Grid-connected control method, device and system of energy storage device and storage medium

Abstract

The embodiment of the invention provides a grid-connected control method of an energy storage device, an energy storage control unit, the energy storage device, an energy storage system and a storage medium, and relates to the technical field of energy storage, and the method comprises the steps: controlling an energy transmission main line to be connected with a DC bus, and controlling the energy storage unit to be disconnected with a corresponding rectification circuit during grid-connected starting, the voltage-sharing capacitor is pre-charged by the power system; controlling the energy storage units of the energy storage sub-modules to be communicated with the corresponding rectification circuits according to a first control strategy under the condition that the voltage-sharing capacitor pre-charging completion condition is satisfied, performing pre-charging processing, and controlling the energy storage units of the energy storage sub-modules to be communicated with the corresponding rectification circuits according to a second control strategy under the condition that the energy storage charging condition is satisfied. And controlling the energy storage units of the energy storage sub-modules to be communicated with the corresponding rectification circuits according to the second control strategy, and carrying out charging processing. According to the embodiment of the invention, the instantaneous impact current and voltage generated in the grid connection process can be effectively reduced, the charging process is more stable, smooth grid connection can be ensured, and the reliability and safety of grid connection are improved.

Description

Grid-connected control method, device, system and storage medium for energy storage device Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to a grid-connected control method for an energy storage device, an energy storage control unit, an energy storage device, an energy storage system, and a storage medium. Background Art

[0002] Currently, energy storage devices can be charged by connecting to the DC bus of the power system. The energy storage device can be of various types, for example, an energy storage device including multiple energy storage sub-modules connected in series. By connecting the energy storage device to the DC bus, the power system outputs electrical energy through the DC bus to charge the energy storage device. When the DC bus is energized, transient surge currents and surge voltages are generated during the process of connecting the energy storage device to the DC bus for grid connection. If the transient surge currents and surge voltages are too large, they will cause significant damage to the energy storage device, reducing its service life and affecting its safety. In addition, during the process of connecting the energy storage device to the grid, it may cause damage to the connected power grid and other equipment in the grid.

[0003] Summary of the Invention

[0004] The present disclosure provides a grid-connected control method for an energy storage device, an energy storage control unit, an energy storage device, an energy storage system, and a storage medium, which can effectively improve the reliability and safety of the grid connection of the energy storage device.

[0005] A first aspect of the present disclosure provides a grid-connected control method for an energy storage device, wherein the energy storage device includes multiple energy storage sub-modules, each of which includes a power unit and an energy storage unit; the power unit includes a rectifier circuit and a grading capacitor; the energy storage unit and the grading capacitor are respectively connected in parallel to the output end of the rectifier circuit, and the energy storage unit and the output end of the rectifier circuit can be connected and disconnected; the input ends of the respective rectifier circuits are connected in series to form an energy transmission main line, and the energy transmission main line can be connected and disconnected to the DC bus of the power system; the method includes: at grid-connected startup, controlling the energy transmission main line to be connected to the DC bus and controlling the energy storage unit to be disconnected from the corresponding rectifier circuit, so that the power system pre-charges the grading capacitor; when it is determined that the pre-charging completion condition of the grading capacitor is met, controlling the energy storage unit of the energy storage sub-module to be connected to the corresponding rectifier circuit according to a first control strategy to perform pre-charging processing, and when it is determined that the energy storage charging condition is met, controlling the energy storage unit of the energy storage sub-module to be connected to the corresponding rectifier circuit according to a second control strategy to perform charging processing.

[0006] The grid-connected control method disclosed in the present invention controls the connection of the energy transmission main line with the power system and controls the disconnection of the energy storage unit with the corresponding rectifier circuit at the time of grid-connected startup, pre-charges the equalizing capacitor, and reduces the voltage difference between the voltage of the energy transmission main line and the DC bus voltage by increasing the voltage of the equalizing capacitor, thereby reducing the instantaneous impact current and instantaneous impact voltage generated during the grid-connected process, reducing damage to the energy storage device, improving the service life of the energy storage device and the safety of use of the energy storage device, and reducing damage to the connected power grid and other equipment in the power grid; after completing the pre-charging process of the equalizing capacitor, the energy storage submodule is controlled to perform pre-charging and charging according to the control strategy, which can make the charging process more stable, reduce damage to the power grid and other equipment in the power grid, ensure smooth grid connection, and improve the reliability and safety of the grid connection of the energy storage device.

[0007] Optionally, controlling the energy storage unit of the energy storage submodule to be connected to the corresponding rectifier circuit according to the first control strategy to perform pre-charging processing includes: selecting the energy storage submodule as the pre-charging energy storage submodule according to the capacitor voltage information of the equalizing capacitor, controlling the energy storage unit of the pre-charging energy storage submodule to be connected to the corresponding rectifier circuit, and performing pre-charging processing.

[0008] The energy storage submodule is selected as the pre-charge energy storage submodule according to the capacitor voltage information of the voltage-equalizing capacitor for pre-charging, which can adjust the voltages of the energy storage units of the energy storage submodule to be similar, thereby improving the reliability of grid connection and extending the service life of the energy storage device.

[0009] Optionally, an energy storage submodule is selected as a pre-charge energy storage submodule based on the capacitor voltage information of the equalizing capacitor: a first participating number corresponding to the energy storage submodules participating in pre-charging is determined; when the first participating number is less than the total number of the energy storage submodules, a first change in the number of energy storage submodules participating in pre-charging is determined based on the first participating number; and the energy storage submodule is selected as the pre-charge energy storage submodule by utilizing a capacitor voltage sorting balancing strategy and based on the capacitor voltage information of the equalizing capacitor and the first change.

[0010] By using the capacitor voltage sorting and balancing strategy to select the energy storage submodule as the pre-charge energy storage submodule for pre-charging, the voltages of the energy storage units of the energy storage submodule can be adjusted to be similar, thereby improving the reliability of grid connection and extending the service life of the energy storage device.

[0011] Optionally, the method of utilizing the capacitor voltage sorting balancing strategy and selecting the energy storage submodule as the pre-charge energy storage submodule based on the capacitor voltage information of the equalizing capacitor and the first change amount includes: if the first change amount is equal to 0 and the maximum capacitor voltage deviation is greater than the voltage deviation threshold, then selecting the energy storage submodule with the smallest equalizing capacitor voltage from all energy storage submodules that are not used as pre-charge energy storage submodules as the new pre-charge energy storage submodule; and selecting the pre-charge energy storage submodule with the largest equalizing capacitor voltage from all pre-charge energy storage submodules as the removed pre-charge energy storage submodule.

[0012] Based on the change in the number of energy storage submodules participating in pre-charging, the voltage ranking of the grading capacitors, and the voltage deviation of the grading capacitors, the energy storage submodules are selected and controlled for pre-charging when the change is equal to 0. This can adjust the voltages of the energy storage units of the energy storage submodules to be similar, thereby improving the reliability and service life of the energy storage units in the grid.

[0013] Optionally, the method of utilizing the capacitor voltage sorting balancing strategy and selecting the energy storage submodule as the pre-charge energy storage submodule based on the capacitor voltage information of the equalizing capacitor and the first change amount includes: when the first change amount is greater than 0 and the power system outputs electric energy to the main energy transmission line, selecting the energy storage submodule with the lowest equalizing capacitor voltage and the same number as the first change amount from all energy storage submodules that are not used as pre-charge energy storage submodules as new pre-charge energy storage submodules; when the first change amount is greater than 0 and the main energy transmission line outputs electric energy to the power system, selecting the energy storage submodule with the highest equalizing capacitor voltage and the same number as the first change amount from all energy storage submodules that are not used as pre-charge energy storage submodules as new pre-charge energy storage submodules.

[0014] Based on the change in the number of energy storage submodules participating in pre-charging and the voltage sorting of the balancing capacitors, when the change is greater than 0, the energy storage submodules are selected and controlled for pre-charging. This can adjust the voltages of the energy storage units of the energy storage submodules to be similar, thereby improving the reliability and service life of the energy storage units when connected to the grid.

[0015] Optionally, the utilization of the capacitor voltage sorting balancing strategy and selection of the energy storage submodule as the pre-charge energy storage submodule based on the capacitor voltage information of the equalizing capacitor and the first change amount includes: when the first change amount is less than 0 and the power system outputs electric energy to the main energy transmission line, selecting the energy storage submodule with the highest equalizing capacitor voltage and the same number as the absolute value of the first change amount from all pre-charge energy storage submodules as the pre-charge energy storage submodule to be cut off; when the first change amount is less than 0 and the main energy transmission line outputs electric energy to the power system, selecting the energy storage submodule with the lowest equalizing capacitor voltage and the same number as the absolute value of the first change amount from all pre-charge energy storage submodules as the cut-off energy storage submodule.

[0016] Based on the change in the number of energy storage submodules participating in pre-charging and the voltage sorting of the balancing capacitors, when the change is less than 0, the energy storage submodules are selected and controlled for pre-charging. This can adjust the voltages of the energy storage units of the energy storage submodules to be similar, thereby improving the reliability and service life of the energy storage units when connected to the grid.

[0017] Optionally, controlling the energy storage unit of the energy storage submodule to be connected to the corresponding rectifier circuit according to the second control strategy for charging processing includes: controlling the energy storage unit of the energy storage submodule to be connected to the corresponding rectifier circuit; selecting the energy storage submodule as the charging energy storage submodule according to the SOC information of the energy storage unit, and controlling the energy storage unit of the charging energy storage submodule to be connected to the corresponding rectifier circuit for charging processing.

[0018] By selecting the energy storage submodule as the charging energy storage submodule based on the SOC information of the energy storage unit for charging, the stability of the DC bus voltage and the voltage of the main energy transmission line can be maintained, and the SOC of each energy storage submodule can be adjusted to be similar, making the charging process more stable, thereby improving the reliability of the energy storage device connected to the grid and the stability and safety of charging.

[0019] Optionally, selecting the energy storage submodule as the charging energy storage submodule based on the SOC information of the energy storage unit includes: determining a second participating number corresponding to the energy storage submodules participating in charging; when the second participating number is less than the total number of the energy storage submodules, determining a second change in the number of energy storage submodules participating in charging based on the second participating number; and selecting the energy storage submodule as the charging energy storage submodule by utilizing an SOC sorting balancing strategy and based on the SOC information of the energy storage submodule and the second change.

[0020] By using the SOC sorting and balancing strategy to select the energy storage submodule as the charging energy storage submodule for charging, the stability of the DC bus voltage and the voltage of the main energy transmission line can be maintained, and the SOC of each energy storage submodule can be adjusted to be similar, making the charging process more stable and improving the reliability of the energy storage device's grid connection and the stability of charging.

[0021] Optionally, the method of utilizing the SOC sorting and balancing strategy and selecting the energy storage submodule as the charging energy storage submodule based on the SOC information of the energy storage submodule and the second variation, and controlling the energy storage unit of the charging energy storage submodule to charge includes: if the second variation is equal to 0 and the maximum SOC deviation is greater than the SOC deviation threshold, selecting the energy storage submodule with the smallest SOC from all energy storage submodules that are not used as charging energy storage submodules as the new charging energy storage submodule; and selecting the energy storage submodule with the largest SOC from all charging energy storage submodules as the removed energy storage submodule; wherein the maximum SOC deviation is the difference between the maximum SOC and the minimum SOC of the energy storage submodule.

[0022] Based on the change in the number of energy storage submodules involved in charging, the battery SOC ranking, and the SOC deviation, the energy storage submodule can be selected and controlled for charging when the change is equal to 0. This can maintain the stability of the DC bus voltage and the voltage of the main energy transmission line, adjust the SOC of each energy storage submodule to be similar, make the charging process more stable, and improve the reliability of the energy storage unit's grid connection.

[0023] Optionally, the utilizing the SOC sorting and balancing strategy and selecting the energy storage submodule as the charging energy storage submodule based on the SOC information of the energy storage submodule and the second variation, and controlling the energy storage unit of the charging energy storage submodule to charge includes: when the second variation is greater than 0 and the power system outputs electric energy to the main energy transmission line, selecting the energy storage submodule with the lowest SOC and the same number as the second variation from all energy storage submodules that are not used as charging energy storage submodules as new charging energy storage submodules; when the second variation is greater than 0 and the main energy transmission line outputs electric energy to the power system, selecting the energy storage submodule with the highest SOC and the same number as the second variation from all energy storage submodules that are not used as charging energy storage submodules as new charging energy storage submodules.

[0024] Based on the change in the number of energy storage submodules involved in charging and the battery SOC ranking, the energy storage submodules can be selected and controlled for charging when the change is less than 0. This can maintain the stability of the DC bus voltage and the voltage of the main energy transmission line, adjust the SOC of each energy storage submodule to be similar, make the charging process more stable, and improve the reliability of the energy storage unit's grid connection.

[0025] Optionally, the use of the SOC sorting and balancing strategy and based on the SOC information of the energy storage submodule and the second variation, selecting the energy storage submodule as the charging energy storage submodule, and controlling the energy storage unit of the charging energy storage submodule to charge includes: when the second variation is less than 0 and the power system outputs electric energy to the main energy transmission line, selecting the energy storage submodule with the highest SOC and the same number as the absolute value of the second variation from all the charging energy storage submodules as the cut-off energy storage submodules; when the second variation is less than 0 and the main energy transmission line outputs electric energy to the power system, selecting the energy storage submodule with the lowest SOC and the same number as the absolute value of the second variation from all the charging energy storage submodules as the cut-off energy storage submodules.

[0026] Based on the change in the number of energy storage submodules involved in charging and the battery SOC ranking, the energy storage submodules can be selected and controlled for charging when the change is less than 0. This can maintain the stability of the DC bus voltage and the voltage of the main energy transmission line, adjust the SOC of each energy storage submodule to be similar, make the charging process more stable, and improve the reliability of the energy storage unit's grid connection.

[0027] Optionally, PI control processing is performed based on a reference current and a real-time current on the main energy transmission line to determine the first participating number and the second participating number.

[0028] PI control processing is performed based on the reference current and the real-time current on the main energy transmission line to determine the number of energy storage sub-modules involved in pre-charging and charging. This can improve the accuracy of controlling the voltage of the main energy transmission line and enhance the stability of the charging process.

[0029] Optionally, the energy storage unit includes: a battery pack; the battery pack and a switchable pre-charging circuit are connected in series to form an energy storage circuit, and the energy storage circuit is connected in parallel to the output end of the corresponding rectifier circuit; the pre-charging circuit includes a first switchable circuit and a second switchable circuit in parallel, and a first starting resistor is provided in the first circuit; the method includes: when the energy storage unit of the energy storage sub-module participating in pre-charging is connected to the corresponding rectifier circuit, controlling the first circuit to be connected and controlling the second circuit to be disconnected, so as to use the first starting resistor for current limiting; or, when the energy storage unit of the energy storage sub-module participating in charging is connected to the corresponding rectifier circuit, controlling the second circuit to be connected, so as to short-circuit the first starting resistor.

[0030] By using the first starting resistor to limit the current in the pre-charging stage, the peak current can be limited, the impact current of the battery pack can be reduced, the safety of the battery pack can be improved, and the service life of the battery pack can be extended; short-circuiting the first starting resistor in the charging stage can reduce the consumption of electrical energy.

[0031] Optionally, controlling the energy storage unit of the energy storage sub-module to be connected to the corresponding rectifier circuit includes: controlling the energy storage units of all energy storage sub-modules to be connected to the corresponding rectifier circuit, and using all first starting resistors for current limiting; determining the delay period based on the charging time constant of the equalizing capacitor; after the delay period, short-circuiting all first starting resistors while all energy storage sub-modules are connected to the corresponding rectifier circuit.

[0032] By limiting the current through the first starting resistor, the peak current can be limited, the safety of the battery pack can be improved, and a protective effect can be played; after the delay time, all the first starting resistors are short-circuited to reduce the power consumed by the first starting resistors.

[0033] Optionally, the conditions for completing the pre-charging of the equalizing capacitor include: the voltage of the main energy transmission line is greater than the voltage threshold of the main energy transmission line; and / or, the energy storage charging conditions include: the difference between the average voltage of the equalizing capacitor and the average voltage of the corresponding energy storage unit is less than the voltage difference threshold.

[0034] By setting the conditions for completing the pre-charging of the equalizing capacitor and the energy storage charging conditions, the difference between the voltage of the main energy transmission line and the voltage of the DC bus can be reduced, and the damage caused to the energy storage device by the instantaneous impact current and instantaneous impact voltage generated during the grid connection process can be reduced, making the charging process more stable and improving the reliability of the energy storage device's grid connection.

[0035] Optionally, the main energy transmission line is connected to the DC bus through a current limiting circuit that can be switched on and off; the current limiting circuit includes a second starting resistor and a cut-off switch connected in parallel with the second starting resistor; the method includes: at grid-connected startup, controlling the cut-off switch to be disconnected to use the second starting resistor for current limiting; when it is determined that the conditions for pre-charging of the equalizing capacitor are met, controlling the cut-off switch to be closed to short-circuit the second starting resistor.

[0036] By setting a second starting resistor, the damage to the energy storage device caused by the instantaneous surge current and instantaneous surge voltage generated during the grid connection process is reduced, making the charging process more stable and improving the reliability of the energy storage device's grid connection; when it is determined that the conditions for pre-charging the equalizing capacitor are met, the second starting resistor is short-circuited to reduce the power consumed by the second starting resistor.

[0037] A second aspect of the present disclosure provides an energy storage control unit, wherein the energy storage device includes multiple energy storage sub-modules, the energy storage sub-module includes a power unit and an energy storage unit; the power unit includes a rectifier circuit and a grading capacitor; the energy storage unit and the grading capacitor are respectively connected in parallel with the output end of the rectifier circuit, and the energy storage unit and the output end of the rectifier circuit can be connected and disconnected; the input ends of the respective rectifier circuits are connected in series to form an energy transmission main line, and the energy transmission main line can be connected and disconnected with the DC bus of the power system; the energy storage control unit includes: a grading capacitor pre-charging module, which is used to control the energy transmission main line to be connected to the DC bus and control the energy storage unit to be disconnected from the corresponding rectifier circuit during grid-connected startup, so that the power system pre-charges the grading capacitor; a pre-charging control module, which is used to control the energy storage unit of the energy storage sub-module to be connected to the corresponding rectifier circuit according to a first control strategy for pre-charging processing; and a charging control module, which is used to control the energy storage unit of the energy storage sub-module to be connected to the corresponding rectifier circuit according to a second control strategy for charging processing.

[0038] The energy storage control unit disclosed in the present invention controls the connection of the energy transmission main line with the power system and controls the disconnection of the energy storage unit with the corresponding rectifier circuit at the time of grid-connected startup, and pre-charges the voltage-equalizing capacitor, which can reduce the difference between the voltage of the energy transmission main line and the voltage of the DC bus, and can reduce the damage to the energy storage device caused by the transient impact current and transient impact voltage generated during the grid-connected process, thereby improving the service life of the energy storage device and the safety of the use of the energy storage device, and can reduce the damage to the connected power grid and other equipment in the power grid; after completing the pre-charging process of the voltage-equalizing capacitor, the energy storage sub-module is selected for pre-charging and charging based on the control strategy, which can make the charging process more stable, reduce the damage to the power grid and other equipment in the power grid, ensure smooth grid connection, and improve the reliability and safety of the grid connection of the energy storage device.

[0039] A third aspect of the present disclosure provides an energy storage control unit, comprising: a memory; and a processor coupled to the memory, wherein the processor is configured to execute the method provided by the first aspect of the present disclosure based on instructions stored in the memory.

[0040] The energy storage control unit disclosed in the present invention has the advantages of the grid-connected control method of the energy storage device disclosed in the present invention.

[0041] A fourth aspect of the present disclosure provides an energy storage system, comprising an energy storage device and the energy storage control unit provided in the second aspect or the third aspect of the present disclosure.

[0042] The energy storage system disclosed herein has the advantages of the energy storage control unit and the energy storage device disclosed herein.

[0043] A fifth aspect of the present disclosure provides an energy storage device, comprising: a plurality of energy storage submodules, wherein the energy storage submodules include a power unit and an energy storage unit; the power unit includes a rectifier circuit and a voltage-equalizing capacitor; the energy storage unit and the voltage-equalizing capacitor are respectively connected in parallel with the output end of the rectifier circuit, and the energy storage unit and the output end of the rectifier circuit can be connected in an on-off manner; the input ends of the respective rectifier circuits are connected in series to form a main energy transmission line, and the main energy transmission line can be connected in an on-off manner to the DC bus of the power system.

[0044] The energy storage device disclosed herein adopts a modular multi-level cascade structure, which can improve the configuration capacity of the energy storage device and enable independent control of each energy storage module subunit. The power unit and voltage-sharing capacitor can improve charging stability, have advantages such as good harmonic characteristics and low equivalent switching frequency, and can control the pre-charging and charging of each energy storage module subunit, which can improve the safety of the energy storage device.

[0045] Optionally, a switchable pre-charging circuit is provided in the connection circuit between the energy storage unit and the output end of the rectifier circuit.

[0046] By setting up a pre-charge circuit, the peak current can be limited, the impact current of the battery pack can be reduced, and the safety of the battery pack can be improved.

[0047] Optionally, the energy storage unit includes: a battery pack; the battery pack and the pre-charging circuit are connected in series to form an energy storage circuit; and the energy storage circuit is connected in parallel to the output end of the corresponding rectifier circuit.

[0048] The energy storage unit uses a battery pack as its energy source. Through the charging and discharging functions of the battery pack, it can provide stable electricity for a long time. The peak current of the battery pack is limited by the pre-charging circuit, which plays a protective role and reduces the impact current of the battery pack, which can improve the safety of the battery pack and extend the service life of the battery pack.

[0049] Optionally, the pre-charging circuit includes a first circuit that can be switched on and off and a second circuit that can be switched on and off in parallel; a first starting resistor and a first switch that are connected in series are provided in the first circuit; and a second switch is provided in the second circuit.

[0050] The pre-charge circuit set up can start the first starting resistor by closing the first switch when the battery pack is in the initial stage of charging and discharging, and close the second switch to short-circuit the starting resistor after the battery pack is working normally. It can limit the peak current, reduce the impact current of the battery pack, and improve the safety of the battery pack.

[0051] Optionally, the main energy transmission line is connected to the DC bus through a switchable current limiting circuit.

[0052] By setting a current limiting circuit, the instantaneous impact current generated when the energy storage device is switched to the DC bus in parallel can be reduced, which can improve the safety of the energy storage device.

[0053] The current limiting circuit includes a second starting resistor and a cut-off switch connected in parallel with the second starting resistor.

[0054] The peak current can be limited by the second starting resistor to play a protective role; when the energy storage device is in the working state, the second starting resistor is short-circuited to reduce the power consumed by the starting resistor.

[0055] A sixth aspect of the present disclosure provides a computer-readable storage medium, which stores computer instructions, and the instructions are executed by a processor to execute the grid-connected control method for the energy storage device provided in the first aspect of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0057] FIG1A is a schematic diagram of the structure of an energy storage system in the prior art; FIG1B is a schematic diagram of the connection between a control subunit and other units in an energy storage submodule in the prior art; FIG1C is another schematic diagram of the structure of a power unit in an energy storage submodule in the prior art;

[0058] FIG2 is a flow chart of some embodiments of the grid-connected control method for an energy storage device disclosed herein;

[0059] FIG3A is a schematic diagram of the structure of some embodiments of the energy storage system of the present disclosure; FIG3B is a schematic diagram of the connection between the control subunit and other units in the energy storage submodule of the energy storage system of the present disclosure; FIG3C is another schematic diagram of the structure of the current limiting circuit of the present disclosure;

[0060] FIG4 is a schematic diagram of a process of precharging according to capacitor voltage information of a grading capacitor in some embodiments of the grid-connected control method of an energy storage device disclosed herein;

[0061] FIG5 is a schematic diagram of a flow chart of controlling pre-charging of an energy storage unit using a capacitor voltage sequencing and balancing strategy in some embodiments of the grid-connected control method of an energy storage device disclosed herein;

[0062] FIG6 is a schematic diagram of a process of charging according to SOC information of an energy storage submodule in some embodiments of the grid-connected control method of an energy storage device disclosed herein;

[0063] FIG7 is a schematic diagram of a flow chart of charging control according to an SOC sorting and balancing strategy in some embodiments of the grid-connected control method of an energy storage device disclosed herein;

[0064] FIG8 is a schematic diagram of a control principle for determining a first participant quantity and a second participant quantity based on a PI control process;

[0065] FIG9 is a schematic diagram of a first module of some embodiments of an energy storage control unit disclosed herein;

[0066] FIG10 is a schematic diagram of a second module of some embodiments of the energy storage control unit disclosed herein;

[0067] FIG11 is a schematic diagram of a third module of some embodiments of the energy storage control unit disclosed herein. DETAILED DESCRIPTION

[0068] The following detailed description of the embodiments of the present application is provided in conjunction with the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present application, but are not intended to limit the scope of the present application, that is, the present application is not limited to the described embodiments.

[0069] 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).

[0070] This application uses descriptions of directions or positional relationships such as "up", "down", "top", "bottom", "front", "back", "inside" and "outside" to facilitate the description of this application, and does not indicate or imply that the device referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, it should not be understood as limiting the scope of protection of this application.

[0071] Furthermore, the terms "first," "second," and "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. "Perpendicular" does not strictly refer to perpendicularity, but rather to the tolerances allowed. "Parallel" does not strictly refer to parallelism, but rather to the tolerances allowed. The directional terms used in the following description refer to the directions shown in the figures and are not intended to limit the specific structure of this application.

[0072] It should also be noted that, in the description of this application, unless otherwise specified or limited, the terms "installed," "connected," and "connected" should be understood broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to direct connections or indirect connections through an intermediary. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.

[0073] In related technologies known to the inventors, as shown in FIG1A , an energy storage system includes an energy storage control unit 11 and an energy storage device. The energy storage device employs a modular multi-level cascade structure, comprising series-connected energy storage submodules 121, 122, ..., 12n. The power system can be any of a variety of power systems, such as a flexible direct current transmission system.

[0074] The power system includes a DC bus, etc. The DC bus includes a positive DC bus 21 and a negative DC bus 22. The two ends of the energy storage device are respectively connected to the positive DC bus 21 and the negative DC bus 22. The two ends of the energy storage device can also be respectively connected to the positive DC bus 21 and the neutral metal return line. A switch K0 is set on the line connecting one end of the energy storage device and the positive DC bus 21. It can be a variety of switches. When the energy storage device is charging, the energy storage control unit 11 controls K0 to close, and the electric energy of the power system is input into the energy storage device through the DC bus to charge the energy storage device.

[0075] Reactors can be installed at one or both ends of the energy storage device. For example, reactors 13 and 14 are connected to the positive DC bus 21 and the negative DC bus 22 at both ends of the energy storage device, respectively, to reduce the instantaneous surge current generated when the energy storage device is connected to the grid. The energy storage submodule includes a power unit 1221 and an energy storage unit 1222. Energy storage unit 1222 and power unit 1221 can be connected via a bus, etc. Energy storage unit 1222 transmits electrical energy and is charged through power unit 1221. Energy storage unit 1222 includes a battery pack 1223, which can be a lithium battery pack, etc.

[0076] Power unit 1221 can adopt various circuit structures. For example, power unit 1221 includes switch K5, a rectifier circuit, a grading capacitor C0, and a grading resistor R0. K5 is a bypass switch and can be a variety of switch devices. Energy storage unit 1222, grading capacitor C0, and grading resistor R0 are all connected in parallel with the output of the rectifier circuit. The inputs of the rectifier circuits are connected in series to form a main energy transmission line 15 connected to the DC bus of the power system.

[0077] The rectifier circuit can be a half-bridge, full-bridge, or quasi-full-bridge rectifier circuit. As shown in FIG1A , power unit 1221 includes a half-bridge rectifier circuit composed of transistors T1 and T2 and diodes D1 and D2. As shown in FIG1C , power unit 1221 includes a full-bridge rectifier circuit composed of transistors T1, T2, T3, and T4 and diodes D1, D2, D3, and D4.

[0078] As shown in Figure 1B, each energy storage submodule is equipped with a control subunit 1224, which is connected to the energy storage control unit 11. Control subunits 1224 receive control instructions from the energy storage control unit 11 and execute corresponding functions based on the control instructions. When the DC bus is energized, the energy storage control unit 11 controls K0 to close and sends a charging control instruction to control subunit 1224. Based on the charging control instruction, control subunit 1224 controls switch K5 to open and turns the rectifier circuit on.

[0079] During the process of connecting the energy storage device to the DC bus for grid connection, instantaneous surge current and surge voltage are generated. If the instantaneous surge current and surge voltage are too large, they will cause significant damage to the energy storage device, reducing its service life and affecting its safety. In addition, during the process of grid connection, the energy storage device may cause damage to the connected power grid and other equipment in the power grid. A current or voltage acquisition device can be set on the main energy transmission line 15, and the current or voltage acquisition device sends the collected voltage or current information to the energy storage control unit 11. If the instantaneous surge current and surge voltage generated during the grid connection process are too large, the energy storage control unit 11 determines that the energy storage device needs to be protected and controls the switch K0 to be disconnected, causing the energy storage device to fail to connect to the grid, affecting the stability of the grid connection.

[0080] The present disclosure provides a technical solution for grid-connected control of an energy storage device. When grid-connected startup occurs, the power system is controlled to pre-charge a grading capacitor. When it is determined that the pre-charging conditions of the energy storage unit are met, the energy storage unit is controlled to perform pre-charging based on a first control strategy. When it is determined that the charging conditions of the energy storage unit are met, the energy storage unit is controlled to perform charging based on a second control strategy. This solution can reduce the transient surge current and transient surge voltage generated during the grid-connected process, thereby increasing the service life and safety of the energy storage device, and reducing damage to the connected power grid and other equipment in the power grid, thereby making the charging process more stable, ensuring smooth grid connection, and improving the reliability and safety of the grid connection of the energy storage device.

[0081] FIG2 is a flow chart of some embodiments of the grid-connected control method for an energy storage device disclosed herein, as shown in FIG2 :

[0082] Step 201 , during grid-connected startup, the main energy transmission line is controlled to be connected to the DC bus and the energy storage unit is controlled to be disconnected from the corresponding rectifier circuit, so that the power system pre-charges the grading capacitor.

[0083] Step 202: Control the energy storage unit of the energy storage submodule to be connected to the corresponding rectifier circuit according to the first control strategy to perform pre-charging processing. When it is determined that the energy storage charging conditions are met, control the energy storage unit of the energy storage submodule to be connected to the corresponding rectifier circuit according to the second control strategy to perform charging processing.

[0084] At the time of grid connection startup, the main energy transmission line is controlled to be connected to the power system and the energy storage unit is controlled to be disconnected from the corresponding rectifier circuit, and the equalizing capacitor is pre-charged. This can reduce the difference between the voltage of the main energy transmission line and the DC bus voltage, reduce the damage to the energy storage device caused by the instantaneous impact current and instantaneous impact voltage generated during the grid connection process, improve the service life of the energy storage device and the safety of the use of the energy storage device, and reduce the damage to the connected power grid and other equipment in the power grid; after completing the pre-charging of the equalizing capacitor, the energy storage sub-module is controlled to perform pre-charging and charging according to the control strategy, which can make the charging process more stable, reduce the damage to the power grid and other equipment in the power grid, ensure smooth grid connection and improve the reliability and safety of the energy storage device connected to the grid.

[0085] In some embodiments, the first control strategy can be a variety of control strategies. In addition to the first control strategy in the embodiment of the present disclosure, the first control strategy can also be a variety of other control strategies. For example, controlling the energy storage unit of the energy storage submodule to perform pre-charging processing according to the first control strategy includes: when it is determined that the pre-charging completion condition of the equalizing capacitor is met, selecting the energy storage submodule as the pre-charging energy storage submodule according to the capacitor voltage information of the equalizing capacitor, controlling the energy storage unit of the pre-charging energy storage submodule to be connected to the corresponding rectifier circuit, and performing pre-charging processing.

[0086] The second control strategy can be a variety of control strategies. In addition to the second control strategy in the embodiment of the present disclosure, the second control strategy can also be a variety of other control strategies. For example, controlling the energy storage unit of the energy storage submodule to perform charging processing according to the second control strategy includes: when it is determined that the energy storage charging conditions are met, selecting the energy storage submodule as the charging energy storage submodule according to the SOC information of the energy storage submodule, and controlling the energy storage unit of the charging energy storage submodule to be connected to the corresponding rectifier circuit for charging processing. The SOC (State of Charge) information of the energy storage submodule is the SOC information of the energy storage unit 1222 of the energy storage submodule, that is, the SOC information of the battery pack 1223 in the energy storage unit 1222.

[0087] After completing the pre-charging of the equalizing capacitor, the energy storage submodule is selected for pre-charging and charging according to the capacitor voltage information of the equalizing capacitor and the SOC information of the energy storage unit. This can make the charging process more stable, ensure smooth grid connection, and improve the reliability and safety of the energy storage device connected to the grid.

[0088] In some embodiments, a first switching circuit is provided in the connection between the energy storage unit 1222 and the output end of the rectifier circuit to enable on / off connection between the energy storage unit 1222 and the rectifier circuit. By controlling the first switching circuit, the energy storage unit 1222 and the output end of the rectifier circuit can be connected and disconnected. The first switching circuit can be a variety of switching circuits, for example, the first switching circuit includes a pre-charge circuit.

[0089] Energy storage unit 1222 can adopt various circuit structures. For example, as shown in Figures 3A and 3B, energy storage unit 1222 includes a battery pack 1223 for storing electrical energy. Battery pack 1223 and a pre-charge circuit are connected in series to form an energy storage circuit. The number of pre-charge circuits can be one or more, and can be provided on one or both sides of battery pack 1223.

[0090] The pre-charge circuit can adopt a variety of structures. For example, the pre-charge circuit includes a first circuit 1225 and a second circuit 1226 connected in parallel. A first starting resistor R2 and a first switching device K3 are provided in series in the first circuit 1225, and a second switching device K4 is provided in the second circuit 1226. When the energy storage unit of the energy storage submodule participating in the pre-charge is connected to the corresponding rectifier circuit, the first circuit 1225 is controlled to control the second circuit 1226 to use the first starting resistor R2 to limit the current. By enabling the starting resistor R2 for current limiting, the peak current of the charge can be limited, thereby protecting the battery pack 1223. By enabling the first starting resistor R2 to short-circuit, the energy consumed by enabling the first starting resistor R2 can be reduced.

[0091] The main energy transmission line 15 is connected to the DC bus via a second switching circuit, so that the main energy transmission line 15 and the DC bus can be connected and disconnected. By controlling the second switching circuit, the main energy transmission line 15 and the DC bus can be connected and disconnected. The second switching circuit can be a variety of switching circuits. For example, the second switching circuit includes a current limiting circuit. For example, a current limiting circuit is provided on the connection line between the first end of the energy storage device and the positive DC bus 21 or the connection line between the second end of the energy storage device and the negative DC bus 22. The current limiting circuit can reduce the instantaneous inrush current generated during grid-connected switching, thereby improving the safety of the energy storage system and extending the service life of the energy storage device.

[0092] The current limiting circuit can have a variety of structures. The current limiting circuit includes a second starting resistor and a cut-off switch connected in parallel with the second starting resistor. During grid-connected startup, the cut-off switch is controlled to be disconnected to use the second starting resistor for current limiting; when it is determined that the conditions for pre-charging the equalizing capacitor are met, the cut-off switch is controlled to be closed to short-circuit the second starting resistor. For example, as shown in FIG3A , the current limiting circuit includes a third line 16 and a fourth line 17 connected in parallel; a second starting resistor R1 is provided in the third line 16, a third switch device K1 connected in series with the second starting resistor R1 is provided in the third line 16, and a fourth switch device K2 is provided in the fourth line 17, and K2 is a cut-off switch. R1 and K2 are connected in parallel; during grid-connected startup, K3 is controlled to be disconnected to use R1 for current limiting; when it is determined that the conditions for pre-charging the equalizing capacitor are met, K2 is controlled to be closed to short-circuit R1. By setting the second starting resistor R1, the peak current during the grid-connected process can be limited, which plays a protective role. Another structure of the current limiting circuit is shown in FIG3C . K2, K3, K4 can use a variety of switch devices.

[0093] As shown in FIG3B , a voltage sensor can be set to collect the total voltage U of the energy storage device, that is, the voltage of the main energy transmission line; the energy storage control unit 11 obtains the total voltage U collected by the voltage sensor; a current sensor can be set to collect the real-time current (bridge arm current) I on the main energy transmission line arm The energy storage control unit 11 obtains the I collected by the current sensor arm As shown in FIG3B , the capacitor voltage U of the voltage-equalizing capacitor C0 can be collected by setting a voltage sensor. c , battery voltage U of battery pack 1223 bat And obtain the SOC information of the battery pack 1223, control the power subunit 1224 to obtain the U collected by the voltage sensor c 、U bat , and U c 、U bat , SOC information is sent to the energy storage control unit 11. The grid-connected control method of the energy storage device disclosed in the present disclosure is applied to the energy storage control unit 11. The energy storage control unit 11 controls K0, K1, and K2 to be connected or disconnected; and controls the power subunit 1224 to control the power unit 1221 to be connected or disconnected, and controls K5, K4, and K3 to be connected or disconnected according to the control instructions sent by the energy storage control unit 11.

[0094] The control subunit 1221 can be implemented in a variety of ways. For example, the control subunit 1221 includes one or more processors and memory. The memory can be a volatile memory and / or a non-volatile memory for storing one or more computer program instructions. The processor can execute the program instructions to communicate with the energy storage control unit and complete other functions that the control subunit needs to process.

[0095] The conditions for completing the pre-charging of the equalizing capacitor can be a variety of conditions. For example, the conditions for completing the pre-charging of the equalizing capacitor include: the voltage of the energy transmission main line is greater than the voltage threshold of the energy transmission main line. As shown in Figures 3A and 3B, at the time of grid-connected startup, the energy storage control unit 11 controls K0 to close, closes K1 and disconnects K2, and uses R1 for current limiting to connect the energy transmission main line 15 to the positive DC bus 21 and the negative DC bus 22. The energy storage control unit 11 sends a control instruction to the control subunit 1221. The control subunit 1221 controls K3, K4, and K5 to be in the disconnected state based on the control instruction, and controls the energy storage unit 1222 to be disconnected from the corresponding rectifier circuit. The equalizing capacitor C0 of each energy storage submodule can be charged uncontrolled through the diode D1, so that the power system pre-charges the equalizing capacitor C0.

[0096] In one embodiment, a second starting resistor is used for current limiting during grid-connected startup. When it is determined that the pre-charging conditions of the voltage-sharing capacitor are met, the second starting resistor is short-circuited. As shown in Figures 3A and 3B, the energy storage control unit 11 detects the voltage U of the energy transmission main line (the overall voltage of the energy storage device) in real time. When it is detected that U is greater than the voltage threshold U of the energy transmission main line, the energy storage control unit 11 detects the voltage U of the energy transmission main line (the overall voltage of the energy storage device) in real time. set1 When the voltage-sharing capacitor pre-charge completion condition is met, U set1 The minimum allowable voltage U between the DC busbars 21 and 22 can be min , or the rated voltage U between the DC busbars 21 and 22 n When the energy storage control unit 11 determines that the conditions for precharging the equalizing capacitors are met, it controls K2 to close, short-circuiting R1. Alternatively, after K2 is successfully closed, it controls K1 to open, removing the starting resistor R1. When the conditions for precharging the equalizing capacitors are met, the energy storage control unit 11 controls the energy storage device to charge.

[0097] FIG4 is a schematic diagram of a process of precharging based on capacitor voltage information of a grading capacitor in some embodiments of the grid-connected control method of the energy storage device disclosed herein, as shown in FIG4 :

[0098] Step 401: Determine a first participating quantity corresponding to energy storage submodules participating in pre-charging.

[0099] Step 402 : When the first participating number is less than the total number of energy storage submodules, determine a change in the number of energy storage submodules participating in pre-charging based on the first participating number.

[0100] Step 403 : Using the capacitor voltage sorting and balancing strategy and based on the capacitor voltage information and variation of the voltage-sharing capacitor, select the energy storage submodule as the pre-charge energy storage submodule and control the energy storage units of the pre-charge energy storage submodule to perform pre-charging.

[0101] By using the capacitor voltage sorting and balancing strategy to select the energy storage submodule as the pre-charge energy storage submodule for pre-charging, the voltage of the energy storage unit of the energy storage submodule can be adjusted to be similar, thereby improving the reliability of the energy storage unit grid connection, ensuring smooth grid connection, and increasing the service life of the energy storage device.

[0102] There are many ways to control the pre-charging of energy storage units using the capacitor voltage sorting and balancing strategy. Figure 5 is a schematic diagram of the process of controlling the pre-charging of energy storage units using the capacitor voltage sorting and balancing strategy in some embodiments of the grid-connected control method of the energy storage device disclosed herein, as shown in Figure 5:

[0103] Step 501: Determine the first number of participants N on .

[0104] Step 502, if N on =0, then go to step 503; if N on =N SM , then go to step 504; if 0 <N on <N SM , then proceed to step 505. N SM is the total number of energy storage submodules.

[0105] Step 503: Remove all energy storage submodules. When removing an energy storage submodule, the energy storage control unit 11 sends a control instruction to the corresponding control subunit 1221. The control subunit 1221 controls K3 and K4 to be in the off state based on the control instruction; or controls K5 to be in the on state based on the control instruction.

[0106] Step 504: All energy storage submodules are put into operation. When one energy storage submodule is put into operation, the energy storage control unit 11 sends a control instruction to the corresponding control submodule 1221. The control submodule 1221 controls K3 to be in a connected state and controls K4 to be in a disconnected state based on the control instruction.

[0107] Step 505: Calculate the change in the number of energy storage submodules N diff =N on -N on_old , that is, in the first number of participants N onLess than the total number N of energy storage submodules SM In the case of the first participation number N on Determine the (first) change N in the number of energy storage submodules participating in pre-charging diff N on -N on_old . N on_old is the first number of participants determined last time, where N is calculated for the first time diff When N on_old The value of is 0.

[0108] Step 506, if N diff >0, then go to step 507; if N diff =0, then go to step 508; if N diff <0, then go to step 509.

[0109] Step 507, determine i arm Is it greater than 0? If i arm >0, then go to step 510, if i arm <0 or i arm =0, then go to step 511. If I arm >0, it is determined that the current direction on the main energy transmission line is the current flowing into the energy storage device, and the energy storage device is in a charging state; if i arm <0 or i arm = 0, the current direction on the main energy transmission line is determined to be the current flowing to the DC bus, and the energy storage device is in the discharge state; if i arm =0, the pre-charged energy storage submodule is nearly fully charged. In this case, the current direction on the main energy transmission line is considered to be the current flowing toward the DC bus.

[0110] Step 510, in the removed (N SM -N on_old ) energy storage submodules |N diff |The energy storage submodule with the lowest capacitor voltage.

[0111] Step 511, in the removed (N SM -N on_old ) modules invested in |N diff |The energy storage submodule with the highest capacitor voltage.

[0112] In some embodiments, the voltage of the voltage-equalizing capacitor of the energy storage submodule is the voltage of the voltage-equalizing capacitor in the energy storage submodule. diff When the power system is greater than 0 and outputs electric energy to the main transmission line, select the energy storage submodule that is not used as a pre-charge energy storage submodule and the one with the lowest voltage of the voltage-sharing capacitor, the number and the change N diffThe same energy storage submodule is used as a new pre-charge energy storage submodule, and the energy storage unit of the new pre-charge energy storage submodule is controlled to be connected to the corresponding rectifier circuit for pre-charging. diff When the voltage of the voltage-sharing capacitor is greater than 0 and the main energy transmission line outputs electric energy to the power system, the voltage-sharing capacitor with the highest voltage and the highest number and change N is selected from all energy storage submodules that are not used as pre-charged energy storage submodules. diff The same energy storage submodule is used as a new pre-charge energy storage submodule, and the energy storage unit of the new pre-charge energy storage submodule is controlled to be connected to the corresponding rectifier circuit for pre-charging.

[0113] Based on the change in the number of energy storage submodules participating in pre-charging and the voltage sorting of the balancing capacitors, it is possible to select and control the energy storage submodules for pre-charging when the change is greater than 0. The voltages of the energy storage units of the energy storage submodules can be adjusted to be similar, thereby improving the reliability and service life of the energy storage units when connected to the grid.

[0114] Step 508, if ⊿U max >⊿U max_ref , then go to step 512, if ⊿U max <⊿U max_ref or ⊿U max =⊿U max_ref , then go to step 513. ΔU max ΔU is the real-time maximum capacitance voltage deviation value between the grading capacitors of the energy storage submodule, that is, the difference between the maximum voltage value and the minimum voltage value of the capacitance voltage values ​​of all grading capacitors; max_ref is the maximum voltage deviation allowed between the capacitors of the energy storage submodule, that is, the voltage deviation threshold, ΔU max_ref Determined according to system requirements.

[0115] Step 512 : Select the energy storage submodules with the highest and lowest capacitor voltages from among the energy storage submodules that have been put into operation (turned on) and removed (turned off) for switching.

[0116] Step 513: Maintain the current state.

[0117] In some embodiments, all capacitor voltages Uc are acquired in real time, and the difference between the maximum voltage value and the minimum voltage value of the capacitor voltages Uc of all grading capacitors is calculated as the maximum capacitor voltage deviation ΔU max If the change N diff Equal to 0 and the maximum capacitor voltage deviation ΔU max Greater than the voltage deviation threshold ΔU max_ref, then, from all the energy storage submodules that are not used as pre-charge energy storage submodules, the energy storage submodule with the smallest voltage on the balancing capacitor is selected as a new pre-charge energy storage submodule, and the energy storage unit of the new pre-charge energy storage submodule is controlled to be connected to the corresponding rectifier circuit; and, from all the pre-charge energy storage submodules, the pre-charge energy storage submodule with the largest voltage on the balancing capacitor is selected (this pre-charge energy storage submodule is used as the removed pre-charge energy storage submodule), and the energy storage unit of this pre-charge energy storage submodule is controlled to be disconnected from the corresponding rectifier circuit.

[0118] Based on the change in the number of energy storage submodules participating in pre-charging, the voltage ranking of the grading capacitors, and the voltage deviation of the grading capacitors, the energy storage submodules can be selected and controlled for pre-charging when the change is equal to 0. The voltages of the energy storage units of the energy storage submodules can be adjusted to be similar, thereby improving the reliability and service life of the energy storage units when connected to the grid.

[0119] Step 509, determine i arm Is it greater than 0? If i arm >0, then go to step 514, if i arm <0 or i arm =0, then go to step 515.

[0120] Step 514, after the N on_old Removal of energy storage submodules |N diff |The energy storage submodule with the highest capacitor voltage.

[0121] Step 515, after the N on_old Removal of energy storage submodules |N diff |The energy storage submodule with the lowest capacitor voltage.

[0122] In some embodiments, the change N diff When the value is less than 0 and the power system outputs electric energy to the main transmission line, the absolute value of the number and change of the voltage-sharing capacitor with the highest voltage among all pre-charged energy storage submodules is selected. diff The same energy storage submodule is used as the pre-charge energy storage submodule, and the energy storage unit of the pre-charge energy storage submodule is controlled to be disconnected from the corresponding rectifier circuit to stop pre-charging; in the variation N diff When the value is less than 0 and the main energy transmission line outputs electric energy to the power system, the absolute value of the number and change of the voltage-sharing capacitor with the lowest voltage among all pre-charged energy storage submodules is selected. diff The same energy storage submodule serves as a cut-off energy storage submodule, controlling the energy storage unit of the cut-off energy storage submodule to be disconnected from the corresponding rectifier circuit, and stopping pre-charging.

[0123] Based on the change in the number of energy storage submodules participating in pre-charging and the voltage sorting of the balancing capacitors, it is possible to select and control the energy storage submodules for pre-charging when the change is less than 0. The voltages of the energy storage units of the energy storage submodules can be adjusted to be similar, thereby improving the reliability and service life of the energy storage units when connected to the grid.

[0124] In some embodiments, when the energy storage unit of the energy storage submodule participating in pre-charging is connected to the corresponding rectifier circuit, a first starting resistor is used for current limiting. As shown in Figures 3A and 3B, the energy storage control unit 11 sends a control instruction to the corresponding control subunit 1221. Based on the control instruction, the control subunit 1221 controls K3 to be connected and K4 to be disconnected, and uses R2 for current limiting.

[0125] There are many methods for controlling the energy storage submodule to charge based on the SOC information of the energy storage unit. Figure 6 is a schematic diagram of the process of charging based on the SOC information of the energy storage submodule in some embodiments of the grid-connected control method of the energy storage device disclosed in the present invention, as shown in Figure 6:

[0126] Step 601: Control the energy storage units of all energy storage submodules to be connected to corresponding rectifier circuits.

[0127] Step 602: Determine a second participating quantity corresponding to the energy storage submodules participating in charging.

[0128] Step 603 : When the second participating number is less than the total number of energy storage submodules, determine a second change in the number of energy storage submodules participating in charging based on the second participating number.

[0129] Step 604 : Using the SOC sorting and balancing strategy and based on the SOC information of the energy storage submodule and the second variation, select the energy storage submodule as the charging energy storage submodule, and control the energy storage units of the charging energy storage submodule to charge.

[0130] By using the SOC sorting and balancing strategy to select the energy storage submodule as the charging energy storage submodule for charging, the stability of the DC bus voltage and the voltage of the main energy transmission line can be maintained, and the SOC of each energy storage submodule can be adjusted to be similar, making the charging process more stable and improving the reliability of the energy storage device's grid connection and the stability of charging.

[0131] The energy storage charging condition can be a variety of energy storage charging conditions. For example, the energy storage charging condition is that the difference between the average voltage of the equalizing capacitor and the average voltage of the corresponding energy storage unit is less than the voltage difference threshold. Real-time detection of the capacitor voltage U of the equalizing capacitor of each energy storage submodule c , battery voltage U of the battery pack bat , calculate the average voltage of the grading capacitor as:

[0132]

[0133] Wherein, Uci is the capacitance voltage of the i-th grading capacitor, that is, the capacitance voltage of the grading capacitor in the i-th energy storage submodule, and N is the number of energy storage submodules.

[0134] Calculate the average voltage of the energy storage unit, that is, the battery voltage of the battery pack is

[0135]

[0136] Wherein, Ubati is the battery voltage of the i-th battery pack, that is, the battery voltage of the battery pack in the i-th energy storage submodule, and N is the number of energy storage submodules.

[0137] In one embodiment, when it is determined that the energy storage charging conditions are met, various methods can be used to control the connection of the energy storage units of all energy storage submodules to the corresponding rectifier circuits. For example, the energy storage units of all energy storage submodules can be controlled to be connected to the corresponding rectifier circuits, and all first startup resistors can be used for current limiting. The delay duration is determined based on the charging time constant of the voltage-sharing capacitor. After the delay duration, all first startup resistors are short-circuited while all energy storage submodules are connected to the corresponding rectifier circuits.

[0138] As shown in Figures 3A and 3B, when the average voltage U c_avg and the average voltage U of the energy storage unit bat_avg Satisfaction|U c_avg -U bat_avg |≤ΔU1, all control sub-units 1224 close K3 in the corresponding energy storage sub-module and disconnect K4 based on the control instruction sent by the energy storage control unit 11, control the battery pack 1223 to be connected through the first starting resistor R2, so that the energy storage unit 1222 is connected to the corresponding rectifier circuit, and use the first starting resistor R2 for current limiting.

[0139] The delay time ΔT is determined based on the charging time constant τ = R2 * C0 of the voltage-equalizing capacitor, where ΔT ≥ 3τ. After the delay ΔT, all control subunits 1224 close K4 and short-circuit all first starting resistors R2 (bypass R2) based on the control instruction sent by the energy storage control unit 11. Alternatively, after K4 is closed, K3 can be disconnected to remove the first starting resistor R2. After all battery packs 1223 are connected through K4, the SOC sorting and balancing strategy is used and based on the SOC information and second variation of the energy storage submodule, the energy storage submodule is selected as the charging energy storage submodule, and the position of the charging energy storage submodule is determined.

[0140] In one embodiment, there are multiple methods for controlling the charging of the energy storage units of the energy storage submodule using the SOC sorting and balancing strategy. FIG7 is a flow chart of charging control according to the SOC sorting and balancing strategy in some embodiments of the grid-connected control method of the energy storage device disclosed herein, as shown in FIG7:

[0141] Step 701: Determine the second number of participants N on .

[0142] Step 702, if N on =0, then go to step 703; if N on =N SM , then go to step 704; if 0 <N on <N SM , then proceed to step 705. N SM is the total number of energy storage submodules.

[0143] Step 703: Remove all energy storage submodules. When removing an energy storage submodule, the energy storage control unit 11 sends a control instruction to the corresponding control subunit 1221. The control subunit 1221 controls K3 and K4 to be disconnected based on the control instruction; or controls K5 to be connected based on the control instruction.

[0144] Step 704: All energy storage submodules are put into operation. When one energy storage submodule is put into operation, the energy storage control unit 11 sends a control instruction to the corresponding control submodule 1221. The control submodule 1221 controls K4 to be connected and controls K3 to be disconnected or connected based on the control instruction.

[0145] Step 705: Calculate the change in the number of energy storage submodules N diff =N on -N on_old ,

[0146] That is, in the first number of participants N on Less than the total number N of energy storage submodules SM In the case of the second participation number N on Determine the (second) change N in the number of energy storage submodules diff N on -N on_old , N on_old is the second number of participants determined last time, where N is the number of participants in the first calculation. diff When N on_old The value of is 0.

[0147] Step 706, if N diff >0, then go to step 707; if N diff =0, then go to step 708; if Ndiff <0, then go to step 709.

[0148] Step 707, determine i arm Is it greater than 0? If i arm >0, then go to step 710, if i arm <0 or i arm =0, then go to step 711. If I arm >0, it is determined that the current direction on the main energy transmission line is the current flowing into the energy storage device, and the energy storage device is in a charging state. If i arm <0 or i arm =0, it is determined that the current direction on the main energy transmission line is that the current flows toward the DC bus, and the energy storage device is in a discharging state.

[0149] Step 710, after the cut (N SM -N on_old ) energy storage submodules |N diff |The energy storage submodule with the lowest SOC.

[0150] Step 711, in the removed (N SM -N on_old ) energy storage submodules |N diff |The energy storage submodule with the highest SOC.

[0151] In one embodiment, the SOC of the energy storage submodule is the SOC value of the battery pack in the energy storage submodule. diff When the power system is greater than 0 and outputs electric energy to the main transmission line, the energy storage submodule with the lowest SOC, quantity and change N is selected from all energy storage submodules that are not used as charging energy storage submodules. diff The same energy storage submodule is used as a new charging energy storage submodule, and the energy storage unit of the new charging energy storage submodule is controlled to be connected to the corresponding rectifier circuit for charging; diff When the SOC is greater than 0 and the main energy transmission line outputs electric energy to the power system, the energy storage submodule with the highest SOC and the highest number and change N is selected from all energy storage submodules that are not used as charging energy storage submodules. diff The same energy storage submodule is used as a new charging energy storage submodule, and the energy storage unit of the new charging energy storage submodule is controlled to be connected to the corresponding rectifier circuit for charging.

[0152] Based on the change in the number of energy storage submodules involved in charging and the battery SOC ranking, the energy storage submodules can be selected and controlled for charging when the change is greater than 0. This can maintain the stability of the DC bus voltage and the voltage of the main energy transmission line, adjust the SOC of each energy storage submodule to be similar, make the charging process more stable, and improve the reliability of the energy storage unit's grid connection.

[0153] Step 708, if ⊿SOC max >⊿SOC max_ref , then go to step 712, if ⊿SOC max <⊿SOC max_ref or ⊿SOC max =⊿SOC max_ref , then go to step 713. ⊿SOC max The maximum real-time SOC deviation of the energy storage submodule, that is, the difference between the maximum SOC value and the minimum SOC value of all battery modules, is the maximum SOC deviation; ⊿SOC max_ref is the maximum allowed SOC deviation value, is the SOC deviation threshold, Δ⊿SOC max_ref Determined according to system requirements.

[0154] Step 712: Select the energy storage submodule with the highest SOC and the energy storage submodule with the lowest SOC from the energy storage submodules that have been put into operation (turned on) and removed (turned off) respectively for switching.

[0155] Step 713: Maintain the current state.

[0156] In some embodiments, if the change is equal to 0 and the maximum SOC deviation ⊿SOC max Greater than SOC deviation threshold ⊿SOC max_ref , then, from all the energy storage submodules that are not used as charging energy storage submodules, the energy storage submodule with the smallest SOC is selected as the new charging energy storage submodule, and the energy storage unit of the new charging energy storage submodule is controlled to be connected to the corresponding rectifier circuit; and, from all the charging energy storage submodules, the energy storage submodule with the largest SOC is selected (this charging submodule serves as the cut-off energy storage submodule), and the energy storage unit of this charging energy storage submodule is controlled to be disconnected from the corresponding rectifier circuit; wherein the maximum SOC deviation is the difference between the maximum SOC and the minimum SOC of the energy storage submodule.

[0157] Based on the change in the number of energy storage submodules involved in charging, the battery SOC ranking, and the SOC deviation, the energy storage submodule can be selected and controlled for charging when the change is equal to 0. This can maintain the stability of the DC bus voltage and the voltage of the main energy transmission line, adjust the SOC of each energy storage submodule to be similar, make the charging process more stable, and improve the reliability of the energy storage unit's grid connection.

[0158] Step 709, determine i arm Is it greater than 0? If i arm >0, then go to step 714, if i arm <0 or i arm =0, then go to step 715.

[0159] Step 714, after the Non_old Removal of energy storage submodules |N diff |The energy storage submodule with the highest SOC.

[0160] Step 715, in the N on_old Removal of energy storage submodules |N diff |The energy storage submodule with the lowest SOC.

[0161] In some embodiments, the change N diff When it is less than 0 and the power system outputs electric energy to the main transmission line, the absolute value of the number and change of the highest SOC among all charging energy storage submodules is selected. diff |The same energy storage submodule is used as the cut-off energy storage submodule, and the cut-off energy storage submodule is controlled to be disconnected from the corresponding rectifier circuit; in the variation N diff When it is less than 0 and the main energy transmission line outputs electric energy to the power system, the absolute value of the number and change of the lowest SOC among all charging energy storage submodules is selected. diff The same energy storage submodule is used as the cut-off energy storage submodule, and the cut-off energy storage submodule is controlled to be disconnected from the corresponding rectifier circuit.

[0162] Based on the change in the number of energy storage submodules involved in charging and the battery SOC ranking, the energy storage submodules can be selected and controlled for charging when the change is less than 0. This can maintain the stability of the DC bus voltage and the voltage of the main energy transmission line, adjust the SOC of each energy storage submodule to be similar, make the charging process more stable, and improve the reliability of the energy storage unit's grid connection.

[0163] In some embodiments, when the energy storage unit of the energy storage submodule participating in the charging is connected to the corresponding rectifier circuit, the first starting resistor is short-circuited. As shown in Figures 3A and 3B, the energy storage control unit 11 sends a control instruction to the corresponding control subunit 1221. Based on the control instruction, the control subunit 1221 controls K4 to be connected, short-circuiting R2. Alternatively, K3 can be controlled to be disconnected, disconnecting R2.

[0164] After selecting an energy storage submodule as a charging energy storage submodule for charging using the SOC sorting and balancing strategy and based on the SOC information of the energy storage submodule and the second variation, a determination is made as to whether a charging completion condition is satisfied. When the charging completion condition is satisfied, it is determined that grid-connected startup of the energy storage device is complete. The charging completion condition can be various, for example, the charging completion condition can be that the average SOC of all energy storage submodules is greater than an SOC threshold, or that the duration of charging using the SOC sorting and balancing strategy is greater than a duration threshold.

[0165] In some embodiments, various methods can be used to determine the first number of energy storage subunits participating in pre-charging and the second number of energy storage subunits participating in charging. For example, PI control processing can be performed based on a reference current and the real-time current I on the main energy transmission line 15 to determine the first number of energy storage subunits participating in pre-charging or the second number of energy storage subunits participating in charging.

[0166] PI control uses the existing PI algorithm to control the controlled object by linearly combining the proportion and integral of the deviation based on the control deviation between the given value and the actual output value. ref is the set reference current, I is the actual measured real-time current I on the energy transmission main line 15 arm , the PI algorithm used in PI control processing is:

[0167]

[0168] Wherein, Nref is the number of energy storage subunits to be put into operation, i.e., the first participating number or the second participating number; kp is the proportional adjustment parameter, T is the integral adjustment parameter; err(t) is the real-time current (real-time charging current) I on the energy transmission main line 15 arm The difference between I and the reference current (reference charging current) Iref; the first or second participating quantity is modified according to the PI control process until I and Iref are equal, or the difference between I and Iref is less than a preset voltage difference threshold. When calculating the first and second participating quantities, the parameter values ​​of kp, T, and Iref can be the same or adjusted accordingly.

[0169] PI control processing is performed based on the reference current and the real-time current on the main energy transmission line to determine the number of energy storage sub-units participating in pre-charging and charging. This can improve the accuracy of controlling the voltage of the main energy transmission line, so that the electric energy charging the energy storage sub-units is stable, thereby improving the stability of the charging process.

[0170] In some embodiments, the present disclosure provides an energy storage device, as shown in Figures 3A and 3B, the energy storage device includes multiple energy storage sub-modules, the multiple energy storage sub-modules are energy storage sub-module 121, energy storage sub-module 122...energy storage sub-module 12n; the energy storage sub-module 122 includes a power unit 1221 and an energy storage unit 1222; the power unit 1221 includes a rectifier circuit and a voltage-equalizing capacitor C0; the rectifier circuit can be a variety of rectifier circuits, for example, the rectifier circuit is a half-bridge rectifier circuit composed of transistors T1, T2 and diodes D1, D2; the energy storage unit 1222 and the voltage-equalizing capacitor C0 are respectively connected in parallel with the output end of the rectifier circuit, and the energy storage unit 1222 can be connected to the output end of the rectifier circuit in an on-off manner; the input ends of each rectifier circuit are connected in series to form an energy transmission main line 15, and the energy transmission main line 15 can be connected to the DC bus 21 of the power system in an on-off manner. For example, a first switching circuit is provided in the connection line between the energy storage unit 1222 and the output end of the rectifier circuit; the energy storage control unit 11 controls the first switching circuit to control the connection and disconnection between the energy storage unit 1222 and the output end of the rectifier circuit. The first switching circuit can be a variety of switching circuits, for example, the first switching circuit includes a pre-charge circuit, etc.

[0171] The main energy transmission line 15 is connected to the DC bus through a second switching circuit. The energy storage control unit 11 controls the second switching circuit to connect and disconnect the main energy transmission line 15 from the DC bus. The second switching circuit can be a variety of switching circuits, for example, the second switching circuit includes a current limiting circuit.

[0172] The energy storage device disclosed herein adopts a modular multi-level cascade structure, which can improve the configuration capacity of the energy storage device and can independently control each energy storage module subunit; the power unit and the voltage-equalizing capacitor can improve the stability of charging, and have advantages such as good harmonic characteristics and low equivalent switching frequency; by setting a switching circuit, the pre-charging and charging of each energy storage module subunit can be controlled, which can improve the safety of the energy storage device. The pre-charging circuit can limit the peak current of the charging, play a protective role, reduce the impact current of the battery pack, improve the safety of the battery pack, and extend the service life of the battery pack; the current limiting circuit can reduce the instantaneous impact current generated when the energy storage device is switched to the DC bus grid, which can improve the safety of the energy storage device.

[0173] In some embodiments, as shown in FIG9 , the present disclosure provides an energy storage control unit 90, comprising a grading capacitor pre-charging module 91, a pre-charging control module 92, and a charging control module 93. During grid-connected startup, the grading capacitor pre-charging module 91 controls the connection between the main energy transmission line and the DC bus and disconnects the energy storage unit from the corresponding rectifier circuit, allowing the power system to pre-charge the grading capacitor.

[0174] The pre-charge control module 92 controls the energy storage unit of the energy storage submodule to connect to the corresponding rectifier circuit according to the first control strategy to perform pre-charge processing. The charging control module 93 controls the energy storage unit of the energy storage submodule to connect to the corresponding rectifier circuit according to the second control strategy to perform charging processing.

[0175] In some embodiments, the pre-charge control module 92 selects an energy storage submodule as a pre-charge energy storage submodule based on the capacitor voltage information of the voltage-sharing capacitor, controls the energy storage unit of the pre-charge energy storage submodule to connect to the corresponding rectifier circuit, and performs pre-charge processing. The charging control module 93 selects an energy storage submodule as a charging energy storage submodule based on the SOC information of the energy storage unit, and controls the energy storage unit of the charging energy storage submodule to connect to the corresponding rectifier circuit for charging processing.

[0176] In some embodiments, the pre-charge control module 92 determines a first participating number corresponding to the energy storage submodules participating in pre-charging. If the first participating number is less than the total number of energy storage submodules, the pre-charge control module 92 determines a first change in the number of energy storage submodules participating in pre-charging based on the first participating number. The pre-charge control module 92 utilizes a capacitor voltage sorting and balancing strategy and, based on the capacitor voltage information and the first change of the voltage-sharing capacitor, selects an energy storage submodule as a pre-charge energy storage submodule and controls the energy storage units of the pre-charge energy storage submodule for pre-charging. When the energy storage units of the energy storage submodules participating in pre-charging are connected to the corresponding rectifier circuit, the pre-charge control module 92 uses a first starting resistor for current limiting.

[0177] The charging control module 93 controls the connection of the energy storage units of all energy storage submodules to their corresponding rectifier circuits. For example, the charging control module 93 controls the connection of the energy storage units of all energy storage submodules to their corresponding rectifier circuits and uses all first startup resistors for current limiting. The charging control module 93 determines a delay time based on the charging time constant of the voltage-sharing capacitor. After the delay time, while all energy storage submodules are connected to their corresponding rectifier circuits, the charging control module 93 short-circuits all first startup resistors.

[0178] The charging control module 93 determines a second number of participating energy storage submodules corresponding to the energy storage submodules participating in the charging operation. If the second number of participating energy storage submodules is less than the total number of energy storage submodules, the charging control module 93 determines a second change in the number of energy storage submodules participating in the charging operation based on the second number of participating energy storage submodules. The charging control module 93 utilizes an SOC sorting and balancing strategy and, based on the SOC information of the energy storage submodules and the second change, selects an energy storage submodule as the charging energy storage submodule and controls the energy storage cells of the charging energy storage submodule to charge. When the energy storage cells of the energy storage submodules participating in the charging operation are connected to the corresponding rectifier circuit, the charging control module 93 short-circuits the first starting resistor.

[0179] In one embodiment, as shown in Figure 10, the energy storage control unit 90 further includes a participant quantity determination module 94 and a current limiting control module 95. The participant quantity determination module 94 performs PI control based on a reference current and the real-time current on the main energy transmission line to determine the first participant quantity and the second participant quantity. During grid-connected startup, the current limiting control module 95 uses a second startup resistor for current limiting. If the conditions for precharging the grading capacitor are met, the current limiting control module 95 short-circuits the second startup resistor.

[0180] FIG11 is a schematic diagram of a third module of some embodiments of an energy storage control unit of the present disclosure. As shown in FIG11 , the energy storage control unit may include a memory 1101, a processor 1102, a communication interface 1103, and a bus 1104. The memory 1101 is used to store instructions. The processor 1102 is coupled to the memory 1101 and is configured to execute the grid-connected control method for the energy storage device according to any of the above-described embodiments based on the instructions stored in the memory 1101.

[0181] Memory 1101 may be a high-speed RAM memory, a non-volatile memory, or the like. Memory 1101 may also be a memory array. Memory 1101 may also be divided into blocks, and the blocks may be combined into virtual volumes according to certain rules. Processor 1102 may be a central processing unit (CPU), an application-specific integrated circuit (ASIC), or one or more integrated circuits configured to implement the grid-connected control method for an energy storage device disclosed herein.

[0182] In some embodiments, the present disclosure provides an energy storage system, comprising the energy storage device and energy storage control unit as described in any of the above embodiments.

[0183] In one embodiment, the present disclosure provides a computer-readable storage medium storing computer instructions, which are executed by a processor to implement the grid-connected control method for an energy storage device in any of the above embodiments.

[0184] The computer-readable storage medium can adopt any combination of one or more readable media. The readable medium can be a readable signal medium or a readable storage medium. The readable storage medium can, for example, include but is not limited to a system, device or component of electricity, magnetism, light, electromagnetic, infrared, or semiconductor, or any combination thereof. More specific examples (non-exhaustive enumeration) of readable storage media can include: an electrical connection with one or more wires, a portable disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof.

[0185] The present disclosure is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems) and computer program products according to the embodiments of the present disclosure. It should be understood that each process and / or box in the flowchart and / or block diagram and the combination of the processes and / or boxes in the flowchart and / or block diagram can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate a device for implementing the functions specified in one or more processes in the flowchart and / or one or more boxes in the block diagram.

[0186] These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce a product including an instruction device that implements the functions specified in one or more processes in the flowchart and / or one or more boxes in the block diagram.

[0187] The methods and systems of the present disclosure may be implemented in many ways. For example, the methods and systems of the present disclosure may be implemented by software, hardware, firmware, or any combination of software, hardware, and firmware. The above order of steps for the method is for illustration only, and the steps of the method of the present disclosure are not limited to the order specifically described above unless otherwise specified. In addition, in some embodiments, the present disclosure may also be implemented as programs recorded in a recording medium, which include machine-readable instructions for implementing the methods according to the present disclosure. Therefore, the present disclosure also covers recording media that store programs for executing the methods according to the present disclosure.

[0188] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and components may be substituted with equivalents without departing from the scope of the present application. In particular, the various technical features described in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. A method for controlling grid connection of an energy storage device, wherein the energy storage device includes a plurality of energy storage submodules, each of the energy storage submodules including a power unit and an energy storage unit; the power unit including a rectifier circuit and a voltage-sharing capacitor; the energy storage unit and the voltage-sharing capacitor are respectively connected in parallel to an output terminal of the rectifier circuit, and the energy storage unit and the output terminal of the rectifier circuit are connected in a disconnectable manner; the input terminals of the rectifier circuits are connected in series to form a main energy transmission line, and the main energy transmission line is connected in a disconnectable manner to a DC bus of a power system; the method comprising: During grid-connected startup, controlling the main energy transmission line to be connected to the DC bus and controlling the energy storage unit to be disconnected from the corresponding rectifier circuit, so that the power system pre-charges the grading capacitor; When it is determined that the conditions for completing pre-charging of the equalizing capacitor are met, the energy storage unit of the energy storage submodule is controlled to be connected to the corresponding rectifier circuit according to the first control strategy to perform pre-charging processing, and when it is determined that the energy storage charging conditions are met, the energy storage unit of the energy storage submodule is controlled to be connected to the corresponding rectifier circuit according to the second control strategy to perform charging processing.

2. The method according to claim 1, wherein the controlling the energy storage unit of the energy storage submodule to be connected to the corresponding rectifier circuit according to the first control strategy to perform pre-charging processing comprises: An energy storage submodule is selected as a pre-charge energy storage submodule according to the capacitor voltage information of the voltage-equalizing capacitor, and the energy storage unit of the pre-charge energy storage submodule is controlled to be connected to the corresponding rectifier circuit to perform pre-charging processing.

3. The method according to claim 2, wherein selecting the energy storage submodule as the pre-charge energy storage submodule according to the capacitor voltage information of the voltage balancing capacitor comprises: Determining a first participating quantity corresponding to the energy storage submodules participating in pre-charging; When the first participating number is less than the total number of the energy storage submodules, determining a first change in the number of energy storage submodules participating in pre-charging based on the first participating number; The energy storage submodule is selected as the pre-charge energy storage submodule by utilizing a capacitor voltage sorting and balancing strategy and according to the capacitor voltage information of the grading capacitor and the first variation.

4. The method according to claim 3, wherein the step of selecting the energy storage submodule as the pre-charge energy storage submodule by utilizing the capacitor voltage sorting and balancing strategy and based on the capacitor voltage information of the grading capacitor and the first variation comprises: If the first change is equal to 0 and the maximum capacitor voltage deviation is greater than the voltage deviation threshold, then the energy storage submodule with the smallest voltage balancing capacitor among all the energy storage submodules that are not used as pre-charge energy storage submodules is selected as the new pre-charge energy storage submodule; and the pre-charge energy storage submodule with the largest voltage balancing capacitor among all the pre-charge energy storage submodules is selected as the removed pre-charge energy storage submodule; The maximum capacitor voltage deviation is the difference between the maximum balancing capacitor voltage and the minimum balancing capacitor voltage of the energy storage submodule.

5. The method according to claim 3, wherein the method of selecting the energy storage submodule as the pre-charge energy storage submodule by utilizing the capacitor voltage sorting and balancing strategy and based on the capacitor voltage information of the grading capacitor and the first variation comprises: When the first variation is greater than 0 and the power system outputs electric energy to the main energy transmission line, selecting energy storage submodules with the lowest voltage of the grading capacitor and the same number as the first variation from all energy storage submodules that are not used as pre-charge energy storage submodules as new pre-charge energy storage submodules; or When the first change is greater than 0 and the main energy transmission line outputs electric energy to the power system, energy storage submodules with the highest voltage of the equalizing capacitor and the same number as the first change are selected from all energy storage submodules that are not used as pre-charged energy storage submodules as new pre-charged energy storage submodules.

6. The method according to claim 3, wherein the step of utilizing a capacitor voltage sorting and balancing strategy and selecting the energy storage submodule as the pre-charge energy storage submodule based on the capacitor voltage information of the grading capacitor and the first variation comprises: When the first variation is less than 0 and the power system outputs electric energy to the main energy transmission line, selecting, from all pre-charged energy storage submodules, energy storage submodules with the highest voltage of the grading capacitor and the same number as the absolute value of the first variation as the removed pre-charged energy storage submodules; or When the first change is less than 0 and the main energy transmission line outputs electric energy to the power system, energy storage submodules with the lowest voltage of the grading capacitor and the same number as the absolute value of the first change are selected from all pre-charged energy storage submodules as the removed pre-charged energy storage submodules.

7. The method according to claim 1, wherein controlling the energy storage unit of the energy storage submodule to be connected to the corresponding rectifier circuit according to the second control strategy to perform charging processing comprises: Controlling the energy storage unit of the energy storage submodule to be connected to the corresponding rectifier circuit; The energy storage submodule is selected as the charging energy storage submodule according to the SOC information of the energy storage unit, and the energy storage unit of the charging energy storage submodule is controlled to be connected to the corresponding rectifier circuit for charging processing.

8. The method according to claim 7, wherein selecting the energy storage submodule as the charging energy storage submodule according to the SOC information of the energy storage unit comprises: determining a second participating quantity corresponding to the energy storage submodules participating in charging; When the second participating number is less than the total number of the energy storage submodules, determining a second change in the number of energy storage submodules participating in charging based on the second participating number; The energy storage submodule is selected as the charging energy storage submodule by utilizing the SOC sorting and balancing strategy and according to the SOC information of the energy storage submodule and the second variation.

9. The method according to claim 8, wherein the selecting the energy storage submodule as the charging energy storage submodule by utilizing the SOC sorting and balancing strategy and based on the SOC information of the energy storage submodule and the second variation comprises: If the second variation is equal to 0 and the maximum SOC deviation is greater than the SOC deviation threshold, then selecting the energy storage submodule with the smallest SOC from all energy storage submodules that are not used as charging energy storage submodules as the new charging energy storage submodule; and selecting the energy storage submodule with the largest SOC from all charging energy storage submodules as the removed energy storage submodule; The maximum SOC deviation is the difference between the maximum SOC and the minimum SOC of the energy storage submodule.

10. The method according to claim 8, wherein the selecting the energy storage submodule as the charging energy storage submodule by utilizing the SOC sorting and balancing strategy and based on the SOC information of the energy storage submodule and the second variation comprises: When the second change is greater than 0 and the power system outputs electric energy to the main energy transmission line, the energy storage submodules with the lowest SOC and the same number as the second change are selected from all energy storage submodules that are not used as charging energy storage submodules as new charging energy storage submodules; or When the second change is greater than 0 and the main energy transmission line outputs electric energy to the power system, energy storage submodules with the highest SOC and the same number as the second change are selected from all energy storage submodules that are not used as charging energy storage submodules as new charging energy storage submodules.

11. The method according to claim 8, wherein the selecting the energy storage submodule as the charging energy storage submodule by utilizing the SOC sorting and balancing strategy and based on the SOC information of the energy storage submodule and the second variation comprises: When the second variation is less than 0 and the power system outputs electric energy to the main energy transmission line, the energy storage submodules with the highest SOC and the same number as the absolute value of the second variation are selected from all the charging energy storage submodules as the removed energy storage submodules; or When the second change is less than 0 and the main energy transmission line outputs electric energy to the power system, energy storage submodules with the lowest SOC and the same number as the absolute value of the second change are selected from all charging energy storage submodules as cut-off energy storage submodules.

12. The method of claim 3 or 8, comprising: A PI control process is performed based on a reference current and a real-time current on the energy transmission main line to determine the first participant quantity or the second participant quantity.

13. The method according to claim 2 or 7, wherein: The energy storage unit includes: a battery pack; the battery pack and a switchable pre-charge circuit are connected in series to form an energy storage circuit, and the energy storage circuit is connected in parallel to the output end of the corresponding rectifier circuit; the pre-charge circuit includes a first switchable circuit and a second switchable circuit connected in parallel, and a first starting resistor is provided in the first circuit; the method includes: When the energy storage unit of the energy storage submodule participating in pre-charging is connected to the corresponding rectifier circuit, the first circuit is controlled to be connected and the second circuit is controlled to be disconnected, so as to use the first starting resistor for current limiting; or When the energy storage unit of the energy storage submodule participating in charging is connected to the corresponding rectifier circuit, the second circuit is controlled to be connected to perform a short-circuit process on the first starting resistor.

14. The method according to claim 7, wherein controlling the energy storage unit of the energy storage submodule to be connected to the corresponding rectifier circuit comprises: Controlling the energy storage units of all energy storage submodules to be connected to corresponding rectifier circuits, and using all first starting resistors for current limiting; Determining a delay time based on a charging time constant of the voltage grading capacitor; After the delay time, all first starting resistors are short-circuited in a state where all energy storage submodules are connected to corresponding rectifier circuits.

15. The method of claim 1, wherein: The conditions for completing the pre-charging of the voltage-sharing capacitor include: the voltage of the main energy transmission line is greater than the voltage threshold of the main energy transmission line; and / or The energy storage charging condition includes: a difference between an average voltage of all grading capacitors and an average voltage of all corresponding energy storage units is less than a voltage difference threshold.

16. The method of claim 1, wherein: The energy transmission main line is connected to the DC bus through a switchable current limiting circuit; the current limiting circuit includes a second starting resistor and a disconnect switch connected in parallel with the second starting resistor; the method includes: During grid-connected startup, controlling the disconnect switch to be disconnected so as to use the second startup resistor for current limiting; When it is determined that the pre-charging completion condition of the voltage-sharing capacitor is met, the cut-off switch is controlled to be closed to short-circuit the second starting resistor.

17. An energy storage control unit, wherein: The energy storage device includes a plurality of energy storage submodules, each of which includes a power unit and an energy storage unit; the power unit includes a rectifier circuit and a voltage-sharing capacitor; the energy storage unit and the voltage-sharing capacitor are respectively connected in parallel to the output end of the rectifier circuit, and the energy storage unit and the output end of the rectifier circuit can be connected in an on-off manner; The input ends of the rectifier circuits are connected in series to form a main energy transmission line, which is connected to the DC bus of the power system in an on-off manner; The energy storage control unit includes: A grading capacitor pre-charging module, configured to control the connection between the main energy transmission line and the DC bus and the disconnection between the energy storage unit and the corresponding rectifier circuit during grid-connected startup, so that the power system pre-charges the grading capacitor; a pre-charging control module, configured to control the energy storage unit of the energy storage submodule to be connected to the corresponding rectifier circuit according to a first control strategy to perform pre-charging processing; The charging control module is used to control the energy storage unit of the energy storage submodule to be connected to the corresponding rectifier circuit according to the second control strategy to perform charging processing.

18. An energy storage control unit, comprising: Memory; and a processor coupled to the memory, wherein the processor is configured to execute the method according to any one of claims 1 to 16 based on instructions stored in the memory.

19. An energy storage system comprising: An energy storage device and an energy storage control unit as claimed in claim 17 or 18.

20. An energy storage device comprising: Multiple energy storage submodules, each of which includes a power unit and an energy storage unit; the power unit includes a rectifier circuit and a voltage-sharing capacitor; The energy storage unit and the voltage-equalizing capacitor are respectively connected in parallel to the output end of the rectifier circuit, and the energy storage unit and the output end of the rectifier circuit can be connected in an on-off manner; the input ends of the respective rectifier circuits are connected in series to form a main energy transmission line, and the main energy transmission line can be connected in an on-off manner to the DC bus of the power system.

21. The energy storage device according to claim 20, wherein: A switchable pre-charging circuit is provided in the connection circuit between the energy storage unit and the output end of the rectifier circuit.

22. The energy storage device according to claim 21, wherein The energy storage unit includes: a battery pack; the battery pack and the pre-charge circuit are connected in series to form an energy storage circuit; and the energy storage circuit is connected in parallel to the output end of the corresponding rectifier circuit.

23. The energy storage device according to claim 21, wherein The pre-charge circuit includes a first circuit and a second circuit that are connected in parallel and can be switched on and off. A first starting resistor and a first switch are provided in series in the first circuit. A second switch is provided in the second circuit.

24. The energy storage device according to claim 20, wherein: The energy transmission main circuit is connected to the DC bus through a switchable current limiting circuit.

25. The energy storage device according to claim 24, wherein: The current limiting circuit includes a second starting resistor and a cut-off switch connected in parallel with the second starting resistor. 26 . A computer-readable storage medium storing computer instructions, wherein the instructions are executed by a processor to execute the method according to claim 1 .

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