Method and device for allocating virtual inertia of photovoltaic cluster

Abstract

The present disclosure provides a method and device for allocating virtual inertia of a photovoltaic cluster. The method includes: determining the required virtual inertia to be provided according to the rate of change of frequency monitored at the grid connection point of the photovoltaic grid-connected system; obtaining the numerical values of the indicators affecting the provision of virtual inertia by each VSG control unit in the photovoltaic cluster of the photovoltaic grid-connected system; determining the function values corresponding to each indicator by using a pre-determined function equation; and determining the allocation ratio of the required virtual inertia to be provided among each VSG control unit according to the function values corresponding to each indicator. In this way, the problem of difficult conversion between multiple performances during the operation of the power system can be overcome, multiple objectives of inertia allocation are taken into account, the rate of change of frequency can be suppressed to a certain extent and quickly restored to a stable state, and the method is simple and practical.

Description

Technical Field

[0001] Embodiments of the present disclosure generally relate to the field of photovoltaic power generation, and more particularly, to a method and apparatus for allocating virtual inertia of a photovoltaic cluster. Background Art

[0002] Data shows that as of the end of 2020, the installed capacity of renewable energy power generation nationwide reached 934 million kilowatts, with a year-on-year growth of about 17.5%. Among them, the installed capacity of wind power was 281 million kilowatts, and the installed capacity of photovoltaic power generation was 253 million kilowatts. Therefore, the large-scale development of photovoltaic power generation has become an irresistible trend.

[0003] Photovoltaic power generation mainly relies on power electronic devices to send the absorbed energy into the power grid. However, when a load mutation occurs, the power electronic devices do not have the inertia control like that in a traditional generator, which may cause a large and rapid change in frequency and seriously affect the stability of the power system in severe cases. For this reason, some scholars have proposed virtual synchronous generator (VSG) control, aiming to simulate the inertia characteristics of a traditional generator during a load mutation, provide virtual inertia for the system, and ensure that the frequency can quickly recover to a stable state.

[0004] In the existing research field of VSG control, most studies focus on the characteristics of virtual generator control itself and inertia allocation. However, with the gradual expansion of the photovoltaic market and the increasing scale of photovoltaic power generation, a single VSG control unit is no longer sufficient to maintain the safety and stability of a large-scale photovoltaic grid-connected system. Therefore, multiple VSG control units need to coordinate and cooperate to ensure the stable operation of the whole system. In a photovoltaic grid-connected system controlled by multiple VSG control units, how to allocate the virtual inertia provided by each unit has become an urgent problem to be solved. Summary of the Invention

[0005] According to an embodiment of the present disclosure, a method for allocating virtual inertia of a photovoltaic cluster is provided, which can convert objective functions with different dimensions and different degrees of satisfaction into objective functions with the same dimension and the same degree of satisfaction, overcome the problem of difficult conversion between multiple performances during the operation of a power system, take into account multiple objectives in inertia allocation, and can also suppress the rate of change of frequency to a certain extent and quickly recover to a stable state. The method is simple and practical.

[0006] In a first aspect of the present disclosure, a method for allocating virtual inertia of a photovoltaic cluster is provided, including:

[0007] Determining the virtual inertia to be provided according to the rate of change of frequency monitored at the grid connection point of the photovoltaic grid-connected system;

[0008] Obtaining the numerical values of the indicators in the photovoltaic cluster of the photovoltaic grid-connected system that affect the virtual inertia provided by each VSG control unit;

[0009] Determine the function values corresponding to each index using a pre-determined function equation, where the function equation is determined by the following method: construct an objective function, determine the membership function corresponding to each VSG control unit according to the objective function, establish a small-signal model of the system, perform stability analysis on the parameters in the membership function using the root locus analysis method, determine the optimal parameters, and obtain the function equation;

[0010] Determine the allocation ratio of the required virtual inertia provided in each VSG control unit according to the function values corresponding to each index.

[0011] In some embodiments, obtaining the numerical values of the indices that affect the provision of virtual inertia by each VSG control unit in the photovoltaic cluster of the photovoltaic grid-connected system includes:

[0012] Obtain the remaining energy storage capacity of the supercapacitor, the rated power of the converter, and the adjustable power of energy storage charge and discharge of the photovoltaic units corresponding to each VSG control unit in the photovoltaic cluster of the photovoltaic grid-connected system.

[0013] In some embodiments, the determining the function values corresponding to each index using the pre-determined function equation includes:

[0014] Determine the function values corresponding to each index using the following function equation:

[0015]

[0016] where x is the index, u(x) is the function value, p 10 , q 10 , C 10 , p 11 , q 11 , C 11 are determined parameters, and a, b, c, d are the boundaries for dividing the working regions of the energy storage state of charge, where the ab segment is the energy storage discharge state, the bc segment is the normal energy storage state, and the cd segment is the energy storage charging state.

[0017] In some embodiments, the determining the allocation ratio of the required virtual inertia provided in each VSG control unit according to the function values corresponding to each index includes:

[0018] Determine the virtual inertia allocated to each VSG control unit according to the ratio of the sum of the function values corresponding to each index in each photovoltaic unit.

[0019] In some embodiments, it further includes:

[0020] Preset a threshold for the frequency change rate, and in response to the frequency change rate exceeding the threshold, initiate virtual inertia control.

[0021] In some embodiments, determining the required virtual inertia to be provided according to the rate of change of frequency occurring in the photovoltaic grid-connected system includes:

[0022] Determine the required virtual inertia to be provided using the following function:

[0023]

[0024] where H 0 is the normal inertia value, M is the threshold of the rate of change of frequency, k 1 and k 2 are control parameters, and df / dt is the value of the frequency change.

[0025] In some embodiments, the value range of the remaining energy storage capacity of the super capacitor is from 10% to 90%.

[0026] In a second aspect of the present disclosure, there is provided an apparatus for allocating virtual inertia of a photovoltaic cluster, including:

[0027] A virtual inertia determination module, configured to determine the required virtual inertia to be provided according to the rate of change of frequency monitored at the grid connection point of the photovoltaic grid-connected system;

[0028] An index value determination module, configured to obtain the values of the indexes that affect the provision of virtual inertia by each VSG control unit in the photovoltaic cluster of the photovoltaic grid-connected system;

[0029] An index function value determination module, configured to determine the function values corresponding to each index using a pre-determined function equation, and the function equation is determined by the following method: constructing an objective function, determining the membership function corresponding to each VSG control unit according to the objective function, establishing a system small-signal model, performing stability analysis on the parameters in the membership function using the root locus analysis method, determining the optimal parameters, and obtaining the function equation;

[0030] A virtual inertia allocation module, configured to determine the allocation ratio of the required virtual inertia to be provided in each VSG control unit according to the function values corresponding to each index.

[0031] In a third aspect of the present disclosure, there is provided an electronic device, including a memory and a processor, where a computer program is stored on the memory, and when the processor executes the program, the method as described above is implemented.

[0032] In a fourth aspect of the present disclosure, there is provided a computer-readable storage medium, on which a computer program is stored, and when the program is executed by a processor, the method as described above is implemented.

[0033] Through the method for allocating virtual inertia of a photovoltaic cluster according to the present disclosure, the problem of difficult conversion between multiple performances during the operation of a power system is overcome, multiple objectives in inertia allocation are taken into account, the rate of change of frequency can be suppressed to a certain extent, and the system can quickly return to a stable state. The method is simple and practical.

[0034] The content described in the section of the invention content is not intended to limit the key or important features of the embodiments of the present disclosure, nor to limit the scope of the present disclosure. Other features of the present disclosure will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] With reference to the accompanying drawings and the following detailed description, the above and other features, advantages, and aspects of the embodiments of the present disclosure will become more apparent. In the drawings, the same or similar reference numerals represent the same or similar elements, where:

[0036] Figure 1 FIG. shows a flowchart of a method for allocating virtual inertia of a photovoltaic cluster according to Embodiment 1 of the present disclosure;

[0037] Figure 2 FIG. shows a schematic structural diagram of an apparatus for allocating virtual inertia of a photovoltaic cluster according to Embodiment 2 of the present disclosure;

[0038] Figure 3 FIG. shows a schematic structural diagram of a device for allocating virtual inertia of a photovoltaic cluster according to Embodiment 3 of the present disclosure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present disclosure. Obviously, the described embodiments are some, but not all, of the embodiments of the present disclosure. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present disclosure without creative efforts fall within the scope of the present disclosure.

[0040] In addition, the term "and / or" in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0041] The technical solutions of the present disclosure will be described below with reference to specific embodiments. As Figure 1 shown, it is a flowchart of a method for allocating virtual inertia of a photovoltaic cluster according to Embodiment 1 of the present disclosure. It can be seen from Figure 1 that the method for allocating virtual inertia of a photovoltaic cluster in this embodiment may include the following steps:

[0042] S101: Determine the virtual inertia to be provided according to the rate of change of frequency monitored at the grid connection point of the photovoltaic grid-connected system.

[0043] In a photovoltaic grid-connected system controlled by multiple VSG control units, a single VSG control unit is no longer sufficient to maintain the safety and stability of a large-scale photovoltaic grid-connected system. Multiple VSG control units need to cooperate in coordination to ensure the overall stable operation. In a photovoltaic grid-connected system, since the frequencies of the output charges of the photovoltaic power source and the energy storage device are unstable and change in real time, it will cause instability of the photovoltaic grid-connected system. The embodiments of the present disclosure adopt the coordinated cooperation of VSG control units to ensure the overall stable operation. That is, corresponding virtual inertia is allocated to different VSG control units to stabilize the photovoltaic grid-connected system.

[0044] First, it is necessary to determine the virtual inertia to be provided according to the overall rate of change of frequency occurring in the photovoltaic grid-connected system. The virtual inertia can achieve an effect similar to that of a synchronous generator by combining an inverter with a corresponding control algorithm. Regarding how to determine the virtual inertia to be provided, reference can be made to the methods involved in the subsequent embodiments of the present disclosure, and this embodiment will not be elaborated in detail.

[0045] S102: Obtain the numerical values of the indicators that affect the provision of virtual inertia by each VSG control unit in the photovoltaic cluster of the photovoltaic grid-connected system.

[0046] In this embodiment, since a photovoltaic grid-connected system usually includes multiple VSG control units, and the virtual inertia to be allocated to each VSG control unit is usually different, it is necessary to determine the virtual inertia to be allocated to each VSG control unit. Specifically, the numerical values corresponding to the indicators that affect the virtual inertia to be provided can be obtained. In this embodiment, to obtain the numerical values corresponding to the indicators that affect the virtual inertia to be provided in each unit of the target photovoltaic cluster, the remaining energy storage capacity of the supercapacitor, the rated power of the converter, and the adjustable power of energy storage charge and discharge in each photovoltaic unit of the target photovoltaic cluster can be obtained. Since during the implementation of the technical solution of the present disclosure, the applicant found that the main indicators affecting the virtual inertia to be provided in each unit are the remaining energy storage capacity of the supercapacitor, the rated power of the converter, and the adjustable power of energy storage charge and discharge, therefore, in this embodiment, corresponding virtual inertia is allocated to different VSG control units according to the influence of each indicator on the virtual inertia.

[0047] As an alternative embodiment of the embodiments of the present disclosure, the following objective function is used to determine the influence of the remaining energy storage capacity of the supercapacitor, the rated power of the converter, and the adjustable power of energy storage charge and discharge on the virtual inertia to be allocated to the VSG control unit:

[0048]

[0049] Wherein, F is the virtual inertia value to be allocated, SOC is the remaining energy storage capacity of the supercapacitor, and ΔP N is the rated power of the converter, ΔP t is the adjustable power for energy storage charging and discharging, and df / dt is the frequency change value.

[0050] Moreover, the function values corresponding to each index are determined by using a pre-determined functional equation, where the functional equation is:

[0051]

[0052] Wherein, x is the index, u(x) is the function value, and p 10 , q 10 , C 10 , p 11 , q 11 , C 11 are determined parameters, and a, b, c, d are the boundaries for dividing the working regions of the energy storage state of charge. Among them, the ab segment is the energy storage discharging state, the bc segment is the normal state of the energy storage, and the cd segment is the energy storage charging state. The values of a, b, c, d need to be selected according to specific situations.

[0053] The above functional equation is determined in the following way: construct an objective function, determine the membership function corresponding to each VSG control unit according to the objective function, establish a small-signal model of the system, perform stability analysis on the parameters in the membership function by using the root locus analysis method, determine the optimal parameters, and obtain the functional equation.

[0054] Specifically, in this embodiment, p 10 , q 10 , C 10 , p 11 , q 11 , C 11 can be obtained by analyzing the small-signal model of the photovoltaic grid-connected system. The modeling object is a six-terminal AC system, and root locus analysis is performed on the parameters. Specifically, the six-terminal AC system can be divided into three modules: a generator set, a frequency regulation unit, and a VSG control unit. Among them, the VSG control unit includes three independent VSG control units. Small-signal models are established for the above three modules respectively. On this basis, root locus analysis is performed to obtain the influence of each function parameter (p 10 , q 10 , C 10 , p 11 , q 11 , C 11 etc.) on the system stability, and the parameter values are determined by comprehensively considering the function vertex, concavity and convexity, etc.

[0055] As an alternative embodiment of the present disclosure, the above function equation may be the membership function of the virtual inertia corresponding to each index, and the value range of the membership function is [0, 1].

[0056] S103: Determine the function values corresponding to each index using a pre-determined function equation.

[0057] In this embodiment, after determining the above parameter values, they can be substituted into the function equation to determine the function values corresponding to each index.

[0058] S104: Determine the allocation ratio of the virtual inertia to be provided in each unit according to the ratio of the function values corresponding to each index, and then determine the allocation amount of the virtual inertia to be provided in each unit of the target photovoltaic cluster.

[0059] In this embodiment, after determining the function values corresponding to each index, the allocation ratio of the virtual inertia to be provided in each VSG control unit can be determined according to the ratio of the function values corresponding to each index, and then the allocation amount of the virtual inertia to be provided in each VSG control unit of the target photovoltaic cluster can be determined.

[0060] Specifically, the virtual inertia allocated to each VSG control unit can be determined according to the ratio of the sum of the function values corresponding to each index in each VSG control unit. For example, the target photovoltaic cluster includes 3 VSG control units A, B, and C, and the function values corresponding to the indexes in each VSG control unit are A1, A2, A3, B1, B2, B3, C1, C2, and C3 respectively, and the total virtual inertia is Q. Then the virtual inertia allocated to unit A is (A1 + A2 + A3) / (A1 + A2 + A3 + B1 + B2 + B3 + C1 + C2 + C3)*Q, and the virtual inertia allocated to unit B and unit C is determined by referring to the above method.

[0061] The method for allocating the virtual inertia of the photovoltaic cluster of the present disclosure overcomes the problem that it is difficult to convert between multiple performances during the operation of the power system, takes into account multiple objectives in inertia allocation, can also suppress the rate of change of frequency to a certain extent and quickly return to a stable state, and the method is simple and practical.

[0062] As an alternative embodiment of the present disclosure, in the above embodiment, a threshold value of the rate of change of the system frequency can also be preset in advance. In response to the rate of change of the frequency exceeding the threshold value, virtual inertia control is started. Specifically, the following function can be used for virtual inertia control:

[0063]

[0064] where H 0 is the normal inertia value, M is the threshold value of the rate of change of the frequency, k 1 and k 2is a control parameter.

[0065] As an alternative embodiment of the present disclosure, in the above embodiment, the value range of the remaining energy storage capacity of the super capacitor is from 10% to 90%.

[0066] It should be noted that for the foregoing method embodiments, for the sake of simple description, they are all expressed as a series of action combinations. However, those skilled in the art should know that the present disclosure is not limited by the described action sequence, because according to the present disclosure, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all optional embodiments, and the actions and modules involved are not necessarily essential to the present disclosure.

[0067] The above is the introduction of the method embodiments. The following further illustrates the solution of the present disclosure through device embodiments.

[0068] As Figure 2 shown, it is a schematic structural diagram of the photovoltaic cluster virtual inertia distribution device according to the second embodiment of the present disclosure. The photovoltaic cluster virtual inertia distribution device of this embodiment includes:

[0069] A virtual inertia determination module 201, configured to determine the required virtual inertia according to the frequency change rate monitored at the grid connection point of the photovoltaic grid-connected system.

[0070] An index value determination module 202, configured to obtain the values of the indexes that affect each VSG control unit to provide virtual inertia in the photovoltaic cluster of the photovoltaic grid-connected system.

[0071] An index function value determination module 203, configured to determine the function values corresponding to each index by using a pre-determined function equation, and the function equation is determined by the following method: constructing an objective function, determining the membership function corresponding to each VSG control unit according to the objective function, establishing a system small-signal model, performing stability analysis on the parameters in the membership function by using the root locus analysis method, determining the optimal parameters, and obtaining the function equation.

[0072] A virtual inertia distribution module 204, configured to determine the distribution ratio of the required virtual inertia in each VSG control unit according to the function values corresponding to each index.

[0073] In the embodiments of the present application, the photovoltaic unit is a well-known photovoltaic power generation device in the art. The VSG control unit may be one or more controllers or chips having a communication interface capable of implementing a communication protocol; the controller or chip executes code related to a program to implement corresponding functions. The virtual inertia determination module 201, the index value determination module 202, the index function value determination module 203, and the virtual inertia allocation module 204 may each be one or more controllers or processors having a communication interface capable of implementing a communication protocol; if necessary, a memory and related interfaces, a system transmission bus, etc. may also be included; the processor or chip executes code related to a program to implement corresponding functions. Alternatively, as a replaceable solution, the virtual inertia determination module 201, the index value determination module 202, the index function value determination module 203, and the virtual inertia allocation module 204 share an integrated chip or share devices such as a processor or controller and a memory. The shared processor or controller, or the integrated chip, executes code related to a program to implement corresponding functions.

[0074] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the described modules can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein.

[0075] Figure 3 FIG. shows a schematic block diagram of an electronic device 300 that can be used to implement the embodiments of the present disclosure. As shown in the figure, the device 300 includes a central processing unit (CPU) 301, which can execute various appropriate actions and processes according to computer program instructions stored in a read-only memory (ROM) 302 or computer program instructions loaded from a storage unit 308 into a random access memory (RAM) 303. In the RAM 303, various programs and data required for the operation of the device 300 can also be stored. The CPU 301, the ROM 302, and the RAM 303 are connected to each other through a bus 304. An input / output (I / O) interface 305 is also connected to the bus 304.

[0076] A plurality of components in the device 300 are connected to the I / O interface 305, including: an input unit 306, such as a keyboard, a mouse, etc.; an output unit 307, such as various types of displays, speakers, etc.; a storage unit 308, such as a magnetic disk, an optical disc, etc.; and a communication unit 309, such as a network card, a modem, a wireless communication transceiver, etc. The communication unit 309 allows the device 300 to exchange information / data with other devices through a computer network such as the Internet and / or various telecommunication networks.

[0077] The central processing unit (CPU) 301 executes the various methods and processes described above, which are tangibly embodied in a machine-readable medium, such as storage unit 308. In some embodiments, portions or all of the computer program may be loaded and / or installed onto the device 300 via the ROM 302 and / or the communication unit 309. When the computer program is loaded into the RAM 703 and executed by the CPU 301, one or more steps of the methods described above may be performed. Alternatively, in other embodiments, the CPU 301 may be configured to execute the above-described methods by any other suitable means (e.g., by means of firmware).

[0078] The functions described above herein may be performed, at least in part, by one or more hardware logic components. By way of example, and not limitation, the types of hardware logic components that may be used include: field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), application specific standard products (ASSPs), systems on a chip (SOCs), complex programmable logic devices (CPLDs), and the like.

[0079] The program code for implementing the methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus such that the program codes, when executed by the processor or controller, cause the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code may be executed entirely on the machine, partly on the machine, as a stand-alone software package partly on the machine and partly on a remote machine, or entirely on the remote machine or server.

[0080] In the context of this disclosure, a machine-readable medium may be a tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. A machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium may include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of a machine-readable storage medium would include an electrical connection based on one or more wires, a portable computer diskette, 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 disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0081] In addition, although the operations are depicted in a particular order, this should be understood as requiring that the operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed to achieve the desired result. In certain environments, multitasking and parallel processing may be advantageous. Similarly, although several specific implementation details are included in the foregoing description, these should not be construed as limiting the scope of the present disclosure. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single implementation. Conversely, the various features that are described in the context of a single implementation may also be implemented separately or in any suitable sub-combination in multiple implementations.

[0082] Although the subject matter has been described in language specific to structural features and / or methodological acts, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are merely example forms of implementing the claims.

Claims

1. A method for allocating virtual inertia of a photovoltaic cluster, characterized in that, it includes: Determining the virtual inertia to be provided according to the frequency change rate monitored at the grid connection point of the photovoltaic grid-connected system; Obtaining the numerical values of the indicators that affect the provision of virtual inertia by each VSG control unit in the photovoltaic cluster of the photovoltaic grid-connected system; Among them, it includes: obtaining the remaining energy storage capacity of the supercapacitor, the rated power of the converter, and the adjustable power of energy storage charge and discharge of the photovoltaic units corresponding to each VSG control unit in the photovoltaic cluster of the photovoltaic grid-connected system; Determine the function values corresponding to each index using a pre-determined function equation, and the function equation is determined by the following method: construct an objective function, determine the membership function corresponding to each VSG control unit according to the objective function, establish a small-signal model of the system, use the root locus analysis method to perform stability analysis on the parameters in the membership function, determine the optimal parameters, and obtain the function equation; wherein, the objective function is: wherein, F is the virtual inertia value to be allocated, SOC is the remaining energy storage capacity of the supercapacitor, and ΔP N is the rated power of the converter, and ΔP t is the adjustable power of the energy storage for charging and discharging, and df / dt is the frequency change value; Determining the allocation ratio of the virtual inertia to be provided in each VSG control unit according to the function values corresponding to each indicator.

2. The method for allocating virtual inertia of a photovoltaic cluster according to claim 1, characterized in that, The step of determining the function values corresponding to each indicator by using a pre-determined function equation includes: Determining the function values corresponding to each indicator by using the following function equation: Among them, x is an index, u(x) is the function value, p 10 , q 10 , C 10 , p 11 , q 11 , C 11 are determined parameters, and a, b, c, and d are the boundaries for dividing the working regions of the energy storage state of charge. Among them, the ab segment is the energy storage discharge state, the bc segment is the normal state of the energy storage, and the cd segment is the energy storage charging state.

3. The method for allocating virtual inertia of a photovoltaic cluster according to claim 2, characterized in that, The step of determining the allocation ratio of the virtual inertia to be provided in each VSG control unit according to the function values corresponding to each indicator includes: Determining the virtual inertia allocated to each VSG control unit according to the ratio of the sum of the function values corresponding to each indicator in each photovoltaic unit; wherein, the ratio is the ratio of the sum of the indicator function values of each VSG control unit to the sum of the indicator function values of all VSG control units.

4. The method for allocating virtual inertia of a photovoltaic cluster according to claim 3, characterized in that, It further includes: Pre-setting a threshold value of the frequency change rate, and in response to the frequency change rate exceeding the threshold value, starting virtual inertia control.

5. The method for allocating virtual inertia of a photovoltaic cluster according to claim 4, characterized in that, The step of determining the virtual inertia to be provided according to the frequency change rate occurring in the photovoltaic grid-connected system includes: Using the following function to determine the virtual inertia to be provided: Among them, H 0 is the normal inertia value, M is the threshold value of the frequency change rate, k 1 and k 2 are control parameters, and df / dt is the frequency change value.

6. The method for allocating virtual inertia of a photovoltaic cluster according to claim 5, characterized in that, The value range of the remaining energy storage capacity of the supercapacitor is 10% to 90%.

7. A device for allocating virtual inertia of a photovoltaic cluster, characterized in that, it includes: A virtual inertia determination module for determining the virtual inertia to be provided according to the frequency change rate monitored at the grid connection point of the photovoltaic grid-connected system; An indicator numerical value determination module for obtaining the numerical values of the indicators that affect the provision of virtual inertia by each VSG control unit in the photovoltaic cluster of the photovoltaic grid-connected system; Among them, it includes: obtaining the remaining energy storage capacity of the supercapacitor, the rated power of the converter, and the adjustable power of energy storage charge and discharge of the photovoltaic units corresponding to each VSG control unit in the photovoltaic cluster of the photovoltaic grid-connected system; The index function value determination module is used to determine the function values corresponding to each index by using a pre-determined function equation, and the function equation is determined by the following method: constructing an objective function, determining the membership function corresponding to each VSG control unit according to the objective function, establishing a system small-signal model, using the root locus analysis method to perform stability analysis on the parameters in the membership function, determining the optimal parameters, and obtaining the function equation; wherein, the objective function is: Among them, F is the value of the virtual inertia to be allocated, SOC is the remaining energy storage capacity of the supercapacitor, and ΔP N is the rated power of the converter, and ΔP t is the adjustable power for energy storage charging and discharging, and df / dt is the frequency change value; The virtual inertia distribution module is used to determine the distribution ratio of the required virtual inertia in each VSG control unit according to the function values corresponding to each index.

8. An electronic device, comprising a memory and a processor, and a computer program is stored on the memory, characterized in that, when the processor executes the program, the method described in any one of claims 1 to 6 is implemented.

9. A computer-readable storage medium, on which a computer program is stored, characterized in that, when the program is executed by the processor, the method described in any one of claims 1 to 6 is implemented.

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