New energy-containing power grid section tidal current out-of-limit safety control method and system

Abstract

The invention discloses a new energy-containing power grid section load flow out-of-limit safety control method and system. The method comprises the following steps: carrying out incremental iteration on DG power, increasing a fixed power value each time, carrying out load flow calculation by using a Newton-Raphson method after each iteration, outputting calculation results of an over-limit bus, a generator and a branch, and stopping iteration; analyzing the power transmission relation between the current out-of-limit node and the branch in the power grid; calculating the power transmission distribution factor sensitivity of each generator to the out-of-limit line according to the PTDF matrix in combination with the generators in the nodes; and 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 performing power adjustment on the generators. Valuable power flow control guidance information is provided for dispatchers, the determined control scheme reasonably stipulates the removal amount of the section controlled end, and the section out-of-limit problem caused by the new energy characteristics after the new energy is connected to the power grid is effectively solved.

Description

Technical Field

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

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

[0004] Therefore, in the actual system operation, the control of section flow has always been the focus of dispatching and operating personnel. At present, the common practice at home and abroad is to calculate various possible operating modes offline and determine the power transmission limit values ​​under various N-1 / / N-2 conditions of the section, but the results are relatively conservative, and once special operating conditions occur due to various reasons, it is difficult for dispatching personnel to quickly determine a reasonable control plan to reduce the load shedding at the receiving end of the section. Long-term operating experience and theoretical analysis of power grid operation show that the section flow distribution is not only affected by the structural characteristics of the section, but also by the output of the power plant near the node of the section. 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 flow of a section of a power grid containing new energy, which solves the problem of over-limit flow 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 over-limit flow 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 a power flow in a section of a power grid containing new energy is provided, the method comprising:

[0007] Simulate the situation of DG access to the power system and calculate the initial power flow, initialize the access parameters of DG, specifically the active power, reactive power and its limit, etc., and then incrementally iterate the active power of DG, specifically, add a fixed power value on the basis of the previous iteration value each time and repeatedly use the Newton method to calculate the power flow, record the node voltage and branch current ratio of this iteration, when it is detected that the node voltage or branch current ratio exceeds the limit, output the calculation results and iteration number of the bus, generator, branch that exceeds the limit, and stop the iteration, and obtain the line limit situation when DG is connected; select multiple nodes that exceed the limit as reference nodes, and analyze the relationship between the current node and the branch in the power grid, which is expressed by the PTDF matrix;

[0008] According to the PTDF matrix combined with 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, so as to adjust 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 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 active power value.

[0012] Further, including;

[0013] The relationship between the power transfer between the current node and the branch in the power grid is expressed 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 method of calculating the sensitivity of each generator to the power transmission distribution factor of the over-limit line according to the PTDF matrix combined with 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 numbered g1, g2, ..., g l ,…,g k According to the node number gl where the generator is located, obtain the branches b1, b2, ..., b1 of the node that exceed the limit of all power flows 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] In the formula, R l is the generator g l The ratio of sensitivity to the total sensitivity.

[0023] Further, including;

[0024] The step of 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 is 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 cross-section power flow over-limit of a new energy power grid, 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, initialize the access parameters of DG, specifically the active power, reactive power and its limit, etc., and then incrementally iterate the active power of DG. Specifically, each time a fixed power value is added to the previous iteration value, the Newton method is repeatedly used to calculate the power flow, and 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 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;

[0030] The representation module is used to select multiple over-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 transmission distribution factor of the over-limit line according to the PTDF matrix combined with the generators in the node, and then obtain the power transmission 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, so as to adjust the power of the generator.

[0033] Further, including;

[0034] In the over-limit judgment module, the line over-limit situation obtained when 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 according to the PTDF matrix combined with the generators in the node, and then the power transmission distribution factor sensitivity ratio of each generator is obtained, which specifically includes:

[0041] For each generator numbered g1, g2, ..., g l ,…,g k According to the node number gl where the generator is located, obtain the branches b1, b2, ..., b1 of the node that exceed the limit of all power flows 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] In the formula, R l is the generator g l The ratio of sensitivity to the 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, so as to adjust the power of the generator, which specifically includes:

[0048] The ratio of the sensitivity of each generator to the total sensitivity is 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] The present invention proposes a power flow over-limit safety control method based on power sensitivity analysis. Through the sensitivity analysis of section power, the output and load distribution are optimized, or a decision-making optimization basis is provided for emergency control measures after a fault, so as to determine the section operation control strategy and propose a section limit power control scheme. The simulation example results of the present invention prove the effectiveness and feasibility of the index algorithm.

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

[0054] Figure 1 It is a flow chart of a method for controlling the over-limit safety of 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 current carrying ratios of various branches of the simulation results described in the embodiment of the present invention;

[0056] Figure 3 It is a schematic diagram of the structure 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 be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] like Figure 1As shown, the present invention proposes a method for controlling the over-limit power flow of a section of a power grid 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, and the node voltage and branch current ratio at the initial and over-limit times are output. The access value of the distributed power source (DG) is gradually increased, and the power flow calculation of the system is performed, 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 re-performed to verify the adjustment effect.

[0059] The specific steps are as follows:

[0060] S1 iterates the connected DG power incrementally and uses the Newton method to calculate the power flow after each iteration. 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 are output and the iteration is stopped.

[0061] Specifically, it includes: initializing the DG access parameters, such as node number and initial power value, and iterating the DG power incrementally, increasing the fixed power value each time. After each iteration, the Newton method is used to calculate the power flow, record the node voltage and branch current ratio, and 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 are output and the iteration is stopped. The line over-limit situation under DG access is obtained, specifically the branches b1, b2, b3... where the power flow exceeds the limit and the nodes n1, n2, n3... where the voltage exceeds the limit.

[0062] S2. Select the generator of the reference node as the 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 that is used to generate 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 in the , 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 over-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 absolute value sum of the PTDF elements corresponding to all overload branches b1, b2, b3, etc. is obtained according to the node where the generator is located, and this is taken 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 derive the ratio of each generator's sensitivity to the total sensitivity.

[0080] S4. Calculate the power adjustment amount of each generator according to the sensitivity ratio, issue a power reduction instruction according to the calculated adjustment amount, adjust the power of the generator, recalculate the power flow to verify the adjustment effect, and solve the problem of over-limit power flow in the branch of the adjusted system, that is, the branch current ratio is reduced to less than 1. That is, the present invention detects the branch current and node voltage simultaneously in the simulation of the cross-section over-limit caused by DG access. In actual calculation, the branch current always exceeds the limit first, and the active power has a small impact on the node voltage, so the node voltage does not exceed the limit. The node voltage detection is only a part of the over-limit judgment module below, and the only real improvement is the over-limit power flow of the branch.

[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 the sensitivity of each generator 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] Specific:

[0085] In this embodiment, the sensitivity of the power transmission distribution factor of each generator to the over-limit line is calculated according to the PTDF matrix combined with 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 numbered g1, g2, ..., g l ,...,g k , according to the node number g where the generator is located l And obtain the node for all branches b1, b2, ..., b that exceed 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] In the formula, R l is the generator g l The ratio of sensitivity to the 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, so as to adjust the power of the generator, which specifically includes:

[0092] The ratio of the sensitivity of each generator to the total sensitivity is 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 by 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 provides a specific example to further verify the feasibility and effectiveness of the proposed power transmission distribution factor-based cross-section power flow safety control method for power grids containing new energy sources. The classic IEEE 39-node network used in this example includes 10 generators and 46 transmission lines, of which 31 nodes are balancing nodes.

[0096] At nodes 15 and 16, a distributed power source DG with an initial value of 50MW is connected, and its value is continuously incremented and iterated until an over-limit situation occurs. The iteration step is 20MW. Specifically, the current of branch 13 exceeds the limit in the 8th iteration. The basic power flow sensitivity matrix is ​​calculated. The total dimension of the matrix is ​​39×46. Each element corresponds to the change in the active power flow of the line due to the node output adjustment.

[0097] When adjusting the active 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 branches 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 the proportion of power reduction command, 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 output of the generator according to the calculation results in the above table, the over-limit situation of the line can be finally solved. Figure 2 As shown, 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 allocation method of the present invention and updating the power flow calculation results, the over-limit situation of the branch was solved, and the branch current ratio was within a safe range.

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

[0107] The over-limit judgment module is used to initialize the access parameters of the DG, iterate the DG power incrementally, increase the fixed power value each time, use the Newton method to calculate the power flow after each iteration, record the node voltage and branch current ratio at this time, and when it is detected that the node voltage or branch current ratio exceeds the limit, output the calculation results of the bus, generator and branch that exceed the limit and stop the iteration, and obtain the line over-limit situation when the DG is connected;

[0108] The representation module is used to select multiple over-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 transmission distribution factor of the over-limit line according to the PTDF matrix combined with the generators in the node, and then obtain the power transmission 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, so as to adjust 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 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 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 according to the PTDF matrix combined with the generators in the node, and then the power transmission distribution factor sensitivity ratio of each generator is obtained, which specifically includes:

[0119] For each generator numbered g1, g2, ..., g l ,…,g k , according to the node number g where the generator is located l And obtain the node for all branches b1, b2, ..., b that exceed 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] In the formula, R l is the generator g l The ratio of sensitivity to the 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, so as to adjust the power of the generator, which specifically includes:

[0126] The ratio of the sensitivity of each generator to the total sensitivity is 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 by 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 section of a power grid containing new energy sources described in the present invention are similar to the corresponding safety control method for over-limit power flow in a section of a power grid containing new energy sources, and will not be repeated here.

[0130] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, 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 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 other 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 can 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 these modifications and variations 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 also intended to include these modifications and variations.

Claims

1. A method for controlling the over-limit safety of power flow in a section of a power grid 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 access parameters of DG, specifically: access the distributed power generation DG to several nodes in the current network, and iterate the active power of DG incrementally, specifically: each time a fixed power value is added to the previous iteration value, and the Newton method is repeatedly used to calculate the power flow, 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, and when it is detected that the node voltage or branch current ratio exceeds the limit, the calculation results and iteration times 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 the power transmission distribution factor of each generator to the over-limit line is calculated, and then the sensitivity ratio of the power transmission distribution factor of each generator is obtained; 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; 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 section containing new energy sources according to claim 1 is characterized in that: The line over-limit situation obtained when the DG is connected specifically includes: the branch numbers of the over-limit flow b1, b2, ..., b N and the node numbers 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 active power value.

3. The method for controlling the over-limit safety of power flow in a power grid section containing new energy sources according to claim 2 is characterized in that: The relationship between the power transfer between the current node and the branch in the power grid is expressed 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 section of a power grid containing new energy sources according to claim 3 is characterized in that: The method of calculating the sensitivity of each generator to the power transmission distribution factor of the over-limit line according to the PTDF matrix combined with 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 numbered 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 corresponding node of the generator for all branches b1, b2, ..., b 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 generators participating in the dispatch is calculated, and the ratio of the sensitivity of each generator to the total sensitivity is obtained: In the formula, R l is the generator g l The ratio of sensitivity to the total sensitivity.

5. The method for controlling the over-limit safety of power flow in a section of a power grid containing new energy sources according to claim 4 is characterized in that: The step of 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 is R l Based on this, the output reduction command issued 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 limit crossing 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 power 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, initialize the access parameters of DG, specifically: access the distributed power generation DG to several nodes in the current network, and iterate the active power of DG incrementally, specifically: each time a fixed power value is added to the previous iteration value, and the Newton method is repeatedly used to calculate the power flow, 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, and when it is detected that the node voltage or branch current ratio exceeds the limit, the calculation results and iteration times of the busbar, generator, and branch that exceed the limit 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 over-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; A sensitivity ratio calculation module is used to calculate the sensitivity of each generator to the power transmission distribution factor of the over-limit line according to the PTDF matrix combined with 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 according to the sensitivity ratio, and issue a power reduction instruction according to the calculated adjustment amount, so as to adjust the power of the generator; analyze the power adjustment amount of the generator corresponding to other nodes in the power grid, and adjust the power of the corresponding generator, so as to recalculate the power flow of the power system to verify the effect after adjustment.

7. The cross-section power flow over-limit safety control system of the 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 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 active power value.

8. The cross-section power flow over-limit safety control system of the 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 of the power grid containing new energy sources according to claim 8 is characterized in that: In the sensitivity ratio calculation module, According to the PTDF matrix combined with the generators in the node, the sensitivity of each generator to the power transmission distribution factor of the over-limit line is calculated, and then the sensitivity ratio of the power transmission distribution factor of each generator is obtained, which includes: For each generator numbered 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 corresponding node of the generator for all branches b1, b2, ..., b 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 generators participating in the dispatch is calculated, and the ratio of the sensitivity of each generator to the total sensitivity is obtained: In the formula, R l is the generator g l The ratio of sensitivity to the total sensitivity.

10. The cross-section power flow over-limit safety control system of the 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, so as to adjust the power of the generator, which specifically includes: The ratio of the sensitivity of each generator to the total sensitivity is 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 limit crossing occurs, P l is the corresponding generator g l The power reduction amount is g l The generator power is reduced by P l .

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