Reliability assessment method and system for main connection of converter station in UHVDC system

Abstract

A method and system for evaluating the reliability of a UHVDC system converter station main wiring connection includes: calculating four state probabilities, namely, the normal state probability P0, the accident-removed state probability P1, the accident-unremoved state probability P2, and the maintenance state probability P3, for all components in a set N of components in the converter station main wiring system; obtaining an adjacency matrix A corresponding to the converter station main wiring system topology, directing adjacency matrix A to obtain a flow adjacency matrix C; then, using a deep search method to obtain a minimum path set for the converter station main wiring system, performing fault determination on the components in the minimum path set to obtain a minimum path cut set for the converter station main wiring system; and combining the minimum path cut set and the four state probabilities of all components in the component set N to calculate reliability evaluation indicators, including system failure probability and system failure frequency. Using a deep search algorithm to traverse the minimum path set for the converter station main wiring connection improves computational efficiency and ensures that no power paths are missed.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system safety, and in particular relates to a method and system for evaluating the reliability of main connections of a converter station in an ultra-high voltage direct current system based on a minimum path algorithm. Background Art

[0002] With the rise of large-scale DC energy transmission systems, an increasing number of projects are using UHVDC systems for long-distance, high-capacity power transmission. Converter stations are the core of the entire UHVDC system, and their proper operation is a prerequisite for safe and stable DC transmission. Faults such as DC blocking and commutation failure in converter stations can cause transient overvoltages on the converter station busbars of the sending grid and voltage drops in the receiving grid, threatening the stable operation of both the sending and receiving grids and, consequently, the safety of large-capacity, long-distance, interregional power transmission. Therefore, it is crucial to establish a converter station main connection reliability assessment method applicable to DC transmission systems to ensure safe and stable system operation and prevent DC system outages. Summary of the Invention

[0003] The present invention provides a method and system for evaluating the reliability of a main connection in a converter station of a UHVDC system. Based on a three-state component model, a four-state model is established for the main connection components. The four states include a normal state, a fault-uncleared state, a repaired state after fault clearing, and a planned maintenance state. Based on the four-state component model and in conjunction with state probability theory, a state transition matrix for each component is established and the state probabilities corresponding to the component states are calculated. An adjacency matrix A is established based on the converter station main connection topology. A is directed to obtain a flow adjacency matrix C. A deep search algorithm is then used to determine the minimum path set for the converter station main connection. Fault determination is performed on the minimum path set to obtain a minimum path cut set. A reliability evaluation index is constructed, including system failure probability and system failure frequency. Finally, based on the minimum path cut set, the four state probabilities of all components are input to calculate the reliability index for the converter station main connection. The present invention utilizes a deep search algorithm to traverse the minimum path set for the converter station main connection, significantly improving computational efficiency and ensuring that no power paths are missed. The method is applicable, comprehensive, and superior.

[0004] According to a first aspect of an embodiment of the present invention, a method for evaluating the reliability of a main connection of a converter station in an ultra-high voltage direct current system is provided, comprising:

[0005] Calculating four state probabilities of all components in the set N of components of the converter station main connection system, the four state probabilities including normal state probability P0, accident removal state probability P1, accident non-removal state probability P2, and maintenance state probability P3;

[0006] Determine an adjacency matrix A corresponding to the topological structure of the converter station main connection system, perform directionality processing on the adjacency matrix A to obtain a flow adjacency matrix C, use the flow adjacency matrix C to determine a minimum path set of the converter station main connection system through a depth search method, perform fault diagnosis on components in the minimum path set, and obtain a minimum path cut set set of the converter station main connection system;

[0007] Calculate reliability evaluation indicators of the converter station main connection system, where the reliability evaluation indicators include a system failure probability and a system failure frequency. The system failure probability is the sum of the failure probabilities of all minimum path cut sets in the minimum path cut set set, and the system failure frequency is the sum of the failure frequencies of all minimum path cut sets. A minimum path cut set includes n components, including m faulty components and nm normal components. The failure probability of this minimum path cut set is the product of the failure state probabilities of the m faulty components and the normal state probabilities of the nm normal components. The failure frequency of this minimum path cut set is the product of the system failure probability and the sum of the repair rates of the m faulty components. The failure state probability of the component is the probability corresponding to all states except the normal state.

[0008] According to a second aspect of an embodiment of the present invention, a system for evaluating the reliability of a main connection of a converter station in an ultra-high voltage direct current system is provided, comprising:

[0009] a state probability calculation module configured to calculate four state probabilities of all components in a set N of components of a main connection system of a converter station, wherein the four state probabilities include a normal state probability P0, an accident cleared state probability P1, an accident uncleared state probability P2, and a maintenance state probability P3;

[0010] a minimum path cut set acquisition module configured to determine an adjacency matrix A corresponding to a topological structure of a main connection system of a converter station, perform directionality processing on the adjacency matrix A to obtain a flow adjacency matrix C, use the flow adjacency matrix C to determine a minimum path set of the main connection system of the converter station through a depth search method, perform fault diagnosis on components in the minimum path set, and obtain a minimum path cut set of the main connection system of the converter station;

[0011] A reliability evaluation index calculation module is configured to calculate a reliability evaluation index of a converter station main connection system, wherein the reliability evaluation index includes a system failure probability and a system failure frequency. The system failure probability is the sum of the failure probabilities of all minimum path cut sets in the minimum path cut set set. The system failure frequency is the sum of the failure frequencies of all minimum path cut sets. A minimum path cut set includes n elements, including m faulty elements and nm normal elements. The failure probability of this minimum path cut set is the product of the failure state probabilities of the m faulty elements and the normal state probabilities of the nm normal elements. The failure frequency of this minimum path cut set is the product of the system failure probability and the sum of the repair rates of the m faulty elements. The failure state probability of the element is the probability corresponding to all states except the normal state.

[0012] According to a third aspect of an embodiment of the present invention, a device for evaluating the reliability of a main connection of a converter station in an ultra-high voltage direct current system is provided, comprising: a processor; and a memory for storing instructions executable by the processor; wherein the processor is configured to execute all or part of the steps of the method.

[0013] According to a fourth aspect of an embodiment of the present invention, there is provided a non-transitory computer-readable storage medium having a computer program stored thereon, wherein the computer program implements all or part of the steps of the method when executed by a processor. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments are briefly introduced below.

[0015] Figure 1 This is a flow chart of a method for evaluating the reliability of main connections in a converter station of an ultra-high voltage direct current system provided by one embodiment of the present invention.

[0016] Figure 2 A four-state relationship transition model diagram provided by one embodiment of the present invention.

[0017] Figure 3 A flowchart of obtaining the minimum path using a depth search method provided by one embodiment of the present invention.

[0018] Figure 4 This is the main wiring diagram of a converter station with dual 12-pulse series converters provided in one embodiment of the present invention.

[0019] Figure 5 、 Figure 6 This is a comparison chart of the result indicators of other methods provided in one embodiment of the present invention and the method of the present invention. DETAILED DESCRIPTION

[0020] The present invention is directed to the main wiring system of a converter station of an ultra-high voltage direct current system, and proposes a reliability assessment method, system, device and storage medium for the main wiring of a converter station of an ultra-high voltage direct current system based on a minimum path algorithm. First, a state model is established for the components in the main wiring. In order to fully consider the different states of the components in actual operation, a four-state model is adopted. This model fully considers the state characteristics of the components as well as factors such as the switching sequence and the operating mode. Secondly, the state probability of all states of each component is determined based on the state probability theory combined with the four-state model of the components. Then, based on the depth search method, a minimum path traversal is performed on the main wiring system of the converter station, and a minimum path cut set set in the system is obtained based on the fault analysis of the minimum path set. Finally, a reliability assessment index is constructed to calculate the reliability index of the obtained minimum path cut set set. The calculation results show the effectiveness and simplicity of the present invention.

[0021] Figure 1 The following is a flow chart of a method for evaluating the reliability of the main connection of a UHVDC system converter station. Figure 1 Each step shown is described in detail.

[0022] Step 1: Build a four-state model for all individual components in the main wiring system set N within the converter station. The four-state model includes the normal state N, the fault-cleared state R, the fault-uncleared state S, and the maintenance state M. Calculate the probability of each state for each individual component in set N: normal state probability P0, fault-cleared state probability P1, fault-uncleared state probability P2, and maintenance state probability P3. N includes the converter transformer, AC circuit breaker, signal collector, relay protection device, converter valve arm, DC circuit breaker, converter valve arrester, and smoothing reactor / filter.

[0023] Figure 2 A four-state relationship transition model diagram is shown, where λ1 is the probability of a component not being removed due to an accident, λ2 is the probability of a component being removed due to an accident, λ3 is the probability of a component planned maintenance, μ1 is the component planned maintenance and repair rate, μ2 is the maintenance and repair rate after the component accident is removed, and μ3 is the component accident removal and repair rate.

[0024] Combined with the state probability theory, the state transfer matrix H of any component is calculated from the probability λ1 of the component not being removed due to an accident, the probability λ2 of the component being removed due to an accident, the probability λ3 of the component planned maintenance, as well as the component accident removal and repair rate μ3, the component repair and overhaul rate μ2 after accident removal, and the component planned maintenance and repair rate μ1. By combining the mutually exclusive relationship between the four state probabilities, the probability values ​​P0, P1, P2 and P3 of the four states of all components are obtained.

[0025] The state transition matrix H of any element

[0026]

[0027] The mutually exclusive relationship between the four state probabilities is expressed as

[0028]

[0029] The method to obtain the probability values ​​of the four states of all components is:

[0030]

[0031] Step 2: Obtain the adjacency matrix A corresponding to the converter station main connection topology. Direct the adjacency matrix A to obtain the flow adjacency matrix C. Then, use the depth search method to obtain the minimum path set of the converter station main connection. Perform fault diagnosis on the components in the minimum path set to obtain the minimum path cut set.

[0032] The basic principle of using the deep search method to find the minimum path set of the main connection of the converter station is: after setting the starting node and the end node, use the defined flow adjacency matrix C to traverse each node, and by traversing and searching each row and column of the matrix, all the power propagation paths of each starting point and end point are obtained. Figure 3 The process of obtaining the minimum path in step 2 is explained in detail.

[0033] Step 2.1: Obtain the adjacency matrix A based on the components of the UHVDC converter station system topology. Direct the adjacency matrix A with the power transmission direction as the positive direction to obtain the flow adjacency matrix C.

[0034] Step 2.2: After the flow adjacency matrix C is input, set the number of the first minimum path search to i=1, assign the number of the system sending power supply to j=1, and define the number of the element adjacent to the sending power supply as k, and the original input of k is 1.

[0035] Step 2.3: Flow to the element C of the adjacency matrix jk Perform "0-1" judgment; if C jk =1, it indicates that the component with the original input number k is adjacent to the source node. Otherwise, k is reassigned. If the judgment result is an adjacent relationship, component k is used as the new source node and a new component adjacent to component k is searched.

[0036] The first element connected to the sending power supply j in the i-th minimum path is k. After finding element k, use k as the "sending power supply" in the second iteration, and let n = k. Here n means the "sending power supply" of each subsequent iteration starting from k, and l is the element used to determine whether the "sending power supply" is connected in each new iteration.

[0037] Step 2.4: Set the receiving-end power source of the UHVDC transmission system as a confluence node, and repeat the above steps 2.2-2.3 until it is determined whether the current search element is a confluence node to determine the end of the search for this minimum path channel.

[0038] Step 2.5: Determine whether the number of source nodes has been completely traversed. If not, reassign i and j, and run the above steps 2.2, 2.3, and 2.4 again to search.

[0039] Step 2.6: Change the direction of the undirected component and repeat the minimum path search work of the above five steps 2.2, 2.3, 2.4, and 2.5.

[0040] Step 3: The minimum path cut sets for the converter station main wiring are obtained through Step 2. A reliability evaluation index is constructed, which includes the system failure probability and system failure frequency. To calculate the reliability evaluation index, the minimum path cut sets for the converter station main wiring must be substituted into the minimum path cut sets. For example, if a minimum path cut set contains n components, including m faulty components and nm normal components, the failure probability of this minimum path cut set is the product of the fault state probabilities of the m faulty components and the normal state probabilities of the nm normal components. The failure frequency of this minimum path cut set is the product of the system failure probability and the sum of the repair rates of the m faulty components. A fault state is any state other than the normal operating state. The fault state probability is one of the following: the probability of the accident-cleared state P1, the probability of the accident-uncleared state P2, and the probability of the maintenance state P3. The sum of the failure probabilities of all minimum path cut sets in the minimum path cut set is the system failure probability. Similarly, the sum of the failure frequencies of all minimum path cut sets is the system failure frequency.

[0041] The calculation formulas for system failure probability and system failure frequency in step 3 are:

[0042]

[0043]

[0044] Where, P F is the failure probability in the minimum path cut set failure, m is the number of faulty components, P k (x j ) is the state probability corresponding to the fault state of the faulty component, n is the number of components involved in the minimum path, P0(i) is the normal state probability of the remaining normal components in the minimum path cut set, μ k (x j ) is the repair probability corresponding to the faulty component, j is the number of the faulty component involved in the fault of this minimum path cut set, i is the number of the normal component in this minimum path cut set except the faulty component, x mAccording to the minimum path cut set, the four state probability values ​​of all components are input and the reliability index results of the main connection of the converter station are calculated.

[0045] In an exemplary embodiment, a reliability assessment system for a UHVDC system converter station main connection is also provided. The system includes a state probability calculation module, a minimum path cut set acquisition module, and a reliability assessment index calculation module. The state probability calculation module is configured to perform all or part of step 1 above. The minimum path cut set acquisition module is configured to perform all or part of step 2 above. The reliability assessment index calculation module is configured to perform all or part of step 3 above.

[0046] In an exemplary embodiment, a device for evaluating the main connection reliability of a converter station in an ultra-high voltage direct current system is also provided, the device comprising: a processor; a memory for storing instructions executable by the processor; wherein the processor is configured to execute all or part of the steps of the above method.

[0047] In an exemplary embodiment, a non-transitory computer-readable storage medium is further provided, on which a computer program is stored. When the computer program is executed by a processor, the computer program implements all or part of the steps of the above method. For example, the non-transitory computer-readable storage medium may be a ROM, RAM, CD-ROM, magnetic tape, floppy disk, or optical data storage device.

[0048] Figure 4 The main wiring diagram of a converter station with dual 12-pulse series converters is shown. The following uses a bipolar dual 12-pulse series main wiring method for a high-voltage direct current transmission system as an example to calculate the reliability parameters of converter station equipment components published by the National Energy Administration of China, including the failure rate and repair rate of each equipment component in different states and the repair time of various faults, as shown in Table (1).

[0049] Due to the influence of complex factors such as the actual operation of equipment, in order to simplify the calculation process, when conducting reliability assessment of the main wiring components of the HVDC transmission system, it is necessary to assume the following prerequisites:

[0050] (1) The failure rate and repair rate of the component are averaged over a period of time, that is, steady-state values, rather than variables that change over time;

[0051] (2) The connection mode of the converter station only considers bipolar dual 12-pulse series connection, and the operating states include bipolar operation, bipolar operation with monopole and one converter unit outage, monopole operation, monopole operation with monopole and one converter unit outage, and bipolar outage;

[0052] (3) The shutdown of any component after failure will not affect the normal operation of other equipment;

[0053] (4) Consider the case of double faults at most and ignore the set of outage events of triple faults and above.

[0054] Table (1) Component reliability parameters (times·(year·unit) -1 , h)

[0055]

[0056] Table (2) Annual time distribution of each operating status

[0057]

[0058] The reliability index of the main connection of the converter station is calculated based on the minimum path state model algorithm with a time period of one year. The probability of each operating mode of the HVDC system and the frequency of switching between each mode are obtained, as well as the continuous operating time in each operating mode, as shown in Table (2). The calculation indexes of the exponential distribution simulation method and the Wilson distribution simulation method are compared.

[0059] Table (2) above is the calculation of the operation mode of the bipolar dual 12-pulse series operation mode. Based on the four-state model and state probability of the components, the minimum path algorithm is combined to determine the path of each minimum path for the minimum cut set of this wiring mode. Based on the path, the state probability of each component included in each path channel is calculated. The calculated probabilities and frequencies of bipolar operation, unipolar operation, and bipolar shutdown operation modes are shown in Table (2). In order to verify this calculation result, it is compared with the calculation results of the exponential distribution simulation method and the Wilson distribution simulation method ( Figure 5 、 6 (Comparison diagram), the probability and frequency under bipolar operation mode are consistent, indicating that the calculation method based on the minimum path model and component state space has obvious advantages in the reliability assessment of HVDC transmission projects. It can reflect the reliability change trend of DC transmission projects under different operation modes and provide a reliability basis for the maintenance and operation of HVDC transmission projects.

Claims

1. A method for evaluating the reliability of main connections in a UHVDC system converter station, characterized in that: include: Calculating four state probabilities of all components in the set N of components of the converter station main connection system, the four state probabilities including normal state probability P0, accident removal state probability P1, accident non-removal state probability P2, and maintenance state probability P3; Determine an adjacency matrix A corresponding to the topological structure of the converter station main connection system, perform directionality processing on the adjacency matrix A to obtain a flow adjacency matrix C, use the flow adjacency matrix C to determine a minimum path set of the converter station main connection system through a depth search method, perform fault diagnosis on components in the minimum path set, and obtain a minimum path cut set set of the converter station main connection system; Calculate reliability evaluation indicators of the converter station main connection system, where the reliability evaluation indicators include a system failure probability and a system failure frequency. The system failure probability is the sum of the failure probabilities of all minimum path cut sets in the minimum path cut set set, and the system failure frequency is the sum of the failure frequencies of all minimum path cut sets. A minimum path cut set includes n components, including m faulty components and nm normal components. The failure probability of this minimum path cut set is the product of the failure state probabilities of the m faulty components and the normal state probabilities of the nm normal components. The failure frequency of this minimum path cut set is the product of the system failure probability and the sum of the repair rates of the m faulty components. The failure state probability of the component is the probability corresponding to all states except the normal state.

2. The method for evaluating the reliability of the main connection of a UHVDC system converter station according to claim 1, characterized in that: The state transfer matrix H of any element in the element set N is calculated based on the probability λ1 of the component not being removed due to an accident, the probability λ2 of the component being removed due to an accident, and the probability λ3 of the component planned maintenance, as well as the component accident removal and repair rate μ3, the component repair and overhaul rate μ2 after accident removal, and the component planned maintenance and repair rate μ1. The mutually exclusive relationship between the four state probabilities is combined to obtain the probability values ​​P0, P1, P2 and P3 of the four states of all elements in the element set N.

3. The method for evaluating the reliability of the main connection of a UHVDC system converter station according to claim 2, characterized in that: The state transfer matrix H: The mutually exclusive relationship between the four state probabilities is expressed as: The four state probabilities P0, P1, P2 and P3 are:

4. The method for evaluating the reliability of the main connection of a UHVDC system converter station according to claim 1, characterized in that: The method for obtaining the minimum path set of the main connection system of the converter station through the deep search method is as follows: after setting the starting node and the end node, traverse each node of the flow adjacency matrix C, and by traversing and searching each row and column of the matrix, all the power propagation paths between each starting point and end point are obtained, which are the minimum path set.

5. A UHVDC system converter station main connection reliability assessment system, characterized in that: include: a state probability calculation module configured to calculate four state probabilities of all components in a set N of components of a main connection system of a converter station, wherein the four state probabilities include a normal state probability P0, an accident cleared state probability P1, an accident uncleared state probability P2, and a maintenance state probability P3; a minimum path cut set acquisition module configured to determine an adjacency matrix A corresponding to a topological structure of a main connection system of a converter station, perform directionality processing on the adjacency matrix A to obtain a flow adjacency matrix C, use the flow adjacency matrix C to determine a minimum path set of the main connection system of the converter station through a depth search method, perform fault diagnosis on components in the minimum path set, and obtain a minimum path cut set of the main connection system of the converter station; A reliability evaluation index calculation module is configured to calculate a reliability evaluation index of a converter station main connection system, wherein the reliability evaluation index includes a system failure probability and a system failure frequency. The system failure probability is the sum of the failure probabilities of all minimum path cut sets in the minimum path cut set set. The system failure frequency is the sum of the failure frequencies of all minimum path cut sets. A minimum path cut set includes n elements, including m faulty elements and nm normal elements. The failure probability of this minimum path cut set is the product of the failure state probabilities of the m faulty elements and the normal state probabilities of the nm normal elements. The failure frequency of this minimum path cut set is the product of the system failure probability and the sum of the repair rates of the m faulty elements. The failure state probability of the element is the probability corresponding to all states except the normal state.

6. The UHVDC system converter station main connection reliability assessment system according to claim 5, characterized in that: The state transfer matrix H of any element in the element set N is calculated based on the probability λ1 of the component not being removed due to an accident, the probability λ2 of the component being removed due to an accident, and the probability λ3 of the component planned maintenance, as well as the component accident removal and repair rate μ3, the component repair and overhaul rate μ2 after accident removal, and the component planned maintenance and repair rate μ1. The mutually exclusive relationship between the four state probabilities is combined to obtain the probability values ​​P0, P1, P2 and P3 of the four states of all elements in the element set N.

7. The UHVDC system converter station main connection reliability assessment system according to claim 6, characterized in that: The state transfer matrix H: The mutually exclusive relationship between the four state probabilities is expressed as: The four state probabilities P0, P1, P2 and P3 are:

8. The UHVDC system converter station main connection reliability assessment system according to claim 6, characterized in that: The method for obtaining the minimum path set of the main connection system of the converter station through the deep search method is as follows: after setting the starting node and the end node, traverse each node of the flow adjacency matrix C, and by traversing and searching each row and column of the matrix, all the power propagation paths between each starting point and end point are obtained, which are the minimum path set.

9. A device for evaluating the reliability of main connections of a converter station in a UHVDC system, characterized in that: include: processor; a memory for storing instructions executable by the processor; The processor is configured to execute the steps of the method according to any one of claims 1 to 4.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 4 are implemented.

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