Distributed power supply capacity limiting method based on original protection constant value of power distribution network

Abstract

The embodiment of the invention provides a distributed power supply capacity limiting method based on an original protection constant value of a power distribution network, and belongs to the field of power distribution networks. Comprises: acquiring a distributed power supply; partitioning the distributed power supply to obtain the distributed power supply of each region; obtaining the access position of an equivalent distributed power supply according to the access position of the distributed power supply in each area; acquiring a protection constant value under the condition of no distributed current access, and acquiring a protection range under the current protection constant value according to the access position; establishing a current protection constraint boundary; obtaining the maximum current of the distributed power supply according to the current protection constraint boundary; according to the maximum current of the distributed power supply, obtaining a first maximum capacity of the distributed power supply in the same direction as the system power supply current and a second maximum capacity opposite to the system power supply current; obtaining a first maximum accessible capacity, and obtaining 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 invention relates to the field of distribution networks, and in particular to a method for limiting the capacity of a distributed power source based on an original protection setting of the distribution network. Background Art

[0002] With the gradual deepening of the construction of new power systems, a large number of new energy sources are connected to low-voltage distribution networks. The access of distributed power sources to the distribution network is characterized by multi-point, scattered and dense, which brings challenges to the protection of traditional distribution networks.

[0003] In terms of protection, the current protection of the traditional distribution network detects the current level after the fault and acts quickly to remove the fault. After the distributed power supply is connected, the amplitude and direction of the fault current change, resulting in the risk of false operation and refusal of the original protection. In addition, the current output by the distributed power supply after the fault is subject to multiple nonlinear constraints such as the current withstand level of the power electronic device and the low voltage ride-through control strategy, which leads to severe challenges for the traditional staged current protection. Summary of the invention

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

[0005] In order to achieve the above object, an embodiment of the present invention provides a method for limiting the capacity of a distributed power supply based on an original protection setting of a distribution network, the method comprising: 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; According to the access position, a protection range under the current protection setting value and a protection setting value without distributed current access are obtained; Establishing a current protection constraint boundary according to the protection setting value; Acquire the maximum current of the distributed power source according to the current protection constraint boundary; According to the maximum current of the distributed power source, obtain a first maximum capacity of the distributed power source 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; 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.

[0006] Optionally, partitioning the distributed power source to obtain the distributed power source in each area includes: dividing the distributed power source into an auxiliary boosting area, an extraction area, and an adjacent feeder area.

[0007] Optionally, according to the access location of the distributed power source in each area, obtaining the access location 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, For the absorption area, Represents a distributed power generation device.

[0008] Optionally, obtaining a protection range under a current protection setting value and a protection setting value without distributed current access 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.

[0009] Optionally, establishing a current protection constraint boundary according to the protection setting 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 .

[0010] Optionally, obtaining the maximum current of the distributed power source according to the current protection constraint boundary 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; 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.

[0011] Optionally, 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.

[0012] Optionally, 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 further 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).

[0013] Optionally, 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 further 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.

[0014] Optionally, 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.

[0015] Through the above technical scheme, the present invention obtains the maximum accessible capacity of the existing distributed power grid connection point under the premise of ensuring the safety and stability of the distribution network, under the complex fault current distribution characteristics of the distributed power sources with multi-point dense access, without changing the existing protection setting and ensuring that the protection range is within the requirements of the relay protection rules. Taking into account the distributed power sources with multi-point scattered and dense access, the present invention proposes a partitioning principle for distributed power sources with consistent protection current influence, and obtains the access position of equivalent distributed power sources for the differentiated distributed power sources. After performing equivalent operations on the distributed power sources, the maximum accessible capacity of each grid connection point is obtained under the condition that the protection setting remains unchanged and the distribution network operation safety is optimal. Compared with the accessible capacity calculation method of the prior art, the present invention performs partitioning and unified calculation according to the influence of the distributed power sources on the protection current, which greatly reduces the complexity of the solution 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 under the re-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, thereby speeding up the calculation speed; and considering the safest distributed power access capacity under the premise of unchanged protection constants, the accessible capacity of distributed power sources is provided with decision support.

[0016] Other features and advantages of the embodiments of the present invention will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying 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 implementations, they are used to explain the embodiments of the present invention, but do not constitute a limitation on the embodiments of the present invention. In the accompanying drawings: Figure 1 It is a flow chart of a method for limiting the capacity of a distributed power source based on the original protection setting of a distribution network according to an embodiment of the present invention; Figure 2 It is a flow chart of establishing a current protection constraint boundary according to a protection setting in a method for limiting capacity of a distributed power source based on an original protection setting of a distribution network according to an embodiment of the present invention; Figure 3 It is a flowchart of obtaining the first maximum accessible capacity in a method for limiting the capacity of a distributed power source based on the original protection setting of a distribution network according to an embodiment of the present invention; Figure 4It is a flowchart of obtaining the second maximum accessible capacity in a method for limiting the capacity of a distributed power source based on the original protection setting of a distribution network according to an embodiment of the present invention; Figure 5 It is a schematic diagram of the distributed power source partitions before and after merging of the second switch in a specific embodiment of a method for limiting the capacity of a distributed power source based on the original protection setting of a distribution network according to an embodiment of the present invention; Figure 6 A distribution line model in a specific embodiment of a method for limiting capacity of a distributed power source based on an original protection setting of a distribution network according to an embodiment of the present invention; Figure 7 It is a schematic diagram of calculation results of original access capacity and maximum access capacity in a specific embodiment of a method for limiting capacity of a distributed power source based on original protection setting of a distribution network according to an embodiment of the present invention; Figure 8 It is a fault current curve flowing through the second switch at the maximum access capacity and a fault current curve diagram of 1.5 times the DG5 capacity in a specific embodiment of a distributed power generation capacity limiting method based on the original protection setting of the distribution network according to an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The specific implementation of the embodiment of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the embodiment of the present invention, and is not used to limit the embodiment of the present invention.

[0019] In the embodiments of the present application, certain software, components, models and other existing solutions in the industry may be mentioned, which should be regarded as exemplary. Their purpose is only to illustrate the feasibility of implementing the technical solution of the present application, but it does not mean that the applicant has or will necessarily use the solution.

[0020] like Figure 1 As shown, Figure 1 The present invention is a flowchart of a method for limiting the capacity of a distributed power source based on the original protection setting of the distribution network according to an embodiment of the present invention. Figure 1 In the method, the method comprises the following steps: In step S01, the distributed power sources currently connected to the distribution network are obtained.

[0021] In step S02, the distributed power sources are divided into zones to obtain the distributed power sources in each zone.

[0022] In step S03, the access locations of equivalent distributed power sources are obtained according to the access locations of the distributed power sources in each area.

[0023] In step S04, a protection setting value is obtained without distributed current access, and a protection range under the current protection setting value is obtained according to the access position.

[0024] In step S05, a current protection constraint boundary is established according to the protection setting.

[0025] In step S06, the maximum current of the distributed power source is obtained according to the current protection constraint boundary.

[0026] In step S07, a first maximum capacity of the distributed power source in the same direction as the system power current and a second maximum capacity in the opposite direction to the system power current are obtained according to the maximum current of the distributed power source.

[0027] In step S08, the first maximum accessible capacity is acquired according to the first maximum capacity and the second maximum capacity, and the second maximum accessible capacity is acquired when the voltage deviation is minimized.

[0028] In step S09, 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.

[0029] In this implementation, first, obtain the existing distributed power sources connected in the distribution network; then partition the distributed power sources to obtain the distributed power sources in each area; secondly, according to the access position of the distributed power sources in each area, obtain the access position of the equivalent distributed power sources; then obtain the protection setting value without distributed current access, and obtain the protection range under the current protection setting value according to the access position; then, establish the current protection constraint boundary according to the protection setting value; then obtain the maximum current of the distributed power source according to the current protection constraint boundary; according to the maximum current of the distributed power source, obtain the first maximum capacity of the distributed power source in the same direction as the system power current and the second maximum capacity in the opposite direction of the system power current; then obtain the first maximum accessible capacity according to the first maximum capacity and the second maximum capacity, and obtain the second maximum accessible capacity when the voltage deviation is minimum; finally, obtain 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. Under the premise of ensuring the safety and stability of the distribution network, the present invention obtains the maximum accessible capacity of the existing distributed power source grid connection point under the complex fault current distribution characteristics of the distributed power sources with multi-point intensive access, without changing the existing protection setting value and ensuring that the protection range is within the requirements of the relay protection rules. Taking into account the distributed power sources' multi-point scattered and dense access, the present invention proposes a zoning principle for distributed power sources based on the consistent impact of protection current, and obtains the access position of equivalent distributed power sources for the differentiated distributed power sources. After performing equivalent operations on the distributed power sources, the maximum accessible capacity of each grid connection point is obtained, considering that the protection setting remains unchanged and the distribution network operation safety is optimal. Compared with the accessible capacity calculation method of the prior art, the present invention performs zoning and unified calculation according to the impact of distributed power sources on the protection current, which greatly reduces the complexity of the solution 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 under the restriction of re-access capacity.

[0030] In this implementation, 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 boost zone bz, an extraction zone dz and an adjacent feeder zone af. In one embodiment of the present invention, for a certain protection, the feeders other than the feeder where the protection is located are regarded as adjacent feeder zones af, the area from the power source to the upstream of the protection is the auxiliary boost zone bz, and the protection range of this section of the line is the extraction zone dz.

[0031] In this implementation, all distributed power sources in each area are considered as an equivalent distributed power source. The access location of the distributed power source in each area can be obtained in a variety of ways known to those skilled in the art. In one embodiment of the present invention, the access location of the equivalent distributed power source is calculated using line impedance weighted average power. The distance between the grid connection point and the power source point of the equivalent distributed power source in the adjacent feeder area af, booster area bz and extraction area dz is obtained according to formulas (1) to (3). , (1) , (2) , (3) in, is the distance between the grid connection point and the power supply point of the equivalent distributed generation in the adjacent feeder area af, To help increase the distance between the grid connection point and the power supply point of the equivalent distributed power generation in area bf, is the distance between the grid connection point and the power source point of the equivalent distributed generation in the extraction area df, 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.

[0032] In this implementation, the method for 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 can be a variety of methods known to those skilled in the art. In one embodiment of the present invention, the protection of the second switch R2 is taken as a specific embodiment, that is, When it is 2, the protection range under the current protection setting value and the protection setting value without distributed current connection are obtained according to the access position. The protection setting value without distributed current connection is calculated according to formula (4). 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 when a fault occurs at a certain location. , (4) in, , , are respectively the reliability coefficients of the first, second and third stages 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 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; , (5) in, and It is the current protection range of the first section and the second section of the second switch R2.

[0033] In this implementation, there may be many ways known to those skilled in the art on how to establish the current protection constraint boundary according to the protection setting value. In one embodiment of the present invention, for example, Figure 2 and Figure 5 As shown, the constraint conditions are established by using the first and second current protections of the second switch R2, and the current protection constraint boundary is established according to the protection setting, including the following steps: In step S051, the correlation between the current flowing through the protection after the distribution network fails is obtained. After the distribution network fails, the current flowing through the protection can be divided into two parts. The first part is the current provided by the system power supply. , the second part is provided by all distributed power sources , according to formula (6), , (6) in, For relevance, The current provided by all distributed power sources, The current supplied to the system power supply.

[0034] In step S052, a first value range of the correlation is determined according to the protection range of the first segment, and a second value range of the correlation is determined according to the protection range of the second segment.

[0035] The first protection range must be between 15% and 80%. The first value range is determined based on the protection range boundary and formula (7): If it is necessary to coordinate with the branch protection at the lower level y, the protection range can be changed to 15%-y% and substituted into formula (7).

[0036] For the second protection, its protection range covers the entire length of the line but cannot exceed the first protection range of the next level. In one embodiment of the present invention, the second protection range is 100%-115%. The second value range is determined according to the protection range boundary and formula (8): .

[0037] , (7) , (8) In step S053, the value range of the final correlation is determined according to the first value range and the second value range. There are many ways known to those skilled in the art for determining the value range of the final correlation according to the first value range and the second value range. In one embodiment of the present invention, in order to meet the constraints of the first and second current protections, the value range of the final correlation is determined according to formulas (9) and (10): , , (9) , (10). In this implementation, the method of obtaining the maximum current of the distributed power source according to the current protection constraint boundary can be a variety of methods known to those skilled in the art. In one embodiment of the present invention, for example Figure 3 As shown in the figure, the specific steps for obtaining the maximum current of the distributed power source according to the current protection constraint boundary are as follows: In step S061, it is determined whether the currents provided by all distributed power sources and the current provided by the system power source are in the same direction.

[0038] In step S062, 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 maximum current is obtained. The first maximum current is determined according to formula (11): , (11) In step S063, when it is determined that the current provided by all distributed power sources is opposite 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): , (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 According to the current protection constraints of the first and second sections, the maximum current affected by the distributed power source is obtained. , all distributed power supplies provide current The current provided by the system power supply In the same direction, according to The second switch is provided with the first maximum current by the distributed power source; the current provided by all distributed power sources The current provided by the system power supply In the reverse direction, the maximum directional current flowing into the second switch is the second maximum current.

[0039] In this embodiment, the maximum current amplitude of the second switch in a given direction When calculating the maximum output current of the adjacent feeder area af, booster area bz and extraction area dz, it is considered that it is impossible to determine that the maximum output of the distributed power source appears in the current provided by all the distributed power sources. The current provided by the system power supply In the same or reverse direction, therefore, the first maximum capacity of the distributed power supply in the same direction as the system power supply current and the second maximum capacity in the reverse direction of the system power supply current are obtained according to the maximum current of the distributed power supply. The first maximum capacity and the second maximum capacity are the maximum access capacity of the distributed power supply in the area calculated under the premise that the protection setting remains unchanged. The first maximum capacity and the second maximum capacity comprehensively consider the impact of each partition on the protection current after the fault, and are the results of the calculation with the coordination of the upper and lower protection ranges as constraints.

[0040] like Figure 3 As shown, the specific steps of obtaining the first maximum accessible capacity according to the first maximum capacity and the second maximum capacity are as follows: In step S061, it is determined whether the currents provided by all distributed power sources and the current provided by the system power source are in the same direction.

[0041] In step S072, 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 according to the first maximum current to obtain a first maximum capacity.

[0042] According to formula (13), the first mathematical model is established to obtain the first maximum capacity. , (13) in, , , are the total capacity of distributed generation devices in the booster area, adjacent feeder area and extraction area of ​​the second switch, respectively. , , are the total rated currents of distributed power sources in the auxiliary area, adjacent feeder area and extraction area, respectively. , , are the maximum current coefficients of the booster zone, adjacent feeder zone and extraction zone, respectively. , Feeder and The normal load, is the transformer capacity of the previous level. In formula (10), the first constraint is the protection range constraint, the second constraint is the power and current relationship constraint, the third and fourth constraints are that the total current of the distributed power source of each feeder is less than the third segment constant, the fourth and fifth constraints are that the output current of the distributed power source does not exceed 1.5 times the feeder load, and the last constraint is that the total capacity of the distributed power source is less than the transformer capacity of the previous level.

[0043] In step S073, when it is determined that the current provided by all the distributed power sources is opposite to the current provided by the system power source, a second mathematical model is established according to the second maximum current to obtain the second maximum capacity.

[0044] According to formula (14), a second mathematical model is established to obtain the second maximum capacity. , (14). That is, the first constraint on the left side of the equal sign in formula (13) Replace with , another optimal solution can be obtained.

[0045] In step S074, the first maximum accessible capacity is obtained according to the first maximum capacity and the second maximum capacity. Compare the optimal solutions obtained by formula (13) and formula (14) to obtain the larger The total capacity of the distributed generation devices in the auxiliary area, adjacent feeder area and extraction area of ​​the corresponding second switch, that is, , , The value of .

[0046] In this implementation, how to obtain the second maximum accessible capacity when the voltage deviation is minimized can be a variety of methods known to those skilled in the art. In one embodiment of the present invention, the second maximum accessible capacity takes the maximum accessible distributed power capacity in the region and the optimal safe operation of the distribution network as constraints, constructs the maximum capacity of the single-point accessible distributed power source, and solves the second maximum accessible capacity of the distributed power source grid connection point while ensuring that it does not exceed the maximum distributed power access capacity in the region. The specific steps for obtaining the second maximum accessible capacity when the voltage deviation is minimized are as follows: In step S075, the area to be measured is acquired and a third mathematical model is established.

[0047] 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. It is related to the current carrying capacity of the current conductor. It is related to the grid voltage level.

[0048] In step S076, the minimum voltage deviation is obtained according to the third mathematical model. The voltage deviation of the three-phase power grid of 20 kV and below cannot exceed 7% of the rated voltage, and the objective function represents the minimum sum of the voltage deviations of all nodes.

[0049] In step S077, the second maximum accessible capacity of each grid-connected point in the tested area is obtained according to the minimum voltage deviation. It can be seen from formula (15) that the first constraint is the regional distributed power capacity constraint, the second constraint is the power conservation condition; the third constraint is the voltage deviation constraint, that is, the single-point voltage cannot exceed the safety requirements of the power grid; the fourth constraint is the current carrying capacity constraint, which cannot exceed the maximum current limit of the installed conductor.

[0050] The distributed power capacity allocation is completed while ensuring the safe operation of the system, and the node voltage deviation caused by the access of distributed power 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 given protection setting.

[0051] In this implementation, the method of obtaining the maximum accessible capacity of the distributed power supply in the entire area according to the first maximum accessible capacity and the second maximum accessible capacity can be a variety of methods known to those skilled in the art. In one embodiment of the present invention, the above operation is repeated to traverse all protections, and the maximum accessible capacity of each network point can be obtained for each switch according to the first maximum accessible capacity and the second maximum accessible capacity of each grid point. The minimum maximum accessible capacity is the final single-point maximum accessible capacity. The maximum accessible capacity is obtained according to formula (16). , (16) in, is an integer code, The maximum accessible capacity.

[0052] Specifically, in one embodiment of the present invention, in order to verify the distributed power generation capacity limiting method based on the original protection setting of the distribution network, such as Figure 6 As shown, a distribution line model was built using Matleb / simulink to divide the impact area based on the impact of the first switch in the protection diagram. For the protection of the first switch, distributed power generation is divided into zones, where DG5 belongs to the adjacent feeder zone, and DG1 and DG4 belong to the extraction zone. The access positions of equivalent distributed power sources are calculated for these zones, and the protection range under the current protection setting and the protection setting without distributed current access are obtained according to the access position. The current protection constraint boundary is established according to the protection setting 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 is solved; then, with the goal of minimizing the voltage deviation of the grid connection point during normal operation, the second maximum access capacity of each distributed power source in the area is solved. The fault current curve flowing through the second switch under the maximum access capacity and the fault current curve of 1.5 times the DG5 capacity are shown as follows Figure 8 As shown. Figure 7 and Figure 8 As shown in the figure, after the capacity is increased, the first protection range under the original fixed value increases from 60% to nearly 100%. In engineering, the first fixed value protection range should be between 15% and 80%. If the protection range is too large, it is not conducive to the coordination of the lower protection and branch protection, and it is very easy to lose selectivity. The test results also prove the correctness of the maximum capacity calculation results.

[0053] Through the above technical scheme, the present invention obtains the maximum accessible capacity of the existing distributed power grid connection point under the premise of ensuring the safety and stability of the distribution network, under the complex fault current distribution characteristics of the distributed power sources with multi-point dense access, without changing the existing protection setting and ensuring that the protection range is within the requirements of the relay protection rules. Taking into account the distributed power sources with multi-point scattered and dense access, the present invention proposes a partitioning principle for distributed power sources with consistent protection current influence, and obtains the access position of equivalent distributed power sources for the differentiated distributed power sources. After performing equivalent operations on the distributed power sources, the maximum accessible capacity of each grid connection point is obtained under the condition that the protection setting remains unchanged and the distribution network operation safety is optimal. Compared with the accessible capacity calculation method of the prior art, the present invention performs partitioning and unified calculation according to the influence of the distributed power sources on the protection current, which greatly reduces the complexity of the solution 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 under the re-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, thereby speeding up the calculation speed; and considering the safest distributed power access capacity under the premise of unchanged protection constants, the accessible capacity of distributed power sources is provided with decision support.

[0054] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application may adopt 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.) containing computer-usable program codes.

[0055] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0056] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0057] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0058] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0059] The memory may include non-permanent memory in a computer-readable medium, random access memory (RAM) and / or non-volatile memory in the form of read-only memory (ROM) or flash RAM. The memory is an example of a computer-readable medium.

[0060] 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.

[0061] 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.

[0062] 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; According to the maximum current of the distributed power source, obtain a first maximum capacity of the distributed power source 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; 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 Acquiring the maximum current of the distributed power source according to the current protection constraint boundary 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; 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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