Multi-stage cascade control method of alternating current-direct current conversion device applied to active voltage support

Abstract

The invention discloses a multi-stage cascade control method for an AC / DC conversion device applied to active voltage support, and relates to the field of converter grid-connected operation control, and the method comprises the steps: calculating a current load side power factor and a power factor variation based on a current parameter and a voltage parameter; performing staged division on a load side power factor region based on a preset optimal power factor; analyzing a power factor interval to which a current load side power factor absolute value belongs, and judging a power compensation mode in combination with the power factor variation; and calculating an initial power compensation value by using a variable parameter mode, and correcting the initial power compensation value in combination with a predefined constraint condition to obtain a final power compensation value. According to the method, the grid-connected point power factor, the residual capacity of the energy storage system and the voltage fluctuation are comprehensively considered, and active power and reactive power compensation is added before traditional grid-following control, so that the residual capacity of the AC-DC conversion device is fully utilized to realize stable control on the grid-connected point voltage.

Description

TECHNICAL FIELD

[0001] The application relates to the field of grid-connected operation control of a converter, in particular to a multi-stage cascaded control method applied to a voltage active support AC-DC conversion device. BACKGROUND

[0002] With the large access of distributed photovoltaic and the continuous increase of power load types, at the end of the distribution network and in the weak grid area, voltage problems such as voltage out-of-limit and voltage fluctuation caused by load fluctuation are becoming increasingly prominent.

[0003] At present, the main solution to the voltage problem in the weak grid area is to replace the on-load voltage regulating transformer and configure the dynamic reactive power compensation device, but the on-load voltage regulating transformer tap operates every 2000 times, and the insulation oil, tap switch and the like need to be checked, the service life is limited, the maintenance workload is large, the maintenance cost is high and the maintenance is complex;

[0004] In addition, the on-load voltage regulating transformer has slow regulation speed, and the fastest speed is five to six seconds, and cannot respond to dynamic changes of voltage, and the dynamic reactive power compensation device compensates reactive power at the key power supply node to reduce voltage fluctuation, but can only reduce voltage fluctuation caused by reactive power, and cannot reduce voltage fluctuation caused by active power.

[0005] Therefore, it is urgent to design a multi-stage cascaded control method applied to an AC-DC conversion device for voltage active support, so as to comprehensively treat voltage fluctuation caused by different factors of active power / reactive power. SUMMARY

[0006] In view of the problems in the related art, the application provides a multi-stage cascaded control method applied to an AC-DC conversion device for voltage active support, so as to overcome the above technical problems existing in the prior art.

[0007] Therefore, the specific technical scheme adopted by the application is as follows:

[0008] A multi-stage cascaded control method applied to an AC-DC conversion device for voltage active support, the method comprising:

[0009] Collecting current parameters and voltage parameters of the AC-DC conversion device after being connected to the power grid, and calculating the current load side power factor and the power factor change based on the current parameters and the voltage parameters;

[0010] Dividing the load side power factor region into stages based on the preset optimal power factor, generating a plurality of power factor intervals; analyzing the power factor interval to which the absolute value of the current load side power factor belongs, and judging the power compensation mode in combination with the power factor change;

[0011] Based on the power compensation mode, the initial power compensation value is calculated by using the variable parameter mode, and the initial power compensation value is corrected combined with the predefined constraint condition to obtain the final power compensation value, so as to realize the multi-stage cascade control of the AC-DC conversion device.

[0012] Preferably, the load side power factor region is divided into stages based on the preset optimal power factor, and a plurality of power factor intervals are generated; the power factor interval to which the absolute value of the current load side power factor belongs is analyzed, and the power compensation mode is judged combined with the power factor change amount, including:

[0013] Based on the preset power factor, the load side power factor region is divided to generate a plurality of power factor intervals, and the power factor interval to which the absolute value of the current load side power factor belongs is judged,

[0014] The power factor interval includes a first power factor interval, a second power factor interval, a third power factor interval, a first dead zone interval and a second dead zone interval.

[0015] If the absolute value of the current load side power factor is located in the first power factor interval, reactive power compensation is performed, and the power compensation control flag at the current time is set to 0; if the absolute value of the current load side power factor is located in the third power factor interval, active power compensation is performed, and the power compensation control flag at the current time is set to 1.

[0016] If the absolute value of the current load side power factor is located in the second power factor interval, the power compensation mode is judged according to the power factor change amount, including active power compensation and reactive power compensation.

[0017] Preferably, based on the power compensation mode, the initial power compensation value is calculated by using the variable parameter mode, and the initial power compensation value is corrected combined with the predefined constraint condition to obtain the final power compensation value, so as to realize the multi-stage cascade control of the AC-DC conversion device, including:

[0018] Based on the active power compensation mode, the initial active power compensation value is calculated by using the variable parameter mode, and the initial active power compensation value is corrected combined with the predefined constraint condition to obtain the final active power compensation value.

[0019] Based on the reactive power compensation mode, the initial reactive power compensation value is calculated by using the variable parameter mode, and the initial reactive power compensation value is corrected combined with the predefined constraint condition to obtain the final reactive power compensation value.

[0020] Preferably, based on the active power compensation mode, the initial active power compensation value is calculated by using the variable parameter mode, and the initial active power compensation value is corrected combined with the predefined constraint condition to obtain the final active power compensation value, including:

[0021] With the DC side to the AC side of the AC-DC conversion device as the positive direction, the active power upper limit and the active power lower limit at the current time when the power compensation control flag is 1 are calculated;

[0022] Based on the voltage deviation, the active power deviation value P parameter at the current time is calculated by using the variable parameter method, and the initial active power compensation value at the current time is calculated according to the active power deviation value P parameter;

[0023] The active power upper limit and the active power lower limit are taken as the constraint condition, and the initial active power compensation value at the current time is corrected to obtain the final active power compensation value at the current time.

[0024] Preferably, based on the reactive power compensation mode, the initial reactive power compensation value is calculated by using the variable parameter method, and the initial reactive power compensation value is corrected in combination with the predefined constraint condition to obtain the final reactive power compensation value, which includes:

[0025] With the DC side to the AC side of the AC-DC conversion device as the positive direction, the reactive power upper limit and the reactive power lower limit at the current time when the power compensation control flag is 0 are calculated;

[0026] Based on the voltage deviation, the reactive power deviation value P parameter at the current time is calculated by using the variable parameter method, and the initial reactive power compensation value at the current time is calculated according to the reactive power deviation value P parameter;

[0027] The reactive power upper limit and the reactive power lower limit are taken as the constraint condition, and the initial reactive power compensation value at the current time is corrected to obtain the final reactive power compensation value at the current time.

[0028] Preferably, the load side power factor region is divided based on the preset power factor, a plurality of power factor intervals are generated, and the current load side power factor absolute value belongs to the power factor interval before:

[0029] The historical operation data of the AC-DC conversion device accessing the power grid is obtained, the historical operation data is input into the pre-constructed resonance sparse decomposition model, and the voltage fluctuation component is output through the resonance sparse decomposition model, and the fluctuation index of the voltage fluctuation component is calculated;

[0030] The power grid topology network model is constructed, the disturbance propagation characteristics of the voltage fluctuation in the power grid topology network model are simulated, and the node vulnerability degree and the power grid performance retention degree under the voltage disturbance state are analyzed in combination with the fluctuation index;

[0031] The node vulnerability and the power grid performance retention degree are integrated to generate the power grid operation sequence, and the power grid operation sequence is input into the fractional order state space model, and the initial confidence degree of the power grid operation sequence is distributed through the fractional order state space model;

[0032] Screening power grid operation sequences with conflicts based on initial confidence assignment results, introducing a predefined hybrid combination rule to fuse the initial confidence of the conflict sequences, and taking the fusion result as the preset power factor.

[0033] Preferably, the historical operation data is input into a pre-constructed resonance sparse decomposition model, and the voltage fluctuation component is output by the resonance sparse decomposition model. The fluctuation index of the voltage fluctuation component includes:

[0034] Wavelet transform is performed on the historical operation data to identify the linear relationship of the low-pass coefficients, high-pass coefficients and redundant coefficients of the historical operation data.

[0035] A resonance sparse decomposition model distinguishing the resonance frequency of the historical operation data is constructed with the minimum error between the historical operation data and the real-time operation data as the target and the proportional linear relationship as the constraint condition.

[0036] The resonance sparse decomposition model is solved by using the Lagrange shrinkage method to obtain high resonance characteristics and low resonance characteristics, and the high resonance characteristics and the low resonance characteristics are inversely transformed to output high resonance voltage fluctuation components and low resonance voltage fluctuation components.

[0037] A high-pass filter and a low-pass filter are constructed, and the high resonance voltage fluctuation components and the low resonance voltage fluctuation components are input into the corresponding filters respectively to generate the spectral kurtosis of the high resonance voltage fluctuation components and the low resonance voltage fluctuation components by a two-section filtering method.

[0038] The spectral kurtosis is summarized to form a spectral kurtosis map, the distribution characteristics of different frequency band spectral kurtosis in the spectral kurtosis map are analyzed, the frequency band distribution characteristics of the high resonance voltage fluctuation components and the low resonance voltage fluctuation components are extracted, and the mean value of the frequency band distribution characteristics is taken as the fluctuation index of the voltage fluctuation component.

[0039] Preferably, the resonance sparse decomposition model is solved by using the Lagrange shrinkage method to obtain high resonance characteristics and low resonance characteristics, and the high resonance characteristics and the low resonance characteristics are inversely transformed to output high resonance voltage fluctuation components and low resonance voltage fluctuation components, including:

[0040] The resonance sparse decomposition model is converted into an optimization objective function containing high resonance component sparsity constraints and low resonance component smoothness constraints, and a Lagrange multiplier is introduced into the optimization objective function to generate an augmented Lagrange function.

[0041] The starting point and the termination condition of the iterative shrinkage algorithm are set, the augmented Lagrange function is iteratively solved by using the iterative shrinkage algorithm, and the minimum value of the high resonance voltage fluctuation component and the low resonance voltage fluctuation component is continuously output in each round of iterative solving process.

[0042] The soft threshold shrinkage operator is used to continuously update the minimum value, and the iteration is stopped when the termination condition is met, and the optimal solution of high resonance characteristics and low resonance characteristics is obtained respectively.

[0043] The optimal solution is inversely transformed by a wavelet to obtain a high resonance voltage fluctuation component and a low resonance voltage fluctuation component.

[0044] Preferably, the node susceptibility and the grid performance retention degree are integrated to generate a grid operation sequence, and the grid operation sequence is input into the fractional order state space model to assign an initial confidence degree of the grid operation sequence, including:

[0045] The node susceptibility sequence and the grid performance retention degree sequence are constructed respectively, and the node susceptibility sequence and the grid performance retention degree sequence are segmented and aggregated to generate a plurality of grid operation sequence pairs.

[0046] The discrete space state of each grid operation sequence pair is mined by using a sequence mining algorithm, and a discrete space state set of the fractional order state space model is generated based on the discrete space state.

[0047] Based on the discrete space state of each grid operation sequence pair, a fractional calculus operator is introduced to estimate the transition probability between the discrete space states, and a fractional order state transition matrix is fitted according to the transition probability.

[0048] The grid operation sequence pair at the current time is taken as an observation value, and the initial confidence degree of the grid operation sequence at the current time is inferred in reverse through the fractional order state transition matrix.

[0049] Preferably, the discrete space state of each grid operation sequence pair is mined by using a sequence mining algorithm, including:

[0050] The candidate motifs in each grid operation sequence pair are screened by an enumeration strategy, and the candidate motif frequency of the candidate motifs in all grid operation sequences is counted.

[0051] The candidate motif frequency is compared with a preset threshold, and the candidate motifs corresponding to the candidate motif frequency in the preset range are selected and composed into a significant motif set.

[0052] The morphological similarity and the evolution logic similarity between the motifs in the significant motif set are calculated, the similar motifs are divided into the same group by using a spectral clustering technology, and the motifs of each type of clustering center are selected and abstracted as the discrete space state.

[0053] The beneficial effects of the present application are:

[0054] 1. The application comprehensively considers the power factor of the grid connection point, the remaining capacity of the energy storage system and the voltage fluctuation, and increases active power and reactive power compensation before the traditional grid control, so as to fully utilize the remaining capacity of the AC / DC conversion device to realize the stable control of the grid connection point voltage, solve the problem of weak area of power distribution network at the end of mountainous area, island and other areas, because the transmission line is long and the line impedance is large, the user side voltage is greatly affected by the load, especially with the access of a large number of distributed photovoltaic and electric vehicle charging piles, the user side voltage fluctuation and over-limit problem, and then improve the power supply quality.

[0055] 2. The application is based on the AC / DC conversion device, combined with the operation state of the energy storage system and the current power factor change trend, through the real-time compensation of the output active power and reactive power, the voltage fluctuation caused by different factors of active / reactive power can be comprehensively treated, the power real-time compensation is not dependent on the specific parameters of line impedance, the operation amount is greatly reduced, at the same time, the application can accelerate the power compensation under the condition of large voltage deviation, stabilize the grid connection point voltage, reduce the compensation coefficient under the condition of small voltage deviation, prevent the voltage fluctuation caused by power fluctuation again, and then improve the power supply quality. BRIEF DESCRIPTION OF DRAWINGS

[0056] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0057] Figure 1 It is an AC / DC voltage compensation access topology diagram applied to the multi-stage cascade control method of the AC / DC conversion device for voltage active support according to the embodiment of the application.

[0058] Figure 2 It is a power factor region division schematic diagram applied to the multi-stage cascade control method of the AC / DC conversion device for voltage active support according to the embodiment of the application.

[0059] Figure 3 It is an AC / DC operation control topology diagram applied to the multi-stage cascade control method of the AC / DC conversion device for voltage active support according to the embodiment of the application.

[0060] Figure 4 It is an AC / DC power compensation calculation flowchart applied to the multi-stage cascade control method of the AC / DC conversion device for voltage active support according to the embodiment of the application.

[0061] Figure 5It is a schematic diagram of a voltage active support test system in a multi-stage cascaded control method of an AC / DC conversion device applied to voltage active support according to an embodiment of the application.

[0062] Figure 6 It is a voltage and current waveform diagram when the load is 0 in a multi-stage cascaded control method of an AC / DC conversion device applied to voltage active support according to an embodiment of the application.

[0063] Figure 7 It is an inductive reactive power regulation voltage waveform diagram of an AC / DC conversion device output in a multi-stage cascaded control method of an AC / DC conversion device applied to voltage active support according to an embodiment of the application.

[0064] Figure 8 It is an active power regulation voltage waveform diagram of an AC / DC conversion device output in a multi-stage cascaded control method of an AC / DC conversion device applied to voltage active support according to an embodiment of the application.

[0065] Figure 9 It is a flowchart of a multi-stage cascaded control method of an AC / DC conversion device applied to voltage active support according to an embodiment of the application. DETAILED DESCRIPTION

[0066] To further illustrate the embodiments, the present application provides drawings which are part of the disclosure of the present application, mainly used to illustrate the embodiments, and can explain the operating principle of the embodiments in conjunction with the related description of the specification. With reference to these contents, those skilled in the art should understand other possible embodiments and advantages of the present application.

[0067] According to an embodiment of the present application, a multi-stage cascaded control method of an AC / DC conversion device applied to voltage active support is provided.

[0068] The present application will be further described in conjunction with the drawings and specific embodiments. As shown in the drawings, according to the multi-stage cascaded control method of an AC / DC conversion device applied to voltage active support according to an embodiment of the present application, the method comprises: Figure 9

[0069] S1, collecting current parameters and voltage parameters of an AC / DC conversion device after being connected to a power grid, and calculating a current load side power factor and a power factor variation based on the current parameters and the voltage parameters.

[0070] It should be noted that after the AC / DC conversion device (AC / DC conversion device) is connected to a weak grid environment, the port voltage u abc (t) and current i abc (t) are collected in real time, and the current load side power factor Φ(t) and the power factor variation ΔΦ(t) are calculated based on this, and the calculation formula is: ​

[0071] ;

[0072] In the formula, Φ(t) is the current load side power factor; ΔΦ(t) is the power factor change amount; t is the time vector.

[0073] S2, based on the preset optimal power factor, the load side power factor region is divided into stages, generating several power factor intervals; analyze the power factor interval to which the absolute value of the current load side power factor belongs, and judge the power compensation mode in combination with the power factor change amount.

[0074] Among them, based on the preset optimal power factor, the load side power factor region is divided into stages, generating several power factor intervals; analyze the power factor interval to which the absolute value of the current load side power factor belongs, and judge the power compensation mode in combination with the power factor change amount, including:

[0075] Based on the preset power factor, the load side power factor region is divided into several power factor intervals, and the power factor interval to which the absolute value of the current load side power factor belongs is judged,

[0076] Among them, the power factor interval includes a first power factor interval, a second power factor interval, a third power factor interval, a first dead zone interval and a second dead zone interval;

[0077] If the absolute value of the current load side power factor is located in the first power factor interval, then execute reactive power compensation, and set the current time power compensation control flag to 0; if the absolute value of the current load side power factor is located in the third power factor interval, then execute active power compensation, and set the current time power compensation control flag to 1;

[0078] If the absolute value of the current load side power factor is located in the second power factor interval, then judge the power compensation mode according to the power factor change amount, and the power compensation mode includes active power compensation and reactive power compensation.

[0079] It should be noted that the load side power factor region is divided into three sections, the first power factor interval, the second power factor interval and the third power factor interval, and the division method is as shown in Figure 2 The power factor judgment dead zone threshold value is When located in the first power factor interval (equivalent to the region 1 in Figure 2 , reactive power compensation is performed, and the current time power compensation control flag is set to 0, that is ; when located in the third power factor interval (equivalent to the region 3 in Figure 2 , active power compensation is performed, and the current time power compensation control flag is set to 1, that is . ​

[0080] wherein, when located in the secondary power factor interval (equivalent to Figure 2 region 2 in the formula), the discrimination is carried out according to △Φ(t), and the calculation formula is:

[0081] ;

[0082] wherein, is the power compensation control flag of the last time, is the power compensation control flag of the current time, is the power factor change dead zone threshold.

[0083] when located in the primary dead zone interval (equivalent to Figure 2 dead zone 1 in the formula), the calculation formula of the power compensation control flag is:

[0084] ;

[0085] when located in the secondary dead zone interval (equivalent to Figure 2 dead zone 2 in the formula), the calculation formula of the power compensation control flag is:

[0086] ;

[0087] wherein, is the power compensation control flag of the last time, is the power compensation control flag of the current time, and t is the time vector.

[0088] wherein, based on the preset power factor, the load side power factor region is divided to generate a plurality of power factor intervals, and before judging the power factor interval to which the absolute value of the current load side power factor belongs, the following is included:

[0089] The historical operation data of the AC-DC conversion device accessing the power grid is obtained, the historical operation data is input into a pre-constructed resonance sparse decomposition model, and the voltage fluctuation component is output through the resonance sparse decomposition model, and the fluctuation index of the voltage fluctuation component is calculated.

[0090] wherein, the historical operation data is input into a pre-constructed resonance sparse decomposition model, and the voltage fluctuation component is output through the resonance sparse decomposition model, and the fluctuation index of the voltage fluctuation component is calculated, including:

[0091] The historical operation data is wavelet transformed to identify the linear relationship of the low-pass coefficient, the high-pass coefficient and the redundant coefficient of the historical operation data.

[0092] It should be noted that obtaining the historical operation data of the AC-DC conversion device accessing the power grid and performing wavelet transform can effectively decompose different frequency components in the data, identify the linear relationship between the low-pass coefficients (corresponding to the smooth, low-frequency basic operation characteristics in the data), the high-pass coefficients (corresponding to the abnormal or disturbance information in the data with fluctuations and high frequencies), and the redundant coefficients (corresponding to the noise or invalid components in the data), which not only realizes accurate deconstruction of the historical operation data, but also provides a reliable basis for subsequent extraction of key operation characteristics, filtering of data noise, and analysis of power grid operation state change rules, helping to improve the cognitive accuracy of the power grid operation after the AC-DC conversion device is accessed.

[0093] A resonance sparse decomposition model is constructed to distinguish the resonance frequency of the historical operation data, with the minimization of the error between the historical operation data and the real-time operation data as the target, and the proportional linear relationship as the constraint condition.

[0094] The mathematical model that can separate different resonance frequency components from the historical operation data is obtained by taking the minimization of the error between the historical and real-time operation data as the target and taking the proportional linear relationship as the constraint. The working principle of the model is to decompose the historical operation data into components with different resonance characteristics (high and low resonance) by the sparsity constraint of the model, to distinguish different resonance frequencies, to determine the variables and parameters of the model by combining the voltage, current and other parameters of the historical operation data, and to complete the model construction.

[0095] The Lagrange shrinkage method is used to solve the resonance sparse decomposition model, and high resonance characteristics and low resonance characteristics are obtained. The high resonance characteristics and the low resonance characteristics are inversely transformed to output high resonance voltage fluctuation components and low resonance voltage fluctuation components.

[0096] It should be noted that the purpose of solving the resonance sparse decomposition model by the Lagrange shrinkage method is to convert the constrained optimization problem into an unconstrained problem by introducing the Lagrange multiplier, and then efficiently solve the high resonance characteristics and low resonance characteristics parameters in the model. The specific implementation includes:

[0097] A Lagrange function is constructed including the objective function, the constraint condition and the Lagrange multiplier. The partial derivative of the function is calculated and set to zero to obtain the iterative formula of the optimal solution. Through iterative calculation until convergence, high and low resonance characteristics are obtained. Finally, the corresponding fluctuation components are output by inverse transformation. Compared with the conventional Lagrange method, the Lagrange shrinkage method increases the shrinkage operation, which can adjust the sparsity of the solution variables during the iteration process, better meet the sparsity requirement of the resonance sparse decomposition model, improve the decomposition accuracy and solution efficiency, and avoid the problem that the solution does not meet the sparsity constraint in the conventional method.

[0098] Wherein, the resonance sparse decomposition model is solved by using Lagrange shrinkage method, high resonance characteristics and low resonance characteristics are obtained respectively, and the high resonance voltage fluctuation component and the low resonance voltage fluctuation component are output by inverse transformation of the high resonance characteristics and the low resonance characteristics.

[0099] The resonance sparse decomposition model is converted into an optimization objective function containing high resonance component sparsity constraint and low resonance component smoothness constraint, and a Lagrange multiplier is introduced into the optimization objective function to generate an augmented Lagrange function;

[0100] The starting point and the termination condition of the iterative shrinkage algorithm are set, and the augmented Lagrange function is iteratively solved by using the iterative shrinkage algorithm, and the minimum values of the high resonance voltage fluctuation component and the low resonance voltage fluctuation component are continuously output in each round of iterative solving process.

[0101] It should be noted that the iterative shrinkage algorithm includes:

[0102] The starting point of the iterative shrinkage algorithm is set, that is, the initial values of the high resonance voltage fluctuation component, the low resonance voltage fluctuation component and the Lagrange multiplier are initialized; the termination condition is set, that is, the difference between the minimum values of the high resonance voltage fluctuation component and the low resonance voltage fluctuation component output by adjacent two rounds of iteration is less than a preset threshold value, or the number of iterations reaches a preset maximum number; the iteration process is entered, and in each round, the unconstrained optimization solution of the augmented Lagrange function with respect to the high resonance voltage fluctuation component and the low resonance voltage fluctuation component is calculated based on the current Lagrange multiplier; then the shrinkage operation is performed on the optimization solution to retain the component values meeting the sparsity requirement and suppress redundant components, and the high resonance voltage fluctuation component and the low resonance voltage fluctuation component of the current round are obtained; then the minimum values of the two components are calculated and output; the Lagrange multiplier is updated and adjusted to a value closer to the constraint condition; then it is judged whether the termination condition is met, if not, the unconstrained optimization solution is recalculated and the iteration is continued, if the termination condition is met, the iteration is stopped, and finally the minimum values of the high resonance voltage fluctuation component and the low resonance voltage fluctuation component continuously obtained in the iteration process are output.

[0103] The soft threshold shrinkage operator is used to continuously update the minimum value, and the iteration is stopped when the termination condition is met, and the optimal solutions of the high resonance characteristics and the low resonance characteristics are obtained respectively;

[0104] The optimal solutions are subjected to wavelet inverse transformation to obtain the high resonance voltage fluctuation component and the low resonance voltage fluctuation component.

[0105] High-pass filters and low-pass filters are constructed, the high resonance voltage fluctuation component and the low resonance voltage fluctuation component are input into the corresponding filters respectively, and the spectral kurtosis of the high resonance voltage fluctuation component and the low resonance voltage fluctuation component is generated by two-section filtering method.

[0106] The spectral kurtosis is summarized to form a spectral kurtosis diagram, distribution characteristics of spectral kurtosis in different frequency bands in the spectral kurtosis diagram are analyzed, frequency band distribution characteristics of the high-resonance voltage fluctuation component and the low-resonance voltage fluctuation component are extracted, and the average of the frequency band distribution characteristics is taken as a fluctuation index of the voltage fluctuation component.

[0107] A power grid topology network model is constructed, propagation characteristics of voltage fluctuation disturbance in the power grid topology network model are simulated, and node fragility degree and power grid performance maintenance degree in the voltage disturbance state are analyzed in combination with the fluctuation index.

[0108] It should be noted that the power grid topology network model is constructed, the propagation characteristics of voltage fluctuation disturbance are simulated, the node fragility degree and the power grid performance maintenance degree are analyzed in combination with the fluctuation index, so that the diffusion path and the influence range of the voltage disturbance in the power grid can be clearly presented, the vulnerable nodes in the power grid that are easily affected by disturbance can be accurately identified, and the maintenance ability of the overall performance of the power grid under disturbance can be quantitatively evaluated, thereby providing a basis for stable operation and regulation of the power grid. The specific implementation is that first, a topology network model is constructed based on the connection relationship of power grid elements and parameters (such as line impedance and node load), high and low resonance voltage fluctuation components are input to simulate the disturbance propagation process, and a fluctuation index (such as voltage fluctuation amplitude and propagation speed) is calculated. Then, a calculation model of the node fragility degree (such as the degree of deviation of the node voltage from the threshold value and the anti-disturbance ability) and the power grid performance maintenance degree (such as the power grid load satisfaction rate and the proportion of voltage qualified nodes) is established through the fluctuation index, and the simulation data is substituted into the calculation model to obtain the analysis result. The purpose of analyzing the node fragility degree and the power grid performance maintenance degree in the voltage disturbance state is that the node fragility degree is used to locate the weak nodes in the power grid, thereby providing a target for targeted strengthening of the anti-disturbance ability of the nodes, and the power grid performance maintenance degree is used to quantitatively evaluate the influence of the disturbance on the overall function of the power grid, thereby supporting the adjustment of the power grid operation strategy and the prevention of faults.

[0109] The node susceptibility and the power grid performance maintenance degree are integrated to generate a power grid operation sequence, and the power grid operation sequence is input into a fractional order state space model to assign an initial confidence degree of the power grid operation sequence through the fractional order state space model.

[0110] The node susceptibility and the power grid performance maintenance degree are integrated to generate a power grid operation sequence, and the power grid operation sequence is input into a fractional order state space model to assign an initial confidence degree of the power grid operation sequence through the fractional order state space model.

[0111] The node susceptibility sequence and the power grid performance maintenance degree sequence are constructed respectively, and the node susceptibility sequence and the power grid performance maintenance degree sequence are segmented and aggregated to generate a plurality of power grid operation sequence pairs.

[0112] The sequence mining algorithm is used to mine the discrete space state of each power grid operation sequence pair, and a discrete space state set of the fractional order state space model is generated based on the discrete space state.

[0113] The discrete space state of each power grid operation sequence pair is mined by using a sequence mining algorithm, and the discrete space state includes:

[0114] The candidate motifs are screened in each power grid operation sequence pair by enumeration strategy, and the candidate motif frequency of the candidate motifs in all power grid operation sequences is counted.

[0115] It should be noted that the enumeration strategy means that all possible candidate motifs are listed one by one, and the candidate motifs meeting specific characteristics (such as length and change trend) are screened in each power grid operation sequence pair; the motif refers to a subsequence fragment in the power grid operation sequence that has a repeated occurrence feature or a specific meaning. This step is specifically implemented as follows: for each power grid operation sequence pair, all possible subsequences are traversed as candidate motifs by enumeration strategy, and then the number of times of occurrence of these candidate motifs in all power grid operation sequences is counted to obtain the candidate motif frequency, so as to screen representative motifs.

[0116] The candidate motif frequency is compared with a preset threshold, and the candidate motifs corresponding to the candidate motif frequency in the preset range are selected and composed into a significant motif set;

[0117] The morphological similarity and evolution logic similarity between the motifs in the significant motif set are calculated, the similar motifs are divided into the same group by using spectral clustering technology, and the motifs of each type of clustering center are abstracted as the discrete space state.

[0118] It should be noted that the morphological similarity can be calculated by comparing the waveform characteristics (such as peak value, valley value and fluctuation amplitude) of the motifs or by using dynamic time warping algorithm to quantify the similarity degree between the motif sequences, and the evolution logic similarity can be calculated by analyzing the change trend of the motifs over time, for example, the rising / descending law, the mutation node and the associated meaning in the power grid operation scene, for example, the corresponding disturbance type and compensation action to determine the degree of similarity.

[0119] Spectral clustering is a technology of mapping data samples to a low-dimensional feature space, constructing an adjacency matrix by calculating the similarity between samples, performing feature decomposition on the matrix to obtain a low-dimensional embedding vector, and finally clustering based on the embedding vector; in specific implementation, the morphological similarity and the evolution logic similarity of the significant motifs are fused as the similarity measurement between the motifs, a motif similarity matrix is constructed, the spectral clustering technology is used to perform feature decomposition and low-dimensional mapping on the similarity matrix, the motifs with close distances after mapping are divided into the same group, the feature mean of all motifs in each type of group is calculated, the motif closest to the mean is selected as the clustering center, and the feature parameters of the clustering center motif are abstracted as the discrete space state.

[0120] Based on the discrete space state of each power grid operation sequence pair, a fractional order calculus operator is introduced to estimate the transition probability between the discrete space states, and a fractional order state transition matrix is fitted according to the transition probability.

[0121] The initial confidence of the power grid operation sequence at the current moment is inferred in reverse through the fractional order state transition matrix based on the power grid operation sequence at the current moment as an observation value.

[0122] The power grid operation sequence with conflict is screened based on the initial confidence allocation result, a predefined mixed combination rule is introduced to perform fusion calculation on the initial confidence of the conflict sequence, and the fusion calculation result is taken as the preset power factor.

[0123] It should be noted that by obtaining the historical operation data of the AC-DC conversion device accessing the power grid and outputting the voltage fluctuation component through the resonance sparse decomposition model and calculating the fluctuation index, the voltage fluctuation characteristics can be accurately extracted, providing a reliable data basis for subsequent power grid state analysis; the power grid topology network model is constructed and the voltage fluctuation disturbance propagation is simulated, and the node vulnerability degree and the power grid performance retention degree are analyzed combined with the fluctuation index, which can comprehensively master the influence of voltage disturbance on the power grid and clearly understand the weak link and overall operation state of the power grid; the node susceptibility and the power grid performance retention degree are integrated to generate the power grid operation sequence and the initial confidence is allocated through the fractional order state space model, which can provide quantitative basis for power grid operation state evaluation and improve the accuracy of state judgment;

[0124] Based on the initial confidence, the conflict sequence is screened and the confidence is fused through the predefined mixed combination rule to obtain the preset power factor, which can effectively solve the confidence conflict problem and ensure that the preset power factor meets the actual operation demand of the power grid, providing a scientific and reasonable reference standard for subsequent load side power factor interval division and power compensation mode judgment, and further ensuring the accuracy and effectiveness of the multi-stage cascade control of the AC-DC conversion device.

[0125] S3, based on the power compensation mode, an initial power compensation value is calculated using a variable parameter method (the variable parameter method is a variable PI method), and the initial power compensation value is corrected combined with predefined constraints to obtain a final power compensation value, to realize multi-stage cascade control of the AC-DC conversion device.

[0126] Among them, based on the power compensation mode, an initial power compensation value is calculated using a variable parameter method, and the initial power compensation value is corrected combined with predefined constraints to obtain a final power compensation value, to realize multi-stage cascade control of the AC-DC conversion device, including:

[0127] Based on the active power compensation mode, an initial active power compensation value is calculated using a variable parameter method, and the initial active power compensation value is corrected combined with predefined constraints to obtain a final active power compensation value, specifically including:

[0128] Taking the DC side to the AC side of the AC-DC conversion device as the positive direction, the active power upper limit and the active power lower limit at the current moment are calculated when the power compensation control flag is 1;

[0129] Based on the voltage deviation, the active power deviation value P parameter at the current time is calculated by using a variable parameter method, and the initial active power compensation value at the current time is calculated according to the current active power deviation value P parameter;

[0130] The upper limit of the active power and the lower limit of the active power are taken as constraint conditions to correct the initial active power compensation value at the current time, and the final active power compensation value at the current time is obtained.

[0131] Based on the reactive power compensation method, the initial reactive power compensation value is calculated by using a variable parameter method, and the final reactive power compensation value is obtained by correcting the initial reactive power compensation value in combination with the predefined constraint conditions.

[0132] It should be noted that, as shown in Figure 4 , taking the positive direction from the DC side to the AC side of the AC / DC conversion device, if The upper and lower limits of the current available active power are calculated, and the calculation formula is:

[0133] ;

[0134] ;

[0135] In the formula, is the upper limit of the active power compensation, is the lower limit of the active power compensation, , , soc value, soc upper limit value and soc lower limit value at the current time, respectively; , are the rated apparent power and the current active power value of the AC / DC conversion device, respectively, is the reactive power value at the current time t.

[0136] The active power compensation value at the current time is calculated preliminarily, and the calculation formula is:

[0137] ;

[0138] ;

[0139] In the formula, is the initial active power compensation value at the current time t; is the active power deviation value calculation P parameter at the current time t, is the active power deviation value calculation I parameter, is the given value of the grid-connected point voltage U d , is the value of the grid-connected point voltage U d at the current time t, The integral value is calculated for the active power compensation at the current time t.

[0140] To improve the control response speed when the voltage deviation is large, while taking into account the voltage fluctuation in the steady state, The design adopts a variable parameter method based on voltage deviation, and the calculation formula is:

[0141] ;

[0142] In the formula, The upper limit of the P parameter for stable operation of the device under active power regulation.

[0143] The active power compensation value at the current time is calculated, and the calculation formula is:

[0144] ;

[0145] In the formula, The final active power compensation value at the current time t is corrected, The upper limit of the active power compensation, The lower limit of the active power compensation, The initial active power compensation value at the current time t.

[0146] Among them, based on the reactive power compensation method, the initial reactive power compensation value is calculated by using the variable parameter method, and the initial reactive power compensation value is corrected combined with the predefined constraint condition to obtain the final reactive power compensation value, including:

[0147] Taking the DC side to the AC side of the AC / DC converter as the positive direction, the upper limit and the lower limit of the reactive power at the current time when the power compensation control flag is 0 are calculated;

[0148] Based on the voltage deviation, the reactive power deviation value P parameter at the current time is calculated by using the variable parameter method, and the initial reactive power compensation value at the current time is calculated according to the reactive power deviation value P parameter;

[0149] The upper limit and the lower limit of the reactive power are used as the constraint condition to correct the initial reactive power compensation value at the current time, and the final reactive power compensation value at the current time is obtained.

[0150] It should be noted that if The upper and lower limits of the reactive power compensation at the current time are calculated, and the calculation formula is:

[0151] ;

[0152] ;

[0153] In the formula, Qcomp(t) is the upper limit of reactive power compensation at the current time, Qcomp(t) is the lower limit of reactive power compensation at the current time, , Pnom and P(t) are respectively the rated apparent power and the current active power value of the AC / DC conversion device, Q(t) is the reactive power value at the current time t

[0154] The preliminary calculation of the reactive power compensation value at the current time t is as follows:

[0155] ;

[0156] ;

[0157] In the formula, Q0(t) is the initial reactive power compensation value at the current time t, P is the reactive power deviation value calculation P parameter (equivalent to the reactive power deviation value P parameter) at the current time t, I is the reactive power deviation value calculation I parameter, Iint is the integral value of the reactive power compensation at the current time t, U is the given value of the grid connection point voltage U d , U is the value of the grid connection point voltage U d at the current time t.

[0158] The control response speed is improved when the voltage deviation is large, and the voltage fluctuation in the steady state is considered, The variable parameter method is designed based on the voltage deviation, and the calculation formula is as follows:

[0159] ;

[0160] In the formula, Pmax is the upper limit value of the P parameter for stable operation of the device under reactive power regulation.

[0161] The calculation of the reactive power compensation value at the current time t is as follows:

[0162] ;

[0163] In the formula, Q(t) is the final reactive power compensation value after correction at the current time t, Q0(t) is the initial reactive power compensation value at the current time t, Qcomp(t) is the upper limit of reactive power compensation at the current time, Qcomp(t) is the lower limit of reactive power compensation at the current time.

[0164] It should be noted that the AC / DC conversion device (AC / DC) is connected to the topology in a weak grid environment asFigure 1 As shown, the AC / DC alternating current side is connected to the power grid through the grid connection point switch QS1, the direct current side can be connected to the electrochemical energy storage or super capacitor according to the design requirement, and real-time communication can be performed between the energy storage system and the device. In order to facilitate power regulation, a CT is installed at the grid connection point to collect current information, which is used to calculate the current power factor value. In order to facilitate control, the power factor is divided into three regions as shown in the figure Figure 2 The overall operation control block diagram of the AC / DC is shown in the figure Figure 3 As shown, the present application first judges the active and reactive power compensation mode according to the current value and variation of the power factor at the grid connection point, and combines the set power factor interval division. On this basis, the variable PI method is used for active-voltage and reactive-voltage control, the active and reactive power compensation values are preliminarily calculated, and the preliminary power values are corrected in combination with the capacity limit value of the device itself and the available capacity of the energy storage system, so as to obtain the final active and reactive power compensation values.

[0165] On the one hand, the present application can perform real-time power compensation without depending on the specific parameters of the line impedance, greatly reducing the calculation amount, and on the other hand, the power compensation can be accelerated in the case of large voltage deviation, the voltage at the grid connection point is stabilized, and the compensation coefficient is reduced in the case of small voltage deviation, so as to prevent voltage fluctuation caused by power fluctuation.

[0166] In order to reduce the voltage fluctuation and voltage deviation caused by load fluctuation, distributed new energy access and other factors, the present application proposes a multi-stage cascade control method of AC / DC conversion device applied to voltage active support. On the one hand, the power factor at the grid connection point, the power factor variation trend, the remaining capacity of the energy storage system and the voltage fluctuation are comprehensively considered to increase the active power and reactive power compensation before the traditional grid control, so as to stabilize the voltage at the grid connection point and improve the power supply quality. On the other hand, in the process of calculating the active power and reactive power compensation values, the variable PI control algorithm based on the voltage deviation value and the capacity constraint is adopted, which can calculate the power compensation value without depending on the line impedance parameters, and can also consider the compensation speed and the stability of the device operation.

[0167] In order to verify the application effect of the control method proposed in the present application, the test environment as shown in the figure Figure 5 is constructed, which includes a 200kVA power grid simulator, a 200m line impedance simulator, a 100kWh lithium iron phosphate energy storage system, a 100kVA RLC adjustable load and a 100kVA AC / DC conversion device. During the system operation, the size of the RLC load is adjusted to change the port voltage of the AC / DC conversion device. It can be seen from the test results that the AC / DC conversion device can adjust the power output according to the change of the port voltage and the power factor, and effectively control the voltage at the grid connection point.

[0168] Figure 6 The voltage and current waveforms for the case of RLC load of 0, in which the voltage amplitude is 220V.

[0169] When the system is put into capacitive load, as shown in Figure 7 , the AC / DC device port voltage rises to 230V, and the power factor decreases, at t1, the conversion device adjusts the voltage by outputting 20kVar inductive reactive power, and the voltage decreases from 230V to 220V.

[0170] When the resistive load is put in, as shown in Figure 8 , the AC / DC port voltage decreases to 210V and the power factor remains unchanged, at t2, the conversion device outputs 20kW active power to adjust the port voltage, and the voltage increases from 210V to 220V.

[0171] The above only describes the preferred embodiments of the present application and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A multi-stage cascaded control method for AC / DC converters with active voltage support, characterized in that, The method includes: Collect current and voltage parameters after the AC / DC converter is connected to the power grid, and calculate the current load-side power factor and power factor change based on the current and voltage parameters; The load-side power factor region is divided into stages based on the preset optimal power factor, generating several power factor intervals; the power factor interval to which the absolute value of the current load-side power factor belongs is analyzed, and the power compensation method is determined in combination with the power factor change. Based on the power compensation method, the initial power compensation value is calculated using a variable parameter method, and the initial power compensation value is corrected by combining predefined constraints to obtain the final power compensation value, so as to realize the multi-stage cascaded control of the AC-DC converter.

2. The multi-stage cascaded control method for an AC / DC converter with active voltage support according to claim 1, characterized in that, The load-side power factor region is divided into several power factor intervals based on a preset optimal power factor. Analyze the power factor range to which the absolute value of the current load-side power factor belongs, and determine the power compensation method based on the change in power factor, including: The load-side power factor region is divided based on a preset power factor, generating several power factor intervals, and the power factor interval to which the current absolute value of the load-side power factor belongs is determined. The power factor range includes a first-level power factor range, a second-level power factor range, a third-level power factor range, a first-level dead zone range, and a second-level dead zone range. If the absolute value of the current load-side power factor is within the first-level power factor range, reactive power compensation is performed, and the current power compensation control flag is set to 0; if the absolute value of the current load-side power factor is within the third-level power factor range, active power compensation is performed, and the current power compensation control flag is set to 1. If the absolute value of the current load-side power factor is within the second-level power factor range, the power compensation method is determined based on the change in power factor. The power compensation method includes active power compensation and reactive power compensation.

3. The multi-stage cascaded control method for an AC / DC converter with active voltage support according to claim 2, characterized in that, The method based on power compensation, which calculates the initial power compensation value using a variable parameter approach and corrects the initial power compensation value by combining predefined constraints to obtain the final power compensation value, thereby realizing multi-stage cascaded control of the AC / DC converter, includes: Based on the active power compensation method, the initial active power compensation value is calculated using a variable parameter method, and the initial active power compensation value is corrected by combining predefined constraints to obtain the final active power compensation value. Based on the reactive power compensation method, the initial reactive power compensation value is calculated using a variable parameter approach, and then corrected by combining predefined constraints to obtain the final reactive power compensation value.

4. The multi-stage cascaded control method for an AC / DC converter with active voltage support according to claim 3, characterized in that, The active power compensation method, which calculates the initial active power compensation value using a variable parameter approach and corrects the initial active power compensation value based on predefined constraints, yields the final active power compensation value, including: Taking the DC side to AC side of the AC-DC converter as the positive direction, calculate the upper limit and lower limit of active power at the current moment when the power compensation control flag is set to 1; Based on the voltage deviation, the active power deviation value P parameter at the current moment is calculated using a variable parameter method, and the initial active power compensation value at the current moment is calculated based on the current active power deviation value P parameter. By using the upper and lower limits of active power as constraints, the initial active power compensation value at the current moment is corrected to obtain the final active power compensation value at the current moment.

5. The multi-stage cascaded control method for an AC / DC converter with active voltage support according to claim 4, characterized in that, The reactive power compensation method involves calculating the initial reactive power compensation value using a variable parameter approach, and then correcting the initial reactive power compensation value based on predefined constraints to obtain the final reactive power compensation value, including: Taking the DC side to AC side of the AC-DC converter as the positive direction, calculate the upper limit and lower limit of reactive power at the current moment when the power compensation control flag is set to 0; Based on the voltage deviation, the reactive power deviation value P parameter at the current moment is calculated using a variable parameter method, and the initial reactive power compensation value at the current moment is calculated based on the reactive power deviation value P parameter. By using the upper and lower limits of reactive power as constraints, the initial reactive power compensation value at the current moment is corrected to obtain the final reactive power compensation value at the current moment.

6. The multi-stage cascaded control method for an AC / DC converter with active voltage support according to claim 5, characterized in that, Before dividing the load-side power factor region based on a preset power factor to generate several power factor intervals, and determining the power factor interval to which the current absolute value of the load-side power factor belongs, the process further includes: The historical operating data of the AC / DC converter connected to the power grid is obtained, the historical operating data is input into the pre-constructed resonant sparse decomposition model, and the voltage fluctuation component is output through the resonant sparse decomposition model to calculate the fluctuation index of the voltage fluctuation component. A power grid topology model is constructed to simulate the disturbance propagation characteristics of voltage fluctuations in the power grid topology model, and the node fragility and power grid performance retention under voltage disturbance conditions are analyzed in combination with the fluctuation index. The node vulnerability and grid performance retention are integrated to generate a grid operation sequence, and the grid operation sequence is input into a fractional-order state-space model. The initial confidence level of the grid operation sequence is assigned through the fractional-order state-space model. Based on the initial confidence level allocation results, conflicting power grid operation sequences are screened, and predefined hybrid combination rules are introduced to perform fusion calculation on the initial confidence levels of conflicting sequences. The fusion calculation results are used as the preset power factor.

7. The multi-stage cascaded control method for an AC / DC converter with active voltage support according to claim 6, characterized in that, The process of inputting historical operating data into a pre-built resonant sparse decomposition model, and outputting voltage fluctuation components through the resonant sparse decomposition model, and calculating the fluctuation index of the voltage fluctuation components includes: Wavelet transform is applied to historical operational data to identify the linear relationship between low-pass coefficients, high-pass coefficients, and redundancy coefficients in the historical operational data. With the goal of minimizing the error between historical and real-time operational data, and with the linear relationship of proportion as a constraint, a resonant sparse decomposition model that distinguishes the resonant frequency of historical operational data is constructed. The Lagrange contraction method is used to solve the resonance sparse decomposition model to obtain the high resonance characteristics and low resonance characteristics respectively. The high resonance characteristics and low resonance characteristics are then inversely transformed to output the high resonance voltage fluctuation component and the low resonance voltage fluctuation component. Construct high-pass and low-pass filters, and input the high-resonance voltage fluctuation component and the low-resonance voltage fluctuation component into the corresponding filters respectively. Generate the spectral kurtosis of the high-resonance voltage fluctuation component and the low-resonance voltage fluctuation component through a two-segment filtering method. The spectral kurtosis is summarized to form a spectral kurtosis map. The distribution characteristics of spectral kurtosis in different frequency bands in the spectral kurtosis map are analyzed. The frequency band distribution characteristics of high resonance voltage fluctuation components and low resonance voltage fluctuation components are extracted. The mean of the frequency band distribution characteristics is used as the fluctuation index of the voltage fluctuation component.

8. A multi-stage cascaded control method for an AC / DC converter with active voltage support according to claim 7, characterized in that, The Lagrange contraction method is used to solve the resonance sparse decomposition model to obtain high resonance characteristics and low resonance characteristics. Inverse transformations are then performed on the high and low resonance characteristics to output the high and low resonance voltage fluctuation components, which include: The resonant sparse decomposition model is transformed into an optimization objective function that includes sparsity constraints of high resonant components and smoothness constraints of low resonant components. Lagrange multipliers are introduced into the optimization objective function to generate an augmented Lagrange function. The starting and ending conditions of the iterative shrinkage algorithm are set, and the augmented Lagrangian function is solved iteratively using the iterative shrinkage algorithm. In each round of iterative solution, the minimum values ​​of the high resonance voltage fluctuation component and the low resonance voltage fluctuation component are continuously output. The minimum value is continuously updated using a soft threshold shrinkage operator. The iteration stops when the termination condition is met, and the optimal solutions for high resonance characteristics and low resonance characteristics are obtained respectively. By performing an inverse wavelet transform on the optimal solution, the high-resonance voltage fluctuation component and the low-resonance voltage fluctuation component are obtained.

9. A multi-stage cascaded control method for an AC / DC converter with active voltage support as described in claim 8, characterized in that, The process of integrating node vulnerability and grid performance retention to generate a grid operation sequence, and inputting the grid operation sequence into a fractional-order state-space model, includes allocating the initial confidence level of the grid operation sequence through the fractional-order state-space model: Node susceptibility sequences and grid performance retention sequences are constructed separately, and then the node susceptibility sequences and grid performance retention sequences are aggregated in segments to generate several grid operation sequence pairs; The discrete spatial state of each power grid operation sequence pair is mined using a sequence mining algorithm, and a set of discrete spatial states of a fractional-order state-space model is generated based on the discrete spatial states. Based on the discrete spatial state of each power grid operation sequence pair, a fractional-order calculus operator is introduced to estimate the transition probability between discrete spatial states, and a fractional-order state transition matrix is ​​fitted according to the transition probability. Using the current power grid operation sequence as an observation, the initial confidence level of the current power grid operation sequence is inferred in reverse through the fractional state transition matrix.

10. A multi-stage cascaded control method for an AC / DC converter with active voltage support according to claim 9, characterized in that, The step of using sequence mining algorithms to mine the discrete spatial state of each power grid operation sequence pair includes: Candidate modalities are selected from each power grid operation sequence pair using an enumeration strategy, and the frequency of candidate modalities in all power grid operation sequences is statistically analyzed. The candidate motif frequencies are compared with preset thresholds, and candidate motifs corresponding to the candidate motif frequencies within a pre-range range are selected and formed into a significant motif set. The morphological similarity and evolutionary logical similarity between motifs in the salient motif set are calculated. Spectral clustering technology is used to divide similar motifs into the same group. At the same time, the motifs at the center of each cluster are selected and abstracted into discrete spatial states.

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