Energy storage system and control method thereof

Abstract

The invention discloses an energy storage system and a control method thereof. The energy storage system comprises a battery cluster, and the battery cluster comprises a first battery pack, a second battery pack, a first positive direct current bus, a first negative direct current bus, a second positive direct current bus, a second negative direct current bus and a DC / DC conversion circuit. The positive electrode of the first battery pack is connected with the first positive DC bus through the first switch and connected with the second positive DC bus through the third switch. The cathode of the first battery pack is connected with the first negative DC bus through the second switch and is connected with the second negative DC bus through the fourth switch. And the positive electrode of the second battery pack is connected with the first positive direct-current bus through a fifth switch and is also connected with the second positive direct-current bus through a seventh switch. The negative electrode of the second battery pack is connected with the first negative DC bus through a sixth switch and is also connected with the second negative DC bus through an eighth switch. The DC / DC conversion circuit is connected between the first DC bus and the second DC bus. Therefore, energy balance between the battery packs can be realized, and the cost of the battery cluster is reduced.

Description

Technical Field

[0001] This application relates to the field of power technology, and in particular to an energy storage system and its control method. Background Technology

[0002] Energy storage systems store or release energy through battery clusters, and the "weakest link" effect exists when battery clusters store or release energy. Specifically, when a battery cluster releases energy, the energy that the cluster can release depends on the battery pack with the lowest energy level within the cluster; when a battery cluster stores energy, the energy that the cluster can store depends on the battery pack with the highest energy level within the cluster.

[0003] Currently, in order to reduce the capacity degradation of energy storage systems caused by the "weakest link" effect, energy storage systems mainly adopt... Figure 1 The battery cluster shown. (As shown in the image) Figure 1 As shown, the battery cluster includes battery packs PACK1, PACK2, ..., PACKn, a positive DC bus BUS+, a negative DC bus BUS-, and n active balancing modules (i.e., DC / DC converter circuits) corresponding to the above n battery packs. The n battery packs are connected in series between the positive terminal BAT+ and the negative terminal BAT- of the battery cluster. The positive and negative terminals of each battery pack are connected to the two ends of the active balancing module corresponding to each battery pack, and the other two ends of the active balancing module corresponding to each battery pack are connected to the positive DC bus BUS+ and the negative DC bus BUS-, respectively. When the energy of one of the n battery packs is high, the corresponding active balancing module transfers the energy of that battery pack to the positive DC bus BUS+ and the negative DC bus BUS-. When the energy of one of the n battery packs is low, the corresponding active balancing module transfers the energy of the positive DC bus BUS+ and the negative DC bus BUS- to that battery pack, thereby achieving energy balance among the battery packs and reducing the capacity decay of the energy storage system caused by the weakest link effect.

[0004] While the aforementioned battery clusters can achieve energy balance among battery packs, n battery packs require n active balancing modules, resulting in excessively high costs for the battery clusters. Summary of the Invention

[0005] This application provides an energy storage system and its control method, which can not only achieve energy balance among battery packs, but also effectively reduce the cost of battery clusters.

[0006] In a first aspect, this application provides an energy storage system comprising a battery cluster, the battery cluster including multiple battery packs, a first positive DC bus, a first negative DC bus, a second positive DC bus, a second negative DC bus, and a DC / DC converter circuit. The multiple battery packs are connected in series between the positive and negative terminals of the battery cluster, and the multiple battery packs include a first battery pack and a second battery pack. The positive terminal of the first battery pack is connected to the first positive DC bus via a first switch, and the negative terminal of the first battery pack is connected to the first negative DC bus via a second switch. The positive terminal of the first battery pack is also connected to the second positive DC bus via a third switch, and the negative terminal of the first battery pack is also connected to the second negative DC bus via a fourth switch. The positive terminal of the second battery pack is connected to the first positive DC bus via a fifth switch, and the negative terminal of the second battery pack is connected to the first negative DC bus via a sixth switch. The positive terminal of the second battery pack is also connected to the second positive DC bus via a seventh switch, and the negative terminal of the second battery pack is also connected to the second negative DC bus via an eighth switch. One end of the DC / DC converter circuit is connected to the first positive DC bus and the first negative DC bus, respectively, and the other end of the DC / DC converter circuit is connected to the second positive DC bus and the second negative DC bus, respectively.

[0007] In this embodiment, since multiple battery packs in the battery cluster share a single DC / DC converter circuit, and the switching between the battery packs and the DC bus has low cost, the cost of the battery cluster can be effectively reduced. Furthermore, based on the structure of the battery cluster in this embodiment, when there is an imbalance in energy (e.g., state of charge) among the internal battery packs, the switching operation between the battery packs and the DC bus, along with the DC / DC converter circuit, can transfer energy from the battery pack with a higher state of charge to the battery pack with a lower state of charge, thereby achieving energy balance among the battery packs.

[0008] In conjunction with the first aspect, in a first possible implementation, the first switch, the second switch, the seventh switch, and the eighth switch are configured to close when the difference between the state of charge of the first battery pack and the state of charge of the second battery pack exceeds a threshold, thereby forming an energy balancing circuit between the first battery pack and the second battery pack. The DC / DC converter circuit is configured to transfer electrical energy stored between the first positive DC bus and the first negative DC bus to the space between the second positive DC bus and the second negative DC bus when the difference between the state of charge of the first battery pack and the second battery pack exceeds the threshold.

[0009] In this embodiment, when there is an energy imbalance among the internal battery packs, an energy balancing circuit can be formed by switching between the battery packs and the DC bus, and the electrical energy of the battery pack with a higher state of charge can be transferred to the battery pack with a lower state of charge through a DC / DC conversion circuit, thereby achieving energy balance among the battery packs.

[0010] In conjunction with the first possible implementation of the first aspect, in the second possible implementation, the first battery pack is the battery pack with the highest state of charge among the multiple battery packs, and the second battery pack is the battery pack with the lowest state of charge among the multiple battery packs.

[0011] In this embodiment, the battery cluster selects two battery packs with the largest difference among the differences that are greater than the threshold for energy balancing each time, thereby enabling the capacity of the battery cluster to increase rapidly.

[0012] In conjunction with the first possible implementation of the first aspect or the second possible implementation of the first aspect, in the third possible implementation, the first switch, the second switch, the seventh switch and the eighth switch are further configured to disconnect when the absolute value of the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is less than or equal to a threshold, that is, when the state of charge between the first battery pack and the second battery pack reaches equilibrium.

[0013] In this embodiment, the switch in the energy balancing circuit of the first battery pack and the second battery pack is opened when the state of charge between the first battery pack and the second battery pack is balanced. This can effectively prevent the next energy balancing from starting directly without opening the switch, which could lead to a short circuit between the battery packs, thereby improving the safety of the battery packs when performing energy balancing.

[0014] In conjunction with the first to third possible embodiments of the first aspect, in the fourth possible embodiment, the DC / DC conversion circuit is further configured to stop operating when the absolute value of the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is less than or equal to a threshold.

[0015] In this embodiment, the DC / DC conversion circuit stops working when the state of charge between the first battery pack and the second battery pack reaches equilibrium, which can effectively reduce the energy loss between the first battery pack and the second battery pack, thereby reducing the energy loss of the battery cluster.

[0016] In conjunction with the first possible implementation of the first aspect, in the fifth possible implementation, the battery cluster further includes a battery management unit, which is configured to control the first switch, the second switch, the seventh switch and the eighth switch to close when the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is greater than a threshold, and to control the DC / DC conversion circuit to transfer the electrical energy stored between the first positive DC bus and the first negative DC bus to the second positive DC bus and the second negative DC bus.

[0017] In this embodiment, when there is an energy imbalance among the internal battery packs, the battery management unit can control the switching action between the battery packs and the DC bus, and control the DC / DC conversion circuit to transfer the electrical energy of the first battery pack with a higher state of charge to the second battery pack with a lower state of charge, thereby achieving energy balance among the battery packs.

[0018] In conjunction with the third possible implementation of the first aspect, in the sixth possible implementation, the battery cluster further includes a battery management unit, which is configured to control the first switch, the second switch, the seventh switch and the eighth switch to be disconnected when the absolute value of the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is less than or equal to a threshold.

[0019] In this embodiment, when the state of charge of the battery pack reaches equilibrium between the first and second battery packs, the battery management unit controls the switch in the energy balancing circuit between the first and second battery packs to be disconnected. This effectively avoids the situation where the next energy balancing begins directly without the switch being disconnected, which could lead to a short circuit between the battery packs, thereby improving the safety of the battery pack during energy balancing.

[0020] In conjunction with the fourth possible implementation of the first aspect, in the seventh possible implementation, the battery cluster further includes a battery management unit, which is used to control the DC / DC conversion circuit to stop working when the absolute value of the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is less than or equal to a threshold.

[0021] In this embodiment, when the state of charge of the battery pack reaches equilibrium between the first and second battery packs, the DC / DC converter circuit is stopped by the battery management unit, which can effectively reduce the energy loss between the first and second battery packs, thereby reducing the energy loss of the battery pack.

[0022] Secondly, this application provides a control method for an energy storage system, applied to the energy storage system. The energy storage system includes a battery cluster, which includes a first battery pack, a second battery pack, a first positive DC bus, a first negative DC bus, a second positive DC bus, a second negative DC bus, and a DC / DC converter circuit. The method includes: when the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is greater than a threshold, the battery cluster connects the positive terminal of the first battery pack to the first positive DC bus, the negative terminal of the first battery pack to the first negative DC bus, the positive terminal of the second battery pack to the second positive DC bus, and the negative terminal of the second battery pack to the second negative DC bus; and controls the DC / DC converter circuit to transfer the electrical energy stored between the first positive DC bus and the first negative DC bus to the second positive DC bus and the second negative DC bus.

[0023] In conjunction with the second aspect, in a first possible implementation, the positive terminal of the first battery pack is connected to the first positive DC bus via a first switch, the negative terminal of the first battery pack is connected to the first negative DC bus via a second switch, the positive terminal of the first battery pack is also connected to the second positive DC bus via a third switch, and the negative terminal of the first battery pack is also connected to the second negative DC bus via a fourth switch. The positive terminal of the second battery pack is connected to the first positive DC bus via a fifth switch, the negative terminal of the second battery pack is connected to the first negative DC bus via a sixth switch, the positive terminal of the second battery pack is also connected to the second positive DC bus via a seventh switch, and the negative terminal of the second battery pack is also connected to the second negative DC bus via an eighth switch. The battery cluster controls the first, second, seventh, and eighth switches to all close, thereby establishing the electrical connections between the positive and first positive DC bus, the negative and first negative DC bus, the positive and second positive DC bus, and the negative and second negative DC bus of the first battery pack.

[0024] In conjunction with the second aspect or the first possible implementation of the second aspect, in the second possible implementation, the first battery pack is the battery pack with the highest state of charge among the multiple battery packs, and the second battery pack is the battery pack with the lowest state of charge among the multiple battery packs.

[0025] In conjunction with any of the second aspects to the second possible implementations of the second aspect, in the third possible implementation, when the absolute value of the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is less than or equal to a threshold, the battery cluster disconnects the electrical connection between the positive terminal of the first battery pack and the first positive DC bus, the electrical connection between the negative terminal of the first battery pack and the first negative DC bus, the electrical connection between the positive terminal of the second battery pack and the second positive DC bus, and the electrical connection between the negative terminal of the second battery pack and the second negative DC bus.

[0026] In conjunction with the third possible implementation of the second aspect, in the fourth possible implementation, the positive terminal of the first battery pack is connected to the first positive DC bus via a first switch, the negative terminal of the first battery pack is connected to the first negative DC bus via a second switch, the positive terminal of the first battery pack is also connected to the second positive DC bus via a third switch, and the negative terminal of the first battery pack is also connected to the second negative DC bus via a fourth switch. The positive terminal of the second battery pack is connected to the first positive DC bus via a fifth switch, the negative terminal of the second battery pack is connected to the first negative DC bus via a sixth switch, the positive terminal of the second battery pack is also connected to the second positive DC bus via a seventh switch, and the negative terminal of the second battery pack is also connected to the second negative DC bus via an eighth switch. The battery cluster controls the first, second, seventh, and eighth switches to all be disconnected, thereby disconnecting the electrical connections between the positive and first positive DC bus, the negative and first negative DC bus, the positive and second positive DC bus, and the negative and second negative DC bus of the first battery pack.

[0027] In conjunction with any of the second to fourth possible implementations of the second aspect, in the fifth possible implementation, if the absolute value of the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is less than or equal to a threshold, the battery cluster control DC / DC conversion circuit stops operating.

[0028] It should be understood that the implementations and beneficial effects of the above-mentioned aspects of this application can be referenced from each other. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of a battery cluster provided by existing technology;

[0030] Figure 2 This is a schematic diagram illustrating the application scenario of the energy storage system provided in this application;

[0031] Figure 3 This is a structural schematic diagram of the energy storage system provided in this application;

[0032] Figure 4 This is another structural schematic diagram of the energy storage system provided in this application;

[0033] Figure 5 This is a flowchart illustrating the control method for the energy storage system provided in this application. Detailed Implementation

[0034] The energy storage system provided in this application is applicable to various fields, including energy storage backup power (such as residential energy storage, industrial and commercial energy storage, power plant energy storage, and power battery backup power), new energy smart microgrids, and power transmission and distribution. It is suitable for different application scenarios, such as energy storage power supply scenarios, photovoltaic-energy storage hybrid power supply scenarios, and UPS power supply scenarios. The following explanation uses the energy storage power supply scenario as an example.

[0035] See Figure 2 , Figure 2 This is a schematic diagram illustrating an application scenario of the energy storage system provided in this application. In the energy storage power supply scenario, the energy storage system provided in this application is... Figure 2 The energy storage system 1 shown includes a battery cluster 11, a DC / DC converter 12, and an energy storage inverter 13. The two DC terminals of the DC / DC converter 12 are connected to the positive terminal (BAT+) and the negative terminal (BAT-) of the battery cluster 11, respectively. The other two DC terminals of the DC / DC converter 12 are connected to the DC terminals of the energy storage inverter 13. The AC terminals of the energy storage inverter 13 are connected to the AC power grid and the AC load. The specific circuit structure of the battery cluster 11 is shown below. Figure 3As shown, the system includes battery pack PACK1 and its corresponding first switch S11, second switch S12, third switch S13 and fourth switch S14; battery pack PACK2 and its corresponding fifth switch S21, sixth switch S22, seventh switch S23 and eighth switch S24, ...; battery pack PACKn and its corresponding (4n-3)th switch Sn1, (4n-2)th switch Sn2, (4n-1)th switch Sn3 and 4nth switch Sn4; first positive DC bus BUS1+; first negative DC bus BUS1-; second positive DC bus BUS2+; second negative DC bus BUS2-; DC / DC converter circuit 111; and battery management unit 112, where n is an integer greater than 1. Each battery pack consists of multiple cells connected in series. Battery packs PACK1, PACK2, ..., PACKn are connected in series between the positive terminal BAT+ and the negative terminal BAT- of battery cluster 11. The positive terminal of battery pack PACK1 is connected to the first positive DC bus BUS1+ via the first switch S11, and the negative terminal of battery pack PACK1 is connected to the first negative DC bus BUS1- via the second switch S12. The positive terminal of battery pack PACK1 is connected to the second positive DC bus BUS2+ via the third switch S13, and the negative terminal of battery pack PACK1 is connected to the second negative DC bus BUS2- via the fourth switch S14. The positive terminal of battery pack PACK2 is connected to the first positive DC bus BUS1+ via the fifth switch S21, and the negative terminal of battery pack PACK2 is connected to the first negative DC bus BUS1- via the sixth switch S22. The positive terminal is connected to the second positive DC bus BUS2+ via the seventh switch S23, and the negative terminal of battery pack PACK2 is connected to the second negative DC bus BUS2- via the eighth switch S24; ...; the positive terminal of battery pack PACKn is connected to the first positive DC bus BUS1+ via the (4n-3)th switch Sn1, the negative terminal of battery pack PACKn is connected to the first negative DC bus BUS1- via the (4n-2)th switch Sn2, the positive terminal of battery pack PACKn is connected to the second positive DC bus BUS2+ via the (4n-1)th switch Sn3, and the negative terminal of battery pack PACKn is connected to the second negative DC bus BUS2- via the 4nth switch Sn4. One end of the DC / DC converter circuit 111 (i.e., DC terminals dc13 and dc14) is connected to the first positive DC bus BUS1+ and the first negative DC bus BUS1-, respectively, and the other end of the DC / DC converter circuit 111 (i.e., DC terminals dc11 and dc12) is connected to the second positive DC bus BUS2+ and the second negative DC bus BUS2-, respectively.In addition, the switches corresponding to each battery pack in battery cluster 11 can be mechanical switches (such as relays) or semiconductor switches, such as metal oxide semiconductor field-effect transistors (MOSFETs), insulated gate bipolar transistors (IGBTs), or gallium nitride (GaN) transistors.

[0036] After the energy storage system 1 starts operating, the DC / DC converter 12 converts the voltage of the battery cluster 11 into a stable DC voltage and outputs it to the DC terminal of the energy storage converter 13. The energy storage converter 13 inverts the DC voltage at its DC terminal into AC power and outputs it to the AC power grid and AC loads to provide power to the AC power grid and AC loads. Meanwhile, the battery management unit 112 in battery cluster 11 monitors the state of charge (SOC) of the n battery packs in real time. If it detects that the difference in SOC between any two battery packs (such as battery pack PACK1 and battery pack PACK2) is greater than a threshold, it controls the first switch S11 and the second switch S12 corresponding to battery pack PACK1 to close, controls the seventh switch S23 and the eighth switch S24 corresponding to battery pack PACK2 to close, and controls the DC / DC conversion circuit 111 to transfer the electrical energy stored between the first positive DC bus BUS1+ and the first negative DC bus BUS1- to the second positive DC bus BUS2+ and the second negative DC bus BUS2-. That is, the electrical energy stored in battery pack PACK1 with a higher SOC is transferred to battery pack PACK1 with a lower SOC, so as to reduce the absolute value of the difference between the SOC of battery pack PACK1 and the SOC of battery pack PACK2.

[0037] Understandably, when there is an imbalance in energy (such as State of Charge) among the internal battery packs of battery cluster 11, energy balance can be achieved by controlling the switching actions of the corresponding battery packs and controlling the DC / DC conversion circuit 111 to transfer electrical energy from the battery pack with higher State of Charge to the battery pack with lower State of Charge. Furthermore, since the n battery packs in battery cluster 11 share a single DC / DC conversion circuit, and the switching costs of the corresponding battery packs are low, the cost of battery cluster 11 can be effectively reduced, thereby reducing the cost of energy storage system 1.

[0038] The above are merely examples of application scenarios for the energy storage system provided in this application, and are not exhaustive. This application does not limit the application scenarios.

[0039] The following is combined with Figure 3 and Figure 4 The working principle of the energy storage system provided in this application is illustrated with examples.

[0040] See Figure 3 , Figure 3 This is a structural schematic diagram of the energy storage system provided in this application. Figure 3 As shown, the energy storage system 1 includes a battery cluster 11. The specific circuit structure of the battery cluster 11 is described in the corresponding section of the above embodiments and will not be repeated here. Optionally, the energy storage system 1 also includes an energy storage converter; see [link to relevant documentation] for details. Figure 4 .like Figure 4 As shown, the energy storage system 1 also includes an energy storage converter 13. The DC terminal i131 of the energy storage converter 13 is connected to the positive terminal BAT+ of the battery cluster 11, and the DC terminal i132 of the energy storage converter 13 is connected to the negative terminal BAT- of the battery cluster 11. The AC terminals o131 and o132 of the energy storage converter 13 are used to connect to the power grid or a load. The number of battery clusters and the number of energy storage converters in the energy storage system 1 may or may not correspond one-to-one; this application does not impose any restrictions on this. Optionally, the energy storage system 1 also includes a DC / DC converter connected between the battery cluster 11 and the DC terminal of the energy storage converter 13. Furthermore, the energy storage system 1 can also be a power supply system providing DC power. In this case, the energy storage system 1 includes the battery cluster 11 and the DC / DC converter, but no longer includes the energy storage converter 13.

[0041] In one embodiment, please also refer to Figure 3 During the process of energy storage system 1 supplying power to the grid or load, battery management unit 112 monitors the SOC of each battery pack in battery pack PACK1, battery pack PACK2, ..., battery pack PACKn in real time. When the battery management unit 112 detects that the difference between the SOC of the first battery pack and the SOC of the second battery pack in the above n battery packs is greater than a threshold, it controls the two switches connected between the first battery pack and the first positive DC bus BUS1+ and the first negative DC bus BUS1-, and the two switches connected between the second battery pack and the second positive DC bus BUS2+ and the second negative DC bus BUS2- to close, and controls the DC / DC conversion circuit 111 to transfer the electrical energy stored between the first positive DC bus BUS1+ and the first negative DC bus BUS1- to the second positive DC bus BUS2+ and the second negative DC bus BUS2-. That is, the electrical energy stored in the battery pack with the higher SOC in the first battery pack and the second battery pack is transferred to the battery pack with the lower SOC, so as to reduce the absolute value of the difference between the SOC of the first battery pack and the SOC of the second battery pack.

[0042] The DC / DC converter circuit 111 can be either a unidirectional or bidirectional DC / DC converter circuit. Here, unidirectional and bidirectional refer to whether the energy flow direction of the DC / DC converter circuit 111 is singular or non-singular. The first battery pack and the second battery pack are any two battery packs from the aforementioned n battery packs whose SOC difference is greater than a threshold. Typically, to improve the energy balancing speed of the battery packs and rapidly increase the capacity of the battery cluster 11, the two battery packs corresponding to the largest difference among the differences exceeding the threshold are identified as the first and second battery packs. Since the method of achieving battery pack energy balancing in the battery cluster 11 is consistent regardless of whether the difference between the SOC of the first and second battery packs is the largest difference among the differences exceeding the threshold, for ease of description, the following explanation will use the example of the difference between the SOC of the first and second battery packs being the largest difference among the differences exceeding the threshold.

[0043] Specifically, the battery management unit 112 monitors the SOC of each of the n battery packs in real time and calculates the difference in SOC between any two battery packs to obtain multiple differences. If the number of differences that satisfy a threshold is greater than 1, the battery management unit 112 determines the battery pack PACK1 and battery pack PACK2 corresponding to the largest difference among the differences that satisfy the threshold as the first battery pack and the second battery pack, respectively. Regardless of whether the SOC of battery pack PACK1 is greater than or less than the SOC of battery pack PACK2, the battery management unit 112 controls the first switch S11 and the second switch S12 corresponding to battery pack PACK1, and the seventh switch S23 and the eighth switch S24 corresponding to battery pack PACK2 to be closed. It also controls the DC / DC converter circuit 111 to transfer the electrical energy stored in the battery pack with the higher SOC from battery pack PACK1 to the battery pack with the lower SOC, thereby reducing the absolute value of the difference between the SOC of battery pack PACK1 and battery pack PACK2. If the absolute value of the difference between the SOC of battery pack PACK1 and battery pack PACK2 is less than or equal to a threshold, the battery management unit 112 controls the first switch S11 and the second switch S12 corresponding to battery pack PACK1, and the seventh switch S23 and the eighth switch S24 corresponding to battery pack PACK2 to be opened, and controls the DC / DC converter circuit 111 to stop operating. Optionally, if the absolute value of the difference between the SOC of battery pack PACK1 and the SOC of battery pack PACK2 is less than or equal to a threshold, the battery management unit 112 controls the first switch S11 and the second switch S12 corresponding to battery pack PACK1, as well as the seventh switch S23 and the eighth switch S24 corresponding to battery pack PACK2, to be disconnected. This achieves energy balance between battery pack PACK1 and battery pack PACK2.

[0044] It should be noted that, assuming the SOC of battery pack PACK1 is greater than that of battery pack PACK2, and the DC / DC converter circuit 111 is a unidirectional DC / DC converter circuit, then the DC terminals dc11 and dc12 of the DC / DC converter circuit 111 are low-voltage terminals, and the DC terminals dc13 and dc14 of the DC / DC converter circuit 111 are high-voltage terminals. Correspondingly, the first positive DC bus BUS1+ and the first negative DC bus BUS1- can be understood as discharge buses, and the second positive DC bus BUS2+ and the second negative DC bus BUS2- can be understood as charging buses. Assuming that the SOC of battery pack PACK1 is less than that of battery pack PACK2, and that the DC / DC converter circuit 111 is a unidirectional DC / DC converter circuit, then the DC terminals dc11 and dc12 of the DC / DC converter circuit 111 are high-voltage terminals, and the DC terminals dc13 and dc14 of the DC / DC converter circuit 111 are low-voltage terminals. Correspondingly, the first positive DC bus BUS1+ and the first negative DC bus BUS1- can be understood as charging buses, and the second positive DC bus BUS2+ and the second negative DC bus BUS2- can be understood as discharging buses. In short, when the DC / DC converter circuit 111 is a unidirectional DC / DC converter circuit, the battery management unit 112 controls the corresponding switching actions of battery packs PACK1 and PACK2 to connect the positive and negative terminals of the battery packs with higher SOC in battery packs PACK1 and PACK2 to the positive and negative DC bus of the discharge bus, respectively, and to connect the positive and negative terminals of the battery packs with lower SOC in battery packs PACK1 and PACK2 to the positive and negative DC bus of the charging bus, respectively, thereby forming an energy balancing loop between battery packs PACK1 and PACK2. Furthermore, when the DC / DC converter circuit 111 is a bidirectional DC / DC converter circuit, the battery management unit 112 controls the corresponding switching actions of battery packs PACK1 and PACK2 to connect the positive and negative terminals of battery pack PACK1 to the positive and negative DC bus of one of the charging and discharging buses, respectively, and to connect the positive and negative terminals of battery pack PACK2 to the positive and negative DC bus of the other of the charging and discharging buses, respectively, thereby forming an energy balancing loop between battery packs PACK1 and PACK2. Clearly, when the DC / DC converter circuit 111 is a bidirectional DC / DC converter circuit, in the process of forming the energy balancing loop between battery packs PACK1 and PACK2, it is only necessary to ensure that the buses connected to battery packs PACK1 and PACK2 are different, making the implementation simpler and more flexible.

[0045] After achieving energy balancing between battery packs PACK1 and PACK2, the battery management unit 112 recalculates the SOC difference between any two battery packs among the n battery packs to obtain multiple differences. Battery packs PACK3 and PACK5, corresponding to the largest difference among those exceeding a threshold, are redefined as the first and second battery packs, respectively, and the energy balancing steps between the first and second battery packs are repeated. When the SOC difference between any two battery packs among the n battery packs is less than or equal to the threshold, the battery management unit 112 stops balancing the energy between the battery packs.

[0046] Furthermore, by replacing the SOC of the battery pack in this embodiment with the voltage of the battery pack, the replaced embodiment can also achieve energy balancing between battery packs. In this embodiment, when the SOC between the two battery packs is balanced, the battery management unit 112 controls the switch in the energy balancing circuit between the two battery packs to open, in order to effectively avoid the situation where the next energy balancing starts directly without the switch being opened, which could lead to a short circuit between the battery packs. Optionally, after detecting that the difference in SOC between the two battery packs is greater than a threshold, and before performing energy balancing on the two battery packs, the battery management unit 112 controls the switches corresponding to n battery packs to open, which can also effectively avoid the situation where the next energy balancing starts directly without the switch being opened, which could lead to a short circuit between the battery packs.

[0047] In this application, when energy imbalance occurs among the internal battery packs of the battery cluster 11, energy balance can be achieved by controlling the switching actions of the corresponding battery packs and controlling the DC / DC conversion circuit 111 to transfer the electrical energy of the battery pack with higher SOC to the battery pack with lower SOC. Furthermore, since the n battery packs in the battery cluster 11 share a single DC / DC conversion circuit, and the corresponding switches for the battery packs are low-cost, the utilization rate of the DC / DC conversion circuit 111 can be effectively improved, and the cost of the battery cluster 11 can be effectively reduced, thereby reducing the cost of the energy storage system 1. Moreover, since the n battery packs share a single DC / DC conversion circuit, the available space for the DC / DC conversion circuit 111 within the battery cluster 11 is large, allowing for the selection of a high-power circuit as the DC / DC conversion circuit 111, thereby effectively shortening the battery pack energy balancing time and thus effectively improving the battery pack energy balancing speed.

[0048] It should be noted that in the above embodiments, the operation of the switch and the DC / DC conversion circuit 111 in the battery cluster 11 are both controlled by the battery management unit 112. In reality, the operation of the switch in the battery cluster 11 can also be independently performed by a switch with integrated control functions, and the DC / DC conversion circuit 111 can also be independently performed by a circuit with integrated control functions. Furthermore, the operation of the switch and the DC / DC conversion circuit 111 in the battery cluster 11 can also be controlled by other devices in the energy storage system 1 besides the battery management unit 112, such as the energy storage converter 13.

[0049] See Figure 5 , Figure 5 This is a flowchart illustrating the control method for the energy storage system provided in this application. The control method for the energy storage system provided in this application is applicable to... Figure 3 and Figure 4 The energy storage system 1 is shown. The control method for the energy storage system may include the following steps:

[0050] S101, detect the SOC of the first and second battery packs in the battery cluster.

[0051] S102, when the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is greater than a threshold, the electrical connection between the positive terminal of the first battery pack and the first positive DC bus, the electrical connection between the negative terminal of the first battery pack and the first negative DC bus, the electrical connection between the positive terminal of the second battery pack and the second positive DC bus, and the electrical connection between the negative terminal of the second battery pack and the second negative DC bus are connected, and the DC / DC conversion circuit is controlled to transfer the electrical energy stored between the first positive DC bus and the first negative DC bus to the second positive DC bus and the second negative DC bus.

[0052] Specifically, the positive terminal of the first battery pack is connected to the first positive DC bus via a first switch, and the negative terminal of the first battery pack is connected to the first negative DC bus via a second switch. The positive terminal of the first battery pack is also connected to the second positive DC bus via a third switch, and the negative terminal of the first battery pack is also connected to the second negative DC bus via a fourth switch. The positive terminal of the second battery pack is connected to the first positive DC bus via a fifth switch, and the negative terminal of the second battery pack is connected to the first negative DC bus via a sixth switch. The positive terminal of the second battery pack is also connected to the second positive DC bus via a seventh switch, and the negative terminal of the second battery pack is also connected to the second negative DC bus via an eighth switch.

[0053] When the difference between the SOC of the first battery pack and the SOC of the second battery pack exceeds a threshold, the battery cluster control switches one, two, seven, and eight are all closed. This controls the DC / DC converter circuit to transfer the electrical energy stored between the first positive DC bus and the first negative DC bus to the second positive DC bus and the second negative DC bus, thereby reducing the absolute value of the difference between the SOC of the first and second battery packs. For example, the first battery pack is the one with the highest SOC among the multiple battery packs in the battery cluster, and the second battery pack is the one with the lowest SOC among the aforementioned multiple battery packs.

[0054] Furthermore, if the absolute value of the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is less than or equal to a threshold, the battery cluster controls the first, second, seventh, and eighth switches to all open. Optionally, if the absolute value of the difference between the state of charge of the first and second battery packs is less than or equal to a threshold, the battery cluster also controls the DC / DC converter circuit to stop operating.

[0055] It should be noted that the specific implementation methods for connecting or disconnecting the electrical connection between the battery pack and the DC bus in the above embodiments include, but are not limited to, setting a switch between the battery pack and the DC bus and controlling the switch operation. For example, a variable resistor can also be set between the battery pack and the DC bus, and the electrical connection between the battery pack and the DC bus can be connected or disconnected by controlling the resistance value of the variable resistor.

[0056] In specific implementation, further details regarding the operations performed by the battery clusters in the energy storage system control method provided in this application can be found in [reference needed]. Figure 3 and Figure 4 The implementation method of the battery cluster 11 shown will not be described in detail here.

[0057] In this application, when energy imbalance occurs among the internal battery packs of a battery cluster, energy balance can be achieved by controlling the switching actions of the corresponding battery packs and controlling the DC / DC conversion circuit to transfer energy from the battery pack with a higher SOC to the battery pack with a lower SOC. Furthermore, since multiple battery packs in the battery cluster share a single DC / DC conversion circuit, and the corresponding switches for the battery packs are low-cost, the utilization rate of the DC / DC conversion circuit can be effectively improved, and the cost of the battery cluster can be effectively reduced. Moreover, because multiple battery packs share a single DC / DC conversion circuit, there is ample space available for the DC / DC conversion circuit within the battery cluster. Therefore, a high-power circuit can be selected as the DC / DC conversion circuit, which can effectively shorten the energy balancing time of the battery packs and thus effectively improve the energy balancing speed.

[0058] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. An energy storage system, characterized in that, The energy storage system includes a battery cluster, which comprises multiple battery packs, a first positive DC bus, a first negative DC bus, a second positive DC bus, a second negative DC bus, and a DC / DC converter circuit, wherein: The plurality of battery packs are connected in series between the positive and negative terminals of the battery cluster, and the plurality of battery packs include a first battery pack and a second battery pack; The positive terminal of the first battery pack is connected to the first positive DC bus via a first switch, the negative terminal of the first battery pack is connected to the first negative DC bus via a second switch, the positive terminal of the first battery pack is also connected to the second positive DC bus via a third switch, and the negative terminal of the first battery pack is also connected to the second negative DC bus via a fourth switch. The positive terminal of the second battery pack is connected to the first positive DC bus via the fifth switch, the negative terminal of the second battery pack is connected to the first negative DC bus via the sixth switch, the positive terminal of the second battery pack is also connected to the second positive DC bus via the seventh switch, and the negative terminal of the second battery pack is also connected to the second negative DC bus via the eighth switch. One end of the DC / DC converter circuit is connected to the first positive DC bus and the first negative DC bus, respectively, and the other end of the DC / DC converter circuit is connected to the second positive DC bus and the second negative DC bus, respectively.

2. The energy storage system according to claim 1, characterized in that, The first switch, the second switch, the seventh switch, and the eighth switch are configured to close when the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is greater than a threshold. The DC / DC converter circuit is configured to transfer the electrical energy stored between the first positive DC bus and the first negative DC bus to the second positive DC bus and the second negative DC bus when the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is greater than the threshold.

3. The energy storage system according to claim 2, characterized in that, The first battery pack is the battery pack with the highest state of charge among the plurality of battery packs, and the second battery pack is the battery pack with the lowest state of charge among the plurality of battery packs.

4. The energy storage system according to claim 2 or 3, characterized in that, The first switch, the second switch, the seventh switch, and the eighth switch are further configured to disconnect when the absolute value of the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is less than or equal to the threshold.

5. The energy storage system according to any one of claims 2-4, characterized in that, The DC / DC converter circuit is further configured to stop operating when the absolute value of the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is less than or equal to the threshold.

6. The energy storage system according to claim 2, characterized in that, The battery cluster also includes a battery management unit; The battery management unit is configured to control the first switch, the second switch, the seventh switch, and the eighth switch to close when the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is greater than a threshold, and to control the DC / DC conversion circuit to transfer the electrical energy stored between the first positive DC bus and the first negative DC bus to the second positive DC bus and the second negative DC bus.

7. The energy storage system according to claim 4, characterized in that, The battery cluster also includes a battery management unit; The battery management system is configured to control the first switch, the second switch, the seventh switch, and the eighth switch to all be disconnected when the absolute value of the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is less than or equal to the threshold.

8. A control method for an energy storage system, characterized in that, The energy storage system includes a battery pack, which includes a first battery pack, a second battery pack, a first positive DC bus, a first negative DC bus, a second positive DC bus, a second negative DC bus, and a DC / DC converter circuit. The method includes: When the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is greater than a threshold, the electrical connection between the positive terminal of the first battery pack and the first positive DC bus, the electrical connection between the negative terminal of the first battery pack and the first negative DC bus, the electrical connection between the positive terminal of the second battery pack and the second positive DC bus, and the electrical connection between the negative terminal of the second battery pack and the second negative DC bus are connected, and the DC / DC conversion circuit is controlled to transfer the electrical energy stored between the first positive DC bus and the first negative DC bus to the second positive DC bus and the second negative DC bus.

9. The method according to claim 8, characterized in that, The positive terminal of the first battery pack is connected to the first positive DC bus via a first switch, the negative terminal of the first battery pack is connected to the first negative DC bus via a second switch, the positive terminal of the first battery pack is also connected to the second positive DC bus via a third switch, and the negative terminal of the first battery pack is also connected to the second negative DC bus via a fourth switch. The positive terminal of the second battery pack is connected to the first positive DC bus via the fifth switch, the negative terminal of the second battery pack is connected to the first negative DC bus via the sixth switch, the positive terminal of the second battery pack is also connected to the second positive DC bus via the seventh switch, and the negative terminal of the second battery pack is also connected to the second negative DC bus via the eighth switch. The connection of the positive terminal of the first battery pack to the first positive DC bus, the connection of the negative terminal of the first battery pack to the first negative DC bus, the connection of the positive terminal of the second battery pack to the second positive DC bus, and the connection of the negative terminal of the second battery pack to the second negative DC bus includes: Control the first switch, the second switch, the seventh switch, and the eighth switch to all be closed.

10. The method according to claim 8 or 9, characterized in that, The first battery pack is the battery pack with the highest state of charge among the plurality of battery packs, and the second battery pack is the battery pack with the lowest state of charge among the plurality of battery packs.

11. The method according to any one of claims 8-10, characterized in that, The method further includes: If the absolute value of the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is less than or equal to the threshold, disconnect the electrical connection between the positive terminal of the first battery pack and the first positive DC bus, the electrical connection between the negative terminal of the first battery pack and the first negative DC bus, the electrical connection between the positive terminal of the second battery pack and the second positive DC bus, and the electrical connection between the negative terminal of the second battery pack and the second negative DC bus.

12. The method according to claim 11, characterized in that, The positive terminal of the first battery pack is connected to the first positive DC bus via a first switch, the negative terminal of the first battery pack is connected to the first negative DC bus via a second switch, the positive terminal of the first battery pack is also connected to the second positive DC bus via a third switch, and the negative terminal of the first battery pack is also connected to the second negative DC bus via a fourth switch. The positive terminal of the second battery pack is connected to the first positive DC bus via the fifth switch, the negative terminal of the second battery pack is connected to the first negative DC bus via the sixth switch, the positive terminal of the second battery pack is also connected to the second positive DC bus via the seventh switch, and the negative terminal of the second battery pack is also connected to the second negative DC bus via the eighth switch. Disconnecting the electrical connection between the positive terminal of the first battery pack and the first positive DC bus, the electrical connection between the negative terminal of the first battery pack and the first negative DC bus, the electrical connection between the positive terminal of the second battery pack and the second positive DC bus, and the electrical connection between the negative terminal of the second battery pack and the second negative DC bus, includes: The first switch, the second switch, the seventh switch, and the eighth switch are all disconnected.

13. The method according to any one of claims 8-12, characterized in that, The method further includes: If the absolute value of the difference between the state of charge of the first battery pack and the state of charge of the second battery pack is less than or equal to the threshold, the DC / DC conversion circuit is controlled to stop working.

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