Method, system and equipment for evaluating grid-connected system of network-forming converter and medium

Abstract

The invention belongs to the technical field of new energy power, and discloses a method, a system, equipment and a medium for evaluating a grid-connected system of a grid-forming converter, and the method comprises the steps: building an equipment-side impedance model and a grid-side impedance model according to dynamic equations of an inner ring and an outer ring of the grid-connected system, a dynamic equation of a synchronous control link and a dynamic control equation of a power grid; performing joint linear analysis on the equipment-side impedance model and the grid-side impedance model, and constructing a closed-loop characteristic equation of the grid-connected system based on a joint linear analysis result; the closed-loop characteristic equation is utilized, and the Nyquist stability criterion is combined to evaluate the grid-connected system of the grid-forming converter; and the evaluation result is verified in a time domain simulation mode. According to the method, the synchronous control link is put on the grid side, the inner and outer rings are put on the equipment side, the impedance modeling method is adopted to evaluate the small interference stability of the grid-connected system of the grid-forming converter, and the problem of high modeling complexity is solved.

Description

Technical Field

[0001] The present invention relates to the field of new energy power technology, and in particular to a method, system, equipment and medium for evaluating a grid-connected system of a grid-connected converter. Background Art

[0002] With the increasing installed capacity of new energy sites such as photovoltaic and wind power in my country, my country is gradually transitioning to a "double high" power system with a high proportion of renewable energy and a high proportion of power electronic equipment. However, due to the lack of frequency and inertial support for new energy grid connection, strong oscillation problems and even instability will occur between power electronic equipment and power systems. In order to better analyze the stability of new energy power systems, a simple, accurate and reliable small disturbance stability assessment method is needed.

[0003] It is generally believed that one of the main reasons for the oscillation of new energy power systems is the insufficient system damping. The main method for studying the stability of new power systems that reflect the system damping level is the eigenvalue method. The eigenvalue method first establishes a small signal model of the system, and then solves the eigenvalue of the model, and judges the system stability by analyzing the changes in the damping of the eigenvalue oscillation mode. In addition, the traditional impedance modeling method jointly models the synchronous control link and the current inner loop, which is highly complex.

[0004] Therefore, how to provide a grid-connected converter grid-connected system evaluation method, system, equipment and medium is a problem that needs to be solved urgently. Summary of the invention

[0005] The embodiments of the present invention provide a method, system, device and medium for evaluating a grid-connected system of a grid-connected converter, so as to solve the problem of high complexity in the prior art of jointly modeling a synchronous control link and a current inner loop using impedance modeling.

[0006] In order to have a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. This summary is not intended to be a general review, nor is it intended to identify key / important components or to delineate the scope of protection of these embodiments. Its only purpose is to present some concepts in a simple form as a preface to the detailed description that follows.

[0007] According to a first aspect of an embodiment of the present invention, a method for evaluating a grid-connected system of a grid-connected converter is provided.

[0008] In one embodiment, a method for evaluating a grid-connected system of a grid-connected converter includes:

[0009] According to the dynamic equations of the internal and external loops of the grid-connected system, the dynamic equations of the synchronous control link and the dynamic control equations of the power grid, the equipment side impedance model and the grid side impedance model are established;

[0010] Perform joint linear analysis on the device-side impedance model and the grid-side impedance model, and build a closed-loop characteristic equation of the grid-connected system based on the joint linear analysis results;

[0011] The grid-connected system of the grid-connected converter is evaluated by using the closed-loop characteristic equation and combining the Nyquist stability criterion. The evaluation results are verified by time domain simulation.

[0012] In one embodiment, according to the dynamic equations of the inner and outer loops of the grid-connected system, the dynamic equations of the synchronous control link and the dynamic control equations of the power grid, establishing the device side impedance model and the grid side impedance model includes:

[0013] The inner and outer loops of the grid-connected system are configured on the equipment side, and the synchronous control link is configured on the grid side; the inner loop dynamic equation of the grid-connected system, the outer loop dynamic equation of the grid-connected system and the filter inductor circuit equation are linearized and connected in parallel to obtain the equipment side impedance model;

[0014] The dynamic equation of the virtual synchronous control link, the dynamic equation of the transmission line inductance, the component formula of the grid voltage under the virtual synchronous link and the analysis formula of the grid-type converter are linearized and connected in parallel to obtain the grid-side impedance model.

[0015] In one embodiment, a joint linear analysis is performed on the device-side impedance model and the grid-side impedance model, and based on the joint linear analysis result, a closed-loop characteristic equation of the grid-connected system is constructed, including:

[0016] After linearizing the device side impedance model and the grid side impedance model, the device side impedance model and the grid side impedance model are combined to obtain a comprehensive impedance model;

[0017] The comprehensive impedance model is converted into an impedance matrix, and the determinant of the impedance matrix is ​​solved to obtain the closed-loop characteristic equation of the grid-connected system.

[0018] In one embodiment, the impedance matrix is ​​a 2*2 impedance matrix.

[0019] In one embodiment, the evaluation of the grid-connected system of the grid-connected converter using the closed-loop characteristic equation and the Nyquist stability criterion includes:

[0020] According to the simulation experiments with different simulation parameters, the Nyquist diagram under stable conditions and the Nyquist diagram under unstable conditions are drawn for the closed-loop characteristic equation;

[0021] According to the Nyquist diagram under stable conditions and the Nyquist diagram under unstable conditions, the stability of the grid-connected system of the grid-connected converter is evaluated accordingly.

[0022] In one embodiment, the simulation parameters include: filter inductance parameters, grid-side inductance parameters, inertia parameters, damping parameters, current inner loop PI link parameters, voltage outer loop PI link parameters, current feedforward filter link parameters and voltage feedforward filter link parameters.

[0023] In one embodiment, according to simulation experiments with different simulation parameters, for a closed-loop characteristic equation, when the Nyquist diagram under stable conditions and the Nyquist diagram under unstable conditions are plotted, it is determined whether the Nyquist diagram surrounds the origin. If so, the Nyquist diagram under unstable conditions is obtained; if not, the Nyquist diagram under stable conditions is obtained.

[0024] In one embodiment, verifying the evaluation result by means of time domain simulation includes:

[0025] According to different evaluation results of the grid-connected system of the grid-building converter, time domain simulation is performed respectively to obtain the corresponding time domain simulation waveform diagram;

[0026] When the time domain simulation uses simulation parameters under stable conditions, the waveform in the obtained simulation waveform graph converges, and the time domain simulation uses simulation parameters under unstable conditions, the waveform in the obtained simulation waveform graph does not converge, then the evaluation result is correct.

[0027] According to a second aspect of an embodiment of the present invention, a grid-connected converter system evaluation system is provided.

[0028] In one embodiment, the grid-connected converter system evaluation system comprises:

[0029] The impedance model building module is used to build the equipment side impedance model and the grid side impedance model according to the dynamic equations of the internal and external loops of the grid-connected system, the dynamic equations of the synchronous control link and the dynamic control equations of the power grid;

[0030] A closed-loop characteristic equation construction module is used to perform joint linear analysis on the device-side impedance model and the grid-side impedance model, and to construct a closed-loop characteristic equation of the grid-connected system based on the joint linear analysis results;

[0031] The stability evaluation and verification module is used to evaluate the grid-connected system of the grid-connected converter using the closed-loop characteristic equation in combination with the Nyquist stability criterion; and to verify the evaluation results by means of time domain simulation.

[0032] In one embodiment, according to the dynamic equations of the inner and outer loops of the grid-connected system, the dynamic equations of the synchronous control link and the dynamic control equations of the power grid, establishing the device side impedance model and the grid side impedance model includes:

[0033] The inner and outer loops of the grid-connected system are configured on the equipment side, and the synchronous control link is configured on the grid side; the inner loop dynamic equation of the grid-connected system, the outer loop dynamic equation of the grid-connected system and the filter inductor circuit equation are linearized and connected in parallel to obtain the equipment side impedance model;

[0034] The dynamic equation of the virtual synchronous control link, the dynamic equation of the transmission line inductance, the component formula of the grid voltage under the virtual synchronous link and the analysis formula of the grid-type converter are linearized and connected in parallel to obtain the grid-side impedance model.

[0035] In one embodiment, a joint linear analysis is performed on the device-side impedance model and the grid-side impedance model, and based on the joint linear analysis result, a closed-loop characteristic equation of the grid-connected system is constructed, including:

[0036] After linearizing the device side impedance model and the grid side impedance model, the device side impedance model and the grid side impedance model are combined to obtain a comprehensive impedance model;

[0037] The comprehensive impedance model is converted into an impedance matrix, and the determinant of the impedance matrix is ​​solved to obtain the closed-loop characteristic equation of the grid-connected system;

[0038] The impedance matrix is ​​a 2*2 impedance matrix.

[0039] In one embodiment, the evaluation of the grid-connected system of the grid-connected converter using the closed-loop characteristic equation and the Nyquist stability criterion includes:

[0040] According to the simulation experiments with different simulation parameters, the Nyquist diagram under stable conditions and the Nyquist diagram under unstable conditions are drawn for the closed-loop characteristic equation;

[0041] According to the Nyquist diagram under stable conditions and the Nyquist diagram under unstable conditions, the stability of the grid-connected system of the grid-connected converter is evaluated accordingly;

[0042] Among them, the simulation parameters include: filter inductance parameters, grid-side inductance parameters, inertia parameters, damping parameters, current inner loop PI link parameters, voltage outer loop PI link parameters, current feedforward filter link parameters and voltage feedforward filter link parameters.

[0043] In one embodiment, according to simulation experiments with different simulation parameters, for a closed-loop characteristic equation, when the Nyquist diagram under stable conditions and the Nyquist diagram under unstable conditions are plotted, it is determined whether the Nyquist diagram surrounds the origin. If so, the Nyquist diagram under unstable conditions is obtained; if not, the Nyquist diagram under stable conditions is obtained.

[0044] In one embodiment, verifying the evaluation result by means of time domain simulation includes:

[0045] According to different evaluation results of the grid-connected system of the grid-building converter, time domain simulation is performed respectively to obtain the corresponding time domain simulation waveform diagram;

[0046] When the time domain simulation uses simulation parameters under stable conditions, the waveform in the obtained simulation waveform graph converges, and the time domain simulation uses simulation parameters under unstable conditions, the waveform in the obtained simulation waveform graph does not converge, then the evaluation result is correct.

[0047] According to a third aspect of an embodiment of the present invention, a computer device is provided.

[0048] In some embodiments, the computer device includes a memory and a processor, the memory stores a computer program, and the processor implements the steps of the above method when executing the computer program.

[0049] According to a fourth aspect of embodiments of the present invention, a computer-readable storage medium is provided.

[0050] In one embodiment, the computer-readable storage medium stores a computer program, and the computer program implements the steps of the above method when executed by a processor.

[0051] The technical solution provided by the embodiment of the present invention may have the following beneficial effects:

[0052] The present invention places the synchronous control link on the grid side, places the inner and outer loops on the device side, and adopts an impedance modeling method to evaluate the small disturbance stability of the grid-connected system of the grid-connected converter. First, according to the dynamic equations of the inner and outer loops and the synchronous control loop, combined with the dynamic control equations of the power grid, the impedance model of the grid side and the device is established; secondly, the determinant of the impedance model system matrix is ​​solved; finally, the simulation tool is used to examine its stability through the Nyquist stability criterion, which proposes a new idea for the small disturbance stability evaluation of the grid-connected system of the grid-connected converter, which is simpler than the traditional impedance modeling.

[0053] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0055] Figure 1 is a flow chart of a method for evaluating a grid-connected system of a grid-connected converter according to an exemplary embodiment;

[0056] Figure 2 is a structural block diagram of a grid-connected converter system evaluation system according to an exemplary embodiment;

[0057] Figure 3 is a structural schematic diagram of a computer device according to an exemplary embodiment;

[0058] Figure 4 is a single machine infinite equivalent circuit shown according to an exemplary embodiment;

[0059] Figure 5 is a Nyquist diagram in a stable condition according to an exemplary embodiment;

[0060] Figure 6 is a Nyquist diagram in an unstable situation according to an exemplary embodiment;

[0061] Figure 7 is a time domain simulation waveform diagram under a stable condition according to an exemplary embodiment;

[0062] Figure 8 is a time domain simulation waveform diagram under unstable conditions according to an exemplary embodiment;

[0063] Fig. 9 It is a technical route flow chart of a stability assessment method according to an exemplary embodiment. DETAILED DESCRIPTION

[0064] The following description and accompanying drawings fully illustrate the specific embodiments of this article so that those skilled in the art can practice them. Parts and features of some embodiments may be included in or replace parts and features of other embodiments. The scope of the embodiments of this article includes the entire scope of the claims, as well as all available equivalents of the claims. Herein, the terms "first", "second", etc. are only used to distinguish one element from another, without requiring or implying any actual relationship or order between these elements. In fact, the first element can also be called the second element, and vice versa. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that the structure, device or equipment including a series of elements includes not only those elements, but also other elements that are not explicitly listed, or also include elements inherent to such structure, device or equipment. In the absence of more restrictions, the elements defined by the sentence "including one..." do not exclude the existence of other identical elements in the structure, device or equipment including the elements. Each embodiment is described in a progressive manner herein, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the embodiments can be referred to each other.

[0065] The terms "longitudinal", "lateral", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like used herein to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this article and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In the description herein, unless otherwise specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a mechanical connection or an electrical connection, it can also be the internal connection of two elements, it can be a direct connection, or it can be an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0066] As used herein, the term "plurality" means two or more than two, unless otherwise specified.

[0067] In this document, the character " / " indicates that the preceding and following objects are in an "or" relationship. For example, A / B means: A or B.

[0068] In this article, the term "and / or" is a description of the association relationship between objects, indicating that three relationships may exist. For example, A and / or B means: A or B, or, A and B.

[0069] It should be understood that, although the various steps in the flow chart are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear description in this article, the execution of these steps is not strictly limited in order, and these steps can be executed in other orders. Moreover, at least a portion of the steps in the figure may include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these sub-steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a portion of the sub-steps or stages of other steps.

[0070] Each module in the device or system of the present application can be implemented in whole or in part by software, hardware, or a combination thereof. The above modules can be embedded in or independent of a processor in a computer device in the form of hardware, or can be stored in a memory in a computer device in the form of software, so that the processor can call and execute operations corresponding to the above modules.

[0071] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0072] Figure 1An embodiment of the grid-connected converter system evaluation method of the present invention is shown.

[0073] In this optional embodiment, the grid-connected converter grid-connected system evaluation method includes:

[0074] Step S101, establishing a device side impedance model and a grid side impedance model according to the dynamic equations of the inner and outer loops of the grid-connected system, the dynamic equations of the synchronous control link and the dynamic control equations of the power grid;

[0075] Step S103: performing a joint linear analysis on the device-side impedance model and the grid-side impedance model, and constructing a closed-loop characteristic equation of the grid-connected system based on the joint linear analysis result;

[0076] Step S105: using the closed-loop characteristic equation and combining with the Nyquist stability criterion, the grid-connected system of the grid-connected converter is evaluated; and the evaluation result is verified by means of time domain simulation.

[0077] Figure 2 An embodiment of the grid-connected converter system evaluation system of the present invention is shown.

[0078] In this optional embodiment, the grid-connected converter system evaluation system comprises:

[0079] The impedance model establishment module 201 is used to establish the device side impedance model and the grid side impedance model according to the dynamic equations of the inner and outer loops of the grid-connected system, the dynamic equations of the synchronous control link and the dynamic control equations of the power grid;

[0080] A closed-loop characteristic equation construction module 203 is used to perform a joint linear analysis on the device-side impedance model and the grid-side impedance model, and to construct a closed-loop characteristic equation of the grid-connected system based on the joint linear analysis result;

[0081] The stability evaluation and verification module 205 is used to evaluate the grid-connected system of the grid-connected converter by using the closed-loop characteristic equation and combining the Nyquist stability criterion; and to verify the evaluation result by means of time domain simulation.

[0082] In order to facilitate understanding of the above technical solutions of the present invention, the above technical solutions of the present invention are further described below from the perspective of architecture and principle, as follows:

[0083] The present invention aims at the problem of small disturbance synchronous stability of new energy power system, and derives a small disturbance stability evaluation method of grid-connected converter system through a new impedance modeling method. The impedance model of the traditional evaluation method models the inner loop and the synchronous control link. The present invention models the outer loop and the inner loop together, and the synchronous control link is combined with the external power grid, thereby proposing a new small disturbance stability evaluation method. First, according to the dynamic equations of the inner and outer loops and the synchronous control link of the grid-connected system, the impedance models of the equipment side and the grid side are established respectively after linearization and parallelization; secondly, the impedance model is converted into a 2*2 impedance matrix, and its determinant is solved; finally, the impedance model is analyzed by the Nyquist stability criterion using simulation tools (such as Matlab and other tools). Based on the Nyquist stability criterion, the present invention provides a new method and idea for the small signal interference stability evaluation of the grid-connected converter system through an innovative impedance model construction method.

[0084] Inner loop dynamic equation:

[0085]

[0086] In the formula, PI CC (s) is the current inner loop PI link, I d and I q are the control currents of the d-axis and q-axis of the inner current loop, L f is the filter inductor, I dref and I qref are the reference voltages of the d-axis and q-axis of the inner current loop, E d and E q are the command values ​​for PWM control of the d-axis and q-axis, ω0 is the power frequency, and f VF (s) is the voltage feedforward filter link, U d and U q are the d-axis and q-axis components of the grid-connected point voltage.

[0087] Outer loop dynamic equation:

[0088]

[0089] In the formula, C f is the filter capacitor, f IF (s) is the current feedforward filter link. PI VC (s) is the transfer function of the PI regulator in the voltage loop, U d and U q are the d-axis and q-axis voltages at the grid connection point, U dref and U qref They are the reference voltages for the d-axis and q-axis of the voltage outer loop respectively.

[0090] Dynamic equation of virtual synchronous control link:

[0091]

[0092] In the formula, ω JD is the virtual synchronous control angular frequency, J is the inertia parameter, D is the damping parameter, ω is the synchronous speed of the AC power grid, and f PQ (s) is the power measurement filter link, P M is the mechanical power, P E is the electrical power, s is an s-domain complex variable, and θ is the power angle.

[0093] Filter inductor circuit equation:

[0094]

[0095] Where, L f is the filter inductor, U sd and U sq They are the d-axis and q-axis components of the voltage on the high-voltage side of the converter filter inductor.

[0096] Ignoring the filter capacitor, the transmission line inductance L g The dynamic equation is:

[0097]

[0098] In the formula, E d and E q They are the d-axis and q-axis components of the grid voltage respectively.

[0099] In addition, the grid voltage The components under the virtual synchronization link are:

[0100]

[0101] Where θ is the power angle and E is the grid voltage amplitude.

[0102] When using the synchronous machine method to analyze GFM (grid-forming), there is (grid-forming converter analysis formula):

[0103]

[0104] Where U is the voltage amplitude at the grid connection point, X g is the external grid reactance.

[0105] By linearizing equations (1), (2) and (4) together, we can obtain the current and voltage output relationship of the device side taking into account the voltage outer loop:

[0106]

[0107] In the formula, ZVSM This is the device side impedance.

[0108] By linearizing equations (3), (5), (6) and (7), we can obtain the relationship between the dq axis voltage and the dq axis input current:

[0109]

[0110] In the formula, Z grid This is the grid side impedance.

[0111] 1. System impedance modeling

[0112] For a single-machine infinite power grid system, its equipment side is equivalent to impedance and power supply, and the grid side is equivalent to load. Its equivalent circuit can be drawn, such as Figure 4 As shown, Figure 4 In the figure, U(s) is the GFM (grid-forming) equivalent voltage source, Z1(s) is the device side equivalent impedance, and Z2(s) is the grid side equivalent impedance.

[0113] In order to use the Nyquist stability criterion for analysis, we can Figure 4 , the transfer function matrix of the device side impedance model is used as the forward transfer function G(s), and the inverse matrix of the transfer function matrix of the grid side impedance model is used as the feedback transfer function H(s), thus forming a complete closed-loop multivariable feedback system. According to the Nyquist stability criterion, it is only necessary to examine whether the Nyquist diagram of the characteristic equation of the closed-loop system contains the origin.

[0114] 2. System transfer function

[0115] According to the theoretical method provided by the present invention, the impedance models of the inner and outer loops on the equipment side and the synchronous control link on the grid side are established respectively, and the impedance models can be obtained by linearizing and connecting them in parallel as follows:

[0116]

[0117] Among them, PI CC (s) is the PI link of the current inner loop, PI VC (s) is the voltage outer loop PI link, L f is the filter inductance, f IF (s) is the current feedforward filter link, f VF (s) is the voltage feedforward filter link, J is the inertia parameter, D is the damping parameter, L g is the inductance of the external grid, X g is the external grid reactance, ΔU d , ΔU q , ΔI d , ΔI qis the small signal of the voltage and current at the grid connection point, s is a complex variable in the s domain, ω0 is the power frequency, and f PQ (s) is the power measurement filter link.

[0118] Extracting the impedance matrix in the above equation (10) and finding its determinant can obtain the closed-loop characteristic equation of the system:

[0119]

[0120] Here, det represents the determinant of the matrix.

[0121] 3. Nyquist stability criterion to examine stability

[0122] After obtaining the determinant of the impedance, the impedance model is analyzed for stability using simulation software using the Nyquist stability criterion and verified using time domain simulation.

[0123] First, the parameters set in the simulation experiment are given in Table 1.

[0124] Table 1 Parameters set in the simulation experiment

[0125]

[0126] By setting different parameters, we can get Nyquist diagrams under stable and unstable conditions, as shown in the following figure: Figure 5-Figure 6 shown.

[0127] Figure 5-Figure 6 The Nyquist diagrams in two different cases are shown in Figure 1. After solving the closed-loop characteristic equation of the system, according to the above theory, the Nyquist diagram is drawn for the closed-loop characteristic equation to check whether it surrounds the origin. First, the grid reactance is set to 0.5 pu (where pu represents the per-unit value) and the damping parameter D is set to 42, and the corresponding Nyquist diagram can be obtained, as shown in Figure 1. Figure 5 As shown. Figure 5 It can be seen that the Nyquist plot does not surround the origin at this time, so it is stable. Set the grid reactance to 0.05pu and adjust the damping parameter to 12, and you can get the corresponding Nyquist plot as follows Figure 6 As shown in the figure, it can be seen that the Nyquist diagram surrounds the origin at this time, so it is unstable. Figure 5-Figure 6 It can be seen that the damping parameters of the system and the strength of the power grid have a certain impact on the stability of the system, and the feasibility of the evaluation method is also verified.

[0128] The time domain simulation waveforms for the above two situations are as follows: Figure 7-Figure 8 As shown. Substitute the values ​​of system stability and instability into the single-machine infinite model to obtain the corresponding results. Figure 7-Figure 8It can be seen that when the parameters under stable conditions are used, the waveform converges and the system is stable; when the parameters under unstable conditions are used, the waveform does not converge and the system is unstable. The time domain simulation results are consistent with expectations, further verifying the correctness of the theory. Figure 7-Figure 8 In the equation, P represents the active power output by the converter.

[0129] In one embodiment, a computer device is provided. The computer device may be a server, and its internal structure diagram may be as follows: Figure 3 As shown. The computer device includes a processor, a memory and a network interface connected through a system bus. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store static information and dynamic information data. The network interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, the steps in the above method embodiment are implemented.

[0130] Those skilled in the art will understand that Figure 3 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present invention, and does not constitute a limitation on the computer device to which the solution of the present invention is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components.

[0131] The technical route of the present invention is summarized as follows Fig. 9 As shown, Fig. 9 Includes: small disturbance stability of grid-type control grid - impedance modeling of grid-type control grid - characteristic equation of grid-type control grid system - using Nyquist stability criterion;

[0132] When the Nyquist plot surrounds the origin, the grid is stable, otherwise the grid is unstable.

[0133] In addition, the present invention also provides a computer device, including a memory and a processor, wherein a computer program is stored in the memory, and the processor implements the steps in the above method embodiment when executing the computer program.

[0134] In addition, the present invention further provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps in the above method embodiment are implemented.

[0135] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided by the present invention can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory or optical memory, etc. Volatile memory can include random access memory (RAM) or external cache memory. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM).

[0136] The present invention is not limited to the structures which have been described above and shown in the drawings, and various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for evaluating a grid-connected system of a grid-connected converter, characterized in that: include: According to the dynamic equations of the internal and external loops of the grid-connected system, the dynamic equations of the synchronous control link and the dynamic control equations of the power grid, the equipment side impedance model and the grid side impedance model are established; Perform joint linear analysis on the device-side impedance model and the grid-side impedance model, and build a closed-loop characteristic equation of the grid-connected system based on the joint linear analysis results; The grid-connected system of the grid-connected converter is evaluated by using the closed-loop characteristic equation and combining the Nyquist stability criterion. The evaluation results are verified by time domain simulation.

2. The grid-connected system evaluation method of a grid-connected converter according to claim 1, characterized in that: The establishment of the device side impedance model and the grid side impedance model according to the dynamic equations of the inner and outer loops of the grid-connected system, the dynamic equations of the synchronous control link and the dynamic control equations of the power grid includes: The inner and outer loops of the grid-connected system are configured on the equipment side, and the synchronous control link is configured on the grid side; the inner loop dynamic equation of the grid-connected system, the outer loop dynamic equation of the grid-connected system and the filter inductor circuit equation are linearized and connected in parallel to obtain the equipment side impedance model; The dynamic equation of the virtual synchronous control link, the dynamic equation of the transmission line inductance, the component formula of the grid voltage under the virtual synchronous link and the analysis formula of the grid-type converter are linearized and connected in parallel to obtain the grid-side impedance model.

3. The grid-connected system evaluation method of a grid-connected converter according to claim 1, characterized in that: The joint linear analysis of the device side impedance model and the grid side impedance model is performed, and based on the joint linear analysis result, a closed-loop characteristic equation of the grid-connected system is constructed, including: After linearizing the device side impedance model and the grid side impedance model, the device side impedance model and the grid side impedance model are combined to obtain a comprehensive impedance model; The comprehensive impedance model is converted into an impedance matrix, and the determinant of the impedance matrix is ​​solved to obtain the closed-loop characteristic equation of the grid-connected system.

4. The grid-connected system evaluation method of a grid-connected converter according to claim 3, characterized in that: The impedance matrix is ​​a 2*2 impedance matrix.

5. The grid-connected system evaluation method of a grid-connected converter according to claim 1, characterized in that: The evaluation of the grid-connected system of the grid-connected converter using the closed-loop characteristic equation and combining the Nyquist stability criterion includes: According to the simulation experiments with different simulation parameters, the Nyquist diagram under stable conditions and the Nyquist diagram under unstable conditions are drawn for the closed-loop characteristic equation; According to the Nyquist diagram under stable conditions and the Nyquist diagram under unstable conditions, the stability of the grid-connected system of the grid-connected converter is evaluated accordingly.

6. The grid-connected system evaluation method of a grid-connected converter according to claim 5, characterized in that: The simulation parameters include: filter inductance parameters, grid-side inductance parameters, inertia parameters, damping parameters, current inner loop PI link parameters, voltage outer loop PI link parameters, current feedforward filter link parameters and voltage feedforward filter link parameters.

7. The grid-connected system evaluation method of a grid-connected converter according to claim 5, characterized in that: According to the simulation experiment with different simulation parameters, when the Nyquist diagram under stable conditions and the Nyquist diagram under unstable conditions are drawn for the closed-loop characteristic equation, it is determined whether the Nyquist diagram surrounds the origin. If so, the Nyquist diagram under unstable conditions is obtained, and if not, the Nyquist diagram under stable conditions is obtained.

8. The grid-connected system evaluation method of a grid-connected converter according to claim 5, characterized in that: The verification of the evaluation result by means of time domain simulation includes: According to different evaluation results of the grid-connected system of the grid-building converter, time domain simulation is performed respectively to obtain the corresponding time domain simulation waveform diagram; When the time domain simulation uses simulation parameters under stable conditions, the waveform in the obtained simulation waveform graph converges, and the time domain simulation uses simulation parameters under unstable conditions, the waveform in the obtained simulation waveform graph does not converge, then the evaluation result is correct.

9. A grid-connected converter system evaluation system, characterized in that: include: The impedance model building module is used to build the equipment side impedance model and the grid side impedance model according to the dynamic equations of the internal and external loops of the grid-connected system, the dynamic equations of the synchronous control link and the dynamic control equations of the power grid; A closed-loop characteristic equation construction module is used to perform joint linear analysis on the device-side impedance model and the grid-side impedance model, and to construct a closed-loop characteristic equation of the grid-connected system based on the joint linear analysis results; The stability evaluation and verification module is used to evaluate the grid-connected system of the grid-connected converter using the closed-loop characteristic equation in combination with the Nyquist stability criterion; and to verify the evaluation results by means of time domain simulation.

10. The grid-connected converter system evaluation system according to claim 9, characterized in that: The establishment of the device side impedance model and the grid side impedance model according to the dynamic equations of the inner and outer loops of the grid-connected system, the dynamic equations of the synchronous control link and the dynamic control equations of the power grid includes: The inner and outer loops of the grid-connected system are configured on the equipment side, and the synchronous control link is configured on the grid side; the inner loop dynamic equation of the grid-connected system, the outer loop dynamic equation of the grid-connected system and the filter inductor circuit equation are linearized and connected in parallel to obtain the equipment side impedance model; The dynamic equation of the virtual synchronous control link, the dynamic equation of the transmission line inductance, the component formula of the grid voltage under the virtual synchronous link and the analysis formula of the grid-type converter are linearized and connected in parallel to obtain the grid-side impedance model.

11. The grid-connected converter system evaluation system according to claim 9, characterized in that: The joint linear analysis of the device side impedance model and the grid side impedance model is performed, and based on the joint linear analysis result, a closed-loop characteristic equation of the grid-connected system is constructed, including: After linearizing the device side impedance model and the grid side impedance model, the device side impedance model and the grid side impedance model are combined to obtain a comprehensive impedance model; The comprehensive impedance model is converted into an impedance matrix, and the determinant of the impedance matrix is ​​solved to obtain the closed-loop characteristic equation of the grid-connected system; Among them, the impedance matrix is ​​a 2*2 impedance matrix.

12. The grid-connected converter system evaluation system according to claim 9, characterized in that: The evaluation of the grid-connected system of the grid-connected converter using the closed-loop characteristic equation and combining the Nyquist stability criterion includes: According to the simulation experiments with different simulation parameters, the Nyquist diagram under stable conditions and the Nyquist diagram under unstable conditions are drawn for the closed-loop characteristic equation; According to the Nyquist diagram under stable conditions and the Nyquist diagram under unstable conditions, the stability of the grid-connected system of the grid-connected converter is evaluated accordingly; Among them, the simulation parameters include: filter inductance parameters, grid-side inductance parameters, inertia parameters, damping parameters, current inner loop PI link parameters, voltage outer loop PI link parameters, current feedforward filter link parameters and voltage feedforward filter link parameters.

13. The grid-connected converter system evaluation system according to claim 12, characterized in that: According to the simulation experiment with different simulation parameters, when the Nyquist diagram under stable conditions and the Nyquist diagram under unstable conditions are drawn for the closed-loop characteristic equation, it is determined whether the Nyquist diagram surrounds the origin. If so, the Nyquist diagram under unstable conditions is obtained, and if not, the Nyquist diagram under stable conditions is obtained.

14. The grid-connected converter system evaluation system according to claim 12, characterized in that: The verification of the evaluation result by means of time domain simulation includes: According to different evaluation results of the grid-connected system of the grid-building converter, time domain simulation is performed respectively to obtain the corresponding time domain simulation waveform diagram; When the time domain simulation uses simulation parameters under stable conditions, the waveform in the obtained simulation waveform graph converges, and the time domain simulation uses simulation parameters under unstable conditions, the waveform in the obtained simulation waveform graph does not converge, then the evaluation result is correct.

15. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 8 are implemented.

16. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 8 are implemented.

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