CN111652469B - Weak link identification method and system for alternating current-direct current hybrid power grid - Google Patents

Weak link identification method and system for alternating current-direct current hybrid power grid Download PDF

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CN111652469B
CN111652469B CN202010358036.2A CN202010358036A CN111652469B CN 111652469 B CN111652469 B CN 111652469B CN 202010358036 A CN202010358036 A CN 202010358036A CN 111652469 B CN111652469 B CN 111652469B
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饶宇飞
崔惟
李程昊
高泽
王建波
田春笋
王骅
高昆
刘巍
方舟
潘雪晴
刘芳冰
李晓萌
赵华
曹晓璐
黎量子
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Electric Power Research Institute of State Grid Henan Electric Power Co Ltd
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Abstract

The application relates to a weak link identification method and system for an alternating current-direct current hybrid power grid, and a vulnerability index calculation model for identifying the weak link of the alternating current-direct current hybrid power grid is constructed; establishing an equivalent topological structure of the alternating current-direct current series-parallel power grid to be identified; calculating identification parameters according to the equivalent topological structure, namely: counting the probability of faults of the power transmission lines in the power grid to be identified, calculating the ratio of the power flow transfer relevance of each power transmission line, calculating the voltage ratio of each bus node, and determining the relevance of each power transmission line and each bus node; and inputting the identification parameters into a vulnerability index calculation model, and calculating the vulnerability index of each power transmission link, wherein the higher the value of the vulnerability index is, the weaker the corresponding power transmission link is, so that the identification of the weak link is realized.

Description

Weak link identification method and system for alternating current-direct current hybrid power grid
Technical Field
The application belongs to the technical field of intelligent power grids, and particularly relates to a weak link identification method and system for an alternating current-direct current series-parallel power grid.
Background
The power resource is a resource which needs to be used in all industries nowadays, and has very important effects on the development of society and the construction of economy. Especially, in the aspects of enterprise production and daily life power consumption, higher requirements are placed on the reliability of the power grid, and the key for realizing the better development of the power distribution network work safety and the enterprise economy is that the power grid can normally run.
With the continuous development of social economy, the scale of the power grid in China is continuously enlarged, and particularly, the operation process of the power grid is continuously complicated by newly developed technical equipment such as extra-high voltage and large units. Therefore, management departments and personnel need to strengthen management work on the aspects of the operation safety and reliability of the power grid, not only need to strengthen supervision on the operation technology of the power grid, but also need to periodically evaluate the operation safety of the power grid, so that the operation safety degree of the power grid is continuously improved.
In the operation process of the power grid, a plurality of weak links often appear, and the links not only influence the normal operation of the power grid, but also bring great potential safety hazards to the operation of the power grid. Relevant managers need to take corresponding preventive measures for weak links in the operation process of the power grid, so that the occurrence of operation faults of the power grid system and the maintenance cost of the operation faults of the power grid are reduced, and the power grid is enabled to operate more economically, reliably and safely.
With the upgrade of the power grid structure in China, the ultra-high voltage alternating current and direct current hybrid connection becomes an important characteristic of power grid operation. The alternating current-direct current hybrid mode brings new challenges to the dispatching and running of the power grid, and increases the risk of cascading failures of the power grid and the difficulty of identification of weak links of the power grid. At present, the influence of direct current transmission is not fully considered in the identification of weak links of a power grid, the relevance of the weak links is not considered, and the direct current hybrid power grid is difficult to adapt to.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the method solves the problems that before cascading failures of the existing power system occur, weak links are difficult to identify, the direct-current transmission influence is not fully considered in the identification of the weak links of the existing power grid, the relevance of the weak links is not considered, and the alternating-current and direct-current series-parallel power grid is difficult to adapt.
The technical scheme adopted by the invention for solving the technical problems is as follows:
the invention provides a weak link identification method for an alternating current-direct current hybrid power grid, which comprises the following steps:
constructing a vulnerability index calculation model for identifying weak links of the AC/DC hybrid power grid, namely:
R ij ＝1000*C i L(i)U(j)Q ij
wherein R is ij The vulnerability index of the power transmission link; u (j) is the ratio of the voltage of the jth bus node; q ij Representing the degree of association between the ith transmission line and the jth bus node; l (i) represents the ratio of the power flow transfer relevance degree of the ith transmission line; c i Representing the probability of the fault of the ith transmission line;
establishing an equivalent topological structure of the alternating current-direct current series-parallel power grid to be identified;
calculating identification parameters according to the equivalent topological structure, namely: counting the probability of faults of the power transmission lines in the power grid to be identified, calculating the ratio of the power flow transfer relevance of each power transmission line, calculating the voltage ratio of each bus node, and determining the relevance of each power transmission line and each bus node;
and inputting the identification parameters into a vulnerability index calculation model, and calculating the vulnerability index of each power transmission link, wherein the higher the value of the vulnerability index is, the weaker the corresponding power transmission link is, so that the identification of the weak link is realized.
The invention provides a weak link identification system for an alternating current-direct current hybrid power grid in a second aspect, which comprises the following steps:
the model building module is used for building a vulnerability index calculation model for identifying weak links of the AC/DC hybrid power grid, namely:
R ij ＝1000*C i L(i)U(j)Q ij
wherein R is ij The vulnerability index of the power transmission link; u (j) is the ratio of the voltage of the jth bus node; q ij Representing the degree of association between the ith transmission line and the jth bus node; l (i) represents the ratio of the power flow transfer correlation degree of the ith transmission line; c i Representing the probability of the fault of the ith transmission line;
the equivalent topology module is used for establishing an equivalent topology structure of the alternating current-direct current series-parallel power grid to be identified;
a parameter calculating module, configured to calculate an identification parameter according to the equivalent topological structure, that is: counting the probability of faults of the power transmission lines in the power grid to be identified, calculating the ratio of the load flow transfer association degree of each power transmission line, calculating the voltage ratio of each bus node, and determining the association degree of each power transmission line and each bus node;
and the identification module is used for inputting the identification parameters into a vulnerability index calculation model and calculating the vulnerability index of each power transmission link, wherein the larger the value of the vulnerability index is, the weaker the corresponding power transmission link is, and therefore the identification of the weak link is realized.
The invention has the beneficial effects that: the method fully considers the influence of direct current transmission, identifies the weak link of the alternating current-direct current hybrid power grid, and provides reference for risk control and operation early warning of the power system.
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The technical solution of the present application is further explained below with reference to the drawings and the embodiments.
FIG. 1 is a flow chart of a method of an embodiment of the present application;
fig. 2 is a schematic diagram of an equivalent topology of a to-be-identified power grid according to an embodiment of the present application.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.
The technical solutions of the present application will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.
Example 1
The embodiment provides a weak link identification method for an alternating current-direct current hybrid power grid, which comprises the following steps:
s1, constructing a vulnerability index calculation model for identifying weak links of the AC/DC series-parallel power grid, namely:
R ij ＝1000C* i L(i)U(j)Q ij
wherein R is ij Is the vulnerability index of the power transmission link(ii) a U (j) is the ratio of the voltage of the jth bus node; q ij Representing the degree of association between the ith transmission line and the jth bus node; l (i) represents the ratio of the power flow transfer relevance degree of the ith transmission line; c i Representing the probability of the fault of the ith transmission line;
s2, establishing an equivalent topological structure of the alternating current-direct current hybrid power grid to be identified, and calculating identification parameters according to the equivalent topological structure, namely: counting the probability of faults of the power transmission lines in the power grid to be identified, calculating the ratio of the power flow transfer relevance of each power transmission line, calculating the voltage ratio of each bus node, and determining the relevance of each power transmission line and each bus node;
and S3, inputting the identification parameters into a vulnerability index calculation model, and calculating the vulnerability index of each power transmission link, wherein the higher the value of the vulnerability index is, the weaker the corresponding power transmission link is, so that the identification of the weak link is realized.
The step of establishing the equivalent topology structure of the alternating current-direct current hybrid power grid to be identified in this embodiment specifically includes:
firstly, determining a boundary range of a power grid to be identified; then, the power flow direction and the transmission power of a tie line in the alternating current and direct current hybrid power grid to be identified are counted, load equivalence is carried out, and an equivalent topology structure diagram of the alternating current and direct current hybrid power grid is formed.
Optionally, the step of counting the probability of the failure of the power transmission line in the power grid to be identified includes:
s201, counting the times of the power transmission line in different historical operating states to obtain the total times of the alternating current-direct current hybrid power grid to be identified in different historical operating states;
s202, counting the frequency of faults of each transmission line;
and S203, calculating the fault probability of each transmission line according to the total historical running state frequency and the fault frequency.
The operating state of the power system refers to the operating conditions of the system and the equipment of the power system under different operating conditions (such as load level, output configuration, system wiring, faults and the like). The operation state of the power system may be classified into a normal state, an abnormal state, and a fault state according to different operation conditions.
The counted times of the historical operating states in the embodiment are the sum of the times of occurrence of normal states, abnormal states and fault states in the counted historical operating conditions.
In this embodiment, count the frequency of shutting of every transmission line, the frequency of taking place the broken string and the frequency of short circuit trip to obtain the probability that every transmission line broke down, promptly:
Figure BDA0002474123800000061
wherein, C i Indicates the probability of the fault of the ith transmission line, N i Frequency of occurrence of blocking of ith transmission line, N i,d Frequency number N representing the disconnection of the ith transmission line i,t And the frequency of the short circuit trip of the ith power transmission line is represented, and N represents the total frequency of different historical operating states of the alternating-current and direct-current hybrid power grid to be identified.
Optionally, the step of calculating the ratio of the power flow transfer association degrees of the power transmission lines in this embodiment includes:
s211, setting the weight of each power transmission line;
this embodiment sets the weight α of the kth transmission line k 。
S212, calculating the power flow transfer rate of each power transmission line according to the weight of each power transmission line;
the load flow transfer rate of each power transmission line is calculated to be L in the embodiment ik Namely:
L ik ＝α k F k P i
wherein L is ik The power flow transfer rate is the power flow transfer rate and represents the power flow transfer relevance degree of the power transmission line i to the power transmission line k after the power transmission line i is out of operation due to faults, and the power transmission line i is directly connected with the power transmission line k; f k The absolute value of the change of the load factor k of the power transmission line caused by the fault of the power transmission line i is obtained; p i Is a transmission line i isAnd the active power per unit value in normal operation.
S213, calculating the ratio of the power flow transfer correlation degree of each transmission line, namely:
Figure BDA0002474123800000071
in the formula: n is a radical of 0 Total number of lines connected to transmission line i, N l The total number of lines included in the AC/DC power grid to be identified.
Optionally, the step of calculating the voltage ratio of each bus node includes:
s221, calculating the voltage sensitivity of each bus node in the power grid to be identified;
Figure BDA0002474123800000072
U lj after the reactive compensation capacity of the bus node l is changed, the voltage of the bus node j is changed, a direct connection line delta Q exists between the bus node l and the bus node j l For increased reactive compensation capacity, Δ U, at bus node l j To increase Δ Q l The corresponding voltage change value of the post bus node j.
S222, calculating the voltage ratio of each bus node, namely:
Figure BDA0002474123800000073
wherein M is 0 The total number of bus nodes M which are directly connected with one bus node l l The total number of bus nodes included in the power grid to be identified.
Optionally, the step of determining the association degree between each power transmission line and each bus node includes:
if the current power transmission line is directly connected with the corresponding bus node, determining that the association degree of the current power transmission line and the corresponding bus node is 1;
and if the current power transmission line is not directly connected with the corresponding bus node, determining that the association degree of the current power transmission line and the corresponding bus node is 0.5.
In this embodiment, the calculated identification parameters are input into a vulnerability index calculation model, and the vulnerability index of each power transmission link is calculated, wherein the larger the value of the vulnerability index is, the weaker the corresponding power transmission link is.
The following describes an embodiment of the present invention with a regional power grid as an identification object:
step 1: and establishing an equivalent topological structure of the AC/DC power grid to be identified.
As shown in fig. 2, in the equivalent topology structure established in this embodiment, there are 7 bus bar nodes (B1, B2, B3, B4, B5, B6, B7) and 6 transmission lines ((1), (2), (3), (4), (5), (6)), where the transmission line (1) between B1 and B2 is a dc transmission circuit, and the remaining 5 transmission lines ((2), (3), (4), (5), (6)) are ac transmission lines.
Step 2: and calculating the probability of the faults of the alternating current and direct current transmission lines.
The total number of times of historical operation states N =1000, and the frequency and probability of the faults of 6 transmission lines are shown in table 1:
TABLE 1 frequency and probability statistics
Frequency N i Frequency N i,d Frequency N i,t Probability C i
Line 1 2 0 0 2‰
Line 2 0 4 5 9‰
Line 3 0 2 0 2‰
Line 4 0 1 2 3‰
Line 5 0 2 2 4‰
Line 6 0 2 3 5‰
And step 3: and calculating the ratio of the power transmission line load flow transfer correlation degree.
Firstly, the power flow transfer rate of each power transmission line is calculated, as shown in table 2, a sparse matrix is formed, and then the ratio of each power transmission line is calculated.
TABLE 2 statistical table of power flow transfer rate and ratio
Line 1 Line 2 Line 3 Line 4 Line 5 Line 6 Ratio of
Line 1 / / / / / L 16 ＝0.5 L (1) ＝0.517
Line 2 / / L 23 ＝0.7 / L 25 ＝0.3 / L (2) ＝1.034
Line 3 / L 32 ＝0.4 / L 34 ＝0.2 L 35 ＝0.8 / L (3) ＝1.448
Line 4 / / L 43 ＝0.3 / / / L (4) ＝0.310
Line 5 / L 52 ＝0.4 L 53 ＝0.5 / / L 56 ＝0.5 L (5) ＝1.448
Line 6 L 61 ＝0.6 / / / L 65 ＝0.6 / L (6) ＝1.241
And 4, step 4: and calculating the voltage ratio of the bus bar nodes.
The voltage sensitivity was first calculated, as shown in table 3, to form a sparse matrix, and the voltage ratio was then calculated.
TABLE 3 statistical table of voltage sensitivity and ratio
Node 1 Node 2 Node 3 Node 4 Node 5 Node 6 Node 7 Ratio of
Node 1 / U 12 ＝0.5 / / / / / U (1) ＝0.625
Node 2 U 21 ＝0.8 / / / / / U 27 ＝0.6 U (2) ＝1.750
Node 3 / / / / / U 36 ＝0.4 / U (3) ＝0.500
Node 4 / / / / U 45 ＝0.2 / / U (4) ＝0.250
Node 5 / / / U 54 ＝0.3 / U 56 ＝0.3 U 57 ＝0.5 U (5) ＝1.375
Node 6 / / U 63 ＝0.7 / U 65 ＝0.6 / / U (6) ＝1.625
Node 7 / U 72 ＝0.3 / / U 75 ＝0.4 / / U (7) ＝0.875
And 5: and calculating the association degree of each transmission line and each bus node as shown in table 4.
TABLE 4 statistical table of degree of association
Node 1 Node 2 Node 3 Node 4 Node 5 Node 6 Node 7
Line 1 Q 11 ＝1 Q 12 ＝1 Q 13 ＝0.5 Q 14 ＝0.5 Q 15 ＝0.5 Q 16 ＝0.5 Q 17 ＝0.5
Line 2 Q 21 ＝0.5 Q 22 ＝0.5 Q 23 ＝0.5 Q 24 ＝1 Q 25 ＝1 Q 26 ＝0.5 Q 27 ＝0.5
Line 3 Q 31 ＝0.5 Q 32 ＝0.5 Q 33 ＝0.5 Q 34 ＝0.5 Q 35 ＝1 Q 36 ＝1 Q 37 ＝0.5
Line 4 Q 41 ＝0.5 Q 42 ＝0.5 Q 43 ＝1 Q 44 ＝0.5 Q 45 ＝0.5 Q 46 ＝1 Q 47 ＝0.5
Line 5 Q 51 ＝0.5 Q 52 ＝0.5 Q 53 ＝0.5 Q 54 ＝0.5 Q 55 ＝1 Q 56 ＝0.5 Q 57 ＝1
Line 6 Q 61 ＝0.5 Q 62 ＝1 Q 63 ＝0.5 Q 64 ＝0.5 Q 65 ＝0.5 Q 66 ＝0.5 Q 67 ＝1
Step 6: and identifying weak links.
Calculating the vulnerability index R ij As shown in table 5.
TABLE 5 vulnerability index statistics Table
Figure BDA0002474123800000091
Figure BDA0002474123800000101
As can be seen from Table 5, R 25 The value of =12.80 is the weakest link.
Example 2:
the embodiment provides a weak link identification system of alternating current-direct current series-parallel connection electric wire netting, includes:
the model building module is used for building a vulnerability index calculation model for identifying weak links of the AC/DC hybrid power grid, namely:
R ij ＝1000*C i L(i)U(j)Q ij
wherein R is ij The vulnerability index of the power transmission link; u (j) is the ratio of the voltage of the jth bus node; q ij Representing the degree of association between the ith transmission line and the jth bus node; l (i) represents the ratio of the power flow transfer relevance degree of the ith transmission line; c i Representing the probability of the fault of the ith transmission line;
the equivalent topology module is used for establishing an equivalent topology structure of the alternating current-direct current series-parallel power grid to be identified;
a parameter calculation module, configured to calculate an identification parameter according to the equivalent topological structure, that is: counting the probability of faults of the power transmission lines in the power grid to be identified, calculating the ratio of the load flow transfer association degree of each power transmission line, calculating the voltage ratio of each bus node, and determining the association degree of each power transmission line and each bus node;
and the identification module is used for inputting the identification parameters into a vulnerability index calculation model and calculating the vulnerability index of each power transmission link, wherein the larger the value of the vulnerability index is, the weaker the corresponding power transmission link is, and therefore the identification of the weak link is realized.
Further, the parameter calculation module comprises a failure probability statistic unit, which is used for counting the probability of failure of each transmission line in the power grid to be identified:
counting the times of the different historical operating states of the power transmission line to obtain the total times of the different historical operating states of the power grid to be identified;
counting the frequency of faults of each transmission line;
and calculating the probability of each transmission line failing according to the total historical operating state frequency and the frequency of the failures.
Further, the parameter calculation module includes a power transmission line ratio calculation unit, configured to calculate a ratio of the power transmission line load flow transfer association degrees:
setting the weight of each transmission line;
calculating the power flow transfer rate of each power transmission line according to the weight of each power transmission line;
calculating the ratio of the power flow transfer relevance of each transmission line, namely
Figure BDA0002474123800000111
In the formula: l is ik The power flow transfer rate is the power flow transfer rate and represents the power flow transfer relevance degree of the power transmission line i to the power transmission line k after the power transmission line i is out of operation due to faults, and the power transmission line i is directly connected with the power transmission line k; n is a radical of 0 The total number of the transmission lines connected with the transmission line i is; n is a radical of l The total number of the transmission lines included in the power grid to be identified.
Further, the parameter calculation module includes a bus node voltage ratio value for calculating the bus node voltage ratio value, namely:
calculating the voltage sensitivity of each bus node in the power grid to be identified;
calculating the voltage ratio of each bus node, namely:
Figure BDA0002474123800000121
wherein, U lj For the voltage sensitivity of the bus nodes, M 0 Total number of bus nodes M for a direct connection line to bus node l l And a direct connection line exists between the bus node l and the bus node j for the total number of the bus nodes contained in the power grid to be identified.
Further, the parameter calculation module includes a relevance determination unit, configured to determine a relevance between each power transmission line and each bus node:
if the current power transmission line is directly connected with the corresponding bus node, determining that the association degree of the current power transmission line and the corresponding bus node is 1;
and if the current power transmission line is not directly connected with the corresponding bus node, determining that the association degree of the current power transmission line and the corresponding bus node is 0.5.
Please refer to embodiment 1 for an implementation process of each module in this embodiment.
In light of the foregoing description of the preferred embodiments according to the present application, it is to be understood that various changes and modifications may be made without departing from the spirit and scope of the invention. The technical scope of the present application is not limited to the content of the specification, and must be determined according to the scope of the claims.

Claims (10)

1. A weak link identification method for an alternating current-direct current hybrid power grid is characterized by comprising the following steps:
constructing a vulnerability index calculation model for identifying weak links of the AC/DC hybrid power grid, namely:
R ij ＝1000*C i L(i)U(j)Q ij
wherein R is ij The vulnerability index of the power transmission link; u (j) is the ratio of the voltage of the jth bus node; q ij Representing the degree of association between the ith transmission line and the jth bus node; l (i) represents the ratio of the power flow transfer correlation degree of the ith transmission line; c i Representing the probability of the fault of the ith transmission line;
establishing an equivalent topological structure of the alternating current-direct current series-parallel power grid to be identified;
calculating identification parameters according to the equivalent topological structure, namely: counting the fault probability of each power transmission line in a power grid to be identified, calculating the ratio of the power flow transfer relevance of each power transmission line, calculating the voltage ratio of each bus node, and determining the relevance of each power transmission line and each bus node;
and inputting the identification parameters into a vulnerability index calculation model, and calculating the vulnerability index of each power transmission link, wherein the higher the value of the vulnerability index is, the weaker the corresponding power transmission link is, so that the identification of the weak link is realized.
2. The method for identifying the weak link of the alternating-current and direct-current hybrid power grid according to claim 1, wherein the step of counting the probability of the fault of the power transmission line in the power grid to be identified comprises the following steps:
counting the times of the different historical operating states of the power transmission line to obtain the total times of the different historical operating states of the alternating current-direct current hybrid power grid to be identified;
counting the frequency of faults of each transmission line;
and calculating the probability of each transmission line failing according to the total historical operating state frequency and the frequency of the failures.
3. The method for identifying the weak link of the alternating current-direct current hybrid power grid according to claim 1, wherein the step of calculating the ratio of the power flow transfer association degrees of the power transmission lines comprises the following steps of:
setting the weight of each transmission line;
calculating the power flow transfer rate of each power transmission line according to the weight of each power transmission line;
calculating the ratio of the power flow transfer relevance of each transmission line, namely
Figure FDA0003830093350000021
In the formula: l is ik The power flow transfer rate is the power flow transfer rate and represents the power flow transfer relevance degree of the power transmission line i to the power transmission line k after the power transmission line i is out of operation due to faults, and the power transmission line i is directly connected with the power transmission line k; n is a radical of 0 The total number of the transmission lines connected with the transmission line i is; n is a radical of l The total number of the transmission lines included in the power grid to be identified.
4. The method for identifying the weak link of the alternating-current and direct-current hybrid power grid according to claim 1, wherein the step of calculating the voltage ratio of each bus node comprises the following steps:
calculating the voltage sensitivity of each bus node in the power grid to be identified;
Figure FDA0003830093350000022
U lj after the reactive compensation capacity of the bus node l is changed, the voltage of the bus node j is changed, a direct connection line delta Q exists between the bus node l and the bus node j l For increased reactive compensation capacity, Δ U, at bus node l j To increase Δ Q l The corresponding voltage change value of the post bus node j;
and calculating the voltage ratio of each bus node, namely:
Figure FDA0003830093350000031
wherein, U lj For the voltage sensitivity of the bus nodes, M 0 Total number of bus nodes M for a direct connection line to bus node l l And a direct connection line exists between the bus node l and the bus node j for the total number of the bus nodes contained in the power grid to be identified.
5. The method for identifying the weak link of the alternating-current and direct-current hybrid power grid according to claim 1, wherein the step of determining the association degree between each power transmission line and each bus node comprises the following steps:
if the current power transmission line is directly connected with the corresponding bus node, determining that the association degree of the current power transmission line and the corresponding bus node is 1;
and if the current power transmission line is not directly connected with the corresponding bus node, determining that the association degree of the current power transmission line and the corresponding bus node is 0.5.
6. The utility model provides a weak link identification system of alternating current-direct current series-parallel connection electric wire netting which characterized in that includes:
the model building module is used for building a vulnerability index calculation model for identifying weak links of the AC/DC hybrid power grid, namely:
R ij ＝1000*C i L(i)U(j)Q ij
wherein R is ij For transmitting electricityVulnerability indexes of links; u (j) is the ratio of the voltage of the jth bus node; q ij Representing the degree of association between the ith transmission line and the jth bus node; l (i) represents the ratio of the power flow transfer relevance degree of the ith transmission line; c i Representing the probability of the fault of the ith transmission line;
the equivalent topology module is used for establishing an equivalent topology structure of the alternating current-direct current series-parallel power grid to be identified;
a parameter calculation module, configured to calculate an identification parameter according to the equivalent topological structure, that is: counting the probability of faults of the power transmission lines in the power grid to be identified, calculating the ratio of the load flow transfer association degree of each power transmission line, calculating the voltage ratio of each bus node, and determining the association degree of each power transmission line and each bus node;
and the identification module is used for inputting the identification parameters into a vulnerability index calculation model and calculating the vulnerability index of each power transmission link, wherein the larger the value of the vulnerability index is, the weaker the corresponding power transmission link is, and therefore the identification of the weak link is realized.
7. The weak link identification system of the alternating current-direct current hybrid power grid according to claim 6, wherein the parameter calculation module comprises a fault probability statistic unit for calculating the probability of each power transmission line in the power grid to be identified failing:
counting the times of the different historical operating states of the power transmission line to obtain the total times of the different historical operating states of the power grid to be identified;
counting the frequency of faults of each transmission line;
and calculating the probability of each transmission line failing according to the total historical operating state frequency and the frequency of the failures.
8. The weak link identification system of the ac-dc hybrid power grid according to claim 6, wherein the parameter calculation module includes a power transmission line ratio calculation unit, configured to calculate a ratio of the power flow transfer relevance degrees of the power transmission lines:
setting the weight of each transmission line;
calculating the power flow transfer rate of each power transmission line according to the weight of each power transmission line;
calculating the ratio of the power flow transfer relevance of each transmission line, namely
Figure FDA0003830093350000051
Wherein: l is ik The power flow transfer rate is the power flow transfer rate and represents the power flow transfer relevance degree of the power transmission line i to the power transmission line k after the power transmission line i is out of operation due to faults, and the power transmission line i is directly connected with the power transmission line k; n is a radical of 0 The total number of the transmission lines connected with the transmission line i is; n is a radical of l The total number of the transmission lines included in the power grid to be identified.
9. The weak link identification system for the ac-dc hybrid power grid according to claim 6, wherein the parameter calculation module includes a voltage ratio of the bus node, and is configured to calculate the voltage ratio of the bus node, that is:
calculating the voltage sensitivity of each bus node in the power grid to be identified;
Figure FDA0003830093350000052
U lj after the reactive compensation capacity of the bus node l is changed, the voltage of the bus node j is changed, a direct connection line delta Q exists between the bus node l and the bus node j l For increased reactive compensation capacity, Δ U, at bus node l j To increase Δ Q l The corresponding voltage change value of the post bus node j;
calculating the voltage ratio of each bus node, namely:
Figure FDA0003830093350000053
wherein, U lj For the voltage sensitivity of the bus nodes, M 0 Total number of bus nodes M for a direct connection line to bus node l l And a direct connection line exists between the bus node l and the bus node j for the total number of the bus nodes contained in the power grid to be identified.
10. The weak link identification system of the ac-dc hybrid power grid according to claim 6, wherein the parameter calculation module includes an association degree determination unit configured to determine an association degree between each transmission line and each bus node:
if the current power transmission line is directly connected with the corresponding bus node, determining that the association degree of the current power transmission line and the corresponding bus node is 1;
and if the current power transmission line is not directly connected with the corresponding bus node, determining that the association degree of the current power transmission line and the corresponding bus node is 0.5.
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