Online stability evaluation and regulation method and system for hybrid system based on improved short circuit ratio

Abstract

The application relates to the technical field of power system stability control, in particular to a hybrid system online stability evaluation and regulation method and system based on an improved short-circuit ratio, which comprises the following steps: constructing an equivalent model of a hybrid system with a grid-connected type and a grid-constructing type, calculating an improved short-circuit ratio of a new energy multi-station to quantify the grid strength of each grid-connected point based on the voltage source characteristics of the grid-constructing type equipment, constructing a characteristic polynomial based on an impedance matrix, quickly searching for a dominant characteristic root by using a circular ring theorem, avoiding high-dimensional calculation, and obtaining a critical short-circuit ratio. If the real-time short-circuit ratio is lower than the critical value, the instability risk is determined, and the regulation strategy of increasing the capacity of the grid-constructing type equipment or adjusting the grid-connected point is triggered. The method realizes online quantitative evaluation and closed-loop regulation of small disturbance stability of the hybrid system with the grid-connected type and the grid-constructing type by combining the improved short-circuit ratio and the circular ring theorem.

Description

Technical Field

[0001] This application relates to the field of power system stability control technology, specifically to a method and system for online stability assessment and control of hybrid systems based on improved short-circuit ratio. Background Technology

[0002] As the proportion of renewable energy continues to rise, grid-following (GFL) equipment is prone to broadband oscillations under weak grid conditions, while grid-forming (GFM) equipment can provide active support. How to assess the grid strength and small-signal stability of hybrid GFL / GFM systems is an important issue facing new power systems.

[0003] Existing short-circuit ratio (SCR) metrics are primarily applicable to single-infeed systems, failing to account for multi-device coupling. While multi-infeed short-circuit ratio (MISCR) reflects voltage support strength, it insufficiently considers small-disturbance stability and lacks characterization of ground fault tolerance (GFM). Generalized short-circuit ratio (gSCR) is complex to calculate and has low online applicability. The multi-station short-circuit ratio (MRSCR) for renewable energy does not account for the GFM effect and lacks research on critical values ​​under small-disturbance stability conditions.

[0004] Furthermore, the order of small-signal models in large-scale new energy systems can reach thousands, posing a "curse of dimensionality" challenge to eigenvalue calculation. Existing order reduction methods still struggle to balance efficiency. While the ring theorem can avoid directly solving high-dimensional characteristic polynomials, current research only focuses on stability assessment and lacks methods for searching and precisely locating dominant eigenvalues.

[0005] Therefore, how to accurately quantify the grid strength of a hybrid grid system and achieve rapid online assessment and control is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] This invention provides a method and system for online stability assessment and control of hybrid systems based on improved short-circuit ratio, which overcomes the shortcomings of existing technologies such as failure to consider the supporting role of grid-connected equipment in grid strength assessment and heavy computational burden due to the "curse of dimensionality" in small disturbance stability analysis, and realizes efficient online stability assessment and optimized control of hybrid systems connected to / connected to the grid.

[0007] In a first aspect, the present invention provides a method for online stability assessment and control of a hybrid system based on an improved short-circuit ratio, comprising the following steps: S1: Construct an equivalent superposition model of a hybrid grid-connected system containing grid-connected equipment and grid-building equipment, taking into account the voltage source characteristics of grid-building equipment, and calculate the improved short-circuit ratio of new energy multi-site stations to characterize the grid strength at each grid connection point; S2: Construct a characteristic polynomial based on the system impedance matrix, use the circular ring theorem to construct a circular region of eigenvalue distribution on the complex plane, quickly search and locate the dominant eigenvalue, and obtain the critical improved short-circuit ratio of new energy multi-stations; S3: If the short-circuit ratio of the improved new energy multi-station is less than the critical improved new energy multi-station short-circuit ratio, it is determined that the system has an instability risk, triggering the site selection and capacity control strategy of the grid-type equipment, and improving the system stability by increasing the capacity of the grid-type equipment or adjusting the grid connection point.

[0008] As a further limitation of the technical solution of the present invention, in S1, constructing the equivalent superposition model of the hybrid grid-connected system includes: The Thevenin model equates network-connected devices to controlled current sources and network-connected devices to voltage sources in series impedance. Based on the node impedance matrix, the grid node voltage equations are established, which include all grid-connected devices, network-structured devices, and synchronous machine nodes.

[0009] By distinguishing the equivalent models of grid-connected and grid-structured equipment, a theoretical foundation is laid for subsequent calculations of their respective short-circuit capacity contributions. The decomposition method based on the superposition principle simplifies the complex multi-infeed system into the superposition of multiple single-infeed subsystems, simplifying the analysis process and improving computational feasibility.

[0010] As a further limitation of the technical solution of this invention, the calculation formula for the short-circuit ratio of the improved new energy multi-station in S1 is as follows:

[0011] in, For the synchronous machine at the grid connection point Provided short-circuit capacity, For network-type equipment To the grid connection point Provided short-circuit capacity, To connect the grid-type equipment at the grid connection point Equivalent grid-connected capacity at the location, This is the collection of all grid-connected devices and their connection points.

[0012] The numerator takes into account both the short-circuit capacity provided by the synchronous machine and the short-circuit capacity provided by all grid-connected equipment, while the denominator takes into account the equivalent grid-connected capacity of the grid-connected equipment. This can comprehensively reflect the grid strength of the hybrid system. Compared with the traditional multiple infeed short-circuit ratio (MISCR), which mistakenly treats grid-connected equipment as grid-connected equipment, this method can accurately reflect the role of grid-connected equipment in improving system strength and avoid misjudging the system strength.

[0013] As a further limitation of the technical solution of the present invention, the method of constructing an annular region of eigenvalue distribution using the annular theorem in S2 to quickly search and locate the dominant eigenvalue includes: Transform the characteristic polynomial into a friendly matrix form; Calculate at least one of the Frobenius norm, 1-norm, and ∞-norm of the friend matrix, and determine the global boundary of the eigenvalue magnitude based on the ring theorem, wherein the global boundary defines the distribution range of the eigenvalues ​​in the complex plane; Within the scope defined by the global boundary, a series of scanning circle centers are set along the imaginary axis of the complex plane, and coordinate translation transformations are performed respectively: with the current scanning circle center as the new coordinate origin, the translated characteristic polynomial is reconstructed and transformed into the corresponding translated affine matrix; the scanning circle center refers to the coordinate point preset on the complex plane for constructing the search benchmark of the annulus theorem.

[0014] Calculate the radius of the inner circle within the annular region of each translated friend matrix, locate the center position of the scan circle corresponding to the minimum inner circle radius, and use the imaginary part at this position as the candidate region of the imaginary part of the dominant feature root. Within the identified imaginary candidate region, a series of scanning circle centers are set along the real axis direction. The coordinate translation transformation and inner circle radius calculation steps are repeatedly executed, and the scanning circle center position and the corresponding minimum inner circle radius when the inner circle radius is minimized are recorded. The location of the scan center and its neighborhood corresponding to the minimum inner circle radius are determined as the distribution area of ​​the dominant feature roots.

[0015] By scanning along both the imaginary and real axes, the center position corresponding to the minimum inner circle radius is determined as the region where the dominant eigenvalue is located, thus achieving rapid and accurate localization of the dominant eigenvalue. This solves the technical problem that existing research on the ring theorem only focuses on stability judgment and lacks eigenvalue search methods.

[0016] As a further limitation of the technical solution of the present invention, the critical improved short-circuit ratio of multiple new energy power stations obtained in S2 includes: Based on the current operating point, the short-circuit ratio values ​​of multiple new energy power stations are gradually adjusted and improved, and the dominant characteristic roots after adjustment are searched again using the circular theorem. When the real part of the dominant characteristic root crosses the imaginary axis, the short-circuit ratio of the improved new energy multi-station corresponding to this critical state is determined as the critical short-circuit ratio of the improved new energy multi-station.

[0017] The critical improved short-circuit ratio (cIMRSCR) of new energy multi-stations is explicitly defined as the improved short-circuit ratio value corresponding to the real part of the dominant eigenvalue crossing the imaginary axis. This definition directly links the grid strength index (IMRSCR) with the mathematical criterion for small disturbance stability, making cIMRSCR a critical threshold for measuring whether the system meets the small disturbance stability constraint, and providing a clear quantitative basis for instability risk early warning.

[0018] In the process of gradually adjusting the IMRSCR values, this method uses the ring theorem to re-search and locate the dominant eigenvalues, rather than directly solving for all eigenvalues. Since the ring theorem only requires simple operations such as calculating the matrix norm to quickly locate the dominant eigenvalues, it significantly reduces the computational burden of each iteration, enabling the entire cIMRSSCR solution process to be completed online. This solves the problem that traditional eigenvalue analysis methods cannot be applied online due to the "curse of dimensionality".

[0019] As a further limitation of the technical solution of the present invention, the addressing and capacity control strategy of the trigger-networked device in S3 includes: When the system is determined to have a risk of instability, the grid connection point where the short-circuit ratio of the improved new energy multi-station is lower than the critical improved new energy multi-station short-circuit ratio is identified and defined as the weak grid connection point. In the weak grid connection point or its electrical proximity area, identify new energy equipment to be put into operation or switched to grid-type control; Based on the determined equipment, control commands are generated for the commissioning of network-type equipment or the reconfiguration of control modes.

[0020] By identifying weak grid-connected points where the IMRSCCR is below the critical value, the control scope is precisely focused on key nodes with insufficient grid strength. This strategy avoids blindly deploying grid-connected equipment across the entire network, and can improve system stability with minimal control costs.

[0021] Extending the control range from weak grid-connected points to their electrical proximity areas fully accounts for the electrical coupling effects between different grid-connected points in multi-feed systems through network impedance. Since the IMRSCR index itself takes into account the mutual influence between multiple substations through mutual impedance, extending the control range to the electrical proximity areas can more effectively improve the overall grid strength of weak nodes and their surrounding areas, avoiding the limitations of controlling only a single node while ignoring the influence of the vicinity.

[0022] As a further limitation of the technical solution of the present invention, the method further includes: S4: After the control strategy is executed, return to S1 and recalculate the improved short-circuit ratio of new energy multi-site at each grid connection point until the grid strength of all grid connection points meets the stability requirements.

[0023] By combining real-time calculations with IMRSCR and the circular theorem, rapid assessment of instability risk and instant generation of control commands were achieved, solving the technical challenge of online control of hybrid systems.

[0024] As a further limitation of the technical solution of the present invention, the short-circuit capacity provided by the grid-connected equipment to the grid connection point is calculated using a voltage source series impedance model in non-current limiting mode, and using an overcurrent capacity limiting calculation in current limiting mode:

[0025] in, Nominal voltage, For network-type equipment k The internal potential, For grid-connected nodes of network-type equipment k With nodes Network mutual impedance between them The equivalent impedance for network-type equipment. This represents the amplitude of the short-circuit current.

[0026] The two working modes of the network-type equipment are distinguished, making the calculation of IMRSCCR more accurate and able to reflect the support capacity of the network-type equipment under actual fault conditions; the calculation in the current-limiting mode only requires the overcurrent capacity limit value, avoiding the complex calculation of internal potential and impedance parameters, and improving the practicality of engineering.

[0027] As a further limitation of the technical solution of the present invention, the step size of the scanning center is set along the imaginary axis direction and the real axis direction, and is set according to the system scale or real-time requirements; the scanning center position corresponding to the minimum value of the inner circle radius is determined as the positioning result of the dominant feature root.

[0028] The adaptive step size adjustment can achieve a balance between computational speed and search accuracy, taking into account both the real-time and accuracy requirements of online applications.

[0029] Secondly, the present invention also provides an online stability assessment and control system for hybrid systems based on an improved short-circuit ratio, comprising: The data acquisition module is used to obtain information on the power grid network structure, the output of new energy equipment, and the operating mode of the equipment. The short-circuit ratio calculation module is used to construct an equivalent superposition model of a hybrid grid-connected system containing grid-connected equipment and grid-building equipment. Based on the voltage source characteristics of the grid-building equipment, it calculates the improved short-circuit ratio of new energy multi-site at each grid connection point. The eigenvalue search module is used to construct a characteristic polynomial based on the system impedance matrix, construct a circular region of eigenvalue distribution on the complex plane using the circular ring theorem, quickly search and locate the dominant eigenvalue, and obtain the critical improved short-circuit ratio of new energy multi-stations. The stability judgment and control module is used to compare the improved short-circuit ratio of multiple new energy power stations with the critical improved short-circuit ratio of multiple new energy power stations. When it is determined that there is a risk of instability, it triggers the location and capacity control strategy of the grid-type equipment and generates control instructions for the commissioning or control mode reconfiguration of the grid-type equipment. The feedback verification module is used to re-call the short-circuit ratio calculation module and the characteristic value search module after the control strategy is executed to verify whether the grid strength of each grid connection point meets the stability requirements.

[0030] As can be seen from the above technical solutions, this application has the following advantages: By improving the short-circuit ratio index to take into account the voltage source characteristics of grid-connected equipment, it can more accurately characterize the grid strength of the hybrid system and make up for the deficiency of the traditional short-circuit ratio index in not considering the active support role of grid-connected equipment; The eigenvalue search method based on the ring theorem does not require direct solution of high-dimensional characteristic polynomials, avoiding the "curse of dimensionality" problem, and has high computational efficiency, making it suitable for online applications; By comparing IMRSCR and cIMRSCR, a clear instability criterion is formed, providing a quantitative basis for system operation scheduling and solving the technical problem that existing technologies are unable to evaluate the stability of hybrid systems under small disturbances online. Attached Figure Description

[0031] To more clearly illustrate the technical solution of this application, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a flowchart illustrating the method provided in an embodiment of the present invention.

[0033] Figure 2 This is a structural diagram of a multi-feed system.

[0034] Figure 3 The diagram shows the result of decoupling a multi-feed system using the superposition principle. Figure 3 In this diagram, A represents the Thevenin equivalent circuit containing only a synchronous machine. Figure 3 In this context, B represents the Thevenin equivalent circuit containing only network-type devices. Figure 3 C in the diagram represents the Norton equivalent circuit containing only root-net devices.

[0035] Figure 4 For grid connection point i The equivalent single-feed system model of the AC system containing only a synchronous machine.

[0036] Figure 5 For grid connection point i The AC system includes only the equivalent single-feed system model of network-type equipment.

[0037] Figure 6 A schematic diagram illustrating the application of coordinate transformations to the theorem of rings, wherein... Figure 6 In this context, A represents the inner radius of the circle. Diagram Figure 6 In this context, B represents the inner radius of the circle. Diagram Figure 6 C in the diagram represents the transformed image.

[0038] Figure 7 To form a parallel system of two machines connected to the network.

[0039] Figure 8 The calculation results and time-domain waveforms of IMRSCR and MRSSCR under different operating conditions of the two-machine system are shown.

[0040] Figure 9 A diagram illustrating the rapid search of the imaginary axis of the eigenvalues ​​of a two-machine system based on the circular ring theorem.

[0041] Figure 10 A diagram illustrating the fast search of the real axis of the eigenvalues ​​of a two-machine system based on the circular ring theorem.

[0042] Figure 11 A three-machine, nine-node system diagram is shown to verify the proposed small-disturbance stability enhancement strategy.

[0043] Figure 12 This diagram illustrates the search for the dominant eigenvalue of the system on the imaginary axis after a sudden change in the external power grid.

[0044] Figure 13 This is a diagram illustrating the search for the dominant eigenvalue real axis of the system after a sudden change in the external power grid.

[0045] Figure 14 The calculation results and time-domain waveforms of IMRSCR and MRSCR under different operating conditions of the IEEE9 system are shown. Detailed Implementation

[0046] To make the purpose, features, and advantages of this application more apparent and understandable, specific embodiments and accompanying drawings will be used to clearly and completely describe the technical solution protected by this application. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0047] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this application and in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0048] like Figure 1 As shown in the figure, this invention provides an online stability assessment and control method for a hybrid system based on an improved short-circuit ratio, comprising the following steps: S1: Construct an equivalent superposition model of a hybrid grid-connected system containing grid-connected equipment and grid-building equipment. Based on the voltage source characteristics of the grid-building equipment, calculate the improved short-circuit ratio of multiple new energy power stations to characterize the grid strength at each grid connection point. This invention establishes a novel universal equivalent superposition model for multi-infeed power systems with mixed grid-connected and grid-connected equipment. A typical multi-infeed renewable energy system is shown below. Figure 2 As shown, Figure 2 Multiple GFM and GFL devices can be connected to the same PCC point or multiple PCC points.

[0049] In a hybrid renewable energy grid-connected system, nodes are categorized according to the type of equipment they connect to. Assume the total number of nodes in the system is... n , where: Node 1 p For grid-connected equipment, the number is p ;node p +1 p + q The number of connection points for network-connected devices is [number]. q ;node p + q +1 n There are synchronization machine nodes, the number of which is n ( p + q ).

[0050] Synchronous generators (SG) are equivalent to voltage sources, and gas flow meters (GFMs) are equivalent to voltage sources with series equivalent impedance; gas flow meters (GFLs) are equivalent to current sources. Therefore, SG and GFMs, which provide short-circuit capacity for AC systems, should use the Thevenin equivalent, while GFLs, representing new energy sources, should use the Norton equivalent. According to the superposition theorem, a multi-infeed system containing multiple GFMs and GFLs can be decomposed into a superposition of multiple single-infeed systems, such as... Figure 3 As shown.

[0051] In a multi-feedback system for new energy sources, the voltage at each PCC point is supported by the SG and all GFM devices, and is affected by the injected current from all GFL devices. Based on Figure 3 After decomposition, the node voltage equations are established using the node impedance matrix: (1) In the formula, for n A 1×1 dimension column vector of node voltages; for n A 1×1 dimension column vector of node injected currents; Z Here is the node impedance matrix; Inject a current vector into the synchronous machine; Inject current vectors into network-type devices; Inject current vectors into grid-connected devices.

[0052] Combination Figure 3 In the A-analysis, when only considering the current injected into each node by the synchronous machine through the impedance network, the node voltage equations can be written in conjunction with equation (1): (2) In the formula, The voltages of each node in a network containing only SG; the off-diagonal elements of the node impedance matrix. Reflecting two nodes i , j Electrical distance between; diagonal elements For multi-port Thevenin equivalent post-node i Self-impedance.

[0053] To assess the short-circuit capacity contributed by different power sources and derive an improved short-circuit ratio for multi-power-generation renewable energy systems, a multi-grid-connected system can be decomposed into an equivalent single-grid-connected subsystem composed of different power sources. Combined with... Figure 3 In the diagram, A obtains an AC system composed of SG at the grid connection point. i The equivalent single-feed system at the location is as follows: Figure 4 As shown. Combined with Figure 3 B in the diagram obtains an AC system composed of GFM at the grid connection point. i The equivalent single-feed system at the location is as follows: Figure 5 As shown.

[0054] Grid connection point before new energy grid connection i The voltage is equal to... Figure 4 and Figure 5 The AC system potential shown : (3) Short-circuit current at grid connection point It equals the open-circuit voltage before the short circuit at that point divided by the equivalent impedance of the system at that point. Combining with equation (3), we can obtain: (4) SG to grid connection point i The provided short-circuit capacity is equal to the short-circuit current multiplied by the nominal voltage at that point. Combining equation (4), we can obtain: (5) Referring to the calculation of the short-circuit capacity of synchronous machines, the short-circuit capacity of grid-connected equipment can be further calculated. If the current limiting condition triggered by the grid-connected converter during a short-circuit fault is not considered, based on... Figure 5 The voltage source equivalent model of the GFM device in the hybrid system shown can be used to derive the node... k The GFM equipment at the location connects to the grid point. i The provided short-circuit capacity is: (6) in, Nominal voltage, For network-type equipment k The internal potential, For grid-connected nodes of network-type equipment k With nodes Network mutual impedance between them The equivalent impedance for network-type equipment.

[0055] When a power grid fault occurs, at the instant of the fault, the nodes k The internal potential of the GFM remains constant, injecting capacitive reactive power into the system and providing voltage support. A significant drop in grid voltage causes the converter output current to exceed the converter's overcurrent capacity limit. Then it enters current limiting mode. At this time, the PCC bus... i The short-circuit current amplitude provided by GFM is When entering the rate limiting state, k The short-circuit capacity provided by the GFM to the AC system is: (7) Combining equations (5), (6), and (7), calculate the SG pairs of nodes. i Short-circuit capacity and nodes k GFM i The sum of the short-circuit capacities can be used to obtain the active support power supply at the grid connection point. i The total short-circuit capacity provided is: (8) In the formula, This is the collection of all grid-connected devices and their connection points.

[0056] Since multiple injection sources exist in a multi-feed system, this section derives the equivalent grid-connected capacity of the GFL device to support the impact of GFLs directly connected to nodes of interest. This is done considering the impact of GFL integration on nodes. i Voltage has an impact. Analysis of the impact of GFL renewable energy access on... Figure 2 Grid connection point p +1 p + q When considering the impact, combine Figure 3 In the equation C, according to Kirchhoff's laws and the superposition theorem, the node... i The voltage change is: (9) In the formula, for Figure 2 The nodes shown Self-impedance, for Figure 3 The nodes shown With nodes The mutual impedance.

[0057] It can be seen that the GFL equipment is connected to the grid node. i and j The injected current will affect the node. i The voltage change. Grid connection point. i The current injected by the equivalent current source of the GFL device in the system is: (10) Furthermore, the grid connection point can be calculated by combining equation (9). i The equivalent grid-connected capacity of GFL equipment is: (11) In the formula, Represents conjugate computation; , Representative grid connection point i and j The capacity of the connected GFL equipment. From equation (11), it can be seen that due to the mutual influence between multiple feed-in branches, the equivalent grid-connected capacity of new energy includes the capacity of directly connected new energy and the new energy capacity of other feed-in branches.

[0058] In new power systems, the ratio of the AC system short-circuit capacity to the grid-connected capacity of new energy equipment is generally defined as the short-circuit ratio. Therefore, when analyzing the grid strength of a hybrid system with integrated / connected grids, the improved short-circuit ratio index for multiple new energy power plants can be calculated by using the ratio of the total AC system short-circuit capacity after the GFM equipment is connected to the equivalent grid-connected capacity of the GFL equipment, denoted as IMRSCR (Improved-MRSCR). Based on this, by dividing equation (8) by equation (11), we can obtain: (12) When GFM enters rate-limiting mode, It should be revised to .

[0059] The IMRSCR defined by Equation (12) can be used to characterize the active support strength of the system for GFL equipment. The numerator of this index takes into account the influence of GFM, including both the short-circuit capacity provided by SG and the short-circuit capacity provided by GFM equipment. Therefore, it can more accurately reflect the grid strength of the multi-feed system connected to / integrated with the grid.

[0060] From the perspective of small disturbance stability, a higher SCR usually means that the equivalent impedance seen from the grid connection point of the GFL equipment is smaller. According to the impedance stability criterion, when the grid equivalent impedance is much smaller than the equipment output impedance, the system is less likely to cause resonance instability due to impedance mismatch. Therefore, maintaining a suitable IMRSCCR level is a prerequisite for ensuring the small disturbance stability of the new energy grid-connected system. Based on equation (12), it can be seen that by reasonably configuring the GFM equipment, the IMRSCCR level of the system can be effectively improved, thereby enhancing the voltage support capability of weak nodes, restoring the system strength to above the safety threshold, and ultimately improving the small disturbance stability of the hybrid system.

[0061] S2: Construct a characteristic polynomial based on the system impedance matrix, use the circular ring theorem to construct a circular region of eigenvalue distribution on the complex plane, quickly search and locate the dominant eigenvalue, and obtain the critical improved short-circuit ratio of the corresponding weak grid connection point for new energy multi-stations. After obtaining the IMRSCCR at each node using equation (12), in order to explicitly describe the impact of IMRSCCR on small-signal stability, the GFL access point is used as an example. i Taking an example, we analyze its small-signal stability. Considering transmission lines where inductance is dominant, i.e., the line's impedance-to-inductance ratio... R / X Since the value is much smaller than 1, for simplicity, the effect of resistance on the stability of small disturbances can be ignored in the analysis, and the circuit can be considered to consist only of inductance.

[0062] Therefore, in a pure inductive network, by combining equation (12), the relationship between its impedance value and the improved short-circuit ratio of multiple new energy power stations can be obtained as follows: (13) At this point, the impedance matrix in the dq coordinate system corresponding to the dynamic line reactance is: (14) For stability analysis of GFL equipment, its impedance matrix is ​​defined as follows: The closed-loop characteristic equation of the system at this point is: (15) Substitute equation (13) into equation (14), and then... Substituting the closed-loop characteristic equation (15) and combining them, we can obtain: (16) Small-disturbance stability analysis of other equivalent single-feed systems can be performed by analogy to the above process. Therefore, the small-disturbance stability of complex multi-feed systems depends on the small-disturbance stability of each equivalent single-feed system after its decomposition, and is affected by IMRSCR.

[0063] According to linear system theory, a system is stable under small disturbances if and only if the system's characteristic roots, i.e., the solutions to the closed-loop characteristic equation in equation (15), are all located in the left half-plane of the complex plane. When the device impedance matrix in the system remains unchanged, the solution to the closed-loop characteristic equation depends only on the value of IMRSCR. Therefore, the IMRSCR that makes the solution to the closed-loop characteristic equation lie on the imaginary axis is defined as the critical improved short-circuit ratio cIMRSCR for multi-station renewable energy.

[0064] When IMRSCR is less than the critical value, it is in a weak power grid scenario. The equivalent impedance increases, the coupling resonance between GFL and the power grid is enhanced, and the real part of the solution of Equation (15) shifts to the right, crossing the imaginary axis and entering the right half-plane. The system faces the risk of oscillation and instability. When IMRSCR is equal to the critical value, the solution of Equation (15) falls exactly on the imaginary axis. The system is in a small disturbance stability boundary. At this time, small disturbances may cause oscillations.

[0065] The improved short-circuit ratio of multiple renewable energy power plants reflects the magnitude of the system's equivalent impedance. When the control parameters of each renewable energy device remain unchanged, the IMRSCR can determine the distribution range of the eigenvalues; the distribution of the eigenvalues ​​directly reflects the system's stable state under small disturbances. By combining the improved short-circuit ratio index of multiple renewable energy power plants with the search for the system's dominant eigenvalues, the deficiency of the improved short-circuit ratio index in directly reflecting the details of oscillation modes can be compensated for.

[0066] For multi-feed systems, after constructing the node admittance matrix containing the device impedance matrix, a characteristic polynomial of the following form can be obtained. Solving for its small-signal stability is essentially solving for the eigenvalues ​​of this characteristic polynomial: (17) In the formula, These are complex coefficients, all functions of IMRSCRI. Improving the short-circuit ratio of multi-generation renewable energy power stations directly alters the coefficient values, thus affecting the eigenvalue distribution.

[0067] When the number of wind turbines in the system reaches dozens, equation (17) contains s Polynomials can reach hundreds or even thousands of orders, and solving polynomials is quite time-consuming. To solve this problem, this invention uses the ring theorem, based on... s The coefficients of the polynomial can be used to quickly determine the location of the zero point through numerical calculation alone.

[0068] To transform the problem of solving the higher-order characteristic polynomials in equation (17) into the problem of solving the matrix eigenvalues, a method is constructed. n The order-friend matrix is ​​as follows: (18) The characteristic polynomial of matrix A can then be derived as follows: (19) It can be seen that the eigenvalues ​​of matrix A λ The eigenvalues ​​are consistent with those in equation (17). For matrix A shown in equation (18), its compatibility matrix norm is... The spectral radius of each is not less than that of A. , Right now ≤ .

[0069] Wherein, the spectral radius is the maximum value of the modulus of all eigenvalues ​​of the matrix: .

[0070] To provide an easily computable upper and lower bound for the eigenvalue modulus of matrix A and to achieve a rough location of the eigenvalue region in equation (17), this invention introduces the Frobenius norm.

[0071] The Frobinius norm of matrix A can be expressed as: (20) The corresponding ring theorem based on the F-norm is defined as follows: For a univariate... n Multiple terms ,in ,but The roots must all lie within the annulus of the complex plane: (twenty one) in, Let be the radius of the inner circle, denoted as . , Let be the radius of the outer circle.

[0072] The F-norm can reflect the overall distribution characteristics of matrix elements well, but its characterization of the matrix's structural information in the row and column directions is relatively limited. To further study the distribution characteristics of matrix elements in different row and column directions, this invention introduces the 1-norm and ∞-norm based on the F-norm. The formulas for the 1-norm and ∞-norm are as follows: (twenty two) (twenty three) Based on the ring theorem based on the F-norm described in equation (21), the ring theorem based on the 1-norm and ∞-norm can be derived similarly based on equations (22) and (23).

[0073] The annular results corresponding to the Frobenius norm, 1-norm, and ∞-norm can constrain the eigenvalue distribution region from different perspectives. By comparing the calculation results of the three, the maximum inner ring and the minimum outer ring can be extracted to construct the annular region where the eigenvalues ​​are located, providing a theoretical basis for subsequent fast eigenvalue search.

[0074] The stability of a system can be determined by the characteristic polynomial of A: if all the roots of the characteristic polynomial lie in the left half of the complex plane, then the system is stable under small disturbances. Considering the computational efficiency of online applications, this invention does not solve for all eigenvalues, but focuses on the dominant eigenvalues ​​near the imaginary axis. Therefore, stability analysis can be achieved by locating the dominant eigenvalues ​​near the imaginary axis based on the ring theorem.

[0075] Applying the inner-loop property of the ring theorem—that is, the property that no eigenvalues ​​exist within the inner loop centered at the origin—requires extending the application of the inner loop to the imaginary axis and its neighborhood to determine the location of the dominant eigenvalues. The original equation... f ( s The radius of the inner circle is determined by the ring theorem. ,like Figure 6 The black inner circle in A is shown in the diagram. (Using ( s 1 j Replace the characteristic polynomial f ( s In ) s Reconstructing the monistic n A polynomial of degree n. Further analysis based on the ring theorem yields a radius of... The inner circle of the circle has its center at the origin on the complex plane, such as... Figure 6 As shown in B in the diagram. The dashed line represents the real axis before the transformation, and the solid line represents the real axis after the transformation. Through coordinate transformation, the radius is... Replace the inner circle with the original coordinate system, keeping the radius of the inner circle unchanged. At this time, the inner circle... The center of the circle becomes (0, 1 j )like Figure 6 The red inner circle in C is shown in the diagram. This method involves performing coordinate transformations on the original characteristic polynomial at arbitrary positions, and then translating the resulting new annulus back into the original coordinate axes. Based on this, it is possible to construct an inner circle at any position in the complex plane. When the radius of the inner circle at a certain position rapidly decreases, it can be determined that an eigenvalue exists near that position.

[0076] The process of searching for the location of the dominant eigenvalue is as follows: (1) Searching along the imaginary axis: such as Figure 6 As shown in C, starting from the origin, different centers are successively selected along the imaginary axis, and the radius of the inner circle of the annulus is calculated multiple times. If, during the search along the imaginary axis, the radii of the inner circles of all the annulus do not change significantly, and all the inner circles of the annulus can cover the imaginary axis and its nearby complex plane region, it indicates that the current dominant eigenvalue is far from the imaginary axis. If the inner circle radius decreases significantly at a certain position, it indicates that a dominant eigenvalue exists near that region. Assume that the position of the center of the circle at this time is ( ).

[0077] (2) Real axis search: In the region where the radius of the detected annulus decreases, the same method can be used. Figure 6 The search method is from ( Continue searching left or right along the real axis, calculating the radius of the inner circle of the annulus multiple times.

[0078] (3) Determining the dominant eigenvalue: If the radius of the inner circle of the annulus gradually approaches zero during the search process, it can be determined that the dominant eigenvalue is located near the current inner circle region. Let the position at this time be ( If the radius of the annulus is at this time... The location of the dominant eigenvalue is ( )or( ).

[0079] In practical applications, the Frobenius norm, 1-norm, and ∞∞-norm can be directly calculated from the matrix elements, and the computational cost per operation is the same as the number of non-zero elements in the matrix. Considering that the number of non-zero elements in the matrix shown in equation (18) is 2... n 1. The complexity of calculating the one-degree norm can be approximated as: In the process of searching for the dominant eigenvalue, let the number of searches along the imaginary axis be . The number of searches along the real axis is The total number of searches is Therefore, the overall complexity of the eigenvalue search method based on the ring theorem can be expressed as: .

[0080] The critical improved short-circuit ratio of multiple renewable energy power plants was obtained through the following methods: Based on the position of the dominant eigenvalue at the current operating point and its sensitivity to the short-circuit ratio of the new energy multi-power station, the value of the short-circuit ratio of the new energy multi-power station is gradually adjusted, and the ring theorem is used to search for the adjusted dominant eigenvalue again. When the real part of the dominant characteristic root changes from negative to positive and passes through zero, the short-circuit ratio of the improved new energy multi-station at that moment is determined as the critical short-circuit ratio of the improved new energy multi-station.

[0081] Compared to methods that directly solve for the eigenvalues ​​of the nodal admittance matrix, the method that combines the calculation of the critical improved short-circuit ratio of multiple new energy power stations with a search based on the ring theorem does not require direct solution to high-order polynomials. The distribution trend of eigenvalues ​​can be initially predicted, and then the location of the dominant eigenvalues ​​can be quickly identified using the ring theorem, thus obtaining the current critical improved short-circuit ratio of the new energy multi-station system. This online stability assessment method for hybrid systems with small disturbances, based on the improved short-circuit ratio of multiple renewable energy power plants and the ring theorem, avoids the high-dimensionality problem encountered in characteristic polynomial calculations and enhances the engineering practicality of eigenvalue analysis by introducing the improved short-circuit ratio of multiple renewable energy power plants. It enables efficient and accurate assessment of the stability of large-scale hybrid systems with small disturbances. Specifically, based on the relationship between the dominant eigenvalues ​​and the system stability boundary, the critical improved short-circuit ratio of multiple renewable energy power plants is obtained by adjusting system parameters.

[0082] S3: If the short-circuit ratio of the improved new energy multi-station is less than the critical improved new energy multi-station short-circuit ratio, it is determined that the system has an instability risk, triggering the site selection and capacity control strategy of the grid-type equipment, and improving the system stability by increasing the capacity of the grid-type equipment or adjusting the grid connection point (i.e., adjusting the access position of the grid-type equipment).

[0083] When it is determined that the system has a risk of instability (i.e.) < ), triggering the location and capacity control strategy of network-type equipment, specifically including: The focus is on identifying and improving weak grid connection points in multi-generational renewable energy power plants where the short-circuit ratio is below a critical value. The grid connection point with the lowest short-circuit ratio among these power plants will be prioritized for regulation.

[0084] With the goal of improving the power grid strength of the weak grid connection point and its electrical adjacent area to above the critical value, the minimum required grid-type equipment support capacity and the optimal access location are calculated.

[0085] Based on the optimal access location and minimum support capacity, control commands are generated for the commissioning of network-type equipment or the reconfiguration of control modes. Specific methods include: adding network-type equipment at weak grid connection points, or switching existing network-connected equipment at weak grid connection points to network-type control mode.

[0086] In this embodiment of the invention, after the control strategy is executed, the process returns to step S1, recalculates the improved short-circuit ratio of multiple renewable energy power plants at each grid connection point, and uses the circular theorem to re-search for the dominant characteristic root until the grid strength at all grid connection points meets the stability requirements (i.e., all grid connection points...). ≥ , and the dominant eigenvalues ​​are located in the left half of the complex plane.

[0087] This embodiment uses, as follows Figure 7The following is an example of a parallel system of two machines connected in parallel with the network. Figure 7 middle, These are the inverter outlet filter inductor and capacitor, respectively. For line impedance, This represents the power grid impedance.

[0088] Initially, the system is connected to two grid-connected (GFL) wind turbines. Using the conventional multiple infeed short-circuit ratio (MISCR) calculation, the system's MISCR is 2.0, corresponding to... Figure 8 State 1 in the context. For example... Figure 8 As shown, the system operates stably in State 1. At time 4 seconds, the grid impedance undergoes a sudden change, and the system MISCR decreases to 1.8 (State 2). Figure 8 As shown in the State2 time-domain waveform, the system exhibits a wideband oscillation with a frequency of 58.4 Hz, indicating instability under small disturbances.

[0089] To improve the system's stability under small disturbances, one of the GFL wind turbines was switched to grid-connected wind turbine (GFM) control. Based on the improved short-circuit ratio formula (12) proposed in this invention, the IMRSCR at the PCC point increased to 2.32 (State 3). For example... Figure 8 As shown in the State3 time-domain waveform, the system oscillations disappeared, and the system returned to stable operation under small disturbances. However, when using the traditional MISCR calculation, the GFM device is considered as part of the equivalent grid-connected capacity of the GFL, resulting in a MISCR of 1.73, which incorrectly judges the current system as still a weak grid. This embodiment verifies that the IMSCR index proposed in this invention can effectively take into account the improvement effect of GFM on the grid strength of the hybrid system.

[0090] Furthermore, the fast eigenvalue search method based on the annular theorem proposed in this invention is employed. A circular search is performed by gradually changing the center of the circle along the imaginary axis from the origin of the complex plane, with a search step size of 2. For example... Figure 9 As shown, when the center of the circle is taken to (0, 368j), the radius of the annulus reaches its minimum, indicating that a characteristic root exists in the vicinity of this region. Subsequently, in Figure 9 Based on the results, a circular search was performed along the real axis with a step size of 0.5. The results are as follows. Figure 10 As shown, the inner ring gradually increases when searching along the negative real axis, indicating that there are no eigenvalues ​​in the negative real axis direction; when searching along the positive real axis, the inner ring radius decreases, with the smallest ring radius being 0.16 and the center position being (0.5, 368j). Considering the error of the ring theorem, the estimated position of the dominant eigenvalue is (0.34, 367.5j). In contrast, the actual dominant eigenvalue obtained by directly solving the original characteristic polynomial is (0.29, 367.50j), and the comparison of the two results is shown in Table 1.

[0091] Table 1: Calculation Results of Eigenvalues ​​for the Two-Machine System

[0092] Depend on Figure 8 The oscillation frequency shown matches the imaginary part of the dominant eigenvalue obtained by the circular theorem search (367.5j corresponds to approximately 58.5Hz), verifying the accuracy of this method.

[0093] The embodiments of the present invention are as follows Figure 11 The three-machine, nine-node system shown is used as an example for verification. Figure 11 In the diagram, nodes 1 and 10 are grid-connected nodes of the wind farm (connected to GFL wind turbines), nodes 2-9 are internal nodes, and node 11 is an infinite bus. For simplicity, it is assumed that all converters have the same capacity.

[0094] Calculate the IMRSCRI of each renewable energy grid-connected node under the initial stable operating condition State1. For example... Figure 14 As shown, the IMRSCRI of node 1 in State 1 is 2.20, and the IMRSCRI of node 10 is 2.32. Taking node 1, which has a lower short-circuit ratio, as the research object, by constructing the system node admittance matrix containing the equipment impedance matrix and solving its characteristic polynomial, the critical improved short-circuit ratio cIMRSCR1 of node 1 is obtained as 1.92.

[0095] During the 5-6 second period, the system is in State 1 and operates stably. At 6 seconds, the external grid impedance undergoes a sudden change, and the IMRSCR of node 1 drops to 1.83. Since 1.83 < 1.92, according to the analysis based on this invention, the system should enter a small-signal instability state. The dominant eigenvalue search is performed using the ring theorem: as follows... Figure 12 As shown, a circular search is performed by gradually changing the center of the circle along the imaginary axis from the origin, with a step size of 2. When the center is taken as (0, ±38.6×2πj), the radius of the circular search is minimized, indicating the presence of characteristic roots in this region. Further circular searches are then performed along the real axis near this location, with a step size of 0.25. The results are as follows... Figure 13 As shown in Table 2, the size of the annulus remains unchanged when searching along the left side of the imaginary axis, indicating that there are no eigenvalues ​​on the left. When searching along the right side, the annulus first decreases and then increases, reaching its minimum radius when its center is near (0.25, ±32.16×2πj). Considering the error of the annulus theorem, the estimated location of the dominant eigenvalue is (0.25, 202.50j). As shown in Table 2, the eigenvalue obtained by the annulus theorem search is 0.25±202.50j, while the actual eigenvalue obtained by direct solution is 0.24±202.83j, with an absolute error of 0.01. In terms of computational efficiency, the average computation time of the annulus theorem method is 0.27 seconds, while the direct solution method takes 115 seconds, representing an efficiency improvement of approximately 426 times.

[0096] Table 2: Eigenvalue Calculation Results of the Three-Machine Nine-Node System

[0097] Figure 14 The time-domain simulation results further validated the above analysis: during State2, which lasts from 6 to 6.2 seconds, the system exhibits an oscillation with a frequency of approximately 32 Hz, which is consistent with the imaginary part of the dominant eigenvalue obtained by the ring theorem search (202.50j corresponds to approximately 32.2 Hz).

[0098] To restore the system to small disturbance stability, one GFL wind turbine in the wind farm connected to weak node 1 was switched to GFM control. Recalculated according to formula (12), the IMRSCR of node 1 increased to 2.44. The circular ring theorem was used again to search for the dominant eigenvalues, and the results showed that the dominant eigenvalues ​​were located near (-1, ±0.2π), all within the left half-plane of the complex plane, indicating that the system could restore small disturbance stability. Figure 14 As shown, after switching to GFM control for 6.5 seconds (State 3), the system oscillations rapidly decayed and eventually returned to stability. This embodiment verifies the effectiveness of the proposed method in online operation scheduling.

[0099] This invention also provides an online stability assessment and control system for hybrid systems based on an improved short-circuit ratio, used to implement the methods described in the above embodiments. The system includes: The data acquisition module is used to obtain information on the power grid network structure, the output of new energy equipment, and the operating mode of the equipment. The short-circuit ratio calculation module is used to construct an equivalent superposition model of a hybrid grid-connected system containing grid-connected equipment and grid-building equipment. Based on the voltage source characteristics of the grid-building equipment, it calculates the improved short-circuit ratio of new energy multi-site at each grid connection point. The eigenvalue search module is used to construct a characteristic polynomial based on the system impedance matrix, construct a circular region of eigenvalue distribution on the complex plane using the circular ring theorem, quickly search and locate the dominant eigenvalue, and obtain the critical improved short-circuit ratio of new energy multi-stations. The stability judgment and control module is used to compare the improved short-circuit ratio of multiple new energy power stations with the critical improved short-circuit ratio of multiple new energy power stations. When it is determined that there is a risk of instability, it triggers the location and capacity control strategy of the grid-type equipment and generates control instructions for the commissioning or control mode reconfiguration of the grid-type equipment. The feedback verification module is used to re-call the short-circuit ratio calculation module and the characteristic value search module after the control strategy is executed to verify whether the grid strength of each grid connection point meets the stability requirements.

[0100] Those skilled in the art will clearly understand that the techniques in the embodiments of the present invention can be implemented using software plus necessary general-purpose hardware platforms. Based on this understanding, the technical solutions in the embodiments of the present invention, or the parts that contribute to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium such as a USB flash drive, mobile hard drive, read-only memory (ROM), random access memory (RAM), magnetic disk, or optical disk, or other media capable of storing program code. It includes several instructions to cause a computer terminal (which may be a personal computer, server, or a second terminal, network terminal, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention.

[0101] In the embodiments provided by this invention, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0102] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0103] In addition, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0104] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An improved short circuit ratio based hybrid system online stability evaluation and regulation method, characterized in that, Includes the following steps: S1: Construct an equivalent superposition model of a hybrid grid-connected system containing grid-connected equipment and grid-building equipment. Based on the voltage source characteristics of the grid-building equipment, calculate the improved short-circuit ratio of multiple new energy power stations to characterize the grid strength at each grid connection point. S2: Construct a characteristic polynomial based on the system impedance matrix, use the circular ring theorem to construct a circular region of eigenvalue distribution on the complex plane, quickly search and locate the dominant eigenvalue, and obtain the critical improved short-circuit ratio of new energy multi-stations; S3: If the short-circuit ratio of the improved new energy multi-station is less than the critical improved new energy multi-station short-circuit ratio, it is determined that the system has an instability risk, triggering the site selection and capacity control strategy of grid-type equipment, and improving system stability by increasing the capacity of grid-type equipment or adjusting the grid connection point. The formula for calculating the short-circuit ratio of the improved multi-station renewable energy system in S1 is as follows: wherein, the short circuit capacity provided by the synchronous machine at the point of common coupling, the short circuit capacity provided by the synchronous machine at the point of common coupling, the short circuit capacity provided by the grid forming device at the point of common coupling, the short circuit capacity provided by the grid forming device at the point of common coupling, the short circuit capacity provided by the grid forming device at the point of common coupling, the equivalent grid connection capacity of the grid following device at the point of common coupling, the equivalent grid connection capacity of the grid following device at the point of common coupling, the set of points of common coupling for all grid forming devices; The method described in S2, which utilizes the annular theorem to construct an annular region of eigenvalue distribution for rapid search and localization of dominant eigenvalues, includes: The characteristic polynomial is transformed into a friend matrix form; at least one of the Frobenius norm, 1-norm, and ∞-norm of the friend matrix is ​​calculated, and the global boundary of the eigenvalue magnitude is determined based on the annular theorem, which defines the distribution range of the eigenvalues ​​in the complex plane; within the range defined by the global boundary, a series of scanning centers are set along the imaginary axis of the complex plane, and coordinate translation transformations are performed respectively: with the current scanning center as the new coordinate origin, the translated characteristic polynomial is reconstructed and transformed into the corresponding translated friend matrix; the radius of the inner circle within the annular region of each translated friend matrix is ​​calculated, the scanning center position corresponding to the minimum inner circle radius is located, and the imaginary part at this position is used as the candidate region of the imaginary part of the dominant eigenvalue; within the located candidate region of the imaginary part, a series of scanning centers are set along the real axis, and the coordinate translation transformation and inner circle radius calculation steps are repeated, recording the scanning center position when the inner circle radius is at its minimum value and the corresponding minimum inner circle radius; the scanning center position corresponding to the minimum inner circle radius and its neighborhood are determined as the distribution region of the dominant eigenvalue; The critically improved short-circuit ratio of multiple new energy power stations obtained in S2 includes: Based on the current operating point, the short-circuit ratio of the new energy multi-site power station is gradually adjusted and improved, and the dominant characteristic root is re-searched using the ring theorem. When the real part of the dominant characteristic root crosses the imaginary axis, the improved short-circuit ratio of the new energy multi-site power station corresponding to the critical state is determined as the critical improved short-circuit ratio of the new energy multi-site power station.

2. The online stability assessment and control method for hybrid systems based on improved short-circuit ratio according to claim 1, characterized in that, In S1, constructing the equivalent superposition model of the hybrid grid-connected system includes: The Thevenin model equates network-connected devices to controlled current sources and network-connected devices to voltage sources in series impedance. Based on the node impedance matrix, the grid node voltage equations are established, which include all grid-connected devices, network-structured devices, and synchronous machine nodes.

3. The online stability assessment and control method for hybrid systems based on improved short-circuit ratio according to claim 1, characterized in that, The location and capacity control strategies for trigger-based network devices in S3 include: When the system is determined to have a risk of instability, the grid connection point where the short-circuit ratio of the improved new energy multi-station is lower than the critical improved new energy multi-station short-circuit ratio is identified and defined as the weak grid connection point. In the weak grid connection point or its electrical proximity area, identify new energy equipment to be put into operation or switched to grid-type control; Based on the determined equipment, control commands are generated for the commissioning of network-type equipment or the reconfiguration of control modes.

4. The online stability assessment and control method for hybrid systems based on improved short-circuit ratio according to claim 1, characterized in that, The method further includes: S4: After the control strategy is executed, return to S1 and recalculate the improved short-circuit ratio of new energy multi-stations at each grid connection point until the grid strength of all grid connection points meets the stability requirements; the stability requirements are for all grid connection points. ≥ Furthermore, the dominant eigenvalues ​​are located in the left half of the complex plane.

5. The online stability assessment and control method for hybrid systems based on improved short-circuit ratio according to claim 1, characterized in that, The short-circuit capacity provided by grid-connected equipment to the grid connection point is calculated using a voltage source series impedance model in non-current-limiting mode, and using an overcurrent capacity limiting model in current-limiting mode. in, Nominal voltage, For network-type equipment k The internal potential, For grid-connected nodes of network-type equipment k With nodes Network mutual impedance between them The equivalent impedance for network-type equipment. This represents the amplitude of the short-circuit current.

6. The online stability assessment and control method for hybrid systems based on improved short-circuit ratio according to claim 1, characterized in that, Set the step size of the scanning center along the imaginary axis and the real axis, depending on the system size or real-time requirements; determine the scanning center position corresponding to the minimum inner circle radius as the location result of the dominant feature root.

7. A hybrid system online stability assessment and control system based on improved short-circuit ratio, used to implement the method according to any one of claims 1-6, characterized in that, include: The data acquisition module is used to obtain information on the power grid network structure, the output of new energy equipment, and the operating mode of the equipment. The short-circuit ratio calculation module is used to construct an equivalent superposition model of a hybrid grid-connected system containing grid-connected equipment and grid-building equipment. Based on the voltage source characteristics of the grid-building equipment, it calculates the improved short-circuit ratio of new energy multi-site at each grid connection point. The eigenvalue search module is used to construct a characteristic polynomial based on the system impedance matrix, construct a circular region of eigenvalue distribution on the complex plane using the circular ring theorem, quickly search and locate the dominant eigenvalue, and obtain the critical improved short-circuit ratio of new energy multi-stations. The stability judgment and control module is used to compare the improved short-circuit ratio of multiple new energy power stations with the critical improved short-circuit ratio of multiple new energy power stations. When it is determined that there is a risk of instability, it triggers the location and capacity control strategy of the grid-type equipment and generates control instructions for the commissioning or control mode reconfiguration of the grid-type equipment. The feedback verification module is used to re-call the short-circuit ratio calculation module and the characteristic value search module after the control strategy is executed to verify whether the grid strength of each grid connection point meets the stability requirements.

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