A method and system for judging small disturbance stability of a converter single-feed system

Abstract

The present invention belongs to the technical field of power system stability judgment, and specifically discloses a method and system for judging the stability of a converter single-feed system with small disturbances, the method comprising: constructing the admittance matrix of the device side and the network side of the converter single-feed system; obtaining the coupling admittance matrix based on the admittance matrix of the device side and the network side; performing a single frequency sweep on the coupling admittance matrix to obtain the eigenvalue of the coupling admittance matrix; obtaining the critical short-circuit ratio of the converter single-feed system based on the eigenvalue; calculating the short-circuit ratio of the converter single-feed system, if the short-circuit ratio is greater than the critical short-circuit ratio, the converter single-feed system is stable with small disturbances, otherwise, the converter single-feed system is unstable with small disturbances. The present invention does not need to construct a white box model with all parameters known, nor does it need to perform multiple frequency sweeps on the closed-loop system, so as to avoid the problem that the high-frequency band data is easily contaminated and the measurement results are inaccurate; the calculation process is simple, and the stability of the system is improved at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of power system stability judgment, and in particular to a method and system for judging small disturbance stability of a converter single-feed system. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] As the proportion of new energy grid-connected increases year by year, the proportion of renewable energy connected to the grid through voltage source converters (VSC) is gradually increasing. However, due to the complex interaction between converters and AC grids, the strength of the grid is gradually decreasing.

[0004] A converter single-feed system is a system with one input and one output, and contains only one converter. The ability of a system to automatically recover to a stable state without spontaneous oscillation or non-periodic loss of step after a small disturbance such as load change is called small disturbance stability. In actual power grids, poor system stability leads to frequent instability of the power grid, resulting in a decrease in power quality, and even power supply accidents and property losses; therefore, it is necessary to determine the small disturbance stability of the system to ensure the stable and reliable operation of the power grid.

[0005] In the prior art, there are two main methods for judging the stability of a converter single-feed system with small disturbances:

[0006] One is the time-domain eigenvalue analysis based on the state-space method; this method needs to be based on a white-box model in which all parameters are known, and is not very practical.

[0007] The other is the Nyquist stability criterion analysis based on the impedance model, which uses the closed-loop system data to obtain Y ( s ) of the generalized Nyquist or Y ( s ) to evaluate the stability of the system; this method is to sweep the frequency of the closed-loop system, and it is necessary to continuously change the inductance parameters on the grid side to make the grid reach the critical stable state and thus measure the critical short-circuit ratio; high-frequency data is easily contaminated by noise such as sensor errors or grid background harmonics, resulting in inaccurate measurement results; in addition, when calculating the accurate system critical short-circuit ratio (CSCR), it is necessary to continuously change the inductance on the AC grid side. L g , which reduces the stability of the system and requires multiple full-band sweeps to obtain data for the entire frequency band. Summary of the invention

[0008] In order to solve the above problems, the present invention proposes a method and system for judging the small disturbance stability of a single-feed converter system, which performs a single frequency sweep on the device side admittance in the low frequency band (0-50Hz), and then determines the small disturbance critical stability condition of the single-feed converter system according to the relationship between the eigenvalue of the frequency sweep data and the CSCR.

[0009] In some embodiments, the following technical solutions are adopted:

[0010] A method for judging small disturbance stability of a converter single-feed system, comprising:

[0011] Construct the device-side admittance matrix and grid-side admittance matrix of the converter single-feed system at different frequencies;

[0012] Based on the device side admittance matrix and the network side admittance matrix, the coupling admittance matrix at different frequencies is obtained;

[0013] Perform a single frequency sweep on the coupling admittance matrix at different frequencies to obtain the eigenvalue of the coupling admittance matrix at each frequency;

[0014] Based on the characteristic value, a critical short-circuit ratio of the converter single-feed system is obtained;

[0015] The short-circuit ratio of the converter single-feed system is calculated. If the short-circuit ratio is greater than the critical short-circuit ratio, the converter single-feed system is stable under small disturbances. Otherwise, the converter single-feed system is unstable under small disturbances.

[0016] As a further solution, a single frequency sweep is performed on the coupling admittance matrix at different frequencies, specifically:

[0017] A single frequency sweep is performed on the coupling admittance matrix at each frequency in the frequency band of 0-50 Hz to obtain multiple eigenvalues ​​of the coupling admittance matrix at each frequency.

[0018] As a further solution, the device-side admittance matrix of the converter single-feed system is specifically:

[0019] ;

[0020] in, , , , The single-feed system admittance is d / q The four sub-elements obtained after axis decomposition.

[0021] As a further solution, the grid-side admittance matrix of the converter single-feed system is specifically:

[0022] ;

[0023] in, L g is the grid inductance, ω 0 is the system base frequency, is the ratio of resistance to inductance.

[0024] As a further solution, the coupling admittance matrix is ​​specifically:

[0025] ;

[0026] in, is the device side admittance matrix of the converter single-infeed system, ω 0 is the system base frequency, is the ratio of resistance to inductance.

[0027] As a further solution, the critical short-circuit ratio of the converter single-feed system is obtained based on the characteristic value, specifically:

[0028] After obtaining the eigenvalue of the coupling admittance matrix at each frequency, the real and imaginary value curves of each eigenvalue corresponding to different frequencies are established with the frequency as the horizontal coordinate and the specific value as the vertical coordinate;

[0029] Select an eigenvalue whose imaginary part is zero and whose real part is negative, and take the absolute value of its real part as the critical short-circuit ratio CSCR of the system.

[0030] As a further solution, the short-circuit ratio of the converter single-feed system is determined as follows:

[0031] The short-circuit ratio of a single-infeed converter system is the inverse of the product of the grid inductance and the system reference frequency.

[0032] In other embodiments, the following technical solutions are adopted:

[0033] A small disturbance stability judgment system for a converter single-feed system, comprising:

[0034] A matrix construction module is used to construct the device-side admittance matrix and the grid-side admittance matrix at different frequencies of the converter single-feed system;

[0035] An eigenvalue determination module is used to obtain a coupling admittance matrix at different frequencies based on a device-side admittance matrix and a network-side admittance matrix; a single frequency sweep is performed on the coupling admittance matrix at different frequencies to obtain an eigenvalue of the coupling admittance matrix at each frequency;

[0036] A critical short-circuit ratio determination module, used for obtaining a critical short-circuit ratio of a converter single-feed system based on the characteristic value;

[0037] The small disturbance stability judgment module is used to calculate the short circuit ratio of the converter single-feed system. If the short circuit ratio is greater than the critical short circuit ratio, the converter single-feed system is stable with small disturbances; otherwise, the converter single-feed system is unstable with small disturbances.

[0038] In other embodiments, the following technical solutions are adopted:

[0039] A terminal device comprises a processor and a memory, wherein the processor is used to implement instructions; and the memory is used to store a plurality of instructions, wherein the instructions are suitable for being loaded by the processor and executing the above-mentioned method for judging the stability of a converter single-feed system with small disturbances.

[0040] In other embodiments, the following technical solutions are adopted:

[0041] A computer-readable storage medium stores a plurality of instructions, wherein the instructions are suitable for being loaded by a processor of a terminal device and executing the above-mentioned method for determining small disturbance stability of a converter single-feed system.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) The present invention first establishes a grid-side admittance matrix and a device-side admittance matrix, and performs a single frequency sweep on the open-loop converter system to obtain the eigenvalue of the coupling admittance matrix. Then, the CSCR is obtained through the relationship between the eigenvalue of the coupling admittance matrix and the CSCR. There is no need to construct a white box model with all parameters known, nor is there any need to perform multiple frequency sweeps on the closed-loop system, thereby avoiding the problem that high-frequency band data is easily contaminated and causes inaccurate measurement results. The method of the present invention has a simple calculation process, strong practicality, and improves the stability of the system.

[0044] (2) The traditional method uses a method of performing multiple frequency sweeps on the closed-loop transfer function, which requires continuous adjustment of the parameter impedance to obtain the critical short-circuit ratio. The present invention constructs an open-loop coupling admittance matrix, and only requires a single frequency sweep to obtain the critical short-circuit ratio, which has low calculation complexity and does not require closed-loop parameters.

[0045] Other features and additional advantages of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 It is a flow chart of a method for judging small disturbance stability of a converter single-feed system in an embodiment of the present invention;

[0047] Figure 2 Schematic diagram of the structure of a converter single-feed system in an embodiment of the present invention;

[0048] Figure 3 PI in the embodiment of the present inventionPLL Numerical diagram of the real and imaginary parts of the eigenvalues ​​when (s)=150+5300 / s;

[0049] Figure 4 for Figure 3 The enlarged part in the dotted box;

[0050] Figure 5 This is a zero point distribution diagram of det(Y(s))=0 when the SCR drops from 3.3pu to 2p.u. in the embodiment of the present invention;

[0051] Figure 6 for Figure 5 Enlarged view of the part in the dashed box. DETAILED DESCRIPTION

[0052] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0053] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0054] Embodiment 1

[0055] The small-disturbance stability of a system often uses the critical short-circuit ratio (CSCR) as a basis for judging the stability of the system. The current research method using CSCR as a stability criterion requires multiple frequency sweeps in the full frequency band to use the Nyquist criterion, or complete converter parameters to perform eigenvalue analysis.

[0056] This embodiment proves the relationship between CSCR and the eigenvalue of the open-loop converter coupling admittance matrix, and on this basis performs a single frequency sweep on the open-loop converter system to obtain its eigenvalue, and then obtains the CSCR and compares it with the system short-circuit ratio, so as to determine the critical stability condition of the system.

[0057] Based on this, in one or more embodiments, a method for judging the stability of a converter single-feed system with small disturbances is disclosed, combining Figure 1 , specifically including the following process:

[0058] S101: Construct a device-side admittance matrix and a grid-side admittance matrix at different frequencies for a single-feed converter system.

[0059] This embodiment uses a droop-controlled grid-following converter to construct a converter single-feed system, and its synchronization link is controlled by a phase-locked loop; the specific structure is as follows: Figure 2 As shown; Figure 2 The structure of a single-feed system of a grid-following converter with phase-locked loop synchronous control is demonstrated. The three-phase voltage and three-phase current in the grid are transformed to the dq axis through abc / dq, and then controlled by the phase-locked loop, while the converter itself is controlled by PWM.

[0060] In the small disturbance stability analysis, the converter single-feed system in which the converter is interconnected with the grid can be decomposed into the device side and the grid side. The admittance modeling of the grid side and the device side is performed respectively, and the grid side admittance is assumed to be Y grid ( s ), the device side admittance is Y VSC ( s ), so the hysteresis matrix of the system can be obtained as:

[0061] (1)

[0062] in:

[0063] (2)

[0064] In formula (2), L g is the grid inductance, ω 0 is the system base frequency, It is the ratio of resistance to inductance and is constant in the RL tie line.

[0065] , , , The single-feed system admittance is d / q The four sub-elements obtained after axis decomposition; Y dd ( s ) is the system d-axis voltage u d and d-axis current i d The corresponding admittance sub-element; Y dq ( s ) is the system d-axis voltage u d and the system q-axis current i qThe corresponding admittance sub-element; Y qd ( s ) is the system q-axis voltage u q and d-axis current i d The corresponding admittance sub-element; Y qq ( s ) is the system q-axis voltage u q and the system q-axis current i q The corresponding admittance sub-element.

[0066] In this embodiment, the method for determining the device-side admittance matrix is:

[0067] First, at the grid connection point (i.e. Figure 2 The PCC point shown in FIG2 injects two linearly independent harmonic currents, the two harmonic currents are 50- ω and 50+ ω The positive sequence current is ω= Taking 3Hz as an example, the positive sequence current of 47Hz and 53Hz is injected.

[0068] Then measure the device side voltage under each injection, and the relationship between current and voltage can be used to form d / q Four dynamic equations in the coordinate system; by solving the equations, the values ​​of each element of the device side admittance matrix at a frequency of 3 Hz can be obtained.

[0069] The specific process is as follows:

[0070] After the positive-sequence three-phase symmetrical harmonic current is injected into the PCC point, the positive-sequence three-phase harmonic current at two different frequencies can be detected at the device side port as shown below:

[0071] (3)

[0072] Among them, the subscripts a, b, and c represent the phase sequence of the detected three-phase harmonic currents, I + 、I - The frequencies are and 2 ω 0- The harmonic current amplitude, φ、Φ The frequencies are and 2 ω 0- The harmonic current phase.

[0073] Then the detected three-phase current is transformed by Parker to obtain the harmonic current in dq coordinates.

[0074] (4)

[0075] in, , ; The superscript * indicates a conjugate complex number, .

[0076] Similarly, the harmonic voltage in dq coordinates can be obtained:

[0077] (5)

[0078] in, , , V + and V - Represents frequency and The harmonic voltage amplitude, and The frequencies are and The harmonic voltage phase.

[0079] By performing a fast Fourier transform (FFT) on the harmonic current, the harmonic current Fourier coefficients (denoted as a i , b i ); Similarly, the harmonic voltage in the above dq coordinate system can be transformed by fast Fourier transform to obtain the harmonic voltage Fourier coefficient (denoted as c i , d i ). The above four coefficients are all complex numbers, and the subscript i Represents the number of injection frequencies.

[0080] (6)

[0081] in, , , , Respectively represent the injection i After subharmonic d axis / q The change in shaft port current and port voltage.

[0082] According to the method described, 50+ ω and 50- ωThe two harmonic currents can obtain two sets of linearly independent Fourier coefficients, from which the device admittance matrix can be calculated according to the following formula:

[0083] (7)

[0084] Since the device-side admittance matrix is ​​obtained by solving the system dynamic equation, the subscripts of each element correspond to the corresponding variables; for example, i d and U d The associated variable subscript is dd, and so on.

[0085] By evenly selecting several points (such as 1Hz, 3Hz, 5Hz, etc.) in the required frequency band of 50Hz, and using the above-mentioned method for solving the device-side admittance matrix, the device-side admittance matrix at a series of frequency points in the required frequency band can be obtained.

[0086] S102: A coupling admittance matrix A at different frequencies is obtained based on the device-side admittance matrix and the network-side admittance matrix, specifically:

[0087] (8)

[0088] In this embodiment, s = jω i ,in ω i The frequency corresponding to the device side admittance matrix is ​​calculated to obtain the matrix corresponding to each frequency. Then, the device measurement admittance matrix corresponding to the corresponding frequency is Y VSC ( s ) can be multiplied to obtain the coupling admittance matrix at each frequency. A .

[0089] S103: Perform a single frequency sweep on each coupling admittance matrix A calculated in S102 to obtain the eigenvalue of each coupling admittance matrix; and obtain the critical short-circuit ratio of the converter single-feed system based on the real and imaginary parts of these eigenvalues.

[0090] When the system short-circuit ratio is lower than the critical short-circuit ratio CSCR, the system will experience subsynchronous oscillation or supersynchronous oscillation, and the active and reactive signals of the system will have harmonics with a frequency of 0-50Hz.

[0091] Therefore, this embodiment only performs a single frequency sweep on each coupling admittance matrix A in the low frequency band (0-50Hz) to obtain the eigenvalue of each coupling admittance matrix; usually, there is only one eigenvalue in the oscillation frequency band in the low frequency band and with practical application significance. Then, a numerical graph of the real and imaginary parts of the eigenvalues ​​is formed, the horizontal axis of which is the frequency, and the vertical axis is the real and imaginary values ​​of each eigenvalue of the coupling admittance matrix at the corresponding frequency, such as Figure 3 shown.

[0092] For the coupling admittance matrix , select one of the eigenvalues ​​with zero imaginary part and negative real part in the oscillation frequency band (0-50Hz), and use the absolute value of the negative number as the critical short circuit ratio CSCR of the system, such as Figure 4 At the frequency of 11.8Hz shown in the figure, the characteristic value e1=-2.36+j0, and the critical short-circuit ratio CSCR is 2.36.

[0093] The method of determining the critical short circuit ratio in this embodiment does not require multiple changes in grid parameters or multiple full-band sweeps; the critical short circuit ratio can be obtained by performing a single sweep, with low computational complexity and without the need for closed-loop parameters.

[0094] S104: Determine the short-circuit ratio of the converter single-feed system. If the short-circuit ratio is greater than the critical short-circuit ratio, the converter single-feed system is stable under small disturbances. Otherwise, the converter single-feed system is unstable under small disturbances.

[0095] If the converter operates under rated conditions, its short-circuit ratio SCR can be defined as:

[0096] (9)

[0097] in, L g is the grid inductance, ω 0 is the system base frequency.

[0098] When the short-circuit ratio SCR is greater than the critical short-circuit ratio CSCR of the system, the converter single-feed system is stable with small disturbances; conversely, when the short-circuit ratio SCR is less than the critical short-circuit ratio CSCR of the system, the converter single-feed system is unstable with small disturbances.

[0099] The following is a simulation verification of the method of this embodiment. Figure 2 The structure shown is used as a simulation model, and the data of the simulation setting are shown in Table 1.

[0100] Table 1 Simulation data

[0101]

[0102] Assume the PI control loop of PLLPLL ( s )=150+5300 / s, draw the low-frequency eigenvalue tracking curve of the coupling admittance matrix as shown in Figure 3 As shown, the dark blue line and orange line represent e 1, the yellow line and the light blue line represent the amplitudes of the real and imaginary parts of e2, respectively. e 1 satisfies the above theorem, and e The real part of 2 is always greater than 0, so the above theorem does not apply.

[0103] Figure 4 for Figure 3 The enlarged view of the dotted box in the middle shows that at 11.8Hz, e The imaginary part of 1 is 0, and the real part is -2.36. According to the above theorem, the CSCR of the system is 2.36.

[0104] at the same time, Figure 5 and Figure 6 It shows that when the SCR drops from 3.3pu to 2p.u., det( Y ( s ))=0. The results show that when SCR is 2.3725, the system is in a critical stable state, that is, the SCR value when the system is stable in the left half plane is greater than 2.3725. According to the above comparison method, when the SCR of the system is greater than the calculated CSCR, the system is stable. Since the critical SCR (2.3725) is greater than the CSCR (2.36), it is consistent with the above theory, thus verifying the effectiveness of the method of this embodiment.

[0105] In addition, at 2Hz, e The imaginary part of 1 is also equal to 0, but the opposite e The real part of 1 is less than 1. When SCR is less than 1, the actual power grid cannot operate, so there is no need to consider the characteristic value of this frequency point.

[0106] In summary, the method of this embodiment can accurately determine the stability of small disturbances in the converter single-feed system. The process is simple and easy to implement. There is no need to build a white box model with known parameters, nor is there any need to perform multiple frequency sweeps on the closed-loop system. It has strong practicality.

[0107] Embodiment 2

[0108] In one or more embodiments, a small disturbance stability judgment system for a converter single-feed system is disclosed, comprising:

[0109] A matrix construction module is used to construct the device-side admittance matrix and the grid-side admittance matrix at different frequencies of the converter single-feed system;

[0110] An eigenvalue determination module is used to obtain a coupling admittance matrix at different frequencies based on a device-side admittance matrix and a network-side admittance matrix; a single frequency sweep is performed on the coupling admittance matrix at different frequencies to obtain an eigenvalue of the coupling admittance matrix at each frequency;

[0111] A critical short-circuit ratio determination module, used for obtaining a critical short-circuit ratio of a converter single-feed system based on the characteristic value;

[0112] The small disturbance stability judgment module is used to calculate the short circuit ratio of the converter single-feed system. If the short circuit ratio is greater than the critical short circuit ratio, the converter single-feed system is stable with small disturbances; otherwise, the converter single-feed system is unstable with small disturbances.

[0113] The specific implementation of the above modules is the same as that in Example 1 and will not be described in detail.

[0114] Embodiment 3

[0115] In one or more embodiments, a terminal device is disclosed, which includes a processor and a memory, the processor is used to implement instructions; the memory is used to store multiple instructions, and the instructions are suitable for being loaded by the processor and executing the small disturbance stability judgment method of the converter single-feed system described in Example 1.

[0116] It should be understood that in this embodiment, the processor may be a central processing unit CPU, and the processor may also be other general-purpose processors, digital signal processors DSP, application-specific integrated circuits ASIC, off-the-shelf programmable gate arrays FPGA or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or the processor may also be any conventional processor, etc.

[0117] The memory may include a read-only memory and a random access memory, and provide instructions and data to the processor. A portion of the memory may also include a non-volatile random access memory. For example, the memory may also store information about the device type.

[0118] In the implementation process, each step of the above method can be completed by an integrated logic circuit of hardware in a processor or an instruction in the form of software.

[0119] Embodiment 4

[0120] In one or more embodiments, a computer-readable storage medium is disclosed, in which a plurality of instructions are stored, wherein the instructions are suitable for being loaded by a processor of a terminal device and executing the method for determining small disturbance stability of a converter single-feed system described in Embodiment 1.

[0121] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A method for judging the small disturbance stability of a converter single-feed system, characterized in that: include: Construct the device-side admittance matrix and grid-side admittance matrix of the converter single-feed system at different frequencies; Based on the device side admittance matrix and the network side admittance matrix, the coupling admittance matrix at different frequencies is obtained; Perform a single frequency sweep on the coupling admittance matrix at different frequencies to obtain the eigenvalue of the coupling admittance matrix at each frequency; Based on the characteristic value, a critical short-circuit ratio of the converter single-feed system is obtained; Calculating a short-circuit ratio of a converter single-feed system, if the short-circuit ratio is greater than a critical short-circuit ratio, the converter single-feed system is stable under small disturbances, otherwise, the converter single-feed system is unstable under small disturbances; The coupling admittance matrix is ​​specifically: ； in, is the device side admittance matrix of the converter single-feed system, ω0 is the system reference frequency, is the ratio of resistance to inductance; Based on the characteristic value, the critical short-circuit ratio of the converter single-feed system is obtained, which is: After obtaining the eigenvalue of the coupling admittance matrix at each frequency, the real and imaginary value curves of each eigenvalue corresponding to different frequencies are established with the frequency as the horizontal coordinate and the specific value as the vertical coordinate; Select an eigenvalue whose imaginary part is zero and whose real part is negative, and take the absolute value of its real part as the critical short-circuit ratio CSCR of the system.

2. A method for judging small disturbance stability of a converter single-feed system according to claim 1, characterized in that: A single frequency sweep is performed on the coupling admittance matrix at different frequencies, specifically: A single frequency sweep is performed on the coupling admittance matrix at each frequency in the frequency band of 0-50 Hz to obtain multiple eigenvalues ​​of the coupling admittance matrix at each frequency.

3. A method for judging small disturbance stability of a converter single-feed system according to claim 1 or 2, characterized in that: The device-side admittance matrix of the converter single-feed system is as follows: ； in, , , , These are the four sub-elements obtained by decomposing the single-feed system admittance in the d / q axis.

4. A method for judging small disturbance stability of a converter single-feed system according to claim 1, characterized in that: The grid-side admittance matrix of the converter single-feed system is as follows: ； Where, Lg is the grid inductance, ω0 is the system reference frequency, is the ratio of resistance to inductance.

5. The method for judging small disturbance stability of a converter single-feed system according to claim 1, characterized in that: Determine the short-circuit ratio of the converter single-feed system, specifically: The short-circuit ratio of a single-infeed converter system is the inverse of the product of the grid inductance and the system reference frequency.

6. A system for judging the stability of a converter single-feed system with small disturbances, based on a method for judging the stability of a converter single-feed system with small disturbances as claimed in any one of claims 1 to 5, characterized in that: include: A matrix construction module is used to construct the device-side admittance matrix and the grid-side admittance matrix at different frequencies of the converter single-feed system; An eigenvalue determination module, used to obtain a coupling admittance matrix at different frequencies based on a device-side admittance matrix and a network-side admittance matrix; Perform a single frequency sweep on the coupling admittance matrix at different frequencies to obtain the eigenvalue of the coupling admittance matrix at each frequency; A critical short-circuit ratio determination module, used for obtaining a critical short-circuit ratio of a converter single-feed system based on the characteristic value; The small disturbance stability judgment module is used to calculate the short circuit ratio of the converter single-feed system. If the short circuit ratio is greater than the critical short circuit ratio, the converter single-feed system is stable with small disturbances; otherwise, the converter single-feed system is unstable with small disturbances.

7. A terminal device, comprising a processor and a memory, wherein the processor is used to implement instructions; and the memory is used to store multiple instructions, characterized in that: The instructions are suitable for being loaded by a processor and executing the method for judging small disturbance stability of a converter single-feed system according to any one of claims 1 to 5.

8. A computer-readable storage medium storing a plurality of instructions, characterized in that: The instruction is suitable for being loaded by a processor of a terminal device and executing the method for judging small disturbance stability of a converter single-feed system according to any one of claims 1 to 5.

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