A frequency control method and device suitable for UHV flexible DC transmission

Abstract

This invention discloses a frequency control method and device suitable for ultra-high voltage flexible DC transmission systems. The method includes first acquiring the system frequency and various operating parameters of the ultra-high voltage flexible DC transmission system, constructing a frequency time series and an operating time series corresponding to each operating parameter; then calculating the frequency mutation intensity and mutation recovery time of each frequency mutation point in the frequency time series, thereby determining the system inertia level; calculating the frequency sudden change trend index based on the trend change characteristics of the frequency time series and the correlation lag characteristics between the frequency time series and each operating time series, and determining the operating condition disturbance level; dynamically determining the frequency control strategy based on the operating condition disturbance level and the system inertia level, and controlling the frequency of the ultra-high voltage flexible DC transmission system. The frequency control method and device provided by this invention for ultra-high voltage flexible DC transmission systems improve the frequency control effect of ultra-high voltage flexible DC transmission systems.

Description

Technical Field

[0001] This invention relates to the field of flexible DC transmission technology, and in particular to a frequency control method and device suitable for ultra-high voltage flexible DC transmission. Background Technology

[0002] Ultra-high voltage (UHV) flexible direct current (DC) transmission technology boasts advantages such as large transmission capacity, long transmission distance, and flexible control, making it a key technology for large-scale grid connection of new energy sources and cross-regional power transmission. However, with the rapid development of new energy power generation technologies, the grid connection scale of renewable energy sources such as wind power and photovoltaics continues to expand, while the proportion of traditional synchronous units such as thermal power and hydropower is gradually declining, leading to a significant reduction in the inherent inertia of the power system. Inertia is a core factor in maintaining the frequency stability of the power system. When inertia is insufficient, the power system becomes highly susceptible to external disturbances such as load fluctuations, sudden changes in new energy output, and unit start-up and shutdown, resulting in system power fluctuations and frequency instability. This exacerbates the difficulty of frequency control in the power system and seriously threatens the safe and stable operation of the power system.

[0003] Therefore, in order to ensure the stable operation of the power system, it is necessary to control the frequency of the power system. However, in the actual operation of the power system, it often faces complex operating conditions with multiple disturbances superimposed. The existing control methods use fixed control logic, which cannot adapt to the complex and ever-changing operating conditions of the UHV flexible DC system. This leads to problems such as frequency runaway and control strategy failure in scenarios with multiple disturbances superimposed, which seriously threatens the safe and stable operation of the power system.

[0004] Therefore, how to dynamically adjust the control strategy under multiple disturbance scenarios to improve the frequency control effect of UHV flexible DC systems has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] This invention provides a frequency control method and device applicable to UHV flexible DC transmission systems, which solves the technical problem that existing control methods use fixed control logic and cannot adapt to the complex and ever-changing operating conditions of UHV flexible DC transmission systems. This leads to problems such as frequency runaway and control strategy failure under multiple disturbance scenarios, which seriously threaten the safe and stable operation of the power system.

[0006] To address the aforementioned technical problems, embodiments of the present invention provide a frequency control method suitable for ultra-high voltage flexible DC transmission, comprising:

[0007] The system frequency and various operating parameters of the UHV flexible DC system are obtained. A frequency time series is constructed using all the system frequencies within a preset time period. An operating time series corresponding to each operating parameter is constructed using all the operating parameters within the preset time period.

[0008] Extract each frequency mutation point in the frequency time series, calculate the frequency mutation intensity of each frequency mutation point based on the degree to which each frequency mutation point deviates from the overall trend of the frequency time series, obtain the mutation recovery time of each frequency mutation point based on the difference characteristics of the neighborhood frequency trend of each frequency mutation point, and determine the system inertia level based on the frequency mutation intensity and mutation recovery time of all the frequency mutation points.

[0009] The frequency abrupt change trend index is calculated based on the trend change characteristics of the frequency time series and the correlation lag characteristics between the frequency time series and each of the operating time series. The operating condition disturbance level is determined based on the comparison result of the frequency abrupt change trend index and the preset mutation threshold. The frequency abrupt change trend index is used to characterize the potential mutation degree of the system frequency.

[0010] The frequency control strategy is dynamically determined based on the operating condition disturbance level and the system inertia level, and the frequency of the UHV flexible DC system is controlled by the frequency control strategy.

[0011] As one preferred embodiment, calculating the frequency mutation intensity of each frequency mutation point based on the degree to which each frequency mutation point deviates from the overall trend of the frequency time series includes:

[0012] The frequency time series is subjected to polynomial fitting to obtain a frequency fitting curve, and the frequency fitting curve is serialized to obtain a frequency fitting time series corresponding to the frequency time series.

[0013] The frequency time series and the frequency fitting time series are subtracted to obtain the frequency deviation time series.

[0014] The value corresponding to each frequency mutation point in the frequency deviation time series is taken as the absolute frequency deviation value of each frequency mutation point;

[0015] The standard deviation of the frequency time series within a preset sliding window at each frequency mutation point is used as the neighborhood frequency deviation benchmark value for each frequency mutation point.

[0016] The ratio of the absolute frequency deviation value of each frequency mutation point to the corresponding neighborhood frequency deviation reference value is used as the frequency mutation intensity of each frequency mutation point.

[0017] As one preferred embodiment, obtaining the mutation recovery time of each frequency mutation point based on the neighborhood frequency trend difference characteristics of each frequency mutation point includes:

[0018] The Otsu threshold segmentation algorithm is used to process all values ​​in the frequency deviation time series to obtain the deviation segmentation threshold;

[0019] All data points in the frequency deviation time series that are less than the deviation segmentation threshold are taken as trend points;

[0020] The frequency deviation time series is divided according to each frequency mutation point to obtain the left neighbor sequence and the right neighbor sequence of each frequency mutation point;

[0021] The trend point that is closest to the frequency change point in the left neighbor sequence of each frequency change point is taken as the left nearest neighbor trend point of the frequency change point, and the trend point that is closest to the frequency change point in the right neighbor sequence of each frequency change point is taken as the right nearest neighbor trend point of the frequency change point.

[0022] The time interval between the left nearest neighbor trend point and the right nearest neighbor trend point of each frequency mutation point is taken as the mutation recovery time of each frequency mutation point.

[0023] As one preferred embodiment, determining the system inertia level based on the frequency change intensity and the change recovery time of all the frequency change points includes:

[0024] The ratio of the frequency mutation intensity to the mutation recovery time at each frequency mutation point is taken as the current inertial force intensity at each frequency mutation point.

[0025] The current inertia intensity at all frequency abrupt change points is input into the system inertia evaluation expression to obtain the system inertia intensity. Based on the comparison between the system inertia intensity and a preset inertia threshold, the system inertia level is determined. The system inertia evaluation expression is designed as follows:

[0026]

[0027] in, The intensity of the system's inertia. It is an exponential function with the natural constant as its base. The number of frequency abrupt change points. For the first The intensity of the current inertia effect at each frequency abrupt change point.

[0028] As one preferred embodiment, the step of calculating the frequency abrupt change trend index based on the trend change characteristics of the frequency time series and the correlation lag characteristics between the frequency time series and each of the running time series includes:

[0029] The frequency abrupt change index is calculated based on the trend abrupt change characteristics of the frequency time series;

[0030] Each key interference factor is obtained based on the correlation characteristics between the frequency time series and each of the running time series;

[0031] Variational mode decomposition is performed on the frequency time series to obtain the frequency variation mode components;

[0032] The interference delay response index of each frequency-varying mode component is obtained based on the correlation hysteresis characteristics between the running time series of each frequency-varying mode component and each key interference factor;

[0033] The average value of the disturbance delay response exponents of all the frequency-varying mode components is taken as the disturbance delay exponent, and the reciprocal of the disturbance delay exponent is taken as the disturbance urgency factor.

[0034] The frequency change trend index is calculated based on the linear relationship between the frequency change index and the disturbance urgency factor.

[0035] As one preferred embodiment, the calculation of the frequency abrupt change index based on the trend abrupt change characteristics of the frequency time series includes:

[0036] Perform first-order difference on the frequency time series to obtain the frequency change rate series, and extract all first abrupt change points in the frequency change rate series;

[0037] The frequency time series is subjected to second-order difference to obtain the frequency change acceleration series, and all second abrupt change points in the frequency change acceleration series are extracted.

[0038] The third mutation point is determined based on the time interval between the first mutation point and the second mutation point;

[0039] The frequency change velocity sequence and the frequency change acceleration sequence are added together to obtain the frequency abrupt change time sequence;

[0040] The sum of the values ​​of all the third mutation points in the frequency abrupt change time series is taken as the frequency abrupt change factor, and the normalized value of the frequency abrupt change factor is taken as the frequency abrupt change index.

[0041] As one preferred embodiment, the dynamic determination of the frequency control strategy based on the operating condition disturbance level and the system inertia level includes:

[0042] The difference between the system inertia level and the operating condition disturbance level is taken as the operating condition controllability.

[0043] When the controllability of the operating condition is greater than 0, the original frequency control strategy is maintained.

[0044] When the controllability of the operating condition is equal to 0, a virtual inertia priority control strategy is executed. The virtual inertia priority control strategy is designed to adjust the parameter value of the virtual inertia according to the disturbance level of the operating condition, and control the frequency of the UHV flexible DC system with the adjusted virtual inertia until the controllability of the operating condition is greater than 0.

[0045] When the controllability of the operating condition is less than 0, a cooperative control strategy is executed. The cooperative control strategy is designed to first start virtual inertia control to suppress the rate of change of the system frequency. When the rate of change of the system frequency is detected to drop below a preset floating threshold, virtual inertia control is stopped, and a primary frequency modulation control is started to adjust the system frequency until the controllability of the operating condition is greater than 0.

[0046] As a preferred embodiment, obtaining the interference delay response index of each frequency-varying mode component based on the correlation hysteresis characteristics between the running time series of each frequency-varying mode component and each key interference factor includes:

[0047] Calculate the cross-correlation coefficient between the running time series of each frequency variation mode component and each key interference factor at each lag order;

[0048] The maximum value of the cross-correlation coefficient between the running time series of each frequency-varying mode component and each key interference factor is taken as the hysteresis correlation coefficient between each frequency-varying mode component and each key interference factor.

[0049] The lag order corresponding to the lag correlation coefficient of the running time series of each frequency change mode component and each key interference factor is taken as the optimal lag time of each frequency change mode component and each key interference factor.

[0050] The interference delay response index of each frequency-varying mode component is calculated based on the linear relationship between the hysteresis correlation coefficient and the optimal hysteresis duration of each frequency-varying mode component and each key interference factor.

[0051] As a preferred embodiment, the calculation of the interference delay response index for each frequency-varying mode component based on the linear relationship between the hysteresis correlation coefficient and the optimal hysteresis duration of each frequency-varying mode component and each key interference factor includes:

[0052] The sum of the hysteresis correlation coefficients of each frequency-varying mode component and all the key interference factors is used as the reference value of the hysteresis correlation coefficient of each frequency-varying mode component.

[0053] Each frequency-varying mode component is sequentially used as a target frequency-varying mode component. The hysteresis correlation coefficient between the target frequency-varying mode component and each key interference factor is divided by the hysteresis correlation coefficient benchmark value of the target frequency-varying mode component to obtain the correlation weight between the target frequency-varying mode component and each key interference factor.

[0054] The interference delay evaluation expression is designed as follows: All the correlation weights and all the hysteresis correlation coefficients of the target frequency-varying mode component are input into the interference delay evaluation expression, and the interference delay response index of the target frequency-varying mode component is output.

[0055]

[0056] in, For target frequency variation modal components Interference delay response index For target frequency variation modal components With the The association weights of the key interference factors For target frequency variation modal components With the The lag correlation coefficients of key interference factors, For target frequency variation modal components The number of key interfering factors.

[0057] Another embodiment of the present invention provides a frequency control device suitable for UHV flexible DC transmission, 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 a frequency control method suitable for UHV flexible DC transmission as described above.

[0058] Compared with the prior art, the beneficial effects of the embodiments of the present invention are at least one of the following:

[0059] First, the system frequency and various operating parameters of the UHV flexible DC system are obtained. A frequency time series is constructed using all system frequencies within a preset time period, and an operating time series is constructed for each operating parameter within the preset time period. Then, frequency abrupt change points are extracted from the frequency time series. The frequency abrupt change intensity of each frequency abrupt change point is calculated based on its deviation from the overall trend of the frequency time series. The abrupt change recovery time of each frequency abrupt change point is obtained based on the difference characteristics of the neighboring frequency trends. The system inertia level is determined based on the frequency abrupt change intensity and the abrupt change recovery time of all frequency abrupt change points, accurately capturing the dynamic changes in the system inertia level. Through dual quantification of abrupt change intensity and recovery time, random noise interference is effectively eliminated, avoiding bias in inertia level determination, and achieving accurate quantification of the UHV flexible DC system's own anti-fluctuation capability. Next, the trend change characteristics of the frequency time series and the correlation lag characteristics between the frequency time series and each operating time series are analyzed. A frequency abrupt change trend index is calculated. Based on the frequency abrupt change trend index and a preset... The comparison results of mutation thresholds determine the operating condition disturbance level, taking into account both the historical patterns of frequency changes and capturing the lag correlation between operating parameter disturbances and frequency fluctuations. This accurately characterizes the potential mutation degree of the system frequency, enabling a comprehensive and accurate prediction of the intensity of external disturbances and the risk of potential mutations. It accurately identifies disturbance signals under multiple disturbance superposition scenarios, solving the problem that traditional methods only focus on current fluctuations and cannot predict potential risks. Finally, based on the operating condition disturbance level and system inertia level, a frequency control strategy is dynamically determined, and the frequency of the UHV flexible DC system is controlled using this strategy. Taking into account the system's own anti-fluctuation capability and the intensity of external disturbances, the control logic is dynamically adapted according to different combinations of system inertia level and disturbance level. This avoids over-control in high-inertia scenarios and solves the problems of control lag and strategy failure in low-inertia and multiple disturbance scenarios. It can effectively suppress sudden frequency changes in multiple disturbance superposition scenarios, adapt to the power system operation requirements after large-scale grid connection of new energy, avoid the risk of frequency runaway, and improve the frequency control effect of the UHV flexible DC system. Attached Figure Description

[0060] Figure 1 This is a flowchart illustrating a frequency control method applicable to ultra-high voltage flexible DC transmission in one embodiment of the present invention;

[0061] Figure 2 This is a schematic diagram illustrating the acquisition of the frequency abrupt change trend index in one embodiment of the present invention;

[0062] Figure 3 This is a structural block diagram of a frequency control device suitable for ultra-high voltage flexible DC transmission in one embodiment of the present invention;

[0063] Figure label:

[0064] Among them, 21 is the processor; and 22 is the memory. Detailed Implementation

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] It should be noted that in the existing technology, the virtual inertia control and primary frequency regulation control of UHV flexible DC systems mostly adopt fixed parameter control mode, without dynamically adjusting the control strategy according to the system inertia level and the level of operating disturbance. This makes it unable to adapt to the complex and ever-changing operating conditions of UHV flexible DC systems, and it is difficult to effectively suppress frequency fluctuations and quickly restore the system steady state. As a result, under the superposition of multiple disturbances, problems such as frequency runaway and control strategy failure are likely to occur, which seriously threaten the safe and stable operation of the power system.

[0070] One embodiment of the present invention provides a frequency control method suitable for UHV flexible DC transmission. For details, please refer to [link to documentation]. Figure 1 , Figure 1 The diagram shown is a flowchart of a frequency control method for UHVDC flexible DC transmission, which is applicable to one embodiment of the present invention, including steps S1 to S4.

[0071] Step S1: Obtain the system frequency and various operating parameters of the UHV flexible DC system, construct a frequency time series using all system frequencies within a preset time period, and construct an operating time series corresponding to each operating parameter using all operating parameters within a preset time period.

[0072] Specifically, the system frequency and various operating parameters are collected every t minutes within a preset time period. During the collection process, an improved Kalman filter algorithm is first used to denoise the collected data to remove abnormal data caused by power grid interference and equipment errors, ensuring data accuracy. Then, the collected system frequency and various operating parameters are serialized at a preset time period to construct a frequency time series and the corresponding operating time series of each operating parameter, providing a data basis for subsequent inertia assessment and disturbance determination.

[0073] It should be noted that the operating parameters include system power imbalance, UHV flexible line transmission power, new energy output, and operating parameters of energy storage equipment.

[0074] In one embodiment, the new energy output includes wind power output and photovoltaic power output, and the operating parameters of the energy storage device include remaining power, charging and discharging power and operating temperature.

[0075] It should be noted that the length of the preset time period and the interval t are both preset values. In this embodiment, the length of the preset time period is 30 days and the interval t is 15. This application does not impose any special restrictions on the value of the preset time period and the interval t. Implementers can flexibly adjust them according to the disturbance propagation speed and the complexity of the operating conditions of the UHV flexible DC system. For example, in areas where the output of new energy sources fluctuates drastically, the preset time period can be adjusted to 15 days and the interval t can be adjusted to 10 to improve the timeliness of data. In areas where the system is operating stably, the preset time period can be adjusted to 60 days and the interval t can be adjusted to 30 minutes to reduce the data processing pressure.

[0076] Step S2: Extract each frequency mutation point in the frequency time series, calculate the frequency mutation intensity of each frequency mutation point according to the degree of deviation of each frequency mutation point from the overall trend of the frequency time series, obtain the mutation recovery time of each frequency mutation point based on the difference characteristics of the neighborhood frequency trend of each frequency mutation point, and determine the system inertia level according to the frequency mutation intensity and mutation recovery time of all frequency mutation points.

[0077] It should be noted that the inherent inertia of the UHV flexible DC system can suppress frequency fluctuations and quickly restore a steady state when frequency fluctuates. When the inherent inertia is strong, even if the frequency fluctuates significantly, it can quickly restore a steady state. Therefore, the inherent inertia of the UHV flexible DC system needs to be taken into account when controlling the frequency of the UHV flexible DC system.

[0078] Specifically, the Pettitt mutation point detection algorithm is used to extract frequency mutation points in the frequency time series.

[0079] Furthermore, the frequency mutation intensity of each frequency mutation point is calculated based on the degree to which each frequency mutation point deviates from the overall trend of the frequency time series.

[0080] In one embodiment, the specific calculation process for the frequency change intensity of each frequency change point includes:

[0081] A polynomial fit is performed on the frequency time series to obtain a frequency fitting curve. The frequency fitting curve is then serialized to obtain a frequency fitting time series corresponding to the frequency time series. The frequency time series and the frequency fitting time series are subtracted to obtain a frequency deviation time series. The value corresponding to each frequency abrupt change point in the frequency deviation time series is taken as the absolute frequency deviation value of each frequency abrupt change point. The standard deviation of the frequency time series within a preset sliding window at each frequency abrupt change point is taken as the neighborhood frequency deviation benchmark value of each frequency abrupt change point. The ratio of the absolute frequency deviation value of each frequency abrupt change point to the corresponding neighborhood frequency deviation benchmark value is taken as the frequency abrupt change intensity of each frequency abrupt change point.

[0082] It should be noted that, firstly, polynomial fitting is used to fit the overall trend of the frequency time series, generating a smooth frequency fitting curve to extract the long-term, stable variation law of the system frequency. Then, the frequency time series and the frequency fitting time series are calculated point by point using sequence subtraction. The difference between the actual collected system frequency data and the fitted smooth trend data at each collection point is calculated, i.e., the frequency deviation from the time series, quantifying the degree of deviation between the actual frequency and the normal trend frequency. Then, the standard deviation is used to calculate the neighborhood frequency deviation benchmark value, quantifying the intensity of frequency data fluctuation within the sliding window of each frequency mutation point, and establishing a local fluctuation benchmark. This not only eliminates the interference of random noise and local fluctuations, but also takes into account the deviation degree of the mutation point itself and the fluctuation background of the surrounding area, solving the problem of misjudgment of mutation intensity caused by traditional single fixed threshold judgment, and improving the reliability of mutation intensity assessment. Polynomial fitting, sequence subtraction, and standard deviation calculation are all well-known techniques, and will not be elaborated here.

[0083] Furthermore, the mutation recovery time of each frequency mutation point is obtained based on the difference characteristics of the neighborhood frequency trends of each frequency mutation point, specifically including:

[0084] The Otsu threshold segmentation algorithm is used to process all values ​​in the frequency deviation time series to obtain the deviation segmentation threshold. All data points in the frequency deviation time series that are less than the deviation segmentation threshold are taken as trend points. The frequency deviation time series is divided by each frequency abrupt change point to obtain the left neighbor sequence and the right neighbor sequence of each frequency abrupt change point. The trend point in the left neighbor sequence of each frequency abrupt change point that is closest to the frequency abrupt change point is taken as the left nearest neighbor trend point of the frequency abrupt change point, and the trend point in the right neighbor sequence of each frequency abrupt change point that is closest to the frequency abrupt change point is taken as the right nearest neighbor trend point of the frequency abrupt change point. The time interval between the left nearest neighbor trend point and the right nearest neighbor trend point of each frequency abrupt change point is taken as the change recovery time of each frequency abrupt change point.

[0085] It should be noted that the Otsu threshold segmentation algorithm is an adaptive threshold segmentation algorithm. Its core calculation logic eliminates the need for manually preset thresholds. By traversing all possible frequency deviation values ​​in the frequency deviation time series, it calculates the inter-class variance corresponding to each candidate threshold, and determines the candidate threshold with the largest inter-class variance as the final deviation segmentation threshold. The Otsu threshold segmentation algorithm adaptively distinguishes between small deviations when the system frequency is in a steady-state trend and deviations affected by frequency abrupt changes and surrounding abrupt changes. It eliminates the need for manual intervention in threshold setting, avoiding misjudgments of trend points due to improper manual threshold selection. This ensures the accuracy of subsequent extraction of left and right nearest neighbor trend points, precisely capturing the complete cycle from deviation from steady state to recovery of steady state for each frequency abrupt change, thus improving the reliability of subsequent system inertia level assessment. The Otsu threshold segmentation algorithm is a well-known technology and will not be elaborated upon here.

[0086] Furthermore, the system inertia level is determined based on the frequency change intensity and recovery time at all frequency change points, specifically including:

[0087] The ratio of the frequency mutation intensity to the mutation recovery time at each frequency mutation point is used as the current inertial intensity at that point. The current inertial intensity of all frequency mutation points is input into the system inertial evaluation expression to obtain the system inertial intensity. Based on the comparison between the system inertial intensity and a preset inertial threshold, the system inertial level is determined. The system inertial evaluation expression is designed as follows:

[0088]

[0089] in, The intensity of the system's inertia. It is an exponential function with the natural constant as its base. The number of frequency abrupt change points. For the first The intensity of the current inertia effect at each frequency abrupt change point.

[0090] It should be noted that the system inertia level is used to characterize the frequency fluctuation resistance of the UHV flexible DC system. The higher the system inertia level, the stronger the system's ability to suppress frequency fluctuations and quickly recover to steady state; conversely, the lower the system inertia level, the more prone the system frequency is to large fluctuations and the slower the recovery to steady state. The smaller the current inertia intensity at each frequency mutation point, the weaker the inertia of the UHV flexible DC system. Through the convergence characteristics of the exponential function, the current inertia intensity of all frequency mutation points can be effectively summarized, while avoiding excessive interference of a single extreme mutation point on the overall evaluation result. This ensures that the system inertia intensity is always between 0 and 1. Evaluation based on the dynamic characteristics of all frequency mutation points can capture the dynamic changes of the system inertia level in real time, accurately reflect the system's resistance to fluctuations under different disturbance scenarios, improve the accuracy of the system inertia level evaluation, provide precise support for subsequent dynamic adjustment of control strategies, ensure that the control strategy can adapt to the dynamic changes of system inertia, and thus improve the stability and reliability of system frequency control.

[0091] For example, when the frequency mutation intensity at the frequency mutation point is 5.2 and the mutation recovery time is 90 minutes, the calculated current inertial force intensity is 0.058. Substituting the current inertial force intensity at the 12 mutation points into the system inertial evaluation expression, then... It is 12.

[0092] In one embodiment, the preset inertia threshold includes a preset first inertia threshold of 0.5 and a preset second inertia threshold of 0.7. If the calculated system inertia intensity is 0.52, the corresponding system inertia level of the UHV flexible DC system is 2, indicating that the system has a certain ability to resist frequency fluctuations, but the recovery speed is slow when facing strong sudden changes.

[0093] Step S3: Calculate the frequency sudden change trend index based on the trend change characteristics of the frequency time series and the correlation lag characteristics between the frequency time series and each operating time series. Determine the operating condition disturbance level based on the comparison results of the frequency sudden change trend index and the preset mutation threshold. The frequency sudden change trend index is used to characterize the potential mutation degree of the system frequency.

[0094] It should be noted that since the propagation of fluctuations usually takes a period of time, the frequency disturbances of various factors in the UHV flexible DC system have a lag effect. Focusing only on the current fluctuations cannot predict potential disturbance risks. Therefore, when assessing the operating disturbance situation of the UHV flexible DC system, it is necessary to consider not only the historical abrupt changes in the system frequency, but also the trend prediction abrupt changes in the system frequency.

[0095] Specifically, step S3 calculates the frequency abrupt change trend index based on the trend change characteristics of the frequency time series and the correlation lag characteristics between the frequency time series and each running time series, including steps S301 to S304:

[0096] Step S301: Calculate the frequency abrupt change index based on the trend abrupt change characteristics of the frequency time series;

[0097] Step S302: Based on the correlation characteristics between the frequency time series and each running time series, obtain each key interference factor, and perform variational mode decomposition on the frequency time series to obtain each frequency change mode component.

[0098] Step S303: Obtain the interference delay response index of each frequency-varying mode component based on the correlation hysteresis characteristics between the running time series of each frequency-varying mode component and each key interference factor.

[0099] Step S304: The average value of the disturbance delay response index of all frequency change mode components is taken as the disturbance delay index, and the reciprocal of the disturbance delay index is taken as the disturbance urgency factor. The frequency sudden change trend index is calculated based on the linear relationship between the frequency sudden change index and the disturbance urgency factor.

[0100] It should be noted that the trend abrupt change characteristics of the frequency time series reflect the historical abrupt change characteristics of the system frequency change, and the correlation lag characteristics between the frequency time series and each operating time series reflect the trend prediction abrupt change characteristics of the system frequency change. When the frequency abrupt change index is larger and the disturbance urgency factor is larger, it indicates that the historical abrupt change characteristics and trend prediction abrupt change characteristics of the system frequency change are stronger, and the disturbance to the system frequency is stronger. The larger the frequency abrupt change trend index, the more necessary it is to quickly control the frequency of the UHV flexible DC system. By combining the past frequency change patterns with the future fluctuation trends, the accuracy of assessing the operating condition disturbance of the UHV flexible DC system is improved.

[0101] For example, when the interference delay response exponents of the four frequency-varying mode components are 0.38, 0.45, 0.32, and 0.41, respectively, the following calculations are obtained:

[0102] The disturbance delay index = (0.38 + 0.45 + 0.32 + 0.41) / 4 = 0.39;

[0103] The disturbance urgency factor = 1 / 0.39 ≈ 2.56, which is 0.48 after normalization;

[0104] Frequency sudden change trend index = (0.42×0.5+0.48×0.5) / 1 = 0.45.

[0105] The preset mutation thresholds are set to 0.3 and 0.6. Since 0.3 < 0.45 < 0.6, the disturbance level of the current operating condition is determined to be 2.

[0106] For details, please see Figure 2 , Figure 2 The diagram illustrates the acquisition of the frequency abrupt change trend index in one embodiment of the present invention.

[0107] In one embodiment, the specific process for obtaining each key interference factor based on the correlation characteristics between the frequency time series and each running time series is as follows:

[0108] Calculate the Pearson correlation coefficient between the frequency time series and each running time series, and take the running parameters corresponding to the running time series with Pearson correlation coefficients greater than a preset correlation threshold as key interference factors.

[0109] It should be noted that the Pearson correlation coefficient is used to measure the degree of correlation between two variables. Different interference factors have different degrees of interference on the UHV flexible DC system. When the Pearson correlation coefficient is greater than the preset correlation threshold, it indicates that the fluctuation of the operating parameter is strongly linearly correlated with the frequency fluctuation, and its change will significantly affect the system frequency, which is the core factor causing the operating condition disturbance. Conversely, when the Pearson correlation coefficient is less than the preset correlation threshold, it indicates that the corresponding operating parameter has a weak impact on the frequency fluctuation and can be excluded to avoid interfering with subsequent calculations. By calculating the Pearson correlation coefficient, operating parameters with strong correlation to frequency fluctuation are screened out, and interference from uncorrelated or weakly correlated parameters is excluded to ensure the reliability of subsequent assessment of the operating condition disturbance. The calculation of the Pearson correlation coefficient is a well-known technique, and will not be described in detail in this embodiment. The preset correlation threshold is a value preset by the user. In this embodiment, the preset correlation threshold is 0.6. As for the value of the preset correlation threshold, as in other implementation methods, the implementer can choose it at his own discretion, and this application does not impose any special restrictions on it.

[0110] In one embodiment, the frequency abrupt change index and the disturbance urgency factor are weighted and summed, and the weighted summation value is normalized to obtain the frequency abrupt change trend index.

[0111] It should be noted that the weights of the weighted summation are set according to the actual situation. For example, when the output of new energy sources fluctuates moderately and the system operates relatively smoothly, the weights of the frequency change index and the disturbance urgency factor are both set to 0.5.

[0112] In one embodiment, step S301, which calculates the frequency abrupt change index based on the trend abruptness characteristics of the frequency time series, includes:

[0113] Step S3011: Perform first-order difference on the frequency time series to obtain the frequency change rate sequence, and extract all first abrupt change points in the frequency change rate sequence; perform second-order difference on the frequency time series to obtain the frequency change acceleration sequence, and extract all second abrupt change points in the frequency change acceleration sequence; determine the third abrupt change point based on the time interval between the first abrupt change point and the second abrupt change point.

[0114] Step S3012: Add the frequency change velocity sequence and the frequency change acceleration sequence together to obtain the frequency abrupt change time sequence; use the sum of the values ​​of all third abrupt change points in the frequency abrupt change time sequence as the frequency abrupt change factor, and use the normalized value of the frequency abrupt change factor as the frequency abrupt change index.

[0115] It should be noted that first-order differencing, second-order differencing, and extraction of abrupt change points in time series are all well-known techniques, and will not be elaborated upon here. The first abrupt change point corresponds to the moment when the rate of frequency change suddenly intensifies or slows down, such as a sudden drop in wind power output leading to a sudden increase in the rate of frequency decrease. This captures the initial frequency abrupt change signal caused by the disturbance. The second abrupt change point corresponds to the moment when the acceleration of frequency change suddenly changes, such as when multiple disturbances are superimposed, causing the rate of frequency decrease to change from slow to rapid. This captures the secondary abrupt change signal indicating the intensification or weakening of the disturbance. The third abrupt change point is determined based on the time interval between the first and second abrupt change points. This allows for the screening of key nodes where abrupt changes in the rate of frequency change and acceleration of frequency change occur simultaneously. When the time interval between the two is less than a preset threshold, it indicates that the abrupt change is a disturbance. The third mutation point, which is a significant mutation caused by continuous action and possible superposition of other disturbances, effectively eliminates false mutation points caused by instantaneous noise and small fluctuations, avoids false triggering of control strategies caused by false mutation signals, and improves the reliability of mutation point acquisition. The frequency change velocity sequence reflects the instantaneous intensity of the mutation, and the frequency change acceleration sequence reflects the development trend of the mutation. The frequency change velocity sequence and the acceleration sequence are added together to obtain the frequency change time series. The fusion of the two comprehensively quantifies the overall intensity of the frequency mutation at each moment, which can accurately identify significant mutations under the superposition of multiple disturbances and provide a quantitative basis for dynamic control strategy adjustment.

[0116] In one embodiment, step S303, which obtains the interference delay response index of each frequency-varying mode component based on the correlation hysteresis characteristics between the running time series of each frequency-varying mode component and each key interference factor, includes:

[0117] Step S3031: Calculate the cross-correlation coefficient between the running time series of each frequency-varying mode component and each key interference factor at each lag order; take the maximum value of the cross-correlation coefficient between the running time series of each frequency-varying mode component and each key interference factor as the lag correlation coefficient between each frequency-varying mode component and each key interference factor.

[0118] Step S3032: The lag order corresponding to the lag correlation coefficient between each frequency change mode component and each key interference factor is taken as the optimal lag time between each frequency change mode component and each key interference factor.

[0119] Step S3033: The interference delay response index of each frequency-changing mode component is calculated based on the linear relationship between the hysteresis correlation coefficient and the optimal hysteresis duration of each frequency-changing mode component and each key interference factor.

[0120] It should be noted that existing UHV flexible DC systems employ fixed control logic. Under scenarios with multiple superimposed disturbances, they cannot predict the timeliness of potential frequency abrupt changes, easily leading to control strategy response lag and failure, which in turn can cause frequency runaway and threaten the safe and stable operation of the power system. This application provides a frequency control method suitable for UHV flexible DC systems. By calculating the cross-correlation coefficients under different lag orders, it accurately identifies the optimal lag duration and lag correlation coefficient between each frequency change mode component and key disturbance factors. It clearly quantifies the lag correlation strength and time difference between key disturbance factor disturbances and frequency fluctuations, providing core support for the subsequent calculation of disturbance urgency factors and frequency abrupt change trend indices. This allows control strategies to intervene in advance and accurately adapt to lag characteristics, fundamentally solving the problems of control response lag and strategy failure, effectively avoiding the risk of frequency runaway, and ensuring the safe and stable operation of the power system.

[0121] In one embodiment, step S3033, which calculates the interference delay response index of each frequency-varying mode component based on the linear relationship between the hysteresis correlation coefficient and the optimal hysteresis duration of each frequency-varying mode component and each key interference factor, includes:

[0122] The sum of the hysteresis correlation coefficients of each frequency-varying mode component and all key interference factors is used as the benchmark value of the hysteresis correlation coefficient of each frequency-varying mode component.

[0123] Each frequency-varying mode component is sequentially used as the target frequency-varying mode component. The lag correlation coefficient between the target frequency-varying mode component and each key interference factor is divided by the baseline value of the lag correlation coefficient of the target frequency-varying mode component to obtain the correlation weight between the target frequency-varying mode component and each key interference factor.

[0124] The interference delay evaluation expression is designed as follows: All correlation weights and hysteresis correlation coefficients of the target frequency-varying mode component are input into the interference delay evaluation expression, which outputs the interference delay response index of the target frequency-varying mode component.

[0125]

[0126] in, For target frequency variation modal components Interference delay response index For target frequency variation modal components With the The association weights of the key interference factors For target frequency variation modal components With the The lag correlation coefficients of key interference factors, For target frequency variation modal components The number of key interfering factors.

[0127] It should be noted that this embodiment first obtains a baseline value of the hysteresis correlation coefficient based on the hysteresis correlation coefficient between a single frequency change mode component and all key interference factors. This baseline value is used to characterize the total intensity of the hysteresis influence of all key interference factors on a certain frequency change mode component, avoiding the one-sidedness of the correlation intensity of a single interference factor. This provides a quantitative basis for the reasonable allocation of subsequent correlation weights and solves the problem of not being able to distinguish the influence weights of each factor when multiple interference factors are superimposed. It accurately distinguishes the differences in the strength of the hysteresis influence of different key interference factors on the mode component. Then, the interference delay response index is obtained by weighted summation. The correlation weight reflects the strength of the interference factor influence, and the hysteresis correlation coefficient reflects the tightness of the hysteresis correlation. The weighted fusion of the two can comprehensively and accurately quantify the comprehensive intensity of the hysteresis influence of all key interference factors on the frequency change mode component under different modes. This adapts to the complex operating conditions of the system affected by various types of disturbances such as new energy power output fluctuations and line power adjustments. It solves the defects of existing fixed control logic that cannot distinguish the hysteresis characteristics of different disturbances and has poor adaptability. This provides reliable support for the accurate calculation of the frequency change trend index and the accurate determination of the operating condition disturbance level.

[0128] For example, if the lag correlation coefficients between a certain frequency-varying mode component and two key interference factors are 0.82 and 0.76 respectively, then the baseline value of the lag correlation coefficient = 0.82 + 0.76 = 1.58, and the correlation weights of the two key interference factors are 0.82 ÷ 1.58 ≈ 0.52 and 0.76 ÷ 1.58 ≈ 0.48 respectively, indicating that the first key interference factor has a stronger lag effect on the frequency-varying mode component.

[0129] Step S4: Dynamically determine the frequency control strategy based on the operating condition disturbance level and the system inertia level, and control the frequency of the UHV flexible DC system using the frequency control strategy.

[0130] In one embodiment, the frequency control strategy is dynamically determined based on the operating condition disturbance level and the system inertia level, including:

[0131] The difference between the system inertia level and the operating condition disturbance level is taken as the operating condition controllability.

[0132] When the controllability of the operating condition is greater than 0, the original frequency control strategy is maintained.

[0133] When the controllability of the operating condition is equal to 0, the virtual inertia priority control strategy is executed. The virtual inertia priority control strategy is designed to adjust the parameter value of the virtual inertia according to the level of the operating condition disturbance, and use the adjusted virtual inertia to control the frequency of the UHV flexible DC system until the controllability of the operating condition is greater than 0.

[0134] When the controllability of the operating condition is less than 0, a cooperative control strategy is executed. The cooperative control strategy is designed to first start virtual inertia control to suppress the rate of change of the system frequency. When the rate of change of the system frequency is detected to drop below the preset floating threshold, virtual inertia control is stopped, and primary frequency modulation control is started to adjust the system frequency until the controllability of the operating condition is greater than 0.

[0135] It should be noted that both the operating condition disturbance level and the system inertia level are divided into three levels: 1, 2, and 3. Operating condition disturbance level 1 represents a slight disturbance, level 2 represents a moderate disturbance, and level 3 represents a severe disturbance. System inertia level 1 represents low inertia, indicating weak system resistance to frequency fluctuations. Even slight disturbances can cause significant frequency fluctuations, and the recovery speed is slow, requiring rapid intervention from external control strategies. System inertia level 2 represents high inertia, indicating moderate system resistance to frequency fluctuations. It can withstand slight disturbances, but requires adaptive control strategies to maintain frequency stability in the face of moderate to severe disturbances. System inertia level 3 represents high inertia, indicating strong system resistance to frequency fluctuations. It can effectively withstand slight and moderate disturbances, requiring only fine-tuning of the control strategy in severe disturbance scenarios. It also exhibits fast frequency recovery and strong stability.

[0136] It should be further explained that the frequency control method for UHV flexible DC transmission provided in this application constructs the controllability index of the operating condition based on the difference between the system inertia level and the operating condition disturbance level. Taking into account both the system's own anti-fluctuation capability and the intensity of external disturbances, the control strategy is dynamically switched. When the controllability is greater than 0, the system inertia is sufficient to withstand the current disturbance. Maintaining the original strategy avoids excessive control that could exacerbate frequency fluctuations and unnecessary energy consumption. When the controllability is equal to 0, the inertia and disturbance intensity are equal. Frequency fluctuations are precisely suppressed and the system steady state is maintained through dynamic adjustment of virtual inertia parameters. When the controllability is less than 0, the disturbance intensity exceeds the system's own... The system exhibits strong resistance to fluctuations. Through coordinated control of virtual inertia and primary frequency regulation, it first rapidly suppresses the rate of frequency change and avoids sudden increases or decreases in frequency. Then, it precisely adjusts the frequency back. When the system experiences instantaneous noise or minor disturbances, if the positive or negative attribute of the controllability of the operating condition remains unchanged, the current strategy is maintained to avoid erroneous strategy switching caused by spurious disturbances. When the disturbance intensity or inertia level changes significantly, or the controllability of the operating condition switches between positive and negative, it can quickly switch to an adaptive strategy. This effectively resists the impact of random interference and sudden disturbances, improves the robustness of the control strategy, further ensures system frequency stability, effectively avoids the risk of frequency runaway, and ensures the safe and stable operation of the UHV flexible DC system and related power systems.

[0137] In one embodiment, the frequency control method for UHVDC flexible DC transmission provided in this application further includes:

[0138] Before controlling the frequency of the UHV flexible DC system using a frequency control strategy, a simulation model is used to simulate the frequency control strategy, and the frequency control strategy is adjusted based on the simulation results.

[0139] It should be noted that UHV flexible DC transmission systems have complex structures and variable operating conditions. Directly applying frequency control strategies to actual systems may lead to control response deviations, increased frequency fluctuations, or even frequency runaway due to insufficient parameter compatibility with the actual system. Simulation models can accurately replicate the strategy's execution effect under different operating conditions, identifying problems such as unreasonable strategy parameters and inconsistent timing transitions. This avoids frequency overshoot caused by excessively high parameters and control lag caused by excessively low parameters, allowing the optimized frequency control strategy to better fit the actual system conditions. This further improves the strategy's adaptability to dynamic changes in operating conditions and its execution accuracy, ultimately enhancing the frequency control effect on UHV flexible DC transmission systems.

[0140] See Figure 3This is a structural block diagram of a frequency control device suitable for ultra-high voltage flexible DC transmission provided by an embodiment of the present invention. The frequency control device 20 provided by this embodiment includes a processor 21, a memory 22, and a computer program stored in the memory 22 and configured to be executed by the processor 21. When the processor 21 executes the computer program, it implements the steps described in the above embodiment of a frequency control method for ultra-high voltage flexible DC transmission, for example... Figure 1 Steps S1 to S4 as described in the document.

[0141] 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 frequency control method suitable for ultra-high voltage flexible DC transmission, characterized in that, The method includes: The system frequency and various operating parameters of the UHV flexible DC system are obtained. A frequency time series is constructed using all the system frequencies within a preset time period. An operating time series corresponding to each operating parameter is constructed using all the operating parameters within the preset time period. Extract each frequency mutation point in the frequency time series, calculate the frequency mutation intensity of each frequency mutation point based on the degree to which each frequency mutation point deviates from the overall trend of the frequency time series, obtain the mutation recovery time of each frequency mutation point based on the difference characteristics of the neighborhood frequency trend of each frequency mutation point, and determine the system inertia level based on the frequency mutation intensity and mutation recovery time of all the frequency mutation points. The frequency abrupt change trend index is calculated based on the trend change characteristics of the frequency time series and the correlation lag characteristics between the frequency time series and each of the operating time series. The operating condition disturbance level is determined based on the comparison result of the frequency abrupt change trend index and the preset mutation threshold. The frequency abrupt change trend index is used to characterize the potential mutation degree of the system frequency. The frequency control strategy is dynamically determined based on the operating condition disturbance level and the system inertia level, and the frequency of the UHV flexible DC system is controlled by the frequency control strategy.

2. The frequency control method applicable to UHV flexible DC transmission according to claim 1, characterized in that, The calculation of the frequency mutation intensity of each frequency mutation point based on the degree to which each frequency mutation point deviates from the overall trend of the frequency time series includes: The frequency time series is subjected to polynomial fitting to obtain a frequency fitting curve, and the frequency fitting curve is serialized to obtain a frequency fitting time series corresponding to the frequency time series. The frequency time series and the frequency fitting time series are subtracted to obtain the frequency deviation time series. The value corresponding to each frequency mutation point in the frequency deviation time series is taken as the absolute frequency deviation value of each frequency mutation point; The standard deviation of the frequency time series within a preset sliding window at each frequency mutation point is used as the neighborhood frequency deviation benchmark value for each frequency mutation point. The ratio of the absolute frequency deviation value of each frequency mutation point to the corresponding neighborhood frequency deviation reference value is used as the frequency mutation intensity of each frequency mutation point.

3. The frequency control method applicable to UHV flexible DC transmission according to claim 2, characterized in that, The step of obtaining the mutation recovery time of each frequency mutation point based on the neighborhood frequency trend difference features of each frequency mutation point includes: The Otsu threshold segmentation algorithm is used to process all values ​​in the frequency deviation time series to obtain the deviation segmentation threshold; All data points in the frequency deviation time series that are less than the deviation segmentation threshold are taken as trend points; The frequency deviation time series is divided according to each frequency mutation point to obtain the left neighbor sequence and the right neighbor sequence of each frequency mutation point; The trend point that is closest to the frequency change point in the left neighbor sequence of each frequency change point is taken as the left nearest neighbor trend point of the frequency change point, and the trend point that is closest to the frequency change point in the right neighbor sequence of each frequency change point is taken as the right nearest neighbor trend point of the frequency change point. The time interval between the left nearest neighbor trend point and the right nearest neighbor trend point of each frequency mutation point is taken as the mutation recovery time of each frequency mutation point.

4. The frequency control method applicable to UHV flexible DC transmission according to claim 1, characterized in that, The step of determining the system inertia level based on the frequency mutation intensity and mutation recovery time of all the frequency mutation points includes: The ratio of the frequency mutation intensity to the mutation recovery time at each frequency mutation point is taken as the current inertial force intensity at each frequency mutation point. The current inertia intensity at all frequency abrupt change points is input into the system inertia evaluation expression to obtain the system inertia intensity. Based on the comparison between the system inertia intensity and a preset inertia threshold, the system inertia level is determined. The system inertia evaluation expression is designed as follows: in, The intensity of the system's inertia. It is an exponential function with the natural constant as its base. The number of frequency abrupt change points. For the first The intensity of the current inertia effect at each frequency abrupt change point.

5. The frequency control method applicable to UHV flexible DC transmission according to claim 1, characterized in that, The calculation of the frequency abrupt change trend index based on the trend change characteristics of the frequency time series and the correlation lag characteristics between the frequency time series and each of the running time series includes: The frequency abrupt change index is calculated based on the trend abrupt change characteristics of the frequency time series; Each key interference factor is obtained based on the correlation characteristics between the frequency time series and each of the running time series; Variational mode decomposition is performed on the frequency time series to obtain the frequency variation mode components; The interference delay response index of each frequency-varying mode component is obtained based on the correlation hysteresis characteristics between the running time series of each frequency-varying mode component and each key interference factor; The average value of the disturbance delay response exponents of all the frequency-varying mode components is taken as the disturbance delay exponent, and the reciprocal of the disturbance delay exponent is taken as the disturbance urgency factor. The frequency change trend index is calculated based on the linear relationship between the frequency change index and the disturbance urgency factor.

6. The frequency control method applicable to UHV flexible DC transmission according to claim 5, characterized in that, The calculation of the frequency abrupt change index based on the trend abrupt change characteristics of the frequency time series includes: Perform first-order difference on the frequency time series to obtain the frequency change rate series, and extract all first abrupt change points in the frequency change rate series; The frequency time series is subjected to second-order difference to obtain the frequency change acceleration series, and all second abrupt change points in the frequency change acceleration series are extracted. The third mutation point is determined based on the time interval between the first mutation point and the second mutation point; The frequency change velocity sequence and the frequency change acceleration sequence are added together to obtain the frequency abrupt change time sequence; The sum of the values ​​of all the third mutation points in the frequency abrupt change time series is taken as the frequency abrupt change factor, and the normalized value of the frequency abrupt change factor is taken as the frequency abrupt change index.

7. The frequency control method applicable to UHV flexible DC transmission according to claim 1, characterized in that, The dynamic determination of the frequency control strategy based on the operating condition disturbance level and the system inertia level includes: The difference between the system inertia level and the operating condition disturbance level is taken as the operating condition controllability. When the controllability of the operating condition is greater than 0, the original frequency control strategy is maintained. When the controllability of the operating condition is equal to 0, a virtual inertia priority control strategy is executed. The virtual inertia priority control strategy is designed to adjust the parameter value of the virtual inertia according to the disturbance level of the operating condition, and control the frequency of the UHV flexible DC system with the adjusted virtual inertia until the controllability of the operating condition is greater than 0. When the controllability of the operating condition is less than 0, a cooperative control strategy is executed. The cooperative control strategy is designed to first start virtual inertia control to suppress the rate of change of the system frequency. When the rate of change of the system frequency is detected to drop below a preset floating threshold, virtual inertia control is stopped, and a primary frequency modulation control is started to adjust the system frequency until the controllability of the operating condition is greater than 0.

8. A frequency control method applicable to UHV flexible DC transmission according to claim 5, characterized in that, The step of obtaining the interference delay response index of each frequency-varying mode component based on the correlation hysteresis characteristics between the running time series of each frequency-varying mode component and each key interference factor includes: Calculate the cross-correlation coefficient between the running time series of each frequency variation mode component and each key interference factor at each lag order; The maximum value of the cross-correlation coefficient between the running time series of each frequency-varying mode component and each key interference factor is taken as the hysteresis correlation coefficient between each frequency-varying mode component and each key interference factor. The lag order corresponding to the lag correlation coefficient of the running time series of each frequency change mode component and each key interference factor is taken as the optimal lag time of each frequency change mode component and each key interference factor. The interference delay response index of each frequency-varying mode component is calculated based on the linear relationship between the hysteresis correlation coefficient and the optimal hysteresis duration of each frequency-varying mode component and each key interference factor.

9. A frequency control method suitable for UHV flexible DC transmission according to claim 8, characterized in that, The interference delay response index for each frequency-varying mode component is calculated based on the linear relationship between the hysteresis correlation coefficient and the optimal hysteresis duration of each frequency-varying mode component and each key interference factor, including: The sum of the hysteresis correlation coefficients of each frequency-varying mode component and all the key interference factors is used as the reference value of the hysteresis correlation coefficient of each frequency-varying mode component. Each frequency-varying mode component is sequentially used as a target frequency-varying mode component. The hysteresis correlation coefficient between the target frequency-varying mode component and each key interference factor is divided by the hysteresis correlation coefficient benchmark value of the target frequency-varying mode component to obtain the correlation weight between the target frequency-varying mode component and each key interference factor. The interference delay evaluation expression is designed as follows: All the correlation weights and all the hysteresis correlation coefficients of the target frequency-varying mode component are input into the interference delay evaluation expression, and the interference delay response index of the target frequency-varying mode component is output. in, For target frequency variation modal components Interference delay response index For target frequency variation modal components With the The association weights of the key interference factors For target frequency variation modal components With the The lag correlation coefficients of key interference factors, For target frequency variation modal components The number of key interfering factors.

10. A frequency control device suitable for ultra-high voltage flexible DC transmission, characterized in that, The system includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein the processor, when executing the computer program, implements a frequency control method for ultra-high voltage flexible DC transmission as described in any one of claims 1 to 9.

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