Energy storage system

Abstract

The invention provides an energy storage system, and belongs to the technical field of energy storage. The energy storage system includes a plurality of battery packs connected in parallel to a DC bus. Wherein the DC / DC conversion circuit in the first battery pack can transmit excitation current to the direct current bus, and the DC / DC conversion circuit in the second battery pack can transmit the excitation current on the direct current bus to the battery cell. Therefore, the EIS excitation of the battery cell in the second battery pack can be realized, so that the BMU in the second battery pack can detect the EIS of the battery cell. According to the scheme, the excitation current can be directly provided by the DC / DC conversion circuit in the first battery pack, and the excitation current is detected by the BMU in the second battery pack, so that the dependence on the PCS and the cluster control box is effectively reduced, the communication interaction among different parts in the energy storage system is reduced, and the flexibility and reliability of EIS detection are effectively improved.

Description

Technical Field

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

[0002] An energy storage system generally includes an energy storage converter, a cluster control box, and a plurality of battery packs (packs) connected in series. Among them, the energy storage converter is also called a power conversion system (PCS). Each battery pack includes a plurality of battery cells (also called battery monomers) and a battery monitor unit (BMU). In order to improve the reliability of the energy storage system, it is necessary to detect the electrochemical impedance spectroscopy (EIS) of the battery cells in the battery pack.

[0003] Generally, the PCS can inject an excitation current into a plurality of battery packs connected in series through the cluster control box. The cluster control box can detect the excitation current and send the detected excitation current to the BMU in the battery pack. The BMU can detect the response voltage generated at both ends of the battery cell by the excitation current and calculate the EIS of the battery cell based on the excitation current sent by the cluster control box and the detected response voltage.

[0004] However, since the above EIS detection scheme requires the PCS to provide the excitation current and requires the cluster control box to detect and transmit the excitation current, the dependence on the PCS and the cluster control box is relatively high, and the flexibility and reliability of EIS detection are poor. Summary of the Invention

[0005] This application provides an energy storage system, which can solve the technical problems of relatively high dependence on the PCS and the cluster control box in the EIS detection scheme and poor flexibility and reliability of EIS detection.

[0006] A energy storage system is provided, which includes: a plurality of battery packs, a DC bus, and a direct current / alternating current (DC / AC) converter. The plurality of battery packs are connected in parallel to the DC bus, the DC bus is connected to the DC end of the DC / AC converter, and the AC end of the DC / AC converter is used to connect to the power grid or load. Each battery pack in the plurality of battery packs includes: a plurality of battery cells connected in series, a direct current / direct current (DC / DC) conversion circuit, and a BMU. The first end of the DC / DC conversion circuit is connected to the plurality of battery cells, the second end is connected to the DC bus, and is used to charge and discharge the plurality of battery cells. The DC / DC conversion circuit in the first battery pack among the plurality of battery packs is further used to transmit an excitation current to the DC bus. The DC / DC conversion circuit in the second battery pack among the plurality of battery packs is further used to transmit the excitation current to the plurality of battery cells in the second battery pack. The BMU in the second battery pack is used to detect the excitation current flowing through the plurality of battery cells in the second battery pack, detect the voltage generated across each of the plurality of battery cells by the excitation current, and determine the EIS of each of the plurality of battery cells based on the excitation current and the voltage.

[0007] In the solution provided by this application, the DC / DC conversion circuit in the first battery pack can directly provide the excitation current to the battery cells in the second battery pack, so there is no need to rely on the PCS to provide the excitation current anymore. Moreover, the BMU in the battery pack can detect the excitation current and calculate the EIS of the battery cells, so there is no need to rely on the cluster control box to detect and transmit the excitation current. Thus, the dependence of the EIS detection on the PCS and the cluster control box is effectively reduced, and the communication interaction between different components in the energy storage system is reduced to avoid the influence of the communication performance on the reliability of the EIS detection, and the flexibility and reliability of the EIS detection are improved.

[0008] Optionally, the DC / DC conversion circuit in the first battery pack is used to transmit the excitation current to the DC bus by discharging the plurality of battery cells in the first battery pack.

[0009] That is to say, the DC / DC conversion circuit in the first battery pack can discharge the second battery pack through the DC bus, so as to provide the excitation current to the plurality of battery cells in the second battery pack. It can be understood that during the process of the first battery pack discharging and outputting the excitation current, the total current transmitted by the DC / DC conversion circuit in the first battery pack to the DC bus can include a DC component and an AC component. Among them, the DC component is the discharge current, the AC component is the excitation current, and the excitation current can also be called the disturbance current.

[0010] Optionally, before the DC / DC conversion circuit in the first battery pack discharges multiple battery cells in the first battery pack, the voltages output by the DC / DC conversion circuits in the multiple battery packs to the DC bus are all 0.

[0011] It can be understood that before the process of performing EIS detection, the DC / DC conversion circuits in the multiple battery packs can all be in an idle state, that is, the energy storage system is not charging or discharging. When the process of EIS detection starts, that is, when the DC / DC conversion circuit in the first battery pack needs to discharge to the second battery pack and provide an excitation current, the DC / DC conversion circuit in the first battery pack can output a voltage to the DC bus to provide the excitation current. Correspondingly, the voltage of the DC bus will increase accordingly. After the DC / DC conversion circuit in the second battery pack detects the increase in the voltage of the DC bus, it can charge multiple battery cells in the second battery pack and transmit the excitation current from the DC bus during the charging process.

[0012] Optionally, the DC / DC conversion circuit in the first battery pack is configured to modulate the discharge current of multiple battery cells in the first battery pack during the discharge process of the multiple battery cells in the first battery pack to obtain an excitation current.

[0013] Among them, modulating the discharge current may mean: using a preset modulation algorithm to control the on / off states of each switching tube in the DC / DC conversion circuit to adjust the amplitude and frequency of the discharge current of multiple battery cells in the first battery pack, so as to realize the injection of the excitation current.

[0014] Optionally, the first battery pack and the second battery pack are different battery packs, or the first battery pack and the second battery pack are the same battery pack.

[0015] Among them, if the first battery pack and the second battery pack are the same battery pack, it is equivalent to that the DC / DC conversion circuit in the battery pack can directly provide an excitation current for the battery cells in this battery pack. It can be understood that the DC / DC conversion circuit needs to provide an excitation current by charging or discharging the battery pack, and the charging current or discharge current of the battery pack will be transmitted via the DC bus, that is, the DC bus is a part of the current loop of the charging current or discharge current. Therefore, for the scenario where the first battery pack and the second battery pack are the same battery pack, it can also be considered that the DC / DC conversion circuit in the battery pack transmits the excitation current to the DC bus and transmits the excitation current to multiple battery cells in the battery pack.

[0016] Optionally, the first battery pack and the second battery pack are the same battery pack. Moreover, the DC / DC conversion circuit in the first battery pack is configured to charge multiple battery cells in the first battery pack to transmit the excitation current to multiple battery cells in the first battery pack.

[0017] For the scenario where the first battery pack and the second battery pack are the same battery pack, the DC / DC conversion circuit in the battery pack can also provide the excitation current by charging the battery cells. Moreover, the process of the DC / DC conversion circuit providing the excitation current can be synchronized with the charging or discharging process of multiple battery packs.

[0018] Optionally, the DC / DC conversion circuit in the first battery pack is configured to modulate the charging current of multiple battery cells in the first battery pack during the charging process of the multiple battery cells in the first battery pack to obtain the excitation current.

[0019] Among them, modulating the charging current may mean: adopting a preset modulation algorithm to control the on / off states of each switching tube in the DC / DC conversion circuit to adjust the amplitude and frequency of the charging current of multiple battery cells in the battery pack, so as to realize the injection of the excitation current.

[0020] Optionally, the energy storage system provided in this application further includes a battery control unit (BCU), and the BCU is configured to send an instruction to the first battery pack, and the instruction is used to instruct the DC / DC conversion circuit in the first battery pack to transmit the excitation current to the DC bus.

[0021] Among them, the first battery pack can be any battery pack selected by the BCU from multiple battery packs. Moreover, the BCU can send the instruction through the communication connection between it and the BMU in the first battery pack. The communication connection can be a controller area network (CAN) bus connection.

[0022] Optionally, the DC / DC conversion circuits in multiple battery packs all include: an LLC conversion circuit and a buck-boost circuit. Among them, one end of the LLC conversion circuit is connected to multiple battery cells, the other end of the LLC conversion circuit is connected to one end of the buck-boost circuit, and the other end of the buck-boost circuit is connected to the DC bus.

[0023] The DC / DC conversion circuit adopts two cascaded power conversion circuits, which can realize two-stage conversion of power. Thus, on the one hand, it can effectively improve the power conversion range of the DC / DC conversion circuit, and on the other hand, it can effectively reduce the requirements for the power conversion performance of a single power conversion circuit, thereby significantly reducing the cost and structural complexity of the DC / DC conversion circuit. Moreover, the buck-boost circuit in the first battery pack can be used to provide the EIS excitation current to the DC bus.

[0024] It can be understood that for the first battery pack, the buck-boost circuit in the DC / DC conversion circuit can provide the first EIS excitation current to the DC bus.

[0025] Optionally, the BMU includes a battery management integration chip (BMIC) and a control chip. Among them, the BMIC is used to detect the excitation current and the voltage generated across each of the multiple battery cells. The control chip is used to determine the EIS of each of the multiple battery cells based on the excitation current and the voltage.

[0026] Among them, the BMIC may include a voltage detection circuit and a current detection circuit. The voltage detection circuit can detect the voltage across each battery cell. The current detection circuit can detect the excitation current flowing through the battery cell. The control chip is used to perform fast Fourier transform (FFT) analysis on the detection data of the BMIC, calculate the EIS of the battery cell, and analyze the impedance change of the battery cell. Thereby, it can ensure timely detection of potential safety risks of the battery cell or the battery pack, thus effectively improving the safety of the energy storage system.

[0027] Optionally, the energy storage system further includes: a switching circuit, and the DC bus is connected to the DC / AC converter through the switching circuit. The switching circuit is used to control the on / off between the DC bus and the DC / AC converter.

[0028] Among them, the switching circuit can be a switching device such as a relay or a contactor that can be controlled to turn on and off through an electrical signal. By way of example, the energy storage system may further include an auxiliary (AUX) power board, simply referred to as the auxiliary power board. The switching circuit can be arranged on the auxiliary power board. It can be understood that, compared with the cluster control box, since there is no need to arrange a current detection circuit on the auxiliary power board, its structure is relatively simple, and thus the structure of the energy storage system can be effectively simplified.

[0029] In summary, the present application provides an energy storage system. The energy storage system includes a plurality of battery packs connected in parallel to the DC bus. Among them, the DC / DC conversion circuit in the first battery pack can transmit the excitation current to the DC bus, and the DC / DC conversion circuit in the second battery pack can transmit the excitation current on the DC bus to the battery cells. Thereby, the EIS excitation of the battery cells in the second battery pack can be realized, so that the BMU in the second battery pack can detect the EIS of the battery cells. Since the solution provided by the embodiment of the present application can directly provide the excitation current from the DC / DC conversion circuit in the first battery pack to the battery cells in the second battery pack, there is no need to rely on the PCS to provide the excitation current. And, since the BMU in the battery pack can detect the excitation current and calculate the EIS of the battery cells, there is no need to rely on the cluster control box to detect and transmit the excitation current. Thereby, the dependence on the PCS and the cluster control box is effectively reduced, and the communication interaction between different components in the energy storage system is reduced, thus effectively improving the flexibility and reliability of the EIS detection. Description of the Drawings

[0030] Figure 1 is a schematic structural diagram of an energy storage system provided by an embodiment of the present application;

[0031] Figure 2 is a schematic structural diagram of another energy storage system provided by an embodiment of the present application;

[0032] Figure 3 is a schematic structural diagram of yet another energy storage system provided by an embodiment of the present application;

[0033] Figure 4 is a schematic structural diagram of a battery pack provided by an embodiment of the present application;

[0034] Figure 5 is a schematic structural diagram of still another energy storage system provided by an embodiment of the present application;

[0035] Figure 6 is a schematic structural diagram of still another energy storage system provided by an embodiment of the present application;

[0036] Figure 7 is a schematic structural diagram of another battery pack provided by an embodiment of the present application. Detailed Description of the Embodiments

[0037] The energy storage system provided by the embodiments of the present application will be introduced in detail below with reference to the drawings. First, the key terms involved in the embodiments of the present application will be introduced.

[0038] Battery Management System (BMS): It is used to monitor the status of the battery pack (such as temperature, voltage, current, state of charge, etc.), and is used to achieve comprehensive control and protection of the energy storage system, and provide a communication interface for the energy storage system to communicate with external components.

[0039] Battery Monitor Unit (BMU): It is responsible for monitoring the basic parameters of the battery cells, that is, battery monomers (cells) or battery modules, such as monitoring parameters such as voltage, current, and temperature. The BMU mainly includes a Battery Management Integration Chip (BMIC).

[0040] Battery Control Unit (BCU): It is used to manage the BMUs of a battery cluster, and based on the data provided by the BMUs within the battery cluster, execute the control strategy of the battery. Moreover, the BCU and multiple BMUs of a battery cluster form a BMS.

[0041] Electrochemical Impedance Spectroscopy: Apply a small-amplitude alternating sinusoidal potential wave with different frequencies to an electrochemical system, and measure the change of the ratio of the alternating potential to the current signal (i.e., the impedance of the electrochemical system) with the frequency ω of the sinusoidal wave, or the change of the phase angle φ of the impedance with ω.

[0042] In some embodiments, as Figure 1 shown, the energy storage system generally includes multiple battery packs, a cluster control box, and a PCS. Among them, the PCS includes a DC / DC converter and an inverter (i.e., a DC / AC converter). After multiple battery packs are connected in series, one end of the DC / DC converter is connected through the cluster control box. The other end of the DC / DC converter is connected to the DC side of the inverter, and the AC side of the inverter is connected to the power grid and / or load. Among them, the DC / DC converter is used to convert the DC power output by multiple series-connected battery packs and then output it to the inverter, and the inverter is used to convert the DC power into AC power and then output it to the power grid or load. The inverter is also used to convert the AC power of the power grid into DC power and then output it to the DC / DC converter, and the DC / DC converter is also used to convert the voltage of the DC power and then charge the multiple series-connected battery packs.

[0043] As Figure 1 shown, each battery pack may include multiple series-connected battery cells. To improve the reliability of the energy storage system, it is necessary to detect the states of the individual battery cells in the battery pack. The industry usually uses EIS to infer the state of the battery cells. The detection principle of EIS is: Apply a small-amplitude sinusoidal current perturbation signal with different frequencies to an electrochemical system (i.e., a battery cell). Then, measure the voltage response generated by the electrochemical system and perform FFT analysis and impedance calculation to obtain the real part, imaginary part, modulus, and phase angle of the impedance at different frequencies. Plot these points into a curve to obtain the EIS impedance spectrum.

[0044] To implement the EIS detection of the battery cells in the battery pack, the energy storage system usually injects an excitation signal into the battery pack through external devices of the battery pack. For example, referring to Figure 1 , in an energy storage system with multiple series-connected battery packs, usually the DC / DC conversion circuit in the PCS injects an excitation current into the multiple series-connected battery packs. This excitation current can be transmitted to the multiple series-connected battery packs through the cluster control box. And, as Figure 1As shown in the figure, the cluster control box includes a current sensor, a rack power control board (RPCB), and a BCU. Among them, the current sensor can detect the excitation current injected by the DC / DC conversion circuit into the battery pack, and the RPCB can transmit the detected excitation current to the BMU in each battery pack. The BMU (such as BMIC) in each battery pack can detect the response voltage generated by the excitation current across the battery cells, and perform FFT analysis on the excitation current and the response voltage to calculate the EIS of each battery cell.

[0045] However, the above EIS detection scheme requires the PCS to provide the excitation current, and requires the cluster control box to detect the excitation current and transmit the detected excitation current to the BMU in the battery pack. That is to say, the above EIS detection scheme has a high dependence on the PCS and the cluster control box. Moreover, since the above EIS detection process involves communication interactions between different devices in the energy storage system, the reliability of the EIS detection also depends on the communication performance between different devices. As a result, the components in the energy storage system are not decoupled, and the flexibility and reliability of the EIS detection are relatively low.

[0046] The embodiment of the present application provides an energy storage system, in which the battery packs are connected in parallel to the DC bus. Moreover, the battery packs have the ability of active charge and discharge, can inject an excitation signal into the DC bus, and the BMU in the battery packs can detect the excitation current. That is to say, the battery packs in this energy storage system no longer rely on the PCS to provide the excitation signal, and no longer rely on the cluster control box to detect and transmit the excitation current, thus effectively improving the flexibility and reliability of the EIS detection.

[0047] As Figure 2 shown, the energy storage system provided by the embodiment of the present application includes: a plurality of battery packs 10, a DC bus 20, and a DC / AC converter 30. The plurality of battery packs 10 are connected in parallel to the DC bus 20. The DC bus 20 is also called the common bus. Continuing to refer to Figure 2 , the DC bus 20 is also connected to the DC terminal of the DC / AC converter 30. The AC terminal of the DC / AC converter 30 is used to connect to the power grid and / or load. The plurality of battery packs 10 are used to output direct current to the DC bus, and the DC / AC converter 30 is used to convert the direct current on the DC bus into alternating current and then output it to the power grid and / or load. Moreover, the DC / AC converter 30 is also used to convert the alternating current of the power grid into direct current and then output it to the DC bus to charge the plurality of battery packs 10. That is to say, the DC / AC converter 30 can realize bidirectional power conversion between direct current and alternating current. And the DC / AC converter 30 can be an inverter or a PCS.

[0048] Continuing to refer to Figure 2, each of the multiple battery packs 10 includes: a plurality of battery cells 11 connected in series, a DC / DC conversion circuit 12, and a BMU 13. Among them, the first end of the DC / DC conversion circuit 12 is connected to the plurality of battery cells 11, and the second end is connected to the DC bus 20. The DC / DC conversion circuit 12 is used to charge and discharge the plurality of battery cells 11.

[0049] Based on the above analysis, it can be seen that compared with a energy storage system in which multiple battery packs are connected in series such as Figure 1 shown, the energy storage system with multiple battery packs 10 connected in parallel provided by the embodiment of the present application can sink the DC / DC conversion function in the PCS into each battery pack 10. Thus, each battery pack 10 has an independent charge and discharge function. And, there is no need to set up a PCS in the energy storage system, or there is no need to set up a DC / DC converter in the PCS of the energy storage system.

[0050] As Figure 3 shown, the DC / DC conversion circuit 12 in the first battery pack 10 among the multiple battery packs 10 is further used to transmit an excitation current to the DC bus 20. The first battery pack 10 can be any one of the multiple battery packs 10. The excitation current can be an alternating current, and the waveform of the excitation current can be a sine wave, a square wave, or a triangular wave, etc.

[0051] Continuing to refer to Figure 3 , the DC / DC conversion circuit 12 in the second battery pack 10 among the multiple battery packs 10 is further used to transmit the excitation current on the DC bus 20 to the plurality of battery cells 11 in the second battery pack 10. Among them, the second battery pack 10 can be any one of the multiple battery packs 10.

[0052] The BMU 13 in the second battery pack 10 is used to detect the excitation current flowing through the plurality of battery cells 11 in the second battery pack 10, detect the voltage generated at both ends of each of the plurality of battery cells 11 by the excitation current, and determine the EIS of each of the plurality of battery cells 11 based on the excitation current and the voltage.

[0053] In the embodiment of the present application, the DC / DC conversion circuit in the first battery pack can transmit the excitation current to the DC bus, and the DC / DC conversion circuit in the second battery pack can transmit the excitation current on the DC bus to the battery cells. Thus, the EIS excitation of the battery cells in the second battery pack can be realized, so that the BMU in the second battery pack can detect the excitation current and the voltage of the battery cells, and calculate the EIS of the battery cells. Since the solution provided by the embodiment of the present application can directly provide the excitation current from the DC / DC conversion circuit in the first battery pack to the battery cells in the second battery pack, there is no need to rely on the PCS to provide the excitation current anymore. Moreover, since the BMU in the battery pack can detect the excitation current and calculate the EIS of the battery cells, there is no need to rely on the cluster control box to detect and transmit the excitation current. Thus, the dependence on the PCS and the cluster control box is effectively reduced, the communication interaction between different components in the energy storage system is reduced, the influence of the communication performance between components on the reliability of EIS detection is avoided, and the flexibility and reliability of EIS detection are effectively improved.

[0054] It can be understood that the above-mentioned first battery pack and second battery pack can be different battery packs in the energy storage system, that is, the excitation current is transmitted between different battery packs. Or, the above-mentioned first battery pack and second battery pack can also be the same battery pack in the energy storage system, that is, the DC / DC conversion circuit in the battery pack can directly provide the excitation current to multiple battery cells in the battery pack.

[0055] The following describes the first alternative scenario: the scenario where the first battery pack and the second battery pack are different battery packs. It can be understood that in this first alternative scenario, each of the other battery packs 10 in the energy storage system except the first battery pack 10 can perform the operations performed by the second battery pack 10. That is, the DC / DC conversion circuit 12 in each of the other battery packs 10 can transmit the excitation current on the DC bus 20 to multiple battery cells 11, and the BMU 13 in each of the other battery packs 10 can detect the excitation current of the multiple battery cells 11, detect the voltage generated across each of the multiple battery cells 11 by the excitation current, and determine the EIS of each of the multiple battery cells 11 based on the excitation current and the voltage.

[0056] Optionally, the DC / DC conversion circuit 12 in the first battery pack 10 is configured to discharge the multiple battery cells 11 in the first battery pack 10 to transmit the excitation current to the DC bus 20. Correspondingly, the DC / DC conversion circuit 12 in the second battery pack 10 is configured to charge the multiple battery cells 11 in the second battery pack 10 to transmit the excitation current to the multiple battery cells 11 in the second battery pack 10.

[0057] That is, the DC / DC conversion circuit 12 in the first battery pack 10 can discharge to the second battery pack 20 through the DC bus 20, so as to provide an excitation current to a plurality of battery cells 11 in the second battery pack 20.

[0058] It can be understood that during the process of the first battery pack 10 discharging and outputting the excitation current, the total current transmitted by the DC / DC conversion circuit 12 in the first battery pack 10 to the DC bus 20 can include a DC component and an AC component. Among them, the DC component is the discharge current, the AC component is the excitation current, and this excitation current can also be called a perturbation current. And this excitation current is an analog quantity.

[0059] It can also be understood that during the above EIS excitation and detection process, since the first battery pack 10 is in a discharging state and the second battery pack 10 is in a charging state, therefore, this EIS excitation and detection process can be serially executed with the normal charge and discharge process of the energy storage system. That is, the solution provided by the embodiments of the present application can execute the above EIS excitation and detection process before the energy storage system starts charging or discharging. Among them, the charging of the energy storage system can refer to the DC / AC converter 30 converting the alternating current of the power grid into direct current to charge a plurality of battery packs 10. The discharging of the energy storage system can refer to a plurality of battery packs 10 of the energy storage system discharging to the DC bus 20.

[0060] Optionally, before the DC / DC conversion circuit 12 in the first battery pack 10 discharges a plurality of battery cells 11 in the first battery pack 10, the energy storage system has not started working yet. That is, before the EIS detection starts, the energy storage system has not been charged or discharged. At this time, the voltage output by the DC / DC conversion circuit 12 in each battery pack 10 to the DC bus 20 is 0, or it can be understood that the DC / DC conversion circuit 12 in each battery pack 10 does not output voltage to the DC bus 20. When the process of EIS detection starts, that is, when it is necessary for the DC / DC conversion circuit 12 in the first battery pack 10 to discharge to the second battery pack 10 and provide an excitation current, the DC / DC conversion circuit 12 in the first battery pack 10 can output voltage to the DC bus 20 to provide the excitation current. Correspondingly, the voltage of the DC bus 20 will increase accordingly. After the DC / DC conversion circuit 12 in the second battery pack 10 detects the increase in the voltage of the DC bus 20, it can charge a plurality of battery cells 11 in the second battery pack 10 and transmit the excitation current from the DC bus 20 during the charging process.

[0061] It can also be understood that the DC / DC conversion circuit 12 in each battery pack 10 includes at least one switching tube. And, as Figure 4As shown, each battery pack 10 further includes a controller 14 (also referred to as a drive circuit) for driving the DC / DC conversion circuit 12. The controller 14 is capable of providing a pulse-width modulation (PWM) signal to at least one switching transistor in the DC / DC conversion circuit 12, that is, sending a wave to at least one switching transistor in the DC / DC conversion circuit 12 to control the on / off state of the at least one switching transistor.

[0062] In the embodiment of the present application, after the controller 14 in the second battery pack 10 detects that the voltage of the DC bus increases, it can send a wave to the DC / DC conversion circuit 12 according to the wave-sending mode corresponding to the charging state, so as to charge the multiple battery cells 11. And the controller 14 can also appropriately adjust the wave-sending mode corresponding to the charging state to minimize the influence on the excitation current transmitted to the multiple battery cells 11.

[0063] Optionally, the DC / DC conversion circuit 12 in the first battery pack 10 is used to modulate the discharge current of the multiple battery cells 11 in the first battery pack 10 to obtain an excitation current during the discharge process of the multiple battery cells 11 in the first battery pack 10.

[0064] Among them, modulating the discharge current may mean that the controller 14 in the first battery pack 10 uses a preset modulation algorithm to control the on / off state of each switching transistor in the DC / DC conversion circuit 12 to adjust the amplitude and frequency of the discharge current of the multiple battery cells 11 in the first battery pack 10, so as to realize the injection of the excitation current. Thus, an excitation signal (also referred to as a characteristic excitation signal), that is, an excitation current, can be injected in the wave-sending link of the DC / DC conversion circuit 12 in the first battery pack 10.

[0065] Optionally, as Figure 5 shown, the energy storage system may further include a BCU 40, and the BCU 40 is used to send an instruction to the first battery pack 10, and the instruction is used to instruct the DC / DC conversion circuit 12 in the first battery pack 10 to transmit an excitation current to the DC bus 20.

[0066] Refer to Figure 5It can be seen that the BCU 40 can establish communication connections with the BMUs 13 in multiple battery packs 10, and the communication connection can be a controller area network (CAN) bus connection. The BCU 40 and the BMUs 13 in multiple battery packs 10 can form the BMS of the energy storage system. When it is necessary to perform EIS detection on the energy storage system, the BCU 40 can select a battery pack 10 from multiple battery packs 10 as the first battery pack 10, and send an instruction to the BMU 13 in the first battery pack 10 through the above communication connection. The BMU 13 can then, based on the instruction sent by the BCU 40, instruct the DC / DC conversion circuit 12 in the first battery pack 10 to transmit an excitation current to the DC bus 20.

[0067] Exemplarily, the BCU 40 can arbitrarily select a battery pack 10 that can work properly from multiple battery packs 10 as the first battery pack, that is, as the EIS excitation source. Moreover, in different EIS detection processes, the BCU 40 can select different battery packs 10 as the first battery pack to ensure that each battery pack 10 can perform EIS detection based on the received EIS excitation current.

[0068] The following describes the second alternative scenario: the scenario where the first battery pack and the second battery pack are the same battery pack. As Figure 6 shown, in this second alternative scenario, the DC / DC conversion circuit 12 in each battery pack 10 is used to provide an excitation current to multiple battery cells 11 in the battery pack 10 itself. For example, the DC / DC conversion circuit 12 in each battery pack 10 is used to charge or discharge the battery cells 11 in the battery pack 10 itself to provide an excitation current to multiple battery cells 11 in the battery pack 10 itself.

[0069] It can be understood that when the DC / DC conversion circuit 12 charges or discharges the battery cells 11 in the battery pack 10, the charging current or discharging current of the battery cells 11 will be transmitted via the DC bus 20, that is, the DC bus 20 is part of the current loop of the charging current or discharging current. For example, in the discharging scenario, the discharging current flows out from the positive electrode of the battery cell 11, flows into the positive bus in the DC bus 20 through the DC / DC conversion circuit 12, and then flows from the negative bus through the DC / DC conversion circuit 12 into the negative electrode of the battery cell 11. In the charging scenario, the charging current flows into the positive electrode of the battery cell 11 through the positive bus and the DC / DC conversion circuit 12 in the DC bus 20, then flows out from the negative electrode of the battery cell 11, and flows out to the negative bus through the DC / DC conversion circuit 12. Therefore, for the scenario where the first battery pack and the second battery pack are the same battery pack, it can also be considered that the DC / DC conversion circuit 12 in the battery pack 10 transmits an excitation current to the DC bus 20 and transmits an excitation current to multiple battery cells 11 in the battery pack 10.

[0070] Comparison Figure 3 and Figure 6 It can be seen that in this second alternative scenario, the DC / DC conversion circuit 12 in each battery pack 10 can independently provide an excitation current to the battery cells 11 in this battery pack 10, without the need to transmit the excitation current between the battery packs 10 through the DC bus 20. Since the DC / DC conversion circuit 12 in each battery pack 10 can independently generate the excitation current, the excitation of the EIS does not need to rely on other battery packs, thus effectively improving the flexibility of the EIS detection.

[0071] Optionally, in this second alternative scenario, the DC / DC conversion circuit 12 is used to charge or discharge a plurality of battery cells 11 to transmit the excitation current to the DC bus 20 and transmit the excitation circuit to the plurality of battery cells 11.

[0072] For example, the DC / DC conversion circuit 12 is used to modulate the discharge current of a plurality of battery cells 11 to obtain an excitation current during the discharge process of the plurality of battery cells 11. Or, the DC / DC conversion circuit 12 is used to modulate the charging current of a plurality of battery cells 11 to obtain an excitation current during the charging process of the plurality of battery cells 11.

[0073] As described above, each battery pack 10 may further include a controller 14, and the controller 14 may adopt a preset modulation algorithm to control the on / off states of the respective switching tubes in the DC / DC conversion circuit 12 to adjust the amplitude and frequency of the discharge current or charging current of the plurality of battery cells 11, thereby realizing the injection of the excitation current.

[0074] It can be understood that the DC / DC conversion circuit 12 charging a plurality of battery cells 11 may mean that: the DC / DC conversion circuit 12 performs power conversion on the direct current output from the DC / AC converter 30 to the DC bus 20 and charges the plurality of battery cells 11. And, the DC / DC conversion circuit 12 discharging a plurality of battery cells 11 may mean that: the DC / DC conversion circuit 12 performs power conversion on the direct current provided by the plurality of battery cells 11 and then outputs it to the DC bus 20, and then the DC / AC converter 30 performs power conversion on the direct current on the DC bus 20 and outputs it to the power grid and / or load.

[0075] Based on the above analysis, it can be seen that in this second alternative scenario, the process of EIS detection can be executed in parallel with the charge and discharge process of the battery pack 10, that is, the detection of the battery cell EIS can be realized during the normal charge and discharge process of the battery pack 10. This detection scheme does not affect the normal charge and discharge of the battery pack 10, and its application flexibility is relatively high.

[0076] Of course, the above EIS detection process can also be executed when the energy storage system is not charging or discharging. For example, it can be executed before the energy storage system operates. Correspondingly, before the DC / DC conversion circuit 12 in each battery pack 10 provides the excitation current, the voltage output by the DC / DC conversion circuit 12 in each battery pack 10 to the DC bus 20 is 0. Or it can be understood that the DC / DC conversion circuit 12 in each battery pack 10 does not output voltage to the DC bus 20.

[0077] Optionally, in this second alternative scenario, the BCU 40 is used to send instructions to multiple battery packs 10, and the instructions are used to instruct the DC / DC conversion circuits 12 in the multiple battery packs 10 to provide excitation current to multiple battery cells 11.

[0078] For the above two alternative scenarios, a communication connection is also established between the BMU 13 and the controller 14 of the DC / DC conversion circuit 12 in each battery pack 10. Based on this communication connection, the BMU 13 can instruct the controller 14 to send a wave to the DC / DC conversion circuit 12, so that the DC / DC conversion circuit 12 outputs an excitation current. By way of example, as Figure 4 shown, the communication connection between the BMU 13 and the controller 14 of the DC / DC conversion circuit 12 can be a serial communication interface (SCI) connection.

[0079] Optionally, in the above two alternative scenarios, continue to refer to Figure 4 , the BMU 13 may include a BMIC 131 and a control chip 132. Among them, the BMIC 131 is used to detect the excitation current and the voltage generated across each of the multiple battery cells 11 by the excitation current. The control chip 132 is used to determine the EIS of each of the multiple battery cells 11 based on the excitation current and the voltage.

[0080] By way of example, the BMIC 131 may include a voltage detection circuit and a current detection circuit. The voltage detection circuit can detect the voltage across each battery cell 11. The current detection circuit can detect the excitation current flowing through the battery cell 11, that is, detect the analog quantity of current perturbation. The control chip 132 is used to perform FFT analysis on the detection data of the BMIC 131, calculate the EIS of the battery cell 11, and analyze the impedance change of the battery cell 11. For example, the control chip 132 can compare the detected impedance with the original impedance (i.e., the initial impedance or the nominal impedance) to analyze the impedance change of the battery cell 11. Thus, it can ensure timely detection of potential safety risks of the battery cell or the battery pack, thereby effectively improving the safety of the energy storage system.

[0081] It can be understood that the frequency of the excitation current output by the first battery pack 10 can vary within a certain frequency range. The BMU 13 can implement EIS detection at different frequency points within this frequency range, that is, it can detect the impedance of the battery cells 11 at different frequency points.

[0082] It can also be understood that, as Figure 4 and Figure 5 shown, each battery pack 10 can include multiple BMICs 131. Each BMIC 131 can be connected to a part of the battery cells 11 and is used to detect the voltage and current of this part of the battery cells 11.

[0083] Optionally, in the above two alternative scenarios, the DC / DC conversion circuit 12 in each battery pack 10 can include two cascaded power conversion circuits. Among these two cascaded power conversion circuits, the power conversion circuit directly connected to the DC bus can be a non-isolated power conversion circuit. For example, it can be a buck-boost circuit. The power conversion circuit directly connected to multiple battery cells 11 can be an isolated power conversion circuit. For example, it can be an LLC power conversion circuit. Here, L refers to inductor, and C refers to capacitor.

[0084] Exemplarily, as Figure 7 shown, the DC / DC conversion circuit 12 in each battery pack 10 can include: an LLC conversion circuit 121 and a buck-boost circuit 122. Among them, one end of the LLC conversion circuit 121 is connected to multiple battery cells 11, the other end of the LLC conversion circuit 121 is connected to one end of the buck-boost circuit 122, and the other end of the buck-boost circuit 122 is connected to the DC bus 20. The buck-boost circuit 122 can be a half-bridge buck-boost circuit or a full-bridge buck-boost circuit.

[0085] For the scenario where the DC / DC conversion circuit 12 in each battery pack 10 includes two cascaded power conversion circuits, the first battery pack 10 can provide a first EIS excitation current to the DC bus through the non-isolated power conversion circuit (i.e., the power conversion circuit directly connected to the DC bus). For example, the controller 14 of the first battery pack 10 can use a preset modulation algorithm to control the on-off states of the switching tubes in the non-isolated power conversion circuit (such as the buck-boost circuit) to achieve the injection of the excitation current.

[0086] It can be understood that both the LLC conversion circuit 121 and the buck-boost circuit 122 can achieve the conversion of DC power. The DC / DC conversion circuit 12 employs two cascaded power conversion circuits, enabling two-stage power conversion. Thus, on the one hand, the power conversion range of the DC / DC conversion circuit 12 can be effectively increased. On the other hand, the requirements for the power conversion performance of a single power conversion circuit can be effectively reduced, thereby reducing the cost and structural complexity of the DC / DC conversion circuit 12.

[0087] It can also be understood that the LLC conversion circuit 121 is an isolated power conversion circuit, and a transformer is included in this isolated power conversion circuit. This isolated power conversion circuit can not only achieve power conversion, and, as Figure 5 shown, the transformer in this isolated power conversion circuit can also achieve electrical isolation between the BMU 13 and the high-voltage DC bus, as well as electrical isolation between the battery cell 11 and the high-voltage DC bus, thereby effectively improving the safety of the battery pack 10 and the entire energy storage system.

[0088] The above description is made by taking the DC / DC conversion circuit 12 including two cascaded power conversion circuits as an example. Of course, the DC / DC conversion circuit 12 may not need to adopt a cascaded architecture. For example, the DC / DC conversion circuit 12 can be a buck-boost circuit.

[0089] Optionally, as Figure 5 shown, the energy storage system may further include: a switch circuit 50. The DC bus 20 is connected to the DC / AC converter 30 through the switch circuit 50, and the switch circuit 50 is used to control the on / off between the DC bus 20 and the DC / AC converter 30.

[0090] Among them, the switch circuit 50 can be a switch device such as a relay or a contactor that can control on / off through an electrical signal. Exemplarily, the energy storage system may further include an AUX power supply board, abbreviated as an auxiliary power board. The switch circuit 50 can be arranged on this auxiliary power board. It can be understood that compared with the cluster control box, since there is no need to arrange a current detection circuit and a signal transmission circuit on the auxiliary power board, its structure is relatively simple, thereby effectively simplifying the structure of the energy storage system.

[0091] It can also be understood that since the DC / DC conversion circuit 12 in each battery pack 10 can control the charging and discharging of the battery cell 11, that is, the DC / DC conversion circuit 12 can achieve the function of a switch, the switch circuit 50 may not need to be arranged in the energy storage system either. Thus, the cost and structural complexity of the energy storage system can be further reduced.

[0092] The above description is given by taking the example of independently setting the DC / DC conversion circuit 12 in each battery pack 10. It can also be understood that at least two (for example, 2 or 3) battery packs 10 can also share the same DC / DC conversion circuit 12. For example, an LLC conversion circuit 121 is independently set in each battery pack 10, and the other ends of the LLC conversion circuits 121 in at least two battery packs 10 are connected in parallel to one end of the same buck-boost circuit 122, and the other end of the buck-boost circuit 122 is then connected to the DC bus.

[0093] In summary, the embodiment of the present application provides an energy storage system, which includes a plurality of battery packs connected in parallel to the DC bus. Among them, the DC / DC conversion circuit in the first battery pack can transmit the excitation current to the DC bus, and the DC / DC conversion circuit in the second battery pack can transmit the excitation current on the DC bus to the battery cells. Thus, the EIS excitation of the battery cells in the second battery pack can be realized, so that the BMU in the second battery pack can detect the EIS of the battery cells. Since the solution provided by the embodiment of the present application can directly provide the excitation current from the DC / DC conversion circuit in the first battery pack to the battery cells in the second battery pack, there is no need to rely on the PCS to provide the excitation current. And, since the BMU in the battery pack can detect the excitation current and calculate the EIS of the battery cells, there is no need to rely on the cluster control box to detect and transmit the excitation current. Thus, the dependence on the PCS and the cluster control box is effectively reduced, and the communication interaction between different components in the energy storage system is reduced, thereby effectively improving the flexibility and reliability of the EIS detection.

[0094] Moreover, the solution provided by the embodiment of the present application can realize the closed-loop completion of the entire EIS detection process within the energy storage system. During the EIS detection process, the functions of EIS excitation and current detection are decoupled, the implementation is relatively simple, and the reliability is higher. In addition, the solution provided by the embodiment of the present application integrates the function of DC / DC conversion into the battery pack, so there is no need to set a DC / DC converter in the energy storage system, for example, there is no need to set a DC / DC converter in the PCS. And, since the DC / DC conversion circuit in each battery pack can also realize the function of switching, that is, it can control the on / off of the battery cells and the DC bus, there is no need to set a cluster control box in the energy storage system either. Thus, the structure of the energy storage system can be effectively simplified, and the cost of the energy storage system can be reduced.

[0095] It can be understood that the energy storage system provided by the embodiment of the present application can be a household energy storage system. Or, the energy storage system can also be a small energy storage system such as a data center energy storage system or a site energy storage system. The embodiment of the present application does not limit the type of the energy storage system, and only needs to ensure that the battery pack 10 in the energy storage system has the function of independent charge and discharge control (that is, independent control of output buck-boost).

[0096] In addition, it can also be understood that the solution provided in the embodiments of the present application can be applied not only to energy storage systems, but also to other battery systems, such as power battery systems.

[0097] In the embodiments of the present application, the terms "first", "second", and "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance. The term "at least one" means one or more, and "a plurality" means two or more.

[0098] In the embodiments of the present application, the term "and / or" is merely a description of the association relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0099] As mentioned above, the above are only optional implementation manners of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. An energy storage system, characterized in that: The energy storage system comprises: a plurality of battery packs, a DC bus and a DC / AC converter, wherein the plurality of battery packs are connected in parallel to the DC bus, the DC bus is connected to the DC end of the DC / AC converter, and the AC end of the DC / AC converter is used to connect to a power grid or a load; Each of the plurality of battery packs comprises: a plurality of battery cells connected in series, a DC / DC conversion circuit and a battery monitoring unit BMU, wherein a first end of the DC / DC conversion circuit is connected to the plurality of battery cells, a second end of the DC / DC conversion circuit is connected to the DC bus, and is used to charge or discharge the plurality of battery cells; The DC / DC conversion circuit in the first battery pack among the plurality of battery packs is further used to transmit an excitation current to the DC bus; The DC / DC conversion circuit in the second battery pack among the multiple battery packs is further used to transmit the excitation current to the multiple battery cells in the second battery pack; The BMU in the second battery pack is used to detect an excitation current flowing through the multiple battery cells in the second battery pack, detect a voltage generated across each of the multiple battery cells by the excitation current, and determine an electrochemical impedance spectrum (EIS) of each of the multiple battery cells based on the excitation current and the voltage.

2. The energy storage system according to claim 1, characterized in that: The DC / DC conversion circuit in the first battery pack is used to transmit the excitation current to the DC bus by discharging the multiple battery cells in the first battery pack.

3. The energy storage system according to claim 2, characterized in that: The DC / DC conversion circuit in the first battery pack is used to modulate the discharge current of the multiple battery cells in the first battery pack to obtain the excitation current during the process of discharging the multiple battery cells in the first battery pack.

4. The energy storage system according to claim 2 or 3, characterized in that: Before the DC / DC conversion circuit in the first battery pack discharges the multiple battery cells in the first battery pack, the voltages output to the DC bus by the DC / DC conversion circuits in the multiple battery packs are all 0.

5. The energy storage system according to any one of claims 1 to 4, characterized in that: The first battery pack and the second battery pack are different battery packs.

6. The energy storage system according to any one of claims 1 to 4, characterized in that: The first battery pack and the second battery pack are the same battery pack.

7. The energy storage system according to any one of claims 1 to 6, characterized in that: The energy storage system further includes a battery control unit BCU, wherein the BCU is used to send instructions to the first battery pack, wherein the instructions are used to instruct a DC / DC conversion circuit in the first battery pack to transmit the excitation current to the DC bus.

8. The energy storage system according to any one of claims 1 to 7, characterized in that: The DC / DC conversion circuits in the multiple battery packs all include: an LLC conversion circuit and a buck-boost circuit; One end of the LLC conversion circuit is connected to the multiple battery cells, the other end of the LLC conversion circuit is connected to one end of the buck-boost circuit, and the other end of the buck-boost circuit is connected to the DC bus.

9. The energy storage system according to any one of claims 1 to 8, characterized in that: The BMU includes a battery management chip BMIC and a control chip; The BMIC is used to detect the excitation current, and detect the voltage generated by the excitation current at both ends of each battery cell in the plurality of battery cells; The control chip is used to determine the EIS of each battery cell in the plurality of battery cells based on the excitation current and the voltage.

10. The energy storage system according to any one of claims 1 to 9, characterized in that: The energy storage system further includes: a switch circuit, through which the DC bus is connected to the DC / AC converter, and the switch circuit is used to control the on / off between the DC bus and the DC / AC converter.

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