Method, system and equipment for evaluating new energy grid-connected strength based on measured impedance and medium

Abstract

The invention provides a new energy grid connection strength evaluation method, system and device based on measured impedance and a medium, and relates to the field of power system stability analysis. The method comprises the following steps: acquiring three-phase electrical quantities of a plurality of grid-connected devices, and converting the three-phase electrical quantities into a dq coordinate system to obtain corresponding dq impedance; in a preset reference coordinate system, all the dq impedances are aligned; injecting current disturbance at a device grid-connected point, and establishing a full-system dynamic matrix of device and network dynamics; and calculating sensitivity based on the full-system dynamic matrix, and evaluating the equipment grid-connected strength according to the sensitivity. According to the method, the need for detailed parameters of the equipment is avoided, the dynamic model of the grid-connected equipment is obtained only through port measurement, the whole-system dynamic matrix describing the dynamic state of the system is established in combination with the network node admittance matrix, and the new energy grid-connected intensity ASC under the small-interference stability significance is calculated based on the matrix perturbation theory.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system stability analysis, and particularly relates to a new energy grid-connected strength evaluation method, system, device and medium based on measured impedance. BACKGROUND

[0002] New energy power generation is booming in China. A large number of new energy power generation represented by wind power and photovoltaic power is connected to the grid through power electronic converters, and the traditional power system dominated by synchronous machines is gradually changing into a new type of power system with high proportion of new energy and high proportion of power electronic devices.

[0003] With the large number of power electronic devices represented by converters connected to the grid, the dynamic characteristics of the power system have changed profoundly. The oscillation caused by power electronic devices and their control systems shows a wide frequency band characteristic, which is a complex problem involving the interaction of multiple types of devices, the mutual coupling of multiple time scales, and the widespread propagation of multiple oscillation modes. Under this background, whether new energy grid connection will affect system stability has become a problem that must be judged, that is, the grid connection strength of new energy is widely concerned, so it is of great significance to propose an index that can quickly and accurately describe the grid connection strength of new energy.

[0004] The short-circuit ratio is often used in traditional power systems to describe the voltage support strength of the device, which is defined as the ratio of the short-circuit capacity at the grid connection point to the rated capacity of the device. In order to consider the interaction between different devices when a large amount of new energy is connected to the grid, scholars further proposed the multiple renewable energy station short-circuit ratio (MRSCR), which takes into account the influence of impedance ratio in the analysis process, and the analysis result is more accurate. Since the short-circuit characteristics of converters are different from those of synchronous machines, the short-circuit ratio related index is difficult to evaluate the support of non-synchronous power sources, and the voltage stiffness index evaluates the grid connection strength based on the ratio of the voltage after the device is connected to the grid to the no-load voltage. However, the above indexes are all static indexes, and cannot reflect the effect of power electronic device control system, nor can they reflect the small signal stability of the system after disturbance. When the proportion of new energy continues to rise, the system may face small signal stability threat before reaching the static stability limit, so it is of great significance to study the grid connection strength of new energy under small signal stability.

[0005] Small signal stability of high penetration of new energy power system is usually analyzed by state space or impedance. State space judges stability by solving system eigenvalues, and participation factors reflect the relevance of different state variables to oscillation modes, but this method faces the problem of "dimension disaster" when units are added, and it needs to obtain the complete model of the system, while in practice it is usually difficult to obtain the detailed control parameters of the converter. Impedance method is based on the port impedance characteristics of grid-connected equipment and power grid, and uses Nyquist criterion to judge the stability of the system according to impedance ratio. Since the impedance of the equipment can be obtained by measurement, this method belongs to "black box" model, and is widely used in new energy power system.

[0006] When the research object is a multi-machine system, the impedance models of different devices must first be established in the same coordinate system. The impedance matrix after unifying the coordinate axes is fed back to the network node admittance matrix to obtain the full system dynamic matrix describing all dynamic actions. On this basis, the participation degree of device impedance / admittance to system modes can be derived by combining matrix perturbation theory. Some studies have analyzed the maximum change of grid-connected equipment admittance under the premise of small signal stability (i.e. eigenvalues do not cross the imaginary axis to the right half of the complex plane), and defined a new energy grid-connected strength index admittance stability capacity (ASC) for small signal stability. However, the calculation process of ASC is based on detailed modeling of grid-connected converters, which is a model-driven method and has no essential difference in modeling complexity from state space method. It should be noted that it is usually difficult to obtain detailed parameters of grid-connected equipment in practical applications. SUMMARY

[0007] The present application provides a new energy grid-connected strength evaluation method, system, device and medium based on measured impedance to solve the problems in the prior art.

[0008] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0009] Obtain three-phase electrical quantities of a plurality of grid-connected devices, and convert the three-phase electrical quantities into corresponding dq impedances in a dq coordinate system;

[0010] Align all dq impedances in a preset reference coordinate system;

[0011] Inject current disturbance at the device grid connection point to establish a full system dynamic matrix of device and network dynamics;

[0012] Calculate the sensitivity based on the full system dynamic matrix, and evaluate the device grid-connected strength according to the sensitivity.

[0013] In some embodiments, the step of converting the three-phase electrical quantities into corresponding dq impedances in a dq coordinate system comprises:

[0014] measuring the impedance in a phase-locked loop coordinate system to obtain a preliminary impedance;

[0015] establishing a compensation matrix for compensating for a deviation of an output angle of the phase-locked loop from a synchronous speed rotation angle of the power grid;

[0016] compensating for the preliminary impedance based on the compensation matrix to obtain dq impedance in a dq coordinate system.

[0017] In some embodiments, the step of aligning all the dq impedance in a preset reference coordinate system comprises:

[0018] specifying a device grid-connected point voltage phase as a reference to select a reference coordinate system;

[0019] calculating a fixed angle of a local synchronous speed coordinate system and the reference coordinate system;

[0020] aligning the local synchronous impedance to the reference coordinate system according to the fixed angle.

[0021] In some embodiments, the step of injecting a current disturbance at a device grid-connected point to establish a full-system dynamic matrix of device and network dynamics comprises:

[0022] injecting a current disturbance at a device grid-connected point to split between the grid-connected device and the network;

[0023] calculating a node admittance matrix to constrain the injected current disturbance and the bus voltage change of the network;

[0024] constraining the injected current disturbance and the bus voltage change of the grid-connected device by aligning the impedance to the reference coordinate system;

[0025] establishing a full-system dynamic matrix of device and network dynamics based on the current disturbance and the corresponding bus voltage response of the grid-connected device and the network.

[0026] In some embodiments, the step of calculating the sensitivity based on the full-system dynamic matrix comprises:

[0027] solving eigenvalues based on the full-system dynamic matrix to obtain system modes;

[0028] calculating a residue of an element of the full-system dynamic matrix at the eigenvalue;

[0029] establishing a sensitivity constraint relationship between device admittance changes and system mode eigenvalue changes to calculate the sensitivity of the system mode to the device admittance parameter.

[0030] In some embodiments, the grid-connected strength of the device is evaluated according to the sensitivity.

[0031] The correlation strength between the device admittance variation and the system modal eigenvalue shift is quantified by using Frobenius inner product, linear constraint equations are formed, and the absolute value of the real part of the eigenvalue is not out of bounds as a stability boundary condition.

[0032] The maximum allowed value of the admittance variation of a single device at different eigenvalues is calculated by the linear constraint equation and the stability boundary condition as a preliminary indicator.

[0033] The minimum value of the preliminary indicator of the selected grid-connected device at different eigenvalues is selected as the ASC indicator of the device.

[0034] In some embodiments, the ASC value is large, and the grid connection strength is high.

[0035] The ASC value is small, and the grid connection strength is low.

[0036] The present application proposes a new energy grid connection strength evaluation system based on measured impedance,

[0037] A conversion unit is configured to obtain three-phase electrical quantities of a plurality of grid-connected devices, and convert the three-phase electrical quantities into corresponding dq impedances in a dq coordinate system.

[0038] An alignment unit is configured to align all the dq impedances in a preset reference coordinate system.

[0039] A modeling unit is configured to inject current disturbance at a device grid connection point, and establish a full system dynamic matrix of device and network dynamics.

[0040] An evaluation unit is configured to calculate sensitivity based on the full system dynamic matrix, and evaluate the grid connection strength of the device according to the sensitivity.

[0041] The present application proposes a computer device, comprising:

[0042] At least one processor; and a memory storing a computer program executable on the processor, the processor executing the program to perform the steps of the reinsurance contract text historical data processing method.

[0043] The present application proposes a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to perform the steps of the reinsurance contract text historical data processing method.

[0044] Compared with the prior art, the present application has the following beneficial effects:

[0045] The application provides a new energy grid connection strength evaluation method based on measured impedance, which comprises the following steps: acquiring three-phase electrical quantities of multiple grid connection devices, converting the three-phase electrical quantities into corresponding dq impedances in a dq coordinate system, aligning all the dq impedances in a preset reference coordinate system, injecting current disturbance at a grid connection point of the device, establishing a full-system dynamic matrix of the device and network dynamics, calculating sensitivity based on the full-system dynamic matrix, and evaluating the grid connection strength of the device according to the sensitivity.

[0046] The application provides a new energy grid connection strength evaluation method based on impedance measurement. The method avoids the need for detailed parameters of the device, and only obtains a dynamic model of the grid connection device through port measurement, combines a network node admittance matrix to establish a full-system dynamic matrix for describing system dynamics, and calculates the new energy grid connection strength ASC in the sense of small disturbance stability based on the matrix perturbation theory. The research result has strong application value for the grid connection strength analysis of the device in the current high-proportion new energy power system. BRIEF DESCRIPTION OF DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other embodiments can also be obtained from these drawings without creative labor.

[0048] Figure 1 A flow chart of the new energy grid connection strength evaluation method based on measured impedance provided by the present application is provided.

[0049] Figure 2 A module diagram of the new energy grid connection strength evaluation system based on measured impedance provided by the present application is provided.

[0050] Figure 3 A structural schematic diagram of an embodiment of the computer device provided by the present application is provided.

[0051] Figure 4 A structural schematic diagram of an embodiment of the computer readable storage medium provided by the present application is provided.

[0052] Figure 5 A phase-locked loop block diagram of the new energy grid connection strength evaluation method based on measured impedance provided by the present application is provided.

[0053] Figure 6 An impedance measurement schematic block diagram of the new energy grid connection strength evaluation method based on measured impedance provided by the present application is provided.

[0054] Figure 7 A system impedance modeling block diagram of the new energy grid connection strength evaluation method based on measured impedance provided by the present application is provided.

[0055] Figure 8 A single grid type converter grid connected system diagram of the new energy grid strength evaluation method based on measured impedance provided by the application;

[0056] Figure 9 A grid type converter dq impedance measurement and fitting result diagram of the new energy grid strength evaluation method based on measured impedance provided by the application;

[0057] Figure 10 A system disturbed angular velocity time domain waveform diagram of the new energy grid strength evaluation method based on measured impedance provided by the application, with the phase-locked loop proportional coefficient being 1.5;

[0058] Figure 11 A system disturbed angular velocity time domain waveform diagram of the new energy grid strength evaluation method based on measured impedance provided by the application, with the phase-locked loop proportional coefficient being 3;

[0059] Figure 12 A frequency time domain waveform diagram of the new energy grid strength evaluation method based on measured impedance provided by the application, with the A field station disturbed;

[0060] Figure 13 A frequency time domain waveform diagram of the new energy grid strength evaluation method based on measured impedance provided by the application, with the B field station disturbed;

[0061] Figure 14 A frequency time domain waveform diagram of the new energy grid strength evaluation method based on measured impedance provided by the application, with the C field station disturbed. DETAILED DESCRIPTION

[0062] The application will be further described below with reference to the drawings. The following examples are only used to more clearly illustrate the technical solutions of the application, and cannot be used to limit the protection scope of the application. It should be pointed out that the following detailed description is exemplary, and is intended to provide further description of the present application.

[0063] As Figure 1 shown, the application provides a new energy grid strength evaluation method based on measured impedance, comprising:

[0064] Obtaining three-phase electrical quantities of multiple grid-connected devices, converting the three-phase electrical quantities into a dq coordinate system to obtain corresponding dq impedances;

[0065] Aligning all the dq impedances in a preset reference coordinate system;

[0066] Injecting current disturbance at the device grid connection point to establish a full system dynamic matrix of device and network dynamics;

[0067] Calculate sensitivity based on the full system dynamic matrix, and evaluate grid-connection strength of the equipment according to the sensitivity.

[0068] The application provides a new energy grid-connection strength evaluation method based on measured impedance, which comprises the following steps: obtaining a converter impedance model by using dq impedance sweep, aligning different equipment impedances to the same coordinate system based on dynamic embedding, establishing a full system dynamic matrix in combination with a network node admittance matrix, calculating the maximum admittance variation of grid-connection equipment under the premise of small disturbance stability, and evaluating the new energy grid-connection strength. The steps are as follows, and the following steps are sequentially performed: Step 1, measuring the port impedance characteristics of the grid-connection equipment. Step 2, aligning the coordinate systems of different equipment based on dynamic embedding. Step 3, establishing a full system dynamic matrix. Step 4, evaluating the grid-connection strength of the equipment based on the full system dynamic matrix.

[0069] Three-phase electrical quantities contain key information such as voltage and current of the equipment in grid-connection operation, which are core data for analyzing the dynamic characteristics and grid-connection strength of the equipment. However, the three-phase electrical quantities are in a three-phase stationary coordinate system, and their analysis is relatively complex, and it is difficult to directly reflect the dynamic characteristics of the equipment. Therefore, it is particularly necessary to convert these three-phase electrical quantities into the dq coordinate system. The dq coordinate system is a rotating coordinate system, and through a specific coordinate transformation, the electrical quantities in the three-phase stationary coordinate system can be converted into direct current components in the dq coordinate system, thereby simplifying the analysis process and more intuitively reflecting the dynamic characteristics of the equipment. In the conversion process, corresponding dq impedances can be obtained, which can accurately describe the electrical characteristics of the equipment in the dq coordinate system. After obtaining the dq impedances of each equipment, all the dq impedances need to be aligned in a preset reference coordinate system. Since the dq impedances of different equipment may be obtained in their respective local coordinate systems, direct analysis may lead to inaccurate results. By aligning in the preset reference coordinate system, the influence of the difference in coordinate systems can be eliminated, so that the dq impedances of all equipment are in the same analysis framework. Sensitivity reflects the sensitivity of system state variables to parameter changes, and according to the calculated sensitivity, the grid-connection strength of the equipment can be accurately evaluated.

[0070] The application only needs to obtain the impedance characteristics of the grid-connection equipment through port measurement, and after combining with the network node admittance matrix, the full dynamics of the system can be described, and the maximum variation of the admittance of the grid-connection equipment under the premise of small disturbance stability is further calculated, that is, the new energy grid-connection strength index ASC is calculated. Compared with the traditional model-driven calculation index method, the present method avoids the complex theoretical model derivation process, accelerates the analysis speed while ensuring the accuracy of the evaluation results.

[0071] As Figure 1 , Figure 5 and Figure 6As shown, in some embodiments, the step of converting the three-phase electrical quantities into the dq coordinate system to obtain the corresponding dq impedance includes:

[0072] measuring the impedance in the phase-locked loop coordinate system to obtain a preliminary impedance;

[0073] establishing a compensation matrix for compensating for the deviation of the phase-locked loop output angle from the synchronous speed rotation angle;

[0074] compensating for the preliminary impedance based on the compensation matrix to obtain the dq impedance in the dq coordinate system.

[0075] When measuring the dq impedance model of a grid-connected device, the three-phase electrical quantities need to be converted to the dq coordinate system through Park transformation. The Park (inverse) transformation usually uses a phase-locked loop (PLL) to measure the grid point phase information, and the phase-locked loop control block diagram is as shown in Figure 5 . Among them, v a , v b , v c are the a, b, c phase voltages of the grid point, v d and v q are the d-axis and q-axis voltages, and s is the Laplace operator.

[0076] The phase-locked loop itself has dynamics, so when measuring, if the measured dq axis electrical quantities are directly used to calculate the impedance, the impedance value in the phase-locked loop coordinate system is obtained. The phase-locked loop coordinate system can be understood as a coordinate system that rotates at synchronous speed without disturbance and swings around synchronous speed when disturbance occurs, that is, the phase-locked loop coordinate system itself has dynamics, so it is necessary to analyze the influence of the dynamics of the measured phase-locked loop on the impedance calculation. It should be noted that the parameters of the PLL used when measuring electrical quantities can be different from the parameters of the PLL in the control system. Figure 5 The transfer function of the PLL shown is:

[0077] Δθ(s)=H PLL (s)V q (s) (1)

[0078]

[0079] Among them, and are the proportional and integral coefficients of the phase-locked loop.

[0080] Assuming that there is an angle difference between the PLL output angle and the angle of synchronous speed rotation at steady state, the conversion relationship of the electrical quantities in the two coordinate systems is:

[0081]

[0082] Among them, xdq p = [x d p x q p ] T is the dq electrical quantity in the phase-locked loop output angle coordinate system, x dq s = [x d s x q s ] T is the dq electrical quantity in the synchronous speed rotation angle. Taking the small signal and converting to the complex frequency domain, we have:

[0083]

[0084] where subscript "0" represents the steady-state value, and for the convenience of writing, the variables in the complex frequency domain are omitted below except for the steady-state value. The simultaneous equations (4) (1) can be obtained by the transformation of the electrical quantity in different coordinate systems, which satisfies:

[0085]

[0086] Since the grid-connected device dq impedance is a 2*2 matrix, two sets of linearly independent voltage and current signals are required for solving, that is:

[0087]

[0088] Therefore, the impedance transformation formula in different coordinate systems can be obtained by simultaneously solving equations (5) (6):

[0089]

[0090] When measuring impedance, based on the phase-locked loop output angle related voltage and current, the device impedance in the phase-locked loop output angle coordinate system is directly obtained from equation (6), and then the phase-locked loop dynamics is compensated according to equation (7), so that the device impedance frequency response in the synchronous speed coordinate system can be obtained. Unlike the traditional dq impedance scan which limits the phase-locked loop bandwidth, this method allows higher phase-locked loop bandwidth, is more convenient to apply, and can summarize the impedance measurement links as shown in Figure 6 By calculating the device impedance based on the phase-locked loop output angle related voltage and current, and compensating the phase-locked loop dynamics, the device impedance frequency response in the synchronous speed coordinate system can be accurately obtained. The influence of the phase-locked loop dynamics on the measurement results is effectively considered, the potential error is eliminated by compensation, and the accuracy and reliability of the measurement results are ensured.

[0091] As a key component for tracking grid voltage phase in grid-connected equipment, the output angle information of phase-locked loop provides a reference for subsequent coordinate transformation and control. In the measurement process, a disturbance signal with a specific frequency and amplitude is injected into the grid-connected equipment, and the preliminary impedance can be obtained in the phase-locked loop coordinate system by monitoring the response of the port voltage and current of the equipment. When the phase-locked loop tracks the grid phase, there may be a deviation between the output angle of the phase-locked loop and the synchronous speed rotating angle of the grid, which will introduce measurement error and cause the preliminary impedance to be unable to accurately represent the characteristics of the equipment in the dq coordinate system. In order to eliminate this deviation, a compensation matrix is needed to compensate for the deviation between the output angle of the phase-locked loop and the synchronous speed rotating angle of the grid. The compensation matrix is essentially a linear transformation matrix that can convert the electrical quantities in the phase-locked loop coordinate system to a position closer to the ideal dq coordinate system. Based on the established compensation matrix, the preliminary impedance is compensated to obtain the dq impedance in the dq coordinate system. The preliminary impedance data and the compensation matrix are subjected to corresponding matrix operations, and the influence of the deviation of the output angle of the phase-locked loop is eliminated through linear transformation. The compensated dq impedance can more accurately reflect the electrical characteristics of the equipment in the ideal synchronous rotating coordinate system.

[0092] As shown in Figure 1 In some embodiments, the step of aligning all the dq impedances in the preset reference coordinate system comprises:

[0093] selecting a reference coordinate system with the voltage phase of the equipment grid connection point as the reference; calculating the fixed angle between the local synchronous speed coordinate system and the reference coordinate system;

[0094] aligning the local synchronous impedance to the reference coordinate system according to the fixed angle.

[0095] In multi-machine system stability analysis, the voltage phase angles of different units are different, and the impedance of the equipment needs to be transformed to the same coordinate system. Taking the grid-connected converter as an example, due to the dynamic output angle of the phase-locked loop, the phase-locked loop output angle coordinate system is a local dynamic coordinate system, and the impedance can be transformed to the local synchronous speed coordinate system through the transformation formula (7). When the research object is a multi-machine system, the impedance of each equipment is established in the synchronous speed rotating coordinate system with the steady-state phase of its own grid connection point as the initial phase, so a reference coordinate system needs to be specified to transform the impedance of all equipment to this coordinate system. The mapping of the local synchronous speed coordinate system to the reference coordinate system depends on the fixed angle γ between the coordinate systems, and the electrical quantity mapping relationship is:

[0096]

[0097] The subscript "DQ" represents the reference coordinate system, so the impedance transformation relationship is:

[0098]

[0099] It is emphasized that the physical meaning of the fixed angle γ is the phase difference of the different device grid-connected points in steady state, which can be obtained by power flow calculation. The above results show that the disturbance electrical quantity of the grid-connected point measured by the phase-locked loop can be used to obtain the impedance in the local dynamic coordinate system, and then the impedance is unified to the reference coordinate system by using the above transformation process. At this time, the impedance of all devices can be written in a matrix, that is:

[0100] Z s = diag(Z DQ1 …Z DQi …Z DQn ) (10)

[0101] Where the subscript "DQ" represents that all grid-connected devices are in the reference coordinate system, and the device impedance matrix Z s characterizes the constraint relationship between the device port voltage and the current.

[0102] Selecting the reference coordinate system based on the voltage phase of the specified device grid-connected point can ensure that the analysis and comparison of the impedance of all devices are carried out in a unified framework closely related to the actual operation state of the power grid. This makes the impedance data measured at different times and by different devices comparable and consistent, avoiding analysis errors and confusion caused by different reference standards. Since the local synchronous speed coordinate system is determined based on the characteristics of the device itself, and the reference coordinate system is based on the voltage phase of the specified device grid-connected point, there is inevitably a certain angle difference between the two. Accurate calculation of this fixed angle can accurately quantify this difference and provide accurate parameters for subsequent coordinate transformation. The accuracy of this step directly affects the alignment effect of the impedance. Only by accurately calculating the fixed angle can additional errors be avoided in the alignment process, and the aligned impedance data can truly reflect the actual characteristics of the device in the reference coordinate system.

[0103] According to the fixed angle, the local synchronous impedance is aligned to the reference coordinate system, and the impedance data of all devices is unified to the reference coordinate system based on the voltage phase of the grid, so that the impedance characteristics of different devices can be comprehensively analyzed and compared under the same standard. Based on the aligned impedance data, the possible weak links in the system can be more accurately judged, thereby improving the overall stability and reliability of the power system and ensuring the safety and quality of power supply.

[0104] As shown in FIGS. Figure 1 and Figure 7 , in some embodiments, the step of injecting a current disturbance at a device grid-connected point to establish a full-system dynamic matrix of device and network dynamics includes:

[0105] Dividing the current disturbance injected at the device grid-connected point between the grid-connected device and the network;

[0106] The admittance matrix of the nodes, the current disturbance injected into the network is constrained with the bus voltage variation;

[0107] The current disturbance injected into the grid-connected device and the bus voltage variation are constrained by aligning to the impedance in the reference coordinate system;

[0108] The full-system dynamic matrix of the device and the network dynamics is established based on the current disturbance and the corresponding bus voltage response of the grid-connected device and the network.

[0109] After step two, the system can be injected as shown in Figure 7 The current disturbance at the grid connection point as input, and the bus voltage variation of the network as output, that is:

[0110] ΔV = [ΔV1 … ΔV i … ΔV n ] T

[0111] ΔI = [ΔI1 … △I i … △I n ] T (11)

[0112] In the formula, ΔV i is the voltage variation value of bus i, which has two components, namely ΔV i = [ΔV id , ΔV iq ] T The superscript "T" represents the matrix transpose, and ΔI i is the current disturbance value of the device i, which also has two components, namely ΔI i = [ΔI id , ΔI iq ] T , Figure 7 Y b in the formula is the admittance matrix of the network nodes, and Z i is the dq impedance of the device i obtained through steps 1 and 2.

[0113] When the current disturbance is injected at the grid connection point of the device, there is a shunt between the grid-connected device and the network, the current disturbance injected into the network is constrained with the bus voltage variation, and the current disturbance injected into the grid-connected device is constrained with the bus voltage variation by the device impedance matrix formula (9), so the full-system dynamic matrix describing the device and the network dynamics can be obtained:

[0114] ΔV = (E + Z s Y b ) -1 Z s ΔI = ZΔI (12)

[0115] In the formula, E is the identity matrix and Z is the dynamic matrix of the entire system. Equation (12) establishes the dynamic matrix of the entire system, and the grid connection strength of the equipment can be calculated based on this matrix.

[0116] Injecting current disturbances at the grid connection point causes current shunting between the grid-connected equipment and the network. This shunting is not a simple current distribution but reflects a complex dynamic interaction process within the equipment and network. Current disturbances can excite potential dynamic modes in the system, comprehensively capturing the dynamic response characteristics of the grid-connected equipment and network under external stimuli. The node admittance matrix is ​​calculated, and constraints are imposed on the injected current disturbances and bus voltage changes. The node admittance matrix describes the electrical connections and admittance parameters between nodes in the power system. By constraining the injected current disturbances and bus voltage changes, the calculation of the node admittance matrix accurately reflects the electrical characteristics of the system under current operating conditions. Accurately understanding the propagation path of current and the distribution of voltage in the system provides accurate electrical parameters for establishing the dynamic matrix of the entire system, thereby improving the accuracy of the overall system model.

[0117] By aligning the impedance to a reference coordinate system to constrain the current disturbances injected into grid-connected equipment and the changes in bus voltage, a unified analysis of the dynamic characteristics of both equipment and the network is achieved. In power systems, grid-connected equipment and the network often have different dynamic characteristics and coordinate system representations. By aligning the impedance to a reference coordinate system, the differences between different coordinate systems are eliminated, allowing the dynamic characteristics of equipment and the network to be analyzed and compared within the same framework. Accurately assessing the impact of equipment on network dynamic characteristics and the constraints imposed by the network on equipment operation provides strong support for coordinated control and optimized operation of the system. By injecting current disturbances and analyzing the bus voltage response, the voltage changes of the system under different operating conditions can be monitored in real time, facilitating timely and effective measures to ensure the safe and stable operation of the system.

[0118] A full-system dynamic matrix is ​​established based on current disturbances and the corresponding bus voltage responses of grid-connected equipment and networks. This full-system dynamic matrix comprehensively considers all dynamic characteristics of the equipment and network, accurately describing the system's dynamic behavior under disturbances. Analyzing the matrix's eigenvalues ​​can determine system stability; calculating sensitivity reveals the impact of system parameter changes on operating status; and designing control strategies based on the matrix enables optimized system operation and rapid response, contributing to improved power system efficiency and reliability.

[0119] like Figure 1 As shown, in some embodiments, the sensitivity is calculated based on the dynamic matrix of the entire system, and the system modes are obtained by solving the eigenvalues ​​based on the dynamic matrix of the entire system.

[0120] The residues of the elements of the full system dynamic matrix at the eigenvalues are calculated; a sensitivity constraint relationship between the changes in the device admittance and the changes in the eigenvalues of the system modal is established, and the sensitivity of the system modal to the device admittance is calculated.

[0121] The sensitivity relationship between the system modal and the device admittance is:

[0122]

[0123] where λ is the modal to be studied, y is the device admittance, Res λ Z ii is the residue of the i-th 2*2 element of the full system dynamic matrix shown in equation (12).

[0124] The eigenvalues of the full system dynamic matrix are decomposed to obtain the system modal. The system modal contains key information of the dynamic behavior of the system, such as the oscillation frequency and the damping ratio. Through eigenvalue solving, various oscillation modes existing in the system can be accurately identified, and the dominant modal and the non-dominant modal can be distinguished.

[0125] The residues of the elements of the full system dynamic matrix at the eigenvalues are calculated. In an actual power system, the operating state, parameter setting and external environment of the device may cause the device admittance to change, thereby affecting the system stability, and equation (13) shows that the relationship between the modal and the admittance is related to the residue.

[0126] The sensitivity constraint relationship between the changes in the device admittance and the changes in the eigenvalues of the system modal is established, and the sensitivity of the system modal to the device admittance is calculated. The sensitivity reflects the sensitivity of the eigenvalues of the system modal to the changes in the device admittance parameters, and through the calculation of the sensitivity, it can be determined which changes in the device admittance have a greater impact on the system modal and which changes have a smaller impact.

[0127] As Figure 1 shown, in some embodiments, the strength of the device grid-connection is evaluated according to the sensitivity.

[0128] The Frobenius inner product is used to quantify the correlation strength between the changes in the device admittance and the eigenvalue shift of the system modal, linear constraint equations are formed, and the non-boundary condition of the absolute value of the real part of the eigenvalue is taken as the stability boundary condition;

[0129] The maximum allowable value of the admittance change of a single device at different eigenvalues is calculated through the linear constraint equation and the stability boundary condition, serving as a preliminary index;

[0130] The minimum value of the preliminary index calculated at different eigenvalues of the grid-connection device is selected as the ASC index of the device. Therefore, when the device admittance changes, the eigenvalue change is constrained by equation (13), and the small-signal sensitivity relationship is:

[0131]

[0132] where <, > denotes Frobenius inner product, and the superscript * is the conjugate transpose of a matrix. The simultaneous equations (13) and (14) are:

[0133]

[0134] where, ΔY sj (λ i ) is the change of the admittance of the converter j at the i-th eigenvalue, and the quantitative relationship between the change of the device admittance and the change of the eigenvalue is established under the condition of small signal stability. Considering the conservativeness, to ensure the small signal stability of the system, the eigenvalue cannot cross the imaginary axis, and therefore the maximum change is the absolute value of the real part, i.e.:

[0135] |Δλ i | max = |σ i | (16)

[0136] After applying the Cauchy inequality to equation (15) and substituting equation (16), we have:

[0137]

[0138] Equation (17) determines the maximum change of the admittance of the j-th device under the condition of small signal stability of the i-th mode. Since the actual system has many modes, the numerical value of equation (17) is different for each mode, and therefore the minimum value of the numerical value of equation (17) corresponding to different modes can be used to represent the grid-connection strength of the new energy station, i.e. the index ASC describing the grid-connection strength of the new energy station is obtained:

[0139]

[0140] The Frobenius inner product (matrix inner product) is used to quantify the correlation between the change of the device admittance and the shift of the eigenvalue of the system mode. The change of the device admittance will cause the change of the eigenvalue of the system mode, and then affect the stability and dynamic performance of the system. The Frobenius inner product can accurately measure the similarity and correlation between the change vector of the device admittance and the shift vector of the eigenvalue of the system mode from the perspective of vector space.

[0141] The linear constraint equation and the stability boundary condition of absolute value of eigenvalue real part are formed to establish a clear mathematical framework for stability analysis of the system. The linear constraint equation expresses the relationship between the device admittance change and the modal eigenvalue shift in a simple mathematical form, so that the complex system dynamic problem can be solved and analyzed by mathematical methods. When the real part of the eigenvalue is positive, the system will have unstable oscillation. Through this boundary condition, the parameter range of the stable operation of the system can be clearly defined, providing a safety criterion for the grid connection and operation of the device.

[0142] The maximum allowed value of the admittance change of a single device at different eigenvalues is calculated by the linear constraint equation and the stability boundary condition, and is used as a preliminary index to provide a specific quantitative index for evaluating the influence of a single device on the stability of the system. The preliminary index reflects the maximum amplitude of the change of the device admittance that can be changed under the premise of ensuring the stability of the corresponding mode, i.e., the device parameters can be adjusted within a certain range without affecting the stability of the corresponding mode.

[0143] The minimum value of the sensitivity of the device at different eigenvalues is selected as the ASC index of the device, which can comprehensively evaluate the grid connection strength of the system as a whole. The ASC index considers the influence of all grid-connected devices on the stability of the system, and reflects the weakest link of the system when facing the change of the device admittance.

[0144] As shown in Figure 1 , in some embodiments, the ASC value is large, and the grid connection strength is high;

[0145] the ASC value is small, and the grid connection strength is low.

[0146] If the ASC value is large, the device admittance of the system can change greatly under the premise of small disturbance stability, i.e., the grid connection strength is high; if the ASC value is small, the modal sensitivity to the change of the unit is high, and the eigenvalue appears positive real part when the unit admittance changes slightly, and the grid connection strength is low.

[0147] When the ASC index is small, there is a device in the system that is very sensitive to the change of the admittance, and the grid connection strength of the whole system is weak, which is easily affected by the change of the device parameters and becomes unstable; on the contrary, when the ASC index is large, the system has strong anti-interference ability and can accommodate a certain degree of change of the device admittance without losing stability. Through the ASC index, the grid connection strength of different systems or the same system under different operating modes can be compared intuitively. When the power system is upgraded or new devices are connected to the grid, the stability of the system after upgrading or connecting to the grid can be evaluated by calculating the ASC index, and measures can be taken in advance to improve the grid connection strength of the system and ensure the safe and reliable operation of the power system.

[0148] As shown inFigure 2 As shown, this invention proposes a new energy grid connection strength assessment system based on measured impedance.

[0149] The conversion unit 100 is configured to acquire the three-phase electrical quantities of multiple grid-connected devices, convert the three-phase electrical quantities to the dq coordinate system, and obtain the corresponding dq impedance.

[0150] Alignment unit 200 is configured to align all dq impedances in a preset reference coordinate system;

[0151] Modeling unit 300 is configured to inject current disturbances at the grid connection point of the equipment to establish a full-system dynamic matrix of equipment and network dynamics;

[0152] Evaluation unit 400 is configured to calculate sensitivity based on the dynamic matrix of the entire system and evaluate the grid connection strength of the equipment based on the sensitivity.

[0153] This invention avoids the need for detailed equipment parameters, obtaining a dynamic model of the grid-connected equipment only through port measurements. It establishes a full-system dynamic matrix describing the system dynamics by combining the network node admittance matrix, and calculates the new energy grid connection intensity ASC under the small disturbance stability meaning based on matrix perturbation theory. The research results have strong application value for the analysis of equipment grid connection intensity in current high-proportion new energy power systems.

[0154] by Figure 8 The single-connect grid-connected converter system shown is Example 1, used to verify the accuracy of the proposed method for assessing the grid connection strength of a single unit. The impedance measurement results of the grid-connected converter are as follows: Figure 9 As shown in Table 1, the grid connection strength ASC calculated based on the measured impedance and steps three and four is as follows. The ASC calculation result is 0.25 when the phase-locked loop proportional coefficient is 1.5, and the ASC calculation result is 0.1206 when the phase-locked loop proportional coefficient is 3. This indicates that increasing the phase-locked loop proportional coefficient reduces the grid connection strength of the grid-connected converter and worsens the system stability. Figure 10 The time-domain simulation waveforms of the electrical quantities of the system under disturbance before and after increasing the phase-locked loop (PLL) proportional coefficient are presented. It can be seen that after increasing the PLL proportional coefficient, the oscillation convergence time of the system under disturbance is longer and the stability margin is lower. That is, increasing the PLL proportional coefficient reduces the grid connection strength of the grid-connected converter, which verifies the accuracy of the proposed method in a single-machine system.

[0155] by Figure 11The certain regional wind power collection system shown is taken as an embodiment 2 to verify the accuracy of the method for the grid-connection strength evaluation of the multi-machine system. There are 14 wind power plants in the region, each of which is simulated by using a single-machine aggregation equivalent model. Since the control strategy is relatively complex, it is difficult to derive the impedance model by theory, and at this time, the analysis method based on the measured impedance greatly reduces the analysis difficulty. The grid-connection strength of different plants in the region is calculated according to the method shown in Table 2.

[0156] As can be seen from Table 2, the ASC calculation result of the A plant is the smallest, indicating that the grid-connection strength of the plant is the lowest. The third column and the seventh column of Table 2 are the total harmonic distortion (THD) of the grid-connection point after the grid-connection point is disturbed. The harmonic distortion rate of the A plant after the disturbance is the highest, which is 1.04%, indicating that the harmonic content of the electrical quantity after the disturbance is the highest, that is, the grid-connection strength is the lowest, which is consistent with the ASC analysis result. The ASC of the B plant is the highest, which is 0.6473. The THD of the electrical quantity of the grid-connection point of the plant after the disturbance is the lowest, which is 0.07%, which is consistent with the ASC analysis result, proving the accuracy of the ASC in the grid-connection strength analysis of the multi-plant system. The MRSCR calculation result shows that the grid-connection strength of the C plant is the lowest, but the harmonic distortion rate of the grid-connection point of the plant after the disturbance is 0.14%, which is much smaller than that of the A plant, indicating the superiority of the grid-connection strength index adopted. The frequency time-domain waveforms of the A, B and C plants after the disturbance are shown in Figure 12 、 Figure 13 and Figure 14 The time-domain waveforms also show that the grid-connection strength of the A plant is relatively low, while the grid-connection strengths of the B and C plants are relatively high, further proving the accuracy of the method.

[0157] Table 1 Grid-connection strength calculation result of the single-machine grid-connected converter grid-connection system

[0158]

[0159] Table 2 Grid-connection strength calculation result of different plants in a region

[0160]

[0161] Finally, it should be noted that the above content is only used to illustrate the technical solutions of the present application, and is not a limitation on the protection scope of the present application. Simple modifications or equivalent replacements of the technical solutions of the present application made by those skilled in the art do not deviate from the essence and scope of the technical solutions of the present application.

Claims

1. A method for assessing the grid connection intensity of new energy sources based on measured impedance, characterized in that, include: Obtain the three-phase electrical quantities of multiple grid-connected devices, and convert all three-phase electrical quantities to the dq coordinate system to obtain the corresponding dq impedance; Align all dq impedances in the preset reference coordinate system; Inject current disturbances at the grid connection point of the equipment to establish a dynamic matrix of the entire system for both equipment and network dynamics; The sensitivity is calculated based on the dynamic matrix of the entire system, and the grid connection strength of the equipment is evaluated based on the sensitivity.

2. The method for assessing the grid connection intensity of new energy sources based on measured impedance as described in claim 1, characterized in that, The steps for converting the three-phase electrical quantities to the dq coordinate system to obtain the corresponding dq impedance include: The impedance is measured in the phase-locked loop coordinate system to obtain the preliminary impedance. Establish a compensation matrix to compensate for the deviation between the phase-locked loop output angle and the grid synchronous rotation angle; The initial impedance is compensated based on the compensation matrix to obtain the dq impedance in the dq coordinate system.

3. The method for assessing the grid connection intensity of new energy sources based on measured impedance as described in claim 1, characterized in that, The step of aligning all dq impedances in a preset reference coordinate system includes: Select a reference coordinate system based on the voltage phase at the grid connection point of a specified device; Calculate the fixed angles between the local synchronous velocity coordinate system and the reference coordinate system; The local synchronous impedance is aligned to the reference coordinate system according to the fixed angle.

4. The method for assessing the grid connection intensity of new energy sources based on measured impedance as described in claim 1, characterized in that, The steps of injecting current disturbances at the grid connection point of the equipment to establish a dynamic matrix of the entire system for both the equipment and the network include: Inject current disturbances at the grid connection point of the equipment to divert current between the grid-connected equipment and the network; Calculate the node admittance matrix and constrain the current disturbance and bus voltage change in the injected network; Current disturbances and bus voltage changes are injected into grid-connected equipment by impedance constraints aligned to a reference coordinate system. A dynamic matrix of the entire system is established based on the current disturbance and the bus voltage response of the grid-connected equipment and network.

5. The method for assessing the grid connection intensity of new energy sources based on measured impedance as described in claim 1, characterized in that, The steps for calculating sensitivity based on the dynamic matrix of the entire system include: Based on the dynamic matrix of the entire system, the eigenvalues ​​are solved to obtain the system modes; Calculate the residues of the dynamic matrix elements of the entire system at the eigenvalues; establish the sensitivity constraint relationship between the change in equipment admittance and the change in the eigenvalues ​​of the system modes, and calculate the sensitivity of the system modes to the equipment admittance parameters.

6. The method for assessing the grid connection intensity of new energy sources based on measured impedance as described in claim 1, characterized in that, The grid connection strength of the device is evaluated based on the sensitivity. By utilizing the correlation strength between the Frobenius inner product quantization device admittance change and the system modal eigenvalue shift, a linear constraint equation is formed, and the absolute value of the real part of the eigenvalue does not exceed the boundary is used as the stability boundary condition. The maximum allowable value of the admittance change of a single device under different eigenvalues ​​is calculated by linear constraint equations and stability boundary conditions, and is used as a preliminary indicator. The minimum value of the preliminary index calculated under different characteristic values ​​for the grid-connected equipment is selected as the ASC index of the equipment.

7. The method for assessing the grid connection intensity of new energy sources based on measured impedance as described in claim 6, characterized in that, A higher ASC value indicates a higher grid connection strength; A lower ASC value indicates a lower grid connection strength.

8. A new energy grid connection strength assessment system based on measured impedance, characterized in that, The conversion unit is configured to acquire the three-phase electrical quantities of multiple grid-connected devices, convert the three-phase electrical quantities to the dq coordinate system, and obtain the corresponding dq impedance. Alignment unit, configured to align all dq impedances in a preset reference coordinate system; The modeling unit is configured to inject current disturbances at the grid connection point of the equipment to establish a full-system dynamic matrix of equipment and network dynamics. The evaluation unit is configured to calculate sensitivity based on the dynamic matrix of the entire system and evaluate the grid connection strength of the equipment based on the sensitivity.

9. Computer equipment, including: At least one processor; And a memory storing a computer program executable on the processor, characterized in that, when the processor executes the program, it performs the steps of the method for processing historical data of reinsurance contract text as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it performs the steps of the method for processing historical data of reinsurance contract text as described in any one of claims 1 to 7.

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