SOC determination method and device, equipment, storage medium and energy storage system

Abstract

The invention provides an SOC determination method, device and equipment, a computer readable storage medium, a program product and an energy storage system (10). The SOC determination method is applied to a cascaded energy storage system (10), each branch of the cascaded energy storage system (10) comprises a plurality of energy storage sub-modules (13) connected in series, and the method comprises: acquiring a first current value of the branch where the energy storage sub-modules (13) are located; determining a target current value of each energy storage sub-module (13) in the branch according to the first current value; and determining the SOC of the corresponding energy storage sub-module (13) according to the target current value.

Description

SOC determination method, device, equipment, storage medium and energy storage system

[0001] The present application relates to the field of battery energy storage, and specifically to a SOC determination method, device, equipment, storage medium and energy storage system.

[0002] As human demand for energy continues to increase, high-voltage direct-mounted energy storage systems, medium-voltage direct-mounted energy storage systems, and modular multilevel converter (MMC) energy storage systems have attracted widespread attention due to their advantages of large single-machine capacity and high efficiency.

[0003] In the related art, the state of charge (SOC) of each energy storage submodule of the cascaded energy storage system is calculated by the battery management unit of the corresponding energy storage submodule. For example, the battery management unit can estimate the SOC based on the collected parameters such as the branch current of a single electrical cabinet, the battery voltage and the battery temperature.

[0004] However, the accuracy of the SOC estimated in the related art is low.

[0005] Summary of the invention

[0006] In view of the above problems, the present application provides an SOC determination method, apparatus, device, storage medium, program product and energy storage system, which can improve the SOC accuracy of energy storage submodules in a cascade energy storage system.

[0007] In a first aspect, the present application provides an SOC determination method, which is applied to a cascade energy storage system, each branch of the cascade energy storage system includes a plurality of energy storage sub-modules connected in series, and the method includes: obtaining a first current value of the branch where the energy storage sub-module is located; determining a target current value of each of the energy storage sub-modules in the branch according to the first current value; and determining the SOC of the corresponding energy storage sub-module according to the target current value.

[0008] In the technical solution of the embodiment of the present application, the SOC determination method obtains a high-precision first current value of each branch through a current measurement unit, and determines the target current value of each energy storage sub-module based on the first current value. Since the current of each energy storage branch collected by the current measurement unit has the characteristics of high sampling frequency and high precision, and the branch current value is not limited by the energy storage sub-module itself, the SOC is calculated based on the high-precision current value, so the accuracy of the SOC can be improved.

[0009] In some embodiments, determining the SOC of the corresponding energy storage submodule according to the target current value includes: determining the SOC of the corresponding energy storage submodule according to the target current value by using an ampere-hour integration method.

[0010] The target current value in this embodiment is determined based on the current of each energy storage branch. Since the current of each energy storage branch is relatively less restricted by the state of the battery itself and is therefore more accurate, the determined target current value is also more accurate. Therefore, when the target current value has a high accuracy, the SOC determined using the ampere-hour integration method is more reliable.

[0011] In some embodiments, the method of determining the SOC of the corresponding energy storage submodule according to the target current value by using the ampere-hour integration method includes:

[0012] Obtaining the SOC of the energy storage submodule at the last moment, the rated capacity of the battery pack of the energy storage submodule, and the time difference, wherein the time difference is the difference between the last moment and the current moment;

[0013] The SOC of the energy storage submodule at the current moment is determined according to the SOC of the energy storage submodule at the previous moment, the rated capacity of the battery pack, the time difference and the target current value.

[0014] In this embodiment, the ampere-hour integration method calculates the battery state of charge by accumulating the integral of current and time. When the target current value is highly accurate and parameters such as time and rated capacity of the battery pack are relatively accurate and fixed, the SOC calculation method is simpler, more reliable and more efficient.

[0015] In some embodiments, the target current value is a charging current value of each of the energy storage submodules, and determining the SOC of the energy storage submodule at the current moment according to the SOC of the energy storage submodule at the previous moment, the rated capacity of the battery pack, the time difference and the target current value includes:

[0016] determining an SOC change amount according to the rated capacity of the battery pack, the time difference and the target current value;

[0017] The sum of the SOC of the energy storage submodule at the previous moment and the SOC change is determined as the SOC of the energy storage submodule at the current moment.

[0018] In some embodiments, the target current value of each of the energy storage submodules is the discharge current value of each of the energy storage submodules, and determining the SOC of the energy storage submodule at the current moment according to the SOC of the energy storage submodule at the previous moment, the rated capacity of the battery pack, the time difference and the target current value includes:

[0019] determining an SOC change amount according to the rated capacity of the battery pack, the time difference and the target current value;

[0020] The difference between the SOC of the energy storage submodule at the previous moment and the SOC change amount is determined as the SOC of the energy storage submodule at the current moment.

[0021] In this embodiment, the change in SOC is calculated using the rated capacity of the battery pack, the time difference between two moments and the target current value. During charging, the sum of the SOC at the previous moment and the SOC change is determined as the SOC at the current moment. During discharging, the difference between the SOC at the previous moment and the change is determined as the SOC at the current moment. This allows for flexible response to charging and discharging scenarios, and provides greater practicality.

[0022] In some embodiments, the method further includes: obtaining a power-off standstill time of a battery pack corresponding to the energy storage submodule; and determining an initial SOC of the ampere-hour integration method according to the power-off standstill time and a preset time threshold.

[0023] The battery state will become stable only after a long period of rest. The SOC value determined when the battery state is stable will be more accurate. Therefore, this embodiment determines the initial value of the ampere-hour integral in combination with the resting time of the battery, which can improve the accuracy of the SOC.

[0024] In some embodiments, determining the initial SOC of the ampere-hour integration method according to the power-off standstill time and a preset time threshold includes:

[0025] If the power-off standstill time is longer than the preset time threshold, obtaining the SOC value determined by the energy storage submodule using the open circuit voltage as the initial SOC;

[0026] If the power-off standstill time is less than the preset time threshold, the SOC value of the charging terminal of the battery pack corresponding to the energy storage submodule is obtained as the initial SOC.

[0027] In this embodiment, the voltage of the battery is sufficiently stable after the battery pack has been in a state of rest for a long enough time, and the open circuit voltage of the battery has a relatively fixed functional relationship with the SOC. Therefore, when the battery pack is in a state of rest for a period of time exceeding the preset time threshold, the SOC value determined by the open circuit voltage is relatively accurate, thereby improving the accuracy of the initial SOC value. When the battery pack is in a state of rest for an insufficient period of time, the voltage stability of the battery is still insufficient, and the open circuit voltage method is not accurate enough to determine the SOC. Therefore, when the battery pack is in a state of rest for a period of time less than the preset time threshold, the SOC at the charging end of the battery pack is used as the initial SOC of the ampere-hour integration, thereby avoiding the problem of inaccurate SOC determination by the open circuit voltage method. Based on the above method, the initial SOC of the ampere-hour integration method is made more accurate, further improving the calculation accuracy of the SOC of the energy storage submodule.

[0028] In some embodiments, the method for obtaining the power-off idle time includes:

[0029] In response to a power-off instruction of the energy storage system, detecting a voltage value across a capacitor of a power conversion module in the energy storage submodule;

[0030] Determine the moment when the voltage value drops to less than a preset voltage threshold as a first moment;

[0031] In response to a power-on instruction of the energy storage system, determining the time when the energy storage system is powered on as a second time;

[0032] The power-off idle time duration is determined according to the second moment and the first moment.

[0033] In this embodiment, when a power-off instruction of the energy storage system is received, the voltage value across the capacitor of the power conversion module in the energy storage submodule is detected, and a first moment is recorded when the voltage value drops to less than a preset voltage threshold. When a power-on instruction of the energy storage control system is received, a second moment is recorded when the energy storage system is powered on and started. The power-off quiescent time is determined based on the second moment and the first moment. The power-off moment and the power-on start moment of the energy storage system can be accurately determined based on the power-off instruction and the power-on instruction, thereby making the power-off quiescent time more accurate.

[0034] In some embodiments, determining the target current value of each energy storage submodule in the branch according to the first current value includes:

[0035] Acquire a second current value of a voltage balancing resistor of a power conversion module in the energy storage submodule and a third current value of an impedance of a load element of the power conversion module;

[0036] The target current value is determined according to the first current value, the second current value, and the third current value.

[0037] In this embodiment, the first current value is the current value of the series branch where the multiple series energy storage submodules are located, and the charging current flowing into the battery pack through the series branch and the discharging current flowing out of the battery pack must pass through the capacitor, voltage-dividing resistor and other load components of the power conversion module. Therefore, on the basis of the first current value and the current values ​​of the capacitor, voltage-dividing resistor and other load shunted by the power conversion module, the charging current value that flows into the corresponding battery pack and the discharging current value that flows out of the battery pack are calculated, so that the calculation of the target current value of the battery pack is more accurate, thereby improving the accuracy of the calculated SOC.

[0038] In some embodiments, the method further includes: sending the target current value of the energy storage submodule to a battery management unit corresponding to the energy storage submodule.

[0039] This allows the battery management unit to obtain more accurate current data and calibrate the current data according to the target current value (i.e., the charge and discharge current value), which also increases the acquisition channel of the current data source in the battery pack module and improves the reliability of the system. In addition, it can also prevent the battery pack management unit from losing current data due to a failure of the current sampling unit, thereby further improving the reliability of the system.

[0040] In some embodiments, the method further comprises:

[0041] Determining the switching frequency of each energy storage submodule within a preset time according to the switching instruction received by each energy storage submodule;

[0042] Determining whether the switching frequency is greater than a preset frequency threshold;

[0043] If the switching frequency is greater than the preset frequency threshold, a control instruction is sent to the battery management unit corresponding to the energy storage submodule, and the control instruction is used to control the battery management unit to calculate the SOC using the target current value.

[0044] In this embodiment, when the switching frequency of the energy storage submodule is high, and the current sampling unit in the battery pack module has a low sampling frequency and may not be able to sample the current, the battery management unit of the energy storage submodule can determine the SOC based on the received target current value, thereby avoiding the SOC estimation inaccuracy caused by the current sampling unit in the battery pack module failing to sample current data due to high-frequency switching.

[0045] In the second aspect, the present application also provides a cascade energy storage system, which includes multiple branches, each of which includes a current measuring unit and multiple energy storage sub-modules connected in series, and the current measuring unit is used to obtain a first current value of the branch; the first current value is used to determine a target current value of each energy storage sub-module in the branch, and the target current value is used to determine the SOC of the corresponding energy storage sub-module.

[0046] In the cascade energy storage system of this embodiment, a current measurement unit is set on each series branch to obtain the current value of the branch, so as to determine the target current value using the current value of the branch, and then determine the SOC of the energy storage submodule. Since the current of each energy storage branch collected by the current measurement unit has the characteristics of high sampling frequency and high precision, and the branch current value is not limited by the energy storage submodule itself, the accuracy of the SOC can be improved by calculating the SOC based on the high-precision current value.

[0047] In some embodiments, each of the energy storage submodules of the cascade energy storage system includes a power conversion module and a battery pack module; the cascade energy storage system also includes an energy storage control system, which is connected to the current measurement unit and the power conversion module; the energy storage control system is used to obtain the first current value from the current measurement unit and send the first current value to the power conversion module on the corresponding branch; the power conversion module is used to determine the target current value of the energy storage submodule on the corresponding branch according to the first current value, and determine the SOC of the battery pack module of the corresponding energy storage submodule according to the target current value.

[0048] In this embodiment, after the current measurement unit obtains the first current value of the branch where it is located, the first current value is sent to the power conversion module of each energy storage sub-module through the energy storage control system, and the SOC of the battery pack module is calculated in the power conversion module. This can avoid the SOC calculation inaccuracy problem of the battery pack module caused by low current sampling frequency or circuit failure, and also improve the flexibility of the SOC determination method.

[0049] In some embodiments, the cascade energy storage system also includes an energy storage control system, which is connected to the current measurement unit and each of the energy storage sub-modules; the energy storage control system is used to obtain the first current value from the current measurement unit, determine the target current value of the energy storage sub-module on the corresponding branch according to the first current value, and determine the SOC of the battery pack module of the corresponding energy storage sub-module according to the target current value.

[0050] In this embodiment, after the current measurement unit obtains the first current value of the branch where it is located, the energy storage control system determines the target current value and the SOC of the energy storage sub-module based on the first current value. Compared with the traditional method of determining the SOC through the battery management module, it can avoid the SOC calculation inaccuracy problem caused by low current sampling frequency or circuit failure of the battery pack module, and also improves the flexibility of the SOC determination method.

[0051] In a third aspect, the present application provides a SOC determination device, which is applied to a cascade energy storage system, wherein each branch of the cascade energy storage system includes a plurality of energy storage submodules connected in series. The SOC determination device includes:

[0052] An acquisition module, used for acquiring a first current value of a branch where the energy storage submodule is located;

[0053] A first determining module, configured to determine a target current value of each of the energy storage submodules in the branch according to the first current value;

[0054] The second determination module is used to determine the SOC of the corresponding energy storage submodule according to the target current value.

[0055] In a fourth aspect, the present application provides an SOC determination device, including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the SOC determination method in one or more embodiments described above is implemented.

[0056] In a fifth aspect, the present application further provides a computer-readable storage medium having a computer program stored thereon, and when the computer program is executed by a processor, the SOC determination method in one or more embodiments as described above is implemented.

[0057] In a sixth aspect, the present application also provides a computer program product, including a computer program, which, when executed by a processor, implements the SOC determination method in one or more embodiments as described above.

[0058] In the seventh aspect, the present application also provides a cascade energy storage system, each branch of the cascade energy storage system includes a plurality of energy storage sub-modules connected in series, the cascade energy storage system also includes a memory and a processor, the memory stores a computer program, and when the processor executes the computer program, it implements the SOC determination method in one or more embodiments described above.

[0059] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below.

[0060] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0061] FIG1 is a schematic diagram of the architecture of a high-voltage direct-mounted energy storage system in some embodiments of the present application;

[0062] FIG2 is a schematic diagram of the structure of an energy storage submodule in some embodiments of the present application;

[0063] FIG3 is a schematic diagram of the MMC energy storage system architecture in some embodiments of the present application;

[0064] FIG4 is a flow chart of a method for determining SOC in some embodiments of the present application;

[0065] FIG5 is a flow chart of a method for determining the SOC of a corresponding energy storage submodule using the ampere-hour integration method in some embodiments of the present application;

[0066] FIG6 is a flow chart of a method for determining an initial value of an ampere-hour integral in some embodiments of the present application;

[0067] FIG7 is a flow chart of a method for determining an initial SOC using the ampere-hour integration method in some embodiments of the present application;

[0068] FIG8 is a flow chart of a method for obtaining power-off idle time in some embodiments of the present application;

[0069] FIG9 is a flow chart of a method for determining a charging current value of an energy storage submodule in some embodiments of the present application;

[0070] FIG10 is a schematic diagram of current flow of a power conversion module when the energy storage submodule is in a charging state in one embodiment of the present application;

[0071] FIG11 is a flow chart of a method for determining SOC in some other embodiments of the present application;

[0072] FIG12 is a schematic diagram of the structure of an SOC determination device in some embodiments of the present application;

[0073] FIG13 is a schematic diagram of the structure of an SOC determination device in some embodiments of the present application;

[0074] FIG14 is a schematic diagram of a computer-readable storage medium in some embodiments of the present application;

[0075] FIG15 is a schematic diagram of a computer program product in some embodiments of the present application.

[0076] The reference numerals in the specific implementation manner are as follows:

[0077] High-voltage direct-mounted energy storage system 10, energy storage control system 11, current measurement unit 12, energy storage submodule 13, isolation switch 14, starting resistor 15, reactor 16;

[0078] A power conversion module 131, a power module controller 1311, a bypass switch 1312, a first switch device T1, a second switch device T2, a voltage balancing resistor R1, and a capacitor C1;

[0079] Battery pack module 132, battery management unit 1321, current sampling unit 1322, electric box 1323;

[0080] MMC energy storage system 20, energy storage control system 201, current measurement unit 202, energy storage submodule 203;

[0081] SOC determination device 130 , acquisition module 1301 , first determination module 1302 , second determination module 1303 .

[0082] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0083] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0084] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0085] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0086] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0087] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0088] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0089] At present, high-voltage direct-mounted energy storage systems, medium-voltage direct-mounted energy storage systems, and MMC energy storage systems have attracted widespread attention due to their advantages of large capacity and high efficiency. The cascade energy storage system generally includes an energy storage control system and multiple cascaded energy storage submodules, each of which includes a power conversion module and a battery module, and the battery module is connected to the energy storage control system through the power conversion module.

[0090] The applicant has noticed that in a cascade energy storage system, after the battery management unit of each energy storage submodule calculates the SOC of the corresponding energy storage submodule, the SOC is uploaded to the energy storage control system, and the energy storage control system performs actions such as SOC balancing of the entire cascade energy storage system based on the SOC uploaded by each energy storage submodule. The battery management unit calculates the SOC based on the current collected by the current sampling unit of the battery pack module, but the current sampling unit of the battery pack module has a low sampling frequency and low accuracy, resulting in insufficient accuracy of the SOC calculated by each energy storage submodule. On the other hand, if the current sampling unit circuit of a certain energy storage submodule fails, it will seriously affect the SOC calculation of the energy storage submodule where it is located, causing the SOC accuracy of the entire energy storage system to be further affected.

[0091] In order to improve the accuracy of SOC calculation of cascade energy storage system, the applicant has found that a current measurement unit with high sampling rate and high precision can be set on the series branch where each energy storage submodule is located, such as a merging unit (MU), and the current value on the series branch is collected by the current measurement unit, and then the battery pack charge and discharge current of each energy storage submodule is calculated according to the collected series branch current value, and then the SOC of each energy storage submodule is calculated according to the charge and discharge current of the battery pack. Since the current sampling frequency and precision of the series branch are high, the SOC of each energy storage submodule can be calculated using high-precision current without increasing the cost, thereby improving the accuracy of SOC calculation. In addition, it can also effectively avoid the problem of inaccurate SOC calculation caused by failure of the current sampling unit circuit of the energy storage submodule.

[0092] Based on the above considerations, in order to solve the problem of low SOC estimation accuracy in cascade energy storage systems, the inventors have conducted in-depth research and designed a SOC calculation method for cascade energy storage systems, the method comprising: obtaining a first current value of a series branch where multiple energy storage submodules are located; determining the charge and discharge current value of the energy storage submodule according to the first current value; and determining the SOC of the corresponding energy storage submodule according to the charge and discharge current value of the energy storage submodule. In this method, since the current measurement unit configured in the series branch of the cascade energy storage system is used to uniformly collect the current value of the branch where each energy storage submodule is located, the current value has the characteristics of high sampling frequency and high accuracy, and can more accurately calculate the SOC of each energy storage submodule, avoiding various problems caused by low SOC calculation accuracy.

[0093] The SOC determination method disclosed in the embodiment of the present application can be used for, but is not limited to, high-voltage direct-mounted energy storage systems, medium-voltage direct-mounted energy storage systems, MMC energy storage systems, and cascaded energy storage systems. It can be understood that as long as it includes at least one branch, each branch includes a plurality of energy storage submodules connected in series and a current measurement unit for measuring the current of the corresponding branch, the SOC determination method disclosed in the present application can be used. The cascaded energy storage system can be applied between DC transmission lines to achieve energy storage.

[0094] For the convenience of description, the following embodiments are described by taking the cascade energy storage system of one embodiment of the present application as a high-voltage direct-mounted energy storage system as an example.

[0095] Please refer to FIG. 1 , which is a schematic diagram of the structure of a high-voltage direct-mounted energy storage system provided in some embodiments of the present application.

[0096] In some embodiments of the present application, the high-voltage direct-hanging energy storage system 10 is used to be connected between high-voltage direct current transmission lines. When the power demand at the power consumption end is small, the current on the high-voltage direct current transmission line can charge the high-voltage direct-hanging energy storage system 10 and store the electric energy in the high-voltage direct-hanging energy storage system 10. When the power demand at the power consumption end is large, the high-voltage direct-hanging energy storage system 10 can discharge to the high-voltage direct current transmission line to increase the current supply on the high-voltage direct current transmission line. The high-voltage direct-hanging energy storage system 10 mainly includes an energy storage control system 11, a current measurement unit 12, and a plurality of energy storage submodules 13. It can be understood that the energy storage system 10 can also include an isolation switch 14, a starting resistor 15, a reactor 16 and other electronic components. Since other components are not directly related to the content of the present invention, they are not described in detail here.

[0097] The energy storage control system 11 is electrically connected to the multiple energy storage sub-modules 13 respectively, and is used to exchange signals with the multiple energy storage sub-modules 13 and control the multiple energy storage sub-modules 13 .

[0098] The plurality of energy storage submodules 13 are connected in series to form a series branch. The isolating switch 14, the starting resistor 15, the current measuring unit 12, the plurality of energy storage submodules 13 connected in series, and the reactor 16 are connected in series in sequence.

[0099] The current measuring unit 12 is also electrically connected to the energy storage control system 11 , and is used to collect current values ​​of the series branches where the multiple energy storage submodules 13 are located, and send the collected current values ​​to the energy storage control system 11 .

[0100] In some embodiments of the present application, the current measuring unit 12 may be a merging unit MU, which is an interface device of an electronic current and voltage transformer, and is used to perform time-related combination of current and voltage data from a secondary converter. The merging unit collects current data with the characteristics of high sampling frequency and high precision, so high-precision current data can be collected. In some other embodiments of the present application, the current measuring unit 12 may also be a current transformer (CT), or other current measuring components with high sampling frequency and high precision.

[0101] It can be understood that Figure 1 is only a structural diagram of a high-voltage direct-mounted energy storage system, and is not an actual electrical connection diagram. The energy storage control system and the current measurement unit and each energy storage sub-module may also include other electronic components for realizing various functions. The actual high-voltage direct-mounted energy storage system circuit may also include various other components and loops, which are not shown in this application.

[0102] Please refer to FIG2 , which is a schematic diagram of the structure of any energy storage submodule 13 in some embodiments of the present application. The energy storage submodule 13 includes a power conversion module 131 and a battery module 132 .

[0103] The conversion module 131 is connected between the energy storage control system 11 and the battery module 13 , and is used to cascade the battery module 132 to the high-voltage direct-mounted energy storage system 10 .

[0104] In some embodiments of the present invention, the power conversion module 131 is a half-bridge type. The power conversion module 131 includes a power module controller 1311, a bypass switch 1312, a first switch device T1, a second switch device T2, a voltage balancing resistor R1, a capacitor C1, and other loads such as a power supply (not shown).

[0105] The power module controller 1311 is connected to the input end of the first switch device T1 and the input end of the second switch device T2, and is used to receive the switching instruction sent by the energy storage control system 11, and send a switching signal to the first switch device T1 and the second switch device T2 according to the switching instruction, so as to realize the charging and discharging of the battery module 132. The first switch device T1 and the second switch device T2 are connected in series.

[0106] The bypass switch 1312 is connected in parallel with the second switch device T2 and is used to quickly bypass and switch out the energy storage submodule 13 when a fault occurs in the energy storage submodule 13 .

[0107] The capacitor C1 is connected in parallel with the first switch device T1 and the second switch device T2 connected in series, and is used to stabilize the voltage of the power conversion module 131. The voltage balancing resistor R1 is connected in parallel with the capacitor C1, and is used to balance the voltage of the energy storage submodule 13.

[0108] In some other embodiments of the present invention, the power conversion module 131 may also be a full-bridge topology structure or a quasi-full-bridge topology structure, etc. Since the full-bridge topology structure and the quasi-full-bridge topology structure are prior arts in the art, they are not described in detail here.

[0109] The battery pack module 132 includes a battery management unit 1321 , a current sampling unit 1322 , and a plurality of power boxes 1323 .

[0110] The battery management unit 1321 is electrically connected to the power module controller 1311, and is used to calculate the SOC of the energy storage submodule 13 and realize battery balancing between the power boxes 1323. The current sampling unit 1322 is connected to the battery management unit 1321, and is used to collect the current of the energy storage submodule 13. The power box 1323 includes a battery (not shown) and a battery monitoring unit (Cell Supervision Circuit, CSC), and the battery monitoring unit is used to sample the voltage, temperature and humidity of the battery and perform balancing control on the power box.

[0111] Please refer to Figure 3, which is a schematic diagram of the architecture of an MMC energy storage system 20 provided in some other embodiments of the present application. The MMC energy storage system 20 includes an energy storage control system 201, multiple branches, and a current measuring unit 202 arranged on each branch, and each branch includes multiple energy storage sub-modules 203 connected in series. Each of the current measuring units 203 is used to measure the current value of its corresponding branch. The energy storage control system 201 is electrically connected to each of the current measuring units 202 and each energy storage sub-module 203. It can be understood that Figure 3 is only a schematic diagram of the architecture of the MMC energy storage system, not an actual electrical connection diagram. The energy storage control system 201 and the current measuring unit 202 and each energy storage sub-module 203 may also include other electronic components for realizing various functions, but they are not shown in the figure. The structure of the energy storage sub-module 203 can be the same as the structure shown in Figure 2, which will not be repeated here.

[0112] It can be understood that although the topological structures of the MMC energy storage system and the high-voltage direct-mounted energy storage system are different, both cascade energy storage systems have an energy storage control system, a branch including multiple energy storage sub-modules connected in series, each branch is provided with a current measurement unit, and each of the energy storage subsystems can have the same structure. Therefore, both energy storage systems can use the SOC determination method provided in the embodiments of the present application.

[0113] In other embodiments, the cascade energy storage system may also be a medium-voltage direct-mounted energy storage system. Corresponding to different voltages in the power transmission system, the number of cascaded energy storage submodules of the cascaded energy storage system is also different, and the peripheral circuit of the energy storage system will also be adjusted accordingly. In other words, the difference between the medium-voltage direct-mounted energy storage system and the high-voltage direct-mounted energy storage system is that the number of cascaded energy storage submodules is different, and the corresponding peripheral circuits are also different, but the medium-voltage direct-mounted energy storage system also includes a plurality of cascaded energy storage submodules, and the plurality of energy storage submodules are connected in series to form one or more series branches, and each of the series branches is provided with a current measurement unit for measuring branch current. The structure of the energy storage submodule may also be as shown in FIG. 2, including a power conversion module and a battery pack module, and the power conversion module may be a half-bridge topology structure or a full-bridge topology structure as described above. The battery pack module includes a plurality of battery cells connected in series. Therefore, the medium-voltage direct-mounted energy storage system may also use the SOC determination method provided in the present application.

[0114] It can be understood that the cascade energy storage system described in the present application is not limited to the MMC energy storage system, high-voltage direct-mounted energy storage system and medium-voltage cascade energy storage system as described above. As long as it includes one or more branches, and each branch includes multiple energy storage sub-modules connected in series, each energy storage sub-module includes a power conversion module and a battery pack composed of multiple battery cells connected in series, and a cascade energy storage system with a topological structure having a current measurement unit arranged on the series branch, the SOC determination method provided in the present application can be used.

[0115] Referring to FIG. 4 , there is a flow chart of a SOC determination method in some embodiments of the present application. The SOC determination method may be applied in the cascade energy storage system as described above, wherein each branch of the cascade energy storage system includes a plurality of energy storage submodules connected in series. The SOC determination method includes:

[0116] Step S401, obtaining a first current value of a branch where an energy storage submodule is located.

[0117] In some embodiments of the present application, the first current value is collected by a current measuring unit arranged on each branch. The current measuring unit may be a merging unit or a current transformer. Both the merging unit and the current transformer have the characteristics of high sampling rate and high precision, so the collected current value has high precision. It is understandable that the current measuring unit may also be other current measuring elements with high sampling frequency and high precision.

[0118] In some embodiments of the present application, the first current value collected by the current measurement unit is sent to the energy storage control system, and the energy storage control system then forwards the first current value to the power controller of each energy storage submodule, and the power controller performs the subsequent steps of determining the SOC according to the first current value. The energy storage control system can also determine the charge and discharge state of the corresponding branch according to the first current value, and determine the switching instructions of each energy storage submodule according to a preset balancing algorithm. The switching instructions are used to control the energy storage submodule to connect to the energy storage system or cut out of the energy storage system. It can be understood that when the energy storage submodule cuts out of the energy storage system, there is no need to determine the SOC of the energy storage submodule.

[0119] In some other implementations of the present application, after the first current value collected by the current measurement unit is sent to the energy storage control system, the energy storage control system performs subsequent steps of determining the SOC according to the first current value.

[0120] Step S402: determining a target current value of each energy storage submodule in the branch according to the first current value.

[0121] In the embodiment of the present application, the battery pack module of each sub-energy storage module has two processes: charging and discharging. During the charging process, the target current value is the charging current value of the battery pack module; during the discharging process, the target current value is the discharging current value of the battery pack module.

[0122] In some embodiments of the present application, during the charging process of the battery pack module, the charging current value of the corresponding battery pack module can be obtained by subtracting the current value shunted by the capacitor, grading resistor and other loads in the power conversion module from the first current value. During the discharging process of the battery pack module, the discharging current value of the corresponding battery pack module can be obtained by adding the first current value to the current value shunted by the capacitor, grading resistor and other loads in the power conversion module. The specific method for determining the target current value will be described in detail later.

[0123] In some implementations, after the energy storage control system sends the first current value to a power controller of each energy storage submodule, the power controller determines a charging current value and a discharging current value of each energy storage submodule according to the first current value.

[0124] In some other implementations, the energy storage control system can also determine the charging current value and the discharging current value of each energy storage sub-module based on the first current value, wherein the energy storage control system can obtain relevant data such as the capacitance, grading resistor, and load of the power conversion module in each energy storage sub-module and calculate the charging current value and the discharging current value.

[0125] Step S403: determining the SOC of the corresponding energy storage submodule according to the target current value.

[0126] In some embodiments, the power controller in each energy storage submodule determines the SOC of the corresponding energy storage submodule according to the target current value. In other embodiments, the energy storage control system may also determine the SOC of each energy storage submodule according to the target current value.

[0127] Exemplarily, the SOC of the corresponding energy storage submodule can be calculated according to the target current value using the ampere-hour integration method, or the SOC of the corresponding energy storage submodule can be determined according to the target current using a linear model method or a neural network model. For example, a training sample data set is formed by collecting a large amount of historical charge and discharge current data and corresponding SOC data of the energy storage submodule, and then the data set is used to train the neural network model to obtain a trained neural network model, wherein the input value of the neural network model is the charge and discharge current value, and the output of the neural network model is the SOC value. When in use, the target current value is input into the trained neural network model to obtain the SOC of the energy storage submodule. Among them, the neural network model can be a BP neural network model or a convolutional neural network model. Since the use of data sets to train neural network models is a prior art, it will not be described in detail here.

[0128] In an embodiment of the present application, the SOC determination method obtains a high-precision first current value of each branch through a current measurement unit, and determines the charging and discharging current value of each energy storage sub-module based on the first current value. Since the current of each energy storage branch collected by the current measurement unit has the characteristics of high sampling frequency and high precision, the SOC is determined based on the high-precision charging current value, which can improve the accuracy of the SOC.

[0129] It can be seen from the above embodiments that there are multiple methods for determining the SOC according to the charge and discharge current values. The following focuses on the specific implementation method of determining the SOC using the ampere-hour integration method. As shown in Figure 5, the SOC of the corresponding energy storage sub-module is determined according to the target current value, including: according to the target current value, the SOC of the corresponding energy storage sub-module is determined using the ampere-hour integration method.

[0130] The ampere-hour integration method is to dynamically estimate the SOC of the battery by integrating time and current when the battery is charging or discharging. The ampere-hour integration method is less affected by the battery's own conditions, and the calculation method is simple and accurate. Therefore, this embodiment uses the ampere-hour integration method according to the target current value to dynamically estimate the SOC value of the battery pack. The calculation method is simple, more accurate and reliable.

[0131] Further, referring to FIG. 5 , in some embodiments, according to the target current value, the SOC of the corresponding energy storage submodule is determined by using the ampere-hour integration method, including:

[0132] Step S501, obtaining the SOC of the energy storage submodule at the previous moment, the rated capacity of the battery pack of the energy storage submodule, and the time difference, wherein the time difference is the difference between the previous moment and the current moment;

[0133] Step S502: Determine the SOC of the energy storage submodule at the current moment according to the SOC of the energy storage submodule at the previous moment, the rated capacity of the battery pack, the time difference and the target current value.

[0134] Specifically, in some embodiments of the present application, when the battery pack module of the energy storage submodule is in the charging process, the target current value is the charging current value of the battery pack module, then in step S502, the SOC of the energy storage submodule at the previous moment, the rated capacity of the battery pack, the time difference and the target current value are determined, including:

[0135] determining an SOC change amount according to the rated capacity of the battery pack, the time difference and the target current value;

[0136] The sum of the SOC of the energy storage submodule at the previous moment and the SOC change is determined as the SOC of the energy storage submodule at the current moment.

[0137] Specifically, in one embodiment, during the charging process, the SOC of the energy storage submodule at the current moment can be calculated by the following formula:

[0138]

[0139] Among them, SOC t is the SOC of the energy storage submodule at the last moment; SOC t+Δt is the SOC of the energy storage submodule at the current moment, wherein the SOC of the battery pack module when it is in the charging state t+Δt is gradually increased; C is the rated capacity of the battery pack of the energy storage submodule, i E is the charging current value of the energy storage submodule, that is, i E is the current value flowing into the battery module, and Δt is the time difference. The SOC change during the charging process is the charging current value i of the energy storage submodule. E The product of the time difference Δt is then divided by the rated capacity of the battery pack.

[0140] When the battery pack of the energy storage submodule is in the discharge process, the target current value is the discharge current value of the battery pack module, then in step S502, according to the SOC of the energy storage submodule at the previous moment, the rated capacity of the battery pack, the time difference and the target current value, the SOC of the energy storage submodule at the current moment is determined, including:

[0141] determining an SOC change amount according to the rated capacity of the battery pack, the time difference and the target current value;

[0142] The difference between the SOC of the energy storage submodule at the previous moment and the SOC change amount is determined as the SOC of the energy storage submodule at the current moment.

[0143] Specifically, in one embodiment, during the discharge process, the SOC of the energy storage submodule at the current moment can be calculated by the following formula:

[0144]

[0145] Among them, SOC t is the SOC of the energy storage submodule at the last moment; SOC t+Δt is the SOC of the energy storage submodule at the current moment, wherein the SOC of the battery pack module when it is in the discharge state is t+Δt is gradually reduced; C is the rated capacity of the battery pack of the energy storage submodule, i E is the discharge current value of the energy storage submodule, that is, i E is the current value flowing out of the battery pack module, and Δt is the time difference. The SOC change during the discharge process is the charging current value i of the energy storage submodule. E The product of the time difference Δt is then divided by the rated capacity of the battery pack.

[0146] In some embodiments, when the charge and discharge current values ​​are sent by the energy storage control system to the power controller of the energy storage submodule, and then the SOC of the energy storage submodule at the current moment is determined by the power controller, the time difference is the time difference between the energy storage control system sending the charge and discharge current values ​​twice, that is, the time difference can be the communication cycle between the energy storage control system and the power controller.

[0147] In some other embodiments, the time difference may also be the difference between two current sampling times of the current measuring unit. In some further embodiments, the time difference may also be set according to actual needs.

[0148] In some embodiments, the power controller of each energy storage submodule obtains the rated capacity of the battery pack of the corresponding energy storage submodule, the SOC of the energy storage submodule at the previous moment, the time difference and the charge and discharge current value, and determines the SOC of the energy storage submodule at the current moment.

[0149] In other embodiments, when the energy storage control system determines the SOC of the energy storage submodule at the current moment, the power controller of each energy storage submodule first sends the rated capacity of the battery pack of the energy storage submodule, the charging and discharging current values ​​and the time difference to the energy storage control system; or, the power controller of each energy storage submodule sends the rated capacity of the battery pack of the energy storage submodule and the charging current value to the energy storage control system, the time difference is calculated by the energy storage control system, and then the energy storage control system determines the SOC of each energy storage submodule.

[0150] In addition, when calculating SOC using the ampere-hour integration method, the initial SOC is crucial to the calculation result and directly affects the accuracy of the SOC calculation result. Therefore, referring to FIG. 6 , the present application also provides a method for determining the initial SOC of the ampere-hour integration method to further improve the accuracy of SOC. The method for determining the initial SOC of the ampere-hour integration method includes:

[0151] Step S601: Obtain the power-off standby time of the battery pack corresponding to the energy storage submodule.

[0152] Among them, the power-off standby time can be the time between the moment when the last power-off instruction is received and the moment when the power-on instruction is received, or it can be the time between the moment when the voltage value across the capacitor of the power conversion module in the energy storage sub-module drops to a certain specific value after receiving the last power-off instruction and the moment when the power-on instruction is received.

[0153] Step S602: determining an initial SOC using an ampere-hour integration method according to the power-off standstill time and a preset time threshold.

[0154] The preset duration threshold may be a preset specific value, such as 5 days, or a value range, which may be set according to actual needs.

[0155] Specifically, as shown in FIG. 7 , in some embodiments, determining the initial SOC of the ampere-hour integration method according to the power-off standstill time and a preset time threshold includes:

[0156] Step S701: if the power-off standstill time is longer than a preset time threshold, obtaining an SOC value determined by the energy storage submodule using the open circuit voltage as an initial SOC;

[0157] Step S702: If the power-off standstill time is less than a preset time threshold, the SOC value of the charging terminal of the battery pack corresponding to the energy storage submodule is obtained as the initial SOC.

[0158] In some embodiments, if the SOC of the energy storage submodule is determined by the power controller of the energy storage submodule, the power controller sends a first notification instruction to the battery management unit of the corresponding energy storage submodule after determining that the power-off standstill time is greater than the preset time threshold, and the first notification instruction is used to control the battery management unit to upload the SOC value determined by the open circuit voltage. After determining that the power-off standstill time is less than the preset time threshold, the power controller sends a second notification instruction to the battery management unit of the corresponding energy storage submodule, and the second notification instruction is used to control the battery management unit to upload the SOC value of the battery pack charging terminal of the corresponding energy storage submodule.

[0159] In other embodiments, if the SOC of the energy storage submodule is determined by the energy storage control system, then when the energy storage control system determines that the power-off static time of the energy storage submodule is greater than the preset time threshold, a third notification instruction is sent to the power controller of the corresponding energy storage submodule, and the third notification instruction is forwarded to the battery management unit of the corresponding energy storage submodule through the power controller, and the third notification instruction is used to control the battery management unit to upload the SOC value determined by the open circuit voltage. When the energy storage control system determines that the power-off static time of the energy storage submodule is less than the preset time threshold, a fourth notification instruction is sent to the power controller of the corresponding energy storage submodule, and the fourth notification instruction is forwarded to the battery management unit of the corresponding energy storage submodule through the power controller, and the fourth notification instruction is used to control the battery management unit to upload the SOC value of the charging terminal of the battery pack corresponding to the energy storage submodule.

[0160] In some embodiments of the present application, if the power-off standstill time is equal to the preset time threshold, the SOC value determined by the energy storage submodule using the open circuit voltage can be used as the initial SOC, or the SOC value of the battery pack charging terminal corresponding to the energy storage submodule can be used as the initial SOC.

[0161] In this embodiment, the voltage of the battery is sufficiently stable after the battery pack has been in a state of rest for a long enough time, and the open circuit voltage of the battery has a relatively fixed functional relationship with the SOC. Therefore, when the battery pack is in a state of rest for a period of time exceeding the preset time threshold, the SOC value determined by the open circuit voltage is relatively accurate, thereby improving the accuracy of the initial SOC value. When the battery pack is in a state of rest for an insufficient period of time, the voltage stability of the battery is still insufficient, and the open circuit voltage method is not accurate enough to determine the SOC. Therefore, when the battery pack is in a state of rest for a period of time less than the preset time threshold, the SOC at the charging end of the battery pack is used as the initial SOC of the ampere-hour integration, thereby avoiding the problem of inaccurate SOC determination by the open circuit voltage method. Based on the above method, the initial SOC of the ampere-hour integration method is made more accurate, further improving the calculation accuracy of the SOC of the energy storage submodule.

[0162] Specifically, referring to FIG. 8 , in some embodiments, the method for obtaining the power-off idle time may include:

[0163] Step S801, responding to a power-off instruction, detecting the voltage value across the capacitor of the power conversion module in the energy storage submodule.

[0164] When the energy storage control system issues a power-off command, the voltage value across the capacitor of the power conversion module will drop linearly. When the power module controller of each energy storage submodule receives the power-off command of the energy storage system, it starts to monitor the voltage value across the capacitor in the power conversion module.

[0165] Step S802: Determine the moment when the voltage value drops to less than a preset voltage threshold as the first moment.

[0166] In some embodiments, when the voltage across the capacitor drops below the preset voltage threshold, the time is recorded as the first time using a timestamp function. In some embodiments, the determined first time is stored in a FLASH memory built into the power module controller.

[0167] Step S803: respond to the power-on instruction and determine the moment when the energy storage control system is powered on as the second moment.

[0168] If the power-on instruction of the energy storage control system is received, the power conversion module is powered on and started. The power module controller can use a timestamp function to obtain the time value of the powered-on startup moment and use the time value as the second moment.

[0169] Step S804: Determine the power-off idle time according to the second moment and the first moment.

[0170] Specifically, after determining the second moment, the first moment value is read from the FLASH memory built into the power module controller, and the power-off standby time is obtained according to the time difference between the second moment and the first moment.

[0171] In this embodiment, when a power-off instruction of the energy storage control system is received, the voltage value across the capacitor of the power conversion module in the energy storage submodule is detected, and a first moment is recorded when the voltage value drops to less than a preset voltage threshold. When a power-on instruction of the energy storage control system is received, a second moment is recorded when the energy storage system is powered on and started. The power-off quiescent time is determined based on the second moment and the first moment. The power-off moment and the power-on start moment of the energy storage system can be accurately determined based on the power-off instruction and the power-on instruction, thereby making the power-off quiescent time more accurate.

[0172] In other implementations of the present application, the power-off idle time may also be obtained by a timing tool such as a timer.

[0173] In other embodiments, the initial value of the ampere-hour integral may also be determined by other means, such as directly using the SOC value determined by the energy storage submodule using the open circuit voltage as the initial SOC, or directly using the SOC value of the charging terminal of the battery pack corresponding to the energy storage submodule as the initial SOC without calculating the power-off standstill time.

[0174] Further referring to FIG. 9 , in some embodiments of the present application, the method for determining the target current value of each energy storage submodule in the branch according to the first current value includes:

[0175] Step S901, obtaining a second current value of a voltage grading resistor of a power conversion module in an energy storage submodule and a third current value of an impedance of a load element of the power conversion module;

[0176] Step S902: Determine the target current value according to the first current value, the second current value, and the third current value.

[0177] The following describes the calculation methods of the charging and discharging current values ​​of the battery pack module of the energy storage submodule during the charging and discharging process.

[0178] 10 is a schematic diagram of the current flow of the power conversion module during the battery pack charging process. During charging, the first switch device T1 of the power conversion module is turned on, and the second switch device T2 is turned off. CT After flowing into the power conversion module, it flows to the corresponding battery module through the first switch device T1, wherein a part of the current i R The current is divided into the voltage-equalizing resistor R1, and part of the current i ZThe charging current i flowing to the battery pack module is divided into other loads such as the power supply of the power conversion module. E It can be obtained by subtracting the current value divided by the voltage balancing resistor R1 and other loads from the first current value on the branch.

[0179] Specifically, during the charging process, according to the first current value, the second current value and the third current value, determining the target current value can be achieved by the following formula:

[0180] i E＝ i CT -i R -i Z ;

[0181] Among them, i CT is the first current value received by the power module controller; i R is the current value shunted by the voltage-equalizing resistor of the power conversion module, that is, the second current value; i Z The load impedance shunt current value composed of other loads such as the power supply on the power conversion module, that is, the third current value; i E It is the current value flowing into the battery module connected in parallel with the power conversion module, that is, the charging current value.

[0182] Among them, the voltage-equalizing resistance value R of the power conversion module is known, and the loads such as the power supply on the power conversion module are constant power loads. The impedance Z of the load can be determined by design and experiment. The power module controller determines the voltage value U across the capacitor C of the power conversion module by real-time acquisition of the voltage across the capacitor C. The voltage-equalizing resistance, power supply and other loads are connected in parallel with the capacitor C. Therefore, the voltage values ​​across the voltage-equalizing resistance and the load are equal to the voltage value U across the capacitor. Therefore, the second current value i can be calculated by the following formula: R And the third current value i Z :

[0183] i R＝ U / R;

[0184] i Z＝ U / Z;

[0185] Similarly, during the discharge process of the battery pack module of the energy storage submodule, the discharge current i E The current i is diverted through the power supply and other loads Z， And the voltage divider resistor R1 shunt current i R After that, the current i flowing to the branch is obtained. CT , where the branch current i CT That is, the first current value, the current value i of the voltage balancing resistor shunting RThat is, the second current value, the current i shunted by the load impedance Z That is, the third current value. The discharge current value i E The first current value i on the branch can be CT Add the second current value i diverted by the voltage balancing resistor R1 R The third current value i shared with other loads Z Get, that is:

[0186] i E＝ i CT +i R +i Z

[0187] Among them, the second current value i R and the third current value i Z The calculation method of is as described above and will not be repeated here.

[0188] In this embodiment, the first current value is the current value of the series branch where the multiple series energy storage submodules are located, and the charging current flowing into the battery pack through the series branch and the discharging current flowing out of the battery pack must pass through the capacitor, voltage-dividing resistor and other load components of the power conversion module. Therefore, on the basis of the first current value and the current values ​​of the capacitor, voltage-dividing resistor and other load shunted of the power conversion module, the charging current value that net flows into the corresponding battery pack and the discharging current value that net flows out of the battery pack are calculated, so that the calculation of the charging and discharging current values ​​of the battery pack is more accurate, thereby improving the accuracy of calculating the SOC.

[0189] In addition, in the cascade energy storage system, due to the low sampling frequency of the current acquisition unit in the battery module, the current data is not accurate enough, which may lead to low accuracy of data related to the current value. In addition, if the current acquisition unit fails, the current data may be lost, thereby affecting the reliability of the energy storage system. To address this problem, the SOC determination method in some embodiments of the present application also includes:

[0190] The target current value (ie, the charging current value and the discharging current value) is sent to the battery management unit of the corresponding energy storage submodule.

[0191] Specifically, the power module controller determines the charge and discharge current values, and sends the charge and discharge current values ​​to the battery management unit of the corresponding energy storage submodule, so that the battery management unit can obtain more accurate battery pack charge and discharge current data, and can calibrate the current data according to the charge and discharge current values, thereby increasing the acquisition channel of the current data source in the battery pack module and improving the reliability of the system. In addition, it can also prevent the battery pack management unit from losing current data due to a failure of the current sampling unit, thereby further improving the reliability of the system.

[0192] In addition, in a cascade energy storage system, the energy storage control system determines whether each energy storage submodule is connected to or cut out of the energy storage system according to a preset balancing control algorithm, and issues a switching instruction to the corresponding energy storage submodule. The power controller of the energy storage submodule controls the connection or cutting out of the energy storage submodule according to the switching instruction. Among them, the switching control instruction includes an input control instruction and a cut-out control instruction. The input control instruction is used to control the energy storage submodule to connect to the energy storage system, and the cut-out instruction is used to control the energy storage submodule to cut out of the energy storage system. However, if the input and cut-out frequency is too high, the current sampling unit of the battery pack module may not sample the current data, resulting in an inaccurate calculation of the SOC by the battery management unit. In response to this problem, referring to FIG. 11, in some embodiments of the present application, the SOC determination method may also include:

[0193] Step S1001: Determine the switching frequency of each energy storage submodule within a preset time according to the switching instruction received by each energy storage submodule;

[0194] Step S1002, determining whether the switching frequency is greater than a preset frequency threshold;

[0195] Step S1003: If the switching frequency is greater than the preset frequency threshold, a control instruction is sent to the battery management unit of the corresponding energy storage submodule, and the control instruction is used to control the corresponding battery management unit to calculate the SOC using the target current value.

[0196] In some embodiments, the power controller in each energy storage submodule receives the switching instruction and determines the switching frequency, and when it is determined that the frequency exceeds the preset frequency threshold, the power controller sends the control instruction so that the battery management unit calculates the SOC using the received charge and discharge current value. The SOC calculated by the battery management unit can be used for internal display, etc.

[0197] In other embodiments, the energy storage control system may determine the switching frequency according to the switching instruction sent to each energy storage submodule, and when it is determined that the switching frequency of a certain energy storage submodule is greater than the preset frequency threshold, the control instruction is sent to the corresponding energy storage submodule or the battery management unit. It is understandable that the control instruction may also be sent by the energy storage control system to the power controller of the corresponding energy storage submodule, and then forwarded by the power controller to the battery management unit, so that the battery management unit calculates the SOC using the received charge and discharge current value.

[0198] In this way, when the switching frequency of the energy storage sub-module is high, the battery management unit of the energy storage sub-module can determine the SOC based on the received charging and discharging current values, thereby avoiding the SOC estimation inaccuracy caused by the current sampling unit in the battery pack module failing to sample current data due to high-frequency switching.

[0199] According to some embodiments of the present application, referring to FIG. 1 to FIG. 11, the present application provides a method for determining SOC, which can be applied to a cascade energy storage system, wherein each branch of the cascade energy storage system includes a plurality of energy storage submodules connected in series. In some embodiments of the present application, a MU or CT arranged on the branch where the energy storage submodule is located collects the first current value on the branch, and the high sampling rate and high precision characteristics of the MU or CT can obtain the first current value with high precision. The SOC determination method obtains the first current value on the branch where the energy storage submodule is located, determines the charge and discharge current values ​​of each energy storage submodule in the branch according to the first current value, and then determines the SOC of the corresponding energy storage submodule according to the charge and discharge current value using the ampere-hour integration method. The method obtains the first current value with high precision by the current measurement unit to calculate the high-precision charging current value of each energy storage submodule, thereby improving the accuracy of the SOC calculation. In addition, the method also determines the initial value of the ampere-hour integration method according to the power-off standby time and the preset time threshold, and further improves the accuracy of the SOC by improving the accuracy of the initial value of the SOC. In addition, the method can also send the charge and discharge current value to the battery management unit of the energy storage submodule, so that the battery management unit can obtain more accurate current data, and can also avoid the battery pack management unit from losing current data due to a current sampling unit failure, further improving the reliability of the system. Furthermore, the method can also notify the battery management unit to determine the SOC based on the received charge and discharge current value when the switching frequency of each energy storage submodule is greater than a preset frequency threshold, avoiding the SOC estimation inaccuracy caused by the failure to sample current data due to high-frequency switching.

[0200] It should be understood that, although the various steps in the flowcharts involved in the above-mentioned embodiments are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps does not have a strict order restriction, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above-mentioned embodiments can include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0201] Some embodiments of the present application also provide a cascade energy storage system. For example, in one embodiment, the cascade energy storage system may be the high-voltage direct-mounted energy storage system shown in Figures 1-2. The cascade energy storage system includes a plurality of branches, each of which includes a current measuring unit and a plurality of energy storage submodules connected in series. The current measuring unit is used to obtain a first current value of the branch in which it is located. The first current value is used to determine a target current value of each of the energy storage submodules in the branch, and the target current value is used to determine the SOC of the corresponding energy storage submodule.

[0202] In another embodiment, the cascade energy storage system may also be the MMC energy storage system shown in Figure 3. In other embodiments, the cascade energy storage system may also be other cascade energy storage systems such as a medium voltage direct-mounted energy storage system. It can be understood that as long as the cascade energy storage system includes multiple branches, each of which includes a current measurement unit and a plurality of energy storage submodules connected in series, the topological structure is within the protection scope of the present application.

[0203] In one embodiment, the current measuring unit may be a merging unit. In other embodiments, the current measuring unit may be a current transformer, or other current measuring components with high sampling frequency and high precision.

[0204] In this embodiment, a current measurement unit is provided on each series branch to obtain the current value of the branch, so as to determine the target current value by using the current value of the branch, and then determine the SOC of the energy storage submodule. Since the current of each energy storage branch collected by the current measurement unit has the characteristics of high sampling frequency and high precision, and the branch current value is not limited by the energy storage submodule itself, the SOC can be calculated based on the high-precision current value, so that the accuracy of the SOC can be improved.

[0205] In some embodiments, each of the energy storage submodules includes a power conversion module and a battery pack module. The cascade energy storage system also includes an energy storage control system, which is connected to the current measurement unit and the power conversion module. The energy storage control system is used to obtain the first current value from the current measurement unit and send the first current value to the power conversion module on the corresponding branch. The power conversion module is used to determine the target current value of the energy storage submodule on the corresponding branch according to the first current value, and determine the SOC of the battery pack module of the corresponding energy storage submodule according to the target current value.

[0206] Specifically, referring to FIG. 2 , the power conversion module further includes a power module controller and a circuit structure (for example, a half-bridge, full-bridge or quasi-full-bridge circuit topology) composed of electronic components such as a bypass switch, a first switch device, a second switch device, a voltage-equalizing resistor, and a capacitor. The power conversion module uses the power module controller to determine the target current value according to the first current value and determines the SOC of the corresponding energy storage submodule according to the target current value. Among them, the power module controller can be a device with computing and control capabilities such as a microprocessor.

[0207] In other embodiments, the cascade energy storage system further includes an energy storage control system, which is connected to the current measurement unit and each of the energy storage submodules;

[0208] The energy storage control system is used to obtain the first current value from the current measurement unit, determine the target current value of the energy storage submodule on the corresponding branch according to the first current value, and determine the SOC of the battery pack module of the corresponding energy storage submodule according to the target current value.

[0209] By using the first current value on the branch to determine the SOC through the energy storage control system or the power conversion module, on the one hand, it can avoid the SOC calculation inaccuracy problem caused by low current sampling frequency or circuit failure of the battery pack module, and on the other hand, it also improves the flexibility of the SOC determination method.

[0210] In some embodiments, the power conversion module and the energy storage control system can determine the SOC by the ampere-hour integration method. The process of determining the SOC by the ampere-hour integration method can refer to the SOC determination method in one or more embodiments described above, which will not be repeated here.

[0211] In this implementation manner, the method for determining the target current value according to the first current value may refer to the method described in FIG. 9 and the corresponding embodiment, which will not be repeated here.

[0212] Based on the same inventive concept, the embodiment of the present application also provides a SOC determination device for implementing the SOC determination method involved above. The implementation solution provided by the SOC determination device to solve the problem is similar to the implementation solution recorded in the above method, so the specific limitations in one or more SOC determination device embodiments provided below can refer to the limitations of the SOC determination method above, and will not be repeated here.

[0213] As shown in FIG12 , a SOC determination device 130 provided in some embodiments of the present application includes: an acquisition module 1301, a first determination module 1302, and a second determination module 1303. Each module in the SOC determination device 130 can be implemented in whole or in part by software, hardware, or a combination thereof. The above modules can be embedded in or independent of a processor in a computer device in the form of hardware, or can be stored in a memory in a computer device in the form of software, so that the processor can call and execute operations corresponding to the above modules.

[0214] The acquisition module 1301 is used to acquire a first current value of a branch where the energy storage submodule is located;

[0215] The first determination module 1302 is used to determine the target current value of each energy storage submodule in the branch according to the first current value;

[0216] The second determination module 1303 is used to determine the SOC of the corresponding energy storage submodule according to the target current value.

[0217] In some embodiments of the present application, the first determination module 1302 is used to obtain the second current value of the voltage-equalizing resistor of the power conversion module in the energy storage submodule and the third current value of the load element impedance of the power conversion module; and determine the target current value based on the first current value, the second current value and the third current value.

[0218] In some implementations of the present application, the second determination module 1303 determines the SOC of the corresponding energy storage submodule according to the target current value by using an ampere-hour integration method.

[0219] Specifically, the second determination module 1303 determines the SOC of the corresponding energy storage submodule using the ampere-hour integration method, including:

[0220] Obtaining the SOC of the energy storage submodule at the last moment, the capacity of the battery pack of the energy storage submodule, and the time difference, wherein the time difference is the difference between the last moment and the current moment;

[0221] The SOC of the energy storage submodule at the current moment is determined according to the SOC of the energy storage submodule at the previous moment, the capacity of the battery pack, the time difference and the target current value.

[0222] Wherein, during the charging process of the battery pack module of the energy storage submodule, the target current value is the charging current value of the battery pack module, and the SOC of the energy storage submodule at the current moment is determined according to the SOC of the energy storage submodule at the previous moment, the rated capacity of the battery pack, the time difference and the target current value, including:

[0223] determining an SOC change amount according to the rated capacity of the battery pack, the time difference and the target current value;

[0224] The sum of the SOC of the energy storage submodule at the previous moment and the SOC change is determined as the SOC of the energy storage submodule at the current moment.

[0225] Specifically, the SOC of the energy storage submodule at the current moment can be calculated by the following formula during the charging process:

[0226]

[0227] Among them, SOC t is the SOC of the energy storage submodule at the last moment; SOC t+Δt is the SOC of the energy storage submodule at the current moment; C is the rated capacity of the battery pack of the energy storage submodule, i E is the charging current value of the energy storage submodule, that is, i E is the current value flowing into the battery module; Δt is the time difference. The SOC change is the charging current value i of the energy storage submodule. E The product of the time difference Δt is then divided by the rated capacity of the battery pack.

[0228] During the discharge process of the battery pack module of the energy storage submodule, the target current value is the discharge current value of the battery pack module. Determining the SOC of the energy storage submodule at the current moment according to the SOC of the energy storage submodule at the previous moment, the rated capacity of the battery pack, the time difference and the target current value includes:

[0229] determining an SOC change amount according to the rated capacity of the battery pack, the time difference and the target current value;

[0230] The difference between the SOC of the energy storage submodule at the previous moment and the SOC change amount is determined as the SOC of the energy storage submodule at the current moment.

[0231] Specifically, during the discharge process, the SOC of the energy storage submodule at the current moment can be calculated by the following formula:

[0232]

[0233] Among them, SOC t is the SOC of the energy storage submodule at the last moment; SOC t+Δt is the SOC of the energy storage submodule at the current moment, wherein the SOC of the battery pack module when it is in the discharge state is t+Δt is gradually reduced; C is the rated capacity of the battery pack of the energy storage submodule, i Eis the discharge current value of the energy storage submodule, that is, i E is the current value flowing out of the battery module, Δt is the time difference. The SOC change is the charging current value i of the energy storage submodule. E The product of the time difference Δt is then divided by the rated capacity of the battery pack.

[0234] In some implementations of the present application, the second determination module 1303 is further configured to determine an initial SOC using an ampere-hour integration method.

[0235] Specifically, the second determination module 1303 obtains the power-off static time of the battery pack corresponding to the energy storage submodule, and determines the initial SOC of the ampere-hour integration method according to the power-off static time and the preset time threshold. If the power-off static time is greater than the preset time threshold, the second determination module 1303 obtains the SOC value determined by the energy storage submodule using the open circuit voltage as the initial SOC; if the power-off static time is less than the preset time threshold, the second determination module 1303 obtains the SOC value of the charging terminal of the battery pack corresponding to the energy storage submodule as the initial SOC.

[0236] In some implementations of the present application, the method in which the second determining module 1303 obtains the power-off idle time may include:

[0237] In response to the power-off instruction, detecting the voltage value across the capacitor of the power conversion module in the energy storage submodule;

[0238] Determine the moment when the voltage value drops to less than a preset voltage threshold as a first moment;

[0239] In response to a power-on instruction, determining the time when the energy storage system is powered on as a second time;

[0240] The power-off idle time duration is determined according to the second time and the first time.

[0241] In some embodiments of the present application, the second determination module 1303 is also used to send the target current value of the energy storage submodule to the battery management unit of the corresponding energy storage submodule, so that the battery management unit can obtain more accurate current data and can calibrate the current data according to the target current value. It can also avoid the battery pack management unit from losing current data due to a failure of the current sampling unit, thereby further improving the reliability of the system.

[0242] In some embodiments of the present application, the second determination module 1303 is also used to determine the switching frequency of each energy storage submodule within a preset time according to the switching instruction received by each energy storage submodule; determine whether the switching frequency is greater than the preset frequency threshold; if the switching frequency is greater than the preset frequency threshold, send a control instruction to the battery management unit of the corresponding energy storage submodule, and the control instruction is used to control the battery management unit to calculate the SOC using the target value. In this way, the SOC estimation inaccuracy caused by the current sampling unit in the battery pack module failing to sample current data due to high-frequency switching can be avoided.

[0243] 13 , some embodiments of the present application further provide an SOC determination device, including a memory and a processor, wherein a computer program is stored in the memory, and when the processor executes the computer program, the SOC determination method in one or more embodiments described above is implemented.

[0244] In some implementations, the SOC determination device may be the energy storage control system in the cascade energy storage system.

[0245] In other embodiments, the SOC determination device may be a power controller of an energy storage submodule in the cascade energy storage system.

[0246] In other embodiments, the SOC determination device may also include a processor and a memory respectively arranged in the energy storage control system and the power controller of each energy storage submodule in the cascade energy storage system, and the computer program is stored in the memory.

[0247] In some further embodiments, the SOC determination device may also be a separate computer device, which is used to be connected to the cascade energy storage system and to determine the SOC of each energy storage submodule by executing the SOC determination method.

[0248] 14 , some embodiments of the present application further provide a computer-readable storage medium having a computer program stored thereon, and when the computer program is executed by a processor, the SOC determination method in one or more embodiments described above is implemented.

[0249] 15 , some embodiments of the present application further provide a computer program product, including a computer program, which, when executed by a processor, implements the SOC determination method in one or more embodiments described above.

[0250] Some embodiments of the present application also provide a cascade energy storage system, wherein each branch of the cascade energy storage system includes a plurality of energy storage sub-modules connected in series, and the cascade energy storage system also includes a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the SOC determination method in one or more embodiments described above is implemented.

[0251] In some embodiments, the cascade energy storage system may be a high-voltage direct-mounted energy storage system as shown in Figures 1 and 2. In other embodiments, the cascade energy storage system may be an MMC energy storage system as shown in Figure 3. In other embodiments, the cascade energy storage system may also be a cascade energy storage system of other topological structures.

[0252] It can be understood by a person skilled in the art that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited thereto. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but are not limited thereto.

[0253] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

A method for determining a state of charge (SOC), characterized in that: The SOC determination method is applied to a cascade energy storage system, each branch of which includes a plurality of energy storage submodules connected in series. The method includes: obtaining a first current value of the branch where the energy storage submodule is located; determining a target current value of each of the energy storage submodules in the branch according to the first current value; and determining the SOC of the corresponding energy storage submodule according to the target current value. The method for determining the state of charge (SOC) according to claim 1, characterized in that: Determining the SOC of the corresponding energy storage submodule according to the target current value includes: determining the SOC of the corresponding energy storage submodule according to the target current value by using an ampere-hour integration method. The method for determining the state of charge (SOC) according to claim 2, characterized in that: The step of determining the SOC of the corresponding energy storage submodule according to the target current value by using the ampere-hour integration method includes: obtaining the SOC of the energy storage submodule at the previous moment, the rated capacity of the battery pack of the energy storage submodule, and the time difference, wherein the time difference is the difference between the previous moment and the current moment; and determining the SOC of the energy storage submodule at the current moment according to the SOC of the energy storage submodule at the previous moment, the rated capacity of the battery pack, the time difference, and the target current value. The method for determining the state of charge (SOC) according to claim 3 is characterized in that: The target current value is the charging current value of each energy storage submodule, and determining the SOC of the energy storage submodule at the current moment according to the SOC of the energy storage submodule at the previous moment, the rated capacity of the battery pack, the time difference and the target current value includes: determining the SOC change according to the rated capacity of the battery pack, the time difference and the target current value; and determining the sum of the SOC of the energy storage submodule at the previous moment and the SOC change as the SOC of the energy storage submodule at the current moment. The method for determining the state of charge (SOC) according to claim 3 is characterized in that: The target current value of each energy storage submodule is the discharge current value of each energy storage submodule, and determining the SOC of the energy storage submodule at the current moment according to the SOC of the energy storage submodule at the previous moment, the rated capacity of the battery pack, the time difference and the target current value includes: determining the SOC change according to the rated capacity of the battery pack, the time difference and the target current value; and subtracting the difference of the SOC change from the SOC of the energy storage submodule at the previous moment to determine the SOC of the energy storage submodule at the current moment. The method for determining the state of charge (SOC) according to any one of claims 4 or 5, characterized in that: The method further includes: obtaining the power-off static time length of the battery pack corresponding to the energy storage submodule; and determining the initial SOC of the ampere-hour integration method according to the power-off static time length and a preset time length threshold. The method for determining the state of charge (SOC) according to claim 6, characterized in that: The method of determining the initial SOC of the ampere-hour integration method based on the power-off standstill time and the preset time threshold includes: if the power-off standstill time is greater than the preset time threshold, obtaining the SOC value determined by the energy storage submodule using the open circuit voltage as the initial SOC; if the power-off standstill time is less than the preset time threshold, obtaining the SOC value of the charging terminal of the battery pack corresponding to the energy storage submodule as the initial SOC. The method for determining the state of charge (SOC) according to claim 7, characterized in that: The method for obtaining the power-off quiescent time comprises: responding to a power-off instruction, detecting the voltage value across the capacitor of the power conversion module in the energy storage submodule; determining the moment when the voltage value drops to less than a preset voltage threshold as a first moment; responding to a power-on instruction, determining the moment when the energy storage system is powered on as a second moment; and determining the power-off quiescent time according to the second moment and the first moment. The method for determining the state of charge (SOC) according to any one of claims 1 to 8, characterized in that: Determining the target current value of each energy storage sub-module in the branch according to the first current value includes: obtaining the second current value of the voltage-equalizing resistor of the power conversion module in the energy storage sub-module and the third current value of the load element impedance of the power conversion module; determining the target current value according to the first current value, the second current value and the third current value. The method for determining the state of charge (SOC) according to any one of claims 1 to 9, characterized in that: The method further includes: sending the target current value of the energy storage submodule to a battery management unit corresponding to the energy storage submodule. The method for determining the state of charge (SOC) according to claim 10, characterized in that: The method also includes: determining the switching frequency of each energy storage submodule within a preset time according to the switching instruction received by each energy storage submodule; judging whether the switching frequency is greater than a preset frequency threshold; if the switching frequency is greater than the preset frequency threshold, sending a control instruction to the battery management unit corresponding to the energy storage submodule, and the control instruction is used to control the battery management unit to calculate the SOC using the target current value. A cascade energy storage system, characterized in that: The cascade energy storage system includes multiple branches, each of which includes a current measuring unit and multiple energy storage sub-modules connected in series, and the current measuring unit is used to obtain a first current value of the branch; the first current value is used to determine a target current value of each energy storage sub-module in the branch, and the target current value is used to determine the SOC of the corresponding energy storage sub-module. The cascade energy storage system according to claim 12 is characterized in that: Each of the energy storage submodules includes a power conversion module and a battery pack module; the cascade energy storage system also includes an energy storage control system, which is connected to the current measurement unit and the power conversion module; the energy storage control system is used to obtain the first current value from the current measurement unit and send the first current value to the power conversion module on the corresponding branch; the power conversion module is used to determine the target current value of the energy storage submodule on the corresponding branch according to the first current value, and determine the SOC of the battery pack module of the corresponding energy storage submodule according to the target current value. The cascade energy storage system according to claim 12 is characterized in that: The cascade energy storage system also includes an energy storage control system, which is connected to the current measurement unit and each of the energy storage sub-modules; the energy storage control system is used to obtain the first current value from the current measurement unit, determine the target current value of the energy storage sub-module on the corresponding branch according to the first current value, and determine the SOC of the battery pack module of the corresponding energy storage sub-module according to the target current value. A SOC determination device, characterized in that: The SOC determination device is applied to a cascade energy storage system, each branch of the cascade energy storage system includes a plurality of energy storage sub-modules connected in series, and the SOC determination device includes: an acquisition module, used to acquire a first current value of the branch where the energy storage sub-module is located; a first determination module, used to determine a target current value of each of the energy storage sub-modules in the branch according to the first current value; and a second determination module, used to determine the SOC of the corresponding energy storage sub-module according to the target current value. A SOC determination device comprises a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the method for determining the state of charge (SOC) according to any one of claims 1 to 11 is implemented. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method for determining the state of charge (SOC) according to any one of claims 1 to 11 is implemented. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the method for determining the state of charge (SOC) described in any one of claims 1 to 11 is implemented. A cascade energy storage system, characterized in that: Each branch of the cascade energy storage system includes a plurality of energy storage submodules connected in series. The cascade energy storage system also includes a memory and a processor. The memory stores a computer program. When the processor executes the computer program, the method for determining the state of charge (SOC) according to any one of claims 1 to 11 is implemented.

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