A flexible interconnection planning method for substations based on distribution transformer sensitivity analysis

Abstract

The present invention provides a flexible interconnection planning method for substations based on distribution transformer sensitivity analysis. The present invention uses a mathematical model of the substation distribution transformer to calculate the load rate sensitivity of the distribution transformer. Secondly, the substations to be interconnected are screened according to the sensitivity of the distribution transformers in each substation, and the connection mode of the flexible interconnection device (FID) is optimized based on the goal of substation load balancing. Then, an FID sizing and system maximum power supply capacity optimization model is established. With the optimization of the maximum power supply capacity (TSC) as the objective function, the configuration capacity of the FID and the active load distribution of the substation are determined, and redundant capacity is removed by secondary optimization of the FID construction cost. Finally, a case study of 40 substations is used to verify that the proposed method can take into account the goals of improving power supply capacity and balancing distribution transformer load, and a scenario comparison is set up to verify the superiority of the proposed method in enhancing power supply capacity, improving load distribution, and improving economic benefits.

Description

Technical Field

[0001] The present invention belongs to the field of distribution network planning and configuration, and in particular to a flexible interconnection planning method for substations based on distribution transformer sensitivity analysis. Background Art

[0002] With the development and advancement of power electronics technology, flexible interconnection devices (FIDs) based on voltage source converters (VSCs) offer bidirectional power flow and precise power flow control capabilities. These devices enable interconnection and mutual supply between substations, and can flexibly transfer power to the faulty substation in the event of a system failure, effectively improving system power supply capacity and reliability. Compared to medium-voltage flexible interconnections, low-voltage FIDs interconnect substation terminals, directly acting on substation loads and achieving "point-to-point" power coordination. This allows for flexible allocation of substation loads and resources, improving the system's load-carrying capacity.

[0003] Currently, research has focused on the total supply capability (TSC) characteristics of flexible interconnected distribution networks. Some studies have constructed TSC assessment models for low-voltage flexible interconnected distribution networks that meet N-1 security requirements and investigated the impact of low-voltage FID configuration capacity on system TSC. Some studies have proposed low-voltage flexible interconnected distribution networks that achieve energy transfer through interconnected VSCs across different substations, thereby reducing the load factor of distribution transformers and improving power supply capacity. Other studies have constructed master-slave game planning models for flexible interconnected distribution networks. Case studies have shown that interconnected distribution networks can coordinate and optimize system economics and power supply capacity. These studies have demonstrated that flexible interconnected distribution networks can improve the load-bearing capacity and power supply capability of distribution networks, becoming a key factor in ensuring stable distribution network operation and meeting user load demands in future power system development.

[0004] In terms of low-voltage FID planning, its significant difference from medium-voltage SOP planning is that the latter is generally configured at the interconnecting switch in the distribution network. By upgrading and transforming the original switch, an interconnected distribution network with flexible closed-loop operation can be obtained. However, the selected location of the low-voltage FID is not fixed. In theory, it can be installed at any substation. At the same time, it is difficult to clarify how the VSCs are connected, which greatly expands the FID site selection scale and solution complexity. Therefore, effectively screening the substation most suitable for VSC configuration and optimizing the connection method of each VSC have become key elements in the low-voltage FID planning problem. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology and propose a flexible interconnection planning method for substations based on distribution transformer sensitivity analysis. The method can screen the substations most suitable for FID interconnection according to load balancing requirements and optimize the connection mode of each VSC, thereby solving the problems of large-scale FID site selection and low solution efficiency. A more reasonable FID planning and configuration scheme is provided to improve the system power supply capacity and load balancing, providing a reference for planning FIDs in actual projects.

[0006] The present invention is achieved through the following technical solutions:

[0007] The first aspect of the present invention is a method for flexible interconnection planning of substations based on distribution transformer sensitivity analysis, comprising:

[0008] Obtain data related to flexible interconnection devices and substations;

[0009] Construct a flexible interconnection planning model for substations, including site selection, capacity optimization, and constraints. Site selection is based on a mathematical model of the substation's distribution transformers, which is used to calculate the load sensitivity of the distribution transformers. Substations to be interconnected are then selected based on their load sensitivity. Finally, the connection method of the flexible interconnection device is optimized with load balancing in mind.

[0010] The fixed capacity optimization is to optimize the maximum power supply capacity as the objective function, and determine the configuration capacity of the flexible interconnection device and the active load distribution of each substation;

[0011] The constraints include FID interconnection mode constraints, flexible interconnection device operation constraints, distribution transformer operation constraints, distribution network flow constraints and safe operation constraints;

[0012] The flexible interconnection planning model of the substation area is solved based on the flexible interconnection device and the relevant data of the substation area to obtain the site selection connection and capacity configuration plan of the flexible interconnection device.

[0013] Furthermore, the site selection is based on the derivation and calculation of the load factor sensitivity of the distribution transformer in the substation area based on the mathematical model of the distribution transformer in the substation area. Then, the substation areas to be interconnected are selected according to the size of the load factor sensitivity of the distribution transformer in each substation area. Then, the connection method of the flexible interconnection device is optimized with the goal of load balancing in the substation area. The details are as follows:

[0014] First, according to the distribution transformer model of the substation, the distribution transformer load rate at substation i is obtained. The calculation formula is as follows:

[0015] ;

[0016] Where: and They represent the active and reactive power on the low-voltage side of the distribution transformer at station i respectively; represents the capacity of the distribution transformer at station i;

[0017] and The calculation formula is as follows:

[0018] ;

[0019] Where: and They represent the active and reactive power transmitted by the VSC connected to the station i; and are the active load and reactive load supplied by the station area i respectively;

[0020] According to the partial derivative law, the relationship between the change in the load factor of the distribution transformer in the substation and the change in the VSC transmission power is obtained:

[0021] ;

[0022] Where: is the load factor change of the distribution transformer at station i; and are the changes in active power and reactive power transmitted by the connected VSC at station i, respectively;

[0023] The calculation formula for the load factor sensitivity of the distribution transformer in the substation is as follows:

[0024] ;

[0025] The screening method for interconnected areas is as follows:

[0026] According to the above distribution transformer load rate sensitivity calculation formula, the sensitivity of all distribution transformers in the distribution area is calculated and arranged in descending order. Then, given the number of installed FIDs and port types, the distribution areas with the highest sensitivity are selected. The number of interconnected distribution areas selected is calculated as follows:

[0027] Where: Indicates the number of interconnected areas screened out; Indicates the number of connected FIDs; Indicates the FID port type;

[0028] The connection mode of flexible interconnection devices is optimized with the goal of load balancing in the substation area. The method is to build a load balancing optimization model with the following objective function:

[0029] Where: is the variance of the distribution transformer load factor in all substations; is the average value of the load factor of all distribution transformers in the substation area; It is the total number of distribution transformers in the substation area.

[0030] Furthermore, the capacity optimization is to determine the configuration capacity of the flexible interconnection device and the active load distribution of each substation with the optimization of the maximum power supply capacity as the objective function; the details are as follows:

[0031] The objective function of the constant capacity optimization model is as follows:

[0032] ; Where: TSC represents the maximum power supply capacity.

[0033] Specifically, if the substation includes multiple FIDs, the substation FID interconnection mode constraints include:

[0034] ;

[0035] ;

[0036] ;

[0037] Where: Represents the FID interconnection matrix. When the nth FID is connected to the station i, the corresponding matrix element =1, otherwise =0; An identifier indicating whether the FID at station j is connected, with a value of 1 indicating connection and a value of 0 indicating no connection; Representation matrix Sum the values ​​of elements in column j.

[0038] Specifically, the flexible interconnection device includes multiple VSCs. Assuming that the power flow from the VSC bus is in the positive direction, the operation constraints of the flexible interconnection device include:

[0039] ;

[0040] ;

[0041] ; ;

[0042] Where: represents the set of area numbers interconnected by the kth FID; represents the active power loss of the VSC connected to the station i; represents the loss coefficient of VSC; represents the capacity of the VSC connected to the station i; Indicates the sine value of the power factor angle.

[0043] Specifically, the distribution transformer operation constraints in the substation area include:

[0044] Where: and They represent the active and reactive power on the high-voltage side of the distribution transformer at station i respectively; and Respectively represent the no-load loss and rated load loss of the distribution transformer; and They represent the no-load current percentage and short-circuit voltage percentage of the distribution transformer respectively.

[0045] Specifically, the distribution network flow constraints include:

[0046] ;

[0047] ;

[0048] ;

[0049] Where: represents the voltage amplitude of the node where the station i is located; It represents the voltage phase angle difference between the node where the transformer area i is located and the node where the transformer area j is located; and They represent the self-conductance and self-susceptance of the node where the station i is located; and They represent the mutual conductance and mutual susceptance between the node where the station i is located and the node where the station j is located respectively; represents the set of nodes connected to the node where station i is located; and They represent the active and reactive power flowing through line ij respectively; and They represent the resistance and reactance of line ij respectively; Represents the current on line ij.

[0050] Specifically, the safety operation constraints include:

[0051] Where: and They represent the upper and lower voltage limits that can ensure safe operation of the node where the substation i is located; and They represent the upper and lower current limits for line ij to ensure safe operation.

[0052] The second aspect of the present invention provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the method for flexible interconnection planning of substations based on distribution transformer sensitivity analysis is implemented.

[0053] The third aspect of the present invention provides a storage medium containing computer-executable instructions, which, when executed by a computer processor, implement the method for flexible interconnection planning of substations based on distribution transformer sensitivity analysis.

[0054] The beneficial effects of the present invention are as follows:

[0055] The present invention calculates the load rate sensitivity of the distribution transformer according to the mathematical model of the distribution transformer in the substation, and then selects the substations to be interconnected according to the sensitivity of the distribution transformer in each substation, and optimizes the FID interconnection mode based on the goal of substation load balancing; then, an FID sizing and TSC optimization model is established to optimize the maximum power supply capacity of the system, and at the same time determine the configuration capacity of the FID and the active load distribution of the substation; after obtaining the FID planning scheme, the FID redundant capacity is eliminated by the method of secondary optimization of the FID construction cost to improve the planning economy; finally, a case study of 40 substations is used to verify that the proposed method can simultaneously improve the power supply capacity and the load balancing degree of the distribution transformer, and a scenario comparison is set to verify the superiority of the proposed method in enhancing the power supply capacity, improving the load distribution and improving the economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is a flow chart of a flexible interconnection planning method for substations based on distribution transformer sensitivity analysis according to the present invention;

[0057] Figure 2 This is an exemplary back-to-back two-port FID area interconnection diagram of the present invention;

[0058] Figure 3 This is a flow chart for solving the low-voltage station FID planning model of the present invention;

[0059] Figure 4 This is a diagram showing a 40-zone distribution network calculation example in an embodiment of the present invention;

[0060] Figure 5 This is a diagram showing the active load distribution before and after FID planning and the VSC transmission power results of each substation in an embodiment of the present invention. DETAILED DESCRIPTION

[0061] The present invention provides a substation flexible interconnection planning method based on distribution transformer sensitivity analysis, which uses the mathematical model of the substation distribution transformer to calculate the distribution transformer load rate sensitivity, and then screens the substations to be interconnected according to the size of the distribution transformer sensitivity of each substation, and optimizes the FID interconnection method based on the substation load balancing target, thereby significantly reducing the FID site selection scale, and providing an FID interconnection method that can improve the distribution transformer load balancing effect; then establish an FID constant capacity and TSC optimization model to collaboratively improve the system's maximum power supply capacity and distribution transformer load balancing, and eliminate redundant capacity through secondary optimization of the FID construction cost; at the same time, set up a scenario comparison to verify the superiority of the proposed method in enhancing power supply capacity, improving load distribution, and improving economic benefits, and provide a reference for the planning of substation FID in actual projects. In order to make the structure and advantages of the present invention clearer, the content of the present invention will be further described in conjunction with the accompanying drawings. A substation flexible interconnection planning method based on distribution transformer sensitivity analysis of the present invention, such as Figure 1 As shown, the following steps are included:

[0062] Step 1: Obtain data related to the flexible interconnection device and the substation;

[0063] The method of the present invention is to set up several flexible interconnection devices between several substations to form an area interconnection system, thereby realizing interconnection and mutual supply between substations, thereby enhancing the power supply capacity of the substation and improving the distribution transformer load balancing rate. Figure 2 The diagram shows an exemplary back-to-back two-port FID substation interconnection system. The system comprises several substations, some or all of which are connected via interconnection devices, and each of which is connected to active and reactive loads. In one specific embodiment, the flexible interconnection device and substation-related data include at least the topology of each substation (such as the type and location of connected devices), system parameters of the flexible interconnection device and various devices connected to the substation (including the capacity and rating of each device), and substation active and reactive load data.

[0064] Step 2: Construct a flexible interconnection planning model for substations, which includes site selection, capacity optimization and constraints, and then optimize the FID construction cost twice. The site selection part uses the distribution transformer load rate sensitivity to screen out the substations to be interconnected, and optimizes the FID interconnection method based on the substation load balancing target; the capacity optimization part determines the configuration capacity of the FID and the active load distribution of the substation to optimize the maximum power supply capacity of the system; the constraints include substation FID interconnection method constraints, flexible interconnection device operation constraints, substation distribution transformer operation constraints, distribution network flow constraints and safe operation constraints; after fixing the optimal TSC solved by the aforementioned planning model, the secondary optimization model optimizes the FID construction capacity with the goal of minimizing the FID construction cost. In a specific implementation plan, first, a distribution transformer load rate sensitivity calculation formula is established based on the mathematical model of the substation distribution transformer, and the interconnected substations are screened according to the sensitivity of each distribution transformer, and then an FID interconnection method optimization model based on the distribution transformer load balancing target is constructed, which specifically includes:

[0065] First, according to the distribution transformer model of the substation, the distribution transformer load rate at substation i is obtained. The calculation formula is as follows: (1); where: and They represent the active and reactive power on the low-voltage side of the distribution transformer at station i respectively; represents the capacity of the distribution transformer at station i;

[0066] and The calculation formula is as follows: (2); where: and They represent the active and reactive power transmitted by the VSC connected to the station i respectively; and are the active load and reactive load supplied by the station area i respectively;

[0067] According to the partial derivative law, the relationship between the change in the load factor of the distribution transformer in the substation and the change in the VSC transmission power is obtained:

[0068] (3); where: is the load factor change of the distribution transformer at station i; and are the changes in active power and reactive power transmitted by the connected VSC at station i, respectively;

[0069] The calculation formula for the load factor sensitivity of the distribution transformer in the substation is as follows:

[0070] (4).

[0071] Then, a FID location selection model is constructed. This is divided into two steps. The first step is to calculate the sensitivity of all distribution transformers in the distribution network using the sensitivity analysis method mentioned above. Then, the most sensitive distribution transformers are selected based on the number of connected FIDs and port types. The second step is to construct an optimization model based on the load balancing of distribution transformers. The decision variable is the interconnection method of each VSC. The goal is to obtain a VSC interconnection scheme that can achieve the most balanced load among the distribution network substations. The step-by-step description is as follows:

[0072] 1) Interconnected area screening:

[0073] According to the above distribution transformer load rate sensitivity calculation formula, the sensitivity of all distribution transformers in the distribution area is calculated and arranged in descending order. Then, given the number of installed FIDs and port types, the distribution areas with the highest sensitivity are selected. The number of interconnected distribution areas selected is as follows:

[0074] (5) Where: Indicates the number of interconnected areas screened out; Indicates the number of connected FIDs; Indicates the FID port type.

[0075] 2) VSC interconnection optimization:

[0076] The selected FID interconnection methods between substations are not fixed. Here, a load balancing optimization model is used to obtain the optimal interconnection solution. Taking the load balancing effect of all substations as the optimization goal, the following objective function is constructed:

[0077] (6); where: is the variance of the distribution transformer load factor in all substations; is the average value of the load factor of all distribution transformers in the substation area; It is the total number of distribution transformers in the substation area.

[0078] Constructing FID interconnection matrix , when the nth FID is connected to a VSC at station i, the corresponding element =1, otherwise =0.

[0079] (7);

[0080] Other The constraints for the elements are as follows:

[0081] (8);

[0082] (9);

[0083] Where: An identifier indicating whether the FID at station j is connected, with a value of 1 indicating connection and a value of 0 indicating no connection; Representation matrix Sum the values ​​of elements in column j.

[0084] Step 3: Based on the obtained FID access location and interconnection plan, construct the FID sizing and TSC optimization model to determine the FID configuration capacity and active load distribution in the substation area. Specifically, the model includes:

[0085] (1) Objective function

[0086] (10); where TSC represents the maximum power supply capacity.

[0087] (2) Constraints

[0088] (a) Operational constraints of flexible interconnection devices

[0089] (11);

[0090] (12);

[0091] (13);

[0092] (14);

[0093] Where: represents the set of area numbers interconnected by the kth FID; represents the active power loss of the VSC connected to the station i; represents the loss coefficient of VSC; represents the capacity of the VSC connected to the station i; Indicates the sine value of the power factor angle.

[0094] (b) Operation constraints of distribution transformers in substations

[0095] (15);

[0096] Where: and They represent the active and reactive power on the high-voltage side of the distribution transformer at station i respectively; and Respectively represent the no-load loss and rated load loss of the distribution transformer; and They represent the no-load current percentage and short-circuit voltage percentage of the distribution transformer respectively.

[0097] (c) Distribution network flow constraints

[0098] (16);

[0099] (17);

[0100] (18);

[0101] Where: represents the voltage amplitude of the node where the station i is located; It represents the voltage phase angle difference between the node where the transformer area i is located and the node where the transformer area j is located; and They represent the self-conductance and self-susceptance of the node where the station i is located; and They represent the mutual conductance and mutual susceptance between the node where the station i is located and the node where the station j is located respectively; represents the set of nodes connected to the node where station i is located; and They represent the active and reactive power flowing through line ij respectively; and They represent the resistance and reactance of line ij respectively; Represents the current on line ij.

[0102] (d) Safety operation constraints

[0103] (19); where: and They represent the upper and lower voltage limits that can ensure safe operation of the node where the substation i is located; and They represent the upper and lower current limits for line ij to ensure safe operation.

[0104] Step 4: After obtaining the FID planning scheme, construct a quadratic optimization model for FID construction costs to eliminate FID redundant capacity. Considering that the FID construction cost and VSC construction capacity can be considered a linear relationship, the FID construction cost quadratic optimization model is also the quadratic optimization model for VSC construction capacity. Specifically, it includes:

[0105] (20);

[0106] The above-mentioned quadratic optimization model takes minimizing the sum of all VSC capacities as the objective function and Equation (11-19) as the constraint condition. At the same time, the value of the system TSC must be constrained to be consistent with the optimal TSC result solved by the above-mentioned TSC optimization model.

[0107] When using the distribution transformer load rate sensitivity method to screen the substations to be interconnected, considering that the substation load distribution and each VSC capacity have not been determined when the sensitivity is first calculated, this paper adopts the strategy of initialization first and then iterative update, that is, the FID planning operation results and load distribution obtained by the first sensitivity screening and site selection and sizing model are not the final results, but are used to update the parameters of the sensitivity and site selection and sizing model, and output the new FID planning scheme and TSC results obtained after one iteration, and then perform the FID capacity secondary optimization. The overall solution process is as follows Figure 3 As shown, the description is as follows:

[0108] (1) Import the relevant parameters of the distribution network and flexible interconnection device, and initialize the active and reactive load distribution of the substation and the capacity of each VSC.

[0109] (2) Calculate the sensitivity of all distribution transformers in the substation according to the sensitivity calculation formula of the distribution transformer in the substation.

[0110] (3) Given the number of FIDs and port types to be connected, a corresponding number of areas to be interconnected are selected based on the sensitivity.

[0111] (4) Construct an FID interconnection optimization model based on distribution transformer load balancing to determine the optimal FID interconnection method.

[0112] (5) Construct and solve the FID constant capacity and power supply capacity TSC optimization model to determine whether it has been iterated.

[0113] (6) If the iteration has been completed, the FID capacity is optimized twice, and then the FID planning configuration scheme, TSC results, and active load distribution are output; if the iteration has not been completed, the currently solved active load distribution and FID transmission power results are used to update the equivalent load of each substation and the sensitivity of each substation distribution transformer, and the new sensitivity results are passed to step (3); then the currently solved VSC capacity is averaged and passed to the distribution transformer load balancing model in step (4); then the solution is continued from step (3) until the FID planning configuration scheme, TSC results, and active load distribution are output.

[0114] In the site selection part, the present invention uses the substation distribution transformer load rate sensitivity method to select the most suitable substation for interconnection, and then optimizes the FID interconnection method based on the load balancing model. In the capacity optimization part, the system maximum power supply capacity TSC is used as the optimization target, combined with flexible interconnection device operation constraints, distribution network flow constraints, distribution transformer operation constraints, safe operation constraints and other conditions to determine the FID configuration capacity and substation active load distribution. In the FID construction cost secondary optimization model, VSC redundant capacity is eliminated to improve the planning economy. Finally, through 40 substation examples, it is verified that the proposed method can decouple the site selection and capacity determination in the FID planning problem, solve the problems of large-scale FID site selection and difficult solution in substation flexible interconnection planning, and can synergistically improve the system maximum power supply capacity and distribution transformer load balancing effect. At the same time, different scenarios are set up for comparison to verify the superiority of the proposed method in enhancing power supply capacity, improving load distribution and improving economic benefits, providing a reference for the planning of substation FID in actual projects.

[0115] The effects of the present invention will be further described below with reference to a specific embodiment:

[0116] by Figure 2 Based on the flexible interconnection structure of the low-voltage area, a design example is used to verify the effect of the method proposed in this invention:

[0117] This example uses a 40-station distribution network with a base voltage of 12.66 kV, a base capacity of 1 MVA, a VSC loss factor of 0.02, an initial total active load of 4400 kW, a total reactive load of 4400 kVar, and initial VSC capacities of 0. The maximum capacity of a single VSC is 500 kVA. The node voltage safe operating range is set to no more than 5% of the rated voltage. Considering the high investment cost of flexible interconnection devices, the FID planning scheme and indicator results described below are based on three two-port FIDs.

[0118] In order to compare the economic benefits of FID planning, the power supply revenue per unit load is set The unit capacity investment cost of VSC is RMB 300,000 / MW per year. 400 yuan / kVA, discount coefficient is 0.087, then the comprehensive income The calculation formula is as follows: (twenty one);

[0119] The simulation hardware environment is Intel i5-12400F @ 2.50GHz, running 32G internal memory, and the software environment is based on MATLAB 2023b and Gurobi 10.

[0120] The simulation analysis is as follows:

[0121] (1) Planning results and indicator evaluation

[0122] Since three two-port FIDs are connected, the number of interconnected substations required is six. The first six substations selected by the distribution transformer load factor sensitivity method are numbered 8, 15, 16, 18, 24, and 36, respectively. The substation interconnection patterns obtained by solving the load balancing optimization model are (8, 36), (15, 24), and (16, 18). The VSC capacity configured for each substation is shown in Table 1.

[0123] Table 1

[0124] Area No. VSC capacity / (kVA) 8 341.9 15 400.0 16 257.8 18 242.2 24 380.3 36 360.4

[0125] The active load distribution of each substation and the VSC transmission power of each substation before and after flexible interconnection planning are as follows: Figure 5 shown.

[0126] Depend on Figure 5 It can be seen that the active load distribution among substations 8, 15, 16, 18, 24 and 36 interconnected by FID has undergone significant changes. Substation 8 supplies power to substation 36, substation 24 supplies power to substation 15, and substation 18 supplies power to substation 16. As a result, the maximum active load that substations 15, 16 and 36 can carry has increased significantly, while the maximum active load that substations 8, 18 and 24 can supply has decreased.

[0127] The changes in the results of various indicators before and after FID planning are shown in Table 2. The calculation formula for voltage deviation is as follows, which is used to describe the voltage stability of the distribution network before and after flexible interconnection of substations:

[0128] (twenty two);

[0129] Table 2

[0130] index Before planning After planning TSC / (MW) 8.027 9.020 Load factor variance / % 2.885 2.256 Voltage deviation / V 0.0246 0.0190 FID investment cost / 10,000 yuan 0 6.90 Substation power supply income / 10,000 yuan 240.81 270.60 Comprehensive income / 10,000 yuan 240.81 263.70

[0131] As shown in the table above, the system's TSC increased by 12.371% after flexible interconnection planning, demonstrating that the integration of flexible interconnection devices in the substation area significantly improves the system's maximum power supply capacity. The load factor variance decreased by 21.802%. This is because the FIDs screened substations based on the load factor sensitivity of the distribution transformers during site selection. Furthermore, the FID interconnection method was optimized based on load balancing objectives. The resulting FID planning scheme improves the load balance of the distribution transformers, balancing light and heavy loads on the distribution transformers and reducing overloads. Furthermore, because the integration and operation of the FIDs optimizes the load and power flow distribution in the substation area, the system voltage deviation is reduced, thereby improving voltage stability and ensuring safe system operation.

[0132] In terms of economic benefits, the comprehensive income increased by 228,900 yuan after FID planning, while the FID investment cost was only 69,000 yuan. That is, the economic benefits brought by the improvement of power supply in the substation after FID planning significantly exceeded the cost brought by the planned investment, thereby improving the economic efficiency of distribution network planning.

[0133] (2) Comparison of FID planning methods

[0134] The traditional sensitivity-based FID site selection method uses the node voltage sensitivity method. To verify the superiority of the proposed flexible interconnection planning method for substations based on the distribution transformer load factor sensitivity method in improving power supply capacity and economic benefits, the following two scenarios are set for comparison:

[0135] 1) Substation FID planning method based on voltage sensitivity method;

[0136] 2) The FID planning method for substations proposed in this paper is based on the distribution transformer load rate sensitivity method for site selection.

[0137] The FID planning schemes and the results of various indicators under the above two scenarios are shown in Table 3:

[0138] Table 3

[0139] Scenario Scenario 1 Scenario 2 FID site selection plan (13, 18), (14, 17), (15, 16) (8, 36), (15, 24), (16, 18) VSC Capacity 13: 352.2kVA14: 339.0kVA15: 384.3kVA16: 394.3kVA17: 333.0kVA18: 345.1kVA 8: 341.9kVA15: 400.0kVA16: 257.8kVA18: 242.2kVA24: 380.3kVA36: 360.4kVA TSC / (MW) 8.501 9.020 Load factor variance / % 2.332 2.256 Voltage deviation / V 0.0147 0.0190 FID investment cost / 10,000 yuan 7.47 6.90 Substation power supply income / 10,000 yuan 255.03 270.60 Comprehensive income / 10,000 yuan 247.56 263.70

[0140] Table 3 shows that Scenario 2, which uses the load sensitivity method for site selection, improves the maximum power supply capacity (TSC) compared to Scenario 1, which uses the voltage sensitivity method for site selection. This also suppresses the variance of the distribution transformer load factor. This is because the voltage sensitivity values ​​of adjacent substations are similar, so the FID interconnection substation locations determined by the voltage sensitivity method are relatively concentrated. For example, in Scenario 1, the FIDs are concentrated at substations 13 to 18. After flexible interconnection of these adjacent substations, the FIDs can play a very limited role. However, the interconnection substation locations selected based on the substation load sensitivity method are more dispersed, allowing them to better leverage the power transfer function of the FIDs. This fully unleashes the substation power supply potential, overcomes power supply bottlenecks, improves power supply capacity, and optimizes load distribution between substations. However, in terms of voltage stability, the voltage at the nodes of the substations selected using the voltage sensitivity method is more affected by the power transferred by the FIDs, making it easier to adjust its fluctuations, resulting in better voltage stability.

[0141] In terms of economic benefits, while the planning method in Scenario 1 can slightly increase overall revenue compared to not planning FID, it still falls short of the proposed method by 161,400 yuan. Furthermore, while the FID investment cost of the proposed method is slightly lower than that of Scenario 1, it significantly increases the power supply revenue for the substation, thus validating the proposed method's economic benefits.

[0142] In addition, the present invention provides an electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the method for planning flexible interconnection of substations based on distribution transformer sensitivity analysis is implemented; and a storage medium comprising computer executable instructions is provided, wherein when the computer executable instructions are executed by the computer processor, the method for planning flexible interconnection of substations based on distribution transformer sensitivity analysis is implemented.

[0143] In summary, the flexible interconnection planning method for substations proposed in this invention takes into account the substation screening strategy based on the sensitivity analysis of the substation distribution transformer load rate and the FID interconnection optimization model based on the load balancing target, in order to screen the most suitable substations for interconnection and provide the FID interconnection method with the best load balancing effect. In the FID capacity optimization part, the maximum power supply capacity of the system is taken as the goal to determine the FID configuration capacity and the active load distribution of the substation. At the same time, the secondary optimization of the FID construction cost is used to eliminate capacity redundancy and improve the planning economy. The results of the example show that the proposed planning method can take into account the two major goals of improving power supply capacity and improving load balancing. It is compared with other planning methods, verifying the superiority of the proposed method in enhancing power supply capacity, improving load distribution, and improving economic benefits, thereby providing a reference for substation FID planning in actual projects.

Claims

1. A flexible interconnection planning method for substations based on distribution transformer sensitivity analysis, characterized in that: include: Obtain data related to flexible interconnection devices and substations; Construct a flexible interconnection planning model for substations, which includes site selection, capacity optimization, and constraints. The site selection is based on the mathematical model of the substation distribution transformer and calculates the load rate sensitivity of the distribution transformer. Then, the substations to be interconnected are screened according to the size of the distribution transformer load rate sensitivity of each substation. Then, the connection mode of the flexible interconnection device is optimized with the substation load balance as the goal. The site selection is based on the mathematical model of the substation distribution transformer and calculates the load rate sensitivity of the distribution transformer. Then, the substations to be interconnected are screened according to the size of the distribution transformer load rate sensitivity of each substation. Then, the connection mode of the flexible interconnection device is optimized with the substation load balance as the goal. The details are as follows: First, according to the distribution transformer model of the substation, the distribution transformer load rate β at substation i is obtained: i The calculation formula is as follows: Where: and They represent the active and reactive power on the low-voltage side of the distribution transformer at station i; S i,T represents the capacity of the distribution transformer at station i; and The calculation formula is as follows: Where: and They represent the active and reactive power transmitted by the VSC connected to the station i; and are the active load and reactive load supplied by the station area i respectively; According to the partial derivative law, the relationship between the change in the load factor of the distribution transformer in the substation and the change in the VSC transmission power is obtained: Where: Δβ i is the load factor change of the distribution transformer at station i; and are the changes in active power and reactive power transmitted by the connected VSC at station i, respectively; The calculation formula for the load factor sensitivity of the distribution transformer in the substation is as follows: The screening method for interconnected areas is as follows: According to the above distribution transformer load rate sensitivity calculation formula, the sensitivity of all distribution transformers in the distribution area is calculated and arranged in descending order. Then, given the number of installed FIDs and port types, the distribution areas with the highest sensitivity are selected. The number of interconnected distribution areas selected is calculated as follows: n DS =n FID ×T FID Where: n DS Indicates the number of interconnected areas screened out; n FID Indicates the number of connected FIDs; T FID Indicates the FID port type; The connection mode of flexible interconnection devices is optimized with the goal of load balancing in the substation area. The method is to build a load balancing optimization model with the following objective function: Where: D Δβ is the variance of the distribution transformer load factor in all substations; is the average load factor of all distribution transformers in the substation area; n Node is the total number of distribution transformers in the substation area; The fixed capacity optimization is to optimize the maximum power supply capacity as the objective function, and determine the configuration capacity of the flexible interconnection device and the active load distribution of each substation; The constraints include FID interconnection mode constraints, flexible interconnection device operation constraints, distribution transformer operation constraints, distribution network flow constraints and safe operation constraints; The flexible interconnection planning model of the substation area is solved based on the flexible interconnection device and the relevant data of the substation area to obtain the site selection connection and capacity configuration plan of the flexible interconnection device.

2. The method according to claim 1, characterized in that The capacity optimization is to optimize the maximum power supply capacity as the objective function, and determine the configuration capacity of the flexible interconnection device and the active load distribution of each substation. The details are as follows: The objective function of the constant capacity optimization model is as follows: Where: TSC represents the maximum power supply capacity.

3. The method according to claim 1, characterized in that The substation area includes multiple FIDs, and the substation area FID interconnection mode constraints include: Where: U FID Represents the FID interconnection matrix. When the nth FID is connected to the station i, the corresponding matrix element u n,i =1, otherwise u n,i =0; R j The identifier indicating whether the FID at station j is connected, with a value of 1 indicating connection and a value of 0 indicating no connection; u j Represents the matrix U FID Sum the values ​​of elements in column j.

4. The method according to claim 1, wherein The flexible interconnection device includes multiple VSCs. Assuming that the VSC power flows out of the bus in the positive direction, the operating constraints of the flexible interconnection device include: Where: π(k) represents the set of area numbers interconnected by the kth FID; K represents the active power loss of the VSC connected to the station i; VSC,Loss represents the loss coefficient of VSC; represents the capacity of the VSC connected to the station i; η represents the sine value of the power factor angle.

5. The method according to claim 1, wherein The distribution transformer operation constraints in the substation area include: Where: and They represent the active and reactive power on the high-voltage side of the distribution transformer at station i; P T0 and P Tk Respectively represent the no-load loss and rated load loss of the distribution transformer; I T0 and U Tk They represent the no-load current percentage and short-circuit voltage percentage of the distribution transformer respectively.

6. The method according to claim 1, characterized in that The distribution network flow constraints include: Where: U i represents the voltage amplitude of the node where the station i is located; θ ij G represents the voltage phase angle difference between the node where the transformer area i is located and the node where the transformer area j is located; ii and B ii They represent the self-conductance and self-susceptance of the node where the station i is located; G ij and B ij They represent the mutual conductance and mutual susceptance between the node where the station i is located and the node where the station j is located respectively; δ(i) represents the set of nodes connected to the node where the station i is located; P ij and Q ij Respectively represent the active and reactive power flowing through line ij; r ij and x ij Represent the resistance and reactance of line ij respectively; I ij Represents the current on line ij.

7. The method according to claim 1, characterized in that The safe operation constraints include: Where: and They represent the upper and lower voltage limits that can ensure safe operation of the node where the substation i is located; and They represent the upper and lower current limits for line ij to ensure safe operation.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the method for planning flexible interconnection of substations based on distribution transformer sensitivity analysis according to any one of claims 1 to 7 is implemented.

9. A storage medium comprising computer-executable instructions, wherein the computer-executable instructions, when executed by a computer processor, implement the method for flexible interconnection planning of substations based on distribution transformer sensitivity analysis according to any one of claims 1 to 7.

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