A method and system for controlling over-limit safety of power flow in a power grid section containing new energy

Abstract

The present invention discloses a method and system for safely controlling over-limit currents in a power grid section containing new energy sources. The method comprises: incrementally iterating DG power, increasing a fixed power value each time, performing current calculations using the Newton method after each iteration, outputting calculation results for over-limit buses, generators, and branches, and stopping iterations; analyzing the power transfer relationship between the current over-limit node and the branch in the power grid; calculating the sensitivity of each generator to the power transmission distribution factor of the over-limit line based on the generators in the node according to the PTDF matrix; calculating the power adjustment amount of each generator according to the sensitivity ratio, and issuing a power reduction instruction according to the calculated adjustment amount, thereby adjusting the power of the generator. The present invention provides dispatchers with very valuable current control guidance information. The determined control scheme reasonably stipulates the amount of cut-off at the controlled end of the section, effectively solving the over-limit problem of the section caused by the new energy characteristics after the new energy is connected to the power grid.

Description

Technical Field

[0001] The present invention relates to the technical field of power distribution in a power transmission network, and in particular to a method and system for safely controlling over-limit current in a section of a power grid containing new energy. Background Art

[0002] The transmission section in the power system refers to a set of transmission lines with the same active power flow direction and similar electrical distance under a certain base state flow.

[0003] The transmission capacity of a section directly affects the safe operation of the power grid in the affected area of ​​the section. When the flow of some lines with a higher load rate approaches the limit power, the probability of line failure will increase. The redistribution of the flow after the line break may lead to chain failures of the section lines and increase the system safety risk.

[0004] Therefore, in actual system operation, controlling cross-section power flows has always been a key focus for dispatchers and operators. Currently, a common practice both domestically and internationally is to perform offline calculations of various possible operating modes to determine the power transfer limits for each cross-section under various N-1 / N-2 operating conditions. However, these results are relatively conservative, and if unusual operating conditions arise for various reasons, dispatchers struggle to quickly determine a reasonable control solution to reduce load shedding at the receiving end of the cross-section. Long-term operating experience and theoretical analysis of power grid operation indicate that cross-section power flow distribution is influenced not only by the cross-section's structural characteristics but also by the power plant output at nearby nodes. Summary of the Invention

[0005] Purpose of the invention: In order to solve the problems arising from the above-mentioned prior art, the present invention provides a method for safely controlling the over-limit current of a section of a power grid containing new energy, which solves the problem of over-limit current of a section caused by the new energy characteristics after the new energy is connected to the power grid. The present invention also provides a safety control system for the over-limit current of a section of a power grid containing new energy.

[0006] Technical solution: According to a first aspect of the present invention, a method for controlling the over-limit safety of power flow in a power grid section containing new energy is provided, the method comprising:

[0007] The system simulates the situation of DG access to the power system and calculates the initial power flow. The DG access parameters, specifically the active power, reactive power, and their limits, are initialized. The active power of the DG is then iterated incrementally. Specifically, a fixed power value is added to the previous iteration value each time, and the power flow calculation is repeated using the Newton method. The node voltage and branch current ratio of this iteration are recorded. When the node voltage or branch current ratio exceeds the limit, the calculation results and the number of iterations for the bus, generator, and branch that exceed the limit are output and the iteration is stopped. The line out-of-limit situation under the DG access situation is determined. Multiple out-of-limit nodes are selected as reference nodes, and the power transfer relationship between the current node and the branch in the power grid is analyzed and represented by a PTDF matrix.

[0008] According to the PTDF matrix and the generators in the node, the sensitivity of each generator to the power transfer distribution factor of the over-limit line is calculated, and then the sensitivity ratio of the power transfer distribution factor of each generator is obtained;

[0009] The power adjustment amount of each generator is calculated according to the sensitivity ratio, and a power reduction instruction is issued according to the calculated adjustment amount, thereby adjusting the power of the generator.

[0010] Further, including;

[0011] The line over-limit situation obtained when the DG is connected specifically includes the branch numbers b1, b2, ..., b N and the node numbers n1, n2, ..., n where the voltage exceeds the limit M , where N is the total number of branches with excessive power flow, M is the total number of nodes with excessive voltage, and the access parameters of the DG include the node number and the initial active power value.

[0012] Further, including;

[0013] The analysis of the power transfer relationship between the current node and the branch in the power grid is represented by a PTDF matrix, including:

[0014]

[0015] Among them, B y is the node admittance matrix calculated based on Kirchhoff's law, which describes the relationship between node current and voltage. l is the line-node admittance matrix, which describes the relationship between line current and node voltage difference.

[0016] Further, including;

[0017] The calculation of the sensitivity of each generator to the power transmission distribution factor of the over-limit line based on the PTDF matrix and the generators in the node, and then obtaining the sensitivity ratio of the power transmission distribution factor of each generator, specifically includes:

[0018] For each generator number g1, g2, ..., g l ,…,g k According to the node number gl where the generator is located, obtain the branches b1, b2, ..., b1 that exceed the limit of the power flow at this node. N The sum of the absolute values ​​of the corresponding PTDF elements is used as the power transfer factor sensitivity S of a single generator l :

[0019] g l Row b i Column Elements

[0020] The sum of the power transfer factor sensitivities of all generators participating in the dispatch is calculated, and the ratio of the sensitivity of each generator to the total sensitivity is obtained.

[0021]

[0022] Where R l is the generator g l The ratio of sensitivity to total sensitivity.

[0023] Further, including;

[0024] Calculating the power adjustment amount of each generator according to the sensitivity ratio, and issuing a power reduction instruction according to the calculated adjustment amount, thereby adjusting the power of the generator, specifically includes:

[0025] The ratio of the sensitivity of each generator to the total sensitivity R l Based on this, the output reduction instruction is distributed to each generator:

[0026] P l =P*R l

[0027] Where P is the total power reduction instruction issued to all generators when a pre-specified over-limit occurs, P l is the corresponding generator g l The power reduction amount is g. l The generator power is reduced by P l This is the strategy proposed by the present invention to solve the problem of cross-section tidal flow exceeding the limit.

[0028] On the other hand, the present invention also provides a safety control system for over-limit power flow in a power grid section containing new energy, the system comprising:

[0029] The over-limit judgment module is used to simulate the situation of DG access to the power system and calculate the initial power flow. It initializes the DG access parameters, specifically the active power, reactive power and its limit, and then iterates the DG active power incrementally. Specifically, it adds a fixed power value to the previous iteration value each time and repeatedly uses the Newton method to calculate the power flow. The node voltage and branch current ratio of this iteration are recorded. When it is detected that the node voltage or branch current ratio exceeds the limit, the calculation results of the busbar, generator, and branch that exceed the limit and the number of iterations are output, and the iteration is stopped, thereby determining the line over-limit situation when DG is accessed.

[0030] The representation module is used to select multiple out-of-limit nodes as reference nodes and analyze the power transfer relationship between the current node and the branch in the power grid, which is represented by a PTDF matrix;

[0031] A sensitivity ratio calculation module is used to calculate the sensitivity of each generator to the power transfer distribution factor of the over-limit line based on the PTDF matrix and the generators in the node, and then obtain the power transfer distribution factor sensitivity ratio of each generator;

[0032] The adjustment module is used to calculate the power adjustment amount of each generator according to the sensitivity ratio, and issue a power reduction instruction according to the calculated adjustment amount, thereby adjusting the power of the generator.

[0033] Further, including;

[0034] In the over-limit judgment module, the line over-limit situation obtained when the DG is connected specifically includes branches b1, b2, ..., b N and the nodes n1, n2, ..., n whose voltage exceeds the limit M , where N is the total number of branches with excessive power flow, M is the total number of nodes with excessive voltage, and the access parameters of the DG include the node number and the initial power value.

[0035] Further, including;

[0036] In the representation module, the power transfer relationship between the current node and the branch in the power grid is analyzed and represented by a PTDF matrix, including:

[0037]

[0038] Among them, B y is the node admittance matrix calculated based on Kirchhoff's law, which describes the relationship between node current and voltage. lis the line-node admittance matrix, which describes the relationship between line current and node voltage difference.

[0039] Further, including;

[0040] In the sensitivity ratio calculation module, the sensitivity of each generator to the power transmission distribution factor of the over-limit line is calculated based on the PTDF matrix and the generators in the node, thereby obtaining the power transmission distribution factor sensitivity ratio of each generator, which specifically includes:

[0041] For each generator number g1, g2, ..., g l ,…,g k According to the node number gl where the generator is located, obtain the branches b1, b2, ..., b1 that exceed the limit of the power flow at this node. N The sum of the absolute values ​​of the corresponding PTDF elements is used as the power transfer factor sensitivity S of a single generator l :

[0042] No. g l Row b i Column Elements

[0043] Calculate the sum of the power transfer factor sensitivities of all generators and find the ratio of each generator's sensitivity to the total sensitivity:

[0044]

[0045] Where R l is the generator g l The ratio of sensitivity to total sensitivity.

[0046] Further, including;

[0047] In the adjustment module, the power adjustment amount of each generator is calculated according to the sensitivity ratio, and a power reduction instruction is issued according to the calculated adjustment amount, thereby adjusting the power of the generator, which specifically includes:

[0048] The ratio of the sensitivity of each generator to the total sensitivity R l Based on this, the output reduction instruction is distributed to each generator:

[0049] P l =P*R l

[0050] Where P is the total power reduction instruction issued to all generators when a pre-specified over-limit occurs, P l is the corresponding generator g l The power reduction amount is g. lThe generator power is reduced by P l This is the strategy proposed by the present invention to solve the problem of cross-section tidal flow exceeding the limit.

[0051] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0052] This paper proposes a power flow over-limit safety control method based on power sensitivity analysis. By analyzing the sensitivity of section power, this method optimizes output and load distribution, or provides a basis for decision-making optimization for emergency control measures after a fault. This method then determines the section's operational control strategy and proposes a section-specific power limit control scheme. Simulation results demonstrate the effectiveness and feasibility of this indicator algorithm.

[0053] As a method for controlling the over-limit flow of a power grid section containing new energy sources based on a power transmission distribution factor, the present invention provides dispatchers with very valuable guidance information for flow control. The determined control scheme reasonably stipulates the amount of cut-off at the controlled end of the section, thereby reducing the output of other dispatchable units in order to solve the over-limit problem of the section caused by the influence of DG access. It effectively solves the over-limit problem of the section caused by the characteristics of new energy sources after the new energy sources are connected to the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a flow chart of a method for controlling over-limit power flow in a power grid section containing new energy sources based on a power transmission distribution factor according to an embodiment of the present invention;

[0055] Figure 2 A comparison diagram of the current carrying ratio of each branch of the simulation results described in an embodiment of the present invention;

[0056] Figure 3 This is a schematic structural diagram of a power flow over-limit safety control system for a power grid section containing new energy sources based on a power transmission distribution factor according to an embodiment of the present invention. DETAILED DESCRIPTION

[0057] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention and not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0058] like Figure 1As shown, the present invention proposes a safety control method for over-limit power flow in a power grid section containing new energy sources based on a power transmission distribution factor. First, the value N of the DG access to the transmission network is incrementally iterated to output the node voltage and branch current ratio at the initial and over-limit times. The system power flow is calculated by gradually increasing the access value of the distributed power source (DG), and the node voltage and branch current ratio of each iteration are recorded. When the node voltage or branch current ratio exceeds the limit, the relevant information is output. The PTDF matrix is ​​calculated and the sum of the power transmission distribution factors of each generator to the over-limit line is obtained. According to the sum, the ratio of the sensitivity of the power transmission distribution factor of each generator to the sum is obtained. Then, according to the ratio, the power adjustment amount of each generator is calculated, and a power reduction instruction is issued according to the calculated adjustment amount. The power of the generator is adjusted, and the power flow calculation is performed again to verify the adjustment effect.

[0059] The specific steps are as follows:

[0060] S1 iterates the connected DG power incrementally and uses the Newton-Ray method to calculate the power flow after each iteration. When it detects that the node voltage or branch current ratio exceeds the limit, it outputs the calculation results of the bus, generator, and branch that exceed the limit and stops the iteration.

[0061] Specifically, the algorithm initializes DG connection parameters, such as node ID and initial power value, and incrementally increases the DG power by a fixed value. After each iteration, the Newton method is used to calculate power flow, recording node voltages and branch current ratios. If a node voltage or branch current ratio exceeds a limit, the calculation results for the busbar, generator, and branch that exceed the limit are output, and the iteration is terminated. The line out-of-limit conditions under DG connection are determined, specifically branches b1, b2, b3, etc., where power flow exceeds the limit, and nodes n1, n2, n3, etc., where voltage exceeds the limit.

[0062] S2. Select the generator of the reference node as a reference and calculate the PTDF (Power Transfer Distribution Factor, PTDF) matrix.

[0063] The calculation of the PTDF matrix in step B is based on the function in MATLAB's MATPOWER for generating a DC power transfer distribution factor matrix. The PTDF matrix is ​​used to analyze the relationship between power transfer between nodes and branches in the power grid. When performing DC power flow calculations, it is usually necessary to introduce an intermediate variable, namely the voltage phase angle θ, to describe the relationship between the node active power and the line active power flow. Considering that the node active power and the node voltage phase angle are linearly related, and the line power flow and the voltage phase angle difference between the two nodes connected by the line are linearly related, there must be a linear relationship between the node active power and the line active power flow. The linear coefficient matrix that directly describes how the node active power is transferred to the line active power flow is the power transfer distribution factor. The calculation principle is as follows:

[0064] P n =B y θ(1)

[0065] Among them, P n is the node active power flow; B y is the node admittance matrix calculated based on Kirchhoff's law, which describes the relationship between node current and voltage. Here, Xi,j represents the line reactance between node i and node j:

[0066]

[0067] Line flow P l The relationship between the voltage phase angle can be described by the following equation:

[0068] P l =B l θ(3)

[0069] Among them, B l is the line-node admittance matrix, which describes the relationship between line current and node voltage difference. Assuming that there is a line connection relationship between node 1 and node 2, and between node 1 and node 3, then B l It can be expressed as:

[0070]

[0071] Among them, the row represents the line, and the column represents the nodes at both ends of the line. Therefore, the above two equations can be obtained:

[0072] P l =B l (B y ) -1 P n (5)

[0073] PTFD=B l (B y ) -1(6)

[0074] It should be noted that B y It is a singular matrix and cannot be directly inverted. y The corresponding items of the reference nodes are set to zero. This is possible because we default to P n The vector must obey the power balance equation, so there is no need to pass B y To ensure Kirchhoff's current law, we get B y *, so in actual calculation we get PTDF through the following equation:

[0075]

[0076] S3. Calculate the sum of the sensitivity of each generator to the power transfer distribution factor of the out-of-limit line and sum all the sums to obtain the ratio of the sensitivity of each generator to the sum.

[0077] The calculation process given in step S3 is as follows:

[0078] 1) For each generator, the sum of the absolute values ​​of the PTDF elements corresponding to all overload branches b1, b2, b3, etc. is obtained based on the node where the generator is located, and this is used as the power transfer factor sensitivity of the single generator.

[0079] 2) Calculate the sum of the power transfer factor sensitivities of all generators and obtain the ratio of each generator's sensitivity to the total sensitivity.

[0080] S4. Calculate the power adjustment for each generator based on the sensitivity ratio. Issue a power reduction command based on the calculated adjustment, adjust the generator power, and recalculate the power flow to verify the adjustment effect. After the adjustment, the branch power flow over-limit problem in the system is resolved, with the branch current ratio reduced to below 1. Specifically, the present invention simultaneously detects both branch current and node voltage in the simulation of a cross-section over-limit situation caused by DG connection. In actual calculations, branch current always exceeds the limit first, and active power has a smaller impact on node voltage, so node voltage does not exceed the limit. This node voltage detection serves only as part of the over-limit determination module described below; it only improves the branch power flow over-limit situation.

[0081] The power reduction instruction given in step S4 is sent to each generator according to the following process to solve the over-limit problem.

[0082] 1) Based on the ratio of each generator's sensitivity to the total sensitivity, the output reduction command is distributed to each generator.

[0083] 2) Recalculate the system power flow after adjusting the generator output and obtain the result of solving the over-limit problem.

[0084] Specifically:

[0085] In this embodiment, the sensitivity of each generator to the power transmission distribution factor of the out-of-limit line is calculated based on the PTDF matrix and the generators in the node, and then the sensitivity ratio of the power transmission distribution factor of each generator is obtained, which specifically includes:

[0086] For each generator number g1, g2, ..., g l ,...,g k , according to the node number g where the generator is located l And obtain the branches b1, b2, ..., b1 of the node for all the flow exceeding the limit N The sum of the absolute values ​​of the corresponding PTDF elements is used as the power transfer factor sensitivity S of a single generator l :

[0087] No. g l Row b i Column elements (8)

[0088] Calculate the sum of the power transfer factor sensitivities of all generators and find the ratio of each generator's sensitivity to the total sensitivity:

[0089]

[0090] Where R l is the generator g l The ratio of sensitivity to total sensitivity.

[0091] In this embodiment, the power adjustment amount of each generator is calculated according to the sensitivity ratio, and a power reduction instruction is issued according to the calculated adjustment amount, thereby adjusting the power of the generator, which specifically includes:

[0092] The ratio of the sensitivity of each generator to the total sensitivity R l Based on this, the output reduction instruction is distributed to each generator:

[0093] P l =P*R l ;(10)

[0094] Where P is the total power reduction instruction issued to all generators when a pre-specified over-limit occurs, P l is the corresponding generator g l The power reduction amount is g. l The dispatchable generator power is reduced P l This is the strategy proposed by the present invention to solve the problem of cross-section tidal flow exceeding the limit.

[0095] The following is a specific example to further demonstrate the feasibility and effectiveness of the proposed power transmission distribution factor-based cross-section power flow over-limit safety control method for renewable energy power grids. The classic IEEE 39-node network used in this example includes 10 generators and 46 transmission lines, of which 31 are balancing nodes.

[0096] A distributed generation (DG) with an initial value of 50 MW was connected to nodes 15 and 16. Its value was incrementally increased with a 20 MW iteration step until an over-limit condition occurred. Specifically, the current of branch 13 exceeded the limit during the eighth iteration. The basic power flow sensitivity matrix was calculated. The matrix has a total dimension of 39 × 46, with each element corresponding to the change in the line active power flow caused by the node output adjustment.

[0097] When adjusting the active power output of each generator set, the regulation function of the balancing unit is also not considered. The power transmission distribution factors of the dispatchable generators corresponding to the over-limit branch are extracted and summed.

[0098] Specifically, for all generator nodes except the reference node, the proportion of each generator power transmission distribution factor to the total is as follows:

[0099] Table 1 The proportion of the transmission distribution factor corresponding to the generator to the total

[0100]

[0101] According to this ratio, the power reduction command is set to 100MW, and the output of each generator is as follows:

[0102] Table 2 Comparison of generator output before and after

[0103]

[0104]

[0105] By distributing the generator output according to the calculation results in the table above, the over-limit situation of the line can be finally solved. Figure 2 As shown in the figure, in the simulated over-limit scenario, the current of 13 branches exceeded the limit in the 8th iteration when the connected DGs were all 210MW. By reducing the output of each dispatchable generator according to the output distribution method of the present invention and updating the power flow calculation results, the over-limit situation of the branch was resolved, and the branch current ratio was within the safe range.

[0106] On the other hand, the present invention also provides a safety control system for cross-section current exceeding limit of power grid containing new energy, such as Figure 3 As shown, the system includes:

[0107] The over-limit judgment module is used to initialize the DG access parameters and iterate the DG power incrementally, increasing the DG power by a fixed value each time. After each iteration, the Newton method is used to calculate the power flow and record the node voltage and branch current ratio at that time. When the node voltage or branch current ratio is detected to be over-limit, the calculation results of the bus, generator, and branch that exceed the limit are output and the iteration is stopped. The line over-limit situation under the condition of DG access is also determined.

[0108] The representation module is used to select multiple out-of-limit nodes as reference nodes and analyze the power transfer relationship between the current node and the branch in the power grid, which is represented by a PTDF matrix;

[0109] A sensitivity ratio calculation module is used to calculate the sensitivity of each generator to the power transfer distribution factor of the over-limit line based on the PTDF matrix and the generators in the node, and then obtain the power transfer distribution factor sensitivity ratio of each generator;

[0110] The adjustment module is used to calculate the power adjustment amount of each generator according to the sensitivity ratio, and issue a power reduction instruction according to the calculated adjustment amount, thereby adjusting the power of the generator.

[0111] Further, including;

[0112] In the over-limit judgment module, the line over-limit situation obtained when the DG is connected specifically includes the branch numbers b1, b2, ..., b N and the node numbers n1, n2, ..., n where the voltage exceeds the limit M , where N is the total number of branches with excessive power flow, M is the total number of nodes with excessive voltage, and the access parameters of the DG include the node number and the initial active power value.

[0113] Further, including;

[0114] In the representation module, the power transfer relationship between the current node and the branch in the power grid is analyzed and represented by a PTDF matrix, including:

[0115]

[0116] Among them, B y is the node admittance matrix calculated based on Kirchhoff's law, which describes the relationship between node current and voltage. l is the line-node admittance matrix, which describes the relationship between line current and node voltage difference.

[0117] Further, including;

[0118] In the sensitivity ratio calculation module, the sensitivity of each generator to the power transmission distribution factor of the over-limit line is calculated based on the PTDF matrix and the generators in the node, thereby obtaining the power transmission distribution factor sensitivity ratio of each generator, which specifically includes:

[0119] For each generator number g1, g2, ..., g l ,…,g k , according to the node number g where the generator is located l And obtain the branches b1, b2, ..., b1 of the node for all the flow exceeding the limit N The sum of the absolute values ​​of the corresponding PTDF elements is used as the power transfer factor sensitivity S of a single generator l :

[0120] No. g l Row b i Column Elements

[0121] Calculate the sum of the power transfer factor sensitivities of all generators and find the ratio of each generator's sensitivity to the total sensitivity:

[0122]

[0123] Where R l is the generator g l The ratio of sensitivity to total sensitivity.

[0124] Further, including;

[0125] In the adjustment module, the power adjustment amount of each generator is calculated according to the sensitivity ratio, and a power reduction instruction is issued according to the calculated adjustment amount, thereby adjusting the power of the generator, which specifically includes:

[0126] The ratio of the sensitivity of each generator to the total sensitivity R l Based on this, the output reduction instruction is distributed to each generator:

[0127] P l =P*R l ;

[0128] Where P is the total power reduction instruction issued to all generators when a pre-specified over-limit occurs, P l is the corresponding generator g l The power reduction amount is g. l The dispatchable generator power is reduced P l This is the strategy proposed by the present invention to solve the problem of cross-section tidal flow exceeding the limit.

[0129] Other technical features of the safety control system for over-limit power flow in a power grid section containing new energy sources described in the present invention are similar to the corresponding safety control method for over-limit power flow in a power grid section containing new energy sources, and will not be repeated here.

[0130] It will be understood by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0131] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0132] Obviously, those skilled in the art may make various changes and modifications to the embodiments of the present invention without departing from the spirit and scope of the embodiments of the present invention. Thus, if such changes and modifications of the embodiments of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for controlling the over-limit safety of power flow in a power grid section containing new energy, characterized in that: The method includes: Simulate the situation of DG access to the power system and calculate the initial power flow, initialize the DG access parameters, specifically: access distributed power generation DG to several nodes in the current network, and perform incremental iterations on the active power of DG. Specifically, each time a fixed power value is added to the previous iteration value, the power flow calculation is repeatedly performed using the Newton method, and the current node voltage and corresponding branch current ratio of this iteration are recorded. The incremental iteration of the active power of all connected distributed power generation DGs is completed. When it is detected that the node voltage or branch current ratio exceeds the limit, the calculation results and the number of iterations of the busbar, generator, and branch that exceed the limit are output and the iteration is stopped, and the line limit situation under the condition of DG access is obtained; Select multiple nodes that exceed the limit as reference nodes, and analyze the power transfer relationship between the current node and the branch in the power grid, which is represented by the PTDF matrix; According to the PTDF matrix and the generators in the current node, the sensitivity of each generator to the power transfer distribution factor of the over-limit line is calculated, and then the sensitivity ratio of the power transfer distribution factor of each generator is obtained; Calculating a power adjustment amount for each generator based on the sensitivity ratio, and issuing a power reduction instruction according to the calculated adjustment amount, thereby adjusting the power of the generator; Analyze the power adjustment of the generators corresponding to other nodes in the power grid, and adjust the power of the corresponding generators, so as to recalculate the power flow of the power system to verify the effect after adjustment.

2. The method for controlling the over-limit safety of power flow in a power grid containing new energy sources according to claim 1 is characterized in that: The line exceeding limit condition obtained when the DG is connected specifically includes: the branch numbers b1, b2, ..., b N and the node numbers n1, n2, ..., n where the voltage exceeds the limit M , where N is the total number of branches with excessive power flow, M is the total number of nodes with excessive voltage, and the access parameters of the DG include the node number and the initial active power value.

3. The method for controlling the over-limit safety of power flow in a power grid containing new energy sources according to claim 2, characterized in that: The analysis of the power transfer relationship between the current node and the branch in the power grid is represented by a PTDF matrix, including: Among them, B y is the node admittance matrix calculated based on Kirchhoff's law, which describes the relationship between node current and voltage. l is the line-node admittance matrix, which describes the relationship between line current and node voltage difference.

4. The method for controlling the over-limit safety of power flow in a power grid containing new energy sources according to claim 3 is characterized in that: The calculation of the sensitivity of each generator to the power transmission distribution factor of the over-limit line based on the PTDF matrix and the generators in the node, and then obtaining the sensitivity ratio of the power transmission distribution factor of each generator, specifically includes: For each generator number g1, g2, ..., g l ,...,g k , k is the total number of generators corresponding to the current node, according to the number g of each generator l And obtain the branches b1, b2, ..., b corresponding to the generator node for all power flow exceeding the limit N The sum of the absolute values ​​of the corresponding PTDF elements is used as the power transfer factor sensitivity S of a single generator l : g l Row b i Column elements; The sum of the power transfer factor sensitivities of all participating generators is calculated, and the ratio of the power transfer factor sensitivity of each generator to the total sensitivity is obtained: Where R l is the generator g l The ratio of the power transfer factor sensitivity to the total sensitivity.

5. The method for controlling the over-limit safety of power flow in a power grid section containing new energy sources according to claim 4 is characterized in that: Calculating the power adjustment amount of each generator according to the sensitivity ratio, and issuing a power reduction instruction according to the calculated adjustment amount, thereby adjusting the power of the generator, specifically includes: The ratio of the sensitivity of each generator to the total sensitivity R l Based on this, the output reduction instruction is distributed to the generator; P l =P*R l ; Where P is the total power reduction instruction issued to all generators when a pre-specified over-limit occurs, P l is the corresponding generator g l The power reduction amount is g l The generator power is reduced by P l .

6. A safety control system for over-limit current flow in a power grid section containing new energy, characterized in that: The system includes: The over-limit judgment module is used to simulate the situation of DG access to the power system and calculate the initial power flow, and initialize the access parameters of DG. Specifically, distributed power generation DG is connected to several nodes in the current network, and the active power of DG is incrementally iterated. Specifically, a fixed power value is added to the previous iteration value each time, and the power flow calculation is repeatedly performed using the Newton method. The current node voltage and corresponding branch current ratio of this iteration are recorded, and the incremental iteration of the active power of all connected distributed power generation DGs is completed. When it is detected that the node voltage or branch current ratio exceeds the limit, the calculation results of the bus, generator, and branch that exceed the limit and the number of iterations are output and the iteration is stopped, and the line over-limit situation under the condition of DG access is obtained; The representation module is used to select multiple out-of-limit nodes as reference nodes and analyze the power transfer relationship between the current node and the branch in the power grid, which is represented by a PTDF matrix; The sensitivity ratio calculation module is used to calculate the sensitivity of each generator to the power transmission distribution factor of the out-of-limit line based on the PTDF matrix and the generators in the current node, and then obtain the power transmission distribution factor sensitivity ratio of each generator; The adjustment module is used to calculate the power adjustment amount of each generator based on the sensitivity ratio, issue a power reduction instruction according to the calculated adjustment amount, and thus adjust the power of the generator; analyze the power adjustment amounts of the generators corresponding to other nodes in the power grid, and adjust the power of the corresponding generators, so as to recalculate the power flow of the power system to verify the effect after the adjustment.

7. The cross-section power flow over-limit safety control system for a power grid containing new energy sources according to claim 6 is characterized in that: In the over-limit judgment module, the line over-limit situation obtained when the DG is connected specifically includes: the branch numbers b1, b2, ..., b N and the node numbers n1, n2, ..., n where the voltage exceeds the limit M , where N is the total number of branches with excessive power flow, M is the total number of nodes with excessive voltage, and the access parameters of the DG include the node number and the initial active power value.

8. The cross-section power flow over-limit safety control system for a power grid containing new energy sources according to claim 7 is characterized in that: In the representation module, the power transfer relationship between the current node and the branch in the power grid is analyzed and represented by a PTDF matrix, including: Among them, B y is the node admittance matrix calculated based on Kirchhoff's law, which describes the relationship between node current and voltage. l is the line-node admittance matrix, which describes the relationship between line current and node voltage difference.

9. The cross-section power flow over-limit safety control system for a power grid containing new energy sources according to claim 8 is characterized in that: In the sensitivity ratio calculation module, Based on the PTDF matrix and the generators in the node, the sensitivity of each generator to the power transfer distribution factor of the over-limit line is calculated, and then the sensitivity ratio of the power transfer distribution factor of each generator is obtained, which includes: For each generator number g1, g2, ..., g l ,...,g k , k is the total number of generators corresponding to the current node, according to the number g of each generator l And obtain the branches b1, b2, ..., b corresponding to the generator node for all power flow exceeding the limit N The sum of the absolute values ​​of the corresponding PTDF elements is used as the power transfer factor sensitivity S of a single generator l : g l Row b i Column elements; The sum of the power transfer factor sensitivities of all participating generators is calculated, and the ratio of the power transfer factor sensitivity of each generator to the total sensitivity is obtained: Where R l is the generator g l The ratio of the power transfer factor sensitivity to the total sensitivity.

10. The cross-section power flow over-limit safety control system for a power grid containing new energy sources according to claim 9 is characterized in that: In the adjustment module, the power adjustment amount of each generator is calculated according to the sensitivity ratio, and a power reduction instruction is issued according to the calculated adjustment amount, thereby adjusting the power of the generator, which specifically includes: The ratio of the sensitivity of each generator to the total sensitivity R l Based on this, the output reduction instruction is distributed to each generator; P l =P*R l ; Where P is the total power reduction instruction issued to all generators when a pre-specified over-limit occurs, P l is the corresponding generator g l The power reduction amount is g l The generator power is reduced by P l .

Images