Method and system for estimating running state of low-voltage power distribution network

Abstract

The invention discloses a method and a system for estimating the running state of a low-voltage power distribution network, and provides a comprehensive evaluation strategy for the running state of the power distribution network in consideration of the increase of the probability that the low-voltage power distribution network runs in an unsafe and normal state after large-scale distributed photovoltaic access to the low-voltage power distribution network. The method is used for accurately and efficiently knowing the operation state of the high-proportion distributed photovoltaic low-voltage power distribution network. According to the method, the combined weighting method is adopted, the subjective weight and the objective weight are adopted as upper and lower limits of the combined weight, and the variable coefficient maximization combined weighting method is adopted, so that the low-voltage power distribution network operation state evaluation results have relatively large differences, evaluated objects can be effectively distinguished, the evaluation results are conveniently compared, and the evaluation efficiency is improved. And the evaluation result is more accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of power system state assessment, and in particular to a method and system for estimating the operating state of a low-voltage distribution network. Background Art

[0002] With the large-scale access of distributed photovoltaic units to distribution areas, the operating environment of the power system is becoming increasingly complex, and the demand for intelligent management is becoming more urgent. The traditional distribution network management model faces new challenges, especially in the context of high penetration of renewable energy and dynamic changes in power demand. Many low-voltage distribution network operating indicators have different degrees of influence on the operating status of the power grid, but the influence weights of many indicators can be divided into subjective weights and objective weights, and the weighting basis of different weights is different. The current power grid operation status evaluation method has not reasonably considered the impact of the combination of subjective and objective weights of each indicator on the power grid operation status. Summary of the invention

[0003] The technical problem to be solved by the present invention is how to fully consider the subjective and objective weights of various indicators and use them reasonably in the evaluation of power grid operation status.

[0004] The present invention solves the above technical problems through the following technical means:

[0005] A method for estimating the operating state of a low-voltage distribution network comprises the following steps:

[0006] Construct a low-voltage distribution network operation status indicator system;

[0007] Taking into account the degree to which various status indicators reflect the safe operation status of the power grid, a comprehensive priority diagram method and a weighted coefficient method based on indicator correlation are established to calculate the subjective weight ω of each indicator respectively. j and objective weights j The combined weighting method of; where j represents the jth indicator;

[0008] Finally, the evaluation results of the low-voltage distribution network operation status are obtained by the combination weighting method of maximizing the coefficient of variation; specifically, the results obtained by the combination weighting method are:

[0009]

[0010] For this evaluation result vector, the maximum coefficient of variation is used as the objective function:

[0011]

[0012] Among them, Z is the combined weight vector, A is the matrix of the numerical values ​​of the low-voltage distribution network operating status indicators, D is the evaluation result vector, k is the number of indicators, ν is the coefficient of variation, is the mean of the evaluation results; based on the combined weights, the evaluation results of the low-voltage distribution network operation status can be finally obtained;

[0013] The constraint condition of the objective function is z j Between subjective weight ω j and objective weights j between.

[0014] Furthermore, the low voltage distribution network operation status indicator system includes:

[0015] For the operation characteristics of high-proportion distributed photovoltaic low-voltage distribution network, one indicator is selected from each of the five aspects: reliability, safety, quality, adaptability, and economy. The reliability indicator is the average power supply reliability rate, the safety indicator is the available transmission capacity, the quality indicator is the voltage deviation rate, the adaptability indicator is the maximum load imbalance, and the economy indicator is the line loss rate.

[0016] The average power supply reliability is:

[0017]

[0018] Among them, N total is the total number of power users, T i is the power outage time, N i The number of users who experienced power outage;

[0019] The available transmission capacity is:

[0020] S ATC =S TTC -S ETC

[0021] Among them, S TTC is the maximum transmission capacity, S ETC For existing transmission capacity;

[0022] The voltage offset rate is:

[0023]

[0024] Among them, U i is the node voltage during normal operation, U N is the rated voltage;

[0025] The maximum load imbalance is:

[0026]

[0027] Among them, P i is the actual load, P EN is the rated capacity;

[0028] The line loss rate is:

[0029]

[0030] Among them, P S is the power supply, P U For electricity consumption.

[0031] Furthermore, the low voltage distribution network operation status indicator system includes:

[0032] Among the various evaluation indicators constructed for the operation characteristics of high-proportion distributed photovoltaic low-voltage distribution networks, the average power supply reliability rate and available transmission capacity are positive indicators, and the voltage offset rate, maximum load imbalance and line loss rate are negative indicators. In order to unify the various evaluation indicators, all indicators are reversed and standardized, so that the smaller the indicator, the safer the operation status of the substation, and all indicators range between 0-1;

[0033] The standardized formula for the positive indicator is:

[0034]

[0035] Among them, x is a positive indicator, x max is the maximum value of the positive indicator, x max It is the minimum value of the positive indicator;

[0036] The standardized formula for the inverse indicator is:

[0037]

[0038] Among them, y is a positive indicator, y max is the maximum value of the positive indicator, y max It is the minimum value of the positive indicator.

[0039] Furthermore, the calculation process of the priority diagram method in the combined weighting method is:

[0040] a. Decompose the multi-index system into several levels to form a hierarchical structure, including the target level, the criterion level and the program level;

[0041] b. Compare the elements in each layer to form a judgment matrix. For the criteria layer and the solution layer, expert judgment, experimental data or other methods can be used for comparison. Judgment matrix; represented by A, its element a ij Indicates the importance of element i relative to element j.

[0042] c. Calculate the consistency index CI; if CI is greater than a certain threshold, consistency adjustment is required; the calculation formula of the consistency index is:

[0043]

[0044] Among them, λ max is the maximum eigenvalue of the judgment matrix, and n is the order of the judgment matrix.

[0045] d. The judgment matrix is ​​adjusted for consistency through the random consistency index RI and the consistency ratio CR. The calculation formula of the consistency ratio is:

[0046]

[0047] If the CR is greater than a certain threshold (usually 0.1), it is necessary to re-judge the expert or modify the judgment matrix;

[0048] e. According to the judgment matrix passed by consistency, calculate the weight vector W and obtain the subjective weight ω of the jth indicator j

[0049]

[0050] Furthermore, the weighting coefficient method based on indicator correlation specifically includes:

[0051] a. The variability of the calculation indicator is mainly measured by the size of the standard deviation. The larger the standard deviation, the greater the numerical difference of the indicator, the more information it can show, and the stronger the evaluation strength of the indicator itself. More weight should be assigned to the indicator. The calculation formula is:

[0052]

[0053] Among them, σ j represents the standard deviation of the jth indicator, x ij represents the value of the jth indicator of the i-th sample, represents the average value of the jth indicator;

[0054] b. Calculate the conflict between indicators to reflect the correlation between different indicators. Let the conflict between indicator j and other indicators be f j , then:

[0055]

[0056] Among them, r ij represents the Pearson correlation coefficient between indicators i and j;

[0057] c. Calculate the information carrying capacity C j In order to judge the role of the indicator in the entire indicator system, the calculation formula is:

[0058] C j =σ j f j

[0059] When Cj When it is larger, the corresponding indicator should be assigned more weight;

[0060] d. For the jth indicator, its weight calculation formula is:

[0061]

[0062] The present invention also provides a low-voltage distribution network operating state estimation system, comprising the following steps:

[0063] Data collection module: build a low-voltage distribution network operation status indicator system;

[0064] Index processing module: Considering the degree to which various status indicators reflect the safe operation status of the power grid, a comprehensive priority diagram method and a weighted coefficient method based on indicator correlation are established to calculate the subjective weight of each indicator ω j and objective weights j The combined weighting method of; where j represents the jth indicator;

[0065] State estimation module: Finally, the low-voltage distribution network operation state evaluation result is obtained by the combination weighting method of maximizing the coefficient of variation; specifically, the result obtained by the combination weighting method is:

[0066]

[0067] For this evaluation result vector, the maximum coefficient of variation is used as the objective function:

[0068]

[0069] Among them, Z is the combined weight vector, A is the matrix of the numerical values ​​of the low-voltage distribution network operating status indicators, D is the evaluation result vector, k is the number of indicators, ν is the coefficient of variation, is the mean of the evaluation results; based on the combined weights, the evaluation results of the low-voltage distribution network operation status can be finally obtained;

[0070] The constraint condition of the objective function is z j Between subjective weight ω j and objective weights j between.

[0071] Furthermore, the low voltage distribution network operation status indicator system includes:

[0072] For the operation characteristics of high-proportion distributed photovoltaic low-voltage distribution network, one indicator is selected from each of the five aspects: reliability, safety, quality, adaptability, and economy. The reliability indicator is the average power supply reliability rate, the safety indicator is the available transmission capacity, the quality indicator is the voltage deviation rate, the adaptability indicator is the maximum load imbalance, and the economy indicator is the line loss rate.

[0073] The average power supply reliability is:

[0074]

[0075] Among them, N total is the total number of power users, T i is the power outage time, N i The number of users who experienced power outage;

[0076] The available transmission capacity is:

[0077] S ATC =S TTC -S ETC

[0078] Among them, S TTC is the maximum transmission capacity, S ETC For existing transmission capacity;

[0079] The voltage offset rate is:

[0080]

[0081] Among them, U i is the node voltage during normal operation, U N is the rated voltage;

[0082] The maximum load imbalance is:

[0083]

[0084] Among them, P i is the actual load, P EN is the rated capacity;

[0085] The line loss rate is:

[0086]

[0087] Among them, P S is the power supply, P U For electricity consumption.

[0088] Furthermore, the low voltage distribution network operation status indicator system includes:

[0089] Among the various evaluation indicators constructed for the operation characteristics of high-proportion distributed photovoltaic low-voltage distribution networks, the average power supply reliability rate and available transmission capacity are positive indicators, and the voltage offset rate, maximum load imbalance and line loss rate are negative indicators. In order to unify the various evaluation indicators, all indicators are reversed and standardized, so that the smaller the indicator, the safer the operation status of the substation, and all indicators range between 0-1;

[0090] The standardized formula for the positive indicator is:

[0091]

[0092] Among them, x is a positive indicator, x max is the maximum value of the positive indicator, x max It is the minimum value of the positive indicator;

[0093] The standardized formula for the inverse indicator is:

[0094]

[0095] Among them, y is a positive indicator, y max is the maximum value of the positive indicator, y max It is the minimum value of the positive indicator.

[0096] Furthermore, the calculation process of the priority diagram method in the combined weighting method is:

[0097] a. Decompose the multi-index system into several levels to form a hierarchical structure, including the target level, the criterion level and the program level;

[0098] b. Compare the elements in each layer to form a judgment matrix. For the criteria layer and the solution layer, expert judgment, experimental data or other methods can be used for comparison. Judgment matrix; represented by A, its element a ij Indicates the importance of element i relative to element j.

[0099] c. Calculate the consistency index CI; if CI is greater than a certain threshold, consistency adjustment is required; the calculation formula of the consistency index is:

[0100]

[0101] Among them, λ max is the maximum eigenvalue of the judgment matrix, and n is the order of the judgment matrix.

[0102] d. The judgment matrix is ​​adjusted for consistency through the random consistency index RI and the consistency ratio CR. The calculation formula of the consistency ratio is:

[0103]

[0104] If the CR is greater than a certain threshold (usually 0.1), it is necessary to re-judge the expert or modify the judgment matrix;

[0105] e. According to the judgment matrix passed by consistency, calculate the weight vector W and obtain the subjective weight ω of the jth indicator j

[0106]

[0107] Furthermore, the weighting coefficient method based on indicator correlation specifically includes:

[0108] a. The variability of the calculation indicator is mainly measured by the size of the standard deviation. The larger the standard deviation, the greater the numerical difference of the indicator, the more information it can show, and the stronger the evaluation strength of the indicator itself. More weight should be assigned to the indicator. The calculation formula is:

[0109]

[0110] Among them, σ j represents the standard deviation of the jth indicator, x ij represents the value of the jth indicator of the i-th sample, represents the average value of the jth indicator;

[0111] b. Calculate the conflict between indicators to reflect the correlation between different indicators. Let the conflict between indicator j and other indicators be f j , then:

[0112]

[0113] Among them, r ij represents the Pearson correlation coefficient between indicators i and j;

[0114] c. Calculate the information carrying capacity C j In order to judge the role of the indicator in the entire indicator system, the calculation formula is:

[0115] C j =σ j f j

[0116] When C j When it is larger, the corresponding indicator should be assigned more weight;

[0117] d. For the jth indicator, its weight calculation formula is:

[0118]

[0119] The advantages of the present invention are:

[0120] The subjective weight reflects the importance of the indicator itself and is generally not affected by the value. The objective weight is calculated from the actual numerical value and reflects the degree of distinction between the data. The basis for the weighting of subjective and objective weights is different. From the perspective of taking into account the advantages of both subjective and objective weights, it is necessary to combine the subjective and objective weights. The present invention adopts a combined weighting method and uses subjective weights and objective weights as the upper and lower limits of the combined weights. The combined weighting method of maximizing the coefficient of variation can make the evaluation results of the operating status of the low-voltage distribution network have greater differences, can effectively distinguish the evaluated objects, and facilitate comparison of evaluation results, so that the evaluation results are more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0121] Figure 1 It is a flowchart of the method in the embodiment of the present invention. DETAILED DESCRIPTION

[0122] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0123] like Figure 1 As shown, a method for estimating the operating state of a low-voltage distribution network proposed in the present invention comprises the following steps:

[0124] Considering the operating characteristics of low-voltage distribution networks with a high proportion of distributed photovoltaic power generation, a low-voltage distribution network operating status indicator system is constructed;

[0125] Considering the degree to which various status indicators reflect the safe operation status of the power grid, a combined weighting method of the comprehensive priority diagram method and the weighting coefficient method based on the correlation of indicators is established;

[0126] Finally, the evaluation results of the low-voltage distribution network operating status are obtained through the combined weighting method of maximizing the coefficient of variation, which can accurately and efficiently evaluate the operating status of the voltage distribution network.

[0127] The technical solution of the present invention is described in detail below:

[0128] Step 1: For the operating characteristics of a high-proportion distributed photovoltaic low-voltage distribution network, select one indicator from each of the five levels: reliability, safety, quality, adaptability, and economy. The reliability indicator is the average power supply reliability rate, the safety indicator is the available transmission capacity, the quality indicator is the voltage deviation rate, the adaptability indicator is the maximum load imbalance, and the economy indicator is the line loss rate.

[0129] The average power supply reliability is:

[0130]

[0131] Among them, N total is the total number of power users, T i is the power outage time, N i The number of users experiencing power outage.

[0132] The available transmission capacity is:

[0133] S ATC =S TTC -S ETC (2)

[0134] Among them, S TTC is the maximum transmission capacity, S ETC The existing transmission capacity.

[0135] The voltage offset rate is:

[0136]

[0137] Among them, U i is the node voltage during normal operation, U N is the rated voltage.

[0138] The maximum load imbalance is:

[0139]

[0140] Among them, P i is the actual load, P EN is the rated capacity.

[0141] The line loss rate is:

[0142]

[0143] Among them, P S is the power supply, P U For electricity consumption.

[0144] Among the various evaluation indicators constructed for the operating characteristics of high-proportion distributed photovoltaic low-voltage distribution networks, the average power supply reliability rate and available transmission capacity are positive indicators, and the voltage offset rate, maximum load imbalance and line loss rate are reverse indicators. In order to unify the various evaluation indicators, all indicators are reversed and standardized, so that the smaller the indicator, the safer the operating status of the substation, and all indicators range between 0-1.

[0145] The standardized formula for the positive indicator is:

[0146]

[0147] Among them, x is a positive indicator.

[0148] The standardized formula for the inverse indicator is:

[0149]

[0150] Among them, y is a positive indicator.

[0151] Step 2: The priority diagram method is a method for calculating the weights of each indicator in a multi-indicator system. The operating status of the low-voltage distribution network is affected by many factors, including load changes, equipment status, environmental factors, etc. The priority diagram method can effectively prioritize these factors to better estimate the operating status. The operating status of the distribution network often changes dynamically. The priority diagram method can adjust the priority of factors in a timely manner according to actual operating data and changing trends to enhance the accuracy of the estimate. The following introduces the basic process of calculating weights using the priority diagram method:

[0152] a. Decompose the multi-index system into several levels to form a hierarchical structure, which usually includes the target level, criterion level and solution level.

[0153] b. Compare the elements in each layer to form a judgment matrix. For the criteria layer and the solution layer, expert judgment, experimental data or other methods can be used for comparison. The judgment matrix is ​​usually represented by A, and its element a ij Indicates the importance of element i relative to element j.

[0154] c. Calculate the consistency index CI. If the CI is greater than a certain threshold (usually 0.1), consistency adjustment is required. The calculation formula of the consistency index is:

[0155]

[0156] Among them, λ max is the maximum eigenvalue of the judgment matrix, and n is the order of the judgment matrix.

[0157] d. The judgment matrix is ​​adjusted for consistency through the random consistency index RI and the consistency ratio CR. The calculation formula of the consistency ratio is:

[0158]

[0159] If the CR is greater than a certain threshold (usually 0.1), it is necessary to re-judge the expert or modify the judgment matrix.

[0160] e. According to the judgment matrix passed by consistency, calculate the weight vector W and obtain the subjective weight ω of the jth indicator j .

[0161] The weighted coefficient method based on indicator correlation is mainly to comprehensively measure the objective weight of the indicator based on the comparison strength of the evaluation indicators and the conflict between the indicators. This method automatically calculates the weight of each indicator by analyzing the correlation between the indicators. This method is more objective than subjective evaluation and helps to reduce human bias, thereby improving the accuracy of state estimation. The weighted coefficient method based on indicator correlation can identify the factors that have the greatest impact on the operating status of the low-voltage distribution network, which enables power grid managers to focus resources and attention on key indicators and optimize operation management and maintenance strategies.

[0162] a. The variability of the calculation indicator is mainly measured by the size of the standard deviation. The larger the standard deviation, the greater the numerical difference of the indicator, the more information it can show, and the stronger the evaluation strength of the indicator itself. More weight should be assigned to the indicator. The calculation formula is:

[0163]

[0164] Among them, σ j represents the standard deviation of the jth indicator, x ij represents the value of the jth indicator of the i-th sample, Represents the average value of the j-th indicator.

[0165] b. Calculate the conflict between indicators to reflect the correlation between different indicators. Let the conflict between indicator j and other indicators be f j , then:

[0166]

[0167] Among them, r ij Represents the Pearson correlation coefficient between indicators i and j.

[0168] c. Calculate the information carrying capacity C j In order to judge the role of the indicator in the entire indicator system, the calculation formula is:

[0169] C j =σ j f j (12)

[0170] When C j The larger it is, the more weight should be assigned to the corresponding indicator.

[0171] d. For the jth indicator, its weight calculation formula is:

[0172]

[0173] Step 3: The combined weighting method first needs to be determined through the subjective weight ω j and objective weightsj Get the combined weight z j , the combined weight is somewhere in between.

[0174] The combination weighting method of maximizing the coefficient of variation makes the evaluation results of the low-voltage distribution network operation status have greater differences, which is convenient for comparing the evaluation results. The results obtained by the combination weighting method are:

[0175]

[0176] Right now:

[0177] D=ZA T =[d1,d2,...,d n ] (14)

[0178] For this evaluation result vector, the maximum coefficient of variation is used as the objective function:

[0179]

[0180] Among them, Z is the combined weight vector, A is the matrix of the numerical values ​​of the low-voltage distribution network operating status indicators, D is the evaluation result vector, k is the number of indicators, ν is the coefficient of variation, is the mean of the evaluation results; based on the combined weights, the low-voltage distribution network operation status evaluation results can be finally obtained; the constraint condition of the objective function is z j Between subjective weight ω j and objective weights j between.

[0181] In general, this method can analyze the operating status evaluation indicators of the low-voltage distribution network, so as to have a clearer understanding of the operating status of the low-voltage distribution network, timely identify the potential operating risks of the low-voltage distribution network, and ensure the safe and stable operation of the low-voltage distribution network.

[0182] For the above-mentioned low-voltage distribution network operating state estimation method, the applicability of this method is evaluated through specific case analysis.

[0183] The method was verified using a real system and four stations were selected for verification. The results of the priority ranking of the proposed indicators are as follows:

[0184]

[0185]

[0186] Then all the above indicators are reversed and standardized, and the output results are as follows:

[0187]

[0188] The combined weighting method of comprehensive priority diagram method and weighted coefficient method based on index correlation is used to comprehensively evaluate the operation status of low-voltage distribution network. The results are as follows:

[0189]

[0190] Finally, the evaluation results of the operating status of the low-voltage distribution network can be obtained through the combined weighting method of maximizing the coefficient of variation, which can help managers identify the potential operating risks of the low-voltage distribution network and ensure the safe and stable operation of the low-voltage distribution network.

[0191] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for estimating the operating state of a low-voltage distribution network, characterized in that: The following steps are involved: Construct a low-voltage distribution network operation status indicator system; Taking into account the degree to which various status indicators reflect the safe operation status of the power grid, a comprehensive priority diagram method and a weighted coefficient method based on indicator correlation are established to calculate the subjective weight ω of each indicator respectively. j and objective weights j The combined weighting method; Where j represents the jth indicator; Finally, the evaluation results of the low-voltage distribution network operation status are obtained by the combination weighting method of maximizing the coefficient of variation; specifically, the results obtained by the combination weighting method are: For this evaluation result vector, the maximum coefficient of variation is used as the objective function: Among them, Z is the combined weight vector, A is the matrix of the numerical values ​​of the low-voltage distribution network operating status indicators, D is the evaluation result vector, k is the number of indicators, ν is the coefficient of variation, is the mean of the evaluation results; based on the combined weights, the evaluation results of the low-voltage distribution network operation status can be finally obtained; The constraint condition of the objective function is z j Between subjective weight ω j and objective weights j between.

2. The method for estimating the operating state of a low-voltage distribution network according to claim 1, characterized in that: The low voltage distribution network operation status indicator system includes: For the operation characteristics of high-proportion distributed photovoltaic low-voltage distribution network, one indicator is selected from each of the five aspects: reliability, safety, quality, adaptability, and economy. The reliability indicator is the average power supply reliability rate, the safety indicator is the available transmission capacity, the quality indicator is the voltage deviation rate, the adaptability indicator is the maximum load imbalance, and the economy indicator is the line loss rate. The average power supply reliability is: Among them, N total is the total number of power users, T i is the power outage time, N i The number of users who experienced power outage; The available transmission capacity is: S ATC =S TTC -S ETC Among them, S TTC is the maximum transmission capacity, S ETC For existing transmission capacity; The voltage offset rate is: Among them, U i is the node voltage during normal operation, U N is the rated voltage; The maximum load imbalance is: Among them, P i is the actual load, P EN is the rated capacity; The line loss rate is: Among them, P S is the power supply, P U For electricity consumption.

3. The method for estimating the operating state of a low-voltage distribution network according to claim 2, characterized in that: The low voltage distribution network operation status indicator system includes: Among the various evaluation indicators constructed for the operation characteristics of high-proportion distributed photovoltaic low-voltage distribution networks, the average power supply reliability rate and available transmission capacity are positive indicators, and the voltage offset rate, maximum load imbalance and line loss rate are negative indicators. In order to unify the various evaluation indicators, all indicators are reversed and standardized, so that the smaller the indicator, the safer the operation status of the substation, and all indicators range between 0-1; The standardized formula for the positive indicator is: Among them, x is a positive indicator, x max is the maximum value of the positive indicator, x max It is the minimum value of the positive indicator; The standardized formula for the inverse indicator is: Among them, y is a positive indicator, y max is the maximum value of the positive indicator, y max It is the minimum value of the positive indicator.

4. The method for estimating the operating state of a low-voltage distribution network according to claim 1, characterized in that: The calculation process of the priority diagram method in the combined weighting method is: a. Decompose the multi-index system into several levels to form a hierarchical structure, including the target level, the criterion level and the program level; b. Compare the elements in each layer to form a judgment matrix. For the criteria layer and the solution layer, expert judgment, experimental data or other methods can be used for comparison. Judgment matrix; represented by A, its element a ij Indicates the importance of element i relative to element j. c. Calculate the consistency index CI; if CI is greater than a certain threshold, consistency adjustment is required; the calculation formula of the consistency index is: Among them, λ max is the maximum eigenvalue of the judgment matrix, and n is the order of the judgment matrix. d. The judgment matrix is ​​adjusted for consistency through the random consistency index RI and the consistency ratio CR. The calculation formula of the consistency ratio is: If the CR is greater than a certain threshold (usually 0.1), it is necessary to re-judge the expert or modify the judgment matrix; e. According to the judgment matrix passed by consistency, calculate the weight vector W and obtain the subjective weight ω of the jth indicator j 5. The method for estimating the operating state of a low-voltage distribution network according to claim 1, characterized in that: The weighting coefficient method based on indicator correlation specifically includes: a. The variability of the calculation indicator is mainly measured by the size of the standard deviation. The larger the standard deviation, the greater the numerical difference of the indicator, the more information it can show, and the stronger the evaluation strength of the indicator itself. More weight should be assigned to the indicator. The calculation formula is: Among them, σ j represents the standard deviation of the jth indicator, x ij represents the value of the jth indicator of the i-th sample, x j represents the average value of the jth indicator; b. Calculate the conflict between indicators to reflect the correlation between different indicators. Let the conflict between indicator j and other indicators be f j , then: Among them, r ij represents the Pearson correlation coefficient between indicators i and j; c. Calculate the information carrying capacity C j In order to judge the role of the indicator in the entire indicator system, the calculation formula is: C j =σ j f j When C j When it is larger, the corresponding indicator should be assigned more weight; d. For the jth indicator, its weight calculation formula is:

6. A low voltage distribution network operation state estimation system, characterized in that: The following steps are involved: Data collection module: build a low-voltage distribution network operation status indicator system; Index processing module: Considering the degree to which various status indicators reflect the safe operation status of the power grid, a comprehensive priority diagram method and a weighted coefficient method based on indicator correlation are established to calculate the subjective weight of each indicator ω j and objective weights j The combined weighting method; Where j represents the jth indicator; State estimation module: Finally, the low-voltage distribution network operation state evaluation result is obtained by the combination weighting method of maximizing the coefficient of variation; specifically, the result obtained by the combination weighting method is: For this evaluation result vector, the maximum coefficient of variation is used as the objective function: Among them, Z is the combined weight vector, A is the matrix of the numerical values ​​of the low-voltage distribution network operating status indicators, D is the evaluation result vector, k is the number of indicators, ν is the coefficient of variation, is the mean of the evaluation results; based on the combined weights, the evaluation results of the low-voltage distribution network operation status can be finally obtained; The constraint condition of the objective function is z j Between subjective weight ω j and objective weights j between.

7. The low voltage distribution network operation status estimation system according to claim 6, characterized in that: The low voltage distribution network operation status indicator system includes: For the operation characteristics of high-proportion distributed photovoltaic low-voltage distribution network, one indicator is selected from each of the five aspects: reliability, safety, quality, adaptability, and economy. The reliability indicator is the average power supply reliability rate, the safety indicator is the available transmission capacity, the quality indicator is the voltage deviation rate, the adaptability indicator is the maximum load imbalance, and the economy indicator is the line loss rate. The average power supply reliability is: Among them, N total is the total number of power users, T i is the power outage time, N i The number of users who experienced power outage; The available transmission capacity is: S ATC =S TTC -S ETC Among them, S TTC is the maximum transmission capacity, S ETC For existing transmission capacity; The voltage offset rate is: Among them, U i is the node voltage during normal operation, U N is the rated voltage; The maximum load imbalance is: Among them, P i is the actual load, P EN is the rated capacity; The line loss rate is: Among them, P S is the power supply, P U For electricity consumption.

8. A low voltage distribution network operation status estimation system according to claim 7, characterized in that: The low voltage distribution network operation status indicator system includes: Among the various evaluation indicators constructed for the operation characteristics of high-proportion distributed photovoltaic low-voltage distribution networks, the average power supply reliability rate and available transmission capacity are positive indicators, and the voltage offset rate, maximum load imbalance and line loss rate are negative indicators. In order to unify the various evaluation indicators, all indicators are reversed and standardized, so that the smaller the indicator, the safer the operation status of the substation, and all indicators range between 0-1; The standardized formula for the positive indicator is: Among them, x is a positive indicator, x max is the maximum value of the positive indicator, x max It is the minimum value of the positive indicator; The standardized formula for the inverse indicator is: Among them, y is a positive indicator, y max is the maximum value of the positive indicator, y max It is the minimum value of the positive indicator.

9. The low voltage distribution network operation status estimation system according to claim 6, characterized in that: The calculation process of the priority diagram method in the combined weighting method is: a. Decompose the multi-index system into several levels to form a hierarchical structure, including the target level, the criterion level and the program level; b. Compare the elements in each layer to form a judgment matrix. For the criteria layer and the solution layer, expert judgment, experimental data or other methods can be used for comparison. Judgment matrix; represented by A, its element a ij Indicates the importance of element i relative to element j. c. Calculate the consistency index CI; if CI is greater than a certain threshold, consistency adjustment is required; the calculation formula of the consistency index is: Among them, λ max is the maximum eigenvalue of the judgment matrix, and n is the order of the judgment matrix. d. The judgment matrix is ​​adjusted for consistency through the random consistency index RI and the consistency ratio CR. The calculation formula of the consistency ratio is: If the CR is greater than a certain threshold (usually 0.1), it is necessary to re-judge the expert or modify the judgment matrix; e. According to the judgment matrix passed by consistency, calculate the weight vector W and obtain the subjective weight ω of the jth indicator j 10. The low voltage distribution network operation status estimation system according to claim 6, characterized in that: The weighting coefficient method based on indicator correlation specifically includes: a. The variability of the calculation indicator is mainly measured by the size of the standard deviation. The larger the standard deviation, the greater the numerical difference of the indicator, the more information it can show, and the stronger the evaluation strength of the indicator itself. More weight should be assigned to the indicator. The calculation formula is: Among them, σ j represents the standard deviation of the jth indicator, x ij represents the value of the jth indicator of the i-th sample, represents the average value of the jth indicator; b. Calculate the conflict between indicators to reflect the correlation between different indicators. Let the conflict between indicator j and other indicators be f j , then: Among them, r ij represents the Pearson correlation coefficient between indicators i and j; c. Calculate the information carrying capacity C j In order to judge the role of the indicator in the entire indicator system, the calculation formula is: C j =σ j f j When C j When it is larger, the corresponding indicator should be assigned more weight; d. For the jth indicator, its weight calculation formula is:

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