CN110957710B - Traveling wave protection method for hybrid multi-terminal direct current transmission line - Google Patents

Traveling wave protection method for hybrid multi-terminal direct current transmission line Download PDF

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CN110957710B
CN110957710B CN201911356732.3A CN201911356732A CN110957710B CN 110957710 B CN110957710 B CN 110957710B CN 201911356732 A CN201911356732 A CN 201911356732A CN 110957710 B CN110957710 B CN 110957710B
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traveling wave
wave data
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CN110957710A (en
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王栋
杨海山
侯梦倩
刘喜梅
于飞
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Qingdao University of Science and Technology
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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
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/265—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured making use of travelling wave theory
    • 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
    • H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
    • H02H7/268—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured for dc systems
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

Abstract

The invention discloses a traveling wave protection method for a hybrid multi-terminal direct current transmission line, which comprises the following steps: respectively acquiring voltage traveling wave data and current traveling wave data on the power transmission line at each end, 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; acquiring 1-mode modulation voltage traveling wave data or 1-mode modulation current traveling wave data based on 1-mode voltage traveling wave data and 1-mode current traveling wave data of each end; acquiring fault direction judging parameters of each end according to 1-mode modulation current traveling wave data or 1-mode modulation voltage traveling wave data of each end; respectively identifying the fault direction of each end according to the fault direction judging parameters and the fault direction criterion of each end; identifying fault types according to fault directions of all terminals; and executing corresponding protection according to the identified fault type. The invention can improve the reliability of the traveling wave protection of the hybrid multi-terminal direct current transmission line.

Description

Traveling wave protection method for hybrid multi-terminal direct current transmission line
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 multi-terminal direct current transmission line.
Background
A high-voltage direct-current transmission system LCC-HVDC (line communated 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. In order to obtain higher transmission capacity, a multi-terminal direct current (MTDC) topology structure is adopted on the inversion side, so that an LCC-MMC-MTDC hybrid multi-terminal direct current transmission system is formed.
At present, the main protection of the LCC-MMC-MTDC hybrid multi-terminal direct current transmission line still adopts the traditional traveling wave protection method based on voltage variation, voltage variation rate and current variation rate. 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 traveling wave protection method of a hybrid multi-terminal direct current transmission line, aiming at solving the problems of poor reliability and easy misoperation of a traveling wave protection method of an LCC-MMC-MTDC hybrid multi-terminal direct current transmission line in the prior art, and improving the reliability of 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 for a hybrid multi-terminal direct current transmission line 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 a plurality of MMC-HVDC ends 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 plurality of MMC-HVDC ends based on the voltage traveling wave data and the current traveling wave data;
acquiring 1-mode modulation voltage traveling wave data or 1-mode modulation current traveling wave data based on 1-mode voltage traveling wave data and 1-mode current traveling wave data of each end;
acquiring fault direction judging parameters of each end according to 1-mode voltage traveling wave data and 1-mode modulation current traveling wave data of each end or according to 1-mode voltage traveling wave data and 1-mode modulation voltage traveling wave data of each end;
respectively identifying the fault direction of each end according to the fault direction judging parameters and the fault direction criterion of each end;
identifying fault types according to fault directions of all terminals;
and executing corresponding protection according to the identified fault type.
In the method, the obtaining 1-mode modulation current traveling wave data based on the 1-mode voltage traveling wave data and the 1-mode current traveling wave data at each end specifically includes:
acquiring the 1-mode modulation current traveling wave data according to the following formula:
Figure BDA0002336131660000021
wherein t is sampling time, u (t) and i (t) are respectively calculated values of 1-mode voltage traveling wave and 1-mode current traveling wave in a sampling data window at the sampling time, i (t) iskAnd (t) is 1-mode modulation current traveling wave data.
In the above method, the obtaining the fault direction determination parameter of each end according to the 1-mode voltage traveling wave data and the 1-mode modulation current traveling wave data of each end specifically includes:
obtaining a fault direction discrimination parameter alpha of each end according to the following formula1：
Figure BDA0002336131660000031
In the formula, tsAnd tdRespectively the start time of the sampled data window and the data window length.
In the method, the identifying the fault direction of each end according to the fault direction determination parameter and the fault direction criterion of each end specifically includes:
if the fault direction determines the parameter alpha1If the fault direction of the end is less than 0, identifying that the fault direction of the end is a positive direction;
if the fault direction determines the parameter alpha1If the fault direction is larger than 0, the fault direction of the end is identified as reverse.
In the above method, the obtaining 1-mode modulation voltage traveling wave data based on the 1-mode voltage traveling wave data and the 1-mode current traveling wave data at each end specifically includes:
acquiring the 1-mode modulation voltage traveling wave data according to the following formula:
Figure BDA0002336131660000032
wherein t is sampling time, u (t) and i (t) are respectively calculated values of 1-mode voltage traveling wave and 1-mode current traveling wave in a sampling data window at the sampling time, and u (t) is the sampling timekAnd (t) is 1 mode modulation voltage traveling wave data.
In the above method, the obtaining the fault direction determination parameter of each end according to the 1-mode current wave data and the 1-mode modulation voltage traveling wave data of each end specifically includes:
obtaining a fault direction discrimination parameter alpha of each end according to the following formula2：
Figure BDA0002336131660000033
In the formula, tsAnd tdRespectively the start time of the sampled data window and the data window length.
In the method, the identifying the fault direction of each end according to the fault direction determination parameter and the fault direction criterion of each end specifically includes:
if the fault direction determines the parameter alpha2If the fault direction of the end is less than 0, identifying that the fault direction of the end is a positive direction;
if the fault direction determines the parameter alpha2If the fault direction is larger than 0, the fault direction of the end is identified as reverse.
The method described above obtains voltage traveling wave data and current traveling wave data on the power transmission lines of the LCC-HVDC end located on the rectifying side and the plurality of MMC-HVDC ends 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 plurality of MMC-HVDC ends based on the voltage traveling wave data and the current traveling wave data, respectively, 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:
Figure BDA0002336131660000041
wherein t is sampling time; u. of+(t) and u_(t) respectively obtaining a sampling value of the positive voltage traveling wave and a sampling value of the negative voltage traveling wave at the sampling time t in the sampling data window; i.e. i+(t) and i_(t) respectively obtaining a sampling value of the positive electrode current traveling wave and a sampling value of the negative electrode current traveling wave at the sampling time t in the sampling data window; u (t) and i (t) are respectively calculated values of 1-mode voltage traveling wave and 1-mode current traveling wave in a sampling data window at a sampling time t.
The method for identifying the fault type according to the fault directions of all the terminals specifically includes:
if the fault directions of all the terminals are positive, determining the fault type as an intra-area fault; otherwise, determining the fault type as an out-of-area fault.
In the method, the executing corresponding protection according to the identified fault type specifically includes:
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.
Compared with the prior art, the invention has the advantages and positive effects that:
1. the invention fully considers the traveling wave refraction and reflection characteristics of the LCC-MMC-MTDC hybrid multi-terminal direct current transmission system, provides a fault direction distinguishing parameter of each terminal according to 1-mode voltage traveling wave data and 1-mode modulation current traveling wave data of each terminal or according to 1-mode current traveling wave data and 1-mode modulation voltage traveling wave data of each terminal, the fault direction distinguishing parameter embodies the similarity of the voltage traveling wave and the modulation current traveling wave or embodies the similarity of the current traveling wave and the modulation voltage traveling wave, the fault direction distinguishing parameter based on the reaction similarity can correctly distinguish the fault direction of each terminal, accurately judge the fault type according to the fault direction of each terminal, execute protection action based on the fault type, realize the traveling wave protection of the LCC-MMC-MTDC hybrid multi-terminal direct current transmission line, and effectively solve the problem that the traveling wave protection reliability is poor due to the failure direction recognition in the prior art, The problem of easy misoperation is solved, and the traveling wave protection reliability of the LCC-MMC-MTDC hybrid multi-terminal direct current transmission line is improved.
2. By applying the traveling wave protection method provided by the invention, the protection units at each end of the line do not need strict time synchronization, do not need to exchange a large amount of sampling data, only need to exchange fault direction judging parameters or fault direction data, 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 multi-terminal dc transmission line traveling wave protection method according to the present invention;
fig. 2 is a typical architecture diagram of the hybrid multi-terminal dc transmission system of the embodiment of fig. 1;
FIG. 3 is a graph of voltage and current simulated waveforms at each end in the event of a typical in-zone fault; the device comprises a power supply, a controller and a controller, wherein (a) is an LCC-HVDC end positive electrode voltage traveling wave waveform and a negative electrode voltage traveling wave waveform, (b) is an MMC-HVDC-I end positive electrode voltage traveling wave waveform and a negative electrode voltage traveling wave waveform, (c) is an MMC-HVDC-II end positive electrode voltage traveling wave waveform and a negative electrode voltage traveling wave waveform, (d) is an LCC-HVDC end positive electrode current traveling wave waveform and a negative electrode current traveling wave waveform, (e) is an MMC-HVDC-I end positive electrode current traveling wave waveform and a negative electrode current traveling wave waveform, and (f) is an MMC-HVDC-II end positive electrode current traveling wave waveform and a negative electrode current traveling wave waveform;
FIG. 4 is a 1-mode voltage traveling waveform and a 1-mode modulated current traveling waveform at the time of a typical in-zone fault obtained using the method of the embodiment of FIG. 1; the system comprises a power supply, a controller, a power supply controller and a power supply controller, wherein (a) is LCC-HVDC end 1-mode voltage traveling wave waveform and 1-mode modulation current traveling wave waveform, (b) is MMC-HVDC-I end 1-mode voltage traveling wave waveform and 1-mode modulation current traveling wave waveform, and (c) is MMC-HVDC-II end 1-mode voltage traveling wave waveform and 1-mode modulation current traveling wave waveform;
FIG. 5 is a graph of voltage and current simulated waveforms at each end in the event of a typical out-of-band fault; the device comprises a power supply, a controller and a controller, wherein (a) is an LCC-HVDC end positive electrode voltage traveling wave waveform and a negative electrode voltage traveling wave waveform, (b) is an MMC-HVDC-I end positive electrode voltage traveling wave waveform and a negative electrode voltage traveling wave waveform, (c) is an MMC-HVDC-II end positive electrode voltage traveling wave waveform and a negative electrode voltage traveling wave waveform, (d) is an LCC-HVDC end positive electrode current traveling wave waveform and a negative electrode current traveling wave waveform, (e) is an MMC-HVDC-I end positive electrode current traveling wave waveform and a negative electrode current traveling wave waveform, and (f) is an MMC-HVDC-II end positive electrode current traveling wave waveform and a negative electrode current traveling wave waveform;
FIG. 6 is a 1-mode voltage traveling waveform and a 1-mode modulated current traveling waveform at the time of a typical out-of-range fault obtained using the method of the embodiment of FIG. 1; the waveform of the current traveling wave is (a) LCC-HVDC end 1-mode voltage traveling wave and (b) MMC-HVDC-I end 1-mode voltage traveling wave and (c) MMC-HVDC-II end 1-mode voltage traveling wave and (c) 1-mode modulation current traveling wave.
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 hybrid multi-terminal dc transmission line traveling wave protection method according to the present invention, and in particular, is a flowchart of an embodiment of a method for implementing LCC-MMC-MTDC hybrid multi-terminal dc transmission line traveling wave protection. In connection with the typical architecture diagram of the hybrid multi-terminal dc transmission system shown in fig. 2, the embodiment implements the traveling wave protection of the hybrid multi-terminal dc transmission line by using the following procedure.
Step 11: and respectively acquiring voltage traveling wave data and current traveling wave data on the power transmission line at each end, 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, in the LCC-MMC-MTDC hybrid multi-terminal direct current transmission system, the rectifying side is an LCC-HVDC end, the inverting side includes two MMC-HVDC ends, MMC-HVDC-I and MMC-HVDC-II, respectively, 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 calculating modulated current traveling wave data or modulated voltage traveling wave data using 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, and then the modulated data are calculated to eliminate the fault influence caused by electromagnetic coupling between the positive electrode line and the negative electrode line.
Specifically, in the embodiment, a protection unit at an LCC-HVDC end respectively acquires positive voltage traveling wave data, negative voltage traveling wave data, positive current traveling wave data and negative current traveling wave data of a power transmission line at the end through an R1 unit and an R2 unit; the protection unit of the MMC-HVDC-I end respectively acquires positive voltage traveling wave data, negative voltage traveling wave data, positive current traveling wave data and negative current traveling wave data of the power transmission line of the end through an R3 unit and an R4 unit; and the protection unit at the MMC-HVDC-II end respectively acquires positive voltage traveling wave data, negative voltage traveling wave data, positive current wave data and negative current wave data of the power transmission line at the end through an R5 unit and an R6 unit. Then, the three-terminal protection unit intercepts the data window of the same length. In this embodiment, the sampling frequency is set to 1MHz and the data window length is set to 1 ms. In practical applications, the sampling frequency is preferably higher than 100kHz, and the data window length is preferably higher than 0.5 ms. Then, according to the traveling wave data in the data window, respectively acquiring 1-mode voltage traveling wave data and 1-mode current traveling wave data of each end according to the following formula:
Figure BDA0002336131660000071
in the formula, t is sampling time; u. of+(t) and u_(t) respectively obtaining a sampling value of the positive voltage traveling wave and a sampling value of the negative voltage traveling wave at the sampling time t in the sampling data window; i.e. i+(t) and i_(t) respectively obtaining a sampling value of the positive electrode current traveling wave and a sampling value of the negative electrode current traveling wave at the sampling time t in the sampling data window; u (t) and i (t) are respectively calculated values of 1-mode voltage traveling wave and 1-mode current traveling wave in a sampling data window at a sampling time t.
And the data in a section of data window is used for calculation, so that the reliability is higher compared with the traditional traveling wave protection method.
Step 12: and obtaining 1-mode modulation voltage traveling wave data or 1-mode modulation current traveling wave data based on the 1-mode voltage traveling wave data and the 1-mode current traveling wave data at each end.
The similarity of the voltage traveling wave data and the current traveling wave data is low, and the fault direction is difficult to identify by directly solving the similarity. The embodiment creatively provides that firstly, the modulated voltage traveling wave data or the modulated current traveling wave data is determined, the modulated voltage traveling wave data has higher similarity with the 1-mode current traveling wave data, the modulated current traveling wave data also has higher similarity with the 1-mode voltage traveling wave data, and the fault direction can be accurately and reliably identified.
Therefore, the 1-mode modulation voltage traveling wave data is obtained based on the 1-mode voltage traveling wave data and the 1-mode current traveling wave data at each end, and the 1-mode modulation current traveling wave data may be obtained based on the 1-mode voltage traveling wave data and the 1-mode current traveling wave data at each end, and may be used alternatively.
As a preferred embodiment, to simplify the identification process and improve the identification accuracy, the method for obtaining 1-mode modulation current traveling wave data based on 1-mode voltage traveling wave data and 1-mode current traveling wave data at each end specifically includes:
acquiring 1-mode modulation current traveling wave data according to the following formula:
Figure BDA0002336131660000081
wherein t is sampling time, u (t) and i (t) are respectively calculated values of 1-mode voltage traveling wave and 1-mode current traveling wave in a sampling data window at the sampling time, i (t) iskAnd (t) is 1-mode modulation current traveling wave data.
And based on the 1-mode voltage traveling wave data and the 1-mode current traveling wave data of each end, obtaining 1-mode modulation voltage traveling wave data, which specifically comprises the following steps:
acquiring 1-mode modulation voltage traveling wave data according to the following formula:
Figure BDA0002336131660000082
wherein t is sampling time, u (t) and i (t) are respectively calculated values of 1-mode voltage traveling wave and 1-mode current traveling wave in a sampling data window at the sampling time, and u (t) is the sampling timekAnd (t) is 1 mode modulation voltage traveling wave data.
Step 13: and acquiring fault direction judging parameters of each end according to the 1-mode voltage traveling wave data and the 1-mode modulation current traveling wave data of each end or according to the 1-mode voltage traveling wave data and the 1-mode modulation voltage traveling wave data of each end.
In step 12, if 1-mode modulation current traveling wave data is obtained through calculation, a fault direction judgment parameter of each end is obtained according to the 1-mode voltage traveling wave data and the 1-mode modulation current traveling wave data of each end. The specific implementation mode is as follows:
obtaining a fault direction discrimination parameter alpha of each end according to the following formula1：
Figure BDA0002336131660000091
In the formula, tsAnd tdRespectively the start time of the sampled data window and the data window length.
In step 12, if 1-mode modulation voltage traveling wave data is obtained through calculation, a fault direction judgment parameter of each end is obtained according to the 1-mode current traveling wave data of each end and the 1-mode modulation voltage traveling wave data. The specific implementation mode is as follows:
obtaining a fault direction discrimination parameter alpha of each end according to the following formula2：
Figure BDA0002336131660000092
In the formula, tsAnd tdRespectively the start time of the sampled data window and the data window length.
Step 14: and respectively identifying the fault direction of each end according to the fault direction judging parameter 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 fault direction identification parameter, 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:
alpha is less than 0, and is a positive fault; alpha is more than 0, and is reverse fault.
By adopting the fault direction criterion, the fixed value of the threshold value is 0, the fixed value is simple, and the problem that the fixed value of the threshold value is difficult in the traditional protection method does not exist.
More specifically, if the fault direction discriminating parameter is α1If the fault direction of a certain end is judged by the parameter alpha1If the fault direction of the end is less than 0, identifying that the fault direction of the end is a positive direction; if the fault direction of a certain end is judged to be parameter alpha1If the fault direction is larger than 0, the fault direction of the end is identified as reverse.
Similarly, if the fault direction judging parameter is alpha2If the fault direction of a certain end is judged by the parameter alpha2If < 0, identifying the fault side of the terminalThe forward direction is the forward direction; if the fault direction of a certain end is judged to be parameter alpha2If the fault direction is larger than 0, the fault direction of the end is identified as reverse.
By adopting the method, the fault direction of each end on the hybrid multi-end direct current transmission line is respectively identified.
Step 15: and identifying the fault type according to the fault directions of all the terminals.
Specifically, if the fault directions of all the terminals are positive, 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 failure directions of the local terminals may be exchanged between the terminals, and after obtaining the failure directions of all the terminals, each terminal protection unit identifies the failure type of the local terminal. In addition, in some other preferred embodiments, the fault direction determination parameters obtained in step 13 may also be exchanged between the terminals, in which case, in addition to identifying the fault direction according to the fault direction determination parameter of the terminal, each terminal protection unit also identifies the fault direction according to the fault direction determination parameters of the other terminals, and then identifies the fault type of the terminal according to the fault directions of all the terminals. No matter what result exchange mode is adopted, the protection units at all 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 the traveling wave protection, the traveling wave catadioptric characteristic of the LCC-MMC-MTDC hybrid multi-terminal direct current transmission system is fully considered, the fault direction distinguishing parameter of each terminal is obtained according to the 1-mode voltage traveling wave data and the 1-mode modulation current traveling wave data of each terminal or the 1-mode current traveling wave data and the 1-mode modulation voltage traveling wave data of each terminal, the fault direction distinguishing parameter embodies the similarity of the voltage traveling wave and the modulation current traveling wave or embodies the similarity of the current traveling wave and the modulation voltage traveling wave, the fault direction distinguishing parameter based on the reaction similarity can correctly distinguish the fault direction of each terminal, the fault type is accurately judged according to the fault direction of each terminal, the protection action is executed based on the fault type, and the traveling wave protection of the LCC-MMC-MTDC hybrid multi-terminal direct current transmission line is realized, the problems of poor traveling wave protection reliability and easy misoperation caused by the fact that fault directions cannot be identified in the prior art are effectively solved, and the traveling wave protection reliability of the LCC-MMC-MTDC hybrid multi-terminal direct current transmission line is improved.
FIG. 3 illustrates voltage and current simulated waveforms at each end in the event of a typical in-zone fault; the device comprises a power supply, a controller and a controller, wherein (a) is an LCC-HVDC end positive electrode voltage traveling wave waveform and a negative electrode voltage traveling wave waveform, (b) is an MMC-HVDC-I end positive electrode voltage traveling wave waveform and a negative electrode voltage traveling wave waveform, (c) is an MMC-HVDC-II end positive electrode voltage traveling wave waveform and a negative electrode voltage traveling wave waveform, (d) is an LCC-HVDC end positive electrode current traveling wave waveform and a negative electrode current traveling wave waveform, (e) is an MMC-HVDC-I end positive electrode current traveling wave waveform and a negative electrode current traveling wave waveform, and (f) is an MMC-HVDC-II end positive electrode current traveling wave waveform and a negative electrode current traveling wave waveform. FIG. 4 is a 1-mode voltage traveling waveform and a 1-mode modulated current traveling waveform at the time of an exemplary in-zone fault obtained using the method of the embodiment of FIG. 1 and based on the waveform data of FIG. 3; the waveform of the current traveling wave is (a) LCC-HVDC end 1-mode voltage traveling wave and (b) MMC-HVDC-I end 1-mode voltage traveling wave and (c) MMC-HVDC-II end 1-mode voltage traveling wave and (c) 1-mode modulation current traveling wave.
Through calculation, when a fault occurs in a region, the fault direction distinguishing parameter alpha of the LCC-HVDC end, the MMC-HVDC-I end and the MMC-HVDC-II end1The values of the voltage and the current are-0.6887, -0.8366 and-0.7881 respectively, and are negative values, namely, the 1-mode voltage traveling wave data and the 1-mode modulation current traveling wave data at each end are in a negative correlation relationship, and the fault direction of each end is a positive fault, so that the fault type of each end is determined to be an in-region fault. Fault ofThe type identification result is consistent with the actually occurred fault type, which shows the reliability and accuracy of the method of the invention.
FIG. 5 illustrates voltage and current simulated waveforms at each end in the event of a typical out-of-band fault; the device comprises a power supply, a controller and a controller, wherein (a) is an LCC-HVDC end positive electrode voltage traveling wave waveform and a negative electrode voltage traveling wave waveform, (b) is an MMC-HVDC-I end positive electrode voltage traveling wave waveform and a negative electrode voltage traveling wave waveform, (c) is an MMC-HVDC-II end positive electrode voltage traveling wave waveform and a negative electrode voltage traveling wave waveform, (d) is an LCC-HVDC end positive electrode current traveling wave waveform and a negative electrode current traveling wave waveform, (e) is an MMC-HVDC-I end positive electrode current traveling wave waveform and a negative electrode current traveling wave waveform, and (f) is an MMC-HVDC-II end positive electrode current traveling wave waveform and a negative electrode current traveling wave waveform. FIG. 6 is a 1-mode voltage traveling waveform and a 1-mode modulated current traveling waveform at the occurrence of a typical out-of-range fault obtained using the method of the embodiment of FIG. 1 and based on the waveform data of FIG. 5; the waveform of the current traveling wave is (a) LCC-HVDC end 1-mode voltage traveling wave and (b) MMC-HVDC-I end 1-mode voltage traveling wave and (c) MMC-HVDC-II end 1-mode voltage traveling wave and (c) 1-mode modulation current traveling wave.
Through calculation, when an external fault occurs, the fault direction distinguishing parameter alpha of the LCC-HVDC end, the MMC-HVDC-I end and the MMC-HVDC-II end1Values of (a) are 0.9999, -0.8029 and-0.8095, respectively. Then, the 1-mode voltage traveling wave data and the 1-mode modulation current traveling wave data of the LCC-HVDC end are in positive correlation, and the fault direction is reverse; the 1-mode voltage traveling wave data and the 1-mode modulation current traveling wave data at the other two ends are in a negative correlation relationship, and the fault directions are positive faults. And due to the existence of the reverse fault end, determining that the fault type of each end is an out-of-area fault. The fault type identification result is consistent with the actually occurred 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 (8)

1. A traveling wave protection method for a hybrid multi-terminal direct current transmission line 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 a plurality of MMC-HVDC ends 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 plurality of MMC-HVDC ends based on the voltage traveling wave data and the current traveling wave data;
acquiring 1-mode modulation voltage traveling wave data or 1-mode modulation current traveling wave data based on 1-mode voltage traveling wave data and 1-mode current traveling wave data of each end;
acquiring fault direction judging parameters of each end according to 1-mode voltage traveling wave data and 1-mode modulation current traveling wave data of each end or according to 1-mode voltage traveling wave data and 1-mode modulation voltage traveling wave data of each end;
respectively identifying the fault direction of each end according to the fault direction judging parameters and the fault direction criterion of each end;
identifying fault types according to fault directions of all terminals;
executing corresponding protection according to the identified fault type;
the method for obtaining the 1-mode modulation current traveling wave data based on the 1-mode voltage traveling wave data and the 1-mode current traveling wave data at each end specifically comprises the following steps:
acquiring the 1-mode modulation current traveling wave data according to the following formula:
Figure FDA0003154618920000011
wherein t is sampling time, u (t) and i (t) are respectively calculated values of 1-mode voltage traveling wave and 1-mode current traveling wave in a sampling data window at the sampling time, i (t) isk(t) is a 1-mode modulation currentTraveling wave data;
the method for obtaining the 1-mode modulation voltage traveling wave data based on the 1-mode voltage traveling wave data and the 1-mode current traveling wave data at each end specifically comprises the following steps:
acquiring the 1-mode modulation voltage traveling wave data according to the following formula:
Figure FDA0003154618920000012
wherein t is sampling time, u (t) and i (t) are respectively calculated values of 1-mode voltage traveling wave and 1-mode current traveling wave in a sampling data window at the sampling time, and u (t) is the sampling timekAnd (t) is 1 mode modulation voltage traveling wave data.
2. The method according to claim 1, wherein the obtaining of the fault direction determination parameter of each end according to the 1-mode voltage traveling wave data and the 1-mode modulation current traveling wave data of each end specifically comprises:
obtaining a fault direction discrimination parameter alpha of each end according to the following formula1：
Figure FDA0003154618920000021
In the formula, tsAnd tdRespectively the start time of the sampled data window and the data window length.
3. The method according to claim 2, wherein the identifying the fault direction of each end according to the fault direction determination parameter and the fault direction criterion of each end respectively comprises:
if the fault direction determines the parameter alpha1If the fault direction of the end is less than 0, identifying that the fault direction of the end is a positive direction;
if the fault direction determines the parameter alpha1If the fault direction is larger than 0, the fault direction of the end is identified as reverse.
4. The method according to claim 1, wherein the obtaining of the fault direction determination parameter of each end according to the 1-mode current wave data and the 1-mode modulation voltage traveling wave data of each end specifically comprises:
obtaining a fault direction discrimination parameter alpha of each end according to the following formula2：
Figure FDA0003154618920000022
In the formula, tsAnd tdRespectively the start time of the sampled data window and the data window length.
5. The method according to claim 4, wherein the identifying the fault direction of each end according to the fault direction determination parameter and the fault direction criterion of each end respectively comprises:
if the fault direction determines the parameter alpha2If the fault direction of the end is less than 0, identifying that the fault direction of the end is a positive direction;
if the fault direction determines the parameter alpha2If the fault direction is larger than 0, the fault direction of the end is identified as reverse.
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 the rectifying side and the plurality of MMC-HVDC terminals located on the inverting 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 plurality of MMC-HVDC terminals 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:
Figure FDA0003154618920000031
wherein t is sampling time; u. of+(t) and u-(t) respectively obtaining a sampling value of the positive voltage traveling wave and a sampling value of the negative voltage traveling wave at the sampling time t in the sampling data window; i.e. i+(t) and i-(t) respectively obtaining a sampling value of the positive electrode current traveling wave and a sampling value of the negative electrode current traveling wave at the sampling time t in the sampling data window; u (t) and i (t) are respectively calculated values of 1-mode voltage traveling wave and 1-mode current traveling wave in a sampling data window at a sampling time t.
7. The method according to any one of claims 1 to 5, wherein the identifying the fault type according to the fault directions of all the terminals specifically comprises:
if the fault directions of all the terminals are positive, determining the fault type as an intra-area fault; otherwise, determining the fault type as an out-of-area fault.
8. The method according to any one of claims 1 to 5, wherein the performing of 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.
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