Power grid carrying capacity analysis method and system for photovoltaic development in rural areas

Abstract

The grid carrying capacity analysis method and system for photovoltaic development in rural areas are based on the power flow calculation model to establish the inequality constraint of photovoltaic access capacity of photovoltaic access nodes; the difference between the maximum photovoltaic capacity under the inequality constraint of distribution transformer capacity and photovoltaic access capacity and the maximum photovoltaic capacity under the inequality constraint of node photovoltaic access capacity is used to determine whether the bottleneck of the grid in the area is the distribution transformer capacity or the distribution line path; the photovoltaic access capacity of each photovoltaic access node in the inequality constraint is updated to the product of the amplification factor and the unitized photovoltaic capacity, and the updated inequality constraint is solved to determine the upper limit of the unitized photovoltaic capacity; based on the power flow calculation model, the photovoltaic access node corresponding to the highest voltage value is calculated according to the upper limit of the unitized photovoltaic capacity as the bottleneck node of the grid carrying capacity, and the photovoltaic access capacity of the bottleneck node is used as the grid carrying capacity analysis result to realize the full development of the photovoltaic capacity in the grid.

Description

Technical Field

[0001] The present invention belongs to the field of new energy technology, and specifically, relates to a grid carrying capacity analysis method and system for photovoltaic development in rural areas. Background Art

[0002] The distribution and transformation grid in rural areas generally has the characteristics of wide coverage, large scale, unbalanced development between regions, and relatively dispersed load. When distributed photovoltaic power sources with high penetration rate are connected to the power grid in rural areas, when their power generation accounts for a certain proportion of the total capacity of the power grid, this fluctuation will have an adverse impact on the power grid. Therefore, it is necessary to analyze each area, estimate the load distribution of the area, and then calculate the maximum photovoltaic access capacity, so as to provide a scientific basis for the development of rural photovoltaic resources.

[0003] In the prior art, it can be mainly divided into two categories: modeling methods based on mathematical models and specific scenario analysis methods. The first type of modeling method based on mathematical models is a method of modeling the maximum access capacity of distributed photovoltaics in the substation area into a mixed nonlinear programming problem with constraints and solving it. Although this method has a rigorous and reliable mathematical basis and many solution algorithms, it is difficult to summarize a unified mathematical model to model and solve complex substations in reality. It is often only suitable for modeling and solving in simple or pre-set scenarios, and it is difficult to apply to actual engineering applications. The second type of method, the specific scenario analysis method, is a method of conducting example analysis based on actual engineering objects and statistically determining the maximum access capacity of distributed photovoltaics through massive data. This type of algorithm does not require complicated mathematical derivation, and multiple approximate optimal solutions can be obtained through relevant scenario data. However, large-scale substation scenarios require a large amount of data and flow calculations, the optimization speed is too slow, and the calculation time is too long.

[0004] According to the law of power flow in the power grid, under the same photovoltaic access capacity, the closer the photovoltaic power access point is to the node in the central area of ​​the distribution transformer, the smaller the voltage raising effect on each node. In existing projects, the voltage of each node of the distribution line is obtained through the power flow calculation formula, and the upper limit of the photovoltaic access capacity of the substation is calculated based on the voltage fluctuation of each node in the substation according to the limit requirements of the national power quality standard. In order to make full use of the characteristics of this power flow and voltage and reduce the impact on the stability of the distribution network, more photovoltaic power access points are usually designed at the nodes close to the central area of ​​the distribution transformer in the same substation, which leads to a large number of photovoltaic accesses at the nodes close to the distribution transformer, while there is no photovoltaic access at the nodes far from the distribution transformer, resulting in the characteristics of large photovoltaic capacity at the upstream node and small photovoltaic capacity at the downstream node. However, due to the calculation characteristics of the power flow calculation itself, the voltage raising effect of the same photovoltaic capacity at different nodes is not the same, resulting in the characteristics of large photovoltaic capacity at the upstream node and small photovoltaic capacity at the downstream node. The photovoltaic capacity gap between the nodes on the distribution line is large, and the voltage gap between the nodes is also large, resulting in the impact of photovoltaic access on the grid voltage exceeding the limit requirements of the national power quality standard, thereby limiting the photovoltaic capacity accessed by the upstream node and limiting the proportion of new energy. Summary of the invention

[0005] In order to solve the deficiencies in the prior art, the present invention provides a grid carrying capacity analysis method and system for photovoltaic development in rural areas. Based on the grid flow calculation model, the voltage fluctuation restriction condition of the photovoltaic access node is introduced into the inequality constraint of the photovoltaic access capacity of each node, so as to solve the problem that only the nodes close to the distribution transformer in the same area can access more photovoltaic capacity due to the single constraint of the distribution transformer capacity, thereby realizing the reasonable distribution of photovoltaic access nodes in the area and the matching of photovoltaic access capacity and load distribution.

[0006] The present invention adopts the following technical solution.

[0007] On the one hand, the present invention proposes a method for analyzing the carrying capacity of a power grid for photovoltaic development in rural areas, comprising:

[0008] Step 1: Establish a power flow calculation model of the photovoltaic power grid in the substation area using the distribution transformer location, distribution line path, and distribution line parameters; the distribution line parameters include: the load corresponding to the photovoltaic access node, and the impedance of the distribution line between the photovoltaic access node and the corresponding upstream node;

[0009] Step 2: Based on the power flow calculation model, through a linear programming method, using the sum of the impedances of the distribution lines between the photovoltaic access node and the corresponding upstream node and the constraint limit of the voltage fluctuation of the photovoltaic access node, an inequality constraint on the photovoltaic access capacity of the photovoltaic access node is established;

[0010] Step 3, under the constraints of the capacity of the distribution transformer and the inequality constraints of the photovoltaic access capacity of the photovoltaic access node, calculate the first calculated value of the maximum photovoltaic capacity of the substation; under the inequality constraints of the photovoltaic access capacity of the photovoltaic access node, calculate the second calculated value of the maximum photovoltaic capacity of the substation; when the difference between the first calculated value and the second calculated value is greater than the set threshold, it is determined that the bottleneck of the substation power grid is the capacity of the distribution transformer; otherwise, it is determined that the bottleneck of the substation power grid is the path of the distribution line;

[0011] Step 4: Taking the ratio of the number of houses connected to the photovoltaic access node and the distribution line path distance from the photovoltaic access node to the distribution transformer as the magnification factor, the photovoltaic access capacity of each photovoltaic access node in the inequality constraint of the photovoltaic access capacity of the photovoltaic access node is updated to the product of the magnification factor and the unitized photovoltaic capacity, and solving the updated inequality constraint to determine the upper limit value of the unitized photovoltaic capacity;

[0012] Step 5: Based on the power flow calculation model, the voltage of each photovoltaic access node is calculated according to the upper limit value of the unitized photovoltaic capacity, and the photovoltaic access node corresponding to the highest voltage value is used as the bottleneck node of the grid carrying capacity, and the photovoltaic access capacity of the bottleneck node is used as the grid carrying capacity analysis result.

[0013] Preferably, step 1 comprises:

[0014] Step 1.1, input the satellite remote sensing image of the substation area; extract the pixel coordinates of the house distribution, the pixel coordinates of the distribution transformer location and the distribution line path from the satellite remote sensing image by image processing method;

[0015] Step 1.2, according to the positive correlation between house distribution and substation load distribution, the pixel coordinates of house distribution are mapped to the pixel coordinates of substation load distribution;

[0016] Step 1.3, using the K-means clustering method to calculate the center point of the load distribution pixel coordinates, and taking the center point as the photovoltaic access node on the distribution line;

[0017] Step 1.4, taking the pixel coordinates of the distribution transformer in the substation as the root node, image processing technology is used to determine the connectivity and geographical distance between the photovoltaic access node and the corresponding upstream node from the distribution line path;

[0018] Step 1.5, obtaining distribution line parameters, including: active power and reactive power of the load corresponding to the photovoltaic access node, and impedance of the distribution line between the photovoltaic access node and the corresponding upstream node;

[0019] Step 1.6, using the distribution transformer location, distribution line path, and distribution line parameters, establish a power flow calculation model for the photovoltaic power grid in the substation area.

[0020] Preferably, in step 1.5, the active power and reactive power of the load corresponding to the photovoltaic access node are as follows:

[0021]

[0022]

[0023] In the formula,

[0024] P L is the total load power of the substation,

[0025] P L，k , Q L，k are respectively the active power and reactive power of the load corresponding to the photovoltaic access node k,

[0026] m is the total number of houses in the area,

[0027] m k is the number of houses connected to the photovoltaic access node k in the area,

[0028] is the power factor of the area.

[0029] Preferably, in step 1.5, a topological method is used to calculate the connectivity matrix between the photovoltaic access node and the corresponding upstream node, and the impedance of the distribution line between the photovoltaic access node and the corresponding upstream node is calculated using the connectivity matrix and the geographical distance according to the following relationship:

[0030] R k =D k ×R d

[0031] X k =D k ×X d

[0032] In the formula,

[0033] R k , X k are the resistance and reactance of photovoltaic access node k,

[0034] D k is the geographical distance from PV access node k to its upstream node,

[0035] R d , X d are the equivalent resistance and equivalent reactance of the distribution line per unit length,

[0036] k = 1, 2, ..., n, where n is the number of photovoltaic access nodes in the substation.

[0037] Preferably, step 2 comprises:

[0038] Step 2.1, calculating the voltage fluctuation of each photovoltaic access node according to the power flow calculation model;

[0039] Step 2.2: The national power quality standard limit is +7%, and the national power quality standard limit is used as the constraint limit of the voltage fluctuation of each photovoltaic access node;

[0040] Step 2.3, through the linear programming method, using the sum of the impedances of the distribution lines between each photovoltaic access node and the corresponding upstream node and the constraint limit of the voltage fluctuation of each photovoltaic access node, establish the inequality constraint of the photovoltaic access capacity of each photovoltaic access node.

[0041] Preferably, in step 2.3, the inequality constraint of the photovoltaic access capacity of each photovoltaic access node is as follows:

[0042]

[0043] In the formula,

[0044] P PV,k is the photovoltaic access capacity of photovoltaic access node k,

[0045] k = 1, 2, ..., n, where n is the number of photovoltaic access nodes in the area.

[0046] is the sum of the impedances of the distribution lines between the photovoltaic access node k and the corresponding upstream node,

[0047] C k is the load parameter corresponding to the photovoltaic access node k,

[0048] U N is the rated voltage of the distribution transformer.

[0049] Preferably, step 2.3 further includes: taking the photovoltaic capacity connected in the substation as negative power, and updating the load parameter corresponding to the photovoltaic access node k according to the following relationship:

[0050]

[0051] In the formula,

[0052] The subscripts i, j, and k are all node numbers in the power flow calculation model. When calculating the voltage fluctuation of the photovoltaic access node k, i represents the upstream node corresponding to the photovoltaic access node k, i = 1, 2, ..., k, and the node from the upstream node i to n is the downstream node j corresponding to the upstream node i, that is, j = i, i+1, ..., n,

[0053] R i , X iare the resistance and reactance of the distribution line between the photovoltaic access node k and the upstream node i, P L，j , Q L，j are the active power and reactive power of downstream node j respectively,

[0054] P BPV，j is the connected PV capacity of downstream node j;

[0055] When the area is not connected to photovoltaic power, P BPV，j is 0, and C1≤C2≤…≤C k ≤…≤C n .

[0056] Preferably, in step 3, the capacity constraint of the distribution transformer is as follows:

[0057]

[0058] Where P is the capacity of the distribution transformer in the substation, P PV，j is the photovoltaic access capacity of downstream node j.

[0059] Preferably, the maximum photovoltaic capacity of the station area is as follows:

[0060] T=max(P PV，1 +P PV，2 +…+P PV，k +…+P PV，n )

[0061] In the formula, the photovoltaic access capacity of each photovoltaic access node is not less than 0.

[0062] Preferably, the threshold value is set to be no less than 5 kW.

[0063] Preferably, in step 4, the amplification factor is as follows:

[0064]

[0065]

[0066] t k =m′ k / l′ k

[0067] In the formula,

[0068] m′ k is the normalized value of the number of houses connected to PV access node k,

[0069] m k is the number of houses connected to the photovoltaic access node k in the area,

[0070] m is the total number of houses in the area,

[0071] l′ k is the distribution line path distance from the photovoltaic access node k to the distribution transformer, which is the sum of the distribution line paths between the photovoltaic access node k and the corresponding upstream node. i = 1 is the root node, representing the distribution transformer.

[0072] t k is the amplification factor of the photovoltaic access node k.

[0073] Preferably, the photovoltaic access capacity of photovoltaic access node k is updated as follows:

[0074] P PV，k =t k P PV

[0075] Where P PV，k is the photovoltaic access capacity of photovoltaic access node k, P PV is the unitized photovoltaic capacity.

[0076] Preferably, the unitized photovoltaic capacity P PV The upper limits are as follows:

[0077]

[0078] In the formula,

[0079] is the sum of the impedances of the distribution lines between the photovoltaic access node k and the corresponding upstream node,

[0080] C k is the load parameter corresponding to the photovoltaic access node k,

[0081] U N is the rated voltage of the distribution transformer,

[0082] k = 1, 2, ..., n, where n is the number of photovoltaic access nodes in the substation.

[0083] The present invention also proposes a power grid carrying capacity analysis system for rural photovoltaic development, including: a power flow calculation model building module, a photovoltaic access capacity constraint module, and a grid bottleneck identification module.

[0084] PV maximum capacity calculation module, PV capacity upper limit calculation module, existing PV access update module, grid carrying capacity analysis module;

[0085] The power flow calculation model building module is used to establish the power flow calculation model of the photovoltaic power grid in the substation area by using the distribution transformer location, distribution line path, and distribution line parameters; the distribution line parameters include: the load corresponding to the photovoltaic access node, and the impedance of the distribution line between the photovoltaic access node and the corresponding upstream node;

[0086] The photovoltaic access capacity constraint module is used to establish an inequality constraint on the photovoltaic access capacity of the photovoltaic access node based on the power flow calculation model and through a linear programming method, using the sum of the impedances of the distribution lines between the photovoltaic access node and the corresponding upstream node and the constraint limit of the voltage fluctuation of the photovoltaic access node;

[0087] The grid bottleneck identification module of the substation is used to calculate the first calculated value of the maximum photovoltaic capacity of the substation under the inequality constraint of the distribution transformer capacity and the node photovoltaic access capacity; calculate the second calculated value of the maximum photovoltaic capacity of the substation under the inequality constraint of the node photovoltaic access capacity; when the difference between the first calculated value and the second calculated value is greater than the set threshold, it is determined that the bottleneck of the substation grid is the distribution transformer capacity; otherwise, it is determined that the bottleneck of the substation grid is the distribution line route;

[0088] The power grid carrying capacity analysis module is used to update the photovoltaic access capacity of each photovoltaic access node in the inequality constraint of the photovoltaic access capacity of the photovoltaic access node to the product of the amplification factor and the unitized photovoltaic capacity when it is determined that the bottleneck of the power grid in the substation area is the distribution line path. The module is used to solve the updated inequality constraint to determine the upper limit of the unitized photovoltaic capacity. Based on the power flow calculation model, the voltage of each photovoltaic access node is calculated according to the upper limit of the unitized photovoltaic capacity, and the photovoltaic access node corresponding to the highest voltage value is used as the bottleneck node of the power grid carrying capacity, and the photovoltaic access capacity of the bottleneck node is used as the power grid carrying capacity analysis result.

[0089] The system also includes: a photovoltaic access capacity constraint update model, which takes the photovoltaic capacity that has been connected in the substation as negative power, and updates the inequality constraint of the photovoltaic access capacity of the photovoltaic access node by updating the load parameters corresponding to the photovoltaic access node.

[0090] The beneficial effects of the present invention are as follows:

[0091] The present invention is based on a power flow calculation model. By using a linear programming method, the present invention utilizes the sum of the impedances of the distribution lines between the photovoltaic access nodes and the corresponding upstream nodes and the constraint limit of the voltage fluctuation of the photovoltaic access nodes to establish an inequality constraint on the photovoltaic access capacity of the photovoltaic access nodes. This achieves the maximum photovoltaic access capacity of the rural substation under the condition that the node voltage fluctuation does not exceed the limit. This solves the problem that only nodes close to the distribution transformer in the same substation can access more photovoltaic capacity due to the single constraint of the distribution transformer capacity. This achieves full development of the photovoltaic capacity in the substation, reduces the gap in photovoltaic access capacity between nodes on the distribution line, and balances the photovoltaic access capacity of nodes on the distribution line in the substation to ensure that the impact of photovoltaic access on the grid voltage does not exceed the limit requirements of the national power quality standard.

[0092] The present invention uses the ratio of the number of houses connected to the photovoltaic access node and the distribution line path distance from the photovoltaic access node to the distribution transformer as the amplification factor, updates the photovoltaic access capacity of each photovoltaic access node in the inequality constraint of the photovoltaic access capacity of the photovoltaic access node to the product of the amplification factor and the unitized photovoltaic capacity, solves the updated inequality constraint to determine the upper limit of the unitized photovoltaic capacity, and realizes that the more houses there are and the smaller the voltage raising effect is, the larger the photovoltaic capacity is.

[0093] The present invention conducts qualitative analysis and quantitative calculation on the factors that lead to the bottleneck of the substation power grid, and based on the power flow calculation model, calculates the voltage of each photovoltaic access node according to the upper limit value of the unitized photovoltaic capacity, and takes the photovoltaic access node corresponding to the highest voltage value as the bottleneck node of the power grid carrying capacity, and takes the photovoltaic access capacity of the bottleneck node as the power grid carrying capacity analysis result.

[0094] The present invention uses image processing technology to process remote sensing images of substations, laying the foundation for various modeling of power grid carrying capacity analysis. It does not need to rely on any load distribution model and is not restricted by whether the substation data is detailed. It can realize power grid carrying capacity analysis of various rural substations.

[0095] The method proposed in the present invention can analyze the grid carrying capacity of the substation where photovoltaic access has been built. The analysis result is used as a balance indicator of the photovoltaic access capacity corresponding to each photovoltaic access node on the distribution line. At the same time, it can also meet the voltage constraints of each photovoltaic access node, avoid the situation where the upstream node access capacity is large and the downstream node access capacity is small when photovoltaic is newly built or expanded in the substation, and ensure the stable operation of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0096] Figure 1 It is a flow chart of the grid carrying capacity analysis method for photovoltaic development in rural areas proposed by the present invention;

[0097] Figure 2It is a flow chart of a method for extracting the structure and node information of a rural distribution line in an embodiment of the present invention;

[0098] Figure 3 is a high-resolution satellite remote sensing image in an embodiment of the present invention;

[0099] Figure 4 This is a rendering of the power distribution line structure extraction in an embodiment of the present invention;

[0100] Figure 5 is a schematic diagram of the structure of a power flow calculation model in an embodiment of the present invention;

[0101] Figure 6 It is a photovoltaic capacity calculation model for balancing upper and lower nodes in an embodiment of the present invention;

[0102] Figure 7 It is a flowchart of bottleneck factor analysis in an embodiment of the present invention. DETAILED DESCRIPTION

[0103] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only embodiments of a part of the present invention, rather than all embodiments. Based on the spirit of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0104] The present invention proposes a grid carrying capacity analysis method for photovoltaic development in rural areas. Figure 1 As shown, the method includes:

[0105] Step 1: Establish a power flow calculation model for the photovoltaic power grid in the substation using the distribution transformer location, distribution line path, and distribution line parameters; the distribution line parameters include: the load corresponding to the photovoltaic access node, and the impedance of the distribution line between the photovoltaic access node and the corresponding upstream node.

[0106] Specifically, Figure 2 As shown, step 1 includes:

[0107] Step 1.1, input a high-resolution satellite remote sensing image of the substation area; extract pixel coordinates of house distribution, pixel coordinates of distribution transformer locations, and distribution line paths from the satellite remote sensing image by image processing methods;

[0108] Specifically, from Figure 3 It can be seen that the high-resolution satellite remote sensing images include the distribution of houses in the substation area, the distribution line path and the location of distribution transformers.

[0109] Step 1.2, according to the positive correlation between house distribution and substation load distribution, the pixel coordinates of house distribution are mapped to the pixel coordinates of substation load distribution;

[0110] Specifically, one house corresponds to one load, the distribution of houses reflects the distribution of loads, and the geographical distance between houses also reflects the distance between loads. The present invention combines the distribution of houses in the substation area and adopts an algorithm that the houses correspond to the photovoltaic load in direct proportion, so as to achieve the effect that the more houses connected to each node, the greater the photovoltaic capacity in the substation area.

[0111] Steps 1.1 and 1.2 use image processing technology to process the remote sensing images of the substation area and realize the identification of the load resources in the substation area.

[0112] Step 1.3, using the K-means clustering method to calculate the center point of the load distribution pixel coordinates, and taking the center point as the photovoltaic access node on the distribution line;

[0113] Step 1.4, taking the pixel coordinates of the distribution transformer in the substation as the root node, image processing technology is used to determine the connectivity and geographical distance between the photovoltaic access node and the corresponding upstream node from the distribution line path;

[0114] Steps 1.3 and 1.4 realize the load part characteristic analysis and distribution line structure identification.

[0115] Step 1.5, obtaining distribution line parameters, including: active power and reactive power of the load corresponding to the photovoltaic access node, and impedance of the distribution line between the photovoltaic access node and the corresponding upstream node;

[0116] Specifically, the active power and reactive power of the load corresponding to the photovoltaic access node are as follows:

[0117]

[0118]

[0119] In the formula,

[0120] P L is the total load power of the substation,

[0121] P L,k , Q L,k are respectively the active power and reactive power of the load corresponding to the photovoltaic access node k,

[0122] m is the total number of houses in the area,

[0123] m k is the number of houses connected to the photovoltaic access node k in the area,

[0124] is the power factor of the area.

[0125] In the embodiment of the present invention, each node is numbered, such as Figure 4 The topological method is used to calculate the connectivity matrix between the photovoltaic access node and the corresponding upstream node. The connectivity matrix and the geographical distance are used to calculate the impedance of the distribution line between the photovoltaic access node and the corresponding upstream node using the following relationship:

[0126] R k =D k ×R d (3)

[0127] X k =D k ×X d (4)

[0128] In the formula,

[0129] R k , X k are the resistance and reactance of photovoltaic access node k,

[0130] D k is the geographical distance from PV access node k to its upstream node,

[0131] R d , X d are the equivalent resistance and equivalent reactance of the distribution line per unit length,

[0132] k = 1, 2, ..., n, where n is the number of photovoltaic access nodes in the substation.

[0133] Step 1.6, using the distribution transformer location, distribution line path, and distribution line parameters, establish a power flow calculation model for the photovoltaic power grid in the substation area.

[0134] like Figure 5 In the power flow calculation model shown in the figure, each node on the distribution line path is not only the center point of the load distribution of multiple houses, but also the access point of the photovoltaic power generated by multiple houses; the node formed by the center point of the load distribution of multiple houses obtains the load power from the distribution line, that is, the active power P of the load node L,k and reactive power Q L,k , the access point for the photovoltaic power generated by multiple houses, responsible for sending the photovoltaic power generated by the connected houses to the distribution line, that is, the photovoltaic access capacity P of the node Pv,k , k = 1, 2,…, n, where n is the number of all nodes in the area. Figure 5 Starting from the distribution transformer, the photovoltaic access node P Pv,k The active power P of the corresponding load node L,k and reactive power QL,k .

[0135] The present invention uses image processing technology to process remote sensing images of substations, laying the foundation for various modeling of power grid carrying capacity analysis. It does not need to rely on any load distribution model and is not restricted by whether the substation data is detailed. It can realize power grid carrying capacity analysis of various rural substations.

[0136] Step 2: Based on the power flow calculation model, through the linear programming method, using the sum of the impedances of the distribution lines between the photovoltaic access node and the corresponding upstream node and the constraint limit of the voltage fluctuation of the photovoltaic access node, an inequality constraint on the photovoltaic access capacity of the photovoltaic access node is established.

[0137] Specifically, step 2 includes:

[0138] Step 2.1: Calculate the voltage fluctuation of each photovoltaic access node according to the power flow calculation model.

[0139] Specifically, Figure 5 In the power flow calculation model shown, the voltage fluctuations at each node are as follows:

[0140]

[0141] In the formula,

[0142] The subscripts i, j, and k are all node numbers in the power flow calculation model. When calculating the voltage fluctuation of the photovoltaic access node k, i represents the upstream node corresponding to the photovoltaic access node k, i = 1, 2, ..., k, and the node from the upstream node i to n is the downstream node j corresponding to the upstream node i, that is, j = i, i+1, ..., n,

[0143] ΔU k % represents the voltage fluctuation of photovoltaic access node k,

[0144] U N is the rated voltage of the distribution transformer,

[0145] P PV，j is the photovoltaic access capacity of downstream node j. If there is no photovoltaic access, it is 0.

[0146] P L,j , Q L,j are the active power and reactive power of downstream node j respectively,

[0147] R i , X i are the resistance and reactance of the distribution line between the photovoltaic access node k and the upstream node i, respectively.

[0148] In step 2.2, the national power quality standard limit is set to +7%, and the national power quality standard limit is used as the constraint limit of the voltage fluctuation of each photovoltaic access node.

[0149] Specifically, the constraint limits of voltage fluctuations at each photovoltaic access node are as follows:

[0150] ΔU1%≤7%…, ΔU k %≤7%,…ΔU n %≤7% (6)

[0151] Step 2.3, through the linear programming method, using the sum of the impedances of the distribution lines between each photovoltaic access node and the corresponding upstream node and the constraint limit of the voltage fluctuation of each photovoltaic access node, establish the inequality constraint of the photovoltaic access capacity of each photovoltaic access node.

[0152] Substituting the load parameter in the second half of equation (5) yields the following relationship:

[0153]

[0154]

[0155] In the formula, C1, C2, ..., C k ,…,C n They represent the load parameters of photovoltaic access node 1, the load parameters of photovoltaic access node 2, ... the load parameters of photovoltaic access node k, ..., the load parameters of photovoltaic access node n, respectively, and satisfy:

[0156] C1≤C2≤...≤C k ≤...≤C n (9)

[0157] Therefore, the constraints on the voltage fluctuation of photovoltaic access node 1 are as follows:

[0158]

[0159] According to formula (10), the following relationship is obtained:

[0160]

[0161] Therefore, the constraints on the voltage fluctuation of the photovoltaic access node 2 are as follows:

[0162]

[0163] According to formula (12), the following relationship is obtained:

[0164]

[0165] By analyzing the voltage fluctuations of photovoltaic access nodes 1 and 2, referring to equations (11) and (13), the constraints of the voltage fluctuations of the remaining photovoltaic access nodes are derived as follows:

[0166]

[0167] According to formula (14), the following relationship is obtained:

[0168]

[0169] The following relationship is obtained by rearranging formula (15):

[0170]

[0171] Therefore, the inequality constraints of the photovoltaic access capacity of each photovoltaic access node are as follows:

[0172]

[0173] In the formula,

[0174] P PV，k is the photovoltaic access capacity of photovoltaic access node k, which is an unknown number to be determined and solved.

[0175] k = 1, 2, ..., n, where n is the number of photovoltaic access nodes in the area.

[0176] is the sum of the impedances of the distribution lines between the photovoltaic access node k and the corresponding upstream node,

[0177] C k is the load parameter corresponding to the photovoltaic access node k, which is a fixed parameter and is obtained by adding them item by item after calculation.

[0178] If there are nodes in the substation that have been connected to a certain amount of photovoltaic power, it is necessary to calculate the maximum photovoltaic capacity of the substation under the given power. However, if the connected photovoltaic power is directly used as power in the power flow calculation, the calculation complexity increases and it is difficult to solve it through the linear programming algorithm.

[0179] In order to improve the calculation efficiency in the above case, the photovoltaic power connected to the area is taken as negative power to update the relevant power flow calculation. Step 2.3 also includes: taking the photovoltaic capacity connected to the area as negative power, and updating the load parameters corresponding to the photovoltaic access node k according to the following relationship:

[0180]

[0181] In the formula,

[0182] The subscripts i, j, and k are all node numbers in the power flow calculation model. When calculating the voltage fluctuation of the photovoltaic access node k, i represents the upstream node corresponding to the photovoltaic access node k, i = 1, 2, ..., k, and the node from the upstream node i to n is the downstream node j corresponding to the upstream node i, that is, j = i, i+1, ..., n,

[0183] R i , X i are the resistance and reactance of the distribution line between the photovoltaic access node k and the upstream node i, P L，j , Q L，j are the active power and reactive power of downstream node j respectively,

[0184] P BPV，j is the connected PV capacity of downstream node j;

[0185] When the area is not connected to photovoltaic power, P BPV，j is 0, and C1≤C2≤…≤C k ≤…≤C n .

[0186] Step 3, under the constraints of the distribution transformer capacity and the inequality constraints of the photovoltaic access capacity of the photovoltaic access node, calculate the first calculated value of the maximum photovoltaic capacity of the substation; under the inequality constraints of the photovoltaic access capacity of the photovoltaic access node, calculate the second calculated value of the maximum photovoltaic capacity of the substation; when the difference between the first calculated value and the second calculated value is greater than the set threshold, it is determined that the bottleneck of the substation power grid is the distribution transformer capacity; otherwise, it is determined that the bottleneck of the substation power grid is the distribution line route.

[0187] Specifically, in step 3, the capacity constraint of the distribution transformer is as follows:

[0188]

[0189] Where P is the capacity of the distribution transformer in the substation, P PV，j is the photovoltaic access capacity of downstream node j.

[0190] The threshold value is set to be no less than 5kW.

[0191] Under the inequality constraints of the photovoltaic access capacity of each photovoltaic access node, the maximum photovoltaic capacity of the substation is determined.

[0192] The purpose of the present invention is to obtain the maximum photovoltaic capacity of the substation under the condition that the node voltage fluctuation does not exceed the limit, that is, under the inequality constraint condition of the photovoltaic access capacity of each node, the sum of the photovoltaic access capacity of each node is maximized, as follows:

[0193] T=max(P PV，1 +P PV，2 +…+PPV，k +…+P PV，n ) (18)

[0194] Since the photovoltaic capacity of each photovoltaic access node cannot be less than 0, it is also necessary to constrain the lower limit of the photovoltaic access capacity value range of each photovoltaic access node, that is:

[0195]

[0196] In order to reasonably allocate the photovoltaic capacity of the substation area taking into account the number of residential houses at each node on the distribution line and to reduce the gap in photovoltaic access capacity between each node on the distribution line, a coupling relationship between the number of houses connected to the node and the line path distance between the node and the distribution center is established, and the amplification factor is determined according to the coupling relationship; the amplification factor and the unitized photovoltaic capacity are used to update the inequality constraints of the photovoltaic access capacity of each node, the inequality constraints of the updated photovoltaic access capacity of each node are solved, and the upper limit of the unitized photovoltaic capacity of each node is determined.

[0197] In the method of finding the maximum photovoltaic capacity of the substation, the bottleneck limiting factors are mainly: distribution line path and distribution capacity. The existing distribution capacity constraint condition is cancelled, and the objective function is maximized based on the node voltage constraint. In order to analyze the bottleneck factor, this constraint is cancelled and the maximum photovoltaic capacity of the substation is recalculated. Figure 7 As shown in the figure, by comparing the total amount of photovoltaic access before and after the two times, if there is a significant difference, and the difference in photovoltaic access is more than 5kW, then it is determined that the bottleneck factor is the distribution capacity of the substation; if there is no obvious difference, then it is determined that the bottleneck factor is the distribution line path of the substation.

[0198] Step 4: Taking the ratio of the number of houses connected to the photovoltaic access node and the distribution line path distance from the photovoltaic access node to the distribution transformer as the amplification factor, the photovoltaic access capacity of each photovoltaic access node in the inequality constraint of the photovoltaic access capacity of the photovoltaic access node is updated to the product of the amplification factor and the unitized photovoltaic capacity, and the updated inequality constraint is solved to determine the upper limit of the unitized photovoltaic capacity.

[0199] Specifically, in step 4, the amplification factor is as follows:

[0200] m′ k =m k / m (20)

[0201]

[0202] t k =m′ k / l′ k (twenty two)

[0203] In the formula,

[0204] m′ k is the normalized value of the number of houses connected to PV access node k,

[0205] m k is the number of houses connected to the photovoltaic access node k in the area,

[0206] m is the total number of houses in the area,

[0207] l′ k is the distribution line path distance from the photovoltaic access node k to the distribution transformer, which is the sum of the distribution line paths between the photovoltaic access node k and the corresponding upstream node. i = 1 is the root node, representing the distribution transformer.

[0208] t k is the amplification factor of the photovoltaic access node k.

[0209] Furthermore, the rules for establishing the amplification factor are specified according to the demand for photovoltaic access capacity. In the embodiment of the present invention, the amplification factor is determined by combining the number of houses connected to the node and the line path distance between the nodes. The following factors are mainly considered: First, the more houses the node is connected to, the larger the roof area of ​​the node is connected to and the more load it has. Therefore, the demand for photovoltaic access capacity to be developed is also greater. Obviously, the number of houses connected to the node is in direct proportion to the amplification factor. Second, considering that the farther the node is from the distribution transformer center, the greater the effect of raising the node voltage is when the photovoltaic access capacity is the same. Therefore, in order to make the entire substation access as much photovoltaic power as possible, it is necessary to suppress the photovoltaic access capacity of the node far from the distribution transformer to a certain extent, so that the line path distance of the node is inversely proportional to the amplification factor. According to the above analysis, with the maximum photovoltaic access capacity of any node as the goal, a coupling relationship between the number of houses connected to the node and the line path distance of the node from the distribution transformer center is established, and the amplification factor is determined according to the coupling relationship.

[0210] For photovoltaic access capacity, and the effect of greater photovoltaic capacity accessed at locations where the more houses there are and smaller voltage raising effects, explore the appropriate coupling relationship between these two quantities.

[0211] The photovoltaic access capacity of photovoltaic access node k is updated as follows:

[0212] P PV，k =t k P PV (twenty three)

[0213] Where P PV，k is the photovoltaic access capacity of photovoltaic access node k, P PV is the unitized photovoltaic capacity.

[0214] Using the magnification factor and the unitized photovoltaic capacity to construct Figure 6 The balanced upper and lower node photovoltaic capacity calculation model shown. Figure 5 , Figure 6 The photovoltaic access capacity of each photovoltaic access node is expressed as t1P according to formula (23): pv 、t2P pv 、t3P pv 、t4P pv The lengths of the distribution lines between the distribution transformer and each photovoltaic access node ①, ②, ③, and ④ are l1, l2, l3, and l4, respectively.

[0215] The inequality constraints of the photovoltaic access capacity of each node are updated using the magnification factor and the unitized photovoltaic capacity. In the updated inequality constraints of the photovoltaic access capacity of each node, in addition to the unitized photovoltaic capacity P PV is unknown, and other related parameters can be solved by calculation. In this way, n inequalities are derived according to the n nodes in the substation area, and n unitized photovoltaic capacities P are obtained. PV The upper limits are as follows:

[0216]

[0217] In the formula,

[0218] is the sum of the impedances of the distribution lines between the photovoltaic access node k and the corresponding upstream node,

[0219] C k is the load parameter corresponding to the photovoltaic access node k,

[0220] U N is the rated voltage of the distribution transformer,

[0221] k = 1, 2, ..., n, where n is the number of photovoltaic access nodes in the substation.

[0222] Take n units of photovoltaic capacity P PV The minimum value of the upper limit value is taken as the result to ensure that the voltage of each node meets the national power quality standard limit requirements. PV Then, the photovoltaic access capacity of each node can be obtained according to the amplification factor.

[0223] Step 5: Based on the power flow calculation model, the voltage of each photovoltaic access node is calculated according to the upper limit value of the unitized photovoltaic capacity, and the photovoltaic access node corresponding to the highest voltage value is used as the bottleneck node of the grid carrying capacity, and the photovoltaic access capacity of the bottleneck node is used as the grid carrying capacity analysis result.

[0224] In the embodiment of the present invention, bottleneck analysis is performed on the access of photovoltaic capacity in the substation area to analyze the factors that limit the improvement of photovoltaic capacity in the substation area. Specifically, it includes: allocating the photovoltaic access capacity of each node in proportion to the area of ​​the house connected to each node, forward calculating the voltage of each node based on the power flow calculation model, and the node corresponding to the highest voltage value is the bottleneck node of the substation area power grid carrying capacity. The voltage fluctuation calculation formula of formula (5) is used as the basis. Previously, when solving the photovoltaic access capacity P of node k, PV，k When P PV，k is an unknown quantity. We need to take equation (5) as a constraint and transform the formula into a linear programming method to solve it. This is to solve P inversely based on equation (5) as a constraint. PV，k Combined with the method of balancing the photovoltaic capacity of the upper and lower nodes, according to its calculation principle, there is a common unitized photovoltaic capacity P PV , so it is mainly because there is a certain node that limits the photovoltaic access of the entire substation. By combining the minimum value of the unitized photovoltaic capacity with the amplification factor of each node, the photovoltaic capacity accessed by each node can be obtained as a known access power, and the voltage of each node can be calculated. The present invention forward calculates the voltage value of each node based on the calculation results of the photovoltaic capacity of the upper and lower nodes. The node with the highest voltage is the bottleneck node that limits the photovoltaic access of the substation. The present invention analyzes the bottleneck factors and bottleneck nodes that limit the photovoltaic capacity of the substation, and realizes the analysis of the grid carrying capacity of photovoltaic development in rural substations.

[0225] The present invention also proposes a power grid carrying capacity analysis system for rural photovoltaic development, including: a power flow calculation model building module, a photovoltaic access capacity constraint module, and a grid bottleneck identification module.

[0226] PV maximum capacity calculation module, PV capacity upper limit calculation module, existing PV access update module, grid carrying capacity analysis module;

[0227] The power flow calculation model building module is used to establish the power flow calculation model of the photovoltaic power grid in the substation area by using the distribution transformer location, distribution line path, and distribution line parameters; the distribution line parameters include: the load corresponding to the photovoltaic access node, and the impedance of the distribution line between the photovoltaic access node and the corresponding upstream node;

[0228] The photovoltaic access capacity constraint module is used to establish an inequality constraint on the photovoltaic access capacity of the photovoltaic access node based on the power flow calculation model and through a linear programming method, using the sum of the impedances of the distribution lines between the photovoltaic access node and the corresponding upstream node and the constraint limit of the voltage fluctuation of the photovoltaic access node;

[0229] The grid bottleneck identification module of the substation is used to calculate the first calculated value of the maximum photovoltaic capacity of the substation under the inequality constraint of the distribution transformer capacity and the node photovoltaic access capacity; calculate the second calculated value of the maximum photovoltaic capacity of the substation under the inequality constraint of the node photovoltaic access capacity; when the difference between the first calculated value and the second calculated value is greater than the set threshold, it is determined that the bottleneck of the substation grid is the distribution transformer capacity; otherwise, it is determined that the bottleneck of the substation grid is the distribution line route;

[0230] The power grid carrying capacity analysis module is used to update the photovoltaic access capacity of each photovoltaic access node in the inequality constraint of the photovoltaic access capacity of the photovoltaic access node to the product of the amplification factor and the unitized photovoltaic capacity when it is determined that the bottleneck of the power grid in the substation area is the distribution line path. The module is used to solve the updated inequality constraint to determine the upper limit of the unitized photovoltaic capacity. Based on the power flow calculation model, the voltage of each photovoltaic access node is calculated according to the upper limit of the unitized photovoltaic capacity, and the photovoltaic access node corresponding to the highest voltage value is used as the bottleneck node of the power grid carrying capacity, and the photovoltaic access capacity of the bottleneck node is used as the power grid carrying capacity analysis result.

[0231] The system also includes: a photovoltaic access capacity constraint update model, which takes the photovoltaic capacity that has been connected in the substation as negative power, and updates the inequality constraint of the photovoltaic access capacity of the photovoltaic access node by updating the load parameters corresponding to the photovoltaic access node.

[0232] The present disclosure may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0233] Computer readable storage medium can be a tangible device that can hold and store instructions used by an instruction execution device. Computer readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination thereof. More specific examples (non-exhaustive lists) of computer readable storage medium include: portable computer disks, hard disks, random access memories (RAM), read-only memories (ROM), erasable programmable read-only memories (EPROM or flash memory), static random access memories (SRAM), portable compact disk read-only memories (CD-ROM), digital versatile disks (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or convex structures in grooves on which instructions are stored, and any suitable combination thereof. Computer readable storage medium used here is not interpreted as a transient signal itself, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagated by waveguides or other transmission media (e.g., light pulses by optical fiber cables), or electrical signals transmitted by wires.

[0234] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, optical fiber transmissions, wireless transmissions, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0235] The computer program instructions for performing the operation of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-related instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as "C" language or similar programming languages. Computer-readable program instructions may be executed completely on a user's computer, partially on a user's computer, as an independent software package, partially on a user's computer, partially on a remote computer, or completely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., using an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), may be personalized by utilizing the state information of the computer-readable program instructions, and the electronic circuit may execute the computer-readable program instructions, thereby realizing various aspects of the present disclosure.

[0236] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for analyzing the carrying capacity of a power grid for photovoltaic development in rural areas, characterized in that: include: Step 1: Establish a power flow calculation model for the photovoltaic power grid in the substation area using the distribution transformer location, distribution line path, and distribution line parameters; The distribution line parameters include: the load corresponding to the photovoltaic access node, the impedance of the distribution line between the photovoltaic access node and the corresponding upstream node; Step 2: Based on the power flow calculation model, through a linear programming method, using the sum of the impedances of the distribution lines between the photovoltaic access node and the corresponding upstream node and the constraint limit of the voltage fluctuation of the photovoltaic access node, an inequality constraint on the photovoltaic access capacity of the photovoltaic access node is established; Step 3, under the constraints of the capacity of the distribution transformer and the inequality constraints of the photovoltaic access capacity of the photovoltaic access node, calculate the first calculated value of the maximum photovoltaic capacity of the substation; under the inequality constraints of the photovoltaic access capacity of the photovoltaic access node, calculate the second calculated value of the maximum photovoltaic capacity of the substation; when the difference between the first calculated value and the second calculated value is greater than the set threshold, it is determined that the bottleneck of the substation power grid is the capacity of the distribution transformer; otherwise, it is determined that the bottleneck of the substation power grid is the path of the distribution line; Step 4: Taking the ratio of the number of houses connected to the photovoltaic access node and the distribution line path distance from the photovoltaic access node to the distribution transformer as the magnification factor, the photovoltaic access capacity of each photovoltaic access node in the inequality constraint of the photovoltaic access capacity of the photovoltaic access node is updated to the product of the magnification factor and the unitized photovoltaic capacity, and solving the updated inequality constraint to determine the upper limit value of the unitized photovoltaic capacity; Step 5: Based on the power flow calculation model, the voltage of each photovoltaic access node is calculated according to the upper limit value of the unitized photovoltaic capacity, and the photovoltaic access node corresponding to the highest voltage value is used as the bottleneck node of the grid carrying capacity, and the photovoltaic access capacity of the bottleneck node is used as the grid carrying capacity analysis result.

2. The grid carrying capacity analysis method for rural photovoltaic development according to claim 1 is characterized in that: Step 1 includes: Step 1.1, input the satellite remote sensing image of the substation area; extract the pixel coordinates of the house distribution, the pixel coordinates of the distribution transformer location and the distribution line path from the satellite remote sensing image by image processing method; Step 1.2, according to the positive correlation between house distribution and substation load distribution, the pixel coordinates of house distribution are mapped to the pixel coordinates of substation load distribution; Step 1.3, using the K-means clustering method to calculate the center point of the load distribution pixel coordinates, and taking the center point as the photovoltaic access node on the distribution line; Step 1.4, taking the pixel coordinates of the distribution transformer in the substation as the root node, image processing technology is used to determine the connectivity and geographical distance between the photovoltaic access node and the corresponding upstream node from the distribution line path; Step 1.5, obtaining distribution line parameters, including: active power and reactive power of the load corresponding to the photovoltaic access node, and impedance of the distribution line between the photovoltaic access node and the corresponding upstream node; Step 1.6, using the distribution transformer location, distribution line path, and distribution line parameters, establish a power flow calculation model for the photovoltaic power grid in the substation area.

3. The grid carrying capacity analysis method for rural photovoltaic development according to claim 2 is characterized in that: In step 1.5, the active power and reactive power of the load corresponding to the photovoltaic access node are as follows: In the formula, P L is the total load power of the substation, P L,k , Q L,k are respectively the active power and reactive power of the load corresponding to the photovoltaic access node k, m is the total number of houses in the area, m k is the number of houses connected to the photovoltaic access node k in the area, is the power factor of the area.

4. The grid carrying capacity analysis method for rural photovoltaic development according to claim 2 is characterized in that: In step 1.5, a topological method is used to calculate the connectivity matrix between the photovoltaic access node and the corresponding upstream node. The impedance of the distribution line between the photovoltaic access node and the corresponding upstream node is calculated using the connectivity matrix and the geographical distance according to the following relationship: R k =D k ×R d X k =D k ×X d In the formula, R k , X k are the resistance and reactance of photovoltaic access node k, D k is the geographical distance from PV access node k to its upstream node, R d , X d are the equivalent resistance and equivalent reactance of the distribution line per unit length, k = 1, 2, ..., n, where n is the number of photovoltaic access nodes in the substation.

5. The grid carrying capacity analysis method for rural photovoltaic development according to claim 1 is characterized in that: Step 2 includes: Step 2.1, calculating the voltage fluctuation of each photovoltaic access node according to the power flow calculation model; Step 2.2: The national power quality standard limit is +7%, and the national power quality standard limit is used as the constraint limit of the voltage fluctuation of each photovoltaic access node; Step 2.3, through the linear programming method, using the sum of the impedances of the distribution lines between each photovoltaic access node and the corresponding upstream node and the constraint limit of the voltage fluctuation of each photovoltaic access node, establish the inequality constraint of the photovoltaic access capacity of each photovoltaic access node.

6. The grid carrying capacity analysis method for rural photovoltaic development according to claim 5 is characterized in that: In step 2.3, the inequality constraints of the photovoltaic access capacity of each photovoltaic access node are as follows: In the formula, P PV,k is the photovoltaic access capacity of photovoltaic access node k, k=1,2,…,n, n is the number of photovoltaic access nodes in the area, is the sum of the impedances of the distribution lines between the photovoltaic access node k and the corresponding upstream node, C k is the load parameter corresponding to the photovoltaic access node k, U N is the rated voltage of the distribution transformer.

7. The grid carrying capacity analysis method for rural photovoltaic development according to claim 6 is characterized in that: Step 2.3 also includes: taking the connected photovoltaic capacity in the area as negative power, and updating the load parameter corresponding to the photovoltaic access node k according to the following relationship: In the formula, The subscripts i, j, and k are all node numbers in the power flow calculation model. When calculating the voltage fluctuation of the photovoltaic access node k, i represents the upstream node corresponding to the photovoltaic access node k, i = 1, 2, ..., k, and the node from the upstream node i to n is the downstream node j corresponding to the upstream node i, that is, j = i, i+1, ..., n. R i , X i are the resistance and reactance of the distribution line between the photovoltaic access node k and the upstream node i, P L,j , Q L,j are the active power and reactive power of downstream node j respectively, P BPV,j is the connected PV capacity of downstream node j; When the area is not connected to photovoltaic power, P BPV,j is 0, and C1≤C2≤…≤C k ≤…≤C n .

8. The grid carrying capacity analysis method for rural photovoltaic development according to claim 7 is characterized in that: In step 3, the distribution transformer capacity constraint is as follows: Where, P is the capacity of the distribution transformer in the substation, P PV,j is the photovoltaic access capacity of downstream node j.

9. The grid carrying capacity analysis method for rural photovoltaic development according to claim 8 is characterized in that: The maximum photovoltaic capacity of the station area is as follows: T=max(P PV,1 +P PV,2 +…+P PV,k +…+P PV,n ) In the formula, the photovoltaic access capacity of each photovoltaic access node is not less than 0.

10. The grid carrying capacity analysis method for rural photovoltaic development according to claim 1, characterized in that: The threshold value is set to be no less than 5kW.

11. The method for analyzing the grid carrying capacity for photovoltaic development in rural areas according to claim 1, characterized in that: In step 4, the amplification factor is as follows: m′ k =m k / m t k =m′ k / l′ k In the formula, m′ k is the normalized value of the number of houses connected to PV access node k, m k is the number of houses connected to the photovoltaic access node k in the area, m is the total number of houses in the area, l′ k is the distribution line path distance from the photovoltaic access node k to the distribution transformer, which is the sum of the distribution line paths between the photovoltaic access node k and the corresponding upstream node. i = 1 is the root node, representing the distribution transformer. t k is the amplification factor of the photovoltaic access node k.

12. The method for analyzing the grid carrying capacity for photovoltaic development in rural areas according to claim 11, characterized in that: The photovoltaic access capacity of photovoltaic access node k is updated as follows: P PV,k =t k P PV Where P PV,k is the photovoltaic access capacity of photovoltaic access node k, P PV is the unitized photovoltaic capacity.

13. The grid carrying capacity analysis method for rural photovoltaic development according to claim 12, characterized in that: Unitized photovoltaic capacity P PV The upper limits are as follows: In the formula, is the sum of the impedances of the distribution lines between the photovoltaic access node k and the corresponding upstream node, C k is the load parameter corresponding to the photovoltaic access node k, U N is the rated voltage of the distribution transformer, k = 1, 2, ..., n, where n is the number of photovoltaic access nodes in the substation.

14. A grid carrying capacity analysis system for photovoltaic development in rural areas, used to implement the method described in any one of claims 1 to 13, It is characterized in that Including: power flow calculation model building module, photovoltaic access capacity constraint module, grid bottleneck identification module, PV maximum capacity calculation module, PV capacity upper limit calculation module, existing PV access update module, grid carrying capacity analysis module; The power flow calculation model building module is used to establish the power flow calculation model of the photovoltaic power grid in the substation area by using the distribution transformer location, distribution line path, and distribution line parameters; the distribution line parameters include: the load corresponding to the photovoltaic access node, and the impedance of the distribution line between the photovoltaic access node and the corresponding upstream node; The photovoltaic access capacity constraint module is used to establish an inequality constraint on the photovoltaic access capacity of the photovoltaic access node based on the power flow calculation model and through a linear programming method, using the sum of the impedances of the distribution lines between the photovoltaic access node and the corresponding upstream node and the constraint limit of the voltage fluctuation of the photovoltaic access node; The grid bottleneck identification module of the substation is used to calculate the first calculated value of the maximum photovoltaic capacity of the substation under the inequality constraint of the distribution transformer capacity and the node photovoltaic access capacity; calculate the second calculated value of the maximum photovoltaic capacity of the substation under the inequality constraint of the node photovoltaic access capacity; when the difference between the first calculated value and the second calculated value is greater than the set threshold, it is determined that the bottleneck of the substation grid is the distribution transformer capacity; otherwise, it is determined that the bottleneck of the substation grid is the distribution line route; The power grid carrying capacity analysis module is used to update the photovoltaic access capacity of each photovoltaic access node in the inequality constraint of the photovoltaic access capacity of the photovoltaic access node to the product of the amplification factor and the unitized photovoltaic capacity when it is determined that the bottleneck of the power grid in the substation area is the distribution line path. The module is used to solve the updated inequality constraint to determine the upper limit of the unitized photovoltaic capacity. Based on the power flow calculation model, the voltage of each photovoltaic access node is calculated according to the upper limit of the unitized photovoltaic capacity, and the photovoltaic access node corresponding to the highest voltage value is used as the bottleneck node of the power grid carrying capacity, and the photovoltaic access capacity of the bottleneck node is used as the power grid carrying capacity analysis result.

15. The grid carrying capacity analysis system for rural photovoltaic development according to claim 14, characterized in that: The system also includes: a photovoltaic access capacity constraint update model, which takes the photovoltaic capacity that has been connected in the substation as negative power, and updates the inequality constraint of the photovoltaic access capacity of the photovoltaic access node by updating the load parameters corresponding to the photovoltaic access node.

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