Transformer substation AVC system voltage threshold optimization method

Abstract

The invention provides a transformer substation AVC system voltage threshold optimization method, and relates to the field of transformer substation automation control in an intelligent power grid. According to the method, voltage data of medium-voltage users and low-voltage users in different time periods of a typical day of a transformer substation are collected, a voltage upper limit exceeding index, a voltage lower limit exceeding index and a qualified index in each time period are accurately calculated, and a comprehensive voltage quality index is obtained according to integration of weight coefficients. And based on the index, determining an initial voltage adjustment demand, carrying out smooth optimization processing, simulating the optimized bus voltage by combining a main shift gear adjustment quantity, a voltage adjustment coefficient and a position voltage transfer coefficient, and solving the optimal bus voltage by taking the maximum comprehensive voltage qualification index as a target function. The method can effectively improve the voltage qualification level of medium-voltage and low-voltage users under the transformer substation, prolongs the service life of equipment, enhances the stability and reliability of a power system, and has remarkable practical application value.

Description

Technical Field

[0001] This invention relates to the field of substation AVC system technology, specifically a method for optimizing the voltage threshold of a substation AVC system. Background Technology

[0002] With the construction and development of new power systems, the proportion of distributed photovoltaic power and fluctuating loads in the power grid is constantly increasing, leading to frequent voltage fluctuations in the distribution network and seriously affecting the voltage quality of medium-voltage and low-voltage users. In traditional substations, the 10kV bus voltage is typically adjusted automatically by the automatic voltage control system (AVC) based on preset, relatively broad, and fixed voltage thresholds. This fails to flexibly adjust voltage thresholds according to the real-time voltage quality of the users under the substation's jurisdiction, resulting in problems such as voltage exceeding the upper limit during off-peak hours and voltage exceeding the lower limit during peak hours, affecting the overall voltage compliance level of users under the substation.

[0003] Currently, the existing AVC strategies for substations in the industry mainly include the following:

[0004] 1. Traditional AVC Control Strategy: This strategy relies solely on the substation bus voltage level, failing to adequately consider the actual power consumption and voltage demand differences of the connected users. During off-peak hours, the substation bus voltage may be too high due to excess reactive power, causing medium- and low-voltage users to exceed their voltage limits. Conversely, during peak hours, the bus voltage may decrease due to insufficient reactive power, causing user voltages to fall below their lower limits. This can lead to a decline in user voltage qualification rates and negatively impact power supply quality. This control method is common in some small substations and early-built power grid systems, but it is increasingly unable to meet the high voltage quality requirements of modern power grids.

[0005] 2. Reactive Power and Voltage Nine-Zone Diagram Control Method: Existing substation AVC strategies employ a reactive power and voltage nine-zone diagram control, forming nine zones based on voltage and power factor thresholds. Different zones correspond to different reactive power compensation and transformer tap changer control schemes. However, this method primarily focuses on reactive power compensation and power factor adjustment, without addressing the need to set voltage thresholds based on the acceptable voltage levels of all users under the substation. This makes it difficult to effectively guarantee voltage quality for medium- and low-voltage users.

[0006] 3. Optimization Method for 10kV Bus Voltage Control Target Value: This method calculates the 10kV bus voltage control target at different time sections using distribution network topology information and operational data. However, this target mainly focuses on distribution network losses and transformer voltage qualification rate, and is not directly used for AVC system voltage threshold setting. Furthermore, it lacks a specific method to convert the section target into AVC voltage threshold, thus failing to meet the need for dynamically optimizing substation AVC system voltage thresholds to improve user voltage qualification rate.

[0007] 4. AVC control method based on voltage stability assessment: This method focuses on analyzing voltage stability issues in the power system and using the assessment of system voltage stability to assist AVC control decisions. However, its main focus is on maintaining the overall voltage stability of the power grid, without delving into the voltage quality of users served by substations. Therefore, its effectiveness in optimizing the voltage threshold of the substation AVC system to improve the voltage qualification rate for medium- and low-voltage users is limited.

[0008] 5. AVC control strategies considering dynamic characteristics: These strategies study the impact of power system dynamic characteristics on AVC control, aiming to improve the dynamic performance and stability of the AVC system. However, these strategies often focus on the dynamic response characteristics of the AVC system itself, failing to fully consider the actual voltage conditions of the users under the substation's jurisdiction to optimize the voltage threshold, resulting in poor improvement in user voltage quality.

[0009] In summary, traditional AVC (Automatic Voltage Controller) systems rely heavily on experience for voltage threshold settings, failing to fully consider actual user voltage quality requirements. This lack of flexibility and precision makes them ill-suited to the complex voltage variations resulting from the large-scale integration of distributed energy resources and fluctuating loads in modern power grids. Therefore, there is an urgent need for an AVC system voltage threshold optimization method based on the voltage quality of medium- and low-voltage users under substations. This method aims to achieve precise and dynamic optimization of the substation AVC system voltage threshold, thereby improving the voltage compliance level for medium- and low-voltage users. This invention addresses these issues by deeply analyzing voltage quality data from medium- and low-voltage users under substations to develop a matching AVC system voltage threshold optimization scheme. Summary of the Invention

[0010] (a) Technical problems to be solved

[0011] To address the shortcomings of existing technologies, this invention provides a method for optimizing the voltage threshold of a substation AVC system, thus solving the problems mentioned in the background section.

[0012] (II) Technical Solution

[0013] To achieve the above objectives, the present invention provides the following technical solution: a method for optimizing the voltage threshold of a substation AVC system, comprising the following steps:

[0014] S1. Calculate the time-of-use voltage quality index for medium and low voltage users before optimization. Collect voltage data of medium-voltage users and low-voltage users at time point i on a typical day in the substation; calculate the over-limit index U for medium-voltage users. ur_zy_i Medium-voltage users exceeding the lower limit index U lr_zy_i and the qualification index U qr_zy_i And the low-voltage user exceeding the upper limit index U ur_dy_i The lower limit index U lr_dy_i and the qualification index Uqr_dy_i Based on the weighting coefficients k1 and k2, calculate the comprehensive upper limit exponent U. ur_zh_i Comprehensive Lower Limit Index U lr_zh_i and the overall pass index U qr_zh_i ;

[0015] S2. Calculation of the time period to be optimized, based on the comprehensive qualification index U. qr_zh_i With target value U qr_tar Based on the relationship and the over-limit index ratio threshold b, the initial voltage adjustment requirement (Need) at time point i is determined. i ; Regarding Need i Perform smoothing optimization: if the length of consecutive identical non-zero demand values ​​is less than 3, set it to 0;

[0016] S3. Calculation of optimal bus voltage, based on the optimized Need i Combined with the main gear adjustment amount tap i Voltage regulation coefficient u k % and location voltage transfer coefficient α, simulated optimized medium-voltage user voltage u' zy_i_n and low-voltage user voltage u' dy_i_n Using the optimized user voltage, recalculate the optimized comprehensive voltage qualification index U' for medium and low voltage users using the calculation method in step one. ur_zh_i With maximizing the comprehensive voltage qualification index as the objective function, under the constraint 10kV≤U' bus_i Solve for the optimal bus voltage U' at ≤10.7kV. bus_i ;

[0017] S4. Calculation of the optimized AVC voltage upper and lower limits: Divide all sampling points throughout the day into N groups, and calculate the voltage lower limit U for each group. l_limit_n and voltage upper limit value U h_limit_n The lower voltage limit is based on the average bus voltage within the group minus the margin β, and is not lower than 10kV. The upper voltage limit is the lower voltage limit plus the minimum adjustment range γ, and does not exceed 10.7kV.

[0018] Preferably, in step S1,

[0019]

[0020] U qr_zy_i =1-U ur_zy_i -U lr_zy_i

[0021]

[0022] U qr_dy_i =1-U ur_dy_i -U lr_dy_i

[0023] U ur_zh_i =k1·U ur_zy_i +k2·U ur_dy_i

[0024] U lr_zh_i =k1·U lr_zy_i +k2·U lr_dy_i

[0025] U qr_zh_i =1-U ur_zh_i -U lr_zh_i

[0026] In the formula, i represents the i-th time point of a typical day, and the range of i is 1 to T, where T represents the total number of user voltage sampling points on a typical day; N ur_zy_i N represents the number of medium-voltage users whose voltage exceeds the upper voltage limit at the i-th time point on a typical day under the substation; lr_zy_i N represents the number of medium-voltage users whose voltage exceeds the lower voltage limit at the i-th time point on a typical day under the substation; zy_i N represents the total number of medium-voltage users with voltage values ​​collected at the i-th time point on a typical day under the substation; ur_dy_i N represents the number of low-voltage users whose voltage exceeds the upper voltage limit at the i-th time point on a typical day under the substation; lr_dy_i N represents the number of low-voltage users whose voltage values ​​exceed the lower voltage limit at the i-th time point on a typical day at the substation; dy_i Let k1 be the total number of low-voltage users with voltage values ​​collected at the i-th time point on a typical day under the substation, k2 be the voltage influence factor of medium-voltage users, and k1 = 0.25 and k2 = 0.75.

[0027] Preferably, in step S2, the initial voltage adjustment requirement is... i The calculation satisfies the following logic:

[0028]

[0029] Among them Need i =1 indicates that a boost adjustment is needed. i =-1 indicates that a voltage reduction adjustment is needed. i =0 means no adjustment is needed, and b is the one-way limit coefficient, which defaults to 10.

[0030] Preferably, in step S3, the optimized medium-voltage user voltage u' is simulated. zy_i_n and low-voltage user voltage u' dy_i_n The calculation formula is as follows:

[0031] u′ zy_i_n = (1+Need) i·tap i ·u k %)·α·u zy_i_n

[0032] u′ dy_i_n = (1+Need) i ·tap i ·u k %)·α·u dy_i_n

[0033] Specifically, when the power supply radius under the substation is no more than 13km, the voltage transfer coefficient α is 1. When the power supply radius under the substation exceeds 13km, the voltage transfer coefficient α for the upstream medium and low voltage users is 1, the voltage transfer coefficient α for the intermediate medium and low voltage users is 1.001, and the voltage transfer coefficient α for the downstream medium and low voltage users is 1.002. i Let u be the number of gears that the main transformer in the substation at the i-th sampling point needs to upgrade or downgrade. k % represents the impact of raising or lowering the voltage level of the main transformer within the substation by one step, u k % is set according to the actual transformer model, u' zy_i_n 、u' dy_i_n Let be the optimized medium-voltage user voltage and low-voltage user voltage for the i-th sampling point, respectively.

[0034] Preferably, in step S3, the objective function is calculated as follows:

[0035] max f i =U′ ur_zh_i

[0036] In the formula, U' ur_zh_i This is the optimized comprehensive voltage qualification index for medium and low voltage users.

[0037] Preferably, in step S3, the optimized formula for calculating the 10kV bus voltage of the main transformer in the substation is as follows:

[0038] U′ bus_i = (1+Need) i ·tap i ·u k %)·U bus_i

[0039] In the formula, U' bus_i U bus_i These represent the 10kV bus voltage of the main transformer in the substation before and after optimization, respectively.

[0040] Preferably, in step S4, each group of lower voltage limit values ​​U l_limit_n The calculation formula is as follows:

[0041]

[0042] Where k is the total number of sampling points in each group, n is the data of the nth group, and β is the downward adjustment margin range of the target value of 10kV bus voltage, which is generally taken in the range of 0.1 to 0.3.

[0043] Preferably, in step S4, the upper limit value U of each group of voltages h_limit_n The calculation formula is as follows:

[0044]

[0045] Among them, U l_limit_n γ is the lower limit of the voltage for the nth group, and γ is the minimum adjustment range of the difference between the upper and lower limits of the 10kV bus voltage, which is generally taken in the range of 0.25 to 0.7.

[0046] (III) Beneficial Effects

[0047] This invention provides a method for optimizing the voltage threshold of a substation AVC system, which has the following beneficial effects:

[0048] 1. By optimizing the calculation of the time-sharing voltage quality index for medium and low-voltage users, this invention accurately collects and analyzes voltage data for both medium and low-voltage users, providing a more targeted basis for subsequent voltage adjustments. Compared to traditional AVC control strategies that rely solely on substation bus voltage levels, this invention more accurately reflects the actual voltage quality, effectively improving the voltage compliance level for medium and low-voltage users under the substation. Furthermore, during the calculation of the time period to be optimized, the relationship between the comprehensive compliance index and the target value is combined to determine the initial voltage adjustment requirements and perform smooth optimization, avoiding over-limit issues for medium and low-voltage users under the substation caused by load or main grid voltage fluctuations, thus improving the rationality and effectiveness of voltage adjustments.

[0049] 2. Based on the full range of user voltage data in the distribution network, the optimal bus voltage curve is simulated with the highest voltage qualification rate to accurately determine the upper and lower limits of the AVC voltage. This invention divides all sampling points throughout the day into N groups, calculates the lower and upper voltage limits for each group, and considers the average bus voltage within the group while taking margin into account, ensuring that the upper and lower voltage limits are within a reasonable range. This method can determine corresponding voltage thresholds according to the voltage characteristics of different time periods, realizing dynamic optimization of the AVC voltage threshold. It solves the problem of fixed and broad voltage thresholds in traditional AVC systems, improves the adaptability of the AVC system to different operating conditions, and better guarantees the voltage quality of medium-voltage and low-voltage users in the distribution network.

[0050] 3. By optimizing the upper and lower limits of AVC voltage and implementing precise bus voltage control, the frequency of voltage fluctuations and reactive power regulation actions is reduced, thereby decreasing losses in equipment such as transformers and extending equipment lifespan. Simultaneously, the operational stability and reliability of the power system are improved. Compared to existing AVC control methods based on voltage stability assessment, this invention not only focuses on the overall voltage stability of the power grid but also delves into the voltage quality of users connected to substations, achieving dual protection of voltage stability and user voltage quality. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the present invention;

[0052] Figure 2 This is a schematic diagram of the low-voltage user voltage quality index in Embodiment 2 of the present invention;

[0053] Figure 3 This is a schematic diagram of the medium-voltage user voltage quality index in Embodiment 2 of the present invention;

[0054] Figure 4 This is a schematic diagram of the comprehensive voltage quality index in Embodiment 2 of the present invention;

[0055] Figure 5 This is a schematic diagram illustrating the voltage regulation requirements of Embodiment 2 of the present invention;

[0056] Figure 6 This is a schematic diagram comparing the overall voltage qualification rate of medium and low voltage users under the three schemes before and after optimization in Embodiment 2 of the present invention. Detailed Implementation

[0057] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0058] Example 1:

[0059] like Figure 1 As shown, this embodiment of the invention provides a method for optimizing the voltage threshold of a substation AVC system, including the following steps:

[0060] S1. Calculation of time-of-use voltage quality index for medium and low voltage users before optimization: Given the voltage values ​​of medium-voltage users and low-voltage users, calculate the voltage qualification index, the index exceeding the upper limit, and the index exceeding the lower limit for medium and low voltage users respectively.

[0061]

[0062] U qr_zy_i =1-U ur_zy_i -U lr_zy_i (3)

[0063]

[0064] U qr_dy_i =1-U ur_dy_i -U lr_dy_i (6)

[0065] In the formula: i represents the i-th time point of a typical day, and the range of i is 1 to T; T represents the total number of user voltage sampling points on a typical day; N ur_zy_i N represents the number of medium-voltage users whose voltage exceeds the upper voltage limit at the i-th time point on a typical day under the substation; lr_zy_i N represents the number of medium-voltage users whose voltage exceeds the lower voltage limit at the i-th time point on a typical day under the substation; zy_i U represents the total number of medium-voltage users with voltage values ​​collected at the i-th time point on a typical day under the substation; ur_zy_i U lr_zy_i These are the indices for medium-voltage users exceeding the upper limit and the lower limit, respectively; N ur_dy_i N represents the number of low-voltage users whose voltage exceeds the upper voltage limit at the i-th time point on a typical day under the substation; lr_dy_i N represents the number of low-voltage users whose voltage values ​​exceed the lower voltage limit at the i-th time point on a typical day at the substation; dy_i U represents the total number of low-voltage users with voltage values ​​collected at the i-th time point on a typical day under the substation; ur_dy_i U lr_dy_i These are the low-voltage user exceeding the upper limit index and the medium-voltage user exceeding the lower limit index at the i-th time point of a typical day under the substation, respectively.

[0066] Based on the user voltage qualification index, upper limit index, and lower limit index for medium and low voltage:

[0067] U ur_zh_i =k1·U ur_zy_i +k2·U ur_dy_i (7)

[0068] U lr_zh_i =k1·U lr_zy_i +k2·U lr_dy_i (8)

[0069] U qr_zh_i =1-U ur_zh_i -U lr_zh_i (9)

[0070] In the formula: k1 and k2 are the voltage influence factors for medium-voltage users and low-voltage users, respectively, with default values ​​of 0.25 and 0.75. qr_zh_i Uur_zh_i U lr_zh_i These are the comprehensive voltage qualification index, comprehensive upper limit exceedance index, and comprehensive lower limit exceedance index for low- and medium-voltage users at the i-th time point of a typical day under the substation.

[0071] S2. Calculation of the time period to be optimized: Compare the user's comprehensive voltage qualification index, upper limit exceedance index, and lower limit exceedance index to calculate the preliminary voltage adjustment requirements at various time points on a typical day.

[0072]

[0073] To eliminate the problem of low- and medium-voltage users exceeding limits under the substation due to load or main grid voltage fluctuations, it is necessary to adjust the calculated preliminary voltage adjustment demand. i Further optimization is achieved by iterating through each point in the array. For each non-zero point, the length of its consecutive identical values ​​before and after it is checked. If the sum of the consecutive lengths is less than 3, the point is set to 0.

[0074] S3. Optimal bus voltage calculation, given the bus voltage adjustment requirement (Need) at the i-th sampling point. i Yes, the optimized voltage values ​​for each medium-voltage and low-voltage user under the substation can be calculated, as detailed below:

[0075] u' zy_i_n = (1+Need) i ·tap i ·u k %)·α·u zy_i_n (11)

[0076] u' dy_i_n = (1+Need) i ·tap i ·u k %)·α·u dy_i_n (12)

[0077] In the formula: tap is the number of taps that the main transformer needs to upgrade or downgrade in the substation at the i-th sampling point, u k % represents the impact of raising or lowering the voltage level of the main transformer within the substation by one step, u k The percentage is set according to the actual transformer model. α is the voltage transfer coefficient to low- and medium-voltage users at different locations after voltage regulation at the substation, generally 1. When the power supply radius under the substation exceeds 13km, α is 1 for low- and medium-voltage users at the front end, 1.001 for low- and medium-voltage users in the middle, and 1.002 for low- and medium-voltage users at the end. zy_i_n 、u' dy_i_n Let be the optimized medium-voltage user voltage and low-voltage user voltage for the i-th sampling point, respectively.

[0078] Using the optimized user voltage, the optimized comprehensive voltage qualification index U' for medium and low voltage users is recalculated according to formulas (1) to (9). ur_zh_i .

[0079] The objective function, for the i-th sampling point, aims to maximize the comprehensive voltage qualification index for medium and low voltage users after optimization. The objective function is as follows:

[0080] max f i =(1-|Need i |)·U ur_zh_i +(1-|Need i |)·U' ur_zh_i (13)

[0081] In the formula, U' ur_zh_i This is the optimized comprehensive voltage qualification index for medium and low voltage users.

[0082] Constraints: Due to the specific requirements on the operating range of the substation bus voltage, the optimized bus voltage should meet the following conditions:

[0083] U' bus_i = (1+Need) i ·tap i ·u k %)·U bus_i (14)

[0084] 10≤U' bus_i ≤10.7 (15)

[0085] In the formula: U' bus_i U bus_i These represent the 10kV bus voltage of the main transformer in the substation before and after optimization, respectively.

[0086] S4. Calculation of the optimized upper and lower limits of AVC voltage, based on the optimized bus voltage data U' under the optimal scheme. bus_i Calculate the upper and lower voltage limits, and then set U' bus_i The data from the first sampling point to the Tth sampling point is divided into N groups on average. Each group corresponds to a voltage limit. First, calculate the lower voltage limit for each group:

[0087]

[0088] In the formula: k is the total number of sampling points in each group, n is the data of the nth group, β is the downward adjustment margin range of the target value of 10kV bus voltage, generally ranging from 0.1 to 0.3, U l_limit_n This is the lower limit of the voltage for the nth group.

[0089] According to U l_limit_n Calculate the upper voltage limit for each group:

[0090]

[0091] In the formula: γ is the minimum adjustment range of the difference between the upper and lower limits of the 10kV bus voltage, which is generally taken in the range of 0.25-0.7.

[0092] Example 2:

[0093] On a typical day, the medium-voltage user qualification index of a certain substation is 100 points, and the low-voltage user qualification rate is 95.606 points. The time-of-use medium and low-voltage user and overall voltage quality indices are as follows: Figure 2 , Figure 3 as well as Figure 4 As shown, the weighting coefficients k1 and k2 for calculating the comprehensive voltage quality index are set to default values ​​of 0.25 and 0.75, respectively.

[0094] Calculate the voltage regulation requirements at various time points, with a unidirectional over-limit coefficient of 10. A voltage regulation requirement of -1 indicates a need for voltage reduction, +1 indicates a need for voltage boost, and 0 indicates no voltage regulation is required. Specific voltage regulation requirements are as follows: Figure 5 .

[0095] Given that the tap change of the main transformer in the substation is 1.25%, meaning that the voltage change is 1.25% when the transformer is raised or lowered by one tap, and that the voltage transfer coefficients for the upstream, intermediate, and downstream users of the line are taken as 1, 1.001, and 1.002, respectively, based on the bus voltage value and voltage adjustment requirements, three main transformer tap adjustment schemes are first formulated using expert experience, as shown in Table 1.

[0096] Table 1. Three Main Transmission Gear Adjustment Schemes

[0097]

[0098]

[0099]

[0100] Based on the comparison, Scheme 1 showed the best improvement in overall voltage qualification rate, therefore Scheme 1 was selected. The comparison of the overall voltage qualification rates for medium and low voltage users before and after optimization is as follows: Figure 6 .

[0101] The optimized bus voltage was obtained based on the calculation of Scheme 1. The number of sampling points on the day was 96. The bus voltage was divided into 12 groups of 8 consecutive sampling values ​​according to the 2-hour time window. The downward adjustment margin range of the 0kV bus voltage target value was set to 0.1, and the minimum adjustment range of the difference between the upper and lower limits of the 10kV bus voltage was 0.3. The calculation results of the upper and lower limits of the bus voltage are shown in Table 2.

[0102] Table 2. Optimized upper and lower limits of bus voltage

[0103]

[0104]

[0105]

[0106] Based on calculations, it is recommended to set the AVC voltage limit from 0:00 to 2:00 to 10.15-10.45kV, and the AVC voltage limit from 2:00 to 24:00 to 10.1-10.4kV.

[0107] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for optimizing the voltage threshold of a substation AVC system, characterized in that, Includes the following steps: S1. Calculate the time-of-use voltage quality index for medium and low voltage users before optimization. Collect voltage data of medium-voltage users and low-voltage users at time point i on a typical day in the substation; calculate the over-limit index U for medium-voltage users. ur_zy_i Medium-voltage users exceeding the lower limit index U lr_zy_i and the qualification index U qr_zy_i And the low-voltage user exceeding the upper limit index U ur_dy_i The lower limit index U lr_dy_i and the qualification index U qr_dy_i Based on the weighting coefficients k1 and k2, calculate the comprehensive upper limit exponent U. ur_zh_i Comprehensive Lower Limit Index U lr_zh_i and the overall pass index U qr_zh_i ; S2. Calculation of the time period to be optimized, based on the comprehensive qualification index U. qr_zh_i With target value U qr_tar Based on the relationship and the over-limit index ratio threshold b, the initial voltage adjustment requirement (Need) at time point i is determined. i ; Regarding Need i Perform smoothing optimization: if the length of consecutive identical non-zero demand values ​​is less than 3, set it to 0; S3. Calculation of optimal bus voltage, based on the optimized Need i Combined with the main gear adjustment amount tap i Voltage regulation coefficient u k % and location voltage transfer coefficient α, simulated optimized medium-voltage user voltage u' zy_i_n and low-voltage user voltage u' dy_i_n Using the optimized user voltage, recalculate the optimized comprehensive voltage qualification index U' for medium and low voltage users using the calculation method in step one. ur_zh_i With maximizing the comprehensive voltage qualification index as the objective function, under the constraint 10kV≤U' bus_i Solve for the optimal bus voltage U' at ≤10.7kV. bus_i ; S4. Calculation of the optimized AVC voltage upper and lower limits: Divide all sampling points throughout the day into N groups, and calculate the voltage lower limit U for each group. l_limit_n and voltage upper limit value U h_limit_n The lower voltage limit is based on the average bus voltage within the group minus the margin β, and is not lower than 10kV. The upper voltage limit is the lower voltage limit plus the minimum adjustment range γ, and does not exceed 10.7kV.

2. The method for optimizing the voltage threshold of a substation AVC system according to claim 1, characterized in that: In step S1: IN qr_zy_i =1-U ur_zy_i -IN lr_zy_i IN qr_dy_i =1-U ur_dy_i -IN lr_dy_i IN ur_zh_i =k1·U ur_zy_i +k2·U ur_dy_i IN lr_zh_i =k1·U lr_zy_i +k2·U lr_dy_i IN qr_zh_i =1-U ur_zh_i -IN lr_zh_i In the formula, i represents the i-th time point of a typical day, and the range of i is 1 to T, where T represents the total number of user voltage sampling points on a typical day; N ur_zy_i N represents the number of medium-voltage users whose voltage exceeds the upper voltage limit at the i-th time point on a typical day under the substation; lr_zy_i N represents the number of medium-voltage users whose voltage exceeds the lower voltage limit at the i-th time point on a typical day under the substation; zy_i N represents the total number of medium-voltage users with voltage values ​​collected at the i-th time point on a typical day under the substation; ur_dy_i N represents the number of low-voltage users whose voltage exceeds the upper voltage limit at the i-th time point on a typical day under the substation; lr_dy_i N represents the number of low-voltage users whose voltage values ​​exceed the lower voltage limit at the i-th time point on a typical day at the substation; dy_i k1 represents the total number of low-voltage users with voltage values ​​collected at the i-th time point on a typical day under the substation, k2 represents the voltage influence factor of medium-voltage users, and k2 represents the voltage influence factor of low-voltage users. The default values ​​of k1 and k2 are 0.25 and 0.75, respectively.

3. The method for optimizing the voltage threshold of a substation AVC system according to claim 1, characterized in that: In step S2, the initial voltage adjustment requirement is... i The calculation satisfies the following logic: Among them Need i =1 indicates that a boost adjustment is needed. i =-1 indicates that a voltage reduction adjustment is needed. i =0 means no adjustment is needed, and b is the one-way limit coefficient, which defaults to 10.

4. The method for optimizing the voltage threshold of a substation AVC system according to claim 1, characterized in that: In step S3, the optimized medium-voltage user voltage u' is simulated. zy_i_n and low-voltage user voltage u' dy_i_n The calculation formula is: u’ zy_i_n =(1+Need i ·tap i ·u k %)·α·u zy_i_n u’ dy_i_n =(1+Need i ·tap i ·u k %)·α·u dy_i_n Specifically, when the power supply radius under the substation is no more than 13km, the voltage transfer coefficient α is 1. When the power supply radius under the substation exceeds 13km, the voltage transfer coefficient α for the upstream medium and low voltage users is 1, the voltage transfer coefficient α for the intermediate medium and low voltage users is 1.001, and the voltage transfer coefficient α for the downstream medium and low voltage users is 1.

002. i Let u be the number of gears that the main transformer in the substation at the i-th sampling point needs to upgrade or downgrade. k % represents the impact of raising or lowering the voltage level of the main transformer within the substation by one step, u k % is set according to the actual transformer tap position voltage adjustment step size, u' zy_i_n 、u' dy_i_n Let be the optimized medium-voltage user voltage and low-voltage user voltage for the i-th sampling point, respectively.

5. The method for optimizing the voltage threshold of a substation AVC system according to claim 1, characterized in that: In step S3, the objective function is calculated as follows: max f i =U ur_zh_i In the formula, U' ur_zh_i This is the optimized comprehensive voltage qualification index for medium and low voltage users.

6. The method for optimizing the voltage threshold of a substation AVC system according to claim 1, characterized in that: In step S3, the optimized formula for calculating the 10kV bus voltage of the main transformer in the substation is as follows: U’ bus_i =(1+Need i ·tap i ·u k %)·U bus_i In the formula, U' bus_i U bus_i These represent the 10kV bus voltage of the main transformer in the substation before and after optimization, respectively.

7. The method for optimizing the voltage threshold of a substation AVC system according to claim 1, characterized in that: In step S4, the lower voltage limit value U for each group l_limit_n The calculation formula is: Where k is the total number of sampling points in each group, n is the data of the nth group, and β is the downward adjustment margin range of the 10kV bus voltage target value, with a value range of 0.1 to 0.

3.

8. The method for optimizing the voltage threshold of a substation AVC system according to claim 1, characterized in that: In step S4, the upper limit value U of each group of voltages h_limit_n The calculation formula is: Among them, U l_limit_n γ is the lower limit of the voltage for the nth group, and γ is the minimum adjustment range of the difference between the upper and lower limits of the 10kV bus voltage, with a value range of 0.25 to 0.7.

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