CN109687458B - Grid planning method considering regional distribution network risk bearing capacity difference - Google Patents
Grid planning method considering regional distribution network risk bearing capacity difference Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H—ELECTRICITY
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- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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Abstract
The invention relates to a net rack planning method considering regional power distribution network risk bearing capacity difference, which comprises the following steps: aiming at the problems of large difference of risk bearing capacity between distribution networks in rural areas and large load fluctuation of the rural areas in rural network reconstruction engineering, a nonparametric kernel density estimation method is adopted to represent load uncertainty; calculating the difference of the capability of each distribution network in the village and town to bear the operation risk caused by the uncertainty of the load, and establishing an evaluation index system of the risk bearing capability of the distribution network in the region by combining the characteristics of the distribution network in the village and town; evaluating by adopting a combined weighting method based on an analytic hierarchy process and an entropy weight method; and establishing an opportunity constraint planning model for line upgrading and selection, and differentially selecting the confidence level of opportunity constraint conditions according to the risk bearing capacity evaluation result of each distribution network in the villages and towns, so that the mutual coordination of the risk bearing capacity and the investment cost of the distribution network in the region is realized, and the investment is lean.
Description
Technical Field
The invention relates to the technical field of power distribution networks, in particular to a net rack planning method considering the difference of risk bearing capacity of a regional power distribution network.
Background
The power distribution network planning theory in China is not complete, and due to the influence of various factors, partial rural power distribution networks still have the problems of weak grid structure, high line load rate, low risk bearing capacity, low line terminal voltage and the like at present, upgrading and transforming the 10kV lines of the rural power distribution networks is an important measure for solving the problems, and the method has important significance for developing and exploring more effective rural power distribution network planning and transforming methods in order to better solve the problems in a new round of rural power distribution network planning and transforming engineering;
the rural power distribution network has the characteristics of large load random fluctuation, large difference of risk bearing capacity of the power distribution networks in various rural areas, and the like, most of the current researches are to select the model of a line and optimize a path under the condition of determining a load predicted value, and for the power distribution networks in the rural areas with large load fluctuation and uncertainty, the network frame planning scheme obtained by the deterministic planning method has poor adaptability and high investment cost; uncertainty planning methods based on a probability model, a fuzzy theory, multi-scenario analysis and an interval theory all require strict satisfaction of inequality constraint conditions of the model, so that investment is possibly greatly increased, and the economy of a planning scheme is inferior to that of the uncertainty planning method based on an opportunity constraint theory; however, the existing planning method based on the opportunity constraint planning theory mostly adopts a method of uniformly taking the confidence level of the opportunity constraint condition, the difference between regional power distribution networks is not considered, and the opportunity constraint planning theory is relatively rarely used for the research of line optimization and model selection;
the grid planning method considering the difference of the risk bearing capacity of the regional power distribution network effectively establishes a probability model of uncertain load prediction errors by adopting a non-parameter kernel density estimation method based on a Gaussian kernel function; an evaluation index system of the risk bearing capacity of the regional power distribution network is established, and the risk bearing capacity of the regional power distribution network of each village and town is effectively evaluated by adopting a combined weighting method based on an analytic hierarchy process and an entropy weight method; an opportunity constraint planning model of the net rack is established, confidence levels of opportunity constraint conditions are selected in a differentiated mode according to risk bearing capacity evaluation results of distribution networks in villages and towns, and an upgrading selection scheme of distribution lines in villages and towns is determined, so that the mutual coordination of the risk bearing capacity and the investment cost of the distribution networks in the villages and towns is realized to a certain extent, and investment refinement of rural power network transformation is realized better.
Disclosure of Invention
The invention aims to provide a scientific, reasonable, simple, practical and effective grid planning method considering the difference of the risk bearing capacity of a regional power distribution network;
the technical scheme adopted for achieving the purpose of the invention is that the net rack planning method considering the difference of the risk bearing capacity of the regional power distribution network is characterized by comprising the following steps of:
1) uncertainty modeling of load
Due to the uncertainty of the load change of the distribution network in the village and town area, the uncertainty of various factors influencing the load and the uncertainty of the load prediction method, the load prediction has an error and the load prediction error has certain uncertainty; selecting a Gaussian function as a kernel function, and performing uncertainty modeling on historical sample data of a load prediction error of a reference year by adopting a non-parameter kernel density estimation method; the probability density model of the load prediction error based on the non-parametric kernel density estimation is shown as formula (1) and formula (2),
where φ (LE, l) is a probability density function of the load prediction error; n is the number of load prediction error samples; g (LE, l) is a Gaussian kernel function; LEiPredicting the ith sample value in the error sample for the load; l is a bandwidth parameter of the non-parametric kernel density estimation model, the smaller the value of l, the greater the volatility of the probability density function, the higher the accuracy of the real condition of the data can be reflected, and the greater the value of l, the smaller the volatility of the probability density function, the smoother the curve, but the lower the accuracy;
the probability model of the load prediction error based on the non-parameter kernel density estimation is obtained by historical sample data of the load prediction error and the formula (1) and the formula (2) and is shown as the formula (3),
2) regional power distribution network risk tolerance assessment based on combined weighting method
The method comprises the steps of fully considering the influence of the difference of the risk bearing capacity of the distribution networks in the villages and towns on line upgrading and selection, combining the characteristics of the distribution networks in the villages and towns, establishing a risk bearing capacity evaluation index system of the distribution networks in the villages and towns on the basis of the actual demand of rural power network reconstruction, and evaluating the risk bearing capacity of the distribution networks in the villages and towns by adopting a combined weighting method based on an analytic hierarchy process and an entropy weight method;
firstly, establishing an evaluation index system for risk bearing capacity of regional power distribution network
The evaluation result of the risk bearing capacity of the regional power distribution network is used as a reference basis for determining the confidence level value of the opportunity constraint condition in the grid planning model, and an evaluation index system established by the evaluation index system is required to be capable of fully reflecting the actual demand of rural power network reconstruction engineering and all factors influencing the risk bearing capacity of the regional power distribution network in the villages and towns; in view of the characteristics of the power distribution network in the village and town area and the feasibility of acquiring field data, the risk bearing capacity of the power distribution network in the village and town area is comprehensively evaluated from three aspects of load supply capacity, grid structure level and power distribution network operation level, and an evaluation index system of the risk bearing capacity of the power distribution network in the village and town area is established;
a. capacity of load supply
The load supply capacity of the regional power distribution network means that the maximum load of power supply can be guaranteed under the condition that various technical and economic constraint conditions are met, the larger the numerical value of the maximum load is, the more likely the regional power distribution network meets the power consumption requirement of a user under the condition that uncertain load prediction errors are considered, and correspondingly, the stronger the capacity of the regional power distribution network for bearing operation risks caused by load uncertainty is;
the maximum load rate, the heavy-load distribution ratio and the heavy-load operation time of the line can reflect the load supply capacity of the regional power distribution network to different degrees; the higher the maximum load rate of a line is, the larger the duty ratio of the heavy load distribution transformer is, the longer the line heavy load operation time is, the smaller the available power supply capacity margin of the regional power distribution network is when the load fluctuation changes, and the situation that the voltage at the tail end of the line is lower than the requirement of a national power grid company is more likely to occur when the equipment is heavily loaded, the weaker the load supply capacity of the regional power distribution network is under the condition of considering the load prediction error, and the worse the corresponding capability of the regional power distribution network for bearing the operation risk caused by the uncertainty of the load is; therefore, the load supply capacity of the regional power distribution network is measured by adopting a line maximum load rate index, a heavy load distribution ratio index and a line heavy load operation time index;
b. grid structure level
The net rack plays a key role in electric energy transmission and is an important guarantee for safe and reliable power supply of a regional power distribution network to loads; the higher the grid structure level is, the stronger the ability of the power distribution network in areas with higher grid structure level to bear the operation risk caused by uncertainty of load under normal or fault conditions is;
the 10kV distribution lines mostly run outdoors, the electrical equipment is aged quickly under the influence of natural environment and heavy-load running, the frequency of power failure caused by failure due to equipment aging is increased remarkably in recent years, and the capacity of a regional power distribution network for bearing running risks caused by load uncertainty is reduced; the power distribution network in the village and town area is mostly of a non-contact radial structure, the load of the line cannot be transferred through other connecting lines after a fault occurs, if the line is reasonably segmented, the power failure range during the fault can be effectively reduced through the matching operation of a load switch, and the power supply of part of the load of the upper layer fault-free section is recovered, so that the risk bearing capacity of the area power distribution network is improved by reasonably segmenting the line; the overlong power supply radius of the line not only increases the fault probability, but also increases the loss of the line to cause the voltage at the tail end of the line to be lower, so that the capacity of a regional power distribution network for bearing the operation risk caused by load uncertainty is reduced; therefore, the equipment aging rate index, the main line segment number index and the power supply radius overrun line duty ratio index are adopted to measure the grid structure level of the regional power distribution network;
c. operation level of distribution network
The comprehensive voltage qualification rate, the power failure time per household, the power supply reliability and the comprehensive line loss rate index can reflect the integral operation condition of the regional power distribution network to a certain extent; the better each index of the operation level of the regional distribution network is, the stronger the capability of the regional distribution network for bearing the operation risk caused by load uncertainty is;
the comprehensive voltage qualification rate reflects the quality of the power supply voltage of the regional power distribution network, and also reflects the magnitude of the load supply capacity and the height of the grid structure level of the regional power distribution network to a certain extent, and when the comprehensive voltage qualification rate is lower than the relevant regulations of the national grid company, the smaller the value of the comprehensive voltage qualification rate is, the weaker the capacity of the regional power distribution network for bearing the operation risk caused by load uncertainty is; under the condition that the grid structures of the regional distribution networks are the same, if the power failure time of each household is shorter within a certain observation time range, the stronger the adaptability of the regional distribution network to load uncertainty is, the stronger the risk bearing capacity is; the reliable power supply means that under the condition of normal or fault of a system, the system can ensure uninterrupted power supply to users according to a certain quality standard, and the higher the power supply reliability of the regional power distribution network is, the more reasonable the planning scheme of the regional power distribution network is, the stronger the capability of bearing the operation risk caused by load uncertainty is; the comprehensive line loss rate not only reflects the operating economy of the regional power distribution network, but also can reflect the load distribution and net rack planning scheme rationality of the regional power distribution network to a certain extent, the higher the comprehensive line loss rate is, the worse the operating economy of the regional power distribution network is, the more unreasonable the load distribution and net rack planning scheme is, and the weaker the capability of the regional power distribution network for bearing the operating risk caused by the uncertainty of the load is; therefore, the operation level of the regional power distribution network is measured by adopting the comprehensive voltage qualification rate index, the power failure time index of the household, the power supply reliability index and the comprehensive line loss rate index;
second, index weight calculation based on combined weighting method
The index weight can measure the relative importance of the evaluation indexes, the size of the index weight can reflect the relative importance of the indexes, and whether the determination of the index weight coefficient in an evaluation system is scientific and reasonable directly influences the credibility of an evaluation result; the subjective weighting method and the objective weighting method have the advantages and the disadvantages respectively, so that the final weight of each index is coordinated subjectively and objectively in order to avoid the disadvantages and give full play to the advantages respectively, and the final weight of each index is determined by adopting a combined weighting method combining the subjective weighting method based on an analytic hierarchy process and the objective weighting method based on an entropy weight method so as to ensure the credibility of the comprehensive weight of the index;
a. subjective weight calculation
Calculating subjective weights of indexes at all levels by adopting an analytic hierarchy process, wherein experts mainly combine with self field work experience to give out relative importance ranking among the indexes and form a judgment matrix, and then the weights of the corresponding indexes are obtained according to the maximum eigenvalue of the judgment matrix and the corresponding eigenvector thereof; forming a relative importance degree judgment matrix between indexes of each level by adopting a 9-level scale expansion method;
for the first-level index, the load supply capacity of the regional power distribution network is one of important standards for measuring the planning and transformation work effect of the power distribution network, and the guarantee of safe and reliable power supply to the load to the maximum extent is also the core target of the regional power distribution network, so that the index is considered as the most important first-level index; the net rack is a key component of the regional power distribution network and is an important bridge for the regional power distribution network to transmit electric energy to the load, the level of the net rack structure is an important theoretical basis for evaluating whether the planning scheme of the regional power distribution network is reasonable or not, and the net rack structure also needs to be highly emphasized, but the importance degree of the net rack structure is slightly weaker compared with the load supply capacity index; the operation level of the power distribution network reflects the overall safety and economy of the system, is a visual reflection of whether the planning scheme of the grid structure of the regional power distribution network is reasonable or not, is a visual reflection of the strength of the capability of the regional power distribution network for bearing the operation risk caused by load uncertainty, and is considered to be weaker than the importance degree of the level index of the grid structure; that is, the relative importance degree of the primary index is ranked as: capacity of load supply>Grid structure level>The operation level of the power distribution network forms a first-level index judgment matrix A based on a 9-level scale extension method1；
The maximum load rate, the heavy-load distribution ratio and the heavy-load operation time of the line have certain influence on the power supply reliability, the voltage qualification rate and the comprehensive line loss rate of the system, and the relative importance sequence of the secondary indexes is as follows: line maximum load rate>Line heavy load operation time>Rate of equipment aging>Number of line segments>Power supply radius overrun line ratio>Integrated voltage yield>Power supply reliability rate>Synthesizing the line loss rate, and forming a second-level index judgment matrix A based on a 9-level scale expansion method2；
Due to the adoption of the 9-level scale extension method, the condition that the numerical values in the judgment matrix are inconsistent due to the complexity of multi-level judgment can be effectively avoided, and the judgment matrix A does not need to be subjected to the judgment1And A2The consistency test is carried out, the whole evaluation process is simplified, and the calculated amount is reduced;
b. objective weight calculation
The objective weight of each index is calculated by adopting an entropy weight method so as to fully consider the influence of the actual value of each index on the risk bearing capacity of the power distribution network, the dimensionless processing mode of the index adopts a form of a formula (4),
in the formula, sijIs the value of the jth index of the scheme i after non-dimensionalization; r isijThe actual value of the jth index of the scheme i; min (r)j) Is the minimum value of the index j; max (r)j) Is the maximum value of the index j;
c. integrated weight calculation
In consideration of subjectivity of the subjective weight of the index and the problem that the objective weight of the index cannot reflect the importance degree of the index in the actual problem, in order to enable the evaluation result of the risk bearing capacity of the regional distribution network to be more objective and reasonable, the comprehensive weight of each index is calculated by a formula (5) by adopting a linear weighted combined weighting method so as to more comprehensively reflect the influence of each factor on the risk bearing capacity of the regional distribution network;
in the formula, mujAs the j-th evaluation indexA composite weight; w is ajAnd vjSubjective weight and objective weight of the jth evaluation index are respectively;
risk bearing capacity assessment of regional distribution network
Although the single index can reflect the strength of the operation risk of the regional power distribution network caused by load uncertainty on one aspect to a certain extent, the single index is not enough to explain the overall situation of the risk bearing capacity of the regional power distribution network; therefore, the risk bearing capacity of the distribution network in each village and town area is evaluated by a method of combining the comprehensive weight of each index and the value after the comprehensive weight is subjected to dimensionless, and the calculation of the risk bearing capacity of the distribution network in each area is shown as a formula (6); the larger the evaluation value of the risk bearing capacity of the regional power distribution network is, the stronger the capacity of the regional power distribution network for bearing the risk caused by load uncertainty is;
in the formula: zmEvaluating the risk tolerance of the power distribution network in the mth area; smjThe value of the jth evaluation index of the mth regional distribution network after dimensionless; mu.sjThe comprehensive weight of the jth evaluation index;
differentiated value of confidence level
According to the value range of the confidence level and by combining the risk bearing capacity evaluation results of the distribution networks in the villages and towns, the confidence level values of the branch power opportunity constraint conditions are selected in a differentiated mode, and meanwhile the confidence level values meeting all opportunity constraint conditions are not less than 80%; the rural area power distribution network with the larger risk bearing capacity estimated value shows that the rural area power distribution network has stronger adaptability to load uncertainty and can bear larger risk, so that the confidence level value of the opportunity constraint condition of the grid model is smaller than that of the area power distribution network with the smaller risk bearing capacity estimated value, and the reserved capacity margin required for line upgrading and model selection can also be smaller;
3) opportunity constrained planning model for net rack
When uncertainty factors are considered in the power distribution network planning process, if the objective function and the constraint conditions of the model are still processed according to the traditional deterministic planning model, a planning scheme with higher investment cost and more conservative investment cost can be obtained; therefore, by taking the minimum investment cost of upgrading the line as an objective function, taking various requirements which must be met by the safe and reliable operation of the system as constraint conditions, establishing an opportunity constraint planning model of the net rack on the basis of considering the uncertainty of the load predicted value, and allowing the planning scheme to have the situation that the constraint conditions are not met under certain conditions, wherein the possibility that the opportunity constraint conditions are met can meet the requirement of a certain confidence level;
(ii) an objective function of the model
The objective function of the model is to minimize the investment cost for upgrading the line, as shown in equation (7)
In the formula, FinvInvestment cost for line upgrade; x is the number oflThe decision variable is a decision variable for judging whether the line l is upgraded, the value is 1 during upgrading, and the value is 0 otherwise; cline,lThe material cost and installation cost of upgrading a line l, which is generally determined by the type of the line; llTo upgrade the length of line l; n is a radical oflThe total number of the upgrading lines;
constraint conditions of model-
When planning the network frame of the power distribution network, certain technical constraint conditions and operation constraint conditions need to be met, the following constraint conditions are considered,
a. branch power constraint
In order to improve the capability of the grid planning scheme to bear the operation risk caused by the uncertainty of the load, based on the opportunity constraint planning theory, the deterministic branch power constraint in the traditional planning model is described as the opportunity constraint, so that the probability that the branch power meets the constraint condition is not less than a certain confidence level, as shown in formula (8),
in the formula, Pi TActive power of a T line i for planning a target year; pimaxMaximum power allowed to pass for line i; alpha is alphampDetermining the confidence level of line power opportunity constraint in the mth village and town area power distribution network according to the risk tolerance evaluation result of the village and town area power distribution network; wherein P isi TObtained by formula (9);
in the formula, PiBIs the reference active power of line i; r isiThe annual average load growth rate of the line i; t is the planning year limit; LE is the random load prediction error; bringing formula (9) into formula (8) to obtain formula (10), and further deforming to obtain formula (11);
Pr{PiB[(1+ri)T+LE]≤Pimax}≥αmP (10)
obtaining a probability density function phi (LE) and a probability distribution function phi (LE) of a load prediction error LE by adopting a nonparametric kernel density estimation method; branch power opportunity constraint condition confidence level alpha of village and town area mmpDetermining according to a risk tolerance evaluation result of the regional power distribution network; reference active power P of line iiB、riAfter the load annual average growth rate and the planning age limit T of the line i are determined, P is determined by the related knowledge of probability theory and an equation (11)imaxAnd determining the model of the line after upgrading and transformation according to the value range, as shown in formula (12);
Pimax≥PiB[Φ-1(αmP)+(1+r)T] (12)
in the formula (I), the compound is shown in the specification,Ф-1(. cndot.) represents an inverse function of the distribution function Φ (·) of the load prediction error;
b. upper and lower limit constraints of node voltage
Ujmin≤Uj≤Ujmax (13)
In the formula of UjIs the voltage value of node j; u shapejmaxAnd UjminThe upper limit value and the lower limit value of the voltage allowed by the node j respectively, and the node voltage allowed deviation of the distribution network in the general township area is 7 percent, then UjminThe value is 9.3 kV;
step of planning net rack
a. According to load prediction error historical sample data of a reference year, a nonparametric kernel density estimation method is adopted to obtain a probability density function phi (LE) and a probability distribution function phi (LE) of the load prediction error;
b. establishing a risk bearing capacity evaluation index system of the regional power distribution network by combining the characteristics of the rural regional power distribution network, obtaining the comprehensive weight of each index by adopting a combined weighting method, and obtaining the risk bearing capacity evaluation value of each rural regional power distribution network according to the comprehensive weight of each index and the nondimensionated index value;
c. establishing an opportunity constraint planning model of the net rack, selecting the confidence level of the branch power opportunity constraint condition in combination with the difference of the risk bearing capacity evaluation value of each rural area power distribution network, determining the load prediction error corresponding to the corresponding confidence level according to the probability distribution function phi (LE) of the load prediction error obtained in the step a, obtaining the load prediction value of each rural area power distribution line in different planning years, determining the requirement which the maximum allowable load capacity of the line should meet according to the formula (12), and determining the model of the line after upgrading according to the requirement;
d. modeling simulation analysis is carried out on the upgrading model selection scheme of the distribution lines in each village and town area under different planning age conditions, whether constraint conditions meet requirements is verified, and finally the line optimization model selection scheme with the minimum investment total cost is determined.
The invention relates to a net rack planning method considering regional distribution network risk bearing capacity difference, which comprises the steps of firstly, establishing a probability model of uncertain load prediction errors by adopting a nonparametric kernel density estimation method; secondly, considering the influence of the difference of the risk bearing capacity of the power distribution network in the township area on the line upgrading model selection, and establishing an evaluation index system of the risk bearing capacity of the area power distribution network by combining the characteristics of the power distribution network in the township area; then, evaluating the risk bearing capacity of each village and town area by adopting a combined weighting method based on an analytic hierarchy process and an entropy weight method; finally, an opportunity constraint planning model of the net rack is established, and confidence levels of opportunity constraint conditions are selected in a differentiation mode according to risk bearing capacity evaluation results of the distribution networks in the villages and towns; the method has the advantages of being scientific, reasonable, simple, practical, good in effect, good in economy of the net rack planning scheme, capable of achieving investment refinement and the like.
Drawings
Fig. 1 is a flowchart of a grid planning method considering differences in risk tolerance of a regional distribution network;
FIG. 2 is a probability density function plot of load prediction error;
FIG. 3 is a graph of a probability distribution function of load prediction error;
FIG. 4 is a system of risk tolerance evaluation indicators for a regional distribution network;
FIG. 5 is a distribution diagram of importance and satisfaction of distribution network indexes in each village and town area;
FIG. 6 shows the simulation result of 1 mother tide when the planning year is 10 years;
FIG. 7 shows the simulation results of 2 tidal flows when the planning year is 10 years;
FIG. 8 is a simulation result of 1 mother tide when the planning year is 15 years;
FIG. 9 shows the simulation results of 2 tidal flows when the planning year is 15 years;
FIG. 10 shows the simulation result of 1 mother tide when the planning year is 20 years;
fig. 11 is a simulation result of 2-generation tidal current when the planned age is 20 years.
Detailed Description
Referring to fig. 1, the method for planning the grid structure based on the difference of the risk tolerance of the regional distribution network of the present invention includes the following steps:
1) load uncertainty modeling
Due to the uncertainty of the load change of the distribution network in the village and town area, the uncertainty of various factors influencing the load and the uncertainty of the load prediction method, the load prediction has an error and the load prediction error has certain uncertainty; selecting a Gaussian function as a kernel function, and performing uncertainty modeling on historical sample data of a load prediction error of a reference year by adopting a non-parameter kernel density estimation method; the probability density model of the load prediction error based on the non-parametric kernel density estimation is shown as formula (1) and formula (2),
where φ (LE, l) is a probability density function of the load prediction error; n is the number of load prediction error samples; g (LE, l) is a Gaussian kernel function; LEiPredicting the ith sample value in the error sample for the load; l is a bandwidth parameter of the non-parametric kernel density estimation model, the smaller the value of l, the greater the volatility of the probability density function, the higher the accuracy of the real condition of the data can be reflected, and the greater the value of l, the smaller the volatility of the probability density function, the smoother the curve, but the lower the accuracy;
the probability model of the load prediction error based on the non-parameter kernel density estimation is obtained by historical sample data of the load prediction error and the formula (1) and the formula (2) and is shown as the formula (3),
2) regional power distribution network risk tolerance assessment based on combined weighting method
The method comprises the steps of fully considering the influence of the difference of the risk bearing capacity of the distribution networks in the villages and towns on line upgrading and selection, combining the characteristics of the distribution networks in the villages and towns, establishing a risk bearing capacity evaluation index system of the distribution networks in the villages and towns on the basis of the actual demand of rural power network reconstruction, and evaluating the risk bearing capacity of the distribution networks in the villages and towns by adopting a combined weighting method based on an analytic hierarchy process and an entropy weight method;
firstly, establishing an evaluation index system for risk bearing capacity of regional power distribution network
The evaluation result of the risk bearing capacity of the regional power distribution network is used as a reference basis for determining the confidence level value of the opportunity constraint condition in the grid planning model, and an evaluation index system established by the evaluation index system is required to be capable of fully reflecting the actual demand of rural power network reconstruction engineering and all factors influencing the risk bearing capacity of the regional power distribution network in the villages and towns; in view of the characteristics of the power distribution network in the village and town area and the feasibility of acquiring field data, the risk bearing capacity of the power distribution network in the village and town area is comprehensively evaluated from three aspects of load supply capacity, grid structure level and power distribution network operation level, and an evaluation index system of the risk bearing capacity of the power distribution network in the village and town area is established;
a. capacity of load supply
The load supply capacity of the regional power distribution network means that the maximum load of power supply can be guaranteed under the condition that various technical and economic constraint conditions are met, the larger the numerical value of the maximum load is, the more likely the regional power distribution network meets the power consumption requirement of a user under the condition that uncertain load prediction errors are considered, and correspondingly, the stronger the capacity of the regional power distribution network for bearing operation risks caused by load uncertainty is;
the maximum load rate, the heavy-load distribution ratio and the heavy-load operation time of the line can reflect the load supply capacity of the regional power distribution network to different degrees; the higher the maximum load rate of a line is, the larger the duty ratio of a heavy load distribution transformer is, the longer the line heavy load operation time is, the smaller the available power supply capacity margin of the regional power distribution network is when the load fluctuation changes, and the situation that the voltage at the tail end of the line is lower than the requirement of a national power grid company is more likely to occur when the equipment is heavily loaded, the weaker the load supply capacity of the regional power distribution network is under the condition of considering load prediction errors, and the worse the capacity of the corresponding regional power distribution network for bearing the operation risk caused by load uncertainty is; therefore, the load supply capacity of the regional power distribution network is measured by adopting a line maximum load rate index, a heavy load distribution ratio index and a line heavy load operation time index;
b. grid structure level
The net rack plays a key role in electric energy transmission and is an important guarantee for safe and reliable power supply of a regional power distribution network to loads; the higher the grid structure level is, the stronger the ability of the regional distribution network to bear the operation risk caused by load uncertainty under normal or fault conditions is;
the 10kV distribution lines mostly run outdoors, the electrical equipment is aged quickly under the influence of natural environment and heavy-load running, the frequency of power failure caused by failure due to equipment aging is increased remarkably in recent years, and the capacity of a regional power distribution network for bearing running risks caused by load uncertainty is reduced; the power distribution network in the village and town area is mostly of a non-contact radial structure, the load of the line cannot be transferred through other connecting lines after a fault occurs, if the line is reasonably segmented, the power failure range during the fault can be effectively reduced through the matching operation of a load switch, and the power supply of part of the load of the upper layer fault-free section is recovered, so that the risk bearing capacity of the area power distribution network is improved by reasonably segmenting the line; the overlong power supply radius of the line not only increases the fault probability, but also increases the loss of the line to cause the voltage at the tail end of the line to be lower, so that the capacity of a regional power distribution network for bearing the operation risk caused by load uncertainty is reduced; therefore, the equipment aging rate index, the main line segment number index and the power supply radius overrun line duty ratio index are adopted to measure the grid structure level of the regional power distribution network;
c. operation level of distribution network
The comprehensive voltage qualification rate, the power failure time per household, the power supply reliability and the comprehensive line loss rate index can reflect the integral operation condition of the regional power distribution network to a certain extent; the better each index of the operation level of the regional distribution network is, the stronger the capability of the regional distribution network for bearing the operation risk caused by load uncertainty is;
the comprehensive voltage qualification rate reflects the quality of the power supply voltage of the regional power distribution network, and also reflects the magnitude of the load supply capacity and the height of the grid structure level of the regional power distribution network to a certain extent, and when the comprehensive voltage qualification rate is lower than the relevant regulations of the national grid company, the smaller the value of the comprehensive voltage qualification rate is, the weaker the capacity of the regional power distribution network for bearing the operation risk caused by load uncertainty is; under the condition that the grid structures of the regional distribution networks are the same, if the power failure time of each household is shorter within a certain observation time range, the stronger the adaptability of the regional distribution network to load uncertainty is, the stronger the risk bearing capacity is; the reliable power supply means that under the condition of normal or fault of a system, the system can ensure uninterrupted power supply to users according to a certain quality standard, and the higher the power supply reliability of the regional power distribution network is, the more reasonable the planning scheme of the regional power distribution network is, the stronger the capability of bearing the operation risk caused by load uncertainty is; the comprehensive line loss rate not only reflects the operating economy of the regional power distribution network, but also can reflect the load distribution and net rack planning scheme rationality of the regional power distribution network to a certain extent, the higher the comprehensive line loss rate is, the worse the operating economy of the regional power distribution network is, the more unreasonable the load distribution and net rack planning scheme is, and the weaker the capability of the regional power distribution network for bearing the operating risk caused by the uncertainty of the load is; therefore, the operation level of the regional power distribution network is measured by adopting the comprehensive voltage qualification rate index, the power failure time index of the household, the power supply reliability index and the comprehensive line loss rate index;
second, index weight calculation based on combined weighting method
The index weight can measure the relative importance of the evaluation indexes, the size of the index weight can reflect the relative importance of the indexes, and whether the determination of the index weight coefficient in an evaluation system is scientific and reasonable directly influences the credibility of an evaluation result; the subjective weighting method and the objective weighting method have the advantages and the disadvantages respectively, so that the final weight of each index is coordinated subjectively and objectively in order to avoid the disadvantages and give full play to the advantages respectively, and the final weight of each index is determined by adopting a combined weighting method combining the subjective weighting method based on an analytic hierarchy process and the objective weighting method based on an entropy weight method so as to ensure the credibility of the comprehensive weight of the index;
a. subjective weight calculation
Calculating subjective weights of indexes at all levels by adopting an analytic hierarchy process, wherein experts mainly combine with self field work experience to give out relative importance ranking among the indexes and form a judgment matrix, and then the weights of the corresponding indexes are obtained according to the maximum eigenvalue of the judgment matrix and the corresponding eigenvector thereof; forming a relative importance degree judgment matrix between indexes of each level by adopting a 9-level scale expansion method;
for the first-level index, the load supply capacity of the regional power distribution network is one of important standards for measuring the planning and transformation work effect of the power distribution network, and the guarantee of safe and reliable power supply to the load to the maximum extent is also the core target of the regional power distribution network, so that the index is considered as the most important first-level index; the net rack is a key component of the regional power distribution network and is an important bridge for the regional power distribution network to transmit electric energy to the load, the level of the net rack structure is an important theoretical basis for evaluating whether the planning scheme of the regional power distribution network is reasonable or not, and the net rack structure also needs to be highly emphasized, but the importance degree of the net rack structure is slightly weaker compared with the load supply capacity index; the operation level of the power distribution network reflects the overall safety and economy of the system, is a visual reflection of whether the planning scheme of the grid structure of the regional power distribution network is reasonable or not, is a visual reflection of the strength of the capability of the regional power distribution network for bearing the operation risk caused by load uncertainty, and is considered to be weaker than the importance degree of the level index of the grid structure; that is, the relative importance degree of the primary index is ranked as: capacity of load supply>Grid structure level>The operation level of the power distribution network forms a first-level index judgment matrix A based on a 9-level scale extension method1；
The maximum load rate, the heavy-load distribution ratio and the heavy-load operation time of the line have certain influence on the power supply reliability, the voltage qualification rate and the comprehensive line loss rate of the system, and secondary indexes are adopted for sequencing, namely: line maximum load rate>Line heavy load operation time>Rate of equipment aging>Number of line segments>Power supply radius overrun line ratio>Integrated voltage yield>Power supply reliability rate>Synthesizing the line loss rate, and forming a two-level index judgment matrix based on a 9-level scale extension methodA2；
Due to the adoption of the 9-level scale extension method, the condition that the numerical values in the judgment matrix are inconsistent due to the complexity of multi-level judgment can be effectively avoided, and the judgment matrix A does not need to be subjected to the judgment1And A2The consistency test is carried out, the whole evaluation process is simplified, and the calculated amount is reduced;
b. objective weight calculation
The objective weight of each index is calculated by adopting an entropy weight method so as to fully consider the influence of the actual value of each index on the risk bearing capacity of the power distribution network, the dimensionless processing mode of the index adopts a form of a formula (4),
in the formula, sijIs the value of the jth index of the scheme i after non-dimensionalization; r isijThe actual value of the jth index of the scheme i; min (r)j) Is the minimum value of the index j; max (r)j) Is the maximum value of the index j;
c. integrated weight calculation
In consideration of subjectivity of the subjective weight of the index and the problem that the objective weight of the index cannot reflect the importance degree of the index in the actual problem, in order to enable the evaluation result of the risk bearing capacity of the regional distribution network to be more objective and reasonable, the comprehensive weight of each index is calculated by a formula (5) by adopting a linear weighted combined weighting method so as to more comprehensively reflect the influence of each factor on the risk bearing capacity of the regional distribution network;
in the formula, mujThe comprehensive weight of the jth evaluation index; w is ajAnd vjSubjective weight and objective weight of the jth evaluation index are respectively;
risk bearing capacity assessment of regional distribution network
Although the single index can reflect the strength of the operation risk of the regional power distribution network caused by load uncertainty on one aspect to a certain extent, the single index is not enough to explain the overall situation of the risk bearing capacity of the regional power distribution network; therefore, the risk bearing capacity of the distribution network in each village and town area is evaluated by a method of combining the comprehensive weight of each index and the value after the comprehensive weight is subjected to dimensionless, and the calculation of the risk bearing capacity of the distribution network in each area is shown as a formula (6); the larger the evaluation value of the risk bearing capacity of the regional power distribution network is, the stronger the capacity of the regional power distribution network for bearing the risk caused by load uncertainty is;
in the formula: zmEvaluating the risk tolerance of the power distribution network in the mth area; smjThe value of the jth evaluation index of the mth regional distribution network after dimensionless; mu.sjThe comprehensive weight of the jth evaluation index;
differentiated value of confidence level
According to the value range of the confidence level and by combining the risk bearing capacity evaluation results of the distribution networks in the villages and towns, the confidence level values of the branch power opportunity constraint conditions are selected in a differentiated mode, and meanwhile the confidence level values meeting all opportunity constraint conditions are not less than 80%; the rural area power distribution network with the larger risk bearing capacity estimated value shows that the rural area power distribution network has stronger adaptability to load uncertainty and can bear larger risk, so that the confidence level value of the opportunity constraint condition of the grid model is smaller than that of the area power distribution network with the smaller risk bearing capacity estimated value, and the reserved capacity margin required for line upgrading and model selection can also be smaller;
3) opportunity constrained planning model for net rack
When uncertainty factors are considered in the power distribution network planning process, if the objective function and the constraint conditions of the model are still processed according to the traditional deterministic planning model, a planning scheme with higher investment cost and more conservative investment cost can be obtained; therefore, by taking the minimum investment cost of upgrading the line as an objective function, taking various requirements which must be met by the safe and reliable operation of the system as constraint conditions, establishing an opportunity constraint planning model of the net rack on the basis of considering the uncertainty of the load predicted value, and allowing the planning scheme to have the situation that the constraint conditions are not met under certain conditions, wherein the possibility that the opportunity constraint conditions are met can meet the requirement of a certain confidence level;
(ii) an objective function of the model
The objective function of the model is to minimize the investment cost for upgrading the line, as shown in equation (7)
In the formula, FinvInvestment cost for line upgrade; x is the number oflThe decision variable is a decision variable for judging whether the line l is upgraded, the value is 1 during upgrading, and the value is 0 otherwise; cline,lThe material cost and installation cost of upgrading a line l, which is generally determined by the type of the line; llTo upgrade the length of line l; n is a radical oflThe total number of the upgrading lines;
constraint conditions of model-
When planning the network frame of the power distribution network, certain technical constraint conditions and operation constraint conditions need to be met, the following constraint conditions are considered,
a. branch power constraint
In order to improve the capability of the grid planning scheme to bear the operation risk caused by the uncertainty of the load, based on the opportunity constraint planning theory, the deterministic branch power constraint in the traditional planning model is described as the opportunity constraint, so that the probability that the branch power meets the constraint condition is not less than a certain confidence level, as shown in formula (8),
in the formula, Pi TActive power of a T line i for planning a target year; pimaxAllowed by line iA maximum value of power passed; alpha is alphampDetermining the confidence level of line power opportunity constraint in the mth village and town area power distribution network according to the risk tolerance evaluation result of the village and town area power distribution network; wherein P isi TObtained by formula (9);
in the formula, PiBIs the reference active power of line i; r is the annual average growth rate for load prediction; t is the planning year limit; LE is the random load prediction error; bringing formula (9) into formula (8) to obtain formula (10), and further deforming to obtain formula (11);
Pr{PiB[(1+ri)T+LE]≤Pimax}≥αmP (10)
obtaining a probability density function phi (LE) and a probability distribution function phi (LE) of a load prediction error LE by adopting a nonparametric kernel density estimation method; branch power opportunity constraint condition confidence level alpha of village and town area mmpDetermining according to a risk tolerance evaluation result of the regional power distribution network; reference active power P of line iiB、riAfter the load annual average growth rate and the planning age limit T of the line i are determined, P is determined by the related knowledge of probability theory and an equation (11)imaxAnd determining the model of the line after upgrading and transformation according to the value range, as shown in formula (12);
Pimax≥PiB[Φ-1(αmP)+(1+r)T] (12)
in the formula, phi-1(. cndot.) represents an inverse function of the distribution function Φ (·) of the load prediction error;
b. upper and lower limit constraints of node voltage
Ujmin≤Uj≤Ujmax (13)
In the formula of UjIs the voltage value of node j; u shapejmaxAnd UjminThe upper limit value and the lower limit value of the voltage allowed by the node j respectively, and the node voltage allowed deviation of the distribution network in the general township area is 7 percent, then UjminThe value is 9.3 kV;
step of planning net rack
a. According to load prediction error historical sample data of a reference year, a nonparametric kernel density estimation method is adopted to obtain a probability density function phi (LE) and a probability distribution function phi (LE) of the load prediction error;
b. establishing a risk bearing capacity evaluation index system of the regional power distribution network by combining the characteristics of the rural regional power distribution network, obtaining the comprehensive weight of each index by adopting a combined weighting method, and obtaining the risk bearing capacity evaluation value of each rural regional power distribution network according to the comprehensive weight of each index and the nondimensionated index value;
c. establishing an opportunity constraint planning model of the net rack, selecting the confidence level of the branch power opportunity constraint condition in combination with the difference of the risk bearing capacity evaluation value of each rural area power distribution network, determining the load prediction error corresponding to the corresponding confidence level according to the probability distribution function phi (LE) of the load prediction error obtained in the step a, obtaining the load prediction value of each rural area power distribution line in different planning years, determining the requirement which the maximum allowable load capacity of the line should meet according to the formula (12), and determining the model of the line after upgrading according to the requirement;
d. modeling simulation analysis is carried out on the upgrading model selection scheme of the distribution lines in each village and town area under different planning age conditions, whether constraint conditions meet requirements is verified, and finally the line optimization model selection scheme with the minimum investment total cost is determined.
The specific embodiment is as follows:
establishing a probability model of load prediction errors
Obtaining load prediction error statistical data of each month in 2017 according to a load predicted value and a load actual value data of each month in 2017 provided by a power supply company in a certain city of Jilin province, taking a Gaussian function as a kernel function for establishing a load prediction error probability model, and obtaining a probability density function phi (LE) and a probability distribution function phi (LE) of the load prediction error based on a nonparametric kernel density estimation method; the probability density function curve of the load prediction error is shown in figure 2, and the probability distribution function curve of the load prediction error is shown in figure 3;
assessment result of risk tolerance of regional distribution network
The established risk tolerance evaluation index system of the regional power distribution network is shown in figure 4, the comprehensive weight of each index is obtained by calculating the subjective weight and the objective weight of each index, the risk tolerance evaluation is carried out on the power distribution network of each village and town to be planned and transformed by combining the dimensionless value of the actual value of each index, and the confidence level of the opportunity constraint condition of the grid planning model is determined according to the evaluation result;
calculating the subjective weight
Comparing the indexes with each other by adopting an analytic hierarchy process, sequencing the indexes in a mode of decreasing the importance degree, and obtaining a judgment matrix A of the first-level indexes by a 9-level scale expansion method1As shown in equation (14), the judgment matrix A of the second-level index2As shown in formula (15);
the judgment matrix obtained by the 9-level scale extension method meets the consistency requirement, and the judgment matrix A of the first-level index is directly solved1And a judgment matrix A of the second-level index2The subjective weight of each index can be obtained by the maximum eigenvalue and the corresponding eigenvector; the subjective weight calculation results of each level of indexes are detailed in a table 3;
second, objective weight calculation result
Actual values of risk bearing capacity evaluation indexes of the distribution network in each village and town area are obtained by certain analysis and statistics of field operation data provided by a power supply company and are shown in table 1, values of each index after dimensionless are obtained by calculation through an entropy weight method and are shown in table 2, and objective weight calculation results of each index are shown in table 3;
TABLE 1 actual values of risk tolerance evaluation indexes of distribution networks in various villages and towns
TABLE 2 nondimensionalized values of the respective indices
Third, the result of the comprehensive weight calculation
Calculating the comprehensive weight of each index by adopting a linear weighting method according to the subjective weight and the objective weight of each index through a formula (5), wherein the comprehensive weight is shown in a table 3;
determining the risk bearing capacity and confidence level of the distribution network in each area
Calculating the risk bearing capacity evaluation value of the distribution network in each village and town area by the formula (6) according to the comprehensive weight of each index and the dimensionless value of each index, wherein the risk bearing capacity evaluation value is shown in table 4;
TABLE 3 calculation results of index weights at various levels
TABLE 4 Risk bearing ability assessment values of distribution networks in various villages and towns
As seen from the risk tolerance evaluation results of the distribution networks in the village and town areas in table 4, the maximum risk tolerance evaluation value of the distribution network in the village and town 3 area is 0.7769, and when the three aspects of load supply capacity, grid structure level and distribution network operation level are considered comprehensively, the capacity of the distribution network in the village and town area for bearing the operation risk caused by load uncertainty is better than that of the distribution networks in the other village and town areas; the estimated risk tolerance of the distribution network in the area of villages and towns 4 is 0.2080 at the minimum, and the risk tolerance of the distribution network is relatively weak due to the operation risk caused by load uncertainty; therefore, when the confidence level of the opportunity constraint condition of the line upgrading model of each rural area is determined, the confidence level value of the opportunity constraint condition of the rural area power distribution network with the larger risk bearing capacity evaluation value is smaller but not lower than 80%; referring to the risk tolerance evaluation results of the power distribution networks in the village and town areas, the confidence level of the village and town 3 is 80%; the confidence level of village and town 1 and village and town 2 is 90%; confidence level of village and town 4 is 95%;
the comprehensive weights of the indexes of the distribution networks in the village and town areas are the same, and the reason for causing the difference of the risk bearing capacity of the distribution networks in the village and town areas is that the actual values of the indexes are different, the satisfaction degree of the indexes of the distribution networks in the village and town areas is represented by the index value after the dimensionless of the distribution networks in the village and town areas and is taken as a vertical coordinate, the importance degree of the index is represented by the comprehensive weight of the index and is taken as a horizontal coordinate, and the distribution diagram of the importance degree and the satisfaction degree of the evaluation index of the risk bearing capacity of the distribution networks in the village and town areas is drawn, as shown in figure 5;
the distribution conditions of the index satisfaction degrees of the distribution networks in the villages and towns can be visually seen through the table 5, and the main weak links which cause the low risk bearing capacity of the distribution networks in the areas under the condition of load uncertainty are found out, so that the corresponding weak links of the distribution networks in the areas are improved in a targeted manner while the lines are upgraded and reformed; as can be seen from fig. 5, the indexes with higher importance degree, i.e., the maximum load rate a1 of the line and the heavy-load operation time A3 of the line, are very low in satisfaction degree, and are the main reasons for the weaker risk bearing capacity of the villages and towns 4, and upgrading and model selection of the power supply line of the villages and towns 4 can not only effectively meet the future load increase demand, but also effectively improve the satisfaction degree of the two indexes with higher importance degree, and improve the risk bearing capacity of the distribution network in the villages and towns area;
3) line optimization and model selection scheme for regional power distribution network
The greater the confidence level value of the opportunity constraint condition in the power distribution network frame planning model in the rural area, the weaker the ability of bearing the operation risk caused by load uncertainty, and the larger load prediction error should be considered when carrying out line upgrade and model selection in the next year so as to ensure that enough capacity margin is reserved to ensure the feasibility of the planning scheme; determining the maximum allowable load capacity of each line according to the formula (12), and determining the model number of the line after upgrading; the load prediction conditions of distribution lines in the village and town areas under different planning age conditions are shown in table 5; because the distribution lines of all village and town areas in the power supply range of the 66kV transformer substation are single-radiation lines without contact, 50% of capacity margin is not required to be reserved for transferring loads of other lines when a fault occurs; therefore, the maximum allowable load capacity of the line can be 60% of the rated capacity of the line when the line model is determined by combining field experience and comprehensively considering the economical efficiency and the safety of the operation of the system;
TABLE 5 load forecasting for different planning years
Simulation analysis is carried out on the line upgrading model selection scheme under different planning age conditions, and the power flow simulation results of 1 st and 2 nd of the 66kV transformer substation under different planning age conditions are shown in the graphs in fig. 6 to 11; in the figure, the darker the green color of a bus/node voltage result display frame indicates that the bus/node voltage is closer to a rated value, the darker the blue color of the bus/node voltage result display frame indicates that the bus/node voltage is lower, and the darker the red color of an element indicates that the heavy load condition of the equipment is more serious; as can be seen from fig. 6 to 11, the load predicted value of the line is larger when the planning age is longer, the number of the heavy-load distribution transformers is gradually increased, the line upgrading and model selection schemes under different planning age conditions obtained by the method provided by the present disclosure can meet the voltage requirement of the end of the line, and the positions and capacities of the distribution transformers which need to be subjected to capacity expansion and transformation can be obtained through the simulation result;
under the condition of considering uncertainty of load prediction errors, the network frame planning method considering the difference of the risk bearing capacity of the regional power distribution network provided by the invention is adopted to obtain a line upgrading selection scheme of the power distribution network in each village and town area as shown in table 6, and the line upgrading cost is shown in table 7;
TABLE 6 upgrade and model selection scheme for distribution network line in villages and towns
TABLE 7 upgrade cost of distribution lines in various villages and towns areas (Unit: Wanyuan)
As can be seen from tables 6 and 7, as the load of the distribution network in each rural area increases with the increase of the planning age, the section of the selected conductor becomes larger and larger during the line upgrade and reconstruction, and the investment cost of the line also increases; according to the risk tolerance assessment results of distribution networks in villages and towns in table 4, the risk tolerance assessment value of the village and town 4 is the smallest, and the risk tolerance of the distribution network in the region is the weakest, so that a conservative line model selection scheme is considered in order to guarantee the effectiveness of the line upgrading and transformation scheme under the condition of considering load uncertainty, and the investment cost is high; because the village and town 1 is far away from the 66kV transformer substation, the power supply radius of the line 1 and the branch line are both long, and in order to ensure that the voltage at the tail end of the line meets the requirement, the branch line of the line needs to adopt a lead with a large section to reduce the voltage loss along the line, so the investment cost is the highest;
in order to verify the effectiveness of the method, the upgrading and model selection scheme of distribution lines of each village and town area supplied with power by the 66kV transformer substation is obtained by the following methods;
the method comprises the following steps: the planning method simultaneously considers the uncertainty of the load and the difference of the risk bearing capacity of the regional distribution network, namely the method provided by the invention;
the method 2 comprises the following steps: the planning method only considers the uncertainty of the load but does not consider the difference of the risk bearing capacity of the regional distribution network, namely, the risk bearing capacity of the 4 distribution networks in the villages and towns is considered to be the same, and the confidence level is uniformly valued to be 95%;
the method 3 comprises the following steps: the planning method does not consider uncertainty of the load and also does not consider the difference of the risk bearing capacity of the regional distribution network, namely the predicted value of the load in the next year is determined according to the maximum load prediction error of 21.56 percent, namely the conventional method;
load prediction results of different planning years obtained by respectively adopting the 3 planning methods are shown in a table 8, and line upgrading selection schemes and planning costs of different planning years are respectively shown in a table 9, a table 10, a table 11 and a table 12;
TABLE 8 load prediction results of different planning methods in different planning years
TABLE 9 line upgrade and model selection scheme with planning age of 10 years
Table 10 line upgrading and model selection scheme for planning 15 years of years
Table 11 line upgrading and model selection scheme for planning 20 years of years
TABLE 12 line upgrade costs for different planning years
As can be seen from table 12, under the constraint condition of node voltage, the line upgrade costs of the planning schemes obtained by the method 1 under the condition of different planning years are all lower than those of the methods 2 and 3; the reason for the analysis is that the method 2 only considers the influence of load prediction errors and does not consider the difference of risk bearing capacity of the distribution network in each village and town area, and the cost of the planning scheme is increased by uniformly valuing the confidence level of the opportunity constraint condition of the net rack planning model; the method 3 does not consider the difference of the risk bearing capacity of the distribution network in each village and town area nor the influence of the load prediction error, the maximum load prediction error is considered in the planning process to ensure that enough capacity margin is available to ensure the effectiveness of the planning scheme, and the upgrading and modifying scheme of the line is conservative, so that the line upgrading cost of the planning scheme obtained by the method 3 is the highest; the grid planning method considering the difference of the risk bearing capacity of the regional power distribution network, provided by the invention, considers the uncertainty of the load and the difference of the risk bearing capacity of the power distribution network in each village and town simultaneously, and performs differentiated value taking on the confidence level difference of the opportunity constraint condition of the grid planning model, so that the obtained planning scheme has the best economy.
While the present invention has been described in detail with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof as defined in the appended claims.
Claims (1)
1. A net rack planning method considering regional distribution network risk bearing capacity difference is characterized by comprising the following steps:
1) uncertainty modeling of load
Due to uncertainty of load change of a distribution network in a village and town area, uncertainty of various factors influencing loads and uncertainty of a load prediction method, errors exist in load prediction, and uncertainty exists in the load prediction errors; selecting a Gaussian function as a kernel function, and performing uncertainty modeling on historical sample data of a load prediction error of a reference year by adopting a non-parameter kernel density estimation method; the probability density model of the load prediction error based on the non-parametric kernel density estimation is shown as formula (1) and formula (2),
in the formula (I), the compound is shown in the specification,
a probability density function for the load prediction error; n is the number of load prediction error samples; g (LE, l) is a Gaussian kernel function; LEiPredicting the ith sample value in the error sample for the load; l is a bandwidth parameter of the non-parametric kernel density estimation model, the smaller the value of l, the greater the volatility of the probability density function, the higher the accuracy of the real condition of the data can be reflected, and the greater the value of l, the smaller the volatility of the probability density function, the smoother the curve, but the lower the accuracy;
the probability model of the load prediction error based on the non-parameter kernel density estimation is obtained by historical sample data of the load prediction error and the formula (1) and the formula (2) and is shown as the formula (3),
2) regional power distribution network risk tolerance assessment based on combined weighting method
The method comprises the steps of fully considering the influence of the difference of the risk bearing capacity of the distribution networks in the villages and towns on line upgrading and selection, combining the characteristics of the distribution networks in the villages and towns, establishing a risk bearing capacity evaluation index system of the distribution networks in the villages and towns on the basis of the actual demand of rural power network reconstruction, and evaluating the risk bearing capacity of the distribution networks in the villages and towns by adopting a combined weighting method based on an analytic hierarchy process and an entropy weight method;
firstly, establishing an evaluation index system for risk bearing capacity of regional power distribution network
The evaluation result of the risk bearing capacity of the regional power distribution network is used as a reference basis for determining the confidence level value of the opportunity constraint condition in the grid planning model, and an evaluation index system established by the evaluation index system is required to be capable of fully reflecting the actual demand of rural power network reconstruction engineering and all factors influencing the risk bearing capacity of the regional power distribution network in the villages and towns; in view of the characteristics of the power distribution network in the village and town area and the feasibility of acquiring field data, the risk bearing capacity of the power distribution network in the village and town area is comprehensively evaluated from three aspects of load supply capacity, grid structure level and power distribution network operation level, and an evaluation index system of the risk bearing capacity of the power distribution network in the village and town area is established;
a. capacity of load supply
The load supply capacity of the regional power distribution network means that the maximum load of power supply can be guaranteed under the condition that various technical and economic constraint conditions are met, the larger the numerical value of the maximum load is, the more likely the regional power distribution network meets the power consumption requirement of a user under the condition that uncertain load prediction errors are considered, and correspondingly, the stronger the capacity of the regional power distribution network for bearing operation risks caused by load uncertainty is;
the maximum load rate, the heavy-load distribution ratio and the heavy-load operation time of the line can reflect the load supply capacity of the regional power distribution network; the higher the maximum load rate of a line is, the larger the duty ratio of a heavy load distribution transformer is, the longer the line heavy load operation time is, the smaller the available power supply capacity margin of the regional power distribution network is when the load fluctuation changes, and the situation that the voltage at the tail end of the line is lower than the requirement of a national power grid company is more likely to occur when the equipment is heavily loaded, the weaker the load supply capacity of the regional power distribution network is under the condition of considering load prediction errors, and the worse the capacity of the corresponding regional power distribution network for bearing the operation risk caused by load uncertainty is; therefore, the load supply capacity of the regional power distribution network is measured by adopting a line maximum load rate index, a heavy load distribution ratio index and a line heavy load operation time index;
b. grid structure level
The net rack plays a key role in electric energy transmission and is an important guarantee for safe and reliable power supply of a regional power distribution network to loads; the higher the grid structure level is, the stronger the ability of the power distribution network in areas with higher grid structure level to bear the operation risk caused by uncertainty of load under normal or fault conditions is;
the 10kV distribution lines mostly run outdoors, the electrical equipment is aged quickly under the influence of natural environment and heavy-load running, the frequency of power failure caused by failure due to equipment aging is increased remarkably in recent years, and the capacity of a regional power distribution network for bearing running risks caused by load uncertainty is reduced; the power distribution network in the village and town area is mostly of a non-contact radial structure, the load of the line cannot be transferred through other connecting lines after a fault occurs, if the line is reasonably segmented, the power failure range during the fault can be effectively reduced through the matching operation of a load switch, and the power supply of part of the load of the upper layer fault-free section is recovered, so that the risk bearing capacity of the area power distribution network is improved by reasonably segmenting the line; the overlong power supply radius of the line not only increases the fault probability, but also increases the loss of the line to cause the voltage at the tail end of the line to be lower, so that the capacity of a regional power distribution network for bearing the operation risk caused by uncertainty of load is reduced; therefore, the equipment aging rate index, the main line segment number index and the power supply radius overrun line duty ratio index are adopted to measure the grid structure level of the regional power distribution network;
c. operation level of distribution network
The comprehensive voltage qualification rate, the power failure time per household, the power supply reliability and the comprehensive line loss rate can reflect the integral operation condition of the regional power distribution network; the better each index of the operation level of the regional distribution network is, the stronger the capability of the regional distribution network for bearing the operation risk caused by the uncertainty of the load is;
the comprehensive voltage qualification rate reflects the quality of the power supply voltage of the regional power distribution network and also reflects the size of the load supply capacity and the level of the grid structure of the regional power distribution network, and when the comprehensive voltage qualification rate is lower than the relevant regulations of the national grid company, the smaller the value of the comprehensive voltage qualification rate is, the weaker the capacity of the regional power distribution network for bearing the operation risk caused by the uncertainty of the load is; under the condition that the grid structures of the regional distribution networks are the same, if the power failure time of each household is shorter within a certain observation time range, the stronger the adaptability of the regional distribution network to load uncertainty is, the stronger the risk bearing capacity is; the reliable power supply means that under the condition of normal or fault of a system, the system can ensure uninterrupted power supply to users according to a certain quality standard, the higher the power supply reliability of the regional power distribution network is, the more reasonable the planning scheme of the regional power distribution network is, and the stronger the capability of bearing the operation risk caused by the uncertainty of the load is; the comprehensive line loss rate not only reflects the operating economy of the regional power distribution network, but also reflects the rationality of the load distribution and grid planning scheme of the regional power distribution network, and the higher the comprehensive line loss rate is, the poorer the operating economy of the regional power distribution network is, the more unreasonable the load distribution and grid planning scheme is, and the weaker the capability of the regional power distribution network for bearing the operating risk caused by the uncertainty of the load is; therefore, the operation level of the regional power distribution network is measured by adopting the comprehensive voltage qualification rate index, the power failure time index of the household, the power supply reliability index and the comprehensive line loss rate index;
second, index weight calculation based on combined weighting method
The index weight can measure the relative importance of the evaluation indexes, the size of the index weight can reflect the relative importance of the indexes, and whether the determination of the index weight coefficient in an evaluation system is scientific and reasonable directly influences the credibility of an evaluation result; the subjective weighting method and the objective weighting method have the advantages and the disadvantages respectively, so that the final weight of each index is coordinated subjectively and objectively in order to avoid the disadvantages and give full play to the advantages respectively, and the final weight of each index is determined by adopting a combined weighting method combining the subjective weighting method based on an analytic hierarchy process and the objective weighting method based on an entropy weight method so as to ensure the credibility of the comprehensive weight of the index;
a. subjective weight calculation
Calculating subjective weights of indexes at all levels by adopting an analytic hierarchy process, wherein experts give out relative importance sequences among the indexes by combining with self field work experience to form a judgment matrix, and then calculating the weight of the corresponding index according to the maximum eigenvalue of the judgment matrix and the corresponding eigenvector thereof; forming a relative importance degree judgment matrix between indexes of each level by adopting a 9-level scale expansion method;
for the first-level index, the load supply capacity of the regional power distribution network is one of important standards for measuring the planning and transformation work effect of the power distribution network, and the safe and reliable power supply of the load is guaranteed to the maximum extent and is also the core target of the regional power distribution network, so that the index is considered as the most important first-level index; the net rack is a key component of the regional power distribution network and is an important bridge for the regional power distribution network to transmit electric energy to the load, the level of the net rack structure is an important theoretical basis for evaluating whether the planning scheme of the regional power distribution network is reasonable or not, and the net rack structure also needs to be highly emphasized, but the importance degree of the net rack structure is slightly weaker compared with the load supply capacity index; the operation level of the power distribution network reflects the overall safety and economy of the system, is a visual reflection of whether the grid planning scheme of the regional power distribution network is reasonable or not, is a visual reflection of the strength of the capability of the regional power distribution network for bearing the operation risk caused by the uncertainty of the load, and is considered to be weaker than the importance degree of the grid structure level index; that is, the relative importance degree of the primary index is ranked as: capacity of load supply>Grid structure level>The operation level of the power distribution network forms a first-level index judgment matrix A based on a 9-level scale extension method1；
The maximum load rate, the heavy-load distribution ratio and the heavy-load operation time of the line have influence on the power supply reliability, the voltage qualification rate and the comprehensive line loss rate of the system, and the relative importance ranking of the secondary indexes is as follows: line maximum load rate>Line heavy load operation time>Rate of equipment aging>Number of line segments>Power supply radius overrun line ratio>Integrated voltage yield>Power supply reliability rate>Synthesizing the line loss rate, and forming a second-level index judgment matrix A based on a 9-level scale expansion method2；
Due to miningThe 9-level scale extension method is adopted, so that the condition that the numerical values in the judgment matrix are inconsistent due to the complexity of multi-level judgment can be effectively avoided, and the judgment matrix A does not need to be subjected to1And A2The consistency test is carried out, the whole evaluation process is simplified, and the calculated amount is reduced;
b. objective weight calculation
The objective weight of each index is calculated by adopting an entropy weight method so as to fully consider the influence of the actual value of each index on the risk bearing capacity of the power distribution network, the dimensionless processing mode of the index adopts a form of a formula (4),
in the formula, sijIs the value of the jth index of the scheme i after non-dimensionalization; r isijThe actual value of the jth index of the scheme i; min (r)j) Is the minimum value of the index j; max (r)j) Is the maximum value of the index j;
c. integrated weight calculation
In consideration of subjectivity of the subjective weight of the index and the problem that the objective weight of the index cannot reflect the importance degree of the index in the actual problem, in order to enable the evaluation result of the risk bearing capacity of the regional distribution network to be more objective and reasonable, the comprehensive weight of each index is calculated by a formula (5) by adopting a linear weighted combined weighting method so as to more comprehensively reflect the influence of each factor on the risk bearing capacity of the regional distribution network;
in the formula, mujThe comprehensive weight of the jth evaluation index; w is ajAnd vjSubjective weight and objective weight of the jth evaluation index are respectively;
risk bearing capacity assessment of regional distribution network
Although the single index can reflect the strength of the operation risk of the regional distribution network caused by load uncertainty on one aspect, the single index is not enough to explain the overall situation of the risk bearing capacity of the regional distribution network; therefore, the risk bearing capacity of the distribution network in each village and town area is evaluated by a method of combining the comprehensive weight of each index and the value after the comprehensive weight is subjected to dimensionless, and the calculation of the risk bearing capacity of the distribution network in each area is shown as a formula (6); the larger the evaluation value of the risk bearing capacity of the regional power distribution network is, the stronger the capacity of the regional power distribution network for bearing the risk caused by load uncertainty is;
in the formula: zmEvaluating the risk tolerance of the power distribution network in the mth area; smjThe value of the jth evaluation index of the mth regional distribution network after dimensionless; mu.sjThe comprehensive weight of the jth evaluation index;
differentiated value of confidence level
According to the value range of the confidence level and by combining the risk bearing capacity evaluation results of the distribution networks in the villages and towns, the confidence level values of the branch power opportunity constraint conditions are selected in a differentiated mode, and meanwhile the confidence level values meeting all opportunity constraint conditions are not less than 80%;
3) opportunity constrained planning model for net rack
When uncertainty factors are considered in the power distribution network planning process, the minimum upgrade investment cost of a line is taken as a target function, various requirements which must be met by safe and reliable operation of a system are taken as constraint conditions, an opportunity constraint planning model of a net rack is established on the basis of considering uncertainty of a load predicted value, the situation that the constraint conditions are not met in a planning scheme is allowed to occur, and the possibility that the opportunity constraint conditions are met is met to meet the requirement of a certain confidence level;
(ii) an objective function of the model
The objective function of the model is to minimize the investment cost for upgrading the line, as shown in equation (7)
In the formula, FinvInvestment cost for line upgrade; x is the number oflThe decision variable is a decision variable for judging whether the line l is upgraded, the value is 1 during upgrading, and the value is 0 otherwise; cline,lThe material cost and the installation cost for upgrading the line l, wherein the material cost of the line is determined by the type of the line; llTo upgrade the length of line l; n is a radical oflThe total number of the upgrading lines;
constraint conditions of model-
When planning the network frame of the power distribution network, certain technical constraint conditions and operation constraint conditions need to be met, the following constraint conditions are considered,
a. branch power constraint
In order to improve the capability of the grid planning scheme to bear the operation risk caused by the uncertainty of the load, based on the opportunity constraint planning theory, the deterministic branch power constraint in the traditional planning model is described as the opportunity constraint, so that the probability that the branch power meets the constraint condition is not less than a certain confidence level, as shown in formula (8),
Pr{0≤Pi T≤Pimax}≥αmP (8)
in the formula, Pi TThe active power of the line i when the planning age is T; pimaxMaximum power allowed to pass for line i; alpha is alphampDetermining the confidence level of branch power opportunity constraint in the mth village and town area power distribution network according to the risk tolerance evaluation result of the village and town area power distribution network; wherein P isi TObtained by formula (9);
Pi T＝PiB[(1+ri)T+LE] (9)
in the formula, PiBIs the reference active power of line i; r isiThe annual average load growth rate of the line i; t is the planning year limit; LE is the random load prediction error; bringing formula (9) into formula (8) to obtain formula (10), and further deforming to obtain formula (11);
Pr{PiB[(1+ri)T+LE]≤Pimax}≥αmP (10)
obtaining a probability density function phi (LE) and a probability distribution function phi (LE) of a load prediction error LE by adopting a nonparametric kernel density estimation method; branch power opportunity constraint condition confidence level alpha of village and town area mmpDetermining according to a risk tolerance evaluation result of the regional power distribution network; reference active power P of line iiB、riAfter the load annual average growth rate and the planning age limit T of the line i are determined, P is determined by the related knowledge of probability theory and an equation (11)imaxAnd determining the model of the line after upgrading and transformation according to the value range, as shown in formula (12);
Pimax≥PiB[Φ-1(αmP)+(1+ri)T] (12)
in the formula, phi-1(. cndot.) represents an inverse function of the distribution function Φ (·) of the load prediction error;
b. upper and lower limit constraints of node voltage
Ujmin≤Uj≤Ujmax (13)
In the formula of UjIs the voltage value of node j; u shapejmaxAnd UjminThe upper and lower limit values of the voltage allowed by the node j, and the allowable deviation of the 10kV voltage of the power distribution network is 7 percent, then UjminThe value is 9.3 kV;
step of planning net rack
a. According to load prediction error historical sample data of a reference year, a nonparametric kernel density estimation method is adopted to obtain a probability density function phi (LE) and a probability distribution function phi (LE) of the load prediction error;
b. establishing a risk bearing capacity evaluation index system of the regional power distribution network by combining the characteristics of the rural regional power distribution network, obtaining the comprehensive weight of each index by adopting a combined weighting method, and obtaining the risk bearing capacity evaluation value of each rural regional power distribution network according to the comprehensive weight of each index and the nondimensionated index value;
c. establishing an opportunity constraint planning model of the net rack, selecting the confidence level of the branch power opportunity constraint condition in combination with the difference of the risk bearing capacity evaluation value of each rural area power distribution network, determining the load prediction error corresponding to the corresponding confidence level according to the probability distribution function phi (LE) of the load prediction error obtained in the step a, obtaining the load prediction value of each rural area power distribution line in different planning years, determining the requirement which the maximum allowable load capacity of the line should meet according to the formula (12), and determining the model of the line after upgrading according to the requirement;
d. modeling simulation analysis is carried out on the upgrading model selection scheme of the distribution lines in each village and town area under different planning age conditions, whether constraint conditions meet requirements is verified, and finally the line optimization model selection scheme with the minimum investment total cost is determined.
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