848 minutes, the SOC of battery pack 1 reaches balance, and when t = 896 minutes, the SOC of battery pack 2 reaches balance. This shows the effectiveness of the proposed power allocation method in balancing the SOC of battery cells.

[0055] The response of BESS to its power regulation command is shown in the attached figure. Figure 4 As shown in the figure, it can be seen that there will be some moments of insufficient power supply during the initial operation, which is mainly caused by the balance of the SOH of the battery cells. However, since the power deviation is small, it will not cause a serious impact. After the SOH is balanced, the BESS can accurately track its power regulation instructions.

[0056] In summary, the dual-layer power distribution method for a dual-battery energy storage system based on balanced control proposed in the present invention can quickly bring the health status and charge status of the battery cells in the group into line while ensuring that the BESS accurately responds to its power regulation instructions.

Claims

1. A double-layer power distribution method for a dual-battery energy storage system based on balanced control, characterized in that: The following steps are involved: (1) Determine the charging group and the discharging group, assign the battery energy storage system power adjustment instructions to the charging group and the discharging group, realize the upper power distribution of the battery energy storage system, calculate the health status imbalance of the two battery groups, and determine the power distribution mode of the two battery groups respectively; (2) Calculate the imbalance index of the battery pack battery cell. The calculation formula of the imbalance index of the battery cell is as follows: Among them, f UHC,i and represents the imbalance index of battery cell i, f 1,i and f 2,i They represent the health status index and charge status index of the current battery cell i, respectively. λ1 and λ2 represent weight coefficients, whose values ​​are related to the power allocation mode. S cd It is the charge and discharge status flag, which takes 1 when discharging and -1 when charging. max and SOH min Respectively represent the maximum and minimum health status of all battery cells, SOH i Indicates the health status of the i-th battery cell; The power regulation instructions of the battery pack are distributed to the battery cells in the pack according to the power distribution mode and the imbalance index. The calculation method of the power distribution mode and the power regulation instructions of the battery cells is as follows: Power allocation mode 1: In mode 1, the health status of the battery cells in the battery pack varies greatly. Therefore, the values ​​of λ1 and λ2 are set to 50% and 50%, respectively. This allows the calculation of the imbalance index of all battery cells in the battery pack. In this case, the power adjustment command for battery cell i is as follows: Power distribution mode 2: In mode 2, the health status of the battery cells in the battery pack is almost the same. Therefore, the main consideration is to balance the state of charge. Therefore, the values ​​of λ1 and λ2 are 0 and 100%, respectively. This can be used to calculate the imbalance index of all battery cells in the battery pack. In this case, the power adjustment command for battery cell i is as follows: 。 2. A double-layer power distribution method for a dual-battery energy storage system based on balanced control according to claim 1, characterized in that: The method for calculating the health status imbalance of the battery pack in step (1) is as follows: Among them, f USOH SOH is the imbalance degree of the battery pack health status. F1 is the extremely poor health status of all battery cells in the battery pack. F2 is the imbalance degree of the health status of all battery cells. max and SOH min Respectively represent the maximum and minimum health status of all battery cells, SOH i and SOH j Represent the health status of the i-th and j-th battery cells respectively, and N is the number of battery cells in the battery pack; When f USOH When it is 1, the battery pack adopts mode 1 to distribute the power of the battery cells in the battery pack. USOH When it is 0, the battery pack adopts mode 2 to distribute the power of the battery cells in the battery pack.

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