Battery energy storage system and charging method thereof

Abstract

The invention discloses a battery energy storage system and a charging method thereof, the battery energy storage system comprises a battery stack, the battery stack comprises at least two battery clusters, each battery cluster comprises a plurality of single batteries connected in series, and an active equalization module is arranged between adjacent single batteries; the battery management system is used for controlling the at least two battery clusters to operate in a grid-connected manner when the battery stack starts to charge and discharge, and sequentially switching each battery cluster to an off-grid state when the charging rate of the battery stack meets a preset condition, the active equalization modules in the battery clusters in the off-grid state are controlled to be alternately in a first equalization state and a second equalization state which are opposite in energy flow direction, so that the single batteries in the battery clusters are sequentially subjected to a discharge working condition, then the battery clusters are switched to the grid-connected state again, and the next battery cluster is switched to the off-grid state; therefore, the service life of the single battery can be prolonged.

Description

Technical Field

[0001] This invention relates to the field of battery equalization technology, and in particular to a battery energy storage system and its charging method. Background Technology

[0002] In the process of global energy structure transformation towards cleaner and lower-carbon energy, the new energy industry has achieved vigorous development, accompanied by a continuous increase in the demand for battery energy storage. Due to its advantages such as high energy density, long cycle life, and low environmental pollution, lithium batteries have become the core carrier in the current energy storage field, and are widely used in many scenarios such as new energy vehicles, portable electronic devices, and large-scale energy storage power stations.

[0003] As users increasingly demand greater ease of use for energy storage devices, high-rate, high-current fast charging, which significantly shortens charging time and improves efficiency, has become a key direction for improving the user experience of lithium batteries, and thus a research hotspot in the field of lithium battery technology. However, while high-rate charging brings convenience, it also poses a serious challenge to the performance and safety of lithium batteries: under prolonged high-rate charging conditions, lithium batteries are prone to a series of violent physicochemical reactions, such as rapid growth of lithium dendrites, destruction of the active material structure, and accelerated electrolyte decomposition. These reactions significantly accelerate the battery aging process, leading to a substantial reduction in battery cycle life and severely decreasing the overall utilization efficiency of the battery. More importantly, the large amount of Joule heat generated during high-rate charging is difficult to dissipate quickly, which can easily cause a sharp rise in local battery temperature, leading to thermal runaway and other safety accidents, posing a significant threat to equipment and personnel safety.

[0004] Therefore, effectively extending lithium battery life, improving overall battery efficiency, and simultaneously enhancing safety during long-term high-rate charging have become core technological challenges for current battery management systems (BMS). Currently, most technical solutions focus on optimizing the battery cell itself, i.e., improving the cell manufacturing process (such as electrode material modification, separator structure optimization, and electrolyte formulation adjustment) to enhance the cell's adaptability to high-rate charging and discharging, thereby improving the cell's performance and indirectly extending battery life and improving safety. However, such solutions require disruptive adjustments to the cell manufacturing process, resulting in high costs and limited adaptability, making them difficult to efficiently promote and apply in existing battery energy storage systems. Therefore, it is urgent to explore more feasible solutions from other technological dimensions. Summary of the Invention

[0005] In view of the above problems, the purpose of this invention is to provide a battery energy storage system and a charging method thereof, thereby extending the service life of the battery.

[0006] According to one aspect of the present invention, a battery energy storage system is provided, comprising a battery stack, including at least two battery clusters, each battery cluster including a plurality of individual cells connected in series, and an active balancing module disposed between adjacent individual cells; a battery management system, configured to control the at least two battery clusters to operate in grid-connected mode when the battery stack begins to charge and discharge, and to sequentially disconnect each battery cluster to an off-grid state when the charging rate of the battery stack meets a preset condition, and to control the active balancing modules in the off-grid battery clusters to alternately be in a first balancing state and a second balancing state with opposite energy flow directions, so that each individual cell in the battery cluster sequentially experiences a discharge condition, and then the battery cluster is reconnected to the grid-connected state and the next battery cluster is disconnected to the off-grid state.

[0007] Optionally, the preset condition is that the charging rate of the battery stack is greater than a preset rate and the duration is greater than a preset time.

[0008] Optionally, the active balancing module is in the first balancing state and the second balancing state for the same amount of time, and the balancing states of adjacent active balancing modules are different.

[0009] Optionally, the battery energy storage system further includes a power management system for increasing the power of other battery clusters while switching any battery cluster out of the grid, so as to keep the total power of the battery stack stable; the battery management system also controls the active balancing module in the battery cluster in the off-grid state to be turned off before switching the battery cluster back into the grid state.

[0010] Optionally, the battery management system uses a grid-connected or off-grid control unit to switch any battery cluster to grid-connected or off-grid status.

[0011] Optionally, the battery management system numbers the at least two battery clusters, and when the charging rate first meets the preset condition, selects any numbered battery cluster as the first battery cluster to be switched off-grid, and then switches each battery cluster off-grid in a preset order. When the charging rate meets the preset condition again, the battery cluster that follows the previous battery cluster switched off-grid in the preset order is selected as the first battery cluster to be switched off-grid, and then switches each battery cluster off-grid in a preset order.

[0012] According to another aspect of the present invention, a charging method for a battery energy storage system is provided, comprising: operating at least two battery clusters in a battery stack in parallel with the grid; detecting the charging rate of the battery stack, and when the charging rate meets a preset condition, sequentially disconnecting each battery cluster to an off-grid state; and when the charging rate does not meet the preset condition, maintaining the at least two battery clusters in parallel operation; controlling the active balancing module in the off-grid battery cluster to alternately be in a first balancing state and a second balancing state with opposite energy flow directions, so that each individual battery cell in the battery cluster sequentially experiences a discharge condition; and reconnecting the off-grid battery cluster to the grid-connected state and continuing to disconnect the next battery cluster to the off-grid state, and returning to the previous step.

[0013] Optionally, the preset condition is that the charging rate of the battery stack is greater than a preset rate and the duration is greater than a preset time.

[0014] Optionally, before the battery cluster is switched back to the grid-connected state, the active balancing module in the battery cluster that is in the off-grid state is also turned off.

[0015] Optionally, the active balancing module is in the first balancing state and the second balancing state for the same amount of time, and the balancing states of adjacent active balancing modules are different.

[0016] The battery energy storage system and charging method provided by this invention, when the charging rate of the battery stack reaches a preset condition, sequentially disconnects each battery cluster in the battery stack to an off-grid state, and controls the active balancing module within the off-grid battery cluster to alternately be in a first balancing state and a second balancing state with opposite energy flow directions. This allows each individual battery cell within the battery cluster to sequentially experience a discharge condition, enabling the battery stack to periodically apply a reverse discharge current to the individual batteries in each battery cluster during high-rate charging, thereby effectively extending the lifespan of individual batteries. Furthermore, by simultaneously disconnecting any battery cluster from the battery stack to an off-grid state and increasing the power of the remaining battery clusters, the overall operating power of the battery stack can be stabilized.

[0017] In a preferred embodiment, the active balancing module alternates between the first balancing state and the second balancing state for the same amount of time, which can theoretically keep the energy of each individual battery cell unchanged during the process of switching the battery cluster from the off-grid state to the grid-connected state, resulting in low energy loss and no need for a special circuit to absorb the lost energy. Attached Figure Description

[0018] The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments of the invention with reference to the accompanying drawings, in which: Figure 1 A schematic diagram of a battery energy storage system according to an embodiment of the present invention is shown; Figure 2 A schematic diagram showing the connection between a single cell and an active balancing module in a battery cluster according to an embodiment of the present invention is shown. Figures 3a-3b The diagram illustrates the balanced current of each individual cell within a battery cluster in an off-grid state according to an embodiment of the present invention. Figure 4 A schematic diagram showing the current change during alternating charging and discharging of any single cell according to an embodiment of the present invention is shown; Figure 5 A schematic flowchart of a charging method for a battery energy storage system according to an embodiment of the present invention is shown. Detailed Implementation

[0019] Various embodiments of the invention will now be described in more detail with reference to the accompanying drawings. In the various drawings, the same elements or modules are indicated by the same or similar reference numerals. For clarity, the various parts in the drawings are not drawn to scale.

[0020] It should be understood that, in the following description, "circuit" may include single or combined hardware circuits, programmable circuits, state machine circuits, and / or elements capable of storing instructions executed by the programmable circuit. When an element or circuit is said to be "connected" to another element or "connected" between two nodes, it may be directly coupled or connected to the other element, or there may be intermediate elements; the connection between elements may be physical, logical, or a combination thereof. Conversely, when an element is said to be "directly coupled to" or "directly connected" to another element, it means that there are no intermediate elements between them.

[0021] Furthermore, certain terms are used in this patent specification and claims to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This patent specification and claims do not distinguish components based on differences in name, but rather on differences in function.

[0022] Furthermore, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0023] Operating a battery energy storage system at high charging rates for extended periods negatively impacts the electrochemical reactions and physical stability of individual cells. Furthermore, high-current charging intensifies polarization within individual cells, increasing the likelihood of lithium dendrite formation on the negative electrode, accelerating cell aging, and shortening battery lifespan. Applying a reverse discharge current during high-rate charging can improve internal battery polarization and reduce irreversible capacity decay. This bidirectional pulse charging mechanism enhances battery safety and extends its lifespan. Based on these findings, this application proposes a battery energy storage system and its charging method.

[0024] Figure 1 A schematic diagram of a battery energy storage system according to an embodiment of the present invention is shown.

[0025] See Figure 1 The battery energy storage system 100 provided in this embodiment of the invention includes a battery stack, a battery management system (not shown in the figure), a power management system (not shown in the figure), and a switching network (S1-S2N). The battery stack includes at least two battery clusters 110. When the battery stack starts charging and discharging, at least two battery clusters 110 are connected in parallel, so that at least two battery clusters 110 are connected to the grid for operation.

[0026] Taking constant power operation mode as an example, the battery management system and power management system in the battery energy storage system 100 can control at least two battery clusters 110 to operate in parallel with the grid at the same power to meet the total power demand. They can also switch a certain battery cluster 110 to an off-grid state to stop charging and discharging, while simultaneously increasing the power of other battery clusters 110, so that the total operating power does not fluctuate significantly. Here, off-grid state means that the battery cluster 110 is no longer connected in parallel with other battery clusters 110, and grid-connected state means that the battery cluster 110 is connected in parallel with other battery clusters 110 again.

[0027] For example, this application uses a grid-connected or off-grid control unit (not shown in the figure) to switch any battery cluster 110 to a grid-connected state or an off-grid state. The grid-connected or off-grid control unit achieves the grid-connected or off-grid state switching of any battery cluster 110 by controlling a network of switches (switches S1-S2N).

[0028] Figure 2 A schematic diagram showing the connection between a single cell and an active balancing module in a battery cluster according to an embodiment of the present invention is shown.

[0029] See Figure 2 Each battery cluster 110 includes multiple individual cells 111 connected in series, and an active balancing module 112 is provided between two adjacent individual cells 111. That is, each battery cluster 110 includes m individual cells 111 and m-1 active balancing modules 112. For example, the multiple individual cells 111 use individual cells of the same specification.

[0030] The battery management system (BMS) sequentially disconnects each battery cluster 110 to an off-grid state when the charging rate of the battery stack meets preset conditions. It then controls the active balancing module 112 within each off-grid battery cluster 110 to alternately operate in a first balancing state and a second balancing state with opposite energy flow directions. This allows each individual battery cell 111 within the battery cluster 110 to sequentially undergo discharge. Subsequently, the active balancing module 112 within the battery cluster 110 is shut down, and the battery cluster 110 is reconnected to the grid, while the system continues to disconnect the next battery cluster 110 to an off-grid state. During the off-grid state, the battery cluster 110 ceases charging and discharging, and the total current is zero.

[0031] Furthermore, the preset conditions are that the charging rate of the battery stack is greater than a preset rate, and the duration is greater than a preset time. For example, the preset rate is 0.5~5C, and the preset time is 10-300s.

[0032] Furthermore, each active balancing module 112 is connected to an adjacent first cell 111 and second cell 111. When it is in a first balancing state, the energy flow direction is from the first cell 111 to the second cell 111, that is, the first cell 111 charges the second cell 111. When it is in a second balancing state, the energy flow direction is from the second cell 111 to the first cell 111, that is, the second cell 111 charges the first cell 111. It is understood that in this application, the time that the active balancing module 112 is in the first balancing state and the second balancing state can be set according to the actual situation.

[0033] Preferably, the active balancing module 112 is in the first balancing state and the second balancing state for the same amount of time, for example, both for 10-100 seconds. When the active balancing module 112 is in the first balancing state and the second balancing state for the same amount of time, the energy of each individual battery cell 111 can cancel each other out during the process of switching from the off-grid state to the grid-connected state of the battery cluster 110, thus theoretically remaining unchanged. Therefore, there will be no problem of large energy loss and inconsistent state of charge.

[0034] Furthermore, the balance states of adjacent active balance modules 112 are different.

[0035] Furthermore, the formula for calculating the charging rate of a battery stack is: R = I / Cap, where Cap refers to the nominal capacity of a battery cluster of 110, in Ah; I represents the stack current, which is + when it is the charging current and - when it is the discharging current, in A; and the unit of the charge / discharge rate R is C.

[0036] Furthermore, the power management system is used to maintain a stable total power of the battery stack. While the battery management system controls any battery cluster 110 to switch off-grid, it increases the power of the other battery clusters 110 to keep the total power of the battery stack essentially stable. Conversely, while the battery management system controls any battery cluster 110 to switch back to grid-connected mode, it decreases the power of the other battery clusters 110, ensuring that the power of the newly switched-in cluster is equal to the power of the other clusters, thus maintaining a relatively stable total power of the battery stack.

[0037] Furthermore, the battery management system numbers at least two battery clusters 110, and when the charging rate first meets the preset conditions, it selects any numbered battery cluster 110 as the first battery cluster 110 to be switched off-grid. Then, it switches each battery cluster 110 off-grid in a preset order. When the charging rate meets the preset conditions again, it selects the battery cluster 110 that is after the battery cluster 110 that was switched off-grid in the previous time as the first battery cluster 110 to be switched off-grid. Then, it switches each battery cluster 110 off-grid in a preset order.

[0038] Figures 3a-3b The diagram illustrates the balanced current of individual cells within a battery cluster in an off-grid state according to an embodiment of the present invention. Figure 4 A schematic diagram illustrating the current change during alternating charging and discharging of any single cell according to an embodiment of the present invention is shown.

[0039] Taking a battery cluster 110 comprising 20 individual cells 111, with the individual cells numbered 1-20 sequentially from the positive to the negative terminal, and the active balancing module 112 numbered 1-19 sequentially, and the battery cluster 110 having a first balancing mode and a second balancing mode as an example, when the battery cluster 110 alternates between the first balancing mode and the second balancing mode multiple times, the current change of any individual cell 111 within it is as follows: Figure 4 As shown.

[0040] See Figure 3a The table shows the balancing current of each individual cell when the battery cluster 110 is in the first balancing mode, i.e., the active balancing module 112 with odd numbers is in the first balancing state, and the active balancing module 112 with even numbers is in the second balancing state. Table 1 shows the energy flow direction of each active balancing module 112 when the battery cluster 110 is in the first balancing mode.

[0041] Table 1

[0042] See Figure 3b This refers to the equalization current of each individual cell when the battery cluster 110 is in the second equalization mode, i.e., the active equalization module 112 with odd numbers is in the second equalization state, and the active equalization module 112 with even numbers is in the first equalization state. Table 2 shows the energy flow direction of each active equalization module 112 when the battery cluster 110 is in the second equalization mode.

[0043] Table 2

[0044] Figure 5 A schematic flowchart of a charging method for a battery energy storage system according to an embodiment of the present invention is shown.

[0045] See Figure 5 The charging method of the battery energy storage system in this embodiment of the invention includes steps S01-S05.

[0046] In step S01, at least two battery clusters in the battery stack are connected to the grid.

[0047] In step S02, the charging rate of the battery stack is detected.

[0048] In step S03, it is determined whether the charging rate meets the preset conditions. If the determination result is yes, the process switches to step S04, and if the determination result is no, it returns to step S01.

[0049] The preset conditions are that the charging rate of the battery stack is greater than a preset rate and the duration is greater than a preset time.

[0050] In step S04, each battery cluster is sequentially cut off to the off-grid state.

[0051] Furthermore, while cutting any battery cluster out of the grid, the power of other battery clusters can be increased to keep the total power of the battery stack stable.

[0052] In step S05, the active balancing module in the off-grid battery cluster is controlled to alternately be in a first balancing state and a second balancing state with opposite energy flow, so that each individual cell in the battery cluster experiences the discharge condition in sequence.

[0053] Furthermore, the active balancing modules are in the first and second balancing states for the same amount of time, and the balancing states of adjacent active balancing modules are different.

[0054] In step S06, the active balancing module in the battery cluster that is in an off-grid state is turned off.

[0055] In step S07, the battery cluster that was in the off-grid state is switched back to the grid-connected state, and the next battery cluster is switched out to the off-grid state. After step S07, return to step S05.

[0056] The battery energy storage system and charging method provided in this invention, when the charging rate of the battery stack meets a preset condition, sequentially disconnects each battery cluster in the battery stack to an off-grid state, and controls the active balancing module within the off-grid battery cluster to alternately be in a first balancing state and a second balancing state with opposite energy flow directions. This allows each individual battery cell within the battery cluster to sequentially experience a discharge condition, enabling the battery stack to periodically apply a reverse discharge current to the individual batteries in each battery cluster during high-rate charging. This effectively extends the lifespan of individual batteries and ensures the overall operating power of the battery stack remains stable. Furthermore, by simultaneously disconnecting any battery cluster from the grid to an off-grid state and increasing the power of the remaining battery clusters, the overall operating power of the battery stack can be stabilized.

[0057] Furthermore, the active balancing module alternates between the first balancing state and the second balancing state for the same amount of time, which allows the energy of each individual battery cell to remain theoretically unchanged during the process of switching from off-grid to grid-connected state and then back to grid-connected state. This results in low energy loss and eliminates the need for a dedicated circuit to absorb the lost energy.

[0058] In addition, the charging method of the battery energy storage system is implemented using the existing main control equalization module and grid-connected / off-grid control unit in the battery energy storage system, without the need for additional hardware equipment, and has a wide range of applications.

[0059] As described above, these embodiments of the present invention do not exhaustively describe all details, nor do they limit the invention to specific embodiments. Clearly, many modifications and variations can be made based on the above description. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to effectively utilize the invention and its modifications. The scope of protection of this invention should be determined by the scope defined in the claims and their equivalents.

Claims

1. A battery energy storage system, comprising: A battery stack includes at least two battery clusters, each battery cluster including multiple individual cells connected in series, and an active balancing module is provided between adjacent individual cells. The battery management system is used to control the grid-connected operation of at least two battery clusters when the battery stack begins to charge and discharge, and to sequentially disconnect each battery cluster to an off-grid state when the charging rate of the battery stack meets a preset condition. The system also controls the active balancing module in the off-grid battery cluster to alternately be in a first balancing state and a second balancing state with opposite energy flow directions, so that each individual cell in the battery cluster experiences the discharge condition in sequence. Then, the battery cluster is reconnected to the grid-connected state and the next battery cluster is disconnected to the off-grid state.

2. The battery energy storage system according to claim 1, wherein, The preset condition is that the charging rate of the battery stack is greater than a preset rate and the duration is greater than a preset time.

3. The battery energy storage system according to claim 1, wherein, The active balancing module is in the first balancing state and the second balancing state for the same amount of time, and the balancing states of adjacent active balancing modules are different.

4. The battery energy storage system according to claim 1, further comprising: A power management system is used to increase the power of other battery clusters while cutting any battery cluster out of the grid, so as to keep the total power of the battery stack stable. Before reconnecting the battery cluster to the grid, the battery management system also controls the active balancing module in the off-grid battery cluster to shut down.

5. The battery energy storage system according to claim 1, wherein, The battery management system uses a grid-connected or off-grid control unit to switch any battery cluster to either grid-connected or off-grid status.

6. The battery energy storage system according to claim 1, wherein, The battery management system numbers the at least two battery clusters, and when the charging rate first meets the preset condition, selects any numbered battery cluster as the first battery cluster to be switched off-grid, and then switches each battery cluster off-grid in a preset order. When the charging rate meets the preset condition again, the battery cluster that follows the previous battery cluster switched off-grid is selected as the first battery cluster to be switched off-grid, and then switches each battery cluster off-grid in a preset order.

7. A charging method for a battery energy storage system, comprising: At least two battery clusters in the battery stack are connected to the grid; The charging rate of the battery stack is detected, and when the charging rate meets a preset condition, each battery cluster is sequentially disconnected from the grid and placed in an off-grid state; and when the charging rate does not meet the preset condition, at least two battery clusters are kept in grid-connected operation. The active balancing module in the off-grid battery cluster is controlled to alternately be in a first balancing state and a second balancing state with opposite energy flow directions, so that each individual cell in the battery cluster experiences the discharge condition in sequence. as well as The battery cluster that was in the off-grid state is switched back to the grid-connected state, and the next battery cluster is switched out to the off-grid state, and then the previous step is returned.

8. The method according to claim 7, wherein, The preset condition is that the charging rate of the battery stack is greater than a preset rate and the duration is greater than a preset time.

9. The method according to claim 7, wherein, Before the battery cluster is reconnected to the grid, the active balancing module in the battery cluster that is in the off-grid state is also turned off.

10. The method according to claim 7, wherein, The active balancing module is in the first balancing state and the second balancing state for the same amount of time, and the balancing states of adjacent active balancing modules are different.

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