Power distribution network extension planning method and system based on improved reliability explicit expression

Abstract

The invention discloses a power distribution network extension planning method and system based on improved reliability explicit expression, and belongs to the technical field of power distribution network planning. The method comprises the following steps that source load time-varying characteristics are considered, a reliability explicit expression model is provided, constraint conditions comprise fault influence recognition constraint, recovery strategy modeling constraint, DG operation constraint, energy storage operation constraint and power flow constraint, model variables comprise control variables and state variables, and the model variables are used for representing reliability indexes; embedding the reliability index into the power distribution network expansion planning model in a constraint form, wherein constraint conditions comprise equipment construction constraint, reliability index constraint and normal operation power flow constraint; and solving the model to generate a planning scheme which meets the reliability constraint and is optimal in economical efficiency. According to the method provided by the invention, the reliability evaluation refinement level of the active power distribution network can be effectively improved, redundant investment is avoided, the planning economy is improved, the solving time is remarkably shortened, and the method has good expandability and engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of distribution network planning technology, and in particular relates to a distribution network extended planning method and system based on improved reliability explicit expression. Background Technology

[0002] To balance the economic efficiency and reliability of the planning scheme, the planning model should incorporate a reliability assessment process during optimization. Network reconfiguration and islanding operation, as key means of restoring power supply after a fault, should also be included in the reliability assessment process.

[0003] There are three main types of distribution network expansion planning methods that consider reliability: using "N-1" rigid reliability constraints, heuristic optimization planning, and reliability explicit expression model embedded planning.

[0004] The "N-1" rigid reliability constraint ensures that all loads can be transferred through network reconfiguration in the event of a failure in any feeder, but it is prone to excessive margin. Heuristic optimization planning methods, which first randomly generate planning schemes, then verify reliability indicators, and iteratively solve for the optimal network structure, result in excessively long solution times, difficulty in convergence, and inability to guarantee global optimality.

[0005] To overcome the limitations of traditional reliability assessment algorithms that rely on pre-defined network topologies, explicit analytical expressions can be constructed between network topology configuration variables and system reliability indices. These expressions embed reliability constraints into the planning model, achieving synergistic optimization of economy and reliability, and avoiding the risk of suboptimal solutions and convergence uncertainties caused by decoupled solutions. However, existing research on explicit reliability expressions has not yet considered the potential for active islanding operation of distributed generation (DG), which may underestimate the reliability of the distribution network and lead to redundant planning investments. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a distribution network expansion planning method and system based on improved reliability explicit expression.

[0007] The technical problem solved by this invention is achieved through the following technical solution:

[0008] A distribution network expansion planning method based on improved reliability explicit expression specifically includes the following steps:

[0009] (1) Taking into account the time-varying characteristics of source load, a reliability explicit expression model is proposed that considers the collaborative restoration of load power supply by network reconstruction and multi-node islanding operation after a fault. The constraints of the reliability explicit expression model include fault impact identification constraints, recovery strategy modeling constraints, DG operation constraints, energy storage operation constraints and power flow constraints. The model variables include control variables and state variables, which are used to represent reliability indicators.

[0010] (2) The reliability index is embedded into the distribution network extended planning model in the form of constraints, with the goal of minimizing the total cost of each planning stage. The constraints of the distribution network extended planning model include equipment construction constraints, reliability index constraints and normal operation power flow constraints.

[0011] (3) Solve the model to generate a planning scheme that satisfies the reliability constraints and is economically optimal.

[0012] Furthermore, the model variables mentioned in step (1) include control variables and state variables, as detailed below:

[0013] Control variables include device configuration variables. ij : Indicates whether a branch road is planned for construction; branch road connectivity variable Indicates whether the main supply restoration area branch roads are connected and Indicates whether the branch roads in the isolated operating area are connected; node recovery variable

[0014] Indicates whether the main power supply recovery zone nodes are supplying power normally and Indicates whether the nodes in the isolated operation area are receiving power normally;

[0015] State variables include power flow variables P, Q, and V: representing the electrical operating states such as node voltages and branch power flows; branch state variables... Indicates whether a branch is connected; node status. Are nodes affected by faults and Whether the node is powered; auxiliary variables Indicates the affiliation of nodes, branch feeders, and This indicates whether DG can constitute an isolated source;

[0016] Equipment configuration variables are restricted by activation constraints that allow connection only after construction, limiting branch connectivity variables. Branch connectivity variables and node recovery variables are coupled together to determine the power supply path selection of nodes after a fault, i.e. whether the load can achieve power supply recovery through network reconfiguration or islanding operation. Control variables further determine the branch connectivity status and node power supply status, thereby determining the system power flow and reliability indicators. Therefore, power flow constraints, voltage constraints, and reliability constraints limit the feasible values ​​of control variables, forming a closed-loop coupling mechanism.

[0017] Furthermore, the constraints of the reliability explicit expression model, wherein the fault impact identification constraint is specifically as follows:

[0018] The fault impact identification constraints include:

[0019] variable The definition is as follows: When a fault occurs in branch xy and causes a power outage at node i, then

[0020] otherwise, Based on network topology, the above logic can be further expressed as follows: if and only if node i and the faulty branch xy belong to the same feeder f, then Conversely, Load power supply state variables Line state variables and auxiliary variables The mathematical relationship between them is as follows;

[0021]

[0022] In the formula: Ψ N For a set of nodes; Ψ F For the feeder set; Ψ L For the set of branches; Ψ SL This is the first section of the branch road assembly; Ψ LN For load nodes; NO is the normal scenario index; f is the feeder index;

[0023] Equations (1)-(2) ensure that each branch and each node belongs to only a single feeder; Equation (3) uses the connectivity of the first branch to determine its feeder affiliation; Equation (4) stipulates that a branch can only belong to a feeder when it is in a connected state; Equations (5)-(6) transmit the feeder affiliation based on the connectivity of the branch; Equation (7) gives the fault impact judgment condition, that is, when the faulty branch and the node belong to the same feeder, the node will lose power due to the fault impact.

[0024] Furthermore, the constraints of the reliability explicit expression model, wherein the modeling constraints of the recovery strategy are specifically as follows:

[0025] The modeling constraints for the recovery strategy include:

[0026]

[0027] In the formula: xy is the scenario index. When xy corresponds to branch ij, it represents the fault scenario of branch ij. When xy = NO, it represents the normal operating state of the system. In this section, xy represents the fault scenario. Variables The definition is: if node i's DG actively runs in an isolated state, then Conversely,

[0028] Equation (8) restricts only the constructed branch lines to be connected; Equations (9)-(10) constrain the connection states of the main power restoration area and the isolated area branch lines to be mutually exclusive; Equation (11) stipulates that nodes unaffected by faults should maintain power supply; Equations (12)-(13) ensure that both the main power restoration area and the isolated area operate radially; Equation (14) defines the overall connection state of the branch line, that is, when it is connected in the main power restoration area or the isolated area, it is considered connected; Equation (15) defines the power supply state of the node, that is, when it is supplying power in any area, it is considered to be supplying power normally; Equation (16) stipulates that the faulty branch line should remain disconnected until the fault is repaired.

[0029] Furthermore, the constraints of the reliability explicit expression model, including the DG operation constraints, energy storage operation constraints, and power flow constraints between the main power recovery zone and the islanded zone, are as follows:

[0030] The DG operating constraints include:

[0031]

[0032] In the formula: The parameter is used to characterize whether the DG output of node i can meet the load demand of that node; when the DG generation power of node i is not less than its load power, otherwise,

[0033] This section of constraints is used to characterize the grid-connected and islanded operation strategies of DG, ensuring that the operation logic is reasonable and limiting its output range: Equation (17) indicates that grid-connected operation and islanded operation of DG cannot occur simultaneously, and islanding can only be formed when the output of DG is sufficient; Equations (18)-(19) constrain the upper and lower limits of DG output in any operation mode; Equation (20) further stipulates that nodes with islanded operation capability can restore power supply when islanding is formed;

[0034] The energy storage operation constraints include:

[0035]

[0036] Equations (21)-(22) are the upper and lower limits of energy storage output; Equation (23) reflects that the energy storage output state is activated and controlled by the node power supply state; Equation (24) is the upper and lower limits of SOC; Equation (25) gives the dynamic update relationship of SOC in each time period; Equations (26)-(27) together limit the rate of change of energy storage active power.

[0037] The power flow constraints of the main supply recovery area and the islanded area include:

[0038]

[0039] Equation (28) defines that the power flow of the first branch of the feeder is consistent with the power flow of the feeder; Equations (29)-(30) describe the power balance constraints of the nodes; Equations (31)-(33) are voltage drop equations, the activation state of which is determined by the branch connectivity; Equations (34)-(35) are branch capacity limits.

[0040] Furthermore, the reliability metrics include two categories: node reliability metrics and system reliability metrics. Node reliability metrics include the client outage duration (CID) at node i. i ) and Customer Interruption Frequency (CIF) i System reliability metrics include the System Average Interruption Duration Index (SAIDI), the System Average Interruption Frequency Index (SAIFI), and the Expected Energy Shortage (EENS). When a fault occurs at time t0, the calculation expressions for each metric are as follows:

[0041]

[0042] In the formula: λ xy The probability of a fault occurring in the xy branch; For fault isolation time, For fault repair time; NC i Let i be the number of users at node i; Let be the average active power of the load at node i.

[0043] Furthermore, the total cost mentioned in step (2) includes investment cost, operation and maintenance cost, and reliability cost, as detailed below:

[0044]

[0045] In the formula: Inv is the investment cost of stage s; OP is the operating cost; RRC is the reliability cost; r is the discount rate used to calculate the present value; s is the set of planning stages; s is the stage index;

[0046]

[0047] In the formula: L N For the newly constructed branch road set; K l For branch line options, rr represents the capital recovery rate; CC represents the set of available models. l，k EC n IC n，k These represent the construction cost coefficients for new branch roads, substations, and transformers, respectively; x indicates whether equipment investment is required; k is the branch road or transformer selection index; l is the branch road index; and n is the substation index.

[0048]

[0049] In the formula: L F For the set of existing fixed branches; Ψ S For the set of substation nodes; O C M is the operating cost coefficient; C The maintenance cost coefficient; y indicates whether the equipment participates in operation;

[0050] RRC s =ER s ·EENS s (44)

[0051] Where: ER s Cost per unit of electricity loss; EENS s Phase s is expected to have no energy supplied.

[0052] Furthermore, the constraints of the power distribution network expansion planning model include equipment construction constraints, reliability index constraints, and normal operation power flow constraints, as detailed below:

[0053] The constraints on equipment construction include:

[0054]

[0055] x ij,k,s ,x n,k,s ,x n,s ,l ij,s ∈{0,1} (51)

[0056] Where: K n This is a set of optional transformer models;

[0057] Equations (45) and (46) stipulate that only one model of each type of equipment can be selected for construction at each stage; Equation (47) restricts each substation to be constructed only once during the entire planning cycle; Equation (48) embodies the logical constraint that transformers can only be configured after the substation construction is completed; Equations (49) and (50) define the branch construction status at each stage; Equation (51) stipulates that all equipment construction decision variables are binary variables;

[0058] In addition to the constraints mentioned above, branch road construction decisions are subject to the existing network structure; if a branch road is to be constructed, it must form a connecting path to the substation with existing branch roads; define LPM i，s ∈{0,1} indicates whether node i is connected to the established network in stage s:

[0059] LPM i,s =x i,s ,i∈Ψ S (52)

[0060]

[0061] Equation (52) specifies that the initial connectivity state of the substation node is set to 1; Equation (53) requires that the construction of the branch can only proceed when at least one node at both ends of the branch is already connected; Equation (54) ensures that for an initially existing branch, the connectivity state of the nodes at both ends is consistent; Equations (55)-(56) constrain that the connectivity state of the nodes at both ends of an initially unbuilt branch is the same after construction.

[0062] The reliability index constraints include:

[0063] To systematically evaluate the system reliability under different equipment configuration schemes, a full time series method is used to traverse failure scenarios at each planning stage, and reliability indices are calculated in conjunction with an explicit reliability expression model to achieve reliability assessment of the planning scheme:

[0064]

[0065] In the formula: Let ω be a reliability index function, representing scenario ω in stage s. k The calculation results of various reliability indicators, It is its time resolution value at time t; ω is the scene index, ω∈Ψ Se ;

[0066] To ensure the system's reliability level at each stage, the average reliability index calculated based on the scenario sets for each stage is constrained to not exceed a threshold ε. s ;

[0067] ∑p k ·g(s,ω k )≤ε s (58)

[0068] To ensure the feasibility of the expansion planning schemes at each stage under normal operating conditions, constraints are imposed on the power flow state of the system at peak loads at each stage to ensure that the voltage and power operating states meet safety requirements. These normal operating power flow constraints include:

[0069]

[0070] Under normal operating conditions, each branch in the distribution network can flexibly adjust its connectivity through network reconfiguration. The system is unaffected by faults, islanding, or changes in recovery strategies. All nodes maintain normal power supply, and the distributed generation (DG) operates at maximum power. The impact of energy storage devices on system operation under normal conditions is not taken into account.

[0071] An extended planning system for a distribution network based on improved reliability explicit expression includes: a planning model construction module and a planning model solution module, as detailed below:

[0072] The planning model construction module is used to construct an extended planning model for the distribution network with the goal of minimizing the comprehensive cost, including investment costs, operation and maintenance costs, and reliability costs at each stage of distribution network planning, and subject to constraints on equipment construction, reliability indicators, and normal operation power flow.

[0073] The planning model solving module uses the Cplex solver to solve the model and obtain the optimal planning scheme for each stage.

[0074] A computer storage medium storing computer instructions for causing a computer to execute a distribution network expansion planning method based on improved reliability explicit expression as described above.

[0075] Beneficial effects

[0076] 1. The method proposed in this application first constructs an explicit expression method for the reliability of active distribution networks considering the synergistic effect of network reconfiguration and islanded operation, and performs refined modeling of the coupling relationship between network topology and post-fault recovery strategy; secondly, it embeds reliability indicators as constraints into the planning model and proposes structural dependency modeling constraints, stipulating that newly built branches must be connected to the existing network, thereby reducing the redundant solution space and improving the solution efficiency; finally, it uses the solution module to generate a planning scheme that satisfies the reliability constraints and is economically optimal, and verifies the effectiveness of the proposed method on 54-node and large-scale systems.

[0077] 2. The method proposed in this application can effectively improve the accuracy of reliability assessment of active distribution networks, avoid redundant investment, improve planning economy, and significantly shorten the solution time. It has good scalability and engineering application value. Attached Figure Description

[0078] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0079] Figure 1 This is a planning model framework diagram in an embodiment of the present invention;

[0080] Figure 2 This is a diagram showing the coupling relationship between variables in the reliability explicit expression model of this invention. Detailed Implementation

[0081] To make the objectives, technical solutions, and advantages of this application clearer and easier to understand, the present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit the scope of this application.

[0082] As attached Figure 1 As shown, a distribution network extended planning method and system based on improved reliability explicit expression includes the following steps:

[0083] (1) Taking into account the time-varying characteristics of source load, a reliability explicit expression model is proposed that considers the collaborative restoration of load power supply by network reconfiguration and multi-node islanding operation after a fault. The model variables include control variables and state variables, and the constraints include fault impact identification constraints, recovery strategy modeling constraints, DG operation constraints, energy storage operation constraints and power flow constraints. The reliability index can be represented by variables.

[0084] (2) Reliability indicators are embedded into the distribution network extended planning model in the form of constraints, and structural dependency constraints are introduced in the equipment construction part. The goal is to minimize the total cost of each planning stage. The constraints include equipment construction constraints, reliability indicator constraints and normal operation power flow constraints.

[0085] (3) Use the solver module to generate a planning scheme that satisfies reliability constraints and is economically optimal.

[0086] The specific process of step (1) is as follows:

[0087] 1) Construct an explicit expression model for reliability indices

[0088] Control variables include device configuration variables. ij : Indicates whether a branch road is planned for construction; branch road connectivity variable Indicates whether the main supply restoration area branch roads are connected and Indicates whether the branch roads in the isolated operating area are connected; node recovery variable

[0089] Indicates whether the main power supply recovery zone nodes are supplying power normally and Indicates whether the nodes in the isolated operation area are receiving power normally;

[0090] State variables include power flow variables P, Q, and V: representing the electrical operating states such as node voltages and branch power flows; branch state variables... Indicates whether a branch is connected; node status. Are nodes affected by faults and Whether the node is powered; auxiliary variables Indicates the affiliation of nodes, branch feeders, and This indicates whether DG can constitute an isolated source;

[0091] The coupling relationships between variables are shown in the appendix. Figure 2 As shown, the equipment configuration variable restricts the branch connectivity variable through activation constraints that require connection after construction; the branch connectivity variable and the node recovery variable are coupled to jointly determine the power supply path selection of the node after a fault, i.e. whether the load can achieve power supply recovery through network reconstruction or islanding operation. The control variable further determines the branch connectivity status and the node power supply status, thereby determining the system power flow and reliability indicators. Therefore, power flow constraints, voltage constraints and reliability constraints will limit the feasible values ​​of the control variable, forming a closed-loop coupling mechanism.

[0092] The constraints include: fault impact identification constraints, recovery strategy modeling constraints, DG operation constraints, energy storage operation constraints, and power flow constraints between the main power supply recovery zone and the islanded zone; specifically as follows:

[0093] The fault impact identification constraints include:

[0094] variable The definition is as follows: When a fault occurs in branch xy and causes a power outage at node i, then

[0095] otherwise, Based on network topology, the above logic can be further expressed as follows: if and only if node i and the faulty branch xy belong to the same feeder f, then Conversely, Load power supply state variables Line state variables and auxiliary variables The mathematical relationship between them is as follows;

[0096]

[0097] In the formula: Ψ N For a set of nodes; Ψ F For the feeder set; Ψ L For the set of branches; Ψ SL This is the first section of the branch road assembly; Ψ LN For load nodes; NO is the normal scenario index; f is the feeder index;

[0098] Equations (1) and (2) ensure that each branch and each node belongs to only a single feeder; Equation (3) uses the connectivity of the first branch to determine its feeder affiliation; Equation (4) stipulates that a branch can only belong to a feeder when it is in a connected state; Equations (5) and (6) transmit the feeder affiliation based on the connectivity of the branch; Equation (7) gives the fault impact judgment condition, that is, when the faulty branch and the node belong to the same feeder, the node will lose power due to the fault.

[0099] The modeling constraints for the recovery strategy are as follows:

[0100]

[0101] In the formula: xy is the scenario index. When xy corresponds to branch ij, it represents the fault scenario of branch ij. When xy = NO, it represents the normal operating state of the system. In this section, xy represents the fault scenario. Variables The definition is: if node i's DG actively runs in an isolated state, then Conversely,

[0102] Equation (8) restricts only the constructed branch lines to be connected; Equations (9)-(10) constrain the connection states of branch lines in the main power recovery area and the isolated area to be mutually exclusive; Equation (11) stipulates that nodes unaffected by faults should maintain power supply; Equations (12)-(13) ensure that both the main power recovery area and the isolated area operate radially; Equation (14) defines the overall connection state of a branch line, that is, when it is connected in the main power recovery area or the isolated area, it is considered connected; Equation (15) defines the power supply state of a node, that is, when it is supplying power in any area, it is considered to be supplying power normally; Equation (16) stipulates that the faulty branch line should remain disconnected until the fault repair is completed;

[0103] The DG operating constraints are as follows:

[0104]

[0105] In the formula: The parameter is used to characterize whether the DG output of node i can meet the load demand of that node; when the DG generation power of node i is not less than its load power, otherwise,

[0106] This section of constraints is used to characterize the grid-connected and islanded operation strategies of DG, ensuring that the operation logic is reasonable and limiting its output range: Equation (17) indicates that grid-connected operation and islanded operation of DG cannot occur simultaneously, and islanding can only be formed when the output of DG is sufficient; Equations (18)-(19) constrain the upper and lower limits of DG output in any operation mode; Equation (20) further stipulates that nodes with islanded operation capability can restore power supply when islanding is formed;

[0107] The energy storage operation constraints are as follows:

[0108]

[0109] Equations (21)-(22) are the upper and lower limits of energy storage output; Equation (23) reflects that the energy storage output state is activated and controlled by the node power supply state; Equation (24) is the upper and lower limits of SOC; Equation (25) gives the dynamic update relationship of SOC in each time period; Equations (26)-(27) together limit the rate of change of energy storage active power.

[0110] The power flow constraints for the main supply recovery zone and the islanded zone are as follows:

[0111]

[0112]

[0113] Equation (28) defines that the power flow of the first branch of the feeder is consistent with the power flow of the feeder; Equations (29)-(30) describe the power balance constraints of the nodes; Equations (31)-(33) are voltage drop equations, the activation state of which is determined by the branch connectivity; Equations (34)-(35) are branch capacity limits.

[0114] Reliability metrics are categorized into two types: node-level and system-level. Node reliability metrics include the customer interruption duration at node i (CID). i ) and customer interruption frequency at node i, CIF i The system reliability indicators include the system average interruption duration index (SAIDI), the system average interruption frequency index (SAIFI), and the expected energy not supplied (EENS). When a fault occurs at time t0, the calculation expressions for each indicator are as follows:

[0115]

[0116] In the formula: λ xy The probability of a fault occurring in the xy branch; For fault isolation time, For fault repair time; NC i Let i be the number of users at node i; Let be the average active power of the load at node i.

[0117] 2) Distribution network expansion planning model

[0118] The reliability index is embedded as a constraint in the extended planning model of the distribution network. The key point is to create an objective function that minimizes the sum of the total costs of each planning stage. The feature is that the total cost includes investment cost, operation and maintenance cost, and reliability cost, as detailed below:

[0119]

[0120] In the formula: Inv is the investment cost of stage s; OP is the operating cost; RRC is the reliability cost; r is the discount rate used to calculate the present value; s is the set of planning stages; s is the stage index;

[0121]

[0122] In the formula: L N For the newly constructed branch road set; K l For branch line options, rr represents the capital recovery rate; CC represents the set of available models. l，k EC n IC n，k These represent the construction cost coefficients for new branch roads, substations, and transformers, respectively; x indicates whether equipment investment is required; k is the branch road or transformer selection index; l is the branch road index; and n is the substation index.

[0123]

[0124] In the formula: L F For the set of existing fixed branches; Ψ S Let represent the set of substation nodes; OC is the operating cost coefficient; MC is the maintenance cost coefficient; y indicates whether the equipment participates in operation;

[0125] RRC s =ER s ·EENS s (44)

[0126] Where: ER s Cost per unit of electricity loss; EENS s Phase s is expected to have no energy supplied.

[0127] The constraints of the distribution network expansion planning model include equipment construction constraints, reliability index constraints, and normal operation power flow constraints, as detailed below:

[0128] The constraints on equipment construction include:

[0129]

[0130] x ij,k,s ,x n,k,s ,x n,s ,l ij,s ∈{0,1} (51)

[0131] Where: K n This is a set of optional transformer models;

[0132] Equations (45) and (46) stipulate that only one model of each type of equipment can be selected for construction at each stage; Equation (47) restricts each substation to be constructed only once during the entire planning cycle; Equation (48) embodies the logical constraint that transformers can only be configured after the substation construction is completed; Equations (49) and (50) define the branch construction status at each stage; Equation (51) stipulates that all equipment construction decision variables are binary variables;

[0133] In addition to the constraints mentioned above, branch road construction decisions are subject to the existing network structure; if a branch road is to be constructed, it must form a connecting path to the substation with existing branch roads; define LPM i，s ∈{0,1} indicates whether node i is connected to the established network in stage s:

[0134] LPM i,s =x i,s ,i∈Ψ S (52)

[0135]

[0136] Equation (52) specifies that the initial connectivity state of the substation node is set to 1; Equation (53) requires that the construction of the branch can only proceed when at least one node at both ends of the branch is already connected; Equation (54) ensures that for an initially existing branch, the connectivity state of the nodes at both ends is consistent; Equations (55)-(56) constrain that the connectivity state of the nodes at both ends of an initially unbuilt branch is the same after construction.

[0137] The reliability index constraints include:

[0138] To systematically evaluate the system reliability under different equipment configuration schemes, a full time series method is used to traverse failure scenarios at each planning stage, and reliability indices are calculated in conjunction with an explicit reliability expression model to achieve reliability assessment of the planning scheme:

[0139]

[0140] In the formula: Let ω be a reliability index function, representing scenario ω in stage s. k The calculation results of various reliability indicators, It is its time resolution value at time t; ω is the scene index, ω∈Ψ Se ;

[0141] To ensure the system's reliability level at each stage, the average reliability index calculated based on the scenario sets for each stage is constrained to not exceed a threshold ε. s ;

[0142] ∑p k ·g(s,ω k )≤εs (58)

[0143] To ensure the feasibility of the expansion planning schemes at each stage under normal operating conditions, constraints are imposed on the power flow state of the system at peak loads at each stage to ensure that the voltage and power operating states meet safety requirements. These normal operating power flow constraints include:

[0144]

[0145] Under normal operating conditions, each branch in the distribution network can flexibly adjust its connectivity through network reconfiguration. The system is unaffected by faults, islanding, or changes in recovery strategies. All nodes maintain normal power supply, and the distributed generation (DG) operates at maximum power. The impact of energy storage devices on system operation under normal conditions is not taken into account.

[0146] The solver module is used to generate a planning scheme that satisfies reliability constraints and is economically optimal.

[0147] Based on the above method embodiments, the present invention provides corresponding system embodiments.

[0148] One embodiment of the present invention provides a distribution network extended planning system based on improved reliability explicit expression, characterized in that it includes: a planning model construction module and a planning model solving module;

[0149] The planning model construction module is used to construct an extended planning model for the distribution network with the goal of minimizing the comprehensive cost, including investment costs, operation and maintenance costs, and reliability costs at each stage of distribution network planning, and subject to constraints on equipment construction, reliability indicators, and normal operation power flow.

[0150] The planning model solving module uses the Cplex solver to solve the model and obtain the optimal planning scheme for each stage.

[0151] The serial numbers in the above embodiments are for descriptive purposes only and do not represent the chronological order of assembly or use of the components. Those skilled in the art will understand that the embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented 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.

[0152] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. 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... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0153] The above description is merely an embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A power distribution network expansion planning method based on improved reliability explicit expression, characterized in that, Specifically comprising the following steps: (1) Taking into account the source load time-varying characteristics, a reliability explicit expression model considering the coordination of post-fault network reconfiguration and multi-node island operation for load power supply recovery is proposed, the constraint conditions of the reliability explicit expression model include fault influence identification constraints, recovery strategy modeling constraints, DG operation constraints, energy storage operation constraints and power flow constraints, and the model variables include control variables and state variables, which are used to represent reliability indicators; (2) The reliability indicators are embedded in the distribution network expansion planning model in the form of constraints, and the total cost of each planning stage is minimized, the constraint conditions of the distribution network expansion planning model include device construction constraints, reliability indicator constraints and normal operation power flow constraints; (3) Solving the model generates a planning scheme that meets the reliability constraints and is optimal in economy.

2. The power distribution network expansion planning method based on improved reliability explicit expression of claim 1, wherein, The model variables in step (1) include control variables and state variables, which are as follows: Control variables include equipment configuration variable l ij : indicates whether the branch is planned to be constructed; branch connectivity variable : indicates whether the branch in the main supply recovery area is connected and : indicates whether the branch in the island operation area is connected; node recovery variable : indicates whether the node in the main supply recovery area is normally powered and : indicates whether the node in the island operation area is normally powered; The state variables include power flow variables P, Q, V: representing node voltage, branch power flow and other electrical operating states; Branch state variable Indicates whether the branch is connected; Node state Whether the node is affected by a fault and Whether the node is powered; auxiliary variables representing node, branch feeder ownership and representing whether a DG can form an island source; The device configuration variable is limited by the activation constraint that can only be connected after construction; the branch connectivity variable and the node recovery variable are coupled with each other, and together determine the selection of the power supply path of the node after the fault, that is, whether the load realizes power supply recovery through network reconfiguration or island operation, the control variable further determines the branch connectivity state and the node power supply state, thereby determining the system power flow and the reliability indicator, therefore, the power flow constraint, the voltage constraint and the reliability constraint will limit the feasible values of the control variable, forming a closed-loop coupling mechanism.

3. The power distribution network expansion planning method based on improved reliability explicit expression of claim 2, wherein, The constraint conditions of the reliability explicit expression model, wherein the fault influence identification constraints are as follows: The fault influence identification constraints include: Variables are defined as follows: when a branch xy fails and causes node i to lose power, then Otherwise, Based on the network topology relationship, the above logic can be further expressed as: if and only if node i and failed branch xy belong to the same feeder f, then Conversely, then Load power supply state variable Line state variable And auxiliary variable The mathematical relationship between them is as follows; where: Ψ N is a set of nodes; Ψ F is a set of feeders; Ψ L is a set of branches; Ψ SL is a set of initial branches; Ψ LN is a set of load nodes; NO is a normal scenario index; f is a feeder index; Equations (1)-(2) ensure that each branch and each node belongs to a single feeder; Equation (3) determines the feeder affiliation of the first branch using its connectivity state; Equation (4) specifies that a branch belongs to a certain feeder only when it is in a connected state; Equations (5)-(6) transfer the feeder affiliation based on the branch connectivity; Equation (7) gives the fault influence judgment condition, that is, when the fault branch and the node belong to the same feeder; the node will be disconnected due to the fault influence.

4. The power distribution network expansion planning method based on improved explicit expression of reliability according to claim 3, characterized in that, The constraint conditions of the reliability explicit expression model, wherein the recovery strategy modeling constraints are as follows: The recovery strategy modeling constraints include: wherein: xy is the scenario index, which represents the fault scenario of branch ij when xy corresponds to branch ij, and represents the normal operation state of the system when xy = NO; in this section, xy represents the fault scenario; the variable is defined as: if the DG of node i is actively islanded, then otherwise, then Equation (8) limits that only the constructed branch can be connected; Equations (9)-(10) constrain the branch connectivity states of the main supply recovery area and the island area to be mutually exclusive; Equation (11) specifies that the nodes not affected by the fault remain powered; Equations (12)-(13) ensure that the main supply recovery area and the island area are both radial operation; Equation (14) defines the overall connectivity state of the branch, that is, it is considered to be connected when it is connected in the main supply recovery area or the island area; Equation (15) defines the power supply state of the node, that is, it is considered to be normally powered when it is powered in any area; Equation (16) specifies that the fault branch remains disconnected before the fault is repaired.

5. The power distribution network expansion planning method based on improved explicit expression of reliability according to claim 4, characterized in that, The constraint conditions of the reliability explicit expression model, wherein the DG operation constraints, the energy storage operation constraints and the power flow constraints of the main supply recovery area and the island area are as follows: The DG operation constraints include: In the formula: is a parameter, used to represent whether the DG output of node i can meet the load demand of the node; when the DG power generation of node i is not less than its load power, Otherwise, The part constraints are used to describe the grid-connected and island operation strategy of the DG, ensure the operation logic is reasonable and limit the output range: formula (17) indicates that the DG grid-connected operation and island operation cannot occur at the same time, and the island can only be formed when the DG output is sufficient; formula (18)-formula (19) constrain the upper and lower limits of the DG output in any operation mode; formula (20) further provides that the node with island operation capability can restore power supply when the island is formed; The energy storage operation constraints include: Formula (21)-formula (22) are the upper and lower limits of the energy storage output; formula (23) reflects that the energy storage output state is activated and controlled by the node power supply state; formula (24) is the upper and lower limit constraint of SOC; formula (25) gives the dynamic updating relationship of SOC in each period; formula (26)-formula (27) jointly limit the active power change rate of the energy storage; The main supply recovery area and island area power flow constraints include: Formula (28) defines that the branch power flow of the first section of the feeder is consistent with the feeder power flow; formula (29)-formula (30) describe the node power balance constraint; formula (31)-formula (33) are the voltage drop equations, and the activation state is determined by the branch connectivity; formula (34)-formula (35) are the branch capacity constraints.

6. The power distribution network expansion planning method based on improved explicit expression of reliability according to claim 5, characterized in that, The reliability indexes include two types of node reliability indexes and system reliability indexes: the node reliability indexes include customer interruption duration (CID i ) and customer interruption frequency (CIF i ) at node i; the system reliability indexes include system average interruption duration index (SAIDI), system average interruption frequency index (SAIFI) and expected energy not supplied (EENS); when a fault occurs at time t0, the calculation expressions of each index are as follows: where λ xy is the probability of the occurrence of the xy branch failure scenario; is the fault isolation time, is the fault repair time; NC i is the number of users at node i; is the load average active power of node i.

7. The power distribution network expansion planning method based on improved reliability explicit expression of claim 6, wherein, The total cost in step (2) includes investment cost, operation and maintenance cost and reliability cost, which are as follows: In the formula: Inv is the investment cost of stage s; OP is the operation cost; RRC is the reliability cost; r is the discount rate for calculating the present value; S is the set of planning stages; s is the stage index; In the formula: L N is a newly added set of constructable branch roads; K l is a set of branch road optional models; rr is a capital recovery rate; CC l，k , EC n , IC n，k are respectively a newly added branch road construction cost coefficient, a substation construction cost coefficient, and a transformer construction cost coefficient; x indicates whether an equipment is invested; k is a branch road or transformer selection index; and l is a branch road index; and n is a substation index. wherein: L F is the set of existing fixed branches; Ψ S is the set of substation nodes; OC is the operating cost coefficient; MC is the maintenance cost coefficient; y indicates whether the equipment participates in operation; RRC s = ER s • EENS s (44) where: ER s is the cost of loss of one unit of energy; EENS s is the expected unserved energy for period s.

8. The power distribution network expansion planning method based on improved reliability explicit expression of claim 7, wherein, The constraint conditions of the distribution network expansion planning model include device construction constraints, reliability index constraints and normal operation power flow constraints, which are as follows: The device construction constraints include: x ij,k,s ,x n,k,s ,x n,s ,l ij,s ∈{0,1} (51) In the formula: K n is a set of selectable transformer models; Formula (45)-formula (46) provide that only one type of each device can be selected for construction in each stage; formula (47) limits that each substation can only be constructed once in the entire planning period; formula (48) embodies the logical constraint, that is, the transformer can only be configured after the substation construction is completed; formula (49)-formula (50) define the branch construction state in each stage; formula (51) provides that all device construction decision variables are binary variables; In addition to the above constraints, the branch construction decision is constrained by the existing network structure; if a branch is to be constructed, it must form a connected path to the substation with the constructed branches; define LPM i,s ∈ {0, 1} indicates whether node i is connected to the constructed network at stage s: LPM i,s = x i,s i e Ψ S (52) Formula (52) provides that the initial connectivity state of the substation node is 1; formula (53) requires that the branch construction can only be carried out when at least one node at both ends of the branch has been connected; formula (54) ensures that for the existing branch, the connectivity states of the nodes at both ends are consistent; formula (55)-formula (56) constrain the connectivity states of the nodes at both ends of the initial non-constructed branch to be the same after construction; The reliability index constraints include: In order to evaluate the reliability level of the system under different device configuration schemes, the full time sequence method is used to traverse the fault scenarios in each planning stage, and the reliability index is calculated by combining the explicit expression model of reliability, so as to realize the reliability evaluation of the planning scheme: In the formula: g(s, ω k ) is a reliability index function, indicating the reliability index calculation result of stage s scene ω k , g(s, ω k , t) is the time resolution value thereof at time t; ω is a scene index, ω ∈ Ψ Se ; To ensure the reliability level of the system in each stage, the average reliability index calculated according to the scenario set of each stage is constrained to be less than or equal to a threshold value ε s ; ∑p k • g(s, ω k )≤ ε s (58) In order to ensure the feasibility of the expansion planning scheme in each stage under normal operation conditions, the power flow state of the system at the load peak in each stage is constrained to ensure that the voltage and power operation state meets the safety requirements, and the normal operation power flow constraint includes: Under normal operating conditions, each branch in the distribution network adjusts its connectivity state through network reconstruction, the system has no fault influence, island division and recovery strategy changes, each node maintains normal power supply, and the DG operates at maximum power. The influence of the energy storage device on the system operation under normal state is not considered.

9. A power distribution network expansion planning system based on improved reliability explicit representation, characterized by, The method comprises the following steps: The planning model construction module is used to construct a distribution network expansion planning model with the minimum comprehensive cost of investment cost, operation and maintenance cost and reliability cost of each stage of distribution network planning as the target, and subject to equipment construction constraints, reliability index constraints and normal operating flow constraints. The planning model solving module uses a Cplex solver to solve the model to obtain an optimal planning scheme of each stage. The computer readable storage medium stores computer instructions for causing a computer to execute the method of any one of claims 1 to 8.

10. A computer storage medium, characterized in that: ​

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