CN107968398A - A kind of node merger simplifies modeling method - Google Patents
A kind of node merger simplifies modeling method Download PDFInfo
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- H—ELECTRICITY
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Abstract
A kind of node merger simplifies modeling method, including node low-voltage judges, main line and branch line division, endpoint node do not occur the branch sort method of low-voltage and low voltage end node sequencing method and uses load node merger equivalent algorithm by node load merger.The node merger of the present invention simplifies modeling method by by node load merger, reduce load bus quantity, there is stronger equivalence before ensureing the calculation of tidal current of the electric network model after simplifying and simplifying, and can be by control errors within the limits prescribed, power distribution network Equivalent Modeling is combined with physical emulation platform, below 400V distributions " low-voltage " are simplified into modeling and matter emulation models coupling, " low-voltage " governance process is verified with simplified physical emulation platform.
Description
Technical Field
The invention relates to a node merging simplified modeling method, in particular to a node merging simplified modeling method for a low-voltage physical simulation platform of a power distribution network below 400V, and belongs to the technical field of power grid operation.
Background
Along with the development of Chinese economy and electric power, the scales of urban and rural power grids in China are continuously enlarged, and the power distribution grids of 400V and below have the problems of more branch lines, numerous load nodes, larger load grade difference, complex load distribution and the like, so that the power distribution grid area has the characteristic of complex power grid structure. Due to the characteristic of complex structure of the power grid, the situation of numerous branch lines and nodes can occur when a topological graph of the power grid of the transformer area is drawn, so that the situation of numerous nodes and branch lines when a physical simulation platform of low voltage of a power distribution network below 400V is built is caused, and the physical simulation platform is difficult to accurately verify the low voltage treatment process.
Therefore, the invention provides a node merging simplified modeling method, which merges node loads, reduces the number of load nodes, ensures that the load flow calculation result of a simplified power grid model has stronger equivalence with that before simplification, can control errors within a specified range, combines the equivalent modeling of a power distribution network with a physical simulation platform, combines the 'low voltage' simplified modeling of a distribution network with the voltage of below 400V with the physical simulation model, and ensures that the 'low voltage' governing process can be verified by the simplified physical simulation platform.
Disclosure of Invention
The invention aims to merge node loads and provide a node merging simplified modeling method aiming at the defects of the prior art.
The technical scheme for realizing the invention is as follows: the method comprises the steps of judging node low voltage, dividing a main line and a branch line, and sequencing branches without low voltage at a tail end node and sequencing low voltage tail end nodes before simplifying modeling; when the branch nodes and the end nodes are reserved after sorting, merging the node loads by adopting a load node merging equivalent algorithm, and equating the loads between the branch nodes and the end nodes into a load. The load node number is reduced, the power flow calculation result of the simplified power grid model is ensured to have stronger equivalence with the power flow calculation result before simplification, and the error can be controlled within a specified range.
The invention discloses a node merging and simplifying modeling method, which comprises the following steps:
(1) and carrying out load flow calculation on the distribution network platform area. And (4) carrying out load flow calculation by adopting a three-phase four-wire system implicit Gaussian method (the load flow calculation is carried out by adopting the method later), and judging whether the node voltage has a low voltage condition. The judging method comprises the following steps: if the node is a three-phase node, a low voltage is generated when the voltage of the node is lower than 353.4V; if the node is a single phase node, a low voltage is present when its voltage is below 198V.
(2) And judging a main line of the distribution transformer area.
The method for judging the main line of the distribution transformer area comprises the following steps of ①, if only one line is connected with an initial node (a node connected with a distribution transformer), determining the line between the initial node and a terminal node with the lowest voltage as the main line and the other lines as branch lines, ②, if a plurality of lines are connected with the initial node, enabling the main line to be composed of two parts, finding out a first part of the main line (namely the line between the initial node and the terminal node with the lowest voltage is the first part of the main line) by the method, recording the first part of the main line into the main line, then enabling the line between the other lines connected with the initial node and the terminal node with the lowest voltage to be the second part of the main line, enabling the first part and the second part of the main line to form the main line, and enabling the rest lines to be branch lines.
(3) A branch sequence judging method. And judging the branch sequence according to the branch condition of the power grid topological structure line and the voltage of the terminal node of the load flow calculation result. The branch line from the main line branch point to the end node of the line is a 1-stage branch line, and the specific judgment method is to set the line from the main line node to the end node with the lowest voltage as the 1-stage branch line and set the other branch lines as lower-stage branch lines. The branch point of the 1-level branch to the end node of the line is a 2-level branch, and the specific judgment method is that the line between the 1-level branch and the end node with the lowest voltage is the 2-level branch, and the other branches are lower branch lines … …; and repeating the method to divide the branches.
(4) The branch ordering method with low voltage at the end node does not occur. Calculating branches without low voltage according to the following formula, and sorting calculation results according to the requirements of reserved nodes and the number of the branches:
wherein Y is a branch calculation value, YjCalculating the load calculation value from the jth end node to the main branch node on the branch, wherein n is the number of end nodes contained in the branch,for the L-th line from the j-th end node to the main line branch nodejThe apparent power on the individual nodes is,for the L-th line from the j-th end node to the main line branch nodejLine impedance of the individual nodes to the branch node.
(5) Low voltage end node sequencing method
The total voltage of the low voltage end node is counted by the following formula:
wherein, VlowIs the total voltage value of the low voltage end node, ViThe voltage value of the ith tail end node is obtained, and n is the voltage number of the tail end node;
calculating the branches with low voltage according to the following formula, and sorting the calculation results according to the requirements of reserved nodes and the number of the branches:
wherein X is a calculated value of the end node,for the ith end low voltage node to the L-th line of the main line branch nodeiThe apparent power on the individual nodes is,for the ith end node to the line of the main line branch nodeiLine impedance of the individual nodes to the branch node.
(6) And (5) according to the sequencing results in the step (4) and the step (5), if the branch node and the end node are not reserved, adopting a direct equivalent method to equivalent the load on the branch line to the branch node. If the branch node and the end node are reserved, a load node merging equivalent algorithm is adopted to enable the load between the branch node and the end node to be equivalent to a load.
The specific equivalent method is as follows:
fig. 2 shows a typical distribution network line, and a and B are two nodes on the line.
From the load flow calculation, UA，UAp，UB，UBpThe voltage amplitude (kV) and the phase angle of the voltage on the two nodes A and B respectively; sA，SAp，SB，SBpAt the two nodes a and B, respectively, is the power load (kVA) and its phase angle; z is the impedance per unit length of the line between a and B (Ω/km), r + jx; the total length of the line between a and B is l (km).
FIG. 3 is a simplified model of an equivalent algorithm employing load node merge, where SkAnd SkpThe amplitude (kVA) and the phase angle of the equivalent load node expressed by apparent power are respectively adopted; l is1And L2The length (km) of the line from the two nodes A and B, respectively, to the equivalent load node (node K), obviously L1+L2＝L；IA，IAp，IB，IBp，IK，IKpThe amplitude (a) and the phase angle of each branch current shown in fig. 2 are shown.
Referring to fig. 3, the voltage magnitude at the equivalent load node can be calculated from node a as:
wherein, PAAnd QARespectively, active power (kW) and reactive power (kVar) flowing through node a.
Calculating the voltage amplitude at the equivalent load node according to the node B as follows:
wherein, PBAnd QBRespectively active power (kW) and reactive power (kVar) flowing through the node B.
Design equivalent error UerrComprises the following steps: u shapeerr＝UK-U′K；
Determination of L by iterative method1And L2The value of (c). When U is turnederrWhen the absolute value of (a) is less than the specified error limit, the iteration is considered to have converged, i.e. the equivalence has been completed; otherwise, when UerrWhen the value is more than zero, L is properly increased in the next iteration1Taking the value of (A); when U is turnederrLess than zero, then L is reduced appropriately at the next iteration1The value of (a).
Solving the value of the equivalent load node according to the following expression:
UK＝UA-IAzL1；
wherein,i.e. the initial apparent power value S at point BB，Is the initial voltage value U of the point BB，I.e. the initial apparent power value S at point AA，Is the initial voltage value U of the point AA，Namely the current value I from the point K to the equivalent terminal node calculated according to the formulaK，UKNamely the equivalent K point voltage value, SKNamely the equivalent K point apparent power value.
All parameters of the simplified model based on the load equivalence method can be obtained by the formula.
(7) And carrying out load flow calculation on the distribution network area subjected to the equivalent modeling to obtain the voltage value of each node, and calculating the low-voltage error of the node subjected to the equivalent.
The node merging simplified modeling method has the advantages that the number of load nodes is reduced by merging node loads, the fact that the load flow calculation result of the simplified power grid model has strong equivalence with that before simplification is guaranteed, errors can be controlled within a specified range, equivalent modeling of a power distribution network is combined with a physical simulation platform, low-voltage simplified modeling of a distribution network with the voltage of below 400V is combined with the physical simulation model, and the low-voltage governing process can be verified by the simplified physical simulation platform.
Drawings
FIG. 1 is a flow chart of a simplified modeling method for node merging according to the present invention;
FIG. 2 is a section of a typical distribution grid line;
FIG. 3 is an equivalent circuit using equivalent load nodes instead of all the loads on the line of FIG. 1;
FIG. 4 is a structural diagram of a left lining camp plot of Huanglong institute 945 in Jiangxi province;
FIG. 5 is a diagram of a result of a power flow calculation in a district in a farm;
FIG. 6 is an equivalent diagram of a region in a field camp without a "low voltage" node;
fig. 7 is an equivalent diagram of a platform region node in a field camp.
Detailed Description
A specific embodiment of the present invention is shown in fig. 1.
As shown in fig. 1, the node merging simplified modeling method of the embodiment includes the following steps:
(1) and carrying out load flow calculation on the distribution network platform area. And carrying out load flow calculation by adopting a three-phase four-wire system implicit Gaussian method, and judging whether the node voltage has a low-voltage condition or not.
(2) And judging a main line of the distribution transformer area.
(3) And branch sequence judgment, namely branch sequence judgment is carried out according to the branch condition of the power grid topological structure line and the voltage of the terminal node of the load flow calculation result.
(4) The branches with no low voltage appearing at the end node are sorted.
(5) The low voltage end nodes are sorted.
(6) According to the sequencing result, if the branch node and the end node are reserved, a load node merging equivalent algorithm is adopted to equate the load between the branch node and the end node into a load; and solving the value of the equivalent load node.
(7) And carrying out load flow calculation on the distribution network area subjected to the equivalent modeling to obtain the voltage value of each node, and calculating the low-voltage error of the node subjected to the equivalent.
This embodiment is implemented by taking a left-line-drawing field camp area of huanglonginstitute 945 in Jiangxi province as an example.
It is known that the capacity of a distribution transformer in a district in rural areas is 50KVA, and the main line is mainly LGJ-25. The structure of the camp site is shown in fig. 4.
Step 1, obtaining a load distribution condition of a platform area according to detection historical data of the platform area in the field camp, drawing a distribution transformer, a tower, a load and a line of a topological graph of the platform area in the field camp according to a graph 4, and performing load flow calculation, wherein the load flow calculation result is shown in a graph 5, the voltage of all the tail ends of black lines is lower than a low-voltage threshold value of 0.354KV, the black area is a low-voltage area, and the lowest voltage reaches 0.336 KV.
Step 2, judging the main line, and as can be seen from fig. 5, the main line from the distribution and transformation outlet to the node 39 is the first part of the main line, and the main line from the distribution and transformation outlet to the node 9 is the second part of the main line; thus, the main line is from node 9 to node 39.
Step 3, branch line sequence judgment, as can be seen from fig. 5, the nodes from the branch point on the main line to 1Y25, 9a1, and 9B1 are all 1-level branches.
Step 4, sequencing branches without low voltage at the end node, combining the load flow calculation result from the graph 5, wherein the length from the distribution transformer outlet to the node 1Y25 is 0.5km, and the load connected with the node 1Y25 is 3kW + j1.45kVar; the length of the line from the distribution transformer outlet to the 9 nodes is 0.45km, and the load connected to the 9 nodes is 4.8KW + j2.32kVar. The node 1A25 is reserved, the load connected to the node 9 is directly equivalent to the node 9, and the load equivalent between the distribution transformer outlet and the node 9 is equivalent by adopting a load node merging equivalent algorithm.
Step 5, merging the equivalent load of the district in rural areas according to the step 4 and the load nodes, and calculating the equivalent load of the district in rural areas as shown in fig. 6, wherein the load on the node 9 is 9kW + j4.35kVar, the load on the node 6 is 9kW + j4.35kVar, the voltage of the node 9 is 0.371kV, and compared with the 0.372kV before the equivalent, the voltage error is 2.688 × 10-3。
And 6, sequencing the low-voltage end nodes. According to the equivalent result of fig. 6, the load from the distribution transformer outlet to the 39 nodes can be directly equivalent by adopting a load node merging equivalent algorithm. The equivalent load flow calculation results are shown in FIG. 7, in which the load on the node 34 is 8.4kW + j4.06kVar, the load on the node 39 is 3.6kW + j1.74kVar, the voltage on the node 39 is 0.339kV, and the equivalent error is 2.959 × 10 compared with the 0.338kV before the equivalence-3。
Claims (5)
1. A node merging simplified modeling method comprises node low voltage judgment, main line and branch line division, and is characterized in that the method also comprises the steps of sorting branches without low voltage at end nodes and sorting low-voltage end nodes before simplified modeling; when the branch nodes and the end nodes are reserved after sorting, merging the node loads by adopting a load node merging equivalent algorithm, and equating the loads between the branch nodes and the end nodes into a load.
2. The method according to claim 1, wherein the branch circuit sorting method in which the low voltage does not occur at the end node is performed by counting a sum of products of an apparent power at a node in the line from the end node to the main line branch node and a line impedance at a node in the line from the end node to the main line branch node to sort the nodes according to a calculation result;
<mrow> <mi>Y</mi> <mo>=</mo> <munderover> <mo>&Sigma;</mo> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>n</mi> </munderover> <msub> <mi>Y</mi> <mi>j</mi> </msub> <mo>=</mo> <munderover> <mo>&Sigma;</mo> <mrow> <mi>j</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>n</mi> </munderover> <mrow> <mo>(</mo> <munder> <mo>&Sigma;</mo> <msub> <mi>L</mi> <mi>j</mi> </msub> </munder> <msub> <mi>S</mi> <msub> <mi>L</mi> <mi>j</mi> </msub> </msub> <mo>&times;</mo> <msub> <mi>z</mi> <msub> <mi>L</mi> <mi>j</mi> </msub> </msub> <mo>)</mo> </mrow> </mrow>
wherein Y is a branch calculation value; y isjCalculating the load calculation value from the jth tail end node to the main line branch node on the branch; n is the number of end nodes contained in the branch;for the L-th line from the j-th end node to the main line branch nodejApparent power on the individual nodes;for the L-th line from the j-th end node to the main line branch nodejFrom node to pointThe line impedance of the branch node.
3. The node merging simplified modeling method according to claim 1, wherein the low voltage end node sorting method is to count a total voltage of the low voltage end nodes, count a sum of an apparent power on a node in a line from the end low voltage node to the main line branch node and a product of a node in the line from the node to the main line branch node and a line impedance to the branch node, and sort according to a product of a ratio of the voltage of the end node in the total voltage and the sum of the products;
the total voltage expression of the low-voltage end node is counted as:
<mrow> <msub> <mi>V</mi> <mrow> <mi>l</mi> <mi>o</mi> <mi>w</mi> </mrow> </msub> <mo>=</mo> <munderover> <mo>&Sigma;</mo> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>n</mi> </munderover> <msub> <mi>V</mi> <mi>i</mi> </msub> </mrow>
wherein, VlowIs the total voltage value of the low voltage end node, ViThe voltage value of the ith tail end node is obtained, and n is the voltage number of the tail end node;
the expression for the calculation of the branch in which the low voltage occurs is:
<mrow> <mi>X</mi> <mo>=</mo> <mfrac> <msub> <mi>V</mi> <mi>i</mi> </msub> <msub> <mi>V</mi> <mrow> <mi>l</mi> <mi>o</mi> <mi>w</mi> </mrow> </msub> </mfrac> <mo>&CenterDot;</mo> <munder> <mo>&Sigma;</mo> <msub> <mi>L</mi> <mi>i</mi> </msub> </munder> <msub> <mi>S</mi> <msub> <mi>L</mi> <mi>i</mi> </msub> </msub> <mo>&times;</mo> <msub> <mi>z</mi> <msub> <mi>L</mi> <mi>i</mi> </msub> </msub> </mrow>
wherein X is a calculated value of the end node,for the ith end low voltage node to the L-th line of the main line branch nodeiThe apparent power on the individual nodes is,for the ith end node to the line of the main line branch nodeiLine impedance of the individual nodes to the branch node.
4. The node merging simplified modeling method according to claim 1, characterized in that the load node merging equivalent algorithm is adopted, and the method is as follows:
A. b are two nodes of a typical distribution network area line respectively, and U is known from load flow calculationA，UAp，UB，UBpThe voltage amplitude and the phase angle of the voltage on the two nodes A and B are respectively; sA，SAp，SB，SBpAt the two nodes a and B, respectively, is the power load and its phase angle; z is the impedance per unit length of the line between A and B; the total length of the line between A and B is L; simplified model using load node merging equivalent algorithm, where SkAnd SkpRespectively representing the amplitude and the phase angle of the equivalent load node by adopting the apparent power; l is1And L2The lengths of the lines from the two nodes A and B to the equivalent load node K, respectively, are obviously L1+L2＝L；IA，IAp，IB，IBp，IK，IKpRespectively representing the amplitude and phase angle of each branch current;
from node a, the voltage magnitude at the equivalent load node is calculated by:
<mrow> <msub> <mi>U</mi> <mi>K</mi> </msub> <mo>=</mo> <msqrt> <mrow> <msup> <mrow> <mo>(</mo> <msub> <mi>U</mi> <mi>A</mi> </msub> <mo>-</mo> <mfrac> <mrow> <msub> <mi>P</mi> <mi>A</mi> </msub> <mi>r</mi> <mi>L</mi> <mo>+</mo> <msub> <mi>Q</mi> <mi>A</mi> </msub> <msub> <mi>xL</mi> <mn>1</mn> </msub> </mrow> <msub> <mi>U</mi> <mi>A</mi> </msub> </mfrac> <mo>)</mo> </mrow> <mn>2</mn> </msup> <mo>+</mo> <msup> <mrow> <mo>(</mo> <mfrac> <mrow> <msub> <mi>P</mi> <mi>A</mi> </msub> <msub> <mi>xL</mi> <mn>1</mn> </msub> <mo>-</mo> <msub> <mi>Q</mi> <mi>A</mi> </msub> <msub> <mi>rL</mi> <mn>1</mn> </msub> </mrow> <msub> <mi>U</mi> <mi>A</mi> </msub> </mfrac> <mo>)</mo> </mrow> <mn>2</mn> </msup> </mrow> </msqrt> </mrow>
wherein, PAAnd QARespectively the active power and the reactive power flowing through the node A;
from node B, the voltage magnitude at the equivalent load node is calculated by:
<mrow> <msubsup> <mi>U</mi> <mi>K</mi> <mo>&prime;</mo> </msubsup> <mo>=</mo> <msqrt> <mrow> <msup> <mrow> <mo>&lsqb;</mo> <msub> <mi>U</mi> <mi>B</mi> </msub> <mo>+</mo> <mfrac> <mrow> <msub> <mi>P</mi> <mi>B</mi> </msub> <mi>r</mi> <mrow> <mo>(</mo> <mi>L</mi> <mo>-</mo> <msub> <mi>L</mi> <mn>1</mn> </msub> <mo>)</mo> </mrow> <mo>+</mo> <msub> <mi>Q</mi> <mi>B</mi> </msub> <mi>x</mi> <mrow> <mo>(</mo> <mi>L</mi> <mo>-</mo> <msub> <mi>L</mi> <mn>1</mn> </msub> <mo>)</mo> </mrow> </mrow> <msub> <mi>U</mi> <mi>B</mi> </msub> </mfrac> <mo>&rsqb;</mo> </mrow> <mn>2</mn> </msup> <mo>+</mo> <msup> <mrow> <mo>&lsqb;</mo> <mfrac> <mrow> <msub> <mi>P</mi> <mi>B</mi> </msub> <mi>x</mi> <mrow> <mo>(</mo> <mi>L</mi> <mo>-</mo> <msub> <mi>L</mi> <mn>1</mn> </msub> <mo>)</mo> </mrow> <mo>-</mo> <msub> <mi>Q</mi> <mi>b</mi> </msub> <mi>r</mi> <mrow> <mo>(</mo> <mi>L</mi> <mo>-</mo> <msub> <mi>L</mi> <mn>1</mn> </msub> <mo>)</mo> </mrow> </mrow> <msub> <mi>U</mi> <mi>B</mi> </msub> </mfrac> <mo>&rsqb;</mo> </mrow> <mn>2</mn> </msup> </mrow> </msqrt> </mrow>
wherein, PBAnd QBActive power and reactive power flowing through the node B, respectively;
equivalent error UerrComprises the following steps: u shapeerr＝UK-U′K；
Determination of L by iterative method1And L2A value of (d); when U is turnederrWhen the absolute value of (a) is less than the specified error limit, the iteration is considered to have converged, i.e. the equivalence has been completed; otherwise, when UerrWhen the value is more than zero, L is properly increased in the next iteration1Taking the value of (A); when U is turnederrLess than zero, then L is reduced appropriately at the next iteration1Taking the value of (A);
solving equivalent load nodes:
<mrow> <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mrow> <msub> <mi>I</mi> <mi>B</mi> </msub> <mo>=</mo> <mfrac> <msubsup> <mi>S</mi> <mi>B</mi> <mo>*</mo> </msubsup> <msubsup> <mi>U</mi> <mi>B</mi> <mo>*</mo> </msubsup> </mfrac> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>I</mi> <mi>A</mi> </msub> <mo>=</mo> <mfrac> <msubsup> <mi>S</mi> <mi>A</mi> <mo>*</mo> </msubsup> <msubsup> <mi>U</mi> <mi>A</mi> <mo>*</mo> </msubsup> </mfrac> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>I</mi> <mi>K</mi> </msub> <mo>=</mo> <msub> <mi>I</mi> <mi>A</mi> </msub> <mo>-</mo> <msub> <mi>I</mi> <mi>B</mi> </msub> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>;</mo> </mrow>
UK＝UA-IAzL1；
<mrow> <msub> <mi>S</mi> <mi>K</mi> </msub> <mo>=</mo> <msub> <mi>U</mi> <mi>K</mi> </msub> <msubsup> <mi>I</mi> <mi>K</mi> <mo>*</mo> </msubsup> <mo>;</mo> </mrow>
wherein,i.e. the initial apparent power value S at point BB，Is the initial voltage value U of the point BB，I.e. the initial apparent power value S at point AA，Is the initial voltage value U of the point AA，Namely the current value I from the point K to the equivalent terminal node calculated according to the formulaK，UKNamely the equivalent K point voltage value, SKThe equivalent K point apparent power value is obtained;
from the above expressions, all parameters of the simplified model based on the load equivalence method can be derived.
5. The node merging simplified modeling method according to claim 1, characterized in that the method steps are as follows:
(1) carrying out load flow calculation on a distribution network region, carrying out load flow calculation by adopting a three-phase four-wire system implicit Gaussian method, and judging whether the node voltage has a low-voltage condition or not;
(2) judging a main line of a distribution transformer area;
(3) judging the branch sequence of the distribution transformer area, and judging the branch sequence according to the branch condition of the power grid topological structure line and the voltage of the terminal node of the load flow calculation result;
(4) sorting branches of which the end nodes do not have low voltage;
(5) sequencing the low-voltage end nodes;
(6) according to the sequencing result, if the branch node and the end node are reserved, a load node merging equivalent algorithm is adopted to equate the load between the branch node and the end node into a load; solving the value of the equivalent load node;
(7) and carrying out load flow calculation on the distribution network area subjected to the equivalent modeling to obtain the voltage value of each node, and calculating the low-voltage error of the node subjected to the equivalent.
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