Transformer area flexible interconnection planning method based on distribution transformer sensitivity analysis

Abstract

The invention provides a transformer area flexible interconnection planning method based on distribution transformer sensitivity analysis. The method comprises the following steps: calculating distribution transformer load rate sensitivity by using a mathematical model of a transformer area distribution transformer; secondly, screening out transformer areas to be interconnected according to the sensitivity of the distribution transformer of each transformer area, and optimizing the connection mode of the flexible interconnection device FID based on the target of transformer area load balancing; then, establishing an FID constant volume and system maximum power supply capacity optimization model, taking optimization of the maximum power supply capacity TSC as a target function, deciding the configuration capacity of the FID and the distribution of the active load of the transformer area, and removing the redundant capacity through secondary optimization of the construction cost of the FID; and finally, 40 transformer area examples verify that the method can give consideration to the goals of improving the power supply capacity, balancing the load of the distribution transformer and the like, and scene comparison verifies the superiority of the method in the aspects of enhancing the power supply capacity, improving the load distribution, improving the economic benefit and the like.

Description

Technical Field

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

[0002] With the development and progress of power electronic technology, a flexible interconnection device (FID) based on a voltage source converter (VSC) has the capabilities of bidirectional power flow and precise power flow control. It can realize interconnection and mutual power supply between distribution transformer areas, and flexibly transfer power to the power-outage distribution transformer area during system faults, thereby effectively improving the power supply capacity and reliability of the system. Compared with medium-voltage flexible interconnection, the interconnection object of low-voltage FID is the end of the distribution transformer area, which can directly act on the load of the distribution transformer area to achieve "point-to-point" power mutual assistance, so as to flexibly allocate the load and resources of the distribution transformer area and improve the load-carrying capacity of the system.

[0003] At present, there have been relevant studies on the total supply capability (TSC) characteristics of the low-voltage FID-based flexible interconnection distribution network. Some literature has constructed a TSC evaluation model for the low-voltage distribution transformer area flexible interconnection distribution network that meets N-1 security, and studied the action law of the configuration capacity of low-voltage FID on the system TSC. In some literature, the low-voltage distribution transformer area flexible interconnection distribution network realizes power transfer through the VSCs interconnected by different distribution transformer areas, thereby reducing the load rate of the distribution transformer and improving the power supply capacity. Some literature has constructed a master-slave game planning model for the flexible interconnection of distribution transformer areas. The case results show that the interconnection of distribution transformer areas can coordinately optimize the economy and power supply capacity of the system. The above-mentioned literature has verified that the flexible interconnection of distribution transformer areas can improve the load-carrying capacity and power supply capacity of the distribution network, and become a key factor in ensuring the stable operation of the distribution network and meeting the load demand of users in the future development of the power system.

[0004] In terms of the low-voltage FID planning, its significant difference from the medium-voltage SOP planning is that the latter is generally configured at the tie switch in the distribution network, and the original switch is upgraded and transformed to obtain a flexibly and flexibly closed-loop operating interconnection distribution network. However, the candidate locations of the low-voltage FID are not fixed. Theoretically, it can be installed at any distribution transformer area, and it is also difficult to clarify how to connect between the VSCs, which greatly expands the siting scale and solution complexity of the FID. Therefore, effectively screening out the most suitable distribution transformer area for configuring the VSC and optimizing the connection mode of each VSC has become a key element in the low-voltage FID planning problem. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and propose a flexible interconnection planning method for distribution transformer areas based on distribution transformer sensitivity analysis, which can screen out the most suitable distribution transformer areas for FID interconnection according to the load balancing requirements, and optimize the connection methods of each VSC, so as to solve the problems of large FID site selection scale and low solution efficiency, and give a more reasonable FID planning and configuration scheme to improve the system power supply capacity and load balancing degree, providing a reference for FID planning in practical engineering.

[0006] The present invention is realized through the following technical solutions: The first aspect of the present invention: A flexible interconnection planning method for distribution transformer areas based on distribution transformer sensitivity analysis, including: Obtain relevant data of flexible interconnection devices and distribution transformer areas; Construct a flexible interconnection planning model for distribution transformer areas. The model includes site selection, capacity determination optimization, and constraint conditions. The site selection is to deduce and calculate the distribution transformer load rate sensitivity based on the mathematical model of the distribution transformer in the distribution transformer area, and then screen out the distribution transformer areas to be interconnected according to the magnitude of the distribution transformer load rate sensitivity of each distribution transformer area, and then optimize the connection method of the flexible interconnection device with the goal of load balancing in the distribution transformer area; The capacity determination optimization takes optimizing the maximum power supply capacity as the objective function to determine the configuration capacity of the flexible interconnection device and the active load distribution of each distribution transformer area; The constraint conditions include distribution transformer area FID interconnection method constraints, flexible interconnection device operation constraints, distribution transformer operation constraints in the distribution transformer area, distribution network power flow constraints, and safe operation constraints; Solve the flexible interconnection planning model for distribution transformer areas based on the relevant data of flexible interconnection devices and distribution transformer areas to obtain the site selection connection and capacity configuration scheme of the flexible interconnection device.

[0007] Furthermore, the site selection is to deduce and calculate the distribution transformer load rate sensitivity based on the mathematical model of the distribution transformer in the distribution transformer area, and then screen out the distribution transformer areas to be interconnected according to the magnitude of the distribution transformer load rate sensitivity of each distribution transformer area, and then optimize the connection method of the flexible interconnection device with the goal of load balancing in the distribution transformer area; specifically as follows: First, according to the distribution transformer model in the distribution transformer area, obtain the distribution transformer load rate at distribution transformer i in the distribution transformer area. The calculation formula is as follows: ; In the formula: and respectively represent the active and reactive powers at the low-voltage side of the distribution transformer at distribution transformer i in the distribution transformer area; represents the capacity of the distribution transformer at distribution transformer i in the distribution transformer area; and The calculation formulas are as follows: ; In the formula: and respectively represent the active and reactive powers transmitted by the VSC connected to Substation Area i; and are respectively the active load and reactive load supplied by Substation Area i; According to the partial derivative rule, the relationship between the change in the load rate of the distribution transformer in the substation area and the change in the transmission power of the VSC is obtained: ; In the formula: is the change in the load rate of the distribution transformer at Substation Area i; and are respectively the change in the active power transmitted by the VSC connected to Substation Area i and the change in the reactive power; Then the calculation formula for the sensitivity of the load rate of the distribution transformer in the substation area in the formula is as follows: ; The method for screening interconnected substation areas is as follows: Calculate the sensitivities of all distribution transformers in the substation areas according to the above calculation formula for the sensitivity of the load rate of the distribution transformer, and arrange them in descending order. Then, after specifying the installation quantity and port type of the FID, select the substation areas with the top sensitivities. The number of interconnected substation areas screened is calculated as follows: ; In the formula: represents the number of interconnected substation areas screened; represents the quantity of FIDs connected; represents the FID port type; Optimize the connection method of the flexible interconnection device with the goal of load balancing in the substation area. The method is to construct a load balancing optimization model, and the objective function is as follows: ; In the formula: is the variance of the load rates of all distribution transformers in the substation areas; is the mean value of the load rates of all distribution transformers in the substation areas; is the total number of distribution transformers in the substation area.

[0008] Furthermore, the fixed-capacity optimization aims 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 area; specifically as follows: The objective function of the fixed-capacity optimization model is as follows: ; In the formula: TSC represents the maximum power supply capacity.

[0009] Specifically, if the substation area includes multiple FIDs, the constraints on the FID interconnection method in the substation area include: ; ; ; In the formula: represents the FID interconnection matrix. When the nth FID is connected to the substation area i, the corresponding matrix element = 1; otherwise = 0; is an identifier indicating whether the FID is connected to the substation area j. The value 1 indicates connection, and the value 0 indicates non - connection; represents the matrix the sum of the elements in the jth column.

[0010] Specifically, the flexible interconnection device includes multiple VSCs. Assuming that the positive direction is the power flowing out of the busbar of the VSC, the operating constraints of the flexible interconnection device include: ; ; ; ; In the formula: represents the set of substation area numbers interconnected by the kth FID; represents the active power loss of the VSC connected to the substation area i; represents the loss coefficient of the VSC; represents the capacity of the VSC connected to the substation area i; represents the sine value of the power factor angle.

[0011] Specifically, the operating constraints of the distribution transformer in the substation area include: ; In the formula: and respectively represent the active and reactive powers on the high - voltage side of the distribution transformer in the substation area i; and respectively represent the no - load loss and rated load loss of the distribution transformer; and respectively represent the no - load current percentage and short - circuit voltage percentage of the distribution transformer.

[0012] Specifically, the power flow constraints of the distribution network include: ; ; ; In the formula: represents the voltage amplitude of the node where the substation area i is located; represents the voltage phase angle difference between the node where the substation area i is located and the node where the substation area j is located; and respectively represent the self - conductance and self - susceptance of the node where the substation area i is located; and respectively represent the mutual conductance and susceptance between the node where the i-th distribution area is located and the node where the j-th distribution area is located; represents the set of nodes connected to the node where the i-th distribution area is located; and respectively represent the active and reactive powers flowing through the line ij; and respectively represent the resistance and reactance of the line ij; represents the current on the line ij.

[0013] Specifically, the safe operation constraints include: ; where: and respectively represent the upper and lower voltage limits for ensuring safe operation of the node where the i-th distribution area is located; and respectively represent the upper and lower current limits for ensuring safe operation of the line ij.

[0014] The second aspect of the present invention: provides an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, it implements the above-mentioned method for flexible interconnection planning of distribution areas based on distribution transformer sensitivity analysis.

[0015] The third aspect of the present invention: provides a storage medium containing computer-executable instructions, and when the computer-executable instructions are executed by a computer processor, they implement the above-mentioned method for flexible interconnection planning of distribution areas based on distribution transformer sensitivity analysis.

[0016] The beneficial effects of the present invention are as follows:

[0017] The present invention calculates the sensitivity of the distribution transformer load rate according to the mathematical model of the distribution transformer in the distribution area. Secondly, it screens out the distribution areas to be interconnected according to the magnitude of the distribution transformer sensitivity of each distribution area, and optimizes the FID interconnection method based on the goal of load balance in the distribution area; then it establishes an FID sizing and TSC optimization model, optimizes the maximum power supply capacity of the system, and simultaneously determines the configuration capacity of the FID and the active load distribution in the distribution area; after obtaining the FID planning scheme, it eliminates the redundant capacity of the FID by the method of secondary optimization of the FID construction cost to improve the planning economy; finally, through a 40-distribution area example, it is verified that the proposed method can improve the power supply capacity and the distribution transformer load balance degree at the same time, and sets up a scenario comparison to verify the superiority of the method proposed by the present invention in enhancing the power supply capacity, improving the load distribution, and enhancing the economic benefits. Description of the Drawings

[0018] Figure 1 is a flowchart of a method for flexible interconnection planning of distribution areas based on distribution transformer sensitivity analysis according to the present invention; Figure 2 This is a schematic diagram of the back-to-back type two-port FID area interconnection for an exemplary embodiment of the present invention; Figure 3 This is a flow chart for solving the FID planning model of the low-voltage area of the present invention; Figure 4 This is a structural diagram of a 40-area distribution network calculation example in an embodiment of the present invention; Figure 5 This is a diagram showing the active load distribution before and after FID planning and the results of the VSC transmission power of each area in an embodiment of the present invention. Detailed implementation manners

[0019] The present invention provides a flexible interconnection planning method for areas based on the analysis of the sensitivity of distribution transformers. The method calculates the sensitivity of the load rate of the distribution transformer by using the mathematical model of the distribution transformer in the area. Secondly, the areas to be interconnected are selected according to the magnitudes of the sensitivities of the distribution transformers in each area, and the FID interconnection method is optimized based on the goal of load balancing in the area, thereby significantly reducing the FID site selection scale and giving an FID interconnection method that can improve the load balancing effect of the distribution transformer; then an FID capacitance determination and TSC optimization model is established to synergistically improve the maximum power supply capacity of the system and the load balancing degree of the distribution transformer, and the FID construction cost is secondarily optimized to eliminate redundant capacity; at the same time, scenario comparisons are set to verify the superiority of the proposed method in aspects such as enhancing the power supply capacity, improving the load distribution, and increasing the economic benefits, providing a reference for the planning of FID in the area in actual engineering. To make the structure and advantages of the present invention clearer, the content of the present invention will be further described below with reference to the accompanying drawings. A flexible interconnection planning method for areas based on the analysis of the sensitivity of distribution transformers according to the present invention, as Figure 1 shown, includes the following steps:

[0020] Step 1: Obtain relevant data of the flexible interconnection device and the area;

[0021] The method of the present invention sets a number of flexible interconnection devices among a number of areas to form an area interconnection system, thereby realizing the interconnection and mutual power supply between the areas, enhancing the power supply capacity of the area and improving the load balancing rate of the distribution transformer. Figure 2 Shown is a structural diagram of an exemplary back-to-back type two-port FID area interconnection system. The entire area interconnection system includes a number of areas, among which some or all of the areas are connected by interconnection devices, and active and reactive loads are connected in the area. In a specific implementation manner, the relevant data of the flexible interconnection device and the area at least includes the topological structure of each area (such as the types of devices connected and the connection positions, etc.), the system parameters of various devices connected to the flexible interconnection device and the area (including the capacity / rated value of various devices, etc.), and the active and reactive load data of the area.

[0022] Step 2: Construct a flexible interconnection planning model for the distribution area. The flexible interconnection planning model for the distribution area includes site selection, capacity determination optimization, and constraint conditions, and then the construction cost of the FID is optimized for the second time. Among them, in the site selection part, the distribution areas to be interconnected are screened out by using the sensitivity of the distribution transformer load rate, and the FID interconnection method is optimized based on the goal of load balance in the distribution area; in the capacity determination optimization part, the configuration capacity of the FID and the active power load distribution in the distribution area are determined to optimize the maximum power supply capacity of the system; the constraint conditions include the constraint of the FID interconnection method in the distribution area, the operation constraint of the flexible interconnection device, the operation constraint of the distribution transformer in the distribution area, the power flow constraint of the distribution network, and the safe operation constraint; the second optimization model, after fixing the optimal TSC solved by the previous planning model, aims to minimize the construction cost of the FID and optimize the construction capacity of the FID. In a specific implementation plan, first, a calculation formula for the sensitivity of the distribution transformer load rate is established based on the mathematical model of the distribution transformer in the distribution area, and the interconnected distribution areas are screened according to the sensitivity of each distribution transformer, and then an optimization model for the FID interconnection method based on the goal of distribution transformer load balance is constructed, specifically including: First, according to the distribution transformer model in the distribution area, the distribution transformer load rate at location i in the distribution area is obtained The calculation formula is as follows: (1); where: and respectively represent the active and reactive powers on the low-voltage side of the distribution transformer at location i in the distribution area; represents the capacity of the distribution transformer at location i in the distribution area; and The calculation formulas are as follows: (2); where: and respectively represent the active and reactive powers transmitted by the VSC connected to location i in the distribution area; and respectively represent the active load and reactive load supplied by location i in the distribution area; According to the partial derivative rule, the relationship between the change in the distribution transformer load rate and the change in the VSC transmission power is obtained: (3); where: is the change in the distribution transformer load rate at location i in the distribution area; and respectively represent the change in the active power transmitted by the VSC connected to location i in the distribution area and the change in the reactive power transmitted; Then the calculation formula for the sensitivity of the distribution transformer load rate in the formula is as follows: (4).

[0023] Then, an FID site selection model is constructed in two steps. In the first step, the sensitivities of all distribution transformers in the substations are calculated through the above sensitivity analysis method, and then several substations with the highest sensitivities are selected according to the number of connected FIDs and the port types. In the second step, an optimization model based on distribution transformer load balancing is constructed, with the decision variable being the interconnection method of each VSC, aiming to obtain a VSC interconnection scheme that can make the load carried by the distribution network substations the most balanced. The steps are described as follows: 1) Screening of interconnected substations: Calculate the sensitivities of all distribution transformers in the substations according to the above formula for the sensitivity of the distribution transformer load rate, and arrange them in descending order. Then, after specifying the installation quantity and port type of the FIDs, select the substations with the top sensitivities. The number of selected interconnected substations is as follows: In formula (5): represents the number of selected interconnected substations; represents the number of connected FIDs; represents the FID port type.

[0024] 2) Optimization of VSC interconnection method: The FID interconnection methods among the selected substations are not fixed. Here, a load balancing optimization model is used to obtain the optimal interconnection scheme. Taking the load balancing effect of all substations as the optimization objective, the following objective function is constructed: (6); In the formula: is the variance of the load rates of all distribution transformers in the substations; is the mean value of the load rates of all distribution transformers in the substations; is the total number of distribution transformers in the substations.

[0025] Construct an FID interconnection matrix , when the nth FID is connected to a VSC at substation i, the corresponding element = 1, otherwise = 0.

[0026] (7); Other constraint conditions for elements are as follows: (8); (9); In the formula: represents the identifier indicating whether an FID is connected at substation j, with a value of 1 indicating connection and a value of 0 indicating non - connection; represents the sum of the element values in the jth column of the matrix .

[0027] Step 3: Based on the obtained FID access locations and interconnection schemes, construct an FID sizing and TSC optimization model to determine the FID configured capacity and the active power load distribution in the distribution substation area, specifically including: (1) Objective function (10); where: TSC represents the maximum power supply capacity.

[0028] (2) Constraints (a) Flexible interconnection device operation constraints (11); (12); (13); (14); Where: represents the set of distribution substation area numbers interconnected by the kth FID; represents the active power loss of the VSC connected to distribution substation area i; represents the loss coefficient of the VSC; represents the capacity of the VSC connected to distribution substation area i; represents the sine value of the power factor angle.

[0029] (b) Distribution transformer operation constraints in the distribution substation area (15); Where: and respectively represent the active and reactive powers on the high-voltage side of the distribution transformer at distribution substation area i; and respectively represent the no-load loss and rated load loss of the distribution transformer; and respectively represent the no-load current percentage and short-circuit voltage percentage of the distribution transformer.

[0030] (c) Distribution network power flow constraints (16); (17); (18); Where: represents the voltage amplitude of the node where distribution substation area i is located; represents the voltage phase difference between the node where distribution substation area i is located and the node where distribution substation area j is located; and respectively represent the self-conductance and self-susceptance of the node where distribution substation area 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.

[0031] (d) Safety operation constraints (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.

[0032] 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: (20);

[0033] 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.

[0034] 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:

[0035] (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.

[0036] (2) Calculate the sensitivity of all distribution transformers in the substation according to the sensitivity calculation formula of the distribution transformer in the substation.

[0037] (3) Given the number of access FIDs and port types, and screen the corresponding number of to-be-interconnected substations according to the sensitivity magnitude.

[0038] (4) Construct an optimization model for the FID interconnection method based on distribution transformer load balancing to determine the optimal FID interconnection method.

[0039] (5) Construct and solve the FID fixed-capacity and power supply capacity TSC optimization model, and determine whether iteration has been performed.

[0040] (6) If iteration has been performed, conduct secondary optimization of the FID capacity, and then output the FID planning and configuration scheme, the TSC result, and the active load distribution; if iteration has not been performed, use the currently solved active load distribution and FID transmission power result to update the equivalent load of each substation and the distribution transformer sensitivity of each substation, and transfer the new sensitivity result to step (3); then take the average value of the currently solved VSC capacity and transfer it to the distribution transformer load balancing model in step (4); then continue to solve from step (3) until the FID planning and configuration scheme, the TSC result, and the active load distribution are output.

[0041] In the site selection part of the present invention, the most suitable substations for interconnection are screened by the distribution transformer load rate sensitivity method of the substation area, and then the FID interconnection method is optimized based on the load balancing model; in the fixed-capacity optimization part, with the system's maximum power supply capacity TSC as the optimization goal, combined with conditions such as the operation constraints of the flexible interconnection device, the distribution network power flow constraints, the distribution transformer operation constraints, and the safe operation constraints, to determine the FID configuration capacity and the active load distribution of the substation area; in the FID construction cost secondary optimization model, the redundant capacity of the VSC is eliminated to improve the planning economy. Finally, through a 40-substation example, it is verified that the proposed method can decouple the site selection and fixed capacity in the FID planning problem, solve the problems of large FID site selection scale and difficult solution in the flexible interconnection planning of the substation area, and can synergistically improve the system's maximum power supply capacity and the distribution transformer load balancing effect. At the same time, different scenarios are set to compare and verify the superiority of the method proposed in this paper in enhancing power supply capacity, improving load distribution, and increasing economic benefits, providing a reference for the planning of FID in substations in actual projects.

[0042] The following further illustrates the effect of the present invention in combination with a specific embodiment:

[0043] Taking Figure 2 the flexible interconnection structure of the low-voltage substation area as the basis, a design example is used to verify the effect of the method proposed in the present invention:

[0044] In this example, a 40-district power distribution network is adopted. The system base voltage is 12.66 kV, the base capacity is 1 MVA, the VSC loss coefficient is 0.02, the total initial active load of the districts is 4400 kW, the total reactive load is 4400 kVar, the initial VSC capacity of each is 0, the maximum capacity of a single VSC is 500 kVA, and the safe operating range of the node voltage is set not to exceed 5% of the rated voltage. Considering the high investment cost of the flexible interconnection device, the planning scheme and index results of the FID in the following text are obtained based on 3 two-port FIDs.

[0045] To compare the economic benefits of FID planning, the power supply income per unit load of the districts is set to be 300,000 yuan / MW per year, and the investment cost per unit capacity of the VSC is 400 yuan / kVA, and the discount factor is 0.087. Then the comprehensive income is calculated as follows: (21);

[0046] The hardware environment for the example simulation is Intel i5-12400F @ 2.50 GHz, with 32G of running memory, and the software environment is based on MATLAB2023b and Gurobi 10.

[0047] The simulation analysis is as follows:

[0048] (1) Planning results and index evaluation

[0049] Since 3 two-port FIDs are connected, the number of interconnected districts required is 6. The numbers of the first 6 districts selected by the distribution transformer load rate sensitivity method are 8, 15, 16, 18, 24, and 36 respectively. The district interconnection methods obtained by solving the load balancing optimization model are (8, 36), (15, 24), and (16, 18). The VSC capacity results configured for each district are shown in Table 1.

[0050] Table 1 Substation Area Number VSC Capacity / (kVA) 8 341.9 15 400.0 16 257.8 18 242.2 24 380.3 36 360.4

[0051] The active load distribution of each district before and after the flexible interconnection planning and the VSC transmission power of each district are as Figure 5 shown.

[0052] As Figure 5 can be seen, there are significant changes in the active load distribution among the interconnected districts 8, 15, 16, 18, 24, and 36 after FID interconnection. Among them, district 8 supplies power to district 36, district 24 supplies power to district 15, and district 18 supplies power to district 16. Therefore, the maximum active load that districts 15, 16, and 36 can carry has increased significantly, while the maximum active load that districts 8, 18, and 24 can supply has decreased.

[0053] The result changes of each index before and after FID planning are shown in Table 2. The calculation formula of voltage deviation is as follows, which is used to describe the voltage stability of the distribution network before and after the flexible interconnection of the distribution transformer area: (22);

[0054] Table 2 Index Before Planning After Planning TSC / (MW) 8.027 9.020 Variance of Load Factor / % 2.885 2.256 Voltage Deviation / V 0.0246 0.0190 FID Investment Cost / 10,000 yuan 0 6.90 Substation Area Power Supply Income / 10,000 yuan 240.81 270.60 Comprehensive Income / 10,000 yuan 240.81 263.70

[0055] As can be seen from the above table, after the flexible interconnection planning, the TSC of the system has increased by 12.371%, indicating that the access of the flexible interconnection device in the distribution transformer area can significantly improve the maximum power supply capacity of the system. The variance of the load rate has decreased by 21.802%. This is because when selecting the location of FID, the distribution transformer areas are screened according to the sensitivity of the distribution transformer load rate, and the interconnection method of FID is also optimized based on the load balancing goal. Therefore, the obtained FID planning scheme can improve the load balancing degree of the distribution transformer to balance the heavy and light loads of the distribution transformer and reduce the occurrence of overload phenomena. In addition, due to the access and operation of FID optimizing the load and power flow distribution in the distribution transformer area, the voltage deviation of the system has also been reduced, thus improving the voltage stability and ensuring the safe operation of the system.

[0056] In terms of economic benefits, the comprehensive income has increased by 228,900 yuan after FID planning, while the investment cost of FID is only 69,000 yuan. That is, the economic benefits brought by improving the power supply of the distribution transformer area after planning FID significantly exceed the cost brought by the planning investment, improving the economy of the distribution network planning.

[0057] (2) Comparison of FID planning methods

[0058] The traditional FID location selection method based on sensitivity uses the node voltage sensitivity method. To verify the superiority of the flexible interconnection planning method for distribution transformer areas based on the sensitivity of distribution transformer load rate proposed in this paper in terms of improving power supply capacity and economic benefits, the following two scenarios are set for comparison:

[0059] 1) The FID planning method for distribution transformer areas based on voltage sensitivity method for location selection;

[0060] 2) The FID planning method for distribution transformer areas based on the sensitivity of distribution transformer load rate proposed in this paper for location selection.

[0061] The FID planning schemes and the results of each index in the above two scenarios are shown in Table 3:

[0062] Table 3 Scenario Scenario 1 Scenario 2 FID Site Selection Scheme (13, 18), (14, 17), (15, 16) (8, 36), (15, 24), (16, 18) VSC Capacity 13: 352.2 kVA 14: 339.0 kVA 15: 384.3 kVA 16: 394.3 kVA 17: 333.0 kVA 18: 345.1 kVA 8: 341.9 kVA 15: 400.0 kVA 16: 257.8 kVA 18: 242.2 kVA 24: 380.3 kVA 36: 360.4 kVA TSC / (MW) 8.501 9.020 Variance of Load Factor / % 2.332 2.256 Voltage Deviation / V 0.0147 0.0190 FID Investment Cost / 10,000 yuan 7.47 6.90 Substation Area Power Supply Income / 10,000 yuan 255.03 270.60 Comprehensive Income / 10,000 yuan 247.56 263.70

[0063] As can be seen from Table 3, compared with Scenario 1 where the voltage sensitivity method is used for site selection, Scenario 2 where the load rate sensitivity method is used for site selection improves the maximum power supply capacity TSC and suppresses the variance of the distribution transformer load rate. This is because the voltage sensitivity values of adjacent substations are close. Therefore, the FID interconnected substation positions given by the voltage sensitivity method are relatively concentrated. For example, the FIDs in Scenario 1 are concentratedly connected at substations 13 - 18. After the flexible interconnection of these adjacent substations, the role that the FIDs can play is very limited. However, the interconnected substation positions selected according to the substation load rate sensitivity are relatively dispersed, which can better play the power transfer role of the FIDs, thereby fully releasing the power supply potential of the substations, overcoming the power supply bottleneck, improving the power supply capacity, and optimizing the load distribution among the substations. In terms of voltage stability, the voltage of the nodes where the substations are located screened by the voltage sensitivity method is more affected by the power transferred by the FIDs, so it is easier to adjust its fluctuation and better voltage stability is obtained.

[0064] In terms of economic benefits, compared with not planning FIDs, using the planning method of Scenario 1 can also slightly improve the comprehensive income, but there is still a gap of 161,400 yuan compared with the planning method proposed in this paper. In addition, the FID investment cost of the planning method proposed in this paper is slightly lower than that of the Scenario 1 planning method, but it can greatly improve the power supply income of the substations, thus verifying that the method in this paper can improve the economy.

[0065] In addition, the present invention also provides an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, it implements the method for flexible interconnection planning of substations based on distribution transformer sensitivity analysis; it also provides a storage medium containing computer-executable instructions, and when the computer-executable instructions are executed by a computer processor, they implement the method for flexible interconnection planning of substations based on distribution transformer sensitivity analysis.

[0066] In summary, the method for flexible interconnection planning of substations proposed in the present invention considers the substation screening strategy based on the analysis of the distribution transformer load rate sensitivity of substations and the optimization model of the FID interconnection method based on the load balancing goal to screen the most suitable substations for interconnection and give the FID interconnection method with the best load balancing effect; in the part of FID capacity determination and optimization, the maximum power supply capacity of the system is used as the goal to determine the FID configuration capacity and the active power load distribution of the substations, and at the same time, the quadratic optimization of the FID construction cost is used to eliminate the capacity redundancy and improve the planning economy. The calculation example results show that the proposed planning method can take into account the two goals of improving the power supply capacity and the load balancing degree, and compare with other planning methods, verifying the superiority of the method proposed in this paper in enhancing the power supply capacity, improving the load distribution, and improving the economic benefits, thus providing a reference for the FID planning of substations in actual projects.

Claims

1. A flexible interconnection planning method for a distribution transformer area based on distribution transformer sensitivity analysis, characterized in that Including: Obtain the relevant data of the flexible interconnection device and the distribution area; Construct a flexible interconnection planning model for the distribution area. The model includes site selection, capacity determination optimization, and constraint conditions. The site selection is to derive and calculate the sensitivity of the distribution transformer load rate based on the mathematical model of the distribution transformer in the distribution area. Secondly, the distribution areas to be interconnected are screened according to the magnitudes of the distribution transformer load rate sensitivities of each distribution area. Then, the connection method of the flexible interconnection device is optimized with the goal of load balancing in the distribution area; The capacity determination optimization takes the optimization of the maximum power supply capacity as the objective function to determine the configuration capacity of the flexible interconnection device and the active load distribution of each distribution area; The constraint conditions include the constraint of the FID interconnection method in the distribution area, the operation constraint of the flexible interconnection device, the operation constraint of the distribution transformer in the distribution area, the distribution network power flow constraint, and the safe operation constraint; Solve the flexible interconnection planning model for the distribution area based on the relevant data of the flexible interconnection device and the distribution area to obtain the site selection connection and capacity configuration scheme of the flexible interconnection device.

2. The method according to claim 1, wherein The site selection is to derive and calculate the sensitivity of the distribution transformer load rate based on the mathematical model of the distribution transformer in the distribution area. Secondly, the distribution areas to be interconnected are screened according to the magnitudes of the distribution transformer load rate sensitivities of each distribution area. Then, the connection method of the flexible interconnection device is optimized with the goal of load balancing in the distribution area. Specifically as follows: First, according to the distribution transformer model in the substation area, the load rate of the distribution transformer at location i in the substation area is obtained. The calculation formula is as follows: ； Where: and respectively represent the active and reactive power at the low-voltage side of the distribution transformer in district i; represents the capacity of the distribution transformer in district i; and The calculation formula is as follows: ； Wherein: and respectively represent the active and reactive powers transmitted by the VSC connected to the i-th distribution area; and are respectively the active load and reactive load supplied by the i-th distribution area; According to the partial derivative rule, obtain the relationship between the change in the distribution transformer load rate in the distribution area and the change in the VSC transmission power: ； In the formula: is the change in the load rate of the distribution transformer at substation area i; and are respectively the change in active power transmitted by the VSC connected to substation area i and the change in reactive power; Then the calculation formula for the distribution transformer load rate sensitivity in the formula is as follows: ； The method for screening interconnected distribution areas is as follows: Calculate the sensitivities of all distribution transformers in the distribution area according to the above distribution transformer load rate sensitivity calculation formula, and sort them in descending order. Then, after specifying the installation quantity and port type of the FID, select the distribution areas with the top sensitivities. The number of interconnected distribution areas screened is calculated as follows: ； Wherein: represents the number of interconnected substations selected; represents the number of FIDs accessed; represents the FID port type; Optimize the connection method of the flexible interconnection device with the goal of load balancing in the distribution area. The method is to construct a load balancing optimization model, and the objective function is as follows: ； Where: is the variance of the load ratios of all distribution transformers in the substations; is the mean value of the load ratios of all distribution transformers in the substations; is the total number of distribution transformers in the substations.

3. The method according to claim 1, characterized in that, The capacity determination optimization takes the optimization of the maximum power supply capacity as the objective function to determine the configuration capacity of the flexible interconnection device and the active load distribution of each distribution area. Specifically as follows: The objective function of the capacity determination optimization model is as follows: ； In the formula: TSC represents the maximum power supply capacity.

4. The method according to claim 1, characterized in that, If the distribution area contains multiple FIDs, the FID interconnection method constraint in the distribution area includes: ； ； ； In the formula: represents the FID interconnection matrix. When the nth FID is connected to the i-th substation area, the corresponding matrix element = 1; otherwise = 0; is an identifier indicating whether an FID is connected to the j-th substation area. A value of 1 indicates connection, and a value of 0 indicates non-connection; represents the matrix the sum of the element values in the j-th column.

5. The method according to claim 1, characterized in that If the flexible interconnection device contains multiple VSCs, assuming that the positive direction of the VSC power flowing out of the bus, the operation constraint of the flexible interconnection device includes: ； ； ； ； In the formula: represents the set of substation area numbers interconnected by the k-th FID; represents the active power loss of the VSC connected at substation area i; represents the loss coefficient of the VSC; represents the capacity of the VSC connected at substation area i; represents the sine value of the power factor angle.

6. The method according to claim 1, characterized in that The operation constraint of the distribution transformer in the distribution area includes: ； Wherein: and respectively represent the active and reactive powers on the high-voltage side of the distribution transformer at the i-th substation area; and respectively represent the no-load loss and rated load loss of the distribution transformer; and respectively represent the percentage of no-load current and percentage of short-circuit voltage of the distribution transformer.

7. The method according to claim 1, wherein The distribution network power flow constraint includes: ； ； ； 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.

8. The method according to claim 1, characterized in that, The safe operation constraint includes: ； 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.

9. An electronic device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements a flexible interconnection planning method for a distribution area based on distribution transformer sensitivity analysis as described in any one of claims 1-8.

10. A storage medium containing computer-executable instructions, which implement a flexible interconnection planning method for a distribution area based on distribution transformer sensitivity analysis as described in any one of claims 1-8 when executed by a computer processor.

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