Method for constructing multi-working-condition external admittance model of grid-connected inverter based on interpolation algorithm

Abstract

The invention discloses a grid-connected inverter multi-working-condition external admittance model construction method based on an interpolation algorithm, and relates to the field of new energy grid-connected small signal modeling, and the method comprises the steps: determining a to-be-modeled working condition range, selecting a typical operation working condition, and obtaining an external admittance model of a grid-connected inverter under the selected typical operation working condition through a frequency scanning method; carrying out interpolation processing on the external admittance models under different voltage and current working conditions on the premise of fixing current and voltage; and further interpolating by using the data obtained by interpolation under the non-selected working condition to obtain an inverter model in the whole working condition range. According to the multi-working-condition external admittance modeling method of the grid-connected inverter, the structure and parameter information of equipment are not needed, and meanwhile, the workload of using a large amount of measurement data is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of small signal modeling for new energy grid-connected inverters, and in particular to a method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm. Background Art

[0002] In modern power systems, more and more renewable energy sources are connected to the grid through inverters, such as wind power generation and photovoltaic power generation. Due to the volatility of new energy and the diversity of grid operation modes, the working conditions of grid-connected inverters are changeable. The external admittance model of the grid-connected inverter is closely related to the working conditions. The interaction between different external admittance characteristics and grid impedance may produce different stability results. Therefore, studying the construction method of the multi-condition external admittance model of the grid-connected inverter has important theoretical significance and technical value for the stability assessment of the power system.

[0003] In the prior art, the methods for constructing multi-operating condition external admittance models of grid-connected inverters are mostly based on white-box models, that is, mathematical modeling is performed under the premise that the structure and parameters of the inverter and its controller are known. However, in actual engineering, due to commercial confidentiality, manufacturers often do not provide the structure and parameters of the equipment, so the grid-connected inverter presents black box characteristics. On the other hand, the data-driven multi-operating condition modeling method requires a large amount of measurement data, is complex to implement, lacks theoretical basis, and has poor interpretability. Summary of the invention

[0004] In view of the above existing problems, the present invention is proposed.

[0005] Therefore, the present invention provides a method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm, which does not require the structure and parameter information of the device and reduces the workload of using a large amount of measurement data.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: a method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm, comprising:

[0007] Determine the range of operating conditions to be modeled and select typical operating conditions, and use the frequency scanning method to obtain the external admittance model of the grid-connected inverter under the selected typical operating conditions; interpolate the external admittance models under different voltage and current conditions under the premise of fixed current and voltage; use the interpolated data under non-selected conditions to further interpolate to obtain the inverter model within the entire operating condition range.

[0008] As a preferred solution of the method for constructing a multi-condition external admittance model of a grid-connected inverter based on an interpolation algorithm described in the present invention, wherein: the operating conditions include the inverter outlet voltage U1 and the current I1; the selection of typical operating conditions needs to include a complete range of operating conditions, and the selected conditions in the same group need to satisfy the same voltage or the same current. Under the premise of meeting the preset frequency standard, when the voltage remains unchanged, the inverter admittance model is proportional to the current; when the current remains unchanged, the admittance model is monotonically related to the voltage.

[0009] As a preferred solution of the method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm described in the present invention, the external admittance model includes: by superimposing a small signal voltage or current of different frequencies on the port of the grid-connected inverter, and then performing FFT analysis on the response current or voltage and the input voltage or current, the ratio of the current component to the voltage component is the measured inverter admittance, and the external admittance Y of the grid-connected inverter is obtained by measuring the signal inv The calculation method of (s) is:

[0010]

[0011] Where: ω is the angular frequency, corresponding to the Laplace operator s, and s = jω; i p1,1 、i p2,1 、u p1,1 、u p2,1 with i p1,2 、i p2,2 、u p1,2 、u p2,2 They are respectively the first and second groups of current and voltage signals of corresponding frequencies extracted by FFT.

[0012] As a preferred solution of the method for constructing a multi-operating condition external admittance model of a grid-connected inverter based on an interpolation algorithm according to the present invention, the interpolation processing of the external admittance model under different voltage and current operating conditions includes interpolating the external admittance model under different voltage or current operating conditions under the premise of a fixed current or voltage to obtain a new operating condition model. The theoretical basis is described as follows:

[0013] The mathematical model of the inverter main circuit is expressed as:

[0014]

[0015] Among them, U d , U q ,I d and I q are the voltage and current dq components at the grid connection point; U dc is the DC bus voltage; ω1 is the power frequency angular frequency; D d and D qRepresent the duty cycle of the d-axis and q-axis respectively;

[0016] The linearized model of the circuit is:

[0017] (Ls+jω1L)ΔI dq =ΔD dq U dc -ΔU dq

[0018] Where the subscript dq represents a complex vector, that is, X dq =X d +jX q , X is the corresponding state quantity.

[0019] As a preferred solution of the method for constructing a multi-condition external admittance model of a grid-connected inverter based on an interpolation algorithm according to the present invention, the interpolation processing of the external admittance model under different voltage and current conditions includes, for the inverter controller, since the phase-locked loop and the current loop are basic control links, taking into account the influence, the small signal model of the control circuit is expressed as:

[0020]

[0021] Among them, G c (s) is the transfer function of the inner current loop; U cr is the carrier amplitude of the inverter; Δθ PLL (s) is the small phase disturbance of the phase-locked loop output, expressed as:

[0022]

[0023] Among them, T pll (s) is the transfer function of the phase-locked loop.

[0024] As a preferred solution of the method for constructing a multi-condition external admittance model of a grid-connected inverter based on an interpolation algorithm according to the present invention, wherein: the interpolation processing of the external admittance model under different voltage and current conditions includes introducing I dq =I1 and D dq =(U1+jω1LI1) / U dc , and we get the following formula:

[0025] A(s)ΔI dq (s)=B1(s)ΔU dq (s)

[0026]

[0027] The specific expansion is as follows:

[0028]

[0029] Among them, U1 and I1 represent the inverter output voltage and current respectively; L is the inverter filter inductor; K d is the feedforward decoupling coefficient of the inner current loop; the other symbols have been defined above.

[0030] As a preferred solution of the method for constructing a multi-condition external admittance model of a grid-connected inverter based on an interpolation algorithm according to the present invention, the interpolation processing of the external admittance model under different voltage and current conditions also includes that the external admittance matrix elements of the grid-connected inverter can be obtained by sorting:

[0031]

[0032] For the grid-connected inverter, when the frequency is constant, the specific formula is as follows:

[0033]

[0034] in, is the element of the inverter external admittance model matrix, which is a function of the operating conditions U1 and I1; a, b, c, d and e are all constants;

[0035] Under the premise of fixed voltage or current, the external admittance model under different currents or voltages is interpolated.

[0036] As a preferred solution of the method for constructing a multi-operating condition external admittance model of a grid-connected inverter based on an interpolation algorithm described in the present invention, wherein: the further interpolation includes: the operating condition of the inverter admittance model obtained is the same as one of the selected operating conditions, that is, the voltage or current is the same, and the inverter admittance whose voltage and current are different from the selected operating condition is obtained by further interpolation, thereby completing the external admittance modeling of the grid-connected inverter within the complete operating condition range.

[0037] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and is characterized in that when the processor executes the computer program, steps of a method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm are implemented.

[0038] A computer-readable storage medium having a computer program stored thereon, characterized in that when the computer program is executed by a processor, the steps of a method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm are implemented.

[0039] The beneficial effects of the present invention are as follows: 1) It is suitable for modeling grid-connected inverters with black box controllers. The present invention first obtains the external admittance model under typical working conditions by frequency scanning, and then obtains the external admittance model of the inverter under multiple working conditions by interpolation algorithm. The detailed structure and parameters of the controller are not required, and the applicability is strong. 2) The algorithm is simple and requires less measurement data. The modeling method disclosed in the present invention is based on the general modeling of grid-connected inverters, has model-driven characteristics, and can improve modeling efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0041] Figure 1 A schematic flow chart of a method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm provided in accordance with an embodiment of the present invention.

[0042] Figure 2 A schematic diagram of an admittance model obtained by frequency scanning of a method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm provided in one embodiment of the present invention.

[0043] Figure 3 A schematic diagram of an inverter external admittance model under different current conditions obtained by interpolation of a method for constructing a multi-operating condition external admittance model of a grid-connected inverter based on an interpolation algorithm provided in one embodiment of the present invention.

[0044] Figure 4 A schematic diagram of verifying an external admittance model obtained by interpolation in a method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm provided in one embodiment of the present invention. DETAILED DESCRIPTION

[0045] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0046] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0047] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0048] The present invention is described in detail with reference to schematic diagrams. When describing the embodiments of the present invention, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0049] At the same time, in the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "upper, lower, inner and outer" are based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first, second or third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0050] In the present invention, unless otherwise clearly specified and limited, the terms "install, connect, connect" should be understood in a broad sense, for example: it can be a fixed connection, a detachable connection or an integral connection; it can also be a mechanical connection, an electrical connection or a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0051] Example 1, reference Figure 1 , which is the first embodiment of the present invention, provides a method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm, comprising:

[0052] Determine the range of operating conditions to be modeled and select typical operating conditions, and use the frequency scanning method to obtain the external admittance model of the grid-connected inverter under the selected typical operating conditions; interpolate the external admittance models under different voltage and current conditions under the premise of fixed current and voltage; use the interpolated data under non-selected conditions to further interpolate to obtain the inverter model within the entire operating condition range.

[0053] The operating conditions include the inverter outlet voltage U1 and current I1; the selection of typical operating conditions needs to include a complete range of operating conditions, and the selected conditions in the same group must meet the same voltage or the same current. Under the premise of meeting the preset frequency standard, when the voltage remains unchanged, the inverter admittance model is proportional to the current; when the current remains unchanged, the admittance model is monotonically related to the voltage.

[0054] The external admittance model includes: by superimposing a small signal voltage or current of different frequencies on the grid-connected inverter port, and then performing FFT analysis on the response current or voltage and the input voltage or current, the ratio of the current component to the voltage component is the measured inverter admittance, and the grid-connected inverter external admittance Y is obtained by measuring the signal. inv The calculation method of (s) is:

[0055]

[0056] Where: ω is the angular frequency, corresponding to the Laplace operator s, and s = jω; i p1,1 、i p2,1 、u p1,1 、u p2,1 with i p1,2 、i p2,2 、u p1,2 、u p2,2 They are respectively the first and second groups of current and voltage signals of corresponding frequencies extracted by FFT.

[0057] Under the premise of fixed current or voltage, the theoretical basis for interpolating the external admittance model under different voltage or current conditions to obtain a new operating condition model is described as follows:

[0058] The mathematical model of the inverter main circuit is expressed as:

[0059]

[0060] Among them, U d , U q ,I d and I q are the voltage and current dq components at the grid connection point; U dc is the DC bus voltage; ω1 is the power frequency angular frequency; D d and D q Represent the duty cycle of the d-axis and q-axis respectively;

[0061] The linearized model of the circuit is:

[0062] (Ls+jω1L)ΔI dq =ΔD dq U dc -ΔU dq

[0063] Where the subscript dq represents a complex vector, that is, X dq =X d +jX q , X is the relevant state quantity.

[0064] For the inverter controller, since the phase-locked loop and current loop are the basic control links, taking into account the influence, the small signal model of the control circuit is expressed as:

[0065]

[0066] Among them, G c (s) is the transfer function of the inner current loop; U cr is the carrier amplitude of the inverter; Δθ PLL (s) is the small phase disturbance of the phase-locked loop output, expressed as:

[0067]

[0068] Among them, T pll (s) is the transfer function of the phase-locked loop.

[0069] Introduction dq =I1 and D dq =(U1+jω1LI1) / U dc , and we get the following formula:

[0070] A(s)ΔI dq (s)=B1(s)ΔU dq (s)

[0071]

[0072] The specific expansion is as follows:

[0073]

[0074] Among them, U1 and I1 represent the inverter output voltage and current respectively; L is the inverter filter inductor; K d is the feedforward decoupling coefficient of the inner current loop; the other symbols have been defined above.

[0075] By sorting out, the external admittance matrix elements of the grid-connected inverter can be obtained as follows:

[0076]

[0077] For the grid-connected inverter, when the frequency is constant, the specific formula is as follows:

[0078]

[0079] in, is the element of the inverter external admittance model matrix, which is a function of operating conditions U1 and I1; a, b, c, d and e are all constants.

[0080] Under the premise of fixed voltage or current, the external admittance model under different currents or voltages is interpolated. For example, under the premise of fixed voltage U1, the external admittance model of different currents I1 can be interpolated to obtain the external admittance model of all current conditions under this fixed voltage, and the same is true for the case of fixed current and different voltages.

[0081] The further interpolation includes: the inverter admittance model operating condition obtained is the same as one of the selected operating conditions, that is, the voltage or current is the same, and the inverter admittance with voltage and current different from the selected operating condition is obtained by further interpolation, thereby completing the external admittance modeling of the grid-connected inverter within the complete operating condition range.

[0082] Example 2, reference Figure 1-Figure 4 , which is an embodiment of the present invention, provides a method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm. In order to verify the beneficial effects of the present invention, scientific demonstration is carried out through experiments.

[0083] Step 1: Determine the range of operating conditions to be modeled and select several typical operating conditions.

[0084] The target inverter rated voltage U1 = 0.69kV, rated current I1 = 1.75kA. The operating conditions include the inverter output voltage U1 and current I1, and the operating condition range is U1: 0.9-1.1pu; I1: 0.2-1.0pu; the selection of typical operating conditions needs to include the entire operating condition range, and the same group of conditions must meet the same voltage or current. To this end, for this embodiment, the selected typical operating conditions are shown in Table 1, where set r represents the operating condition number.

[0085] Table 1 Typical operating conditions

[0086]

[0087] Step 2: Use the frequency scanning method to obtain the external admittance model of the grid-connected inverter under the selected typical operating conditions.

[0088] In this embodiment, by superimposing small signal voltages of different frequencies on the grid-connected inverter port, the selected scanning frequency is [-994-841-708-596-502-422-355-299-251-211-178-151-126-106-89-75-63-53-45-38-32-26-21-17-13-9-7-5- 3-1,1:2:99,102108117127137149161174189204221239259281304329356386418452489531574621672728788853924995]Hz, a total of 110 frequency points, covering the frequency range of (-1000,1000)Hz. Then the response current and input voltage are analyzed by FFT respectively, and the ratio of the current component to the voltage component is the measured inverter admittance. The external admittance Y of the grid-connected inverter is obtained by measuring the signal inv The calculation method of (s) is:

[0089]

[0090] Where: ω is the angular frequency, corresponding to the Laplace operator s, and s = jω; i p1,1 、i p2,1 、u p1,1 、u p2,1 with i p1,2 、i p2,2 、u p1,2 、u p2,2 They are the first and second groups of current and voltage signals of corresponding frequencies extracted by FFT. Figure 3 As shown, this is the inverter admittance model at different voltages obtained by scanning when I1 = 1.0 pu. Includes amplitude and phase.

[0091] Step 3: Under the premise of fixed voltage, interpolate the external admittance model under different current conditions.

[0092] According to the analysis in the invention content, for the grid-connected inverter, when the frequency is constant, there are:

[0093]

[0094] Where: is the element of the inverter external admittance model matrix, which is a function of the working conditions U1 and I1; a, b, c, d and e are all constants. Therefore, under the premise of fixed voltage, the external admittance model under different current working conditions is interpolated to obtain other working condition models. Figure 4 The external admittance model of the inverter under different current conditions obtained by interpolation when U1 = 1.0pu

[0095] Step 4: Use the interpolated data under non-selected operating conditions to further interpolate the inverter model within the entire operating range.

[0096] The inverter admittance model obtained by interpolation in step 3 is always the same as the selected voltage condition U1 in any operating condition. The inverter admittance with voltage and current different from the selected operating condition can be further interpolated. In order to verify the correctness of the interpolated model, the operating condition of U1 = 0.9pu & I1 = 0.51pu is selected, and the interpolated model is compared with the model obtained by frequency scanning. Figure 4 As shown, it can be seen that the two are basically consistent. So far, the external admittance modeling of the grid-connected inverter in the entire operating range has been completed.

[0097] In summary, the present invention discloses a method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm. Multi-operating-condition admittance modeling can be performed for an inverter containing a black box controller. Compared with the existing multi-operating-condition modeling method, the present invention obtains the external admittance model of the inverter under multiple operating conditions through an interpolation algorithm, and does not require the detailed structure and parameters of the controller, and has strong applicability. At the same time, the algorithm of the present invention is based on the general modeling of the grid-connected inverter, has a model-driven feature, and can improve the modeling efficiency.

[0098] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

[0099] Embodiment 3, the third embodiment of the present invention, is different from the first two embodiments in that:

[0100] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc., which can store program codes.

[0101] The present application 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 application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0102] These computer program instructions may also be stored in a computer-readable memory capable of directing 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 an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0103] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0104] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0105] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm, characterized in that: include, Determine the range of operating conditions to be modeled and select typical operating conditions, and use the frequency scanning method to obtain the external admittance model of the grid-connected inverter under the selected typical operating conditions; Under the premise of fixed current and voltage, the external admittance model under different voltage and current conditions is interpolated; The interpolated data under non-selected operating conditions are used to further interpolate the inverter model within the entire operating range.

2. The method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm according to claim 1, characterized in that: The operating conditions include the inverter outlet voltage U1 and current I1; the selection of typical operating conditions needs to include a complete range of operating conditions, and the selected conditions in the same group must meet the same voltage or the same current. Under the premise of meeting the preset frequency standard, when the voltage remains unchanged, the inverter admittance model is proportional to the current; when the current remains unchanged, the admittance model is monotonically related to the voltage.

3. The method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm according to claim 2, characterized in that: The external admittance model includes: by superimposing a small signal voltage or current of different frequencies on the grid-connected inverter port, performing FFT analysis on the response current or voltage and the input voltage or current, the ratio of the current component to the voltage component is the measured inverter admittance, and the external admittance Y of the grid-connected inverter is obtained by measuring the signal. inv The calculation method of (s) is: Where: ω is the angular frequency, corresponding to the Laplace operator s, and s = jω; i p1,1 、i p2,1 、u p1,1 、u p2,1 with i p1,2 、i p2,2 、u p1,2 、u p2,2 They are respectively the first and second groups of current and voltage signals of corresponding frequencies extracted by FFT.

4. The method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm according to claim 3, characterized in that: The interpolation processing of the external admittance model under different voltage and current working conditions includes interpolating the external admittance model under different voltage or current working conditions under the premise of fixed current or voltage to obtain a new working condition model. The theoretical basis is described as follows: The mathematical model of the inverter main circuit is expressed as: Among them, U d , U q ,I d and I q are the voltage and current dq components at the grid connection point; U dc is the DC bus voltage; ω1 is the power frequency angular frequency; D d and D q Represent the duty cycle of the d-axis and q-axis respectively; The linearized model of the circuit is: (Ls+jω1L)ΔI dq =ΔD dq U dc -ΔU dq Where the subscript dq represents a complex vector, that is, X dq =X d +jX q , X is the corresponding state quantity.

5. The method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm according to claim 4, characterized in that: The interpolation processing of the external admittance model under different voltage and current conditions includes, for the inverter controller, since the phase-locked loop and the current loop are basic control links, taking into account the influence, the small signal model of the control circuit is expressed as: Among them, G c (s) is the transfer function of the inner current loop; U cr is the carrier amplitude of the inverter; Δθ PLL (s) is the small phase disturbance of the phase-locked loop output, expressed as: Among them, T pll (s) is the transfer function of the phase-locked loop.

6. The method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm according to claim 5, characterized in that: The interpolation processing of the external admittance model under different voltage and current conditions includes introducing I dq =I1 and D dq =(U1+jω1LI1) / U dc , and we get the following formula: A(s)ΔI dq (s)=B1(s)ΔU dq (with) Among them, A(s), B1(s) and B2(s) are specifically expanded as follows: Among them, U1 and I1 represent the inverter output voltage and current respectively; L is the inverter filter inductor; K d is the feedforward decoupling coefficient of the inner current loop.

7. The method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm according to claim 6, characterized in that: The interpolation processing of the external admittance model under different voltage and current conditions also includes that the external admittance matrix elements of the grid-connected inverter can be obtained by sorting: For the grid-connected inverter, when the frequency is constant, the specific formula is as follows: in, is the element of the inverter external admittance model matrix, which is a function of the operating conditions U1 and I1; a, b, c, d and e are all constants; Under the premise of fixed voltage or current, the external admittance model under different currents or voltages is interpolated.

8. The method for constructing a multi-operating-condition external admittance model of a grid-connected inverter based on an interpolation algorithm according to claim 7, characterized in that: The further interpolation includes: the inverter admittance model operating condition obtained is the same as one of the selected operating conditions, that is, the voltage or current is the same, and the inverter admittance with voltage and current different from the selected operating condition is obtained by further interpolation, thereby completing the external admittance modeling of the grid-connected inverter within the complete operating condition range.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 8 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 8 are implemented.

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