Island division method for power distribution network comprising distributed power supply

Abstract

The invention provides a method for dividing an island of a power distribution network containing a distributed power supply, which comprises the following steps of: acquiring and classifying data, carrying out weight modeling, carrying out assignment on weights of edges of a connected graph according to known data information, carrying out island division, and formulating a minimum spanning tree of the connected graph according to four principles followed by the island division. The invention provides an island division method for a power distribution network containing a distributed power supply, which comprises the following steps of: applying a Kruskal algorithm, comprehensively considering edges of a connected graph, obtaining a splitting point of island operation, and outputting an island division scheme. According to the method, the DG with the frequency modulation capability and the DG with the frequency modulation capability are combined, the load shedding position and the load shedding amount are adjusted through a cplex algorithm, the DG without the frequency modulation capability is communicated with the DG with the frequency modulation capability, influences caused by load fluctuation and uncertainty of output of the DGs such as a draught fan and a photovoltaic device are reduced, and therefore a stable island division scheme is obtained, and influences caused by unstable electrical energy in extreme weather are weakened.

Description

Technical Field

[0001] The present invention relates to the field of distributed power sources, and in particular to a method for islanding a distribution network including distributed power sources. Background Art

[0002] Meeting the growing load demand, optimizing the energy structure, and improving the comprehensive energy utilization capacity through extensive access to distributed power sources has received increasing attention. When power shortages in the superior power grid cause insufficient regional power supply, severe weather conditions cause distribution system equipment failures, and the superior power grid collapses, the distribution area and the superior power grid can achieve power restoration to the loads in the island area through reasonable island division, improve power supply reliability, and reserve sufficient time for fault inspection and repair.

[0003] At present, island division is usually carried out based on the ideas of power balance, load priority and controllability, giving priority to the power consumption of important loads and expanding the scope of the island as much as possible to ensure the power consumption of users. However, during the operation of the island area, extreme weather may cause changes in the power energy used by DG, resulting in load fluctuations, which will reduce the operating stability of the island area, unstable power, affect power use, and reduce the utilization rate of distributed power sources. Therefore, in order to try to improve the stability of power consumption, it is of great significance to study stable island division. Summary of the invention

[0004] In order to solve the above technical problems, an object of the present invention is to provide a method for islanding a distribution network including distributed power sources.

[0005] Based on this, the present invention proposes a method for islanding a distribution network including distributed power sources, comprising the following steps:

[0006] Step 1: Obtain and classify data;

[0007] Step 2: Weight modeling, assigning weights to the edges of the connected graph based on known data information;

[0008] Step 3: Island division: formulate the minimum spanning tree of the connected graph according to the four principles followed by island division, and adjust the position and amount of load shedding to divide the island area;

[0009] Step 4: Check the feasibility of island partitioning and whether it meets the conditions for stable operation;

[0010] Step 5: If the island division is feasible, proceed to step 6; if the island division is not feasible, proceed to step 3 again;

[0011] Step 6: Output the island division plan.

[0012] Optionally, the data in the acquired and classified data includes:

[0013] Fault location information, power supply information at the time of fault, power outage time information, and load level information;

[0014] The classified data is classified according to the different energy sources used by DG: small gas turbine power generation, photovoltaic power generation, and wind power generation.

[0015] Optionally, the known data information includes:

[0016] The active power of user load and the importance of user load, among which the power size has no direct correlation with the importance. The smaller the power, the greater the importance, the smaller the weight, the higher the priority, and the easier it is to be included in the island. In this way, when the rated capacity of DG does not change, more small-capacity user loads can be retained to expand the scope of the island to ensure user electricity consumption and facilitate the free switching of the distribution network between the island operation mode and the grid-connected operation mode.

[0017] Optionally, the four major principles followed by the island division include:

[0018] Important load priority principle: Important loads are powered first, and the first and second level loads are first placed in the island with DG;

[0019] Maximum load principle: As long as the user load in the island does not exceed the capacity of all DGs, as many user loads as possible will be included in the island;

[0020] Minimum network loss principle: In order to provide continuous and uninterrupted power supply to the distribution network as much as possible when a system failure occurs, the user load close to the DG is incorporated into the DG, which can minimize the network loss of island operation;

[0021] Principle of remote loads connected first: In order to facilitate the restoration of power grid operation, user loads near the tail end of the distribution network are considered to be connected to the divided islands first. Because the distribution network presents a radial structure, after the power supply is restored, the power supply of the upper-level line is restored first, and then the independently operated islands are connected to the grid at the same time. When an island is formed in the middle area of ​​the distribution network, in order to achieve island operation and grid-connected operation, a reclosing device is required to restore the user loads at the tail end. Therefore, in order to quickly restore power supply, the user loads near the tail end of the distribution network should be connected first;

[0022] According to the four principles, the Kruskal algorithm is used to find the minimum spanning tree of the connected graph. Each time a new edge is selected, all edges in the connected graph are considered, not just the adjacent edges of the current node. The union-find set can be used to determine whether a ring is formed. At the same time, it is also convenient to maintain the connected blocks. According to the rated capacity of the DG, the weight of the connected graph edge, and the size of the user load power, the power balance area is determined as the power island, and the decoupling point of the island operation is obtained, providing a stable solution for the island division. Among them, the Kruskal algorithm includes:

[0023] Arrange each edge in the edge set E by weight, where the weight is sorted from small to large according to the comparison rule in the cmp function. E is an Edge structure containing the start point, end point, and edge weight.

[0024] Create an empty tree T whose initial state is 0;

[0025] For each edge in E, add it to the tree T, provided that it does not cause the tree T to form a cycle. If an edge connects the tree T into a cycle, discard the edge;

[0026] When the variable equals -1, the algorithm ends.

[0027] Optionally, the stable operation conditions include:

[0028] Power balance: The total power generation capacity of the DG in the island must be greater than the total capacity of the power load;

[0029]

[0030] In the above formula: P Gi is the power generation of the ith DG in the island; P Lj is the power of the electrical load in the island;

[0031] Transmission safety: The voltage and current of the lines and electrical equipment in the island should be within the steady-state safety range;

[0032] I maxij <I ratedij

[0033] 0.95U ratedi i <1.05U ratedi

[0034] In the above formula: I maxij is the maximum current flowing through the line and transformer, I ratedij The rated current flowing through the line and transformer is specified as: U i Refers to the real-time voltage of the busbar, U ratedi Refers to the rated voltage of the busbar.​

[0035] Optionally, the adjusting the load shedding position and load shedding amount includes:

[0036] The cplex algorithm is used to adjust the location and amount of load shedding, sacrificing a portion of the Class II load to ensure that the DG without frequency regulation capability is connected to the DG with frequency regulation capability. This can ensure that a certain proportion of spare capacity is reserved for each island area, reduce the impact of load fluctuations and the uncertainty of the output of DGs such as wind turbines and photovoltaics, and ensure that the island area can continue to operate safely and stably under certain extreme working conditions.

[0037] The present invention has the following advantages: The present invention provides a method for islanding a distribution network including distributed power sources through improvement, which has the following improvements compared with similar devices:

[0038] Advantages: The present invention provides a method for islanding a distribution network including distributed power sources. It combines the four principles of islanding, uses the Kruskal algorithm, comprehensively considers the edges with weights in the connected graph, obtains the decoupling point of the island operation, and adjusts the position and amount of load shedding through the cplex algorithm, connects the DG without frequency regulation capability with the DG with frequency regulation capability, reduces the impact of load fluctuations and the uncertainty of the output of DGs such as wind turbines and photovoltaics, thereby obtaining a solution with stable islanding and improved utilization of distributed power sources, and reduces the impact of unstable power energy in extreme weather. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a flow chart of the present invention;

[0040] Figure 2 Flow chart of an embodiment of the present invention. DETAILED DESCRIPTION

[0041] In the description of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0042] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] Furthermore, in the description of the present invention, unless otherwise specified, “plurality” means two or more.

[0044] For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0045] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0046] The present invention provides an improved method for islanding a distribution network including distributed power sources, and its working principle is as follows:

[0047] First, obtain the fault location information, power supply information at the time of the fault, power outage time information, and load level information, and classify them according to the different energy sources used by DG: small gas turbine power generation, photovoltaic power generation, and wind power generation;

[0048] Second, the weight of the edge of the connected graph is determined according to the active power of the user load and the importance of the user load;

[0049] Third, based on the important load priority principle, the maximum load principle, the minimum network loss principle, and the remote load first access principle, the Kruskal algorithm is used to find the minimum spanning tree of the connected graph, and combined with the cplex algorithm, the load shedding position and load shedding amount are adjusted to generate a stable island partitioning scheme;

[0050] Fourth, check the feasibility of island execution. Starting from power generation and load power consumption, provide reference for the stable operation of island execution through power balance and transmission safety, mainly:

[0051] Power balance: The total power generation capacity of the DG in the island must be greater than the total capacity of the power load;

[0052]

[0053] In the above formula: P Gi is the power generation of the ith DG in the island; P Lj is the power of the electrical load in the island;

[0054] Transmission safety: The voltage and current of the lines and electrical equipment in the island should be within the steady-state safety range;

[0055] I maxij <I ratedij

[0056] 0.95U ratedi i <1.05U ratedi

[0057] In the above formula: I maxij is the maximum current flowing through the line and transformer, I ratedij The rated current flowing through the line and transformer is specified as: U i Refers to the real-time voltage of the busbar, U ratedi Refers to the rated voltage of the busbar

[0058] Fifth, if the island division does not meet the requirements of power balance and transmission safety, go back to the island division and recalculate. If the island division meets the requirements of power balance and transmission safety, the island division plan can be output.

[0059] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.​

Claims

1. A method for islanding a distribution network including distributed power sources, characterized in that: The following steps are involved: Step 1: Obtain and classify data; Step 2: Weight modeling, assigning weights to the edges of the connected graph based on known data information; Step 3: Island division: formulate the minimum spanning tree of the connected graph according to the four principles followed by island division, and adjust the position and amount of load shedding to divide the island area; Step 4: Check the feasibility of island partitioning and whether it meets the conditions for stable operation; Step 5: If the island division is feasible, proceed to step 6; if the island division is not feasible, proceed to step 3 again; Step 6: Output the island division plan.

2. A method for islanding a distribution network including distributed power sources according to claim 1, characterized in that: The data in the acquisition and classification data include: Fault location information, power supply information at the time of fault, power outage time information, and load level information; The classified data is classified according to the different energy sources used by DG: small gas turbine power generation, photovoltaic power generation, and wind power generation.

3. A method for islanding a distribution network including distributed power sources according to claim 1, characterized in that: The known data information includes: The active power of user load and the importance of user load.

4. The method for islanding a distribution network including distributed power sources according to claim 1, characterized in that: The four major principles followed by the island division are: Important load priority principle: Important loads are powered first, and the first and second level loads are first placed in the island with DG; Maximum load principle: put as many user loads as possible into the island; Minimum network loss principle: In order to ensure continuous and uninterrupted power supply as much as possible, user loads close to the DG are included in the island; The principle of connecting distant loads first: In order to facilitate the restoration of power grid operation, user loads close to the tail end of the distribution network are given priority in connecting to the divided islands.

5. The method for islanding a distribution network including distributed power sources according to claim 1, characterized in that: The conditions for stable operation include: Power balance: The total power generation capacity of the DG in the island must be greater than the total capacity of the power load; In the above formula: P Gi is the power generation of the ith DG in the island; P Lj is the power of the electrical load in the island; Transmission safety: The voltage and current of the lines and electrical equipment in the island should be within the steady-state safety range; I maxij <I ratedij 0.95U ratedi <U i <1.05U ratedi In the above formula: I maxij is the maximum current flowing through the line and transformer, I ratedij The rated current flowing through the line and transformer is specified as U i Refers to the real-time voltage of the busbar, U ratedi Refers to the rated voltage of the busbar.

6. A method for islanding a distribution network including distributed power sources according to claim 1, characterized in that: The adjustment of the load shedding position and load shedding amount comprises: The cplex algorithm is used to adjust the position and amount of load shedding, sacrificing a part of the second-class load to ensure that the DG without frequency regulation capability is connected with the DG with frequency regulation capability.

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