Method for evaluating influence of converter grid-connected system parameters on small interference stability

Abstract

The invention belongs to the field of electric power, and discloses a method for evaluating the influence of converter grid-connected system parameters on small interference stability, which comprises the following steps: constructing a grid-following type single-machine infinite system impedance model which comprises a converter side and an alternating current grid side; according to the converter side admittance matrix and the AC network side admittance matrix of the model, calculating a return difference matrix of the following network type single-machine infinite bus system, and determining a dominant characteristic value of the system; drawing a Pode diagram corresponding to the return difference matrix, and determining the frequency corresponding to the lowest point of an amplitude curve in the Pode diagram as the frequency corresponding to the system dominant characteristic value; and in combination with a sensitivity analysis theory, evaluating the influence of parameter change on the small-interference stability of the system according to whether a frequency increment real part is greater than 0.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electric power, and particularly relates to a method for evaluating influence of grid-connected system parameters of a converter on small signal stability. BACKGROUND

[0002] With the development of new energy power generation technology in China, the power system in China gradually presents the characteristics of a 'double high' power grid with high proportion of new energy and high proportion of power electronic equipment. With the gradual increase of the proportion of power electronic devices in the alternating current power grid, the power system has small signal stability problems such as wideband oscillation, which seriously affects the safe operation of the system. System parameter changes have a great influence on the small signal stability of the system, so it is necessary to explore the mechanism of the influence of system parameters on the small signal stability.

[0003] In the related art, the methods for analyzing the influence of parameters on the small signal stability of the system mainly include eigenvalue analysis method, time domain simulation method, and frequency domain impedance analysis method. The eigenvalue analysis method can accurately identify the system modal parameters by analyzing the system stability through system eigenvalues, but the calculation is time-consuming, and the 'dimension disaster' problem is easy to occur for high-dimensional systems. The time domain analysis method solves the differential equation through numerical integration and observes the dynamic response of the system, but it needs to be simulated multiple times and cannot quantify the parameter sensitivity. The frequency domain impedance analysis method is based on the impedance model and depends on the Nyquist criterion analysis, but it has high requirements for the accuracy of the system modeling, and is easily affected by noise in actual engineering, so the practicability is not strong. SUMMARY

[0004] Therefore, the present application discloses a method for evaluating the influence of grid-connected system parameters of a converter on small signal stability, which can solve the problems in the related art.

[0005] To achieve the above-mentioned purpose, the technical solutions of the present application are as follows: According to a first aspect of the present application, a method for evaluating the influence of grid-connected system parameters of a converter on small signal stability is provided, which comprises the following steps: constructing an impedance model of a grid-following single-machine infinite system, wherein the impedance model of the grid-following single-machine infinite system comprises a converter side and an alternating current grid side; calculating a return difference matrix of the grid-following single-machine infinite system according to the admittance matrix of the converter side and the admittance matrix of the alternating current grid side of the model, and determining a dominant eigenvalue of the system; drawing a Bode plot corresponding to the return difference matrix, and determining a frequency corresponding to the lowest point of the amplitude curve in the Bode plot as a frequency corresponding to the dominant eigenvalue of the system; combining the sensitivity analysis theory, and evaluating the influence of parameter changes on the small signal stability of the system according to whether the real part of the frequency increment is greater than 0.

[0006] According to a second aspect of the present application, an evaluation device for the influence of grid-connected converter system parameters on small signal stability is provided, the device comprising: a construction unit that constructs a grid-following single-machine infinite system impedance model, the grid-following single-machine infinite system impedance model comprising a converter side and an AC grid side; a calculation unit that calculates a return difference matrix of the grid-following single-machine infinite system according to a converter side admittance matrix and an AC grid side admittance matrix of the model, and determines a dominant eigenvalue of the system; a drawing unit that draws a Bode plot corresponding to the return difference matrix, and determines a frequency corresponding to a lowest point of an amplitude curve in the Bode plot as a frequency corresponding to the dominant eigenvalue of the system; an evaluation unit that combines a sensitivity analysis theory, and evaluates the influence of parameter changes on small signal stability of the system according to whether a real part of the frequency increment is greater than 0.

[0007] According to a third aspect of the present application, an electronic device is provided, comprising: a processor; a memory for storing processor-executable instructions; wherein the processor implements the steps of the method of the first aspect by running the executable instructions.

[0008] According to a fourth aspect of the present application, a computer-readable storage medium is provided, having stored thereon computer instructions that, when executed by a processor, implement the steps of the method of the first aspect.

[0009] As can be seen from the above technical solutions, the evaluation method for the influence of grid-connected converter system parameters on small signal stability disclosed in the present application is based on a grid-following single-machine infinite system impedance model, determines a frequency corresponding to a dominant eigenvalue by calculating a determinant of a return difference matrix of the system and drawing a Bode plot, and then combines a parameter sensitivity analysis theory to determine the influence of parameters on small signal stability of the system, thereby efficiently and accurately evaluating the influence of system parameters on small signal stability of the system. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 is a flowchart of an evaluation method for the influence of grid-connected converter system parameters on small signal stability provided by an exemplary embodiment; Figure 2 is a schematic diagram of a grid-following single-machine infinite system impedance model provided by an exemplary embodiment; Figure 3 is a schematic diagram of an evaluation process for the influence of system parameters on small signal stability provided by an exemplary embodiment; Figure 4 is a schematic diagram of system zero-pole points provided by an exemplary embodiment; Figure 5 is a schematic diagram of a system admittance matrix determinant Bode chart provided by an example embodiment; Figure 6 is a schematic diagram of left and right eigenvectors and eigenvalues of a selected frequency point system provided by an example embodiment; Figure 7 is a schematic diagram of an active power image when the integral coefficient is 8000 provided by an example embodiment; Figure 8 is a schematic diagram of an active power image when the integral coefficient is 8800 provided by an example embodiment; Figure 9 is a schematic structural diagram of a device provided by an example embodiment; Figure 10 is a block diagram of an evaluation device for the influence of grid-connected system parameters of a converter on small signal stability provided by an example embodiment. DETAILED DESCRIPTION

[0011] The example embodiments will be described in detail herein with reference to the attached drawings. In the following description, like reference numerals refer to like elements, unless the context clearly dictates otherwise. The implementations described in the following example embodiments are not meant to represent all implementations consistent with one or more embodiments of the present application. Rather, they are simply meant to represent some examples of apparatuses and methods consistent with some aspects of one or more embodiments of the present application as detailed in the appended claims.

[0012] It should be noted that the order of the steps of the methods in other embodiments can not necessarily be the same as those illustrated and described in the present application. In some other embodiments, the steps included in the methods can be more or less than those described in the present application. In addition, a single step described in the present application can be divided into multiple steps for description in other embodiments, and multiple steps described in the present application can be combined into a single step for description in other embodiments.

[0013] To further illustrate the present application, the following examples are provided: With the development of new energy power generation technology in China, the power system in China gradually presents the characteristics of "double high" power grid with high proportion of new energy and high proportion of power electronic equipment. With the gradual increase of the proportion of power electronic devices in the alternating current power grid, the power system has small signal stability problems such as wide frequency oscillation, which seriously affects the safe operation of the system. System parameter changes have a great influence on the small signal stability of the system, so it is necessary to explore the mechanism of the influence of system parameters on the small signal stability.

[0014] In the related art, methods for analyzing the influence of parameters on the small signal stability of a system mainly include eigenvalue analysis, time domain simulation, and frequency domain impedance analysis. The eigenvalue analysis can accurately identify the modal parameters of the system by analyzing the system stability through system eigenvalues, but the calculation is time-consuming and prone to the curse of dimensionality for high-dimensional systems. The time domain analysis observes the dynamic response of the system by numerically integrating differential equations, but it needs to be simulated multiple times and cannot quantify the parameter sensitivity. The frequency domain impedance analysis is based on the impedance model and relies on the Nyquist criterion for analysis, but it requires high accuracy for system modeling and is easily affected by noise in actual engineering, which is not practical.

[0015] To solve the problems in the related art, the present application provides a method for evaluating the influence of parameters of a converter grid-connected system on small signal stability.

[0016] Figure 1 A flowchart of a method for evaluating the influence of parameters of a converter grid-connected system on small signal stability according to an example embodiment is shown in FIG. 1. As shown in FIG. 1, the method can include the following steps: Figure 1 Step 101: Construct an impedance model of a grid-connected single-machine infinite system, which includes a converter side and an AC grid side. Step 102: Calculate the return difference matrix of the grid-connected single-machine infinite system according to the admittance matrix of the converter side and the admittance matrix of the AC grid side, and determine the dominant eigenvalue of the system. Step 103: Draw a Bode plot corresponding to the return difference matrix, and determine the frequency corresponding to the lowest point of the amplitude curve in the Bode plot as the frequency corresponding to the dominant eigenvalue of the system. Step 104: Combine the sensitivity analysis theory and evaluate the influence of parameter changes on the small signal stability of the system according to whether the real part of the frequency increment is greater than 0.

[0017] In this embodiment, based on the impedance model of the grid-connected single-machine infinite system, the dominant eigenvalue corresponding frequency is determined by calculating the determinant of the return difference matrix and drawing a Bode plot, and then the influence of parameters on the small signal stability of the system is determined by combining the parameter sensitivity analysis theory, thereby efficiently and accurately evaluating the influence of system parameters on the small signal stability of the system.

[0018] In an embodiment, the impedance model of the grid-connected single-machine infinite system includes: a voltage vector at the outlet side of the converter, a filter inductance and capacitance, a DC side capacitance, an equivalent inductance of the grid, a current vector flowing through the equivalent inductance of the grid, an infinite bus voltage phasor, a voltage vector and a current vector at the point of common coupling.

[0019] As shown in FIG. 2, the impedance model of the grid-connected single-machine infinite system includes a voltage vector at the outlet side of the converter, a filter inductance and capacitance, a DC side capacitance, an equivalent inductance of the grid, a current vector flowing through the equivalent inductance of the grid, an infinite bus voltage phasor, a voltage vector and a current vector at the point of common coupling. Figure 2 ​As shown, Vs is the voltage vector at the converter outlet side; Lf and Cf are the filter inductance and capacitance respectively; Cdc is the DC side capacitance; Lg is the grid equivalent inductance; Ig represents the current vector flowing through Lg; E is the infinite bus voltage phasor; V and I are the voltage vector and current vector at the Point of Common Coupling (PCC) respectively.

[0020] In an embodiment, the step of calculating the return difference matrix of the single-machine infinite-bus system according to the converter-side admittance matrix and the AC grid-side admittance matrix of the model comprises: adding the converter-side admittance matrix and the AC grid-side admittance matrix of the model to obtain the return difference matrix.

[0021] The admittance matrix Y GFL (s) of the system can be obtained through its return difference matrix (RDM): ; wherein Y VSC (s) is the converter-side admittance matrix, Y grid (s) is the AC grid-side admittance matrix.

[0022] The converter-side admittance matrix and the AC grid-side admittance matrix of the model can be obtained through impedance measurement. For example, a series of frequency points can be selected within 0-100 Hz with a step of 1 Hz ω n (n=1, 2, 3... 100), and a sweep is performed at each frequency point to obtain the system admittance matrix Y GFL (j ω n )(n=1, 2, 3... 100) corresponding to each frequency point.

[0023] In an embodiment, the calculation expression of the dominant eigenvalue is: s = σ + jω ; When σ ω, the following formula is satisfied: ; wherein Y GFL (s) is the admittance matrix of the single-machine infinite-bus system, i.e., the return difference matrix.

[0024] To meet the condition of formula (2), it is necessary to find the frequency point with the highest risk of system instability. The system Bode diagram (Porter diagram) is composed of an amplitude curve and a phase curve, reflecting the stability margin of the system. The lowest point of the amplitude curve of the system Bode diagram is the point with the smallest damping, and the system has the highest risk of instability. The point corresponds to the dominant eigenvalue of Y GFL (s).

[0025] In an embodiment, the drawing of the Porter diagram corresponding to the return difference matrix comprises: defining a function: ; wherein det(.) represents calculating the determinant of a matrix, Y GFL (s) is the return difference matrix. Draw the Porter diagram of F(s), which is the Porter diagram corresponding to the return difference matrix.

[0026] In an embodiment, the combination of sensitivity analysis theory and the evaluation of the influence of parameter change on the small disturbance stability of the system according to whether the real part of the frequency increment is greater than 0 comprises: The lowest point of the amplitude curve in the Porter diagram is denoted as s1, and the frequency corresponding to this point is denoted as ω1; The sensitivity of the frequency point s1 in the system to any parameter k can be expressed as follows: ; wherein Y GFL (s) is the return difference matrix, v1 and u1 are the left and right eigenvectors of Y GFL (s) at s=jω1, and the left and right eigenvectors are realized by the function [V, D, W]=eig(.), wherein V and W correspond to the left and right eigenvectors of the matrix to be solved, and are given in the form of column vectors; D corresponds to the eigenvalue of the matrix to be solved, and is given in the form of a diagonal matrix; The partial derivative of the system admittance matrix with respect to the system parameter k is calculated as follows: ; wherein k1 and k2 are different values of the same parameter, with a difference of 10%, and are the admittance matrices at point s1 when the parameter is k1 and k2, respectively; Two perturbations are performed on point s1 to obtain the perturbed frequencies ω A and ω B : ; wherein Δω is the perturbation; Since the frequency point s1 satisfies σ ω, the following formula is obtained: ; wherein Y GFL (jω A ) and Y GFL (jω B ) are the admittance matrix of the system at frequency points ω A and ω B , respectively; Convert the formula to the incremental calculation formula: ; wherein Δk is the increment of the system parameter, Δs is the increment of the system frequency point at s1, and is a complex number; After setting the variation of the parameter to be solved, the corresponding frequency point increment Δs is calculated by the incremental calculation formula (8); In the case of positive increment of Δk, if the real part Re(Δs) of the frequency increment is > 0, it is evaluated that the increase of the parameter k makes the small signal stability of the system worse; if the real part Re(Δs) of the frequency increment is < 0, it is evaluated that the increase of the parameter k makes the small signal stability of the system better.

[0027] The overall process of calculating the comprehensive score of the power distribution network carrying capacity is shown in the following more specific embodiments: Figure 3 According to the parameter values in Table 1, and according to the model structure shown in Figure 2 , a grid-connected converter grid-connected system model is built in Matlab / Simulink software.

[0028] Table 1

[0029] The parameters of the grid-connected single-machine infinite system are adjusted so that the dominant eigenvalue is close to the imaginary axis, as shown in Figure 4 . As can be seen from Figure 4 , the dominant eigenvalue of the system is , which satisfies the requirement of σ ω, and the frequency corresponding to the dominant eigenvalue is 10.2 Hz at this time.

[0030] The determinant of the admittance matrix of the grid-connected single-machine infinite system is solved by Matlab, and its Bode plot is drawn, and the Bode plot image is shown in Figure 5 . It can be seen that the frequency corresponding to the lowest point of the Bode plot amplitude is 10.8 Hz, which is consistent with the frequency corresponding to the dominant eigenvalue of the system.

[0031] ​The frequency point is perturbed twice, the perturbation amount Δω is set to 1 Hz, and then the proportional coefficient of the phase-locked loop of the system is selected for sensitivity analysis. The left and right eigenvectors of the matrix at this time are calculated by the [V, U, W] = eig() function as shown in Figure 6 .

[0032] The integral coefficient is set to increase from 8000 to 8800 (i.e., an increment of 10%), and finally Δs = 2.0547 + 0.0420j is obtained, Re(Δs) > 0, indicating that the increase of the integral coefficient of the phase-locked loop PI link will make the small disturbance stability of the system worse.

[0033] In the Simulink simulation software, the integral coefficient is adjusted from 8000 to 8800, and a small disturbance is applied at 5s, and the time domain simulation images of the integral coefficient under 8000 and 8800 are shown in Figure 7 and Figure 8 . It can be seen that when the integral coefficient increases, the system instability speed becomes faster, and the small disturbance characteristics become worse, verifying the reliability of the aforementioned evaluation criterion.

[0034] Figure 9 is a schematic structural diagram of a device provided by an exemplary embodiment. Please refer to Figure 9 , at the hardware level, the device includes a processor 901, an internal bus 902, a network interface 903, a memory 904, and a non-volatile memory 905, and of course, it can also include other hardware required by functions. One or more embodiments of the present application can be implemented in a software manner, such as reading a corresponding computer program from the non-volatile memory 905 into the memory 904 by the processor 901 and then running. Of course, in addition to the software implementation, one or more embodiments of the present application do not exclude other implementation manners, such as logic devices or a combination of software and hardware, etc., that is, the execution subject of the following processing flow is not limited to the logical units, but can also be hardware or logic devices.

[0035] Please refer to Figure 10 , an evaluation device for the influence of grid-connected system parameters of a converter on small disturbance stability can be applied to a device as shown in Figure 10 to implement the technical solutions of the present application, and the device includes: A construction unit 1001 is configured to construct a grid-following single-machine infinite system impedance model, and the grid-following single-machine infinite system impedance model includes a converter side and an alternating current grid side. A calculation unit 1002 is configured to calculate a return difference matrix of the grid-following single-machine infinite system according to a converter side admittance matrix and an alternating current grid side admittance matrix of the model, and determine a dominant eigenvalue of the system. The drawing unit 1003 is configured to draw a Bode plot corresponding to the return difference matrix, and determine a frequency corresponding to a lowest point of an amplitude curve in the Bode plot as a frequency corresponding to a dominant eigenvalue of the system. The evaluation unit 1004 is configured to combine a sensitivity analysis theory, and evaluate an influence of a parameter change on small disturbance stability of the system according to whether a real part of a frequency increment is greater than 0.

[0036] Optionally, the calculation unit 1002 is specifically configured to: add the converter-side admittance matrix and the AC grid-side admittance matrix of the model to obtain the return difference matrix.

[0037] Optionally, a calculation expression of the dominant eigenvalue is as follows: s = σ + jω ; When σ ω is satisfied, the following formula is satisfied: ; wherein Y GFL (s) is a grid-following system admittance matrix, that is, the return difference matrix.

[0038] Optionally, the drawing unit 1003 is specifically configured to: define a function as follows: ; wherein det(.) represents a determinant of a matrix, Y GFL (s) is the return difference matrix; draw a Bode plot of F(s), and the Bode plot of F(s) is a Bode plot corresponding to the return difference matrix.

[0039] Optionally, the evaluation unit 1004 is specifically configured to: record a lowest point of an amplitude curve in the Bode plot as s1, and record a frequency corresponding to the point as ω1; A sensitivity of a frequency point s1 in the system to an arbitrary parameter k can be represented as follows: ; wherein Y GFL (s) is the return difference matrix, v1 and u1 are respectively left and right eigenvectors of Y GFL (s) at s=jω1, the left and right eigenvectors are obtained by a function [V, D, W]=eig(.), wherein V and W respectively correspond to left and right eigenvectors of a matrix to be solved, and are given in the form of column vectors; D corresponds to an eigenvalue of the matrix to be solved, and is given in the form of a diagonal matrix; A partial derivative of the system admittance matrix with respect to the system parameter k is calculated as follows: ; wherein k1 and k2 are different values of the same parameter preselected, with a difference of 10%, and are the admittance matrices at point s1 when the parameter is k1 and k2 respectively; Two perturbations are made to point s1 to obtain the perturbed frequencies ω A and ω B : ; wherein Δω is the perturbation; Since the frequency point s1 satisfies σ ω, there is the following formula: ; wherein Y GFL (jω A ) and Y GFL (jω B ) are the admittance matrices of the system at the frequency points ω A and ω B respectively; The formula is converted into an incremental calculation formula: ; wherein Δk is the increment of the corresponding system parameter, and Δs is the increment of the system frequency point at s1, which is a complex number; After the variation of the parameter to be solved is set, the incremental calculation formula (8) is used to calculate the corresponding frequency point increment Δs; In the case of positive increment Δk, if the real part Re(Δs) of the frequency increment is greater than 0, it is evaluated that the increase of the parameter k makes the small signal stability of the system worse; if the real part Re(Δs) of the frequency increment is less than 0, it is evaluated that the increase of the parameter k makes the small signal stability of the system better.

[0040] Optionally, the impedance model of the grid-connected single-machine infinite system comprises: a voltage vector at the outlet side of the converter, a filter inductance and a capacitor, a DC side capacitor, an equivalent inductance of the power grid, a current vector flowing through the equivalent inductance of the power grid, an infinite bus voltage phasor, a voltage vector and a current vector at a point of common coupling.

[0041] Optionally, the impedance model further comprises: An acquisition unit 1005 is configured to acquire a converter side admittance matrix and an AC grid side admittance matrix of the model according to an impedance measurement method.

[0042] The systems, apparatuses, modules, or units illustrated in the above embodiments can be specifically implemented by computer chips or entities, or by products with certain functions. A typical implementation device is a computer, and the specific form of the computer can be a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0043] In a typical configuration, a computer includes one or more processors (CPUs), input / output interfaces, network interfaces, and memory.

[0044] The memory can include non-persistent memory in computer readable media, random access memory (RAM), and / or non-volatile memory, such as read-only memory (ROM) or Flash memory. The memory is an example of computer readable media.

[0045] Computer readable media includes permanent and non-permanent, removable and non-removable media implemented by any method or technology for storing information. Information can be computer readable instructions, data structures, program modules or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read only memory (ROM), electrically erasable programmable read only memory (EEPROM), flash memory or other memory technologies, compact disc read only memory (CD-ROM), digital versatile disc (DVD) or other optical storage, magnetic cassette, disk storage, quantum memory, graphene-based storage medium or other magnetic storage device, or any other non-transmission medium that can be used to store information accessible by a computing device. According to the definition herein, computer readable media does not include transitory media, such as modulated data signals and carriers.

[0046] For the computer readable medium (or computer readable storage medium) as described above or any other form, computer instructions can be stored thereon, which are executed by a processor to implement one or more of the above embodiments, thereby realizing the technical solutions of the present application.

[0047] The present application also proposes a computer program, which is executed by a processor to implement one or more of the above embodiments, thereby realizing the technical solutions of the present application. The computer program can be specifically recorded on the computer readable medium as described above or any other form, and the present application does not limit this.

[0048] It is also important to note that the terms "comprises", "comprising", or other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the presence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0049] The above described embodiments of the application have been described in connection with what are presently considered to be the most practical and preferred embodiments from a present practical viewpoint. However, it is to be understood that the application is not to be limited to the disclosed embodiments, but instead, is intended to cover various arrangements of the present application that are different from those described, which fall within the scope of the appended claims and their equivalents.

[0050] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of one or more embodiments of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0051] It is to be understood that the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. Preferred embodiments of the application are described herein, including the best mode known to the inventors of practicing the application. Of course, modifications will occur to those skilled in the art to which the present application pertains, and it is understood that within the scope of the appended claims, the application can be practiced otherwise than is specifically described herein. For example, the present application can be implemented in either hardware or software, or a combination of both hardware and software. Any portion of the present application can be implemented as code resident in a "carrier medium", which carries machine readable instructions for execution by a machine. In this context, a "carrier medium" can be a machine-readable medium that carries program code for use by a machine to execute instructions that cause the machine to perform a desired action. Examples of carrier media include magnetic storage media (e.g., magnetic disks), optical storage media (e.g., optical discs), electrical storage media (e.g., the circuits of a computer), and forms of electrical signals (e.g., carrier waves, infrared signals, microwave signals, etc.). The embodiments of the present application described herein are not limited to any particular carrier medium.

[0052] The foregoing is considered as illustrative only of the principles of the one or more embodiments of the application. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the one or more embodiments of the present application to the exact one or more embodiments described above. Accordingly, the one or more embodiments of the present application set forth herein are susceptible to numerous modifications and alternative methods of use. It is therefore desired that the one or more embodiments of the present application be measured by the breadth of the following claims rather than the limited scope of the foregoing disclosure.

Claims

1. A method for evaluating the influence of grid-connected converter system parameters on small signal stability, characterized in that, The method comprises: constructing a grid-following single-machine infinite system impedance model, the grid-following single-machine infinite system impedance model comprising a converter side and an alternating current grid side; calculating a return difference matrix of the grid-following single-machine infinite system according to a converter side admittance matrix and an alternating current grid side admittance matrix of the model, and determining a system dominant eigenvalue; drawing a Bode plot corresponding to the return difference matrix, and determining a frequency corresponding to a lowest point of an amplitude curve in the Bode plot as a frequency corresponding to the system dominant eigenvalue; combining a sensitivity analysis theory, and evaluating an influence of parameter variation on small disturbance stability of the system according to whether a real part of the frequency increment is greater than 0.

2. The method of claim 1, wherein, The calculating of the return difference matrix of the grid-following single-machine infinite system according to the converter side admittance matrix and the alternating current grid side admittance matrix of the model comprises: adding the converter side admittance matrix and the alternating current grid side admittance matrix of the model to obtain the return difference matrix.

3. The method of claim 1, wherein, The expression for calculating the dominant eigenvalue is: s = σ + jω ； σ The following equation is satisfied when ω is satisfied. ； where Y GFL (s) is the netted system admittance matrix, i.e., the back difference matrix.

4. The method of claim 1, wherein, The drawing of the Bode plot corresponding to the return difference matrix comprises: defining a function: ； where det(.) denotes the determinant of a matrix, Y GFL (s) is the backoff matrix; drawing a Bode plot of F(s), the Bode plot of F(s) being the Bode plot corresponding to the return difference matrix.

5. The method of claim 1, wherein, The combining of the sensitivity analysis theory, and the evaluating of the influence of parameter variation on small disturbance stability of the system according to whether the real part of the frequency increment is greater than 0 comprises: recording the lowest point of the amplitude curve in the Bode plot as s1, and recording a frequency corresponding to the point as ω1; a sensitivity of a frequency point s1 in the system to any parameter k can be expressed as follows: ； where Y GFL (s) is the back-difference matrix, vi and ui are the left and right eigenvectors of Y GFL (s) at s = jωi, said left and right eigenvectors are implemented by the function [V, D, W] = eig(.) where V and W correspond to the left and right eigenvectors of the sought matrix, both given in the form of column vectors; D corresponds to the eigenvalues of the sought matrix, given in the form of a diagonal matrix; a partial derivative of a system admittance matrix to a system parameter k is calculated according to the following formula: ； where k1 and k2 are different values of the same parameter preselected to differ by 10%, and Ys1(k1) and Ys1(k2) are the admittance matrices at point s1 for parameters k1 and k2, respectively. Twice perturbation is made to point s1, and the perturbed frequency ω A and ω B is obtained ； wherein, Δω is a perturbation; Since the frequency point s1satisfies σ ω, there is the following equation: ； where Y GFL (jω A ) and Y GFL (jω B ) are the admittance matrices of the system at frequency points ω A and ω B , respectively. the formula is converted into an incremental calculation formula: ； wherein, Δk is an increment of the corresponding system parameter, Δs is an increment of the frequency point at s1, and is a complex number; after setting the variation of the parameter to be solved, the corresponding frequency point increment Δs is calculated through the incremental calculation formula (8); in the case that Δk is a positive increment, if a real part Re(Δs) of the frequency increment is greater than 0, it is evaluated that the increase of the parameter k makes the small disturbance stability of the system worse; if the real part Re(Δs) of the frequency increment is less than 0, it is evaluated that the increase of the parameter k makes the small disturbance stability of the system better.

6. The method of claim 1, wherein, The grid-following single-machine infinite system impedance model comprises: a converter outlet side voltage vector, a filter inductance and a capacitor, a direct current side capacitor, a grid equivalent inductance, a current vector flowing through the grid equivalent inductance, an infinite bus voltage phasor, a voltage vector and a current vector of a point of common coupling.

7. The method of claim 1, wherein, Further comprising: obtaining the converter side admittance matrix and the alternating current grid side admittance matrix of the model according to an impedance measurement mode.

8. An apparatus for evaluating the influence of grid-connected system parameters on small signal stability of a converter, characterized in that The device comprises: a construction unit: constructing a grid-following single-machine infinite system impedance model, the grid-following single-machine infinite system impedance model comprising a converter side and an alternating current grid side; a calculation unit: calculating a return difference matrix of the grid-following single-machine infinite system according to a converter side admittance matrix and an alternating current grid side admittance matrix of the model, and determining a system dominant eigenvalue; a drawing unit: drawing a Bode plot corresponding to the return difference matrix, and determining a frequency corresponding to a lowest point of an amplitude curve in the Bode plot as a frequency corresponding to the system dominant eigenvalue; The evaluation unit: combined with the sensitivity analysis theory, and according to whether the real part of the frequency increment is greater than 0, the influence of the parameter change on the small disturbance stability of the system is evaluated.

9. An electronic device, comprising: Comprise: a processor; a memory for storing processor-executable instructions; wherein the processor, by running the executable instructions, implements the steps of the method of any one of claims 1-7.

10. A computer readable storage medium having stored thereon computer instructions, wherein, The instructions, when executed by the processor, implement the steps of the method of any one of claims 1-7.

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