DC line protection method and system based on the similarity of current traveling wave time-frequency matrix

Abstract

This invention discloses a DC line protection method and system based on the similarity of current traveling wave time-frequency matrices. The method includes: calculating the line-mode current on either side of the DC line based on the positive and negative currents at the protection installation points on both sides; determining whether the protection on both sides of the line is activated based on the line-mode current; when both protections on both sides are activated, determining the current traveling wave time-frequency matrix corresponding to either side of the line based on the line-mode current within a preset sampling time period; calculating the left characteristic real matrix of the current traveling wave on either side based on the current traveling wave time-frequency matrix; calculating the similarity of the current traveling wave time-frequency matrices on both sides of the line based on the equivalent left characteristic real matrix of the current traveling wave, and identifying faults inside and outside the line area based on the similarity. This invention is applicable to DC power grids without DC filters or where DC inductors are installed at the converter station outlet, and has stronger resistance to transition resistance and noise immunity.

Description

Technical Field

[0001] This invention relates to the field of power system relay protection technology, and more specifically, to a DC line protection method and system based on the similarity of current traveling wave time-frequency matrix. Background Technology

[0002] Direct current (DC) transmission boasts advantages such as flexible control, low harmonic content, high transmission power, and the ability to transmit over long distances, making it a crucial method for achieving large-scale renewable energy grid integration, asynchronous grid interconnection, and isolated power supply. However, DC transmission lines operate in harsh environments and are prone to faults. When a line fault occurs, each converter station feeds short-circuit current to the fault point. This fault current rises rapidly and has a large amplitude, severely jeopardizing the DC system. Therefore, reliable, fast, and sensitive line protection is of paramount importance for the safe and stable operation of the DC transmission network.

[0003] Existing main protection methods for DC transmission lines mainly fall into two categories. One category is based on the boundary elements of the DC line, relying on the blocking effect of DC inductors on high-frequency components or the low resistance of DC filters at resonant frequencies. Since flexible DC transmission systems typically do not require DC filters, protection methods based on the boundary effects of DC filters are only applicable to traditional HVDC transmission systems. Furthermore, protection methods based on the boundary effects of DC inductors are only applicable to DC grids where DC inductors are installed at both ends of the line, and cannot be applied to DC grids where DC inductors are installed at the converter station outlet. The other category of protection methods is not based on the boundary elements of the DC line. This type of protection method has a wider range of engineering applications, but existing protection methods not based on DC line boundary elements suffer from problems such as not being able to protect the entire line length, being unsuitable for various line lengths, having long operating times, and being susceptible to transition resistance and noise. Summary of the Invention

[0004] This invention proposes a DC line protection method and system based on the similarity of the time-frequency matrix of current traveling wave, in order to solve the problem of how to efficiently protect DC transmission lines.

[0005] To address the aforementioned problems, according to one aspect of the present invention, a DC line protection method based on the time-frequency matrix similarity of current traveling waves is provided, the method comprising:

[0006] Based on the positive and negative currents at the protection installation points on both sides of the DC line, calculate the corresponding line-mode current on either side of the line.

[0007] Based on the line current, determine whether the protection on both sides of the line is activated;

[0008] When it is determined that the protection on both sides of the line is activated, for any side of the line, the current traveling wave time-frequency matrix corresponding to that side is determined based on the line mode current within the preset sampling time period corresponding to that side.

[0009] Calculate the left characteristic real matrix of the current traveling wave corresponding to each side based on the current traveling wave time-frequency matrix;

[0010] The similarity between the time-frequency matrices of the current traveling waves on both sides of the line is calculated by equivalent calculation of the left characteristic real matrix of the current traveling waves on both sides of the line, and the fault inside or outside the line area is determined based on the similarity.

[0011] Preferably, the method calculates the line-mode current corresponding to either side of the line in the following manner:

[0012]

[0013] Where I0 and I1 represent the zero-mode current and line-mode current, respectively, I p I n These represent the positive current and the negative current, respectively.

[0014] Preferably, the method determines whether the protection on either side of the line is activated by means of:

[0015] For either side of the line, if the following conditions are met If the condition is not met, the protection will be activated; otherwise, the protection will not be activated. Here, I(k) is the sampled value of the line-mode current corresponding to either side of the line, and d... set This is the first preset threshold.

[0016] Preferably, the current traveling wave time-frequency matrix acquisition unit, for any side p(q) of the line, determines the current traveling wave time-frequency matrix corresponding to side p(q) based on the initial current traveling wave of the line mode within a preset sampling time period corresponding to side p(q), including:

[0017]

[0018]

[0019] Among them, S p(q) This is the two-dimensional traveling wave time-frequency matrix corresponding to the p(q) side of the line. This represents the initial current traveling wave signal of the p(q) side line mode. for The Fourier transform form; f→n / NT, τ→jT, T is the sampling interval, j,m=0,1,…,N-1; n=0,1,…,fix(N / 2), fix refers to taking the largest integer not exceeding N / 2; S p(q) The row vector represents the time-domain characteristics of the signal at a certain frequency, and the column vector represents the frequency-domain characteristics of the signal at a certain moment. The element S... p(q) (a,b) represents the value of the b-th sampling point at the a-th frequency corresponding to side p(q); where the frequency difference between two adjacent rows is: fs The sampling frequency is denoted by ; the frequency of the a-th row is:

[0020] Preferably, the step of calculating the left eigenvalue matrix of the current traveling wave corresponding to any side based on the current traveling wave time-frequency matrix includes:

[0021] The time-frequency matrix S of the traveling current on the p(q) side of the line p(q) Perform singular value decomposition to obtain the left eigenma matrix U. p(q) And take the left feature matrix U p(q) The real part is used to obtain the left characteristic real matrix U of the current traveling wave corresponding to the p(q) side. real_p(q) ;

[0022] The left feature matrix is ​​obtained using the following methods:

[0023]

[0024] Among them, U p(q) V is the left characteristic matrix corresponding to the p(q) side of the line; p(q) The right characteristic matrix; Λ p(q) With Λ 1-p(q) It is a diagonal matrix whose diagonal elements are the time-frequency matrix S of the current traveling wave. p(q) The singular values;

[0025] Preferably, the step of calculating the similarity of the time-frequency matrices of the current traveling waves on both sides of the line based on the equivalent left characteristic real matrix of the current traveling waves on both sides includes:

[0026] Similarity can be calculated using the following methods:

[0027]

[0028] The following methods are used to determine faults inside and outside the line area based on the similarity:

[0029]

[0030] Where, α U For similarity; U real_p and U real_q These are the left characteristic real matrices of the current traveling waves on the p-side and q-side of the line, respectively; ρ set The second preset threshold is used; if the fault is determined to be within the zone, a trip signal is sent to the DC circuit breakers on both sides of the line; if the fault is determined to be outside the zone, the protection is reset.

[0031] According to another aspect of the present invention, a DC line protection system based on the time-frequency matrix similarity of current traveling waves is provided, the system comprising:

[0032] The line model current acquisition unit is used to calculate the line model current on either side of the line based on the positive and negative pole currents at the protection installation points on both sides of the DC line.

[0033] The protection activation judgment unit is used to determine whether the protection on both sides of the line is activated based on the line mode current.

[0034] The current traveling wave time-frequency matrix acquisition unit is used to determine the current traveling wave time-frequency matrix corresponding to any side of the line based on the line mode current within the preset sampling time period corresponding to any side when it is determined that the protection on both sides of the line is activated.

[0035] The current traveling wave left characteristic real matrix determination unit is used to calculate the current traveling wave left characteristic real matrix corresponding to any side based on the current traveling wave time-frequency matrix.

[0036] The fault identification unit inside and outside the line area calculates the left characteristic real matrix of the current traveling wave corresponding to any side based on the current traveling wave time-frequency matrix, and determines the fault inside and outside the line area based on the similarity.

[0037] Preferably, the line-mode current determining unit calculates the line-mode current corresponding to any side of the line in the following manner:

[0038]

[0039] Where I0 and I1 represent the zero-mode current and line-mode current, respectively, I p I n These represent the positive current and the negative current, respectively.

[0040] Preferably, the protection activation judgment unit determines whether the protection on either side of the line is activated using the following method:

[0041] For either side of the line, if the following conditions are met If the condition is not met, the protection will be activated; otherwise, the protection will not be activated. Here, I(k) is the sampled value of the line-mode current corresponding to either side of the line, and d... set This is the first preset threshold.

[0042] Preferably, the current traveling wave time-frequency matrix acquisition unit, for any side p(q) of the line, determines the current traveling wave time-frequency matrix corresponding to side p(q) based on the initial current traveling wave of the line mode within a preset sampling time period corresponding to side p(q), including:

[0043]

[0044]

[0045] Among them, S p(q)This is the two-dimensional traveling wave time-frequency matrix corresponding to the p(q) side of the line. This represents the initial current traveling wave signal of the p(q) side line mode. for The Fourier transform form; f→n / NT, τ→jT, T is the sampling interval, j,m=0,1,…,N-1; n=0,1,…,fix(N / 2), fix refers to taking the largest integer not exceeding N / 2; S p(q) The row vector represents the time-domain characteristics of the signal at a certain frequency, and the column vector represents the frequency-domain characteristics of the signal at a certain moment. The element S... p(q) (a,b) represents the value of the b-th sampling point at the a-th frequency corresponding to side p(q); where the frequency difference between two adjacent rows is: f s The sampling frequency is denoted by ; the frequency of the a-th row is:

[0046] Preferably, the current traveling wave left characteristic real matrix determination unit calculates the current traveling wave left characteristic real matrix corresponding to any side based on the current traveling wave time-frequency matrix, including:

[0047] The time-frequency matrix S of the traveling current on the p(q) side of the line p(q) Perform singular value decomposition to obtain the left eigenma matrix U. p(q) And take the left feature matrix U p(q) The real part is used to obtain the left characteristic real matrix U of the current traveling wave corresponding to the p(q) side. real_p(q) ;

[0048] The left feature matrix is ​​obtained using the following methods:

[0049]

[0050] Among them, U p(q) V is the left characteristic matrix corresponding to the p(q) side of the line; p(q) The right characteristic matrix; Λ p(q) With Λ 1-p(q) It is a diagonal matrix whose diagonal elements are the time-frequency matrix S of the current traveling wave. p(q) The singular values;

[0051] Preferably, the step of calculating the similarity of the time-frequency matrices of the current traveling waves on both sides of the line based on the equivalent left characteristic real matrix of the current traveling waves on both sides includes:

[0052] Similarity can be calculated using the following methods:

[0053]

[0054] The following methods are used to determine faults inside and outside the line area based on the similarity:

[0055]

[0056] Where, α U For similarity; U real_p and U real_q These are the left characteristic real matrices of the current traveling waves on the p-side and q-side of the line, respectively; ρ set The second preset threshold is used; if the fault is determined to be within the zone, a trip signal is sent to the DC circuit breakers on both sides of the line; if the fault is determined to be outside the zone, the protection is reset.

[0057] According to another aspect of the present invention, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any one of the DC line protection methods based on the similarity of the time-frequency matrix of current traveling waves.

[0058] According to another aspect of the present invention, the present invention provides an electronic device, comprising:

[0059] The aforementioned computer-readable storage medium; and one or more processors for executing the program in the computer-readable storage medium.

[0060] This invention provides a DC line protection method and system based on the similarity of current traveling wave time-frequency matrix, comprising: calculating the line-mode current corresponding to either side of the line based on the current at the protection installation points on both sides of the DC line; determining whether the protection on both sides of the line is activated based on the line-mode current; when it is determined that the protection on both sides of the line is activated, for either side of the line, determining the current traveling wave time-frequency matrix corresponding to that side based on the line-mode current within a preset sampling time period corresponding to that side; calculating the left characteristic real matrix of the current traveling wave corresponding to that side based on the current traveling wave time-frequency matrix; calculating the similarity of the current traveling wave time-frequency matrices on both sides of the line based on the equivalent left characteristic real matrix of the current traveling wave on both sides of the line, and determining the fault inside or outside the line area based on the similarity. This invention identifies faults inside and outside the protection zone based on the similarity of the initial current traveling waves on both sides of the line. It does not rely on line boundary components and is applicable to DC power grids without DC filters or with DC inductors installed at the converter station outlet. It can protect the entire line length and is applicable to DC power grids of different line lengths. At the same time, by utilizing the time-domain and frequency-domain characteristics of the initial current traveling waves, it can effectively avoid the defects caused by using only time-domain fault feature information, and has stronger resistance to transition resistance and noise immunity. The sampling time window is short, which can meet the speed requirements of the main protection of DC transmission lines. Attached Figure Description

[0061] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures:

[0062] Figure 1This is a flowchart of a DC line protection method 100 based on the time-frequency matrix similarity of current traveling waves according to an embodiment of the present invention;

[0063] Figure 2 This is a flowchart of the protection algorithm according to an embodiment of the present invention;

[0064] Figure 3 This is a topology diagram of a four-terminal bipolar flexible DC power grid according to an embodiment of the present invention;

[0065] Figure 4 This is a time-frequency characteristic diagram of the initial current traveling wave at both ends of the line under PGF at F1 according to an embodiment of the present invention;

[0066] Figure 5 This is a time-frequency characteristic diagram of the initial current traveling wave at both ends of the line under PPF at F3 according to an embodiment of the present invention;

[0067] Figure 6 This is a schematic diagram of the structure of a DC line protection system 600 based on the similarity of the time-frequency matrix of current traveling wave according to an embodiment of the present invention. Detailed Implementation

[0068] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0069] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0070] This invention is based on the analysis of the initial current traveling wave fault characteristics at both ends of a DC transmission line, and concludes that the frequency domain similarity of the initial current traveling waves at both ends of the line under faults within the fault zone is much higher than that under faults outside the fault zone. Therefore, within a specific time window after the fault occurs and before the subsequent reflected traveling waves reach the protection device, the similarity of the initial current traveling waves at both ends at different sampling times and frequencies can be comprehensively considered, and the faults inside and outside the fault zone can be identified based on the magnitude of this value.

[0071] Figure 1 This is a flowchart of a DC line protection method 100 based on the time-frequency matrix similarity of current traveling waves according to an embodiment of the present invention. Figure 1As shown, the DC line protection method based on the time-frequency matrix similarity of current traveling waves provided by the embodiments of the present invention identifies faults inside and outside the protection zone based on the similarity of the initial current traveling waves on both sides of the line. It does not rely on line boundary elements and is applicable to DC power grids without DC filters or where DC inductors are installed at the converter station outlet. It can protect the entire line length and is applicable to DC power grids of different line lengths. Simultaneously, by utilizing the time-domain and frequency-domain characteristics of the initial current traveling waves, it effectively avoids the defects caused by solely using time-domain fault characteristic information, exhibiting stronger resistance to transition resistance and noise immunity. The short sampling time window meets the speed requirements of the main protection of DC transmission lines. The DC line protection method 100 based on the time-frequency matrix similarity of current traveling waves provided by the embodiments of the present invention, starting from step 101, calculates the corresponding line-mode current on either side of the line based on the positive and negative currents at the protection installation points on both sides of the DC line.

[0072] Preferably, the method calculates the line-mode current corresponding to either side of the line in the following manner:

[0073]

[0074] Where I0 and I1 represent the zero-mode current and line-mode current, respectively, I p I n These represent the positive and negative currents, respectively. (Combined) Figure 2 As shown, in this invention, the positive and negative currents at the protection installation points at both ends of a DC line are measured, and the line-mode components of the current at both ends of the line are calculated based on the acquired currents. The calculation formula is:

[0075]

[0076] Where I0 and I1 represent the zero-mode current and line-mode current, respectively, I p I n These represent the positive current and the negative current, respectively.

[0077] Considering that linear mode components exist in various fault types and have a smaller attenuation and faster propagation speed, this invention is based on linear mode components.

[0078] In step 102, based on the line current, it is determined whether the protection on both sides of the line is activated.

[0079] Preferably, the method determines whether the protection on either side of the line is activated by means of:

[0080] For either side of the line, if the following conditions are met If the condition is not met, the protection will be activated; otherwise, the protection will not be activated. Here, I(k) is the sampled value of the line-mode current corresponding to either side of the line, and d... set This is the first preset threshold.

[0081] Combination Figure 2 As shown, in this invention, after obtaining the line mode current, the rate of change of the line mode current traveling wave at both ends of the line is calculated and the absolute value is taken. Based on the magnitude of this value, it is determined whether the protection at both ends is activated.

[0082] Among them, for either side of the line, if the following conditions are met... If the condition is not met, the protection will be activated; otherwise, the protection will not be activated. Here, I(k) is the sampled value of the line-mode current corresponding to either side of the line, and d... set This is the first preset threshold.

[0083] In step 103, when it is determined that the protection on both sides of the line is activated, for any side of the line, the time-frequency matrix of the current traveling wave corresponding to that side is determined based on the initial current traveling wave of the line mode within the preset sampling time period corresponding to that side.

[0084] Preferably, the step of determining the current traveling wave time-frequency matrix corresponding to the p(q) side based on the initial current traveling wave of the line mode within a preset sampling time period corresponding to the p(q) side includes:

[0085]

[0086]

[0087] Among them, S p(q) This is the two-dimensional traveling wave time-frequency matrix corresponding to the p(q) side of the line. This represents the initial current traveling wave signal of the p(q) side line mode. for The Fourier transform form; f→n / NT, τ→jT, T is the sampling interval, j,m=0,1,…,N-1; n=0,1,…,fix(N / 2), fix refers to taking the largest integer not exceeding N / 2; S p(q) The row vector represents the time-domain characteristics of the signal at a certain frequency, and the column vector represents the frequency-domain characteristics of the signal at a certain moment. The element S... p(q) (a,b) represents the value of the b-th sampling point at the a-th frequency corresponding to side p(q); where the frequency difference between two adjacent rows is: f s The sampling frequency is denoted by ; the frequency of the a-th row is:

[0088] Combination Figure 2 As shown, in this invention, within a relatively short sampling time window, the S-transform is performed on the initial line-mode current traveling waves at both ends of the line to obtain the time-frequency matrices S of the current traveling waves on the p-side and q-side of the line, respectively. p and S q .

[0089] The time-frequency matrix of the current traveling wave is obtained for either side using the following methods:

[0090]

[0091]

[0092] In step 104, the left characteristic real matrix of the current traveling wave corresponding to each side is calculated based on the current traveling wave time-frequency matrix.

[0093] Preferably, the step of calculating the left eigenvalue matrix of the current traveling wave corresponding to any side based on the current traveling wave time-frequency matrix includes:

[0094] For any side p(q), the time-frequency matrix S of the current traveling wave corresponding to that side p(q) Perform singular value decomposition to obtain the left eigenma matrix U. p(q) And take the left feature matrix U p(q) The real part is used to obtain the left characteristic real matrix U of the current traveling wave corresponding to the p(q) side. real_p(q) ;

[0095] The left feature matrix is ​​obtained using the following methods:

[0096]

[0097] Among them, U p(q) V is the left characteristic matrix corresponding to the p(q) side of the line; p(q) Λ is the right characteristic matrix corresponding to the p(q) side of the line; p(q) With Λ 1-p(q) It is a diagonal matrix whose diagonal elements are the time-frequency matrix S of the current traveling wave. p(q) The singular values ​​of .

[0098] In this invention, the S on both sides p S q Perform singular value decomposition to obtain the left characteristic matrix, and take its real part to obtain the left characteristic real matrix U of the current traveling wave on both sides. real_p and U real_q .

[0099] Among them, for matrix S p S q Perform singular value decomposition using the following formula:

[0100]

[0101] Among them, U p(q) V is the left characteristic matrix corresponding to the p(q) side of the line; p(q) Λ is the right characteristic matrix corresponding to the p(q) side of the line;p(q) With Λ 1-p(q) It is a diagonal matrix whose diagonal elements are the time-frequency matrix S of the current traveling wave. p(q) Singular values; with U p(q) As S p(q) The product of feature extraction, take U p(q) The real part of the current traveling wave is obtained by the left characteristic real matrix U. real_p(q) .

[0102] In step 105, the similarity between the time-frequency matrices of the current traveling waves on both sides of the line is calculated based on the equivalent real matrix of the left characteristic feature of the current traveling waves on both sides of the line, and the fault inside or outside the line area is determined based on the similarity.

[0103] Preferably, the step of calculating the similarity between the time-frequency matrices of the current traveling waves on both sides of the line based on the equivalent left characteristic real matrix of the current traveling waves on both sides of the line, and determining the fault within the line area based on the similarity, includes:

[0104] Similarity can be calculated using the following methods:

[0105]

[0106] The following methods are used to determine faults inside and outside the line area based on the similarity:

[0107]

[0108] Where, α U For similarity; U real_p and U real_q These are the left characteristic real matrices of the current traveling waves on the p-side and q-side of the line, respectively; ρ set The second preset threshold is used; if the fault is determined to be within the zone, a trip signal is sent to the DC circuit breakers on both sides of the line; if the fault is determined to be outside the zone, the protection is reset.

[0109] Combination Figure 2 As shown, in this invention, the left characteristic real matrix U of the current traveling wave on the p-side and q-side of the line is calculated. real_p U real_q Similarity α between U And according to α U The size of the fault determines whether it is inside or outside the line area.

[0110] in,

[0111] The criteria for identifying faults inside and outside the line area are:

[0112]

[0113] Where, α U For similarity; U real_pand U real_q These are the time-frequency matrices of the traveling current waves on the p-side and q-side of the line, respectively; ρ set The second preset threshold is used; if the fault is determined to be within the zone, a trip signal is sent to the DC circuit breakers on both sides of the line; if the fault is determined to be outside the zone, the protection is reset.

[0114] The method of the present invention has high reliability, fast response, no protection dead zone, can withstand higher transition resistance and noise, and is a DC transmission line main protection method that does not rely on boundary elements.

[0115] To verify the method of this invention, a system was built on PSCAD / EMTDC as follows: Figure 3 The model shown is a detailed representation of a ±500kV flexible DC power grid. The solid squares at both ends of the line represent protection devices R. ij With DC circuit breakers, each converter station outlet is equipped with a DC inductor L. i The DC line adopts an overhead line frequency-dependent distributed parameter model. The specific locations of typical fault points F1-F3 are: F1 and F2 are respectively located on Line... AB At distances of 3% and 50% from converter station A, F3 is on line line. BD The midpoint.

[0116] To accurately acquire the initial current traveling wave and ensure the fastness of the method, the sampling time window T is set to 0.2 ms. Considering the reliability of the principle and other factors in practical engineering, the sampling frequency is set to 100 kHz. Threshold d set Take 5kA / ms, ρ set Take 0.1.

[0117] Simulations of different fault locations and fault types:

[0118] A metallic positive ground fault (PGF), a bipolar fault (PPF), and a negative ground fault (NGF) are respectively set at points F1, F2, and F3, with a fault duration of 1.2s. To visually represent the time-frequency matrix of the initial current, this invention uses a time-frequency characteristic diagram to characterize the time-frequency matrix. Taking the PGF at F1 and the PGF at F3 as examples, R... AB With R BA The time-frequency characteristic diagrams of the initial current traveling wave are as follows: Figure 4 (a), (b) and Figure 5 As shown in (a) and (b). R under all the above faults AB With R BA Rate of change of traveling wave of line mode current at location |dI AB / dt|、|dI BA / dt| and α U The calculation results are shown in Table 1.

[0119] Simulation results show that the protection system can start quickly under different locations and types of faults, both inside and outside the fault zone. Under internal faults, the initial current traveling waves on both sides are highly similar, α... U The value is equal to or close to 1, indicating high sensitivity. Under external fault conditions, the waveforms of the initial current traveling waves on both sides of the DC line exhibit opposite characteristics and low similarity. α U The value is much smaller than the threshold, so the protection is reliable and does not activate. Therefore, this invention is not affected by the fault location or fault type, and can accurately identify faults inside and outside the zone within a 0.2ms sampling time window.

[0120] Table 1 Simulation results for different fault locations and fault types.

[0121]

[0122] Simulation of different transition resistances:

[0123] Transition resistors of 500Ω are set at points F1 and F2 within the zone and at point F3 outside the zone, respectively. AB / dt|、|dI BA / dt| and α U The values ​​are shown in Table 2.

[0124] Table 2 Simulation results for different transition resistances

[0125]

[0126] Simulation results show that the present invention has a high resistance to transition resistance and can accurately identify faults inside and outside the high resistance region.

[0127] Table 3 Simulation results for different line lengths

[0128]

[0129] Simulation of different line lengths:

[0130] Each Figure 3 The four DC lines in the simulation were set to 50km and 800km. Metallic PGF and PPF were installed at F1 and F2 within the zone and F3 outside the zone. The simulation results are shown in Table 3.

[0131] Simulation results show that when the line length is between 50km and 800km, the present invention can reliably identify faults inside and outside the area, and has a wide range of engineering applications.

[0132] Simulation under noise:

[0133] Gaussian white noise with a signal-to-noise ratio of 30dB was added to the simulation, and metallic PGF and PPF were set at F1, F2 and F3 respectively. The simulation results are shown in Table 4.

[0134] Table 4 Simulation results of 30dB white noise

[0135]

[0136]

[0137] Simulation results show that the present invention can still reliably identify faults inside and outside the region under 30dB white noise, demonstrating high robustness.

[0138] In summary, this invention offers high reliability and sensitivity, is independent of line boundary elements, can protect the entire length of lines of varying lengths, and can withstand high transition resistance and noise. Furthermore, its short sampling time window meets the speed requirements of DC power grid main protection.

[0139] Figure 6 This is a schematic diagram of the structure of a DC line protection system 600 based on the time-frequency matrix similarity of current traveling waves according to an embodiment of the present invention. Figure 6 As shown, the DC line protection system 600 based on the similarity of the time-frequency matrix of the current traveling wave provided by the present invention includes: a line model current acquisition unit 601, a protection start judgment unit 602, a current traveling wave time-frequency matrix acquisition unit 603, a current traveling wave left characteristic real matrix determination unit 604, and a line zone internal and external fault discrimination unit 605.

[0140] Preferably, the line model current acquisition unit 601 is used to calculate the line model current corresponding to any side of the line based on the current at the protection installation points on both sides of the DC line.

[0141] Preferably, the line mode current determining unit 601 calculates the line mode current corresponding to any side of the line in the following manner:

[0142]

[0143] Where I0 and I1 represent the zero-mode current and line-mode current, respectively, I p I n These represent the positive current and the negative current, respectively.

[0144] Preferably, the protection activation judgment unit 602 is used to determine whether the protection on both sides of the line is activated based on the line mode current.

[0145] Preferably, the protection activation judgment unit 602 determines whether the protection on either side of the line is activated using the following method:

[0146] For either side of the line, if the following conditions are met If the condition is not met, the protection will be activated; otherwise, the protection will not be activated. Here, I(k) is the sampled value of the line-mode current corresponding to either side of the line, and d... set This is the first preset threshold.

[0147] Preferably, the current traveling wave time-frequency matrix acquisition unit 603 is used to determine the two-dimensional time-frequency matrix corresponding to any side of the line based on the line mode current within a preset sampling time period corresponding to any side of the line when it is determined that the protection on both sides of the line is activated.

[0148] Preferably, the current traveling wave time-frequency matrix acquisition unit 603, for any side p(q) of the line, determines the current traveling wave time-frequency matrix corresponding to side p(q) based on the initial current traveling wave of the line mode within a preset sampling time period corresponding to side p(q), including:

[0149]

[0150]

[0151] Among them, S p(q) This is the two-dimensional traveling wave time-frequency matrix corresponding to the p(q) side of the line. This represents the initial current traveling wave signal of the p(q) side line mode. for The Fourier transform form; f→n / NT, τ→jT, T is the sampling interval, j,m=0,1,…,N-1; n=0,1,…,fix(N / 2), fix refers to taking the largest integer not exceeding N / 2; S p(q) The row vector represents the time-domain characteristics of the signal at a certain frequency, and the column vector represents the frequency-domain characteristics of the signal at a certain moment. The element S... p(q) (a,b) represents the value of the b-th sampling point at the a-th frequency corresponding to side p(q); where the frequency difference between two adjacent rows is: f s The sampling frequency is denoted by ; the frequency of the a-th row is:

[0152] Preferably, the current traveling wave left characteristic real matrix determination unit 604 is used to calculate the current traveling wave left characteristic real matrix corresponding to any side based on the current traveling wave time-frequency matrix.

[0153] Preferably, the current traveling wave left characteristic real matrix determination unit 604 calculates the current traveling wave left characteristic real matrix corresponding to any side based on the current traveling wave time-frequency matrix, including:

[0154] For any side p(q), the time-frequency matrix S of the current traveling wave corresponding to that side p(q) Perform singular value decomposition to obtain the left eigenma matrix U. p(q)And take the left feature matrix U p(q) The real part is used to obtain the left characteristic real matrix U of the current traveling wave corresponding to the p(q) side. real_p(q) ;

[0155] The left feature matrix is ​​obtained using the following methods:

[0156]

[0157] Among them, U p(q) V is the left characteristic matrix corresponding to the p(q) side of the line; p(q) Λ is the right characteristic matrix corresponding to the p(q) side of the line; p(q) With Λ 1-p(q) It is a diagonal matrix whose diagonal elements are the time-frequency matrix S of the current traveling wave. p(q) The singular values ​​of .

[0158] Preferably, the fault discrimination unit 605 inside and outside the line area calculates the similarity of the time-frequency matrix of the current traveling wave on both sides of the line based on the equivalent left characteristic real matrix of the current traveling wave on both sides of the line, and judges the fault inside and outside the line area based on the similarity.

[0159] Preferably, the fault discrimination unit 605 inside and outside the line area calculates the similarity of the time-frequency matrices of the current traveling waves on both sides of the line based on the equivalent left characteristic real matrix of the current traveling waves on both sides of the line, including:

[0160] Similarity can be calculated using the following methods:

[0161]

[0162] The following methods are used to determine faults inside and outside the line area based on the similarity:

[0163]

[0164] Where, α U For similarity; U real_p and U real_q These are the left characteristic real matrices of the current traveling waves on the p-side and q-side of the line, respectively; ρ set The second preset threshold is used; if the fault is determined to be within the zone, a trip signal is sent to the DC circuit breakers on both sides of the line; if the fault is determined to be outside the zone, the protection is reset.

[0165] The DC line protection system 600 based on the similarity of the time-frequency matrix of the current traveling wave in an embodiment of the present invention corresponds to the DC line protection method 100 based on the similarity of the time-frequency matrix of the current traveling wave in another embodiment of the present invention, and will not be described again here.

[0166] According to another aspect of the present invention, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of any one of the DC line protection methods based on the similarity of the time-frequency matrix of current traveling waves.

[0167] According to another aspect of the present invention, the present invention provides an electronic device, comprising:

[0168] The aforementioned computer-readable storage medium; and

[0169] One or more processors for executing a program in the computer-readable storage medium.

[0170] The invention has been described with reference to a few embodiments. However, as will be known to those skilled in the art, and as defined in the appended claims, other embodiments besides those disclosed above fall equivalently within the scope of the invention.

[0171] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the art, unless otherwise expressly defined herein. All references to “a / the / the [device, component, etc.]” ​​are openly interpreted as at least one instance of said device, component, etc., unless otherwise expressly stated. The steps of any method disclosed herein need not be performed in the exact order disclosed unless explicitly stated otherwise.

[0172] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0173] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0174] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0175] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0176] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A DC line protection method based on the time-frequency matrix similarity of current traveling waves, characterized in that, The method includes: Based on the positive and negative currents at the protection installation points on both sides of the DC line, calculate the corresponding line-mode current on either side of the line. Based on the line current, determine whether the protection on both sides of the line is activated; When it is determined that the protection on both sides of the line is activated, for any side of the line, the time-frequency matrix of the current traveling wave corresponding to that side is determined based on the initial current traveling wave of the line mode within the preset sampling time period corresponding to that side. Calculate the left characteristic real matrix of the current traveling wave corresponding to each side based on the current traveling wave time-frequency matrix; The similarity between the time-frequency matrices of the current traveling waves on both sides of the line is calculated by equivalent calculation of the left characteristic real matrix of the current traveling waves on both sides of the line, and the fault inside and outside the line area is determined based on the similarity. The method determines whether the protection on either side of the line is activated using the following means: For either side of the line, if the following conditions are met If the condition is met, then protection is activated; otherwise, protection is deactivated. I ( k ) represents the sampled value of the line-mode current corresponding to either side of the line. d set The first preset threshold; Specifically, for any side of the line, the time-frequency matrix of the current traveling wave corresponding to that side is determined based on the initial current traveling wave of the line mode within a preset sampling time period, including: ， in, S p(q) This is the two-dimensional current traveling wave time-frequency matrix corresponding to the p(q) side of the line. This represents the initial current traveling wave signal of the p(q) side line mode. for The Fourier transform form; , , T The sampling interval is... j , m =0,1,…, N -1; n =0,1,…,fix( N / 2), fix refers to no more than N The largest integer that is 2 / 2; S p(q) The row vector represents the time-domain characteristics of the signal at a certain frequency, and the column vector represents the frequency-domain characteristics of the signal at a certain moment. The elements... S p(q) ( a , b ) represents the first side corresponding to p(q). a The first frequency b The values ​​of each sampling point; where the frequency difference between two adjacent rows is: , f s The sampling frequency; the first a The frequency of the rows is: .

2. The method according to claim 1, characterized in that, The method calculates the line-mode current corresponding to either side of the line in the following manner: ， in, I 0 、I 1 These represent zero-mode current and line-mode current, respectively. I p 、I n These represent the positive current and the negative current, respectively.

3. The method according to claim 1, characterized in that, The step of calculating the left characteristic real matrix of the current traveling wave corresponding to each side based on the current traveling wave time-frequency matrix includes: The time-frequency matrix of the traveling current on the p(q) side of the line S p(q) Perform singular value decomposition to obtain the left eigenma matrix. U p(q) And take the left feature matrix U p(q) The real part is used to obtain the left characteristic real matrix of the current traveling wave corresponding to the p(q) side. U real_p(q) ; The left feature matrix is ​​obtained using the following methods: ， in, U p(q) Let be the left characteristic matrix corresponding to the p(q) side of the line; V p(q) The right-hand characteristic matrix; Λ p(q) and Λ 1-p(q) It is a diagonal matrix, whose diagonal elements are the time-frequency matrix of the current traveling wave. S p(q) The singular values ​​of .

4. The method according to claim 1, characterized in that, The step of calculating the similarity between the time-frequency matrices of the current traveling waves on both sides of the line based on the equivalent left characteristic real matrix of the current traveling waves on both sides of the line, and determining faults inside and outside the line area based on the similarity, includes: Similarity can be calculated using the following methods: ， The following methods are used to determine faults inside and outside the line area based on the similarity: in, α U Similarity; U real_p and U real_q These are the left characteristic real matrices of the current traveling wave corresponding to the p-side and q-side of the line, respectively; ρ set The second preset threshold is used; if the fault is determined to be within the zone, a trip signal is sent to the DC circuit breakers on both sides of the line; if the fault is determined to be outside the zone, the protection is reset.

5. A DC line protection system based on the time-frequency matrix similarity of current traveling waves, characterized in that, The system includes: The line model current acquisition unit is used to calculate the line model current on either side of the line based on the positive and negative pole currents at the protection installation points on both sides of the DC line. The protection activation judgment unit is used to determine whether the protection on both sides of the line is activated based on the line mode current. The current traveling wave time-frequency matrix acquisition unit is used to determine the current traveling wave time-frequency matrix corresponding to any side of the line based on the initial current traveling wave of the line mode within the preset sampling time period corresponding to any side of the line when it is determined that the protection on both sides of the line is activated. The current traveling wave left characteristic real matrix determination unit is used to calculate the current traveling wave left characteristic real matrix corresponding to any side based on the current traveling wave time-frequency matrix. The fault discrimination unit inside and outside the line area is used to calculate the similarity of the time-frequency matrix of the current traveling wave on both sides of the line based on the equivalent left characteristic real matrix of the current traveling wave on both sides of the line, and to discriminate faults inside and outside the line area based on the similarity. The protection activation judgment unit determines whether the protection on either side of the line is activated using the following method: For either side of the line, if the following conditions are met If the condition is met, then protection is activated; otherwise, protection is deactivated. I ( k ) represents the sampled value of the line-mode current corresponding to either side of the line. d set The first preset threshold; The current traveling wave time-frequency matrix acquisition unit, for any side p(q) of the line, determines the current traveling wave time-frequency matrix corresponding to side p(q) based on the initial current traveling wave of the line mode within a preset sampling time period corresponding to side p(q), including: ， in, S p(q) This is the two-dimensional current traveling wave time-frequency matrix corresponding to the p(q) side of the line. This represents the initial current traveling wave signal of the p(q) side line mode. for The Fourier transform form; , , T The sampling interval is... j , m =0,1,…, N -1; n =0,1,…,fix( N / 2), fix refers to no more than N The largest integer that is 2 / 2; S p(q) The row vector represents the time-domain characteristics of the signal at a certain frequency, and the column vector represents the frequency-domain characteristics of the signal at a certain moment. The elements... S p(q) ( a , b ) represents the first side corresponding to p(q). a The first frequency b The values ​​of each sampling point; where the frequency difference between two adjacent rows is: , f s The sampling frequency; the first a The frequency of the rows is: .

6. The system according to claim 5, characterized in that, The line-mode current determination unit calculates the line-mode current corresponding to any side of the line using the following method: ， in, I 0 、I 1 represents the zero-mode current and the line-mode current, respectively. I p 、I n These represent the positive current and the negative current, respectively.

7. The system according to claim 5, characterized in that, The current traveling wave left characteristic real matrix determination unit calculates the current traveling wave left characteristic real matrix corresponding to any side based on the current traveling wave time-frequency matrix, including: The time-frequency matrix of the traveling current on the p(q) side of the line S p(q) Perform singular value decomposition to obtain the left eigenma matrix. U p(q) And take the left feature matrix U p(q) The real part is used to obtain the left characteristic real matrix of the current traveling wave corresponding to the p(q) side. U real_p(q) ; The left feature matrix is ​​obtained using the following methods: ， in, U p(q) Let be the left characteristic matrix corresponding to the p(q) side of the line; V p(q) The right-hand characteristic matrix; Λ p(q) and Λ 1-p(q) It is a diagonal matrix, whose diagonal elements are the time-frequency matrix of the current traveling wave. S p(q) The singular values ​​of .

8. The system according to claim 5, characterized in that, The fault discrimination unit inside and outside the line area calculates the similarity of the time-frequency matrices of the current traveling waves on both sides of the line based on the equivalent left characteristic real matrix of the current traveling waves on both sides of the line, and determines the fault type based on the similarity, including: Similarity can be calculated using the following methods: The following methods are used to determine faults inside and outside the line area based on the similarity: in, α U Similarity; U real_p and U real_q These are the left characteristic real matrices of the current traveling wave corresponding to the p-side and q-side of the line, respectively; ρ set The second preset threshold is used; if the fault is determined to be within the zone, a trip signal is sent to the DC circuit breakers on both sides of the line; if the fault is determined to be outside the zone, the protection is reset.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps of the method as described in any one of claims 1-4.

10. An electronic device, characterized in that, include: The computer-readable storage medium as described in claim 9; and one or more processors for executing the program in the computer-readable storage medium.

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