CN110797863B - Economic dispatching method considering safety constraints of N-1 and N-2 of power grid - Google Patents

Economic dispatching method considering safety constraints of N-1 and N-2 of power grid Download PDF

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CN110797863B
CN110797863B CN201911008395.9A CN201911008395A CN110797863B CN 110797863 B CN110797863 B CN 110797863B CN 201911008395 A CN201911008395 A CN 201911008395A CN 110797863 B CN110797863 B CN 110797863B
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黄丽平
狄方涛
龙洁
王逸飞
郭俊韬
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Abstract

The application discloses an economic dispatching method considering the safety constraints of a power grid N-1 and a power grid N-2, heavy load lines which are easy to have cascading failures are screened out by carrying out power grid N-1 power flow analysis on an economic dispatching model P0 which does not consider the safety constraints, N-2 fault pairs are formed by the heavy load lines and corresponding branches which are analyzed by the N-1 one by one to generate a new N-2 fault set, then power flow verification is carried out on the fault set based on branch breaking distribution factors to obtain harmful fault scenes, the harmful fault scenes are added to P0 to obtain a new economic dispatching model P1, P1 is updated through continuous verification and re-verification steps until the number of the harmful N-1 and N-2 fault scenes is zero to obtain a final dispatching model P2, a dispatching scheme meeting the criteria of the line N-1 and the N-2 is obtained by solving P2, the further propagation and development of the initial fault of the power grid N-1 are effectively avoided, and the problem that the power grid cascading failure power failure is caused by the fact that the secondary fault is easy to occur on a heavy-load line after the N-1 fault is not considered in the existing economic dispatching method considering the safety constraint of the power grid N-1 is solved.

Description

Economic dispatching method considering safety constraints of N-1 and N-2 of power grid
Technical Field
The application relates to the technical field of economic dispatching of power systems, in particular to an economic dispatching method considering safety constraints of power grids N-1 and N-2.
Background
The economic dispatching is one of the most basic and important problems in the operation of the power system, and the main task of the economic dispatching is to make a power generation plan of a whole-grid thermal power generating unit with the lowest power generation cost on the premise of meeting certain power system safe operation constraints and meet the safe and reliable power utilization requirements of users.
In a conventional economic dispatching method aiming at economic optimization, an operation state of a power grid is generally optimized and adjusted under the condition that a structure state of the power grid is assumed to be unchanged. The optimization result obtained in this way usually utilizes the power carrying capacity of some branches in the power grid to the maximum extent, and is digitally embodied, that is, some branches of the power grid in the optimization result are usually adjusted to operate near the operation limit. Such optimization results are possible for research analysis, but if used for practical grid operation adjustment guidance, it is economically redundant and not safe enough. With the increasing frequency of serious natural disasters, information network attacks and other problems, the conventional power system economic dispatching method considering the safety constraint of the power grid N-1 is not enough to ensure the safe operation of the power grid to a certain extent, which causes the attention of the power system industry to multiple faults. However, after the N-1 fault is calculated, a heavy-load line which is easy to have cascading faults can exist in the rest lines of the power grid, and the fault is caused again. Because the power system comprises a large number of power transmission elements, the multiple fault analysis has difficulty in dimension disaster, and the research of the multiple fault analysis method and the operation mode which are feasible and effective in improving the operation safety of the power system has important significance for preventing the power grid blackout accident and ensuring the operation reliability of the power grid. The existing economic dispatching method considering the N-1 safety constraint of the power grid is based on Benders decomposition, the N-1 safety check of the power grid is carried out or a line state indicator is introduced, N groups of line N-1 constraints are directly constructed and added into an economic dispatching model, the method enables the number of constraint conditions of the optimization model to be increased sharply, and the difficulty and the speed of solving the model are greatly increased.
Disclosure of Invention
The application provides an economic dispatching method considering power grid N-1 and N-2 safety constraints, which is used for solving the technical problems that the existing economic dispatching method considering power grid N-1 safety constraints does not analyze the fault of a heavy-load line after not considering the fault of N-1, the cascading failure power failure is easy to generate, the reliability is low, the quantity of constraint conditions of an economic dispatching model of the existing method is large, the solving difficulty of the economic dispatching model is increased, and the solving speed is influenced.
In view of this, the present application provides an economic dispatching method considering the safety constraints of the power grids N-1 and N-2, comprising the following steps:
acquiring network parameters of a power grid, solving an established economic dispatching model P0 without considering fault state constraints, and defining branches for N-1 analysis;
carrying out N-1 fault influence analysis on the branches with the N-1 analysis defined one by one, calculating a first load flow of the rest branches without the N-1 analysis defined, and determining the load rate of the rest branches;
when the remaining branches have heavy load lines, combining the heavy load lines in the remaining branches which are not defined with the N-1 analysis with the branches which are defined with the N-1 analysis one by one to form an N-2 fault pair, wherein the heavy load lines are the branches with the load rate exceeding a first threshold value;
calculating a second load flow of the remaining branch of the non-N-2 fault pair, and determining the load rate of the remaining branch of the non-N-2 fault pair;
when N-1 harmful fault scenes exist, calculating the number of the N-1 harmful fault scenes, wherein the N-1 harmful fault scenes are scenes enabling the load rate of the residual branches which are not defined with the N-1 analysis to exceed a second threshold value, and the second threshold value is larger than the first threshold value;
when N-2 harmful fault scenes exist, calculating the number of the N-2 harmful fault scenes, wherein the N-2 harmful fault scenes are scenes enabling the load rate of the remaining branches of the non-N-2 fault pairs to exceed a third threshold value;
establishing N-1 harmful fault scene constraints of each N-1 harmful fault scene based on the single-branch on-off distribution factors, and establishing N-2 harmful fault scene constraints of each N-2 harmful fault scene based on the double-branch on-off distribution factors;
adding the N-1 harmful fault scene constraint and the N-2 harmful fault scene constraint into the economic dispatching model P0 to obtain a new economic dispatching model P1;
solving the new economic dispatch model P1;
if the sum of the number of the N-2 harmful fault scenes and the number of the N-1 harmful fault scenes is zero, obtaining a power grid safe and economic dispatching scheme according to a solving result of the new economic dispatching model P1, otherwise, returning to the step to carry out N-1 fault influence analysis on the branches with the N-1 analysis defined one by one, calculating a first power flow of the rest branches without the N-1 analysis defined, determining the load rate of the rest branches, and solving the new economic dispatching model P1 until the sum of the number of the N-2 harmful fault scenes and the number of the N-1 harmful fault scenes is zero.
Optionally, the economic dispatch model P0 is:
Figure GDA0002988739910000031
wherein, ai、biAnd ciThe second, first and constant cost coefficients of the generator set i are respectively; PG (Picture experts group)iThe output of the generator set i is obtained;
Figure GDA0002988739910000032
and
Figure GDA0002988739910000033
respectively representing the upper limit and the lower limit of the allowable output of the generator set i; PLjIs the active power flow through line j; SFj,bNode b, line j power flow distribution factor; KGb,iAssociating the elements of the b-th row and the i-th column of the matrix KG for the node generator; KDb,dThe b-th row and d-th column elements of the node load incidence matrix KD; KLb,jThe b th row and j th column elements and PD of the node line incidence matrix KLdIs the active demand of load d;
Figure GDA0002988739910000034
for the maximum active power transfer capacity of line j,
Figure GDA0002988739910000035
maximum active power transfer capacity for line j
Figure GDA0002988739910000036
The opposite of (d); SB is the number set of all nodes of the system; SG is a number set of all generator sets of the system; SD is the number set of all the loads of the system; SL is the number set of all lines of the system, Δ DdA load shedding variable being the load d; cEENSIs the load shedding cost factor.
Optionally, the N-2 nuisance fault scenario constraints are:
Figure GDA0002988739910000037
wherein the content of the first and second substances,
Figure GDA0002988739910000038
after a failure of line p, q, the power flow of line j,
Figure GDA0002988739910000039
for the open distribution factor of the p-line,
Figure GDA00029887399100000310
for the breaking distribution factor, PL, of q linespFor active power flow through line p, PLqIs the active power flow through line q.
Optionally, the N-1 nuisance fault scenario constraints are:
Figure GDA00029887399100000311
wherein the content of the first and second substances,
Figure GDA00029887399100000312
after a fault on line l, the power flow on line j,
Figure GDA00029887399100000313
is the breaking distribution factor of the l lines.
Optionally, the new economic dispatch model P1 is:
Figure GDA0002988739910000041
wherein, Δ DdA load shedding variable being the load d; cEENSIs the load shedding cost factor.
Optionally, the first threshold is 0.8.
Optionally, the second threshold and the third preset are both 1.
Optionally, the performing N-1 fault impact analysis on the branches with the N-1 analysis defined one by one, calculating a first power flow of the remaining branches without the N-1 analysis defined, and determining a load rate of the remaining branches specifically includes:
and carrying out N-1 fault influence analysis on the branches with the N-1 analysis defined one by one based on the single-branch cut-off distribution factor, calculating a first load flow of the rest branches without the N-1 analysis defined, and determining the load rate of the rest branches.
Optionally, the calculation formula of the first power flow is as follows:
Figure GDA0002988739910000042
wherein the content of the first and second substances,
Figure GDA0002988739910000043
the power flow of the line j after the line l has a fault; PLjIs the active power flow through line j;
Figure GDA0002988739910000044
is the breaking distribution factor of the l line; PLlIs the active power flow through line i.
Optionally, the calculating a second power flow of the remaining branch of the non-N-2 fault pair and determining a load rate of the remaining branch of the non-N-2 fault pair specifically include:
calculating a second load flow of the remaining branch of the non-N-2 fault pair based on the double-branch cut-off distribution factor, and determining the load rate of the remaining branch of the non-N-2 fault pair;
the calculation formula of the second power flow is as follows:
Figure GDA0002988739910000045
wherein the content of the first and second substances,
Figure GDA0002988739910000051
the power flow of the line j is obtained after the line p and the line q simultaneously have faults;
Figure GDA0002988739910000052
is the break distribution factor of the p lines;
Figure GDA0002988739910000053
is the break distribution factor of q lines; PLjIs the active power flow through line j; PLpIs the active power flow through line p; PLqIs the active power flow through line q.
According to the technical scheme, the embodiment of the application has the following advantages:
the economic dispatching method considering the safety constraints of the power grid N-1 and the power grid N-2 comprises the steps of firstly, carrying out fault verification on the power grid N-1, calculating the power flow of the rest lines, screening out the heavy-load lines which are easy to generate cascading faults, then forming N-2 fault pairs by the heavy-load lines and branches which are defined to be analyzed by the N-1 one by one, constructing N-2 fault safety constraints by combining the N-2 fault pairs which can cause the power flow of the power grid to exceed the limit and the corresponding lines which generate the power flow to exceed the limit, adding the N-2 fault safety constraints into an economic dispatching model P0, effectively avoiding further propagation and development of the initial fault of the power grid N-1, obtaining a new economic dispatching model P1, continuously verifying, adding and verifying steps to update P1, obtaining a final economic dispatching model P2 until the number of harmful fault scenes is zero, solving the P2 to obtain a power grid safe economic dispatching scheme which meets the N-1 and the N-2, the method solves the technical problems that the existing economic dispatching method considering the N-1 safety constraint of the power grid does not analyze the fault of the heavy-load line after not considering the N-1 fault, the cascading fault is easy to generate, the reliability is low, the quantity of the constraint conditions of the economic dispatching model of the existing method is large, and the solving difficulty and the solving speed of the economic dispatching model are increased.
Drawings
FIG. 1 is a schematic flow chart diagram illustrating an embodiment of an economic dispatch method considering grid N-1 and N-2 safety constraints according to the present disclosure;
FIG. 2 is a topological diagram of an IEEE-RTS79 test system according to an application example of the economic dispatching method considering the safety constraints of the power grids N-1 and N-2.
Detailed Description
In order to make the technical solutions of the present application better understood, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
For easy understanding, please refer to fig. 1 and fig. 2, an embodiment of an economic dispatching method considering safety constraints of power grids N-1 and N-2 provided by the present application includes:
step 101, obtaining network parameters of a power grid, solving the established economic dispatching model P0 without considering fault state constraints, and defining branches for N-1 analysis.
It should be noted that, first, the network parameters of the power grid need to be acquired, and the network parameters of the power grid may include: node number, branch number, node numbers corresponding to two sides of the branch, electrical parameters and operation limit values of the branch, cost coefficient of power generation, operation parameters, node numbers of the branch, and active requirements of system load. And establishing an economic dispatching model P0 without considering fault state constraints, defining branches needing N-1 analysis in advance, wherein the branches without N-1 analysis defined are residual branches. The N-1 fault in the power grid means that after any one independent element (a generator, a transmission line, a transformer and the like) in N elements of the power system is cut off due to a fault, no power failure of a user due to overload tripping of other lines is caused, the stability of the system is not damaged, and accidents such as voltage breakdown and the like do not occur.
And 102, performing N-1 fault influence analysis on the branches with the N-1 analysis defined one by one, calculating a first load flow of the rest branches without the N-1 analysis defined, and determining the load rate of the rest branches.
It should be noted that the first power flow of the remaining branches not defined with N-1 analysis may be calculated based on a single branch open distribution factor (LODF), where a Line Output Distribution Factor (LODF) refers to a proportional relation value between a current increment (current transfer component) on the remaining branches except the open branch and an original power flow of the opened branch when a current injected into the network by a node in the network remains unchanged before and after the cut of the grid fault branch and the network is a linear element. And (4) carrying out N-1 fault influence analysis on the branches with the N-1 analysis defined one by one based on the single-branch cut-off distribution factor, and calculating the first load flow of the rest branches without the N-1 analysis defined. The disconnection distribution factor of single or multiple branches can be obtained by the following formula:
LODFM,O＝PTDFM,O(E-PTDFO,O)；
PTDFM,O＝XM -1ΦTB0 -1Ψ；
PTDFO,O＝XO -1ΨTB0 -1Ψ；
when N-1 fault analysis is carried out on the preselected lines one by one, the distribution factor of the disconnection of a certain line j to a single line l is obtained by using the formula
Figure GDA0002988739910000061
At this time, LODFM,OIs a 1 × 1 vector; xMIs a 1 × 1 vector with the element xjThe reactance of branch j; phi is a node-branch correlation NB multiplied by 1 vector of the branch j, the corresponding position of the branch starting node is +1, the corresponding position of the branch ending node is-1, and the rest are 0 elements; psi is a node-branch association NB x 1 vector of the branch l, and the meaning of the elements is the same as phi; b is0And the NB x NB order susceptance matrix is established for the power grid by using the reactance as a branch parameter.
Calculating the breaking distribution factor of line j to line l
Figure GDA0002988739910000071
Then, the power flow of the line j after the line l has a fault is obtained according to the following formula
Figure GDA0002988739910000072
Figure GDA0002988739910000073
And 103, when the remaining branches have the heavy load lines, combining the heavy load lines in the remaining branches which are not defined with the N-1 analysis with the branches which are defined with the N-1 analysis one by one to form an N-2 fault pair, wherein the heavy load lines are the branches of which the load rate exceeds a first threshold value.
It should be noted that the N-2 fault in the power grid means that after any two independent elements (generator, transmission line, transformer, etc.) in N elements of the power system are cut off due to a fault, no power failure of a user due to overload tripping of other lines should be caused, the stability of the system is not damaged, and accidents such as breakdown do not occur. If for all lines
Figure GDA0002988739910000074
Where 0.8 is the first threshold, the procedure is concluded, demonstrating that the scheduling scheme meets the N-1 requirements and there are no potentially harmful N-2 failures. If there is a line
Figure GDA0002988739910000075
Step 104 is executed next.
And 104, calculating a second load flow of the remaining branch circuit of the non-N-2 fault pair, and determining the load rate of the remaining branch circuit of the non-N-2 fault pair.
And 105, when N-1 harmful fault scenes exist, calculating the number of the N-1 harmful fault scenes, wherein the N-1 harmful fault scenes are scenes enabling the load rate of the residual branches which are not defined to be analyzed by the N-1 to exceed a second threshold, and the second threshold is larger than the first threshold.
And 106, when an N-2 harmful fault scene exists, calculating the number of the N-2 harmful fault scenes, wherein the N-2 harmful fault scenes are scenes enabling the load rate of the remaining branches of the non-N-2 fault pairs to exceed a third threshold value.
It should be noted that, whether an N-2 harmful fault scenario exists is determined, that is, after the power grid N-2 fault is determined, whether a line with a load factor greater than 1 exists in the remaining lines of the power grid, where 1 is a third threshold, and if not, the N-2 harmful fault scenario number Cn2 is made to be 0; if yes, enabling Cn2 to be N-2 harmful fault scenes, namely after the power grid N-2 fails, enabling lines with power flows exceeding the limit in the rest lines of the power grid to form harmful fault pairs with the N-2 line groups.
The line load rate in the rest lines of the power grid exceeds 0.8 after the N-1 fault of the power grid
Figure GDA0002988739910000076
In combination with the N-1 lines to form a potential N-2 fault pair. And analyzing the influence of each N-2 fault according to a double-branch disconnection distribution factor (LODF) on each N-2 fault. The double branch disconnection distribution factor can be obtained by 3 formulas given in step 102, for example, assuming that line p and line q are a certain N-2 fault pair, when line p and line q are disconnected simultaneously, the disconnection distribution factor of line j on line p and line q respectively is obtained
Figure GDA0002988739910000081
At this point in step 102, the formula, LODFM,OIs a 2 x 1 vector, the first element represents that when the line p and the line q are simultaneously disconnected, the line j respectively disconnects the line p and distributes the factors
Figure GDA0002988739910000082
The second element represents the distribution factor of line j on line q when line p and line q are open simultaneously
Figure GDA0002988739910000083
XMIs a 1 × 1 vector with the element xjThe reactance of branch j; phi is a node-branch correlation NB multiplied by 1 vector of the branch j, the corresponding position of the branch starting node is +1, the corresponding position of the branch ending node is-1, and the rest are 0 elements; psi is a node-branch correlation NB x 2 vector of the branches p and q, and the meaning of the elements is the same as phi; b is0And the NB x NB order susceptance matrix is established for the power grid by using the reactance as a branch parameter.
When the line p and the line q are simultaneously disconnected, the disconnection distribution factor of the line j to the line p and the line q is obtained
Figure GDA0002988739910000084
Then, the power flow of the line j after the line p and the line q simultaneously have faults is obtained according to the following formula
Figure GDA0002988739910000085
Figure GDA0002988739910000086
It should be noted that, for the power flow calculated in step 102, it is determined whether an N-1 harmful fault scenario exists, that is, after it is determined that the power grid N-1 has a fault, whether a line with a load rate greater than 1, that is, a second threshold exists in the remaining lines of the power grid, and if not, the N-1 harmful fault scenario Cn1 is made equal to 0; if yes, enabling Cn1 to be N-1 harmful fault scenes, namely after the power grid N-1 fails, enabling lines with power flow exceeding the limit in the rest lines of the power grid to form harmful fault pairs with the N-1 lines.
And 107, establishing N-1 harmful fault scene constraints of each N-1 harmful fault scene based on the single branch disconnection distribution factors, and establishing N-2 harmful fault scene constraints of each N-2 harmful fault scene based on the double branch disconnection distribution factors.
It should be noted that, whether the total number of the N-2 and N-1 fault scenes is 0 is judged, that is, whether Cn2+ Cn1 is 0, if yes, the program is ended, it is proved that the economic dispatching scheme meets the requirements of N-1 and N-2, if not, the N-1 harmful fault scene constraint of each N-1 harmful fault scene is established based on the single branch disconnection distribution factor, and the N-2 harmful fault scene constraint of each N-2 harmful fault scene is established based on the double branch disconnection distribution factor. The N-1 harmful fault scene constraint established based on the single branch disconnection distribution factor is as follows:
Figure GDA0002988739910000087
wherein the content of the first and second substances,
Figure GDA0002988739910000088
for line j after line l has failedIn the course of tidal current,
Figure GDA0002988739910000089
is the breaking distribution factor of the l lines.
The N-2 harmful fault scene constraint established based on the double-branch disconnection distribution factor is as follows:
Figure GDA0002988739910000091
wherein the content of the first and second substances,
Figure GDA0002988739910000092
after a failure of line p, q, the power flow of line j,
Figure GDA0002988739910000093
for the open distribution factor of the p-line,
Figure GDA0002988739910000094
for the breaking distribution factor, PL, of q linespFor active power flow through line p, PLqIs the active power flow through line q.
And 108, adding the N-1 harmful fault scene constraint and the N-2 harmful fault scene constraint into the economic dispatching model P0 to obtain a new economic dispatching model P1.
It should be noted that the economic dispatch model P0 may specifically be:
Figure GDA0002988739910000095
in the formula, ai、biAnd ciThe second, first and constant cost coefficients of the generator set i are respectively; PG (Picture experts group)iThe output of the generator set i is taken as a control variable in the economic dispatching model;
Figure GDA0002988739910000096
and
Figure GDA0002988739910000097
respectively representing the upper limit and the lower limit of the allowable output of the generator set i; PLjIs the active power flow through line j; SFj,bThe node b and the line j have power flow distribution factors, namely, active components flowing through the line j when the node b injects unit power; KGb,iAssociating the elements of the b-th row and the i-th column of the matrix KG for the node generator; KDb,dThe b-th row and d-th column elements of the node load incidence matrix KD; KLb,jThe node line incidence matrix KL comprises the b-th row and j-th column elements; KG. The specific definitions of KD and KL are as follows: the node generator association matrix KG is a (NG multiplied by NB) matrix, wherein NG is the total number of thermal power generating units of the system, and NB is the number of nodes of the system; the line of KG corresponds to the node, the column corresponds to the generator, any element KG of itjkThe definition is as follows: KG jk1, the node where the generator k is located is j; KGjk0 indicates that generator k is not at node j. The node load incidence matrix KD is an (ND multiplied by NB) matrix, wherein ND is the system load number; the rows of KD correspond to nodes, the columns correspond to loads, any element of KDjkThe definition is as follows: KD jk1, the node where the load k is located is j; KDjk0 indicates that the load k is not present at the node j. The node line association matrix KL is an (NL multiplied by NB) matrix, wherein NL is the number of system lines; KL has a row corresponding to a node, a column corresponding to a line, and any element KLjkThe definition is as follows: KL jk1, meaning that line k is associated with node j and its direction is away from node; KLjk-1, meaning that line k is associated with node j and it points to a node; KLjk0 indicates that line k is not associated with node j. PD (photo diode)dIs the active demand of load d.
Figure GDA0002988739910000101
SB is the number set of all nodes of the system, and is the maximum active power transmission capacity of the line j; SG is a number set of all generator sets of the system; SD is the number set of all the loads of the system; SL is the set of numbers for all lines of the system,
Figure GDA0002988739910000102
maximum power transfer capacity for line j
Figure GDA0002988739910000103
The opposite number of (c).
Adding the N-1 harmful fault scene constraint and the N-2 harmful fault scene constraint into the established economic dispatching model P0, wherein the obtained new economic dispatching model P1 specifically comprises the following steps:
Figure GDA0002988739910000104
wherein, Δ DdA load shedding variable being the load d; cEENSThe load shedding cost coefficient is a relatively large constant, so that the load shedding is avoided as much as possible by the optimization result. Introducing variable Δ DdAnd the model can be guaranteed to have solutions under each fault scene.
And 109, solving a new economic dispatching model P1, when the sum of the number of the N-2 harmful fault scenes and the number of the N-1 harmful fault scenes is zero, taking a dispatching scheme corresponding to the solution of the new economic dispatching model P1 as a target power grid safe economic dispatching scheme, and when the sum of the number of the N-2 harmful fault scenes and the number of the N-1 harmful fault scenes is not zero, returning to the steps 102 to 109 until the sum of the number of the N-2 harmful fault scenes and the number of the N-1 harmful fault scenes is zero.
It should be noted that, the optimization solver solution model P1 may be called, after the model P1 is solved, if the sum of the number of N-2 harmful fault scenes and the number of N-1 harmful fault scenes is zero, a power grid safe and economic dispatching scheme is obtained according to the solution result of the new economic dispatching model P1, otherwise, the steps 102 to 109 are returned until the sum of the number of N-2 harmful fault scenes and the number of N-1 harmful fault scenes is zero, and the dispatching scheme corresponding to the solution result of the new economic dispatching model P1 is used as the power grid safe and economic dispatching scheme when the sum of the number of N-2 harmful fault scenes and the number of N-1 harmful fault scenes is zero.
The economic dispatching method considering the safety constraints of the power grids N-1 and N-2 provided in the embodiment of the application screens out heavy-load lines which are easy to have cascading failures by carrying out power grid N-1 power flow analysis on an economic dispatching model P0 which does not consider the safety constraints, forms N-2 fault pairs with corresponding branches analyzed by the N-1 one by one to generate a new N-2 fault set, carries out power flow verification on the fault set based on branch breaking distribution factors to obtain a harmful fault scene, adds the harmful fault scene to P0 to obtain a new economic dispatching model P1, updates P1 by continuous verification adding and re-verification steps until the number of the harmful N-1 and N-2 fault scenes is zero to obtain a final dispatching model P2, solves P2 to obtain a dispatching scheme meeting the criteria of the lines N-1 and N-2, the further propagation and development of the initial fault of the power grid N-1 are effectively avoided, and the problem that the power grid cascading failure power failure is caused by the fact that the secondary fault is easy to occur on a heavy-load line after the N-1 fault is not considered in the existing economic dispatching method considering the safety constraint of the power grid N-1 is solved.
Referring to fig. 2 and tables 1 to 6, in order to more specifically describe that the economic dispatching method considering the safety constraints of the power grids N-1 and N-2 provided in the embodiment of the present application can effectively improve the safety of power dispatching, taking an improved IEEE-RTS79 test system as an example, the economic dispatching method considering the safety constraints of the power grids N-1 and N-2 provided in the embodiment of the present application is used to optimize power dispatching of the test system. Node test system node 13 is defined as a balanced node. Table 1, table 2, table 3 list the parameters required for step 101 in the previous method example, respectively. Table 4 is a comparison of the results of the scheduling schemes obtained by the economic scheduling method considering the security constraints of the power grid N-1 and N-2 and the conventional economic scheduling method provided in the embodiment of the present application.
The IEEE-RTS79 test system in the present example has a total of 38 branches, a split system of branches L11, thus excluding L11 when performing the N-1 test analysis. And (4) disconnecting the 37 lines one by one, and then calculating and analyzing the load flow distribution condition of the rest lines of the power grid after each line is disconnected. When the scheduling result obtained by the traditional scheduling method is used for N-1 fault analysis, 2 times of line overload are generated in total, and the steps are as follows: when the line L10 is disconnected, the load factor of the line L5 in the rest lines is 1.55, which greatly exceeds the operation limit of the line; when the line L17 is disconnected, the load factor of the line L3 in the remaining lines is 1.007, which also exceeds the line operation limit. And secondly, 13 heavy-load lines with the load rate exceeding 0.8 in the rest lines of the power grid after each N-1 fault. When the scheduling result obtained by the invention is used for analyzing the N-1 fault, the N-1 fault of each line and no overload generated by the rest lines of the power grid are generated, and the scheduling result meets the requirement of the N-1 standard. Secondly, after each N-1 fault, the load rate of the heavy load lines exceeding 0.8 in the rest lines of the power grid is only 5 times, and compared with the traditional scheduling scheme, the load rate is reduced by half. These two schemes, specifically reloading the line number and its load, are listed in table 5.
The heavy haul line pairs given in Table 5 were each individually subjected to N-2 analysis. Obviously, in the economic dispatching method considering the safety constraints of the power grids N-1 and N-2 in the embodiment of the application, in 5 pairs of N-2 fault detection given in the table 5, the power flow of the remaining lines of the power grids does not exceed the operation limit. For the conventional economic dispatch scheme, 13 pairs of N-2 fault pair analyses are given for table 5, and a total of 10 line overloads occur, with the results shown in table 6.
According to the analysis, the economic dispatching method considering the safety constraints of the power grid N-1 and N-2 can effectively improve the safety of power dispatching.
TABLE 1
Figure GDA0002988739910000121
Figure GDA0002988739910000131
TABLE 2
Figure GDA0002988739910000132
Figure GDA0002988739910000141
Figure GDA0002988739910000151
TABLE 3
Figure GDA0002988739910000152
Figure GDA0002988739910000161
TABLE 4
Figure GDA0002988739910000162
Figure GDA0002988739910000171
TABLE 5
Figure GDA0002988739910000172
Figure GDA0002988739910000181
TABLE 6
Figure GDA0002988739910000182
Figure GDA0002988739910000191
The above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions in the embodiments of the present application.

Claims (9)

1. An economic dispatching method considering safety constraints of N-1 and N-2 of a power grid is characterized by comprising the following steps:
acquiring network parameters of a power grid, solving an established economic dispatching model P0 without considering fault state constraints, and defining branches for N-1 analysis;
carrying out N-1 fault influence analysis on the branches with the N-1 analysis defined one by one, calculating a first load flow of the rest branches without the N-1 analysis defined, and determining the load rate of the rest branches;
when the remaining branches have heavy load lines, combining the heavy load lines in the remaining branches which are not defined with the N-1 analysis with the branches which are defined with the N-1 analysis one by one to form an N-2 fault pair, wherein the heavy load lines are the branches with the load rate exceeding a first threshold value;
calculating a second load flow of the remaining branch of the non-N-2 fault pair, and determining the load rate of the remaining branch of the non-N-2 fault pair;
when N-1 harmful fault scenes exist, calculating the number of the N-1 harmful fault scenes, wherein the N-1 harmful fault scenes are scenes enabling the load rate of the residual branches which are not defined with the N-1 analysis to exceed a second threshold value, and the second threshold value is larger than the first threshold value;
when N-2 harmful fault scenes exist, calculating the number of the N-2 harmful fault scenes, wherein the N-2 harmful fault scenes are scenes enabling the load rate of the remaining branches of the non-N-2 fault pairs to exceed a third threshold value;
establishing N-1 harmful fault scene constraints of each N-1 harmful fault scene based on the single-branch on-off distribution factors, and establishing N-2 harmful fault scene constraints of each N-2 harmful fault scene based on the double-branch on-off distribution factors;
adding the N-1 harmful fault scene constraint and the N-2 harmful fault scene constraint into the economic dispatching model P0 to obtain a new economic dispatching model P1;
solving the new economic dispatch model P1, the new economic dispatch model P1 being:
Figure FDA0002988739900000021
wherein, ai、biAnd ciThe second, first and constant cost coefficients of the generator set i are respectively; PG (Picture experts group)iThe output of the generator set i is obtained;
Figure FDA0002988739900000022
and
Figure FDA0002988739900000023
respectively representing the upper limit and the lower limit of the allowable output of the generator set i; PLjIs the active power flow through line j; SFj,bNode b, line j power flow distribution factor; KGb,iAssociating the elements of the b-th row and the i-th column of the matrix KG for the node generator; KDb,dThe b-th row and d-th column elements of the node load incidence matrix KD; KLb,jThe b th row and j th column elements and PD of the node line incidence matrix KLdIs the active demand of load d;
Figure FDA0002988739900000024
for the maximum active power transfer capacity of line j,
Figure FDA0002988739900000025
maximum active power transfer capacity for line j
Figure FDA0002988739900000026
The opposite of (d); SB is the number set of all nodes of the system; SG is a number set of all generator sets of the system; SD is the number set of all the loads of the system; SL is the number set of all lines of the system, Δ DdA load shedding variable being the load d; cEENSA load shedding cost factor;
Figure FDA0002988739900000027
after a failure of line p, q, the power flow of line j,
Figure FDA0002988739900000028
for the open distribution factor of the p-line,
Figure FDA0002988739900000029
for the breaking distribution factor, PL, of q linespFor active power flow through line p, PLqIs the active power flow through line q;
Figure FDA00029887399000000210
after a fault on line l, the power flow on line j,
Figure FDA00029887399000000211
is the breaking distribution factor of the l line;
if the sum of the number of the N-2 harmful fault scenes and the number of the N-1 harmful fault scenes is zero, obtaining a power grid safe and economic dispatching scheme according to a solving result of the new economic dispatching model P1, otherwise, returning to the step to carry out N-1 fault influence analysis on the branches with the N-1 analysis defined one by one, calculating a first power flow of the rest branches without the N-1 analysis defined, determining the load rate of the rest branches, and solving the new economic dispatching model P1 until the sum of the number of the N-2 harmful fault scenes and the number of the N-1 harmful fault scenes is zero.
2. The economic dispatch method considering grid N-1 and N-2 safety constraints as claimed in claim 1, wherein the economic dispatch model P0 is:
Figure FDA0002988739900000031
wherein, ai、biAnd ciSecondary, primary and constant of the generator set iThe coefficient; PG (Picture experts group)iThe output of the generator set i is obtained;
Figure FDA0002988739900000032
and
Figure FDA0002988739900000033
respectively representing the upper limit and the lower limit of the allowable output of the generator set i; PLjIs the active power flow through line j; SFj,bNode b, line j power flow distribution factor; KGb,iAssociating the elements of the b-th row and the i-th column of the matrix KG for the node generator; KDb,dThe b-th row and d-th column elements of the node load incidence matrix KD; KLb,jThe b th row and j th column elements and PD of the node line incidence matrix KLdIs the active demand of load d;
Figure FDA0002988739900000034
for the maximum active power transfer capacity of line j,
Figure FDA0002988739900000035
maximum active power transfer capacity for line j
Figure FDA0002988739900000036
The opposite of (d); SB is the number set of all nodes of the system; SG is a number set of all generator sets of the system; SD is the number set of all the loads of the system; SL is the number set of all the lines of the system.
3. The economic dispatching method considering power grid N-1 and N-2 safety constraints as claimed in claim 2, wherein the N-2 harmful fault scenario constraints are:
Figure FDA0002988739900000037
wherein the content of the first and second substances,
Figure FDA0002988739900000038
after a failure of line p, q, the power flow of line j,
Figure FDA0002988739900000039
for the open distribution factor of the p-line,
Figure FDA00029887399000000310
for the breaking distribution factor, PL, of q linespFor active power flow through line p, PLqIs the active power flow through line q.
4. The economic dispatching method considering power grid N-1 and N-2 safety constraints as claimed in claim 3, wherein the N-1 harmful fault scenario constraints are:
Figure FDA00029887399000000311
wherein the content of the first and second substances,
Figure FDA00029887399000000312
after a fault on line l, the power flow on line j,
Figure FDA00029887399000000313
is the breaking distribution factor of the l lines.
5. The economic dispatch method considering grid N-1 and N-2 safety constraints as claimed in claim 1, wherein the first threshold is 0.8.
6. The economic dispatch method considering grid N-1 and N-2 safety constraints as claimed in claim 5, wherein the second threshold and the third threshold are both 1.
7. The economic dispatching method considering safety constraints of N-1 and N-2 of the power grid as claimed in claim 1, wherein the step of performing N-1 fault impact analysis on the branches with defined N-1 analysis one by one, calculating a first load flow of the remaining branches without defined N-1 analysis, and determining the load ratios of the remaining branches comprises:
and carrying out N-1 fault influence analysis on the branches with the N-1 analysis defined one by one based on the single-branch cut-off distribution factor, calculating a first load flow of the rest branches without the N-1 analysis defined, and determining the load rate of the rest branches.
8. The economic dispatch method considering grid N-1 and N-2 safety constraints as claimed in claim 1, wherein the first power flow is calculated by the following formula:
Figure FDA0002988739900000041
wherein the content of the first and second substances,
Figure FDA0002988739900000042
the power flow of the line j after the line l has a fault; PLjIs the active power flow through line j;
Figure FDA0002988739900000043
is the breaking distribution factor of the l line; PLlIs the active power flow through line i.
9. The economic dispatching method considering grid N-1 and N-2 safety constraints as claimed in claim 1, wherein the calculating the second power flow of the remaining branches of the non-N-2 fault pair and determining the load rate of the remaining branches of the non-N-2 fault pair specifically comprises:
calculating a second load flow of the remaining branch of the non-N-2 fault pair based on the double-branch cut-off distribution factor, and determining the load rate of the remaining branch of the non-N-2 fault pair;
the calculation formula of the second power flow is as follows:
Figure FDA0002988739900000044
wherein the content of the first and second substances,
Figure FDA0002988739900000045
the power flow of the line j is obtained after the line p and the line q simultaneously have faults;
Figure FDA0002988739900000046
is the break distribution factor of the p lines;
Figure FDA0002988739900000047
is the break distribution factor of q lines; PLjIs the active power flow through line j; PLpIs the active power flow through line p; PLqIs the active power flow through line q.
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