Power secondary system island LEMP failure risk assessment method based on functional decomposition

Abstract

The invention discloses an electric power secondary system island LEMP failure risk assessment method based on functional decomposition, and the method comprises the steps: constructing a lightning electromagnetic pulse environment model with sea surface characteristics, and simulating the characteristics of lightning electromagnetic pulses; the energy density in the lightning discharge process is calculated based on the environment model, the equipment failure probability in the secondary system is determined, and a system state coefficient is obtained through mapping calculation; the method comprises the following steps: constructing a power secondary system function tree, decomposing the power secondary system function tree to obtain a system layer and n function layers, constructing a function diagram for each function in the nth function layer, carrying out failure probability evaluation based on the function diagram to obtain a failure probability of each function in the nth function layer, and then recurring from the nth function layer to the first function layer to obtain a failure probability of each function in the nth function layer; and the failure risk value of the whole power secondary system is obtained. According to the invention, cascading and systematic fault risk assessment on the whole system level can be realized. And the risk assessment precision and the engineering guiding significance can be improved.

Description

Technical Field

[0001] This invention relates to the field of power system secondary system risk assessment, and in particular to a method for assessing the failure risk of power secondary system islands based on functional decomposition (LEMP). Background Technology

[0002] Island microgrids, as independent power supply systems, play a vital role in ensuring energy supply and economic development on islands. However, due to their unique geographical location and climate, island microgrids are vulnerable to lightning electromagnetic pulses (LEMPs). LEMPs can affect the normal operation of the secondary power system through conduction and radiation. The safety risks of the secondary power system introduce many uncertainties to the safe operation of the primary power system, making the assessment of the risks of the secondary power system an urgent issue.

[0003] Current research on risk assessment for power secondary systems mainly explores three aspects: its impact on individual secondary equipment, information security, and human-caused risks. Regarding secondary equipment, various studies have been conducted on the impact of relay protection systems, control systems, and power communication networks on power system security risks. Regarding information security, cyber-physical system (CPS) network attack patterns have been studied. Based on quantitative assessments of cognitive reliability and human-caused reliability, a preliminary reliability assessment method for fully digital protection systems, considering both failure and repair, has been developed.

[0004] However, most of the above methods and studies are limited to single-dimensional risk assessment and do not propose a comprehensive assessment method for the impact of power secondary system failures on the power secondary system itself and the power primary system. Establishing a reliability block diagram of a system or equipment requires the experience of experts, which is highly subjective and has low universality. Summary of the Invention

[0005] To address the problems existing in the aforementioned background technology, this invention proposes a method for assessing the failure risk of secondary systems in island microgrids based on functional decomposition and LEMP (Lead-of-Mechanism for Electromagnetic Pulse) to describe the impact of lightning electromagnetic pulses on secondary systems. This invention constructs a mathematical model of a lightning electromagnetic pulse environment with sea surface characteristics to simulate the characteristics of lightning electromagnetic pulse LEMP. Based on the functional diagram obtained after functional decomposition, the concept of functional failure in the secondary system of an island microgrid is defined. The reliability block diagram-based assessment method is generalized, allowing direct calculation of the failure probability of functions from the functional diagram, thereby overcoming the aforementioned shortcomings.

[0006] This invention is achieved using the following technical solution:

[0007] A method for assessing the failure risk of a power secondary system island based on functional decomposition (LEMP) includes the following steps:

[0008] (1) Analyze the lightning electromagnetic pulse environment of the island microgrid, construct a lightning electromagnetic pulse environment model with sea surface characteristics, and simulate the characteristics of lightning electromagnetic pulse; calculate the energy density during the lightning discharge process based on the lightning electromagnetic pulse environment model with sea surface characteristics, determine the failure probability of equipment in the secondary system, and calculate the system state coefficients by mapping.

[0009] (2) Construct a functional tree of the power secondary system and decompose it to obtain a system layer and n functional layers. Construct a functional diagram for each function in the nth functional layer. Based on the functional diagram, evaluate the failure probability to obtain the failure probability of each function in the nth functional layer. Then, recursively deduce from the nth functional layer to the 1st functional layer to obtain the failure risk value of the entire power secondary system.

[0010] In the above technical solution, further, in (1), the Pierson-Moscowit sea spectrum model is used to simulate the energy of lightning electromagnetic pulses on the sea surface, and the fractal Brownian motion model is used to simulate the energy of lightning electromagnetic pulses on the natural land surface, so as to obtain the energy density of the environment in which the power secondary system is located.

[0011] Furthermore, in step (1), the electric field strength generated by lightning discharge is calculated based on the energy density during the lightning discharge process. This allows for the estimation of overvoltage generated in the primary power system. The transmission coupling voltage entering the secondary power system can be calculated based on the ratio of overvoltage to the secondary power system. By comparing this voltage with the equipment interference threshold and the equipment damage threshold, the failure probability of the equipment in the secondary power system can be obtained. The system state coefficient can be obtained through mapping calculation.

[0012] Furthermore, in (2), a power secondary system function tree is constructed; specifically, the power secondary system function tree includes systems and functions; the system is specifically defined as: based on business, it includes software and hardware, and is a set of functions with physical boundaries that can perform a series of comprehensive tasks; the function is specifically defined as a set of information and physical devices in the system that independently perform a certain task.

[0013] Furthermore, step (2) of constructing a function graph for each function in the nth functional layer is specifically as follows:

[0014] The function diagram is obtained by decomposing each function. The elements in the function diagram include: entities, logical nodes and logical connections.

[0015] The entities specifically refer to: secondary equipment and power software that objectively exist in the power secondary system;

[0016] Specifically, the logical node is the smallest part of the power secondary system that exchanges data or performs tasks; it is an abstraction of the behavior and methods of secondary equipment and power software.

[0017] Logical connection: The communication link between logical nodes is the path for information transmission.

[0018] Furthermore, failure probability assessment is performed based on the functional diagram to obtain the failure probability of each function in the nth functional layer. Then, the risk value of the entire system is obtained by recursively calculating from the nth functional layer to the 1st functional layer.

[0019] For a power secondary system containing n functional layers, the calculation of the risk value of the entire system is specifically expressed as follows:

[0020]

[0021] In the formula: R SYS S represents the risk value of the entire system. condition These are the system state coefficients; Let be the failure probability of the j-th function in the first functional layer. Its weight; k1 is the total number of functions in the first functional layer of the system; k represents the failure probability of the i-th function in the m-th functional layer. m,i Let be the number of functions in the next functional layer contained in the i-th function of the m-th functional layer; Let be the failure probability of the j-th function in the next functional layer corresponding to the i-th function in the (m+1)-th functional layer. Its weight.

[0022] Furthermore, the method for calculating the failure probability of each function in the nth functional layer includes: 1) evaluating the failure probability of each logical node and logical connection in the functional diagram, 2) then constructing a function describing the functional state with respect to the logical node and logical connection states, and 3) finally calculating the functional failure probability of each function.

[0023] Furthermore, 1) calculate the failure probability U of logical nodes and logical connections:

[0024]

[0025] In the formula: f represents the number of times the power supply has failed since it was put into operation; T MTTR The mean repair time (h) for each power outage; T is the operating time since power was put into operation; e ij It is a variable that represents the logical connection state from logical node i to logical node j, v i This refers to the state of logical node i.

[0026] Furthermore, 2) Construct a function describing the functional state with respect to the logical node state and logical connection state: First, establish its adjacency matrix based on the topological relationship of the functional graph to represent the interconnection between logical nodes; the order of the adjacency matrix is ​​equal to the number of logical nodes in the functional graph; all diagonal elements of the adjacency matrix are 1, and the off-diagonal elements are N. ij It is given by the following formula:

[0027]

[0028] Among them, e ij It is a variable that represents the logical connection state from logical node i to logical node j, e ij ∈{0,1};

[0029] Next, the rows and columns corresponding to the intermediate nodes of the function graph in the adjacency matrix are eliminated one by one, resulting in the off-diagonal elements N′ of the new adjacency matrix. ij The off-diagonal elements N of the original adjacency matrix ij The following relationship exists:

[0030] N′ ij =N ij +N ik ·N kj

[0031] Where, N ik This represents the connection between logical node i in the original adjacency matrix and the eliminated intermediate node k, with a value of 1 or 0, N. kj This represents the connection between the eliminated intermediate node k and the logical node j in the original adjacency matrix, with a value of 1 or 0; the diagonal elements of the new adjacency matrix are 1;

[0032] Let the nodes numbered 1 to p in the functional graph be the first nodes, and the nodes numbered q to n be the last nodes. After eliminating all the intermediate nodes, we obtain a new adjacency matrix, specifically represented as follows:

[0033]

[0034] In the formula, N pn N′ represents the probability of effective information transmission from the first node p to the last node n; u Perform a logical AND operation on all non-zero elements in the array to obtain the function expression of the transition state G' with respect to the logical connection state N when all logical nodes V are working normally:

[0035]

[0036] Rewriting the transition state G' as an AND-OR expression yields the following equation:

[0037]

[0038] In the formula, G′ i =Πe ij In the G' expression, each logical connection is recorded only once.

[0039] The functional state G is expressed as a function of the logical node state V and the logical connection state N:

[0040]

[0041] G i =Πe ij v i v j

[0042] v i and v j These represent the states of the two logical nodes at the two ends of the logical connection, with values ​​of either 0 or 1.

[0043] Furthermore, 3) calculate the failure probability of the function:

[0044] Calculate the probability of the function being in a normal state using the probability formula for the sum of events:

[0045]

[0046] Subtracting the result of the above formula from 1 gives the probability of functional failure.

[0047] The beneficial effects of this invention are as follows:

[0048] 1. This invention proposes a modeling method based on functional decomposition, replacing traditional equipment-level modeling methods that rely on expert experience with functional diagrams, and describing the operational structure of the power secondary system from the perspective of system function. This method overcomes the problems of strong subjectivity and large structural limitations in the modeling process of existing technologies, making the model more universal and scalable, while also facilitating standardization and promotion, effectively improving the scientific nature, repeatability, and cross-scenario adaptability of system modeling.

[0049] 2. This invention addresses the unique geographical and climatic conditions of island microgrids by constructing a targeted mathematical model of a lightning electromagnetic pulse environment specific to the sea surface, realistically simulating the interference characteristics of lightning electromagnetic pulses on secondary systems. Based on this, the concept of "functional failure" is proposed, and a quantifiable method for assessing the probability of functional failure is developed. This method can directly calculate the risk level of each function of the system under disturbance, thereby improving the accuracy of risk assessment and its engineering guidance significance.

[0050] 3. This invention automatically derives the failure probability of system functions based on functional diagram structures, enabling cascading and systemic fault risk assessment at the entire system level. Compared to existing analysis methods that focus on single devices or attack points, this method can capture global system risks caused by local functional failures, improving the comprehensiveness, foresight, and efficiency of fault analysis, and providing quantitative support and theoretical basis for the anti-disturbance design and operation and maintenance strategies of island power systems. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the tree structure of the system functions in this invention;

[0052] Figure 2 This is a flowchart of the functional failure probability assessment process in this invention;

[0053] Figure 3 This is a functional diagram of a specific example of the present invention. Detailed Implementation

[0054] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0055] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0056] According to a specific embodiment of the present invention, a method for assessing the failure risk of a power secondary system island based on functional decomposition (FD) is as follows:

[0057] First, the lightning electromagnetic pulse environment of the island microgrid is analyzed, and the evaluation method based on reliability block diagrams is extended to construct a mathematical model of the lightning electromagnetic pulse environment with sea surface characteristics. This allows for the direct calculation of the functional failure probability based on the functional diagram. Finally, the calculation process of the proposed evaluation method is illustrated using the measurement data acquisition function of the island microgrid's secondary system as an example.

[0058] 1. Construct a mathematical model of a lightning electromagnetic pulse environment with sea surface characteristics to simulate the properties of lightning electromagnetic pulses.

[0059] The Pierson-Moscowit ocean spectral model was used to simulate the energy of lightning electromagnetic pulses at the sea surface, as shown in the following formula:

[0060]

[0061] in This represents the energy density in the lightning electromagnetic pulse environment. γ and η are the radial wavenumbers along the x and y directions, respectively. αα and β are dimensionless empirical constants, α = 8.1×10 -3 , β = 0.74. g is the acceleration due to gravity, represents the wind speed at 19.5 m above the sea surface. θ is the angle between the wind direction and the wave propagation direction, and N(θ) is the directional distribution function related to the sea wind propagation direction.

[0062] The fractal Brownian motion model is used to simulate the magnitude of the lightning electromagnetic pulse energy on the natural land surface:

[0063] V(γ,η) = V0(γ 2 + η 2 ) -a / 2

[0064] where V0 = h / 2πL. a = 8 - 2D, D is the fractal dimension, and its value range is 2 < D < 3, which is used to characterize the roughness of the fractal rough surface. L and h are the root mean squares representing the correlation length and the correlation height respectively. The correlation length and the correlation height are both technical terms in topography and the field of fractal analysis. The correlation length is an index describing the self-similarity in space, indicating the maximum distance of the continuation of the self-similarity of the surface features within a certain scale range; the correlation height is used to quantify the height change or roughness of the surface within a specific scale range, and is used to reflect the vertical change of the terrain.

[0065] The lightning electromagnetic pulse causes overvoltage surges to the overhead lines in the primary power system. The overvoltage surges affect the equipment in the secondary power system through the cables, and the influence is reflected by the system status coefficient. The greater the energy density during the lightning discharge process, the stronger the generated electric field, and correspondingly, there will be a higher failure probability for the equipment and connecting cables in the secondary power system.

[0066] The calculation method of the system status coefficient is as follows:

[0067] First, calculate the electric field intensity from the energy density,

[0068]

[0069] estimate the overvoltage generated in the primary system,

[0070] V ov = k1·E·L

[0071] where k1 is the lightning coupling constant, and its general value range is 0.3 - 1.0. In this paper, the value is 0.5; L is the effective length of the overhead line, and the unit is meter.

[0072] Calculate the transfer coupling voltage transmitted to the secondary system,

[0073] V2nd =η·V ov

[0074] η is the ratio of overvoltage coupling to the secondary system, which is generally taken as 0.01-0.2, and is taken as 0.05 in this paper.

[0075] Finally, the probability of equipment failure is calculated, and the system state coefficients are calculated through mapping.

[0076]

[0077] S condition =S min +(S max -S min )·P fail

[0078] V th1 The interference threshold for the equipment is set to 30V in this paper; V th2 The equipment damage threshold is set at 200V in this paper; S min The minimum value of the system state coefficient is taken as 1 in this paper; S max The maximum value of the system state coefficient is 10, which is taken as the value in this paper; S condition That is, the system state coefficients.

[0079] 2. Decomposition of the power secondary system

[0080] 1) Construct the functional tree of the power secondary system

[0081] System: Distinguished by business function, it includes both software and hardware, has physical boundaries, and is a collection of functions capable of performing a series of integrated tasks. Specifically, it may include protection systems, measurement systems, control systems, communication systems, etc.

[0082] Function: A collection of information and physical devices that independently perform a specific task within a system. Specifically, for example: a protection system includes overcurrent protection, overvoltage protection, undervoltage protection, and differential protection; a measurement system includes the functions of energy meters, metering instruments, and oscilloscopes; a control system includes automation control, remote control, and telemetry functions; and a communication system includes digital communication, wireless communication, and fiber optic communication functions. For a complex system, a single function may encompass multiple functions. For instance, overcurrent protection in a protection system can be further subdivided into definite-time overcurrent protection, inverse-time overcurrent protection, directional overcurrent protection, and undervoltage-blocked overcurrent protection.

[0083] Based on the above definitions of system and function, such as Figure 1 The diagram shows a tree structure of system functions. As can be seen from the diagram, the system can be decomposed into a system layer and n functional layers.

[0084] 2) Construct a function diagram for each function in the nth functional layer.

[0085] Calculating the failure probability of the function is a crucial part of the entire risk assessment. Further decomposition of each function in the final functional layer yields a functional diagram, whose elements include entities, logical nodes, and logical connections.

[0086] Physical entities: The objectively existing secondary equipment and power software in the power secondary system.

[0087] Logical node: The smallest unit in a power secondary system that exchanges data or performs tasks. A logical node is an abstraction of the behavior and methods of secondary equipment and power software. For example, in a substation automation system, intelligent electronic devices responsible for collecting analog signals can be abstracted as current transformer logical nodes, voltage transformer logical nodes, etc.

[0088] Logical connection: A communication link between logical nodes, which is the path for information transmission. A logical connection can be viewed as an abstraction of a communication channel.

[0089] Functional diagrams reveal the logical connections, logical nodes, and information flow between each function.

[0090] (3) Based on the functional diagram, the failure probability is evaluated to obtain the failure probability of each function in the nth functional layer. Then, the failure probability is deduced from the nth functional layer to the 1st functional layer to obtain the risk value of the entire system.

[0091] First, we make the following assumptions:

[0092] Without considering the cascading effects of functional failures, each logical node and logical connection in a functional diagram has exactly two states: normal and failed. A functional diagram typically contains several head nodes and several tail nodes. If information can be correctly transmitted from a head node to a tail node, the connection is considered normal; otherwise, the connection is considered failed. If information received by a node can be correctly processed and sent to all subsequent connections of that node, the node is considered normal; otherwise, the node is considered failed. The states of each node and connection in a functional diagram are independent of each other.

[0093] If a path exists in the functional diagram from the first node to the last node, then the first node and the last node are said to be connected. If any last node in the functional diagram can correctly receive information from each first node connected to it, then the function is said to be completed normally; otherwise, the function is said to be failed. In the functional diagram, if all logical nodes and logical connections on a certain path are not failed, then the path is said to be valid, that is, the information generated by the first node can be correctly transmitted to the last node through this path.

[0094] Based on the above analysis, the necessary and sufficient condition for the function to complete normally is that there is at least one valid path between any pair of connected head nodes and tail nodes in the function graph.

[0095] Then, the failure probability of each logical node and logical connection in the function diagram is evaluated. Then, a function describing the functional state (functional normal or functional failure) with respect to the state of logical nodes and logical connections is constructed. Finally, the functional failure probability of each function is obtained.

[0096] For a power secondary system containing n functional layers, its risk value can be expressed by the following two formulas:

[0097]

[0098] In the formula: R SYS S represents the risk value of the entire system. condition The system state coefficient represents the current system status and characterizes the impact of the energy density in the electromagnetic field environment of the space where the current power secondary system is located on the system risk. The method of taking the value is shown in the table above. This refers to the risk of the j-th function in the first layer. Its weight; k1 is the total number of functions in the first layer of the system. Risk of the i-th function at layer m; k m,i Let be the number of sub-functions in the next layer contained in the i-th function of the m-th layer; The risk of the j-th sub-function of the i-th function at the m-th layer; Its weight.

[0099] In the above technical solution, the method for calculating the failure probability of each function in the nth functional layer is as follows:

[0100] 1) Calculate the failure probability of logical node V and logical connection E.

[0101] Currently, there is relatively little research on the reliability of power software operation. Historical statistics can be used to obtain the failure probability, which is assumed to be a constant value expressed as:

[0102]

[0103] In the formula: f represents the number of times the power supply has failed since it was put into operation; T MTTR The average repair time (h) for each power failure; T is the operating time since the power was put into operation.

[0104] 2) Construct a function describing the functional state G with respect to the logical node state V and the logical connection state N.

[0105] For ease of understanding, we first consider the function expression of the transition state G' with respect to the logical connection state N when all logical nodes are operating normally. We then construct an adjacency matrix based on the topological relationships of the function graph to represent the interconnections between logical nodes. The adjacency matrix is ​​a square matrix whose order is equal to the number of logical nodes in the function graph. Its diagonal elements are all 1s, and its off-diagonal elements are N. ij It is given by the following formula:

[0106]

[0107] Where e ij It is a variable that represents the logical connection state from node i to node j, e ij ∈{0,1}.

[0108] Next, the rows and columns corresponding to the intermediate nodes (neither the first nor the last node) in the adjacency matrix are eliminated one by one. After eliminating the intermediate node k, the rows and columns corresponding to node k in the original adjacency matrix are eliminated, and the order of the adjacency matrix is ​​reduced by 1. Let N′ ij N represents the off-diagonal elements of the new adjacency matrix. ij Let represent the off-diagonal elements of the original adjacency matrix, and the two have the following relationship:

[0109] N′ ij =N ij +N ik ·N kj

[0110] Where, N ik This represents the connection between logical node i in the original adjacency matrix and the eliminated intermediate node k, with a value of 1 or 0, N. kj This represents the connection between the eliminated intermediate node k and the logical node j in the original adjacency matrix. Its value is 1 or 0, and the diagonal elements of the new adjacency matrix remain unchanged at 1.

[0111] Let the nodes numbered 1 to p in the functional graph be the first nodes, and the nodes numbered q to n be the last nodes. After eliminating all the intermediate nodes, we obtain a new adjacency matrix, specifically represented as follows:

[0112]

[0113] In the above formula, N pn A non-zero value indicates the existence of a message transmission path from the first node p to the last node n. Since a functioning node is defined as all last nodes correctly receiving information from each first node connected to it, the block matrix N′ is... u Perform a logical AND operation on all non-zero elements in the expression to obtain the following formula:

[0114]

[0115] The above formula is the function of the transition state G' with respect to the logical connection state N when all logical nodes V are working normally.

[0116] After obtaining the functional expression of the transition state G' with respect to the logical connection state N, considering that the logical node V also has a certain failure probability, we obtain the functional expression of the functional state G with respect to the logical node state V and the logical connection state N.

[0117] To more concisely and clearly represent the influence of logical node V on functional state G, the transition state G' is rewritten as an AND-OR expression, resulting in the following formula:

[0118]

[0119] above formula G i 'by e ij The product of G constitutes i '=Πe ij In the expression G', each logical connection is recorded only once. The states of the logical nodes at both ends of the logical connection are v. i and v j The value can be either 0 or 1. Logical node v i and logical node v j The effect on the functional state G is expressed in a product form, i.e., G i =Πe ij v i v j e ij v i v j The specific value is calculated from the formula in the above-mentioned valid probabilities of logical nodes and logical connections.

[0120]

[0121] The above equation is a function of the functional state G with respect to the logical node state V and the logical connection state N. The necessary and sufficient condition for the function to complete normally is that at least one term on the right-hand side of the above equation has a value of 1.

[0122] 3) Probability of failure of calculation function

[0123] The following is a precise method for calculating the probability of functional failure. After obtaining the expression for the functional state G with respect to the logical node state V and the logical connection state N, the probability of the functional state being normal can be calculated using the probability formula for the sum of events:

[0124]

[0125] In the above equation, each term on the right-hand side of the second equal sign can be represented as the product of the probabilities of the corresponding logical nodes and logical connections functioning normally, thus yielding the probability of normal functionality. Subtracting the result from the above equation by 1 gives the probability of functional failure.

[0126] like Figure 2 The diagram shows the flowchart for assessing the probability of functional failure. The flowchart illustrates the entire process of calculating the probability of functional failure.

[0127] like Figure 3 The diagram shown is a functional diagram for a specific example, illustrating the relationship between logical links and logical nodes. The failure probabilities of logical nodes and logical links are shown in Tables 1 and 2. Uppercase letters V and E represent logical nodes and logical links in the functional diagram, respectively, while lowercase letters v and e represent the states of the corresponding nodes or links. Notably, the communication channel from node V7 to node V6 has redundant configuration, thus the failure probability of link E9 is relatively low.

[0128] Table 1 Failure Probability of Logical Nodes

[0129]

[0130] Table 2 Failure Probability of Logical Connections

[0131]

[0132] Eliminating nodes 4, 5, and 6 yields the simplified adjacency matrix.

[0133]

[0134] Therefore, G and H are shown in Table 3.

[0135] Table 3G′ i With Gi value

[0136]

[0137] The probability of the function being in normal condition can be obtained by precise calculation method, which is 0.982096, and the probability of the function failing is 0.017904.

[0138] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0139] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0140] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0141] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0142] The embodiments described above are merely some preferred embodiments of the present invention, and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for assessing the failure risk of a power secondary system island based on functional decomposition (FDM), characterized in that, Includes the following steps: (1) Analyze the lightning electromagnetic pulse environment of the island microgrid, construct a lightning electromagnetic pulse environment model with sea surface characteristics, and simulate the characteristics of lightning electromagnetic pulse; calculate the energy density during the lightning discharge process based on the lightning electromagnetic pulse environment model with sea surface characteristics, determine the failure probability of equipment in the secondary system, and calculate the system state coefficients by mapping. (2) Construct a functional tree of the power secondary system and decompose it to obtain a system layer and n functional layers. Construct a functional diagram for each function in the nth functional layer. Based on the functional diagram, evaluate the failure probability to obtain the failure probability of each function in the nth functional layer. Then, recursively deduce from the nth functional layer to the 1st functional layer to obtain the failure risk value of the entire power secondary system.

2. The method for assessing the failure risk of a power secondary system island based on functional decomposition, as described in claim 1, is characterized in that... In (1), the Pierson-Moscowit sea spectrum model is used to simulate the energy of lightning electromagnetic pulses on the sea surface, and the fractal Brownian motion model is used to simulate the energy of lightning electromagnetic pulses on the natural land surface, so as to obtain the energy density of the environment in which the power secondary system is located.

3. The method for assessing the failure risk of a power secondary system island based on functional decomposition, as described in claim 1, is characterized in that... In (1), the electric field strength generated by lightning discharge is calculated based on the energy density during the lightning discharge process. This allows for the estimation of overvoltage generated in the primary power system. The transmission coupling voltage entering the secondary power system can be calculated based on the ratio of overvoltage to the secondary power system. By comparing this voltage with the equipment interference threshold and the equipment damage threshold, the failure probability of the equipment in the secondary power system can be obtained. The system state coefficient can be obtained through mapping calculation.

4. The method for assessing the failure risk of a power secondary system island based on functional decomposition, as described in claim 1, is characterized in that... In (2), a power secondary system function tree is constructed; specifically, the power secondary system function tree includes systems and functions; the system is specifically defined as: based on business, it includes software and hardware, and is a set of functions with physical boundaries that can perform a series of comprehensive tasks; the function is specifically defined as: a set of information and physical devices in the system that independently perform a certain task.

5. The method for assessing the failure risk of a power secondary system island based on functional decomposition, as described in claim 1, is characterized in that... The process of constructing a function diagram for each function in the nth functional layer, as described in (2), is as follows: The function diagram is obtained by decomposing each function. The elements in the function diagram include: entities, logical nodes and logical connections. The entities specifically refer to: secondary equipment and power software that objectively exist in the power secondary system; Specifically, the logical node is the smallest part of the power secondary system that exchanges data or performs tasks; it is an abstraction of the behavior and methods of secondary equipment and power software. Logical connection: The communication link between logical nodes is the path for information transmission.

6. The method for assessing the failure risk of a power secondary system island based on functional decomposition, as described in claim 5, is characterized in that... Failure probability assessment is performed based on the functional diagram to obtain the failure probability of each function in the nth functional layer. Then, the risk value of the entire system is obtained by recursively deriving from the nth functional layer to the 1st functional layer. For a power secondary system containing n functional layers, the calculation of the risk value of the entire system is specifically expressed as follows: In the formula: R SYS S represents the risk value of the entire system. condition These are the system state coefficients; Let be the failure probability of the j-th function in the first functional layer. Its weight; k1 is the total number of functions in the first functional layer of the system; k represents the failure probability of the i-th function in the m-th functional layer. m,i Let be the number of functions in the next functional layer contained in the i-th function of the m-th functional layer; Let be the failure probability of the j-th function in the next functional layer corresponding to the i-th function in the (m+1)-th functional layer. Its weight.

7. The method for assessing the failure risk of a power secondary system island based on functional decomposition, as described in claim 5, is characterized in that... The calculation method for the failure probability of each function in the nth functional layer includes: 1) evaluating the failure probability of each logical node and logical connection in the functional diagram, 2) then constructing a function describing the functional state with respect to the logical node and logical connection states, and 3) finally calculating the functional failure probability of each function.

8. The method for assessing the failure risk of a power secondary system island based on functional decomposition according to claim 7, characterized in that, 1) Calculate the failure probability U of logical nodes and logical connections: In the formula: f represents the number of times the power supply has failed since it was put into operation; T MTTR The mean repair time (h) for each power outage; T is the operating time since power was put into operation; e ij It is a variable that represents the logical connection state from logical node i to logical node j, v i This refers to the state of logical node i.

9. The method for assessing the failure risk of a power secondary system island based on functional decomposition, as described in claim 8, is characterized in that... 2) Construct a function describing the functional state with respect to the logical node state and logical connection state: First, establish the adjacency matrix based on the topological relationship of the functional graph to represent the interconnections between logical nodes; the order of the adjacency matrix is ​​equal to the number of logical nodes in the functional graph; all diagonal elements of the adjacency matrix are 1, and the off-diagonal elements are N. ij It is given by the following formula: Among them, e ij It is a variable that represents the logical connection state from logical node i to logical node j, e ij ∈{0,1}; Next, the rows and columns corresponding to the intermediate nodes of the function graph in the adjacency matrix are eliminated one by one, resulting in the off-diagonal elements N′ of the new adjacency matrix. ij The off-diagonal elements N of the original adjacency matrix ij The following relationship exists: N′ ij =N ij +N ik ·N kj Where, N ik This represents the connection between logical node i in the original adjacency matrix and the eliminated intermediate node k, with a value of 1 or 0, N. kj This represents the connection between the eliminated intermediate node k and the logical node j in the original adjacency matrix, with a value of 1 or 0; the diagonal elements of the new adjacency matrix are 1; Let the nodes numbered 1 to p in the functional graph be the first nodes, and the nodes numbered q to n be the last nodes. After eliminating all the intermediate nodes, we obtain a new adjacency matrix, specifically represented as follows: In the formula, N pn N represents the probability of effective information transmission from the first node p to the last node n; u Perform a logical AND operation on all non-zero elements in G' to obtain the function expression of the transition state G' with respect to the logical connection state N when all logical nodes V are working normally: Rewriting the transition state G' as an AND-OR expression yields the following equation: In the formula, G' i =Πe ij In the G' expression, each logical connection is recorded only once. The functional state G is expressed as a function of the logical node state V and the logical connection state N: G i =Πe ij v i v j v i and v j These represent the states of the two logical nodes at the two ends of the logical connection, with values ​​of either 0 or 1.

10. The method for assessing the failure risk of a power secondary system island based on functional decomposition, as described in claim 9, is characterized in that... 3) Probability of failure of calculation function: Calculate the probability of the function being in a normal state using the probability formula for the sum of events: Subtracting the result of the above formula from 1 gives the probability of functional failure.

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