Line overload emergency control method based on power flow tracking and power sensitivity

Abstract

The invention relates to a line overload emergency control method based on power flow tracking and power sensitivity, and belongs to the technical field of power grids. The method comprises the steps of calculating the power flow of a line in an emergency state; searching an overload line; determining a control node group; and calculating the power sensitivity of each node to the overload line. A power flow tracking method is used to determine a generator node and a load node which have great influence on an overload line. Meanwhile, in order to avoid load shedding, the power flow tracking method can also provide power allocation information from the load to the generator, and a control node group is determined. Solving of the branch-node power sensitivity is simplified, the control speed is further improved, the branch-node power sensitivity method is adopted to judge the power adjustment direction of the control node group, and the problem that the power adjustment direction of the power flow tracking method is uncertain is solved. The adjustment amount of the control node group is calculated in combination with the adjustment rate of the generator, and the control node group is controlled by adopting a reverse equivalent pairing principle, so that the operation is closer to reality.

Description

Technical Field

[0001] The invention belongs to the technical field of power grids, and in particular relates to a line overload emergency control method based on power flow tracking and power sensitivity. Background Art

[0002] Major power outages caused by extreme events such as natural disasters, chain accidents, and cyber attacks will not only cause damage to power system equipment and power outages, but may also seriously affect industrial production and commercial activities, and even affect social stability and national energy security.

[0003] In summary, these extreme events with low probability and high risk will cause the performance of the power system to drop sharply, seriously affecting people's daily life. In modern production and life, we are increasingly dependent on electricity and are increasingly inseparable from it. Therefore, it is of great significance to ensure the continuous supply of electricity in extreme events such as natural disasters, chain accidents, and cyber attacks.

[0004] At present, the emergency control methods for solving line overload are: mathematical programming method, sensitivity method and power flow tracking method. The mathematical programming method regards the elimination of overloaded lines as an optimization problem. It constructs an optimization model through the control of each node on the overloaded line and the constraints of each line in the system, and solves the model by using the planning method. However, in the process of solving the problem, many devices are adjusted and the calculation is complicated. There may also be problems such as multiple solutions or non-convergence of calculation. There are usually two types of sensitivity methods. The traditional sensitivity method mostly uses the DC power flow method when calculating the sensitivity, and the balancing machine does not participate in the adjustment; the other sensitivity method derives the branch-node power sensitivity based on the current correlation coefficient matrix, and uses the branch-node power sensitivity and reverse adjustment method to obtain an emergency control method for solving line overload. However, these two sensitivity methods have a greater relationship with the power grid topology and network parameters when calculating the sensitivity, and have a smaller relationship with the actual operating parameters of the power grid, which will bring about a large calculation error. The power flow tracking method mainly analyzes the active distribution relationship between the generator output and the transmission line and the load. The overloaded line is eliminated by adjusting the generator nodes and load nodes with large line occupancy. However, the power flow tracking method cannot determine the power adjustment direction of the adjustment node group. Therefore, how to overcome the shortcomings of the existing technology is an urgent problem to be solved in the field of power grid technology. The above three methods do not consider the problem of the active power regulation rate of the generator. In actual operation, the output of the generator may be difficult to adjust in time due to the constraints of the generator regulation rate, especially when encountering severe overload. Summary of the invention

[0005] The purpose of the present invention is to solve the deficiencies of the prior art and to provide a line overload emergency control method based on power flow tracking and power sensitivity.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A line overload emergency control method based on power flow tracking and power sensitivity comprises the following steps:

[0008] Step (1), calculating the power flow of the line in an emergency state;

[0009] Step (2), finding the overloaded line;

[0010] Step (3), determining the control node group;

[0011] Step (4), calculating the power sensitivity of each node to the overloaded line and determining the power adjustment direction of the control node group;

[0012] Step (5), calculating the adjustment amount of the control node group in combination with the generator adjustment rate;

[0013] Step (6), determine whether the line overload can be eliminated by adjusting the generator output only; if so, formulate a generator adjustment plan; if not, proceed to the next step;

[0014] Step (7), determine the generator set G + Is there upward adjustment capability? If so, increase the generator set G + Output and increase The load power is determined to determine whether the overload line is eliminated, and the process goes to step (10); if not, the process goes to the next step;

[0015] Step (8), determine the generator set G - Is there downward adjustment capability? If so, reduce the generator set G - Output and reduction The load power is determined to determine whether the overload line is eliminated, and the process goes to step (10); if not, the process goes to the next step;

[0016] Among them, G + To increase the output node, G - Reduced output node; is the node L in the power grid n For branch b Approximate sensitivity of λ b-n For line l b The current phasor of the node L n The current correlation coefficient between the injected current phasors;

[0017] Step (9), removal Generators and cuts Load;

[0018] Step (10), whether the overload line is eliminated, if so, end the calculation, if not, go to step (6).

[0019] Further, preferably, the specific method of step (3) is:

[0020] (3.1) Find the nodes that affect the overloaded line:

[0021] The set of generator nodes and load nodes to be adjusted is obtained through power flow tracking:

[0022]

[0023] In the formula, G l is the set of generator nodes that provide power to branch l, m is the number of generator nodes that provide power to branch l; L l is the set of load nodes that draw power from branch l, and n is the number of corresponding load nodes; G l,m is the mth generator node that provides power to branch l; L l,n is the nth load node that draws power from branch l;

[0024]

[0025] P l-G P is the set of power flow contributions of all generator nodes that provide power to branch l; l,Gm The power flow contribution of the mth generator node providing power to branch l to branch l;

[0026] P l-L is the set of power flow contributions to branch l from all generator nodes drawing power from branch l;

[0027] P l,Ln is the power flow contribution of the nth load node drawing power from branch l to branch l;

[0028] (3.2) Determine the nodes that have a greater impact on the overloaded line:

[0029] Occupancy rate of generator G on branch l α G,l It is defined as the power supplied by generator G to line l and the total power P on branch l. l The ratio of

[0030]

[0031] Calculate the load L's occupancy rate β for line l L,l

[0032]

[0033] Take the load node set L l As the target node, the power flow tracking method is used to obtain the set of generator nodes G that provide power to the target node. l ';

[0034] G′ l = {G′ l,1 ,G′ l,2 ,……G′ l,m} (9)

[0035] Among them, G' l,m The mth generator node that provides power to the target node;

[0036] In G l and G l 'Select the generator node set with large occupancy rate as the appropriate control node group G'(G + G - ), and use the power sensitivity to determine the power adjustment direction of the control node group.

[0037] Further, preferably, the specific method of step (4) is:

[0038] Calculate the node L in the power grid n For branch b Sensitivity S b-n for:

[0039]

[0040] Among them, U b-l and Line l b The voltage modulus and phase angle of the first end; U n-L and The nodes N i The voltage magnitude and phase angle of b-n For line l b The current phasor of the node L n The current correlation coefficient between the injected current phasors is obtained by formula (11);

[0041]

[0042] Among them, for a power grid with n nodes and b transmission lines, C(λ) is a b×n-order real matrix, C(λ) is the power grid correlation coefficient matrix; Y B is the branch susceptance matrix; A is the node association matrix; Y N is the node susceptance matrix;

[0043] According to the trigonometric identity transformation formula, equation (10) is transformed into equation (12):

[0044]

[0045] Formula (12) is approximately equivalent to formula (13):

[0046]

[0047] in, is the node L in the power grid n For branch b Approximate sensitivity of It means that when the generator output of the node decreases or the load power increases, the power of the overloaded line can be reduced; It means that when the generator output of the node increases or the load power decreases, the power of the overloaded line can be increased;

[0048] It means that the power of the overloaded line can be reduced when the generator output of the node decreases or the load power increases; It means that the power of the overloaded line can be increased when the generator output of the node increases or the load power decreases;

[0049] The nodes in the system are divided into two categories: the first category is the nodes for reducing output or increasing load, represented by the set D1; the second category is the nodes for increasing output or shedding load, represented by the set D2; the control node group G'(G + G - ) + To increase the output node, G - Reduce output node.

[0050] Further, preferably, the specific method of step (5) is:

[0051] To eliminate the overload on the line, the power adjusted by the generator is recorded as ΔP G , then the generator G i Power adjustment ΔP Gi for:

[0052] ΔP Gi =α Gi,l ΔP l ·P Gi / P l (14)

[0053] Among them, α Gi，l For the generator G i Occupancy rate; ΔP l is the overload branch power that exceeds the limit; P G,i is the power of the adjusted generator; P l is the power on the overloaded line;

[0054] Total adjustment ΔP G for:

[0055]

[0056] According to the regulation rate and emergency control time limit of each generator, the control node group G'(G + G - )'s maximum adjustment capability;

[0057] ΔP Ga =θ×t (16)

[0058] Where θ represents the generator regulation rate, t represents the emergency control time; according to the reverse equal amount pairing adjustment method, the adjustment amount ΔP of the increased output node i in each control node group is i and the adjustment amount ΔP of the reduced output node j j should be equal, then the actual adjustment limit of the control node group increase output node i and decrease output node j is:

[0059]

[0060] ΔP Gai To increase the maximum regulation capacity of output node i;

[0061] ΔP Gaj is the maximum regulation capacity of the reduced output node j.

[0062] Furthermore, preferably, in step (6), the adjustment scheme is to only adjust the generator output without cutting the load.

[0063] Compared with the prior art, the present invention has the following beneficial effects:

[0064] To eliminate line overload, it is necessary not only to determine the control node group, but also to judge the power adjustment direction of the control node group, which is not fully considered in the above methods. In view of the shortcomings of the above methods, the present invention combines the advantages of the power sensitivity method and the power flow tracking method, and proposes a line overload emergency control strategy based on power flow tracking and power sensitivity. The present invention uses the power flow tracking method to determine the generator nodes and load nodes that have a greater impact on the overloaded line. At the same time, in order to avoid load shedding, the power flow tracking method can also provide power sharing information from the load to the generator to determine the control node group. The solution of branch-node power sensitivity is simplified, and the control speed is further improved. The branch-node power sensitivity method is used to judge the power adjustment direction of the control node group, which solves the problem of uncertain power adjustment direction of the power flow tracking method. The adjustment amount of the control node group is calculated in combination with the adjustment rate of the generator, and the control node group is controlled by the reverse equal pairing principle, which makes it closer to actual operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 This is a schematic diagram of the proportional allocation principle;

[0066] Figure 2 It is the emergency control flow chart;

[0067] Figure 3 This is the IEEE39 node system diagram. DETAILED DESCRIPTION

[0068] The present invention is further described in detail below in conjunction with embodiments.

[0069] Those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the art or the product specifications are used. If the manufacturer of the materials or equipment used is not specified, they are all conventional products that can be purchased.

[0070] Example 1

[0071] A line overload emergency control method based on power flow tracking and power sensitivity comprises the following steps:

[0072] Step (1), calculating the power flow of the line in an emergency state;

[0073] Step (2), finding the overloaded line;

[0074] Step (3), determining the control node group;

[0075] Step (4), calculating the power sensitivity of each node to the overloaded line and determining the power adjustment direction of the control node group;

[0076] Step (5), calculating the adjustment amount of the control node group in combination with the generator adjustment rate;

[0077] Step (6), determine whether the line overload can be eliminated by adjusting the generator output only; if so, formulate a generator adjustment plan; if not, proceed to the next step;

[0078] Step (7), determine the generator set G + Is there upward adjustment capability? If so, increase the generator set G + Output and increase The load power is determined to determine whether the overload line is eliminated, and the process goes to step (10); if not, the process goes to the next step;

[0079] Step (8), determine the generator set G - Is there downward adjustment capability? If so, reduce the generator set G - Output and reduction The load power is determined to determine whether the overload line is eliminated, and the process goes to step (10); if not, the process goes to the next step;

[0080] Among them, G + To increase the output node, G - Reduced output node; is the node L in the power grid n For branch b Approximate sensitivity of λ b-n For line l b The current phasor of the node L n The current correlation coefficient between the injected current phasors;

[0081] Step (9), removal Generators and cuts Load;

[0082] Step (10), whether the overload line is eliminated, if so, end the calculation, if not, go to step (6).

[0083] Example 2

[0084] A line overload emergency control method based on power flow tracking and power sensitivity comprises the following steps:

[0085] Step (1), calculating the power flow of the line in an emergency state;

[0086] Step (2), finding the overloaded line;

[0087] Step (3), determining the control node group;

[0088] Step (4), calculating the power sensitivity of each node to the overloaded line and determining the power adjustment direction of the control node group;

[0089] Step (5), calculating the adjustment amount of the control node group in combination with the generator adjustment rate;

[0090] Step (6), determine whether the line overload can be eliminated by adjusting the generator output only; if so, formulate a generator adjustment plan; if not, proceed to the next step;

[0091] Step (7), determine the generator set G + Is there upward adjustment capability? If so, increase the generator set G + Output and increase The load power is determined to determine whether the overload line is eliminated, and the process goes to step (10); if not, the process goes to the next step;

[0092] Step (8), determine the generator set G -Is there downward adjustment capability? If so, reduce the generator set G - Output and reduction The load power is determined to determine whether the overload line is eliminated, and the process goes to step (10); if not, the process goes to the next step;

[0093] Among them, G + To increase the output node, G - Reduced output node; is the node L in the power grid n For branch b Approximate sensitivity of λ b-n For line l b The current phasor of the node L n The current correlation coefficient between the injected current phasors;

[0094] Step (9), removal Generators and cuts Load;

[0095] Step (10), whether the overload line is eliminated, if so, end the calculation, if not, go to step (6).

[0096] The specific method of step (3) is:

[0097] (3.1) Find the nodes that affect the overloaded line:

[0098] The set of generator nodes and load nodes to be adjusted is obtained through power flow tracking:

[0099]

[0100] In the formula, G l is the set of generator nodes that provide power to branch l, m is the number of generator nodes that provide power to branch l; L l is the set of load nodes that draw power from branch l, and n is the number of corresponding load nodes; G l,m is the mth generator node that provides power to branch l; L l,n is the nth load node that draws power from branch l;

[0101]

[0102] P l-G P is the set of power flow contributions of all generator nodes that provide power to branch l; l,Gm The power flow contribution of the mth generator node providing power to branch l to branch l;

[0103] P l-Lis the set of power flow contributions to branch l from all generator nodes drawing power from branch l;

[0104] P l,Ln is the power flow contribution of the nth load node drawing power from branch l to branch l;

[0105] (3.2) Determine the nodes that have a greater impact on the overloaded line:

[0106] Occupancy rate of generator G on branch l α G,l It is defined as the power supplied by generator G to line l and the total power P on branch l. l The ratio of

[0107]

[0108] Calculate the load L's occupancy rate β for line l L,l

[0109]

[0110] Take the load node set L l As the target node, the power flow tracking method is used to obtain the set of generator nodes G that provide power to the target node. l ';

[0111] G′ l = {G′ l,1 ,G′ l,2 ,……G′ l,m} (9)

[0112] Among them, G' l,m The mth generator node that provides power to the target node;

[0113] In G l and G l 'Select the generator node set with large occupancy rate as the appropriate control node group G'(G + G - ), and use the power sensitivity to determine the power adjustment direction of the control node group.

[0114] The specific method of step (4) is:

[0115] Calculate the node L in the power grid n For branch b Sensitivity S b-n for:

[0116]

[0117] Among them, U b-l and Line l bThe voltage modulus and phase angle of the first end; U n-L and The nodes N i The voltage magnitude and phase angle of b-n For line l b The current phasor of the node L n The current correlation coefficient between the injected current phasors is obtained by formula (11);

[0118]

[0119] Among them, for a power grid with n nodes and b transmission lines, C(λ) is a b×n-order real matrix, C(λ) is the power grid correlation coefficient matrix; Y B is the branch susceptance matrix; A is the node association matrix; Y N is the node susceptance matrix;

[0120] According to the trigonometric identity transformation formula, equation (10) is transformed into equation (12):

[0121]

[0122] Formula (12) is approximately equivalent to formula (13):

[0123]

[0124] in, is the node L in the power grid n For branch b Approximate sensitivity of It means that when the generator output of the node decreases or the load power increases, the power of the overloaded line can be reduced; It means that when the generator output of the node increases or the load power decreases, the power of the overloaded line can be increased;

[0125] It means that the power of the overloaded line can be reduced when the generator output of the node decreases or the load power increases; It means that the power of the overloaded line can be increased when the generator output of the node increases or the load power decreases;

[0126] The nodes in the system are divided into two categories: the first category is the nodes for reducing output or increasing load, represented by the set D1; the second category is the nodes for increasing output or shedding load, represented by the set D2; the control node group G'(G + G - ) + To increase the output node, G - Reduce output node.

[0127] The specific method of step (5) is:

[0128] To eliminate the overload on the line, the power adjusted by the generator is recorded as ΔP G , then the generator G i Power adjustment ΔP Gi for:

[0129] ΔP Gi =α Gi,l ΔP l ·P Gi / P l (14)

[0130] Among them, α Gi，l For the generator G i Occupancy rate; ΔP l is the overload branch power that exceeds the limit; P G,i is the power of the adjusted generator; P l is the power on the overloaded line;

[0131] Total adjustment ΔP G for:

[0132]

[0133] According to the regulation rate and emergency control time limit of each generator, the control node group G'(G + G - )'s maximum adjustment capability;

[0134] ΔP Ga =θ×t (16)

[0135] Where θ represents the generator regulation rate, t represents the emergency control time; according to the reverse equal amount pairing adjustment method, the adjustment amount ΔP of the increased output node i in each control node group is i and the adjustment amount ΔP of the reduced output node j j should be equal, then the actual adjustment limit of the control node group increase output node i and decrease output node j is:

[0136]

[0137] ΔP Gai To increase the maximum regulation capacity of output node i;

[0138] ΔP Gaj is the maximum regulation capacity of the reduced output node j.

[0139] In step (6), the adjustment plan is to only adjust the generator output without cutting the load.

[0140] Example 3

[0141] 1. Trend tracking method

[0142] Power flow tracking is to find the power distribution relationship in the network through analysis and calculation of a specific operating state in the system, and to clarify which loads the power of a specific generator is sent to, and which generators the power of a specific load node comes from. Power flow tracking is based on the principle of proportional distribution. The principle of proportional distribution is shown in Figure 1 Define P as the power flowing through the node, which is equal to the total power flowing into the node and also equal to the total power flowing out of the node. The proportional distribution principle defines the inflow power P a , P b At the outgoing power P c , P d The shares of are shown in formulas (1), (2), (3) and (4) respectively.

[0143]

[0144]

[0145]

[0146]

[0147] Pac is the inflow power P a At the outgoing power P c the share of

[0148] Pad is the inflow power P a At the outgoing power P d the share of

[0149] Pbc is the inflow power P b At the outgoing power P c the share of

[0150] Pbd is the inflow power P b At the outgoing power P d The share of .

[0151] The power flow tracing method can provide the power ratio of the damaged component in the load and calculate the loss of each load. Before power flow tracing, the system needs to be converted into a lossless network.

[0152] 2. Combined methods to eliminate line overload

[0153] Eliminating overloaded lines is generally divided into three steps:

[0154] (1) Determine the control node group;

[0155] (2) Determine the power adjustment direction of the control node group;

[0156] (3) Calculate the adjustment amount of the control node group.

[0157] Specifically:

[0158] (1) Determine the control node group

[0159] When calculating power sensitivity using the sensitivity method, it is mainly related to the topological structure and parameters of the power grid, and the actual operating parameters of the power grid have little effect on it. However, the power flow distribution of the overload line is not only related to the topological structure of the power grid, but also to the actual operation of the power grid. Therefore, the control node group determined by the sensitivity method is not necessarily the best one. Because the operating conditions of different units are different in practice, the adjustment schemes are also different, and the scope of application is naturally different. Therefore, the present invention uses the power flow tracking method to determine the control node group.

[0160] Before power flow tracing, the system needs to be transformed into a lossless network, and the overloaded line is taken as the target branch for power flow tracing. The generator nodes and load nodes are tracked separately to obtain the set of generator nodes that provide power to the target branch and the set of load nodes that draw power from the target branch.

[0161] (1.1) Find the nodes that affect the overloaded line

[0162] The set of generator nodes and load nodes to be adjusted is obtained through power flow tracking:

[0163]

[0164] In the formula, G l is the set of generator nodes that provide power to branch l, m is the number of generator nodes that provide power to branch l; L l is the set of load nodes that draw power from branch l, and n is the number of corresponding load nodes; G l,m is the mth generator node that provides power to branch l; L l,n is the nth load node that draws power from branch l;

[0165] Branch i, i=1, 2, ..., l, refers to the set of all branches in the network, that is, branch 1, branch 2 ... branch l; the target branch refers to the overloaded line after the overload occurs.

[0166] G can be obtained through trend tracking l and L l The power flow contributions of each node to branch l are:

[0167]

[0168] P l-GP is the set of power flow contributions of all generator nodes that provide power to branch l; l,Gm The power flow contribution of the mth generator node providing power to branch l to branch l;

[0169] P l-L is the set of power flow contributions to branch l from all generator nodes drawing power from branch l;

[0170] P l,Ln is the power flow contribution of the nth load node drawing power from branch l to branch l;

[0171] In actual power systems, eliminating an overloaded line requires adjusting G l and L l The output of the generator nodes and load nodes in the system usually only adjusts the generator nodes and load nodes that contribute more to the overloaded line, and there is no need to adjust all of them. Therefore, it is necessary to find out the nodes that have a greater impact on the overloaded line and adjust them.

[0172] (1.2) Determine the nodes that have the greatest impact on the overloaded line

[0173] The present invention introduces the concept of occupancy rate in the control process, and only the generator nodes and load nodes with larger occupancy rates need to be adjusted.

[0174] Occupancy rate of generator G on branch l α G,l It is defined as the power supplied by generator G to line l and the total power P on branch l. l ratio.

[0175]

[0176] Similarly, the occupancy rate β of load L on line l can be calculated L,l

[0177]

[0178] In order to avoid load shedding, find the generator node that provides power to the load node, with the load node set L l As the target node, the power flow tracking method is used to obtain the set of generator nodes G that provide power to the target node. l '.

[0179] G′ l = {G′ l,1 ,G′ l,2 ,……G′ l,m} (9)

[0180] G' l,m It is the mth generator node that provides power to the target node.

[0181] In G l and G l 'Select the generator node set with large occupancy rate as the appropriate control node group G'(G + G - ), and use power sensitivity to determine the power adjustment direction of the control node group. The large occupancy rate is used as the standard for selecting the generator node set; when adjusting, only the output of the generator can be adjusted.

[0182] The advantage of the power flow tracking method is that it can clearly know the contribution of each generator output to the power transmission line and load power of the power grid. The power flow tracking method can accurately obtain the nodes that affect the overloaded line, but these nodes may be negatively correlated with the power change of the overloaded line, that is, reducing the output of the node will lead to an increase in the power of the overloaded line. Therefore, the power flow tracking method cannot determine the power adjustment direction of the control node group. The branch-node power sensitivity method can divide the nodes that affect the overloaded line into two categories, one is the nodes that are positively correlated with the active power change of the overloaded line; the other is the nodes that are negatively correlated with the active power change of the overloaded line. The branch-node power sensitivity method is used to determine the direction of the power adjustment of the control node group.

[0183] (2) Determine the power adjustment direction of the control node group

[0184] The branch-node power sensitivity method is based on the current correlation coefficient matrix and derives the power sensitivity matrix between the node injection power variable and the line power variable according to the grid topology and node voltage data provided in real time by the wide area measurement system. n For branch b Sensitivity S b-n for:

[0185]

[0186] Among them, U b-l and Line l b The voltage modulus and phase angle of the first end; U n-L and The nodes N i The voltage magnitude and phase angle of b-n For line l b The current phasor of the node L n The current correlation coefficient between the injected current phasors is obtained by formula (11);

[0187]

[0188] Among them, for a power grid with n nodes and b transmission lines, C(λ) is a b×n-order real matrix, C(λ) is the power grid correlation coefficient matrix; Y B is the branch susceptance matrix; A is the node association matrix; Y N is the node susceptance matrix.

[0189] According to the trigonometric identity transformation formula, equation (10) is transformed into equation (12):

[0190]

[0191] In the power system flow calculation, the voltage amplitude and phase angle of each node are not much different, so is a value close to 1. is also a value close to 1. The multiplication of these two values ​​close to 1 has little effect on the result, so formula (12) can be approximately equivalent to formula (13).

[0192]

[0193] in, is the node L in the power grid n For branch b The sensitivity approximation of ; From the simplified formula (13), it can be seen that the calculation amount is greatly simplified and the calculation speed is improved, which provides a guarantee for the rapid identification of faulty components.

[0194] According to formula (13), we can get: It means that the power of the overloaded line can be reduced when the generator output of the node decreases or the load power increases; It means that when the generator output of the node increases or the load power decreases, the power of the overloaded line can be increased. Therefore, the nodes in the system can be divided into two categories: the first category is the nodes with reduced output or increased load, represented by the set D1; the second category is the nodes with increased output or reduced load, represented by the set D2. The control node group G'(G + G - ) + To increase the output node, G - It is the node for reducing output.

[0195] It means that the power of the overloaded line can be reduced when the generator output of the node decreases or the load power increases; It means that the power of the overloaded line can be increased when the generator output of the node increases or the load power decreases;

[0196] The nodes in the system are divided into two categories: the first category is the nodes for reducing output or increasing load, represented by the set D1; the second category is the nodes for increasing output or shedding load, represented by the set D2; the control node group G'(G+ G - ) + To increase the output node, G - Reduce output node.

[0197] Step (3) aims to select the adjustment node, and step (4) determines the adjustment direction of the output node by calculation. When When, reduce the load.

[0198] (3) Calculate the adjustment amount of the control node group

[0199] When the system is overloaded, the control node group G'(G + G - ), according to the overload ratio of the line and the line occupancy rate, and combined with the generator adjustment rate, the output is increased or decreased proportionally, thereby eliminating the over-limit power on the overloaded line.

[0200] To eliminate the overload on the line, the power adjusted by the generator is recorded as ΔP G , then the generator G i The power adjustment is:

[0201] ΔP Gi =α Gi,l ΔP l ·P Gi / P l (14)

[0202] Among them, α Gi，l For the generator G i Occupancy rate; ΔP l is the overload branch power that exceeds the limit; P G,i is the power of the adjusted generator; P l is the power on the overloaded line.

[0203] Total adjustment ΔP G for:

[0204]

[0205] ΔP Gi is the adjustment of generator i, ΔP G is the total adjustment amount;

[0206] According to the regulation rate and emergency control time limit of each generator, the control node group G'(G + G - )'s maximum adjustment capability.

[0207] ΔP Ga =θ×t (16)

[0208] Among them, θ represents the generator regulation rate, and t represents the emergency control time. According to the reverse equal amount pairing adjustment method, the adjustment amount ΔP of the increased output node i in each control node group is i and the adjustment amount ΔP of the reduced output node j j should be equal, then the actual adjustment limit of the control node group increase output node i and decrease output node j is:

[0209]

[0210] 3. Emergency control process to eliminate line overload

[0211] When a line is overloaded, in order to protect the safety of other transmission lines, an emergency control strategy needs to be adopted in a short time to eliminate the overloaded line and restore the system to a safe state. The emergency control steps are as follows:

[0212] (1) Calculate the power flow of the line in an emergency;

[0213] (2) Find the overloaded circuit;

[0214] (3) Determine the control node group;

[0215] (4) Calculate the power sensitivity of each node to the overloaded line and determine the power adjustment direction of the control node group;

[0216] (5) Calculate the adjustment amount of the control node group in combination with the generator adjustment rate;

[0217] (6) Can the line overload be eliminated by adjusting the generator output only? If yes, formulate a generator adjustment plan (plan: only adjust the generator output without cutting the load), if not, proceed to the next step;

[0218] (7) Generator set G + Is there upward adjustment capability? If so, increase the generator G + Output and increase Load power, if not, proceed to the next step;

[0219] (8) Generator set G - Is there downward adjustment capability? If so, reduce the generator G - Output and reduction Load power, if not, proceed to the next step;

[0220] (9) Resection Generators and cuts Load;

[0221] (10) Is the overload line eliminated? If so, end the calculation; if not, go to (6).

[0222] Emergency control flow chart Figure 2 shown.

[0223] Application Examples

[0224] To verify the effectiveness of the present invention, three methods are used as emergency control strategies to eliminate line overload. In the IEEE39 node system, line 6-11 is disconnected due to a fault, causing overloads on lines 14-4, 10-13 / 13-14. The overload line power is shown in Table 1. In order to be closer to actual operation, the time of the emergency control strategy is set to 2 minutes. For grid-connected thermal power generating units, it is usually required that the output adjustment speed per minute is greater than 5% of the maximum output; the IEEE39 node system diagram is as follows Figure 3 As shown, the relevant data of the active output of 10 generators are shown in Table 2. In the following, method 1 is the power flow tracking method; method 2 is the branch-node power sensitivity method; method 3 is the power flow tracking and power sensitivity combination method of the present invention.

[0225] Table 1 Overload of faulty lines in IEEE39 system

[0226] Overload line Normal power / MW Fault power / MW Maximum transmission power / MW Overload rate 14-4 265.42 528.16 500 1.056 10-13 322.10 617.40 600 1.029 13-14 317.18 639.88 600 1.066

[0227] Table 2 IEEE39 bus system generator data

[0228] Generator Node Maximum output / MW Real-time output / MW Regulation capacity / MW 30 1040 250 104 31 745.94 677.87 74.594 32 725 650 72.5 33 652 632 65.2 34 508 508 50.8 35 687 650 68.7 36 580 560 58 37 564 540 56.4 38 865 830 86.5 39 1100 1000 110

[0229] The control node groups are determined using three methods as shown in Table 3, Table 4, and Table 5 respectively.

[0230] Table 3 Control node groups determined by method 1

[0231]

[0232]

[0233] Table 4 Method 2 determines the control node group

[0234]

[0235] Table 5 Method 3 determines the control node group

[0236]

[0237] Taking the three overload lines as the target lines, the control node group is determined by three methods respectively. As shown in Table 3, method 1 selects the nodes with large occupancy rate of the overload line, the generator node No. 32 and the load node No. 4 as the control node group; as shown in Table 4, method 2 selects the nodes with large power sensitivity to the overload line, the output reduction node No. 32 and the output increase node No. 39 as the control node group; as shown in Table 5, method 3 first selects the generator node No. 32 and the load nodes No. 4, 15, and 8 with large occupancy rate of the overload line, and then selects the generator No. 31 that has an impact on the three overload lines according to the generator nodes No. 31, 32, and 33 that provide power to the load, and finally selects the generator node No. 32 and the generator node No. 31 as the control node group, and uses the power sensitivity to determine the direction of power adjustment.

[0238] Three methods are used to calculate the power adjustment amount of the control node group. The emergency control strategies of the three methods are shown in Table 6.

[0239] Table 6 Emergency control strategies of three methods

[0240]

[0241] As shown in Table 6, all three methods can eliminate line overload. Method 3 has the same adjustment amount as Method 1, but different control node groups. Method 1 needs to reduce load node 4 by 40.51MW, while Method 3 does not need to reduce load and avoids load shedding. Method 3 has different control node groups and adjustment amounts from Method 2. The adjustment amount of Method 2 is 52.8MW, while the adjustment amount of Method 3 is 40.51MW. The adjustment amount of Method 3 is less than that of Method 2.

[0242] The present invention verifies the effectiveness of the combined method of power flow tracking and power sensitivity. Compared with method 1, this method avoids load shedding. Compared with method 2, the power adjustment amount obtained by this method is smaller, which means that the control node group determined by this method is better than the control node group determined by method 2. If the time of the emergency control strategy is set to 1 minute, the conventional method needs to cut off the generator No. 32 and reduce the load node No. 15 by 320MW, and reduce the load node No. 16 by 50MW to eliminate the line overload. With the method of the present invention, it is only necessary to cut off the generator No. 32 and reduce the load node No. 12 by 370MW to eliminate the overload. The present invention only adjusts one load.

[0243] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A line overload emergency control method based on power flow tracking and power sensitivity, characterized in that: The steps include: Step (1), calculating the power flow of the line in an emergency state; Step (2), finding the overloaded line; Step (3), determining the control node group; Step (4), calculating the power sensitivity of each node to the overloaded line and determining the power adjustment direction of the control node group; Step (5), calculating the adjustment amount of the control node group in combination with the generator adjustment rate; Step (6), determine whether the line overload can be eliminated by adjusting the generator output only; if so, formulate a generator adjustment plan; if not, proceed to the next step; Step (7), determine the generator set G + Is there upward adjustment capability? If so, increase the generator set G + Output and increase S' K-i >0 load power, determine whether the overload line is eliminated, and then go to step (10); if not, proceed to the next step; Step (8), determine the generator set G - Is there downward adjustment capability? If so, reduce the generator set G - Output and reduction S' K-i <0 load power, determine whether the overload line is eliminated, and then proceed to step (10); if not, proceed to the next step; Among them, G + To increase the output node, G - Reduced output node; S' b-n is the node L in the power grid n For branch b Approximate sensitivity of S' b-n =λ b-n ,λ b-n For line l b The current phasor of the node L n The current correlation coefficient between the injected current phasors; Step (9), remove S' K-i >0 generator and cut S K-i Load <0; Step (10), whether the overload line is eliminated, if so, end the calculation, if not, go to step (6).

2. The line overload emergency control method based on power flow tracking and power sensitivity according to claim 1 is characterized in that: The specific method of step (3) is: (3.1) Find the nodes that affect the overloaded line: The set of generator nodes and load nodes to be adjusted is obtained through power flow tracking: In the formula, G l is the set of generator nodes that provide power to branch l, m is the number of generator nodes that provide power to branch l; L l is the set of load nodes that draw power from branch l, and n is the number of corresponding load nodes; G l,m is the mth generator node that provides power to branch l; L l,n is the nth load node that draws power from branch l; P l-G ={P l,G1 ,P l,G2 ......P l,Gi ......P l,Gm } (6) P l-L ={P l,L1 ,P l,L2 ......P l,Li ......P l,Ln } P l-G P is the set of power flow contributions of all generator nodes that provide power to branch l; l,Gm The power flow contribution of the mth generator node that provides power to branch l to branch l; P l-L is the set of power flow contributions to branch l from all generator nodes drawing power from branch l; P l,Ln is the power flow contribution of the nth load node drawing power from branch l to branch l; (3.2) Determine the nodes that have a greater impact on the overloaded line: Occupancy rate of generator G on branch l α G,l It is defined as the power supplied by generator G to line l and the total power P on branch l l The ratio of Calculate the load L's occupancy rate β for line l L,l Take the load node set L l As the target node, the power flow tracking method is used to obtain the set of generator nodes G that provide power to the target node. l '; G' l ={G' l,1 ,G' l,2 ,……G' l,m } (9) Among them, G' l,m The mth generator node that provides power to the target node; In G l and G' l Select the generator node set with large occupancy rate as the appropriate control node group G'(G + G - ), and use the power sensitivity to determine the power adjustment direction of the control node group.

3. The line overload emergency control method based on power flow tracking and power sensitivity according to claim 1 is characterized in that: The specific method of step (4) is: Calculate the node L in the power grid n For branch b Sensitivity S b-n for: Among them, U b-l and Line l b The voltage modulus and phase angle of the first end; U n-L and The nodes N i The voltage magnitude and phase angle of b-n For line l b The current phasor of the node L n The current correlation coefficient between the injected current phasors is obtained by formula (11); Among them, for a power grid with n nodes and b transmission lines, C(λ) is a b×n-order real matrix, C(λ) is the power grid correlation coefficient matrix; Y B is the branch susceptance matrix; A is the node association matrix; Y N is the node susceptance matrix; According to the trigonometric identity transformation formula, equation (10) is transformed into equation (12): Formula (12) is approximately equivalent to formula (13): S' b-n =λ b-n (13) Among them, S' b-n is the node L in the power grid n For branch b Approximate sensitivity of S' b-n >0 means that when the generator output of the node decreases or the load power increases, the power of the overloaded line can be reduced; S' b-n <0 means that when the generator output of the node increases or the load power decreases, the power of the overloaded line can be increased; S' K-i >0 means that the power of the overloaded line can be reduced when the generator output of the node decreases or the load power increases; S' K-i <0 means that the power of the overloaded line can be increased when the generator output of the node increases or the load power decreases; The nodes in the system are divided into two categories: the first category is the nodes for reducing output or increasing load, represented by the set D1; the second category is the nodes for increasing output or shedding load, represented by the set D2; the control node group G'(G + G - ) + To increase the output node, G - Reduce output node.

4. The line overload emergency control method based on power flow tracking and power sensitivity according to claim 1 is characterized in that: The specific method of step (5) is: To eliminate the overload on the line, the power adjusted by the generator is recorded as ΔP G , then the generator G i Power adjustment ΔP Gi for: ΔP Gi =a Gi,l ·ΔP l ·P Gi / P l (14) Among them, α Gi，l For the generator G i Occupancy rate; ΔP l is the overload branch power that exceeds the limit; P G,i is the power of the adjusted generator; P l is the power on the overloaded line; Total adjustment ΔP G for: According to the regulation rate and emergency control time limit of each generator, the control node group G'(G + G - )'s maximum adjustment capability; ΔP Ga =θ×t (16) Where θ represents the generator regulation rate, t represents the emergency control time; according to the reverse equal amount pairing adjustment method, the adjustment amount ΔP of the increased output node i in each control node group is i and the adjustment amount ΔP of the reduced output node j j should be equal, then the actual adjustment limit of the control node group increase output node i and decrease output node j is: ΔP Gai To increase the maximum regulation capacity of output node i; ΔP Gaj is the maximum regulation capacity of the reduced output node j.

5. The line overload emergency control method based on power flow tracking and power sensitivity according to claim 1 is characterized in that: In step (6), the adjustment plan is to only adjust the generator output without cutting the load.

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