Stable region adjustment method for typical network configuration control strategy based on sequence impedance analysis

Abstract

The application relates to the technical field of typical network configuration control, and discloses a stability domain adjustment method of a typical network configuration control strategy based on sequence impedance analysis, which aims to solve the shortcomings of a non-uniform stability domain framework, unclear MC control impedance characteristics, unclear parameter influence law and insufficient solution precision; the method establishes a control model of the typical network configuration control strategy, constructs a full-order small signal model based on small signal linearization disturbance processing, deduces a sequence impedance model in combination with the conversion relationship between positive and negative sequences and dq axis components, establishes a parameter-stability mapping relationship based on sequence impedance amplitude and phase characteristics in combination with gain margin and phase margin criteria, demarcates a stability domain range through two-dimensional parameter scanning and boundary fitting, and finally simulates and corrects the stability domain, so that the VSG control and the MC control stability domain can be accurately demarcated and compared horizontally, and the network configuration control parameter optimization and the power grid adaptability are improved.

Description

Technical Field

[0001] This invention relates to the field of typical network control technology, and in particular to a stability domain adjustment method for typical network control strategies based on sequence impedance analysis. Background Technology

[0002] Grid-connected control strategies, by simulating the self-synchronization characteristics and inertia support capabilities of synchronous generators, have become a core technology for solving the stability problem of new energy grid connection. Among them, VSG control (Virtual Synchronous Generator Control) and MC control (Matching Control) are two typical grid-connected control strategies. VSG control replicates the rotor motion equations and electromagnetic characteristics of synchronous generators and has good inertia support capabilities, but it suffers from problems such as complex parameter tuning and limited adaptability under weak grid conditions. MC control, based on the similarity between the dynamics of DC capacitor voltage and the rotor motion equations of synchronous generators, achieves self-synchronization through DC voltage-frequency mapping, and has gradually become a research hotspot in recent years. However, related research has mostly focused on the verification of control principles and lacks systematic analysis of its stability domain.

[0003] Currently, the sequence impedance method is an effective tool for broadband stability analysis, capable of revealing the impedance characteristics of a system under disturbances at different frequencies, providing a quantitative basis for the stability evaluation of network control strategies. However, it still has the following key shortcomings: First, it lacks a unified framework for solving the stability domain; the stability analysis methods for VSG control and MC control are independent of each other, making it impossible to conduct horizontal comparisons and performance evaluations. Second, the derivation of the sequence impedance model does not fully consider small-signal nonlinear coupling terms, leading to deviations in the stability criteria and affecting the accuracy of the stability domain solution. Third, it does not systematically reveal the influence of key parameters on the stability domain, making it difficult to guide parameter optimization in engineering practice. Fourth, the stability domain solution often uses single-parameter scanning, failing to consider the coupling effects between parameters, resulting in inaccurate descriptions of the stability domain boundaries.

[0004] Therefore, there is an urgent need for a unified and precise method for the stability domain regulation of grid control strategies that combines sequence impedance analysis, so as to provide technical support for the stable operation of high-proportion renewable energy grid-connected systems. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing typical grid control strategies, such as inconsistent stability domain solution frameworks, unclear MC control impedance characteristics, unclear parameter influence laws, and insufficient solution accuracy. The proposed method is a stability domain adjustment method for typical grid control strategies based on sequence impedance analysis. This method enables accurate delineation and horizontal comparison of the stability domains of VSG control and MC control, providing a theoretical basis for optimizing grid control parameters and improving grid adaptability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] Stability-domain regulation methods based on typical network control strategies using sequence impedance analysis include:

[0008] Establish control models for typical network control strategies;

[0009] A full-order small-signal model is constructed by linearizing and perturbating the small-signal signal;

[0010] By combining the conversion relationship between positive and negative sequence and dq axis components, the sequence impedance model is derived;

[0011] Based on the magnitude and phase characteristics of the sequence impedance, and combined with the gain margin and phase margin criteria, a parameter-stability mapping relationship is established.

[0012] The stability region is defined by two-dimensional parameter scanning and boundary fitting, and the stability region is corrected by simulation.

[0013] As a further preferred embodiment of the present invention, the control model based on a typical network control strategy includes:

[0014] Active power-frequency control and reactive power-voltage control;

[0015] The voltage reference value is obtained through dual-loop control of voltage and current.

[0016] A modulation wave is generated by combining the phase angle and the voltage amplitude.

[0017] As a further preferred embodiment of the present invention, based on the steady-state operating point linearization method, the control equations of the control loop and the main circuit are subjected to small-signal perturbation processing, the small-signal components of all variables are defined, the small-signal quadratic terms are ignored, and the full-order small-signal model covering the control equations, coordinate transformation, LCL filter and power conservation is established.

[0018] The control equations include DC voltage-power control equations, active power-frequency control equations, and reactive power-voltage control equations.

[0019] The voltage and current variables generated by the control system are transformed to the electrical system coordinate system through coordinate transformation.

[0020] Using an LCL filter as the main circuit of a grid-type converter, the output voltage disturbance on the inverter side is obtained through the LCL filter;

[0021] Based on the steady-state calculation equations for active and reactive power, small-signal disturbances in active and reactive power are obtained after small-signal linearization.

[0022] As a further preferred embodiment of the present invention, the sequence impedance model is derived by combining the conversion relationship between positive and negative sequence and dq axis components, including:

[0023] Positive-sequence and negative-sequence small-signal disturbances are added to the three-phase voltage and current to establish time-domain expressions for voltage and current;

[0024] Convert the time-domain expression to the frequency-domain expression, ignoring nonlinear coupling terms;

[0025] By combining the conversion relationship between positive and negative sequence and dq axis components, the expressions for positive sequence impedance and negative sequence impedance are derived, and the sequence impedance expressions for VSG and MC are constructed.

[0026] Analyze the amplitude-frequency and phase-frequency characteristics of the sequence impedance to determine the inductive and capacitive ranges and the impedance amplitude fluctuation range.

[0027] As a further preferred embodiment of the present invention, the parameter-stability mapping relationship is established based on the order impedance amplitude-phase characteristics and combined with the gain margin and phase margin criteria, as follows:

[0028] When the sequence impedance phase reaches -180°, the difference between the corresponding impedance amplitude and 0dB is expressed by the following gain margin expression:

[0029]

[0030] in, For loop gain, The angular frequency at which the phase reaches -180°, with a gain margin > 0, has an amplitude stability margin at this frequency;

[0031] When the sequence impedance amplitude reaches 0dB, the corresponding impedance phase difference from -180° is expressed as the phase margin expression:

[0032]

[0033] in, Angular frequency at 0dB The value is an imaginary unit; when the phase margin is greater than 0, there is a phase stability margin at this frequency.

[0034] By traversing the range of control parameters and grid parameters, sequence impedance analysis is performed on each parameter combination to extract gain margin and phase margin, and a parameter-stability mapping relationship is established.

[0035] If the gain margin is greater than 0 and the phase margin is greater than 0, it is considered stable.

[0036] If the gain margin is 0 or the phase margin is 0 and neither of these conditions is less than 0, the system is considered critically stable.

[0037] If the gain margin is less than 0 or the phase margin is less than 0, it is considered unstable.

[0038] As a further preferred embodiment of the present invention, the two-dimensional parameter scanning and boundary fitting are used to define the stable region range as follows:

[0039] Select control parameters and grid parameters that have a significant impact on the stability of grid control as the scanning objects, and set the scanning range and step size of the control parameters and grid parameters.

[0040] Using a fixed set of parameter combinations as a reference value, a gradient scan is performed on another set of parameter combinations. The gain margin and phase margin of each parameter combination are obtained through sequence impedance analysis. The stability is judged and the critical parameter values ​​for stability and instability are recorded.

[0041] A cubic polynomial is used to fit the critical parameter values ​​to obtain the stability domain boundary curve. Based on the goodness of fit of the stability domain boundary curve, the stable region and the unstable region of the stability domain boundary curve are delineated.

[0042] As a further preferred embodiment of the present invention, the simulation-corrected stability region includes:

[0043] Set the main circuit parameters, control parameters, and power grid parameters;

[0044] Set the power grid strength condition and load condition;

[0045] Set a judgment threshold and compare the simulation results with the stability domain analysis results. If all stable parameter combinations in the simulation fall within the stability domain and all unstable parameter combinations fall within the instability domain, and the critical parameter deviation does not exceed the judgment threshold, then the stability domain is valid.

[0046] If the critical parameter deviation exceeds the judgment threshold, the sequence impedance model is revised, the nonlinear coupling term is reconsidered, or the approximate conditions in the derivation process of the sequence impedance model are adjusted until the critical parameter deviation meets the judgment threshold requirements.

[0047] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention establishes a sequence impedance model for MC control and clearly analyzes the impedance characteristics of MC control; it establishes a unified stability domain solution framework, realizing a horizontal comparison of the stability domains of two typical grid control strategies, VSG control and MC control, providing a basis for the selection of different grid control strategies; in the derivation of the sequence impedance model, the system considers the influence of small-signal disturbances and coordinate transformations, and improves the accuracy of stability domain solution by combining the dual criteria of gain margin and phase margin; through two-dimensional parameter scanning and polynomial fitting, it reveals the coupling influence law of key control parameters and grid parameters on the stability domain, accurately adjusts the stability domain boundary, provides clear guidance for parameter optimization of grid control strategies, and can significantly improve the stability of the system under weak grid conditions; this method is applicable to different grid strengths and different load conditions, has strong engineering practicality, and can be directly applied to the design and commissioning of high-proportion renewable energy grid-connected systems, reducing the risk of system oscillation and instability. Attached Figure Description

[0048] Figure 1 This is a flowchart of the stability domain adjustment of a typical network control strategy in Embodiment 1 of the present invention; Figure 2 This is a block diagram of VSG control active power-frequency control in Embodiment 1 of the present invention; Figure 3 This is a block diagram of MC-controlled DC voltage-frequency control in Embodiment 1 of the present invention; Figure 4 This is the circuit topology diagram used in the actual simulation of Embodiment 1 of the present invention; Figure 5 This is a power grid frequency waveform diagram under the actual simulation of the operating conditions mentioned in Embodiment 2 of the present invention; Figure 6 This is a power grid frequency waveform diagram under the actual simulation of the working conditions mentioned in Embodiment 3 of the present invention. Detailed Implementation

[0049] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the specific embodiments of this invention will be described in detail below with reference to the accompanying drawings. These embodiments are merely preferred examples of this invention, used to aid in understanding the inventive concept, and do not constitute a limitation on the scope of protection.

[0050] Example 1

[0051] A stability-domain regulation method based on a typical network control strategy using sequence impedance analysis, referring to... Figure 1 The stability region adjustment method includes the following steps:

[0052] Step S1: Establish a control model for a typical network control strategy;

[0053] Typical grid control strategies include virtual synchronous generator (VSG) control and matching control (MC) control. The core mathematical models of VSG control and MC control cover four major aspects: active power-frequency control, reactive power-voltage control, voltage and current dual-loop control, and modulation wave generation.

[0054] Step S11, Active-Frequency Control;

[0055] Reference Figure 2 For VSG control, the rotor motion equation of the synchronous generator is simulated to achieve dynamic adjustment of active power and frequency. The active power-frequency control expression of VSG control is as follows:

[0056]

[0057] in, and These are the reference value and the measured value of active power, respectively. The rated angular frequency; This is a virtual moment of inertia; The damping coefficient; Represents the Laplace operator. The phase angle is the result of integration.

[0058] Reference Figure 3 For MC control, based on the similarity between the dynamics of the DC capacitor voltage and the motion equations of the synchronous generator rotor, self-synchronization is achieved through DC voltage-frequency mapping. The active power-frequency control expression for MC control is:

[0059]

[0060] in, and These are the reference and measured DC voltage values ​​for the grid-type converter, respectively. This is the DC voltage-frequency adjustment coefficient; The phase angle is the result of integration.

[0061] Step S12, reactive power-voltage control;

[0062] For VSG control: reactive power-voltage droop control is adopted to achieve coordinated regulation of reactive power and AC voltage. The reactive power-voltage control expression for VSG control is:

[0063]

[0064] in, This is the reactive power-voltage droop factor. This is the reference value for the d-axis voltage. and These are the reference value and the measured value of reactive power, respectively. The q-axis voltage reference value is set to 0V. The inertia coefficient.

[0065] For MC control: PI control is used to achieve zero steady-state error tracking of reactive power. The reactive power-voltage control expression for MC control is:

[0066]

[0067] in, , These are the proportional coefficient and integral coefficient of the reactive power outer loop, respectively. This is the rated voltage on the AC side of the converter.

[0068] Step S13, voltage and current dual-loop control;

[0069] Voltage outer loop: Employs a PI controller to track the deviation between the dq-axis voltage reference value and the measured value, outputting the inner loop current reference value. The transfer function is:

[0070]

[0071] The governing equations are:

[0072]

[0073] in, This refers to the proportional coefficient of the voltage outer loop PI controller; The integral coefficient of the voltage outer loop PI controller. , These are the current reference values ​​on the d-axis and q-axis of the grid connection point (PCC), respectively. , These are the AC voltage measurements on the d-axis and q-axis of the PCC, respectively. This is the filter capacitor on the inverter side.

[0074] By comparing the voltage reference value and the actual value through the voltage outer loop transfer function, the basic current requirement is calculated. Based on the predicted load demand and decoupling compensation, the cross-coupling effect caused by coordinate system rotation is eliminated, and finally, an accurate current reference value is output.

[0075] The inner current loop uses a PI controller to track the deviation between the current reference value and the measured value, and outputs a modulated wave voltage correction. Its transfer function is:

[0076]

[0077] The governing equations are:

[0078]

[0079] in, The proportional coefficient of the inner loop PI controller; The integral coefficient of the inner loop PI controller; , These are the modulated wave voltage reference values ​​(inverter output voltage command) for the output d-axis and q-axis, respectively. , These are the d-axis and q-axis current measurements of the PCC, respectively. This is the filter inductor on the inverter side.

[0080] The current reference value and the measured current value output from the outer voltage loop of the previous stage are compared. The error is then calculated using the proportional-integral transfer function of the inner current loop. Voltage feedforward and inductive coupling terms are added to cancel out internal interference within the system. The final output voltage reference value is used to generate the modulation wave to drive the inverter.

[0081] Step S14, generating the modulated wave;

[0082] Based on the three-phase sinusoidal expression, and combining the phase angle and voltage amplitude to generate the modulation wave, the mathematical model is as follows:

[0083]

[0084] in, , and The modulated wave voltages for phases A, B, and C. The phase angle is the result of integrating the voltage vector.

[0085] Using the calculated voltage amplitude and phase, the transformation process of the three-phase sinusoidal reference signal from the synchronous rotating coordinate system (dq coordinate system) to the three-phase stationary coordinate system (abc coordinate system) is synthesized, which is used to generate the three-phase modulation wave that ultimately drives the inverter.

[0086] Step S2: Establish a full-order small-signal model;

[0087] Based on the steady-state operating point linearization method, small-signal perturbation processing is applied to the control equations of each control element and the main circuit. Small-signal components of all variables are defined, and small-signal quadratic terms (nonlinear terms) are ignored. A full-order small-signal model covering the control equations, coordinate transformation, LCL filter, and power conservation is established, specifically including:

[0088] Step S21, governing equations;

[0089] By performing small-signal processing on the DC voltage-power control equations of MC, and reducing the active-frequency control and reactive-voltage control of the converter to small-signal values, we can obtain:

[0090]

[0091] In the formula, , , , These are the MC control output phase, DC side voltage, d-axis voltage of the converter output, and small-signal disturbance of the reactive power output of the converter, respectively.

[0092] By performing small-signal processing on the active power-frequency control equations and reactive power-voltage control equations of the VSG, and combining this with the power conservation relationship, we can obtain:

[0093]

[0094] In the formula, , These are the VSG control output phase and the small-signal disturbance of the active power output of the converter, respectively.

[0095] Step S22, coordinate transformation;

[0096] The voltage and current variables generated by the control system need to be transformed to the electrical system coordinate system through coordinate transformation, and there is a steady-state phase angle difference between the two. , This is the small-signal change of the phase angle difference during the dynamic process; the coordinate transformation matrix is:

[0097]

[0098] in, This is the coordinate transformation matrix; , , ;

[0099] in, This represents the small-signal disturbance of the inverter output voltage reference value in the electrical system coordinate system. This represents the PCC voltage disturbance in the control system coordinate system. This represents the current disturbance in the control system coordinate system. This represents the disturbance of the voltage reference value in the control system coordinate system. This represents the PCC voltage disturbance in the electrical system coordinate system. This represents the current disturbance in the electrical system coordinate system.

[0100] , These are the measured steady-state voltage values ​​of the PCC along the d-axis and q-axis in the electrical system coordinate system, respectively. , These are the measured PCC steady-state current values ​​along the d-axis and q-axis in the electrical system coordinate system, respectively. , These are the steady-state voltage reference values ​​for the d-axis and q-axis in the control system coordinate system, respectively. In this embodiment, the superscript "s" represents the transformed coordinate system, the superscript "c" represents the control system coordinate system, and the subscript "0" represents the steady-state value.

[0101] Step S23, LCL filter;

[0102] The LCL filter is the core main circuit of a grid-type converter. Based on Kirchhoff's laws, the LCL filter obtains the output voltage disturbance, current disturbance, and PCC voltage on the inverter side.

[0103]

[0104] in, This indicates the amount of voltage disturbance at the inverter side output. This represents the current disturbance of the current filtering capacitor. Represents the PCC voltage in the electrical system coordinate system; Represents the voltage-current transfer matrix. This represents the admittance matrix of the filter capacitor. This represents the network-side impedance matrix.

[0105] in,

[0106]

[0107] In the formula, , , , , These represent the inverter-side filter inductor, filter capacitor, damping resistor, inverter-side filter inductor series resistance, and grid-side inductor, respectively.

[0108] Step S24, power conservation;

[0109] Based on the steady-state calculation equations for active and reactive power, the small-signal disturbances of active and reactive power are obtained after small-signal linearization:

[0110]

[0111] in, , These are the small-signal disturbances of active power and reactive power, respectively. , These are the measured steady-state PCC current values ​​along the d-axis and q-axis in the control system coordinate system, respectively. , These are the PCC voltage disturbances along the d-axis and q-axis in the control system coordinate system, respectively. , These are the measured values ​​of the PCC steady-state voltage along the d-axis and q-axis in the control system coordinate system, respectively. , These are the current disturbances along the d-axis and q-axis in the control system coordinate system, respectively.

[0112] Step S3: Derive the sequence impedance model;

[0113] The sequence impedance model is the core of broadband stability analysis. By introducing positive and negative sequence small-signal perturbations, the expressions for positive and negative sequence impedances are derived. The specific steps are as follows:

[0114] Step S31, introduce time-domain perturbation;

[0115] Positive and negative sequence small-signal disturbances are added to the three-phase voltage and current to establish time-domain expressions for voltage and current. Taking phase A as an example, the time-domain expression is established as follows:

[0116]

[0117]

[0118] In the formula, Represents the voltage time domain. Represents the time domain of current. Represents a continuous-time variable. , and These are the peak values ​​of the fundamental voltage, positive-sequence perturbation voltage, and negative-sequence perturbation voltage, respectively. , and These are the peak values ​​of the fundamental current, the positive-sequence perturbation current response, and the negative-sequence perturbation current response, respectively. , and These are the fundamental frequency, the positive-sequence perturbation frequency, and the negative-sequence perturbation frequency, respectively. and These are the initial phase angles of the positive-sequence and negative-sequence disturbance voltages, respectively. , and These are the initial phase angles of the fundamental current, the positive-sequence disturbance current response, and the negative-sequence disturbance current response, respectively.

[0119] Step S32, frequency domain conversion;

[0120] In the frequency domain, using the convolution theorem, since the amplitude of the coupling term is extremely small under small signal perturbations, its impact on stability is negligible, therefore it is ignored. and Nonlinear coupling terms, voltage and current It can be written as:

[0121]

[0122]

[0123] In the formula, It represents the imaginary unit.

[0124] Step S33, impedance derivation;

[0125] Combining the positive / negative order with the conversion relationship between dq axis components:

[0126]

[0127]

[0128] in, , These are the frequency domain components of the d-axis and q-axis voltages. , and These are the frequency domain components of the voltages in phases A, B, and C. , These are the positive-sequence voltage phasor and the negative-sequence voltage phasor, respectively.

[0129] Combining the small-signal model equations, positive sequence impedance With negative sequence impedance The mathematical expression is as follows:

[0130]

[0131] in, Indicates positive sequence impedance. Indicates negative sequence impedance; , These are the positive sequence voltage and the positive sequence current, respectively. , These are negative sequence voltage and negative sequence current, respectively. It is the d-axis self-impedance. It is the q-axis self-impedance. It is the mutual impedance between the q-axis and the d-axis. It is the mutual impedance between the d-axis and the q-axis.

[0132] Based on the above analysis, the sequence impedance expression of VSG can be derived as follows:

[0133]

[0134] The sequence impedance expression for MC is:

[0135]

[0136] in, , ;

[0137] in, The voltage amplitude of the mains grid at point PCC. The phase difference between the internal potential of the VSG and the grid voltage. This represents the phase difference of MC during steady-state operation. This is the DC voltage reference value for the grid-type converter. The input DC voltage in the initial state; It is a DC voltage regulator capacitor. The equivalent impedance on the grid side. .

[0138] Step S34, Feature Analysis:

[0139] Based on the derived sequence impedance expression, the amplitude-frequency response curve (amplitude-frequency) and phase-frequency response curve (phase-frequency) are plotted and analyzed as follows:

[0140] Inductive and capacitive ranges: The impedance is inductive when the phase is between 0° and 180°, and capacitive when the phase is between -180° and 0°.

[0141] Amplitude fluctuation range: The trend of impedance amplitude variation at different frequencies reflects the system's ability to suppress broadband disturbances;

[0142] Positive / negative sequence symmetry: The degree of difference between positive and negative sequence impedances affects the system's adaptability to unbalanced disturbances.

[0143] Step S4: Establish the parameter-stability mapping relationship;

[0144] Based on the analysis results of the sequence impedance amplitude and phase characteristics, gain margin (GM) and phase margin (PM) are used as stability criteria to establish a mapping relationship between control parameters and system stability:

[0145] Step S41, Criterion Definition;

[0146] Gain margin (GM): The difference between the impedance magnitude and 0dB when the sequence impedance phase reaches -180°. The mathematical expression is:

[0147]

[0148] in, This is the loop gain, which is the ratio of the source-side output impedance to the load-side input impedance. This is the angular frequency at which the phase reaches -180°. When the value is greater than 0, there is an amplitude stability margin at this frequency, which can suppress oscillations caused by disturbances at this frequency.

[0149] Phase margin (PM): When the sequence impedance magnitude reaches 0dB, the difference between the impedance phase and -180° is expressed mathematically as follows:

[0150]

[0151] in, Angular frequency at which 0dB is reached The imaginary unit, When the value is greater than 0, there is a phase stability margin at this frequency, which avoids system instability caused by phase lag.

[0152] Step S42: Establish the mapping relationship;

[0153] Traverse key control parameters (control parameters include) , , , ) and grid parameters (grid-side inductance) Grid-side resistance The range of values ​​for ) is determined, and sequence impedance analysis is performed on each parameter combination to extract gain margin and phase margin, thus establishing a "parameter combination- - -The mapping relationship of "stability".

[0154] Stablize: >0 and >0;

[0155] Critical stability: =0 or =0 and no single term is less than 0;

[0156] Instability: <0 or <0.

[0157] Step S5: Define the range of the stability region;

[0158] The stable region is accurately defined using a two-dimensional parameter scanning and boundary fitting method. The specific steps are as follows:

[0159] Step S51, parameter selection;

[0160] Select control parameters and power grid parameters that have a significant impact on the stability of grid control as the scanning objects;

[0161] Control parameter: Virtual moment of inertia DC voltage-frequency adjustment coefficient reactive power outer loop proportional coefficient Reactive power outer loop integral coefficient ;

[0162] Grid parameters: Grid-side inductance Grid-side resistance .

[0163] Step S52, gradient value determination;

[0164] Set the scan range and step size for control parameters and power grid parameters:

[0165] Scan range: based on commonly used engineering values. ∈[0.01,0.1]、 ∈[0.005,0.02]、 ∈[0.1mH, 40mH]、 ∈[0Ω,15Ω];

[0166] Step size setting: The gradient step size should not exceed 5% of the maximum parameter value to ensure scanning accuracy, for example... The values ​​are taken in gradients of 0.1mH, 0.5mH, 1mH, 5mH, 10mH, 20mH, and 40mH.

[0167] Step S53: Record critical parameters;

[0168] Using a fixed set of parameter combinations as a baseline, a gradient scan is performed on another set of parameter combinations. This second set of parameters is selected based on commonly used engineering gradient values, with the gradient step size not exceeding 5% of the maximum parameter value. Sequence impedance analysis is used to obtain the gain margin (GM) and phase margin (PM) for each parameter combination. Stability is assessed, and the critical parameter values ​​for stability and instability are recorded. For example, fixing... =0.035, scan At that time, record =0.008H is the critical value between stability and instability.

[0169] Step S54, boundary fitting;

[0170] A cubic polynomial was used to fit the critical parameter values ​​to obtain the stability domain boundary curve. The fitting equation is as follows:

[0171]

[0172] in, There are two types of scanning parameters. , , , The coefficients are the fitting coefficients, and the goodness of fit is required. A value ≥0.95 is used to ensure the accuracy of the stability region boundary curve. Based on the goodness of fit of the stability region boundary curve, the stable region of the stability region boundary curve is defined (satisfying...). >0 and (Parameter combinations >0) and the unstable region.

[0173] Step S6: Simulation verification and model correction;

[0174] A simulation model was built to verify the accuracy of the stability region and the effectiveness of the method. The specific steps are as follows:

[0175] Step S61, Simulation model construction;

[0176] like Figure 4 As shown, the actual simulation circuit topology is constructed; main circuit parameters: inverter rated power 7MW, DC side voltage 35KV, AC side rated voltage 35KV. =20mH, =20μF, =0.6Ω;

[0177] Control parameters:

[0178] VSG control: =0.057 kg·m², =5 N·m·s / rad, =7.1Var / V; MC control: =0.035, =0.01, =0.0026; Voltage and current dual loop =0.5, K iv =5, =0.1606, =208.01;

[0179] Power grid parameters: By adjusting and Simulate different short-circuit ratio (SCR) scenarios, SCR=0.35~0.45.

[0180] Step S62, Simulation condition settings;

[0181] Power grid strength conditions: =0.001H (SCR=0.45) =0.01H (SCR=0.4) =0.04H (SCR=0.37); =0Ω (SCR=0.45) =10Ω (SCR=0.38) =15Ω (SCR=0.35);

[0182] Load conditions: light load (20% of rated power), medium load (50% of rated power), heavy load (80% of rated power) and load cut-in / cut-out (6s cut-in, 7s cut-out).

[0183] Step S63: Result comparison and correction;

[0184] Comparison of simulation results and stability domain analysis results:

[0185] Stability Region Accuracy Assessment: A threshold value for judging the deviation of the critical parameter is set as follows. If all stable parameter combinations in the simulation fall within the stability region, all unstable parameter combinations fall within the instability region, and the critical parameter deviation does not exceed 5%, then the stability region solution is valid.

[0186] Model correction: If the deviation exceeds 5%, return to step S3 to correct the sequence impedance model, reconsider the nonlinear coupling terms or adjust the approximate conditions in the impedance derivation process until the deviation meets the requirements (critical parameter deviation does not exceed 5%).

[0187] Example 2

[0188] VSG control stability domain adjustment and verification.

[0189] Step 1: Establish the core mathematical model of VSG

[0190] Active-frequency control: =0.057 kg·m², =5 N·m·s / rad, =314 rad / s;

[0191] Reactive power-voltage control: =7.1Var / V, =0Var;

[0192] Voltage and current dual loop: =0.5, K iv =5, =0.1606, =208.01;

[0193] Modulated wave generation: based on Generate a three-phase modulated wave.

[0194] Step 2: Establish a full-order small-signal model

[0195] Steady-state operating point: =35KV, =0; =0.9KA, =0.9KA, converter steady-state power angle =0.1 rad;

[0196] Coordinate transformation small signal model: ;

[0197] LCL filter model parameters: =20mH, =0Ω, =20μF, =0.6Ω;

[0198] Power conservation small-signal model:

[0199] , .

[0200] Step 3, Derive the sequence impedance model

[0201] VSG control sequence impedance expression:

[0202]

[0203] Characteristic analysis shows that the positive and negative sequence impedances controlled by the VSG are inductive across the entire frequency band, with a phase range of 0° to 90° and an amplitude that gradually increases with frequency.

[0204] Step 4, Establish mapping relationship

[0205] Scan parameters: ∈[0.1mH, 40mH], ∈[0Ω,15Ω], with step sizes of 0.1mH and 1Ω respectively;

[0206] Application of the criterion: Stable when >0 and PM>0;

[0207] Mapping results: =0.001H, When =0Ω, =3.98dB, =50.76°, the system is stable; =0.01H、 When =0Ω, =-0.06dB, =358.79°, the system is unstable.

[0208] Step 5, Delineate the stability region

[0209] Two-dimensional scanning: fixed =0Ω, scanning ;fixed =0.001H, scan ;

[0210] Critical parameters: When =0Ω, The critical value is 0.0095H; When =0.001H, The critical value is 9.5Ω;

[0211] Boundary fitting, the fitting equation is:

[0212] =-0.000035 3 +0.00045 2 -0.001978 +0.0095;

[0213] Goodness of fit: R 2 =0.951;

[0214] Stability region: <-0.000035 3 +0.00045 2 -0.001978 The parameter combination of +0.0095 represents the stable region.

[0215] Step 6, Simulation Verification:

[0216] Simulation Model: A simulation model of the VSG-controlled converter was built, with grid parameters set according to the scan range. Figure 5 This is a waveform diagram of the power grid frequency under the actual simulation conditions of this embodiment.

[0217] Simulation results:

[0218] =0.001H, =0Ω: The voltage frequency at the grid connection point is stable and there is no oscillation, which is consistent with the stability domain analysis;

[0219] =0.01H、 =10Ω: The grid connection point voltage frequency oscillates continuously with an amplitude exceeding 15% of the rated value, causing system instability, consistent with the stability domain analysis;

[0220] Critical parameter verification: =0.008H, When Ω = 0, the system is in a critical stable state and can recover stability after a small disturbance, verifying the accuracy of the critical parameter.

[0221] Example 3

[0222] MC control stability domain adjustment and verification.

[0223] Step 1: Establish the mathematical model of the MC control core;

[0224] Active-frequency control: =0.035, =35KV, =37.5KV;

[0225] Reactive power-voltage control: =0.01, =0.0026, =0Var;

[0226] Voltage and current dual loop: =0.5, K iv =5, =0.1606, =208.01;

[0227] Modulated wave generation: based on Generate a three-phase modulated wave.

[0228] Step 2: Establish a full-order small-signal model

[0229] Steady-state operating point: =35KV, =0; =0.9KA, =0.9KA; Converter steady-state power angle =0.1 rad;

[0230] Coordinate transformation small signal model: ;

[0231] LCL filter model parameters: =20mH, =0Ω, =20μF, =0.6Ω;

[0232] Power conservation small-signal model:

[0233] , .

[0234] Step 3, Derive the sequence impedance model;

[0235] MC control sequence impedance expression:

[0236]

[0237] Characteristic analysis: MC control exhibits inductive behavior in the low-frequency range for both positive and negative sequence impedances, while the inductive characteristics weaken in the mid-to-high frequency range. The phase range is 0°~60°, and the amplitude is lower than that of VSG control.

[0238] Step 4: Establish mapping relationships;

[0239] Scan parameters: ∈[0.1mH, 40mH], ∈[0Ω,15Ω], with step sizes of 0.1mH and 1Ω respectively;

[0240] Application of the criterion: >0 and Stable when >0;

[0241] Mapping results: =0Ω、 When =0.001H, =4.03dB, =50.45°, the system is stable; =0Ω、 When =0.04H, =-5.49dB, =0.72°, the system is unstable.

[0242] Step 5: Define the stability region;

[0243] Two-dimensional scanning: fixed =0Ω, scanning ;fixed =0.001H, scan ;

[0244] Critical parameters: When =0Ω, The critical value is 0.011H; When =0.001H, The critical value is 7.8Ω;

[0245] Boundary fitting: The fitting equation is:

[0246] =-0.000081 3 +0.00092 2 -0.0038 +0.011;

[0247] The goodness of fit is: R 2 =0.992;

[0248] Stability region: <-0.000081 3 +0.00092 2 -0.0038 The parameter combination of +0.011 represents the stable region.

[0249] Step 6, Simulation verification;

[0250] Simulation Model: Build a simulation model of the MC-controlled converter, setting the control parameters as described above. Figure 6 This is a waveform diagram of the power grid frequency under the actual simulation conditions of this embodiment.

[0251] Simulation results:

[0252] =0Ω、 =0.001H: The grid connection point voltage frequency is stable, the dynamic response is fast, and it is consistent with the stability domain analysis;

[0253] =10Ω =0.011H: The voltage frequency at the grid connection point oscillates significantly, with the amplitude exceeding 20% ​​of the rated value, indicating system instability, consistent with the stability domain analysis;

[0254] Critical parameter verification: Adjust to 0Ω. =0.011H, the system recovered to stability, verifying the guiding role of the stability region in parameter optimization.

[0255] The above scheme verifies that the stability domain adjustment method proposed in this invention has good applicability to both types of network control strategies, and the solution accuracy meets engineering requirements, which can provide effective support for the selection and parameter optimization of network control strategies.

[0256] Although the steps in the above embodiments are described in the above order, those skilled in the art will understand that in order to achieve the effect of this embodiment, different steps do not need to be executed in such an order. They can be executed simultaneously (in parallel) or in a reverse order. These simple variations are all within the protection scope of this invention.

[0257] Those skilled in the art will understand that although some embodiments described herein include certain features but not others included in other embodiments, combinations of features from different embodiments are intended to be within the scope of the invention and form different embodiments. For example, in the claims of this invention, any of the claimed embodiments can be used in any combination.

[0258] It should be noted that the above embodiments are illustrative of the invention and not restrictive, and that those skilled in the art can devise alternative embodiments without departing from the scope of the appended claims. In the claims, the word "comprising" does not exclude the presence of elements or steps not listed in the claims. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by means of hardware comprising several different elements and by means of a suitably programmed PC.

[0259] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it should be noted that the parts not covered in this invention are the same as or can be implemented using existing technology. It will be readily understood by those skilled in the art that the scope of protection of this invention is obviously not limited to these specific embodiments. Without departing from the principles of this invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions resulting from these changes or substitutions will all fall within the scope of protection of this invention.

Claims

1. A stability-domain regulation method based on a typical network control strategy using sequence impedance analysis, characterized in that, include: Establish control models for typical network control strategies; A full-order small-signal model is constructed by linearizing and perturbating the small-signal signal; By combining the conversion relationship between positive and negative sequence and dq axis components, the sequence impedance model is derived; Based on the magnitude and phase characteristics of the sequence impedance, and combined with the gain margin and phase margin criteria, a parameter-stability mapping relationship is established. The stability region is defined by two-dimensional parameter scanning and boundary fitting, and the stability region is corrected by simulation.

2. The stability domain adjustment method for a typical network control strategy based on sequence impedance analysis according to claim 1, characterized in that, The control model based on typical network control strategies includes: Active power-frequency control and reactive power-voltage control; The voltage reference value is obtained through dual-loop control of voltage and current. A modulation wave is generated by combining the phase angle and the voltage amplitude.

3. The stability domain adjustment method for a typical network control strategy based on sequence impedance analysis according to claim 1, characterized in that, Based on the steady-state operating point linearization method, the control equations of the control loop and the main circuit are subjected to small-signal perturbation processing. The small-signal components of all variables are defined, the small-signal quadratic terms are ignored, and the full-order small-signal model covering the control equations, coordinate transformation, LCL filter and power conservation is established. The control equations include DC voltage-power control equations, active power-frequency control equations, and reactive power-voltage control equations. The voltage and current variables generated by the control system are transformed to the electrical system coordinate system through coordinate transformation. Using an LCL filter as the main circuit of a grid-type converter, the output voltage disturbance on the inverter side is obtained through the LCL filter; Based on the steady-state calculation equations for active and reactive power, small-signal disturbances in active and reactive power are obtained after small-signal linearization.

4. The stability domain adjustment method for a typical network control strategy based on sequence impedance analysis according to claim 1, characterized in that, Based on the conversion relationship between positive and negative sequence and dq axis components, the sequence impedance model is derived, including: Positive-sequence and negative-sequence small-signal disturbances are added to the three-phase voltage and current to establish time-domain expressions for voltage and current; Convert the time-domain expression to the frequency-domain expression, ignoring nonlinear coupling terms; By combining the conversion relationship between positive and negative sequence and dq axis components, the expressions for positive sequence impedance and negative sequence impedance are derived, and the sequence impedance expressions for VSG and MC are constructed. Analyze the amplitude-frequency and phase-frequency characteristics of the sequence impedance to determine the inductive and capacitive ranges and the impedance amplitude fluctuation range.

5. The stability domain adjustment method for a typical network control strategy based on sequence impedance analysis according to claim 1, characterized in that, The parameter-stability mapping relationship is established based on the order impedance amplitude and phase characteristics, combined with the gain margin and phase margin criteria, as follows: When the sequence impedance phase reaches -180°, the difference between the corresponding impedance amplitude and 0dB is expressed by the following gain margin expression: ; in, For loop gain, The angular frequency at which the phase reaches -180°, with a gain margin > 0, has an amplitude stability margin at this frequency; When the sequence impedance amplitude reaches 0dB, the corresponding impedance phase difference from -180° is expressed as the phase margin expression: ; in, Angular frequency at 0dB The value is an imaginary unit; when the phase margin is greater than 0, there is a phase stability margin at this frequency. By traversing the range of control parameters and grid parameters, sequence impedance analysis is performed on each parameter combination to extract gain margin and phase margin, and a parameter-stability mapping relationship is established. If the gain margin is greater than 0 and the phase margin is greater than 0, it is considered stable. If the gain margin is 0 or the phase margin is 0 and neither of these conditions is less than 0, the system is considered critically stable. If the gain margin is less than 0 or the phase margin is less than 0, it is considered unstable.

6. The stability domain adjustment method for a typical network control strategy based on sequence impedance analysis according to claim 5, characterized in that, The two-dimensional parameter scanning and boundary fitting are used to define the stable region range as follows: Select control parameters and grid parameters that have a significant impact on the stability of grid control as the scanning objects, and set the scanning range and step size of the control parameters and grid parameters. Using a fixed set of parameter combinations as a reference value, a gradient scan is performed on another set of parameter combinations. The gain margin and phase margin of each parameter combination are obtained through sequence impedance analysis. The stability is judged and the critical parameter values ​​for stability and instability are recorded. A cubic polynomial is used to fit the critical parameter values ​​to obtain the stability domain boundary curve. Based on the goodness of fit of the stability domain boundary curve, the stable region and the unstable region of the stability domain boundary curve are delineated.

7. The stability domain adjustment method for a typical network control strategy based on sequence impedance analysis according to claim 1, characterized in that, The simulation-corrected stability region includes: Set the main circuit parameters, control parameters, and power grid parameters; Set the power grid strength condition and load condition; Set a judgment threshold and compare the simulation results with the stability domain analysis results. If all stable parameter combinations in the simulation fall within the stability domain and all unstable parameter combinations fall within the instability domain, and the critical parameter deviation does not exceed the judgment threshold, then the stability domain is valid. If the critical parameter deviation exceeds the judgment threshold, the sequence impedance model is revised, the nonlinear coupling term is reconsidered, or the approximate conditions in the derivation process of the sequence impedance model are adjusted until the critical parameter deviation meets the judgment threshold requirements.

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