Background
The last circuit breaker of the converter station of the direct current transmission system is a key circuit breaker for connecting the direct current valve group with the alternating current transmission line, and the final circuit breaker mainly prevents overvoltage of the converter station caused by sudden load shedding of the converter station. The problem of insulation matching caused by overvoltage is one of the problems that the safe operation of the alternating current-direct current hybrid system must be considered seriously. The last circuit breaker is a key circuit breaker for connecting the direct current system and the alternating current system, and the tripping of the last circuit breaker can cause the disconnection of the direct current system and the alternating current system. Because a large amount of reactive compensation equipment on the converter bus cannot be cut off immediately, the direct current system can continue to charge the converter station bus. If the direct current system is not stopped in time, high overvoltage is formed in the converter station, and the safety of alternating current and direct current equipment is seriously influenced.
The final breaker protection mainly comprises two modes of lightning arrester type final breaker protection and switch state type final breaker protection. The lightning arrester type final breaker protection utilizes the energy consumption characteristic of the lightning arrester after the fault occurs to identify the fault condition. Therefore, the protection is a passive protection mode. It takes a certain time for the energy integral of the arrester to exceed a fixed value, which means that the equipment of the converter station still has to bear the impact of high-power overvoltage in the period, and the longer the action delay of the arrester type final breaker protection is, the greater the impact of high-power overvoltage is borne by the system equipment. The switch state type final breaker protection is an active protection mode for pre-judging the fault condition by utilizing the information before the fault, and converter station equipment does not need to bear fault threat for a certain time. And (4) protecting the final breaker in a switch state type, and judging which breakers are the last breakers from the valve bank to the AC line in advance according to the switch state information of the AC field uploaded to the pole control host. When the protection system sends a tripping command to the last breaker, an emergency shutdown command of the direct current converter station needs to be started first, the corresponding valve group is shut down, and then the tripping command is executed.
In an ac field of the existing dc engineering, a plurality of 2/3 connected ac lines are generally connected in series and parallel between buses, and in order to prevent an overvoltage problem caused by the false tripping of a final breaker, the final breaker needs to be determined according to the switching state of the ac field. In the initial research of foreign electrical equipment manufacturers, the final breaker of the valve group only needs to consider the switching state of an alternating current string where the valve group is located, and the method is irrelevant to other strings, and the method is proved to judge the incompleteness of logic and has the defect of missing judgment. At present, there are two main technical methods, namely a method for automatically judging the logic of the last circuit breaker based on matrixing and a method for judging the last circuit breaker based on path coincidence. The method for automatically judging the logic of the last circuit breaker in the matrixing mode is complex and low in efficiency. In order to avoid the risk of action tripping of the last circuit breaker caused by misoperation, the prior art designs a last circuit breaker index table, and an operator determines the last circuit breaker of an alternating current field in the operation mode by retrieving the index number of each working condition. The method through enumeration or data statistics has poor flexibility, the whole table needs to be refilled when an exchange string is expanded or the operation is quitted, the workload is large, and omission is easily caused when an index table is manually filled.
In addition, according to the path coincidence-based final breaker judgment method, all paths between the valve bank and the alternating current line are searched through a depth-first search algorithm, and the breaker with the occurrence frequency equal to the number of the paths is judged as the final breaker. The method has a certain reference value for solving the problem of intelligent judgment of the final breaker. However, when the number of paths between the valve block and the ac line is large, the amount of calculation of the final breaker determination method based on the path overlapping is large. In fact, a shortest path can be searched, the circuit breakers on the shortest path can be disconnected in sequence, and the last circuit breaker of the valve bank can be judged in real time by taking whether the shortest path exists from the valve bank to the alternating current line collection point as a judgment basis, so that the number of path searching is reduced, and the operation judgment efficiency is improved.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a valve group final breaker identification method based on Dijkstra algorithm, which can avoid a complicated judgment process of an enumeration identification method, so as to improve final breaker identification efficiency and accuracy. The technical scheme is as follows:
a valve group final breaker identification method based on Dijkstra algorithm comprises the following steps:
step 1: abstracting the alternating current field into a non-directional connected graph, determining the vertex and the edge of the non-directional connected graph according to the configuration of the alternating current field, and constructing an alternating current field adjacency matrix C; correcting the adjacent matrix C of the alternating current field according to the real-time state of the circuit breaker in the alternating current field;
step 2: setting a line collection vertex in an alternating current field as a source point and a certain valve group vertex in the alternating current field as a destination point, and obtaining a shortest path vertex set P between the line collection vertex and the valve group vertex through a Dijkstra algorithm;
and step 3: deleting the non-breaker vertexes in the shortest path vertex set P in the step 2; the shortest path vertex set P and the breaker vertex set U are intersected to obtain a shortest path breaker vertex set V only containing breaker vertexesCBI.e. VCB=P∩U;
And 4, step 4: judging the shortest path breaker peak set VCBWhether the set is an empty set; if the set is an empty set, the valve bank has no last circuit breaker; otherwise, entering step 5;
and 5: sequentially collecting vertexes V of shortest path breakerCBThe middle vertexes are set to be in an open state, and the adjacent moment of the alternating current field is updated according to the real-time state of the breakerC, according to the step 2, executing Dijkstra algorithm to continuously search the shortest path from the line collection vertex to the valve group;
step 6: judging whether the vertex set to be in an open state is the last breaker: if the shortest path exists between the line collection vertex and the valve group vertex, the vertex set to be in an open state is the last breaker; otherwise, the vertex set to the open state is not the last breaker; set V of breaker vertexes in shortest pathCBIf the time is empty, the judgment is finished; otherwise, return to step 5.
Further, the step 1 specifically comprises:
step 11: abstracting a main wiring diagram of the alternating-current field into a non-directional connected diagram G (V, E); wherein V ═ { V ═ V1,v2,…,vNThe vertex set of the undirected communication graph of the alternating current field is represented, N is the number of the vertices, and the vertex set comprises lines, valve banks, buses, junction points and circuit breakers of the alternating current field; e ═ E1,e2,…,eLThe method comprises the steps that (1) an edge set of an alternating-current field undirected connected graph is represented, L is the number of edges, and elements in the edge set represent that two vertexes in the undirected connected graph are directly connected;
step 12: if connection exists between two vertexes in the undirected connected graph and the two vertexes are in a closed state, an edge exists; otherwise, the edge does not exist; all the AC lines in the AC field are collected into a vertex, and the connection relationship between the vertexes is represented by an adjacency matrix C:
wherein, cijRepresenting a vertex viAnd vertex vjThe specific values of the connection relationship are as follows:
step 13: when the edge in the undirected connected graph is in a closed state, namely all the circuit breakers connected with the edge are in a closed state, the value of the edge in the adjacent matrix is kept unchanged; when the edge in the undirected connected graph is in an open state, namely a breaker connected with the edge is in an open state, the value of the edge in the adjacent matrix is modified to be infinity;
wherein, cij' is the value of the ac field adjacency matrix element modified according to the real-time status of the circuit breaker in the ac field.
Further, the specific step of searching the shortest path by using Dijkstra algorithm includes:
step 21: dividing the vertex set V into a vertex set S with the shortest path obtained and a vertex set T with the shortest path not determined, wherein S is the vertex V with the shortest path obtainedsWhere S is { vertex v of the shortest path has already been found }, S ═ vs}; storing Slave vertices v with distance array DsCurrent path length to other vertices, D ═ C (v)s) (ii) a Recording the shortest path by using an array P;
step 22: finding distance vertex v from distance array DsNearest vertex vkAdding it from set T to set S;
step 23: by vertex vkIs the middle point, if the vertex vsTo the vertex in the set T through the vertex vkLater than original without passing through vertex vkShort, the distance is modified, i.e. D [ v ]t]=min{D[vt],D[vk]+C(vk,vt) And modifying the path in the P;
step 24: repeating the steps 22 and 23 until the vertex is the valve group vertex, and terminating the searching process; otherwise, the search process will continue until all of the remaining vertices in set T are added to set S.
The invention has the beneficial effects that: the invention adopts graph theory technology, and converts an alternating current field into a non-directional connected graph by determining the vertex and the edge of the alternating current field in a direct current transmission system, thereby providing a universal modeling method suitable for the alternating current field with different structural characteristics, the change of the running mode of the alternating current field and the extension of direct current engineering; the method for identifying the final breaker is simple, all paths from the line collection vertex to the valve group vertex do not need to be traversed, and the operation efficiency of the self-adaptive judgment of the final breaker is improved. In conclusion, the method is simple and feasible, can adapt to the valve bank final breaker self-adaptive judgment under different alternating current field operation conditions, and is reliable, effective and strong in practicability.
Detailed Description
The invention is described in further detail below with reference to the figures and specific embodiments. Fig. 1 is a flowchart of a valve group final breaker identification method based on Dijkstra algorithm provided by the present invention, and the method includes the following steps:
step one, abstracting an alternating current field into a non-directional connected graph, determining the top point and the edge of the non-directional connected graph according to the configuration of the alternating current field, and correcting an adjacent matrix of the alternating current field according to the real-time state of a breaker in the alternating current field, wherein the concrete steps are as follows:
s1, abstracting the main wiring diagram of the AC field into a non-directional communication diagram G ═ (V, E), wherein V ═ { V ═ E1,v2,…,vNThe vertex set of the undirected communication graph of the alternating current field is represented, N is the number of the vertices, and the vertex set comprises lines, valve banks, buses, junction points and circuit breakers of the alternating current field; e ═ E1,e2,…,eLAnd (4) representing an edge set of the undirected connected graph of the alternating-current field, wherein L is the number of the edges, and elements in the edge set represent that two vertexes in the undirected connected graph are directly connected.
s2, if there is a connection between two vertices in the undirected connected graph and both vertices are in a closed state, an edge exists. Otherwise, the edge does not exist. It is particularly noted that the vertices of the circuit breaker equivalent are considered to be in the closed state, except that the states of the vertices are classified into the closed state and the open state. To simplify the search process, all ac lines in the ac field are collected as one vertex, and the connection relationship between vertices can be represented by an adjacency matrix C:
wherein, cijRepresenting a vertex viAnd vertex vjThe specific values of the connection relationship are as follows:
wherein, when the vertex v isiAnd vertex vjWhen directly connected, then element cij1. Vertex viAnd vertex vjWhen the same vertex is used, i equals j, then cij0. When the vertex v isiAnd vertex vjWhen not directly connected, the element cij=∞。
s3, when the side in the undirected connectivity graph is in a closed state, that is, the breakers connected to the side are in a closed state, the value of the side in the adjacency matrix remains unchanged. When the edge in the undirected connected graph is in an open state, namely the breaker connected with the edge is in an open state, the value of the edge in the adjacent matrix is modified to be infinity.
Wherein, cij' is the value of the ac field adjacency matrix element modified according to the real-time status of the circuit breaker in the ac field.
Step two, setting a line collection vertex in the alternating current field as a source point and a certain valve group vertex in the alternating current field as a destination point, and obtaining a shortest path vertex set P between the line collection vertex and the valve group vertex through a Dijkstra algorithm, wherein the specific search process is as follows:
s1, dividing the vertex set V into a vertex set S for which the shortest path has been found and a vertex set T for which the shortest path has not been determined, and storing the vertex set V by a distance array DsTo other vertexAnd D, recording the shortest path by using the P array according to the previous path length, wherein the matrix C is an adjacent matrix which is obtained in the step one and reflects the running condition of the real-time alternating current field.
S2, initialization, S ═ vertex v for which shortest path has been foundsT ═ T { vertex v for which shortest path has not been determined yett},D=C(vsAnd (b) recording the shortest path by the P array.
s3 finding distance vertex v from distance array DsNearest vertex vkIt is added from set T to set S.
s4, at vertex vkIs the middle point, if the vertex vsTo T middle vertex through vertex vkLater than original without passing through vertex vkShort, the distance is modified, i.e. D [ v ]t]=min{D[vt],D[vk]+C(vk,vt) And modify the path in P.
s5, repeating the steps s3 and s4 until the vertex is the valve group vertex, and terminating the searching process; otherwise, the search process will continue until all of the remaining vertices in set T are added to set S.
And step three, deleting the non-breaker vertexes in the shortest path vertex set P in the step two. The shortest path vertex set P and the breaker vertex set U are intersected to obtain a shortest path breaker vertex set V only containing breaker vertexesCBI.e. VCB=P∩U。
Step four, judging the peak set V of the breaker with the shortest pathCBWhether the set is an empty set; if the set is an empty set, the valve bank has no last circuit breaker; otherwise, go to step five.
Step five, if the shortest path breaker vertex set VCBIf not, sequentially setting all vertexes in the set to be in an open state, updating an adjacent matrix C of the alternating current field according to the real-time state of the breaker in the first step, and then continuously searching the shortest path from the line collection vertex to the valve bank according to the Dijkstra algorithm in the second step; next, the process proceeds to step six, and it is determined whether or not the vertex set to the open state is the last breaker.
Step six, if the circuit is stored between the line collection vertex and the valve group vertexIn the shortest path, the vertex set to the open state in step five is the last breaker, whereas the vertex set to the open state is not the last breaker. Set V of breaker vertexes in shortest pathCBIf the time is empty, the judgment is finished; otherwise, returning to the step five.
Example (c): fig. 2 shows an electrical main connection diagram of an ac farm, which includes 2 valve blocks P1 and P2, 2 buscouple breakers 5101 and 5102, 5011 to 5073 as bay string breakers, lines denoted by L1 to L7, and points of intersection of ac lines or valve blocks and ac strings denoted by T1 to T9.
In the initial stage of the dc engineering construction, only the first 6 intervals in the ac field of fig. 2 are put into operation, and thereby an adjacent matrix C of the ac field is established as follows:
the Dijkstra algorithm is used to obtain the set of shortest path vertices from the valve block P1 to the line collection point L as P ═ P1, T4,5033, B2,5013, T2, L.
This results in the shortest path breaker vertex set U corresponding to this set being {5013,5033 }. Setting the breakers in the set to be in an open state, setting row and column elements where the breakers are located in the adjacent matrix to be 0, continuously searching the shortest path from the valve group P1 to the line collection point L through a Dijkstra algorithm, and judging whether the breaker is the last breaker according to whether a path exists, wherein the judgment result of the last breaker is shown in table 1. Valve block P2 is processed in the same manner as above.
TABLE 1 Final Circuit breaker determination
As can be seen from table 1, after the valve group P1 deletes the breaker vertex in the shortest path breaker vertex set U, there is still a path from the valve group P1 to the line collection vertex L, i.e. the valve group P1 is still in electrical contact with the external ac line. So none of the breakers in the set U is the last breaker. Likewise, valve block P2 has no final circuit breaker.
When the direct current project is expanded, as the 7 th interval string in fig. 2 is put into operation, new row and column elements are added to the last column and the last row of the adjacent matrix of the alternating current field according to the connection relationship between the added vertex and the known vertex. In addition, when a certain interval string in the alternating current field is out of operation, the row and column elements where the string element is located are set to 0 from the adjacent matrix.
When the operation mode of the ac field is changed, as shown in fig. 2, the circuit breakers 5013, 5022, 5023, 5031, 5032, 5042, 5043 and 5052 in the ac field are in an open state, and the rest of the circuit breakers are in a closed state. In this mode of operation, the final breaker search results for the valve block P1 and the valve block P2 are shown in table 2.
TABLE 2 Final Circuit breaker determination
When the circuit breakers 5033, 5102, 5051 are opened, the valve block is disconnected from the ac line sink vertex, so these 3 circuit breakers are the last circuit breakers. After the circuit breakers 5053, 5061 are opened, the valve block remains connected to the ac line collection apex, so neither circuit breaker is the last circuit breaker.