CN112952829B - Power system node operation safety evaluation method and device and power system - Google Patents
Power system node operation safety evaluation method and device and power system Download PDFInfo
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Abstract
According to the method, the device and the power system for evaluating the operation safety of the nodes of the power system, provided by the invention, the fact that the power system comprises networks with different voltage levels is considered, and a certain network topological structure is also formed among the networks with different voltage levels, so that the power grid system is divided into different voltage levels and different areas before the safety evaluation of the nodes is carried out, the calculated amount is reduced, and the real-time evaluation efficiency is improved; in addition, the maximum bearable load of each node is determined by optimizing the power flow model, so that the accuracy of safety assessment is improved, and relevant measures are further taken for links with relatively weak safety, so that the safe and stable operation of a power grid is ensured.
Description
Technical Field
The invention relates to the technical field of electrical automation, in particular to a method and a device for evaluating the operation safety of nodes of an electric power system and the electric power system.
Background
In recent years, safe and stable operation of a power grid and reliable power supply are the most concerned contents of relevant departments of power grid dispatching, and the maintenance of sufficient power supply safety of the power grid is also a powerful guarantee for ensuring stable and effective operation of social economy.
An existing Energy Management System (EMS) mainly depends on scheduling control personnel to perform rough topology analysis on power grid operation data so as to complete safety assessment on the power grid operation state, and then scheduling and controlling an operating power system. However, the existing node safety assessment method tests the professional level and judgment capability of scheduling control personnel, and particularly when aiming at a power grid with large scale at provincial level and above, more nodes, diversified power supply structure and complex structure, the power supply safety of each node is difficult to be accurately assessed due to the lack of scientific assessment standards and judgment bases and the lack of effective safety assessment means.
In addition, in the prior art, most of the topology analysis of the power grid only analyzes a network with one voltage level or equivalently converts a transformer substation into nodes, and the networks with different voltage levels are combined together for analysis, so that the regional characteristic of the power grid is not considered, the calculated amount is too large, and the real-time evaluation requirement of scheduling operation cannot be met.
Disclosure of Invention
The invention aims to solve at least one of the technical defects, in particular to the technical defect that the node safety evaluation method in the prior art is difficult to accurately evaluate the power supply safety of each node, and the calculated amount is too large to meet the real-time evaluation requirement of scheduling operation.
The invention provides a method for evaluating the operation safety of a power system node, which comprises the following steps:
layering network architectures in an electric power system according to voltage levels to obtain a first network architecture and a second network architecture, and partitioning the second network architecture according to the first network architecture and a corresponding power grid topological structure to obtain small network architectures in different areas;
obtaining operation data of the power system, performing ground state power flow calculation according to the operation data, and if the ground state power flow is converged, constructing an optimized power flow model according to the first network architecture, the small network architecture and the operation data;
and respectively calculating the maximum bearable load of each node in the first network architecture and the small network architecture by using the optimized power flow model, and evaluating the operation safety of the nodes according to the maximum bearable load.
Optionally, the first network architecture is a 500kV network architecture, and the second network architecture is a 220kV network architecture;
the step of partitioning the second network architecture according to the first network architecture and the corresponding power grid topological structure to obtain small network architectures in different areas includes:
and partitioning the 220kV network architecture based on the 500kV network architecture and the corresponding power grid topological structure, and determining a small network architecture formed by a plurality of 220kV network architectures in different areas.
Optionally, the optimized power flow model includes an objective function and a constraint condition for maximizing the bearable load capacity of the node.
Optionally, the constraint condition comprises an equality constraint and an inequality constraint;
the equality constraints comprise power flow constraints; the inequality constraints comprise active output constraints and reactive output constraints of the controllable generator, branch active power constraints and section active power constraints.
Optionally, the step of calculating the maximum bearable load of each node in the first network architecture by using the optimized power flow model includes:
and taking a 220kV transformer substation corresponding to the transformer substation node in the 500kV network architecture as a load, and determining the maximum bearable load of the transformer substation node corresponding to the target function by using a tracking center track inner point method in combination with the equality constraint and the inequality constraint.
Optionally, the step of calculating a maximum bearable load of each node in the small network architecture by using the optimized power flow model includes:
and taking a 500kV transformer substation corresponding to a transformer substation node in the 220kV network architecture as a power supply, and determining the maximum bearable load of the transformer substation node corresponding to the target function by using the tracking center track inner point method in combination with the equality constraint, the inequality constraint and the maximum bearable load of the 500kV transformer substation.
Optionally, the step of evaluating the operation security of the node according to the maximum bearable load includes:
acquiring the real-time load quantity of the node, and calculating the power supply adequacy of the node according to the maximum bearable load of the node and the real-time load quantity;
and evaluating the operation safety of the node according to the power supply adequacy.
Optionally, after the step of evaluating the operation security of the node according to the maximum bearable load, the method further includes:
and (4) counting the power supply adequacy of each node, and performing warning operation on the node with the minimum power supply adequacy.
The invention also provides a device for evaluating the operation safety of the nodes of the power system, which comprises:
the system comprises a layering and partitioning module, a first network architecture and a second network architecture, wherein the layering and partitioning module is used for layering the network architectures in the power system according to voltage grades to obtain the first network architecture and the second network architecture, and partitioning the second network architecture according to the first network architecture and a corresponding power grid topological structure to obtain small network architectures in different areas;
the model building module is used for obtaining operation data of the power system, performing ground state power flow calculation according to the operation data, and building an optimized power flow model according to the first network architecture, the small network architecture and the operation data if the ground state power flow is converged;
and the safety evaluation module is used for respectively calculating the maximum bearable load of each node in the first network architecture and the small network architecture by using the optimized power flow model and evaluating the operation safety of the node according to the maximum bearable load.
The invention also provides a power system, and when the power system evaluates the operation safety of each node, the steps of the method for evaluating the operation safety of the nodes of the power system according to any one of the embodiments are executed.
According to the technical scheme, the embodiment of the invention has the following advantages:
the invention provides a method, a device and a power system for evaluating the running safety of nodes of the power system, wherein the method comprises the following steps: layering network architectures in an electric power system according to voltage levels to obtain a first network architecture and a second network architecture, and partitioning the second network architecture according to the first network architecture and a corresponding power grid topological structure to obtain small network architectures in different areas; obtaining operation data of the power system, performing ground state power flow calculation according to the operation data, and if the ground state power flow is converged, constructing an optimized power flow model according to the first network architecture, the small network architecture and the operation data; and respectively calculating the maximum bearable load of each node in the first network architecture and the small network architecture by using the optimized power flow model, and evaluating the operation safety of the nodes according to the maximum bearable load.
Compared with the prior art, the invention considers that the power system comprises networks with different voltage levels, and a certain network topology structure is also arranged among the networks with different voltage levels, so that the power grid system is divided into different voltage levels and different areas before the node safety evaluation is carried out, thereby reducing the calculated amount and improving the real-time evaluation efficiency; in addition, the maximum bearable load of each node is determined by optimizing the power flow model, so that the accuracy of safety assessment is improved, and relevant measures are further taken for links with relatively weak safety, so that the safe and stable operation of the power grid is ensured.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the description of the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without inventive labor.
Fig. 1 is a schematic flow chart illustrating a node operation safety evaluation of an electrical power system according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a process of calculating a maximum node load according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a power system node operation safety evaluation according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
As used herein, the singular forms "a", "an", "the" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It will be understood by those within the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
In recent years, safe and stable operation of a power grid and reliable power supply are the most concerned contents of relevant departments of power grid dispatching, and the maintenance of sufficient power supply safety of the power grid is also a powerful guarantee for ensuring stable and effective operation of social economy.
An existing Energy Management System (EMS) mainly depends on scheduling control personnel to perform rough topology analysis on power grid operation data so as to complete safety assessment on the power grid operation state, and then scheduling and controlling an operating power system. However, the existing node safety assessment method tests the professional level and judgment capability of scheduling control personnel, and particularly when aiming at a power grid with large scale at provincial level and above, more nodes, diversified power supply structure and complex structure, the power supply safety of each node is difficult to be accurately assessed due to the lack of scientific assessment standards and judgment bases and the lack of effective safety assessment means.
In addition, in the prior art, most of the topology analysis of the power grid only analyzes the network of one voltage class or equivalently converts a transformer substation into nodes, and the networks of different voltage classes are combined together for analysis, so that the regional characteristic of the power grid is not considered, the calculated amount is too large, and the real-time evaluation requirement of scheduling operation cannot be met.
Therefore, the invention aims to solve the technical problems that the node safety evaluation method in the prior art is difficult to accurately evaluate the power supply safety of each node, the calculated amount is too large, and the real-time evaluation requirement of scheduling operation cannot be met, and the specific technical scheme is as follows:
referring to fig. 1, fig. 1 is a schematic flow chart of a method for evaluating operation safety of a node of an electrical power system according to an embodiment of the present invention, and the present invention provides a method for evaluating operation safety of a node of an electrical power system, which includes the following steps:
s110: the method comprises the steps of layering network architectures in an electric power system according to voltage levels to obtain a first network architecture and a second network architecture, and partitioning the second network architecture according to the first network architecture and a corresponding power grid topological structure to obtain small network architectures in different areas.
In the step, most of traditional topology analysis of the power grid only analyzes a network with one voltage level or equivalently converts a transformer substation into nodes, the networks with different voltage levels are combined together for analysis, the regional characteristic of the power grid is not considered, the calculated amount is too large, and the real-time evaluation requirement of scheduling operation cannot be met.
Therefore, compared with the traditional node operation safety evaluation, the method divides the power grid into a plurality of areas according to different voltage levels and the same voltage level, so that the calculation amount during the node operation safety evaluation is reduced.
For example, the provincial grid voltage regulation range generally includes grid structure of 500kV and 220kV voltage levels of the power grid, and by adopting the hierarchical partitioning strategy in this step, the network architecture of the power system is firstly divided into two network architectures of 500kV and 220kV, and then the 220kV network architecture is partitioned to obtain small network architectures of different areas, which have the following two characteristics compared with the conventional simple network:
(1) Delamination property: the 500kV transformer substation is basically a power supply of a 220kV network, namely, electric energy flows from the 500kV network to the 220kV network, the phenomenon of 'backward transmission' of the electric energy only occurs under a very special condition, and the networks of two voltage classes have independence.
Therefore, when the node safety degree is evaluated, the system nodes are divided into a 500kV network and a 220kV network for calculation respectively. When a 500kV network is calculated, a 220kV transformer substation network is equivalent to the load of a 500kV transformer substation; when the 220kV transformer substation is calculated, the 500kV transformer substation is considered as a power supply of the 220kV network by combining the calculation result of the 500kV network, so that the calculation workload is reduced, and the calculation speed is increased.
(2) Zoning: although the power grid as a whole can be regarded as a common network, the nodes are connected by lines. However, especially for 220kV networks, there is a clear "regional" property, i.e. several 220kV class substations are clustered around a certain 500kV substation, and most of the 500kV substations are the "power supply", and these 220kV substations are less connected to the 220kV substations around other 500kV substations.
Based on the proposed evaluation concept of hierarchical zoning, on one hand, when a 500kV transformer substation is calculated, the influence of 220kV nodes is considered in the form of load, and a network with a 220kV voltage level is not introduced for calculation, so that the calculation amount is reduced; in addition, the number of nodes of the level above 500kV in the power grid is not large, so that the calculation is performed on the whole when the 500kV network is calculated.
On the other hand, the number of 220kV nodes is several times of the number of 500kV nodes, and the network structure is more complicated. When the power supply safety degree of the 220kV voltage level node is calculated, the 220kV node is further partitioned, and the power supply safety degree of the 220kV node in each area is calculated based on the partitioned small network architecture, so that the calculation amount is further reduced, and the real-time evaluation efficiency is improved.
It should be noted that, the node operation safety degree index performs power supply safety degree evaluation on each node (i.e., a substation with a voltage level of 220kV or more) of the system from two aspects of real-time power balance and strong network topology structure.
S120: and obtaining operation data of the power system, performing ground state power flow calculation according to the operation data, and if the ground state power flow is converged, constructing an optimized power flow model according to the first network architecture, the small network architecture and the operation data.
In this step, after the network architecture in the power system is layered according to the voltage class through step S110 to obtain a first network architecture and a second network architecture, the second network architecture is partitioned according to the first network architecture and a corresponding power grid topology structure to obtain small network architectures in different areas, then the operation data of the power system is obtained, the ground state power flow is calculated according to the operation data, and if the ground state power flow is converged, a corresponding optimized power flow model is constructed.
Specifically, before performing the ground state power flow calculation, it is necessary to obtain operation data of the power system, where the operation data is model data in a power grid operation model, and the model data includes, but is not limited to, voltage (amplitude and phase angle) on each bus, power distribution in the network, power loss, and the like. After the operation data of the power system is obtained, the ground state power flow can be calculated; further, under the condition that the ground state power flow is converged, an optimized power flow model is established according to the first network architecture, the small network architecture and the operation data, and the maximum load amount supplied by the current node can be determined through the optimized power flow model.
It is understood that power system load flow calculation belongs to the category of steady state analysis and does not involve the dynamics and transients of system components. Therefore, the mathematical model does not contain differential equations and is a set of high-order nonlinear equations. The solution of the nonlinear algebraic equation set cannot be iterated, so the trend calculation method firstly requires that it be capable of reliably converging and giving correct answers.
S130: and respectively calculating the maximum bearable load of each node in the first network architecture and the small network architecture by using the optimized load flow model, and evaluating the operation safety of the node according to the maximum bearable load.
In this step, after the optimized power flow model is constructed in step S120, the optimized power flow model may be used to calculate the maximum bearable load of each node in the first network architecture and the small network architecture, so as to evaluate the operation security of the node according to the maximum bearable load.
Specifically, the calculation of the maximum bearable load of each node in the optimized power flow model is basically a whole-network optimized calculation problem. Therefore, in the optimized load flow calculation, the maximum bearable load of the nodes is calculated as a target, the loads of other nodes are kept unchanged, the adjustable generator set is set as a control quantity, the active and reactive constraints of the generator, the voltage constraints of the nodes and the branch power constraints are considered, the load flow equation condition is met at the same time, and then all the loaded nodes in the region are scanned to obtain the maximum bearable load of all the loaded nodes.
Referring to fig. 2 schematically, fig. 2 is a schematic diagram of a calculation flow of a maximum bearing capacity of a node according to an embodiment of the present invention, and in fig. 2, first, model data in a power grid operation model is obtained, then, a power flow calculation is performed, and in a case of power flow convergence, a line transformer limit value, a section limit value, a controllable unit, an upper limit and a lower limit are set, so as to form an optimized power flow model, and an optimized calculation is performed to obtain the maximum bearing capacity of a certain node.
For example, according to the aforementioned 500kV and 220kV hierarchical partition calculation method, the network scale does not exceed 50 nodes in the process of calculating the maximum bearable load of a single node each time, so that the real-time requirement of the system can be completely satisfied by adopting the optimized load flow calculation.
In conclusion, the safety index evaluation algorithm with higher system robustness, which is established by the invention, can quantitatively evaluate the operation safety of the power system, provides most of sensing capabilities for scheduling personnel and auxiliary decision units, establishes a corresponding index system, and provides effective and accurate evaluation results of the operation safety of the power grid for the scheduling personnel and the auxiliary decision units.
In one embodiment, the first network architecture is a 500kV network architecture and the second network architecture is a 220kV network architecture; in step S110, the step of partitioning the second network architecture according to the first network architecture and the corresponding power grid topology structure to obtain small network architectures in different areas may include:
and partitioning the 220kV network architecture based on the 500kV network architecture and the corresponding power grid topological structure, and determining a small network architecture formed by a plurality of 220kV network architectures in different areas.
In this embodiment, due to the "regional" characteristic of the power grid, the power grid may be divided into network architectures of different voltage levels, so as to reduce the amount of calculation in the node operation security evaluation.
For example, the network architecture of the power system may be divided into a 500kV network architecture and a 220kV network architecture, and then the 220kV network architecture is continuously partitioned based on the 500kV network architecture and the corresponding power grid topology, so as to determine a small network architecture composed of a plurality of 220kV network architectures in different areas.
Specifically, when a 500kV network is calculated, a 220kV transformer substation network is equivalent to a load of a 500kV transformer substation; when the 220kV transformer substation is calculated, the 500kV transformer substation is considered as a power supply of the 220kV network by combining the calculation result of the 500kV network, so that the calculation workload is reduced, and the calculation speed is increased.
In one embodiment, the optimized power flow model includes an objective function and constraints that maximize the loadable load capacity of the node.
In this embodiment, the objective function selected by the node security degree is the maximum bearable capability of the node. Can be expressed as:
maxf＝λ
in the formula, λ is the maximum bearable load of the node.
In addition, constraint conditions are also included in the optimized power flow model, and the constraint conditions include, but are not limited to, equality constraints and inequality constraints.
Further, as can be seen from the objective function expression and the system constraint conditions, the objective function parameter control variables need to be paid attention in the optimization load flow calculation, so that the part of the objective function and the equation constraint related to the parameter λ needs to be redefined, which is still an optimization problem in theory, and therefore, many special processes are performed in the implementation process. The main implementation details are as follows:
(1) Use of sparse techniques:
sparse techniques are techniques that avoid storing the zero elements in the sparse matrix and avoiding performing computations on these zero elements as much as possible when programming. So as to greatly reduce the memory occupation and the solving time.
In the application, the admittance matrix of the power grid is adopted for calculation, and compared with the impedance matrix, the admittance matrix has high sparsity and contains a lot of 0 elements. During programming, whether the element is 0 or not is judged firstly, and if the element is 0, the element does not participate in calculation so as to reduce the memory occupation and the solving time.
(2) Selection of constraint conditions:
since the actual system may be very large in scale, the number of branches is also very large. Therefore, not all branch constraints are added to the optimization model in the optimization calculations. By doing so, the optimization problem can be greatly simplified, so that the optimization calculation time is greatly reduced, and the convergence of the optimization calculation can be improved. Typically only a set of branch constraints (called critical constraints) that are out of bounds or close to out of bounds (e.g., greater than 80% line rating) are introduced into the optimization calculations.
In addition, after an adjustment, some additional line violations or impending violations may be caused, in which case a new set of critical constraints is identified and the optimization calculations are re-performed until there are no violations.
For the power flow section constraints, the same treatment as the branch constraints is performed in principle, but considering that the number of the section constraints in the system is not large, all the power flow section constraints and the key branch constraints are taken as a key constraint set together. The key constraint set comprises branches which are out of limit and are about to be out of limit, and the branches with relatively light loads are excluded, so that an initial feasible solution is easily obtained, and the purpose of the optimal solution of the maximum bearable load of the nodes can be realized, so that the performance of the optimal power flow algorithm is improved.
(3) And (4) constraint limit processing:
for the selected controllable variable, such as an active controllable unit, if the current output value is very close to the upper limit of the active output value, that is, the output value is likely to reach the upper limit by a little, the adjustment amount of the adjustment is very small, and in order to avoid the adjustment with the very small adjustment amount in the result, the upper limit of the active output of the unit is changed into the current output value before the optimization calculation. Therefore, unnecessary small adjustment is avoided, and the adjustment result is more practical.
In one embodiment, the constraint condition includes an equality constraint and an inequality constraint; the equality constraints comprise power flow constraints; the inequality constraints comprise active output constraints and reactive output constraints of the controllable generator, branch active power constraints and section active power constraints.
In this embodiment, the constraint conditions in the optimized power flow model include equality constraints and inequality constraints, where the equality constraints include power flow constraints, and in any case, the power flow equation of the power system must be satisfied, that is, the generated power always keeps balanced with the system load, and the equation is as follows:
P Gi -(1+λ)P Di ＝U i ∑U j [G ij cos(δ i -δ j )+B ij sin(δ i -δ j )]
Q Gi -(1+λ)Q Di ＝-U i ∑U j [B ij cos(δ i -δ j )-G ij sin(δ i -δ j )]
wherein, the left side of the equation is the active power P flowing into a certain node Gi And load power P Di (1 + λ) times of (a), i.e. maximum bearing capacity; the right side of the equation is the power flow out of the node, a power flow equation in a polar coordinate form is adopted, i represents the node, and j represents another node (any node) related to i; and summing the power flows flowing to all nodes related to the node i to obtain the total power flow flowing out of the node i.
The inequality constraints comprise active output constraints and reactive output constraints of the controllable generator, branch active power constraints and section active power constraints, and specifically comprise the following steps:
1. active power output constraint of controllable generator
During the active power adjustment process of the generator, the maximum active power and the minimum active power are limited. The maximum active power of the generator set is generally a rated value of the active output of the generator; the minimum generated active power is limited by technical conditions. The inequality constraints on the active output of the controllable generator are expressed as follows:
P minGi ≤P Gi ≤P maxGi i∈S G
in the formula, P minGi -a maximum capacity lower limit for unit i; p maxGi -minimum technical output upper limit of the unit i.
2. Reactive power output constraint for controllable generator
During the reactive power adjustment process of the generator, the maximum reactive power and the minimum reactive power are limited. The inequality constraint on the active power output of the controllable generator is expressed as follows:
Q minGi ＜Q Gi ＜Q maxGi i∈S G
in the formula, Q minGi -maximum capacity upper limit of unit i; q maxGi -minimum technical output lower limit of the unit i.
3. Branch active power constraint
The adjustment of the generator power necessarily results in a change of the branch flow, and the changed branch power should be constrained by the upper and lower limit values of the branch.
The power limit of the transmission line is a reflection of the transmission capacity, the transmission capacity of the line may be limited by various stability factors, and the transmission line limit adopted by safety constraint scheduling depends on different network safety standards, such as: n-0 standard, N-1 standard, N-2 standard, etc., with different safety standards corresponding to different power limits and different operating costs.
The inequality constraint of the branch active power constraint is expressed as follows:
P minij ≤P ij ≤P maxij
in the formula, P minij 、P maxij Respectively is the lower limit and the upper limit of the branch active power flow, and the following formula is P in the above formula ij In the specific representation of (a), a branch represents a line connecting a node i and a node j, e and f represent vertical components of a voltage U in the directions of an x axis and a y axis, respectively, in a rectangular coordinate system, and G and B represent conductance and susceptance, respectively.
4. Active power constraint of the section:
in addition to being concerned about the crossing of the power line flow, operators sometimes wish to monitor the flow profile. When faults such as short circuit, disconnection and the like of different types occur, the active power flow of the control section is within a safety limit value, and the transient stability of a power grid when the faults occur can be guaranteed to a certain extent.
The active inequality constraint of the section is expressed as follows:
in the formula (I), the compound is shown in the specification,
the upper limit and the lower limit of the active power of the section T are respectively; p ij Is the active power of branch ij in the section T;
the resultant power (directional) of the cross section T is shown.
In one embodiment, the step of calculating the maximum bearable load of each node in the first network architecture by using the optimized power flow model in step S130 may include:
and taking a 220kV transformer substation corresponding to the transformer substation node in the 500kV network architecture as a load, and determining the maximum bearable load of the transformer substation node corresponding to the target function by combining the equality constraint and the inequality constraint through a tracking center track inner point method.
In the embodiment, when a 500kV network is calculated, a 220kV transformer substation network is equivalent to the load of a 500kV transformer substation; namely, when calculating the node of the 500kV transformer substation, the 220kV transformer substation related to the same subarea grid frame is taken as the load (P) Di ，Q Di ) And processing is carried out, so that the calculation workload is reduced, and the calculation speed is improved.
Further, when solving the objective function in combination with the equality constraint and the inequality constraint, the solution may be performed using a tracking center trajectory interior point method.
Because the most core part of the node safety index calculation is the calculation of the maximum bearable load of the node, for optimization problems, the primal-dual interior point method has strong convergence and high calculation speed, but for large-scale practical problems, it is often very difficult to find a feasible initial point. The following introduced tracking center trajectory interior point method only requires that the relaxation variables and the Lagrange multiplier meet simple conditions of being more than or less than zero in the optimization process, and can replace the original requirement of solving in a feasible domain, so that the calculation process is greatly simplified.
For ease of discussion, the optimized power flow model is simplified to the following general nonlinear optimization model, described in detail below:
obj.min.f(x) (1)
s.t.h(x)＝0 (2)
wherein, the formula (1) is an objective function and is a nonlinear function; the formula (2) is a nonlinear equation constraint condition, wherein h (x) = [ h = 1 (x),h 2 (x),…,h m (x)] T M is the number of equality constraint conditions; the formula (3) is an inequality constraint condition, wherein g (x) = [ g = 1 (x),g 2 (x),…,g r (x)] T R is the number of equality constraints, the upper limit is
The lower limit isg＝[g 1 ,g 2 ,…,g r ] T 。
The basic idea of the tracking center trajectory interior point method is as follows, firstly, an inequality constraint formula (3) is converted into an equality constraint:
where l, u are relaxation variables, l = [ l = 1 ,l 2 ,…,l r ] T ，u＝[u 1 ,u 2 ,…,u r ] T L > 0 and u > 0 should be satisfied.
Thus, the original problem becomes the optimization problem a:
the objective function is then transformed into a barrier function that should approximate the original objective function f (x) in the feasible domain, but become very large at the boundary. An optimization problem B can thus be obtained:
wherein, the perturbation factor (or barrier constant) mu is more than 0; in the Σ function, j =1 indicates that the summation is performed from 1 with j as a variable; r represents summing up to r; j after Σ is a variable, meaning entirely for In (l) j ) J is summed from all cases 1 to r.
When l is i Or u i When approaching the boundary, the objective function tends to infinity, so a minimal solution satisfying the above barrier objective function cannot be found on the boundary, and an optimal solution can only be obtained when l > 0, u > 0 are satisfied. Therefore, the optimization problem A containing inequality limitation is changed into the optimization problem B only containing equality constraint through the transformation of the objective function, and therefore the Lagrange multiplier method can be directly used for solving.
In one embodiment, the step of calculating the maximum bearable load of each node in the small network architecture by using the optimized power flow model in step S130 may include:
and determining the maximum bearable load of the substation node corresponding to the target function by using the tracking center track interior point method by taking the 500kV substation corresponding to the substation node in the 220kV network architecture as a power supply and combining the equality constraint, the inequality constraint and the maximum bearable load of the 500kV substation.
In this embodiment, when calculating a 220kV substation, the 500kV substation is considered as a power supply of the 220kV network in combination with the calculation result of the 500kV network, that is, when calculating a node of the 220kV substation, the 500kV substation connected to the node in the partitioned grid is used as a power supply (P) Gi ，Q Gi ) And processing is carried out, so that the calculation workload is reduced, and the calculation speed is improved.
In one embodiment, the step of evaluating the operation security of the node according to the maximum bearable load in step S130 includes:
s131: acquiring the real-time load quantity of the node, and calculating the power supply adequacy of the node according to the maximum bearable load of the node and the real-time load quantity;
s132: and evaluating the operation safety of the node according to the power supply adequacy.
In this embodiment, when the operation safety of the node is evaluated, the power supply adequacy of the node is mainly used as a basis, and therefore, a calculation formula of the node operation safety degree algorithm may be expressed as:
C(i)＝f(P max,i ,P Cur,i )
wherein C (i) is the result of evaluating the power supply safety degree of the node i, P max,i Is the maximum bearable load, P, of node i under the current condition of the system Cur,i Is the real-time load amount of node i.
The node operation safety degree provided by the application evaluates the power supply safety degree by calculating the allowance of the power supply capacity and the power supply requirement of each operation node under the real-time condition, and by combining a pre-established intelligent scheduling index system, the calculation result of C (i) is reduced to the interval of 0-1, and then the specific expression of C (i) is as follows:
in the above-mentioned expression, the expression,
and representing the power supply margin of the node i under the real-time condition, and accordingly influencing the power supply safety degree calculation result of the node i.
In an embodiment, after the step of evaluating the operation security of the node according to the maximum bearable load in step S130, the method may further include:
s140: and (4) counting the power supply adequacy of each node, and performing warning operation on the node with the minimum power supply adequacy.
This exampleAfter the power supply adequacy of each node is calculated, integrating the power supply adequacy index C of each node i And the minimum value is recommended to reflect the worst condition, so that the minimum value plays a warning role for the dispatcher, and meanwhile, the nodes with low power supply adequacy can be displayed as required.
In an embodiment, as shown in fig. 3, fig. 3 is a schematic structural diagram of an apparatus for evaluating operation safety of a node of an electrical power system according to an embodiment of the present invention; the invention also provides a device for evaluating the operation safety of the nodes of the power system, which comprises a layered partition module 110, a model construction module 120 and a safety evaluation module 130, and specifically comprises the following components:
the hierarchical partitioning module 110 is configured to hierarchy a network architecture in an electric power system according to voltage levels to obtain a first network architecture and a second network architecture, and partition the second network architecture according to the first network architecture and a corresponding power grid topology structure to obtain small network architectures in different areas;
the model building module 120 is configured to obtain operation data of the power system, perform ground state power flow calculation according to the operation data, and build an optimized power flow model according to the first network architecture, the small network architecture and the operation data if the ground state power flow is converged;
and a security evaluation module 130, configured to separately calculate maximum loadable loads of each node in the first network architecture and the small network architecture by using the optimized power flow model, and evaluate the operation security of the node according to the maximum loadable loads.
In the embodiment, considering that the power system comprises networks with different voltage levels and a certain network topology structure is arranged among the networks with different voltage levels, the power system is divided into different voltage levels and different areas before node safety evaluation is performed, so that the calculation amount is reduced and the real-time evaluation efficiency is improved; in addition, the maximum bearable load of each node is determined by optimizing the power flow model, so that the accuracy of safety assessment is improved, and relevant measures are further taken for links with relatively weak safety, so that the safe and stable operation of the power grid is ensured.
In an embodiment, the invention further provides a power system, and when the power system evaluates the operation safety of each node, the steps of the method for evaluating the operation safety of the nodes of the power system according to any one of the above embodiments are executed.
The above-mentioned embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will 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 of the embodiments of the present invention.
Claims (10)
1. A method for evaluating the operation safety of nodes of an electric power system is characterized by comprising the following steps:
layering network architectures in an electric power system according to voltage levels to obtain a first network architecture and a second network architecture, and partitioning the second network architecture according to the first network architecture and a corresponding power grid topological structure to obtain small network architectures in different areas; wherein the first network architecture is a 500kV network architecture and the second network architecture is a 220kV network architecture;
acquiring operation data of the power system, performing ground state power flow calculation according to the operation data, and if the ground state power flow is converged, constructing an optimized power flow model according to the 500kV network architecture, the small network architecture and the operation data;
and calculating the maximum bearable load of each node in the small-sized network architecture by using the optimized load flow model and the maximum bearable load of the 500kV transformer substation corresponding to the transformer substation node in the 500kV network architecture as a power supply, and evaluating the operation safety of the node according to the maximum bearable load.
2. The method according to claim 1, wherein the step of partitioning the second network architecture according to the first network architecture and the corresponding grid topology to obtain small network architectures in different areas comprises:
and partitioning the 220kV network architecture based on the 500kV network architecture and the corresponding power grid topological structure, and determining a small network architecture formed by a plurality of 220kV network architectures in different areas.
3. The method of claim 1, wherein the optimized power flow model comprises an objective function and constraints that maximize the loadable load capacity of the node.
4. The power system node operation safety evaluation method according to claim 3, wherein the constraint condition includes an equality constraint and an inequality constraint;
the equality constraints comprise power flow constraints; the inequality constraints comprise active output constraints and reactive output constraints of the controllable generator, branch active power constraints and section active power constraints.
5. The method for evaluating the operation safety of the nodes in the power system according to claim 4, wherein the step of calculating the maximum bearable load of each node in the 500kV network architecture by using the optimized power flow model comprises:
and determining the maximum bearable load of the substation node corresponding to the objective function by combining the equality constraint and the inequality constraint and using a tracking center track inner point method.
6. The method for evaluating the operation safety of the power system nodes according to claim 4, wherein the step of calculating the maximum bearable load of each node in the small network architecture by using the optimized power flow model and the maximum bearable load of the 500kV substation comprises the following steps:
and determining the maximum bearable load of the substation node corresponding to the objective function by using a tracking center track inner point method in combination with the equality constraint, the inequality constraint and the maximum bearable load of the 500kV substation.
7. The method for evaluating the operation safety of the power system node according to claim 1, wherein the step of evaluating the operation safety of the node according to the maximum bearable load comprises:
acquiring the real-time load quantity of the node, and calculating the power supply adequacy of the node according to the maximum bearable load of the node and the real-time load quantity;
and evaluating the operation safety of the node according to the power supply adequacy.
8. The method for evaluating operational safety of a node in a power system according to claim 7, further comprising, after the step of evaluating operational safety of the node according to the maximum bearable load:
and counting the power supply adequacy of each node, and performing warning operation on the node with the minimum power supply adequacy.
9. An electric power system node operation safety evaluation device, comprising:
the system comprises a layering and partitioning module, a first network architecture and a second network architecture, wherein the layering and partitioning module is used for layering the network architectures in the power system according to voltage grades to obtain the first network architecture and the second network architecture, and partitioning the second network architecture according to the first network architecture and a corresponding power grid topological structure to obtain small network architectures in different areas; wherein the first network architecture is a 500kV network architecture and the second network architecture is a 220kV network architecture;
the model building module is used for obtaining operation data of the power system, performing ground state power flow calculation according to the operation data, and building an optimized power flow model according to the 500kV network architecture, the small network architecture and the operation data if the ground state power flow is converged;
and the safety evaluation module is used for calculating the maximum bearable load of each node in the 500kV network architecture by using the optimized load flow model with the 220kV transformer substation corresponding to the transformer substation node in the 500kV network architecture as a load, calculating the maximum bearable load of each node in the small network architecture by using the optimized load flow model and the maximum bearable load of the 500kV transformer substation with the 500kV transformer substation corresponding to the transformer substation node in the 220kV network architecture as a power supply, and evaluating the operation safety of the node according to the maximum bearable load.
10. An electrical power system, characterized by: when the power system carries out operation safety evaluation on each node, the steps of the operation safety evaluation method of the power system node according to any one of claims 1 to 8 are executed.
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