A method for limiting the capacity of distributed power sources based on the original protection setting values of the distribution network

Abstract

An embodiment of the present invention provides a method for limiting the capacity of distributed power sources based on the original protection settings of a distribution network, belonging to the field of distribution networks. The method includes: obtaining distributed power sources; partitioning the distributed power sources to obtain the distributed power sources in each area; obtaining the access positions of equivalent distributed power sources according to the access positions of the distributed power sources in each area; obtaining the protection settings in the case of no distributed current access, and obtaining the protection range under the current protection settings according to the access positions; establishing a current protection constraint boundary; obtaining the maximum current of the distributed power sources according to the current protection constraint boundary; obtaining a first maximum capacity in the same direction as the system power source current and a second maximum capacity in the opposite direction to the system power source current of the distributed power sources according to the maximum current of the distributed power sources; obtaining a first maximum accessible capacity and a second maximum accessible capacity; and obtaining the maximum accessible capacity according to the first maximum accessible capacity and the second maximum accessible capacity.

Description

Technical Field

[0001] The present invention relates to the field of distribution networks, and particularly to a method for limiting the capacity of distributed power sources based on the original protection settings of the distribution network. Background Art

[0002] With the gradual deepening of the construction of the new power system, a large number of new energy sources are connected to the low-voltage distribution network. The access of distributed power sources in the distribution network shows the characteristics of multi-point, decentralized and intensive, which brings challenges to the traditional distribution network protection.

[0003] For protection, the current protection configured in the traditional distribution network detects the current level after a fault and quickly operates to cut off the fault. After the access of distributed power sources, the amplitude and direction of the fault current change, resulting in the risk of misoperation and refusal to operate of the original protection. In addition, the current output by the distributed power source after a fault is subject to multi-condition non-linear constraints such as the current-carrying capacity of power electronic devices and the low-voltage ride-through control strategy, which all pose severe challenges to the traditional stage current protection. Summary of the Invention

[0004] The purpose of the embodiments of the present invention is to provide a method for limiting the capacity of distributed power sources based on the original protection settings of the distribution network, which solves the problem that when the amplitude and direction of the fault current change, the original protection may misoperate and refuse to operate.

[0005] To achieve the above purpose, the embodiments of the present invention provide a method for limiting the capacity of distributed power sources based on the original protection settings of the distribution network, and the method includes:

[0006] Obtain the existing distributed power sources connected in the distribution network;

[0007] Partition the distributed power sources to obtain the distributed power sources in each area;

[0008] According to the access positions of the distributed power sources in each area, obtain the access positions of the equivalent distributed power sources;

[0009] According to the access positions, obtain the protection range under the current protection settings and the protection settings without distributed current access;

[0010] Establish a current protection constraint boundary according to the protection settings;

[0011] Obtain the maximum current of the distributed power sources according to the current protection constraint boundary;

[0012] According to the maximum current of the distributed power sources, obtain the first maximum capacity in the same direction as the system power source current and the second maximum capacity in the opposite direction to the system power source current of the distributed power sources;

[0013] Obtain the first maximum accessible capacity according to the first maximum capacity and the second maximum capacity, and obtain the second maximum accessible capacity under the condition of minimum voltage deviation;

[0014] Obtain the maximum accessible capacity of the distributed power sources in the whole area according to the first maximum accessible capacity and the second maximum accessible capacity.

[0015] Optionally, partitioning the distributed power sources to obtain the distributed power sources in each area includes: dividing the distributed power sources into a boosting area, a drawing area, and an adjacent feeder area.

[0016] Optionally, obtaining the access positions of the equivalent distributed power sources according to the access positions of the distributed power sources in each area includes:

[0017] Obtain the distances between the connection points of the equivalent distributed power sources and the power source points in the adjacent feeder area, the boosting area, and the drawing area according to formulas (1) to (3),

[0018] , (1)

[0019] , (2)

[0020] , (3)

[0021] Wherein, is the distance between the connection point of the equivalent distributed power source in the adjacent feeder area and the power source point, is the distance between the connection point of the equivalent distributed power source in the boosting area and the power source point, is the distance between the connection point of the equivalent distributed power source in the drawing area and the power source point, is the current capacity of the th distributed power source currently, is the th distance between the distributed generation device and the power source node, is the protection code, is the integer code, represents the adjacent feeder area, is the drawing area, represents the distributed generation device.

[0022] Optionally, obtaining the protection range under the current protection setting value and the protection setting value without distributed current access according to the access position includes:

[0023] Calculate the protection setting value without distributed current access according to formula (4),

[0024] , (4)

[0025] Among them, , , are the reliability coefficients of the first, second, and third stages of the three-stage current protection respectively, is the transformer impedance, is the system rated voltage, is the system nominal voltage coefficient, , , are the lengths between the first switch and the second switch, the second switch and the third switch, and the third switch and the line end respectively, and are the self-starting and return coefficients respectively, is the maximum load current, , , are the protection settings of the first, second, and third stages of the three-stage current protection of the second switch respectively, is the line impedance per unit length;

[0026] Calculate the protection range under the current protection setting according to formula (5),

[0027] , (5)

[0028] Among them, and are the current protection ranges of the first and second stages of the second switch.

[0029] Optionally, establishing the current protection constraint boundary according to the protection setting includes:

[0030] Obtain the correlation between the currents flowing through the protection after the distribution network fails, and determine the correlation according to formula (6),

[0031] , (6)

[0032] Among them, is the correlation, is the current provided by all distributed power sources, is the current provided by the system power source;

[0033] Determine the first value range of the correlation according to the protection range of the first stage, determine the second value range of the correlation according to the protection range of the second stage, determine the first value range according to formula (7), and determine the second value range according to formula (8),

[0034] , (7)

[0035] , (8)

[0036] Determine the value range of the final correlation according to the first value range and the second value range, and determine the value range of the final correlation according to formulas (9) and (10).

[0037] , (9)

[0038] , (10)

[0039] Among them, the value range of the final correlation is .

[0040] Optionally, obtaining the maximum current of the distributed power source according to the current protection constraint boundary includes:

[0041] Judge whether the currents provided by all the distributed power sources are in the same direction as the current provided by the system power source;

[0042] When it is judged that the currents provided by all the distributed power sources are in the same direction as the current provided by the system power source, obtain the first maximum current;

[0043] When it is judged that the currents provided by all the distributed power sources are in the opposite direction to the current provided by the system power source, obtain the second maximum current;

[0044] Determine the first maximum current according to formula (11), and determine the second maximum current according to formula (12).

[0045] , (11)

[0046] , (12)

[0047] Among them, is the first maximum current, is the second maximum current, is to obtain when the fault occurs at the proportion of the position, is to obtain when the fault occurs at the proportion of the position.

[0048] Optionally, obtaining the first maximum accessible capacity according to the first maximum capacity and the second maximum capacity, and obtaining the second maximum accessible capacity under the condition of the minimum voltage deviation includes:

[0049] Judge whether the currents provided by all the distributed power sources are in the same direction as the current provided by the system power source;

[0050] When it is determined that the currents provided by all the distributed power sources are in the same direction as the current provided by the system power source, a first mathematical model is established to obtain the first maximum capacity;

[0051] When it is determined that the currents provided by all the distributed power sources are in the opposite direction to the current provided by the system power source, a second mathematical model is established to obtain the second maximum capacity;

[0052] The final first maximum accessible capacity is obtained according to the first maximum capacity and the second maximum capacity.

[0053] Optionally, obtaining the first maximum accessible capacity according to the first maximum capacity and the second maximum capacity, and obtaining the second maximum accessible capacity under the condition of minimum voltage deviation further includes:

[0054] A first mathematical model is established according to formula (13) to obtain the first maximum capacity,

[0055] , (13)

[0056] wherein, 、 、 are respectively the total capacities of the distributed generation devices in the boosting area, the adjacent feeder area, and the drawing area of the second switch, 、 、 are respectively the total rated currents of the distributed power sources in the boosting area, the adjacent feeder area, and the drawing area, 、 、 are respectively the maximum overcurrent coefficients of the boosting area, the adjacent feeder area, and the drawing area, 、 are respectively the normal loads of the feeders and ;

[0057] A second mathematical model is established according to formula (14) to obtain the second maximum capacity,

[0058] , (14).

[0059] Optionally, obtaining the first maximum accessible capacity according to the first maximum capacity and the second maximum capacity, and obtaining the second maximum accessible capacity under the condition of minimum voltage deviation further includes:

[0060] Obtain the area to be measured and establish a third mathematical model;

[0061] Obtain the minimum value of the voltage deviation according to the third mathematical model;

[0062] Obtain the second maximum accessible capacity of each grid connection point in the area to be measured according to the minimum value of the voltage deviation;

[0063] Obtain the area to be measured according to formula (15) and establish a third mathematical model,

[0064] , (15)

[0065] wherein, and are respectively the active power and reactive power generated by the power source connected to node , and are respectively the active power and reactive power absorbed by the load connected to node , and are respectively the voltages of node and node , and are respectively the conductance and susceptance of branch , is the voltage phase angle difference between node and node , is the maximum line current, is the voltage deviation coefficient.

[0066] Optionally, obtaining the maximum accessible capacity of the distributed power sources in the entire area according to the first maximum accessible capacity and the second maximum accessible capacity includes:

[0067] Obtain the maximum accessible capacity according to formula (16),

[0068] , (16)

[0069] wherein, is an integer code, is the maximum accessible capacity of each grid connection point in each protection switch .

[0070] Through the above technical solutions, on the premise of ensuring the safe and stable operation of the distribution network, under the complex fault current distribution characteristics of multi-point dense access of distributed power sources, without changing the existing protection setting values and ensuring that the protection range meets the requirements of relay protection rules, the maximum accessible capacity of the existing distributed power source connection points is obtained. Considering the multi-point dispersed and dense access of distributed power sources, the present invention proposes a zoning principle for distributed power sources based on the consistent influence of protection currents, and obtains the access positions of equivalent distributed power sources for the distinguished distributed power sources. After performing equivalent operations on the distributed power sources, considering that the protection setting values remain unchanged and the operation safety of the distribution network is optimal, the maximum accessible capacity of each connection point is obtained. Compared with the existing accessible capacity calculation method, in the present invention, zoning and unified calculation are performed according to the influence of distributed power sources on protection currents, greatly reducing the complexity of solving caused by dispersed and dense distributed power sources in the distribution network, and ensuring the effectiveness and reliability of the original protection setting values under the access capacity limit. The present invention also transforms the multi-objective optimization problem into two single-objective optimizations, namely, the first maximum accessible capacity and the second maximum accessible capacity, to accelerate the calculation speed; and considering the safest distributed power source access capacity on the premise that the protection setting values remain unchanged, it provides decision support for the accessible capacity of distributed power sources.

[0071] Other features and advantages of the embodiments of the present invention will be described in detail in the subsequent specific implementation part. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] The drawings are used to provide a further understanding of the embodiments of the present invention, and constitute a part of the specification. Together with the following specific implementation, they are used to explain the embodiments of the present invention, but do not constitute a limitation to the embodiments of the present invention. In the drawings:

[0073] Figure 1 is a flowchart of a method for limiting the capacity of distributed power sources based on the original protection setting values of a distribution network according to an embodiment of the present invention;

[0074] Figure 2 is a flowchart of establishing a current protection constraint boundary according to protection setting values in a method for limiting the capacity of distributed power sources based on the original protection setting values of a distribution network according to an embodiment of the present invention;

[0075] Figure 3 is a flowchart of obtaining the first maximum accessible capacity in a method for limiting the capacity of distributed power sources based on the original protection setting values of a distribution network according to an embodiment of the present invention;

[0076] Figure 4 is a flowchart of obtaining the second maximum accessible capacity in a method for limiting the capacity of distributed power sources based on the original protection setting values of a distribution network according to an embodiment of the present invention;

[0077] Figure 5 Schematic diagrams before and after the merger of distributed power supply zones of the second switch in a specific embodiment of a method for limiting the capacity of distributed power sources based on the original protection settings of a distribution network according to an embodiment of the present invention;

[0078] Figure 6 Distribution line model in a specific embodiment of a method for limiting the capacity of distributed power sources based on the original protection settings of a distribution network according to an embodiment of the present invention;

[0079] Figure 7 Schematic diagram of the calculation results of the original access capacity and the maximum access capacity in a specific embodiment of a method for limiting the capacity of distributed power sources based on the original protection settings of a distribution network according to an embodiment of the present invention;

[0080] Figure 8 Fault current curve flowing through the second switch under the maximum access capacity and fault current curve diagram of 1.5 times the capacity of DG5 in a specific embodiment of a method for limiting the capacity of distributed power sources based on the original protection settings of a distribution network according to an embodiment of the present invention. Specific embodiments

[0081] The following will describe in detail the specific embodiments of the embodiments of the present invention with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for the purpose of illustrating and explaining the embodiments of the present invention, and are not used to limit the embodiments of the present invention.

[0082] In the embodiments of the present application, certain industry-existing solutions such as software, components, models, etc. may be mentioned. They should be regarded as exemplary, and their purpose is only to illustrate the feasibility in the implementation of the technical solutions of the present application, but it does not mean that the applicant has already or necessarily used this solution.

[0083] As Figure 1 shown, Figure 1 is a flowchart of a method for limiting the capacity of distributed power sources based on the original protection settings of a distribution network according to an embodiment of the present invention. In this Figure 1 method, the method includes the following steps:

[0084] In step S01, the existing distributed power sources connected to the distribution network are obtained.

[0085] In step S02, the distributed power sources are partitioned to obtain the distributed power sources in each region.

[0086] In step S03, according to the access positions of the distributed power sources in each region, the access positions of the equivalent distributed power sources are obtained.

[0087] In step S04, obtain the protection setting values in the case of no distributed current access, and obtain the protection range under the current protection setting values according to the access location.

[0088] In step S05, establish the current protection constraint boundary according to the protection setting values.

[0089] In step S06, obtain the maximum current of the distributed power source according to the current protection constraint boundary.

[0090] In step S07, obtain the first maximum capacity in the same direction as the system power source current and the second maximum capacity in the opposite direction to the system power source current of the distributed power source according to the maximum current of the distributed power source.

[0091] In step S08, obtain the first maximum accessible capacity according to the first maximum capacity and the second maximum capacity, and obtain the second maximum accessible capacity under the condition of the minimum voltage deviation.

[0092] In step S09, obtain the maximum accessible capacity of the distributed power sources in the whole region according to the first maximum accessible capacity and the second maximum accessible capacity.

[0093] In this embodiment, first, the existing distributed power sources connected to the distribution network are obtained; then the distributed power sources are partitioned to obtain the distributed power sources in each area; second, according to the connection positions of the distributed power sources in each area, the connection positions of the equivalent distributed power sources are obtained; then the protection setting values are obtained under the condition of no distributed current connection, and the protection range under the current protection setting values is obtained according to the connection positions; then, the current protection constraint boundary is established according to the protection setting values; then the maximum current of the distributed power source is obtained according to the current protection constraint boundary; the first maximum capacity in the same direction as the system power source current and the second maximum capacity in the opposite direction to the system power source current of the distributed power source are obtained according to the maximum current of the distributed power source; then the first maximum accessible capacity is obtained according to the first maximum capacity and the second maximum capacity, and the second maximum accessible capacity is obtained under the condition of the minimum voltage deviation; finally, the maximum accessible capacity of the distributed power sources in the whole area is obtained according to the first maximum accessible capacity and the second maximum accessible capacity. On the premise of ensuring the safe and stable operation of the distribution network, under the complex fault current distribution characteristics of the multi-point dense connection of distributed power sources, without changing the existing protection setting values and ensuring that the protection range meets the requirements of the relay protection rules, the maximum accessible capacity of the existing distributed power source connection points is obtained. Considering the multi-point dispersed and dense connection of distributed power sources, the present invention proposes a partitioning principle of distributed power sources based on the consistent influence on protection current, and obtains the connection positions of equivalent distributed power sources for the partitioned distributed power sources. After performing the equivalent operation on the distributed power sources, considering that the protection setting values remain unchanged and the operation safety of the distribution network is optimal, the maximum accessible capacity of each connection point is obtained. Compared with the existing accessible capacity calculation method, in the present invention, partitioning and unified calculation are performed according to the influence of distributed power sources on protection current, which greatly reduces the complexity of solving caused by the dispersed and dense distributed power sources in the distribution network, and can ensure the effectiveness and reliability of the original protection setting values under the access capacity limit.

[0094] In this embodiment, partitioning the distributed power sources to obtain the distributed power sources in each area includes: dividing the distributed power sources into a boosting area bz, a drawing area dz, and an adjacent feeder area af. In an embodiment of the present invention, for a certain protection, the other feeders except the feeder where the protection is located are used as the adjacent feeder area af, the area from the power source to the upstream of the protection is the boosting area bz, and the protection range of this section of the line is the drawing area dz.

[0095] In this embodiment, all distributed power sources within each area are considered as an equivalent distributed power source. For the access location of the equivalent distributed power source obtained according to the access location of the distributed power sources in each area, there are various methods known to those skilled in the art. In an embodiment of the present invention, the access location of the equivalent distributed power source is calculated by weighted average power of line impedance, and the distances between the connection points of the equivalent distributed power sources and the power points in the adjacent feeder area af, boosting area bz, and drawing area dz are obtained according to formulas (1) to (3).

[0096] , (1)

[0097] , (2)

[0098] , (3)

[0099] wherein, is the distance between the connection point of the equivalent distributed power source and the power point in the adjacent feeder area af, is the distance between the connection point of the equivalent distributed power source and the power point in the boosting area bf, is the distance between the connection point of the equivalent distributed power source and the power point in the drawing area df, is the current th capacity of the distributed power source, is the distance between the th distributed generation device and the power node, is the protection code, is the integer code, represents the adjacent feeder area, represents the boosting area, represents the drawing area, represents the distributed generation device.

[0100] In this embodiment, for obtaining the protection setting value in the case of no distributed current access and the protection range under the current protection setting value according to the access location, there are various methods known to those skilled in the art. In an embodiment of the present invention, taking the protection of the second switch R2 as a specific example, that is When it is 2, the protection range under the current protection setting value and the protection setting value in the case of no distributed current access are obtained according to the access location. The protection setting value in the case of no distributed current access is calculated according to formula (4), and the protection range under the current protection setting value is calculated according to formula (5), that is, the protection range when the current flowing through the protection is equal to the setting value in the case of a fault at a certain place.

[0101] , (4)

[0102] Among them, , , are respectively the first, second, and third reliability coefficients of the three-stage current protection for protecting the second switch R2. is the transformer impedance, is the system rated voltage, is the system nominal voltage coefficient, , , are respectively the lengths between the first switch and the second switch, the second switch and the third switch, and the third switch and the line end. and are respectively the self-starting and return coefficients. is the maximum load current. , , are respectively the protection setting values of the first, second, and third stages of the three-stage current protection of the second switch. is the line impedance per unit length;

[0103] , (5)

[0104] Among them, and are the current protection ranges of the first and second stages of the second switch R2.

[0105] In this embodiment, for the method of establishing the current protection constraint boundary according to the protection setting value, there can be various methods known to those skilled in the art. In one embodiment of the present invention, as Figure 2 and Figure 5 shown, taking the first and second stage current protections of the second switch R2 to establish constraint conditions, establishing the current protection constraint boundary according to the protection setting value includes the following steps:

[0106] In step S051, obtain the correlation between the currents flowing through the protection after the distribution network fails. After the distribution network fails, the currents flowing through the protection can be divided into two parts. The first part is the current provided by the system power supply , and the second part is provided by all distributed power sources . Determine the correlation according to formula (6),

[0107] , (6)

[0108] Among them, is the correlation, is the current provided by all distributed power sources, is the current provided by the system power supply.

[0109] In step S052, a first value range of the correlation is determined according to the protection range of the first section, and a second value range of the correlation is determined according to the protection range of the second section.

[0110] The protection range of the first section must be within 15% - 80%. The first value range is determined according to this protection range boundary and formula (7). If it is necessary to cooperate with the branch protection at the lower - level y, the protection range is changed to 15% - y% and then brought into formula (7).

[0111] For the second - section protection, its protection range covers the entire line length but cannot exceed the protection range of the first section of the next - level. In an embodiment of the present invention, the protection range of the second section is 100% - 115%. The second value range is determined according to this protection range boundary and formula (8). 。

[0112] ,(7)

[0113] ,(8)

[0114] In step S053, the value range of the final correlation is determined according to the first value range and the second value range. For the method of determining the value range of the final correlation from the first value range and the second value range, there are various methods known to those skilled in the art. In an embodiment of the present invention, in order to meet the constraint conditions of the first - section and second - section current protections, the value range of the final correlation is determined according to formulas (9) and (10). ,

[0115] ,(9)

[0116] ,(10)。

[0117] In this embodiment, for the method of obtaining the maximum current of the distributed power source according to the current - protection constraint boundary, there are various methods known to those skilled in the art. In an embodiment of the present invention, as Figure 3 shown, the specific steps of obtaining the maximum current of the distributed power source according to the current - protection constraint boundary are as follows:

[0118] In step S061, it is judged whether the currents provided by all distributed power sources are in the same direction as the current provided by the system power source.

[0119] In step S062, when it is judged that the currents provided by all distributed power sources are in the same direction as the current provided by the system power source, the first maximum current is obtained. The first maximum current is determined according to formula (11).

[0120] , (11)

[0121] In step S063, when it is determined that the currents provided by all distributed power sources are in the opposite direction to the current provided by the system power source, the second maximum current is obtained. The second maximum current is determined according to formula (12).

[0122] , (12)

[0123] Wherein, is the first maximum current, is the second maximum current, is for obtaining when the fault occurs at the position ratio, is for obtaining when the fault occurs at the position ratio. The maximum current affected by the distributed power source is obtained according to the current protection constraints in the first and second paragraphs. When all the currents provided by the distributed power sources are in the same direction as the current provided by the system power source and the current provided by the system power source , according to the inflow of the value of , the second switch is supplied with the first maximum current by the distributed power source; when all the currents provided by the distributed power sources are in the opposite direction to the current provided by the system power source , the maximum directional current flowing into the second switch is the second maximum current.

[0124] In this embodiment, when the maximum value of the given maximum current amplitude flowing to the second switch is the largest, when calculating the maximum output currents of the adjacent feeder area af, the boosting area bz, and the drawing area dz, considering that it is impossible to determine whether the maximum output of the distributed power source appears when all the currents provided by the distributed power sources are in the same direction or in the opposite direction to the current provided by the system power source , therefore, according to the maximum current of the distributed power source, the first maximum capacity in the same direction as the system power source current and the second maximum capacity in the opposite direction to the system power source current of the distributed power source are obtained. The first maximum capacity and the second maximum capacity are the maximum access capacities of the distributed power sources in the region calculated on the premise that the protection setting values remain unchanged, and the first maximum capacity and the second maximum capacity comprehensively consider the influence of each partition on the protection current after the fault, and are the results calculated with the coordination of the protection ranges of the upper and lower levels as the constraint conditions.

[0125] As Figure 3 shown, the specific steps for obtaining the first maximum access capacity according to the first maximum capacity and the second maximum capacity are as follows:

[0126] In step S061, it is determined whether the currents provided by all distributed power sources are in the same direction as the current provided by the system power source.

[0127] In step S072, when it is determined that the currents provided by all distributed power sources are in the same direction as the current provided by the system power source, a first mathematical model is established based on the first maximum current to obtain the first maximum capacity.

[0128] A first mathematical model is established according to formula (13) to obtain the first maximum capacity.

[0129] , (13)

[0130] Wherein, 、 、 are respectively the total capacities of the distributed generation devices in the boosting area, adjacent feeder area, and drawing area of the second switch. 、 、 are respectively the total rated currents of the distributed power sources in the boosting area, adjacent feeder area, and drawing area. 、 、 are respectively the maximum overcurrent coefficients of the boosting area, adjacent feeder area, and drawing area. 、 are respectively the and normal loads of the feeder. is the capacity of the upper-level transformer. In formula (10), the first constraint is the protection range constraint, the second constraint is the power-current relationship constraint, the third and fourth constraints are that the total current of the distributed power sources on each feeder is less than the third-segment setting value, the fourth and fifth constraints are that the output current of the distributed power source does not exceed 1.5 times the feeding load, and the last constraint is that the total capacity of the distributed power sources is less than the capacity of the upper-level transformer.

[0131] In step S073, when it is determined that the currents provided by all distributed power sources are in the opposite direction to the current provided by the system power source, a second mathematical model is established based on the second maximum current to obtain the second maximum capacity.

[0132] A second mathematical model is established according to formula (14) to obtain the second maximum capacity.

[0133] , (14). That is, on the left side of the equal sign of the first constraint in formula (13) is replaced with , and another optimal solution can be obtained.

[0134] In step S074, obtain the first maximum accessible capacity according to the first maximum capacity and the second maximum capacity. Compare the magnitudes of the optimal solutions obtained from formula (13) and formula (14), and obtain the larger one the total capacity of the distributed generation devices in the boosting area, adjacent feeder area, and drawing area of the corresponding second switch below, that is 、 、 values of

[0135] In this embodiment, for how to obtain the second maximum accessible capacity under the condition of minimum voltage deviation, there can be various methods known to those skilled in the art. In an embodiment of the present invention, the second maximum accessible capacity is constructed with the maximum accessible distributed power capacity in the area and the best safe operation of the distribution network as constraints, and the maximum capacity of the single-point accessible distributed power source is constructed. Under the condition of ensuring that the limit of the maximum distributed power access capacity in the area is not exceeded, the second maximum accessible capacity of the distributed power connection point is solved. The specific steps to obtain the second maximum accessible capacity under the condition of minimum voltage deviation are as follows:

[0136] In step S075, obtain the area to be measured and establish a third mathematical model.

[0137] Obtain the area to be measured and establish a third mathematical model according to formula (15),

[0138] , (15)

[0139] where and are the active power and reactive power generated by the power source connected to node respectively, and are the active power and reactive power absorbed by the load connected to node respectively, and are the voltages of node and node respectively, and are the conductance and susceptance of branch respectively, is the voltage phase angle difference between node and node , is the maximum line current, is the voltage deviation coefficient. is related to the current-carrying capacity of the current conductor, is related to the grid voltage level.

[0140] In step S076, the minimum voltage deviation is obtained according to the third mathematical model. The voltage deviation of a three-phase power grid with a voltage of 20 kV or less shall not exceed 7% of the rated voltage. The objective function represents the minimum of the sum of voltage deviations of all nodes.

[0141] In step S077, the second maximum accessible capacity of each grid connection point in the area to be measured is obtained according to the minimum voltage deviation. As can be seen from formula (15), the first constraint is the capacity constraint of the regional distributed power source, the second constraint is the power conservation condition; the third constraint is the voltage deviation constraint, that is, the single-point voltage shall not exceed the safety requirements of the power grid; the fourth is the current-carrying capacity constraint, which shall not exceed the maximum current limit of the installed wire.

[0142] Under the condition of ensuring the safe operation of the system, the distributed power source capacity allocation is completed, and the node voltage deviation caused by the access of the distributed power source is minimized. For a certain area x (x = bz2, af2, dz2), a third mathematical model is established to obtain the second maximum accessible capacity of each grid connection point under the minimum voltage deviation and the given protection setting value.

[0143] In this embodiment, for the method of obtaining the maximum accessible capacity of the distributed power source in the whole area according to the first maximum accessible capacity and the second maximum accessible capacity, there are various methods known to those skilled in the art. In an embodiment of the present invention, the above operations are repeated to traverse all protections, and for each switch, the maximum accessible capacity of each grid connection point can be obtained according to the first maximum accessible capacity and the second maximum accessible capacity of each grid connection point. The minimum maximum accessible capacity is the final single-point maximum accessible capacity, and the maximum accessible capacity is obtained according to formula (16).

[0144] , (16)

[0145] Among them, is integer coding, is the maximum accessible capacity.

[0146] Specifically, in an embodiment of the present invention, in order to verify the distributed power source limit capacity method based on the original protection setting value of the distribution network, such as Figure 6As shown in the figure, a distribution line model was built using Matleb / simulink to divide the influence area on the first switch in the protection diagram. For protecting the first switch, distributed power sources were partitioned. Among them, DG5 belongs to the adjacent feeder area, and DG1 and DG4 belong to the extraction area. The access positions of the equivalent distributed power sources in these areas were calculated. Based on the access positions, the protection range under the current protection setting value and the protection setting value without distributed current access were obtained. And according to the protection setting value, the current protection constraint boundary was established to obtain the maximum current of the distributed power source, and the first maximum access capacity of the equivalent distributed power source in each area was solved. Then, with the goal of minimizing the voltage deviation at the grid connection point during normal operation, the second maximum access capacity of each distributed power source in the area was solved. The fault current curves flowing through the second switch under the maximum access capacity and the fault current curve of 1.5 times the capacity of DG5 are as Figure 8 shown. As Figure 7 and Figure 8 shown, after the capacity increased, the protection range of the first section under the original setting value increased from 60% to nearly 100%. In engineering, the protection range of the first section setting value should be between 15% and 80%. An overly large protection range is not conducive to the coordination of downstream protection and branch protection and is extremely likely to lose selectivity. This test result also proves the correctness of the maximum capacity calculation result.

[0147] Through the above technical solution, on the premise of ensuring the safe and stable operation of the distribution network, under the complex fault current distribution characteristics of multi-point dense access of distributed power sources, without changing the existing protection setting value and ensuring that the protection range meets the requirements of the relay protection rules, the maximum accessible capacity of the existing distributed power source grid connection points is obtained. Considering the multi-point dispersed and dense access situations of distributed power sources, the present invention proposes a partitioning principle for distributed power sources based on the consistent influence of protection current, and obtains the access positions of the equivalent distributed power sources for the distinguished distributed power sources. After performing equivalent operations on the distributed power sources, considering that the protection setting value remains unchanged and the operation safety of the distribution network is optimal, the maximum accessible capacity of each grid connection point is obtained. Compared with the existing accessible capacity calculation method, in the present invention, partitioning and unified calculation are performed according to the influence of distributed power sources on protection current, which greatly reduces the complexity of solving caused by distributed and dense distributed power sources in the distribution network, and can ensure the effectiveness and reliability of the original protection setting value under the access capacity limit. The present invention also transforms the multi-objective optimization problem into two single-objective optimizations, that is, it is divided into the first maximum accessible capacity and the second maximum accessible capacity, which speeds up the calculation speed; and considering the safest distributed power source access capacity on the premise that the protection setting value remains unchanged, it provides decision support for the accessible capacity of the distributed power source.

[0148] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0149] The present application is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram, as well as the combination of flows and / or blocks in the flowchart and / or block diagram, can be realized by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0150] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer-readable memory generate a manufactured article including instruction means, and the instruction means implements the functions specified in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0151] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in Figure 1 one flow or multiple flows and / or blocks Figure 1 one block or multiple blocks.

[0152] In a typical configuration, a computing device includes one or more processors (CPUs), an input / output interface, a network interface, and a memory.

[0153] The memory may include non-permanent memory in a computer-readable medium, in the form of random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash memory (flash RAM). The memory is an example of a computer-readable medium.

[0154] Computer readable media include permanent and non-permanent, removable and non-removable media that can be implemented by any method or technology to store information. Information can be computer readable instructions, data structures, program modules or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disk read-only memory (CD-ROM), digital versatile disk (DVD) or other optical storage, magnetic cassettes, magnetic tape disk storage or other magnetic storage devices or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined herein, computer readable media does not include temporary computer readable media (transitory media), such as modulated data signals and carrier waves.

[0155] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0156] The above are only embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included within the scope of the claims of the present application.

Claims

1. A method for limiting the capacity of distributed power sources based on the original protection setting of the distribution network, characterized in that: The method comprises: Obtain the existing distributed power sources connected to the distribution network; Partitioning the distributed power source to obtain a distributed power source in each area; According to the access position of the distributed power source in each area, obtaining the access position of the equivalent distributed power source; Obtaining a protection setting value without distributed current access, and obtaining a protection range under the current protection setting value according to the access position; Establishing a current protection constraint boundary according to the protection setting value and the protection range; Acquire the maximum current of the distributed power source according to the current protection constraint boundary, where the maximum current of the distributed power source includes a first maximum current in the same direction and a second maximum current in the opposite direction; Acquire a corresponding first maximum capacity according to the first maximum current, and acquire a corresponding second maximum capacity according to the second maximum current; Acquire a first maximum accessible capacity according to the first maximum capacity and the second maximum capacity, and acquire a second maximum accessible capacity when the voltage deviation is minimal; The maximum accessible capacity of the distributed power sources in the entire area is obtained according to the first maximum accessible capacity and the second maximum accessible capacity.

2. The method according to claim 1, characterized in that: The distributed power source is divided into zones to obtain the distributed power source in each zone, including: the distributed power source is divided into an auxiliary boosting zone, an extraction zone and an adjacent feeder zone.

3. The method according to claim 2, characterized in that According to the access position of the distributed power source in each area, obtaining the access position of the equivalent distributed power source includes: According to formulas (1) to (3), the distance between the grid connection point and the power source point of the equivalent distributed power generation in the adjacent feeder area, boosting area and extraction area is obtained. ，（1） ，（2） ，（3） in, is the distance between the grid connection point and the power source point of the equivalent distributed generation in the adjacent feeder area, To help increase the distance between the grid connection point and the power supply point of the equivalent distributed power generation in the area, is the distance between the grid connection point and the power source point of the equivalent distributed power generation in the extraction area, For the current The current capacity of distributed power generation, For the The distance between a distributed generation device and the power node, To protect the code, is an integer code, Represented as adjacent feeder area, It is indicated as the boosting zone. Represents the absorption area, Represents a distributed power generation device.

4. The method according to claim 2, characterized in that: Obtaining the protection setting value without distributed current access, and obtaining the protection range under the current protection setting value according to the access position includes: According to formula (4), the protection setting value without distributed current connection is calculated: ，（4） in, , , They are the reliability coefficients of the first, second and third stages of the three-stage current protection. is the transformer impedance, is the system rated voltage, is the system nominal voltage coefficient, , , are the lengths between the first switch and the second switch, the second switch and the third switch, and the third switch and the end of the line, respectively. and are the self-start and return coefficients, is the maximum load current, , , are the protection settings of the first, second and third stages of the three-stage current protection of the second switch, is the line impedance per unit length; According to formula (5), the protection range under the current protection setting value is calculated: ，（5） in, and It is the current protection range of the first section and the second section of the second switch.

5. The method according to claim 4, characterized in that Establishing the current protection constraint boundary according to the protection setting value and the protection range includes: Obtain the correlation between the currents flowing through the protection after the distribution network fails, and determine the correlation according to formula (6): ，（6） in, For relevance, The current provided by all distributed power sources, The current provided to the system power supply; Determine a first value range of the correlation according to the protection range of the first segment, determine a second value range of the correlation according to the protection range of the second segment, determine the first value range according to formula (7), and determine the second value range according to formula (8), ，（7） ，（8） Determine the value range of the final correlation according to the first value range and the second value range, and determine the value range of the final correlation according to formulas (9) and (10). ，（9） ，（10） Among them, the value range of the final correlation is .

6. The method according to claim 5, characterized in that The maximum current of the distributed power source is obtained according to the current protection constraint boundary, wherein the maximum current of the distributed power source includes a first maximum current in the same direction and a second maximum current in the opposite direction, including: Determining whether the currents provided by all the distributed power sources are in the same direction as the current provided by the system power supply; When it is determined that the currents provided by all the distributed power sources are in the same direction as the current provided by the system power supply, obtaining a first maximum current; In the case where it is determined that the currents provided by all the distributed power sources are opposite to the current provided by the system power source, obtaining a second maximum current; The first maximum current is determined according to formula (11), and the second maximum current is determined according to formula (12). ，（11） ，（12） in, is the first maximum current, is the second largest current, To obtain The fault occurs when The position proportion, To obtain The fault occurs when The position proportion.

7. The method according to claim 6, characterized in that Acquiring a first maximum accessible capacity according to the first maximum capacity and the second maximum capacity, and acquiring a second maximum accessible capacity when the voltage deviation is minimal includes: Determining whether the currents provided by all the distributed power sources are in the same direction as the current provided by the system power supply; In the case where it is determined that the currents provided by all the distributed power sources are in the same direction as the current provided by the system power supply, a first mathematical model is established to obtain a first maximum capacity; In the case where it is determined that the currents provided by all the distributed power sources are opposite to the current provided by the system power source, a second mathematical model is established to obtain a second maximum capacity; A final first maximum accessible capacity is acquired according to the first maximum capacity and the second maximum capacity.

8. The method according to claim 7, characterized in that Acquiring a first maximum accessible capacity according to the first maximum capacity and the second maximum capacity, and acquiring a second maximum accessible capacity when the voltage deviation is minimal also includes: According to formula (13), a first mathematical model is established to obtain the first maximum capacity. ，（13） in, , , are the total capacities of the distributed generation devices in the boosting area, the adjacent feeder area and the extraction area of ​​the second switch, respectively, , , are the total rated currents of the distributed power sources in the booster area, the adjacent feeder area and the extraction area, respectively. , , are the maximum current coefficients of the booster zone, the adjacent feeder zone and the extraction zone, respectively, , Feeder and Normal load; A second mathematical model is established according to formula (14) to obtain the second maximum capacity. ，（14）。 9. The method according to claim 8, characterized in that Acquiring a first maximum accessible capacity according to the first maximum capacity and the second maximum capacity, and acquiring a second maximum accessible capacity when the voltage deviation is minimal also includes: Acquire the area to be measured and establish a third mathematical model; Acquire a minimum voltage deviation value according to the third mathematical model; Acquire the second maximum accessible capacity of each grid connection point in the test area according to the minimum voltage deviation; According to formula (15), the area to be tested is obtained and the third mathematical model is established. ，（15） in, and Node The active power and reactive power generated by the connected power supply, and Node The active power and reactive power absorbed by the connected load, and Node and nodes The voltage, and Branch The conductance and susceptance of For Node and nodes The voltage phase angle difference, is the maximum line current, is the voltage deviation coefficient.

10. The method according to claim 9, characterized in that Acquiring the maximum accessible capacity of the distributed power source in the entire area according to the first maximum accessible capacity and the second maximum accessible capacity includes: According to formula (16), the maximum accessible capacity is obtained: ，（16） in, is an integer code, For each protection switch The maximum accessible capacity of each grid connection point.

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