CN110988602A - S-transformation-based traveling wave protection method for hybrid direct current transmission line - Google Patents
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
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Abstract
The invention discloses a mixed direct current transmission line traveling wave protection method based on S transformation, which comprises the following steps: respectively acquiring voltage traveling wave data and current traveling wave data of power transmission lines at two ends, and respectively acquiring 1-mode voltage traveling wave data and 1-mode current traveling wave data of each end based on the voltage traveling wave data and the current traveling wave data; s transformation is carried out on the 1-mode voltage traveling wave data and the 1-mode current traveling wave data of each end, and an S transformation matrix corresponding to each end is obtained; acquiring an amplitude-frequency traveling wave matrix corresponding to each end according to the S transformation matrix of each end, and calculating amplitude-frequency traveling wave energy corresponding to each end according to the amplitude-frequency traveling wave matrix of each end; identifying the fault direction of each end according to the amplitude-frequency traveling wave energy of each end; identifying fault types according to fault directions at two ends; and executing corresponding protection according to the identified fault type. The invention can improve the reliability of the traveling wave protection of the hybrid direct current transmission line.
Description
Technical Field
The invention belongs to the technical field of electric power, particularly relates to a protection method of an electric power system, and more particularly relates to a traveling wave protection method of a hybrid direct current transmission line based on S conversion.
Background
A high-voltage direct-current transmission system LCC-HVDC (line communtated converter based HVDC) based on a line current commutation principle has long transmission distance, large transmission capacity and high transmission efficiency. However, the LCC-HVDC inverter station is prone to phase commutation failure, which in turn leads to transmission reliability problems. The flexible high-voltage direct-current transmission system MMC-HVDC (modular multilevel converter based HVDC) based on the modular multilevel principle has no commutation failure risk and can realize certain power flow control. However, the MMC-HVDC system has smaller transmission capacity and higher construction cost. Therefore, the LCC-MMC-HVDC hybrid direct-current power transmission system adopting the LCC-HVDC principle on the rectification side and the MMC-HVDC principle on the inversion side can simultaneously have the advantages of a traditional high-voltage direct-current power transmission system and a flexible direct-current power transmission system, and is widely applied.
At present, the traditional traveling wave protection method based on voltage variation, voltage variation rate and current variation rate is still adopted for main protection of the LCC-MMC-HVDC hybrid direct current transmission line. The traditional traveling wave protection method is used as a single-terminal quantity protection method, has no direction identification capability, cannot distinguish an internal fault from an external fault, has poor fault identification reliability, is easy to generate protection misoperation, and particularly has the risk of misoperation when the external fault occurs. Therefore, it is necessary to develop a new traveling wave direction protection method.
Disclosure of Invention
The invention provides a mixed direct current transmission line traveling wave protection method based on S transformation, aiming at solving the problems of poor reliability and easy misoperation of an LCC-MMC-HVDC mixed direct current transmission line traveling wave protection method in the prior art, and improving the reliability of the mixed direct current transmission line traveling wave protection.
In order to realize the purpose of the invention, the invention is realized by adopting the following technical scheme:
a traveling wave protection method of a hybrid direct current transmission line based on S transformation comprises the following steps:
respectively acquiring voltage traveling wave data and current traveling wave data on a power transmission line of an LCC-HVDC end positioned on a rectification side and an MMC-HVDC end positioned on an inversion side, and respectively acquiring 1-mode voltage traveling wave data and 1-mode current traveling wave data of the LCC-HVDC end and the MMC-HVDC end based on the voltage traveling wave data and the current traveling wave data;
s conversion is carried out on the 1-mode voltage traveling wave data and the 1-mode voltage traveling wave data of the LCC-HVDC end and the MMC-HVDC end, and an S conversion matrix corresponding to each end is obtained;
acquiring an amplitude-frequency traveling wave matrix corresponding to each end according to the S transformation matrix of each end, and calculating amplitude-frequency traveling wave energy corresponding to each end according to the amplitude-frequency traveling wave matrix of each end;
respectively identifying the fault direction of an LCC-HVDC end and the fault direction of an MMC-HVDC end according to the amplitude-frequency traveling wave energy and the fault direction criterion of each end;
identifying the fault type according to the fault direction of the LCC-HVDC end and the fault direction of the MMC-HVDC end;
and executing corresponding protection according to the identified fault type.
The method described above obtains the amplitude-frequency traveling wave matrix corresponding to each end according to the S transformation matrix of each end, and calculates the amplitude-frequency traveling wave energy corresponding to each end according to the amplitude-frequency traveling wave matrix of each end, and specifically includes:
obtaining an amplitude-frequency traveling wave matrix P corresponding to each end according to the following formula:
and calculating the amplitude-frequency traveling wave energy E corresponding to each end according to the following formula:
k is a sampling point serial number when the 1-mode voltage traveling wave data and the 1-mode current traveling wave data are acquired; t is sampling step length; j is a variable used for iterative calculation, j is 1,2, …, and N is a known frequency discrimination degree in S transformation; f. ofsIs a reference frequency, the value of which is equal to 1/NT; suAnd SiRespectively an S transformation matrix of the 1-mode voltage traveling wave and an S transformation matrix of the 1-mode current traveling wave at the end; a. themAnd AnAre respectively provided withThe amplitude and the phase angle of the amplitude-frequency traveling wave matrix P are obtained; abs is a modulus function, and angle is a phase angle function; f. ofminAnd fmaxKnown minimum and maximum frequency values, respectively; w is the data window length.
According to the method, the fault direction of the LCC-HVDC end and the fault direction of the MMC-HVDC end are respectively identified according to the amplitude-frequency traveling wave energy and the fault direction criterion of each end, and the method specifically comprises the following steps:
if the amplitude-frequency traveling wave energy E meets the condition that E is more than or equal to delta, identifying that the fault direction of the end is a forward direction;
if the amplitude-frequency traveling wave energy E meets the condition that E is less than delta, identifying that the fault direction of the end is reverse;
Δ is a known threshold value.
According to the method, the fault type is identified according to the fault direction of the LCC-HVDC end and the fault direction of the MMC-HVDC end, and the method specifically comprises the following steps:
if the fault direction of the LCC-HVDC end and the fault direction of the MMC-HVDC end are both positive directions, determining that the fault type is an intra-area fault; otherwise, determining the fault type as an out-of-area fault.
According to the method, corresponding protection is executed according to the identified fault type, and the method specifically comprises the following steps:
if the fault type is an intra-area fault, the protection unit executes protection action;
and if the fault type is an out-of-area fault, the protection unit executes protection locking.
The method described above obtains voltage traveling wave data and current traveling wave data on the power transmission line of the LCC-HVDC end located on the rectifying side and the MMC-HVDC end located on the inverting side, respectively, and obtains 1-mode voltage traveling wave data and 1-mode current traveling wave data of the LCC-HVDC end and the MMC-HVDC end, respectively, based on the voltage traveling wave data and the current traveling wave data, and specifically includes:
respectively acquiring positive electrode voltage traveling wave data, negative electrode voltage traveling wave data, positive electrode current traveling wave data and negative electrode current traveling wave data of each end, and respectively acquiring 1-mode voltage traveling wave data and 1-mode current traveling wave data of each end according to the following formulas:
wherein k is the serial number of the sampling point; t is sampling step length; u. of+(kT) and u-(kT) is respectively a sampling value of the positive voltage traveling wave and a sampling value of the negative voltage traveling wave at the kT sampling moment; i.e. i+(kT) and i- (kT) are respectively a sampling value of the positive electrode current traveling wave and a sampling value of the negative electrode current traveling wave at the kT sampling moment; u. of1(kT) and i1(kT) are respectively calculated values of the 1-mode voltage traveling wave and the 1-mode current traveling wave at the kT sampling moment.
The method for performing S-transformation on the 1-mode voltage traveling wave data and the 1-mode voltage prevailing wave data of the LCC-HVDC end and the MMC-HVDC end to obtain an S-transformation matrix corresponding to each end specifically includes:
and (3) processing the 1-mode voltage traveling wave data and the 1-mode current traveling wave data at each end by using S conversion according to the following formula:
wherein N is a known frequency discrimination; e is a natural constant, i is an imaginary number unit, N is a sampling frequency number, and N is 1,2, … and N; j is a variable used for iterative computation, j is 1,2, …, N; u. of1And i11 mode voltage traveling wave data and 1 mode voltage traveling wave data are respectively obtained; suAnd SiRespectively an S transformation matrix of 1-mode voltage traveling waves and an S transformation matrix of 1-mode current traveling waves.
Compared with the prior art, the invention has the advantages and positive effects that:
(1) the invention fully considers the traveling wave catadioptric characteristic of LCC-MMC-HVDC hybrid direct current transmission system, performs S transformation on 1-mode voltage traveling wave data and 1-mode current traveling wave data of each end of the line by utilizing S transformation to obtain an S transformation matrix corresponding to each end, extracts amplitude information and phase information contained in the voltage traveling wave and the current traveling wave based on the S transformation matrix to form an amplitude-frequency traveling wave matrix, further obtains amplitude-frequency traveling wave energy according to the amplitude-frequency traveling wave matrix, correctly identifies the fault direction of each end based on the amplitude-frequency traveling wave energy and fault direction criterion, accurately judges the fault type according to the fault directions of the two ends, executes protection action based on the fault type, realizes traveling wave protection of the LCC-MMC-HVDC hybrid direct current transmission line, and effectively solves the problem that the traveling wave protection reliability is poor due to the failure direction identification in the prior art, The problem of easy misoperation is solved, and the reliability of traveling wave protection of the LCC-MMC-HVDC hybrid direct current transmission line is improved.
(2) By applying the traveling wave protection method provided by the invention, the protection units at two ends of the line do not need strict time synchronization, do not need to exchange a large amount of sampling data, only amplitude-frequency traveling wave energy data or fault direction data need to be exchanged, the data transmission pressure of a communication channel is small, and the protection method is easier to be applied practically.
Other features and advantages of the present invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are 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 flow chart of an embodiment of a hybrid direct current transmission line traveling wave protection method according to the present invention;
FIG. 2 is a diagram of an exemplary architecture of the hybrid DC power transmission system of the embodiment of FIG. 1;
FIG. 3 is a voltage traveling wave simulation waveform and a current traveling wave simulation waveform at both ends in the event of a typical in-zone fault using the method of the embodiment of FIG. 1; wherein, (a) is a positive voltage traveling wave waveform and a negative voltage traveling wave waveform at two ends, and (b) is a positive current traveling wave waveform and a negative current traveling wave waveform at two ends;
FIG. 4 is the 1-mode voltage traveling wave calculation waveform and the 1-mode current traveling wave calculation waveform of FIG. 3; the method comprises the following steps that (a) a 1-mode voltage traveling wave calculation waveform and a 1-mode current wave calculation waveform of an LCC-HVDC end are obtained, and (b) a 1-mode voltage traveling wave calculation waveform and a 1-mode current wave calculation waveform of an MMC-HVDC end are obtained;
FIG. 5 is a two-terminal amplitude-frequency traveling wave matrix waveform corresponding to FIG. 4; wherein, (a) is amplitude-frequency traveling wave matrix waveform of LCC-HVDC end, and (b) is amplitude-frequency traveling wave matrix waveform of MMC-HVDC end.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings and examples.
Fig. 1 shows a flowchart of an embodiment of a method for protecting a traveling wave of a hybrid direct current transmission line according to the present invention, and in particular, an embodiment of a method for protecting a traveling wave of an LCC-MMC-HVDC hybrid direct current transmission line based on S transform. In connection with the typical architecture diagram of the hybrid dc transmission system shown in fig. 2, this embodiment implements hybrid dc transmission line traveling wave protection using the following procedure.
Step 11: and respectively acquiring voltage traveling wave data and current traveling wave data on the power transmission lines at two ends, and respectively acquiring 1-mode voltage traveling wave data and 1-mode current traveling wave data at each end based on the voltage traveling wave data and the current traveling wave data.
As shown in the architecture diagram of fig. 2, for an LCC-MMC-HVDC hybrid dc transmission system, the rectifying side is an LCC-HVDC end, the inverting side is an MMC-HVDC end, each end is provided with a protection unit, and the protection unit can obtain voltage traveling wave data and current traveling wave data of the end where the protection unit is located. In addition, in this embodiment, to solve the problem of electromagnetic coupling between the positive electrode line and the negative electrode line, instead of directly performing S-conversion on the voltage traveling wave data and the current traveling wave data, 1-mode voltage traveling wave data and 1-mode current traveling wave data are acquired based on the voltage traveling wave data and the current traveling wave data, so as to eliminate the fault influence caused by electromagnetic coupling between the positive electrode and the negative electrode.
Specifically, IN this embodiment, the protection unit at the LCC-HVDC end acquires the positive voltage traveling wave data, the negative voltage traveling wave data, the positive current traveling wave data, and the negative current traveling wave data on the power transmission line at the LCC-HVDC end through the RP unit and the RN unit, and the protection unit at the MMC-HVDC end acquires the positive voltage traveling wave data, the negative voltage traveling wave data, the positive current traveling wave data, and the negative current traveling wave data on the power transmission line at the LCC-HVDC end through the IP unit and the IN unit. Then, 1-mode voltage traveling wave data and 1-mode voltage traveling wave data of each end are respectively obtained according to the following formula:
in the formula, k is the serial number of the sampling point; t is a sampling step length, and is set according to needs; u. of+(kT) and u-(kT) is respectively a sampling value of the positive voltage traveling wave and a sampling value of the negative voltage traveling wave at the kT sampling moment; i.e. i+(kT) and i-(kT) is respectively a sampling value of the positive electrode current traveling wave and a sampling value of the negative electrode current traveling wave at the kT sampling moment; u. of1(kT) and i1(kT) are respectively calculated values of the 1-mode voltage traveling wave and the 1-mode current traveling wave at the kT sampling moment.
Step 12: and S transformation is carried out on the 1-mode voltage traveling wave data and the 1-mode current traveling wave data of each end, and an S transformation matrix corresponding to each end is obtained.
The S transformation is used as an excellent time-frequency analysis tool and applied to a hybrid direct-current power transmission system, and amplitude values and phase angles of different frequency components at different sampling moments in the transient traveling wave can be obtained. Based on this feature of S transformation, in step 12, the 1-mode voltage traveling wave data and 1-mode current traveling wave data at each end obtained in step 11 are processed by using the following formula:
wherein k and T have the same meanings as in step 11. N is the known frequency discrimination, and the N has a large value, good discrimination but low calculation speed; when N is small, the discrimination is poor, but the calculation speed is high, and the specific value can be determined according to the actual situation. e is a natural constant, i is an imaginary unit, N is a sampling frequency number, N is 1,2, …, N, j is a variable for iterative computation, j is 1,2, …, N；u1And i11 mode voltage traveling wave data and 1 mode voltage traveling wave data are respectively obtained; suAnd SiRespectively an S transformation matrix of 1-mode voltage traveling waves and an S transformation matrix of 1-mode current traveling waves. And each end respectively calculates to obtain an S transformation matrix of the 1-mode voltage traveling wave and an S transformation matrix of the 1-mode current traveling wave.
Step 13: and obtaining the amplitude-frequency traveling wave matrix corresponding to each end according to the S transformation matrix of each end, and calculating the amplitude-frequency traveling wave energy corresponding to each end according to the amplitude-frequency traveling wave matrix of each end.
Specifically, firstly, the amplitude-frequency traveling wave matrix P corresponding to each end is obtained according to the following formula:
in the formula, k, T and j have the same meanings as above. f. ofsThe reference frequency is equal to 1/NT. SuAnd SiThe S transformation matrix of the 1-mode voltage traveling wave and the S transformation matrix of the 1-mode current traveling wave are respectively arranged at the ends. A. themAnd AnRespectively the amplitude and the phase angle of the amplitude-frequency traveling wave matrix P; abs is a modulo function and angle is a phase angle function.
Then, the amplitude-frequency traveling wave energy E corresponding to each end is calculated according to the amplitude-frequency traveling wave matrix P and the following formula:
fminand fmaxRespectively determining the value of the known minimum frequency value and the known maximum frequency value according to the actually-desired frequency interval; generally, the minimum frequency is preferably 1kHz or more, and the maximum frequency is preferably 500kHz or less. W is the data window length and is also known.
Step 14: and respectively identifying the fault direction of each end according to the amplitude-frequency traveling wave energy and the fault direction criterion of each end.
The fault direction criterion is a known criterion, and is a criterion that the fault direction of the terminal can be identified based on the amplitude-frequency traveling wave energy, and the embodiment does not limit the concrete expression of the fault direction criterion.
As a preferred embodiment, in order to simplify the identification process and improve the identification accuracy, the following criteria are preferably used to identify the fault direction:
that is, if the amplitude-frequency traveling wave energy E of a certain end meets the condition that E is more than or equal to delta, the fault direction of the end is identified as the forward direction; and if the amplitude-frequency traveling wave energy E of a certain end meets the condition that E is less than delta, identifying that the fault direction of the end is reverse. Where Δ is a known threshold value, and an appropriate value can be determined according to the actual system architecture and the recognition accuracy. For example, Δ ═ 50MVA · rad (megavolt ampere · rad).
By adopting the method, the fault direction of the LCC-HVDC end and the fault direction of the MMC-HVDC end are respectively identified.
Step 15: and identifying the fault type according to the fault directions at the two ends.
Specifically, if the fault direction of the LCC-HVDC end and the fault direction of the MMC-HVDC end are both positive directions, determining that the fault type is an intra-area fault; otherwise, determining the fault type as an out-of-area fault.
In some preferred embodiments, the protection unit of the LCC-HVDC terminal and the protection unit of the MMC-HVDC terminal may exchange a fault direction of the local terminal, and each terminal protection unit identifies a fault type of the local terminal after obtaining the fault direction of the local terminal and the fault direction of the opposite terminal. Besides, in some other preferred embodiments, the LCC-HVDC-end protection unit and the MMC-HVDC-end protection unit may also exchange the amplitude-frequency traveling wave energy E obtained in step 13, in this case, each end protection unit identifies the fault direction according to the amplitude-frequency traveling wave energy of the end, identifies the fault direction according to the amplitude-frequency traveling wave energy of the opposite end, and then identifies the fault type of the end according to the two fault directions. No matter what result exchange mode is adopted, the protection units at two ends of the circuit do not need strict time synchronization or exchange a large amount of sampling data, the data transmission pressure of a communication channel is low, and the protection method is easier to be applied practically.
Step 16: and executing corresponding protection according to the identified fault type.
The failure type is generally an intra-area failure or an extra-area failure, and each failure corresponds to a different protection strategy. If the fault type is an intra-area fault, the protection unit executes protection action; if the fault type is an out-of-area fault, the protection unit will perform protection lockout. After the fault type is determined, the protection unit executes corresponding protection according to the known corresponding relation.
The method of the embodiment is adopted to execute traveling wave protection, the traveling wave catadioptric characteristic of an LCC-MMC-HVDC hybrid direct current power transmission system is fully considered, S transformation is carried out on 1-mode voltage traveling wave data and 1-mode current traveling wave data of each end of the line by utilizing S transformation to obtain an S transformation matrix corresponding to each end, amplitude information and phase information contained in voltage traveling waves and current traveling waves are extracted based on the S transformation matrix to form an amplitude-frequency traveling wave matrix, amplitude-frequency traveling wave energy is further obtained according to the amplitude-frequency traveling wave matrix, fault directions of each end are correctly identified based on the amplitude-frequency traveling wave energy and fault direction criterion, fault types are accurately judged according to the fault directions of the two ends, protection actions are executed based on the fault types, traveling wave protection of the LCC-MMC-HVDC hybrid power transmission line is realized, and the problem that traveling wave protection reliability is poor due to the fact that the fault directions cannot be identified in the prior art is effectively solved, The problem of easy misoperation is solved, and the reliability of traveling wave protection of the LCC-MMC-HVDC hybrid direct current transmission line is improved.
Fig. 3 shows a voltage traveling wave simulation waveform and a current traveling wave simulation waveform at two ends of an LCC-MMC-HVDC hybrid direct current transmission line when a typical intra-area fault is transmitted by using the method of the embodiment of fig. 1. Wherein, (a) is a positive voltage traveling wave waveform and a negative voltage traveling wave waveform at two ends, and (b) is a positive current traveling wave waveform and a negative current traveling wave waveform at two ends. Fig. 4 is a 1-mode voltage traveling wave calculation waveform and a 1-mode current traveling wave calculation waveform of fig. 3. Wherein, (a) is waveform u calculated for 1-mode voltage traveling wave of LCC-HVDC terminallccAnd 1-mode electric epidemic wave calculation waveform ilcc(b) calculating a waveform u for 1-mode voltage traveling wave of the MMC-HVDC endmmcAnd 1-mode electric epidemic wave calculation waveform immc. Calculation methodThe method adopts the method of the embodiment of figure 1. Fig. 5 is a two-end amplitude-frequency traveling wave matrix waveform corresponding to the 1-mode voltage traveling wave calculation waveform and the 1-mode voltage traveling wave calculation waveform of fig. 4. Wherein, (a) is amplitude-frequency traveling wave matrix waveform of the LCC-HVDC terminal, specifically, amplitude-frequency traveling wave matrix waveform obtained by the method of the embodiment of fig. 1 for 1-mode voltage traveling wave calculation waveform and 1-mode current traveling wave calculation waveform in fig. 4 (a); (b) the method is an amplitude-frequency traveling wave matrix waveform of an MMC-HVDC terminal, and specifically is an amplitude-frequency traveling wave matrix waveform obtained by the method in the embodiment of fig. 1 for a 1-mode voltage traveling wave calculation waveform and a 1-mode voltage traveling wave calculation waveform in fig. 4 (b). In the amplitude-frequency traveling wave matrix waveform of fig. 5, the X-axis is time t (different sampling times within the data window); the Y axis is a frequency component, and each sampling moment comprises a complex frequency component; and the Z axis is an amplitude-frequency traveling wave energy value obtained according to the amplitude-frequency traveling wave matrix.
Through calculation, the amplitude-frequency row wave energy value of the LCC-HVDC end is 8004.4 MVRad, and the amplitude-frequency row wave energy value of the MMC-HVDC end is 600.3 MVRad. Under the condition that the threshold value delta is 50 MVA-rad, the actual amplitude-frequency traveling wave energy values at two ends are both larger than the threshold value delta, and the fault direction criterion can know that the two ends are both positive faults, so that the fault type is determined to be an intra-area fault, and the fault type identification result is consistent with the actually generated fault type, and the reliability and the accuracy of the method are shown.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions.
Claims (7)
1. A traveling wave protection method of a hybrid direct current transmission line based on S conversion is characterized by comprising the following steps:
respectively acquiring voltage traveling wave data and current traveling wave data on a power transmission line of an LCC-HVDC end positioned on a rectification side and an MMC-HVDC end positioned on an inversion side, and respectively acquiring 1-mode voltage traveling wave data and 1-mode current traveling wave data of the LCC-HVDC end and the MMC-HVDC end based on the voltage traveling wave data and the current traveling wave data;
s conversion is carried out on the 1-mode voltage traveling wave data and the 1-mode voltage traveling wave data of the LCC-HVDC end and the MMC-HVDC end, and an S conversion matrix corresponding to each end is obtained;
acquiring an amplitude-frequency traveling wave matrix corresponding to each end according to the S transformation matrix of each end, and calculating amplitude-frequency traveling wave energy corresponding to each end according to the amplitude-frequency traveling wave matrix of each end;
respectively identifying the fault direction of an LCC-HVDC end and the fault direction of an MMC-HVDC end according to the amplitude-frequency traveling wave energy and the fault direction criterion of each end;
identifying the fault type according to the fault direction of the LCC-HVDC end and the fault direction of the MMC-HVDC end;
and executing corresponding protection according to the identified fault type.
2. The method according to claim 1, wherein obtaining an amplitude-frequency traveling wave matrix corresponding to each end according to the S transform matrix of each end, and calculating an amplitude-frequency traveling wave energy corresponding to each end according to the amplitude-frequency traveling wave matrix of each end specifically includes:
obtaining an amplitude-frequency traveling wave matrix P corresponding to each end according to the following formula:
and calculating the amplitude-frequency traveling wave energy E corresponding to each end according to the following formula:
k is a sampling point serial number when the 1-mode voltage traveling wave data and the 1-mode current traveling wave data are acquired; t is sampling step length; j is a variable used for iterative computation,j is 1,2, …, N is the known frequency discrimination in S transform; f. ofsIs a reference frequency, the value of which is equal to 1/NT; suAnd SiRespectively an S transformation matrix of the 1-mode voltage traveling wave and an S transformation matrix of the 1-mode current traveling wave at the end; a. themAnd AnRespectively the amplitude and the phase angle of the amplitude-frequency traveling wave matrix P; abs is a modulus function, and angle is a phase angle function; f. ofminAnd fmaxKnown minimum and maximum frequency values, respectively; w is the data window length.
3. The method according to claim 2, wherein the step of identifying the fault direction of the LCC-HVDC end and the fault direction of the MMC-HVDC end according to the amplitude-frequency traveling wave energy and the fault direction criterion of each end comprises:
if the amplitude-frequency traveling wave energy E meets the condition that E is more than or equal to delta, identifying that the fault direction of the end is a forward direction;
if the amplitude-frequency traveling wave energy E meets the condition that E is less than delta, identifying that the fault direction of the end is reverse;
Δ is a known threshold value.
4. The method according to claim 3, wherein identifying the fault type according to the fault direction of the LCC-HVDC terminal and the fault direction of the MMC-HVDC terminal comprises:
if the fault direction of the LCC-HVDC end and the fault direction of the MMC-HVDC end are both positive directions, determining that the fault type is an intra-area fault; otherwise, determining the fault type as an out-of-area fault.
5. The method according to claim 1, wherein performing the corresponding protection according to the identified fault type specifically comprises:
if the fault type is an intra-area fault, the protection unit executes protection action;
and if the fault type is an out-of-area fault, the protection unit executes protection locking.
6. The method according to any one of claims 1 to 5, wherein voltage traveling wave data and current traveling wave data on the transmission line of the LCC-HVDC terminal located on a rectification side and the MMC-HVDC terminal located on an inversion side are respectively obtained, and based on the voltage traveling wave data and the current traveling wave data, 1-mode voltage traveling wave data and 1-mode current traveling wave data of the LCC-HVDC terminal and the MMC-HVDC terminal are respectively obtained, and the method specifically comprises the following steps:
respectively acquiring positive electrode voltage traveling wave data, negative electrode voltage traveling wave data, positive electrode current traveling wave data and negative electrode current traveling wave data of each end, and respectively acquiring 1-mode voltage traveling wave data and 1-mode current traveling wave data of each end according to the following formulas:
wherein k is the serial number of the sampling point; t is sampling step length; u. of+(kT) and u-(kT) is respectively a sampling value of the positive voltage traveling wave and a sampling value of the negative voltage traveling wave at the kT sampling moment; i.e. i+(kT) and i-(kT) is respectively a sampling value of the positive electrode current traveling wave and a sampling value of the negative electrode current traveling wave at the kT sampling moment; u. of1(kT) and i1(kT) are respectively calculated values of the 1-mode voltage traveling wave and the 1-mode current traveling wave at the kT sampling moment.
7. The method according to claim 6, wherein performing S-transformation on 1-mode voltage traveling wave data and 1-mode voltage traveling wave data of the LCC-HVDC end and the MMC-HVDC end to obtain an S-transformation matrix corresponding to each end specifically comprises:
and (3) processing the 1-mode voltage traveling wave data and the 1-mode current traveling wave data at each end by using S conversion according to the following formula:
wherein N is a known frequency discrimination; e is a natural constant, i is an imaginary number unit, N is a sampling frequency number, and N is 1,2, … and N; j is a variable used for iterative computation, j is 1,2, …, N; u. of1And i1Are respectively provided with1 mode voltage traveling wave data and 1 mode voltage traveling wave data; suAnd SiRespectively an S transformation matrix of 1-mode voltage traveling waves and an S transformation matrix of 1-mode current traveling waves.
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