Method, device and equipment for station modeling and harmonic resonance analysis of flexible interconnection system

Abstract

The application relates to a flexible interconnection system station modeling and harmonic resonance analysis method, device and equipment, the method comprising the following steps: acquiring electrical parameters, power station topology data and operation condition data of a flexible interconnection system; performing model construction according to the electrical parameters, the power station topology data and the operation condition data to obtain a station-level simplified impedance network model; acquiring array variable parameters; inputting the array variable parameters, the electrical parameters and the operation condition data into the station-level simplified impedance network model to obtain grid-connected point current amplitudes; drawing a three-dimensional frequency domain graph according to all variable parameters and corresponding grid-connected point current amplitudes; and performing identification analysis according to the three-dimensional frequency domain graph to obtain a harmonic resonance analysis result. The method can construct a station-level simplified impedance network model from a device layer to a system layer, then acquire a three-dimensional frequency domain graph capable of analyzing harmonic resonance based on the station-level simplified impedance network model, and finally identify accurate harmonic resonance analysis results through the three-dimensional frequency domain graph.

Description

Technical Field

[0001] This application relates to the field of resonance analysis technology for flexible interconnected systems, and in particular to a method, apparatus and equipment for field modeling and harmonic resonance analysis of flexible interconnected systems. Background Technology

[0002] Flexible interconnected systems are characterized by multi-level parallel access of grid-connected inverters and high-order coupling networks formed by the impedance of components in each power station. To improve the grid-connected capacity and inverter efficiency of large-scale flexible interconnections, multiple LCL-type grid-connected inverters are typically connected in parallel at the point of common coupling, forming a complex multi-inverter grid-connected system. However, the circuit structure of LCL filters results in inherent resonant frequencies, leading to additional resonant peaks in the frequency band of the flexible interconnected system. Simultaneously, the parallel distribution of multiple inverters causes mutual coupling between them. In the topology of the flexible interconnected system, the LCL filter circuits of each inverter are interconnected. Under the combined influence of the split transformer, main transformer, and transmission lines at the inverter's AC port, the grid-connected current is affected by multiple resonant bands, and is amplified by harmonics at the intersection of these bands. This easily leads to power quality problems such as overvoltage current and excessive harmonic content, seriously affecting the stable operation of the power grid and even causing accidents such as power station disconnection.

[0003] Harmonic resonance analysis presupposes the establishment of an equivalent system model and the abstraction of mathematical formulas. Existing power system modeling often focuses on local components or subsystems, failing to adequately consider the overall impedance interaction at the power station level. While existing power system modeling employs clustering or aggregation equivalence strategies, it does not cover the influence of key components such as transmission line impedance and transformer stray capacitance, leading to insufficient model accuracy. Furthermore, existing models often neglect the non-ideal characteristics of inverter switching devices, making it difficult to comprehensively reflect the harmonic resonance situation of the actual system. Therefore, research on harmonic resonance characteristics using power system models suffers from inaccurate results because the established bus models do not fully consider the comprehensive impact of components such as transmission line distributed capacitance and transformer stray capacitance on the wide-frequency resonance band. They only focus on the suppression of resonance by inverter control strategies, neglecting the interaction between the source-side and grid-side electrical structures. This makes it difficult to fully reveal the distribution patterns and influencing mechanisms of the resonance band at the power system grid connection point.

[0004] The following problems exist when using existing harmonic resonance analysis methods to analyze harmonic resonance in flexible interconnected systems: First, existing modeling methods are mostly limited to local inverters or single feeders, lacking system-level impedance aggregation of the entire power station electrical structure (including multiple feeders, multiple transformers, and multiple cable segments), making it difficult to accurately characterize the resonance characteristics at the grid connection point; Second, the coupling effect between internal structural parameters of the power station (such as line length and the number of parallel inverters) and grid impedance is ignored, failing to reveal the law of resonance band variation with parameters; Third, the classification and generation mechanism of resonance bands are unclear, and suppression measures lack specificity; Fourth, suppression methods mostly rely on adjustments to a single control strategy, failing to form resonance avoidance schemes from the system design and parameter planning levels, thus limiting applicability. Summary of the Invention

[0005] This application provides a method, apparatus, and equipment for field modeling and harmonic resonance analysis of flexible interconnected systems, which solves the technical problem that the analysis results are inaccurate due to the single model when using existing harmonic resonance analysis methods to analyze the harmonic resonance of flexible interconnected systems.

[0006] To achieve the above objectives, this application provides the following technical solution:

[0007] On the one hand, a method for station modeling and harmonic resonance analysis of a flexible interconnected system is provided, including the following steps:

[0008] Acquire electrical parameters of grid-connected inverters, split transformers, main transformers, and transmission lines in flexible interconnection systems, as well as power plant topology and operating condition data;

[0009] Based on the electrical parameters, the power plant topology data, and the operating condition data, a simplified impedance network model at the plant level is constructed to obtain the model.

[0010] Obtain array variable parameters, input the array variable parameters, the electrical parameters, and the operating condition data into the station-level simplified impedance network model to obtain the grid connection point current amplitude corresponding to each set of variable parameters; plot the three-dimensional frequency domain diagram of the grid connection point current amplitude-frequency characteristic based on all the variable parameters and the corresponding grid connection point current amplitude.

[0011] Based on the three-dimensional frequency domain diagram, the harmonic resonance analysis results are obtained.

[0012] Optionally, the site modeling and harmonic resonance analysis method for the flexible interconnection system further includes: determining a resonance suppression strategy based on the harmonic resonance analysis results; the content of determining the resonance suppression strategy includes:

[0013] If the harmonic resonance analysis result indicates that the resonance band of the three-dimensional frequency domain diagram is the inverter resonance band, then the resonance suppression strategy is to introduce an adjustable active damping coefficient into the simplified impedance network model at the station level.

[0014] If the harmonic resonance analysis result shows that the resonance band of the three-dimensional frequency domain diagram is a superimposed resonance band containing an inverter resonance band and an arc-shaped resonance band, and the critical feeder length of the superimposed resonance band is obtained, then the resonance suppression strategy is to set the feeder length of the flexible interconnect system to be less than the critical feeder length.

[0015] Optionally, the operating condition data includes the number of feeders, the number of generating units, and the equivalent harmonic impedance at the grid connection point; based on the electrical parameters, the power station topology data, and the operating condition data, a simplified impedance network model at the plant level is constructed, including:

[0016] Norton equivalent modeling is performed based on the electrical quantity parameters of the grid-connected inverter to obtain the Norton equivalent model of the grid-connected inverter.

[0017] A simplified equivalent model of the double-split transformer winding is obtained by performing a simplified equivalent model based on the electrical parameters of the double-split transformer; a simplified equivalent model of the main transformer winding is obtained by performing a simplified equivalent model based on the electrical parameters of the main transformer.

[0018] Based on the electrical quantity parameters of the transmission line, a parameter equivalent model is performed to obtain the distributed parameter model of the transmission line;

[0019] Based on the number of power generation units, the feeder topology of each feeder in the power station topology data, the Norton equivalent model of the grid-connected inverter, the equivalent model of the double-split transformer winding, the equivalent model of the main transformer winding, and the distributed parameter model of the transmission line, Norton equivalent model is performed to obtain a single feeder aggregate impedance model corresponding to each feeder topology.

[0020] Norton equivalent modeling is performed based on the number of feeders, the equivalent harmonic impedance of the grid connection point, and the aggregated impedance model of all single feeders to obtain a simplified impedance network model at the site level.

[0021] Optionally, Norton equivalent modeling is performed based on the number of feeders, the equivalent harmonic impedance of the grid connection point, and all the single feeder aggregated impedance models to obtain a simplified impedance network model at the site level, including:

[0022] Based on the number of feeders, all the single-feeder aggregate impedance models are processed by Norton equivalent parallel connection to obtain the photovoltaic equivalent circuit on the photovoltaic side of the flexible interconnect system.

[0023] Based on the power plant topology data and the equivalent harmonic impedance of the grid connection point, the grid side of the flexible interconnection system is subjected to Thevenin equivalent processing to obtain the grid equivalent circuit.

[0024] The photovoltaic equivalent circuit is connected in parallel with the power grid equivalent circuit to obtain a simplified impedance network model at the station level;

[0025] In the simplified impedance network model at the station level, the grid-side equivalent impedance is obtained by equating the inverter winding impedance, filter winding impedance, and passive filter impedance of the main transformer to the grid side. The grid-side equivalent impedance is then input into the simplified impedance network model at the station level for derivation, resulting in the grid-connection point harmonic current expression of the simplified impedance network model at the station level.

[0026] Optionally, the expression for the harmonic current at the grid connection point is:

[0027] ;

[0028] In the formula, I PCCh U is the grid-connected harmonic current of the h-th harmonic. Sh For the equivalent harmonic voltage source of the h-th harmonic power grid equivalent circuit, i feqh Z is the equivalent Norton harmonic current source for the h-th harmonic single-feeder aggregate impedance model. feqh The equivalent Norton harmonic impedance of the h-th harmonic single-feed aggregate impedance model is given by N1, N2, N3, and Z, where N1 is the number of turns in the main transformer grid-side winding, N2 is the number of turns in the main transformer inverter-side winding, and N3 is the number of turns in the main transformer filter winding. 1h Z represents the harmonic impedance of the grid-side winding of the h-th harmonic main transformer. 2h Z represents the harmonic impedance of the inverter winding of the main transformer for the h-th harmonic. 3h Z represents the harmonic impedance of the filter winding of the main transformer for the h-th harmonic. 3fh Z represents the grid-side equivalent impedance of the h-th harmonic, n is the number of feed lines, and Z is the value of Z. Sh Let be the equivalent harmonic impedance at the grid connection point of the h-th harmonic.

[0029] On the other hand, a site modeling and harmonic resonance analysis device for a flexible interconnected system is provided, including a data acquisition module, a model building module, a spectrum drawing module and an analysis module;

[0030] The data acquisition module is used to acquire electrical parameters of grid-connected inverters, double-split transformers, main transformers, and transmission lines in the flexible interconnection system, as well as power plant topology data and operating condition data.

[0031] The model building module is used to build a model based on the electrical parameters, the power station topology data and the operating condition data to obtain a simplified impedance network model at the station level.

[0032] The graph plotting module is used to obtain array variable parameters, input the array variable parameters, the electrical parameters and the operating condition data into the station-level simplified impedance network model, and obtain the grid connection point current amplitude corresponding to each set of variable parameters; and plot the three-dimensional frequency domain graph of the grid connection point current amplitude-frequency characteristic based on all the variable parameters and the corresponding grid connection point current amplitude.

[0033] The analysis module is used to perform identification and analysis based on the three-dimensional frequency domain diagram to obtain harmonic resonance analysis results.

[0034] Optionally, the site modeling and harmonic resonance analysis device of the flexible interconnection system further includes a resonance suppression module, which is used to determine a resonance suppression strategy based on the harmonic resonance analysis results; the content of determining the resonance suppression strategy includes:

[0035] If the harmonic resonance analysis result indicates that the resonance band of the three-dimensional frequency domain diagram is the inverter resonance band, then the resonance suppression strategy is to introduce an adjustable active damping coefficient into the simplified impedance network model at the station level.

[0036] If the harmonic resonance analysis result shows that the resonance band of the three-dimensional frequency domain diagram is a superimposed resonance band containing an inverter resonance band and an arc-shaped resonance band, and the critical feeder length of the superimposed resonance band is obtained, then the resonance suppression strategy is to set the feeder length of the flexible interconnect system to be less than the critical feeder length.

[0037] Optionally, the operating condition data includes the number of feeders, the number of power generation units, and the equivalent harmonic impedance at the grid connection point; the model construction module includes a first construction submodule, a second construction submodule, a third construction submodule, a fourth construction submodule, and a fifth construction submodule;

[0038] The first construction submodule is used to perform Norton equivalent modeling based on the electrical quantity parameters of the grid-connected inverter to obtain the Norton equivalent model of the grid-connected inverter;

[0039] The second construction submodule is used to perform simplified equivalent modeling based on the electrical quantity parameters of the double-split transformer to obtain an equivalent model of the double-split transformer winding; and to perform simplified equivalent modeling based on the electrical quantity parameters of the main transformer to obtain an equivalent model of the main transformer winding.

[0040] The third construction submodule is used to perform parameter equivalent modeling based on the electrical quantity parameters of the transmission line to obtain the distributed parameter model of the transmission line;

[0041] The fourth construction submodule is used to perform Norton equivalent modeling based on the number of power generation units, the feeder topology of each feeder in the power station topology data, the Norton equivalent model of the grid-connected inverter, the equivalent model of the double-split transformer winding, the equivalent model of the main transformer winding, and the transmission line distributed parameter model, to obtain a single feeder aggregate impedance model corresponding to each feeder topology;

[0042] The fifth construction submodule is used to perform Norton equivalent modeling based on the number of feeders, the equivalent harmonic impedance of the grid connection point, and all the single feeder aggregate impedance models to obtain a simplified impedance network model at the site level.

[0043] Optionally, Norton equivalent modeling is performed based on the number of feeders, the equivalent harmonic impedance of the grid connection point, and all the single feeder aggregated impedance models to obtain a simplified impedance network model at the site level, including:

[0044] Based on the number of feeders, all the single-feeder aggregate impedance models are processed by Norton equivalent parallel connection to obtain the photovoltaic equivalent circuit on the photovoltaic side of the flexible interconnect system.

[0045] Based on the power plant topology data and the equivalent harmonic impedance of the grid connection point, the grid side of the flexible interconnection system is subjected to Thevenin equivalent processing to obtain the grid equivalent circuit.

[0046] The photovoltaic equivalent circuit is connected in parallel with the power grid equivalent circuit to obtain a simplified impedance network model at the station level;

[0047] In the simplified impedance network model at the station level, the grid-side equivalent impedance is obtained by equating the inverter winding impedance, filter winding impedance, and passive filter impedance of the main transformer to the grid side of the main transformer. The grid-side equivalent impedance is then input into the simplified impedance network model at the station level for derivation, resulting in the grid-connection point harmonic current expression of the simplified impedance network model at the station level.

[0048] The expression for the harmonic current at the grid connection point is:

[0049] ;

[0050] In the formula, I PCCh U is the grid-connected harmonic current of the h-th harmonic. Sh For the equivalent harmonic voltage source of the h-th harmonic power grid equivalent circuit, i feqh Z is the equivalent Norton harmonic current source for the h-th harmonic single-feeder aggregate impedance model. feqh The equivalent Norton harmonic impedance of the h-th harmonic single-feed aggregate impedance model is given by N1, N2, N3, and Z, where N1 is the number of turns in the main transformer grid-side winding, N2 is the number of turns in the main transformer inverter-side winding, and N3 is the number of turns in the main transformer filter winding. 1hZ represents the harmonic impedance of the grid-side winding of the h-th harmonic main transformer. 2h Z represents the harmonic impedance of the inverter winding of the main transformer for the h-th harmonic. 3h Z represents the harmonic impedance of the filter winding of the main transformer for the h-th harmonic. 3fh Z represents the grid-side equivalent impedance of the h-th harmonic, n is the number of feed lines, and Z is the value of Z. Sh Let be the equivalent harmonic impedance at the grid connection point of the h-th harmonic.

[0051] On the other hand, a terminal device is provided, including a processor and a memory;

[0052] The memory is used to store program code and transmit the program code to the processor;

[0053] The processor is used to execute the site modeling and harmonic resonance analysis method of the flexible interconnection system described above, according to the instructions in the program code.

[0054] This invention discloses a method, apparatus, and equipment for site modeling and harmonic resonance analysis of a flexible interconnected system. The method includes: acquiring electrical parameters of the grid-connected inverter, dual-split transformer, main transformer, and transmission lines, as well as power plant topology and operating condition data; constructing a simplified impedance network model at the site level based on the electrical parameters, power plant topology, and operating condition data; acquiring arrays of variable parameters; inputting these arrays, electrical parameters, and operating condition data into the simplified impedance network model to obtain the grid-connected point current amplitude corresponding to each set of variable parameters; plotting the three-dimensional frequency domain diagram of the grid-connected point current amplitude-frequency characteristics based on all variable parameters and corresponding grid-connected point current amplitudes; and performing identification and analysis based on the three-dimensional frequency domain diagram to obtain the harmonic resonance analysis results.

[0055] As can be seen from the above technical solutions, this application has the following advantages: The site modeling and harmonic resonance analysis method of the flexible interconnection system constructs a site-level simplified impedance network model from the equipment layer to the system layer, and then obtains a three-dimensional frequency domain diagram that can analyze harmonic resonance based on the site-level simplified impedance network model. The accurate wave resonance analysis results are obtained by identifying the three-dimensional frequency domain diagram, which solves the technical problem that the analysis results are inaccurate due to the single modeling when using the existing harmonic resonance analysis method to analyze the harmonic resonance of the flexible interconnection system.

[0056] The site modeling and harmonic resonance analysis device of the flexible interconnection system constructs a site-level simplified impedance network model from the equipment layer to the system layer through a data acquisition module, a model construction module, a spectrum drawing module, and an analysis module. Then, based on the site-level simplified impedance network model, a three-dimensional frequency domain map capable of analyzing harmonic resonance is obtained, and accurate wave resonance analysis results are obtained by identifying the three-dimensional frequency domain map. Attached Figure Description

[0057] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0058] Figure 1 This is a flowchart illustrating the steps of the site modeling and harmonic resonance analysis method for the flexible interconnected system described in the embodiments of this application.

[0059] Figure 2 This is a schematic diagram of the topology of the flexible interconnection system in the site modeling and harmonic resonance analysis method of the flexible interconnection system described in the embodiments of this application;

[0060] Figure 3 This is a circuit diagram of a simplified impedance network model at the field station level in the field station modeling and harmonic resonance analysis method for the flexible interconnection system described in this application embodiment;

[0061] Figure 4 This is a three-dimensional frequency domain diagram of the grid connection point current frequency domain characteristics under the change of the line length of the power generation unit in the site modeling and harmonic resonance analysis method of the flexible interconnection system described in the embodiments of this application.

[0062] Figure 5 This is a three-dimensional frequency domain diagram of the frequency domain characteristics of the grid connection point current under the change of feeder length in the field modeling and harmonic resonance analysis method of the flexible interconnection system described in the embodiments of this application.

[0063] Figure 6 This is a three-dimensional frequency domain diagram of the grid connection point current frequency domain characteristics when the number of power generation units changes under a single feeder in the field modeling and harmonic resonance analysis method of the flexible interconnection system described in the embodiments of this application.

[0064] Figure 7 This is a three-dimensional frequency domain diagram of the grid connection point current frequency domain characteristics under the change of the number of feeders in a single power generation unit in the field modeling and harmonic resonance analysis method of the flexible interconnection system described in the embodiments of this application.

[0065] Figure 8 This is a flowchart illustrating the steps of a site modeling and harmonic resonance analysis method for a flexible interconnected system according to another embodiment of this application.

[0066] Figure 9 Norton equivalent circuit diagram of the grid-connected inverter Norton equivalent model in the site modeling and harmonic resonance analysis method of the flexible interconnection system described in the embodiments of this application;

[0067] Figure 10This is a simplified equivalent circuit diagram of the double-split transformer winding equivalent model in the field station modeling and harmonic resonance analysis method of the flexible interconnection system described in the embodiments of this application;

[0068] Figure 11 This is the equivalent circuit diagram of the main transformer winding equivalent model in the site modeling and harmonic resonance analysis method of the flexible interconnection system described in the embodiments of this application.

[0069] Figure 12 This is an equivalent circuit diagram of the transmission line distributed parameter model in the site modeling and harmonic resonance analysis method for the flexible interconnected system described in this application embodiment;

[0070] Figure 13 The circuit diagram of the single-feeder aggregate impedance model in the site modeling and harmonic resonance analysis method of the flexible interconnection system described in the embodiments of this application;

[0071] Figure 14 This is a schematic diagram of the framework of the site modeling and harmonic resonance analysis device for the flexible interconnection system described in the embodiments of this application;

[0072] Figure 15 This is a schematic diagram of the terminal device described in an embodiment of this application. Detailed Implementation

[0073] To make the inventive objectives, features, and advantages of this application more apparent and understandable, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0074] In the description of the embodiments of this application, 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. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0075] In the embodiments of this application, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "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 the embodiments of this application according to the specific circumstances.

[0076] Patent terminology used in this application:

[0077] LCL filters are a type of third-order filter widely used in power electronic grid-connected systems. They mainly consist of inverter-side inductors, filter capacitors, and grid-side inductors, and are designed to efficiently suppress high-frequency switching harmonics and optimize power quality.

[0078] This application provides a method, apparatus, and equipment for field modeling and harmonic resonance analysis of flexible interconnected systems, which solves the technical problem that the analysis of harmonic resonance of flexible interconnected systems using existing harmonic resonance analysis methods is inaccurate due to the single model.

[0079] Example 1:

[0080] Figure 1 This is a flowchart illustrating the steps of the site modeling and harmonic resonance analysis method for the flexible interconnected system described in this application. Figure 2 This is a schematic diagram of the topology of the flexible interconnected system in the site modeling and harmonic resonance analysis method of the flexible interconnected system described in the embodiments of this application.

[0081] like Figure 1 As shown in the figure, this application provides a method for field station modeling and harmonic resonance analysis of a flexible interconnected system, including the following steps:

[0082] S1. Obtain electrical parameters of grid-connected inverters, dual-split transformers, main transformers, and transmission lines in the flexible interconnection system, as well as power plant topology data and operating condition data.

[0083] It should be noted that in the site modeling and harmonic resonance analysis of the flexible interconnected system, step S1 involves acquiring multi-dimensional data, including electrical parameters of the grid-connected inverter, the dual-split transformer, the main transformer, and the transmission lines, as well as power station topology and operating condition data. This data is provided to understand the harmonic characteristics and resonance mechanism of the flexible interconnected system and to conduct accurate modeling and analysis. In this embodiment, as... Figure 2As shown, step S1 can be understood as acquiring the electrical parameters of the grid-connected inverter, double-split transformer, main transformer, and transmission line in the flexible interconnection system, as well as the power station topology data and the operating condition data composed of data such as the number of feeders, the number of power generation units, and the length of each cable segment.

[0084] In this embodiment, the electrical parameters of the grid-connected inverter include filter parameters, switching and control parameters, and control parameters. Specifically, the electrical parameters of the grid-connected inverter are: filter parameters include values ​​for inverter-side inductance L1, grid-side inductance L2, and filter capacitor C; the switching and control parameters include the switching frequency f of the grid-connected inverter. s Delay time t d Active damping coefficient k d etc.; controller parameters include the proportional gain k of the current loop PR controller. p Integral coefficient k h Cutoff angular frequency ω c And the fundamental angular frequency ω0, etc.

[0085] It should be noted that filter parameters have a significant impact on the output waveform quality and harmonic suppression capability of grid-connected inverters.

[0086] In the embodiments of this application, the electrical parameters of the double-split transformer include rated voltage, short-circuit impedance percentage, rated capacity, and splitting factor. The electrical parameters of the main transformer include the rated voltage, rated capacity, equivalent impedance percentage, and connection group of each winding of the main transformer (such as the grid side, inverter side, and filter winding).

[0087] It should be noted that the rated capacity of a double-split transformer represents its power handling capacity and is the basis for transformer selection and design. The splitting factor of a double-split transformer reflects the impedance relationship between the split windings, which is crucial for analyzing the current distribution and harmonic transmission characteristics of double-split transformers in flexible interconnection systems. The short-circuit impedance of a double-split transformer represents its impedance under short-circuit conditions and is an important basis for evaluating the transformer's short-circuit current withstand capability and the short-circuit protection design of flexible interconnection systems. The rated voltage and rated capacity of each winding of the main transformer (such as the grid side, inverter side, and filter winding) typically have larger capacities and higher voltage levels to meet the overall power transmission and voltage transformation requirements of flexible interconnection systems.

[0088] In this embodiment of the application, the electrical parameters obtained in step S1 further include passive filter parameters, which include a filter inductor L tuned to the 5th harmonic. f With filter capacitor C f The value.

[0089] In the embodiments of this application, the electrical parameters of the transmission line include the cable type and cross-sectional area of ​​each section of underground cable in the power station of the flexible interconnection system, as well as the resistance r0, inductance l0, capacitance c0 per unit cable length and the actual length l of each cable section.

[0090] It should be noted that the electrical parameters of a transmission line are the line's ability to impede current and support voltage, and are an important basis for analyzing the voltage drop, power transmission capacity, and harmonic transmission characteristics of a transmission line.

[0091] In this embodiment of the application, the power station topology structure in the power station topology data of the flexible interconnection system is as follows: Figure 2 As shown, the total installed capacity of the power station (e.g., 7×7MW), the total number of feeders connected to the 10.5kV bus (e.g., a maximum of 7), the total number of parallel generating units on each feeder (e.g., a maximum of 7), and the specific composition of each generating unit, which includes 2 grid-connected inverters and 1 double-split transformer. Based on the power station topology data, the operating condition data includes the number of generating units currently in operation (m) and the number of feeders (n), as well as the specific length parameters of each cable segment. The specific length parameters of each cable segment include: within each generating unit, the cable length from the parallel connection point of the two grid-connected inverters to the low-voltage side connection point of its corresponding double-split transformer; the cable length from the high-voltage side output end of the double-split transformer of each generating unit to the 10.5kV feeder access point it is connected to; and the total cable length of each 10.5kV feeder from its first generating unit access point to its end connecting to the 10.5kV bus. Operating condition data also includes system equivalent parameters, including the equivalent harmonic impedance Z on the grid side at the point of common coupling (PCC). Sh It is used to establish the subsequent power grid equivalent circuit.

[0092] It should be noted that the power plant topology data represents the electrical connection methods and topology between various power devices in a flexible interconnection system, and is the basis for establishing a model of the flexible interconnection system and analyzing harmonic resonance.

[0093] Figure 3 This is a circuit diagram of a simplified impedance network model at the field station level, used in the field station modeling and harmonic resonance analysis method for the flexible interconnected system described in this application embodiment.

[0094] S2. Based on electrical parameters, power plant topology data, and operating condition data, a simplified impedance network model at the plant level is constructed to obtain the model.

[0095] It should be noted that in step S2, based on the data obtained in step S1, equivalent models of each power device in the power plant topology structure of the power plant topology data are established (such as the Norton equivalent model of the grid-connected inverter, the equivalent model of the double-split transformer winding, the equivalent model of the main transformer winding, and the distributed parameter model of the transmission line, etc.). Based on all the equivalent models, through multi-port network aggregation, all power generation units and feeders in the operating condition data are equivalently converted into photovoltaic equivalent circuits on the photovoltaic side and grid equivalent circuits on the grid side, forming a structure as follows: Figure 3 The simplified impedance network model at the station level is shown. In this embodiment, the station modeling and harmonic resonance analysis method of the flexible interconnection system constructs a simplified impedance network model at the station level by equivalently constructing the impedances of components such as grid-connected inverters, transformers, and transmission lines under a unified framework through step S2. This model can more comprehensively and accurately characterize the impedance interaction characteristics of the entire power station and the power grid in the flexible interconnection system, providing a reliable foundation for resonance analysis and solving the problem of unclear resonant mechanisms and laws.

[0096] For example, before establishing a simplified impedance network model at the plant level, to improve the accuracy of the model, data preprocessing and parameter normalization operations can be performed on the electrical parameters, plant topology data, and operating condition data obtained in step S1. Data preprocessing includes missing value handling, outlier / outlier detection, noise smoothing, and / or duplicate data processing. Missing value handling refers to deleting records with missing values, filling with the mean / median / mode, using interpolation methods (such as Lagrange multiplication), and model prediction (such as random forest or KNN). Outlier / outlier detection refers to identifying outliers using Z-Score (30% accuracy), IQR (interquartile range), box plots, density-based methods, or clustering, and then determining whether to retain or correct them based on business logic. Noise smoothing refers to reducing random fluctuations through binning (equal width / equal frequency), moving averages, regression fitting, etc. Duplicate data processing refers to data deduplication, paying attention to distinguishing between true duplication and approximate duplication.

[0097] In other embodiments, in step S2, a simplified impedance network model at the station level can be constructed using a hierarchical modeling strategy based on the electrical parameters, power plant topology data, and operating condition data obtained in step S1. The hierarchical modeling strategy includes first establishing models of each power device in the equipment layer based on the data obtained in step S1, then establishing a system layer model based on the power plant topology structure of the power plant topology data (e.g., connecting the equipment layer models based on the topology data to form a station-level impedance network), and injecting harmonic current sources into the inverter ports of the system layer model to form a simplified impedance network model at the station level capable of analyzing interconnected systems and harmonic resonance.

[0098] S3. Obtain array variable parameters. Input the array variable parameters, electrical parameters, and operating condition data into the simplified impedance network model at the station level to obtain the grid connection point current amplitude corresponding to each set of variable parameters. Plot the three-dimensional frequency domain diagram of the grid connection point current amplitude-frequency characteristic based on all variable parameters and the corresponding grid connection point current amplitude.

[0099] It should be noted that the variable parameters include the resonant frequency and the line length. The array of variable parameters can be understood as being composed of resonant frequencies and line lengths with different values. In step S3, based on the simplified impedance network model at the station level constructed in step S2, a three-dimensional frequency domain diagram related to the current amplitude characteristics at the grid connection point is plotted with harmonic frequency and line length as variables, providing data for subsequent identification and analysis of station modeling and harmonic resonance in flexible interconnected systems. In this embodiment, based on the simplified impedance network model at the station level established in step 2, a three-dimensional frequency domain diagram of the frequency domain characteristics of the current amplitude at the grid connection point with harmonic frequency and critical line length as variables is plotted. In the process of obtaining the current amplitude at the grid connection point through the simplified impedance network model at the station level, the electrical parameters obtained in step S1 and the current operating conditions (number of connected generating units m, number of feeders n) are substituted into the simplified impedance network model at the station level.

[0100] For example, step S3 can be understood as inputting electrical parameters and operating condition data into the simplified impedance network model at the site level, then modifying the resonant frequency and line length according to each set of variable parameters. The simplified impedance network model at the site level outputs the grid-connected point current amplitude corresponding to each set of variable parameters. Then, based on each set of variable parameters and the corresponding grid-connected point current amplitude, a three-dimensional surface plot is generated using matplotlib as a three-dimensional frequency domain plot. The three-dimensional frequency domain plot shows the dynamic relationship between frequency, line length, and current amplitude.

[0101] In this embodiment, the current I at the grid connection point is obtained through a simplified impedance network model at the station level. PCC The amplitude response at different harmonic frequencies is used to identify the resonant peaks in the flexible interconnect system and to determine their generation mechanism and frequency distribution characteristics.

[0102] S4. Based on the three-dimensional frequency domain diagram, identify and analyze the harmonic resonance to obtain the results of the analysis.

[0103] It should be noted that step S4 extracts the resonant bands and data for each resonant band from the three-dimensional frequency domain diagram obtained in step S3. This data includes harmonic frequencies, current amplitudes, and line lengths, yielding harmonic resonance analysis results. This provides a basis for subsequently developing resonance suppression strategies to suppress harmonic resonance in flexible interconnection systems. In this embodiment, the site modeling and harmonic resonance analysis method for this flexible interconnection system achieves accurate impedance modeling from local components to the entire site system through step S2. Steps S3 and S4 reveal the distribution patterns and formation mechanisms of the resonant bands through harmonic resonance analysis results.

[0104] Figure 4 This is a three-dimensional frequency domain diagram of the grid connection point current frequency domain characteristics under varying line lengths of the power generation unit in the site modeling and harmonic resonance analysis method for the flexible interconnected system described in this application embodiment. Figure 5 This is a three-dimensional frequency domain plot of the grid connection point current frequency domain characteristics under varying feeder length in the field modeling and harmonic resonance analysis method for the flexible interconnected system described in this application embodiment. Figure 6 This is a three-dimensional frequency domain diagram of the grid connection point current frequency domain characteristics when the number of power generation units is changed under a single feeder in the field modeling and harmonic resonance analysis method for the flexible interconnected system described in this application embodiment. Figure 7 This is a three-dimensional frequency domain diagram of the grid connection point current frequency domain characteristics under the change of the number of feeders in a single power generation unit in the field modeling and harmonic resonance analysis method of the flexible interconnection system described in the embodiments of this application.

[0105] In the embodiments of this application, during the process of obtaining harmonic resonance analysis results based on the three-dimensional frequency domain diagram, such as Figure 4 and Figure 5 As shown, the harmonic resonance analysis results include the arc-shaped resonance band, the inverter resonance band, and the superimposed resonance band.

[0106] It should be noted that, as Figure 4 and Figure 5 As shown, the arc-shaped resonance band refers to the resonance caused by the series or parallel resonance of the distributed capacitance, line inductance, and system equivalent inductance of the transmission line at a specific frequency. The characteristic of the arc-shaped resonance band is that, in a three-dimensional frequency domain diagram with harmonic frequency and line length as variables, the trajectory of the resonance peaks exhibits an arc-shaped distribution. The inverter resonance band refers to the resonance caused by the inherent resonance characteristics of the LCL filter in the grid-connected inverter and its control delay. The characteristic of the inverter resonance band is that the resonance peaks are concentrated at the switching frequency f. s The resonant band is located near the edge band, specifically at the 6k±1st harmonic frequency (where k is a positive integer), and does not significantly change with external line parameters. The superimposed resonant band refers to the band formed when the arc-shaped resonant band and the inverter resonant band intersect or overlap in frequency. Due to the superposition of multiple resonance mechanisms, the superimposed resonant band will exhibit severe harmonic amplification, potentially leading to instability in the flexible interconnect system.

[0107] In this embodiment, the number of parallel inverters in the fixed flexible interconnect system (i.e., the fixed number of power generation units m and the number of feeders n) is used to change the length of the power generation unit connection cable or the feeder cable, and step S3 is executed to obtain a similar result. Figure 4 (Changing the length of the power generation unit line) and Figure 5 The three-dimensional frequency domain diagram shown (with changes in feeder length) also includes the analysis of the influence of changes in line length on the distribution of the resonant band.

[0108] It should be noted that the specific methods for sharing the influence of changes in line length on the resonant band distribution include: analyzing the center frequency f of the arc-shaped resonant band. arc The law of shifting towards lower frequencies as the line length l increases; the center frequency f of the inverter resonant band. inv It remains essentially constant and is unaffected by changes in line length.

[0109] In this embodiment of the application, the line length of the fixed flexible interconnection system is changed sequentially, and the number of connected power generation units m and / or the number of feeders n are changed. The operation of step S3 is then performed to obtain a result similar to... Figure 6 (Changing the number of power generation units) and Figure 7 The three-dimensional frequency domain diagram shown (with the number of feeders changed) also includes the analysis of the influence of the number of parallel inverters on the distribution of the resonant band.

[0110] It should be noted that the analysis of the impact of changes in the number of parallel inverters on the resonant band distribution specifically includes: analyzing the photovoltaic-side equivalent output impedance Z of the simplified impedance network model at the site level as the total number of parallel inverters increases. pvh The decrease leads to the center frequency f of the arc-shaped resonant band. arc The pattern of shifting towards lower frequencies; the center frequency f of the inverter resonant band. inv It remains constant and is unaffected by changes in the number of parallel inverters.

[0111] In this embodiment, based on the analysis of the influence of changes in line length on the resonant band distribution and the analysis of the influence of changes in the number of parallel inverters on the resonant band distribution, operating conditions and parameter combinations that may produce superimposed resonant bands (i.e., the intersection of the arc-shaped resonant band and the inverter resonant band) are identified. Given different combinations of the number of generator units m and the number of feeders n in the flexible interconnected system, the critical feeder length l that triggers superimposed resonance can be extracted from the superimposed resonant band. critical and its corresponding harmonic frequency f overlap .

[0112] It should be noted that the site modeling and harmonic resonance analysis method of this flexible interconnection system reveals the causes of various resonance bands such as arc resonance band, inverter resonance band and superimposed resonance band through the harmonic resonance analysis results obtained in step S4 (caused by line distributed capacitance, grid-connected inverter LCL filter, and the superposition of the two respectively) and the quantitative law of their distribution changing with line length and the number of parallel inverters.

[0113] In the embodiments of this application, the site modeling and harmonic resonance analysis method of the flexible interconnection system not only clarifies the physical causes of the three types of resonance bands, namely the arc resonance band, the inverter resonance band and the superimposed resonance band, through steps S3 and S4, but also reveals the quantitative law of the frequency change with the line length and the number of parallel inverters, so that the resonance analysis moves from qualitative judgment to quantitative prediction.

[0114] In this embodiment, the site modeling and harmonic resonance analysis method for the flexible interconnection system constructs a complete technical process from model building, theoretical analysis, countermeasure proposal to simulation verification through steps S1 to S4. The process of this site modeling and harmonic resonance analysis method for the flexible interconnection system is clear and highly repeatable, ensuring not only the reliability of theoretical conclusions but also forming a standard analysis method for harmonic resonance in flexible interconnection systems that can guide engineering practice.

[0115] It should be noted that the site modeling and harmonic resonance analysis method for this flexible interconnected system, through step S2, systematically simplifies the complex flexible interconnected system, which includes multiple grid-connected inverters, multiple feeders, multiple types of transformers, and transmission lines with distributed parameters, into a site-level simplified impedance network model that can be used for frequency domain analysis. This model utilizes Norton and Thevenin equivalences, providing a foundation for accurate resonance analysis of the flexible interconnected system. In constructing the site-level simplified impedance network model, a complete technical loop, from accurate modeling and mechanism analysis to effective suppression, systematically solves the fragmentation problem in harmonic resonance analysis of flexible interconnected systems.

[0116] This application provides a method for site modeling and harmonic resonance analysis of a flexible interconnected system, including acquiring electrical parameters of the grid-connected inverter, double-split transformer, main transformer, and transmission lines in the flexible interconnected system, as well as power plant topology data and operating condition data; constructing a model based on the electrical parameters, power plant topology data, and operating condition data to obtain a site-level simplified impedance network model; acquiring array variable parameters, inputting the array variable parameters, electrical parameters, and operating condition data into the site-level simplified impedance network model to obtain the grid-connected point current amplitude corresponding to each set of variable parameters; plotting the three-dimensional frequency domain diagram of the grid-connected point current amplitude-frequency characteristics based on all variable parameters and corresponding grid-connected point current amplitudes; and performing identification and analysis based on the three-dimensional frequency domain diagram to obtain the harmonic resonance analysis results. The site modeling and harmonic resonance analysis method for flexible interconnected systems constructs a site-level simplified impedance network model from the equipment layer to the system layer. Then, based on the site-level simplified impedance network model, a three-dimensional frequency domain diagram capable of analyzing harmonic resonance is obtained. Accurate harmonic resonance analysis results are obtained by identifying the three-dimensional frequency domain diagram. This solves the technical problem that the analysis results are inaccurate due to the single model when using existing harmonic resonance analysis methods to analyze the harmonic resonance of flexible interconnected systems.

[0117] Figure 8 This is a flowchart illustrating the steps of a site modeling and harmonic resonance analysis method for a flexible interconnected system according to another embodiment of this application.

[0118] like Figure 8 As shown, in one embodiment of this application, the site modeling and harmonic resonance analysis method for the flexible interconnection system further includes: S5. Determining a resonance suppression strategy based on the harmonic resonance analysis results; the content of determining the resonance suppression strategy includes:

[0119] If the harmonic resonance analysis result shows that the resonance band of the three-dimensional frequency domain diagram is the inverter resonance band, then the resonance suppression strategy is to introduce an adjustable active damping coefficient into the simplified impedance network model at the station level.

[0120] If the harmonic resonance analysis result shows that the resonance band of the three-dimensional frequency domain diagram is a superimposed resonance band containing the inverter resonance band and the arc resonance band, and the critical feeder length of the superimposed resonance band is obtained, then the resonance suppression strategy is to set the feeder length of the flexible interconnect system to be less than the critical feeder length.

[0121] It should be noted that in determining the resonance suppression strategy based on the harmonic resonance analysis results, the site modeling and harmonic resonance analysis method of this flexible interconnection system first performs harmonic resonance analysis on the flexible interconnection system and generates a three-dimensional frequency domain diagram. The type of the resonance band is determined by obtaining the characteristics of the resonance band from this three-dimensional frequency domain diagram. Then, corresponding resonance suppression measures are selected according to different resonance band types to suppress the harmonic resonance of the flexible interconnection system. In this embodiment, the resonance suppression strategy is formulated for different resonance band types. For example, when the resonance band shown in the three-dimensional frequency domain diagram is the inverter resonance band, the resonance suppression strategy is to introduce an adjustable active damping coefficient into the simplified impedance network model at the site level. Using active damping technology, a specific control loop is added to the grid-connected inverter control of the flexible interconnection system to simulate the damping resistance effect, increasing the system's damping characteristics. Furthermore, the adjustable active damping coefficient can be flexibly adjusted according to the actual operating conditions of the flexible interconnection system, effectively suppressing the resonance caused by the inverter resonance band. Feeder length affects the impedance characteristics of flexible interconnect systems. When the feeder length exceeds a critical length, resonance is easily triggered. By controlling the feeder length, resonance can be avoided at the structural level of the flexible interconnect system. That is, if the resonance band in the three-dimensional frequency domain diagram is formed by the superposition of the inverter resonance band and the arc resonance band, the resonance suppression strategy is to determine the critical feeder length of this superimposed resonance band and set the feeder length of the flexible interconnect system to be less than the critical feeder length.

[0122] In this embodiment of the application, based on the harmonic resonance analysis results, an active damping coefficient is introduced and configured in the grid-connected inverter control of the flexible interconnected system to suppress the resonance generated by the grid-connected inverter.

[0123] It should be noted that by introducing an active damping coefficient to suppress resonance generated by the grid-connected inverter, a filter capacitor current feedback path can be introduced into the inner current loop of the Norton equivalent model of the grid-connected inverter in the simplified impedance network model at the site level, and an adjustable active damping coefficient k can be set. d Among them, the active damping coefficient k d The initial value and adjustment range of the adjustable active damping coefficient can be determined based on system stability criteria and resonance suppression requirements. For example, based on the actual system conditions and simulation analysis, the initial value and adjustment range of the active damping coefficient can be reasonably determined. Typically, the active damping coefficient k... d A value around 0.01 achieves a good balance between effectively suppressing resonance and maintaining the stability of the flexible interconnect system. This active damping coefficient k... d By directly substituting into the control equation of the Norton equivalent model of the grid-connected inverter, the peak value of the inverter's output impedance at the resonant frequency can be reduced by increasing the damping. The adjustable active damping coefficient k... d Introduced into the controller of the Norton equivalent model of a grid-connected inverter, control theory, such as proportional-integral-derivative (PID) control and fuzzy control, can be used to control the active damping coefficient k. dPrecise adjustments are made to achieve the best resonance suppression effect.

[0124] In other embodiments, steps S3 and S4 are re-executed based on the updated model after introducing the active damping coefficient; the grid-connected point current spectrum before and after applying damping is compared to verify the suppression effect of the peak amplitude of the inverter resonant band.

[0125] In this embodiment, the resonance band based on the harmonic resonance analysis results is a superimposed resonance band. To avoid the superimposed resonance caused by the intersection of the arc-shaped resonance band and the inverter resonance band of the flexible interconnect system, the feeder length of the flexible interconnect system can be reasonably planned and designed.

[0126] It should be noted that if setting the feeder length of the flexible interconnection system to be less than the critical feeder length still cannot avoid the generation of superimposed resonance zone, then it is necessary to consider adjusting the power plant access scheme in the flexible interconnection system (such as changing the initial combination of the number of power generation units m or the feeder data n) or restricting the switching of certain power generation units during operation, so that the operating point of the flexible interconnection system is far away from the superimposed resonance risk zone.

[0127] In other embodiments, if the feeder length of the flexible interconnect system exceeds a critical value (such as a critical feeder length), methods such as adding reactors or changing the system topology can be considered to adjust the impedance characteristics of the flexible interconnect system to avoid resonance.

[0128] In the embodiments of this application, the resonance suppression strategy also includes a comprehensive suppression strategy consisting of introducing an adjustable active damping coefficient and setting the feed line length to be less than the critical feed line length.

[0129] It should be noted that the active damping coefficient is used to suppress inherent resonance at the device level under normal conditions, while parameter avoidance (such as feeder length being less than the critical feeder length) is used to prevent superimposed resonance at the network level from a physical perspective during the planning stage. However, in special operating conditions where the resonance region cannot be avoided due to objective space constraints or dynamic system reconfiguration, a comprehensive suppression strategy combining both must be adopted to ensure stability. In this embodiment, the active damping coefficient, as a general and active resonance suppression strategy control means, is mainly used to suppress inherent inverter resonance; parameter avoidance (such as feeder length being less than the critical feeder length), as a planning and design means for the primary system, is mainly used to prevent superimposed resonance, which is more harmful. In special operating conditions where the risk cannot be completely eliminated through parameter avoidance (such as feeder length being less than the critical feeder length), the active damping coefficient can indirectly reduce the harmonic amplification at the superimposed resonance by reducing the amplitude of the inverter resonance peak, thereby improving the stability margin of the flexible interconnect system. The site modeling and harmonic resonance analysis method for this flexible interconnected system combines active control (configuring active damping coefficients in inverter control) with primary system planning and design (parameter avoidance where feeder length is less than the critical feeder length) through the resonance suppression strategy in step S5. This achieves synergy between active control and primary system design, effectively suppressing resonance during operation and avoiding high-risk operating conditions from the planning stage. This significantly improves the applicability and system reliability of the site modeling and harmonic resonance analysis method for this flexible interconnected system, overcomes the limitation that a single control strategy may fail under specific operating conditions, and provides a more reliable solution for resonance suppression.

[0130] In one embodiment of this application, the operating condition data includes the number of feeders, the number of generating units, and the equivalent harmonic impedance at the grid connection point; based on the electrical parameters, power plant topology data, and operating condition data, a simplified impedance network model at the plant level is constructed, including:

[0131] Norton equivalent modeling is performed based on the electrical quantity parameters of the grid-connected inverter to obtain the Norton equivalent model of the grid-connected inverter.

[0132] A simplified equivalent model of the winding of the double-split transformer is obtained by performing a simplified equivalent model based on the electrical parameters of the main transformer; a simplified equivalent model of the winding of the main transformer is obtained by performing a simplified equivalent model based on the electrical parameters of the main transformer.

[0133] Based on the electrical quantity parameters of the transmission line, a parametric equivalent model is performed to obtain the distributed parameter model of the transmission line;

[0134] Based on the number of power generation units, the feeder topology of each power plant topology data, the Norton equivalent model of the grid-connected inverter, the equivalent model of the double-split transformer winding, the equivalent model of the main transformer winding, and the distributed parameter model of the transmission line, Norton equivalent model is performed to obtain the single feeder aggregate impedance model corresponding to each feeder topology.

[0135] Norton equivalent modeling is performed based on the number of feeders, the equivalent harmonic impedance at the grid connection point, and the aggregated impedance model of all single feeders to obtain a simplified impedance network model at the station level.

[0136] It should be noted that constructing a simplified impedance network model at the plant level can be understood as constructing a simplified impedance network model at the plant level through a series of step-by-step equivalent modeling steps based on electrical parameters, power plant topology data, and operating condition data.

[0137] Figure 9 This is the Norton equivalent circuit diagram of the Norton equivalent model of the grid-connected inverter in the site modeling and harmonic resonance analysis method for the flexible interconnected system described in this application embodiment. Figure 9 middle, I refh This is the h-th harmonic reference current command value for the grid-connected inverter.

[0138] like Figure 9 As shown in the embodiments of this application, in the process of constructing the Norton equivalent model of the grid-connected inverter, the electrical quantity parameters of the grid-connected inverter are used to perform Norton equivalent modeling to obtain the Norton equivalent model of the grid-connected inverter. This Norton equivalent model of the grid-connected inverter can characterize the electrical characteristics of the grid-connected inverter in the circuit in a concise form.

[0139] It should be noted that Norton's theorem states that any linear two-terminal network containing a source can be equivalently replaced by a parallel combination of a current source and a resistor for the external circuit. In this embodiment, according to Norton's equivalence principle, a single grid-connected inverter can be equivalently represented as follows: Figure 9 The controlled current source and the parallel circuit of the grid-connected inverter output impedance shown are used as the Norton equivalent model of the grid-connected inverter. From the transfer function of the Norton equivalent model of the grid-connected inverter, the equivalent transfer function G0 of the controlled current source and the calculated output equivalent impedance Z can be obtained. oh The first equivalent formula is: The equivalent transfer function is:

[0140] ;

[0141] ;

[0142] The first equivalent formula is:

[0143] ;

[0144] In the formula, s is the Laplace operator, and G inv For the inverter transfer function, G c The current loop PR controller transfer function is shown in the equivalent transfer function G0; L1 is the inverter-side inductance of the grid-connected inverter, L2 is the grid-side inductance of the grid-connected inverter, C is the filter capacitor of the grid-connected inverter, and kd k is the active damping coefficient. p k is the proportional gain of the current loop PR controller. h ω is the integral coefficient of the current loop PR controller. c Z is the cutoff angular frequency of the current loop PR controller, ω0 is the fundamental angular frequency of the current loop PR controller, and Z is the cutoff angular frequency. oh K is the output equivalent impedance of the h-th harmonic of the grid-connected transformer. PWM The gain of the grid-connected inverter is given. The equivalent transfer function G0 and the first equivalent formula serve as the control formula for the controller of the Norton equivalent model of the grid-connected inverter.

[0145] Figure 10 This is a simplified equivalent circuit diagram of the double-split transformer winding equivalent model in the site modeling and harmonic resonance analysis method for the flexible interconnection system described in this application embodiment. Figure 10 (a) indicates the winding connection method of a double-split transformer. Figure 10 (b) represents the equivalent circuit of a double-split transformer.

[0146] like Figure 10 As shown in the embodiments of this application, in the process of constructing the equivalent model of the double-split transformer winding, the electrical quantity parameters of the double-split transformer (including winding voltage, current, turns ratio and other parameters) are used to perform simplified equivalent modeling (the complex structure and electrical characteristics of the transformer are reasonably simplified) to obtain the equivalent model of the double-split transformer winding, which facilitates the analysis of its impact on the circuit in the overall model.

[0147] It should be noted that, according to the winding connection method of the double-split transformer (corresponding to...), Figure 10 (a) establishes its simplified equivalent circuit (corresponding to) Figure 10 (b) is used as the equivalent model of the double-split transformer winding. The equivalent impedance of each winding in the equivalent model of the double-split transformer winding is denoted as the first equivalent impedance Z1 of the primary winding, the second equivalent impedance Z2' of the secondary winding, and the third equivalent impedance Z3' of the secondary winding. The formula for calculating each equivalent impedance in the equivalent model of the double-split transformer winding is denoted as the second equivalent formula, which is:

[0148] ;

[0149] In the formula, Z k For the split impedance, k f k is the splitting coefficient. When the double-split transformer operates under ideal conditions, k f ≈4, Z1≈0, Z2'=Z3'≈2Z k .

[0150] Figure 11This is the equivalent circuit diagram of the main transformer winding equivalent model in the site modeling and harmonic resonance analysis method of the flexible interconnection system described in the embodiments of this application.

[0151] like Figure 11 As shown in the embodiments of this application, in the process of constructing the equivalent model of the main transformer winding, the electrical quantity parameters of the main transformer (similar to the double-split transformer, but with different specific parameter values) are also simplified for equivalent modeling to obtain the equivalent model of the main transformer winding, which is used to describe the equivalent characteristics of the main transformer in the circuit.

[0152] It should be noted that an equivalent circuit for a three-winding transformer, including the grid-side winding, load-side winding, and filter winding of the main transformer, is established, such as... Figure 11 As shown. The equivalent harmonic impedance of each winding is obtained and denoted as Z. 1h Z 2h and Z 3h And obtain the harmonic impedance Z of the filtering branch (5th single-tuned filter). fh In the formula, h in the table below represents the harmonic order.

[0153] Figure 12 This is an equivalent circuit diagram of the distributed parameter model of the transmission line in the site modeling and harmonic resonance analysis method for the flexible interconnected system described in this application embodiment. Figure 12 (a) represents the distributed parameter module of the transmission line. Figure 12 (b) represents the π-type two-port equivalent circuit of the transmission line.

[0154] like Figure 12 As shown in the embodiments of this application, in the process of constructing the transmission line distributed parameter model, the electrical quantity parameters of the transmission line (such as line resistance, inductance, capacitance, length, etc.) are used to perform parameter equivalent modeling (the actual parameters of the transmission line are equivalent to parameter forms that are easy to analyze and calculate), and the transmission line distributed parameter model is obtained. This transmission line distributed parameter model takes into account the distribution of transmission line parameters along the line.

[0155] It should be noted that a distributed parameter model of the transmission line is established based on the electrical quantity parameters of the transmission line obtained in step S1. Specifically, for a line with an actual cable length of l, a distributed parameter model of the transmission line is established using... Figure 12 The equivalent circuit of distributed parameters shown in (a) serves as a schematic diagram of the parameter distribution for a transmission line distributed parameter model. Equivalence processing is performed on this schematic diagram, specifically at the harmonic frequency ω. h The series impedance Z L With parallel admittance Y P The equivalent circuit is used as the distributed parameter model for the transmission line. In this embodiment, the distributed parameter model for the transmission line includes calculating the series impedance Z. L With parallel admittance Y PThe formula for the distribution parameters is:

[0156] ;

[0157] ;

[0158] ;

[0159] In the formula, Z L Y represents the series impedance of the series elements in the distributed parameter model of the transmission line. P Z represents the parallel admittance of parallel elements in the distributed parameter model of the transmission line; l represents the actual length of the cable; Z represents the parallel admittance of parallel elements in the distributed parameter model of the transmission line. c γ and ω represent the line wave impedance and line propagation constant, respectively. The equivalent impedance, inductance, and capacitance per unit length of the transmission line are r0, l0, and c0, respectively. h Let ω be the angular frequency corresponding to the h-th harmonic, and j represent an imaginary number.

[0160] Figure 13 This is a circuit diagram of the single-feeder aggregate impedance model in the site modeling and harmonic resonance analysis method of the flexible interconnection system described in the embodiments of this application.

[0161] like Figure 13 As shown in this embodiment, in the process of constructing the single feeder aggregated impedance model, the Norton equivalent model is performed by integrating the number of power generation units (affecting the power distribution on the feeder), the topology of each feeder in the power plant topology data (clarifying the connection method and direction of the feeders), the previously obtained Norton equivalent model of the grid-connected inverter, the equivalent model of the double-split transformer winding, the equivalent model of the main transformer winding, and the transmission line distributed parameter model. This yields a single feeder aggregated impedance model corresponding to each feeder topology. This single feeder aggregated impedance model aggregates the equivalent models of each device on the feeder, reflecting the overall impedance characteristics of a single feeder.

[0162] It should be noted that a single feeder impedance model is established based on the component models of the grid-connected inverter Norton equivalent model, the double-split transformer winding equivalent model, the main transformer winding equivalent model, and the transmission line distributed parameter model, as well as the single feeder topology obtained in step S1. Based on the single feeder impedance model, the m parallel generating units and their connecting lines under a single feeder are aggregated using Norton equivalent models to obtain... Figure 13 The single-feeder aggregated impedance model is shown. Based on the single-feeder impedance model, Norton equivalent aggregation of m generator units connected in parallel under a single feeder and their connecting lines includes: equating a single generator unit (containing 2 inverters and 1 double-split transformer) to a current source and impedance in parallel; considering the impedance Z of the connecting cables between generator units. Lh and admittance Y PhAfter connecting m power generation units in parallel sequentially, and then connecting them in series with the harmonic impedance Z of the feeder cable... FLh and parallel harmonic impedance Z FPh Connection; finally, the entire feeder is equivalent to a Norton circuit, which consists of an equivalent current source I for the h-th harmonic of a generator unit. eqh The equivalent output harmonic impedance Z of a power generation unit eqh The system is constructed using a parallel connection. In this embodiment, the equivalent current source I is calculated using a single-feeder aggregate impedance model. eqh Equivalent output impedance Z of a single feeder eqh The formula is denoted as the third equivalent formula, which is:

[0163] ;

[0164] ;

[0165] In the formula, I eqh Z is an equivalent current source that presents h-th harmonics to the outside world for a single power generation unit. eqh Z represents the equivalent output harmonic impedance of a single power generation unit exhibiting the h-th harmonic. 0h Z represents the output harmonic impedance of a single grid-connected inverter for its h-th harmonic. Th Z is the equivalent harmonic impedance of the h-th harmonic of a double-split transformer. Ph For the parallel branch harmonic impedance of the h-th harmonic of the connecting cable between power generation units, i refh，n I is the reference current command value for the h-th harmonic of the nth grid-connected inverter. feqh Z is the equivalent Norton harmonic current source for the h-th harmonic of a single feeder. FLh Z is the series harmonic impedance of the h-th harmonic of the feeder cable. FPh is the parallel harmonic impedance of the h-th harmonic of the feeder cable, and m is the total number of generating units.

[0166] like Figure 3 As shown, in one embodiment of this application, Norton equivalent modeling is performed based on the number of feeders, the equivalent harmonic impedance at the grid connection point, and the aggregated impedance model of all single feeders to obtain a simplified impedance network model at the site level, including:

[0167] Based on the number of feeders, all single-feeder aggregate impedance models are processed by Norton equivalent parallel connection to obtain the photovoltaic equivalent circuit on the photovoltaic side of the flexible interconnect system.

[0168] Based on the power plant topology data and the equivalent harmonic impedance of the grid connection point, the grid side of the flexible interconnection system is processed by Thevenin equivalent treatment to obtain the grid equivalent circuit.

[0169] By connecting the photovoltaic equivalent circuit and the power grid equivalent circuit in parallel, a simplified impedance network model at the station level is obtained.

[0170] In the simplified impedance network model at the station level, the grid-side equivalent impedance is obtained by equating the inverter winding impedance, filter winding impedance, and passive filter impedance of the main transformer to the grid side. The grid-side equivalent impedance is then input into the simplified impedance network model at the station level for derivation, resulting in the grid-connection point harmonic current expression of the simplified impedance network model at the station level.

[0171] The expression for the harmonic current at the grid connection point is:

[0172] ;

[0173] In the formula, I PCCh U is the grid-connected harmonic current of the h-th harmonic. Sh For the equivalent harmonic voltage source of the h-th harmonic power grid equivalent circuit, i feqh Z is the equivalent Norton harmonic current source for the h-th harmonic single-feeder aggregate impedance model. feqh The equivalent Norton harmonic impedance of the h-th harmonic single-feed aggregate impedance model is given by N1, N2, N3, and Z, where N1 is the number of turns in the main transformer grid-side winding, N2 is the number of turns in the main transformer inverter-side winding, and N3 is the number of turns in the main transformer filter winding. 1h Z represents the harmonic impedance of the grid-side winding of the h-th harmonic main transformer. 2h Z represents the harmonic impedance of the inverter winding of the main transformer for the h-th harmonic. 3h Z represents the harmonic impedance of the filter winding of the main transformer for the h-th harmonic. 3fh Z represents the grid-side equivalent impedance of the h-th harmonic, n is the number of feed lines, and Z is the value of Z. Sh Z is the equivalent harmonic impedance at the grid connection point for the h-th harmonic. 3fh =(N1 / N3) 2 ×(3Z fh +Z 3h Z fh The harmonic impedance of the h-th harmonic of the main transformer.

[0174] It should be noted that during the construction of the simplified impedance network model at the station level, Norton equivalent and Thevenin equivalent modeling is performed based on the number of feeders (determining the overall scale of feeders within the station), the equivalent harmonic impedance at the grid connection point (reflecting the harmonic characteristics of the station's grid connection point), and all single-feeder aggregated impedance models. This results in the simplified impedance network model at the station level, which describes the impedance characteristics of the station as a whole, providing a basic model for subsequent analysis of harmonic resonance and other issues at the station. In this embodiment, based on the constructed single-feeder aggregated impedance model of n feeders, combined with the parameters of the main transformer (main transformer) in step S1 and the equivalent harmonic impedance at the grid connection point, the entire flexible interconnection system is established as follows: Figure 3The simplified impedance network model at the field station level is shown. Specifically, the single-feeder aggregated impedance models of n feeders are connected in parallel to obtain the total equivalent current source I of the photovoltaic equivalent circuit on the photovoltaic side of the flexible interconnect system. pvh (The algebraic sum of the current sources of all feeders) and the total output impedance Z pvh The grid side of the flexible interconnected system (including the grid-side windings of the main transformer and the grid equivalent impedance) is represented by the Thevenin equivalent circuit, i.e., by the equivalent harmonic voltage source U. Sh Equivalent harmonic impedance Z at grid connection point Sh The equivalent circuit of a power grid that forms a flexible interconnected system in series, such as Figure 3 As shown. The site modeling and harmonic resonance analysis method of this flexible interconnection system yields the expression for the harmonic current at the grid connection point, which is used to analyze the harmonic resonance characteristics of the flexible interconnection system.

[0175] In this embodiment, the simplified impedance network model at the field station level includes calculating the total output impedance Z of the photovoltaic equivalent circuit. pvh The calculation formula is given, and it is denoted as the fourth equivalent formula. The fourth equivalent formula is:

[0176] ;

[0177] In the formula, n is the total number of feeders.

[0178] In this embodiment, the site modeling and harmonic resonance analysis method of the flexible interconnection system reveals the classification, mechanism and distribution law of the resonance band through step S4, and achieves effective suppression of harmonic resonance through resonance avoidance design in step S5, thereby improving the grid connection stability and power quality of the power station in the flexible interconnection system.

[0179] Example 2:

[0180] Figure 14 This is a schematic diagram of the framework of the site modeling and harmonic resonance analysis device for the flexible interconnection system described in the embodiments of this application.

[0181] like Figure 14 As shown, this application provides a field station modeling and harmonic resonance analysis device for a flexible interconnection system, including a data acquisition module 10, a model building module 20, a spectrum drawing module 30, and an analysis module 40;

[0182] The data acquisition module 10 is used to acquire electrical parameters of grid-connected inverters, double-split transformers, main transformers, and transmission lines in the flexible interconnection system, as well as power plant topology data and operating condition data.

[0183] The model building module 20 is used to build a model based on electrical parameters, power plant topology data and operating condition data to obtain a simplified impedance network model at the plant level.

[0184] The graph plotting module 30 is used to obtain array variable parameters, input array variable parameters, electrical parameters and operating condition data into the station-level simplified impedance network model, and obtain the grid connection point current amplitude corresponding to each set of variable parameters; and plot the three-dimensional frequency domain graph of the grid connection point current amplitude-frequency characteristic based on all variable parameters and corresponding grid connection point current amplitude values.

[0185] Analysis module 40 is used to perform identification and analysis based on the three-dimensional frequency domain diagram to obtain harmonic resonance analysis results.

[0186] It should be noted that the modules in the device of Embodiment 2 correspond to the steps described in the method of Embodiment 1. Since the steps in the method of Embodiment 1 have already been described, the contents of the data acquisition module 10, model construction module 20, spectrum drawing module 30, and analysis module 40 in the flexible interconnection system site modeling and harmonic resonance analysis device will not be described again in this embodiment. The flexible interconnection system site modeling and harmonic resonance analysis device constructs a site-level simplified impedance network model from the equipment layer to the system layer through the data acquisition module 10, model construction module 20, spectrum drawing module 30, and analysis module 40. Then, based on the site-level simplified impedance network model, a three-dimensional frequency domain diagram capable of analyzing harmonic resonance is obtained, and accurate wave resonance analysis results are obtained by identifying the three-dimensional frequency domain diagram.

[0187] In one embodiment of this application, the site modeling and harmonic resonance analysis device of the flexible interconnection system further includes a resonance suppression module 50. The resonance suppression module is used to determine a resonance suppression strategy based on the harmonic resonance analysis results. The content of determining the resonance suppression strategy includes:

[0188] If the harmonic resonance analysis result shows that the resonance band of the three-dimensional frequency domain diagram is the inverter resonance band, then the resonance suppression strategy is to introduce an adjustable active damping coefficient into the simplified impedance network model at the station level.

[0189] If the harmonic resonance analysis result shows that the resonance band of the three-dimensional frequency domain diagram is a superimposed resonance band containing the inverter resonance band and the arc resonance band, and the critical feeder length of the superimposed resonance band is obtained, then the resonance suppression strategy is to set the feeder length of the flexible interconnect system to be less than the critical feeder length.

[0190] In one embodiment of this application, the operating condition data includes the number of feeders, the number of power generation units, and the equivalent harmonic impedance at the grid connection point; the model building module 20 includes a first building submodule, a second building submodule, a third building submodule, a fourth building submodule, and a fifth building submodule;

[0191] The first construction submodule is used to perform Norton equivalent modeling based on the electrical quantity parameters of the grid-connected inverter to obtain the Norton equivalent model of the grid-connected inverter.

[0192] The second construction submodule is used to perform simplified equivalent modeling based on the electrical quantity parameters of the double-split transformer to obtain the equivalent model of the double-split transformer winding; and to perform simplified equivalent modeling based on the electrical quantity parameters of the main transformer to obtain the equivalent model of the main transformer winding.

[0193] The third construction submodule is used to perform parametric equivalent modeling based on the electrical quantity parameters of the transmission line to obtain the distributed parameter model of the transmission line;

[0194] The fourth submodule is used to perform Norton equivalent modeling based on the number of power generation units, the feeder topology of each power plant topology data, the Norton equivalent model of the grid-connected inverter, the equivalent model of the double-split transformer winding, the equivalent model of the main transformer winding, and the distributed parameter model of the transmission line, so as to obtain the single feeder aggregate impedance model corresponding to each feeder topology.

[0195] The fifth submodule is used to perform Norton equivalent modeling based on the number of feeders, the equivalent harmonic impedance of the grid connection point, and the aggregate impedance model of all single feeders, to obtain a simplified impedance network model at the site level.

[0196] In one embodiment of this application, Norton equivalent modeling is performed based on the number of feeders, the equivalent harmonic impedance at the grid connection point, and the aggregated impedance model of all single feeders to obtain a simplified impedance network model at the site level, including:

[0197] Based on the number of feeders, all single-feeder aggregate impedance models are processed by Norton equivalent parallel connection to obtain the photovoltaic equivalent circuit on the photovoltaic side of the flexible interconnect system.

[0198] Based on the power plant topology data and the equivalent harmonic impedance of the grid connection point, the grid side of the flexible interconnection system is processed by Thevenin equivalent treatment to obtain the grid equivalent circuit.

[0199] By connecting the photovoltaic equivalent circuit and the power grid equivalent circuit in parallel, a simplified impedance network model at the station level is obtained.

[0200] In the simplified impedance network model at the station level, the grid-side equivalent impedance is obtained by equating the inverter winding impedance, filter winding impedance, and passive filter impedance of the main transformer to the grid side. The grid-side equivalent impedance is then input into the simplified impedance network model at the station level for derivation, resulting in the grid-connection point harmonic current expression of the simplified impedance network model at the station level.

[0201] The expression for the harmonic current at the grid connection point is:

[0202] ;

[0203] In the formula, I PCCh U is the grid-connected harmonic current of the h-th harmonic. Sh For the equivalent harmonic voltage source of the h-th harmonic power grid equivalent circuit, i feqhZ is the equivalent Norton harmonic current source for the h-th harmonic single-feeder aggregate impedance model. feqh The equivalent Norton harmonic impedance of the h-th harmonic single-feed aggregate impedance model is given by N1, N2, N3, and Z, where N1 is the number of turns in the main transformer grid-side winding, N2 is the number of turns in the main transformer inverter-side winding, and N3 is the number of turns in the main transformer filter winding. 1h Z represents the harmonic impedance of the grid-side winding of the h-th harmonic main transformer. 2h Z represents the harmonic impedance of the inverter winding of the main transformer for the h-th harmonic. 3h Z represents the harmonic impedance of the filter winding of the main transformer for the h-th harmonic. 3fh Z represents the grid-side equivalent impedance of the h-th harmonic, n is the number of feed lines, and Z is the value of Z. Sh Let be the equivalent harmonic impedance at the grid connection point of the h-th harmonic.

[0204] Example 3:

[0205] Figure 15 This is a schematic diagram of the terminal device described in an embodiment of this application.

[0206] like Figure 15 As shown, this application provides a terminal device, including a processor and a memory;

[0207] Memory is used to store program code and transfer the program code to the processor;

[0208] The processor is used to execute the above-mentioned site modeling and harmonic resonance analysis method for flexible interconnected systems according to the instructions in the program code.

[0209] It should be noted that the processor is used to execute the steps in the above-described embodiment of a method for site modeling and harmonic resonance analysis of a flexible interconnected system according to the instructions in the program code. Alternatively, when the processor executes the computer program, it implements the functions of each module / unit in the above-described system / device embodiments.

[0210] For example, a computer program can be divided into one or more modules / units, one or more of which are stored in memory and executed by a processor to complete this application. One or more modules / units can be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of the computer program in a terminal device.

[0211] Terminal devices can be computing devices such as desktop computers, laptops, handheld computers, and cloud servers. Terminal devices may include, but are not limited to, processors and memory. Those skilled in the art will understand that this does not constitute a limitation on the terminal device, which may include more or fewer components than illustrated, or combinations of certain components, or different components. For example, a terminal device may also include input / output devices, network access devices, buses, etc.

[0212] The processor can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor.

[0213] Memory can be an internal storage unit of a terminal device, such as a hard drive or RAM. Memory can also be an external storage device, such as a plug-in hard drive, SmartMedia Card (SMC), Secure Digital (SD) card, or Flash Card. Furthermore, memory can include both internal and external storage units. Memory is used to store computer programs and other programs and data required by the terminal device. Memory can also be used to temporarily store data that has been output or will be output.

[0214] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0215] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between apparatuses or units through some interfaces, and may be electrical, mechanical, or other forms.

[0216] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0217] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0218] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0219] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for station modeling and harmonic resonance analysis of a flexible interconnected system, characterized in that, Includes the following steps: Acquire electrical parameters of grid-connected inverters, split transformers, main transformers, and transmission lines in flexible interconnection systems, as well as power plant topology and operating condition data; Based on the electrical parameters, the power plant topology data, and the operating condition data, a simplified impedance network model at the plant level is constructed to obtain the model. Obtain array variable parameters, input the array variable parameters, the electrical parameters, and the operating condition data into the station-level simplified impedance network model to obtain the grid connection point current amplitude corresponding to each set of variable parameters; plot the three-dimensional frequency domain diagram of the grid connection point current amplitude-frequency characteristic based on all the variable parameters and the corresponding grid connection point current amplitude. Based on the three-dimensional frequency domain diagram, the harmonic resonance analysis results are obtained.

2. The method for station modeling and harmonic resonance analysis of a flexible interconnected system according to claim 1, characterized in that, Also includes: Based on the harmonic resonance analysis results, a resonance suppression strategy is determined; The content of determining the resonance suppression strategy includes: If the harmonic resonance analysis result indicates that the resonance band of the three-dimensional frequency domain diagram is the inverter resonance band, then the resonance suppression strategy is to introduce an adjustable active damping coefficient into the simplified impedance network model at the station level. If the harmonic resonance analysis result shows that the resonance band of the three-dimensional frequency domain diagram is a superimposed resonance band containing an inverter resonance band and an arc-shaped resonance band, and the critical feeder length of the superimposed resonance band is obtained, then the resonance suppression strategy is to set the feeder length of the flexible interconnect system to be less than the critical feeder length.

3. The method for station modeling and harmonic resonance analysis of a flexible interconnected system according to claim 1 or 2, characterized in that, The operating condition data includes the number of feeders, the number of power generation units, and the equivalent harmonic impedance at the grid connection point. Based on the electrical parameters, the power plant topology data, and the operating condition data, a simplified impedance network model at the power plant level is constructed, including: Norton equivalent modeling is performed based on the electrical quantity parameters of the grid-connected inverter to obtain the Norton equivalent model of the grid-connected inverter. A simplified equivalent model of the double-split transformer winding is obtained by performing a simplified equivalent model based on the electrical parameters of the double-split transformer; a simplified equivalent model of the main transformer winding is obtained by performing a simplified equivalent model based on the electrical parameters of the main transformer. Based on the electrical quantity parameters of the transmission line, a parameter equivalent model is performed to obtain the distributed parameter model of the transmission line; Based on the number of power generation units, the feeder topology of each feeder in the power station topology data, the Norton equivalent model of the grid-connected inverter, the equivalent model of the double-split transformer winding, the equivalent model of the main transformer winding, and the distributed parameter model of the transmission line, Norton equivalent model is performed to obtain a single feeder aggregate impedance model corresponding to each feeder topology. Norton equivalent modeling is performed based on the number of feeders, the equivalent harmonic impedance of the grid connection point, and the aggregated impedance model of all single feeders to obtain a simplified impedance network model at the site level.

4. The method for station modeling and harmonic resonance analysis of a flexible interconnected system according to claim 3, characterized in that, Based on the number of feeders, the equivalent harmonic impedance of the grid connection point, and all the single feeder aggregated impedance models, Norton equivalent modeling is performed to obtain a simplified impedance network model at the site level, including: Based on the number of feeders, all the single-feeder aggregate impedance models are processed by Norton equivalent parallel connection to obtain the photovoltaic equivalent circuit on the photovoltaic side of the flexible interconnect system. Based on the power plant topology data and the equivalent harmonic impedance of the grid connection point, the grid side of the flexible interconnection system is subjected to Thevenin equivalent processing to obtain the grid equivalent circuit. The photovoltaic equivalent circuit is connected in parallel with the power grid equivalent circuit to obtain a simplified impedance network model at the station level; In the simplified impedance network model at the station level, the grid-side equivalent impedance is obtained by equating the inverter winding impedance, filter winding impedance, and passive filter impedance of the main transformer to the grid side. The grid-side equivalent impedance is then input into the simplified impedance network model at the station level for derivation, resulting in the grid-connection point harmonic current expression of the simplified impedance network model at the station level.

5. The method for station modeling and harmonic resonance analysis of a flexible interconnected system according to claim 4, characterized in that, The expression for the harmonic current at the grid connection point is: ； In the formula, I PCCh U is the grid-connected harmonic current of the h-th harmonic. Sh For the equivalent harmonic voltage source of the h-th harmonic power grid equivalent circuit, i feqh Z is the equivalent Norton harmonic current source for the h-th harmonic single-feeder aggregate impedance model. feqh The equivalent Norton harmonic impedance of the h-th harmonic single-feed aggregate impedance model is given by N1, N2, N3, and Z, where N1 is the number of turns in the main transformer grid-side winding, N2 is the number of turns in the main transformer inverter-side winding, and N3 is the number of turns in the main transformer filter winding. 1h Z represents the harmonic impedance of the grid-side winding of the h-th harmonic main transformer. 2h Z represents the harmonic impedance of the inverter winding of the main transformer for the h-th harmonic. 3h Z represents the harmonic impedance of the filter winding of the main transformer for the h-th harmonic. 3fh Z represents the grid-side equivalent impedance of the h-th harmonic, n is the number of feed lines, and Z is the value of Z. Sh Let be the equivalent harmonic impedance at the grid connection point of the h-th harmonic.

6. A device for station modeling and harmonic resonance analysis of a flexible interconnected system, characterized in that, It includes a data acquisition module, a model building module, a graph drawing module, and an analysis module; The data acquisition module is used to acquire electrical parameters of grid-connected inverters, double-split transformers, main transformers, and transmission lines in the flexible interconnection system, as well as power plant topology data and operating condition data. The model building module is used to build a model based on the electrical parameters, the power station topology data and the operating condition data to obtain a simplified impedance network model at the station level. The graph plotting module is used to obtain array variable parameters, input the array variable parameters, the electrical parameters and the operating condition data into the station-level simplified impedance network model, and obtain the grid connection point current amplitude corresponding to each set of variable parameters; and plot the three-dimensional frequency domain graph of the grid connection point current amplitude-frequency characteristic based on all the variable parameters and the corresponding grid connection point current amplitude. The analysis module is used to perform identification and analysis based on the three-dimensional frequency domain diagram to obtain harmonic resonance analysis results.

7. The site modeling and harmonic resonance analysis device for a flexible interconnected system according to claim 6, characterized in that, It also includes a resonance suppression module, which is used to determine a resonance suppression strategy based on the harmonic resonance analysis results; The content of determining the resonance suppression strategy includes: If the harmonic resonance analysis result indicates that the resonance band of the three-dimensional frequency domain diagram is the inverter resonance band, then the resonance suppression strategy is to introduce an adjustable active damping coefficient into the simplified impedance network model at the station level. If the harmonic resonance analysis result shows that the resonance band of the three-dimensional frequency domain diagram is a superimposed resonance band containing an inverter resonance band and an arc-shaped resonance band, and the critical feeder length of the superimposed resonance band is obtained, then the resonance suppression strategy is to set the feeder length of the flexible interconnect system to be less than the critical feeder length.

8. The site modeling and harmonic resonance analysis device for a flexible interconnected system according to claim 6 or 7, characterized in that, The operating condition data includes the number of feeders, the number of power generation units, and the equivalent harmonic impedance at the grid connection point; the model construction module includes a first construction submodule, a second construction submodule, a third construction submodule, a fourth construction submodule, and a fifth construction submodule; The first construction submodule is used to perform Norton equivalent modeling based on the electrical quantity parameters of the grid-connected inverter to obtain the Norton equivalent model of the grid-connected inverter; The second construction submodule is used to perform simplified equivalent modeling based on the electrical quantity parameters of the double-split transformer to obtain an equivalent model of the double-split transformer winding; and to perform simplified equivalent modeling based on the electrical quantity parameters of the main transformer to obtain an equivalent model of the main transformer winding. The third construction submodule is used to perform parameter equivalent modeling based on the electrical quantity parameters of the transmission line to obtain the distributed parameter model of the transmission line; The fourth construction submodule is used to perform Norton equivalent modeling based on the number of power generation units, the feeder topology of each feeder in the power station topology data, the Norton equivalent model of the grid-connected inverter, the equivalent model of the double-split transformer winding, the equivalent model of the main transformer winding, and the transmission line distributed parameter model, to obtain a single feeder aggregate impedance model corresponding to each feeder topology; The fifth construction submodule is used to perform Norton equivalent modeling based on the number of feeders, the equivalent harmonic impedance of the grid connection point, and all the single feeder aggregate impedance models to obtain a simplified impedance network model at the site level.

9. The site modeling and harmonic resonance analysis device for a flexible interconnected system according to claim 8, characterized in that, Based on the number of feeders, the equivalent harmonic impedance of the grid connection point, and all the single feeder aggregated impedance models, Norton equivalent modeling is performed to obtain a simplified impedance network model at the site level, including: Based on the number of feeders, all the single-feeder aggregate impedance models are processed by Norton equivalent parallel connection to obtain the photovoltaic equivalent circuit on the photovoltaic side of the flexible interconnect system. Based on the power plant topology data and the equivalent harmonic impedance of the grid connection point, the grid side of the flexible interconnection system is subjected to Thevenin equivalent processing to obtain the grid equivalent circuit. The photovoltaic equivalent circuit is connected in parallel with the power grid equivalent circuit to obtain a simplified impedance network model at the station level; In the simplified impedance network model at the station level, the grid-side equivalent impedance is obtained by equating the inverter winding impedance, filter winding impedance, and passive filter impedance of the main transformer to the grid side of the main transformer. The grid-side equivalent impedance is then input into the simplified impedance network model at the station level for derivation, resulting in the grid-connection point harmonic current expression of the simplified impedance network model at the station level. The expression for the harmonic current at the grid connection point is: ； In the formula, I PCCh U is the grid-connected harmonic current of the h-th harmonic. Sh For the equivalent harmonic voltage source of the h-th harmonic power grid equivalent circuit, i feqh Z is the equivalent Norton harmonic current source for the h-th harmonic single-feeder aggregate impedance model. feqh The equivalent Norton harmonic impedance of the h-th harmonic single-feed aggregate impedance model is given by N1, N2, N3, and Z, where N1 is the number of turns in the main transformer grid-side winding, N2 is the number of turns in the main transformer inverter-side winding, and N3 is the number of turns in the main transformer filter winding. 1h Z represents the harmonic impedance of the grid-side winding of the h-th harmonic main transformer. 2h Z represents the harmonic impedance of the inverter winding of the main transformer for the h-th harmonic. 3h Z represents the harmonic impedance of the filter winding of the main transformer for the h-th harmonic. 3fh Z represents the grid-side equivalent impedance of the h-th harmonic, n is the number of feed lines, and Z is the value of Z. Sh Let be the equivalent harmonic impedance at the grid connection point of the h-th harmonic.

10. A terminal device, characterized in that, Including the processor and memory; The memory is used to store program code and transmit the program code to the processor; The processor is configured to execute the site modeling and harmonic resonance analysis method for the flexible interconnected system as described in any one of claims 1-5, according to the instructions in the program code.

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