Energy storage system

Abstract

The present application belongs to the technical field of energy storage. Provided is an energy storage system. A power converter in the energy storage system can not only charge and discharge a battery pack, but can also supply an excitation current to the battery pack. A current sampling circuit in the energy storage system can measure the excitation current flowing through the battery pack, and transmit the measured excitation current to a BMU in the battery pack. The BMU can measure a voltage that is generated across a battery cell by the excitation current, and determine EIS of the battery cell on the basis of the received excitation current and the measured voltage. Since the power converter can supply the excitation current to the battery pack during the charging and discharging of the battery pack, and none of the current measurement process, the voltage measurement process and the EIS measurement process interferes with the normal charging and discharging of the battery pack, the EIS measurement process of the battery cell can be performed synchronously with the charging and discharging process of the battery pack, thereby enabling online EIS measurement of the battery cell.

Description

Energy storage system

[0001] This application claims priority to Chinese Patent Application No. 202510065829.8, filed on January 14, 2025, entitled "Energy Storage System", and also claims priority to Chinese Patent Application No. 202511228645.5, filed on August 28, 2025, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of energy storage technology, and in particular to an energy storage system. Background Technology

[0003] Energy storage systems typically consist of multiple battery packs, each containing multiple battery cells (also known as individual cells). To improve the reliability of energy storage systems, it is necessary to perform electrochemical impedance spectroscopy (EIS) analysis on the battery cells within the battery packs.

[0004] An EIS (Electronic Information System) testing system typically includes: an EIS AC interference master unit, a junction box, and an industrial control computer. The EIS AC interference master unit provides excitation current to the battery cell under test. The junction box samples the excitation current flowing through the battery cell, samples the response voltage generated by this excitation current, and transmits the sampled excitation current and response voltage to the industrial control computer. The industrial control computer then calculates the EIS of the battery cell under test based on the received sampling data.

[0005] However, the above testing method can only perform offline EIS testing of the battery cells, and cannot perform online EIS testing of the battery cells during battery pack operation. Offline testing refers to performing EIS testing on the battery cells before they leave the factory, or performing EIS testing on the battery cells after they have been removed from the battery pack. Summary of the Invention

[0006] This application provides an energy storage system that can solve the technical problem that EIS detection schemes can only achieve offline detection and cannot perform online detection of the EIS of the cells during battery pack operation.

[0007] An energy storage system is provided, comprising: a power converter, a current sampling circuit, and at least one battery pack. The at least one battery pack refers to a single battery pack or multiple battery packs connected in series. Each battery pack includes a battery monitor unit (BMU) and multiple battery cells. The power converter is used to charge and discharge the at least one battery pack and to provide a first excitation current to the at least one battery pack. The current sampling circuit is used to detect a second excitation current flowing through the at least one battery pack and to send the detected second excitation current to the BMU in the at least one battery pack. The second excitation current is the excitation current flowing through the at least one battery pack when the power converter provides the first excitation current to the at least one battery pack. The BMU in the at least one battery pack is used to detect the voltage generated across each of the multiple battery cells by the second excitation current and to determine the energy index (EIS) of each of the multiple battery cells based on the second excitation current and the voltage.

[0008] In the solution provided in this application, the power converter can not only charge and discharge at least one battery pack, but also provide excitation current to the at least one battery pack. Furthermore, the current sampling circuit can detect the excitation current flowing through the at least one battery pack and send the detected excitation current to the BMU in the battery pack. The BMU can detect the voltage generated across the battery cell by the excitation current and determine the cell's EIS based on the excitation current and the detected voltage. Since the power converter can provide excitation current to the battery pack during the charging and discharging process, and the aforementioned current detection, voltage detection, and EIS detection processes do not affect the charging and discharging of the battery pack, the cell EIS detection process can be performed synchronously with the charging and discharging process of the battery pack, thereby enabling online detection of the cell EIS.

[0009] Optionally, the power converter is used to provide charging current to at least one battery pack after converting the output power of the grid or photovoltaic modules during the charging process of at least one battery pack, and to modulate the charging current to obtain a first excitation current. Modulating the charging current can refer to using a preset modulation algorithm to control the on / off state of each switch in the power converter to adjust the amplitude and frequency of the charging current, thereby injecting the first excitation current. It is understood that the first excitation current is an alternating current, and the above modulation process will not affect the normal charging of the battery pack.

[0010] Optionally, the power converter is used to convert the output power of at least one battery pack during its discharge process and output the converted power, and to modulate the discharge current of the at least one battery pack to obtain a first excitation current. Modulating the discharge current can refer to using a preset modulation algorithm to control the on / off state of each switch in the power converter to adjust the amplitude and frequency of the discharge current, thereby injecting the first excitation current. This first excitation current is an alternating current, and the modulation process does not affect the normal discharge of the battery pack.

[0011] It is understandable that the amplitude of the first excitation current can be less than or equal to the amplitude of the charging current or the discharging current in order to avoid affecting the normal charging and discharging of the battery pack.

[0012] Optionally, the second excitation current detected by the current sampling circuit is an analog signal. This current sampling circuit is used to convert the analog signal into a digital signal and then send it to the BMU in the at least one battery pack.

[0013] Because digital signals have strong anti-interference capabilities, the current sampling circuit converts the second excitation current from an analog signal to a digital signal before sending it, which ensures that the signal quality received by the BMU is high, thereby ensuring that the detection accuracy of the EIS is high.

[0014] Optionally, the current sampling circuit is further configured to send a synchronization signal to the BMU in at least one battery pack, the synchronization signal including a detection timestamp of the second excitation current. The BMU in the battery pack is used to synchronize the second excitation current and voltage based on the detection timestamp of the second excitation current and the detection timestamp of the voltage, and to determine the EIS of each of the multiple cells based on the synchronized second excitation current and voltage.

[0015] Synchronizing the excitation current and cell voltage using a synchronization signal ensures high accuracy of the subsequently calculated EIS. Synchronizing the excitation current and cell voltage involves aligning the sampled excitation current and cell voltage data based on the detection timestamp. In other words, excitation currents and cell voltages at the same detection timestamp are treated as a set of sampled data to calculate the cell's EIS.

[0016] Optionally, the energy storage system further includes a battery control unit (BCU). The BCU is used to send an EIS detection command to the power converter, the EIS detection command carrying the amplitude and frequency of the first excitation current.

[0017] The BCU can be located in the cluster control box. The BCU can initiate the EIS detection process by sending an EIS detection command to the power converter.

[0018] Optionally, the BMU in the at least one battery pack is also used to report all detected EIS to the BCU. The BCU is also used to send the EIS reported by the BMU in the at least one battery pack to the cloud server.

[0019] The BCU can report the EIS of each cell to the cloud server via wireless or wired communication. After receiving the EIS of each cell reported by the BCU in the energy storage system, the cloud server can perform big data analysis on the EIS of each cell, thereby enabling more accurate and comprehensive detection of the cell status.

[0020] Optionally, the waveform of the first excitation current is a sine wave, a triangular wave, or a trapezoidal wave. The amplitude range of the first excitation current is 5 amperes (A) to 30 A, meaning the amplitude of the first excitation current is relatively large, thereby reducing the difficulty of voltage and current sampling. The frequency range of the first excitation current is 0.01 Hz to 4 kHz, and the BMU can achieve EIS detection within this frequency range.

[0021] Optionally, the current sampling circuit is located in the cluster control box or in the battery management system (BMS). It is understood that the cluster control box or BMS typically includes a current sampling circuit for sampling the charge and discharge current, and the solution provided in this application can reuse this current sampling circuit to detect the excitation current. This avoids the need to add an extra current sampling circuit to the energy storage system, thereby preventing an increase in the cost and structural complexity of the energy storage system.

[0022] Optionally, the power converter in the energy storage system is a direct current / direct current (DC / DC) converter or a direct current / alternating current (DC / AC) converter. If the power converter is a DC / DC converter, one end of the DC / DC converter can be connected to at least one battery pack, and the other end can be connected to an energy storage converter or inverter, or it can be connected to a DC bus. This DC bus is used to connect DC loads and / or other DC power sources (such as photovoltaic modules). If the power converter is a DC / AC converter, one end of the DC / AC converter is connected to at least one battery pack, and the other end can be connected to an AC load and / or the power grid.

[0023] Optionally, the power converter can be located in the energy storage converter. Alternatively, the power converter is a DC / DC converter located in the BMS, meaning the DC / DC converter in the BMS can charge and discharge the battery pack and provide excitation current to the battery pack.

[0024] In summary, this application provides an energy storage system. The power converter in this energy storage system can not only charge and discharge at least one battery pack, but also provide excitation current to the at least one battery pack. Furthermore, the current sampling circuit in the energy storage system can detect the excitation current flowing through at least one battery pack and send the detected excitation current to the BMU in the battery pack. The BMU can detect the voltage generated across the battery cell by the excitation current and determine the cell's EIS based on the excitation current and the detected voltage. Since the power converter can provide excitation current to the battery pack during the charging and discharging process, and the aforementioned current detection, voltage detection, and EIS detection processes do not affect the charging and discharging of the battery pack, the cell EIS detection process can be performed synchronously with the charging and discharging process of the battery pack, thereby enabling online detection of the cell EIS. Attached Figure Description

[0025] Figure 1 is a schematic diagram of an energy storage system provided in an embodiment of this application;

[0026] Figure 2 is a schematic diagram of a battery pack provided in an embodiment of this application;

[0027] Figure 3 is a schematic diagram of another energy storage system provided in an embodiment of this application;

[0028] Figure 4 is a schematic diagram of another energy storage system provided in an embodiment of this application;

[0029] Figure 5 is a schematic diagram of another energy storage system provided in an embodiment of this application;

[0030] Figure 6 is a schematic diagram of the structure of an EIS detection system provided in an embodiment of this application;

[0031] Figure 7 is a schematic diagram of an application scenario of an energy storage system provided in an embodiment of this application;

[0032] Figure 8 is a schematic diagram of another application scenario of the energy storage system provided in the embodiments of this application. Detailed Implementation

[0033] The energy storage system provided in the embodiments of this application is described in detail below with reference to the accompanying drawings.

[0034] Figure 1 is a schematic diagram of an energy storage system provided in an embodiment of this application. As shown in Figure 1, the energy storage system may include a battery group, which includes multiple battery packs 10 connected in series. Continuing to refer to Figure 1, the energy storage system also includes a cluster control box and a power converter 30. The cluster control box is connected between the battery group and the power converter 30, and serves as the power distribution unit of the energy storage system, used to control the on / off connection between the battery group and the power converter 30.

[0035] In this embodiment, the power converter 30 can be a DC / DC converter, a DC / AC converter, or an AC / DC converter, etc., as a main power circuit. In the scenario where the power converter 30 is a DC / DC converter, one end of the DC / DC converter is connected to the battery pack via a cluster control box, and the other end can be connected to a DC load and / or other DC power sources (e.g., photovoltaic modules) via a DC bus. Alternatively, the energy storage system also includes the power conversion system (PCS). The other end of the DC / DC converter can be connected to the DC terminal of the PCS, and the AC terminal of the PCS is connected to the power grid and / or an AC load. The DC / DC converter is used to convert the DC power output from the battery pack and output it, and to convert the DC power provided by other DC power sources or the PCS and provide it to the battery pack, thereby charging the multiple battery packs 10 in the battery pack.

[0036] In scenarios where the power converter 30 is a DC / AC converter or an AC / DC converter, the DC / AC converter or AC / DC converter can be located in the PCS, and the DC terminal of the PCS is connected to the battery pack via a cluster control box, while the AC terminal is connected to the power grid and / or an AC load. The PCS is used to convert the DC power output from the battery pack into AC power and output it to the power grid or load, and to convert the AC power from the power grid into DC power and supply it to the battery pack, thereby charging the multiple battery packs 10 in the battery pack.

[0037] As shown in Figure 1, each battery pack 10 may include multiple battery cells 11. For example, the number of these multiple battery cells 11 can range from 4 to 100. These multiple battery cells 11 can be connected in series and / or in parallel. Each battery cell 11 can be a lithium-ion battery cell. To improve the reliability of the energy storage system, it is necessary to detect the state of each battery cell 11 in the battery pack 10. The industry typically uses EIS to infer the state of the battery cells. The detection principle of EIS is as follows: small-amplitude sinusoidal current perturbation signals of different frequencies are applied to the electrochemical system (i.e., the battery cell), the corresponding voltage response generated by the electrochemical system is measured, and a fast Fourier transform (FFT) and impedance calculation are performed to obtain the real part, imaginary part, magnitude, and phase angle of the impedance at different frequencies. These points are plotted as curves to obtain the EIS impedance spectrum. There are two commonly used EIS impedance spectra: one is called the Nyquist plot, and the other is called the Bode plot. The EIS impedance spectrum reflects the relationship between the impedance of the electrochemical system and the frequency, providing rich information on interface structure and dynamics.

[0038] In a broad sense, EIS can be understood as a high-precision, high-frequency, and non-destructive sensor. This sensor is sensitive to both external factors (such as temperature, humidity, pressure, flow rate, concentration, and load) and internal factors (such as the material itself, interfaces, composition, and manufacturing process) of an electrochemical system. This sensitivity makes EIS detection highly valuable in the energy storage field.

[0039] The EIS testing system commonly used in the industry is primarily an offline testing system. This offline EIS testing system typically includes: an EIS AC interference main unit, a junction box, and an industrial control computer. The EIS AC interference main unit includes a function generator and an electronic load. The function generator generates the AC excitation signal (i.e., excitation current), and the electronic load superimposes the AC excitation current used for testing. The junction box includes a voltage acquisition device and a current acquisition device. The voltage acquisition device acquires the voltage across the battery cell during testing; the current acquisition device acquires the excitation current during testing. The industrial control computer is equipped with impedance testing and analysis software. This software is used to record and process the data acquired from the junction box both online and offline to obtain the EIS of the battery cell.

[0040] For example, the offline testing system described above can perform DC measurement, fixed frequency test and frequency sweep test on the battery cell, thereby collecting data on the impedance parameters of the battery cell under different disturbance signal (i.e. excitation current) frequencies.

[0041] However, the aforementioned offline testing system is only suitable for testing cells before they leave the factory; it cannot perform EIS testing on cells within the energy storage system after they leave the factory. Alternatively, the cells need to be removed from the battery pack after leaving the factory and then sent to the aforementioned offline testing system for offline testing. Since cells in energy storage systems often only exhibit abnormalities after a period of use following manufacturing, such as lithium plating, abnormal internal resistance, or capacity reduction, online testing is a primary requirement for energy storage systems. Online testing refers to performing EIS testing directly on the cells within the battery pack during battery pack operation. This testing process does not affect the normal charging and discharging of the battery pack, and the battery pack continues to operate normally after the testing.

[0042] This application provides an energy storage system capable of online detection of cell EIS (Energy Information System). As shown in Figure 1, the energy storage system includes a battery group, a current sampling circuit 20, and a power converter 30. The battery group includes at least one battery pack 10. At least one battery pack 10 refers to a single battery pack 10 or multiple battery packs 10 connected in series. Optionally, the number of at least one battery pack 10 included in the battery group can range from 2 to 12.

[0043] Figure 2 is a schematic diagram of a battery pack according to an embodiment of this application. As shown in Figure 2, each battery pack 10 in the at least one battery pack 10 includes a battery monitor unit (BMU) 12 and a plurality of battery cells 11. For example, the number of battery cells 11 in each battery pack 10 can range from 2 to 100. Referring to Figure 2, the plurality of battery cells 11 can be connected in series. Alternatively, the plurality of battery cells 11 can be connected in parallel, or some of the battery cells 11 can be connected in series and some in parallel. This embodiment of the application does not limit the connection method of the plurality of battery cells 11.

[0044] The power converter 30 is used to charge and discharge the at least one battery pack 10 and to provide a first excitation current to the at least one battery pack 10. The first excitation current flows in the direction of the battery pack. This first excitation current, also called the EIS excitation current, is an alternating current, and its waveform can be a sine wave, a triangular wave, or a trapezoidal wave, etc. The power converter 30 is a power converter in the main power loop of the energy storage system. This main power loop is also called the main power circuit. The main power loop can refer to a power loop used to realize bidirectional energy flow in the energy storage system and to exchange energy with the grid or load.

[0045] The current sampling circuit 20 is used to detect the second excitation current flowing through the at least one battery pack 10 and send the detected second excitation current to the BMU 12 in the at least one battery pack 10. The second excitation current is the excitation current flowing through the at least one battery pack 10 when the power converter 30 provides the first excitation current to the at least one battery pack 10. Alternatively, it can be understood that the first excitation current is the actual excitation current output by the power converter 30, and the second excitation current is the actual excitation current flowing through the at least one battery pack 10 after transmission through the line.

[0046] The BMU 12 in each battery pack 10 is used to detect the voltage generated across each of the multiple battery cells 11 by the second excitation current, and to determine the EIS of each of the multiple battery cells 11 based on the second excitation current and the detected voltage. The BMU 12 is also called a BMU board, which may include a battery management integrated circuit (BMIC) and peripheral devices.

[0047] For example, BMU 12 can perform FFT and EIS impedance calculations on the acquired data (i.e., the second excitation current and the voltage across the cell terminals) and obtain key parameters such as frequency, real impedance, and imaginary impedance. Then, based on the acquired key parameters, an EIS curve (such as a Nyquist plot or Bode plot) is plotted, and the characteristic values ​​of the EIS curve are extracted. Finally, based on the extracted characteristic values, the relevant characteristics of cell 11 in the energy storage system can be obtained online, such as one or more of the following characteristics: impedance anomaly, temperature anomaly, capacity anomaly, internal temperature, and SOX. SOX can include state of charge (SOH), state of health (SOP), and state of energy (SOE).

[0048] In summary, this application provides an energy storage system in which the power converter can not only charge and discharge the battery pack, but also provide excitation current to the battery pack. The current sampling circuit in the energy storage system can detect the excitation current flowing through the battery pack and send the detected excitation current to the BMU in the battery pack. The BMU can detect the voltage generated across the battery cell by the excitation current and determine the cell's EIS based on the received excitation current and the detected voltage. Since the power converter can provide excitation current to the battery pack during the charging and discharging process, and the aforementioned current detection, voltage detection, and EIS detection processes do not affect the normal charging and discharging of the battery pack, the cell EIS detection process can be synchronized with the battery pack's charging and discharging process, thereby enabling online detection of the cell EIS.

[0049] Understandably, one end of the power converter 30 is used to connect to the battery pack, and the other end is used to connect to the power grid, load, and / or other DC power sources. Furthermore, the other end of the power converter 30 (also referred to as the user side) has an output capacitor that filters out the first excitation current, thus preventing any additional impact on the energy storage system.

[0050] The power converter 30 includes at least one switching transistor, which can control the on / off state of the at least one switching transistor via a pulse width modulation (PWM) signal, thereby achieving charging and discharging control of at least one battery pack 10. In this embodiment, the power converter 30 can reuse the at least one switching transistor to generate a first excitation current. For example, the power converter 30 can modulate the PWM signal using a software algorithm to generate the first excitation current.

[0051] In this embodiment, the power converter 30 can simultaneously charge or discharge at least one battery pack 10 during EIS excitation, thereby avoiding interference with the normal operation of the energy storage system and achieving online cluster-level EIS detection. For example, the power converter 30 can modulate a PWM signal to generate a current ripple in the charging or discharging current of the at least one battery pack 10. This current ripple is the first excitation current used to achieve EIS excitation. Furthermore, this first excitation current can also be referred to as the EIS excitation current ripple.

[0052] Optionally, the power converter 30 is used to provide charging current to the at least one battery pack 10 after converting the output power of the grid or other DC power source (such as photovoltaic modules) during the charging process. The power converter 30 is also used to modulate the charging current to obtain a first excitation current. Modulating the charging current can refer to using a preset modulation algorithm to control the on / off state of each switch in the power converter 30 to adjust the amplitude and frequency of the charging current, causing current ripple and thus injecting the first excitation current. It is understood that the first excitation current is an alternating current, and the above modulation process will not affect the normal charging of the battery pack.

[0053] Optionally, the power converter 30 is used to convert the output power of at least one battery pack 10 during discharge and output it, for example, to a load and / or the power grid. The power converter 30 is also used to modulate the discharge current of at least one battery pack 10 to obtain a first excitation current and to provide the first excitation current to at least one battery pack 10. Modulating the discharge current may refer to using a preset modulation algorithm to control the on / off state of each switch in the power converter 30 to adjust the amplitude and frequency of the discharge current, causing current ripple in the discharge current, thereby injecting the first excitation current.

[0054] It is also understood that the amplitude of the first excitation current provided by the power converter 30 to at least one battery pack 10 is less than or equal to the amplitude of the charging current, and less than or equal to the amplitude of the discharging current. Furthermore, since this first excitation current is an alternating current, the process of modulating the charging and discharging current and injecting the excitation current described above will not affect the normal discharge of the battery pack 10. Here, the amplitude of the first excitation current can refer to its peak value.

[0055] It is also understandable that the internal resistance of a single cell 11 in an energy storage system is relatively small, typically less than 1 milliohm (mΩ). For example, taking a 280 Ah (AH) cell as an example, the internal resistance of a single cell 11 is approximately 0.2 mΩ. Therefore, during EIS detection, if the amplitude of the excitation current is also small, the amplitude of the voltage generated across the cell 11 by this excitation current will be small. This increases the requirements for the accuracy of current and voltage sampling, and increases the difficulty of current and voltage sampling. In this embodiment, since the excitation current can be provided by the power converter 30, and the current range that the power converter 30 can provide is relatively large, it can ensure that the amplitude of the excitation current it provides is large. Furthermore, the power converter 30 can provide excitation currents of different frequencies with low noise. Therefore, the accuracy requirements of the current sampling circuit and voltage sampling circuit can be effectively reduced, and the cost of the current sampling circuit and voltage sampling circuit can be effectively reduced while ensuring the accuracy of current and voltage sampling.

[0056] For example, the amplitude of the first excitation current provided by the power converter 30 can range from 5A to 30A. The frequency range of the first excitation current can be from 0.01Hz to 4kHz. Furthermore, the frequency of the first excitation current provided by the power converter 30 can vary within this 0.01Hz to 4kHz frequency range to ensure that the energy storage system can detect EIS at different frequency points within this range. In addition, the amplitude of the battery pack's charging current (or discharging current) can be set according to the requirements of the application scenario, for example, it can be 50A, or it can be 280A or 300A.

[0057] As mentioned above, the first excitation current provided by the power converter 30 to at least one battery pack 10 is an alternating current, the direction of which is constantly changing. For example, referring to Figure 4, the direction of the first excitation current in one half-cycle can be from the positive terminal of at least one battery pack 10 to the negative terminal of at least one battery pack 10, and the direction of the first excitation current in the other half-cycle can be from the negative terminal of at least one battery pack 10 to the positive terminal of at least one battery pack 10.

[0058] As one possible implementation, this energy storage system can be applied to relatively large-scale energy storage scenarios such as industrial and commercial applications, power plants, or charging stations. In these scenarios, the battery pack typically includes multiple battery packs 10, and the number of these battery packs 10 is relatively large. Furthermore, as shown in Figure 1, the energy storage system also includes a cluster control box. This cluster control box, also known as a rack power control board (RPCB), is the power distribution unit in the energy storage system, connected between the power converter 30 and the battery pack.

[0059] In this implementation, as shown in Figures 1 and 4, the current sampling circuit 20 is located in the cluster control box. Furthermore, the power converter 30 needs to provide a first excitation current to at least one battery pack 10 in the battery pack through this cluster control box. That is, the first excitation current provided by the power converter 30 flows through the cluster control box, therefore the current sampling circuit 20 in the cluster control box can detect the second excitation current flowing through the at least one battery pack 10.

[0060] As another possible implementation, this energy storage system can be applied to small-scale energy storage scenarios such as data centers, residential applications, or site environments. In these scenarios, the battery pack typically includes a single battery pack 10, or a small number of battery packs 10 connected in series. Furthermore, as shown in Figures 3 and 5, the energy storage system includes a battery management system (BMS), and the current sampling circuit 20 is located within the BMS.

[0061] It is understood that the second excitation current detected by the current sampling circuit 20 is an analog signal. The current sampling circuit 20 can directly send this analog signal to the BMU 12 in at least one battery pack 10. Alternatively, the current sampling circuit 20 can convert the analog signal into a digital signal and then send the digital signal to the BMU 12 in at least one battery pack 10. The current sampling circuit 20 can send the analog or digital signal to the BMU 12 in at least one battery pack 10 via a signal line.

[0062] It is also understood that the cluster control box and BMS are typically equipped with a current sensor for detecting the charging and discharging current of the battery pack. This current sensor can be a shunt. For example, referring to Figures 4 and 5, this current sensor can be equivalent to a sampling resistor R0, and it can be connected in series with the negative terminal of the battery pack. Of course, the current sensor can also be connected in series with the positive terminal of the battery pack; this embodiment does not limit this. In this embodiment, the current sampling circuit 20 in the cluster control box or BMS can reuse the current sensor to detect the second excitation current flowing through at least one battery pack 10.

[0063] As a possible example, the current sampling circuit 20 can directly send the analog signal to the BMU 12 in each battery pack 10. In this example, referring to Figures 4 and 5, the current sampling circuit 20 may further include a first operational amplifier A1, a capacitor C0, a second operational amplifier A2, and an isolation (ISO) circuit. The first operational amplifier A1 amplifies the current signal sampled by the current sensor. The capacitor C0 filters out the DC component of the current signal (i.e., filters out the charging or discharging current) to obtain the AC component (i.e., the second excitation current). The second operational amplifier A2 amplifies the second excitation current output by the capacitor C0 and transmits the amplified second excitation current to the BMU 12 in each battery pack 10 through the isolation circuit. The isolation circuit can be used to achieve signal isolation.

[0064] As another possible example, the current sampling circuit 20 first converts the second excitation current from an analog signal to a digital signal, and then sends the digital signal to the BMU 12 in at least one battery pack 10.

[0065] In this example, continuing to refer to Figures 4 and 5, the current sampling circuit 20 may further include a first operational amplifier A1, a capacitor C0, a second operational amplifier A2, and an analog-to-digital converter (ADC). The first operational amplifier A1 amplifies the current signal sampled by the current sensor. The capacitor C0 filters out the DC component of the current signal, obtaining the AC component (i.e., the second excitation current). The second operational amplifier A2 amplifies the second excitation current output by the capacitor C0. The ADC converts the second excitation current from an analog signal to a digital signal. For example, referring to Figures 4 and 5, the ADC can employ sigma-delta (∑-Δ) modulation technology to implement the analog-to-digital conversion. Furthermore, the ADC can also have signal isolation functionality.

[0066] In this example, the current sampling circuit 20 can send the analog-to-digital converted digital signal to at least one BMU 12 in the battery pack 10 via the low-voltage differential signaling (LVDS) protocol. After receiving the digital signal, the BMU 12 can first decode the digital signal to recover the analog signal before performing subsequent EIS calculations.

[0067] Understandably, because digital signals have stronger anti-interference capabilities, the current sampling circuit 20 converts the detected second excitation current into a digital signal before transmitting it to the BMU 12, which can effectively improve the anti-interference capability of the transmitted signal. This ensures that the signal quality received by the cluster control box is high, thereby ensuring the high accuracy of the subsequently calculated cell EIS.

[0068] Optionally, in scenarios where the current sampling circuit 20 converts the second excitation current from an analog signal to a digital signal before sending it to the BMU 12, the current sampling circuit 20 is also used to send a synchronization signal to the BMU 12 in at least one battery pack 10. This synchronization signal includes a detection timestamp of the second excitation current, also known as a sampling timestamp. The BMU 12 is used to synchronize the second excitation current and voltage based on the detection timestamp of the second excitation current and the detection timestamp of the voltage across the battery cell 11, and to determine the EIS of each of the multiple battery cells 11 based on the synchronized second excitation current and voltage.

[0069] In this embodiment, for scenarios where the current sampling circuit 20 is located in the cluster control box or BMS, since the cluster control box or BMS is used to sample the excitation current, while the BMU 12 is used to sample the voltage generated by the excitation current across the battery cell 11, the excitation current and battery cell voltage signals are sampled by different components in the energy storage system. Therefore, it is necessary to synchronize the two signals to ensure the accuracy of the subsequently calculated EIS. Based on this, when the current sampling circuit 20 in the cluster control box or BMS detects the second excitation current, it can also record the detection timestamp of the detected second excitation current and send the detection timestamp to the BMU 12 in at least one battery pack 10 via a synchronization signal. For example, the detection timestamp recorded by the current sampling circuit 20 can be the sampling timestamp when the second excitation current is analog-to-digital converted.

[0070] After receiving the synchronization signal, BMU 12 can synchronize the second excitation current and voltage based on the detection timestamp of the second excitation current and the detection timestamp of the voltage across the battery cell 11. Synchronization can refer to data alignment of the second excitation current and voltage based on the detection timestamps, or it can be understood as treating second excitation currents and voltages with the same detection timestamps as a set of detection data. Then, BMU 12 can determine the EIS of the battery cell 11 based on the synchronized second excitation current and voltage.

[0071] Optionally, continuing to refer to Figures 4 and 5, the BMU 12 in the battery pack 11 may include a voltage sampling circuit capable of sampling the voltage across each cell 11. For example, this voltage sampling circuit may include multiple sets of sub-circuits connected one-to-one with multiple cells (e.g., n+1 cells as shown in Figures 4 and 5, where n is a positive integer). Each set of sub-circuits is used to sample the voltage across one cell 11 to which it is connected. Each set of sub-circuits may include a third operational amplifier A3 and an analog-to-digital converter (ADC). The third operational amplifier A3 amplifies the voltage across the cell 11, and the ADC converts the voltage output by the third operational amplifier A3 from an analog signal to a digital signal. Correspondingly, the timestamp for detecting the voltage across the cell 11 mentioned above may also refer to the sampling timestamp when the ADC performs analog-to-digital conversion of the voltage.

[0072] Referring to cell n-1 in Figures 4 and 5, the equivalent circuit model of each cell 11 in the battery pack 10 may include an ideal cell C. idle Inductance L, Resistance R Ω Capacitor C sei resistance R sei Capacitor C dl resistance R ct and impedance Z w Among them, capacitor C sei and resistance R sei Parallel connection, resistor R ct and impedance Z w After being connected in series with capacitor C dl Parallel connection. The above two parallel branches are connected to the ideal cell C. idle Inductance L and resistance R Ω Series connection. It is understandable that when the state of cell 11 changes, the parameters of at least one component in the equivalent circuit model will also change, resulting in different response voltages generated after the excitation current passes through the equivalent circuit model. Therefore, the EIS of cell 11 calculated based on the response voltage and excitation current can accurately reflect the state of cell 11.

[0073] Optionally, as shown in Figure 1, the energy storage system may further include a battery control unit (BCU) 40. The BCU 40 and the BMUs 12 in each battery pack 10 can form a battery management system (BMS). Furthermore, if the energy storage system is applied to larger-scale energy storage scenarios such as industrial and commercial applications, power plants, or charging stations, as shown in Figure 1, the BCU 40 can be located in a cluster control box, i.e., the cluster control box includes the BCU 40. The BCU 40 is used to send an EIS detection command to the power converter 30, the EIS detection command carrying the amplitude and frequency of a first excitation current. The power converter 30 is used to generate a first excitation current with the corresponding amplitude and frequency based on the EIS detection command.

[0074] If the energy storage system can be applied to small-scale energy storage scenarios such as data centers, residential applications, or site environments, then since the number of battery packs 10 included in the battery pack is relatively small in these scenarios (e.g., typically one battery pack 10), the functions of both the BMU and BCU can be integrated into the BMU. That is, the BMU 12 combines the functions of a traditional BCU and BMU. Accordingly, the BMU 12 can also be called a BCU. Furthermore, the BMU 12 is also used to send an EIS detection command to the power converter 30, which carries the amplitude and frequency of the first excitation current. The power converter 30 is used to generate a first excitation current with the corresponding amplitude and frequency based on the EIS detection command.

[0075] Therefore, the cell EIS detection process can be initiated and controlled by BCU 40 or BMU 12. Furthermore, BCU 40 (or BMU 12) and power converter 30 can establish a communication connection via a controller area network (CAN) bus, and BCU 40 (or BMU 12) can send EIS detection commands to power converter 30 via the CAN bus.

[0076] Optionally, in scenarios where BMU 12 and BCU 40 are configured independently, BMU 12 in battery pack 10 is also used to report the detected EIS to BCU 40. BCU 40 is also used to send the EIS reported by at least one BMU 12 in battery pack 10 to a cloud server (also called a cloud platform). For example, BCU 40 can report the cell's EIS to the cloud server via wireless or wired communication. The wireless communication connection can be a Wi-Fi connection or mobile communication (such as 4G / 5G), while the wired communication can be a network cable connection or fiber optic connection. For example, the wired communication connection can be a Fast Ethernet (FE) connection.

[0077] In scenarios where the BMU 12 integrates BCU functionality, it can also be used to report detected EIS to a cloud server. For example, the BMU 12 can report the cell's EIS to the cloud server via wireless or wired communication. Wireless communication can be Wi-Fi or mobile communication (such as 4G / 5G), while wired communication can be Ethernet or fiber optic.

[0078] Understandably, after the cloud server obtains the EIS of each cell reported by BCU 40 or BMU 12 in the energy storage system, it can perform big data analysis on the EIS of each cell, thereby enabling more accurate and comprehensive detection of the cell status.

[0079] Optionally, the power converter 30 in the energy storage system can be a DC / DC converter, or it can be a DC / AC converter. This application embodiment does not limit the type of the power converter 30, only requiring that the power converter 30 is the main power circuit in the energy storage system used for charging and discharging the battery pack 10.

[0080] A DC / DC converter is used to convert direct current to voltage. It can be a non-isolated power conversion circuit, such as a buck converter, a boost converter, or a buck-boost converter. Alternatively, a DC / DC converter can be an isolated power conversion circuit, such as an LLC power conversion circuit, where L stands for inductor and C stands for capacitor.

[0081] A DC / AC converter can be used to achieve bidirectional conversion between direct current and alternating current; it can also be called an AC / DC converter. It can be a single-phase inverter circuit, a T-type three-level inverter circuit, a three-phase bridge inverter circuit, or a Heric inverter circuit, etc. Here, Heric refers to the concept of a highly efficient and reliable inverter.

[0082] It is also understood that in the energy storage system provided in this application embodiment, the power converter 30 can be located in the PCS. Alternatively, in the scenario where the power converter 30 is a DC / DC converter, the DC / DC converter can be located in the BMS. For example, in a small energy storage scenario, referring to Figures 3 and 5, the BMS may include a DC / DC converter, a current sampling circuit 20, and a BMU 12 located in the battery pack 10. Furthermore, both the DC / DC converter and the current sampling circuit 20 can be located on a single board, which can be located on a structural component. If the energy storage system includes one battery pack 10, the structural component can be directly attached to the battery pack 10. If the energy storage system includes multiple battery packs 10 connected in series, the DC / DC converter and the current sampling circuit 20 can be set independently of the multiple battery packs 10 and connected to the multiple battery packs 10 connected in series, that is, the multiple battery packs 10 can share the DC / DC converter circuit and the current sampling circuit 20.

[0083] It is also understandable that in large-scale energy storage scenarios, the DC / DC converter can be a device independent of the battery pack and the PCS. Alternatively, the DC / DC converter can be located within the PCS. Furthermore, the cluster control box can be located within the PCS, or within the DC / DC converter, or it can be set up independently.

[0084] Optionally, the current sampling circuit 20 can also be located in the battery pack 10, for example, in the BMU 12. This application embodiment does not limit the arrangement of the various components in the energy storage system.

[0085] Referring to Figure 6, the EIS detection system in the energy storage system provided in this embodiment may include: an excitation unit, a sampling unit, a transmission unit, and an algorithm unit. The following description uses an energy storage system applied to a large-scale energy storage scenario as an example to illustrate each unit in this EIS detection system.

[0086] Excitation Unit: As the excitation source for EIS, it provides excitation current flowing in the direction of the battery pack. Since the internal resistance of the cells in the energy storage system is relatively low, the excitation unit needs to provide the largest possible excitation current to reduce the technical difficulty of high-precision sampling and thus reduce costs. Referring to Figures 4 and 7, this excitation unit can be implemented by a DC / DC converter or a PCS (e.g., a DC / AC converter within a PCS). Furthermore, this excitation unit can be a power converter in the main power loop of the energy storage system. For example, in industrial and commercial scenarios or charging station scenarios, this excitation unit can be implemented by a DC / DC converter. Alternatively, in industrial and commercial scenarios or power station scenarios, this excitation unit can be implemented by a PCS (e.g., a DC / AC converter within a PCS). The aforementioned DC / DC converter or DC / AC converter can generate excitation currents of different frequencies, with low noise and large current flow.

[0087] Sampling Unit: Used to achieve high-precision sampling of cell voltage and EIS excitation current. Referring to Figures 4 and 7, this sampling unit can be implemented jointly by the RPCB (i.e., cluster control box) and the BMU 12 in the battery pack. The cluster control box is used to sample the excitation current, and the BMU 12 is used to sample the cell voltage.

[0088] Transmission Unit: Used to transmit the excitation current sampled by the sampling unit, and implemented by the RPCB (i.e., cluster control box), or by both the RPCB and BMU 12. This transmission unit can also synchronize the cell voltage and excitation current. The excitation current sampled by the sampling unit can be an analog current signal or a digital current signal. For analog current signals, the transmission function can be implemented by the RPCB alone. For digital current signals, as shown in Figure 6, the transmission function can be implemented by both the RPCB and BMU 12. The RPCB is used to convert the excitation current from an analog current signal to a digital current signal, for example, using Σ-Δ modulation technology to achieve analog-to-digital conversion. The BMU 12 is used to decode the digital current signal to recover the analog current signal.

[0089] Algorithm Unit: This unit executes the EIS algorithm on the acquired data (i.e., cell voltage and excitation current) to obtain the electrochemical impedance spectroscopy (EIS) curve of cell 11. As shown in Figures 4 and 7, this algorithm unit can be executed by the BMU 12 inside the battery pack. For example, this algorithm unit mainly performs FFT transformation and EIS impedance calculation, and obtains the following key parameters: frequency, real impedance, and imaginary impedance. Furthermore, this algorithm unit can plot the EIS curve (e.g., Nyquist curve) based on the calculated data and extract the EIS curve feature values. Based on these feature values, the algorithm unit can derive the relevant characteristics of cell 11 in the energy storage system online, such as impedance anomalies, temperature anomalies, capacity anomalies, internal temperature, and SOx.

[0090] The process of EIS inspection performed by the above-mentioned EIS inspection system is as follows:

[0091] First, the BCU inside the RPCB initiates the EIS detection process. This BCU communicates with the DC / DC converter or the DC / AC converter in the PCS to generate EIS excitation. During EIS detection, the battery pack in the energy storage system is either charging or discharging, and the charging or discharging current of the battery pack is greater than 5A. Battery charging includes two states: equalization charging and float charging.

[0092] Subsequently, the DC / DC converter or the DC / AC converter in the PCS generates an excitation current while operating, which flows into the battery pack. For example, the amplitude of this excitation current can be from 5A to 30A, and the frequency can be from 0.01Hz to 4kHz. Furthermore, both the amplitude and frequency of this excitation current can be controlled by the BCU within the RPCB.

[0093] Furthermore, while the DC / DC converter or the DC / AC converter in the PCS generates the excitation current, the BMU 12 inside each battery pack 10 in the battery pack samples the voltage across the two ends of the cell 11, and the RPCB samples the excitation current and transmits it to the BMU 12. The BMU 12 synchronously collects the cell voltage and excitation current, starts the FFT operation, and executes the EIS impedance calculation algorithm to obtain the electrochemical impedance spectrum curve of the cell 11. After obtaining the curve, the BMU 12 uses an internally integrated algorithm to determine the relevant state of the cell, and sends it to a cloud platform (e.g., via the BCU) for big data analysis of the cell to achieve more accurate and comprehensive cell state detection.

[0094] It is understandable that in small-scale energy storage scenarios such as data centers, residential applications, or site applications, the EIS detection system in the energy storage system can also include an excitation unit, sampling unit, transmission unit, and algorithm unit as shown in Figure 6. The functions of each of these units can be found in the description in Figure 6, and will not be repeated here. Furthermore, in the aforementioned small-scale energy storage scenarios, since the BMU 12 in the battery pack 10 is generally considered part of the BMS, referring to Figures 5 and 8, the excitation unit, transmission unit, sampling unit, and algorithm unit in the aforementioned EIS detection system can all be implemented by the BMS. Specifically, the excitation unit is implemented by the DC / DC converter circuit in the BMS, the transmission unit is implemented by the current sampling circuit 20, the sampling unit is implemented by the current sampling circuit 20 and the BMU 12, and the algorithm unit is implemented by the BMU 12. In addition, since the BMU 12 in the BMS can be located inside the battery pack 10 in the battery group, the sampling unit and algorithm unit can also be considered to be implemented by the battery pack 10 in the battery group.

[0095] Optionally, as shown in Figure 8, in site and data center scenarios, one end of the DC / DC conversion circuit in the BMS is connected to the battery pack, and the other end is used to connect to the load and / or other DC power sources (e.g., photovoltaic modules). Continuing to refer to Figure 8, in residential scenarios, one end of the DC / DC conversion circuit in the BMS is connected to the battery pack, and the other end is used to connect to the DC terminal of the inverter (INV). The AC terminal of the inverter can be used to connect to the power grid and / or the load.

[0096] In summary, this application provides an energy storage system in which the power converter can not only charge and discharge the battery pack but also provide excitation current to the battery pack. The current sampling circuit in the energy storage system can detect the excitation current flowing through the battery pack and send the detected excitation current to the BMU in the battery pack. The BMU can detect the voltage generated across the battery cell by the excitation current and determine the cell's EIS based on the received excitation current and the detected voltage. Since the power converter can provide excitation current to the battery pack during charging and discharging, and the aforementioned current detection, voltage detection, and EIS detection processes do not affect the normal charging and discharging of the battery pack, the cell EIS detection process can be synchronized with the battery pack's charging and discharging process, thereby enabling online detection of the cell's EIS. This ensures timely detection of potential safety risks to the battery cell or battery pack, effectively improving the safety of the energy storage system.

[0097] Furthermore, the excitation current provided by the power converter in the energy storage system avoids the increased cost of setting up a separate excitation unit and ensures a large amplitude of the provided excitation current, thereby effectively improving the sampling accuracy of current and voltage, and thus improving the detection accuracy of EIS. In addition, the solution provided in this application embodiment can utilize the original current sampling circuit of the energy storage system to sample the excitation current, which can effectively reduce the structural complexity and cost of the EIS detection system.

[0098] In the embodiments of this application, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The term "at least one" refers to one or more, and "multiple" refers to two or more.

[0099] In the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0100] The above description is merely an optional implementation of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An energy storage system, characterized in that, The energy storage system includes: a power converter, a current sampling circuit, and at least one battery pack; each battery pack in the at least one battery pack includes: a battery monitoring unit (BMU) and multiple battery cells; The power converter is used to charge and discharge the at least one battery pack and to provide a first excitation current to the at least one battery pack. The current sampling circuit is used to detect the second excitation current flowing through the at least one battery pack and send the detected second excitation current to the BMU in the at least one battery pack, wherein the second excitation current is the excitation current flowing through the at least one battery pack when the power converter provides the first excitation current to the at least one battery pack; The BMU is used to detect the voltage generated across each of the plurality of cells by the second excitation current, and to determine the electrochemical impedance spectroscopy (EIS) of each of the plurality of cells based on the second excitation current and the voltage.

2. The energy storage system according to claim 1, characterized in that, The power converter is used to convert the output power of the grid or photovoltaic module during the charging process of the at least one battery pack, and then provide a charging current to the at least one battery pack, and to modulate the charging current to obtain the first excitation current.

3. The energy storage system according to claim 1, characterized in that, The power converter is used to convert the output power of the at least one battery pack during the discharge process and output it, and to modulate the discharge current of the at least one battery pack to obtain the first excitation current.

4. The energy storage system according to any one of claims 1 to 3, characterized in that, The second excitation current detected by the current sampling circuit is an analog signal. The current sampling circuit is used to convert the analog signal into a digital signal and send it to the BMU in the at least one battery pack.

5. The energy storage system according to any one of claims 1 to 4, characterized in that, The current sampling circuit is also used to send a synchronization signal to the BMU in the at least one battery pack, the synchronization signal including a detection timestamp of the second excitation current; The BMU is used to synchronize the second excitation current and the voltage based on the detection timestamp of the second excitation current and the detection timestamp of the voltage, and to determine the EIS of each of the plurality of cells based on the synchronized second excitation current and the voltage.

6. The energy storage system according to any one of claims 1 to 5, characterized in that, The energy storage system also includes: a battery control unit (BCU); The BCU is used to send an EIS detection command to the power converter, the EIS detection command carrying the amplitude and frequency of the first excitation current.

7. The energy storage system according to any one of claims 1 to 6, characterized in that, The waveform of the first excitation current is a sine wave, a triangular wave, or a trapezoidal wave. The amplitude range of the first excitation current is 5 amperes A to 30 A, and the frequency range of the first excitation current is 0.01 Hz to 4 kHz.

8. The energy storage system according to any one of claims 1 to 7, characterized in that, The current sampling circuit is located in the cluster control box or in the battery management system (BMS).

9. The energy storage system according to any one of claims 1 to 8, characterized in that, The power converter is a DC / DC converter, or the power converter is a DC / AC converter.

10. The energy storage system according to any one of claims 1 to 9, characterized in that, The power converter is located in the energy storage converter; Alternatively, the power converter is a DC / DC converter and is located in the BMS.

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