A method and system for gradient energy matching longitudinal protection of wind farm transmission lines

Abstract

The present invention belongs to the technical field of relay protection of electric power system, and is specifically a method and system for gradient energy matching longitudinal protection of wind farm transmission line, S001, collecting the current values ​​on both sides of the line at the installation place of wind farm transmission line protection, and extracting the edge information of current signal from the current values ​​on both sides of the line by using multi-resolution morphological gradient; S002, generating gradient energy values ​​according to the current values ​​on both sides of the line and the edge information of current signal, and calculating the DTW distance of the gradient energy values ​​on both sides based on the gradient energy values; S003, judging whether the DTW distance meets the criterion of gradient energy matching longitudinal protection of wind farm transmission line; adjusting the braking amount adaptively by constructing gradient energy ratio, and improving the reliability and sensitivity of protection. Therefore, it can be unaffected by the frequency offset characteristics of fault current in wind farm, improve the ability of protection to withstand transition resistance, and no threshold needs to be set separately, so the scope of application is wider, which is conducive to the application and engineering realization of actual wind farm outgoing line protection.

Description

Technical Field

[0001] The present invention relates to the technical field of novel power system relay protection, and in particular to a gradient energy matching type longitudinal protection method and system for a wind farm transmission line. Background Art

[0002] Under the background of "dual carbon", a high proportion of renewable energy power stations connected to the grid has become an irreversible trend of the new power system. As one of the important representatives of renewable energy, wind energy plays a key supporting role in building a new power system. However, due to the complexity of wind turbine structure and the differences in control strategies, wind turbines exhibit characteristics that are completely different from traditional synchronous generators when they fail. Such as: frequency offset, impedance fluctuation, high harmonics, weak feed, etc., which lead to a significant decrease in the action performance of traditional line protection and the risk of refusal to operate. Therefore, the study of new protection schemes for wind farm transmission lines has important practical significance and social value for promoting the development of renewable energy and ensuring the safe and stable operation of power systems.

[0003] The existing wind farm transmission line protection can be mainly divided into frequency domain protection and time domain protection. Frequency domain protection mainly compares the power frequency or high frequency information of the current before and after the fault through Fourier and wavelet transforms, constructs directional or differential elements, and isolates the fault line. Time domain protection mainly relies on fault differential current and differential voltage, and equates the internal and external faults to different inductance circuit models and protection based on the distance characteristics of the sampling value.

[0004] Whether it is a doubly-fed wind turbine or a permanent magnet direct-drive wind turbine, the short-circuit current at the moment of fault may show characteristics such as frequency offset, which reduces the reliability of traditional line protection based on industrial frequency and poses a risk of refusal to operate.

[0005] Based on this, a method and system for gradient energy matching longitudinal protection of wind farm transmission lines are studied and developed. Summary of the invention

[0006] The present invention provides a gradient energy matching longitudinal protection method and system for a wind farm transmission line. The method utilizes multi-resolution morphological gradients to extract edge information of currents on both sides, defines gradient energy values ​​to highlight high-frequency energy differences between currents, introduces phase angle differences through dynamic time adjustment, deeply displays the effect of energy changes over time, constructs a gradient energy ratio to adaptively adjust the braking amount, improves the reliability and sensitivity of protection, is not affected by the frequency offset characteristics of fault currents in wind farms, improves the ability of protection to withstand transition resistance, does not need to set a separate threshold, has a wider range of applications, and solves the technical problems in the prior art such as frequency offset of short-circuit currents in wind farms at the time of faults, resulting in reduced reliability of line protection and the risk of refusal to operate.

[0007] A method for gradient energy matching longitudinal protection of a wind farm transmission line comprises the following steps:

[0008] S001, collecting current values ​​on both sides of the line where the wind farm transmission line protection is installed, and extracting edge information of current signals from the current values ​​on both sides of the line using multi-resolution morphological gradient;

[0009] S002, generating a gradient energy value according to the current values ​​on both sides of the line and the edge information of the current signal, and calculating the DTW distance of the gradient energy values ​​on both sides based on the gradient energy value;

[0010] S003, judging whether the DTW distance satisfies the gradient energy matching longitudinal protection criterion of the wind farm transmission line; if so, judging that the fault occurred is within the transmission line area, and the protection is activated; otherwise, judging that the fault occurred is outside the transmission line area, and the protection is restored.

[0011] Optionally, in step S001, current values ​​on both sides of the line at the wind farm transmission line protection installation site are collected, and the current values ​​on both sides of the line are three-phase current signals collected at the station side and the system side of the wind farm transmission line protection installation site.

[0012] Optionally, in step S001, extracting edge information of current signals from the current values ​​on both sides of the line using multi-resolution morphological gradients includes:

[0013] The expansion and corrosion basic operation units of mathematical morphology are used to operate the three-phase current signals on the station side and the system side.

[0014] The dilation operation is:

[0015] The corrosion operation is:

[0016] Among them, f(x) is the original sampled current signal; g(y) is the structure function; D1 and D2 are the variable definition domains of the structure element and the original sampled current signal respectively; represents the expansion operation; ! represents the erosion operation;

[0017] After the basic operations of dilation and erosion basic operation units are performed on the current signal, the single-scale morphological gradient of the current signal is obtained;

[0018] The basic morphological gradient is:

[0019] Among them, G is the morphological gradient structure operator;

[0020] Based on the single-scale morphological gradient, gradient calculation is performed to obtain multi-resolution morphological gradients to represent the edge information of the current signal.

[0021] Optionally, the multi-resolution morphological gradient is:

[0022]

[0023] Among them, g + Indicates rising edge; g - represents the falling edge; l represents the length of the structural element, and its value decreases with the increase of the number of morphological gradient decomposition layers; α represents the number of multi-resolution morphological gradient decomposition layers; is the gradient value of the decomposition layer number corresponding to the rising edge; is the gradient value of the decomposition layer corresponding to the falling edge; P α is the gradient value after decomposition of the α layer; when α=0, P α is the original sampling current signal.

[0024] Optionally, in step S002, a gradient energy value is generated according to the current values ​​on both sides of the line and the edge information of the current signal, and the gradient energy value in the DTW distance of the gradient energy values ​​on both sides is calculated based on the gradient energy value:

[0025]

[0026] Among them, i is the current value after gradient decomposition; n is the number of sampling points of the original signal; i j is the current value corresponding to the nth sampling point; E is the gradient energy value. S002, generating a gradient energy value according to the current values ​​on both sides of the line and the edge information of the current signal, and calculating the DTW distance of the gradient energy values ​​on both sides;

[0027] Optionally, in step S002, calculating the DTW distance of the gradient energy values ​​on both sides based on the gradient energy value includes:

[0028] Arrange the current signal gradient energy value sequences X and Y on both sides of the line in chronological order and construct the distance matrix A m×n ;

[0029] Point x i With point y j The Euclidean distance between them is:

[0030] Among them, A m×n The element a in ij Defined as point x i and j The Euclidean distance of x i ,y j are any points on the sequences X and Y respectively;

[0031] In the matrix A m×n Find a regular path in which the cumulative distance between sequences X and Y is minimized;

[0032] The regular path is: P = {p1, p2, ..., p s}

[0033] Among them, m and n are matrices A m×n The number of points in the horizontal and vertical coordinates; max(m,n)<sm+n; P is the set of paths; P1, P2, ..., P s is the distance of a single path; the constraints that the regular path should satisfy are: monotonicity constraint: i k i k-1 ,j k j k-1 , continuity constraint: i k -i k-1 1,j k -j k-1 ≤1, boundary constraint: i1=j1=1,i s =m,j s =n;

[0034] Since there is more than one path set P that meets the constraints, in order to make the selected path optimal, the global optimal problem is transformed into a local optimal problem, and the cumulative distance of each step is guaranteed to be optimal, so that the global optimal regularized path can be obtained;

[0035] The recursive formula is:

[0036] Among them, D(i,j) is the accumulated optimal distance solved at each step;

[0037] The global optimal planning path is normalized to obtain the DTW distance of the required current signal gradient energy values ​​on both sides. The DTW distance is:

[0038]

[0039] Among them, DTW(X,Y) is the DTW distance before normalization; D xy is the normalized DTW distance.

[0040] Optionally, step S003, judging whether the DTW distance satisfies a criterion for a gradient energy matching type longitudinal protection of a wind farm transmission line, wherein the protection criterion in the criterion for a gradient energy matching type longitudinal protection of a wind farm transmission line is:

[0041]

[0042] Where D is the DTW distance of the current gradient energy value on both sides of the line; D set To protect the startup threshold; E r is the braking amount; E M 、E Nare the gradient energy values ​​of the current signal at the station side and the system side respectively;

[0043] Optionally, S003, it is determined whether the DTW distance meets the gradient energy matching type longitudinal protection criterion of the wind farm transmission line; if so, it is determined that the fault occurred in the transmission line area, and the protection is actuated; otherwise, it is determined that the fault occurred outside the transmission line area, and the protection is restored. The determination method is:

[0044] The calculated DTW distance of the current gradient energy value on both sides of the line is compared with the set protection start threshold value D set For comparison, if D is greater than the set protection start threshold value D set , the protection starts if D is greater than the braking amount E r , it is determined as a fault within the zone and an action signal is issued, otherwise it is reset.

[0045] The present invention also provides a wind farm transmission line gradient energy matching type longitudinal protection system, including a data acquisition module, a current gradient energy value DTW distance calculation module, a fault detection module and a protection action module;

[0046] A data acquisition module is used to collect current data at the wind farm transmission line protection installation location, and extract edge information of current signals from the current data using multi-resolution morphological gradient;

[0047] A current gradient energy value DTW distance calculation module, used to calculate the DTW distance of the gradient energy values ​​on both sides according to the current data and the edge information of the current signal;

[0048] A fault detection module, used to determine whether the DTW distance of the gradient energy values ​​on both sides meets the longitudinal protection criterion of the wind farm transmission line, and determine whether to issue a protection action signal according to the judgment result;

[0049] The protection action module is used to start the corresponding action according to the protection action signal. When the DTW distance of the gradient energy values ​​on both sides meets the protection criterion, it is determined to be a fault within the transmission line area and a protection action signal is issued; otherwise, it is determined to be a fault outside the transmission line area and no protection action signal is issued.

[0050] Optionally, the data acquisition module collects current data at a protection installation location of a wind farm transmission line, where the wind farm includes a double-fed wind farm and a permanent magnet direct-drive wind farm.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] 1) The technical solution of the present application utilizes multi-resolution morphological gradients to extract high-frequency information of the current signal, identifies the edge features of the current waveform, and amplifies the amplitude difference of the signals on both sides through slope structural elements, thereby further improving the protection's transition resistance capability.

[0053] 2) Compared with the traditional power frequency phasor protection using Fourier algorithm, the technical solution of the present application is completely carried out in the time domain and does not require the use of voltage quantities. Therefore, it is not affected by the frequency offset characteristics of the fault current in the wind farm, thereby improving the reliability of the line protection based on the power frequency quantity.

[0054] 3) The technical solution of the present application uses the DTW algorithm to determine whether the longitudinal protection criteria of the wind farm transmission line are met, and determines whether to issue a protection action signal based on the judgment result. It comprehensively utilizes the fault tolerance of DTW to the phase difference of the time series in the dynamic path finding process, and combines the advantages of mathematical morphology in noise resistance to make its matching results more robust in similar channels. Therefore, the criterion can tolerate a certain degree of synchronization error and has good noise resistance performance.

[0055] 4) In the technical solution of the present application, by judging whether the DTW distance of the current gradient energy value on both sides of the line meets the gradient energy matching longitudinal protection criterion of the wind farm transmission line, the braking amount can be adaptively adjusted to further improve the sensitivity and safety of the protection, so that the criterion does not need to set a separate threshold and has a wider scope of application. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 :It is a flow chart of the gradient energy matching type longitudinal protection method of the wind farm transmission line in Example 1 of the present invention;

[0057] Figure 2 : A model diagram of a wind farm transmission line system in Example 1 of the present invention;

[0058] Figure 3 : A-phase current and gradient energy value when AG fault occurs at point f2 of Example 1 of the present invention;

[0059] Figure 4 : A-phase current and gradient energy value when AG fault occurs at point f4 of Example 1 of the present invention;

[0060] Figure 5 : The protection dynamic performance when an AG fault occurs at point f2 of Example 1 of the present invention;

[0061] Figure 6 : The protection dynamic performance when AG fault occurs at point f4 of Example 1 of the present invention;

[0062] Figure 7 : This is the protection dynamic performance when there is a synchronization error in Example 1 of the present invention.

[0063] Specific implementation information,

[0064] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The illustrative implementation modes of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0065] Embodiment 1:

[0066] like Figure 1 As shown, a gradient energy matching longitudinal protection method for a wind farm transmission line comprises the following steps:

[0067] S001, collecting current values ​​on both sides of the line where the wind farm transmission line protection is installed, and extracting edge information of current signals from the current values ​​on both sides of the line using multi-resolution morphological gradient;

[0068] S002, generating a gradient energy value according to the current values ​​on both sides of the line and the edge information of the current signal, and calculating the DTW distance of the gradient energy values ​​on both sides based on the gradient energy value;

[0069] S003, judging whether the DTW distance satisfies the gradient energy matching longitudinal protection criterion of the wind farm transmission line; if so, judging that the fault occurred is within the transmission line area, and the protection is activated; otherwise, judging that the fault occurred is outside the transmission line area, and the protection is restored.

[0070] Preferably, in step S001, current values ​​on both sides of the line where the wind farm transmission line protection is installed are collected, and the current values ​​on both sides of the line are three-phase current signals collected from the station side and the system side of the wind farm transmission line protection installation.

[0071] Wherein, in the step S001, extracting edge information of current signals from the current values ​​on both sides of the line using multi-resolution morphological gradient includes:

[0072] The expansion and corrosion basic operation units of mathematical morphology are used to operate the three-phase current signals on the station side and the system side.

[0073] The dilation operation is:

[0074] The corrosion operation is:

[0075] Among them, f(x) is the original sampled current signal; g(y) is the structure function; D1 and D2 are the variable definition domains of the structure element and the original sampled current signal respectively; represents the expansion operation; ! represents the erosion operation;

[0076] After the basic operations of dilation and erosion basic operation units are performed on the current signal, the single-scale morphological gradient of the current signal is obtained;

[0077] The basic morphological gradient is:

[0078] Among them, G is the morphological gradient structure operator;

[0079] Based on the single-scale morphological gradient, gradient calculation is performed to obtain multi-resolution morphological gradients to represent the edge information of the current signal.

[0080] Specifically, the multi-resolution morphological gradient is:

[0081]

[0082] Among them, g + Indicates rising edge; g - represents the falling edge; l represents the length of the structural element, and its value decreases with the increase of the number of morphological gradient decomposition layers; α represents the number of multi-resolution morphological gradient decomposition layers; is the gradient value of the decomposition layer number corresponding to the rising edge; is the gradient value of the decomposition layer corresponding to the falling edge; P α is the gradient value after decomposition of the α layer; when α=0, P α is the original sampling current signal.

[0083] Preferably, in step S002, a gradient energy value is generated according to the current values ​​on both sides of the line and the edge information of the current signal, and the gradient energy value in the DTW distance of the gradient energy values ​​on both sides is calculated based on the gradient energy value:

[0084]

[0085] Among them, i is the current value after gradient decomposition; n is the number of sampling points of the original signal; i j is the current value corresponding to the nth sampling point; E is the gradient energy value. S002, generating a gradient energy value according to the current values ​​on both sides of the line and the edge information of the current signal, and calculating the DTW distance of the gradient energy values ​​on both sides;

[0086] Based on the generated current gradient energy value, the DTW algorithm is used to calculate the DTW distance of the gradient energy values ​​on both sides.

[0087] The DTW algorithm is a matching algorithm based on dynamic programming, which can be used to measure the overall similarity of two time series. Its core idea is to find the best correspondence between the two sequences through dynamic bending and determine the optimal regular path. The accumulated distance under this path is the distance between the two sequences. The smaller the distance, the higher the similarity.

[0088] The steps of calculating the DTW distance of the gradient energy values ​​on both sides based on the current gradient energy value include:

[0089] Arrange the current signal gradient energy value sequences X and Y on both sides of the line in chronological order and construct the distance matrix A m×n ;

[0090] Point x i With point y j The Euclidean distance between them is:

[0091] Among them, A m×n The element a in ij Defined as point x i and j The Euclidean distance of x i ,y j are any points on the sequences X and Y respectively;

[0092] In the matrix A m×n Find a regular path in which the cumulative distance between sequences X and Y is minimized;

[0093] The regular path is: P = {p1, p2, ..., p s}

[0094] Among them, m and n are matrices A m×n The number of points in the horizontal and vertical coordinates; max(m,n)<sm+n; P is the set of paths; P1, P2, ..., P s is the distance of a single path; the constraints that the regular path should satisfy are: monotonicity constraint: i k i k-1 ,j k j k-1 , continuity constraint: i k -i k-1 1,j k -j k-1 ≤1, boundary constraint: i1=j1=1,i s =m,j s =n;

[0095] Since there is more than one path set P that meets the constraints, in order to select the best path, the global optimal problem is transformed into a local optimal problem, and the accumulated distance of each step is guaranteed to be optimal, so that the global optimal regularized path can be obtained;

[0096] The recursive formula is:

[0097] Among them, D(i,j) is the accumulated optimal distance solved at each step;

[0098] The global optimal planning path is normalized to obtain the DTW distance of the required current signal gradient energy values ​​on both sides. The DTW distance is:

[0099]

[0100] Among them, DTW(X,Y) is the DTW distance before normalization; D xy is the normalized DTW distance.

[0101] Further optimized, step S003, judging whether the DTW distance satisfies the wind farm transmission line gradient energy matching type longitudinal protection criterion, the protection criterion in the wind farm transmission line gradient energy matching type longitudinal protection criterion is:

[0102]

[0103] Where D is the DTW distance of the current gradient energy value on both sides of the line; D set To protect the startup threshold; E r is the braking amount; E M 、E N are the gradient energy values ​​of the current signal at the station side and the system side respectively;

[0104] Specifically, step S003 determines whether the DTW distance meets the gradient energy matching type longitudinal protection criterion of the wind farm transmission line; if so, it is determined that the fault occurred in the transmission line area, and the protection is activated; otherwise, it is determined that the fault occurred outside the transmission line area, and the protection is restored. The determination method is:

[0105] The calculated DTW distance of the current gradient energy value on both sides of the line is compared with the set protection start threshold value D set For comparison, if D is greater than the set protection start threshold value D set , the protection starts if D is greater than the braking amount E r , it is determined as a fault within the zone and an action signal is issued, otherwise it is reset.

[0106] Embodiment 2:

[0107] This embodiment is a specific application of embodiment 1. Figure 2 The specific parameters of the wind farm transmission line system model shown in FIG. 1 are shown in Table 1.

[0108]

[0109] Table 1 Simulation model parameters

[0110] The sampling frequency is 4kHz, the data window length is 10ms, and simulation analysis is performed on different fault scenarios of the transmission line, such as the location of the fault point and the type of fault.

[0111] On the transmission line, fault points are set at 10km, 20km, and 30km away from the station side busbar to simulate faults within the area. At the same time, fault points are set at the station exit and the system side exit to simulate faults outside the area. The above fault points are recorded as f1 to f5 in sequence, and their relative positions are as follows: Figure 2 As shown in . The fault type of each fault point is set to A-phase grounding fault, BC-phase short circuit fault, BC-two-phase grounding fault, and three-phase short circuit fault, which are represented by AG, BC, BCG, and ABC respectively.

[0112] Take the A-phase metallic grounding fault at the middle of the f2 line at t=0s as an example. The A-phase current collected by the CT at the beginning and end of the transmission line of the double-fed wind farm and the permanent magnet direct-drive wind farm, and the gradient energy value generated based on it are as follows: Figure 3 Protection dynamic performance, such as Figure 5 shown.

[0113] from Figure 5 It can be seen that, by adopting the protection criterion, both types of wind farms can start protection within 3ms after the fault occurs, and the action amount is greater than the braking amount within 4ms, and the protection sends an action signal. Therefore, the criterion can correctly identify the fault and has good speed.

[0114] Take the A-phase metallic grounding fault at the exit of f4 station at t=0s as an example. The A-phase current collected by the CT at the beginning and end of the two wind farm transmission lines and the gradient energy generated based on it are as follows: Figure 4 Protection dynamic performance, such as Figure 6 shown.

[0115] Depend on Figure 4 It can be seen that when there is an out-of-zone fault, the fault current amplitudes on both sides of the line are the same and the directions are opposite, and the generated gradient energy values ​​are basically the same. Figure 6 It can be seen that the action amount of both types of wind farms is lower than the protection start value and even lower than the braking amount, so the protection is reliable and does not act.

[0116] Different fault types are simulated for different fault locations, and the action and braking amounts are intercepted 10ms after the fault. The results are shown in Table 2.

[0117]

[0118] Note: √-action ×-no action, the same below.

[0119] Table 2 Protection action when different faults occur at different fault locations

[0120] It can be seen from Table 2 that when an in-zone fault occurs at the station, the protection can be started normally after the fault occurs, and the action amount is greater than the braking amount, and the protection can operate correctly. However, when the non-fault phase and out-of-zone fault occur, the action amount is significantly less than the braking amount, and the protection does not operate reliably. The above results show that the protection principle has good action performance in different fault scenarios and can quickly and reliably identify the faulty line.

[0121] Taking the A phase grounding fault and the BC phase grounding fault at f3 as an example, the transition resistance is set to 25, 50, 75, 100 Ω, respectively. The protection action is shown in Table 3.

[0122]

[0123] Table 3 Protection action at different transition resistances

[0124] Although the difference in short-circuit current amplitude is reduced in the case of high-resistance grounding, it will affect the protection performance to a certain extent. However, the criterion does not rely on the steady-state amplitude of the current on both sides to identify the fault. The gradient energy value generated by the multi-resolution morphological gradient has a spectral shape determined by the transient current morphology, and the high-frequency details of the current are further amplified by the ramp structural elements. Therefore, the criterion can still accurately identify the fault in the high-resistance fault scenario, as shown in Table 3. Considering that the maximum transition resistance of the 220kV system is generally 100Ω, the criterion still has good action performance in different transition resistance scenarios.

[0125] The sampling of the device is not synchronized, which will cause the phase angle error of the sampling signal, and the transmission error of the current transformer will cause the amplitude error and phase angle error. The longitudinal protection judges the fault by comparing the electrical quantities on both sides of the line, which inevitably requires the protection to have a certain ability to resist synchronization errors. The phase angle error on both sides is set to 18°, that is, the communication delay is 1ms, and the CT amplitude error is set to +5% and -5% respectively, to test the ability of the judgment to resist synchronization errors. Taking the three-phase short circuit fault at f5 as an example, the dynamic performance of the protection, such as Figure 7 shown.

[0126] The DTW distance calculation process does not strictly require that the sampling points with the same sequence number be absolutely consistent in clock, but converts the synchronization error of the sampling point into the distance error through flexible matching, which makes the DTW distance have a certain ability to resist synchronization errors in principle. Figure 7 It can be seen that when the two errors are superimposed, although the action amount and the braking amount fluctuate, the protection action amount is still smaller than the starting value and lower than the braking amount. Therefore, the criterion has good anti-synchronization error capability.

[0127] The criterion relies on the edge information extracted by the morphological edge-guided operator, so it is necessary to verify the adaptability of the protection principle under certain noise scenarios. It is generally believed that the signal-to-noise ratio in the power system is not less than 25dB. Taking the fault at f5 outside the zone as an example, Gaussian white noise with signal-to-noise ratios of 15, 20, 25, and 30dB is superimposed on the fault current signal. The protection action is shown in Table 4.

[0128]

[0129] Table 4 Protection actions under different noise scenarios

[0130] It can be seen from Table 4 that the criterion has good noise resistance performance in the face of scenes with different noise intensities. This is because mathematical morphology itself has good noise suppression ability, and the DTW distance dynamically bends the sampling sequence to make its matching results more robust in the similarity channel. The combination of the two makes the criterion more adaptable to noise.

[0131] Embodiment 3:

[0132] This embodiment provides a wind farm transmission line gradient energy matching type longitudinal protection system, including a data acquisition module, a current gradient energy value DTW distance calculation module, a fault detection module and a protection action module;

[0133] A data acquisition module is used to collect current data at the wind farm transmission line protection installation location, and extract edge information of current signals from the current data using multi-resolution morphological gradient;

[0134] A current gradient energy value DTW distance calculation module, used to calculate the DTW distance of the gradient energy values ​​on both sides according to the current data and the edge information of the current signal;

[0135] A fault detection module, used to determine whether the DTW distance of the gradient energy values ​​on both sides meets the longitudinal protection criterion of the wind farm transmission line, and determine whether to issue a protection action signal according to the judgment result;

[0136] The protection action module is used to start the corresponding action according to the protection action signal. When the DTW distance of the gradient energy values ​​on both sides meets the protection criterion, it is determined to be a fault within the transmission line area and a protection action signal is issued; otherwise, it is determined to be a fault outside the transmission line area and no protection action signal is issued.

[0137] The data acquisition module collects current data at the installation location of the wind farm transmission line protection, and the wind farm includes a double-fed wind farm and a permanent magnet direct-drive wind farm.

[0138] In this embodiment, the protection action module uses the DTW algorithm to determine whether the DTW distance of the gradient energy values ​​on both sides meets the longitudinal protection criterion of the wind farm transmission line, and determines whether to issue a protection action signal based on the judgment result. It comprehensively utilizes the fault tolerance of DTW to the phase difference of the time series in the dynamic path finding process, and combines the advantages of mathematical morphology in noise resistance to make its matching result more robust in similar channels. Therefore, the criterion can tolerate a certain degree of synchronization error and has good noise resistance performance.

[0139] In addition, by judging whether the DTW distance of the current gradient energy value on both sides of the line satisfies the current gradient energy value on both sides of the line in the gradient energy matching longitudinal protection criterion of the wind farm transmission line, the braking amount can be adaptively adjusted to further improve the sensitivity and safety of the protection, so that the criterion does not need to set a separate threshold and has a wider scope of application.

[0140] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A gradient energy matching type longitudinal protection method for wind farm transmission lines, characterized in that: The method comprises the following steps: S001, collecting current values ​​on both sides of the line where the wind farm transmission line protection is installed, and extracting edge information of current signals from the current values ​​on both sides of the line using multi-resolution morphological gradient; S002, generating a gradient energy value according to the current values ​​on both sides of the line and the edge information of the current signal, and calculating the DTW distance of the gradient energy values ​​on both sides based on the gradient energy value; specifically, generating a gradient energy value according to the current values ​​on both sides of the line and the edge information of the current signal, and calculating the DTW distance of the gradient energy values ​​on both sides based on the gradient energy value, wherein the gradient energy value is: in, is the current value after gradient decomposition; is the number of sampling points of the original signal; For the The current value corresponding to each sampling point; is the gradient energy value; S002, generating a gradient energy value according to the current values ​​on both sides of the line and the edge information of the current signal, and calculating the DTW distance of the gradient energy values ​​on both sides; The DTW distance of the gradient energy values ​​on both sides calculated based on the gradient energy value includes: The current signal gradient energy value sequence on both sides of the line and Arrange in chronological order and construct a distance matrix ; point With point The Euclidean distance between them is: ; in, Elements in Defined as a point and The Euclidean distance of , Sequence and Any point on In the matrix Find a regular path in which the sequence and The cumulative distance is the smallest; The regularized path is: in, , For the matrix The number of points on the horizontal and vertical coordinates; ; is a set of paths; P1, P2, ..., P s is the distance of a single path; the constraints that the regular path should satisfy are: monotonicity constraint: , continuity constraints: , boundary constraints: ; Since the set of paths that satisfy the constraints More than one, in order to make the selected path optimal, the global optimal problem is transformed into a local optimal problem, ensuring that the cumulative distance of each step is optimal, and the global optimal regularized path can be obtained; The recursive formula is: in, The accumulated optimal distance solved for each step; The global optimal planning path is normalized to obtain the DTW distance of the required current signal gradient energy values ​​on both sides. The DTW distance is: in, is the DTW distance before normalization; is the normalized DTW distance; S003, judging whether the DTW distance satisfies the gradient energy matching longitudinal protection criterion of the wind farm transmission line; if so, judging that the fault occurred is within the transmission line area, and the protection is activated; otherwise, judging that the fault occurred is outside the transmission line area, and the protection is restored.

2. A method for gradient energy matching longitudinal protection of a wind farm transmission line according to claim 1, characterized in that: In the step S001, current values ​​on both sides of the line where the wind farm transmission line protection is installed are collected. The current values ​​on both sides of the line are three-phase current signals collected from the station side and the system side of the wind farm transmission line protection installation.

3. A method for gradient energy matching type longitudinal protection of wind farm transmission lines according to claim 2, characterized in that: In the step S001, extracting edge information of current signals from the current values ​​on both sides of the line using multi-resolution morphological gradient includes: The expansion and corrosion basic operation units of mathematical morphology are used to operate the three-phase current signals on the station side and the system side. The dilation operation is: The corrosion operation is: in, is the original sampling current signal; is the structure function; D1 and D2 are the variable definition domains of the structure element and the original sampling current signal respectively; represents the dilation operation; represents the erosion operation; After the basic operations of dilation and erosion basic operation units are performed on the current signal, the single-scale morphological gradient of the current signal is obtained; The single-scale morphological gradient is: Among them, G is the morphological gradient structure operator; Based on the single-scale morphological gradient, gradient calculation is performed to obtain multi-resolution morphological gradients to represent the edge information of the current signal.

4. A method for gradient energy matching type longitudinal protection of wind farm transmission lines according to claim 3, characterized in that: The multi-resolution morphological gradient is: in, Indicates rising edge; Indicates falling edge; Represents the length of the structural element, and its value decreases with the increase of the number of morphological gradient decomposition layers; Represents the number of multi-resolution morphological gradient decomposition layers; is the gradient value of the decomposition layer number corresponding to the rising edge; is the gradient value of the decomposition layer corresponding to the falling edge; for The gradient value after layer decomposition; when hour, is the original sampling current signal.

5. A method for gradient energy matching longitudinal protection of wind farm transmission lines according to any one of claims 2 to 4, characterized in that: Step S003, judging whether the DTW distance satisfies the wind farm transmission line gradient energy matching type longitudinal protection criterion, wherein the protection criterion in the wind farm transmission line gradient energy matching type longitudinal protection criterion is: in, is the DTW distance of the current gradient energy value on both sides of the line; To protect the startup threshold; is the braking amount; , are the gradient energy values ​​of the current signals on the station side and the system side respectively.

6. A method for gradient energy matching type longitudinal protection of wind farm transmission lines according to claim 5, characterized in that: S003, judging whether the DTW distance satisfies the gradient energy matching type longitudinal protection criterion of the wind farm transmission line; If yes, it is determined that the fault occurred in the transmission line area, and the protection is activated; otherwise, it is determined that the fault occurred outside the transmission line area, and the protection is restored. The judgment method is: The calculated DTW distance of the current gradient energy value on both sides of the line is compared with the set protection start threshold value. For comparison, if Greater than the set protection start threshold , the protection starts, if Greater than the braking amount , it is determined as a fault within the zone and an action signal is issued, otherwise it is reset.

7. A wind farm transmission line gradient energy matching type longitudinal protection system, characterized by: It includes a data acquisition module, a current gradient energy value DTW distance calculation module, a fault detection module and a protection action module; A data acquisition module is used to collect current data at the wind farm transmission line protection installation location, and extract edge information of current signals from the current data using multi-resolution morphological gradient; The current gradient energy value DTW distance calculation module is used to calculate the DTW distance of the gradient energy values ​​on both sides according to the current data and the edge information of the current signal; specifically, the gradient energy value is generated according to the current value on both sides of the line and the edge information of the current signal, and the gradient energy value in the DTW distance of the gradient energy values ​​on both sides obtained by calculation based on the gradient energy value is: in, is the current value after gradient decomposition; is the number of sampling points of the original signal; For the The current value corresponding to each sampling point; is the gradient energy value; Generate a gradient energy value according to the current values ​​on both sides of the line and the edge information of the current signal, and calculate the DTW distance of the gradient energy values ​​on both sides; The DTW distance of the gradient energy values ​​on both sides calculated based on the gradient energy value includes: The current signal gradient energy value sequence on both sides of the line and Arrange in chronological order and construct a distance matrix ; point With point The Euclidean distance between them is: ; in, Elements in Defined as a point and The Euclidean distance of , Sequence and Any point on In the matrix Find a regular path in which the sequence and The cumulative distance is the smallest; The regularized path is: in, , For the matrix The number of points on the horizontal and vertical coordinates; ; is a set of paths; P1, P2, ..., P s is the distance of a single path; the constraints that the regular path should satisfy are: monotonicity constraint: , continuity constraints: , boundary constraints: ; Since the set of paths that satisfy the constraints More than one, in order to make the selected path optimal, the global optimal problem is transformed into a local optimal problem, ensuring that the cumulative distance of each step is optimal, and the global optimal regularized path can be obtained; The recursive formula is: in, The accumulated optimal distance solved for each step; The global optimal planning path is normalized to obtain the DTW distance of the required current signal gradient energy values ​​on both sides. The DTW distance is: in, is the DTW distance before normalization; is the normalized DTW distance; A fault detection module, used to determine whether the DTW distance of the gradient energy values ​​on both sides meets the longitudinal protection criterion of the wind farm transmission line, and determine whether to issue a protection action signal according to the judgment result; The protection action module is used to start the corresponding action according to the protection action signal. When the DTW distance of the gradient energy values ​​on both sides meets the protection criterion, it is determined to be a fault within the transmission line area and a protection action signal is issued; otherwise, it is determined to be a fault outside the transmission line area and no protection action signal is issued.

8. A wind farm transmission line gradient energy matching type longitudinal protection system according to claim 7, characterized in that: The data acquisition module collects current data at the wind farm transmission line protection installation location, and the wind farm includes a double-fed wind farm and a permanent magnet direct-drive wind farm.

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