Droop control method and device of energy storage system in direct current microgrid

Abstract

The application provides a droop control method and device for an energy storage system in a direct-current microgrid, and the method comprises the following steps: obtaining an initial droop curve; determining a boundary condition of a droop control parameter in the droop curve; establishing a target function with the highest cycle efficiency of the energy storage system in full charging and full discharging as a target; establishing a droop curve optimization model according to the target function and the boundary condition; solving the droop curve optimization model to obtain an optimal solution of the droop control parameter, so as to update the initial droop curve; and controlling the energy storage system by using the updated droop curve. The application can improve the power conversion efficiency of the energy storage system, and improve the economy and service life of the energy storage system and even the entire direct-current microgrid.

Description

Technical Field

[0001] This invention relates to the field of DC microgrid control technology, specifically to a droop control method and a droop control device for an energy storage system in a DC microgrid. Background Technology

[0002] In DC microgrids, energy storage inverters typically employ droop control to regulate battery power. Specifically, the energy management system (EMS) within the inverter generates a setpoint for the battery port voltage based on the desired battery power and the droop curve, then controls the inverter to maintain the port voltage at this setpoint. The bidirectional DC / DC converter then samples the current port voltage and adjusts the battery power based on the same droop control curve. This design decouples the inverter's port voltage control from the battery power control, enabling rapid battery power regulation.

[0003] While the aforementioned droop control enables rapid adjustment of battery power, the droop curve used is often only a feasible curve and cannot maximize the system's efficiency. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a droop control method and apparatus for an energy storage system in a DC microgrid, which can improve the power conversion efficiency of the energy storage system and enhance the economy and lifespan of the energy storage system and even the entire DC microgrid.

[0005] The technical solution adopted in this invention is as follows:

[0006] A droop control method for an energy storage system in a DC microgrid includes the following steps: obtaining an initial droop curve; determining the boundary conditions of the droop control parameters in the droop curve; establishing an objective function with the goal of maximizing the cycle efficiency of the energy storage system during full charge and discharge; establishing a droop curve optimization model based on the objective function and the boundary conditions; solving the droop curve optimization model to obtain the optimal solution of the droop control parameters, thereby updating the initial droop curve; and controlling the energy storage system using the updated droop curve.

[0007] The droop control parameters in the droop curve include the discharge initiation voltage, the charging initiation voltage, the discharge droop coefficient, and the charging droop coefficient.

[0008] The charging start voltage is not less than the discharging start voltage.

[0009] The objective function is:

[0010] maxη cycle =η charge *η discharge

[0011]

[0012]

[0013] Where, η cycle η is the cycle efficiency of the energy storage system after full charge and discharge. charge The efficiency of the energy storage system at full power charging, η discharge Let V1, V2, K1, and K2 be the discharge initiation voltage, the charging initiation voltage, the discharge droop coefficient, and the charging droop coefficient, respectively, and P be the discharge droop coefficient. ac_max Let f be the maximum power on the AC side of the energy storage inverter in the DC microgrid, and f() represent the functional relationship between efficiency and the independent variable.

[0014] The optimization model of the drooping curve is solved using the composite method.

[0015] A droop control device for an energy storage system in a DC microgrid includes: an acquisition module for acquiring an initial droop curve; a determination module for determining boundary conditions for droop control parameters in the droop curve; a first establishment module for establishing an objective function with the goal of maximizing the cycle efficiency of the energy storage system during full charge and discharge; a second establishment module for establishing a droop curve optimization model based on the objective function and the boundary conditions; an update module for solving the droop curve optimization model to obtain the optimal solution for the droop control parameters, thereby updating the initial droop curve; and a control module for controlling the energy storage system using the updated droop curve.

[0016] The droop control parameters in the droop curve include the discharge initiation voltage, the charging initiation voltage, the discharge droop coefficient, and the charging droop coefficient.

[0017] The charging start voltage is not less than the discharging start voltage.

[0018] The objective function is:

[0019] maxη cycle =η charge *η discharge

[0020]

[0021]

[0022] Where, η cycle η is the cycle efficiency of the energy storage system after full charge and discharge. chargeThe efficiency of the energy storage system at full power charging, η discharge Let V1, V2, K1, and K2 be the discharge initiation voltage, the charging initiation voltage, the discharge droop coefficient, and the charging droop coefficient, respectively, and P be the discharge droop coefficient. ac_max Let f be the maximum power on the AC side of the energy storage inverter in the DC microgrid, and f() represent the functional relationship between efficiency and the independent variable.

[0023] The update module solves the sag curve optimization model using the composite method.

[0024] The beneficial effects of this invention are:

[0025] This invention establishes an objective function with the goal of maximizing the cycle efficiency of the energy storage system during full charge and discharge, and solves for the optimal droop control parameters based on this objective function, thereby obtaining the optimal droop curve. This improves the power conversion efficiency of the energy storage system and enhances the economy and lifespan of the energy storage system and even the entire DC microgrid. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of a DC microgrid according to an embodiment of the present invention;

[0027] Figure 2 This is a flowchart of the droop control method for an energy storage system in a DC microgrid according to an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of a drooping curve according to an embodiment of the present invention;

[0029] Figure 4 This is a schematic diagram of a droop curve update according to an embodiment of the present invention;

[0030] Figure 5 This is a block diagram of the droop control device of the energy storage system in a DC microgrid according to an embodiment of the present invention. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] like Figure 1As shown, one embodiment of the present invention's DC microgrid includes an energy storage inverter 1, a battery 2, and a photovoltaic panel 3. The battery 2 and the energy storage inverter 1 constitute an energy storage system. The battery 2 and the photovoltaic panel 3 are connected to the DC side of the energy storage inverter 1. The AC side of the energy storage inverter 1 is connected to the power grid 5 and a load 6 respectively through a grid-connected / off-grid switching device 4. The battery 2 includes a battery pack and a bidirectional DC / DC converter. Through the control of control components such as the EMS and inverter controller within the energy storage inverter 1, the battery can both store energy and supply power to the power grid and the load.

[0033] like Figure 2 As shown, the droop control method for an energy storage system in a DC microgrid according to an embodiment of the present invention includes the following steps:

[0034] S1, obtain the initial droop curve.

[0035] In this embodiment of the invention, the drooping curve is a power-voltage curve, which represents the relationship between the battery input power and the battery input port voltage. The battery input port voltage is the voltage at its own port, measured internally by the battery.

[0036] In one embodiment of the present invention, the droop control parameters in the droop curve include a discharge initiation voltage V1, a charging initiation voltage V2, a discharge droop coefficient K1, and a charging droop coefficient K2. The discharge initiation voltage V1 and the charging initiation voltage V2 may be the same or different. In a preferred embodiment of the present invention, as shown... Figure 3 As shown, the charging start voltage V2 can be greater than the discharging start voltage V1. That is, in a preferred embodiment of the present invention, the droop curve can include a charging region, a no-charge / no-discharge region, and a discharging region. In the discharging region, the battery input power is less than or equal to 0, the battery input port voltage is less than or equal to the discharging start voltage V1, and the droop coefficient is K1. In the no-charge / no-discharge region, the battery input power is equal to 0, the battery input port voltage is between the discharging start voltage V1 and the charging start voltage V2, and the droop coefficient can be considered 0. In the charging region, the battery input power is greater than or equal to 0, the battery input port voltage is greater than or equal to the charging start voltage V2, and the droop coefficient is K2. By adding a no-charge / no-discharge region, frequent switching between charging and discharging states can be effectively avoided when the battery's rated charging / discharging state switching voltage value is approaching.

[0037] In one embodiment of the present invention, the initial droop curve may be pre-designed and stored, or it may be the droop curve used during the previous control cycle. This initial droop curve can only ensure that the energy storage system operates normally, but it cannot guarantee that the cycle efficiency of the energy storage system will reach its optimal level.

[0038] S2 determines the boundary conditions for the sag control parameters in the sag curve.

[0039] The boundary conditions of the droop control parameters in the droop curve are the boundaries of the values ​​of each droop control parameter. In one embodiment of the present invention, the boundary values ​​of the discharge initiation voltage V1 and the charging initiation voltage V2 are the same, and the minimum value of both is the minimum allowable value of the bus voltage V. bus_min The maximum values ​​are all the maximum allowable bus voltage V. bus_max .

[0040] In one embodiment of the present invention, the minimum allowable value for the bus voltage is:

[0041]

[0042] Among them, V n V is the rated voltage on the AC side of the energy storage inverter. margin This is a preset voltage margin, for example, it can be set to 30V.

[0043] The maximum allowable bus voltage is:

[0044] V bus_max =k*V transistor -V overshoot_max

[0045] Among them, V transistor The voltage rating of the device is given by k, which is a safety factor. k is less than 1 to ensure device safety; for example, it can be taken as 0.8 V. overshoot_max This is the maximum overcharge voltage.

[0046] The discharge droop coefficient K1 and the charge droop coefficient K2 have the same value boundaries. The maximum and minimum values ​​can be selected by comprehensively considering the accuracy of the battery input port voltage acquisition and the maximum battery input power.

[0047] S3 establishes an objective function with the goal of maximizing the cycle efficiency of the energy storage system during full charging and discharging.

[0048] The charging and discharging efficiency of an energy storage system depends on the bus voltage and the AC power of the energy storage inverter. In other words, the independent variables of the energy storage system's efficiency curve are the bus voltage and the AC power of the energy storage inverter. The specific relationships are as follows:

[0049] η=f(V bus ,P ac )

[0050] Where η is the operating efficiency of the energy storage system, and V bus P is the bus voltage. ac Let f be the AC power of the energy storage inverter, and let f() represent the functional relationship between efficiency and the independent variable.

[0051] In a specific embodiment of the present invention, the operating efficiency η of the energy storage system is related to the bus voltage V.bus and the AC side power P of the energy storage inverter ac The functional relationship is as follows:

[0052]

[0053] Where k is the bus voltage V bus The coefficients, ω is a constant term, and a and b are the AC side power P of the energy storage inverter. ac The coefficients are denoted by c, which is a constant term. k, ω, a, b, and c can be obtained through fitting.

[0054] Therefore, the efficiency of the energy storage system at full power charging is:

[0055]

[0056] The efficiency of the energy storage system at full power discharge is:

[0057]

[0058] The cycle efficiency of the energy storage system after full charge and discharge is:

[0059] η cycle =η charge *η discharge

[0060] Where, η cycle η is the cycle efficiency of the energy storage system after full charge and discharge. charge The efficiency of charging an energy storage system to full power, η discharge For the efficiency of the energy storage system at full power discharge, P ac_max This represents the maximum power on the AC side of the energy storage inverter in a DC microgrid.

[0061] The objective function established in this embodiment of the invention is:

[0062] maxη cycle =η charge *η discharge

[0063] S4. Establish a sag curve optimization model based on the objective function and boundary conditions.

[0064] S5, solve the sag curve optimization model to obtain the optimal solution of the sag control parameters, so as to update the initial sag curve.

[0065] In one embodiment of the present invention, a global optimization search algorithm, such as the composite method, can be used to solve the droop curve optimization model to obtain the optimal solutions for the discharge initiation voltage V1, the charging initiation voltage V2, the discharge droop coefficient K1, and the charging droop coefficient K2, thereby updating the droop curve with the optimal droop control parameters.

[0066] S6 controls the energy storage system using the updated droop curve.

[0067] The droop control method for the energy storage system in the DC microgrid of this invention can calculate the optimal droop curve based on the efficiency curve and achieve control of the energy storage system with the optimal droop curve.

[0068] In one specific embodiment of the present invention, the initial droop curve is as follows: Figure 4 As shown by the dashed line, the discharge initiation voltage V1 is 400V, the charging initiation voltage V2 is 410V, and the discharge droop coefficient K1 and the charging droop coefficient K2 are both 250W / V. After updating the droop curve using the method of this embodiment of the invention, the updated droop curve is as follows. Figure 4 As shown by the solid line, assuming that after the update only the discharge initiation voltage V1 and the charging initiation voltage V2 decrease by 5V, and the discharge droop coefficient K1 and the charging droop coefficient K2 remain unchanged, the efficiency comparison of the energy storage system under the control of the initial droop curve and the updated droop curve is shown in Table 1.

[0069] Table 1

[0070]

[0071] As can be seen from Table 1, the efficiency of the energy storage system under the updated droop curve control is significantly improved.

[0072] The droop control method for energy storage systems in DC microgrids according to embodiments of the present invention establishes an objective function with the goal of maximizing the cycle efficiency of the energy storage system during full charge and discharge, and solves for the optimal droop control parameters based on the objective function to obtain the optimal droop curve. This improves the power conversion efficiency of the energy storage system and enhances the economy and lifespan of the energy storage system and even the entire DC microgrid.

[0073] Corresponding to the droop control method for the energy storage system in the DC microgrid in the above embodiments, the present invention also proposes a droop control device for the energy storage system in the DC microgrid.

[0074] like Figure 5As shown, the droop control device for an energy storage system in a DC microgrid according to an embodiment of the present invention includes an acquisition module 10, a determination module 20, a first establishment module 30, a second establishment module 40, an update module 50, and a control module 60. The acquisition module 10 is used to acquire an initial droop curve; the determination module 20 is used to determine the boundary conditions of the droop control parameters in the droop curve; the first establishment module 30 is used to establish an objective function with the goal of maximizing the cycle efficiency of the energy storage system during full charge and discharge; the second establishment module 40 is used to establish a droop curve optimization model based on the objective function and boundary conditions; the update module 50 is used to solve the droop curve optimization model to obtain the optimal solution of the droop control parameters, thereby updating the initial droop curve; and the control module 60 is used to control the energy storage system using the updated droop curve.

[0075] In this embodiment of the invention, the drooping curve is a power-voltage curve, which represents the relationship between the battery input power and the battery input port voltage. The battery input port voltage is the voltage at its own port, measured internally by the battery.

[0076] In one embodiment of the present invention, the droop control parameters in the droop curve include a discharge initiation voltage V1, a charging initiation voltage V2, a discharge droop coefficient K1, and a charging droop coefficient K2. The discharge initiation voltage V1 and the charging initiation voltage V2 may be the same or different. In a preferred embodiment of the present invention, as shown... Figure 3 As shown, the charging start voltage V2 can be greater than the discharging start voltage V1. That is, in a preferred embodiment of the present invention, the droop curve can include a charging region, a no-charge / no-discharge region, and a discharging region. In the discharging region, the battery input power is less than or equal to 0, the battery input port voltage is less than or equal to the discharging start voltage V1, and the droop coefficient is K1. In the no-charge / no-discharge region, the battery input power is equal to 0, the battery input port voltage is between the discharging start voltage V1 and the charging start voltage V2, and the droop coefficient can be considered 0. In the charging region, the battery input power is greater than or equal to 0, the battery input port voltage is greater than or equal to the charging start voltage V2, and the droop coefficient is K2. By adding a no-charge / no-discharge region, frequent switching between charging and discharging states can be effectively avoided when the battery's rated charging / discharging state switching voltage value is approaching.

[0077] In one embodiment of the present invention, the initial droop curve may be pre-designed and stored, or it may be the droop curve used during the previous control cycle. This initial droop curve can only ensure that the energy storage system operates normally, but it cannot guarantee that the cycle efficiency of the energy storage system will reach its optimal level.

[0078] The boundary conditions of the droop control parameters in the droop curve are the boundaries of the values ​​of each droop control parameter. In one embodiment of the present invention, the boundary values ​​of the discharge initiation voltage V1 and the charging initiation voltage V2 are the same, and the minimum value of both is the minimum allowable value of the bus voltage V. bus_min The maximum values ​​are all the maximum allowable bus voltage V. bus_max .

[0079] In one embodiment of the present invention, the minimum allowable value for the bus voltage is:

[0080]

[0081] Among them, V n V is the rated voltage on the AC side of the energy storage inverter. margin This is a preset voltage margin, for example, it can be set to 30V.

[0082] The maximum allowable bus voltage is:

[0083] V bus_max =k*V transistor -V overshoot_max

[0084] Among them, V transistor The voltage rating of the device is given by k, which is a safety factor. k is less than 1 to ensure device safety; for example, it can be taken as 0.8 V. overshoot_max This is the maximum overcharge voltage.

[0085] The discharge droop coefficient K1 and the charge droop coefficient K2 have the same value boundaries. The maximum and minimum values ​​can be selected by comprehensively considering the accuracy of the battery input port voltage acquisition and the maximum battery input power.

[0086] The charging and discharging efficiency of an energy storage system depends on the bus voltage and the AC power of the energy storage inverter. In other words, the independent variables of the energy storage system's efficiency curve are the bus voltage and the AC power of the energy storage inverter. The specific relationships are as follows:

[0087] η=f(V bus ,P ac )

[0088] Where η is the operating efficiency of the energy storage system, and V bus P is the bus voltage. ac Let f be the AC power of the energy storage inverter, and f() represent the functional relationship between efficiency and the independent variable.

[0089] In a specific embodiment of the present invention, the operating efficiency η of the energy storage system is related to the bus voltage V. bus and the AC side power P of the energy storage inverter ac The functional relationship is as follows:

[0090]

[0091] Where k is the bus voltage V bus The coefficients, ω is a constant term, and a and b are the AC side power P of the energy storage inverter. ac The coefficients are denoted by c, which is a constant term. k, ω, a, b, and c can be obtained through fitting.

[0092] Therefore, the efficiency of the energy storage system at full power charging is:

[0093]

[0094] The efficiency of the energy storage system at full power discharge is:

[0095]

[0096] The cycle efficiency of the energy storage system after full charge and discharge is:

[0097] η cycle =η charge *η discharge

[0098] Where, η cycle η is the cycle efficiency of the energy storage system after full charge and discharge. charge The efficiency of charging an energy storage system to full power, η discharge For the efficiency of the energy storage system at full power discharge, P ac_max This represents the maximum power on the AC side of the energy storage inverter in a DC microgrid.

[0099] The objective function established by the first module 30 is:

[0100] maxη cycle =η charge *η discharge

[0101] In one embodiment of the present invention, the updating module 50 may employ a global optimization search algorithm, such as the composite method, to solve the droop curve optimization model and obtain the optimal solutions for the discharge initiation voltage V1, the charging initiation voltage V2, the discharge droop coefficient K1, and the charging droop coefficient K2, thereby updating the droop curve with the optimal droop control parameters.

[0102] The droop control device for the energy storage system in the DC microgrid of this invention can calculate the optimal droop curve based on the efficiency curve and control the energy storage system with the optimal droop curve.

[0103] In one specific embodiment of the present invention, the initial droop curve is as follows: Figure 4As shown by the dashed line, the discharge initiation voltage V1 is 400V, the charging initiation voltage V2 is 410V, and the discharge droop coefficient K1 and the charging droop coefficient K2 are both 250W / V. After updating the droop curve using the device of this embodiment of the invention, the updated droop curve is as follows. Figure 4 As shown by the solid line, assuming that after the update only the discharge initiation voltage V1 and the charging initiation voltage V2 decrease by 5V, and the discharge droop coefficient K1 and the charging droop coefficient K2 remain unchanged, the efficiency comparison of the energy storage system under the control of the initial droop curve and the updated droop curve is shown in Table 1.

[0104] As can be seen from Table 1, the efficiency of the energy storage system under the updated droop curve control is significantly improved.

[0105] According to an embodiment of the present invention, the droop control device for the energy storage system in a DC microgrid establishes an objective function with the goal of maximizing the cycle efficiency of the energy storage system during full charge and discharge, and solves for the optimal droop control parameters based on the objective function, thereby obtaining the optimal droop curve. This improves the power conversion efficiency of the energy storage system and enhances the economy and lifespan of the energy storage system and even the entire DC microgrid.

[0106] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. "A plurality of" means two or more, unless otherwise explicitly specified.

[0107] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0108] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0109] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0110] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

[0111] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0112] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0113] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

[0114] Furthermore, the functional units in the various embodiments of the present invention can be integrated into a processing module, or each unit can exist physically separately, or two or more units can be integrated into a module. The integrated module can be implemented in hardware or as a software functional module. If the integrated module is implemented as a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium.

[0115] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A droop control method for an energy storage system in a DC microgrid, characterized in that, Includes the following steps: Obtain the initial droop curve; Determine the boundary conditions for the sag control parameters in the sag curve; An objective function is established with the goal of maximizing the cycle efficiency of the energy storage system during full charge and discharge. A sag curve optimization model is established based on the objective function and the boundary conditions. Solve the sag curve optimization model to obtain the optimal solution of the sag control parameters, so as to update the initial sag curve; The energy storage system is controlled using the updated droop curve. The droop control parameters in the droop curve include the discharge initiation voltage, the charging initiation voltage, the discharge droop coefficient, and the charging droop coefficient. The charging initiation voltage is not less than the discharge initiation voltage. The objective function is: max the cycle =h charge or discharge Where, η cycle η is the cycle efficiency of the energy storage system after full charge and discharge. charge The efficiency of the energy storage system at full power charging, η discharge Let V1, V2, K1, and K2 be the discharge initiation voltage, the charging initiation voltage, the discharge droop coefficient, and the charging droop coefficient, respectively, and P be the discharge droop coefficient. ac_max Let f be the maximum power on the AC side of the energy storage inverter in the DC microgrid, and f() represent the functional relationship between efficiency and the independent variable.

2. The droop control method for an energy storage system in a DC microgrid according to claim 1, characterized in that, The optimization model of the drooping curve is solved using the composite method.

3. A droop control device for an energy storage system in a DC microgrid, characterized in that, include: An acquisition module is used to acquire an initial droop curve; A determination module, which is used to determine the boundary conditions of the sag control parameters in the sag curve; The first establishment module is used to establish an objective function with the goal of maximizing the cycle efficiency of the energy storage system during full charging and discharging. The second establishment module is used to establish a sag curve optimization model based on the objective function and the boundary conditions. An update module is used to solve the droop curve optimization model to obtain the optimal solution of the droop control parameters, so as to update the initial droop curve. A control module is configured to control the energy storage system using an updated droop curve. The droop control parameters in the droop curve include the discharge initiation voltage, the charging initiation voltage, the discharge droop coefficient, and the charging droop coefficient. The charging initiation voltage is not less than the discharge initiation voltage. The objective function is: max the cycle =h charge or discharge Where, η cycle η is the cycle efficiency of the energy storage system after full charge and discharge. charge The efficiency of the energy storage system at full power charging, η discharge Let V1, V2, K1, and K2 be the discharge initiation voltage, the charging initiation voltage, the discharge droop coefficient, and the charging droop coefficient, respectively, and P be the discharge droop coefficient. ac_max Let f be the maximum power on the AC side of the energy storage inverter in the DC microgrid, and let f() represent the functional relationship between efficiency and the independent variable.

4. The droop control device for an energy storage system in a DC microgrid according to claim 3, characterized in that, The update module solves the sag curve optimization model using the composite method.

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