A method and system for analyzing coupling characteristics of a flexible direct current feeding receiving end power grid

Abstract

This invention discloses a method and system for analyzing the coupling characteristics of flexible DC-DC fed into a receiving-end power grid, relating to the field of DC transmission technology. The method includes: acquiring node admittance parameters and transient electrical quantities at the AC bus of the converter station during a fault cycle in the receiving-end power grid; acquiring the ideal passive voltage change and the expected passive voltage value based on the node admittance parameters and transient electrical quantities; determining the active control bias based on the expected passive voltage value; superimposing the active control bias, the ideal passive voltage change, and the expected passive voltage value to obtain the ideal passive voltage recovery trajectory; comparing the ideal passive voltage recovery trajectory with the actual voltage recovery trajectory to obtain the active control voltage increment trajectory of each converter station; and performing cross-correlation calculations on the active control voltage increment trajectories corresponding to any two converter stations to determine the transient coupling strength of the converter station pair, which can improve the operational reliability of the receiving-end power grid.

Description

Technical Field

[0001] This invention relates to the field of DC power transmission technology, and in particular to a method and system for analyzing the coupling characteristics of flexible DC power fed into the receiving-end power grid. Background Technology

[0002] Flexible DC transmission technology based on modular multilevel converters has been widely used in fields such as centralized transmission of new energy sources, asynchronous grid interconnection, and long-distance large-capacity power transmission due to its significant advantages, including independent control of active and reactive power, no need for reactive power compensation, and ability to supply power to passive networks.

[0003] As the core link in power consumption, the receiving-end power grid often faces the operational scenario of multiple flexible DC transmission lines densely feeding into it, forming a typical topology of densely fed flexible DC power into the receiving-end power grid. However, there is a tight electrical coupling between flexible DC converter stations through the receiving-end AC power grid. When an AC short-circuit fault occurs in the vicinity of a converter station in the system, not only is the transient behavior of the converter station at the fault point affected, but the voltage recovery and power response of adjacent converter stations also change dynamically. Therefore, analyzing the transient interactive coupling effects between multiple converter stations is crucial to avoiding improper control parameters, cascading instability, and ensuring the safe operation of the receiving-end power grid.

[0004] Existing coupling analysis methods often take a holistic view of the system, and their indicators rely on static parameters. They lack a coupling component decomposition mechanism, making it difficult to identify the interaction relationships between converter stations, resulting in a lack of targeted optimization of control parameters.

[0005] Therefore, how to conduct a detailed analysis of the transient stability coupling characteristics between converter stations in a flexible DC dense feed-in receiving-end power grid has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] This invention provides a method and system for analyzing the coupling characteristics of flexible DC feed into the receiving-end power grid, in order to solve the problem of how to quantify the coupling degree between converter stations by extracting the active control response trajectory, thereby improving the reliability of the receiving-end power grid operation.

[0007] To address the aforementioned technical problems, embodiments of the present invention provide a method for analyzing the coupling characteristics of a flexible DC-fed receiving-end power grid, comprising: During the fault cycle of the receiving-end power grid, obtain the node admittance parameters and the transient electrical quantity sequence at the AC bus of the converter station at the corresponding time. Based on the node admittance parameters and the transient electrical quantity sequence, the ideal passive voltage change and the expected passive voltage at the AC bus of the converter station at the fault clearance time are obtained. The active control bias for the transient recovery process is determined using the expected passive voltage value as a comparison benchmark. The active control bias, the ideal passive voltage change, and the expected passive voltage value are superimposed to obtain the ideal passive voltage recovery trajectory of each converter station bus in the initial stage of fault recovery. The ideal passive voltage recovery trajectory is aligned point by point with the actual voltage recovery trajectory of each converter station measured at the fault clearing time to obtain the active control voltage increment trajectory of each converter station. Cross-correlation calculations are performed on the active control voltage increment trajectories corresponding to any two converter stations to obtain the transient coupling strength of the converter station pair; the transient coupling strength is used to screen converter station pairs.

[0008] Furthermore, the acquisition of node admittance parameters and transient electrical quantity sequences at the AC bus of the converter station during a fault cycle at the receiving end of the power grid includes: Before a fault occurs in the receiving-end power grid, the node admittance parameters of the AC network are obtained; During a power grid fault at the receiving end, electrical instantaneous values ​​corresponding to each fault moment are read from each converter station; the electrical instantaneous values ​​include the instantaneous values ​​of phase voltage and bridge arm current. Based on the instantaneous electrical values, the positive sequence voltage amplitude and active power value during the fault duration are determined; The three-phase voltage sequence is obtained by subtracting the positive sequence voltage amplitude from the preset voltage reference value; The active power value is subtracted from the preset power reference value to obtain the active power sequence.

[0009] Furthermore, the process of obtaining the expected passive voltage value includes: The active power sequence is compared with the voltage reference value to obtain the first equivalent injection current change sequence. Based on the node admittance parameters, the node impedance matrix before the fault is calculated; Using the node impedance matrix as the sensitivity matrix, the passive voltage drop trajectory of each converter station bus during the fault occurrence is determined based on the matrix product between the sensitivity matrix and the first equivalent injected current change sequence. The voltage drop at the time of fault clearance is extracted from the passive voltage drop trajectory. Based on the difference between the voltage drop and the voltage reference value, the expected passive voltage value at the AC bus of the converter station at the time of fault clearance is determined.

[0010] Furthermore, determining the active control bias for the transient recovery process based on the expected passive voltage value includes: Based on the electrical instantaneous value, determine the actual positive sequence voltage amplitude corresponding to the fault clearing time; The difference between the actual positive sequence voltage amplitude and the expected passive voltage value is defined as the active control bias.

[0011] Furthermore, the process of obtaining the ideal passive voltage change includes: Obtain the active power command value frozen at the fault clearing time from each converter station; Starting from the fault clearance time, a delay window is constructed based on the response time constant of the outer loop of the internal control of each converter station. Within the delay window, the active power command value is converted into a second equivalent injection current change sequence; Substituting the sensitivity matrix and the second equivalent injection current change sequence into a preset formula, the ideal passive voltage change corresponding to each moment within the delay window is calculated.

[0012] Furthermore, before performing cross-correlation calculations on the active control voltage increment trajectories corresponding to any two converter stations, the method further includes: The active control voltage increment trajectory is processed to remove the DC component.

[0013] Furthermore, the transient coupling strength of the converter station pair is obtained, including: Within a preset observation time window, calculate the short-time cross-correlation function between any two converter stations corresponding to the active control voltage increment trajectory; Based on the short-time cross-correlation function, obtain the maximum absolute value of cross-correlation between any two converter stations within a preset time lag range and the autocorrelation function values ​​of any two converter stations under zero lag. The transient coupling strength between any two converter stations is determined based on the normalized result between the maximum absolute value of cross-correlation and the value of autocorrelation function.

[0014] Another embodiment of the present invention provides a coupling characteristic analysis system for a flexible DC-fed receiving-end power grid, comprising: The data acquisition module is used to acquire the node admittance parameters and transient electrical quantity sequences at the AC bus of the converter station at the corresponding time during the fault cycle of the receiving-end power grid. The passive response analysis module is used to obtain the ideal passive voltage change and the expected passive voltage at the AC bus of the converter station at the fault clearance time based on the node admittance parameter and the transient electrical quantity sequence. The bias determination module is used to determine the active control bias of the transient recovery process based on the expected passive voltage value as a comparison benchmark. The ideal trajectory synthesis module is used to superimpose the active control bias, the ideal passive voltage change, and the expected passive voltage value to obtain the ideal passive voltage recovery trajectory of each converter station bus in the initial stage of fault recovery. The active incremental extraction module is used to align the ideal passive voltage recovery trajectory with the actual voltage recovery trajectory of each converter station measured at the fault clearing time point by point to obtain the active control voltage incremental trajectory of each converter station. The coupling analysis module is used to perform cross-correlation calculations on the active control voltage increment trajectories corresponding to any two converter stations to obtain the transient coupling strength of the converter station pair; the transient coupling strength is used to screen converter station pairs.

[0015] Another embodiment of the present invention provides a computer device including a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. When the processor executes the computer program, it implements the coupling characteristic analysis method for flexible DC feed into the receiving-end power grid as described above.

[0016] In another embodiment of the present invention, a computer-readable storage medium is provided, the computer-readable storage medium storing a computer program, wherein when the device containing the computer-readable storage medium executes the computer program, it implements the coupling characteristic analysis method for flexible DC feed into the receiving-end power grid as described above.

[0017] Compared with the prior art, the beneficial effects of the embodiments of the present invention are at least one of the following: This invention first collects the node admittance parameters of the receiving-end power grid and the transient electrical quantity sequence at the converter station bus during a fault. By processing these response data, the accuracy of subsequent passive response component analysis can be improved. During the processing, the ideal passive voltage change and the expected passive voltage value at the fault clearing time are calculated using the two types of data, thereby separating the pure passive voltage component unaffected by active control and enhancing the identification of passive response. Then, the active control bias is determined based on the expected passive voltage value, which can quantify the actual contribution of active control to voltage recovery and prevent confusion between active and passive effects. The above quantities are superimposed to obtain the ideal passive voltage recovery trajectory, providing a physically consistent reference line for subsequent incremental stripping. Based on this ideal trajectory, the active control voltage increment trajectory is extracted and cross-correlation analysis is performed, improving the efficiency of coupling identification and reducing the risk of system transient instability. Attached Figure Description

[0018] Figure 1 This is a schematic flowchart of a method for analyzing the coupling characteristics of a flexible DC-fed receiving-end power grid in one embodiment of the present invention. Figure 2This is a schematic diagram of the coupling characteristic analysis system for flexible DC-fed receiving-end power grid in one embodiment of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] In the description of this application, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," "third," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0021] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. The terms "vertical," "horizontal," "left," "right," "upper," "lower," and similar expressions used herein are for illustrative purposes only and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0022] In the description of this application, it should be noted that, unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the invention. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0023] One embodiment of the present invention provides a method for analyzing the coupling characteristics of a flexible DC-fed receiving-end power grid. For details, please refer to [link to relevant documentation]. Figure 1 , Figure 1The diagram shown is a flowchart illustrating the coupling characteristic analysis method for a flexible DC-fed receiving-end power grid in one embodiment of the present invention, including the following steps: S1. During the fault cycle of the receiving-end power grid, obtain the node admittance parameters and the transient electrical quantity sequence at the AC bus of the converter station at the corresponding time.

[0024] In this embodiment, in order to provide accurate basic data for distinguishing between passive voltage drops and active control increments and analyzing transient coupling characteristics, the operating status of the receiving-end power grid is monitored during the receiving-end power grid fault cycle (before and during the fault) to obtain key electrical data such as voltage and power.

[0025] Specifically, before a fault occurs, the node admittance parameters of the AC network are obtained by monitoring the operating status of the receiving-end power grid. These parameters are used to construct the subsequent sensitivity matrix. For example, the AC network topology connection file, the positive sequence impedance parameters of each AC transmission line, the activated capacity of each parallel capacitor reactor, and the tap position data of each synchronous generator step-up transformer can be obtained from the receiving-end power grid energy management system for the scheduling period before the fault occurs.

[0026] The AC network topology connection file can be used to determine the distribution of non-zero, non-diagonal elements in the node admittance matrix, i.e., to identify which node pairs have direct transmission line connections, thus determining the sparse structure of the matrix. The positive-sequence impedance parameters of each AC transmission line, after being inversely calculated, are directly filled into the corresponding mutual admittance elements in the matrix, and the negative value of this mutual admittance is accumulated into the self-admittance diagonal element of the corresponding node. The input capacity of each parallel capacitor reactor needs to be converted into an equivalent ground admittance value before being superimposed onto the self-admittance diagonal element of the corresponding node. The tap position data of each synchronous generator step-up transformer, combined with the transformer's rated turns ratio, corrects the self-admittance and mutual admittance values ​​of the transformer branch at the relevant nodes in the matrix. After the aforementioned processing, the above four types of data directly form the values ​​of each element in the pre-fault steady-state node admittance matrix, and the pre-fault steady-state node admittance matrix is ​​formed based on the acquired data. .

[0027] When a fault is detected in the receiving-end power grid, such as a short-circuit fault on any AC bus, the instantaneous electrical values ​​from the time of the fault occurrence to the time of fault clearance are recorded, thereby determining the three-phase voltage drop depth sequence and active power output obstruction sequence at the AC bus of each flexible DC converter station.

[0028] For example, instantaneous voltage digital messages with a sampling rate of 80 to 256 points per cycle can be read from the output port of the merging unit of the capacitive voltage transformer installed in the grid-side winding of each converter transformer. Then, the read messages are subjected to Clarke transform to obtain the instantaneous phase voltage values ​​corresponding to each fault time (including the fault occurrence time, fault duration, and fault clearance time). At the same time, the instantaneous sampled value of the bridge arm current is read from the valve base controller interface board of the converter station control and protection system, i.e., the instantaneous value of the bridge arm current.

[0029] Furthermore, a positive-sequence Fourier transform is performed on the instantaneous phase voltage values ​​to obtain the positive-sequence voltage amplitude at each fault moment. Similarly, a Parker transform is performed on the instantaneous bridge arm current values ​​to transform them into a synchronous rotating coordinate system to obtain the active power values ​​at each fault moment.

[0030] In this embodiment, in order to obtain the passive voltage drop trajectory of the converter station bus during the fault, it is first necessary to obtain the positive sequence voltage amplitude corresponding to each sampling point during the fault duration. and active power value Next, the positive sequence voltage amplitude is compared with the preset voltage reference value. Taking the difference, we obtain the three-phase voltage sequence, as shown below: Compare the active power value with the preset power reference value. The difference is taken to obtain the active power sequence, as shown below: In one implementation of this embodiment, the average active power and the average positive sequence voltage amplitude calculated within one week prior to the fault occurrence are used as... and Among them, subscript Indicates the first A flexible DC converter station This represents the relative time sampling point during the fault duration, with the fault occurrence time as zero.

[0031] S2. Based on the node admittance parameters and transient electrical quantity sequence, obtain the ideal passive voltage change and the expected passive voltage value at the AC bus of the converter station at the fault clearing time.

[0032] To obtain the expected passive voltage at the AC bus of the converter station at the time of fault clearance, it is necessary to determine the passive voltage sag trajectory of each converter station bus during the fault period. It should be understood that the passive voltage sag trajectory represents the sequence of changes in the bus voltage of each converter station as a function of the active power deficit distribution during the fault, determined solely by the physical topology of the AC grid, assuming complete exclusion of dynamic adjustments by the control systems of each converter station. This trajectory serves as a purely physical voltage response reference for subsequent steps.

[0033] Specifically, the active power sequence is first... With voltage reference value By performing ratio calculations, the sequence of changes in the first equivalent injected current is obtained. Specifically, it is expressed as follows: For the previously obtained nodal admittance parameters, i.e., the nodal admittance matrix Perform the inversion operation to obtain the node impedance matrix before the fault. , The Middle Line 1 Column elements Indicates the first When a unit current is injected into the node, at the first The voltage change generated at each node This is the sensitivity matrix for the constructed pure AC power flow transfer. As can be understood, power flow transfer sensitivity refers to the matrix's ability to linearly map the injected current change to the voltage drop of other nodes when a converter station experiences a power outage due to a fault, which is equivalent to injecting a negative current change into the node. This quantitatively describes the sensitivity of the pure AC network topology to the propagation and distribution of active power deficit.

[0034] Based on the matrix product between the sensitivity matrix and the first equivalent injected current change sequence, the passive voltage drop trajectory of each converter station bus during the fault occurrence period is determined. , means as follows: Extracting fault clearing moments from passive voltage dip trajectories Corresponding voltage drop .

[0035] The difference between the voltage drop and the voltage reference value is then calculated to determine the expected passive voltage at the AC bus of the converter station at the time of fault clearance. Specifically, it is expressed as follows: In this embodiment, the expected value serves to provide a purely physical reference surface, devoid of control dynamics, for the subsequent separation of the active control component. Without constructing this physical reference surface, the contributions of passive power flow transfer and active control regulation in the measured voltage cannot be clearly decoupled over time.

[0036] In this embodiment, the ideal passive voltage change is reflected within a specific control response delay window. Assuming that the control systems of each converter station have not yet made active adjustments to the voltage change after the fault is cleared, and the active power injected into the AC system still maintains the level frozen at the moment the fault is cleared, the voltage change is generated on the bus of each converter station by the constant equivalent injection current change through the AC grid impedance relationship.

[0037] Based on this, a delay window is constructed using the fault clearing time as the starting point and the response time constant of the outer loop control within each converter station. The response time constant includes: the main integral time constant. The equivalent response time constant of the inner loop current controller In this embodiment, the main integral time constant characterizes the response speed of the outer loop power controller's integral link in eliminating the steady-state error of active power. Its value is directly taken from the tuning parameter register of the proportional-integral adjustment module of the outer loop power controller in the control and protection system of each converter station. The equivalent response time constant of the inner loop current controller characterizes the equivalent first-order inertia time required for the inner loop current closed loop to complete the actual current tracking from the given command. This value is obtained from the engineering commissioning report or factory test record of each converter station.

[0038] Furthermore, and The width of the control response delay window is 1.5 to 2 times that of the control window. The sum of these two corresponds to the series action time of the entire control link from the input of the outer loop power deviation to the actual output of the inner loop current. The main integral time constant of the outer loop power controller determines the dominant time scale required for the active power command to respond to the voltage deviation and reach a stable regulation rate, while the equivalent response time constant of the inner loop current controller determines the time required for the bridge arm current to actually track the current after the current command is issued. The two are connected in series in the control loop, thus together constituting a complete control response time delay.

[0039] In the delay window Within this framework, assuming that the active power injected into the AC system by each converter station remains at the frozen level at the moment of fault clearance, and combining this with voltage and power reference values, it is converted into the corresponding second equivalent injection current change. , represented as: In the formula, The active power command value frozen at the time of fault clearing is read from the digital signal processor register of the outer loop controller of each converter station's control and protection system.

[0040] Subsequently, the sensitivity matrix and the aforementioned second equivalent injection current change sequence are substituted into the following preset formula to calculate the ideal passive voltage change at each time point within the delay window. : in, This represents the total number of flexible DC converter stations in the receiving-end power grid. The relative time with the fault clearing time as zero. .

[0041] S3. Using the expected passive voltage value as a comparison benchmark, determine the active control bias for the transient recovery process.

[0042] As is understood, in this embodiment, the active control bias represents the initial voltage deviation accumulated at the time of fault clearance, resulting from the failure of each converter station control system to respond to AC voltage changes during the fault period due to maintaining the active power command frozen. This deviation originates solely from the passive hold-up behavior of the converter station control strategy itself during the fault and does not include power flow transfer information determined by the AC grid topology.

[0043] Based on this, similarly, according to the instantaneous phase voltage values ​​obtained at each fault time previously, the actual positive sequence voltage amplitude corresponding to the fault clearing time is extracted. By further subtracting the voltage amplitude from the expected passive voltage value, the active control bias for the transient recovery process is obtained. Specifically, it is expressed as follows: In this embodiment, the bias amount is actively controlled. Its function is to serve as a constant bias term superimposed when deriving the ideal passive voltage recovery trajectory, thereby embedding the influence already caused by the control loop at the moment of fault clearing into the initial conditions of the recovery process, so that the subsequent active control voltage increment trajectory extracted from the measured recovery trajectory completely covers the additional voltage changes caused by the inner loop current limiting, the outer loop power recovery slope and the dynamic response of the phase-locked loop during the entire recovery stage.

[0044] S4. The active control bias, the ideal passive voltage change, and the expected passive voltage value are superimposed to obtain the ideal passive voltage recovery trajectory of each converter station bus in the early stage of fault recovery.

[0045] The previously calculated active control bias As a constant bias term, it is related to the ideal passive voltage change. and the expected value of the purely passive response voltage at the moment of fault clearing. By superimposing the data, the ideal passive voltage recovery trajectory of each converter station bus during the initial recovery phase is obtained. .

[0046] In this embodiment, the ideal passive voltage recovery trajectory refers to the curve of the positive sequence voltage of each converter station bus over time, determined solely by the physical transfer effect of the AC grid and the control bias formed at the moment of fault clearance, within the control response delay window after fault clearance, assuming that the control systems of each converter station have not yet undergone active adjustment and the injected power remains at a frozen level. Its mathematical expression is as follows: S5. Align the ideal passive voltage recovery trajectory with the actual voltage recovery trajectory of each converter station measured at the fault clearing time point by point to obtain the active control voltage increment trajectory of each converter station.

[0047] In this embodiment, the active control voltage increment trajectory refers to the difference sequence obtained by separating the ideal passive voltage recovery trajectory from the measured voltage recovery trajectory. The physical source of this trajectory is entirely attributable to the active dynamic adjustment behavior of the converter station control system after fault clearance. Specifically, it includes the current limiting action of the inner loop current controller, the difference in the power recovery slope in the outer loop power controller, and the dynamic tracking response of the phase-locked loop to the AC voltage phase angle. Given that the physical transfer effect of the AC grid has been deducted from the ideal passive voltage recovery trajectory, the voltage fluctuation information contained in this trajectory only reflects the additional voltage changes caused by the dynamic characteristics of each converter station control link and the differences in control parameters.

[0048] Based on this, the ideal passive voltage recovery trajectory obtained in the previous deduction will be... Comparison with actual voltage recovery trajectory To perform point-by-point synchronization alignment on the same sampling time series, the following subtraction operation is performed: The above difference sequence This refers to the active control voltage increment trajectory caused entirely by the difference in the inner loop current limiting of the converter station, the outer loop power recovery slope, and the dynamic response of the phase-locked loop.

[0049] Similar to the previous process of obtaining the instantaneous phase voltage values ​​and filtering transformations corresponding to each fault moment, this step involves continuously reading the time window following the fault clearance moment from the merging unit of the capacitive voltage transformers installed on the AC bus of each flexible DC converter station. ( The observation time is measured in milliseconds from 100 to 500 milliseconds after the fault is cleared. The instantaneous three-phase voltage samples within the specified range are then processed using a positive sequence Fourier filter algorithm to obtain the actual voltage recovery trajectory for each converter station. .

[0050] To eliminate the impact of steady-state error on subsequent correlation analysis, the DC component of the active control voltage increment trajectory is further processed. The DC component-removed active control voltage increment trajectory is then expressed as: S6. Perform cross-correlation calculations on the active control voltage increment trajectories corresponding to any two converter stations to obtain the transient coupling strength of the converter station pair.

[0051] Once the key indicator of the active control voltage increment trajectory is obtained, the set of converter stations exhibiting strong control interaction during transient recovery can be identified, guiding the decentralized tuning of control parameters between converter stations. Strong control interaction, as understood, specifically refers to a sufficient magnitude of dynamic coupling between the control systems of two converter stations via an AC network, manifested as highly similar or inversely mapped fluctuation patterns in their active control voltage increment trajectories on the time axis. If this strong control interaction persists, it may lead to control-coupled oscillations between converter stations due to incoordination of control parameters. This manifests as undesirable low-frequency power fluctuations during voltage recovery after fault clearance, significantly prolonged voltage recovery time, or underdamped oscillations during recovery. In severe cases, it may trigger a chain reaction of instability in the converter station control system.

[0052] This embodiment preferably uses a short-time cross-correlation function for identification. Specifically, Within a preset observation time window, such as Within, calculate any two converter stations and The short-time cross-correlation function between the corresponding active control voltage increment trajectories is expressed as follows: in, This is the time lag, and its value range is... ; It is a short-time cross-correlation function; , Converter stations and The corresponding active control voltage increment trajectory.

[0053] Based on the above formula, the maximum absolute value of the short-time cross-correlation function between any two converter stations within a preset time lag range and the autocorrelation function values ​​of any two converter stations at zero lag are obtained. In this embodiment, the preset time lag range is... The maximum absolute value of cross-correlation is expressed by this formula: .

[0054] Based on the normalized result between the maximum absolute value of cross-correlation and the value of autocorrelation function, the transient coupling strength between any two converter stations is determined as follows: in, and The first The and the first The autocorrelation function value of the active control voltage increment trajectory of a converter station under zero hysteresis.

[0055] Traverse all The converter station pair combination yields the normalized transient coupling strength matrix. , the matrix Converter station pairs with a median value greater than 0.7 are identified as having strong control interaction. The identification results are output to the human-machine interface of the power grid dispatch control system in the form of a list of converter station name pairs and corresponding coupling strength values. This is used to guide the differentiated tuning of the proportional-integral parameters of the outer loop controller of each converter station.

[0056] Understandably, a large value for this indicator indicates significant dynamic interaction between the control loops of the two converter stations during the transient recovery process after fault clearance. Specifically, active control voltage fluctuations caused by inner-loop current limiting, outer-loop power recovery slope, or phase-locked loop dynamic response at one converter station are strongly transmitted and mapped onto the active control voltage increment trajectory of the other converter station. This poses a risk of poor interaction between control parameters, potentially inducing subsynchronous oscillations or slow voltage recovery. Conversely, a small value indicates weak correlation between the active control voltage increment trajectories of the two converter stations, with their respective control loops exhibiting largely independent dynamic responses. Mutual disturbances caused by control coupling are negligible, and the transient interaction between the two stations is primarily driven by passive power flow transfer determined by the AC grid's physical topology. Therefore, decoupling and coordinating control parameter tuning for this converter station pair is unnecessary. Because the above operations achieve independent quantification of active coupling strength at the converter station pair level, grid operators can accurately identify the specific converter station combinations requiring distributed control parameter optimization.

[0057] For example: Assume a receiving-end power grid contains three flexible DC converter stations, denoted as station A, station B, and station C. After traversal calculation in step S6, the normalized transient coupling strength matrix shows CAB=0.82, CAC=0.45, and CBC=0.31. Based on the 0.7 threshold, only station A and station B constitute a strong control interactive converter station pair.

[0058] The output of the human-machine interface is formatted as: "Strong control interactive converter station pair: Station A—Station B, transient coupling strength 0.82". Other combinations are not output because they do not exceed the threshold, or are listed separately as "low coupling strength". Based on this result, engineers can perform differentiated tuning of the proportional gain and integral time constant of the outer loop power controllers of Station A and Station B, appropriately widening the difference in their control bandwidth and reducing the overlap in the control time scale, while maintaining the conventional tuning values ​​for Station C. This achieves targeted decoupling optimization rather than uniform conservative tuning across the entire network.

[0059] In summary, this invention acquires admittance and electrical parameter data at different fault times during the receiving-end power grid fault cycle. Using this data as input, it calculates the passive voltage drop trajectory and expected passive voltage value of each converter station, determined solely by the AC network topology. Then, it extracts the active control bias by using the difference between the actual voltage measurement and the expected passive voltage value at the moment the fault is cleared. Based on this, the entire transient recovery voltage trajectory is decomposed into two independent parts: the passive voltage response trajectory and the active control voltage increment trajectory. This allows subsequent coupling characteristic analysis to focus on the interactive behavior of the converter station control system itself, improving the accuracy and relevance of transient coupling assessment.

[0060] One embodiment of the present invention provides a coupling characteristic analysis system for flexible DC-fed receiving-end power grids. For details, please refer to [link to relevant documentation]. Figure 2 , Figure 2 The diagram shown is a schematic of a coupling characteristic analysis system for a flexible DC-fed receiving-end power grid according to one embodiment of the present invention, comprising: The data acquisition module M1 is used to acquire the node admittance parameters and transient electrical quantity sequences at the AC bus of the converter station at the corresponding time during the fault cycle of the receiving-end power grid. The passive response analysis module M2 is used to obtain the ideal passive voltage change and the expected passive voltage at the AC bus of the converter station at the fault clearing time based on the node admittance parameter and the transient electrical quantity sequence. The bias determination module M3 is used to determine the active control bias of the transient recovery process based on the expected passive voltage value as a comparison benchmark. The ideal trajectory synthesis module M4 is used to superimpose the active control bias, the ideal passive voltage change, and the expected passive voltage value to obtain the ideal passive voltage recovery trajectory of each converter station bus in the initial stage of fault recovery. The active incremental extraction module M5 is used to align the ideal passive voltage recovery trajectory with the actual voltage recovery trajectory of each converter station measured at the fault clearing time point by point to obtain the active control voltage incremental trajectory of each converter station. The coupling analysis module M6 is used to perform cross-correlation calculations on the active control voltage increment trajectories corresponding to any two converter stations to obtain the transient coupling strength of the converter station pair; the transient coupling strength is used to screen converter station pairs.

[0061] In one embodiment of this application, a computer device is provided, which includes a memory and a processor. The memory stores machine-executable instructions that can be executed by the processor. When the processor executes a computer program, it implements the above steps. The computer device provided in this embodiment has a similar implementation principle and technical effect to the above method embodiments, and will not be described again here.

[0062] In one embodiment of this application, a computer-readable storage medium is provided, on which a computer program is stored, and when the computer program is executed by a processor, it performs the above steps; the implementation principle and technical effects of the computer-readable storage medium provided in this embodiment are similar to those of the above method embodiments, and will not be repeated here.

[0063] The technical features and effects of the coupling characteristic analysis system for flexible DC-fed receiving-end power grid proposed in this embodiment of the invention are the same as those of the coupling characteristic analysis method for flexible DC-fed receiving-end power grid proposed in this embodiment of the invention, and will not be repeated here.

[0064] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for analyzing the coupling characteristics of flexible DC feed into the receiving-end power grid, characterized in that, include: During the fault cycle of the receiving-end power grid, obtain the node admittance parameters and the transient electrical quantity sequence at the AC bus of the converter station at the corresponding time. Based on the node admittance parameters and the transient electrical quantity sequence, the ideal passive voltage change and the expected passive voltage at the AC bus of the converter station at the fault clearance time are obtained. The active control bias for the transient recovery process is determined using the expected passive voltage value as a comparison benchmark. The active control bias, the ideal passive voltage change, and the expected passive voltage value are superimposed to obtain the ideal passive voltage recovery trajectory of each converter station bus in the initial stage of fault recovery. The ideal passive voltage recovery trajectory is aligned point by point with the actual voltage recovery trajectory of each converter station measured at the fault clearing time to obtain the active control voltage increment trajectory of each converter station. Cross-correlation calculations are performed on the active control voltage increment trajectories corresponding to any two converter stations to obtain the transient coupling strength of the converter station pair; The transient coupling strength is used to screen converter station pairs.

2. The coupling characteristic analysis method for flexible DC-DC fed into the receiving-end power grid as described in claim 1, characterized in that, The acquisition of node admittance parameters and transient electrical quantity sequences at the AC bus of the converter station during a fault cycle at the receiving end of the power grid includes: Before a fault occurs in the receiving-end power grid, the node admittance parameters of the AC network are obtained; During a power grid fault at the receiving end, electrical instantaneous values ​​corresponding to each fault moment are read from each converter station; the electrical instantaneous values ​​include the instantaneous values ​​of phase voltage and bridge arm current. Based on the instantaneous electrical values, the positive sequence voltage amplitude and active power value during the fault duration are determined; The three-phase voltage sequence is obtained by subtracting the positive sequence voltage amplitude from the preset voltage reference value; The active power value is subtracted from the preset power reference value to obtain the active power sequence.

3. The coupling characteristic analysis method for flexible DC-DC fed into the receiving-end power grid as described in claim 2, characterized in that, The process of obtaining the expected value of the passive voltage includes: The active power sequence is compared with the voltage reference value to obtain the first equivalent injection current change sequence. Based on the node admittance parameters, the node impedance matrix before the fault is calculated; Using the node impedance matrix as the sensitivity matrix, the passive voltage drop trajectory of each converter station bus during the fault occurrence is determined based on the matrix product between the sensitivity matrix and the first equivalent injected current change sequence. The voltage drop at the time of fault clearance is extracted from the passive voltage drop trajectory. Based on the difference between the voltage drop and the voltage reference value, the expected passive voltage value at the AC bus of the converter station at the time of fault clearance is determined.

4. The coupling characteristic analysis method for flexible DC-DC fed into the receiving-end power grid as described in claim 2, characterized in that, The determination of the active control bias for the transient recovery process based on the expected passive voltage value includes: Based on the electrical instantaneous value, determine the actual positive sequence voltage amplitude corresponding to the fault clearing time; The difference between the actual positive sequence voltage amplitude and the expected passive voltage value is defined as the active control bias.

5. The coupling characteristic analysis method for flexible DC-DC fed into the receiving-end power grid as described in claim 3, characterized in that, The process of obtaining the ideal passive voltage change includes: Obtain the active power command value frozen at the fault clearing time from each converter station; Starting from the fault clearance time, a delay window is constructed based on the response time constant of the outer loop of the internal control of each converter station. Within the delay window, the active power command value is converted into a second equivalent injection current change sequence; Substituting the sensitivity matrix and the second equivalent injection current change sequence into a preset formula, the ideal passive voltage change corresponding to each moment within the delay window is calculated.

6. The coupling characteristic analysis method for flexible DC-DC fed into the receiving-end power grid as described in claim 1, characterized in that, Before performing cross-correlation calculations on the active control voltage increment trajectories corresponding to any two converter stations, the method further includes: The active control voltage increment trajectory is processed to remove the DC component.

7. The coupling characteristic analysis method for flexible DC-DC fed into the receiving-end power grid as described in claim 1, characterized in that, The step of performing cross-correlation calculations on the active control voltage increment trajectories corresponding to any two converter stations to obtain the transient coupling strength of the converter station pair includes: Within a preset observation time window, calculate the short-time cross-correlation function between any two converter stations corresponding to the active control voltage increment trajectory; Based on the short-time cross-correlation function, obtain the maximum absolute value of cross-correlation between any two converter stations within a preset time lag range and the autocorrelation function values ​​of any two converter stations under zero lag. The transient coupling strength between any two converter stations is determined based on the normalized result between the maximum absolute value of cross-correlation and the value of autocorrelation function.

8. A coupling characteristic analysis system for flexible DC feed into a receiving-end power grid, characterized in that, include: The data acquisition module is used to acquire the node admittance parameters and transient electrical quantity sequences at the AC bus of the converter station at the corresponding time during the fault cycle of the receiving-end power grid. The passive response analysis module is used to obtain the ideal passive voltage change and the expected passive voltage at the AC bus of the converter station at the fault clearance time based on the node admittance parameter and the transient electrical quantity sequence. The bias determination module is used to determine the active control bias of the transient recovery process based on the expected passive voltage value as a comparison benchmark. The ideal trajectory synthesis module is used to superimpose the active control bias, the ideal passive voltage change, and the expected passive voltage value to obtain the ideal passive voltage recovery trajectory of each converter station bus in the initial stage of fault recovery. The active incremental extraction module is used to align the ideal passive voltage recovery trajectory with the actual voltage recovery trajectory of each converter station measured at the fault clearing time point by point to obtain the active control voltage incremental trajectory of each converter station. The coupling analysis module is used to perform cross-correlation calculations on the active control voltage increment trajectories corresponding to any two converter stations to obtain the transient coupling strength of the converter station pair. The transient coupling strength is used to screen converter station pairs.

9. A computer device, characterized in that, It includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein the processor executes the computer program to implement the coupling characteristic analysis method for flexible DC feed into the receiving-end power grid as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program, wherein when the device containing the computer-readable storage medium executes the computer program, it implements the coupling characteristic analysis method for flexible DC-fed receiving-end power grid as described in any one of claims 1 to 7.

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