A method and device for evaluating the oscillation risk of a grid-connected system operation mode of a converter

Abstract

The application belongs to the field of electric power, and discloses a method and device for evaluating oscillation risk of a converter grid-connected system operation mode, comprising: obtaining device-side admittance matrix and grid-side admittance matrix of the converter grid-connected system at multiple frequency points in a preset frequency range through sweep frequency measurement; constructing a closed-loop admittance matrix of the converter grid-connected system by taking the device-side admittance matrix as a forward channel and the inverse matrix of the grid-side admittance matrix as a feedback channel; calculating and drawing maximum singular value curves of the closed-loop admittance matrix in the preset frequency range under at least two different operation modes, and evaluating the oscillation risk degree of the corresponding operation mode according to the maximum singular value curves. By establishing the closed-loop admittance matrix taking the device-side admittance matrix as the forward channel and the inverse matrix of the grid-side admittance matrix as the feedback channel, and taking the drawn maximum singular value curve of the closed-loop admittance matrix as the evaluation standard of the oscillation risk, the decision-making process is simplified, and the complexity of engineering implementation is reduced.

Description

Technical Field

[0001] This invention belongs to the field of power, and in particular relates to a method and apparatus for assessing the oscillation risk of converter grid-connected systems during operation. Background Technology

[0002] Traditional synchronous generators are gradually being replaced by converters based on power electronic conversion technology. However, while this transformation brings high efficiency and flexible control, it also introduces new stability challenges, especially small-disturbance stability. Because power electronic devices lack the inherent rotational inertia and damping characteristics of synchronous machines, the system is more sensitive to external disturbances, easily leading to broadband oscillations, which in severe cases may cause large-scale grid disconnection accidents, threatening the safe operation of the power grid.

[0003] Grid strength is a key factor affecting the stability of renewable energy grid-connected systems. To quantitatively assess grid strength, the Short Circuit Ratio (SCR) and its derivative, the Critical Short Circuit Ratio (CSCR), are commonly used as core criteria in engineering. The SCR reflects the relative relationship between the equivalent impedance of the grid side and the impedance of the renewable energy generation unit; the lower the SCR value, the weaker the grid and the worse the system stability.

[0004] In related technologies, the main analytical methods for the impact of grid strength on the stability of a system under small disturbances include impedance analysis and eigenvalue analysis. Impedance analysis establishes a model of the converter output impedance and grid impedance, applying the Nyquist stability criterion or Bode plot to analyze the system's stability boundary. While this method has clear physical meaning, its analysis becomes complex when dealing with multiple-input multiple-output (MIMO) systems, making it difficult to intuitively reveal the differences in oscillation risk under different operating modes. Eigenvalue analysis requires first establishing a detailed small-signal state-space model of the system. By solving the eigenvalues ​​of the system state matrix, the damping ratio and frequency of each oscillation mode are analyzed. If the damping ratio of a certain mode is too low or negative, it indicates that the system has an instability risk. Although this method is accurate, its modeling process is extremely complex, dependent on the accuracy of system parameters, and for common "black box" or "gray box" devices in practical engineering, it is difficult to obtain their complete internal state equations, limiting its applicability. Furthermore, traditional impedance modeling often dynamically couples synchronous control elements (such as phase-locked loops) with the current inner loop for simultaneous solution, further increasing the complexity and difficulty of the model. Summary of the Invention

[0005] In view of this, the present invention discloses a method and apparatus for assessing the oscillation risk of a converter grid-connected system, which can solve the shortcomings of related technologies.

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

[0007] According to a first aspect of the present application, a method for evaluating the oscillation risk of a converter grid-connected system operation mode is provided, and the method comprises the following steps:

[0008] Obtaining the device-side admittance matrix and the grid-side admittance matrix of the converter grid-connected system at multiple frequency points in a preset frequency range through sweep measurement, respectively;

[0009] Constructing the closed-loop admittance matrix of the converter grid-connected system by taking the device-side admittance matrix as the forward channel and the inverse matrix of the grid-side admittance matrix as the feedback channel;

[0010] Calculating and drawing the maximum singular value curve of the closed-loop admittance matrix in the preset frequency range under at least two different operation modes, and evaluating the oscillation risk degree of the corresponding operation mode according to the maximum singular value curve.

[0011] According to a second aspect of the present application, an evaluation device for the oscillation risk of a converter grid-connected system operation mode is provided, and the device comprises:

[0012] An obtaining unit: obtaining the device-side admittance matrix and the grid-side admittance matrix of the converter grid-connected system at multiple frequency points in a preset frequency range through sweep measurement, respectively;

[0013] A constructing unit: constructing the closed-loop admittance matrix of the converter grid-connected system by taking the device-side admittance matrix as the forward channel and the inverse matrix of the grid-side admittance matrix as the feedback channel;

[0014] An evaluating unit: calculating and drawing the maximum singular value curve of the closed-loop admittance matrix in the preset frequency range under at least two different operation modes, and evaluating the oscillation risk degree of the corresponding operation mode according to the maximum singular value curve.

[0015] According to a third aspect of the present application, an electronic device is provided, and the device comprises:

[0016] A processor;

[0017] A memory for storing processor-executable instructions;

[0018] The processor executes the executable instructions to realize the steps of the method according to the first aspect.

[0019] According to a fourth aspect of the present application, a computer-readable storage medium is provided, and the medium stores computer instructions which are executed by a processor to realize the steps of the method according to the first aspect.

[0020] According to the above technical solutions, the method for evaluating the oscillation risk of a converter grid-connected system operation mode disclosed by the present application has the following advantages:

[0021] (1) Analysis precision and reliability are greatly improved: The traditional eigenvalue analysis method needs to establish an accurate system state space model, and the modeling process is complex and requires high accuracy of parameters. The present application directly obtains the device side and network side admittance matrix through sweep measurement, and systematically measures in the frequency band of 1Hz to 100Hz, effectively avoiding error accumulation in the complex modeling process. By constructing a closed-loop system model with the device side admittance matrix as the forward channel and the inverse matrix of the network side admittance matrix as the feedback channel, the stability characteristics of the system under different operating modes can be accurately captured, significantly improving the accuracy and reliability of the evaluation results.

[0022] (2) Practicality is significantly enhanced: The technical solution of the present application pays special attention to the application needs in engineering practice. By establishing a small signal model of the grid-following converter including the phase-locked loop dynamics, the DC voltage outer loop control, the current inner loop control and the coordinate transformation link, the method can effectively handle the multi-variable coupling problem existing in the actual system. The device side admittance matrix is represented by a 2*2 matrix in the xy coordinate system, which clearly represents the linear relationship between the small signal components of the port current and the small signal components of the port voltage, reducing the complexity of engineering implementation and improving the practical value of the method.

[0023] (3) The risk assessment intuitiveness is obviously improved: The present application innovatively uses the maximum singular value curve as the stability evaluation index, and by comparing the peak value changes of the curve under different operating modes, the relative risk level of each operating mode can be intuitively reflected. This evaluation criterion based on peak value comparison enables engineers to quickly identify high-risk operating regions, providing a scientific basis for optimizing the selection of system operating modes and simplifying the decision-making process.

[0024] (4) Efficiency of multi-operation mode comparison: The method supports simultaneous risk assessment of multiple operating modes, including short-circuit ratio, converter output active power and reactive power, and other key operating parameters. This parallel comparison capability not only improves the evaluation efficiency, but also comprehensively reflects the stability characteristics of the system under different operating conditions, providing multi-dimensional protection for safe system operation.

[0025] (5) Completeness of verification mechanism: The present application establishes a complete verification system by building a time-domain simulation model to compare the dynamic response characteristics of different operating modes under the same disturbance conditions. This waveform analysis-based verification method can objectively reflect the actual stability of the system, ensuring the correctness and reliability of the evaluation results, forming a complete technical closed loop from analysis to verification.

[0026] (6) The significance of technical and economic benefits: the implementation of the present application does not require additional hardware investment, and the comprehensive risk assessment can be completed through software, which has lower implementation cost and higher economic benefit. By identifying and avoiding high-risk operation modes in advance, the occurrence of system oscillation accidents can be effectively prevented, and economic losses caused by system instability can be avoided, which has significant comprehensive benefits. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a flow chart of an evaluation method of oscillation risk of a grid-connected system operation mode of a converter provided by an example embodiment;

[0028] Figure 2 is a schematic diagram of a grid-connected system of a grid-connected converter provided by an example embodiment;

[0029] Figure 3 is a schematic diagram of a multivariable negative feedback system provided by an example embodiment;

[0030] Figure 4 is a schematic diagram of the characteristic value change of a closed-loop admittance matrix provided by an example embodiment;

[0031] Figure 5 is a schematic diagram of the maximum characteristic value curve of a closed-loop admittance matrix under different operation modes provided by an example embodiment;

[0032] Figure 6 is a schematic diagram of time domain simulation results under two operation modes provided by an example embodiment;

[0033] Figure 7 is a schematic structural diagram of a device provided by an example embodiment;

[0034] Figure 8 is a block diagram of an evaluation device of oscillation risk of a grid-connected system operation mode of a converter provided by an example embodiment. DETAILED DESCRIPTION

[0035] The example embodiments will be described in detail here, and the examples are shown in the drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementation described in the following example embodiments does not represent all the implementations consistent with one or more embodiments of the present application. Instead, they are only examples of devices and methods consistent with some aspects of one or more embodiments of the present application as detailed in the appended claims.

[0036] It should be noted that the steps of the corresponding method are not necessarily performed in the order shown and described in the present application in other embodiments. In some other embodiments, the steps included in the method thereof can be more or less than 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 also be combined into a single step for description in other embodiments.

[0037] In related technologies, the analysis methods for the influence of grid strength on system small signal stability mainly include impedance analysis method and eigenvalue method. The impedance analysis method establishes a model of converter output impedance and grid impedance, and applies Nyquist stability criterion or Bode diagram to analyze the stability boundary of the system. This method has clear physical meaning, but when dealing with multiple-input multiple-output (MIMO) systems, the analysis process becomes complex, and it is difficult to intuitively reveal the oscillation risk difference under different operating modes. The eigenvalue method needs to first establish a detailed small signal state space model of the system, and analyzes the damping ratio and frequency of each oscillation mode by solving the eigenvalues of the system state matrix. If the damping ratio of a certain mode is too low or negative, it indicates that the system has instability risk. Although this method is accurate, the modeling process is extremely complex, depends on the accuracy of system parameters, and for the "black box" or "gray box" devices commonly seen in actual engineering, it is difficult to obtain their complete internal state equations, and the applicability is limited. In addition, the traditional impedance modeling usually couples the synchronous control link (such as phase-locked loop) and the current inner loop dynamics together for simultaneous solution, further increasing the complexity and difficulty of the model.

[0038] To solve the problems in the related art, the present application provides an evaluation method for oscillation risk of a converter grid-connected system operating mode.

[0039] Figure 1 is a flowchart of an evaluation method for oscillation risk of a converter grid-connected system operating mode provided by an exemplary embodiment. As Figure 1 shown, the method can include the following steps:

[0040] Step 101, obtain the device-side admittance matrix and the grid-side admittance matrix of the converter grid-connected system at multiple frequency points in a preset frequency range through sweep frequency measurement.

[0041] The grid-connected system of the grid-following converter containing the control link and the main circuit is shown in Figure 2 , wherein V q is the q-axis voltage of the converter, I d , I q are the d-axis and q-axis currents of the converter, I dref , I qref are the d-axis and q-axis current reference values of the converter, and I qref= 0, PI PLL (s) is a phase-locked loop PI link, ω PLL and θ PLL respectively, the frequency and phase angle of the phase-locked loop output, V dc is a DC voltage, L f is a filter inductance, C f is a filter capacitance, L g is the equivalent inductance on the grid side, E d and E q are the PWM d-axis and q-axis voltage commands, s is a complex variable.

[0042] In an embodiment, the preset frequency band of the sweep frequency measurement is 1Hz to 100Hz. Since the device side admittance and the grid side admittance of the system are both black box models, the sweep frequency method is usually used for impedance measurement in engineering. For example, a frequency band of 1-100Hz is selected, and the device side admittance and the grid side admittance under each frequency band are measured in turn with a step of 1Hz, so that the device side admittance and the grid side admittance matrix at each frequency point under 1-100Hz can be obtained.

[0043] In an embodiment, the device side admittance matrix and the grid side admittance matrix of the converter grid-connected system at multiple frequency points in a preset frequency band are obtained respectively, comprising: establishing a small signal model of a grid-following converter containing a phase-locked loop dynamic, a DC voltage outer loop control, a current inner loop control and a coordinate transformation link, and obtaining the device side admittance matrix according to the small signal model of the grid-following converter; wherein the device side admittance matrix is expressed as a 2*2 matrix in the xy coordinate system, which is used to represent the linearized relationship between the port current small signal component and the port voltage small signal component.

[0044] The dynamic equation of the DC voltage outer loop is:

[0045] ;

[0046] wherein PI dc (s) is a PI control link of the DC voltage outer loop, K pdc , K idc are the proportional and integral coefficients of the DC voltage outer loop PI control link, respectively.

[0047] The dynamic equation of the current inner loop is:

[0048] ;

[0049] wherein, ω 0 is the power frequency, ω 0=1; is a voltage feedforward filter link, T h(s) is the time constant of the voltage feed-forward filter loop, PI cc (s) is the current inner loop PI control loop, subscript 0 represents the steady-state value of the corresponding variable, the same below.

[0050] The current inner loop PI control loop PIcc(s) is as follows:

[0051] ;

[0052] Where, K pc (s), K ic (s) are the proportional coefficient and integral coefficient of the current PI loop, respectively.

[0053] The equation for the grid-connected converter to achieve synchronization with the grid through the phase-locked loop is:

[0054] ;

[0055] At the same time, there is a DC side power balance equation:

[0056] ;

[0057] Where, C dc is the DC voltage capacitor.

[0058] The dynamic equations of the above converter control loop are established in the dq coordinate system. In order to obtain the closed-loop transfer function in the global coordinate system, the device-side admittance in the dq axis needs to be converted to the global coordinate system, i.e., the xy coordinate system. This conversion is achieved through the transformation matrix T:

[0059] ;

[0060] Thus we get the transformation formula of voltage and current in xy and dq axes as follows:

[0061] ;

[0062] Where, , , , , represents the inverse of the rotation matrix, V x , V y are the port voltage components of the x-axis and y-axis, I x , I y are the port current components of the x-axis and y-axis.

[0063] By combining the transformation matrix T and the transformation formula and linearizing, the linearized equation can be obtained:

[0064] ;

[0065] wherein, denotes the derivative of the inverse of the rotation matrix θ PLL0 denotes the steady-state value of the inverter output matrix, θ PLL0 =0;Δ represents a small signal of the corresponding electrical quantity, and the same applies below.

[0066] The aforementioned DC voltage outer loop dynamic equation, the current inner loop dynamic equation, the synchronization equation, and the DC side power balance equation are linearized at the equilibrium point, combined with the linearized equations, and arranged and expressed in the form of admittance as follows:

[0067] ;

[0068] wherein, Y xx , Y xy , Y yx , Y yy respectively represent four elements of a 2*2 admittance matrix; Y VSCxy (s) is the device side admittance matrix under the xy axis.

[0069] The specific expressions of the four elements of the admittance matrix are as follows:

[0070] ;

[0071] In addition, the grid side admittance matrix Ygridxy(s) of the inverter can be expressed by the following formula:

[0072] .

[0073] Step 102, constructing a closed-loop admittance matrix of the inverter grid-connected system by taking the device side admittance matrix as a forward channel and the inverse matrix of the grid side admittance matrix as a feedback channel.

[0074] In an embodiment, the closed-loop admittance matrix is the ratio of the device side admittance matrix to a sum matrix, and the sum matrix is the sum of the ratio of the device side admittance matrix to the grid side admittance matrix and a unit matrix.

[0075] The obtained device side admittance matrix and grid side admittance matrix of the inverter can constitute a multivariable negative feedback system as shown in Figure 3 .

[0076] It can be obtained that the closed-loop admittance matrix Yclose(s) of the system is: Figure 3

[0077] ;

[0078] wherein, Y VSCxy (s) represents the device side admittance matrix,​ denotes the inverse of the grid-side admittance matrix, s is a complex frequency variable, and I is an identity matrix.

[0079] Step 103, calculate and draw the maximum singular value curves of the closed-loop admittance matrix in the preset frequency range under at least two different operating modes, and evaluate the oscillation risk degree of the corresponding operating mode according to the maximum singular value curves.

[0080] The maximum singular value reflects the maximum gain of the closed-loop system to any input direction:

[0081] ;

[0082] where σ max (G) denotes the maximum singular value of the closed-loop system transfer function matrix G, and u and y represent the input and output vectors of the closed-loop system, represent the 2-norm of the solution vector. By examining the maximum singular value of the closed-loop transfer function in a certain frequency range, the frequency point with the maximum gain of the system in that frequency range can be determined, and the oscillation risk of that frequency range can be evaluated.

[0083] The short-circuit ratio (SCR) of the rated power output and ignoring the line resistance can be expressed as follows:

[0084] ;

[0085] Therefore, Figure 3 The closed-loop admittance matrix of the system shown can be expressed as an explicit formula containing SCR:

[0086] ;

[0087] It can be seen that the SCR will affect Y close (s), and further affect the maximum singular value of Y close (s). The SCR under different operating modes is usually different, so the maximum singular value curve of Y close (s) under different operating modes is also different. In addition, the system power will affect the current inner loop reference value of the converter, and further affect the maximum singular value peak value of Y close (s).

[0088] If you want to draw the singular value characteristic curve of the closed-loop admittance matrix, you can use the svd function of Matlab combined with a loop statement to calculate the maximum singular value of the closed-loop admittance matrix in a certain frequency range. For example, you can use the svd function to calculate the maximum singular value of the matrix at the frequency point using the closed-loop admittance transfer function matrix obtained by the above frequency sweep in the frequency range of 1-100 Hz, and use a smooth curve to connect them in sequence, and you can get the maximum singular value curve of the closed-loop admittance matrix in the frequency range.

[0089] In this embodiment, by establishing a closed-loop admittance matrix with the device-side admittance matrix as the forward channel and the inverse matrix of the grid-side admittance matrix as the feedback channel, and taking the drawn maximum singular value curve of the closed-loop admittance matrix as the evaluation standard of oscillation risk, the decision-making process is simplified and the complexity of engineering implementation is reduced.

[0090] In an embodiment, the different operating modes are defined by different combinations of system operating parameters, including at least one of short circuit ratio, converter output active power and reactive power.

[0091] In order to explore the oscillation risk of the system under different operating modes, different operating modes can be set and the peak values of the maximum singular value curves of their closed-loop admittance matrices are respectively investigated and compared. For example, the following two operating modes can be set: the first one, SCR=2, P=0.8p.u., Q=0.2p.u.; the second one, SCR=3, P=1p.u., Q=0p.u.

[0092] The maximum singular value curves of the closed-loop admittance matrices under the two operating modes are drawn according to the above method respectively and their peak values are compared, so that the oscillation risks of the two operating modes can be judged.

[0093] In an embodiment, the oscillation risk degree of the corresponding operating mode is evaluated according to the maximum singular value curve, including: comparing the peak values of the maximum singular value curves corresponding to the at least two different operating modes, and evaluating the operating mode with a higher maximum singular value curve peak value as the operating mode with a higher oscillation risk.

[0094] According to the parameter values in Table 1 and the model structure described in the first part, a grid-connected converter grid-connected system model is built in Matlab / Simulink software.

[0095] Table 1

[0096]

[0097] As shown in Figure 4 By drawing the dominant eigenvalue of the closed-loop admittance matrix, it can be seen that the system stability gradually decreases as the SCR decreases. When the system SCR=1.5, the system is critically stable.

[0098] To investigate the oscillation risk of the closed-loop admittance matrix under different operating modes, two operating modes were set up: Operating Mode 1: SCR=1.75, P=0.8pu, Q=0.2pu; Operating Mode 2: SCR=2, P=1p.u., Q=0p.u. The maximum singularity curves for the two different operating modes are plotted as follows: Figure 5 As shown, the peak value of the maximum singularity curve in operating mode 1 is higher than that in operating mode 2, therefore the oscillation risk of operating mode 1 is greater than that of operating mode 2.

[0099] In one embodiment, the method further includes: building a time-domain simulation model of the converter grid-connected system; setting parameters for the at least two different operating modes in the time-domain simulation model and applying the same small disturbance; observing and comparing the dynamic response waveforms output by the system, and verifying that the operating mode with more unstable waveforms or more severe oscillations is the operating mode with a higher risk of oscillation.

[0100] Simulations were performed using a Simulink-based single-machine infinite bus model. For a system with a stable initial state, a small disturbance of 0.1 pu was applied to the grid voltage at time 5 seconds. The converter output active power waveforms under operating modes 1 and 2 were observed as follows. Figure 6 It can be seen that using the parameters of operating mode 1, the system becomes unstable after being subjected to a small disturbance at 5s; however, using operating mode 2, the system does not become unstable after being subjected to a small disturbance at 5s. This time-domain simulation proves the effectiveness of the above evaluation method.

[0101] Figure 7 This is a schematic structural diagram of a device provided in an exemplary embodiment. Please refer to... Figure 7 At the hardware level, the device includes a processor 702, an internal bus 704, a network interface 706, memory 708, and non-volatile memory 710, and may also include other hardware required for its functions. One or more embodiments of the present invention can be implemented in software, for example, the processor 702 reads the corresponding computer program from the non-volatile memory 710 into memory 708 and then runs it. Of course, in addition to software implementation, one or more embodiments of the present invention do not exclude other implementation methods, such as logic devices or a combination of hardware and software, etc. That is to say, the execution subject of the following processing flow is not limited to each logic unit, but can also be hardware or logic devices.

[0102] Please refer to Figure 8 An assessment device for the oscillation risk of a converter grid-connected system can be applied to, for example... Figure 8 The device shown, in order to implement the technical solution of the present invention, includes:

[0103] The acquisition unit 801 is configured to acquire, by means of the sweep frequency measurement, the device-side admittance matrix and the grid-side admittance matrix of the grid-connected converter system at a plurality of frequency points in a preset frequency range, respectively.

[0104] The construction unit 802 is configured to construct a closed-loop admittance matrix of the grid-connected converter system by taking the device-side admittance matrix as a forward channel and taking the inverse matrix of the grid-side admittance matrix as a feedback channel.

[0105] The evaluation unit 803 is configured to calculate and plot a maximum singular value curve of the closed-loop admittance matrix in the preset frequency range under at least two different operating modes, and evaluate the oscillation risk degree of the corresponding operating mode according to the maximum singular value curve.

[0106] Optionally, the preset frequency range of the sweep frequency measurement is 1 Hz to 100 Hz.

[0107] Optionally, the acquisition unit 801 is specifically configured to:

[0108] establish a small-signal model of a grid-following converter including a phase-locked loop dynamic, a direct-current voltage outer loop control, a current inner loop control and a coordinate transformation link, and obtain the device-side admittance matrix according to the small-signal model of the grid-following converter; wherein the device-side admittance matrix is expressed as a 2*2 matrix in an xy coordinate system, and the matrix is used to represent a linearized relationship between a small-signal component of a port current and a small-signal component of a port voltage.

[0109] Optionally, the closed-loop admittance matrix is a ratio of the device-side admittance matrix to a sum matrix, and the sum matrix is a sum of a ratio of the device-side admittance matrix to the grid-side admittance matrix and a unit matrix.

[0110] Optionally, the different operating modes are defined by different combinations of system operating parameters, and the system operating parameters include at least one of a short-circuit ratio, a converter output active power and a converter output reactive power.

[0111] Optionally, the evaluation unit 803 is specifically configured to:

[0112] compare peak values of the maximum singular value curves corresponding to the at least two different operating modes, and evaluate an operating mode with a higher maximum singular value curve peak value as an operating mode with a higher oscillation risk.

[0113] Optionally, the apparatus further includes:

[0114] The construction unit 804 is configured to construct a time-domain simulation model of the grid-connected converter system.

[0115] The interference unit 805 is configured to set parameters of the at least two different operating modes in the time-domain simulation model, respectively, and apply the same small disturbance.

[0116] The verification unit 806 is configured to observe and compare the dynamic response waveforms output by the system, and verify that the operation mode in which the waveform is unstable or oscillates more severely is the operation mode with higher risk of oscillation.

[0117] The system, apparatus, module or unit illustrated in the above embodiments can be specifically implemented by a computer chip or entity, or by a product 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.

[0118] In a typical configuration, a computer includes one or more processors (CPUs), input / output interfaces, network interfaces, and memory.

[0119] 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.

[0120] Computer readable media includes permanent and non-permanent, removable and non-removable media implemented using any method or technology for storage of information such as 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 computer readable media such as modulated data signals and carriers.

[0121] 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 implementing the technical solutions of the present application.

[0122] The present application further provides a computer program which, when executed by a processor, implements one or more of the above-mentioned embodiments, thereby implementing the technical solutions of the present application. The computer program can be recorded on a computer readable medium in any form as mentioned above or any other form, and the present application does not limit this.

[0123] It should also be noted that the terms "comprising", "containing", or any other similar term are intended to encompass non-exclusive inclusions, such that processes, methods, articles, or apparatuses that comprise a list of elements are not limited to those elements, but can also include other elements not expressly listed, or inherent to such processes, methods, articles, or apparatuses. Without more limitations, the element defined by the phrase "comprising a" does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0124] The above describes specific embodiments of the present application. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims can be performed in a different order than the order in which they are recited and still achieve the desired results. In addition, the processes depicted in the figures do not necessarily require the particular order shown, or sequential order, to achieve the desired results. In certain implementations, multitasking and parallel processing can be advantageous or necessary.

[0125] The terms used in one or more embodiments of the present application are merely for the purpose of describing specific embodiments and are not intended to limit one or more embodiments of the present application. The singular forms "a", "an" and "the" used in one or more embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein means and includes any or all possible combinations of one or more associated listed items.

[0126] It should be understood that although the terms first, second, third, etc. can be used in one or more embodiments of the present application to describe various information, these information should not be limited to these terms. These terms are only used to distinguish one type of information from another. For example, without departing from the scope of one or more embodiments of the present application, first information can also be referred to as second information, and similarly, second information can also be referred to as first information. Depending on the context, the word "if" as used herein can be interpreted as "when" or "upon determining" or "in response to determining".

[0127] The above merely provides the preferred embodiment of one or more embodiments of the present application, and is not intended to limit one or more embodiments of the present application. Any modification, equivalent replacement, improvement, and the like made within the spirit and principle of one or more embodiments of the present application shall be included in the scope of protection of one or more embodiments of the present application.

Claims

1. A method for evaluating the risk of oscillation of a variable frequency converter grid-connected system operating mode, characterized in that, The method comprises: obtaining, through sweep frequency measurement, device-side admittance matrix and grid-side admittance matrix of the converter grid-connected system at multiple frequency points in a preset frequency range, respectively; constructing a closed-loop admittance matrix of the converter grid-connected system by taking the device-side admittance matrix as a forward channel and the inverse matrix of the grid-side admittance matrix as a feedback channel; calculating and plotting maximum singular value curves of the closed-loop admittance matrix in the preset frequency range under at least two different operating modes, and comparing peak values of the maximum singular value curves corresponding to the at least two different operating modes, and evaluating the operating mode with a higher peak value of the maximum singular value curve as an operating mode with a higher risk of oscillation; wherein the different operating modes are defined by different combinations of system operating parameters, and the system operating parameters include at least one of short-circuit ratio, converter output active power and reactive power.

2. The method of claim 1, wherein, The preset frequency range of the sweep frequency measurement is 1 Hz to 100 Hz.

3. The method of claim 1, wherein, The obtaining, through sweep frequency measurement, device-side admittance matrix and grid-side admittance matrix of the converter grid-connected system at multiple frequency points in a preset frequency range, respectively, comprises: establishing a small-signal model of a grid-following converter including a phase-locked loop dynamic, a DC voltage outer loop control, a current inner loop control and a coordinate transformation link, and obtaining the device-side admittance matrix according to the small-signal model of the grid-following converter; wherein the device-side admittance matrix is expressed as a 2*2 matrix in an xy coordinate system, which is used to represent the linearized relationship between the small-signal component of the port current and the small-signal component of the port voltage.

4. The method of claim 1, wherein, The closed-loop admittance matrix is the ratio of the device-side admittance matrix to a sum matrix, and the sum matrix is the sum of the ratio of the device-side admittance matrix to the grid-side admittance matrix and a unit matrix.

5. The method of claim 1, wherein, The method further comprises: building a time-domain simulation model of the converter grid-connected system; in the time-domain simulation model, parameters of the at least two different operating modes are set respectively, and the same small disturbance is applied; observing and comparing the dynamic response waveforms of the system output, and verifying that the operating mode with more unstable or more intense oscillation is the operating mode with a higher risk of oscillation.

6. An evaluation device for the risk of oscillation of a variable frequency converter grid-connected system operating mode, characterized in that, The device comprises: an obtaining unit: obtaining, through sweep frequency measurement, device-side admittance matrix and grid-side admittance matrix of the converter grid-connected system at multiple frequency points in a preset frequency range, respectively; a constructing unit: constructing a closed-loop admittance matrix of the converter grid-connected system by taking the device-side admittance matrix as a forward channel and the inverse matrix of the grid-side admittance matrix as a feedback channel; an evaluating unit: calculating and plotting maximum singular value curves of the closed-loop admittance matrix in the preset frequency range under at least two different operating modes, and comparing peak values of the maximum singular value curves corresponding to the at least two different operating modes, and evaluating the operating mode with a higher peak value of the maximum singular value curve as an operating mode with a higher risk of oscillation; wherein the different operating modes are defined by different combinations of system operating parameters, and the system operating parameters include at least one of short-circuit ratio, converter output active power and reactive power.

7. An electronic device, comprising: comprise: a processor; a memory for storing processor-executable instructions; wherein the processor executes the executable instructions to implement the steps of the method of any one of claims 1-5.

8. A computer readable storage medium having stored thereon computer instructions, wherein, The instructions, when executed by the processor, implement steps of the method of any of claims 1-5.

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