CN118232291A

CN118232291A - Pilot protection method and device for flexible direct current transmission line and storage medium

Info

Publication number: CN118232291A
Application number: CN202410271627.4A
Authority: CN
Inventors: 王志杰; 李海锋; 金浩天; 刘海南
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2024-03-11
Filing date: 2024-03-11
Publication date: 2024-06-21

Abstract

The invention discloses a pilot protection method, a pilot protection device and a storage medium for a flexible direct-current transmission line, and belongs to the field of direct-current transmission of power systems. The method comprises the following steps: measuring points are arranged at two ends of the line, and the line voltage of the measuring points at two sides of the line and the current-limiting reactance voltage at two sides of the line are measured; preliminary judgment is carried out according to the polar voltage, and the starting is protected when the starting criterion is met; calculating the ratio of the current limiting reactance voltage at two sides of the line to the voltage of the measuring points at two sides; calculating standard deviation coefficients of the ratio of the current limiting reactance voltage at two sides of the line to the voltage of the measuring points at two sides; and identifying the corresponding fault type according to the obtained standard deviation coefficient, performing fault pole selection, and executing corresponding protection action. The invention utilizes standard deviation coefficient to measure waveform variation trend of the ratio of current limiting reactance to measuring point voltage under positive and negative fault, has simple principle, is not influenced by transition resistance theoretically, and has no protection dead zone. In addition, the protected computation is based on local information only, and a data synchronization system is not required.

Description

Pilot protection method and device for flexible direct current transmission line and storage medium

Technical Field

The invention relates to the field of direct-current transmission of power systems, in particular to a pilot protection method, a pilot protection device and a storage medium for a flexible direct-current transmission line.

Background

The flexible direct current transmission system based on the modularized multi-level converter (modular multilevel converter, MMC) has the advantages of low harmonic content, capability of large-scale consumption of renewable energy sources, no commutation failure and the like, and is widely applied worldwide.

However, the dc power grid belongs to a low inertia network, after a short circuit fault occurs on the dc side, the converter station will feed a short circuit current to the fault point, and the fault current is rapidly discharged in a short time, so that the fault current rises quickly and has a large amplitude. Therefore, rapid and reliable identification of faults in a flexible direct current power grid is still a critical problem to be solved.

The traditional direct current transmission line mainly adopts traveling wave protection, differential undervoltage and voltage mutation protection, and the method has good speediness and is usually used as main protection in direct current line protection; the traditional current differential protection utilizes double-end electric quantity, and has stronger selectivity and sensitivity.

The traveling wave protection and the traditional current differential protection have the following two disadvantages:

1) The traveling wave protection method has the problems of excessive dependence on boundary elements, insufficient transition resistance tolerance, poor anti-interference capability and the like. Furthermore, for a far-end failure, the selectivity may not be satisfied.

2) The current differential protection is easily influenced by the distributed capacitance, so that longer delay is required to avoid the transient discharging process of the distributed capacitance, and the protection speed is influenced.

Therefore, how to improve the capability of traveling wave protection to withstand transition resistance and the rapidity of current differential protection become one of important directions of the prior direct current line fault protection.

Disclosure of Invention

In order to solve at least one of the technical problems existing in the prior art to a certain extent, the invention aims to provide a pilot protection method, a pilot protection device and a storage medium for a flexible direct current transmission line.

The technical scheme adopted by the invention is as follows:

A pilot protection method for a flexible direct current transmission line comprises the following steps:

measuring points are arranged at two ends of the line, and the line voltage of the measuring points at two sides of the line and the current-limiting reactance voltage at two sides of the line are measured;

in the starting unit, preliminary judgment is carried out according to the polar voltage, and the starting is protected when the starting criterion is met;

Calculating the ratio of the current limiting reactance voltage at two sides of the line to the voltage of the measuring points at two sides;

calculating standard deviation coefficients of the ratio of the current limiting reactance voltage at two sides of the line to the voltage of the measuring points at two sides;

And identifying the corresponding fault type according to the obtained standard deviation coefficient, performing fault pole selection, and executing corresponding protection action.

Further, the gradient of the polar voltage traveling wave is used as a starting criterion of protection, and the calculation formula of the gradient of the polar voltage traveling wave is as follows:

(ΔU_p>k_vU_ref)U(ΔU_n>k_vU_ref)＝1

In the formula, deltaU _p is positive DC line voltage variation, deltaU _n is negative DC line voltage variation, j is voltage gradient calculation point number, i is current sampling point, U _ref is rated line voltage, and k _v is voltage fluctuation coefficient.

Further, the calculation formula of the ratio of the current limiting reactance voltage at two sides of the line to the voltage of the measuring point M, N at two sides is as follows:

Wherein U _Ldc1 is the line mode voltage at two ends of a direct current line left-side current-limiting reactor L _dc1, and U _Ldc2 is the line mode voltage at two ends of a direct current line right-side current-limiting reactor L _dc2; u _M1 is the line mode voltage at measurement point M, and U _N1 is the line mode voltage at measurement point N; rat _{Ldc1_M1} is the ratio of U _Ldc1 to U _M1, and Rat _{Ldc2_N1} is the ratio of U _Ldc2 to U _N1.

Further, the calculation formula of the standard deviation coefficient of the ratio of the current limiting reactance voltage at two sides of the line to the measuring point voltage is as follows:

Wherein S _M is the standard deviation coefficient of Rat _{Ldc2_M1}, and S _N is the standard deviation coefficient of Rat _{Ldc2_N1}; n is the number of sampling points in the time window T; and/> Mean values of Rat _{Ldc2_M1} and Rat _{Ldc2_N1} are shown, respectively.

Further, the identifying the corresponding fault type according to the obtained standard deviation coefficient includes:

When the fault occurs in the area, the Rat _{Ldc1_M1}、Rat_{Ldc1_N1} tends to be stable, and S _M and S _N are close to 0; when the positive out-of-zone fault occurs, the Rat _{Ldc2_M1} tends to be stable, the Rat _{Ldc2_N1} changes exponentially, and S _M is close to 0,S _N and is larger; when the reverse region fails, rat _{Ldc2_M1} changes exponentially, rat _{Ldc2_N1} tends to be stable, S _M is larger, and S _N is close to 0; the expression is as follows:

Where K _set is the action threshold.

Further, the criteria for fault pole selection are as follows:

Wherein U ₀ is zero mode voltage; p _set is a preset threshold that is set by the sum of the maximum ground voltages at which line interelectrode faults occur.

Further, the zero mode voltage U ₀ is calculated by:

Wherein U ₁ represents a line mode voltage; u _p represents the positive line voltage; u _n denotes the negative line voltage.

Further, the performing a corresponding protection action includes:

If the fault is the positive pole fault of the circuit, the positive pole protection action is performed; if the circuit negative electrode fails, performing negative electrode protection; if the fault is a line interelectrode fault, the positive electrode protection and the negative electrode protection act together; otherwise, the fault is identified as the out-of-zone fault, and the protection is not operated.

The invention adopts another technical scheme that:

A flexible direct current transmission line pilot protection device, comprising:

at least one processor;

At least one memory for storing at least one program;

the at least one program, when executed by the at least one processor, causes the at least one processor to implement the method described above.

The invention adopts another technical scheme that:

A computer readable storage medium, in which a processor executable program is stored, which when executed by a processor is adapted to carry out the method as described above.

Compared with the prior art, the invention has the following advantages and beneficial effects:

1) The ratio of the current limiting reactance to the voltage of the measuring point is beneficial to amplifying the difference of the fault characteristics inside and outside the area caused by the boundary of the direct current line. And measuring the waveform change trend of the ratio of the current limiting reactance to the voltage of the measuring point under the positive and negative faults by using the standard deviation coefficient. The principle is simple, is not influenced by transition resistance in theory, and does not have protection dead zone.

2) Through simulation test, the effectiveness and reliability of the provided protection scheme are verified. The fault type can be accurately identified under all fault types, the fault type detection device has stronger transition resistance tolerance capability, the sampling frequency requirement on the protection device is lower, and faults inside and outside the area can be identified when the sampling frequency is lower. In addition, under the interference of strong white noise, the protection can still act correctly, and the influence of noise on the scheme is small.

3) The calculation of protection is based on local information only, the fault type can be identified only by switching the fault direction through optical fibers, and the protection scheme does not need a data synchronization system.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following description is made with reference to the accompanying drawings of the embodiments of the present invention or the related technical solutions in the prior art, and it should be understood that the drawings in the following description are only for convenience and clarity of describing some embodiments in the technical solutions of the present invention, and other drawings may be obtained according to these drawings without the need of inventive labor for those skilled in the art.

Fig. 1 is a schematic diagram of a flexible dc power transmission system in one embodiment of the invention;

fig. 2 is a flow chart of a flexible direct current transmission line rapid pilot protection method in an embodiment of the invention.

FIG. 3 is a graph of intra-zone fault results in one example embodiment of the invention.

FIG. 4 is a graph of out-of-zone fault results in one example embodiment of the invention;

FIG. 5 is a graph of intra-zone and extra-zone fault simulation results in one example embodiment of the invention.

Fig. 6 is a schematic diagram of a four-port flexible dc power transmission system in an example embodiment of the invention;

fig. 7 is a flowchart illustrating steps for pilot protection of a flexible dc transmission line based on transient voltage waveform characteristics in an exemplary embodiment of the present invention.

Detailed Description

Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative only and are not to be construed as limiting the invention. The step numbers in the following embodiments are set for convenience of illustration only, and the order between the steps is not limited in any way, and the execution order of the steps in the embodiments may be adaptively adjusted according to the understanding of those skilled in the art.

In the description of the present invention, it should be understood that references to orientation descriptions such as upper, lower, front, rear, left, right, etc. are based on the orientation or positional relationship shown in the drawings, are merely for convenience of description of the present invention and to simplify the description, and do not indicate or imply that the apparatus or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the present invention.

In the description of the present invention, a number means one or more, a number means two or more, and greater than, less than, exceeding, etc. are understood to not include the present number, and above, below, within, etc. are understood to include the present number. The description of the first and second is for the purpose of distinguishing between technical features only and should not be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated or implicitly indicating the precedence of the technical features indicated.

In the description of the present invention, unless explicitly defined otherwise, terms such as arrangement, installation, connection, etc. should be construed broadly and the specific meaning of the terms in the present invention can be reasonably determined by a person skilled in the art in combination with the specific contents of the technical scheme.

Aiming at the prior art, the invention provides a flexible direct current transmission line pilot protection scheme based on transient voltage waveform characteristics, which comprises the following steps: taking a modularized multi-level converter (modular multilevel converter, MMC) flexible direct current transmission system as a research object, and acquiring line pole voltages measured by measuring points at the first end and the tail end of a line; measuring the current limiting reactance voltage at two ends of the line; calculating the gradient of the polar line voltage; calculating the ratio of the current limiting reactance voltage to the measuring point voltage; calculating the standard deviation coefficient of the ratio; calculating the magnitude of the ground voltage; judging whether the polar line voltage gradient criterion meets the condition; and performing preliminary judgment in the starting unit, and protecting starting when the starting criterion is met. Calculating the ratio of the current limiting reactance voltage to the measuring point voltage, calculating a standard deviation coefficient in a certain time window, transmitting standard deviation coefficient information to the opposite side of the direct current line, identifying as an in-area fault if both ends of the direct current line meet the criterion condition, performing fault pole selection, and judging whether the magnitude of the ground mode voltage meets the condition; and in the protection unit, corresponding protection actions are carried out according to the processing results of the fault identification and fault pole selection unit in the area. According to the scheme provided by the invention, the regional faults inside and outside the region are well distinguished, the sensitivity is high, the rapid response to the line faults of the flexible direct current transmission line can be realized, and the situation of misjudgment is not easy to occur. And overcomes the defects of low mobility and insufficient reliability of the existing pilot protection method.

As shown in fig. 7, the embodiment provides a pilot protection method for a flexible direct current transmission line based on transient voltage waveform characteristics, which includes the following steps:

s1, measuring points are arranged at two ends of a line, and the line voltage of the measuring points at two sides of the line and the current-limiting reactance voltage at two sides of the line are measured.

S2, carrying out preliminary judgment according to the polar line voltage, and protecting starting when judging that the starting criterion is met.

The starting unit uses the gradient of the polar voltage traveling wave as a starting criterion for protection, and specifically comprises the following steps:

(ΔU_p>k_vU_ref)U(ΔU_n>k_vU_ref)＝1

Wherein U _ref is the rated line voltage; a represents a fault pole, and k _v is a voltage fluctuation coefficient. In order to avoid the influence of steady-state and transient voltage fluctuation, the value of k _v should be larger than the maximum value of the voltage gradient during the normal operation of the system and smaller than the minimum value possibly occurring during the fault. In some embodiments, k _v takes 0.02.

S3, calculating the ratio of the current limiting reactance voltage at two sides of the line to the voltage of the measuring points at two sides.

The ratio of the measured point voltages obtained by measuring the measured points R12 and R21 to the current limiting reactance voltage is as follows:

s4, calculating standard deviation coefficients of the ratio of the current limiting reactance voltage at two sides of the line to the voltage of the measuring points at two sides.

As an alternative embodiment, the standard deviation coefficient of the ratio of the current limiting reactance voltage at both ends of the line to the voltage at the measuring point is calculated by the following formula:

wherein N is the number of sampling points in the time window T; and/> Mean values of Rat _{Ldc2_M1} and Rat _{Ldc2_N1} are shown, respectively. When the fault occurs in the area, S _M and S _N are close to 0 because the Rat _{Ldc1_M1}、Rat_{Ldc1_N1} tends to be stable; when the forward out-of-zone fault happens, the Rat _{Ldc2_M1} tends to be stable, the Rat _{Ldc2_N1} changes exponentially, S _M is close to 0, and S _N is larger; rat _{Ldc2_M1} changes exponentially and Rat _{Ldc2_N1} stabilizes at reverse out-of-zone faults, S _M is large and S _N is close to 0.

S5, identifying the corresponding fault type according to the obtained standard deviation coefficient, and performing fault pole selection.

The in-region fault identification and fault pole selection unit identifies the in-region fault by using standard deviation coefficients of the ratio of the current limiting reactance voltage at two ends of the line to the voltage of the measuring point, and performs fault pole selection. The fault criteria in the construction area are as follows:

In the formula, K _set is an action threshold, the value of the action threshold is selected according to the maximum value possibly occurring at the measuring points at the two ends during the fault in the area, and during the fault in the area, because Rat _{Ldc2_M1}、Rat_{Ldc2_N1} tends to be stable, S _{M/N_in/ex} is close to 0 theoretically, and multiple simulation tests show that S _{M/N_in/ex} is between 0 and 0.2, so as to avoid measurement errors and noise interference and consider a certain margin. In some alternative embodiments, the action threshold K _set =0.5.

The fault pole selection criteria are constructed as follows:

Wherein p _set is set to the sum of the maximum ground voltages when the line is clear of an inter-pole fault, while taking into account the reliability of the criteria and preserving a certain margin, in some alternative embodiments, p _set = 50kV.

S6, executing corresponding protection actions according to the fault identification result.

Specifically, the protection unit performs corresponding protection actions according to the processing results of the fault identification and fault pole selection unit in the area: if the fault is the positive pole fault of the circuit, the positive pole protection action is performed; if the circuit negative electrode fails, performing negative electrode protection; if the fault is a line interelectrode fault, the positive electrode protection and the negative electrode protection act together; otherwise, the fault is identified as the out-of-zone fault, and the protection is not operated.

The above method is explained in detail below with reference to the drawings and specific examples.

Example 1:

In this embodiment, a true bipolar MMC flexible dc power transmission system is taken as an example, and analysis of a fault voltage traveling wave is performed, where the system topology structure is shown in fig. 1. The direct current transmission line is a bipolar overhead line, L _dc is a current limiting reactor for inhibiting the rising rate of fault current, and M, N is a protection installation place at two ends of the direct current line. Fig. 1 shows typical failure points, where f ₁ is the in-zone failure point on Line1, f ₂ is the out-of-zone failure point on MMC1 side, and f ₃ is the out-of-zone failure point on MMC2 side.

Referring to fig. 2, the pilot protection method for the flexible direct current transmission line based on the transient voltage waveform characteristics provided by the embodiment includes the following steps:

S101, measuring points are arranged at the head and tail ends of the line, and the line voltage at the head and tail ends of the line and the voltage at two ends of the current limiting reactance are measured.

In one embodiment, the setting of the protection measuring point is specifically: the head end of the Line1 is provided with measuring points R12 and L _dc; the device is used for measuring line voltage and current limiting reactance voltage data of the head end of the line; the end of the Line1 is provided with measuring points R21 and L _dc which are used for measuring Line voltage and current-limiting reactance voltage data at the end of the Line.

S102, performing preliminary judgment in a starting unit, and protecting starting when a starting criterion is met.

In one embodiment, the gradient quantity of the polar voltage traveling wave at two ends of the Line1 is used as a starting criterion of protection, and specifically:

(ΔU_p>k_vU_ref)U(ΔU_n>k_vU_ref)＝1

Wherein U _ref is the rated line voltage; a represents a fault pole, and k _v is a voltage fluctuation coefficient. In order to avoid the influence of steady-state and transient voltage fluctuation, the value of the voltage gradient should be larger than the maximum value of the voltage gradient in the normal operation of the system and smaller than the minimum value possibly occurring in the fault, and k _v takes 0.02.

S103, calculating the ratio of the current limiting reactance voltage measured by the protection measuring points R12 and R21 to the voltage of the measuring point.

S104, calculating standard deviation coefficients of the ratio of the current limiting reactance voltage measured by the protection measuring points R12 and R21 to the voltage of the measuring point.

And taking voltage data of 0.5ms after the fault occurs, and calculating the ratio Rat _Ldc1 _M1 and the ratio Rat _{Ldc2_N1} of the two ends of the direct current line by using standard deviation coefficients. When the fault occurs in the area, S _M and S _N are close to 0 because the Rat _{Ldc1_M1}、Rat_{Ldc1_N1} tends to be stable; when the forward out-of-zone fault happens, the Rat _{Ldc2_M1} tends to be stable, the Rat _{Ldc2_N1} changes exponentially, S _M is close to 0, and S _N is larger; during the reverse out-of-zone fault, rat _{Ldc2_M1} changes exponentially, rat _{Ldc2_N1} tends to be stable, S _M is larger, S _N is close to 0, and the method comprises the following steps:

In the formula, K _set is an action threshold, the value of the action threshold is selected according to the maximum value possibly occurring at the measuring points at the two ends during the fault in the area, and during the fault in the area, because Rat _{Ldc2_M1}、Rat_{Ldc2_N1} tends to be stable, S _{M/N_in/ex} is close to 0 theoretically, and multiple simulation tests show that S _{M/N_in/ex} is between 0 and 0.2, so as to avoid measurement errors and noise interference and consider a certain margin. The present embodiment selects the action threshold K _set =0.5.

From the above, it can be seen that: when the protection is used for calculating the electrical quantity information of the side, the opposite side electrical quantity signals are not required to be transmitted to the side, the protection calculation of each side only needs to independently calculate the electrical quantity information of the side, and the fault type can be identified only by transmitting the logic signals obtained by the side to the opposite side. Thus, the protection provided does not need to take into account data communication.

S5, calculating zero mode voltage U ₀ according to the positive and negative pole direct current line voltage:

As can be seen from the formula, when bipolar failure occurs, the zero mode voltage will be 0 due to symmetry between the anode and the cathode; when the positive electrode fails, the positive electrode voltage drops instantaneously, so that the ground voltage is negative; conversely, when the line has a negative electrode grounding fault, the negative electrode voltage is instantaneously reduced, so that the ground voltage is positive. Therefore, the sum of the ground voltages is selected for fault pole selection, namely:

The p _set is set according to the sum of the maximum ground voltages when the line is avoided from interelectrode faults, meanwhile, the reliability of the criterion is considered, a certain margin is reserved, and in the embodiment, p _set =50 kV is selected.

S106, corresponding protection actions are carried out according to the processing results of the fault identification and fault pole selection units in the region.

In one embodiment, if the maximum value of the sum of the positive pole line and the negative pole direct current line is smaller than-p _set and meets the criterion, identifying the fault as the positive pole line fault and performing positive pole protection action; if the maximum value of the sum of the positive electrode line and the negative electrode direct current line is larger than p _set and meets the criterion, identifying the fault as a negative electrode line fault and performing negative electrode protection action; if the maximum value of the sum of the positive pole line and the negative pole direct current line meets the criterion between [ -p _set,p_set ], identifying the fault as the fault between the lines, and enabling the positive pole and the negative pole to act together; if the fault is not satisfied, the fault is identified as the out-of-zone fault, and the protection is not operated.

The invention is further illustrated by a specific simulation example.

In the embodiment, a double-end flexible direct current transmission system model shown in fig. 1 is built in PSCAD/EMTDC for simulation test. The converter stations all adopt MMC models, and specific model parameters are shown in table 1. The direct current transmission line adopts a frequency-dependent parameter model. Taking the protection speed requirement into consideration, taking 0.5ms after the fault occurs as a protection time window. The sampling frequency was chosen to be 10kHz.

TABLE 1 model parameters

Writing a protection algorithm on the MATLAB platform, importing fault simulation data of the built PSCAD model, and verifying the action condition of protection. Since the positive and negative electrode lines have symmetry, positive electrode protection of the Line1 is taken as an example for illustration.

Taking the positive electrode ground fault as an example, when a metallic fault is set 180km away from the protection installation position, the simulation results of the voltage gradient, the ray _{Ldc_M1}、Rat_{Ldc_N1} waveform and the voltage zero-mode component on the M, N side are shown in fig. 3.

As can be seen from fig. 3 (a) and (b), the positive and negative voltage gradients at the measurement point M, N are both greater than the setting value of 10kv, and the protection at m and N is started within 0.5 ms; from the starting point, a 0.5ms data window is cut back, and the standard deviation coefficient of the ray _{Ldc1_M1}、Rat_{Ldc1_N1} in fig. 3 (c) is calculated, so as to obtain S _M＝0.0032、S_N =0.0031, both of which are smaller than the setting value K _set, and the fault can be distinguished as an intra-zone fault, and from fig. 3 (d), the zero mode voltage is smaller than-p _set, and the positive electrode ground fault can be distinguished.

Taking the earth fault of the positive pole of the inversion side current limiting reactance valve side as an example, the simulation results of the voltage gradient, the Rat _{Ldc_M1}、Rat_{Ldc_N1} waveform chart and the voltage zero-mode component of the fault f ₂ and the voltage gradient of the M, N side are shown in fig. 4.

As can be seen from fig. 4 (a) and (b), the positive and negative voltage gradients at the measurement point M, N are both greater than the set value, and the protection at M, N is started within 0.5 ms; from the starting time, a data window of 0.5ms is cut back, and the standard deviation coefficient of Rat _{Ldc1_M1}、Rat_{Ldc1_N1} in fig. 4 (c) is calculated, so that the fault can be judged as an out-of-zone fault when S _M＝0.0028、S_N＝2.9697,S_M is smaller than a setting value K _set,S_N and larger than a setting value K _set, and the fault can be judged as an anode fault when zero mode voltage is smaller than-p _set as can be seen from fig. 4 (d).

And setting the faults inside and outside the areas with different fault types, different positions and different transition resistances. The simulation results are shown in table 2.

Table 2 protection discrimination results

As can be seen from table 2, for different fault distances and different transition resistances under the fault in the region, both S _M and S _N of the measurement points on both sides of the line are smaller than the setting value, and the protection can reliably operate; for the out-of-zone faults at the outlet of the inversion station, S _M is smaller than a setting value, and S _N is larger than the setting value; for out-of-zone faults at the exit of the rectification station, S _M is greater than the set value and S _N is less than the set value. The proposed protection scheme is therefore substantially immune to the transition resistance and the fault distance. Meanwhile, simulation processing is carried out on a protection area of the whole line, 1000 omega is taken as an example of an in-area fault, a metallic grounding fault is taken as an example of an out-of-area fault, and a simulation result is shown in fig. 5.

From the observation of fig. 5, it can be seen that the difference between S _M and S _N in the internal and external faults is obvious, and the proposed protection scheme can still protect the whole length of the line even in the high-resistance ground fault in the area.

Example 2:

In order to further test the adaptability of the scheme to different topological systems, a four-port MMC model shown in FIG. 6 is built, and fault simulation verification is carried out by taking Line1 as an example.

The four-port network shown in fig. 6 is respectively provided with an intra-area fault (f ₁) and an external-area fault (f ₂、f₃), and simulation analysis is carried out on the proposed protection scheme, and the simulation results are shown in table 3.

Table 3 determination result of protection scheme under four-port MMC model

From the data in table 3, it can be seen that: the protection scheme is not influenced by the topological system structure, and has stronger transitional resistance tolerance.

The embodiment also provides a pilot protection device for the flexible direct current transmission line, which comprises:

at least one processor;

At least one memory for storing at least one program;

the at least one program, when executed by the at least one processor, causes the at least one processor to implement the method illustrated in fig. 5.

The pilot protection device for the flexible direct current transmission line can execute any combination implementation steps of the method embodiment of the flexible direct current transmission line pilot protection method provided by the method embodiment of the invention, and has corresponding functions and beneficial effects.

Embodiments of the present application also disclose a computer program product or computer program comprising computer instructions stored in a computer readable storage medium. The computer instructions may be read from a computer-readable storage medium by a processor of a computer device, and executed by the processor, to cause the computer device to perform the method shown in fig. 7.

The embodiment also provides a storage medium which stores instructions or programs for executing the pilot protection method of the flexible direct current transmission line, and when the instructions or programs are operated, the instructions or programs can execute any combination implementation steps of the method embodiment, and the method has corresponding functions and beneficial effects.

In some alternative embodiments, the functions/acts noted in the block diagrams may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Furthermore, the embodiments presented and described in the flowcharts of the present invention are provided by way of example in order to provide a more thorough understanding of the technology. The disclosed methods are not limited to the operations and logic flows presented herein. Alternative embodiments are contemplated in which the order of various operations is changed, and in which sub-operations described as part of a larger operation are performed independently.

Furthermore, while the invention is described in the context of functional modules, it should be appreciated that, unless otherwise indicated, one or more of the described functions and/or features may be integrated in a single physical device and/or software module or one or more functions and/or features may be implemented in separate physical devices or software modules. It will also be appreciated that a detailed discussion of the actual implementation of each module is not necessary to an understanding of the present invention. Rather, the actual implementation of the various functional modules in the apparatus disclosed herein will be apparent to those skilled in the art from consideration of their attributes, functions and internal relationships. Accordingly, one of ordinary skill in the art can implement the invention as set forth in the claims without undue experimentation. It is also to be understood that the specific concepts disclosed are merely illustrative and are not intended to be limiting upon the scope of the invention, which is to be defined in the appended claims and their full scope of equivalents.

The functions, if implemented in the form of software functional units and sold or used as a stand-alone product, may be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention may be embodied essentially or in a part contributing to the prior art or in a part of the technical solution, in the form of a software product stored in a storage medium, comprising several instructions for causing a computer device (which may be a personal computer, a server, a network device, etc.) to perform all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a usb disk, a removable hard disk, a Read-Only Memory (ROM), a random access Memory (RAM, random Access Memory), a magnetic disk, or an optical disk, or other various media capable of storing program codes.

Logic and/or steps represented in the flowcharts or otherwise described herein, e.g., a ordered listing of executable instructions for implementing logical functions, can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. For the purposes of this description, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.

More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic device) having one or more wires, a portable computer diskette (magnetic device), a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). In addition, the computer readable medium may even be paper or other suitable medium on which the program is printed, as the program may be electronically captured, via, for instance, optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner, if necessary, and then stored in a computer memory.

It is to be understood that portions of the present invention may be implemented in hardware, software, firmware, or a combination thereof. In the above-described embodiments, the various steps or methods may be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, may be implemented using any one or combination of the following techniques, as is well known in the art: discrete logic circuits having logic gates for implementing logic functions on data signals, application specific integrated circuits having suitable combinational logic gates, programmable Gate Arrays (PGAs), field Programmable Gate Arrays (FPGAs), and the like.

In the foregoing description of the present specification, reference has been made to the terms "one embodiment/example", "another embodiment/example", "certain embodiments/examples", and the like, means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiments or examples. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

While embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that: many changes, modifications, substitutions and variations may be made to the embodiments without departing from the spirit and principles of the invention, the scope of which is defined by the claims and their equivalents.

While the preferred embodiment of the present application has been described in detail, the present application is not limited to the above embodiments, and various equivalent modifications and substitutions can be made by those skilled in the art without departing from the spirit of the present application, and these equivalent modifications and substitutions are intended to be included in the scope of the present application as defined in the appended claims.

Claims

1. The pilot protection method for the flexible direct current transmission line is characterized by comprising the following steps of:

preliminary judgment is carried out according to the polar voltage, and the starting is protected when the starting criterion is met;

2. The flexible direct current transmission line pilot protection method according to claim 1, wherein a gradient of a polar voltage traveling wave is used as a starting criterion for protection, and a calculation formula of the gradient of the polar voltage traveling wave is as follows:

(ΔU_p>k_vU_ref)U(ΔU_n>k_vU_ref)＝1

3. The pilot protection method of a flexible direct current transmission line according to claim 1, wherein a calculation formula of a ratio of a current limiting reactance voltage at two sides of the line to a voltage at measuring points M, N at two sides is as follows:

Wherein U _Ldc1 is the line mode voltage at two ends of a direct current line left-side current-limiting reactor L _dc1, and U _Ldc2 is the line mode voltage at two ends of a direct current line right-side current-limiting reactor L _dc2; u _M1 is the line mode voltage at measurement point M, and U _N1 is the line mode voltage at measurement point N;

Rat _{Ldc1_M1} is the ratio of U _Ldc1 to U _M1, and Rat _{Ldc2_N1} is the ratio of U _Ldc2 to U _N1.

4. A pilot protection method for a flexible direct current transmission line according to claim 3, wherein a standard deviation coefficient of a ratio of a current limiting reactance voltage to a measuring point voltage at two sides of the line is calculated as follows:

5. The method for pilot protection of a flexible direct current transmission line according to claim 4, wherein the identifying the corresponding fault type according to the obtained standard deviation coefficient comprises:

Where K _set is the action threshold.

6. The flexible direct current transmission line pilot protection method according to claim 5, wherein the criteria for fault pole selection are as follows:

7. The flexible direct current transmission line pilot protection method according to claim 6, wherein the zero mode voltage U ₀ is calculated by:

8. The flexible direct current transmission line pilot protection method according to claim 6, wherein the performing the corresponding protection action comprises:

9. A flexible direct current transmission line pilot protection device, comprising:

at least one processor;

At least one memory for storing at least one program;

when the at least one program is executed by the at least one processor, the at least one processor is caused to implement a flexible direct current transmission line pilot protection method as claimed in any one of claims 1 to 8.

10. A computer readable storage medium, in which a processor executable program is stored, characterized in that the processor executable program is for performing a flexible direct current transmission line pilot protection method according to any of claims 1-8 when being executed by a processor.