CN112147460B - Hybrid direct current transmission line protection method, system and storage medium thereof - Google Patents
Hybrid direct current transmission line protection method, system and storage medium thereof Download PDFInfo
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Abstract
The invention discloses a method, a system and a storage medium for protecting a hybrid direct current transmission line, and aims to solve the technical problems of insufficient accuracy and sensitivity of line protection in the prior art. It comprises the following steps: after protection is started, calculating fault components of line mode voltages at two ends of the line according to voltages at two ends of the direct current transmission line; calculating the high-frequency and low-frequency energy ratio of line mode voltages at two ends of a line according to the synchronous compression wavelet coefficient; and judging the fault occurrence area of the direct current transmission line according to the high-frequency and low-frequency energy ratio. The invention can improve the reliability and the sensitivity of the line protection of the series-parallel direct current transmission system.
Description
Technical Field
The invention relates to a hybrid direct-current transmission line protection method, a system and a storage medium thereof, belonging to the technical field of power transmission and distribution.
Background
In order to integrate the advantages of a grid commutated converter type high voltage direct current transmission system (Line Commuted Converter based High Voltage Direct Current, LCC-HVDC) based on thyristor technology and a flexible direct current transmission system (Voltage Source Converter based High Voltage Direct Current, VSC-HVDC) based on voltage source type converters, a hybrid direct current transmission system becomes an important development direction of the transmission system. One implementation of the hybrid dc power transmission system is: LCC is adopted at the transmitting end, and the receiving end adopts LCC and a plurality of Voltage Source Converters (VSC) in series-parallel connection to carry out direct current transmission; the hybrid direct current transmission system provides a more flexible and rapid transmission mode, improves the voltage stability of the alternating current system at the inversion side, reduces the probability of commutation failure, and can give consideration to economic and technical benefits. The relay protection level of the hybrid direct current transmission system, particularly a circuit, has great influence on the operation stability and the safety of the power system, so that the research on the rapid protection technology of the hybrid direct current transmission system has important theoretical significance and practical application value.
The conventional direct current transmission line protection is generally divided into a main protection and a backup protection, wherein the main protection is configured with traveling wave protection and differential under-voltage protection, and the backup protection is longitudinal current differential protection. An important condition for the implementation of the traveling wave protection scheme is the extraction and analysis of fault transient information. The fault transient signal is a nonlinear and non-stationary transient signal with abrupt change property, and the tools such as wavelet transformation, S transformation, hilbert yellow transformation and the like with time-frequency analysis are suitable for analyzing and processing the fault transient signal, wherein the wavelet transformation has the advantages of a plurality of mathematical analysis methods, the time-frequency resolution capability is better, and the fault transient signal is widely applied.
However, the existing traveling wave protection of the direct current transmission line still has the following defects: 1) As single-side electrical quantity protection, the protection range of the existing traveling wave protection cannot protect the whole length of a line, and the protection is difficult to detect high-resistance ground faults on the line; 2) The existing travelling wave signal is extracted mainly by adopting a wavelet transformation method, but transient wave surges of each fault, which are determined by the fault position and the length of a transmission line, are not mutually independent, even have aliasing, and can influence the accuracy of extracting frequency components; 3) The primary structure of the hybrid direct current transmission system is greatly different from that of the conventional direct current transmission system, and the conventional direct current line protection method is difficult to be suitable for the hybrid direct current transmission line.
Disclosure of Invention
Aiming at the problems of the prior art in the protection of the hybrid direct current transmission line, the invention provides a method, a system and a storage medium for the protection of the hybrid direct current transmission line, which are characterized in that synchronous compression wavelet transformation is utilized to extract high-frequency energy and low-frequency energy in voltage fault components, the ratio of the high-frequency energy to the low-frequency energy in the voltage fault components at two ends of the line is calculated respectively, the ratio of the high-frequency energy to the low-frequency energy is compared with a threshold value, whether the direct current transmission line has faults or not is identified, a fault area is identified, and corresponding protection actions are carried out.
In order to solve the technical problems, the invention adopts the following technical means:
In a first aspect, the invention provides a hybrid direct current transmission line protection method based on synchronous voltage-reduction wave conversion, which is characterized by comprising the following steps:
Step A, calculating fault components of line mode voltages at two ends of a line according to voltages at two ends of a direct current transmission line;
Step B, calculating synchronous compression wavelet coefficients according to fault components of line mode voltages;
Step C, calculating the high-frequency and low-frequency energy ratio of the line mode voltages at two ends of the line according to the synchronous compression wavelet coefficient;
And D, judging a fault occurrence area of the direct current transmission line according to the high-frequency and low-frequency energy ratio.
With reference to the first aspect, further, the step a specifically includes the following steps:
Step A01, acquiring positive and negative voltage signals at two ends of a direct current transmission line in real time, and calculating fault components of the positive and negative voltages at two ends of the line after protection starting;
step A02, adopting a phase-mode transformation technology to decouple the two mutually coupled polar lines into mutually independent single-phase systems, and calculating fault components of line-mode voltages, wherein the specific calculation formula is as follows:
Wherein, deltau l1 (t) represents a line mode voltage fault component of the head end of the direct current transmission line at the moment t, deltau l2 (t) represents a line mode voltage fault component of the tail end of the direct current transmission line at the moment t, deltau p1 (t) represents a fault component of the positive voltage of the head end of the line at the moment t, deltau q1 (t) represents a fault component of the negative voltage of the head end of the line at the moment t, deltau p2 (t) represents a fault component of the positive voltage of the tail end of the line at the moment t, deltau q2 (t) represents a fault component of the negative voltage of the tail end of the line at the moment t.
With reference to the first aspect, further, a calculation formula of the synchronous compression wavelet coefficient in the step B is as follows:
Wherein T s (ω, b) represents a synchronous compression wavelet coefficient corresponding to a fault component of the line mode voltage, Δω is a frequency interval, a k represents a kth scale factor, ω x (a, b) represents an instantaneous frequency corresponding to a fault component of the line mode voltage, ω represents a center frequency of the line mode voltage, W x (a, b) represents a wavelet coefficient corresponding to a fault component of the line mode voltage, (Δa) k represents a difference between the kth scale factor and the kth-1 scale factor, (Δa) k＝ak-ak-1, k is a positive integer.
With reference to the first aspect, further, step B specifically includes the following steps:
Step B01, respectively selecting n center frequencies of high frequency bands of line mode voltage at the head end of the line And n center frequencies of the low frequency band/>Wherein j=1 … n;
step B02, calculating synchronous compression wavelet coefficients of line mode voltage fault components delta u l1 (t) at the head end of the line for the center frequency of the high frequency band: Calculating synchronous compression wavelet coefficients of line mode voltage fault components delta u l1 (t) at the head end of a line for the center frequency of a low frequency band: /(I)
Step B03, respectively selecting n center frequencies of the high frequency band of the line mode voltage at the end of the lineAnd n center frequencies of the low frequency band/>
Step B04, calculating synchronous compression wavelet coefficients of line mode voltage fault components delta u l2 (t) at the tail end of the line for the center frequency of the high frequency band: Calculating synchronous compression wavelet coefficients of line end line mode voltage fault components delta u l2 (t) for low-frequency band center frequencies: /(I)
With reference to the first aspect, further, step C specifically includes the following steps:
And C01, calculating high-frequency energy and low-frequency energy according to synchronous compression wavelet coefficients of line mode voltages at the head end of the line, wherein the specific formulas are as follows:
wherein E 1h represents the high-frequency energy of the line mode voltage at the head end of the line, Represents the j-th center frequency of the high frequency band/>E 1l represents low-frequency energy of line mode voltage at the head end of the line,/>Represents the j-th center frequency of the low frequency band/>Is used for synchronously compressing wavelet coefficients;
Step C02, calculating the ratio R 1 of high-frequency energy and low-frequency energy of the line mode voltage at the head end of the line:
R1＝E1h/E1l (6)
and C03, calculating high-frequency energy and low-frequency energy according to synchronous compression wavelet coefficients of line mode voltages at the tail end of the line, wherein the specific formulas are as follows:
wherein E 2h represents the high-frequency energy of the line mode voltage at the end of the line, Represents the j-th center frequency of the high frequency band/>E 2l represents the low frequency energy of the line mode voltage at the end of the line,/>Represents the j-th center frequency of the low frequency band/>Is used for synchronously compressing wavelet coefficients;
step C04, calculating the ratio R 2 of high-frequency energy to low-frequency energy of the line mode voltage at the end of the line:
R2＝E2h/E2l (9)
With reference to the first aspect, further, the specific operation of step D is as follows:
Setting two thresholds R setH and R setL, wherein R setH＞RsetL;
Comparing R 1 and R 2 with threshold values R setH and R setL respectively, and judging a fault occurrence area of the direct current transmission line according to a criterion, wherein the criterion is as follows:
a first criterion: if R 1＞RsetH or R 2＞RsetH, judging that the fault occurs in the line area and performing line protection action;
A second criterion: if R setH≥R1＞RsetL and R setH≥R2＞RsetL, judging that the fault occurs in the line area and performing line protection action;
Third criterion: if R 1 and R 2 do not meet the first criterion or the second criterion, the fault is judged to occur outside the line area, and the line protection is not operated.
In a second aspect, the present invention provides a hybrid dc transmission line protection device based on synchronous voltage-to-wavelet transform, the device comprising:
The fault component calculation module is used for calculating fault components of line mode voltages at two ends of the line according to voltages at two ends of the direct current transmission line;
The synchronous compression wavelet transformation module is used for calculating synchronous compression wavelet coefficients according to fault components of the line mode voltage;
The energy ratio calculation module is used for calculating the high-frequency and low-frequency energy ratio of the line mode voltages at two ends of the line according to the synchronous compression wavelet coefficient;
and the fault region judging module is used for judging the fault occurrence region of the direct current transmission line according to the high-frequency and low-frequency energy ratio.
In a third aspect, the invention provides a hybrid direct current transmission line protection device based on synchronous voltage-reduction wave conversion, which comprises a processor and a storage medium;
The storage medium is used for storing instructions;
the processor is configured to operate in accordance with the instructions to perform the steps of the method of the first aspect.
In a fourth aspect, the invention proposes a computer-readable storage medium, on which a computer program is stored, which program, when being executed by a processor, carries out the steps of the method according to the first aspect.
The following advantages can be obtained by adopting the technical means:
The invention provides a method, a system and a storage medium for protecting a hybrid direct current transmission line, wherein the method and the system use measurement information at two ends of the line in the hybrid direct current transmission system, compared with single-side electric quantity protection, the method and the system can improve the reliability of the line protection of the hybrid direct current transmission system, and simultaneously, the method and the system also adopt synchronous compression wavelet transformation to extract high-frequency energy and low-frequency energy of signals more accurately, so as to improve the sensitivity of the protection. When judging whether faults occur and the fault occurrence area, the criterion provided by the invention fully utilizes the single-end quantity and the double-end quantity, can effectively solve the problems faced by the existing direct current line protection, and ensures the accuracy of judgment.
Drawings
Fig. 1 is a schematic structural diagram of a hybrid dc power transmission system according to an embodiment of the present invention.
Fig. 2 is a flow chart of steps of a hybrid direct current transmission line protection method based on synchronous voltage-ripple conversion.
Fig. 3 is a flowchart of a hybrid direct current transmission line protection method based on synchronous voltage-ripple conversion according to the present invention.
Fig. 4 is a schematic structural diagram of a hybrid dc transmission line protection device based on synchronous voltage-to-wavelet transform according to the present invention.
In the figure, 1 is a smoothing reactor, 2 is a direct current filter, 3 is a direct current transmission line, 4 is a direct current protection system, 501 is a fault component calculation module, 502 is a synchronous voltage-reduction wave conversion module, 503 is an energy ratio calculation module, and 504 is a fault region discrimination module.
Detailed Description
The technical scheme of the invention is further described below with reference to the accompanying drawings:
Fig. 1 is a schematic structural diagram of a hybrid dc power transmission system according to an embodiment of the present invention, where a power grid commutated converter (LCC) type conventional dc converter station is adopted at a transmitting end of the power transmission system, a power grid commutated converter (LCC) type conventional dc converter station is adopted at a receiving end of the power transmission system, a multi-Voltage Source Converter (VSC) type flexible dc converter station is adopted at a receiving end of the power transmission system, and after the multi-Voltage Source Converter (VSC) type flexible dc converter station is connected in parallel, the multi-Voltage Source Converter (VSC) type flexible dc converter station is connected in series with the conventional dc (LCC) converter station. In the figure, 1 is a smoothing reactor, 2 is a direct current filter, 3 is a direct current transmission line, and 4 is a direct current protection system.
Aiming at the power transmission system in fig. 1, the invention provides a hybrid direct current power transmission line protection method based on synchronous compression wavelet transformation, which specifically comprises the following steps as shown in fig. 2 and 3:
Step A, calculating fault components of line mode voltages at two ends of a line according to voltages at two ends of a direct current transmission line, wherein the specific operation is as follows:
And A01, acquiring positive and negative voltage signals at two ends of the direct current transmission line in real time, and calculating fault components of the positive and negative voltages at two ends of the line after protection starting, namely calculating the difference value between the positive and negative voltages at two ends of the line at the current moment t and the positive and negative voltages at two ends of the line at the steady moment.
Step A02, adopting a phase-mode transformation technology to decouple the two mutually coupled polar lines into mutually independent single-phase systems, and calculating fault components of line-mode voltages, wherein the specific calculation formula is as follows:
Wherein, deltau l1 (t) represents a line mode voltage fault component of the head end of the direct current transmission line at the moment t, deltau l2 (t) represents a line mode voltage fault component of the tail end of the direct current transmission line at the moment t, deltau p1 (t) represents a fault component of the positive voltage of the head end of the line at the moment t, deltau q1 (t) represents a fault component of the negative voltage of the head end of the line at the moment t, deltau p2 (t) represents a fault component of the positive voltage of the tail end of the line at the moment t, deltau q2 (t) represents a fault component of the negative voltage of the tail end of the line at the moment t.
And B, calculating the synchronous compression wavelet coefficient according to the fault component of the line mode voltage.
The derivation process of the synchronous compression wavelet coefficients is as follows:
1) Performing continuous wavelet transformation on fault components of the line mode voltage by using a given mother wavelet function phi to obtain wavelet coefficients:
Wherein W x (a, b) represents a wavelet coefficient corresponding to a fault component of the line mode voltage, a is a scale factor, b is a translation factor, x (t) represents a fault component of the line mode voltage, i.e., x (t) = { Δu l1(t),Δul2 (t) }, t is time, Representation of the wavelet functionConjugation.
2) Calculating instantaneous frequency according to wavelet coefficient:
Wherein omega x (a, b) represents the instantaneous frequency corresponding to the fault component of the line mode voltage, i is an imaginary unit, First order bias for b for W x (a, b).
3) Determining a frequency interval delta omega, selecting a central frequency omega of line mode voltage, compressing wavelet coefficients in a time-frequency plane into a neighborhood of the central frequency omega, wherein the neighborhood is
4) Considering that a computer discretizes a scale factor a in the process of calculating a synchronous compression coefficient, (delta a) k＝ak-ak-1 is set, wherein (delta a) k represents the difference between a kth scale factor and a kth-1 scale factor, a k represents the kth scale factor, a k-1 represents the kth-1 scale factor, and a classical value method of a k is a k＝2k, and k is a positive integer.
The calculation formula of the synchronous compression wavelet coefficient is as follows:
Where T s (ω, b) represents the synchronous compression wavelet coefficient corresponding to the fault component of the line mode voltage.
The synchronous compression can compress the diffusion area of the wavelet transformation coefficient in the frequency/scale direction to an omega-domain, can improve the time-frequency aggregation of the analysis result, and is suitable for accurately extracting the energy of different frequency bands of fault signals.
The step B specifically comprises the following steps:
Step B01, respectively selecting n center frequencies of high frequency bands of line mode voltage at the head end of the line And n center frequencies of the low frequency band/>Where j=1 … n,/>The j-th center frequency of the high frequency band representing the line mode voltage at the line head end,/>The j-th center frequency of the low frequency band representing the line mode voltage at the line head end.
Step B02, calculating synchronous compression wavelet coefficients of line mode voltage fault components delta u l1 (t) at the head end of the line for the center frequency of the high frequency band according to formulas (12) - (14): wherein/> The j-th center frequency of the high-frequency band representing the line mode voltage at the head end of the line/>Is used for synchronously compressing wavelet coefficients; and (3) calculating synchronous compression wavelet coefficients of line head end line mode voltage fault components delta u l1 (t) for low-frequency band center frequencies according to formulas (12) - (14): wherein/> J-th center frequency of low frequency band representing line mode voltage at line head end/>Is used for the synchronous compression wavelet coefficients.
Step B03, respectively selecting n center frequencies of the high frequency band of the line mode voltage at the end of the lineAnd n center frequencies of the low frequency band/>Wherein/>The j-th center frequency of the high-frequency band representing the line-end line mode voltage,/>The j-th center frequency of the low band representing the line end line mode voltage.
Step B04, calculating synchronous compression wavelet coefficients of line end line mode voltage fault components delta u l2 (t) for the center frequency of the high-frequency band according to formulas (12) - (14): wherein/> The j-th center frequency of the high-frequency band representing the line mode voltage at the end of the line/>Is used for synchronously compressing wavelet coefficients; and (3) calculating synchronous compression wavelet coefficients of line end line mode voltage fault components delta u l2 (t) for low-frequency band center frequencies according to formulas (12) - (14): /(I)Wherein/>The j-th center frequency of the low frequency band representing the line mode voltage at the end of the line/>Is used for the synchronous compression wavelet coefficients.
Step C, calculating the high-frequency and low-frequency energy ratio of the line mode voltages at two ends of the line according to the synchronous compression wavelet coefficient; the specific operation is as follows:
And C01, calculating high-frequency energy and low-frequency energy according to synchronous compression wavelet coefficients of line mode voltages at the head end of the line, wherein the specific formulas are as follows:
wherein E 1h represents the high-frequency energy of the line mode voltage at the head end of the line, Represents the j-th center frequency of the high frequency band/>E 1l represents low-frequency energy of line mode voltage at the head end of the line,/>Represents the j-th center frequency of the low frequency band/>Is used for synchronously compressing wavelet coefficients;
Step C02, calculating the ratio R 1 of high-frequency energy and low-frequency energy of the line mode voltage at the head end of the line:
R1＝E1h/E1l (17)
and C03, calculating high-frequency energy and low-frequency energy according to synchronous compression wavelet coefficients of line mode voltages at the tail end of the line, wherein the specific formulas are as follows:
wherein E 2h represents the high-frequency energy of the line mode voltage at the end of the line, Represents the j-th center frequency of the high frequency band/>E 2l represents the low frequency energy of the line mode voltage at the end of the line,/>Represents the j-th center frequency of the low frequency band/>Is used for synchronously compressing wavelet coefficients;
step C04, calculating the ratio R 2 of high-frequency energy to low-frequency energy of the line mode voltage at the end of the line:
R2＝E2h/E2l (20)
step D, judging a fault occurrence area of the direct current transmission line according to the high-frequency and low-frequency energy ratio; the specific operation is as follows:
Considering that a fault occurs in a region, possibly at any position on a dc line, and that the line may have a certain attenuation effect on the high frequency, two thresholds R setH and R setL are set, where R setH＞RsetL.
And respectively comparing R 1 and R 2 with threshold values R setH and R setL, and judging the fault occurrence area of the direct current transmission line according to the criterion.
Taking the hybrid direct current transmission system in the embodiment of the invention as an example, when a fault occurs outside a direct current circuit area, a filter at the head end and a smoothing reactor at the tail end of the direct current circuit can generate an obvious attenuation effect on a high-frequency component in a voltage fault component, and the ratio of the high-frequency energy to the low-frequency energy at the head end and the tail end of the circuit is generally small; when a fault occurs in the direct current line area, the high-frequency component in the fault component does not pass through the filter and the smoothing reactor, the attenuation is smaller, and the ratio of the high-frequency energy to the low-frequency energy at the head end and the tail end of the corresponding line is generally larger.
The criteria in the present invention based on the above analysis are specifically as follows:
a first criterion: if R 1＞RsetH or R 2＞RsetH, judging that the fault occurs in the line area and performing line protection action;
A second criterion: if R setH≥R1＞RsetL and R setH≥R2＞RsetL, judging that the fault occurs in the line area and performing line protection action;
Third criterion: if R 1 and R 2 do not meet the first criterion or the second criterion, the fault is judged to occur outside the line area, and the line protection is not operated.
The invention also provides a mixed direct current transmission line protection device based on synchronous voltage-to-wavelet transform, as shown in fig. 4, comprising a fault component calculation module 501, a synchronous voltage-to-wavelet transform module 502, an energy ratio calculation module 503 and a fault area discrimination module 504, wherein the fault component calculation module is used for calculating fault components of line mode voltages at two ends of a line according to voltages at two ends of the direct current transmission line after protection is started; the synchronous compression wavelet transformation module is used for calculating synchronous compression wavelet coefficients according to fault components of line mode voltages, and specifically comprises the following steps: processing fault components of line mode voltage by utilizing continuous wavelet transformation, calculating wavelet coefficients and instantaneous frequency, and compressing the wavelet coefficients in a time-frequency plane to one field of central frequency to obtain synchronous compression wavelet coefficients; the energy ratio calculation module is used for calculating the high-frequency and low-frequency energy ratio of the line mode voltages at two ends of the line according to the synchronous compression wavelet coefficient; the fault region judging module is used for judging the fault occurrence region of the direct current transmission line according to the high-frequency and low-frequency energy ratio.
The invention also provides a mixed direct current transmission line protection device based on synchronous compression wavelet transformation, which comprises a processor and a storage medium; the storage medium is used for storing instructions; the processor is used for operating according to the instruction to execute the steps of the hybrid direct current transmission line protection method based on synchronous compression wavelet transformation.
The invention also provides a computer readable storage medium, on which a computer program is stored, which when being executed by a processor implements the steps of the hybrid direct current transmission line protection method based on synchronous voltage-to-wavelet transform of the invention.
Compared with the prior art, the invention has the following advantages: 1. the invention can improve the reliability of the line protection of the hybrid direct current transmission system relative to the single-side electrical quantity protection by using the measurement information of the two ends of the line in the hybrid direct current transmission system; 2. synchronous compression wavelet transformation is adopted to more accurately extract high-frequency energy and low-frequency energy of signals, so that the sensitivity of protection is improved; 3. when judging whether faults occur and the fault occurrence area, the criterion provided by the invention fully utilizes the single-end quantity and the double-end quantity, can effectively solve the problems faced by the existing direct current line protection, and ensures the accuracy of judgment.
It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may 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, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may 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, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that modifications and variations could be made by those skilled in the art without departing from the technical principles of the present invention, and such modifications and variations should also be regarded as being within the scope of the invention.
Claims (7)
1. The hybrid direct current transmission line protection method based on synchronous voltage-ripple conversion is characterized by comprising the following steps of:
Step A, calculating fault components of line mode voltages at two ends of a line according to voltages at two ends of a direct current transmission line;
Step B, calculating synchronous compression wavelet coefficients according to fault components of line mode voltages;
Step C, calculating the high-frequency and low-frequency energy ratio of the line mode voltages at two ends of the line according to the synchronous compression wavelet coefficient;
Step D, judging a fault occurrence area of the direct current transmission line according to the high-frequency and low-frequency energy ratio;
The step A specifically comprises the following steps:
Step A01, acquiring positive and negative voltage signals at two ends of a direct current transmission line in real time, and calculating fault components of the positive and negative voltages at two ends of the line after protection starting;
step A02, adopting a phase-mode transformation technology to decouple the two mutually coupled polar lines into mutually independent single-phase systems, and calculating fault components of line-mode voltages, wherein the specific calculation formula is as follows:
Wherein Deltau l1 (t) represents a line mode voltage fault component of the head end of the direct current transmission line at the moment t, deltau l2 (t) represents a line mode voltage fault component of the tail end of the direct current transmission line at the moment t, deltau p1 (t) represents a fault component of the positive voltage of the head end of the line at the moment t, deltau q1 (t) represents a fault component of the negative voltage of the head end of the line at the moment t, deltau p2 (t) represents a fault component of the positive voltage of the tail end of the line at the moment t, deltau q2 (t) represents a fault component of the negative voltage of the tail end of the line at the moment t;
The step C specifically comprises the following steps:
And C01, calculating high-frequency energy and low-frequency energy according to synchronous compression wavelet coefficients of line mode voltages at the head end of the line, wherein the specific formulas are as follows:
wherein E 1h represents the high-frequency energy of the line mode voltage at the head end of the line, Represents the jth center frequency of the high frequency bandE 1l represents low-frequency energy of line mode voltage at the head end of the line,/>Represents the j-th center frequency of the low frequency band/>N is the total number of center frequencies, b represents the translation factor of the fault component of the line mode voltage;
Step C02, calculating the ratio R 1 of high-frequency energy and low-frequency energy of the line mode voltage at the head end of the line:
R1＝E1h/E1l
and C03, calculating high-frequency energy and low-frequency energy according to synchronous compression wavelet coefficients of line mode voltages at the tail end of the line, wherein the specific formulas are as follows:
wherein E 2h represents the high-frequency energy of the line mode voltage at the end of the line, Represents the jth center frequency of the high frequency bandE 2l represents the low frequency energy of the line mode voltage at the end of the line,/>Represents the j-th center frequency of the low frequency band/>Is used for synchronously compressing wavelet coefficients;
step C04, calculating the ratio R 2 of high-frequency energy to low-frequency energy of the line mode voltage at the end of the line:
R2＝E2h/E2l。
2. The method for protecting a hybrid direct current transmission line based on synchronous compression wavelet transform according to claim 1, wherein the calculation formula of the synchronous compression wavelet coefficient in the step B is as follows:
Wherein T s (ω, b) represents a synchronous compression wavelet coefficient corresponding to a fault component of the line mode voltage, Δω is a frequency interval, a k represents a kth scale factor, ω x (a, b) represents an instantaneous frequency corresponding to a fault component of the line mode voltage, ω represents a center frequency of the line mode voltage, W x (a, b) represents a wavelet coefficient corresponding to a fault component of the line mode voltage, (Δa) k represents a difference between the kth scale factor and the kth-1 scale factor, (Δa) k＝ak-ak-1, k is a positive integer.
3. The method for protecting a hybrid direct current transmission line based on synchronous voltage-ripple conversion according to claim 2, wherein the step B specifically comprises the steps of:
Step B01, respectively selecting n center frequencies of high frequency bands of line mode voltage at the head end of the line And n center frequencies of the low frequency band/>Wherein j=1 … n;
step B02, calculating synchronous compression wavelet coefficients of line mode voltage fault components delta u l1 (t) at the head end of the line for the center frequency of the high frequency band: Calculating synchronous compression wavelet coefficients of line mode voltage fault components delta u l1 (t) at the head end of a line for the center frequency of a low frequency band: /(I)
Step B03, respectively selecting n center frequencies of the high frequency band of the line mode voltage at the end of the lineAnd n center frequencies of the low frequency band/>
Step B04, calculating synchronous compression wavelet coefficients of line mode voltage fault components delta u l2 (t) at the tail end of the line for the center frequency of the high frequency band: Calculating synchronous compression wavelet coefficients of line end line mode voltage fault components delta u l2 (t) for low-frequency band center frequencies: /(I)
4. The method for protecting a hybrid direct current transmission line based on synchronous voltage-ripple conversion according to claim 3, wherein the specific operation in the step D is as follows:
Setting two thresholds R setH and R setL, wherein R setH＞RsetL;
Comparing R 1 and R 2 with threshold values R setH and R setL respectively, and judging a fault occurrence area of the direct current transmission line according to a criterion, wherein the criterion is as follows:
a first criterion: if R 1＞RsetH or R 2＞RsetH, judging that the fault occurs in the line area and performing line protection action;
A second criterion: if R setH≥R1＞RsetL and R setH≥R2＞RsetL, judging that the fault occurs in the line area and performing line protection action;
Third criterion: if R 1 and R 2 do not meet the first criterion or the second criterion, the fault is judged to occur outside the line area, and the line protection is not operated.
5. A hybrid direct current transmission line protection device based on synchronous voltage-to-wavelet transformation, the device comprising:
The fault component calculation module is used for calculating fault components of line mode voltages at two ends of the line according to voltages at two ends of the direct current transmission line;
The synchronous compression wavelet transformation module is used for calculating synchronous compression wavelet coefficients according to fault components of the line mode voltage;
The energy ratio calculation module is used for calculating the high-frequency and low-frequency energy ratio of the line mode voltages at two ends of the line according to the synchronous compression wavelet coefficient;
The fault area judging module is used for judging a fault occurrence area of the direct current transmission line according to the high-frequency and low-frequency energy ratio;
wherein the fault component calculation module is configured to:
acquiring positive and negative voltage signals at two ends of a direct current transmission line in real time, and calculating fault components of the positive and negative voltages at two ends of the line after protection starting;
the phase-mode conversion technology is adopted to decouple the two mutually coupled polar lines into a mutually independent single-phase system, and the fault component of the line mode voltage is calculated according to the following specific calculation formula:
Wherein Deltau l1 (t) represents a line mode voltage fault component of the head end of the direct current transmission line at the moment t, deltau l2 (t) represents a line mode voltage fault component of the tail end of the direct current transmission line at the moment t, deltau p1 (t) represents a fault component of the positive voltage of the head end of the line at the moment t, deltau q1 (t) represents a fault component of the negative voltage of the head end of the line at the moment t, deltau p2 (t) represents a fault component of the positive voltage of the tail end of the line at the moment t, deltau q2 (t) represents a fault component of the negative voltage of the tail end of the line at the moment t;
The energy ratio calculation module is configured to:
According to the synchronous compression wavelet coefficient of the line mode voltage at the head end of the line, the high-frequency energy and the low-frequency energy are calculated, and the specific formulas are as follows:
wherein E 1h represents the high-frequency energy of the line mode voltage at the head end of the line, Represents the j-th center frequency of the high frequency band/>E 1l represents low-frequency energy of line mode voltage at the head end of the line,/>Represents the j-th center frequency of the low frequency band/>N is the total number of center frequencies, b represents the translation factor of the fault component of the line mode voltage;
calculating the ratio R 1 of high-frequency energy and low-frequency energy of the line mode voltage at the head end of the line:
R1＝E1h/E1l
The high-frequency energy and the low-frequency energy of the synchronous compression wavelet coefficient are calculated according to the line mode voltage at the end of the line, and the specific formulas are as follows:
wherein E 2h represents the high-frequency energy of the line mode voltage at the end of the line, Represents the jth center frequency of the high frequency bandE 2l represents the low frequency energy of the line mode voltage at the end of the line,/>Represents the j-th center frequency of the low frequency band/>Is used for synchronously compressing wavelet coefficients;
Calculating the ratio R 2 of high-frequency energy to low-frequency energy of the line mode voltage at the end of the line:
R2＝E2h/E2l。
6. The mixed direct current transmission line protection device based on synchronous compression wavelet transformation is characterized by comprising a processor and a storage medium;
The storage medium is used for storing instructions;
The processor being operative according to the instructions to perform the steps of the method according to any one of claims 1 to 4.
7. Computer readable storage medium, on which a computer program is stored, characterized in that the program, when being executed by a processor, implements the steps of the method according to any one of claims 1-4.
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