Impedance modeling method and system of direct current synchronous network-forming static var generator

Abstract

This invention discloses an impedance modeling method and system for a DC synchronous grid-type static var generator (SVM), relating to the field of grid-type SVMs. The method includes: constructing a small-signal model of power disturbance, a small-signal model of DC capacitor, a small-signal model of power control loop, a small-signal model of coordinate transformation, a small-signal model of voltage and current dual closed-loop, and a coupling model of DC and AC sides in the control loop; constructing a network model in the main circuit; combining the small-signal model of power control loop, the small-signal model of voltage and current dual closed-loop, and the coupling model to obtain a first expression; substituting the small-signal model of coordinate transformation into the first expression to obtain a second expression; substituting the small-signal model of power disturbance, the small-signal model of DC capacitor, and the small-signal model of power control loop into the second expression to obtain a third expression; substituting the network model into the third expression to obtain a fourth expression; and determining the impedance model of the grid-type SVM based on the fourth expression.

Description

Technical Field

[0001] This invention relates to the field of grid-type static var generators, and more specifically, to an impedance modeling method and system for a DC synchronous grid-type static var generator. Background Technology

[0002] The high proportion of power electronic equipment connected to the grid results in a power system characterized by "high penetration, low inertia, and weak damping." Since most new energy units are connected to the grid via power electronic converters, their inherent low inertia, weak damping, and random fluctuations expose the system to a greater risk of voltage instability. To improve the voltage stability of a grid with hollowed-out power sources, existing technologies have proposed grid-mounted static var generators (SVMs) with dynamic response speed and high overload capacity to enhance grid voltage support performance while also addressing system inertia support requirements.

[0003] The small-disturbance stability of grid-connected static var generators (SVAs) varies under different grid conditions. Their SVA stability is still affected by many factors, including grid strength, control parameters, and operating conditions. Furthermore, when grid-connected SVAs are connected to grids of varying strengths, the coupling effect between controllers may induce system oscillations or even instability. In scenarios with a high proportion of renewable energy integration and dynamic changes in grid-side impedance, the dynamic behavior of the grid-connected SVA interacting with the grid becomes even more complex. As a typical voltage source converter, the output impedance characteristics of a grid-connected SVA directly determine the dynamic interaction characteristics and stability margin of the power system's source-grid relationship. Constructing an accurate impedance model of a grid-connected SVA is of significant reference value for revealing the oscillation mechanism of the power system and optimizing control parameters.

[0004] Therefore, it is urgent to analyze the small-disturbance stability of grid-type static var generators, reveal their instability mechanism based on impedance models, and guide the rational design of control parameters to reduce the risk of system instability. Summary of the Invention

[0005] The purpose of this invention is to provide an impedance modeling method and system for DC synchronous grid-type static var generators, which solves the problem that the existing technology does not analyze the impedance model of grid-type static var generators under DC synchronization, and cannot clarify the oscillation and instability risk of grid-type static var generators after they are connected to the power grid.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0007] In a first aspect, the present invention provides an impedance modeling method for a grid-type static var generator, the method comprising:

[0008] We construct small-signal models of power disturbance, DC capacitor, power control loop, coordinate transformation, voltage and current dual closed-loop, and coupling model of DC and AC sides for the grid-type static var generator in the control loop.

[0009] A network model of the main circuit section of a grid-type static var generator is constructed; wherein, the main circuit environment includes filter inductors, filter capacitors and damping resistor branches;

[0010] By combining the small-signal model of the power control loop, the small-signal model of the voltage and current dual closed loop, and the coupled model, the first expression characterizing the output voltage of the grid-type static var generator in the system coordinate system on the d and q axes is obtained.

[0011] Substituting the coordinate transformation small-signal model into the first expression, we obtain the second expression for the d and q axis components in the control coordinate system.

[0012] Substituting the small-signal power disturbance model, the small-signal DC capacitor model, and the small-signal power control loop model into the second expression yields the third expression.

[0013] Substituting the network model into the third expression yields the fourth expression characterizing the voltage-current relationship at the grid connection point;

[0014] The impedance model of the grid-type static var generator is determined based on the fourth expression.

[0015] In one implementation, a small-signal model of the power perturbation is constructed, including:

[0016] Establish the steady-state equations for the active and reactive power output of a DC synchronous grid-type static var generator;

[0017] The steady-state equation is linearized to obtain a small-signal model of power disturbance.

[0018] In one implementation scheme, a small-signal model of the DC capacitor is constructed, including:

[0019] Establish the steady-state equations for the DC side;

[0020] By introducing a small-signal disturbance signal on the DC side, a small-signal model of the DC capacitor is obtained.

[0021] In one implementation, a small-signal model of the power control loop is constructed, including:

[0022] Determine the expressions for the synchronization angle and voltage loop reference voltage on the d-axis of a grid-type static var generator for DC synchronization;

[0023] The expressions for the synchronization angle and voltage loop at the d-axis reference voltage are linearized to obtain the small-signal model of the power control loop.

[0024] In one implementation scheme, a dual closed-loop small-signal model of voltage and current is constructed, including:

[0025] Using the internal potential as a reference, a reference signal for the inner current loop is generated based on the feedback of the filter capacitor voltage.

[0026] The current inner loop control is executed based on the reference signal of the current inner loop. The current inner loop tracks the current reference output by the voltage inner loop and generates a modulated wave signal.

[0027] In one implementation, the coupling model between the DC side and the AC side is expressed as follows: ;in, The d-axis component represents the output voltage of the grid-type static var generator in the system coordinate system. The q-axis component represents the output voltage of the grid-type static var generator in the system coordinate system. Represents the DC and AC coupling matrix; This represents the disturbance signal of the d-axis modulated wave in the system coordinate system. This represents the disturbance signal of the q-axis modulated wave in the system coordinate system.

[0028] In one implementation, the expression for the network model is:

[0029] ;in, Represents the identity matrix; Represents the filter inductance transfer matrix; Represents the filter capacitor transfer matrix; This represents the damping resistance transfer matrix; The d-axis component represents the output voltage of the grid-type static var generator in the system coordinate system. The q-axis component represents the output voltage of the grid-type static var generator in the system coordinate system. This represents the disturbance signal of the d-axis inductor current in the system coordinate system. This represents the disturbance signal of the q-axis inductor current in the system coordinate system. This represents the disturbance signal of the grid-connected current along the d-axis in the system coordinate system. This represents the disturbance signal of the grid-connected current along the q-axis in the system coordinate system. This represents the disturbance signal of the grid-connected voltage along the d-axis in the system coordinate system. This represents the disturbance signal of the grid-connected voltage along the q-axis in the system coordinate system.

[0030] A second aspect of the present invention provides an impedance modeling system for a grid-type static var generator, the system comprising:

[0031] The small-signal model construction unit is used to construct the small-signal power disturbance model, DC capacitor small-signal model, power control loop small-signal model, coordinate transformation small-signal model, voltage and current dual closed-loop small-signal model, and DC-AC coupling model of the grid-type static var generator in the control loop.

[0032] The network model building unit is used to build the network model of the main circuit section of the grid-type static var generator; wherein, the main circuit environment includes filter inductors, filter capacitors and damping resistor branches;

[0033] The modeling unit is used to combine the small-signal model of the power control loop, the small-signal model of the voltage and current dual closed loop, and the coupling model to obtain the first expression characterizing the output voltage of the grid-type static var generator (SVM) in the system coordinate system along the d and q axes. Substituting the coordinate transformation small-signal model into the first expression yields the second expression characterizing the d and q axes in the control coordinate system. Substituting the power disturbance small-signal model, the DC capacitor small-signal model, and the power control loop small-signal model into the second expression yields the third expression. Substituting the network model into the third expression yields the fourth expression characterizing the voltage and current relationship at the grid connection point. Based on the fourth expression, the impedance model of the grid-type SVM is determined.

[0034] In one implementation, a small-signal model of the power perturbation is constructed, including:

[0035] Establish the steady-state equations for the active and reactive power output of a DC synchronous grid-type static var generator;

[0036] The steady-state equation is linearized to obtain a small-signal model of power disturbance.

[0037] In one implementation scheme, a small-signal model of the DC capacitor is constructed, including:

[0038] Establish the steady-state equations for the DC side;

[0039] By introducing a small-signal disturbance signal on the DC side, a small-signal model of the DC capacitor is obtained.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] In the technical solution provided by this invention, for a grid-type static var generator based on DC synchronization, small-signal models suitable for small disturbance signal stability analysis are constructed for various control links and main circuit parts of the power system. These models include power disturbance small-signal models, DC capacitor small-signal models, power control loop small-signal models, coordinate transformation small-signal models, voltage and current dual closed-loop small-signal models, coupling models of the DC and AC sides, and network models in the main circuit part. Combining the interaction relationships of various control links and main circuit parts of the power system, the constructed small-signal models and network models are combined. Finally, an impedance model suitable for small disturbance stability analysis of the DC-synchronous grid-type static var generator is constructed. Based on this impedance model, the stability of the grid-type static var generator connected to different grid strengths can be analyzed using the eigenvalue locus method, providing model support for clarifying the instability mechanism of the grid-type static var generator and the grid interaction system. Attached Figure Description

[0042] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0043] Figure 1 A flowchart illustrating an impedance modeling method for a grid-type static var generator provided in an embodiment of the present invention;

[0044] Figure 2 The frequency sweep result diagram of the grid-type static var generator based on DC synchronization provided in the embodiment of the present invention. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0046] It should be noted that the terms "comprising" or "may include" used in the various embodiments of this application indicate the presence of the claimed function, operation, or element, and do not limit the addition of one or more functions, operations, or elements. Furthermore, as used in the various embodiments of this application, the terms "comprising," "having," and their cognates are intended only to indicate a specific feature, number, step, operation, element, component, or combination of the foregoing, and should not be construed as primarily excluding the presence of one or more other features, numbers, steps, operations, elements, components, or combinations of the foregoing, or adding one or more combinations of the foregoing.

[0047] It should be understood that terms such as "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 technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0048] Please refer to Figure 1 This invention provides an impedance modeling method for a grid-type static var generator, the method comprising the following steps:

[0049] S101, construct the small-signal model of power disturbance, DC capacitor, power control loop, coordinate transformation, voltage and current dual closed-loop small-signal model, and coupling model of DC side and AC side of grid-type static var generator in the control loop.

[0050] In this embodiment, the process of constructing the small-signal power disturbance model is as follows: establish the steady-state equations for the active and reactive power output of the DC synchronous grid-type static var generator; linearize the steady-state equations to obtain the small-signal power disturbance model.

[0051] Specifically, the steady-state equations for active power and reactive power are expressed as follows: (1), where, The d-axis component represents the grid-connected voltage; The d-axis component represents the grid-connected current; Represents the q-axis component of the grid-connected voltage; This represents the q-axis component of the grid-connected current.

[0052] Linearization near the steady-state operating point, ignoring higher-order infinitesimals, yields a small-signal model of the power perturbation:

[0053] (2), where, The active power disturbance signal output by the system; The active power disturbance signal output by the system; This represents the disturbance signal of the grid-connected voltage along the d-axis in the system coordinate system. This represents the disturbance signal of the grid-connected voltage along the q-axis in the system coordinate system. This represents the disturbance signal of the grid-connected current along the d-axis in the system coordinate system. This represents the disturbance signal of the grid-connected current along the q-axis in the system coordinate system. The power transfer matrix representing the grid-connected voltage; The power transfer matrix represents the grid-connected current. and The expression is:

[0054] (3), where, This represents the steady-state quantity of the d-axis grid-connected current; This represents the steady-state quantity of the q-axis grid-connected current; This represents the steady-state quantity of the d-axis grid-connected voltage; It represents the steady-state quantity of the q-axis grid-connected voltage.

[0055] The above power disturbance small-signal model establishes the relationship between power disturbance and voltage and current disturbance, laying the foundation for subsequent small-signal analysis of the control loop.

[0056] The process of constructing a small-signal model of a DC capacitor is as follows: establish the steady-state equation on the DC side; introduce a small-signal disturbance signal on the DC side to obtain the small-signal model of the DC capacitor.

[0057] Specifically, the dynamic behavior of the DC-side capacitor directly affects the system's energy balance. Based on the capacitor's charging and discharging characteristics, the steady-state equation for the DC-side capacitor can be expressed as:

[0058] (4), where, Indicates the DC-side capacitor; Indicates the DC side voltage; This represents the derivative of the DC-side voltage with respect to time. After introducing a small-signal perturbation on the DC side, we obtain the small-signal model of the DC capacitor: (5), where, This indicates a disturbance signal in the DC-side voltage. This represents the transfer matrix between power and DC voltage. Wherein, The expression is: (6), where, This represents the steady-state quantity of the DC-side voltage; This represents the Laplace operator.

[0059] This small-signal model of the DC capacitor establishes the relationship between the DC capacitor voltage deviation and power disturbance, and characterizes the energy interaction between the DC side and the AC side.

[0060] The process of constructing the small-signal model of the power control loop is as follows: Determine the synchronization angle and the expression of the voltage loop in the d-axis reference voltage of the DC synchronous grid-type static var generator; Linearize the expression of the synchronization angle and the voltage loop in the d-axis reference voltage to obtain the small-signal model of the power control loop.

[0061] GFM-SVG achieves system synchronization and reactive power regulation through a power control loop. The system synchronization angle θ and the d-axis reference voltage of the voltage loop are also considered. The expression is: (7), where, Indicates the moment of inertia; Indicates the damping coefficient; Indicates virtual coefficients; Indicates the fundamental angular frequency; Indicates the rated voltage; Express the reference value for reactive power; This represents the integral coefficient.

[0062] Linearizing the power loop near the steady-state point yields the small-signal model of the power control loop:

[0063] (8); (9), where, The disturbance signal representing the synchronization angle; This indicates the reactive power control quantity; This represents the disturbance signal of the d-axis reference voltage of the voltage loop; This represents the disturbance signal of the q-axis reference voltage of the voltage loop; This represents the power transfer function matrix. Wherein, The expression is:

[0064] (10) Signal transformation matrix The expression is

[0065] The small-signal model of the power control loop describes the effect of the power control loop on the regulation of the system synchronization angle and voltage control quantity.

[0066] The coordinate transformation small-signal model transforms variables between different coordinate systems during the coordinate transformation process. For the transformation process between different variables, the coordinate transformation small-signal model can be expressed as:

[0067] (11), where, This represents the disturbance signal of the d-axis voltage in the control coordinate system; This represents the disturbance signal of the q-axis voltage in the control coordinate system; This represents the disturbance signal of the d-axis voltage in the system coordinate system. This represents the disturbance signal of the q-axis voltage in the system coordinate system. The coordinate transformation transfer matrix representing voltage; This represents the disturbance signal of the d-axis current in the control coordinate system; This represents the disturbance signal of the q-axis current in the control coordinate system; The coordinate transformation transfer matrix representing the current; This represents the disturbance signal of the modulated wave along the d-axis in the system coordinate system. This represents the disturbance signal of the q-axis modulated wave in the system coordinate system. This represents the disturbance signal of the d-axis modulated wave in the control coordinate system; This represents the disturbance signal of the q-axis voltage in the control coordinate system; The coordinate transformation transfer matrix representing the modulated wave; This represents the disturbance signal of the d-axis inductor current in the control coordinate system. This represents the disturbance signal of the q-axis inductor current in the control coordinate system; This represents the disturbance signal of the inductor current along the d-axis in the system coordinate system. This represents the disturbance signal of the q-axis inductor current in the system coordinate system. This represents the coordinate transformation transfer matrix of the inductor current. Each transfer matrix is ​​determined by the steady-state operating point:

[0068] (12), where, This represents the steady-state quantity of the q-axis inductor current; This represents the steady-state quantity of the d-axis inductor current; This represents the steady-state quantity of the q-axis inductor current; This represents the steady-state quantity of the d-axis inductor current.

[0069] This coordinate transformation small-signal model describes the effect of coordinate transformation on system variables in the presence of phase and amplitude disturbances.

[0070] The process of constructing a voltage and current dual closed-loop small-signal model is as follows: with the internal potential as a reference, a reference signal for the current inner loop is generated based on the voltage feedback of the filter capacitor; the current inner loop control is executed based on the reference signal of the current inner loop, and the current inner loop generates a modulated wave signal by tracking the current reference output by the voltage inner loop.

[0071] Specifically, the outer voltage loop uses the inner potential as a reference and generates a reference signal for the inner current loop based on the feedback of the filter capacitor voltage.

[0072] (13), where, This represents the d-axis reference voltage in the control coordinate system; Control the q-axis reference voltage in the coordinate system; This represents the virtual impedance matrix.

[0073] Based on the current inner loop control of the network-type SVG, we can obtain:

[0074] (14), where, This represents the reference inductor current along the d-axis in the control coordinate system. This represents the q-axis reference inductor current in the control coordinate system; Represents the voltage controller matrix; This represents the capacitor voltage feedforward decoupling matrix; This represents the filter capacitor.

[0075] The inner current loop tracks the current reference output by the voltage loop and generates a modulated wave signal:

[0076] (15), where, For current controller matrix; This represents the transfer function of the current controller; This is the inductor current feedforward decoupling matrix; This represents the filter inductor.

[0077] The expression for the coupling model between the DC and AC sides is: (16); among them, The d-axis component represents the output voltage of the grid-type static var generator in the system coordinate system. The q-axis component represents the output voltage of the grid-type static var generator in the system coordinate system. Represents the DC and AC coupling matrix; This represents the disturbance signal of the d-axis modulated wave in the system coordinate system. This represents the disturbance signal of the q-axis modulated wave in the system coordinate system.

[0078] in, The expression is (17), where, Represents the steady-state quantity of the d-axis modulated wave; It represents the steady-state quantity of the q-axis modulated wave.

[0079] This model reveals the interaction between DC voltage fluctuations and AC-side control quantities, and is an important part of analyzing the dynamic stability of the system.

[0080] S102, Construct a network model of the main circuit section of the grid-type static var generator; wherein, the main circuit environment includes filter inductors, filter capacitors and damping resistor branches.

[0081] Specifically, the main circuit includes a filter inductor, a filter capacitor, and a damping resistor branch. In the synchronous coordinate system, based on the filter's circuit structure and Kirchhoff's voltage and current laws, the expression for the matrix network model of the main circuit in the dq coordinate system can be derived as follows: (18), among which, Represents the identity matrix; Represents the filter inductance transfer matrix; Represents the filter capacitor transfer matrix; This represents the damping resistance transfer matrix; The d-axis component represents the output voltage of the grid-type static var generator in the system coordinate system. The q-axis component represents the output voltage of the grid-type static var generator in the system coordinate system. This represents the disturbance signal of the d-axis inductor current in the system coordinate system. This represents the disturbance signal of the q-axis inductor current in the system coordinate system. This represents the disturbance signal of the grid-connected current along the d-axis in the system coordinate system. This represents the disturbance signal of the grid-connected current along the q-axis in the system coordinate system. This represents the disturbance signal of the grid-connected voltage along the d-axis in the system coordinate system. This represents the disturbance signal of the grid-connected voltage along the q-axis in the system coordinate system.

[0082] in, , and The expression is:

[0083] (19), where, Indicates the filter resistor; This indicates the damping resistance.

[0084] S103, by combining the small-signal model of the power control loop, the small-signal model of the voltage and current dual closed loop, and the coupling model, the first expression characterizing the output voltage of the grid-type static var generator in the d-axis and q-axis components in the system coordinate system is obtained.

[0085] In this embodiment, by combining the above formulas (9), (13), (14), (15), and (16), we can obtain the first expression for the d-axis and q-axis components of the output voltage of the grid-type static var generator in the system coordinate system, namely:

[0086] (20).

[0087] S104, Substitute the coordinate transformation small signal model into the first expression to obtain the second expression for the d and q axis components in the control coordinate system.

[0088] Specifically, by substituting the coordinate transformation small-signal model recorded in formula (11) into the first expression, and transforming the variables in the control coordinate system to the system coordinate system, the second expression can be obtained, namely:

[0089] (twenty one).

[0090] S105, Substitute the small-signal model of power disturbance, the small-signal model of DC capacitor, and the small-signal model of power control loop into the second expression to obtain the third expression.

[0091] Substitute the small-signal models of power disturbance, DC capacitance, and power control loop into the second expression to eliminate intermediate variables. and We can obtain the third expression, which is:

[0092] (twenty two).

[0093] S106, Substitute the network model into the third expression to obtain the fourth expression characterizing the voltage and current relationship at the grid connection point.

[0094] Substitute the network model into the third expression to eliminate intermediate variables. After simplification, a fourth expression characterizing the voltage-current relationship at the grid connection point can be obtained, namely: (23). Among them, and The expressions are as follows:

[0095] (twenty four).

[0096] S107, determine the impedance model of the grid-type static var generator based on the fourth expression.

[0097] Based on Kirchhoff's voltage and current laws and the fourth expression, the impedance model of a grid-type static var generator can be obtained, i.e. (25).

[0098] The derived impedance model fully describes the impedance characteristics of a DC synchronous grid-type static var generator in the frequency domain and can be used for subsequent small-disturbance stability analysis. To verify the correctness of the constructed impedance model, a frequency sweep method was used to verify the theoretical analysis results. Figure 2 As shown, including The impedance component Z in the dd channel dd ; The impedance component Z in the dq channel dq ; The impedance component Z in the qd channel qd ; The impedance component Z in the qq channel qq Observations show that, Figure 2 The frequency sweep results are in good agreement with the theoretical analysis results, demonstrating that the established impedance model accurately reflects the port impedance characteristics of the power system. The stability of grid-connected static var generators (SVMs) connected to different grid strengths can be analyzed, providing model support for clarifying the instability mechanism of the SVM and grid interaction system.

[0099] This invention also provides an impedance modeling system for a grid-type static var generator, the system comprising:

[0100] The small-signal model construction unit is used to construct the small-signal power disturbance model, DC capacitor small-signal model, power control loop small-signal model, coordinate transformation small-signal model, voltage and current dual closed-loop small-signal model, and DC-AC coupling model of the grid-type static var generator in the control loop.

[0101] The network model building unit is used to build the network model of the main circuit section of the grid-type static var generator; wherein, the main circuit environment includes filter inductors, filter capacitors and damping resistor branches;

[0102] The modeling unit is used to combine the small-signal model of the power control loop, the small-signal model of the voltage and current dual closed loop, and the coupling model to obtain the first expression characterizing the output voltage of the grid-type static var generator (SVM) in the system coordinate system along the d and q axes. Substituting the coordinate transformation small-signal model into the first expression yields the second expression characterizing the d and q axes in the control coordinate system. Substituting the power disturbance small-signal model, the DC capacitor small-signal model, and the power control loop small-signal model into the second expression yields the third expression. Substituting the network model into the third expression yields the fourth expression characterizing the voltage and current relationship at the grid connection point. Based on the fourth expression, the impedance model of the grid-type SVM is determined.

[0103] In the impedance modeling system for a grid-type static var generator (SVR) provided in this embodiment of the invention, for a DC-synchronous grid-type SVR, a small-signal model of power disturbance, a small-signal model of DC capacitor, a small-signal model of power control loop, a small-signal model of coordinate transformation, a small-signal model of voltage and current dual closed-loop, a coupling model of DC side and AC side, and a network model in the main circuit are constructed for various control links and main circuit parts of the power system. Combining the interaction relationships of various control links and main circuit parts of the power system, the constructed small-signal models and network models are combined, and finally, an impedance model of a DC-synchronous grid-type SVR suitable for small-disturbance stability analysis is constructed. Based on this impedance model, the stability of the grid-type SVR connected to different grid strengths can be analyzed using the eigenvalue locus method, providing model support for clarifying the instability mechanism of the grid-type SVR and the grid interaction system.

[0104] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An impedance modeling method of a direct current synchronous meshed static var generator, characterized by, The methods include: We construct small-signal models of power disturbance, DC capacitor, power control loop, coordinate transformation, voltage and current dual closed-loop, and coupling model of DC and AC sides for the grid-type static var generator in the control loop. A network model of the main circuit section of a grid-type static var generator is constructed; wherein, the main circuit environment includes filter inductors, filter capacitors and damping resistor branches; By combining the small-signal model of the power control loop, the small-signal model of the voltage and current dual closed loop, and the coupled model, the first expression characterizing the output voltage of the grid-type static var generator in the system coordinate system on the d and q axes is obtained. Substituting the coordinate transformation small-signal model into the first expression, we obtain the second expression for the d and q axis components in the control coordinate system. Substituting the small-signal power disturbance model, the small-signal DC capacitor model, and the small-signal power control loop model into the second expression yields the third expression. Substituting the network model into the third expression yields the fourth expression characterizing the voltage-current relationship at the grid connection point; The impedance model of the grid-type static var generator is determined based on the fourth expression.

2. The impedance modeling method for a DC synchronous grid-type static var generator according to claim 1, characterized in that, Constructing a small-signal model of power perturbation includes: Establish the steady-state equations for the active and reactive power output of a DC synchronous grid-type static var generator; The steady-state equation is linearized to obtain a small-signal model of power disturbance.

3. The impedance modeling method for a DC synchronous grid-type static var generator according to claim 1, characterized in that, Constructing a small-signal model of DC capacitance includes: Establish the steady-state equations for the DC side; By introducing a small-signal disturbance signal on the DC side, a small-signal model of the DC capacitor is obtained.

4. The impedance modeling method for a DC synchronous grid-type static var generator according to claim 1, characterized in that, Construct a small-signal model of the power control loop, including: Determine the expressions for the synchronization angle and voltage loop reference voltage on the d-axis of a grid-type static var generator for DC synchronization; The expressions for the synchronization angle and voltage loop at the d-axis reference voltage are linearized to obtain the small-signal model of the power control loop.

5. The impedance modeling method for a DC synchronous grid-type static var generator according to claim 1, characterized in that, Construct a dual closed-loop small-signal model for voltage and current, including: Using the internal potential as a reference, a reference signal for the inner current loop is generated based on the feedback of the filter capacitor voltage. The current inner loop control is executed based on the reference signal of the current inner loop. The current inner loop tracks the current reference output by the voltage inner loop and generates a modulated wave signal.

6. The impedance modeling method for a DC synchronous grid-type static var generator according to claim 1, characterized in that, The expression for the coupling model between the DC side and the AC side is: ;in, The d-axis component represents the output voltage of the grid-type static var generator in the system coordinate system. The q-axis component represents the output voltage of the grid-type static var generator in the system coordinate system. Represents the DC and AC coupling matrix; This represents the disturbance signal of the d-axis modulated wave in the system coordinate system. This represents the disturbance signal of the q-axis modulated wave in the system coordinate system.

7. The impedance modeling method for a DC synchronous grid-type static var generator according to claim 1, characterized in that, The expression for the network model is: ;in, Represents the identity matrix; Represents the filter inductance transfer matrix; Represents the filter capacitor transfer matrix; This represents the damping resistance transfer matrix; The d-axis component represents the output voltage of the grid-type static var generator in the system coordinate system. The q-axis component represents the output voltage of the grid-type static var generator in the system coordinate system. This represents the disturbance signal of the d-axis inductor current in the system coordinate system. This represents the disturbance signal of the q-axis inductor current in the system coordinate system. This represents the disturbance signal of the grid-connected current along the d-axis in the system coordinate system. This represents the disturbance signal of the grid-connected current along the q-axis in the system coordinate system. This represents the disturbance signal of the grid-connected voltage along the d-axis in the system coordinate system. This represents the disturbance signal of the grid-connected voltage along the q-axis in the system coordinate system.

8. An impedance modeling system for a DC synchronous grid-type static var generator, characterized in that the system... include: The small-signal model construction unit is used to construct the small-signal power disturbance model, DC capacitor small-signal model, power control loop small-signal model, coordinate transformation small-signal model, voltage and current dual closed-loop small-signal model, and DC-AC coupling model of the grid-type static var generator in the control loop. The network model building unit is used to build the network model of the main circuit section of the grid-type static var generator; wherein, the main circuit environment includes filter inductors, filter capacitors and damping resistor branches; The modeling unit is used to combine the small-signal model of the power control loop, the small-signal model of the voltage and current dual closed loop, and the coupling model to obtain the first expression characterizing the output voltage of the grid-type static var generator (SVM) in the system coordinate system along the d and q axes. Substituting the coordinate transformation small-signal model into the first expression yields the second expression characterizing the d and q axes in the control coordinate system. Substituting the power disturbance small-signal model, the DC capacitor small-signal model, and the power control loop small-signal model into the second expression yields the third expression. Substituting the network model into the third expression yields the fourth expression characterizing the voltage and current relationship at the grid connection point. Based on the fourth expression, the impedance model of the grid-type SVM is determined.

9. The impedance modeling system for a DC synchronous grid-type static var generator according to claim 8, characterized in that, Constructing a small-signal model of power perturbation includes: Establish the steady-state equations for the active and reactive power output of a DC synchronous grid-type static var generator; The steady-state equation is linearized to obtain a small-signal model of power disturbance.

10. The impedance modeling system for a DC synchronous grid-type static var generator according to claim 8, characterized in that, Constructing a small-signal model of DC capacitance includes: Establish the steady-state equations for the DC side; By introducing a small-signal disturbance signal on the DC side, a small-signal model of the DC capacitor is obtained.

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