CN105811404A - Stable situation monitoring method for quiescent voltage of distribution network with synergic transmission and distribution - Google Patents

Abstract

The invention discloses a stable situation monitoring method for quiescent voltage of a distribution network with synergic transmission and distribution. The method comprises the following steps of combining an impedance module margin index; carrying out multi-step estimation on load fluctuation of the distribution network within a future period; forecasting a track of the impedance module margin index at the stable quiescent voltage of each node of the distribution network; estimating a stable situation of the quiescent voltage of the distribution network according to a track change trend; calculating a Thevenin equivalent parameter of the node of the distribution network at an estimation state in each step by a Thevenin equivalent method; calculating to obtain the impedance module margin index of a load of the node in each step state; combining the impedance module margin indexes of the nodes in each single-step state to obtain the track of quiescent voltage margin index within an estimated time frame. By the method, a weak node at the stable voltage can be closely monitored so as to prevent voltage instability.

Description

A distribution network static voltage stability monitoring method based on coordinated transmission and distribution

technical field

The invention relates to a method for monitoring the static voltage stability situation of a distribution network in coordination with transmission and distribution.

Background technique

As an integral part of the smart grid, the smart distribution network is moving towards a flexible, reliable and efficient distribution network grid structure, a high reliability and high security communication network, a high penetration rate of distributed power access, distribution The general direction and overall goal development of fast simulation and self-healing control of electrical systems. With the continuous integration of distributed power generation and new energy generation, the smart distribution network is showing a more flexible and changeable trend, making the connection between the transmission network and the distribution network increasingly close. Therefore, the coordinated analysis of transmission and distribution is the key to ensure the economical and safe operation of the power grid. important means.

With the development of intelligent distribution network, a large number of distributed power sources and new energy sources are connected to the distribution network, resulting in frequent fluctuations in the state of the distribution network, threatening the static voltage stability of the distribution network at all times. At present, relevant literatures have studied the monitoring methods of the static voltage stability of the transmission network and the static voltage stability of the distribution network, but most of these studies focus on the stability evaluation of the current state of the system.

However, in fact, the degree of node voltage stability is not only related to the size of the voltage stability index obtained in the current state, but also related to the degree of change in the trajectory of the voltage stability index after the disturbance. Therefore, it is necessary to pay close attention to the static voltage stability of the node to prevent voltage instability. .

Contents of the invention

In order to solve the above-mentioned problems, the present invention proposes a method for monitoring the static voltage stability situation of the distribution network in coordination with transmission and distribution. This method evaluates the static voltage stability situation of the distribution network for transmission and distribution coordination by predicting the static voltage situation trajectory of the multi-step state in the future, and analyzes The change trend of the trajectory accurately judges the voltage weak nodes, which provides a reference for the implementation of preventive and control measures.

In order to achieve the above object, the present invention adopts the following technical solutions:

A distribution network static voltage stability situation monitoring method for coordinated transmission and distribution, comprising the following steps:

(1) Set the load impedance modulus margin index, which reflects the distance between the current state of the power system and the limit transmission state, and represents the voltage stability margin;

(2) Perform multiple single-step predictions for the distribution network load fluctuations in the future to form multi-step predictions, and predict the impedance touch margin index trajectory of the static voltage stability of each node in the distribution network;

(3) Using the Thevenin equivalent method to calculate the Thevenin equivalent parameters of the distribution network nodes in the estimated state of each step, and calculate the load impedance modulus index of the node in each step state;

(4) Synthesize the impedance touch margin indicators of the nodes in each single-step state, and obtain the static voltage margin index trajectory of each node in the estimated time period;

(5) Analyze the change trend of the track of the static voltage margin index, and determine the weak nodes of voltage stability.

In the step (1), the specific method is to define the load impedance modulus index of each node, and its value is the ratio of the difference between the load equivalent impedance of node i and Thevenin equivalent impedance and the load equivalent impedance of node i , which reflects the distance between the current state of the system and the limit transmission state, the maximum value is 1, and the minimum value is 0.

Preferably, in the step (1), when the load impedance modulus margin index of the node is zero, the power system operates at the critical point of voltage stability.

In the step (2), the change of the estimated multi-step distribution network load fluctuation is a continuous process, and for each single-step estimation, multiple single-step estimations are combined into a multi-step estimation.

In described step (2), concrete steps include:

(2-1) The overall equivalent of the distribution network is the PQ load connected to the boundary nodes of the transmission and distribution network;

(2-2) Use the rapid decomposition method to calculate the estimated state of the transmission network, and then use the Thevenin equivalent parameter identification method to calculate the Thevenin equivalent parameter of the transmission network, connect it to the root node of the distribution network, and use the forward pushback method to calculate this The distribution network loss when

(2-3) Add the obtained distribution network loss to the estimated distribution network load net power, update the distribution network equivalent PQ node power information, and regain Thevenin equivalent parameters;

(2-4) Transfer the reacquired Thevenin equivalent parameters to the root node of the distribution network, and then use the forward push-back method to calculate the state of the distribution network after power fluctuations.

In the step (2-1), the power value of the PQ load connected to the node is the sum of the distribution network loss in the current operating state and the estimated net power of the distribution network load.

In the step (3), the specific steps are: use the Thevenin equivalent method to calculate the Thevenin equivalent parameters of the distribution network nodes in the estimated state of each step, and then use the load impedance modulo margin index calculation method of each node to obtain each step The load impedance modulo margin index of the node in the state.

In the step (4), the impedance touch margin indicators of the nodes in each single-step state are comprehensively observed, and the static voltage margin indicator tracks of each node within an estimated time period are obtained.

In the step (5), analyze the trend of trajectory changes in detail to find the weak point of voltage stability: for each single-step estimation, the load impedance modulus index obtained from two adjacent states is compared, and the difference The node with the largest value and the node with the smallest load impedance touch margin index in the estimated state are determined as weak nodes for voltage stability. Closely monitor voltage stability weak nodes to prevent voltage instability.

The beneficial effects of the present invention are:

(1) By predicting the static voltage situation trajectory of the multi-step state in the future, evaluating the static voltage stability situation of the transmission and distribution cooperative distribution network, and analyzing the change trend of the trajectory to accurately judge the voltage weak nodes, which provides a reference for the implementation of preventive and control measures;

(2) Using the Thevenin equivalent method to evaluate the static voltage security situation of the transmission and distribution cooperative distribution network, the calculation results are accurate and the calculation process is simple.

Description of drawings

Fig. 1 is a schematic diagram of situation awareness based on Thevenin equivalent distribution network of the present invention;

Fig. 2 is IEEE9 node system topological diagram of the present invention;

Fig. 3 is a comparison chart of node impedance modulus margin index before and after load lifting of the present invention;

Fig. 4 is a schematic diagram of the trajectory of the node impedance modulus margin index under different load levels according to the present invention.

detailed description:

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 1, the Thevenin equivalent method is mostly used for online assessment of the static voltage security and stability of the power system. The local index method proposed on the basis of Thevenin equivalent is an effective method for online monitoring of the maximum transmission capacity of the system and judging the weak nodes of the system voltage stability one. Therefore, the present invention uses the Thevenin equivalent method to evaluate the static voltage security situation of the transmission and distribution cooperative distribution network, and first defines the load impedance modulus index μ as follows:

${\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; h</span>}\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; |</span>}{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; Z</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; |</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula: |Z _Li |, |Z _thi | represent the load equivalent impedance and Thevenin equivalent impedance of node i. The impedance modulus margin index μ reflects the distance between the current state of the system and the limit transmission state, with a maximum value of 1 and a minimum value of 0. When μ achieves the minimum value of 0, the system operates at the critical point of voltage stability, so μ can effectively reflect the voltage stability margin.

When using the load impedance modulus margin index to analyze the node voltage stability situation, since the corresponding index of each node has different margin index trajectories with the change of the system state, it is easy to misjudge the weak voltage stability by only focusing on the index size corresponding to each node in the current state node, resulting in a deviation between the assessment of the node voltage situation and the actual situation. In order to determine the exact voltage instability node, it is necessary to analyze the change trajectory of the corresponding indicators of each node in detail, find the node that tends to become unstable faster, pay close attention to its voltage situation, and take preventive and control measures in time to prevent voltage instability. Lay the groundwork. For this reason, the present invention combines the impedance modulus margin index, and predicts the impedance modulus margin index trajectory of the static voltage stability of each node in the distribution network through multi-step estimation of the distribution network load fluctuation within a period of time in the future, and then according to the trajectory change trend Evaluate the static voltage stability situation of the distribution network, the specific process is as follows:

(1) For the estimated multi-step distribution network load fluctuation, its change is a continuous process, consisting of multiple single-step estimates. For each single-step estimation, the following method is used to calculate the distribution network status change under each step estimation situation:

a) The overall equivalent of the distribution network is the PQ load connected to the boundary node of the transmission and distribution network, and its power value is the sum of the distribution network loss in the current operating state and the estimated net power of the distribution network load. Calculate the estimated state of the transmission network with the fast decomposition method, and then use the Thevenin equivalent parameter identification method to calculate the Thevenin equivalent parameters E' _th and Z' _th of the transmission network;

b) Connect the Thevenin equivalent parameters E' _th and Z' _th to the root node of the distribution network, as shown in Figure 1, and use the forward push-back method to calculate the distribution network loss at this time;

c) Add the distribution network loss calculated in b) to the estimated net power of the distribution network load to update the equivalent PQ node power information of the distribution network, repeat step a) to obtain the Thevenin equivalent parameters E″ _th , Z″ _th ;

d) Transfer E″ _th and Z″ _th to the root node of the distribution network, and then use the forward push-back method to calculate the state of the distribution network after power fluctuations.

(2) Use the Thevenin equivalent method to calculate the Thevenin equivalent parameters of the distribution network nodes in the estimated state of each step, and then substitute into formula (1) to obtain the load impedance modulus index of the node in each step state;

The static voltage margin index trajectory of each node in the estimated time period can be obtained by synthesizing the impedance touch margin indexes of the nodes in each single-step state. Analyze the trajectory change trend in detail, define the nodes whose trajectory changes rapidly and whose index is too small as the weak node of voltage stability, and closely monitor the weak node of voltage stability to prevent voltage instability.

Taking distribution network load fluctuation as an example to verify the effectiveness of the proposed method for evaluating the static voltage security situation of transmission and distribution coordinated distribution network.

The simulation computing hardware platform is THINKPADW530 workstation, the CPU is i7-3740QM, the main frequency is 2.7GHz, the memory is 8G, and the software platform is MATLAB and PSAT toolbox.

As shown in Figure 2, the IEEE3 machine 9-node transmission network system is combined with the IEEE33-node distribution network system for simulation. Make the following changes to the system: the voltage level of the backbone grid of the IEEE9 node system is set to 121kV, and the IEEE33 node distribution network system is used to replace the node 6 load, and the voltage level of the distribution network system is 35kV.

To simulate load fluctuations by increasing the overall load level, first increase the overall load level to 5 times the initial level, and compare the impedance module margin indicators of each node before and after the load increase, as shown in Figure 3. After the overall load level of the distribution network is increased by 5 times, the impedance mode margin indicators of nodes 1 and 9 are reduced, which are relatively weak nodes for voltage stability. In order to further evaluate the voltage stability of nodes 1 and 9 when the overall load level of the distribution network increases, the distribution network load level is gradually increased with a step size of 5 times the base load level, and the changes in the impedance modulus margin index of these two nodes are obtained track.

As shown in Figure 4, under the initial load level, the impedance mode margin index of node 1 is 0.9938, and the impedance mode margin index of node 9 is 0.9963. Spend. Gradually increase the load level of the distribution network, the impedance mode margin indicators of the two nodes are reduced, the impedance mode margin index of node 1 is lower than that of node 9, and the index of node 1 decreases faster than node 9, node 1 will be ahead of node 9 9 voltage instability. Therefore, for the scenario where the overall load level of the distribution network increases, the voltage support capability of node 1 is weaker than that of node 9, and it is necessary to pay close attention to changes in its voltage security situation to prevent voltage instability.

Through this calculation example, it is verified that the method proposed in the present invention can evaluate and estimate the static voltage security and stability situation of the distribution network under the condition of multi-step distribution network load fluctuation, and judge the voltage stability by analyzing the trajectory curve of the impedance modulus margin index of each node Weak nodes provide a reference for the implementation of voltage prevention and control measures.

Although the specific implementation of the present invention has been described above in conjunction with the accompanying drawings, it does not limit the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, those skilled in the art do not need to pay creative work Various modifications or variations that can be made are still within the protection scope of the present invention.

Claims (9)

1. the distribution static voltage stability situation monitoring method that transmission & distribution are collaborative, is characterized in that: comprise the following steps:

(1) assumed load modulus of impedance margin index, reflection power system current state, from the distance of limited transmission state, characterizes voltage stability margin；

(2) the Distribution Network Load Data fluctuation in following a period of time is carried out multiple single step to estimate, form multistep prediction, it was predicted that margin index track is touched in the impedance of each node static voltage stabilization of distribution；

(3) utilize Thevenin's equivalence method to calculate the Thevenin's equivalence parameter of distribution node under each step predicted state, calculate and obtain the load impedance mould margin index often walking state lower node；

(4) margin index is touched in the impedance of the node of each single step state comprehensive, it is thus achieved that the quiescent voltage margin index track of each node in prediction time horizon；

(5) quiescent voltage margin index trail change trend is analyzed, it is determined that voltage stabilization weak node.

2. the distribution static voltage stability situation monitoring method that a kind of transmission & distribution as claimed in claim 1 are collaborative, it is characterized in that: in described step (1), concrete grammar is, define the load impedance mould margin index of each node, its value is the ratio of the load equiva lent impedance of the load equiva lent impedance of node i and the difference of Thevenin's equivalence impedance and node i, reflecting the system current state distance from limited transmission state, its maximum is 1, and minima is 0.

3. the distribution static voltage stability situation monitoring method that a kind of transmission & distribution as claimed in claim 1 are collaborative, is characterized in that: in described step (1), when the load impedance mould margin index of node is zero, Operation of Electric Systems is in voltage stability critical point.

4. the distribution static voltage stability situation monitoring method that a kind of transmission & distribution as claimed in claim 1 are collaborative, it is characterized in that: in described step (2), to the multistep Distribution Network Load Data fluctuation estimated, its change is continuous process, each single step is estimated, composition multistep prediction is estimated in multiple single steps.

5. the distribution static voltage stability situation monitoring method that a kind of transmission & distribution as claimed in claim 1 are collaborative, is characterized in that: in described step (2), concrete steps include:

(2-1) by distribution entirety equivalence it is the PQ load connect on transmission and distribution network boundary node；

(2-2) calculate the power transmission network state estimated with algorithm quicksort, then calculate power transmission network Thevenin's equivalence parameter with Thevenin's equivalence parameter identification method, accessed distribution root node, calculate distribution loss now with front pushing back with method；

(2-3) the distribution loss obtained is added with estimating Distribution Network Load Data net power, updates the PQ node power information that distribution is equivalent, regain Thevenin's equivalence parameter；

(2-4) the Thevenin's equivalence parameter of reacquisition is delivered to the root node of distribution, pushes back before recycling and calculate the state after distribution power swing with method.

6. the distribution static voltage stability situation monitoring method that a kind of transmission & distribution as claimed in claim 5 are collaborative, it is characterized in that: in described step (2-1), the distribution loss that performance number is current operating conditions of the PQ load that node connects with estimate Distribution Network Load Data net power sum.

7. the distribution static voltage stability situation monitoring method that a kind of transmission & distribution as claimed in claim 1 are collaborative, it is characterized in that: in described step (3), concretely comprise the following steps: calculate the Thevenin's equivalence parameter of distribution node under each step predicted state by Thevenin's equivalence method, then the load impedance mould margin index computational methods of each node are utilized, it is thus achieved that often walk the load impedance mould margin index of state lower node.

8. the distribution static voltage stability situation monitoring method that a kind of transmission & distribution as claimed in claim 1 are collaborative, it is characterized in that: in described step (4), margin index comprehensive observing is touched in the impedance of the node of each single step state, it is thus achieved that the quiescent voltage margin index track of each node in prediction time horizon.

9. the distribution static voltage stability situation monitoring method that a kind of transmission & distribution as claimed in claim 1 are collaborative, it is characterized in that: in described step (5), track variation tendency is carried out labor, find voltage stabilization weak spot: each single step is estimated, the load impedance mould margin index that adjacent two states obtain is done difference, load impedance under node maximum for wherein difference and predicted state is touched the minimum node of margin index and is defined as voltage stabilization weak node.Look over one's shoulder voltage stabilization weak node in case there is Voltage Instability.