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

Abstract

The invention provides a grid-connected control method of an energy storage device, an energy storage control unit, an energy storage system and a storage medium, and relates to the technical field of energy storage, and the method comprises the steps: sequentially controlling an energy storage unit of each energy storage sub-module to be connected with a corresponding voltage-sharing capacitor in a state that an energy transmission main line is disconnected with a DC bus, enabling the energy storage units to pre-charge the corresponding voltage-sharing capacitors (201); and under the condition that the voltage-sharing capacitance of each energy storage sub-module satisfies a voltage-sharing capacitance pre-charging completion condition, controlling the energy transmission main line to be communicated with the DC bus (202). According to the method, the instantaneous impact current and the instantaneous impact voltage generated in the grid connection process can be effectively reduced, so that the charging process is more stable, smooth grid connection can be ensured, and the grid connection reliability and safety of the energy storage device are improved.

Description

Grid-connected control method, unit, 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 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 system, and a storage medium, which can effectively improve the reliability and safety of the grid-connected energy storage device.

[0005] According to a first aspect of the present disclosure, there is provided a grid-connected control method for an energy storage device, wherein the energy storage device comprises a plurality of energy storage submodules, wherein the energy storage submodules comprise a power unit and an energy storage unit; the power unit comprises 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 on and off; 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 on and off to a DC bus of a power system; the method comprises: in a state where the energy transmission main line is disconnected from the DC bus, sequentially controlling the energy storage units of the respective energy storage submodules to be connected to the corresponding voltage-equalizing capacitors, so that the energy storage units pre-charge the corresponding voltage-equalizing capacitors; and when the voltage-equalizing capacitors of the respective energy storage submodules meet the voltage-equalizing capacitor pre-charging completion condition, controlling the energy transmission main line to be connected to the DC bus.

[0006] The grid-connected control method disclosed herein controls the disconnection of the main energy transmission line from the power system and the connection of the energy storage unit to the corresponding voltage-sharing capacitor at the time of grid-connected startup, and pre-charges the voltage-sharing capacitor. 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 transient surge current and transient surge voltage generated during the grid-connected process, increase the service life of the energy storage device and the safety of its use, reduce damage to the connected power grid and other equipment in the power grid, and improve the reliability and safety of the grid-connected energy storage device.

[0007] Optionally, when the main energy transmission line is connected to the DC bus, the energy storage unit of the energy storage submodule is controlled to be connected to the corresponding rectifier circuit according to a control strategy to perform charging processing.

[0008] After completing the pre-charging of the voltage-equalizing capacitor, the energy storage submodule is charged 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 energy storage device connected to the grid.

[0009] Optionally, controlling the energy storage unit of the energy storage submodule to be connected to the corresponding rectifier circuit according to the control strategy for charging processing includes: selecting the energy storage submodule as the charging energy storage submodule according to the SOC information of the energy storage submodule, and controlling the charging energy storage submodule to be connected to the corresponding rectifier circuit for charging processing when the energy transmission main line is connected to the DC bus.

[0010] By selecting the energy storage submodule as the charging energy storage submodule based on the SOC information of the energy storage unit and performing charging processing, 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.

[0011] Optionally, selecting an energy storage submodule as a charging energy storage submodule based on the SOC information of the energy storage submodule includes: determining a participating number corresponding to the energy storage submodules participating in charging; when the participating number is greater than 0 and less than the total number of the energy storage submodules, determining a change in the number of energy storage submodules participating in charging based on the participating number; and selecting the energy storage submodule as the charging energy storage submodule based on the SOC information of the energy storage submodule and the change using an SOC sorting balancing strategy.

[0012] 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.

[0013] Optionally, 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 variation includes: if the variation is equal to 0 and the maximum SOC deviation is greater than an 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.

[0014] 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.

[0015] Optionally, 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 variation includes: when the variation is greater than 0 and the power system outputs electric energy to the main energy transmission line, selecting the energy storage submodules with the lowest SOC and the same number as the variation from all energy storage submodules that are not used as charging energy storage submodules as new charging energy storage submodules; and when the variation is greater than 0 and the main energy transmission line outputs electric energy to the power system, selecting the energy storage submodules with the highest SOC and the same number as the variation from all energy storage submodules that are not used as charging energy storage submodules as new charging energy storage submodules.

[0016] 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.

[0017] Optionally, the use of the SOC sorting and balancing strategy and the selection of the energy storage submodule as the charging energy storage submodule based on the SOC information of the energy storage submodule and the variation includes: when the variation is less than 0 and the power system outputs electric energy to the main energy transmission line, selecting the energy storage submodules with the highest SOC and the same number as the absolute value of the variation from all the charging energy storage submodules as the removed energy storage submodules; when the variation is less than 0 and the main energy transmission line outputs electric energy to the power system, selecting the energy storage submodules with the lowest SOC and the same number as the absolute value of the variation from all the charging energy storage submodules as the removed energy storage submodules.

[0018] 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.

[0019] Optionally, determining the number of participants corresponding to the energy storage submodules participating in charging includes: performing PI control processing based on a reference voltage and a real-time voltage of the energy transmission main line to determine the number of participants.

[0020] 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.

[0021] 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 circuit that can be switched on and off and a second circuit that can be switched on and off in parallel, and a starting resistor is provided in the first circuit; the method includes: when the energy storage unit pre-charges the corresponding equalizing capacitor, by controlling the first circuit to be connected and controlling the second circuit to be disconnected, so as to use the starting resistor for current limiting; when the equalizing capacitor of the energy storage sub-module meets the equalizing capacitor pre-charging completion condition and the charging energy storage sub-module is charged, controlling the second circuit to be connected, so as to short-circuit the starting resistor.

[0022] By using a starting resistor for current limiting 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 starting resistor in the charging stage can reduce energy consumption.

[0023] Optionally, the voltage balancing capacitor full condition includes: a difference between the voltage of the voltage balancing capacitor and the voltage of the corresponding energy storage unit is less than a voltage difference threshold.

[0024] By setting the conditions for completing the pre-charging of the equalizing capacitor, the damage to the energy storage device caused by the instantaneous surge current and instantaneous surge 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.

[0025] 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-modules including 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 on and off; 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 on and off to 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 storage units of each energy storage sub-module to be connected to the corresponding grading capacitors in sequence when the energy transmission main line is disconnected from the DC bus, so that the energy storage units pre-charge the corresponding grading capacitors; a line connection control module, which is used to control the energy transmission main line to be connected to the DC bus when the grading capacitors of each energy storage sub-module meet the grading capacitor pre-charging completion condition.

[0026] The energy storage control unit disclosed herein controls the disconnection of the main energy transmission line from the power system and the connection of the energy storage unit to the corresponding voltage-sharing capacitor during grid-connected startup, thereby precharging the voltage-sharing capacitor. 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 transient surge current and transient surge voltage generated during the grid-connected process, increase the service life of the energy storage device and the safety of its use, and reduce damage to the connected power grid and other equipment in the power grid. This ensures smooth grid connection and improves the reliability and safety of the energy storage device's grid connection.

[0027] Optionally, the energy storage control unit includes: a charging control module, which is used to control the energy storage unit of the energy storage submodule to be connected to the corresponding rectifier circuit according to a control strategy for charging processing when the energy transmission main line is connected to the DC bus.

[0028] After completing the pre-charging of the voltage-equalizing capacitor, the energy storage submodule is controlled to charge 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 energy storage device connected to the grid.

[0029] 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.

[0030] 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.

[0031] A fourth aspect of the present disclosure provides a power transmission 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.

[0032] The power transmission system disclosed in the present invention has the advantages of the energy storage control unit and the energy storage device disclosed in the present invention.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] The pre-charge circuit can start the 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, which can limit the peak current, reduce the impact current of the battery pack, and improve the safety of the battery pack.

[0039] Optionally, the energy storage module subunit includes: a control subunit; the control subunit is respectively connected to the corresponding power unit and pre-charging circuit, and is connected to the energy storage control unit; the control subunit is used to control the state of the power unit and control the on and off of the pre-charging circuit when receiving a control instruction sent by the energy storage control unit.

[0040] By controlling the power unit and pre-charge circuit through the control subunit, the charging and discharging of the battery pack can be controlled, which can improve the stability of the charging and discharging current of the battery pack, and has the advantages of good harmonic characteristics and low equivalent switching frequency. It can effectively prevent the battery pack from overcharging and over-discharging, making the charging and discharging of the battery pack safer and more reliable, and improving the service life of the battery pack.

[0041] Optionally, the control subunit is further configured to obtain the voltage of the grading capacitor, the voltage of the battery pack and SOC information, and send the obtained information to the energy storage control unit.

[0042] By obtaining the voltage of the grading capacitor, the voltage of the battery pack, and the SOC information through the control subunit, the energy storage control unit can determine whether the conditions for pre-charging the grading capacitor are met based on the relevant information, and can use the SOC sorting and balancing strategy to select the energy storage submodule as the charging energy storage submodule, making the charging process more stable and improving the reliability of the energy storage device's grid connection and the stability of charging.

[0043] Optionally, the voltage sensor is used to collect the real-time voltage of the energy transmission main line and send it to the energy storage control unit.

[0044] The real-time voltage of the main energy transmission line is collected through electrical sensors. The energy storage control unit performs PI control processing based on the real-time voltage to determine the number of energy storage sub-modules involved in charging, thereby improving the accuracy of controlling the voltage of the main energy transmission line and enhancing the stability of the charging process.

[0045] A fifth aspect of the present disclosure provides a computer-readable storage medium storing computer instructions, which are executed by a processor in the grid-connected control method for the energy storage device provided in the first aspect of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] 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.

[0047] 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.

[0048] 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;

[0049] FIG2 is a flow chart of some embodiments of the grid-connected control method for an energy storage device disclosed herein;

[0050] 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;

[0051] FIG4 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;

[0052] FIG5 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 the energy storage device disclosed herein;

[0053] FIG6 is a schematic diagram of the control principle for determining the number of charging participants based on PI control processing;

[0054] FIG7 is a schematic diagram of a first module of some embodiments of an energy storage control unit disclosed herein;

[0055] FIG8 is a schematic diagram of a second module of some embodiments of the energy storage control unit disclosed herein;

[0056] FIG9 is a schematic diagram of a third module of some embodiments of the energy storage control unit disclosed herein. DETAILED DESCRIPTION

[0057] 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.

[0058] 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).

[0059] 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.

[0060] 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.

[0061] 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.

[0062] The present disclosure provides a technical solution for grid-connected control of an energy storage device. When the main energy transmission line is disconnected from the DC bus, the energy storage units of each energy storage sub-module are controlled in turn to pre-charge the corresponding equalizing capacitors. When the equalizing capacitors of each energy storage sub-module meet the conditions for completing the pre-charging of the equalizing capacitors, the main energy transmission line is controlled to be connected to the DC bus, and the energy storage sub-modules are controlled to perform charging according to the 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 of the energy storage device and the safety of its use, 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-connected energy storage device.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] Power unit 1221 can adopt a variety of circuit structures. For example, power unit 1221 includes switch K3, a rectifier circuit, a grading capacitor C0, and a grading resistor R0. K3 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 to 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.

[0067] 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.

[0068] 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 bypass switch K3 to open and turns the rectifier circuit on.

[0069] 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.

[0070] 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 :

[0071] Step 201 : When the main energy transmission line is disconnected from the DC bus, the energy storage units of the energy storage submodules are sequentially controlled to be connected to the corresponding grading capacitors, so that the energy storage units pre-charge the corresponding grading capacitors.

[0072] Step 202 : When the grading capacitors of the energy storage submodules all meet the grading capacitor pre-charging completion condition, control the energy transmission main line to be connected to the DC bus.

[0073] At grid-connected startup, the main energy transmission line is controlled to be disconnected from the power system and the energy storage unit is controlled to be connected to the corresponding grading capacitor to pre-charge the grading capacitor. 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-connected process, increase the service life of the energy storage device and the safety of the use of the energy storage device, and reduce damage to the connected power grid and other equipment in the power grid; it can ensure smooth grid connection and improve the reliability and safety of the grid connection of the energy storage device.

[0074] In some embodiments, when the main energy transmission line is connected to the DC bus, the energy storage unit of the energy storage submodule is controlled to connect to the corresponding rectifier circuit according to the control strategy for charging. After the pre-charging of the voltage-sharing capacitor is completed, the power grid is controlled to charge the energy storage submodule according to the control strategy. This 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 energy storage device grid connection.

[0075] The control strategy can be a variety of control strategies, and in addition to the control strategy in the embodiment of the present disclosure, the 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 control strategy includes: selecting the energy storage submodule as the charging energy storage submodule according to the SOC information of the energy storage submodule, and controlling the charging energy storage submodule to perform charging processing when the energy transmission main line is connected to the DC bus, so that the power system charges the charging energy storage submodule. 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.

[0076] After completing the pre-charging process of the voltage-equalizing capacitor, the energy storage submodule is selected for charging according to the SOC information of the energy storage submodule, which can make the charging process more stable, ensure smooth grid connection and improve the reliability and safety of the grid connection of the energy storage device.

[0077] In some embodiments, a switch 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 switch circuit, the energy storage unit 1222 and the output end of the rectifier circuit can be connected and disconnected. The switch circuit can be of various types, for example, including a pre-charge circuit.

[0078] Energy storage unit 1222 can employ various circuit structures. For example, as shown in Figures 3A and 3B , energy storage unit 1222 includes an energy storage circuit formed by a battery pack 1223 for storing electrical energy and a pre-charging circuit in series. The number of pre-charging circuits can be one or more, and they can be provided on one or both sides of battery pack 1223. The pre-charging circuit can employ various structures. For example, the pre-charging circuit includes a first circuit 1225 and a second circuit 1226 connected in parallel. A starting resistor R2 and a first switching device K1 are provided in series in the first circuit 1225, and a second switching device K2 is provided in the second circuit 1226.

[0079] When the energy storage unit pre-charges the corresponding voltage-equalizing capacitor, the first line 1225 is connected and the second line 1226 is disconnected to use the starting resistor R1 for current limiting. Current limiting by starting the starting resistor R2 can limit the peak charging current and protect the battery pack 1223. By short-circuiting the starting resistor R2, the energy consumed by starting the starting resistor R2 can be reduced.

[0080] 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, and 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, the control subunit 1224 obtains 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 to be connected or disconnected. The control subunit 1224 controls the power unit 1221 to be connected or disconnected, and controls K3, K2, and K1 to be connected or disconnected according to the control instructions sent by the energy storage control unit 11.

[0081] The control subunit 1224 can be implemented in a variety of ways. For example, the control subunit 1224 includes one or more processors and memories. The memories can be volatile memories and / or non-volatile memories for storing one or more computer program instructions. The processors can run the program instructions to communicate with the energy storage control unit and complete other functions that need to be processed by themselves. The control subunit 1224 can be integrated or divided into two subunits. For example, the control subunit 1224 includes a power control subunit and a battery control subunit. When the power control subunit receives a control instruction sent by the energy storage control unit, it controls the state of the power unit, etc. When the battery control subunit receives a control instruction sent by the energy storage control unit, it controls the on and off of the pre-charge circuit, etc. The power control subunit obtains the voltage of the equalizing capacitor and sends it to the energy storage control unit. The battery control subunit obtains the voltage and SOC information of the battery pack and sends it to the energy storage control unit.

[0082] 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 that the difference between the voltage of the equalizing capacitor and the voltage of the corresponding energy storage unit is less than the voltage difference threshold. As shown in Figures 3A and 3B, at the time of grid-connected startup, the energy storage control unit 11 controls K0 to disconnect so that the main energy transmission line 15 is disconnected from the positive DC bus 21; the energy storage control unit 11 sends a control instruction, and the control subunit 1224 closes K1 and disconnects K2 according to the control instruction, connects the energy storage unit 1222 to the corresponding equalizing capacitor C0, uses R1 for current limiting, and the energy storage unit 1222 pre-charges the corresponding equalizing capacitor C0, that is, uses the battery pack 1223 to pre-charge the equalizing capacitor C0. When pre-charging the equalizing capacitor C0, the control subunit 1224 can control K3 to close.

[0083] The control subunit 1224 obtains the voltage Uc of the voltage balancing capacitor C0 and the voltage Uc of the battery pack 1223 in real time. bat , U bat That is the voltage of the energy storage unit 1222, and is sent to the energy storage control unit 11. When the voltage Uc of the equalizing capacitor C0 minus the voltage of the energy storage unit 1222 (the voltage of the battery pack 1223) U bat When |≤ΔU1, the energy storage submodule's grading capacitors are determined to have met the grading capacitor pre-charge completion condition. ΔU1 is the voltage difference threshold, predetermined based on the battery's internal resistance and allowable charging current. Upon determining that the grading capacitors have met the grading capacitor pre-charge completion condition, the energy storage control unit 11 sends a control instruction, and control subunit 1224 closes K2 according to the control instruction, short-circuiting R2. After closing K2, control subunit 1224 may disconnect K1.

[0084] The voltage-equalizing capacitors of each energy storage submodule are precharged in turn. When the voltage-equalizing capacitors of each energy storage submodule meet the voltage-equalizing capacitor pre-charging completion conditions, that is, when K2 of each energy storage submodule is closed, the energy storage submodule is selected as the charging energy storage submodule according to the SOC information of the energy storage submodule, and the position of the charging energy storage submodule is determined.

[0085] There are many methods for controlling the energy storage submodule to charge based on the SOC information of the energy storage unit. Figure 4 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 4:

[0086] Step 401: Determine the number of energy storage submodules participating in charging.

[0087] Step 402 : When the participating number is greater than 0 and less than the total number of energy storage submodules, determine a change in the number of energy storage submodules participating in charging based on the participating number.

[0088] Step 403 : Using the SOC sorting and balancing strategy and based on the SOC information and variation of the energy storage submodule, an energy storage submodule is selected as a charging energy storage submodule, and the energy storage unit of the charging energy storage submodule is controlled to perform charging processing while the main energy transmission line is connected to the DC bus.

[0089] 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.

[0090] In one embodiment, various methods can be used to control the charging of the energy storage units of the energy storage submodule using the SOC sorting and balancing strategy. FIG5 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 FIG5:

[0091] Step 501: Determine the number of participants N on .

[0092] 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.

[0093] Step 503: Remove all energy storage submodules. For example, when removing an energy storage submodule, the energy storage control unit 11 sends a control instruction to the corresponding control submodule 1224. Based on the control instruction, the control submodule 1224 controls K1, K2, and K3 to be in the open state, or controls K3 and K2 to be in the closed state and K1 to be in the open state.

[0094] Step 504: All energy storage submodules are put into operation. For example, when one energy storage submodule is put into operation, the energy storage control unit 11 sends a control instruction to the corresponding control submodule 1224. The control submodule 1224 controls K2 to be in a connected state and controls K1 and K3 to be in a disconnected state based on the control instruction.

[0095] Step 505: Calculate the change in the number of energy storage submodules N diff =N on -N on_old , that is, in the number of participants N on Less than the total number N of energy storage submodules SMIn the case of on Determine the change in the number of energy storage submodules N diff N on -N on_old , N on_old The number of participants determined last time, when the number of parameters is calculated for the first time, N on_old The default value is 0.

[0096] Step 506, if N diff >0, then go to step 507; if N diff =0, then go to step 708; if N diff <0, then go to step 509.

[0097] 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.

[0098] Step 510, in the removed (N SM -N on_old ) energy storage submodules |N diff |The energy storage submodule with the lowest SOC.

[0099] Step 511, in the removed (N SM -N on_old ) energy storage submodules |N diff |The energy storage submodule with the highest SOC.

[0100] 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.

[0101] 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.

[0102] Step 508, if ⊿SOC max >⊿SOC max_ref , then go to step 512, if ⊿ SOC max <⊿SOC max_ref or ⊿SOC max =⊿SOC max_ref , then go to step 513. ⊿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.

[0103] Step 512 : Select the energy storage submodules with the highest and lowest SOC from among the energy storage submodules that have been put into operation (turned on) and removed (turned off) respectively for switching.

[0104] Step 513: Maintain the current state.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] Step 514, after the N on_old Removal of energy storage submodules |N diff |The energy storage submodule with the highest SOC.

[0109] Step 515, after the N on_old Removal of energy storage submodules |N diff |The energy storage submodule with the lowest SOC.

[0110] 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.

[0111] 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.

[0112] Using the SOC sorting and balancing strategy and based on the SOC information and change amount of the energy storage submodule, when the energy storage submodule is selected as the charging energy storage submodule for charging for the first time, the energy storage control unit 11 controls K0 to close so that the power system charges the charging energy storage submodule. Then, using the SOC sorting and balancing strategy and based on the SOC information and change amount of the energy storage submodule, continue to select the energy storage submodule as the charging energy storage submodule for charging. Determine whether the charging completion condition is met. When the charging completion condition is met, determine that the energy storage device is connected to the grid and charging is completed. There can be multiple charging completion conditions. For example, the charging completion condition can be that the average value of the SOC of all energy storage submodules is greater than the SOC threshold, or the duration of charging using the SOC sorting and balancing strategy is greater than the duration threshold, etc.

[0113] In some embodiments, when the voltage-sharing capacitor of the energy storage submodule meets the voltage-sharing capacitor pre-charge completion condition and the charging energy storage submodule is charging, the second line 1226 is controlled to be connected to short-circuit the starting resistor R1. As shown in Figures 3A and 3B, the energy storage control unit 11 sends a control instruction to the corresponding control subunit 1224. Based on the control instruction, the control subunit 1224 controls K2 to be connected, short-circuiting R2; it can also control K1 to be disconnected, disconnecting R2.

[0114] In some embodiments, various methods can be used to determine the number of energy storage subunits participating in charging. For example, PI control processing can be performed based on a reference voltage and the real-time voltage of the main energy transmission line 15 to determine the number of energy storage subunits participating in charging.

[0115] PI control processing 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. As shown in Figure 6, U N is the reference voltage, which can be the actual measured or preset voltage U at the connection point between the positive DC bus and the energy storage device. N ; U is the actually measured voltage U of the energy storage device, and the PI algorithm used in the PI control process is:

[0116]

[0117] Where Nref is the number of energy storage sub-units to be put into use, that is, the number of energy storage sub-modules participating in charging; kp is the proportional adjustment parameter, T is the integral adjustment parameter; err(t) is the difference between the voltage U of the energy storage device and the reference voltage U N The difference between I and Iref; according to the PI control process, the number of participants is modified until I and Iref are the same, or U and U NThe difference is less than the preset voltage difference threshold. When calculating the number of participants, the parameter values ​​of kp, T, and Iref can be the same or adjusted accordingly.

[0118] 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.

[0119] In some embodiments, as shown in FIG7 , the present disclosure provides an energy storage control unit 70, comprising a voltage-equalizing capacitor pre-charging module 71 and a line connection control module 72. When the main energy transmission line is disconnected from the DC bus, the voltage-equalizing capacitor pre-charging module 71 sequentially controls the energy storage units of each energy storage submodule to connect with the corresponding voltage-equalizing capacitors, so that the energy storage units pre-charge the corresponding voltage-equalizing capacitors. When the voltage-equalizing capacitors of each energy storage submodule meet the voltage-equalizing capacitor pre-charging completion condition, the line connection control module 72 controls the main energy transmission line to connect with the DC bus.

[0120] As shown in FIG8 , the energy storage control unit 70 further includes a charging control module 73 . When the energy transmission main line is connected to the DC bus, the charging control module 73 controls the energy storage unit of the energy storage submodule to be connected to the corresponding rectifier circuit according to a control strategy for charging.

[0121] In some embodiments, the charging control module 73 selects an energy storage submodule as a charging energy storage submodule based on the SOC information of the energy storage submodule, and controls the charging energy storage submodule to perform charging processing when the main energy transmission line is connected to the DC bus, so that the power system charges the charging energy storage submodule.

[0122] Charging control module 73 determines the number of energy storage submodules participating in charging. If the number of energy storage submodules participating is greater than 0 but less than the total number of energy storage submodules, the module then determines the change in the number of energy storage submodules participating in charging based on the number of energy storage submodules participating. Using the SOC sorting and balancing strategy and based on the SOC information and change of the energy storage submodules, charging control module 73 selects an energy storage submodule as the charging energy storage submodule. It then controls the charging of the energy storage units of the charging energy storage submodule while the main energy transmission line is connected to the DC bus.

[0123] When the energy storage unit pre-charges the corresponding grading capacitor, the grading capacitor pre-charging module 71 uses the starting resistor to limit the current. The charging control module 73 short-circuits the starting resistor when the grading capacitor of the energy storage submodule meets the grading capacitor pre-charging completion condition and the charging energy storage submodule is charged.

[0124] In some embodiments, as shown in FIG8 , the energy storage control unit 70 includes a participant quantity determination module 73 . The quantity determination module 73 performs PI control processing based on a reference voltage and a real-time voltage of the energy transmission main line to determine the participant quantity.

[0125] FIG9 is a schematic diagram of a third module of some embodiments of the energy storage control unit of the present disclosure. As shown in FIG9 , the energy storage control unit may include a memory 901, a processor 902, a communication interface 903, and a bus 904. The memory 901 is used to store instructions. The processor 902 is coupled to the memory 901 and is configured to execute the grid-connected control method of the energy storage device in any of the above-described embodiments based on the instructions stored in the memory 901.

[0126] Memory 901 may be a high-speed RAM memory, a non-volatile memory, or the like. Memory 901 may also be a memory array. Memory 901 may also be divided into blocks, and the blocks may be combined into virtual volumes according to certain rules. Processor 902 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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 block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks 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 produce a device for implementing the functions specified in one or more processes in the flowchart and / or one or more blocks in the block diagram.

[0131] 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.

[0132] 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.

[0133] 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: When the energy transmission main line is disconnected from the DC bus, the energy storage unit of each energy storage submodule is sequentially controlled to be connected to the corresponding grading capacitor, so that the energy storage unit pre-charges the corresponding grading capacitor; When the grading capacitors of the energy storage submodules meet the grading capacitor pre-charging completion condition, the energy transmission main line is controlled to be connected to the DC bus.

2. The method of claim 1, comprising: When the energy transmission main line is connected to the DC bus, the energy storage unit of the energy storage submodule is controlled to be connected to the corresponding rectifier circuit according to the control strategy to perform charging processing.

3. The method according to claim 2, wherein controlling the energy storage unit of the energy storage submodule to be connected to the corresponding rectifier circuit according to the control strategy to perform charging processing comprises: An energy storage submodule is selected as a charging energy storage submodule according to the SOC information of the energy storage submodule, and the charging energy storage submodule is controlled to be connected to the corresponding rectifier circuit when the energy transmission main line is connected to the DC bus for charging processing.

4. The method according to claim 3, wherein selecting the energy storage submodule as the charging energy storage submodule according to the SOC information of the energy storage submodule comprises: Determining the number of participants corresponding to the energy storage submodules participating in the charging; When the participating number is greater than 0 and less than the total number of the energy storage submodules, determining a change in the number of energy storage submodules participating in charging based on the 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 variation.

5. The method according to claim 4, 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 and the variation of the energy storage submodule comprises: If the change is equal to 0 and the maximum SOC deviation is greater than the SOC deviation threshold, then the energy storage submodule with the smallest SOC is selected from all energy storage submodules that are not used as charging energy storage submodules as the new charging energy storage submodule; and the energy storage submodule with the largest SOC is selected 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.

6. The method according to claim 4, 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 and the variation of the energy storage submodule comprises: When the 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 change are selected as new charging energy storage submodules from all energy storage submodules that are not used as charging energy storage submodules; or When the 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 change are selected from all energy storage submodules that are not used as charging energy storage submodules as new charging energy storage submodules.

7. The method according to claim 4, wherein the step of utilizing the SOC sorting and balancing strategy and selecting the energy storage submodule as the charging energy storage submodule according to the SOC information and the variation of the energy storage submodule comprises: When the 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 variation are selected from all the charging energy storage submodules as the removed energy storage submodules; or When the 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 change are selected from all charging energy storage submodules as cut-off energy storage submodules.

8. The method according to claim 4, wherein determining the number of participants corresponding to the energy storage submodules participating in the charging comprises: PI control processing is performed based on a reference voltage and a real-time voltage of the energy transmission main line to determine the participating quantity.

9. The method of claim 1, 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 starting resistor is provided in the first circuit; the method includes: When the energy storage unit pre-charges the corresponding voltage-sharing capacitor, the first circuit is controlled to be connected and the second circuit is controlled to be disconnected, so as to use the starting resistor for current limiting; When the voltage-equalizing capacitor of the energy storage submodule meets the voltage-equalizing capacitor pre-charging completion condition and the charging energy storage submodule is charged, the second circuit is controlled to be connected to short-circuit the starting resistor.

10. The method of claim 1, wherein: The condition that the grading capacitor is fully charged includes: a difference between the voltage of the grading capacitor and the voltage of the corresponding energy storage unit is less than a voltage difference threshold.

11. 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-charge control module is used to control the energy storage unit of each energy storage submodule to be connected to the corresponding grading capacitor in sequence when the energy transmission main line is disconnected from the DC bus, so that the energy storage unit pre-charges the corresponding grading capacitor; The line connection control module is used to control the main energy transmission line to be connected with the DC bus when the grading capacitors of each energy storage sub-module meet the grading capacitor pre-charging completion condition.

12. The apparatus of claim 11, further comprising: 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 control strategy when the energy transmission main line is connected to the DC bus to perform charging processing.

13. 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 10 based on instructions stored in the memory.

14. An energy storage system comprising: An energy storage device and an energy storage control unit according to any one of claims 11 to 13.

15. The energy storage system according to claim 14, 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.

16. The energy storage system according to claim 15, 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.

17. The energy storage system according to claim 16, 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.

18. The energy storage system according to claim 16, wherein: The energy storage module subunit includes: a control subunit; the control subunit is respectively connected to the corresponding power unit and pre-charge circuit, and is connected to the energy storage control unit; The control subunit is used to control the state of the power unit and control the on and off of the pre-charging circuit when receiving the control instruction sent by the energy storage control unit.

19. The energy storage system according to claim 18, wherein: The control subunit is further configured to obtain the voltage of the grading capacitor, the voltage of the battery pack, and SOC information, and send the information to the energy storage control unit.

20. The energy storage system according to claim 14, comprising: The voltage sensor is used to collect the real-time voltage of the energy transmission main line and send it to the energy storage control unit.

21. A computer-readable storage medium storing computer instructions, wherein the instructions are executed by a processor to execute the method according to any one of claims 1 to 10.

Images