CN115411779A - Short-circuit current calculation method, device and equipment considering double-fed fan crowbar input - Google Patents
Short-circuit current calculation method, device and equipment considering double-fed fan crowbar input Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/466—Scheduling the operation of the generators, e.g. connecting or disconnecting generators to meet a given demand
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/28—The renewable source being wind energy
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/40—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation wherein a plurality of decentralised, dispersed or local energy generation technologies are operated simultaneously
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Abstract
The invention relates to the technical field of electric power systems, and discloses a method, a device and equipment for calculating short-circuit current by considering the input of a crowbar of a double-fed fan. According to the method, the crowbar input priority of each double-fed fan of a target large power grid is determined based on the importance degree of the nodes and the initial voltage drop percentage, the crowbar input priority is sequenced from high to low, a corresponding double-fed fan set and a reactive current set are constructed, and the initial value of each element in the reactive current set is made to be a corresponding limit value; and performing short-circuit current iterative computation by updating the values of the first x elements in the reactive current set to zero, taking the current result as a target short-circuit current computation result if the voltage of the grid-connected point of the last n-x double-fed fans in the double-fed fan set is greater than the crowbar input threshold value during convergence, and otherwise, enabling x = x +1 and performing the short-circuit current iterative computation again. According to the method, the prying bar input factor of the double-fed fan is considered, and the accurate calculation of the power grid short-circuit current with high wind power permeability can be realized.
Description
Technical Field
The invention relates to the technical field of electric power systems, in particular to a method, a device and equipment for calculating short-circuit current considering the investment of a crowbar of a double-fed fan.
Background
In the design and operation of power systems and electrical equipment, short circuit calculations are essential basic calculations to solve a series of technical problems.
Existing short circuit current engineering calculation methods only consider synchronous generators, transmission networks and loads, where synchronous generators are considered as a parallel combination of constant current source and admittance, transmission networks are considered as a combination of resistance and reactance, and loads are considered as grounded branches and represented by constant impedance. When the power system is in a normal operation state, the node equation of the power system based on the method can be expressed as follows:
in the formula, Y is a node admittance matrix, V is a node voltage vector, I is a node injection current vector, the current of only the generator end node is not zero, and the currents of the other nodes are all zero.
The node equations for the power system can be transformed into:
V＝ZI
wherein Z is a nodal impedance matrix which is an inverse of the nodal admittance matrix, and can be derived from the nodal admittance matrix, Z = Y -1 。
Assuming that node f in the system is directly shorted to ground, it is equivalent to adding an injection current i to node f f Because of the constant current source of the synchronous generator before and after the faultThe injected current is constant, so the node equation of the network after short circuit is:
in the formula I f The vector of the variation value of the current injected into the node f before and after the short-circuit fault is shown, only the value at the node f is not zero, and the rest values are all zero.
After the short circuit, the voltage of the node f becomes 0, and therefore, the voltage equation in the above equation can be expressed as:
0＝v f +z ff i f
the short-circuit current calculation formula of the node f is as follows:
in the formula, v f Voltage of node f before short circuit, Z ff The self-impedance of node f is represented as an element in the node impedance matrix Z.
Therefore, the conventional short-circuit current engineering calculation method does not consider a crowbar input factor or directly equates the crowbar input to a tripping state (namely disconnection with a power grid). With the increasing wind power permeability, the influence of the double-fed wind turbine on the calculation of the short-circuit current of the power grid cannot be ignored, and particularly the influence on the power grid area with a high wind power generation ratio is obtained. When the voltage of a grid connection point falls below a low-voltage crossing threshold value, the doubly-fed wind turbine needs to provide reactive current for a power grid to support voltage. When the double-fed fan is close to a short-circuit point or the short-circuit fault is serious, the voltage of a grid-connected point of the double-fed fan falls to a crowbar input threshold value, the double-fed fan is input into a crowbar circuit to avoid overcurrent damage of a converter at the rotor side, the short-circuit current characteristic of the double-fed fan at the moment can be approximately regarded as an asynchronous motor, and the characteristic is equivalent to impedance in a short-circuit current calculation program.
Therefore, when the double-fed fan crowbar input factor is considered, the node equation of the network after short circuit and the short-circuit current calculation formula are not applicable any more, and the conventional method is obviously inaccurate in calculation of the short-circuit current of the power grid with high wind power permeability.
In addition, if the crowbar input factor is taken into consideration in the short-circuit current calculation program, that is, the reactive current or the short-circuit impedance which should be provided by the current doubly-fed wind turbine is judged according to the newly calculated grid-connected point voltage in the iterative process, the calculation program is difficult to converge due to factors such as initial value selection, node admittance matrix change, reactive current change, mutual influence among the doubly-fed wind turbines and the like.
Disclosure of Invention
The invention provides a short-circuit current calculation method, a short-circuit current calculation device and short-circuit current calculation equipment considering the input of a crowbar of a double-fed fan, and solves the technical problem that the short-circuit current of a power grid with high wind power permeability is difficult to accurately calculate due to the fact that the input factor of the crowbar of the double-fed fan is not considered in the conventional short-circuit current engineering calculation method.
The invention provides a method for calculating short-circuit current by considering the input of a crowbar of a double-fed fan, which comprises the following steps:
the method comprises the following steps of S1, determining the lever input priority of each double-fed fan of a target large power grid; the larger the value of the lever input priority is, the larger the weighted sum of the importance degree of the corresponding node and the initial voltage drop percentage is;
s2, sequencing the double-fed fans according to the sequence of the crowbar input priority from high to low, constructing a corresponding double-fed fan set and a reactive current set according to the obtained sequencing result, and enabling the value of each element in the reactive current set to be a corresponding limit value; the kth element in the reactive current set represents the reactive current provided by the kth doubly-fed fan in the doubly-fed fan set;
s3, calculating the short-circuit current of the target large power grid, wherein the calculation comprises the following steps: step S3.1, let x =1; step S3.2, assuming that front x double-fed fans in the double-fed fan set are put into a crowbar, updating the values of front x elements in the reactive current set to be zero, calculating corresponding equivalent impedance of the double-fed fans, and updating a node admittance matrix of a target large power grid; s3.3, calculating short-circuit node current and node voltage according to current values of elements in the reactive current set, updating values of corresponding elements in the reactive current set according to calculation results, and performing iterative calculation on the short-circuit node current and the node voltage until a convergence condition is met; and S3.4, judging whether the grid-connected point voltages of the back n-x double-fed fans in the double-fed fan set are all larger than a crowbar input threshold value when the calculation result is converged, if so, taking the current solved short-circuit point current and the voltage of each node as a target short-circuit current calculation result, otherwise, enabling x = x +1, and returning to the step S3.2.
According to an implementation manner of the first aspect of the present invention, the determining the crowbar input priority of each doubly-fed wind turbine of the target large grid includes:
determining various indexes for evaluating the input priority of the crowbar, wherein the indexes comprise indexes representing the importance degree of the nodes and the initial voltage drop percentage of the double-fed fan;
determining the weight of each index;
and calculating the corresponding crowbar input priority by adopting weighted summation according to the weight and the data of each index corresponding to the double-fed fan.
According to an implementation manner of the first aspect of the present invention, the determining indexes for evaluating the investment priority of the crowbar includes:
determining indexes representing the importance degree of the nodes, wherein the indexes comprise the degree centrality, the betweenness centrality and the cohesion degree of the nodes;
the calculating of the corresponding crowbar input priority by adopting weighted summation comprises the following steps:
calculating the corresponding crowbar input priority according to the following formula:
E i ＝a 1 (1-U i )+a 2 D i +a 3 M i +a 4 B i
in the formula, E i Indicating the crowbar throw-in priority, U, of the ith doubly-fed wind turbine i Is the voltage per unit value of the grid-connected point of the ith doubly-fed fan, 1-U i Represents the initial voltage drop percentage of the ith doubly-fed wind turbine, D i Expressing the degree centrality, M, of the ith doubly-fed wind turbine i Showing the ith doubly-fed fanMesomeric centrality of, B i Represents the condensation degree of the ith doubly-fed wind turbine, a 1 Is the weight corresponding to the initial voltage drop percentage, a 2 A weight corresponding to centrality, a 3 Is a weight corresponding to the betweenness centrality, a 4 The weight corresponding to the degree of aggregation.
According to a manner that can be realized in the first aspect of the present invention, the updating the values of the corresponding elements in the reactive current set according to the calculation result, and performing iterative calculation of the short-circuit node current and the voltage of each node until the convergence condition is satisfied includes:
s3.31, calculating correspondingly provided reactive current according to the voltage of the grid-connected point of the back n-x double-fed fans in the double-fed fan set, and updating the value of a corresponding element in the reactive current set according to the calculated reactive current;
step S3.32, calculating short-circuit node current and each node voltage according to the current value of each element in the reactive current set;
and step S3.33, if the voltage difference of each node of the calculation results of the current of the two adjacent short-circuit nodes and the voltage of each node is less than the voltage difference threshold value, judging that the convergence condition is met, otherwise, returning to the step S3.31.
According to a manner that can be realized by the first aspect of the present invention, the updating the value of the corresponding element in the reactive current set according to the calculated reactive current includes:
if the voltage of the grid-connected point of the double-fed fan is not less than the low-voltage crossing threshold, the correspondingly provided reactive current is zero;
if the voltage of the grid-connected point of the double-fed fan is smaller than the low-voltage ride-through threshold, calculating correspondingly provided reactive current according to the following formula:
I q ＝K v (0.9-U)
in the formula I q Representing reactive current, K, correspondingly supplied by doubly-fed wind turbines v And U is a voltage per unit value of a grid-connected point of the double-fed motor.
According to an enabling aspect of the first aspect of the invention, the method further comprises:
setting the input threshold value of the crowbar to be 0.4p.u.;
setting the voltage difference threshold to be 0.001p.u.;
and/or setting the low-voltage crossing threshold value to be 0.9p.u.
According to an implementation manner of the first aspect of the present invention, in the step S3, the short-circuit node current and the node voltages are calculated according to the following formulas:
in the formula I f Injecting a vector of the variation of the current, I, for the node f before and after the short-circuit fault 1 ,I 2 ,...,I n The reactive current Z provided by the 1 st, 2., n doubly-fed wind turbines respectively 1f ,Z 2f ,..., Z nf 1,2, the transfer impedance between n doubly-fed wind turbines and a short-circuit node, v f Voltage at node f before short circuit, Z ff Is the self-impedance of node f, V i Is the voltage of node i, Z 1i ,Z 2i ,...,Z ni The transfer impedance between the n doubly-fed wind turbines and the node i is 1, 2.
The invention provides a short-circuit current calculating device considering the pry bar input of a double-fed fan, which comprises the following components:
the determination module is used for determining the crowbar input priority of each double-fed fan of the target large power grid; the larger the value of the lever input priority is, the larger the weighted sum of the importance degree of the corresponding node and the initial voltage drop percentage is;
the building module is used for sequencing the double-fed fans according to the sequence of the crowbar input priority from high to low, building a corresponding double-fed fan set and a reactive current set according to the obtained sequencing result, and enabling the value of each element in the reactive current set to be a corresponding limit value; the kth element in the reactive current set represents the reactive current provided by the kth doubly-fed fan in the doubly-fed fan set;
the calculation module is used for calculating the short-circuit current of the target large power grid and comprises: an initial value setting unit for letting x =1; the first calculation unit is used for assuming that the front x double-fed fans in the double-fed fan set are put into a crowbar, updating the values of the front x elements in the reactive current set to zero, calculating corresponding equivalent impedance of the double-fed fans, and updating a node admittance matrix of a target large power grid; the second calculation unit is used for calculating short-circuit node current and node voltage according to current values of all elements in the reactive current set, updating values of corresponding elements in the reactive current set according to calculation results, and performing iterative calculation on the short-circuit node current and the node voltage until convergence conditions are met; and the judging unit is used for judging whether the grid-connected point voltages of the back n-x double-fed fans in the double-fed fan set are all larger than a crowbar input threshold value when the calculation result is converged, if so, taking the current solved short-circuit point current and the voltage of each node as a target short-circuit current calculation result, and if not, enabling x = x +1 and returning to the first calculating unit.
According to an implementable manner of the second aspect of the invention, the determining module comprises:
the first determining unit is used for determining various indexes for evaluating the input priority of the crowbar, wherein the indexes comprise indexes representing the importance degree of nodes and the initial voltage drop percentage of the double-fed fan;
the second determining unit is used for determining the weight of each index;
and the third calculating unit is used for calculating the corresponding crowbar input priority by adopting weighted summation according to the weight and the data of each index corresponding to the double-fed fan.
According to an implementable manner of the second aspect of the present invention, the first determining unit is specifically configured to:
determining indexes representing the importance degree of the nodes, wherein the indexes comprise degree centrality, betweenness centrality and cohesion of the nodes;
the third calculating unit is specifically configured to calculate a corresponding crowbar input priority according to the following formula:
E i ＝a 1 (1-U i )+a 2 D i +a 3 M i +a 4 B i
in the formula, E i Indicating the crowbar throw-in priority, U, of the ith doubly-fed wind turbine i Is the voltage per unit value of the grid-connected point of the ith doubly-fed fan, 1-U i The initial voltage drop percentage of the ith doubly-fed wind turbine is expressed, D i The degree centrality, M, of the ith doubly-fed fan is shown i Expressing the betweenness centrality of the ith doubly-fed fan, B i Represents the condensation degree of the ith doubly-fed wind turbine, a 1 Is the weight corresponding to the initial voltage drop percentage, a 2 A weight corresponding to centrality, a 3 A weight corresponding to the betweenness centrality 4 Is the weight corresponding to the degree of aggregation.
According to an implementable manner of the second aspect of the present invention, the second calculation unit includes:
the updating subunit is used for calculating correspondingly provided reactive current according to the voltage of the grid-connected point of the last n-x double-fed fans in the double-fed fan set, and updating the value of the corresponding element in the reactive current set according to the calculated reactive current;
the calculating subunit is used for calculating short-circuit node current and each node voltage according to the current values of each element in the reactive current set;
and the judging subunit is used for judging that the convergence condition is met if the voltage difference of each node of the calculation results of the short-circuit node current and each node voltage of two adjacent times is smaller than the voltage difference threshold value, and otherwise, returning to the updating subunit.
According to an implementable manner of the second aspect of the present invention, the update subunit is specifically configured to:
if the voltage of the grid-connected point of the double-fed fan is not less than the low-voltage crossing threshold, the correspondingly provided reactive current is zero;
if the voltage of the grid-connected point of the double-fed fan is smaller than the low-voltage ride-through threshold, calculating correspondingly provided reactive current according to the following formula:
I q ＝K v (0.9-U)
in the formula I q Representing reactive current, K, correspondingly supplied by the doubly-fed wind turbine v For voltage regulation factor, U is double feedAnd voltage per unit value of the grid-connected point.
According to an implementable manner of the second aspect of the invention, the apparatus further comprises:
the first setting module is used for setting the input threshold value of the crowbar to be 0.4p.u;
a second setting module, configured to set the voltage difference threshold to 0.001p.u.;
and/or a third setting module, configured to set the low voltage crossing threshold to 0.9p.u.
According to an implementation manner of the second aspect of the present invention, the calculating module is specifically configured to calculate the short-circuit node current and the node voltages according to the following formulas:
in the formula I f Vector of variation values of injected current for node f before and after short-circuit fault, I 1 ,I 2 ,...,I n The reactive current Z provided by the 1 st, 2., n doubly-fed wind turbines respectively 1f ,Z 2f ,..., Z nf 1,2, transfer impedance between n doubly-fed wind turbines and a short-circuit node, v f Voltage of node f before short circuit, Z ff Is the self-impedance of node f, V i Is the voltage of node i, Z 1i ,Z 2i ,...,Z ni The transfer impedance between the n doubly-fed wind turbines and the node i is 1, 2.
The third aspect of the invention provides a short-circuit current calculation device considering the crowbar investment of a double-fed fan, which comprises:
a memory to store instructions; the instruction is used for realizing the method for calculating the short-circuit current considering the crowbar input of the double-fed fan in any one realizable mode;
a processor to execute the instructions in the memory.
A fourth aspect of the present invention is a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the method for calculating a short-circuit current considering a crowbar throw of a doubly-fed wind turbine in any one of the above-mentioned implementable manners.
According to the technical scheme, the invention has the following advantages:
according to the method, the crowbar input priority of each double-fed fan of a target large power grid is determined based on the importance degree of the nodes and the initial voltage drop percentage, the double-fed fans are sequenced according to the sequence of the crowbar input priority from high to low, a corresponding double-fed fan set and a reactive current set are constructed, and the initial values of all elements in the reactive current set are enabled to be corresponding limit values; carrying out iterative calculation on the target large power grid short-circuit current by updating the values of the first x elements in the reactive current set to zero, if the grid-connected point voltages of the last n-x double-fed fans in the double-fed fan set are all larger than the crowbar input threshold value when the calculation result is converged, taking the current calculation result as the calculation result of the target short-circuit current, and if the calculation result is not converged, making x = x +1 and carrying out iterative calculation on the short-circuit current again; according to the invention, a crowbar input measure can be preferentially adopted for the double-fed fan with large initial voltage drop percentage and low node importance degree, otherwise, the double-fed fan with small initial voltage drop percentage and high node importance degree is in a normal operation or low-voltage ride-through state as much as possible, the final convergence of short-circuit current calculation is ensured, and the accuracy of the grid short-circuit current calculation with high wind-electricity permeability is improved.
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 flowchart of a short-circuit current calculation method considering a crowbar of a doubly-fed wind turbine according to an alternative embodiment of the present invention;
FIG. 2 is a flowchart illustrating an operation of performing an iterative calculation of the short-circuit node current and the voltage of each node based on the method shown in FIG. 1 until a convergence condition is satisfied according to an alternative embodiment of the present invention;
fig. 3 is a structural connection block diagram of a short-circuit current calculation device considering the crowbar input of the doubly-fed wind turbine according to an alternative embodiment of the present invention.
Reference numerals:
1-a determination module; 2-building a module; and 3, a calculation module.
Detailed Description
The embodiment of the invention provides a short-circuit current calculation method, a short-circuit current calculation device and short-circuit current calculation equipment considering the prying bar input of a double-fed fan, and aims to solve the technical problem that the power grid short-circuit current with high wind power permeability is difficult to accurately calculate due to the fact that the prying bar input factor of the double-fed fan is not considered in the conventional short-circuit current engineering calculation method.
In order to make the objects, features and advantages of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the embodiments described below are only a part of the embodiments of the present invention, 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 invention.
The invention provides a short-circuit current calculation method considering the prying bar input of a double-fed fan.
Referring to fig. 1, fig. 1 shows a flowchart of a method for calculating a short-circuit current considering a crowbar of a doubly-fed wind turbine according to an embodiment of the present invention.
The short-circuit current calculation method considering the double-fed fan crowbar input comprises the steps of S1-S3.
The method comprises the following steps of S1, determining the lever input priority of each double-fed fan of a target large power grid; wherein, the larger the value of the crowbar drop priority is, the larger the weighted sum of the importance degree of the corresponding node and the initial voltage drop percentage is.
In an implementation manner, the determining the crowbar engagement priority of each double-fed wind turbine of the target large power grid includes:
determining various indexes for evaluating the input priority of the crowbar, wherein the indexes comprise indexes representing the importance degree of the nodes and the initial voltage drop percentage of the double-fed fan;
determining the weight of each index;
and calculating the corresponding crowbar input priority by adopting weighted summation according to the weight and the data of each index corresponding to the double-fed fan.
The indexes representing the importance degree of the nodes can be set according to the actual condition of the power grid. In an implementation manner, the index for determining the importance degree of the characteristic node includes a degree-centrality, an betweenness-centrality and an aggregation degree of the node.
The degree centrality of the node is defined as the number of neighbor nodes directly connected with the node, and the index reflects that the importance degree of the node is larger if the number of the neighbors of the node is larger. The degree centrality is a basic index for evaluating the importance degree of the nodes, and the expression of the degree centrality is as follows:
in the formula, D i Expressing the degree centrality, N, of the ith doubly-fed wind turbine i And n-1 is the maximum possible value of the grid node value, and is the number of the neighbor nodes directly connected with the ith double-fed fan.
The betweenness centrality of the nodes is defined as the proportion of the shortest paths among all the nodes of the power grid passing through the nodes, and the index reflects the influence of the nodes on information flow transmitted along the shortest paths in the network. The betweenness centrality index is widely applied to a power grid although the calculation process is complex. Mesomeric centrality M i The expression of (a) is:
in the formula, G st The shortest path from the start node s to the end node t,
the shortest path from the start node s to the end node t and through node i.
Assuming that the total number of nodes of the undirected network is n, the average distance between the nodes is d, the value represents the arithmetic mean of the shortest distances between all the nodes, and the network cohesion is defined as the reciprocal of the product of the number of network nodes and the average distance, the network cohesion C can be represented as:
in the formula (d) ij And N is a power grid node set.
The condensation degree B of the ith doubly-fed fan i Can be expressed as:
in the formula, C i For deleting the network condensation degree rho after the ith doubly-fed fan i Is the number of nodes associated with the ith doubly-fed wind turbine, d i And deleting the average distance between the network nodes after the ith doubly-fed fan is deleted.
As a specific embodiment, when the index representing the importance degree of the node includes the degree centrality, the betweenness centrality and the aggregation degree of the node, the corresponding crowbar input priority is calculated according to the following formula:
E i ＝a 1 (1-U i )+a 2 D i +a 3 M i +a 4 B i
in the formula, E i Indicating the crowbar throw-in priority, U, of the ith doubly-fed wind turbine i The voltage per unit value of the grid-connected point of the ith doubly-fed fan is 1-U i The initial voltage drop percentage of the ith doubly-fed wind turbine is representedRatio, D i Expressing the degree centrality, M, of the ith doubly-fed wind turbine i Expressing the betweenness centrality of the ith doubly-fed fan, B i Represents the condensation degree of the ith doubly-fed wind turbine, a 1 Is the weight corresponding to the initial voltage drop percentage, a 2 A weight corresponding to centrality, a 3 A weight corresponding to the betweenness centrality 4 Is the weight corresponding to the degree of aggregation.
The method for determining the index weight is generally divided into a subjective method and an objective method, and in order to avoid negative influence caused by subjective will, in this embodiment, an entropy method may be used to determine the weight. The entropy method is an objective weighting method for determining the weight of indexes according to the difference of the degree of order of information contained in each index. For a certain index, the smaller the entropy value of the index is, the larger the weight of the index is; conversely, the larger the entropy of the index is, the smaller the weight of the index is.
As a specific implementation manner, an original evaluation value matrix is formed for n nodes of the target large power grid and the 4 evaluation indexes, and further, the objective weight of each index is determined based on an entropy method:
(1) Calculating the proportion p of the index value of the node i under the jth index ij ：
In the formula, V ij Representing the index value of the node i under the jth index;
(2) Calculating the entropy e of the jth index j ：
(3) Calculating an objective weight coefficient of the jth index:
in the formula, ω p_j Representing the j-th indexObjective weighting factor.
S2, sequencing the double-fed fans according to the sequence of the crowbar input priority from high to low, constructing a corresponding double-fed fan set and a reactive current set according to the obtained sequencing result, and enabling the value of each element in the reactive current set to be a corresponding limit value; and the kth element in the reactive current set represents the reactive current provided by the kth doubly-fed fan in the doubly-fed fan set.
In a possible manner, the limit value of each element in the reactive current set is set to be 1.1 to 1.3 times the corresponding rated current. As a specific embodiment, the limit value of each element in the reactive current set is set to be 1.2 times of the corresponding rated current.
Step S3, calculating the short-circuit current of the target large power grid, wherein the calculation comprises the following steps: step S3.1, let x =1; step S3.2, assuming that front x double-fed fans in the double-fed fan set are put into a crowbar, updating the values of front x elements in the reactive current set to be zero, calculating corresponding equivalent impedance of the double-fed fans, and updating a node admittance matrix of a target large power grid; s3.3, calculating short-circuit node current and node voltage according to current values of elements in the reactive current set, updating values of corresponding elements in the reactive current set according to calculation results, and performing iterative calculation on the short-circuit node current and the node voltage until a convergence condition is met; and S3.4, judging whether the grid-connected point voltages of the back n-x double-fed fans in the double-fed fan set are all larger than a crowbar input threshold value when the calculation result is converged, if so, taking the current solved short-circuit point current and the voltage of each node as a target short-circuit current calculation result, otherwise, enabling x = x +1, and returning to the step S3.2.
When the double-fed fan is close to a short-circuit point or the short-circuit fault is serious, when the voltage of a grid-connected point of the double-fed fan drops to a crowbar input threshold value, the double-fed fan is required to be input into a crowbar circuit to avoid overcurrent damage of a rotor side converter, the short-circuit current characteristic of the double-fed fan at the moment can be approximately regarded as an asynchronous motor, the equivalent is impedance in a short-circuit current calculation program, and the calculation formula of the equivalent impedance Z is as follows:
in the formula, R s Is stator resistance, R r Is rotor resistance, X s Is a stator reactance, X r Is rotor reactance, X m For the magnetizing reactance, s is the slip, where j is the imaginary component.
The corresponding equivalent impedance of the doubly-fed wind turbine can be calculated based on a calculation formula of the equivalent impedance Z.
In an implementation manner, as shown in fig. 2, the updating the values of the corresponding elements in the reactive current set according to the calculation result, and performing iterative calculation of the short-circuit node current and the voltage of each node until a convergence condition is satisfied includes:
s3.31, calculating correspondingly provided reactive current according to the voltage of the grid-connected point of the back n-x double-fed fans in the double-fed fan set, and updating the value of a corresponding element in the reactive current set according to the calculated reactive current;
step S3.32, calculating short-circuit node current and each node voltage according to the current value of each element in the reactive current set;
and step S3.33, if the voltage difference of each node of the calculation results of the current of the two adjacent short-circuit nodes and the voltage of each node is less than the voltage difference threshold value, judging that the convergence condition is met, otherwise, returning to the step S3.31.
When the voltage of a grid connection point falls below a low-voltage crossing threshold value, the doubly-fed wind turbine needs to provide reactive current for a power grid to support voltage. Based on this, in an achievable manner, the updating the value of the corresponding element in the reactive current set according to the calculated reactive current includes:
if the voltage of the grid-connected point of the double-fed fan is not less than the low-voltage crossing threshold, the correspondingly provided reactive current is zero;
if the voltage of the grid-connected point of the double-fed fan is smaller than the low-voltage ride-through threshold, calculating correspondingly provided reactive current according to the following formula:
I q ＝K v (0.9-U)
in the formula I q Representing reactive current, K, correspondingly supplied by doubly-fed wind turbines v And U is a voltage per unit value of the grid-connected point of the double-fed motor.
In one implementation, the low voltage crossing threshold is set to range from 0.85 to 0.95p.u. As a specific embodiment, the low voltage crossing threshold is set to 0.9p.u.
In one implementation, the voltage difference threshold is set to a value in a range of 0.001 to 0.002p.u. As a specific embodiment, the voltage difference threshold is set to 0.001p.u.
In one implementation, the value range of the crowbar input threshold is set to be 0.35-0.45p.u. As a specific embodiment, the crowbar input threshold is set to be 0.4p.u.;
in one implementation, in step S3, the short-circuit node current and the node voltages are calculated according to the following formula:
in the formula I f Vector of variation values of injected current for node f before and after short-circuit fault, I 1 ,I 2 ,...,I n The reactive current Z provided by the 1 st, 2., n doubly-fed wind turbines respectively 1f ,Z 2f ,..., Z nf 1,2, transfer impedance between n doubly-fed wind turbines and a short-circuit node, v f Voltage at node f before short circuit, Z ff Is the self-impedance of node f, V i Is the voltage of node i, Z 1i ,Z 2i ,..., Z ni 1,2, transfer impedance between n doubly-fed wind turbines and a node i.
Calculating initial voltage drop without considering the condition that the double-fed fan provides short-circuit current, wherein the calculation method comprises the following steps: setting the reactive current provided by all the double-fed fans to be 0 constantly, and obtaining the voltage of the grid-connected point of each double-fed fan according to the calculation formula of the short-circuit node current and the voltage of each node, namely 1-U i As the i-thInitial voltage drop percentage of the platform doubly-fed wind turbine, wherein U i And the voltage per unit value of the grid-connected point of the ith double-fed fan is obtained. In order to ensure the final convergence of the short-circuit current calculation, it is required to judge which units are in a low-voltage ride-through state finally before iterative calculation, and which units are in a crowbar input measure, which is a permutation and combination problem and has more than one final answer probability, and it is considered that a large amount of reactive power is absorbed from a power grid by a double-fed fan adopting the crowbar input measure, so that negative influence is brought to the voltage recovery of the power grid after a fault.
The invention further provides a short-circuit current calculation device considering the throw-in of the crowbar of the double-fed fan, and the device can be used for executing the short-circuit current calculation method considering the throw-in of the crowbar of the double-fed fan in any embodiment of the invention.
Referring to fig. 3, fig. 3 is a connection block diagram of a short-circuit current calculating device considering the insertion of a crowbar of a doubly-fed wind turbine according to an embodiment of the present invention.
The short-circuit current calculating device considering the double-fed fan crowbar input provided by the embodiment of the invention comprises the following components:
the determination module 1 is used for determining the crowbar input priority of each double-fed fan of the target large power grid; the larger the value of the crowbar input priority is, the larger the weighted sum of the importance degree of the corresponding node and the initial voltage drop percentage is;
the building module 2 is used for sequencing the double-fed fans according to the sequence of the crowbar input priority from high to low, building a corresponding double-fed fan set and a reactive current set according to the obtained sequencing result, and enabling the value of each element in the reactive current set to be a corresponding limit value; the kth element in the reactive current set represents the reactive current provided by the kth doubly-fed fan in the doubly-fed fan set;
the calculation module 3 is used for calculating the short-circuit current of the target large power grid, and comprises: an initial value setting unit for letting x =1; the first calculation unit is used for assuming that the front x double-fed fans in the double-fed fan set are put into a crowbar, updating the values of the front x elements in the reactive current set to zero, calculating corresponding equivalent impedance of the double-fed fans, and updating a node admittance matrix of a target large power grid; the second calculation unit is used for calculating short-circuit node current and node voltage according to current values of all elements in the reactive current set, updating values of corresponding elements in the reactive current set according to calculation results, and performing iterative calculation on the short-circuit node current and the node voltage until convergence conditions are met; and the judging unit is used for judging whether the grid-connected point voltages of the back n-x double-fed fans in the double-fed fan set are all larger than a crowbar input threshold value when the calculation result is converged, if so, taking the current solved short-circuit point current and the voltage of each node as a target short-circuit current calculation result, and if not, enabling x = x +1 and returning to the first calculating unit.
In one possible implementation, the determining module 1 includes:
the first determining unit is used for determining various indexes for evaluating the input priority of the crowbar, wherein the indexes comprise indexes representing the importance degree of nodes and the initial voltage drop percentage of the double-fed fan;
a second determining unit, configured to determine weights of the indexes;
and the third calculating unit is used for calculating the corresponding crowbar input priority by adopting weighted summation according to the weight and the data of each index corresponding to the double-fed fan.
In an implementation manner, the first determining unit is specifically configured to:
determining indexes representing the importance degree of the nodes, wherein the indexes comprise degree centrality, betweenness centrality and cohesion of the nodes;
the third calculating unit is specifically configured to calculate a corresponding crowbar input priority according to the following formula:
E i ＝a 1 (1-U i )+a 2 D i +a 3 M i +a 4 B i
in the formula, E i Represents the crowbar input priority, U, of the ith double-fed fan i The voltage per unit value of the grid-connected point of the ith doubly-fed fan is 1-U i The initial voltage drop percentage of the ith doubly-fed wind turbine is expressed, D i Expressing the degree centrality, M, of the ith doubly-fed wind turbine i Expressing the betweenness centrality of the ith doubly-fed fan, B i Represents the condensation degree of the ith doubly-fed wind turbine, a 1 Is the weight corresponding to the initial voltage drop percentage, a 2 A weight corresponding to centrality, a 3 Is a weight corresponding to the betweenness centrality, a 4 Is the weight corresponding to the degree of aggregation.
In one implementation, the second computing unit includes:
the updating subunit is used for calculating correspondingly provided reactive current according to the voltage of the grid-connected point of the last n-x double-fed fans in the double-fed fan set, and updating the value of the corresponding element in the reactive current set according to the calculated reactive current;
the calculation subunit is used for calculating short-circuit node current and each node voltage according to the current value of each element in the reactive current set;
and the judging subunit is used for judging that the convergence condition is met if the voltage difference of each node of the calculation results of the current of the adjacent two short-circuit nodes and the voltage of each node is less than the voltage difference threshold value, and otherwise, returning to the updating subunit.
In an implementation manner, the update subunit is specifically configured to:
if the voltage of the grid-connected point of the double-fed fan is not less than the low-voltage crossing threshold, the correspondingly provided reactive current is zero;
if the voltage of the grid-connected point of the double-fed fan is smaller than the low-voltage ride-through threshold, calculating correspondingly provided reactive current according to the following formula:
I q ＝K v (0.9-U)
in the formula I q Representing reactive current, K, correspondingly supplied by the doubly-fed wind turbine v And U is a voltage per unit value of a grid-connected point of the double-fed motor.
In one enabling manner, the apparatus further includes:
the first setting module is used for setting the input threshold value of the crowbar to be 0.4p.u;
a second setting module, configured to set the voltage difference threshold to be 0.001p.u.;
and/or a third setting module, configured to set the low voltage crossing threshold to 0.9p.u.
In an implementation manner, the calculating module 3 is specifically configured to calculate the short-circuit node current and the node voltages according to the following formula:
in the formula I f Injecting a vector of the variation of the current, I, for the node f before and after the short-circuit fault 1 ,I 2 ,...,I n The reactive current Z provided by the 1 st, 2., n doubly-fed wind turbines respectively 1f ,Z 2f ,..., Z nf 1,2, the transfer impedance between n doubly-fed wind turbines and a short-circuit node, v f Voltage of node f before short circuit, Z ff Is the self-impedance of node f, vi is the voltage of node i, Z 1i ,Z 2i ,...,Z ni The transfer impedance between the n doubly-fed wind turbines and the node i is 1, 2.
The invention also provides a short-circuit current calculation device considering the double-fed fan crowbar input, which comprises:
a memory to store instructions; the instruction is used for realizing the method for calculating the short-circuit current considering the crowbar input of the double-fed fan according to any one of the above embodiments;
a processor to execute the instructions in the memory.
The invention further provides a computer-readable storage medium, on which a computer program is stored, and when being executed by a processor, the computer program implements the method for calculating the short-circuit current considering the crowbar input of the doubly-fed wind turbine according to any one of the above embodiments.
It can be clearly understood by those skilled in the art that, for convenience and brevity of description, the specific working processes of the above-described apparatuses, devices and modules may refer to the corresponding processes in the foregoing method embodiments, and the specific beneficial effects of the above-described apparatuses, devices and modules may refer to the corresponding beneficial effects in the foregoing method embodiments, which are not described herein again.
In the several embodiments provided in the present application, it should be understood that the disclosed apparatus, device and method may be implemented in other ways. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the modules is only one logical division, and other divisions may be realized in practice, for example, a plurality of modules or components may be combined or integrated into another apparatus, or some features may be omitted, or not executed.
The modules described as separate parts may or may not be physically separate, and parts displayed as modules may or may not be physical modules, may be located in one position, or may be distributed on a plurality of network modules. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment.
In addition, functional modules in the embodiments of the present invention may be integrated into one processing module, or each of the modules may exist alone physically, or two or more modules are integrated into one module. The integrated module can be realized in a hardware mode, and can also be realized in a software functional module mode.
The integrated module, if implemented in the form of a software functional module and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk, or an optical disk, and various media capable of storing program codes.
The above 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 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 of the embodiments of the present invention.
Claims (10)
1. A method for calculating short-circuit current considering double-fed fan crowbar input is characterized by comprising the following steps:
the method comprises the following steps of S1, determining the lever input priority of each double-fed fan of a target large power grid; the larger the value of the crowbar input priority is, the larger the weighted sum of the importance degree of the corresponding node and the initial voltage drop percentage is;
s2, sequencing the double-fed fans according to the sequence of the crowbar input priority from high to low, constructing a corresponding double-fed fan set and a reactive current set according to the obtained sequencing result, and enabling the value of each element in the reactive current set to be a corresponding limit value; the kth element in the reactive current set represents the reactive current provided by the kth doubly-fed fan in the doubly-fed fan set;
s3, calculating the short-circuit current of the target large power grid, wherein the calculation comprises the following steps: step S3.1, let x =1; s3.2, supposing that the front x double-fed fans in the double-fed fan set are put into a crowbar, updating the values of the front x elements in the reactive current set to zero, calculating corresponding equivalent impedance of the double-fed fans, and updating a node admittance matrix of a target large power grid; s3.3, calculating short-circuit node current and node voltage according to current values of elements in the reactive current set, updating values of corresponding elements in the reactive current set according to calculation results, and performing iterative calculation on the short-circuit node current and the node voltage until a convergence condition is met; and S3.4, judging whether the grid-connected point voltages of the back n-x double-fed fans in the double-fed fan set are all larger than a crowbar input threshold value when the calculation result is converged, if so, taking the current solved short-circuit point current and each node voltage as a target short-circuit current calculation result, and if not, making x = x +1 and returning to the step S3.2.
2. The method for calculating the short-circuit current considering the crowbar investment of the doubly-fed wind turbine generator as claimed in claim 1, wherein the determining the crowbar investment priority of each doubly-fed wind turbine generator of the target large power grid comprises:
determining various indexes for evaluating the input priority of the crowbar, wherein the indexes comprise indexes representing the importance degree of the nodes and the initial voltage drop percentage of the double-fed fan;
determining the weight of each index;
and calculating the corresponding crowbar input priority by adopting weighted summation according to the weight and the data of each index corresponding to the double-fed fan.
3. The method for calculating the short-circuit current considering the crowbar investment of the doubly-fed wind turbine as claimed in claim 2, wherein the determining and evaluating indexes of the crowbar investment priority comprises:
determining indexes representing the importance degree of the nodes, wherein the indexes comprise the degree centrality, the betweenness centrality and the cohesion degree of the nodes;
the calculating of the corresponding crowbar input priority by adopting weighted summation comprises the following steps:
calculating the corresponding crowbar input priority according to the following formula:
E i ＝a 1 (1-U i )+a 2 D i +a 3 M i +a 4 B i
in the formula, E i Indicating the crowbar throw-in priority, U, of the ith doubly-fed wind turbine i The voltage per unit value of the grid-connected point of the ith doubly-fed fan is 1-U i Represents the initial voltage drop percentage of the ith doubly-fed wind turbine, D i The degree centrality, M, of the ith doubly-fed fan is shown i Expressing the betweenness centrality of the ith doubly-fed fan, B i Represents the condensation degree of the ith doubly-fed wind turbine, a 1 Is the weight corresponding to the initial voltage drop percentage, a 2 A weight corresponding to centrality, a 3 A weight corresponding to the betweenness centrality 4 Is the weight corresponding to the degree of aggregation.
4. The method for calculating the short-circuit current considering the crowbar investment of the doubly-fed wind turbine as claimed in claim 1, wherein the step of updating the values of the corresponding elements in the reactive current set according to the calculation result, and performing iterative calculation on the short-circuit node current and the voltage of each node until a convergence condition is met comprises the steps of:
s3.31, calculating correspondingly provided reactive current according to the voltage of the grid-connected point of the back n-x double-fed fans in the double-fed fan set, and updating the value of a corresponding element in the reactive current set according to the calculated reactive current;
step S3.32, calculating short-circuit node current and each node voltage according to the current value of each element in the reactive current set;
and step S3.33, if the voltage difference of each node of the calculation results of the current of the two adjacent short-circuit nodes and the voltage of each node is less than the voltage difference threshold value, judging that the convergence condition is met, otherwise, returning to the step S3.31.
5. The method for calculating the short-circuit current with consideration of the crowbar investment of the doubly-fed wind turbine as claimed in claim 4, wherein the step of updating the values of the corresponding elements in the reactive current set according to the calculated reactive current comprises the following steps:
if the voltage of the grid-connected point of the double-fed fan is not less than the low-voltage crossing threshold, the correspondingly provided reactive current is zero;
if the voltage of the grid-connected point of the double-fed fan is smaller than the low-voltage ride-through threshold, calculating correspondingly provided reactive current according to the following formula:
I q ＝K v (0.9-U)
in the formula I q Representing reactive current, K, correspondingly supplied by the doubly-fed wind turbine v And U is a voltage per unit value of a grid-connected point of the double-fed motor.
6. The method for calculating the short-circuit current considering the crowbar throw-in of the doubly-fed wind turbine as claimed in claim 5, wherein the method further comprises the following steps:
setting the input threshold value of the crowbar to be 0.4p.u.;
setting the voltage difference threshold to be 0.001p.u.;
and/or setting the low-voltage crossing threshold value to be 0.9p.u.
7. The method for calculating the short-circuit current considering the crowbar input of the doubly-fed wind turbine as claimed in claim 1, wherein in the step S3, the short-circuit node current and the voltage of each node are calculated according to the following formula:
in the formula I f Injecting a vector of the variation of the current, I, for the node f before and after the short-circuit fault 1 ,I 2 ,...,I n The reactive current Z provided by the 1 st, 2., n doubly-fed wind turbines respectively 1f ,Z 2f ,...,Z nf 1,2, the transfer impedance between n doubly-fed wind turbines and a short-circuit node, v f Voltage at node f before short circuit, Z ff Is the self-impedance of node f, V i Is the voltage of node i, Z 1i ,Z 2i ,...,Z ni The transfer impedance between the n doubly-fed wind turbines and the node i is 1, 2.
8. A short-circuit current calculation device considering double-fed fan crowbar input is characterized by comprising:
the determination module is used for determining the crowbar input priority of each double-fed fan of the target large power grid; the larger the value of the lever input priority is, the larger the weighted sum of the importance degree of the corresponding node and the initial voltage drop percentage is;
the building module is used for sequencing the double-fed fans according to the sequence of the crowbar input priority from high to low, building a corresponding double-fed fan set and a corresponding reactive current set according to the obtained sequencing result, and enabling the value of each element in the reactive current set to be a corresponding limit value; the kth element in the reactive current set represents the reactive current provided by the kth doubly-fed fan in the doubly-fed fan set;
the calculation module is used for calculating the short-circuit current of the target large power grid and comprises: an initial value setting unit for letting x =1; the first calculation unit is used for assuming that the front x double-fed fans in the double-fed fan set are put into a crowbar, updating the values of the front x elements in the reactive current set to zero, calculating corresponding equivalent impedance of the double-fed fans, and updating a node admittance matrix of a target large power grid; the second calculation unit is used for calculating short-circuit node current and node voltage according to current values of all elements in the reactive current set, updating values of corresponding elements in the reactive current set according to calculation results, and performing iterative calculation on the short-circuit node current and the node voltage until convergence conditions are met; and the judging unit is used for judging whether the grid-connected point voltages of the back n-x double-fed fans in the double-fed fan set are all larger than a crowbar input threshold value when the calculation result is converged, if so, taking the current solved short-circuit point current and the voltage of each node as a target short-circuit current calculation result, and if not, enabling x = x +1 and returning to the first calculating unit.
9. A short-circuit current calculation device considering double-fed fan crowbar input is characterized by comprising:
a memory to store instructions; the instructions are used for realizing the short-circuit current calculation method considering the crowbar investment of the double-fed wind turbine as claimed in any one of claims 1 to 7;
a processor to execute the instructions in the memory.
10. A computer-readable storage medium, characterized in that a computer program is stored on the computer-readable storage medium, and when executed by a processor, the computer program implements the method for calculating a short-circuit current considering a crowbar plunge of a doubly-fed wind turbine as claimed in any one of claims 1 to 7.
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