Energy storage system

Abstract

The invention provides an energy storage system which comprises a plurality of energy storage units, and each energy storage unit comprises a first battery cluster, a second battery cluster, a first switch, a second switch, a direct current bus and an energy storage converter. The first switch is used for switching on or switching off circuit connection between the plurality of battery cells in the first battery cluster and the direct current bus, and the second switch is used for switching on or switching off circuit connection between the plurality of battery cells in the second battery cluster and the direct current bus. The direct-current end of the energy storage converter is connected with the direct-current bus, and the energy storage converter controls electric energy to be transferred between the second battery cluster and the power grid under the conditions that the energy storage converter is conductively connected with the power grid, the absolute value of the voltage difference between the first battery cluster and the second battery cluster is larger than a first voltage threshold value, the first switch is switched off and the second switch is switched on. The first switch is closed when the absolute value of the voltage difference between the first battery cluster and the second battery cluster is smaller than or equal to a first voltage threshold value. Therefore, the impact current in the process of merging the plurality of battery clusters into the direct-current bus can be reduced.

Description

Technical Field

[0001] This application relates to the technical field of power supplies, and particularly to an energy storage system. Background Art

[0002] With the large-scale application of energy storage systems, the requirements for the energy storage capacity of energy storage systems have also increased accordingly. Currently, energy storage systems mainly increase the energy storage capacity of energy storage systems by increasing the number of battery clusters connected in parallel to the DC bus. However, there is an inrush current during the process of multiple battery clusters being incorporated into the DC bus, which is likely to damage the battery clusters. Therefore, how to reduce the inrush current during the incorporation of multiple battery clusters is particularly important. Summary of the Invention

[0003] This application provides an energy storage system that can effectively reduce the inrush current during the process of multiple battery clusters being incorporated into the DC bus.

[0004] In a first aspect, this application provides an energy storage system, which includes multiple energy storage units. Each energy storage unit among the multiple energy storage units includes a first battery cluster, a second battery cluster, a first switch, a second switch, a DC bus, and an energy storage converter. Among them, the closing or opening of the first switch is used to conduct or disconnect the circuit connection between multiple battery cells in the first battery cluster and the DC bus, and the closing or opening of the second switch is used to conduct or disconnect the circuit connection between multiple battery cells in the second battery cluster and the DC bus. The DC side of the energy storage converter is connected to the DC bus, and the AC sides of the energy storage converters of multiple energy storage units are connected in parallel and used to connect to the power grid. The energy storage converter is configured to transfer the electric energy of the second battery cluster to the power grid, or transfer the electric energy of the power grid to the second battery cluster, when the energy storage converter is electrically connected to the power grid, the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is greater than a first voltage threshold, the first switch is open, and the second switch is closed, so that the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is less than or equal to the first voltage threshold. The first switch is further configured to close when the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is less than or equal to the first voltage threshold.

[0005] In this embodiment, before the first battery cluster and the second battery cluster in each energy storage unit are incorporated into the DC bus, the voltages of both are detected first. When the power converters in each energy storage unit are electrically connected to the grid (i.e., the energy storage system is in the grid-connected state), and when the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster in each energy storage unit (hereinafter referred to as the absolute value of the voltage difference between the first battery cluster and the second battery cluster) is greater than the first voltage threshold, each energy storage unit first incorporates its respective second battery cluster into the DC bus. Then, through its respective power converter, the electrical energy of the second battery cluster is transferred to the grid, or the electrical energy of the grid is transferred to the second battery cluster, so that the absolute value of the voltage difference between the first battery cluster and the second battery cluster in each energy storage unit is less than or equal to the first voltage threshold. Each energy storage unit incorporates the first battery cluster into the DC bus only when the absolute value of the voltage difference between its respective first battery cluster and second battery cluster is less than or equal to the first voltage threshold. Briefly speaking, in each energy storage unit, both the first battery cluster and the second battery cluster are incorporated into the DC bus only when the absolute value of the voltage difference between them is less than or equal to the first voltage threshold. The inrush current during the process of the first battery cluster and the second battery cluster being incorporated into the DC bus is caused by the voltage difference between the first battery cluster and the second battery cluster, and the magnitude of this inrush current is positively correlated with the absolute value of this voltage difference. Therefore, the inrush current during the process of the first battery cluster and the second battery cluster in each energy storage unit being incorporated into the DC bus can be effectively reduced.

[0006] Combined with the first aspect, in the first possible embodiment, the power converter is configured to control the second battery cluster to be in the charging state when the power converter is electrically connected to the grid, the difference between the voltage of the first battery cluster minus the voltage of the second battery cluster is greater than the first voltage threshold, the first switch is off and the second switch is on. Specifically, the electrical energy of the grid is transferred to the second battery cluster so that the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is less than or equal to the first voltage threshold.

[0007] Combined with the first aspect, in the second possible embodiment, the power converter is configured to control the second battery cluster to be in the discharging state when the power converter is electrically connected to the grid, the difference between the voltage of the second battery cluster minus the voltage of the first battery cluster is greater than the first voltage threshold, the first switch is off and the second switch is on. Specifically, the electrical energy of the second battery cluster is transferred to the grid so that the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is less than or equal to the first voltage threshold.

[0008] Combined with any one of the first aspect to the second possible implementation manner of the first aspect, in the third possible implementation manner, the first battery cluster includes a first voltage sampling unit, and the second battery cluster includes a second voltage sampling unit. The first voltage sampling unit is configured to collect the voltage of the DC bus when the first switch is closed and the second switch is open, so as to obtain a first bus voltage. The second voltage sampling unit is configured to collect the voltage of the DC bus when the first switch is closed and the second switch is open, so as to obtain a second bus voltage; and collect the voltage of the DC bus when the first switch is open and the second switch is closed, so as to obtain a third bus voltage. The voltage of the first battery cluster is the first bus voltage, and the voltage of the second battery cluster is the sum of the difference between the first bus voltage and the second bus voltage and the third bus voltage. Wherein, the difference between the first bus voltage and the second bus voltage can be understood as the sampling error between the first voltage sampling unit and the second voltage sampling unit.

[0009] In this implementation manner, considering that there will be a sampling error even between two voltage sampling circuits with the same circuit structure, and this sampling error will affect the differential pressure control result between the first battery cluster and the second battery cluster, resulting in the problem of connecting both the first battery cluster and the second battery cluster to the DC bus when misjudging that the absolute value of the differential pressure between the first battery cluster and the second battery cluster is less than or equal to the first voltage threshold, thereby leading to a poor control effect of the inrush current. Based on this, the energy storage unit provided in this application can convert the third bus voltage collected by the second voltage sampling circuit into the bus voltage with the first voltage sampling circuit as the sampling reference based on the sampling error between the first voltage sampling unit and the second voltage sampling unit, so that the voltages of both the first battery cluster and the second battery cluster are voltages with the same voltage sampling circuit as the sampling reference, thereby effectively avoiding the sampling error between the voltages of the first battery cluster and the second battery cluster collected by different voltage sampling circuits, and further effectively avoiding the situation of misjudging that the absolute value of the differential pressure between the first battery cluster and the second battery cluster is less than or equal to the first voltage threshold due to this sampling error, so as to effectively reduce the inrush current during the process of connecting the first battery cluster and the second battery cluster to the DC bus.

[0010] Combined with any one of the first aspect to the second possible implementation manner of the first aspect, in the fourth possible implementation manner, the first battery cluster includes a third voltage sampling unit, and the second battery cluster includes a second voltage sampling unit. The second voltage sampling unit is configured to collect the voltage of the DC bus to obtain a second bus voltage when the first switch is closed and the second switch is open; and collect the voltage of the DC bus to obtain a third bus voltage when the first switch is open and the second switch is closed. The third voltage sampling unit is configured to collect the voltage across both ends of the multiple battery cells in series and parallel in the first battery cluster to obtain a first voltage when the first switch is closed and the second switch is open. The voltage of the first battery cluster is the first voltage, and the voltage of the second battery cluster is the sum of the difference between the first voltage minus the second bus voltage and the third bus voltage.

[0011] In this implementation manner, considering that there will be sampling errors even between two voltage sampling circuits with the same circuit structure, and this sampling error will affect the differential pressure control result between the first battery cluster and the second battery cluster, resulting in the problem of connecting both the first battery cluster and the second battery cluster to the DC bus when misjudging that the absolute value of the differential pressure between the first battery cluster and the second battery cluster is less than or equal to the first voltage threshold, thereby leading to poor control effect of the inrush current. Based on this, the energy storage unit provided in this application can convert the multiple voltages collected by the multiple voltage sampling circuits into voltages with the same voltage sampling circuit as the sampling reference based on the sampling errors between any two of the multiple voltage sampling circuits, so as to effectively avoid the sampling error between the voltage of the first battery cluster and the voltage of the second battery cluster collected by different voltage sampling circuits, and further effectively avoid the situation of misjudging that the absolute value of the differential pressure between the first battery cluster and the second battery cluster is less than or equal to the first voltage threshold due to this sampling error, so as to effectively reduce the inrush current during the process of connecting the first battery cluster and the second battery cluster to the DC bus.

[0012] Combined with any one of the first aspect to the fourth possible implementation manner of the first aspect, in the fifth possible implementation manner, the first switch is configured to close when the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is less than or equal to the first voltage threshold, and the current of the second battery cluster is less than or equal to the current threshold. Wherein, the current threshold can be zero or a value close to zero. Thus, it can be ensured that the first switch closes only when the current of the second battery cluster in the trigger condition is approximately zero. Since the polarization voltage of the battery cluster is positively correlated with the current of the battery cluster, the polarization voltage of the second battery cluster can be effectively reduced, thereby reducing the error between the actual voltage value and the detected voltage value of the second battery cluster caused by the polarization voltage of the second battery cluster, so as to effectively reduce the inrush current during the process of connecting the first battery cluster and the second battery cluster to the DC bus.

[0013] Combined with any one of the first to the fourth possible implementation manners of the first aspect, in the sixth possible implementation manner, the energy storage converter is further configured to shut down when the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is less than or equal to the first voltage threshold. The first switch is configured to close when the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is less than or equal to the first voltage threshold after the energy storage converter has been shut down for the first duration. Wherein, the first duration is greater than 0, and preferably, the first duration is greater than or equal to the duration required for the polarization voltage of the second battery cluster to disappear after the charge and discharge of the second battery cluster ends.

[0014] Considering that the polarization voltage of the battery cluster does not disappear immediately after the charge and discharge of the battery cluster ends, based on this, in this implementation manner, both the voltage of the first battery cluster and the voltage of the second battery cluster in the trigger condition for closing the first switch are the voltages of the two battery clusters obtained after waiting for a period of time (i.e., after the polarization voltage of the second battery cluster disappears) after the charge and discharge of the second battery cluster ends. Therefore, the error between the actual voltage value and the detected voltage value of the second battery cluster caused by the polarization voltage of the second battery cluster can be effectively avoided, thereby further effectively reducing the inrush current during the process of the first battery cluster and the second battery cluster being connected to the DC bus.

[0015] Combined with any one of the first to the sixth possible implementation manners of the first aspect, in the seventh possible implementation manner, the energy storage converter is further configured to control the current value of the second battery cluster to be the first current value when the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is greater than or equal to the second voltage threshold during the process of controlling the transfer of electric energy between the second battery cluster and the power grid; and control the current value of the second battery cluster to be the second current value when the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is greater than the first voltage threshold and less than the second voltage threshold, where the second current value is less than the first current value.

[0016] In this implementation manner, during the process of the energy storage converter controlling the transfer of electric energy between the second battery cluster and the power grid, by making the current of the second battery cluster a large current when the absolute value of the pressure difference between the first battery cluster and the second battery cluster is large, and making the current of the second battery cluster a small current when the absolute value of the pressure difference between the first battery cluster and the second battery cluster is small, the absolute value of the pressure difference between the first battery cluster and the second battery cluster can approach the first voltage threshold at a faster speed when the absolute value of the pressure difference is large. Since the magnitude of the polarization voltage of the battery cluster is positively correlated with the current value of the battery cluster, therefore, the influence of the polarization voltage of the second battery cluster when the absolute value of the pressure difference between the first battery cluster and the second battery cluster is small can also be reduced. Furthermore, not only can the first battery cluster and the second battery cluster be quickly connected to the DC bus, but also the influence of the polarization voltage of the second battery cluster on the pressure difference control effect between the first battery cluster and the second battery cluster can be reduced.

[0017] Combined with any one of the first to the seventh possible implementation manners of the first aspect, in the eighth possible implementation manner, the energy storage system further includes a first controller. The first controller is configured to control the energy storage converter to transfer the electric energy of the second battery cluster to the power grid, or transfer the electric energy of the power grid to the second battery cluster when the energy storage converter is electrically connected to the power grid, the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is greater than a first voltage threshold, the first switch is open, and the second switch is closed. The first controller is further configured to control the first switch to close when the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is less than or equal to the first voltage threshold. Wherein, the first controller can be any one of the cluster controller of the first battery cluster, the container controller of the energy storage container including all the battery clusters in the above-mentioned multiple energy storage units, and the system controller of the energy storage system.

[0018] Combined with any one of the first to the eighth possible implementation manners of the first aspect, in the ninth possible implementation manner, both the first battery cluster and the second battery cluster include a cluster control box. The first switch is located in the cluster control box of the first battery cluster, and the second switch is located in the cluster control box of the second battery cluster.

[0019] In this implementation manner, the first switch is placed in the cluster control box of the first battery cluster, and the second switch is placed in the cluster control box of the second battery cluster, which can effectively utilize the existing internal space of the cluster control box, so that the volume of the battery cluster will not be increased additionally, which is beneficial to the miniaturization design of the battery cluster.

[0020] Combined with any one of the first to the ninth possible implementation manners of the first aspect, in the tenth possible implementation manner, the multiple energy storage units include a first energy storage unit and a second energy storage unit. The energy storage converter in the first energy storage unit is further configured to transfer the electric energy of the second battery cluster in the first energy storage unit to the AC terminal of the energy storage converter in the first energy storage unit when the energy storage converter in each energy storage unit is disconnected from the power grid (i.e., the energy storage system is in an off-grid state), the difference between the voltage of the second battery cluster and the voltage of the first battery cluster in the first energy storage unit is greater than the first voltage threshold, the first switch in the first energy storage unit is open, and the second switch is closed. The energy storage converter in the second energy storage unit is further configured to transfer the electric energy at the AC terminal of the energy storage converter in the second energy storage unit to the battery cluster connected to the other switch in the second energy storage unit when the energy storage converter in each energy storage unit is disconnected from the power grid, the difference between the voltage of the second battery cluster and the voltage of the first battery cluster in the first energy storage unit is greater than the first voltage threshold, one switch in the second energy storage unit is open, and the other switch is closed.

[0021] In this embodiment, before the first battery cluster and the second battery cluster in the first energy storage unit are both connected to the DC bus, the voltages of both are detected first. When the energy storage system is in an off-grid state, and the difference between the voltage of the second battery cluster and the voltage of the first battery cluster in the first energy storage unit is greater than the first voltage threshold, the first energy storage unit first connects the second battery cluster to the DC bus, and the second energy storage unit connects the battery cluster connected by the other switch to the DC bus. Then, through the energy storage converters of the first energy storage unit and the second energy storage unit, the electric energy of the second battery cluster in the first energy storage unit is transferred into the battery cluster connected by the other switch in the second energy storage unit, so that the absolute value of the pressure difference between the first battery cluster and the second battery cluster in the first energy storage unit is less than or equal to the first voltage threshold. Then, when the absolute value of the pressure difference between the first battery cluster and the second battery cluster in the first energy storage unit is less than or equal to the first voltage threshold, the first energy storage unit connects the first battery cluster to the DC bus. The first energy storage unit and the second energy storage unit are any two energy storage units in the energy storage system. Based on this embodiment, it can be known that: the first battery cluster and the second battery cluster in each energy storage unit are both connected to the DC bus when the absolute value of the pressure difference between them is less than or equal to the first voltage threshold. Thus, the inrush current during the process of connecting the first battery cluster and the second battery cluster in each energy storage unit to the DC bus can be effectively reduced.

[0022] Combined with any one of the first to the tenth possible embodiments of the first aspect, in the eleventh possible embodiment, the plurality of energy storage units include a first energy storage unit and a second energy storage unit. The energy storage converter in the second energy storage unit is further configured to transfer the electric energy of the battery cluster connected by the other switch in the second energy storage unit to the AC terminal of the energy storage converter in the second energy storage unit when the energy storage converter in each energy storage unit is disconnected from the power grid, the difference between the voltage of the first battery cluster and the voltage of the second battery cluster in the first energy storage unit is greater than the first voltage threshold, and one switch in the second energy storage unit is open and the other switch is closed. The energy storage converter in the first energy storage unit is further configured to transfer the electric energy at the AC terminal of the energy storage converter in the first energy storage unit to the electric energy of the second battery cluster in the first energy storage unit when the energy storage converter in each energy storage unit is disconnected from the power grid, the difference between the voltage of the first battery cluster and the voltage of the second battery cluster in the first energy storage unit is greater than the first voltage threshold, and the first switch in the first energy storage unit is open and the second switch is closed.

[0023] In this embodiment, before the first battery cluster and the second battery cluster in the first energy storage unit are both connected to the DC bus, the voltages of both are detected first. When the energy storage system is in an off-grid state, and the difference between the voltage of the first battery cluster and the voltage of the second battery cluster in the first energy storage unit is greater than the first voltage threshold, the first energy storage unit first connects the second battery cluster to the DC bus, and the second energy storage unit connects the battery cluster connected to the other switch to the DC bus. After that, the power of the battery cluster connected to the other switch in the second energy storage unit is transferred to the second battery cluster in the first energy storage unit through the energy storage inverter of the first energy storage unit and the energy storage inverter of the second energy storage unit, so that the absolute value of the pressure difference between the first battery cluster and the second battery cluster in the first energy storage unit is less than or equal to the first voltage threshold. After that, the first energy storage unit connects the first battery cluster to the DC bus only when the absolute value of the pressure difference between its first battery cluster and the second battery cluster is less than or equal to the first voltage threshold. The first energy storage unit and the second energy storage unit are any two energy storage units in the energy storage system. Based on this embodiment, it can be known that: the first battery cluster and the second battery cluster in each energy storage unit are both connected to the DC bus only when the absolute value of the pressure difference between them is less than or equal to the first voltage threshold. Thus, the inrush current during the process of connecting the first battery cluster and the second battery cluster in each energy storage unit to the DC bus can be effectively reduced.

[0024] Combined with the tenth possible embodiment of the first aspect or the eleventh possible embodiment of the first aspect, in the twelfth possible embodiment, the energy storage system further includes a second controller. The second controller is configured to control the energy storage inverter in the first energy storage unit to transfer the power of the second battery cluster in the first energy storage unit to the AC terminal of the energy storage inverter in the first energy storage unit when the energy storage inverter in each energy storage unit is disconnected from the power grid, the difference between the voltage of the second battery cluster and the voltage of the first battery cluster in the first energy storage unit is greater than the first voltage threshold, and the first switch in the first energy storage unit is open and the second switch is closed. The second controller is further configured to control the energy storage inverter in the second energy storage unit to transfer the power at its AC terminal to the battery cluster connected to the other switch in the second energy storage unit when the energy storage inverter in each energy storage unit is disconnected from the power grid, the difference between the voltage of the second battery cluster and the voltage of the first battery cluster in the first energy storage unit is greater than the first voltage threshold, and one switch in the second energy storage unit is open and the other switch is closed. The second controller is further configured to control the first switch in the first energy storage unit to close when the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster in the first energy storage unit is less than or equal to the first voltage threshold. Wherein, the second controller can be the container controller of the energy storage container including all the battery clusters in the above-mentioned multiple energy storage units or the system controller of the energy storage system. Description of the Drawings

[0025] Figure 1 It is a schematic diagram of the application scenario of the energy storage system provided by this application;

[0026] Figure 2 It is a schematic diagram of the structure of the energy storage system provided by this application;

[0027] Figure 3 It is another schematic diagram of the structure of the energy storage system provided by this application. Detailed implementation manners

[0028] The energy storage system provided by this application can be applied to various application fields such as the energy storage and backup power field (such as household energy storage, industrial and commercial energy storage, power station energy storage, power battery backup power, etc.), the new energy intelligent microgrid field, and the power transmission and distribution field, and can be applied to different application scenarios. For example, energy storage power supply scenarios, photovoltaic-storage hybrid power supply scenarios, UPS power supply scenarios, etc. Hereinafter, the energy storage power supply scenario will be taken as an example for description.

[0029] Refer to Figure 1 , Figure 1 which is a schematic diagram of the application scenario of the energy storage system provided by this application. In the energy storage power supply scenario, the energy storage system provided by this application is Figure 1The energy storage system shown includes energy storage units 1, ……, and energy storage unit n, where n is an integer greater than 1. Energy storage unit 1 includes a first battery cluster 111, a second battery cluster 112, a first switch S11, a second switch S12, a DC bus (including a positive DC bus BUS1+ and a negative DC bus BUS1-), and an energy storage converter 12. Among them, one end of the multiple battery cells in series and parallel in the first battery cluster 111 is connected to the positive DC bus BUS1+ through the first switch S11, and the other end of the multiple battery cells in series and parallel in the first battery cluster 111 is connected to the negative DC bus BUS1-; one end of the multiple battery cells in series and parallel in the second battery cluster 112 is connected to the positive DC bus BUS1+ through the second switch S12, and the other end of the multiple battery cells in series and parallel in the second battery cluster 112 is connected to the negative DC bus BUS1-; the DC end of the energy storage converter 12 is connected to the positive DC bus BUS1+ and the negative DC bus BUS1-. ……. Energy storage unit n includes a first battery cluster 1n1, a second battery cluster 1n2, a first switch Sn1, a second switch Sn2, a DC bus (including a positive DC bus BUSn+ and a negative DC bus BUSn-), and an energy storage converter 1(n + 1). Among them, one end of the multiple battery cells in series and parallel in the first battery cluster 1n1 is connected to the positive DC bus BUSn+ through the first switch Sn1, and the other end of the multiple battery cells in series and parallel in the first battery cluster 1n1 is connected to the negative DC bus BUSn-; one end of the multiple battery cells in series and parallel in the second battery cluster 1n2 is connected to the positive DC bus BUSn+ through the second switch Sn2, and the other end of the multiple battery cells in series and parallel in the second battery cluster 1n2 is connected to the negative DC bus BUSn-; the DC end of the energy storage converter 1(n + 1) is connected to the positive DC bus BUSn+ and the negative DC bus BUSn-. The AC ends of the energy storage converter 12, ……, the AC ends of the energy storage converter 1(n + 1) are connected in parallel to an AC power grid and an AC load.

[0030] Since the working principles of each of the above n energy storage units are the same, for the convenience of introduction, energy storage unit 1 will be taken as an example for introduction below.

[0031] After the energy storage system starts to operate, when the power converters in each energy storage unit of the energy storage inverter 12 are electrically connected to the power grid (i.e., the energy storage system is in a grid-connected state), the absolute value of the difference between the voltage of the first battery cluster 111 and the voltage of the second battery cluster 112 (hereinafter abbreviated as the absolute value of the voltage difference between the first battery cluster 111 and the second battery cluster 112) is greater than the first voltage threshold, the first switch S11 is open, and the second switch S12 is closed, the energy storage inverter 12 transfers the electric energy of the second battery cluster 112 to the power grid, or transfers the electric energy of the power grid to the second battery cluster 112. The first switch S11 closes when the absolute value of the voltage difference between the first battery cluster 111 and the second battery cluster 112 is less than or equal to the first voltage threshold. After the first switch S11 closes, the energy storage inverter 12 performs DC conversion and inversion on the DC voltage between the positive DC bus BUS1+ and the negative DC bus BUS1- in sequence, and outputs alternating current to the AC power grid and AC load to realize power supply to the AC power grid and AC load.

[0032] It can be understood that before the first battery cluster and the second battery cluster in each energy storage unit are incorporated into the DC bus, the voltages of both are detected first. And when the energy storage system is in a grid-connected state and the absolute value of the voltage difference between the first battery cluster and the second battery cluster in each energy storage unit is greater than the first voltage threshold, each energy storage unit first incorporates its own second battery cluster into the DC bus, and then transfers the electric energy of the second battery cluster to the power grid through its own energy storage inverter, or transfers the electric energy of the power grid to the second battery cluster, so that the absolute value of the voltage difference between the first battery cluster and the second battery cluster in each energy storage unit is less than or equal to the first voltage threshold. Each energy storage unit incorporates the first battery cluster into the DC bus only when the absolute value of the voltage difference between its own first battery cluster and the second battery cluster is less than or equal to the first voltage threshold. Simply put, the first battery cluster and the second battery cluster in each energy storage unit are both incorporated into the DC bus only when the absolute value of the voltage difference between them is less than or equal to the first voltage threshold. And the inrush current during the process of the first battery cluster and the second battery cluster being incorporated into the DC bus is caused by the voltage difference between the first battery cluster and the second battery cluster, and the magnitude of this inrush current is positively correlated with the absolute value of this voltage difference. Therefore, the inrush current during the process of the first battery cluster and the second battery cluster in each energy storage unit being incorporated into the DC bus can be effectively reduced.

[0033] The above is only an example of the application scenario of the energy storage system provided by this application, rather than an exhaustive list, and this application does not limit the application scenario.

[0034] The following combines Figure 2 and Figure 3 to exemplify and explain the working principle of the energy storage system provided by this application.

[0035] See Figure 2 ,Figure 2 This is a schematic structural diagram of the energy storage system provided by this application. As Figure 2 shown, the energy storage system includes energy storage unit 1, ……, and energy storage unit n, where n is an integer greater than 1. Among them, energy storage unit 1 includes first battery cluster 111, second battery cluster 112, first switch S11, second switch S12, a DC bus (including positive DC bus BUS1+ and negative DC bus BUS1-), and energy storage converter 12. The first switch S11 is used to conduct or disconnect the circuit connection between multiple battery cells in the first battery cluster 111 and the DC bus in energy storage unit 1. Exemplarily, the position of the first switch S11 is as follows: One end (positive electrode) after the series connection of multiple battery cells in the first battery cluster 111 is connected to the positive DC bus BUS1+ through the first switch S11, and the other end (negative electrode) after the series connection of multiple battery cells in the first battery cluster 111 is connected to the negative DC bus BUS1-; The second switch S12 is used to conduct or disconnect the circuit connection between multiple battery cells in the second battery cluster 112 and the DC bus in energy storage unit 1. Exemplarily, the position of the second switch S12 is as follows: One end (positive electrode) after the series connection of multiple battery cells in the second battery cluster 112 is connected to the positive DC bus BUS1+ through the second switch S12, and the other end (negative electrode) after the series connection of multiple battery cells in the second battery cluster 112 is connected to the negative DC bus BUS1-. ……. Energy storage unit n includes first battery cluster 1n1, second battery cluster 1n2, first switch Sn1, second switch Sn2, a DC bus (including positive DC bus BUSn+ and negative DC bus BUSn-), and energy storage converter 1(n + 1). The first switch Sn1 is used to conduct or disconnect the circuit connection between multiple battery cells in the first battery cluster 1n1 and the DC bus in energy storage unit n. Exemplarily, the position of the first switch Sn1 is as follows: One end (positive electrode) after the series connection of multiple battery cells in the first battery cluster 1n1 is connected to the positive DC bus BUSn+ through the first switch Sn1, and the other end (negative electrode) after the series connection of multiple battery cells in the first battery cluster 1n1 is connected to the negative DC bus BUSn-; One end (positive electrode) after the series connection of multiple battery cells in the second battery cluster 1n2 is connected to the positive DC bus BUSn+ through the second switch Sn2, and the second switch Sn2 is used to conduct or disconnect the circuit connection between multiple battery cells in the second battery cluster 1n2 and the DC bus in energy storage unit n. Exemplarily, the position of the second switch Sn2 is as follows: The other end (negative electrode) after the series connection of multiple battery cells in the second battery cluster 1n2 is connected to the negative DC bus BUSn-. Here, for the connection relationship between the DC bus and the energy storage converter in each energy storage unit, please refer to the description of the corresponding part in the above embodiment, and it will not be elaborated here.

[0036] Optionally, the first switch in each energy storage unit can also be connected between the negative electrode of the series connection of multiple battery cells in the first battery cluster and the negative DC bus, and the second switch can also be connected between the negative electrode of the series connection of multiple battery cells in the second battery cluster and the negative DC bus; alternatively, the number of the first switch and the second switch in each energy storage unit can both be two. One of the two first switches is connected between the positive electrode of the series connection of multiple battery cells in the first battery cluster and the positive DC bus, and the other first switch is connected between the negative electrode of the series connection of multiple battery cells in the first battery cluster and the negative DC bus; one of the two second switches is connected between the positive electrode of the series connection of multiple battery cells in the second battery cluster and the positive DC bus, and the other second switch is connected between the negative electrode of the series connection of multiple battery cells in the second battery cluster and the negative DC bus. In this application, the connection mode of multiple battery cells inside the battery cluster can also be in parallel or in a series-parallel hybrid mode.

[0037] In addition, the first switch S11 can be located inside or outside the first battery cluster 111, and the second switch S12 can be located inside or outside the second battery cluster 112;...; the first switch Sn1 can be located inside or outside the first battery cluster 1n1, and the second switch Sn2 can be located inside or outside the second battery cluster 1n2. The first switch and the second switch in each energy storage unit can be mechanical switches (such as contactors, relays), or semiconductor switches, such as metal oxide semiconductor field effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), or gallium nitride (GaN) transistors, etc.

[0038] Furthermore, Figure 2 each of the shown battery clusters further includes two voltage sampling circuits and a cluster controller. For details, please refer to Figure 3 . As Figure 3As shown, the first battery cluster 111 further includes a first voltage sampling circuit 1111, a third voltage sampling circuit 1112, and a cluster controller 1113. The second battery cluster 112 further includes a second voltage sampling circuit 1121, a fourth voltage sampling circuit 1122, and a cluster controller 1123. A communication connection is established between the cluster controller 1123 and the cluster controller 1113;...; the first battery cluster 1n1 further includes a first voltage sampling circuit 1n11, a third voltage sampling circuit 1n12, and a cluster controller 1n13. The second battery cluster 1n2 further includes a second voltage sampling circuit 1n21, a fourth voltage sampling circuit 1n22, and a cluster controller 1n23. A communication connection is established between the cluster controller 1n23 and the cluster controller 1n13. In addition, the first battery cluster and the second battery cluster in each energy storage unit further include their respective cluster control boxes (not shown in the figure). The first switch, the first voltage sampling circuit, the third voltage sampling circuit, and the cluster controller of the first battery cluster in each energy storage unit may all be located in the cluster control box of the first battery cluster. The second switch, the second voltage sampling circuit, the fourth voltage sampling circuit, and the cluster controller of the second battery cluster may all be located in the cluster control box of the second battery cluster. Optionally, the first battery cluster in each energy storage unit further includes a first protection element, and the second battery cluster in each energy storage unit further includes a second protection element. The first protection element is arranged between the multiple battery cells of the first battery cluster and the DC bus, and the second protection element is arranged between the multiple battery cells of the second battery cluster and the DC bus. Among them, the first protection element and the second protection element are used to achieve fault isolation, including overcurrent protection devices such as fuses, fuse Hifuses, and circuit breakers.

[0039] In an implementation scenario, the energy storage converters in the n energy storage units are all conductively connected to the AC grid, that is, the energy storage system is in a grid-connected state.

[0040] When each energy storage converter is in a grid-connected state of the energy storage system, the absolute value of the pressure difference between the first battery cluster and the second battery cluster in its respective energy storage unit is greater than the first voltage threshold, the first switch is off and the second switch is on, it transfers the electrical energy of the second battery cluster in its respective energy storage unit to the grid, or transfers the electrical energy of the grid to the second battery cluster in its respective energy storage unit, so that the absolute value of the pressure difference between the first battery cluster and the second battery cluster in each energy storage unit is less than or equal to the first voltage threshold. After that, the first switch in each energy storage unit closes when the absolute value of the pressure difference between its first battery cluster and the second battery cluster is less than or equal to the first voltage threshold.

[0041] The energy storage system further includes a first controller, and the first controller can be any one of the cluster controller 1113 of the first battery cluster 111, the container controller of the energy storage container including all the battery clusters in the above n energy storage units (not shown in the figure), and the system controller of the energy storage system (not shown in the figure). Since the operating principles of the multiple battery clusters in each energy storage unit being incorporated into the DC bus are the same, for the sake of convenience in description, hereinafter, the first controller is taken as the cluster controller 1113 and the energy storage unit is taken as the energy storage unit 1 for introduction.

[0042] Specifically, before the energy storage system supplies power to the AC grid, the first switch and the second switch in each energy storage unit are both in the off state, and the energy storage converters in each energy storage unit are in the shutdown state. The cluster controller 1113 controls the first switch S11 to close, and when the first switch S11 is closed and the second switch S12 is open, it collects the voltage of the DC bus in energy storage unit 1 through the first voltage sampling circuit 1111, that is, the voltage between the positive DC bus BUS1+ and the negative DC bus BUS1-, to obtain the first bus voltage Vbus1. When the first switch S11 is closed and the second switch S12 is open, the cluster controller 1113 sends a bus voltage acquisition instruction to the cluster controller 1123. When the cluster controller 1123 receives this bus voltage acquisition instruction, it collects the voltage between the positive DC bus BUS1+ and the negative DC bus BUS1- through the second voltage sampling circuit 1121 to obtain the second bus voltage Vbus2, and returns the second bus voltage Vbus2 to the cluster controller 1113. When the cluster controller 1113 receives the second bus voltage Vbus2, it controls the first switch S11 to open, and by sending a control instruction to the cluster controller 1123, makes the cluster controller 1123 control the second switch S12 to close. When the first switch S11 is open and the second switch S12 is closed, the cluster controller 1113 obtains the voltage between the positive DC bus BUS1+ and the negative DC bus BUS1- collected by the second voltage sampling circuit 1121 by sending a bus voltage acquisition instruction to the cluster controller 1123, to obtain the third bus voltage Vbus3. After that, when the first switch S11 is closed and the second switch S12 is open, the first bus voltage Vbus1 collected by the first voltage sampling circuit 1111 and the second bus voltage Vbus2 collected by the second voltage sampling circuit 1121 are theoretically equal. Based on this, the cluster controller 1113 can calculate the sampling error ε1 = Vbus1 - Vbus2 between the first voltage sampling circuit 1111 and the second voltage sampling circuit 1121, and thus can calculate the voltage Vbus3' after converting the third bus voltage Vbus3 to the sampling reference of the first voltage sampling circuit 1111 as Vbus3' = ε1 + Vbus3 = Vbus1 - Vbus2 + Vbus3. Furthermore, it can be obtained that: when taking the first voltage sampling circuit 1111 as the sampling reference, the voltage of the first battery cluster 111 is Vbus1, and the voltage of the second battery cluster 112 is Vbus3'.

[0043] After that, since the second switch S12 remains closed, when the difference between the voltage of the first battery cluster 111 (Vbus1) and the voltage of the second battery cluster 112 (Vbus3’) is greater than the first voltage threshold, the cluster controller 1113 controls the energy storage converter 12 to charge the second battery cluster 112 by sending a control instruction to the energy storage converter 12. Specifically, it controls the energy storage converter 12 to transfer the electric energy of the AC grid to the second battery cluster 112 so that the absolute value of the voltage difference between the first battery cluster 111 and the second battery cluster 112 is less than or equal to the first voltage threshold; or when the difference between the voltage of the second battery cluster 112 (Vbus3’) and the voltage of the first battery cluster 111 (Vbus1) is greater than the first voltage threshold, the cluster controller 1113 controls the energy storage converter 12 to discharge the second battery cluster 112. Specifically, it controls the energy storage converter 12 to transfer the electric energy of the second battery cluster 112 to the AC grid so that the absolute value of the voltage difference between the first battery cluster 111 and the second battery cluster 112 is less than or equal to the first voltage threshold. The first voltage threshold is the critical voltage value of the absolute value of the voltage difference between the first battery cluster and the second battery cluster when the inrush current will not damage the battery cluster. Exemplarily, the first voltage threshold is 15V. After that, when the absolute value of the voltage difference between the first battery cluster 111 and the second battery cluster 112 is less than or equal to the first voltage threshold, the cluster controller 1113 controls the first switch S11 to close so that both the first battery cluster 111 and the second battery cluster 112 are connected to the DC bus BUS1+ and BUS1-.

[0044] It can be understood that in the above embodiments, the voltage of the battery cluster is taken as the bus voltage at the DC bus to which the battery cluster is connected as an example. In the present application, the voltage of the battery cluster can also be the voltage across both ends after multiple battery cells in the battery cluster are connected in series and parallel. The specific implementation is as follows:

[0045] Before the energy storage system supplies power to the AC grid, the first switch and the second switch in each energy storage unit are in the open state, and the energy storage converters in each energy storage unit are in the shutdown state. The cluster controller 1113 controls the first switch S11 to close, and when the first switch S11 is closed and the second switch S12 is open, the cluster controller 1113 acquires the voltage between the positive DC bus BUS1+ and the negative DC bus BUS1- through the first voltage sampling circuit 1111 to obtain the first bus voltage Vbus1, and acquires the voltage across the two ends after multiple battery cells in the first battery cluster 111 are connected in series through the third voltage sampling circuit 1112 to obtain the first voltage V1. The cluster controller 1113 also acquires the voltage between the positive DC bus BUS1+ and the negative DC bus BUS1- sampled by the second voltage sampling circuit 1121 to obtain the second bus voltage Vbus2 when the first switch S11 is closed and the second switch S12 is open. When the cluster controller 1113 acquires the second bus voltage Vbus2, it controls the first switch S11 to open and controls the second switch S12 to close through the cluster controller 1123. When the first switch S11 is open and the second switch S12 is closed, the cluster controller 1113 acquires the voltage between the positive DC bus BUS1+ and the negative DC bus BUS1- sampled by the second voltage sampling circuit 1121 to obtain the third bus voltage Vbus3, and acquires the voltage across the two ends after multiple battery cells in the second battery cluster 112 are connected in series through the fourth voltage sampling circuit 1122 to obtain the second voltage V2. Then, since the first bus voltage Vbus1 sampled by the first voltage sampling circuit 1111 and the second bus voltage Vbus2 sampled by the second voltage sampling circuit 1121 are theoretically equal when the first switch S11 is closed and the second switch S12 is open, the first bus voltage Vbus1 sampled by the first voltage sampling circuit 1111 and the first voltage V1 sampled by the third voltage sampling circuit 1112 are theoretically equal when the first switch S11 is closed, and the third bus voltage Vbus3 sampled by the second voltage sampling circuit 1121 and the second voltage V2 sampled by the fourth voltage sampling circuit 1122 are theoretically equal when the second switch S12 is closed. Based on this, the cluster controller 1113 can calculate the sampling error ε1 = Vbus1 - Vbus2 between the first voltage sampling circuit 1111 and the second voltage sampling circuit 1121, the sampling error ε2 = V1 - Vbus1 between the third voltage sampling circuit 1112 and the first voltage sampling circuit 1111, and the sampling error ε3 = Vbus3 - V2 between the second voltage sampling circuit 1121 and the fourth voltage sampling circuit 1122.Thus, the cluster controller 1113 can calculate to obtain the voltage V2' after converting the second voltage V2 with the third voltage sampling circuit 1112 as the sampling reference, where V2' = ε1 + ε2 + ε3 + V2 = V1 - Vbus2 + Vbus3. Furthermore, it can be obtained that: when the third voltage sampling circuit 1112 is used as the sampling reference, the voltage of the first battery cluster 111 is V1, and the voltage of the second battery cluster 112 is V2'.

[0046] After that, since the second switch S12 remains closed, when the difference between the voltage (V1) of the first battery cluster 111 and the voltage (V2') of the second battery cluster 112 is greater than the first voltage threshold, the cluster controller 1113 controls the energy storage converter 12 to charge the second battery cluster 112. Specifically, it controls the energy storage converter 12 to transfer the electric energy of the AC grid to the second battery cluster 112, so that the absolute value of the voltage difference between the first battery cluster 111 and the second battery cluster 112 is less than or equal to the first voltage threshold. Or, when the difference between the voltage (V2') of the second battery cluster 112 and the voltage (V1) of the first battery cluster 111 is greater than the first voltage threshold, the cluster controller 1113 controls the energy storage converter 12 to discharge the second battery cluster 112. Specifically, it controls the energy storage converter 12 to transfer the electric energy of the second battery cluster 112 to the AC grid, so that the absolute value of the voltage difference between the first battery cluster 111 and the second battery cluster 112 is less than or equal to the first voltage threshold. After that, when the absolute value of the voltage difference between the first battery cluster 111 and the second battery cluster 112 is less than or equal to the first voltage threshold, the cluster controller 1113 controls the first switch S11 to close, so that both the first battery cluster 111 and the second battery cluster 112 are connected to the DC bus BUS1+ and BUS1-.

[0047] It can be understood that considering that there will be sampling errors even between two voltage sampling circuits with the same circuit structure, and this sampling error will affect the voltage difference control result between the first battery cluster and the second battery cluster, resulting in the problem that the cluster controller misjudges that the absolute value of the voltage difference between the first battery cluster and the second battery cluster is less than or equal to the first voltage threshold and then connects both the first battery cluster and the second battery cluster to the DC bus, which further leads to poor control effect of the inrush current. Based on this, the energy storage unit provided in this application can convert the multiple voltages collected by multiple voltage sampling circuits into voltages with the same voltage sampling circuit as the sampling reference based on the sampling errors between any two of the multiple voltage sampling circuits, thereby effectively avoiding the sampling errors between the voltage of the first battery cluster and the voltage of the second battery cluster collected by different voltage sampling circuits, and further effectively avoiding the situation of misjudging that the absolute value of the voltage difference between the first battery cluster and the second battery cluster is less than or equal to the first voltage threshold due to this sampling error, so as to effectively reduce the inrush current during the process of connecting the first battery cluster and the second battery cluster to the DC bus.

[0048] It should be noted that, in order to completely avoid the sampling error between different voltage sampling circuits, ideally, the same voltage sampling circuit can be directly used to collect the voltages of the first battery cluster and the second battery cluster. However, when the number of battery clusters included in the energy storage unit continuously increases with the increase of the energy storage capacity, the method of using the same voltage sampling circuit to collect the voltages of a large number of battery clusters will make the wiring between the same voltage sampling circuit and multiple battery clusters difficult, resulting in a higher cost of the energy storage system. In addition, the method of using the same voltage sampling circuit to collect the voltages of a large number of battery clusters will cause the failure to spread to other battery clusters when a certain battery cluster fails (such as a short circuit), resulting in a worse safety of the energy storage system. Based on this, considering the cost and safety of the energy storage system, in engineering implementation, a sampling method of using different voltage sampling voltages to collect the voltages of different battery clusters is mostly adopted.

[0049] Furthermore, considering the polarization voltage of the battery cluster, that is, the voltage loss caused by the imbalance of internal electrochemical reactions and material transport during the charge and discharge process of the battery cluster, which will cause an error between the actual voltage value of the battery cluster and the detected voltage value of the battery cluster (i.e., the voltage value collected by the voltage sampling circuit), this error will also affect the control effect of the impact current. Based on this, in order to reduce the influence of the polarization voltage of the battery cluster, during the process of controlling the power transfer between the second battery cluster and the power grid, the energy storage unit also controls the current of the second battery cluster (i.e., the charging current or the discharging current), and also considers the influence of the polarization voltage of the battery cluster in the trigger condition for controlling the closing of the first switch, specifically as follows:

[0050] During the process of the cluster controller 1113 controlling the power transfer between the second battery cluster 112 and the AC power grid, when the absolute value of the voltage difference between the first battery cluster 111 and the second battery cluster 112 is greater than or equal to the second voltage threshold, the current value of the second battery cluster 112 is controlled to be the first current value by controlling the energy storage converter 12; and when the absolute value of the voltage difference between the first battery cluster 111 and the second battery cluster 112 is greater than the first voltage threshold and less than the second voltage threshold, the current of the second battery cluster 112 is controlled to be the second current value by controlling the energy storage converter 12. Among them, the second voltage threshold is greater than the first voltage threshold, and the second current value is less than the first current value. Optionally, during the process of the cluster controller 1113 controlling the power transfer between the second battery cluster 112 and the AC power grid, the current value of the second battery cluster 112 is also controlled to be positively correlated with the absolute value of the voltage difference between the first battery cluster 111 and the second battery cluster 112 by controlling the energy storage converter 12.

[0051] It can be understood that during the process of the cluster controller 1113 controlling the transfer of electric energy between the second battery cluster 112 and the power grid, when the absolute value of the pressure difference between the first battery cluster 111 and the second battery cluster 112 is relatively large, the current of the second battery cluster 112 can be made a large current, and when the absolute value of the pressure difference between the first battery cluster 111 and the second battery cluster 112 is relatively small, the current of the second battery cluster 112 can be made a small current, so that when the absolute value of the pressure difference between the first battery cluster 111 and the second battery cluster 112 is large, the absolute value of this pressure difference approaches the first voltage threshold at a relatively fast speed. Since the polarization voltage of the battery cluster is positively correlated with the current value of the battery cluster, therefore, the influence of the polarization voltage of the second battery cluster 112 when the absolute value of the pressure difference between the first battery cluster 111 and the second battery cluster 112 is small can also be reduced. Furthermore, not only can the first battery cluster 111 and the second battery cluster 112 be quickly incorporated into the DC bus, but also the influence of the polarization voltage of the second battery cluster 112 on the pressure difference control effect between the first battery cluster 111 and the second battery cluster 112 can be reduced.

[0052] After that, when the absolute value of the pressure difference between the first battery cluster 111 and the second battery cluster 112 is less than or equal to the first voltage threshold, and the current of the second battery cluster 112 is less than or equal to the current threshold, the cluster controller 1113 controls the first switch S11 to close, so that both the first battery cluster 111 and the second battery cluster 112 are incorporated into the DC bus BUS1+ and BUS1-. Among them, the current threshold can be zero or a value close to zero. Thus, it can be ensured that the first switch S11 closes only when the trigger condition includes that the current of the second battery cluster 112 is approximately zero, and further, the error between the actual voltage value and the detected voltage value of the second battery cluster 112 caused by the polarization voltage of the second battery cluster 112 can be effectively reduced, so as to effectively reduce the inrush current during the process of the first battery cluster 111 and the second battery cluster 112 being incorporated into the DC bus.

[0053] Considering that the polarization voltage of the battery cluster does not disappear immediately after the charge and discharge of the battery cluster, in order to further reduce the error between the actual voltage value and the detected voltage value of the battery cluster caused by the polarization voltage of the battery cluster, and to further reduce the inrush current during the process of the first battery cluster 111 and the second battery cluster 112 being incorporated into the DC bus, when the absolute value of the voltage difference between the first battery cluster 111 and the second battery cluster 112 is less than or equal to the first voltage threshold, the cluster controller 1113 also controls the energy storage converter 12 to shut down. After the energy storage converter 12 has been shut down for the first duration, when the absolute value of the voltage difference between the first battery cluster 111 and the second battery cluster 112 is less than or equal to the first voltage threshold, the cluster controller 1113 controls the first switch S11 to close, so that both the first battery cluster 111 and the second battery cluster 112 are incorporated into the DC bus BUS1+ and BUS1-. Exemplarily, the first duration is greater than or equal to the duration required for the polarization voltage of the second battery cluster 112 to disappear after the end of charging, such as 30 s. Since the voltages of the first battery cluster 111 and the second battery cluster 112 in the trigger condition for closing the first switch S11 are both obtained after waiting for a period of time (i.e., after the polarization voltage of the second battery cluster 112 has disappeared) after the end of the charge and discharge of the second battery cluster 112, the error between the actual voltage value and the detected voltage value of the second battery cluster 112 caused by the polarization voltage of the second battery cluster 112 can be effectively avoided, thereby further effectively reducing the inrush current during the process of the first battery cluster 111 and the second battery cluster 112 being incorporated into the DC bus.

[0054] In another implementation scenario, the energy storage converters in the n energy storage units are all disconnected from the AC grid, that is, the energy storage system is in an off-grid state.

[0055] Since the battery clusters in each energy storage unit cannot exchange electric energy with the grid when the energy storage system is in an off-grid state, in this implementation scenario, the battery clusters in two different energy storage units are used to exchange electric energy with each other, so that the absolute value of the voltage difference between the two battery clusters in the same energy storage unit is less than or equal to the first voltage threshold, as follows:

[0056] When the energy storage converter in the first energy storage unit transfers the electrical energy of the second battery cluster in the first energy storage unit to the AC terminal of the energy storage converter in the first energy storage unit under the conditions that the energy storage system is in the off-grid state, the difference between the voltage of the second battery cluster and the voltage of the first battery cluster in the first energy storage unit is greater than the first voltage threshold, the first switch in the first energy storage unit is open and the second switch is closed; when the energy storage converter in the second energy storage unit transfers the electrical energy at the AC terminal of the energy storage converter in the second energy storage unit to the battery cluster connected to the other switch in the second energy storage unit under the conditions that the energy storage system is in the off-grid state, the difference between the voltage of the second battery cluster and the voltage of the first battery cluster in the first energy storage unit is greater than the first voltage threshold, and one switch in the second energy storage unit is open and the other switch is closed. Alternatively, when the energy storage converter in the second energy storage unit transfers the electrical energy of the battery cluster connected to the other switch in the second energy storage unit to the AC terminal of the energy storage converter in the second energy storage unit under the conditions that the energy storage system is in the off-grid state, the difference between the voltage of the first battery cluster and the voltage of the second battery cluster in the first energy storage unit is greater than the first voltage threshold, and one switch in the second energy storage unit is open and the other switch is closed; when the energy storage converter in the first energy storage unit transfers the electrical energy at the AC terminal of the energy storage converter in the first energy storage unit to the electrical energy of the second battery cluster in the first energy storage unit under the conditions that the energy storage system is in the off-grid state, the difference between the voltage of the first battery cluster and the voltage of the second battery cluster in the first energy storage unit is greater than the first voltage threshold, the first switch in the first energy storage unit is open and the second switch is closed. After that, the first switch in the first energy storage unit closes when the absolute value of the pressure difference between the first battery cluster and the second battery cluster in the first energy storage unit is less than or equal to the first voltage threshold.

[0057] The energy storage system further includes a second controller, and the second controller can be the container controller of the energy storage container including all the battery clusters in the above-mentioned n energy storage units or the system controller of the energy storage system. Since the working principle of multiple battery clusters in each energy storage unit being incorporated into the DC bus is the same, for the convenience of description, the following takes the second controller as the system controller, the first energy storage unit as energy storage unit 1, and the second energy storage unit as energy storage unit n as an example for introduction.

[0058] Specifically, before the energy storage system supplies power to the AC grid, the first switch and the second switch in each energy storage unit are both in the off state, and the energy storage converters in each energy storage unit are in the shutdown state. The system controller controls the closing or opening of the first switch S11 and the second switch S12, and samples the voltages when the first switch S11 and the second switch S12 are closed or opened through the voltage sampling circuits in the first battery cluster 111 and the second battery cluster 112, and calculates the voltages of the first battery cluster 111 and the second battery cluster 112. Among them, the voltage of the first battery cluster 111 is Vbus1, and the voltage of the second battery cluster 112 is Vbus3'; or the voltage of the first battery cluster 111 is V1, and the voltage of the second battery cluster 112 is V2'. For the specific implementation method of this part, please refer to the description of the corresponding part in the previous implementation scenario, and will not be elaborated here.

[0059] After that, when the absolute value of the voltage difference between the first battery cluster 111 and the second battery cluster 112 is greater than the first voltage threshold, the system controller controls either the first switch Sn1 or the second switch Sn2 in the energy storage unit n to close by sending a control instruction to the cluster controller in the energy storage unit n. Here, taking the control of the first switch Sn1 closing as an example. Since the first switch S11 is in the open state and the second switch S12 is in the closed state, therefore, when the energy storage system is in the off-grid state, the difference between the voltage of the second battery cluster 112 minus the voltage of the first battery cluster 111 is greater than the first voltage threshold, the first switch S11 is open and the second switch S12 is closed, the system controller controls the energy storage converter 12 to make the second battery cluster 112 in the discharge state by sending a control instruction to the energy storage converter 12. Specifically, it controls the energy storage converter 12 to transfer the electric energy of the second battery cluster 112 to the AC side of the energy storage converter 12; the system controller also controls the energy storage converter 1(n+1) to make the first battery cluster 1n1 in the charging state by sending a control instruction to the energy storage converter 1(n+1) when the energy storage system is in the off-grid state, the difference between the voltage of the second battery cluster 112 minus the voltage of the first battery cluster 111 is greater than the first voltage threshold, the first switch Sn1 is closed and the second switch Sn2 is open. Specifically, it controls the energy storage converter 1(n+1) to transfer the electric energy at the AC side of the energy storage converter 1(n+1) to the first battery cluster 1n1, so that the absolute value of the voltage difference between the first battery cluster 111 and the second battery cluster 112 is less than or equal to the first voltage threshold. Or, when the energy storage system is in the off-grid state, the difference between the voltage of the first battery cluster 111 minus the voltage of the second battery cluster 112 is greater than the first voltage threshold, the first switch Sn1 is closed and the second switch Sn2 is open, the system controller controls the energy storage converter 1(n+1) to make the first battery cluster 1n1 in the discharge state by sending a control instruction to the energy storage converter 1(n+1). Specifically, it controls the energy storage converter 1(n+1) to transfer the electric energy of the first battery cluster 1n1 to the AC side of the energy storage converter 1(n+1); the system controller also controls the energy storage converter 12 to make the second battery cluster 112 in the charging state by sending a control instruction to the energy storage converter 12 when the energy storage system is in the off-grid state, the difference between the voltage of the first battery cluster 111 minus the voltage of the second battery cluster 112 is greater than the first voltage threshold, the first switch S11 is open and the second switch S12 is closed. Specifically, it controls the energy storage converter 12 to transfer the electric energy at the AC side of the energy storage converter 12 to the second battery cluster 112, so that the absolute value of the voltage difference between the first battery cluster 111 and the second battery cluster 112 is less than or equal to the first voltage threshold.After that, when the absolute value of the voltage difference between the first battery cluster 111 and the second battery cluster 112 is less than or equal to the first voltage threshold, the system controller controls the first switch S11 to close by sending a control instruction to the cluster controller 1113, so that both the first battery cluster 111 and the second battery cluster 112 are incorporated into the DC bus BUS1+ and BUS1-.

[0060] Similar to the previous implementation scenario, considering the polarization voltage of the battery cluster, an error will occur between the actual voltage value and the detected voltage value of the battery cluster, and this error will also affect the control effect of the inrush current. Based on this, in order to reduce the influence of the polarization voltage of the battery cluster, during the process of the system controller controlling the power transfer between the second battery cluster 112 and the AC side of the energy storage converter 12, the current of the second battery cluster 112 is also controlled, and the influence of the polarization voltage of the battery cluster is also considered in the trigger condition for controlling the first switch S11 to close. The specific implementation method considering the polarization voltage of the battery cluster in this implementation scenario is similar to the specific implementation method considering the polarization voltage of the battery cluster in the previous implementation scenario. Just replace "during the process of controlling the power transfer between the second battery cluster 112 and the power grid" in the specific implementation method considering the polarization voltage of the battery cluster in the previous implementation scenario with "during the process of controlling the power transfer between the second battery cluster 112 and the AC side of the energy storage converter 12", and replace "cluster controller 1113" with "system controller", then the specific implementation method considering the polarization voltage of the battery cluster in this implementation scenario can be obtained, which will not be elaborated here.

[0061] In this application, before the first battery cluster and the second battery cluster in each energy storage unit are incorporated into the DC bus, the voltages of both are detected first. When the absolute value of the voltage difference between the first battery cluster and the second battery cluster in each energy storage unit is greater than the first voltage threshold, each energy storage unit first incorporates its respective second battery cluster into the DC bus. And when the energy storage system is in the grid-connected state, each energy storage unit controls the power exchange between the second battery cluster and the grid through its respective energy storage converter, so that the absolute value of the voltage difference between the first battery cluster and the second battery cluster in each energy storage unit is less than or equal to the first voltage threshold; or, when the energy storage system is in the off-grid state, the two energy storage converters in any two energy storage units control the power exchange between the second battery cluster of one energy storage unit and a battery cluster of another energy storage unit, so that the absolute value of the voltage difference between the first battery cluster and the second battery cluster in each energy storage unit is less than or equal to the first voltage threshold. After that, each energy storage unit incorporates the first battery cluster into the DC bus only when the absolute value of the voltage difference between its respective first battery cluster and second battery cluster is less than or equal to the first voltage threshold. Simply put, the first battery cluster and the second battery cluster in each energy storage unit are both incorporated into the DC bus only when the absolute value of the voltage difference between them is less than or equal to the first voltage threshold. Thus, the inrush current during the process of incorporating the first battery cluster and the second battery cluster into the DC bus in each energy storage unit can be effectively reduced. In addition, based on the first switch and the second switch in each energy storage unit, and the control method for reducing the inrush current when multiple battery clusters are incorporated, the energy storage system can flexibly connect or disconnect individual battery clusters according to actual needs, realizing the infinite expansion of the energy storage system, and making full use of the cycle life of each battery cluster, without being affected by the SOX difference between clusters. Moreover, the energy storage system can also flexibly select and configure the number of energy storage converters for parallel operation according to actual needs to achieve different output powers, so as to achieve arbitrary expansion of the output power of the energy storage system.

[0062] It should be noted that the control method for reducing the inrush current when multiple battery clusters are incorporated in this application is not limited to being applied to energy storage battery clusters. In fact, it can be applied to all application scenarios with voltage parallel operation, such as the parallel operation scenario of DC modules of charging piles, the parallel operation scenario of energy storage converters, the parallel operation scenario of power conversion modules on the output bus side, or the parallel operation scenario of power conversion units and battery clusters, etc.

[0063] The above is only the specific implementation manner of this application, but the protection scope of this application is not limited thereto. Any person skilled in the art within the technical scope disclosed in this application can easily think of changes or substitutions, which should all be covered within the protection scope of this application.

Claims

1. An energy storage system, characterized in that, The energy storage system includes a plurality of energy storage units, and each of the plurality of energy storage units includes a first battery cluster, a second battery cluster, a first switch, a second switch, a DC bus, and an energy storage converter, where: The first switch is closed or opened to conduct or disconnect the circuit connection between a plurality of battery cells in the first battery cluster and the DC bus; The second switch is closed or opened to conduct or disconnect the circuit connection between a plurality of battery cells in the second battery cluster and the DC bus; The DC end of the energy storage converter is connected to the DC bus, and the AC ends of the energy storage converters of the plurality of energy storage units are connected in parallel and used to connect to the power grid; The energy storage converter is configured to transfer the electric energy of the second battery cluster to the power grid, or transfer the electric energy of the power grid to the second battery cluster when the energy storage converter is electrically connected to the power grid, the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is greater than a first voltage threshold, the first switch is opened, and the second switch is closed; The first switch is further configured to be closed when the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is less than or equal to the first voltage threshold.

2. The energy storage system according to claim 1, wherein The energy storage converter is configured to transfer the electric energy of the power grid to the second battery cluster when the energy storage converter is electrically connected to the power grid, the difference between the voltage of the first battery cluster minus the voltage of the second battery cluster is greater than the first voltage threshold, the first switch is opened, and the second switch is closed.

3. The energy storage system according to claim 1, wherein The energy storage converter is configured to transfer the electric energy of the second battery cluster to the power grid when the energy storage converter is electrically connected to the power grid, the difference between the voltage of the second battery cluster minus the voltage of the first battery cluster is greater than the first voltage threshold, the first switch is opened, and the second switch is closed.

4. The energy storage system according to any one of claims 1-3, characterized in that, The first battery cluster includes a first voltage sampling unit, and the second battery cluster includes a second voltage sampling unit; The first voltage sampling unit is configured to collect the voltage of the DC bus to obtain a first bus voltage when the first switch is closed and the second switch is opened; The second voltage sampling unit is configured to collect the voltage of the DC bus to obtain a second bus voltage when the first switch is closed and the second switch is opened; and collect the voltage of the DC bus to obtain a third bus voltage when the first switch is opened and the second switch is closed; The voltage of the first battery cluster is the first bus voltage, and the voltage of the second battery cluster is the sum of the difference between the first bus voltage minus the second bus voltage and the third bus voltage.

5. The energy storage system according to any one of claims 1-3, characterized in that, The first battery cluster includes a third voltage sampling unit, and the second battery cluster includes a second voltage sampling unit; The second voltage sampling unit is configured to collect the voltage of the DC bus to obtain a second bus voltage when the first switch is closed and the second switch is open; and collect the voltage of the DC bus to obtain a third bus voltage when the first switch is open and the second switch is closed. The third voltage sampling unit is configured to collect the voltage across both ends of multiple battery cells in series and parallel connection in the first battery cluster to obtain a first voltage when the first switch is closed and the second switch is open. The voltage of the first battery cluster is the first voltage, and the voltage of the second battery cluster is the sum of the difference between the first voltage and the second bus voltage and the third bus voltage.

6. The energy storage system according to any one of claims 1-5, characterized in that, The first switch is configured to close when the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is less than or equal to the first voltage threshold, and the current of the second battery cluster is less than or equal to the current threshold.

7. The energy storage system according to any one of claims 1-5, characterized in that The energy storage converter is further configured to shut down when the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is less than or equal to the first voltage threshold. The first switch is configured to close when the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is less than or equal to the first voltage threshold after the energy storage converter has been shut down for a first duration, where the first duration is greater than 0.

8. The energy storage system according to any one of claims 1-7, characterized in that, The energy storage converter is further configured to control the current value of the second battery cluster to be a first current value when the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is greater than or equal to a second voltage threshold during the process of controlling the transfer of electric energy between the second battery cluster and the power grid; and control the current value of the second battery cluster to be a second current value when the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is greater than the first voltage threshold and less than the second voltage threshold, where the second current value is less than the first current value.

9. The energy storage system according to any one of claims 1-8, characterized in that, The energy storage system further includes a first controller. The first controller is configured to control the energy storage converter to transfer the electric energy of the second battery cluster to the power grid, or transfer the electric energy of the power grid to the second battery cluster when the energy storage converter is electrically connected to the power grid, the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is greater than the first voltage threshold, the first switch is open, and the second switch is closed. The first controller is further configured to control the first switch to close when the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster is less than or equal to the first voltage threshold.

10. The energy storage system according to any one of claims 1-9, characterized in that, Both the first battery cluster and the second battery cluster include cluster control boxes. The first switch is located in the cluster control box of the first battery cluster, and the second switch is located in the cluster control box of the second battery cluster.

11. The energy storage system according to any one of claims 1-10, characterized in that, The multiple energy storage units include a first energy storage unit and a second energy storage unit. The energy storage converter in the first energy storage unit is further configured to transfer the electric energy of the second battery cluster in the first energy storage unit to the AC terminal of the energy storage converter in the first energy storage unit when the energy storage converters in each energy storage unit are disconnected from the power grid, the difference between the voltage of the second battery cluster and the voltage of the first battery cluster in the first energy storage unit is greater than the first voltage threshold, the first switch in the first energy storage unit is turned off and the second switch is turned on; The energy storage converter in the second energy storage unit is further configured to transfer the electric energy at the AC terminal of the energy storage converter in the second energy storage unit to the battery cluster connected to the other switch in the second energy storage unit when the energy storage converters in each energy storage unit are disconnected from the power grid, the difference between the voltage of the second battery cluster and the voltage of the first battery cluster in the first energy storage unit is greater than the first voltage threshold, and one switch in the second energy storage unit is turned off and the other switch is turned on; 12. The energy storage system according to any one of claims 1-11, characterized in that, The multiple energy storage units include a first energy storage unit and a second energy storage unit; The energy storage converter in the second energy storage unit is further configured to transfer the battery cluster connected to the other switch in the second energy storage unit to the electric energy at the AC terminal of the energy storage converter in the second energy storage unit when the energy storage converters in each energy storage unit are disconnected from the power grid, the difference between the voltage of the first battery cluster and the voltage of the second battery cluster in the first energy storage unit is greater than the first voltage threshold, and one switch in the second energy storage unit is turned off and the other switch is turned on; The energy storage converter in the first energy storage unit is further configured to transfer the electric energy at the AC terminal of the energy storage converter in the first energy storage unit to the electric energy of the second battery cluster in the first energy storage unit when the energy storage converters in each energy storage unit are disconnected from the power grid, the difference between the voltage of the first battery cluster and the voltage of the second battery cluster in the first energy storage unit is greater than the first voltage threshold, the first switch in the first energy storage unit is turned off and the second switch is turned on; 13. The energy storage system according to claim 11 or 12, characterized in that, The energy storage system further includes a second controller; The second controller is configured to control the energy storage converter in the first energy storage unit to transfer the electric energy of the second battery cluster in the first energy storage unit to the AC terminal of the energy storage converter in the first energy storage unit when the energy storage converters in each energy storage unit are disconnected from the power grid, the difference between the voltage of the second battery cluster and the voltage of the first battery cluster in the first energy storage unit is greater than the first voltage threshold, the first switch in the first energy storage unit is turned off and the second switch is turned on; The second controller is further configured to control the energy storage converter in the second energy storage unit to transfer the electric energy at its AC terminal to the battery cluster connected to the other switch in the second energy storage unit when the energy storage converters in each energy storage unit are disconnected from the power grid, the difference between the voltage of the second battery cluster and the voltage of the first battery cluster in the first energy storage unit is greater than the first voltage threshold, and one switch in the second energy storage unit is turned off and the other switch is turned on; The second controller is further configured to control the first switch in the first energy storage unit to close when the absolute value of the difference between the voltage of the first battery cluster and the voltage of the second battery cluster in the first energy storage unit is less than or equal to the first voltage threshold.

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