Battery pack and energy storage system

Abstract

The present application relates to the technical field of energy storage, and provides a battery pack and an energy storage system. A DC / DC conversion circuit in the battery pack provided by the present application is used for providing a first excitation current for a plurality of battery cells. An impedance detection circuit is used for detecting a second excitation current flowing through the plurality of battery cells, detecting a voltage generated by the second excitation current at two ends of the battery pack, and determining the impedance of the battery pack on the basis of the second excitation current and the voltage. The DC / DC conversion circuit and the impedance detection circuit are both provided in the battery pack, and the process in which the DC / DC conversion circuit provides the first excitation current and the process in which the impedance detection circuit detects the second excitation current and the voltage and determines the impedance would not affect the normal operation (such as normal charging and discharging) of the battery pack. Therefore, on-line detection of the impedance of the battery pack is achieved during operation of the battery pack. In this way, on-line monitoring of the state of health of the battery pack can be achieved, thereby ensuring that potential safety risks of the battery pack can be detected in a timely manner.

Description

Battery pack and energy storage system

[0001] The present application claims priority to the Chinese patent application No. 202410874180.X, filed on July 01, 2024, and entitled "Battery pack and energy storage system", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of energy storage, and in particular, to a battery pack and an energy storage system. BACKGROUND

[0003] An energy storage system generally includes a plurality of battery packs, each of which can include a battery management system (BMS) and a plurality of battery cells (also referred to as battery monomers). In order to improve the reliability of the energy storage system, the impedance of the battery pack needs to be detected.

[0004] Generally, before the battery pack is shipped, a detection device can provide an excitation current to the battery pack and detect the voltage of the battery pack. Then, the detection device can analyze the impedance of the battery pack based on the excitation current and the detected voltage.

[0005] However, the above detection scheme can only detect the impedance of the battery pack before the battery pack is shipped, i.e., can only detect the impedance of the battery pack offline, and cannot detect the impedance of the battery pack online during the operation of the battery pack. SUMMARY

[0006] The present application provides a battery pack and an energy storage system, which can solve the technical problem that the impedance detection scheme cannot detect the impedance of the battery pack online during the operation of the battery pack.

[0007] In a first aspect, a battery pack is provided, which includes a plurality of battery cells, a direct current / direct current (DC / DC) conversion circuit, and an impedance detection circuit. The plurality of battery cells are connected in series between the positive electrode and the negative electrode of the battery pack; the first end of the DC / DC conversion circuit is connected with the positive electrode and the negative electrode of the battery pack, and is configured to provide a first excitation current to the plurality of battery cells. The impedance detection circuit is configured to detect a second excitation current flowing through the plurality of battery cells, detect a voltage generated across the battery pack by the second excitation current, and determine the impedance of the battery pack based on the second excitation current and the voltage. The second excitation current is the excitation current flowing through the plurality of battery cells when the DC / DC conversion circuit provides the first excitation current to the plurality of battery cells.

[0008] The battery pack provided by the application can realize online detection of the impedance of the battery pack during the operation of the battery pack, because the DC / DC conversion circuit and the impedance detection circuit are both arranged in the battery pack, and the process of providing the first excitation current by the DC / DC conversion circuit and the process of detecting the second excitation current, the voltage and determining the impedance by the impedance detection circuit do not affect the normal operation (such as normal charging and discharging) of the battery pack. Therefore, the health status of the battery pack can be monitored online to ensure that potential safety risks of the battery pack are detected in time. Moreover, the topology of the battery pack provided by the application is relatively simple, and the volume and cost of the battery pack can be avoided.

[0009] Optionally, the battery pack can further include a first capacitor. The second end of the DC / DC conversion circuit is connected in parallel with the first capacitor, and the DC / DC conversion circuit is configured to alternately charge and discharge the first capacitor to provide the first excitation current to the plurality of battery cells. In this case, when the DC / DC conversion circuit charges the first capacitor, the first excitation current flows from the negative electrode to the positive electrode of the battery pack; and when the DC / DC conversion circuit discharges the first capacitor, the first excitation current flows from the positive electrode to the negative electrode of the battery pack.

[0010] The battery pack provided by the application can alternately charge and discharge the first capacitor by the DC / DC conversion circuit to provide the first excitation current in the form of a sine wave. Since the first excitation current can be provided when the first capacitor is charged and discharged, the energy loss can be effectively reduced. Moreover, the DC / DC conversion circuit can be in the CLLC topology, LLC topology, LLLC topology, dual active bridge topology or bidirectional flyback topology. In this case, C represents capacitor, and L represents inductor. The DC / DC conversion circuit can adopt various types of topologies, and has high flexibility in application.

[0011] Optionally, the DC / DC conversion circuit can be further configured to output power to other battery packs and receive power input from other battery packs to provide the first excitation current to the plurality of battery cells. In this case, the other battery packs are other battery packs in the same energy storage system except the battery pack.

[0012] In this case, when the DC / DC conversion circuit outputs power, the first excitation current flows from the negative electrode to the positive electrode of the battery pack; and when the DC / DC conversion circuit receives power input from other battery packs, the first excitation current flows from the positive electrode to the negative electrode of the battery pack. In this way, on the one hand, the first excitation current provided by the DC / DC conversion circuit to the plurality of battery cells can be ensured to be large, and on the other hand, the energy loss of the energy storage system during the process of providing the first excitation current can be ensured to be small.

[0013] Optionally, the impedance detection circuit can comprise a current sampling circuit, a voltage sampling circuit and a control chip. The current sampling circuit is connected between the first end of the DC / DC conversion circuit and the positive or negative electrode of the battery pack, and is configured to detect the second excitation current flowing through the plurality of battery cells. The voltage sampling circuit is connected to the positive and negative electrodes of the battery pack, and is configured to detect the voltage generated across the battery pack by the second excitation current. The control chip is connected to the current sampling circuit and the voltage sampling circuit, and is configured to determine the impedance of the battery pack based on the second excitation current and the voltage.

[0014] It can be understood that the total current flowing through the plurality of battery cells includes not only the second excitation current, but also the charging current or discharging current of the battery pack itself. Since the current sampling circuit is connected between the first end of the DC / DC conversion circuit and the positive or negative electrode of the battery pack, the second excitation current flowing through the plurality of battery cells can be directly detected. Accordingly, the control chip can directly determine the impedance based on the second excitation current without the need to extract the second excitation current from the total current flowing through the plurality of battery cells. Thus, the processing logic of the control chip is effectively simplified, and the computational complexity of the control chip in determining the impedance is reduced.

[0015] It can be understood that the second excitation current detected by the current sampling circuit and the voltage detected by the voltage sampling circuit are both analog signals. The control chip can simultaneously perform analog-to-digital conversion on the second excitation current and the voltage based on the same clock signal, and then determine the impedance of the battery pack based on the digital signals of the second excitation current and the voltage. Since the control chip can process the second excitation current and the voltage of the battery pack based on the same clock signal, the phase offset of the voltage and the current caused by asynchronous signal processing can be avoided, thereby ensuring high accuracy of impedance detection.

[0016] Optionally, the current sampling circuit can comprise a current sensor and a first operational amplifier. The current sensor is connected between the first end of the DC / DC conversion circuit and the positive or negative electrode of the battery pack, and is configured to convert the second excitation current flowing through the current sensor into a voltage signal. The input end of the first operational amplifier is connected to the current sensor, and the output end of the first operational amplifier is connected to the control chip. The first operational amplifier is configured to amplify the voltage signal and transmit the amplified voltage signal to the control chip.

[0017] Since the first operational amplifier can amplify the voltage signal sampled by the current sensor and transmit the amplified voltage signal to the control chip, it can ensure that the voltage signal received by the control chip for representing the second excitation current has a large amplitude, thereby ensuring high detection accuracy when the impedance is detected based on the second excitation current.

[0018] Optionally, the impedance detection circuit can comprise a current sampling circuit, a voltage sampling circuit and a control chip. The current sampling circuit is connected in series with the plurality of battery cells, and is configured to detect a total current flowing through the plurality of battery cells. The voltage sampling circuit is connected with the positive electrode and the negative electrode of the battery pack, and is configured to detect a voltage generated across the battery pack by the second excitation current. The control chip is connected with the current sampling circuit and the voltage sampling circuit respectively, and is configured to determine the second excitation current based on the total current, and determine the impedance of the battery pack based on the second excitation current and the voltage.

[0019] Since the current sampling circuit is connected in series with the plurality of battery cells, the total current detected by the current sampling circuit includes not only the second excitation current, but also the charging current or discharging current of the battery pack itself. The control chip first determines the second excitation current from the total current, and then determines the impedance of the battery pack based on the second excitation current, which can ensure high accuracy of impedance detection.

[0020] Optionally, the current sampling circuit can comprise a current sensor and a first operational amplifier. The current sensor is connected in series with the plurality of battery cells, and is configured to convert the total current flowing through the current sensor into a voltage signal. The first operational amplifier is connected with the current sensor at the input end, and is connected with the control chip at the output end, and is configured to amplify the voltage signal and transmit the amplified voltage signal to the control chip.

[0021] Since the first operational amplifier can amplify the voltage signal sampled by the current sensor and transmit the amplified voltage signal to the control chip, the control chip can receive a voltage signal with a large amplitude representing the total current, thereby ensuring high detection accuracy when detecting the impedance based on the total current.

[0022] Optionally, the voltage sampling circuit can comprise a second capacitor and a second operational amplifier. The second capacitor is connected in series between the non-inverting input end of the second operational amplifier and the positive electrode of the battery pack, the inverting input end of the second operational amplifier is connected with the negative electrode of the battery pack, and the output end of the second operational amplifier is connected with the control chip.

[0023] The second capacitor has a direct current blocking and alternating current passing function, i.e. the second capacitor can isolate the direct current component in the voltage across the battery pack (i.e. the direct current voltage of the battery pack itself) and transmit the alternating current component (i.e. the ripple voltage generated by the second excitation current) to the second operational amplifier for amplification. In this way, accurate sampling of the ripple voltage generated by the second excitation current is achieved, thereby ensuring high detection accuracy when the control chip detects the impedance based on the amplified ripple voltage.

[0024] Optionally, the DC / DC conversion circuit and the impedance detection circuit can be arranged on the same circuit board. In this way, the integration of the battery pack can be effectively improved, and the volume of the battery pack can be avoided to be increased.

[0025] Optionally, the first excitation current can be positively related to the capacity of any of the plurality of battery cells and negatively related to the number of the plurality of battery cells. It can be understood that the capacity of the battery cell is negatively related to the internal resistance, i.e., the larger the capacity of the battery cell, the smaller the internal resistance. In the scheme provided in the present application, if the capacity of the battery cell is large (i.e., the internal resistance of the battery cell is small), and / or the number of the battery cells is small, the first excitation current can be large to ensure that the second excitation current and the voltage sampled by the impedance detection circuit are large, and thus the accuracy of the impedance detection is high.

[0026] Optionally, the first excitation current can be 2 amperes (A) to 30 A. The first excitation current in this range can ensure accurate detection of the impedance of the battery cell.

[0027] Optionally, the frequency range of the first excitation current can be 0.01 hertz (Hz) to 8 kilohertz (kHz) to realize impedance detection at different frequencies in the frequency range.

[0028] Optionally, the first excitation current can be composed of at least two sine signals of different frequencies. In this way, impedance detection at different frequencies can be realized based on one excitation current, and the efficiency of impedance detection can be improved.

[0029] Optionally, the impedance detection circuit can also be used to report the impedance of the battery pack to a cloud server, and the impedance is used by the cloud server to detect the health of the battery pack. That is, the cloud server can monitor the health of the battery pack in real time based on the impedance, and identify potential safety risks of the battery pack in time.

[0030] In a second aspect, a power storage system is provided, which includes a housing and a plurality of battery packs as provided in the first aspect. The plurality of battery packs can be arranged in the housing.

[0031] Optionally, the second ends of the DC / DC conversion circuits in the plurality of battery packs can be connected in parallel, and the DC / DC conversion circuit in the first battery pack of the plurality of battery packs can be configured to output power to the second battery pack and receive power input from the second battery pack to provide the first excitation current to the plurality of cells in the first battery pack. When the DC / DC conversion circuit in the first battery pack outputs power, the first excitation current flows from the negative electrode to the positive electrode of the first battery pack; when the DC / DC conversion circuit in the first battery pack receives power input from the second battery pack, the first excitation current flows from the positive electrode to the negative electrode of the first battery pack. In this way, on the one hand, the DC / DC conversion circuit can ensure that the first excitation current provided to the cells in the first battery pack is large, and on the other hand, the energy loss of the energy storage system during the process of providing the first excitation current can be small.

[0032] Optionally, the energy storage system can further include a cloud server. The cloud server can be configured to receive the impedance reported by the plurality of battery packs and detect the health degree of the plurality of battery packs based on the received impedance. In this way, the cloud server can realize online monitoring of the impedance of the plurality of battery packs to identify potential safety risks of the plurality of battery packs in time.

[0033] In summary, the present application provides a battery pack and an energy storage system. The battery pack includes a plurality of cells, a DC / DC conversion circuit, and an impedance detection circuit. The DC / DC conversion circuit is configured to provide a first excitation current to the plurality of cells. The impedance detection circuit is configured to detect a second excitation current flowing through the plurality of cells, detect a voltage of the battery pack, and determine an impedance of the battery pack based on the second excitation current and the voltage. Since the DC / DC conversion circuit and the impedance detection circuit are both arranged in the battery pack, and the process of providing the first excitation current by the DC / DC conversion circuit and the process of detecting the second excitation current, the voltage, and determining the impedance by the impedance detection circuit do not affect the normal operation (such as normal charging and discharging) of the battery pack, the online detection of the impedance of the battery pack can be realized during the operation of the battery pack. In this way, the online monitoring of the health state of the battery pack can be realized to ensure that potential safety risks of the battery pack are detected in time. Moreover, the topology of the battery pack provided by the present application is relatively simple, and the volume and cost of the battery pack can be avoided. BRIEF DESCRIPTION OF DRAWINGS

[0034] FIG. 1 is a structural schematic diagram of an application scenario of a battery pack according to an embodiment of the present application;

[0035] FIG. 2 is a structural schematic diagram of a battery pack according to an embodiment of the present application;

[0036] FIG. 3 is a structural schematic diagram of another battery pack according to an embodiment of the present application;

[0037] FIG. 4 is a structural schematic diagram of another battery pack according to an embodiment of the present application;

[0038] FIG. 5 is a structural schematic diagram of another battery pack according to an embodiment of the present application;

[0039] FIG. 6 is a structural schematic diagram of another battery pack according to an embodiment of the present application;

[0040] FIG. 7 is a structural schematic diagram of another battery pack according to an embodiment of the present application;

[0041] FIG. 8 is a structural schematic diagram of a DC / DC conversion circuit according to an embodiment of the present application;

[0042] FIG. 9 is a structural schematic diagram of a current sampling circuit according to an embodiment of the present application;

[0043] FIG. 10 is a structural schematic diagram of another battery pack according to an embodiment of the present application;

[0044] FIG. 11 is a structural schematic diagram of a voltage sampling circuit according to an embodiment of the present application;

[0045] FIG. 12 is a structural schematic diagram of an energy storage system according to an embodiment of the present application;

[0046] FIG. 13 is a structural schematic diagram of another energy storage system according to an embodiment of the present application;

[0047] FIG. 14 is a structural schematic diagram of another energy storage system according to an embodiment of the present application;

[0048] FIG. 15 is a structural schematic diagram of another energy storage system according to an embodiment of the present application;

[0049] FIG. 16 is a structural schematic diagram of another energy storage system according to an embodiment of the present application;

[0050] FIG. 17 is a structural schematic diagram of another energy storage system according to an embodiment of the present application;

[0051] FIG. 18 is a structural schematic diagram of another energy storage system according to an embodiment of the present application. DETAILED DESCRIPTION

[0052] The battery pack and energy storage system according to the embodiments of the present application will be described in detail below with reference to the accompanying drawings. First, the key terms involved in the embodiments of the present application will be introduced.

[0053] In order to maintain the stability of a new energy power generation system (for example, a photovoltaic power generation system), it is often necessary to configure a certain capacity of energy storage system for the new energy power generation system. Moreover, with the rapid development of new energy power generation technology, the capacity of the energy storage system to be configured also gradually becomes larger. Correspondingly, the application of large-capacity battery packs in the energy storage system is becoming more and more common, and the measurability of the state of the battery pack has become a key factor in improving the reliability of the energy storage system.

[0054] FIG. 1 is a schematic diagram of an application scenario of a battery pack according to an embodiment of the present application. As shown in FIG. 1, the application scenario can include a plurality of battery packs 10 and a power conversion system (PCS) 20. The plurality of battery packs 10 are connected in series and connected to the direct current end of the power conversion system 20, and the alternating current end of the power conversion system 20 can be connected to a power grid 30 and / or a load 40. The power conversion system 20 can convert the direct current provided by the plurality of battery packs 10 into alternating current and output to the power grid 30 and / or the load 40. Moreover, the power conversion system 20 can also convert the alternating current provided by the power grid 20 into direct current and output to the plurality of battery packs 10, thereby charging the plurality of battery packs 10.

[0055] Each battery pack 10 can include a plurality of series-connected battery cells 11, which can be lithium-ion battery cells, such as lithium iron phosphate battery cells or ternary lithium battery cells, etc.

[0056] In some embodiments, a detection device, such as an electrochemical impedance spectroscopy (EIS) detection device, can be used to detect the impedance of the battery pack before it is shipped. However, this scheme can only achieve offline detection of the impedance of the battery pack, and cannot achieve real-time detection of the health status of the battery pack during its life cycle, and cannot identify potential safety risks of the battery pack in a timely manner.

[0057] An embodiment of the present application provides a battery pack 10, which can be applied to an application scenario such as that shown in FIG. 1. As shown in FIG. 2, the battery pack 10 includes a plurality of battery cells 11, a DC / DC conversion circuit 12, and an impedance detection circuit 13.

[0058] The plurality of battery cells 11 are connected in series between the positive electrode BAT+ and the negative electrode BAT- of the battery pack 10. The first end of the DC / DC conversion circuit 12 is connected to the positive electrode BAT+ and the negative electrode BAT- of the battery pack 10, and the DC / DC conversion circuit 12 is configured to provide a first excitation current to the plurality of battery cells 11. The first excitation current is an alternating current.

[0059] The impedance detection circuit 13 is configured to detect a second excitation current flowing through the plurality of battery cells 11, the second excitation current being an excitation current flowing through the plurality of battery cells 11 when the DC / DC conversion circuit 12 provides the first excitation current to the plurality of battery cells 11. The impedance detection circuit 13 is also configured to detect a voltage generated across the battery pack 10 by the second excitation current. The impedance detection circuit 13 is further configured to determine the impedance of the battery pack 10 based on the detected second excitation current and voltage.

[0060] It can be understood that the impedance of the battery pack 10 can refer to the total impedance of the plurality of battery cells 11 connected in series in the battery pack 10, i.e., the sum of the internal resistances of the plurality of battery cells 11. It can also be understood that the phase of the second excitation current can be offset compared to the first excitation current, and the frequency of the second excitation current can be superimposed with the frequency of the interference signal.

[0061] In summary, the embodiments of the present application provide a battery pack, in which the DC / DC conversion circuit can provide a first excitation current to the plurality of battery cells, and the impedance detection circuit can detect a second excitation current flowing through the plurality of battery cells and a voltage of the battery pack, and determine the impedance of the battery pack. Since the DC / DC conversion circuit and the impedance detection circuit are both arranged in the battery pack, and the process of providing the first excitation current by the DC / DC conversion circuit and the process of detecting the second excitation current, the voltage, and determining the impedance by the impedance detection circuit do not affect the normal operation (such as normal charging and discharging) of the battery pack, so that the online detection of the impedance of the battery pack can be realized during the operation of the battery pack. Thus, the online monitoring of the health status of the battery pack can be realized to ensure that potential safety risks of the battery pack are detected in time. Moreover, the topology of the battery pack provided by the embodiments of the present application is relatively simple, and the volume and cost of the battery pack can be avoided.

[0062] It can be understood that the battery pack 10 can also include a BMS. In some embodiments, the BMS can provide an excitation current to the battery cells 11, but since the BMS is an integrated chip, to avoid excessive heat of the chip, the excitation current provided by the BMS is usually small. In the embodiments of the present application, since the DC / DC conversion circuit 12 is independent of the BMS, the provision of the first excitation current by the DC / DC conversion circuit 12 does not affect the heat dissipation performance of the BMS. Accordingly, the first excitation current provided by the DC / DC conversion circuit 12 can be large, and thus the amplitudes of the current and the voltage detected by the impedance detection circuit 13 can be large, to realize accurate detection of the impedance of the battery pack 10.

[0063] Optionally, the impedance detection circuit 13 can determine the EIS of the plurality of battery cells 11 in series based on the second excitation current and the voltage of the battery pack 10, i.e., the impedance detection circuit 13 can perform online EIS measurement on the plurality of battery cells 11. The measurement result of the EIS can include a real part and an imaginary part, wherein the real part is the total impedance of the plurality of battery cells 11. That is, the impedance detection circuit 13 can determine the real part in the measurement result of the EIS as the impedance of the battery pack 10.

[0064] As an optional implementation, as shown in FIG. 3, the battery pack 10 can further include a first capacitor C1. The second end of the DC / DC conversion circuit 12 is connected in parallel with the first capacitor C1, and the DC / DC conversion circuit 12 is configured to alternately charge and discharge the first capacitor C1 to provide the first excitation current to the plurality of battery cells 11 in the battery pack 10.

[0065] Wherein, when the DC / DC conversion circuit 12 charges the first capacitor C1, the first excitation current flows from the negative electrode BAT- to the positive electrode BAT+ of the battery pack 10. When the DC / DC conversion circuit 12 discharges the first capacitor C1, the first excitation current flows from the positive electrode BAT+ to the negative electrode BAT- of the battery pack 10. Since the DC / DC conversion circuit 12 can provide the first excitation current when charging and discharging the first capacitor C1, the energy loss during impedance detection can be effectively reduced.

[0066] As another optional implementation, as shown in FIG. 13, the DC / DC conversion circuit 12 can also be configured to output power to other battery packs and receive power input from other battery packs to provide the first excitation current to the plurality of battery cells 11. Wherein, the other battery packs are other battery packs in the same energy storage system except the battery pack.

[0067] Wherein, when the DC / DC conversion circuit 12 outputs power, the first excitation current flows from the negative electrode BAT- to the positive electrode BAT+ of the battery pack 10; when the DC / DC conversion circuit 12 receives power input from other battery packs, the first excitation current flows from the positive electrode BAT+ to the negative electrode BAT- of the battery pack 10. In this way, on the one hand, the DC / DC conversion circuit 12 can ensure that the first excitation current provided to the plurality of battery cells 11 is large, and on the other hand, the energy loss of the energy storage system during the process of providing the first excitation current can be small.

[0068] In the embodiments of the present application, the power conversion topology adopted by the DC / DC conversion circuit 12 can be CLLC topology, LLC topology, LLLC topology, dual active bridge topology or bidirectional flyback topology. C in the above topologies refers to a capacitor, and L refers to an inductor. Since the DC / DC conversion circuit 12 can adopt multiple different types of topologies, it has high application flexibility.

[0069] For example, the DC / DC conversion circuit 12 can be a CLLC topology as shown in FIG. 3, or can be a variant topology of the CLLC topology.

[0070] Alternatively, the DC / DC conversion circuit 12 can be an LLC topology as shown in FIG. 4, or can be a variant topology of the LLC topology.

[0071] Alternatively, the DC / DC conversion circuit 12 can be an LLLC topology as shown in FIG. 5, or can be a variant topology of the LLLC topology.

[0072] Alternatively, the DC / DC conversion circuit 12 can be a dual active bridge (DAB) topology as shown in FIG. 6, or can be a variant topology of the DAB topology.

[0073] Alternatively, the DC / DC conversion circuit 12 can be a bidirectional flyback topology as shown in FIG. 7, or can be a variant topology of the bidirectional flyback topology.

[0074] As shown in FIG. 8, and as can be seen with reference to FIGS. 3-6, the DC / DC conversion circuit 12 can include a first bridge circuit 121, a transformer T0, and a second bridge circuit 122. The primary side of the transformer T0 is connected to the first bridge circuit 121, and the secondary side of the transformer T0 is connected to the second bridge circuit 122.

[0075] The first bridge circuit 121 can be a full-bridge resonant circuit, which can include a first bridge leg 1a, a second bridge leg 1b, and a resonant device 1c. The first bridge leg 1a and the second bridge leg 1b are connected in parallel, and each of the first bridge leg 1a and the second bridge leg 1b includes two switching tubes connected in series. One end of the primary side of the transformer T0 is connected to the bridge leg midpoint of the first bridge leg 1a through the resonant device 1c, and the other end of the primary side of the transformer T0 is connected to the bridge leg midpoint of the second bridge leg 1b through the resonant device 1c. The bridge leg midpoint of a bridge leg can refer to the series node between the two switching tubes of the bridge leg. The resonant device 1c can include at least one inductor and at least one capacitor.

[0076] As one possible example, as shown in FIGS. 4-6 and 8, the second bridge circuit 122 can be a full-bridge circuit, which can include a third bridge leg 2a and a fourth bridge leg 2b connected in parallel. Each of the third bridge leg 2a and the fourth bridge leg 2b includes two switching tubes connected in series. One end of the secondary side of the transformer T0 is connected to the bridge leg midpoint of the third bridge leg 2a, and the other end of the secondary side of the transformer T0 is connected to the bridge leg midpoint of the fourth bridge leg 2b.

[0077] As another possible example, as shown in FIG. 3, the second bridge circuit 122 can be a full-bridge resonant circuit, that is, the second bridge circuit 122 can include a resonant device in addition to the third bridge arm 2a and the fourth bridge arm 2b connected in parallel. For example, the resonant device can include an inductor and a capacitor, one end of the secondary side of the transformer T0 is connected to the bridge arm midpoint of the third bridge arm 2a through the capacitor, and the other end of the secondary side of the transformer T0 is connected to the bridge arm midpoint of the fourth bridge arm 2b through the inductor.

[0078] Since at least one of the first bridge circuit 121 and the second bridge circuit 122 in the DC / DC conversion circuit 12 shown in FIGS. 3 to 6 is a resonant circuit, the DC / DC conversion circuit 12 can also be referred to as a resonant converter.

[0079] As shown in FIG. 7, for the scenario that the DC / DC conversion circuit 12 adopts a bidirectional flyback topology, the DC / DC conversion circuit 12 can include a transformer T0 and two switching tubes. The primary side and the secondary side of the transformer T0 are respectively connected to a switching tube. Optionally, the DC / DC conversion circuit 12 can also include two inductors, and the primary side and the secondary side of the transformer T0 are respectively connected to an inductor.

[0080] Optionally, as shown in FIGS. 2 to 7, the impedance detection circuit 13 can include a current sampling circuit 131, a voltage sampling circuit 132, and a control chip 133.

[0081] The current sampling circuit 131 is connected between the first end of the DC / DC conversion circuit 12 and the positive electrode BAT+ or the negative electrode BAT- of the battery pack 10. In the battery pack 10 shown in FIGS. 2 to 7, the current sampling circuit 131 is connected between the first end of the DC / DC conversion circuit 12 and the negative electrode BAT- of the battery pack 10. The current sampling circuit 131 is used to detect the second excitation current flowing through the plurality of battery cells 11.

[0082] The voltage sampling circuit 132 is connected to the positive electrode BAT+ and the negative electrode BAT- of the battery pack 10, and the voltage sampling circuit 132 is used to detect the voltage generated across the battery pack 10 by the second excitation current.

[0083] The control chip 133 is connected to the current sampling circuit 131 and the voltage sampling circuit 132, respectively, and the control chip 133 is used to determine the impedance of the battery pack 10 according to the second excitation current and the voltage.

[0084] It can be understood that the second excitation current detected by the current sampling circuit 131 and the voltage detected by the voltage sampling circuit 132 are both analog signals. The control chip 133 can first convert the second excitation current and the voltage into digital signals based on the same clock signal, and then determine the impedance of the battery pack 10 based on the second excitation current and the voltage in the form of digital signals.

[0085] In an example, the control chip 133 can include an analog-to-digital converter (ADC) and a processing circuit. The ADC can simultaneously perform analog-to-digital conversion on the second excitation current and the voltage based on the same clock signal, and the processing circuit can determine the impedance of the battery pack 10 based on the second excitation current and the voltage after analog-to-digital conversion.

[0086] In the embodiments of the present application, the control chip 133 (for example, the ADC) can simultaneously process the second excitation current and the voltage of the battery pack 10 based on the same clock signal to obtain the impedance of the battery pack 10. In this way, the phase offset of the voltage and the current caused by asynchronous signal processing can be avoided, and the accuracy of impedance detection can be ensured to be high.

[0087] It can also be understood that the total current flowing through the plurality of battery cells 11 includes not only the second excitation current but also the charging current or discharging current of the battery pack 10 itself. Since the current sampling circuit 131 is connected between the first end of the DC / DC conversion circuit 12 and the positive electrode BAT+ or the negative electrode BAT- of the battery pack 10, the second excitation current flowing through the plurality of battery cells 11 can be directly detected. Accordingly, the control chip 133 can directly determine the impedance of the battery pack 10 based on the second excitation current, without the need to extract the second excitation current from the total current flowing through the plurality of battery cells 11. In this way, the processing logic of the control chip 133 is effectively simplified, and the calculation complexity of the control chip 133 in determining the impedance is reduced.

[0088] Optionally, the control chip 133 can be a micro-controller unit (MCU). Moreover, the control chip 133 can be a control device of the DC / DC conversion circuit 12, that is, the control chip 133 can also control the working states of the switching tubes in the DC / DC conversion circuit 12 to enable the DC / DC conversion circuit 12 to output the first excitation current.

[0089] It can also be understood that the frequency of the first excitation current provided by the DC / DC conversion circuit 12 can be varied within a preset frequency range, and the impedance detection circuit 13 can detect the EIS of the battery pack 10 at different frequencies within the frequency range, and then determine the impedance of the battery pack 10 at different frequencies. Since the frequency of the second excitation current detected by the current sampling circuit 131 can superimpose the frequency of the interference signal, if the control chip 133 directly determines the impedance of the battery pack 10 at different frequencies based on the frequency of the second excitation current detected by the current sampling circuit 131, the accuracy of the detection result will be low. In the embodiment of the present application, since the control chip 133 can control the DC / DC conversion circuit 12 to output the first excitation current, the control chip 133 can directly determine the impedance of the battery pack 10 at different frequencies based on the frequency of the first excitation current, thereby ensuring that the accuracy of the detection result is high.

[0090] FIG. 9 is a structural schematic diagram of a current sampling circuit provided by an embodiment of the present application. As shown in FIG. 9, the current sampling circuit 131 can include a current sensor 1311 and a first operational amplifier 1312.

[0091] The current sensor 1311 is connected between the first end of the DC / DC conversion circuit 12 and the positive electrode BAT+ or the negative electrode BAT- of the battery pack 10, and is used to convert the second excitation current flowing through the current sensor 1311 into a voltage signal.

[0092] The input end of the first operational amplifier 1312 is connected with the current sensor 1311, the output end of the first operational amplifier 1312 is connected with the control chip 132, and the first operational amplifier 1312 is used to amplify the voltage signal and transmit the amplified voltage signal to the control chip 133.

[0093] Since the first operational amplifier 1312 can amplify the voltage signal sampled by the current sensor 1311 and transmit the amplified voltage signal to the control chip 133, it can ensure that the amplitude of the voltage signal received by the control chip 133 for characterizing the second excitation current is large, and thus the detection accuracy of the control chip 133 based on the second excitation current for impedance detection is high.

[0094] Optionally, the current sensor 1311 can be a shunt, or a Hall current sensor, etc., and the type of the current sensor 1311 is not limited in the embodiments of the present application. As shown in FIG. 9, the input end of the first operational amplifier 1312 includes a non-inverting input end (+) and an inverting input end (-). The non-inverting input end (+) is connected with the current sensor 1311 through a resistor R1, and the inverting input end (-) is connected with the current sensor 1311 through a resistor R2. In addition, the non-inverting input end (+) is also connected with the ground GND through a resistor R3, and the inverting input end (-) is also connected with the output end of the first operational amplifier 1312 through a resistor R4. With reference to FIG. 9 continuously, the first operational amplifier 1312 also has a power supply positive pole V+ and a power supply negative pole V-, the power supply negative pole V- is connected with the ground GND, and the power supply positive pole V+ can be connected with a power supply end of 3.3V.

[0095] FIG. 10 is a schematic diagram of a connection mode of another current sampling circuit provided by the embodiments of the present application. As shown in FIG. 10, the current sampling circuit 131 can be connected in series with the plurality of battery cells 11, and the current sampling circuit 131 is used to detect the total current flowing through the plurality of battery cells 11. It can be understood that the total current detected by the current sampling circuit 131 is the current obtained by superimposing the second excitation current and the charging current or discharging current of the battery pack 10 itself.

[0096] The voltage sampling circuit 132 is connected with the positive pole BAT+ and the negative pole BAT- of the battery pack 10, and the voltage sampling circuit 132 is used to detect the voltage generated by the second excitation current across the battery pack 10. The control chip 133 is connected with the current sampling circuit 131 and the voltage sampling circuit 132 respectively, and the control chip 133 is used to determine the second excitation current from the total current detected by the current sampling circuit 131, and is used to determine the impedance of the battery pack 10 according to the second excitation current and the voltage. For example, the control chip 133 can calculate the average value of the total current detected by the current sampling circuit 131 in a period of time, and determine the difference between the total current detected by the current sampling circuit 131 in the period of time and the average value as the second excitation current in the period of time.

[0097] It can be understood that the amplitude of the second excitation current is usually much smaller than the amplitude of the charging current or discharging current of the battery pack 10 itself, and therefore, if the impedance of the battery pack 10 is directly calculated based on the total current detected by the current sampling circuit 131, the second excitation current will be overwhelmed by the charging current or discharging current of the battery pack 10 itself. In the embodiments of the present application, since the control chip 133 can first extract the second excitation current from the total current detected by the current sampling circuit 131, and then calculate the impedance of the battery pack 10 based on the second excitation current, the accuracy of the impedance detection can be effectively ensured.

[0098] The current sampling circuit 131 shown in FIG. 10 can also adopt the structure shown in FIG. 9, that is, the current sampling circuit 131 can also include a current sensor 1311 and a first operational amplifier 1312. The current sensor 1311 is connected in series with the plurality of battery cells 11, and the current sensor 1311 is configured to convert the total current flowing through the current sensor 1311 into a voltage signal. The input end of the first operational amplifier 1312 is connected with the current sensor 1311, and the output end of the first operational amplifier 1312 is connected with the control chip 133. The first operational amplifier 1312 is configured to amplify the voltage signal and transmit the amplified voltage signal to the control chip 133. The structure and working principle of the current sensor 1311 and the first operational amplifier 1312 described above can refer to the description of the current sampling circuit 131 shown in FIG. 9, which will not be repeated here.

[0099] Optionally, as shown in FIG. 11, the voltage sampling circuit 132 can include a second capacitor C2 and a second operational amplifier 1321.

[0100] The second capacitor C2 is connected in series between the non-inverting input end (+) of the second operational amplifier 1321 and the positive electrode BAT+ of the battery pack 10, the inverting input end (-) of the second operational amplifier 1321 is connected with the negative electrode BAT- of the battery pack 10, and the output end of the second operational amplifier 1321 can be connected with the control chip 133.

[0101] Since the second excitation current is a sinusoidal signal, the voltage change of the battery pack 10 caused by the second excitation current is also a sinusoidal signal, that is, the voltage generated by the second excitation current is a sinusoidal voltage, also known as ripple voltage. Since the amplitude of the ripple voltage is much smaller than the amplitude of the direct current voltage of the battery pack 10 itself, if the voltage of the battery pack 10 is directly sampled, the ripple voltage will be overwhelmed by the direct current voltage of the battery pack 10 itself. In order to accurately sample the ripple voltage, as shown in FIG. 11, the second capacitor C2 (also known as a DC blocking capacitor) can be connected in series between the non-inverting input end (+) of the second operational amplifier 1321 and the positive electrode BAT+ of the battery pack 10. The second capacitor C2 has the function of blocking direct current and passing alternating current, that is, the second capacitor C2 can shield the direct current component (i.e., the direct current voltage of the battery pack 10 itself) in the voltage across the battery pack 10 and transmit the alternating current component (i.e., the ripple voltage) to the second operational amplifier 1321 for amplification. In this way, accurate sampling of the ripple voltage is achieved, which in turn ensures accurate detection of the impedance of the battery pack 10.

[0102] Continuing to refer to FIG. 11, the non-inverting input terminal (+) of the second operational amplifier 1321 can be connected with the second capacitor C2 through the resistor R5, the inverting input terminal (-) can be connected with the negative electrode BAT- of the battery pack 10 through the resistor R6, and the inverting input terminal (-) can also be connected with the output terminal of the second operational amplifier 1321 through the resistor R7. In addition, the second operational amplifier 1321 also has a power supply positive electrode V+ and a power supply negative electrode V-, the power supply negative electrode V- is grounded GND, and the power supply positive electrode V+ can be connected with a 3.3V power supply terminal.

[0103] As shown in FIG. 11, the non-inverting input terminal (+) of the second operational amplifier 1321 can also be connected with a bias power supply terminal V0 through the resistor R8, and the bias power supply terminal V0 is used to provide a bias voltage. For example, the bias voltage can be 1.65V. It can be understood that the ripple voltage transmitted to the second operational amplifier 1321 by the second capacitor C2 is constantly changing between a positive voltage and a negative voltage. However, the ADC in the control chip 133 can usually only receive a positive voltage, so it is necessary to provide a bias voltage through the bias power supply terminal V0, so that the ripple voltage received by the second operational amplifier 1321 is a positive voltage, and then the amplified ripple voltage received by the ADC in the control chip 133 is a positive voltage.

[0104] Alternatively, the voltage sampling circuit 132 provided by the embodiment of the present application can also not include the second capacitor C2, that is, the voltage sampling circuit 132 can directly detect the voltage across the battery pack 10. In addition, after the control chip 133 receives the voltage detected by the voltage sampling circuit 132, the control chip 133 can calculate the ripple voltage generated by the second excitation current through a software algorithm. For example, the control chip 133 can calculate the average value of the voltage detected by the voltage sampling circuit 132 within a period of time, and determine the difference between the voltage detected by the voltage sampling circuit 132 within the period of time and the average value as the ripple voltage generated by the second excitation current within the period of time.

[0105] Alternatively, the DC / DC conversion circuit 12 and the impedance detection circuit 13 can be arranged on the same circuit board, that is, the DC / DC conversion circuit 12 and the impedance detection circuit 13 can be integrated. For example, as shown in FIG. 2, the DC / DC conversion circuit 12 and the impedance detection circuit 13 can be integrated in a DC / DC converter (also referred to as a DC / DC module). In this way, the integration of the battery pack 10 can be effectively improved, and the volume and structural complexity of the battery pack 10 can be avoided.

[0106] In the embodiments of the present application, the capacities of the plurality of battery cells 11 in the battery pack 10 can be the same, which can refer to the theoretical capacity, i.e., the nominal capacity, of the battery cells 11. It can be understood that, during the operation of the battery pack 10, if an abnormality occurs in a certain battery cell 11, the actual capacity of the battery cell 11 will be less than the theoretical capacity, i.e., the actual internal resistance of the battery cell 11 will be greater than the theoretical internal resistance. Correspondingly, the impedance of the battery pack 10 detected by the impedance detection circuit 13 (i.e., the actual impedance) will be greater than the theoretical impedance of the battery pack 10, thereby identifying that the battery pack 10 has an abnormality.

[0107] Alternatively, the size of the first excitation current provided by the DC / DC conversion circuit 12 can be positively correlated with the capacity (i.e., the theoretical capacity, and the capacity hereinafter refers to the theoretical capacity of the battery cell 11 unless otherwise specified) of any battery cell 11 in the battery pack 10 and negatively correlated with the number of the plurality of battery cells 11. That is, the greater the capacity of the battery cell 11, the greater the first excitation current can be; the fewer the number of the battery cells 11 included in the battery pack 10, the greater the first excitation current can be.

[0108] It can be understood that, in the case of a certain impedance of the battery pack 10, the greater the first excitation current, the greater the amplitude of the second excitation current detected by the impedance detection circuit 13 and the amplitude of the voltage of the battery pack 10. In the case of a certain detection resolution (also referred to as sampling resolution) of the impedance detection circuit 13, the greater the amplitudes of the current and voltage detected by the impedance detection circuit 13, the higher the detection accuracy. It can also be understood that the capacity of the battery cell 11 is negatively correlated with the internal resistance, i.e., the greater the capacity of the battery cell 11, the smaller the internal resistance. Therefore, if the number of the battery cells 11 included in the battery pack 10 is small and / or the capacity of each battery cell 11 is large, the impedance of the battery pack 10 is small. At this time, the first excitation current provided by the DC / DC conversion circuit 12 can be large to ensure that the amplitudes of the current and voltage detected by the impedance detection circuit 13 are large, thereby ensuring that the detection accuracy of the impedance detection circuit 13 is high.

[0109] For example, assuming that the detection resolution of the impedance detection circuit 13 is 50 millivolts (mV), in order to ensure the voltage detection accuracy, the ripple voltage generated by the second excitation current should be greater than 50 mV. If the battery pack 10 includes n battery cells 11 connected in series, each battery cell 11 is a lithium iron phosphate battery cell with a capacity of 280 ampere-hours (AH) and an internal resistance of 0.25 milliohms (mohm), the effective value I of the first excitation current provided by the DC / DC conversion circuit 12 can satisfy: I > (50 / 0.25) / n = 200 / n A.

[0110] It can also be understood that the detection resolution of the impedance detection circuit 13 can refer to the resolution of the ADC in the control chip 133. Generally, the higher the resolution of the ADC in the control chip 133, the higher the hardware cost of the control chip 133. In the embodiment of the present application, since the DC / DC conversion circuit 12 can provide a first excitation current of a suitable size based on the capacity and number of the battery cell 11, the accuracy of impedance detection can be effectively improved without increasing the resolution of the ADC in the control chip 133, that is, without increasing the hardware cost of the control chip 133.

[0111] Optionally, in the embodiment of the present application, the size of the first excitation current can be 2A to 30A. The first excitation current in this range can ensure accurate detection of the impedance of the battery cell.

[0112] Optionally, the first excitation current provided by the DC / DC conversion circuit 12 can be a sinusoidal signal, that is, the first excitation current is a sinusoidal current, and the frequency range can be 0.01Hz to 8kHz, for example, the frequency range can be 0.1Hz to 2kHz. It can be understood that the frequency of the first excitation current provided by the DC / DC conversion circuit 12 can vary within the frequency range, and the impedance detection circuit 13 can detect the impedance of the battery pack 10 at different frequencies within the frequency range, that is, detect the change of the impedance of the battery pack 10 with the frequency of the first excitation current.

[0113] As a possible example, the first excitation current can be a sinusoidal signal of a single frequency. And the DC / DC conversion circuit 12 can adjust the frequency of the sinusoidal signal within the above frequency range.

[0114] As another possible example, the first excitation current can also be composed of at least two sinusoidal signals of different frequencies, that is, the first excitation current can contain at least two frequencies. The at least two frequencies all belong to the above frequency range, and the DC / DC conversion circuit 12 can adjust the at least two frequencies within the above frequency range.

[0115] As an example, the first excitation current can be a composite signal composed of a basic sinusoidal signal. Wherein, the frequency of the basic sinusoidal signal is a first frequency, and the amplitude is a first amplitude; the composite signal can be a sinusoidal signal or a square wave signal, and the frequency is a second frequency, and the amplitude is a second amplitude. The first frequency is higher than the second frequency, and the first amplitude is smaller than the second amplitude. Or it can be understood that: the basic sinusoidal signal fluctuates within the second amplitude range according to the second frequency, thereby forming a composite signal.

[0116] For the scenario that the first excitation current is composed of sinusoidal signals of at least two different frequencies, after the DC / DC conversion circuit 12 provides a first excitation current, the impedance detection circuit 13 can simultaneously detect the impedance of the battery pack 10 at the at least two different frequencies, thereby effectively improving the efficiency of impedance detection.

[0117] Optionally, the impedance detection circuit 13 can also be used to report the impedance of the battery pack 10 to the cloud server, so that the cloud server can analyze the health of the battery pack 10 based on the impedance. In this way, the cloud server can realize online monitoring of the health of the battery pack 10, so as to identify potential safety risks of the battery pack 10 in time.

[0118] In summary, the embodiments of the present application provide a battery pack, the DC / DC conversion circuit in the battery pack can provide a first excitation current for a plurality of battery cells, and the impedance detection circuit can detect a second excitation current flowing through the plurality of battery cells and a voltage of the battery pack, and determine the impedance of the battery pack. Since the above-mentioned DC / DC conversion circuit and impedance detection circuit are both arranged in the battery pack, and the process of providing the first excitation current by the DC / DC conversion circuit and the process of detecting the second excitation current, voltage and determining the impedance by the impedance detection circuit will not affect the normal operation (such as normal charging and discharging) of the battery pack, so that online detection of the impedance of the battery pack can be realized during the operation of the battery pack. In this way, online monitoring of the health state of the battery pack can be realized to ensure that potential safety risks of the battery pack can be detected in time. Moreover, the topology of the battery pack provided by the embodiments of the present application is relatively simple, and the volume and cost of the battery pack can be avoided.

[0119] The embodiments of the present application also provide a storage energy system, as shown in FIG. 12, which can include a housing 00 and a plurality of battery packs 10 provided by the above-mentioned embodiments. The plurality of battery packs 10 can be arranged in the housing 00.

[0120] Optionally, the plurality of battery packs 10 can be connected in series. Moreover, as shown in FIG. 13, the second ends of the DC / DC conversion circuits 12 in the plurality of battery packs 10 can be connected in parallel. The plurality of battery packs 10 include a first battery pack and a second battery pack, the DC / DC conversion circuit 12 in the first battery pack is used to output power to the second battery pack and receive power input by the second battery pack to provide a first excitation current for the plurality of battery cells 11 in the first battery pack.

[0121] When the DC / DC conversion circuit 12 in the first battery pack outputs power to the second battery pack, the first excitation current provided by the DC / DC conversion circuit 12 in the first battery pack to the plurality of battery cells 11 in the first battery pack can flow from the negative electrode BAT- to the positive electrode BAT+ of the first battery pack 10. When the DC / DC conversion circuit 12 in the first battery pack receives power input from the second battery pack, the first excitation current provided by the DC / DC conversion circuit 12 in the first battery pack to the plurality of battery cells 11 in the first battery pack can flow from the positive electrode BAT+ to the negative electrode BAT- of the first battery pack 10.

[0122] Based on the above manner, on the one hand, the DC / DC conversion circuit 12 can ensure that the first excitation current provided to the plurality of battery cells 11 in the battery pack 10 is large, and on the other hand, the energy loss of the energy storage system during the process of providing the first excitation current can be small.

[0123] It can be understood that the above-mentioned first battery pack and the second battery pack can be any two battery packs 10 included in the energy storage system, that is, the DC / DC conversion circuit 12 in any two battery packs 10 can interact power to provide the first excitation current to the plurality of battery cells 11 in the respective battery pack 10.

[0124] As shown in FIG. 13, the power conversion topology adopted by the DC / DC conversion circuit 12 of each battery pack 10 in the energy storage system can be a CLLC topology and its variant topology. Alternatively, as shown in FIG. 14, the power conversion topology adopted by the DC / DC conversion circuit 12 of each battery pack 10 in the energy storage system can be an LLC topology and its variant topology. Alternatively, as shown in FIG. 15, the power conversion topology adopted by the DC / DC conversion circuit 12 of each battery pack 10 in the energy storage system can be an LLLC topology and its variant topology. Alternatively, as shown in FIG. 16, the power conversion topology adopted by the DC / DC conversion circuit 12 of each battery pack 10 in the energy storage system can be a DAB topology and its variant topology. Alternatively, as shown in FIG. 17, the power conversion topology adopted by the DC / DC conversion circuit 12 of each battery pack 10 in the energy storage system can be a bidirectional flyback topology and its variant topology.

[0125] It can also be understood that for the scenario in which the DC / DC conversion circuits 12 in the two battery packs 10 interact power to provide the first excitation current, the capacitance value of the first capacitor C1 in the two battery packs 10 can be small, or as shown in FIGS. 13-17, the first capacitor C1 can not be required to be provided in the two battery packs 10.

[0126] Since the plurality of battery packs 10 are connected in series in the energy storage system, the plurality of battery packs 10 are simultaneously charged and simultaneously discharged. Ideally, the plurality of battery packs 10 can be simultaneously fully charged and can be simultaneously fully discharged. However, due to the influence of many factors such as preparation process, use environment and use time, the state of charge (SOC) of different battery packs 10 will be different. Therefore, when the plurality of battery packs 10 are simultaneously charged, some battery packs 10 will be fully charged while other battery packs 10 are not fully charged. At this time, in order to avoid the danger of continuing to charge the battery pack 10 that has been fully charged, the energy storage system will stop charging the plurality of battery packs 10. Similarly, when some battery packs 10 are fully discharged while other battery packs 10 still have residual power, in order to avoid damage caused by continuing to discharge the battery pack 10 that has been fully discharged, the energy storage system will stop discharging the plurality of battery packs 10.

[0127] Based on the above analysis, in the scenario where the plurality of battery packs 10 are connected in series, if the SOC of different battery packs 10 is different, some battery packs 10 will not be fully charged or will not be fully discharged, which will seriously affect the operation efficiency of the energy storage system. In the embodiments of the present application, the DC / DC conversion circuit 12 in each battery pack 10 can also have the function of active balancing, that is, the DC / DC conversion circuit 12 can also balance the SOC difference between different battery packs 10.

[0128] For example, if the SOC of the first battery pack 10 is lower than the SOC of the second battery pack 10, the DC / DC conversion circuit 12 in the first battery pack 10 can receive the discharge power output by the second battery pack 10 and input the charging power to the plurality of battery cells 11 in the first battery pack 10. If the SOC of the first battery pack 10 is higher than the SOC of the second battery pack 10, the DC / DC conversion circuit 12 in the first battery pack 10 can receive the discharge power output by the plurality of battery cells 11 in the first battery pack 10 and output the charging power to the second battery pack 10.

[0129] Since the DC / DC conversion circuit 12 in the battery pack 10 provided by the embodiments of the present application not only can provide the first excitation current required for impedance detection, but also can have the function of active balancing, the active balancing circuit does not need to be additionally configured in the battery pack 10, thereby effectively reducing the cost and structural complexity of the battery pack 10.

[0130] Optionally, with reference to FIG. 1, the energy storage system can also include an energy storage converter 20, and the plurality of battery packs 10 connected in series can be connected to the direct current end of the energy storage converter 20, and the alternating current end of the energy storage converter 20 can be connected to the power grid 30 and / or the load 40.

[0131] Optionally, as shown in FIG. 18, the energy storage system can further include a cloud server 50, which can receive the impedance of the battery pack 10 uploaded by the DC / DC conversion circuit 12 in each battery pack 10, and detect the health degree of the battery pack 10 based on the received impedance. For example, the cloud server 50 can compare the impedance of each battery pack 10 with a preset impedance threshold, and determine the health degree of the battery pack 10 based on the difference between the impedance of the battery pack 10 and the impedance threshold. Alternatively, the cloud server 50 can analyze the change of the impedance of each battery pack 10 within a preset period (e.g., one month or one year), and determine the health degree of the battery pack 10 based on the change. The cloud server 50 can identify the potential safety risk of the battery pack 10 in time based on the health degree of the battery pack 10.

[0132] Optionally, the cloud server 50 can further establish a communication connection with a user terminal, and be capable of sending the impedance (or impedance curve) of the battery pack 10 to the user terminal for display in the user interface of the user terminal. Thus, the user can monitor the health status of the battery pack 10 in real time, and identify the potential safety risk of the battery pack 10 in time. The impedance curve can be drawn by the cloud server 50 according to the impedance of the battery pack 10 at different times.

[0133] In the embodiments of the present application, the terms "first", "second" and "third" are only used for descriptive purposes, and cannot be understood or implied as indicating or suggesting relative importance. The term "at least one" refers to one or more, and "multiple" refers to two or more.

[0134] In the embodiments of the present application, the term "and / or" is only used to describe the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can represent the following three cases: A exists alone, A and B exist together, and B exists alone. In addition, the character " / " in this paper generally represents an "or" relationship between the associated objects before and after it.

[0135] The above is only an optional embodiment of the present application, but the protection scope of the present application is not limited thereto, and any skilled person in the art can easily think of various equivalent modifications or replacements within the technical range disclosed in the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A battery pack, characterized by, The battery pack comprises a plurality of battery cells, a DC / DC conversion circuit and an impedance detection circuit; The plurality of battery cells are connected in series between the positive electrode and the negative electrode of the battery pack; The first end of the DC / DC conversion circuit is connected with the positive electrode and the negative electrode of the battery pack, and the DC / DC conversion circuit is configured to provide a first excitation current to the plurality of battery cells; The impedance detection circuit is configured to detect a second excitation current flowing through the plurality of battery cells, the second excitation current being the excitation current flowing through the plurality of battery cells when the DC / DC conversion circuit provides the first excitation current to the plurality of battery cells; The impedance detection circuit is further configured to detect a voltage generated by the second excitation current across the battery pack; The impedance detection circuit is further configured to determine the impedance of the battery pack based on the second excitation current and the voltage.

2. The battery pack of claim 1, wherein, The battery pack further comprises a first capacitor; The second end of the DC / DC conversion circuit is connected in parallel with the first capacitor, and the DC / DC conversion circuit is configured to alternately charge and discharge the first capacitor to provide the first excitation current to the plurality of battery cells; Wherein, when the DC / DC conversion circuit charges the first capacitor, the first excitation current flows from the negative electrode to the positive electrode of the battery pack; and when the DC / DC conversion circuit discharges the first capacitor, the first excitation current flows from the positive electrode to the negative electrode of the battery pack.

3. The battery pack of claim 1, wherein The DC / DC conversion circuit is configured to output power to other battery packs and receive power input from the other battery packs to provide the first excitation current to the plurality of battery cells, the other battery packs being other battery packs in the same energy storage system except the battery pack.

4. The battery pack of any one of claims 1 to 3, wherein, The impedance detection circuit comprises a current sampling circuit, a voltage sampling circuit and a control chip; The current sampling circuit is connected between the first end of the DC / DC conversion circuit and the positive electrode or the negative electrode of the battery pack, and the current sampling circuit is configured to detect the second excitation current flowing through the plurality of battery cells; The voltage sampling circuit is connected with the positive electrode and the negative electrode of the battery pack, and the voltage sampling circuit is configured to detect the voltage; The control chip is connected with the current sampling circuit and the voltage sampling circuit respectively, and the control chip is configured to determine the impedance of the battery pack based on the second excitation current and the voltage.

5. The battery pack of claim 4, wherein, The current sampling circuit comprises a current sensor and a first operational amplifier; The current sensor is connected between the first end of the DC / DC conversion circuit and the positive electrode or the negative electrode of the battery pack, and the current sensor is configured to convert the second excitation current flowing through the current sensor into a voltage signal; The input end of the first operational amplifier is connected with the current sensor, and the output end of the first operational amplifier is connected with the control chip, and the first operational amplifier is configured to amplify the voltage signal and transmit the amplified voltage signal to the control chip.

6. The battery pack of any one of claims 1 to 3, wherein, The impedance detection circuit comprises a current sampling circuit, a voltage sampling circuit and a control chip; The current sampling circuit is connected in series with the plurality of battery cells, and is configured to detect a total current flowing through the plurality of battery cells; The voltage sampling circuit is connected with the positive electrode and the negative electrode of the battery pack, and is configured to detect the voltage; The control chip is connected with the current sampling circuit and the voltage sampling circuit respectively, and is configured to determine the second excitation current according to the total current, and determine the impedance of the battery pack based on the second excitation current and the voltage.

7. The battery pack of claim 6, wherein, The current sampling circuit comprises a current sensor and a first operational amplifier; The current sensor is connected in series with the plurality of battery cells, and is configured to convert the total current flowing through the current sensor into a voltage signal; The input end of the first operational amplifier is connected with the current sensor, and the output end of the first operational amplifier is connected with the control chip, and the first operational amplifier is configured to amplify the voltage signal and transmit the amplified voltage signal to the control chip.

8. The battery pack of any one of claims 4 to 7, wherein, The voltage sampling circuit comprises a second capacitor and a second operational amplifier; The second capacitor is connected in series between the non-inverting input end of the second operational amplifier and the positive electrode of the battery pack, the inverting input end of the second operational amplifier is connected with the negative electrode of the battery pack, and the output end of the second operational amplifier is connected with the control chip.

9. The battery pack of any one of claims 1-8, wherein, The DC / DC conversion circuit and the impedance detection circuit are arranged on the same circuit board.

10. The battery pack of any one of claims 1 to 9, wherein, The size of the first excitation current is positively correlated with the capacity of any battery cell in the plurality of battery cells, and is negatively correlated with the number of the plurality of battery cells.

11. The battery pack of claim 10, wherein, The size of the first excitation current is 2A to 30A.

12. The battery pack of any one of claims 1-11, wherein, The frequency range of the first excitation current is 0.01 Hz to 8 kHz.

13. The battery pack of any one of claims 1-12, wherein, The first excitation current is composed of at least two sine signals with different frequencies.

14. The battery pack of any one of claims 1-13, wherein, The impedance detection circuit is further configured to report the impedance of the battery pack to a cloud server, and the impedance is used by the cloud server to detect the health degree of the battery pack.

15. An energy storage system characterized by, The energy storage system comprises a housing and a plurality of battery packs as claimed in claim 1, and the plurality of battery packs are arranged in the housing.

16. The energy storage system of claim 15, wherein, The battery pack further comprises a first capacitor; The second end of the DC / DC conversion circuit is connected in parallel with the first capacitor, and the DC / DC conversion circuit is configured to alternately charge and discharge the first capacitor to provide the first excitation current to the plurality of battery cells; When the DC / DC conversion circuit charges the first capacitor, the first excitation current flows from the negative electrode to the positive electrode of the battery pack; and when the DC / DC conversion circuit discharges the first capacitor, the first excitation current flows from the positive electrode to the negative electrode of the battery pack.

17. The energy storage system of claim 15, wherein, The second ends of the DC / DC conversion circuits of the plurality of battery packs are connected in parallel, and the DC / DC conversion circuit in the first battery pack of the plurality of battery packs is configured to output power to the second battery pack and receive power input by the second battery pack to provide the first excitation current to the plurality of battery cells in the first battery pack.

18. An energy storage system according to any one of claims 15 to 17, wherein, The impedance detection circuit comprises a current sampling circuit, a voltage sampling circuit and a control chip; The current sampling circuit is connected between the first end of the DC / DC conversion circuit and the positive electrode or the negative electrode of the battery pack, and is used for detecting the second excitation current flowing through the plurality of battery cells; The voltage sampling circuit is connected with the positive electrode and the negative electrode of the battery pack, and is used for detecting the voltage; The control chip is connected with the current sampling circuit and the voltage sampling circuit respectively, and is used for determining the impedance of the battery pack according to the second excitation current and the voltage.

19. The energy storage system of claim 18, wherein, The voltage sampling circuit comprises a second capacitor and a second operational amplifier; The second capacitor is connected in series between the non-inverting input end of the second operational amplifier and the positive electrode of the battery pack, the inverting input end of the second operational amplifier is connected with the negative electrode of the battery pack, and the output end of the second operational amplifier is connected with the control chip.

20. The energy storage system of any one of claims 15 to 19, wherein, The energy storage system further comprises a cloud server; The cloud server is used for receiving the impedance reported by a plurality of battery packs, and detecting the health degree of a plurality of battery packs based on the impedance.

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