CN112564057B

CN112564057B - Adaptive Reclosing Method of DC System Based on Main Frequency of Traveling Wave

Info

Publication number: CN112564057B
Application number: CN202010597438.8A
Authority: CN
Inventors: 李猛; 梁晨光; 张大海; 和敬涵; 许寅; 马为民; 韩柳; 冯腾; 肖智宏; 宫勋; 熊凌飞; 王晨清; 孔祥平; 吴聪颖; 刘文轩
Original assignee: Beijing Jiaotong University; State Grid Economic and Technological Research Institute; Electric Power Research Institute of State Grid Jiangsu Electric Power Co Ltd
Current assignee: Beijing Jiaotong University; State Grid Economic and Technological Research Institute; Electric Power Research Institute of State Grid Jiangsu Electric Power Co Ltd
Priority date: 2020-06-28
Filing date: 2020-06-28
Publication date: 2022-02-15
Anticipated expiration: 2040-06-28
Also published as: CN112564057A

Abstract

The invention provides an adaptive reclosing method for a DC system based on the dominant frequency of traveling waves. The method includes: sampling the positive and negative voltages and positive currents of the line after a fault occurs in the transmission line of the DC system, calculating the main frequency of the line-mode voltage traveling wave of the line by using the MUSIC algorithm, and judging whether the main frequency of the voltage traveling wave is not The main frequency equal to the natural characteristic frequency of the line, if so, determine the instantaneous fault of the line, and the hybrid circuit breaker recloses; otherwise, use the STFT algorithm to extract the voltage amplitude corresponding to the main frequency of the voltage traveling wave and the natural characteristic main frequency, and calculate Eigensignal amplitude ratio. The fault disappearance time is calibrated according to the change of the characteristic signal amplitude ratio, and the specific time of the hybrid circuit breaker reclosing is determined based on the fault disappearance time. By actively judging the nature of the fault, the invention avoids the blind reclosing of the DC circuit breaker on the fault, and realizes the self-adaptive reclosing of the DC circuit breaker.

Description

Traveling wave dominant frequency-based direct current system self-adaptive reclosing method

Technical Field

The invention relates to the technical field of power system protection and control, in particular to a direct current system self-adaptive reclosing method based on traveling wave main frequency.

Background

The high-voltage direct-current transmission is used as a main line for trans-regional energy transmission and has the characteristics of long power transmission corridor, wide coverage area, large transmission capacity and the like. Considering economic factors, the direct current transmission mostly takes an overhead line as a channel for electric energy transmission. The overhead transmission line is exposed to the air, has severe working conditions, is an element with the highest fault probability in a direct current system, and mainly has transient faults. The research on the recovery scheme after the direct-current line fault is particularly important for guaranteeing the safety of equipment, improving the power supply reliability and maintaining the stability of the whole system.

When a line has a fault, a VSC-HVDC (voltage source converted based high voltage direct current) transmission system based on a voltage source converter has a converter outlet connected with a large capacitor in parallel and discharges to a fault point; even if the converter is locked, an alternating current system and a fault point can still form a loop through a freewheeling diode, and the fault cannot be cleared through a control system like a line communated converter based high voltage direct current (LCC-HVDC) system based on a grid commutation converter. Therefore, the flexible direct current system is additionally provided with the direct current circuit breakers at two ends of the line, the isolation of a fault line is realized, and the reliability of the operation of the system is improved.

The fault restarting strategy of the flexible direct current power transmission system based on the overhead line is as follows: converter lockout-circuit breaker trip- (fault nature identification I) -deionization- (fault nature identification II) -restart. The key of success or failure of system recovery is the identification of fault properties, and if the fault is an instantaneous fault, the circuit breaker is controlled to be switched on to establish system voltage; if the fault is a permanent fault, the converter is locked, and line maintenance is carried out. The concept of "adaptive reclosing" was proposed in the 80's of the 20 th century, with the main objective of avoiding reclosing under permanent faults. The relevant scholars further study deeply and clearly understand that the adaptive reclosing should also be able to capture the arc quenching time under transient faults to ensure the reclosing success in the voltage recovery phase. Currently, adaptive reclosure is generally applied to an alternating current power grid, but research on the technology in the field of direct current systems is just started.

At present, the fault recovery research methods of the flexible dc system in the prior art can be summarized into four categories: fault property identification schemes based on alternating current circuit breakers, based on converters, based on direct current circuit breakers, and based on characteristic electrical quantities.

The fault recovery scheme based on the alternating current circuit breaker mainly utilizes the matching of the alternating current circuit breaker and the direct current switch to realize fault isolation and recovery, the strategy can finish the isolation of a fault area without depending on communication, but the whole direct current system can be quitted from operation in a fault clearing stage, and the reclosing speed is slow.

The converter-based reclosing strategy may also be referred to as a restart strategy. The strategy mainly utilizes a converter topology with fault clearing capability, after the fault is isolated, the converter is operated in a specific mode, and the fault property is judged according to related electric quantities such as direct current voltage, direct current, bridge arm current and the like. However, the fault recovery scheme is limited by the structure of the converter, and when the fault recovery scheme is used for a multi-terminal direct-current power grid, the converter valve is locked to cause the whole direct-current system to exit, so that the power failure range is expanded.

Compared with the first two methods, the method has the advantages that fault lines can be selectively removed based on the fault clearing and system recovery strategies of the direct current circuit breakers, the power failure range after the fault is reduced to the maximum extent, the integral shutdown of the direct current system is avoided, single direct current line coincidence is achieved, however, the scheme needs to detect whether voltage is established to judge whether the fault disappears or not through multiple coincidence of the circuit breakers after the dissociation removing time is over, the pre-recognition of the fault property is lacked, and the coincidence strategy has certain blindness.

Disclosure of Invention

The embodiment of the invention provides a direct current system self-adaptive reclosing method based on traveling wave main frequency, which aims to overcome the problems in the prior art.

In order to achieve the purpose, the invention adopts the following technical scheme.

A direct current system self-adaptive reclosing method based on traveling wave main frequency comprises the following steps:

step 1, after a direct current system transmission line breaks down, continuously sampling positive and negative voltages and positive currents of the line, and calculating line mode voltage traveling waves of the line;

step 2, calculating the main frequency of the line mode voltage traveling wave by using the MUSIC algorithm, judging whether the main frequency of the line mode voltage traveling wave is equal to the main frequency of the inherent characteristic frequency of the line, if so, determining the instantaneous fault of the line, wherein the fault is at the midpoint of the line, the hybrid breaker of the line is reclosed, and the process is ended; otherwise, executing step 3;

and step 3: using short-time Fourier transform (STFT) algorithm to carry out linear mode voltage traveling wavePerforming time-frequency transformation, and extracting voltage amplitude U (f) corresponding to main frequency of the traveling wave of the line mode voltage and voltage amplitude U (f) corresponding to main frequency of the inherent characteristic frequency_L) According to said U (f) and U (f)_L) Calculating the amplitude ratio of the characteristic signals:

and 4, calibrating the fault disappearance moment according to the change of the characteristic signal amplitude ratio, and determining the specific reclosing moment of the hybrid circuit breaker based on the fault disappearance moment.

Preferably, after the power transmission line of the dc system fails in step 1, continuously sampling the positive and negative voltages and the positive current of the line, and calculating the line mode voltage traveling wave of the line, includes:

at length L of DC system transmission line t₁After the time is failed, the positive and negative voltages U of the line are applied according to a set time interval_1p、U_1nAnd positive electrode current I_1pContinuously sampling, and calculating the line mode voltage traveling wave U of the line by using a phase-mode conversion formula₁；

Preferably, the line mode voltage traveling wave U is calculated by utilizing the MUSIC algorithm₁Comprises:

after the mixed circuit breakers at two sides of the line are tripped, the positive current I is continuously detected according to a set time interval_1pApplying a positive electrode current I_1pThe time at which the current decays to 0.01 times the rated current is denoted as t₃Intercepting line mode voltage traveling wave U in data window length₁Data, the length of the data window is t-4L/v, v is the traveling wave propagation speed, and U in the length of the data window is calculated by utilizing the MUSIC algorithm₁Power spectrum of data, maximum amplitude U in said data window₁The minimum frequency corresponding to the wave crest is called as the line mode voltage traveling wave U₁The main frequency f of (1).

Preferably, the step 3 of performing time-frequency transformation on the line-mode voltage traveling wave by using a short-time fourier transform (STFT) algorithm to extract the line-mode voltageVoltage amplitude U (f) corresponding to the main frequency of the traveling wave and voltage amplitude U (f) corresponding to the main frequency of the natural characteristic frequency_L) According to said U (f) and U (f)_L) And calculating a characteristic signal amplitude ratio, including:

using STFT algorithm to measure U in data window length₁Performing time-frequency transformation on the data to calculate U₁Extracting the U of the line mode voltage traveling wave₁The main frequency f of the natural characteristic frequency is extracted from the voltage amplitude U (f) corresponding to the main frequency f_LCorresponding voltage amplitude U (f)_L)；

Defining the amplitude ratio of the characteristic signals as K:

preferably, the calibrating the fault disappearance time according to the change of the characteristic signal amplitude ratio in step 4, and determining the specific reclosing time of the hybrid circuit breaker based on the fault disappearance time includes:

at time t₃Then, the anode current U is continuously monitored according to a set time interval_1pAnd calculating the line mode voltage traveling wave U₁The main frequency f and the characteristic signal amplitude ratio K;

judging the condition anode current U_1pLess than 0.01 times of rated voltage, K<1, if yes, determining a permanent fault of the line, locking the hybrid circuit breaker, cutting off the fault line, and ending the process; otherwise, carrying out subsequent processing;

the judgment condition is t₄Time of day t₄>t₃，K>1, and if so, determining that the line has a transient fault, the fault being at a point in the line, t₄The moment is the disappearance moment of the fault, at t₄And the hybrid breaker is reclosed at any moment.

According to the technical scheme provided by the embodiment of the invention, the direct-current circuit breaker is prevented from being blindly superposed on the fault by actively judging the fault property, the self-adaptive reclosing is realized, the reclosing success rate of the direct-current circuit breaker is improved, the closing reliability of the direct-current circuit breaker is improved, and the technical defect of blindly superposing of the direct-current circuit breaker in the prior art is overcome.

Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

Fig. 1 is a processing flow chart of a direct current system adaptive reclosing method based on traveling wave dominant frequency according to an embodiment of the present invention;

fig. 2 is a schematic diagram of a ± 200kV double-ended pseudo bipolar direct-current transmission system based on an MMC according to an embodiment of the present invention;

FIG. 3 is a schematic diagram showing the calculation results of the present invention applied to different faults, wherein FIG. 3(a) corresponds to the calculation result of the permanent fault of example 1, and FIG. 3(b) corresponds to the calculation result of the transient fault of example 2;

FIG. 4 is a diagram illustrating a calculation result of a dead zone detected at a midpoint of a line according to the present invention.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.

As used herein, the singular forms "a", "an", "the" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may also be present. Further, "connected" or "coupled" as used herein may include wirelessly connected or coupled. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

For the convenience of understanding the embodiments of the present invention, the following description will be further explained by taking several specific embodiments as examples in conjunction with the drawings, and the embodiments are not to be construed as limiting the embodiments of the present invention.

The invention provides a method for judging the bipolar short-circuit fault property of the flexible direct-current transmission line actively based on the discharge process of the line to the ground unit capacitor after the fault, aiming at the research requirement of the fault recovery of the flexible direct-current transmission system, and the self-adaptive reclosing is realized by calculating the amplitude ratio of the voltage traveling wave characteristic frequency signal and calibrating the fault disappearance moment.

The invention provides a direct current system self-adaptive reclosing method based on traveling wave main frequency. The main frequency change characteristic of the residual voltage traveling wave of the line after the insulation of the arrester is recovered is calculated, the characteristic frequency voltage signal amplitude ratio K is calculated, the fault disappearance moment is calibrated based on the change of the K value, and the circuit breaker is controlled to be reclosed.

For a DC line of length LWhen the circuit breaker breaks down, the circuit breakers on the two sides of the circuit trip, and the residual voltage traveling wave along the line is reflected between the circuit breakers on the two sides of the circuit and a fault point. Wherein, the breaker is equivalent to an open circuit, and the reflection coefficient of the traveling wave is + 1; and the fault point is short-circuited, and the traveling wave reflection coefficient is approximate to-1. Meter T_L2L/v is the time length of the traveling wave going back and forth on the line; f. of_Lv/2L is the main frequency of the inherent characteristic frequency corresponding to the line, v is the traveling wave propagation speed, and v is 3 × 10⁸m/s。

The processing flow of the direct current system adaptive reclosing method based on the traveling wave main frequency provided by the embodiment of the invention is shown in fig. 1, and the method specifically comprises the following steps:

step 1: line t of length L₁After the fault happens at any moment, the positive and negative voltages U of the line are applied_1p、U_1nAnd positive electrode current I_1pContinuously sampling, and calculating line mode voltage traveling wave U by using a phase mode conversion formula shown in the specification₁。

Step 2: after the mixed circuit breakers positioned at two sides of the line are tripped, the tripping time of the mixed circuit breaker is recorded as t₂. Continuously detecting the anode current I_1pApplying a positive electrode current I_1pThe time at which the current decays to 0.01 times the rated current is denoted as t₃. Thereafter, the U in the time window is intercepted₁And the length of the time window is t-4L/v.

Calculating U in time window by MUSIC (Multiple Signal Classification) algorithm₁Power spectrum of data, U within data window₁The frequency corresponding to the peak with the maximum amplitude is the minimum, and the minimum frequency is called as the line mode voltage traveling wave U₁Is denoted as f, f is also called as fault feature main frequency f. After the line is in fault, the maximum value of the fault voltage traveling wave propagation period is 4L/v, and the maximum value can be used as a time window for FFT calculation.

And step 3: judging line mode voltage traveling wave U₁Whether the main frequency of (A) is equal to the inherent characteristics of the lineDominant frequency f of the eigenfrequency_LIf so, determining the instantaneous fault of the line, enabling the fault to be at the middle point of the line, reclosing the hybrid circuit breaker, and ending the process; otherwise, step 4 is executed.

And 4, step 4: applying STFT (Short Time Fourier Transform) algorithm to U in Time window₁Carrying out time-frequency transformation on the data, and extracting the traveling wave U of the outgoing line mode voltage₁The voltage amplitude corresponding to the main frequency f is marked as U (f), and f is also extracted_LCorresponding voltage amplitude, denoted as U (f)_L) Defining a characteristic signal amplitude ratio K:

the STFT is one of common tools for analyzing signal time-frequency characteristics, has the characteristics of simple calculation and frequency scale linearity, and is an effective algorithm for extracting a specific frequency spectrum. The basic principle is that a section of long signal is divided into a limited number of short signal sections according to the length of a window, and fft (fast Fourier transform) is performed on each divided short signal section, so that the frequency components of each short signal section at different moments can be obtained. Thereafter. And arranging the obtained spectrogram of each short signal segment along a time axis, so as to obtain the time-varying relation of different frequency components of the original signal. The STFT can conveniently construct the change relation of each frequency signal contained in the signal along with time, and the fault characteristic frequency f and the line characteristic frequency f are already obtained_LUnder the condition (2), only the corresponding frequencies f and f are required to be marked in the time-frequency diagram obtained by STFT_LThe signal amplitudes of (d) are U (f) and U (f)_L)。

When the window of the STFT takes a larger value, a very high frequency resolution and a relatively low time resolution can be obtained, but considering that the self-adaptive reclosing strategy has no high requirement on time precision, the problem can be solved through proper time delay.

Taking into account the line mode voltage travelling wave U₁Contains a plurality of frequency components, the frequency spectrum is very complex, and the algorithm is more pursuing the frequency resolution capability, so the Hanning window (Han) is selectedning) as a moving window at the time of STFT calculation, the window length was set to 2000.

And 5: time t₃Then, the anode current U is continuously monitored according to a set time interval_1pAnd calculating the line mode voltage traveling wave U₁And judging the fault property according to the change rule of K by the main frequency f and the characteristic signal amplitude ratio K.

Judging the condition anode current U_1pLess than 0.01 times of rated voltage, K<1, if yes, determining a permanent fault of the line, locking the hybrid circuit breaker, cutting off the fault line, and ending the process; otherwise, step 6 is executed.

Step 6: at t₄Time (t)₄>t₃)，K>1: then a line transient fault is determined, the fault being at a line midpoint, t₄The moment is the disappearance moment of the fault, at t₄And the hybrid breaker is reclosed at any moment.

Fig. 2 is a schematic diagram of a ± 200kV double-ended pseudo bipolar direct-current transmission system based on an MMC according to an embodiment of the present invention, where various parameters of the system are shown in table 1. Suppose the system is at t₁When the time is 0s, a bipolar short-circuit fault occurs, and the direct current breaker is at t₂Put into the arrester 3ms later. Wherein, the total length L of the line is 300kM, and the wave speed v of the travelling wave is 3 multiplied by 10⁸m/s, main frequency f of line natural characteristic frequency_Lv/2L 500 Hz; in addition, the arc resistance R of the fault branch is simulated by utilizing the Thomson arc model shown in the formula (1)_arcWherein u is_aIs the arc voltage; i.e. i_fIs the arc current; i is_s＝10^-18A is ionization current induced by external ionization (light, heat); c. C₁，c₂Is constant at 0.1MPa, c₁≈2.86×10⁶K·cm,c₂≈7.47×10⁴K·kV·cm。R_f20 Ω is the transition resistance of the fault branch; sampling frequency f ₀50 kHZ; STFT time frequency analysis selects Hanning window with window length of 2000.

TABLE 1 System simulation parameters

Example 1: distance to failure L_f60kM, permanent fault (no arc)

Step 1) failure at t₁After 0ms, the positive and negative voltages U_1p、U_1nAnd current I_1pContinuously sampling, and calculating line-mode voltage traveling wave U by using phase-mode conversion₁。

Step 2) lightning arrester at t₂3ms, positive electrode current I_1PAt t₃When the time is 6.2ms, the current is reduced to 0.01 times of rated current; with t₃Intercepting data with the duration of t being 4L/v being 4ms for starting time, and calculating to obtain U by using MUSIC₁The main frequency (frequency minimum) f is 1233 Hz.

Step 3) utilizing STFT to pair U₁Performing time-frequency analysis, and extracting voltage amplitude signals U (f) corresponding to the fault characteristic main frequency f and the line characteristic main frequency f_LCorresponding voltage amplitude signal U (f)_L) And calculating the voltage signal amplitude ratio K.

Example 2: distance to failure L_f60kM, permanent fault (no arc)

Example 2: distance to failure L_f60kM, the nature of the fault is a transient fault (with arc)

Step 2) lightning arrester at t₂3ms, positive electrode current I_1PAt t₃When the time is 6.2ms, the current is reduced to 0.01 times of rated current; with t₃Intercepting data with the duration of t being 4L/v being 4ms for starting time, and calculating to obtain U by using MUSIC₁The main frequency (frequency minimum) f of (c) 1074 Hz.

Step 3) utilizing STFT to pair U₁Performing time-frequencyAnalyzing and extracting voltage amplitude signals U (f) corresponding to the fault characteristic main frequency f and the line characteristic main frequency f_LCorresponding voltage amplitude signal U (f)_L) And calculating the voltage signal amplitude ratio K.

Fig. 3 shows the calculation results of the above-mentioned example, fig. 3(a) corresponds to the calculation result of the permanent fault of example 1, and fig. 3(b) corresponds to the calculation result of the transient fault of example 2.

As shown in FIG. 3(a), the upper portion of FIG. 3(a) is the DC line current I_1pAnd fault branch current I_fComparing the waveforms; the middle part of fig. 3(a) is a voltage U (f) corresponding to a fault main frequency of 1233Hz and a voltage U (f) of a line characteristic main frequency of 500Hz_L) Comparing the waveforms; the lower part of FIG. 3(a) is U (f) and U (f)_L) Is measured.

The calculation result shows that K is at t₃And then, the voltage is always less than 1, so that the detection criterion of permanent faults is met, the circuit breaker is locked, and a fault line is cut off.

As shown in FIG. 3(b), the upper portion of FIG. 3(b) is the DC line current I_1pAnd fault branch current I_fComparing the waveforms; the middle part of fig. 3(b) is the voltage U (f) corresponding to the fault main frequency 1074Hz and the voltage U (f) of the line characteristic main frequency 500Hz_L) Comparing the waveforms; the lower part of FIG. 3(b) is U (f) and U (f)_L) Is measured. Wherein, t₄Representing the actual arc current I resulting from the simulation_fDisappearance time, t₄' denotes the calculated arc current extinction time. Theoretically, t₄＝t₄', but considering that STFT itself has a problem of insufficient time resolution, t₄And t₄There is some error between.

The calculation result shows that K is at t₃Less than 1 after 6.2ms, but at t₄' thereafter, K>1, the detection criterion of the transient fault is met, and the circuit breaker is reclosed.

Further analysis, when the fault occurs at the line midpoint (L)_f150 kM/2), the characteristic frequency f is v/4L due to a fault_fv/2L equals the natural characteristic frequency f of the line_LAt this time, U (f) is U (f)_L) CalculatingThe resulting voltage amplitude ratio K is 1. Therefore, the midpoint of the line is the detection blind zone of the invention.

Example 3: distance to failure L_fCompare permanent faults with transient faults at 150kM (line midpoint).

Step 2) lightning arrester at t₂3ms, positive electrode current I_1PAt t₃When the time is 6.7ms, the current is reduced to 0.01 times of rated current; with t₃Intercepting data with the duration of t being 4L/v being 4ms for starting time, and calculating to obtain U by using MUSIC₁The main frequencies (frequency minimum) of (f) 508Hz (permanent fault) and (f) 521Hz (transient fault).

FIG. 4 is a diagram illustrating a calculation result of a dead zone detected at a midpoint of a line according to the present invention. The calculation result shows that K is at t₃Constantly equal to 1 after 6.7ms, it is difficult to distinguish the nature of the fault, but considering that the probability of the fault occurring exactly at the point in the line is low, it is treated as a transient fault.

In conclusion, the invention avoids the direct current breaker from being blindly superposed on the fault by actively judging the fault property, realizes self-adaptive reclosing, improves the success rate of the reclosing of the direct current breaker, improves the reliability of the closing of the direct current breaker and overcomes the technical defect of the blindly superposing of the direct current breaker in the prior art.

The method of the embodiment of the invention has simple and reliable principle, can accurately identify the bipolar short circuit fault property only by collecting the line voltage and the current magnitude after the fault, and has high identification degree and small detection blind area.

Those of ordinary skill in the art will understand that: the figures are merely schematic representations of one embodiment, and the blocks or flow diagrams in the figures are not necessarily required to practice the present invention.

The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, for apparatus or system embodiments, since they are substantially similar to method embodiments, they are described in relative terms, as long as they are described in partial descriptions of method embodiments. The above-described embodiments of the apparatus and system are merely illustrative, and the units described as separate parts may or may not be physically separate, and the parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. a direct current system adaptive reclosing method based on traveling wave dominant frequency, is characterized in that, comprises:

Step 1. After the DC system transmission line fails, continuously sample the positive and negative voltages and positive current of the line, and calculate the line-mode voltage traveling wave of the line;

Step 2. Use the MUSIC algorithm to calculate the main frequency of the line-mode voltage traveling wave, and judge whether the main frequency of the line-mode voltage traveling wave is equal to the main frequency of the natural characteristic frequency of the line. point, the hybrid circuit breaker of the line is reclosed, and the process ends; otherwise, go to step 3;

Step 3: Use the short-time Fourier transform (STFT) algorithm to perform time-frequency transformation on the line-mode voltage traveling wave, and extract the voltage amplitude U(f) corresponding to the main frequency of the line-mode voltage traveling wave and the main frequency of the natural characteristic frequency. For the corresponding voltage amplitude U(f _L ), the characteristic signal amplitude ratio is calculated according to the U(f) and U(f _L ):

Step 4, calibrating the time of fault disappearance according to the change of the characteristic signal amplitude ratio, and determining the specific time of the hybrid circuit breaker reclosing based on the time of fault disappearance, including:

After time _t3 , the positive voltage U _1p is continuously monitored according to the set time interval, and the main frequency f of the line-mode voltage traveling wave U ₁ and the characteristic signal amplitude ratio K are calculated; where t ₃ is when the positive current I _1p decays to The moment of 0.01 times the rated current;

When the positive voltage U _1p of the judgment condition is less than 0.01 times the rated voltage, whether K<1 is established, if so, it is determined that the line is permanently faulty, the hybrid circuit breaker is blocked, the faulty line is cut off, and the process ends; otherwise, follow-up processing is performed;

Judgment condition is at time t ₄ , t ₄ >t ₃ , K>1 is established, if so, determine the line instantaneous fault, the fault is at the midpoint of the line, time t ₄ is the time when the fault disappears, and the hybrid circuit breaker at time t ₄ Reclosing.

2 . The method according to claim 1 , wherein in the step 1, after the DC system transmission line fails, the positive and negative voltages and the positive current of the line are continuously sampled, and the line mode of the line is calculated. 3 . Voltage traveling waves, including:

After the fault occurs at the time t ₁ of the DC transmission line of length L, the positive and negative voltages U _1p , U _1n and the positive current I _1p of the line are continuously sampled according to the set time interval, and the phase-mode transformation formula is used to calculate the line's line mode voltage traveling wave U ₁ ;

3. method according to claim 2, is characterized in that, described utilizing MUSIC algorithm to calculate the main frequency of line-mode voltage traveling wave U ₁ , comprising:

After the hybrid circuit breaker on both sides of the line trips, the positive current I _1p is continuously detected according to the set time interval, and the time when the positive current I _1p is attenuated to 0.01 times the rated current is recorded as t ₃ , and the line mode within the data window length is intercepted. Voltage traveling wave U1 data, the length _of the data window is t=4L/v, v is the traveling wave propagation speed, use the MUSIC algorithm to calculate the power spectrum _of the U1 data within the data window length, and the amplitude value in the data window The frequency corresponding to the largest U ₁ peak is the smallest, which is called the main frequency f of the line-mode voltage traveling wave U ₁ .

4 . The method according to claim 3 , wherein in the step 3, the short-time Fourier transform (STFT) algorithm is used to perform time-frequency transformation on the line-mode voltage traveling wave, and the line-mode voltage traveling wave is extracted. 5 . The voltage amplitude U(f) corresponding to the main frequency and the voltage amplitude U(f _L ) corresponding to the main frequency of the natural characteristic frequency, the characteristic signal amplitude ratio is calculated according to the U(f) and U(f _L ), include:

Use the STFT algorithm to perform time _- frequency transformation on the U1 data within the data window length, calculate the power spectrum of U1, extract the voltage amplitude U( _f ) corresponding to the main frequency f of U1 _of the line-mode voltage traveling wave, and extract the inherent The voltage amplitude U(f _L ) corresponding to the main frequency f _L of the characteristic frequency;

Define the characteristic signal amplitude ratio as K: