CN105740966A - Expansion planning method of power distribution network containing distributed power sources - Google Patents

Abstract

The invention relates to a distribution network expansion planning method including distributed power sources. The specific steps are as follows: calculate the maximum capacity P _min of distributed power sources that can be accommodated by the existing distribution network; perform load forecasting; source-load coordination; source-network coordination ; Dutch network coordination. The beneficial effects of the present invention are: the present invention enables effective combination of power supply and power grid, complementary advantages, and coordinated development; in the case of a given planned access capacity of distributed power supply, the specific access location of distributed power supply can be determined, and investment in grid expansion can be saved Cost, in order to minimize the adverse impact of distributed power on the power grid, maximize its benefits, fully consider the coordination of load forecasting, distributed power planning capacity, substation capacity and line current carrying capacity, and adapt to load growth At the same time, it can improve the active consumption capacity of the distributed power supply, which has important practical value.

Description

A distribution network expansion planning method with distributed generation

technical field

The invention relates to the technical field of distribution network planning methods, in particular to a distribution network expansion planning method including distributed power sources.

Background technique

With the growth of economy and the rapid development of industrial technology, social power consumption is also increasing rapidly. When the existing network cannot meet the growing load demand in the area under its jurisdiction or some users have higher requirements for power supply reliability, it will A corresponding expansion plan for the system is required. The main task of power distribution system expansion planning is to determine the optimal system construction plan according to the results of space load prediction in the network during the planning period and the basic conditions of the existing network, and to make power distribution The construction and operation costs of the system are minimal. The traditional expansion method is usually to increase the power purchase of conventional power sources, that is, to find a set of optimal decision variables (such as substation location and capacity, feeder path and size, etc.) under the premise of meeting future load growth requirements and network operation constraints. , to minimize the sum of investment, operation, maintenance and network loss.

Distributed power generation is a new type of comprehensive utilization of power generation and energy with great development prospects. It has the advantages of saving investment, reducing losses, improving system reliability, high efficiency, and various energy types. At the same time, its location is flexible and decentralized. The characteristics are excellently adapted to the decentralized power demand and resource distribution. It can not only be used for power peak regulation, construction of backup power stations or combined heat and power power stations, but also realize independent power generation in remote areas. In recent years, it has attracted extensive attention in the field of electric power industry. With the emergence of distributed generation, planners have more choices when formulating capacity expansion plans, not only new substations and feeders, but also new options for incorporating distributed generation to achieve more significant benefits. Combining distributed generation with the grid is an important way to save investment costs, improve energy efficiency, and enhance power system reliability and flexibility. The continuous and rapid development of distributed generation and its unreasonable large penetration in the system will have a serious impact on the power grid. From this perspective, it is also required that grid planners must be forward-looking in the distribution network planning that takes distributed generation into account. Research.

When a large number of distributed power sources appear in the planning scheme, a large number of random changes greatly increase the complexity of the system, and the traditional planning methods do not have sufficient ability to solve the planning problems involving distributed power sources, mainly because the traditional planning These methods simplify the planning problem to varying degrees, and lack a good method for dealing with the uncertain factors that exist objectively in planning and are difficult to express quantitatively. Mainly manifested in the following aspects:

(1) The emergence of distributed power generation will make the load forecasting, planning and operation of the power system face greater uncertainty than in the past. Traditional distribution network planning is generally carried out in accordance with the steps of "load forecasting-power supply planning-network planning". When load forecasting, it is necessary not only to know the total load forecast value, but also to know the law of load distribution and growth. However, a large number of users install distributed power to provide them with electric energy, which will inevitably affect the load growth mode of the entire power system, making it more difficult for distribution network planners to accurately predict the growth of load, thereby affecting distribution network planning.

(2) Distribution network planning generally considers 5 to 20 years. During this period, it is usually assumed that the grid load increases year by year, and new medium-voltage and low-voltage nodes continue to appear, requiring the construction of one or more substations. Since the dynamic properties of the planning problem are closely related to its dimension (usually thousands of nodes need to be considered at the same time), if there are many generator nodes, the optimal network layout scheme can be found in all possible network structures (that is, it can The scheme that minimizes construction cost, maintenance cost and power loss) is even more difficult.

(3) For users or independent power generation companies who want to install distributed power in the distribution network, there is a certain conflict between them and the distribution network company who want to maintain the existing level of safety and quality of the system. Because a large number of distributed power sources are connected to the power distribution system for grid-connected operation, this will have a profound impact on the structure of the distribution network system, and the dependence on large-scale power plants and power transmission will gradually decrease, and the original unidirectional power feed flow characteristics will occur. A series of comprehensive problems including voltage adjustment, reactive power balance, relay protection, etc. will affect the operation of the system. In order to maintain the safe and stable operation of the power grid, it is necessary to enable distributed power generation to be dispatched. To achieve this goal, it is necessary to carry out necessary control and adjustment through power electronic equipment, and integrate distributed power supply units into the existing power distribution system, which not only requires the transformation of the existing power distribution automation system, but also requires Manage the grid from passive to active (voltage regulation, protection policies, disturbances and interface issues).

In addition, the types of distributed power units and the diversification of energy sources used make how to determine a reasonable power source structure in the distribution network and how to coordinate and effectively utilize various types of power sources become urgent problems to be solved.

Reasonable access of distributed power to the distribution network can effectively improve the voltage of the distribution network, reduce the system active network loss, and increase the system load rate; on the contrary, if the access location and capacity are unreasonable, it will affect the safe and stable operation of the distribution network . How to coordinate distributed generation configuration with distribution network planning is of great significance to effectively improve resource utilization and ensure safe and reliable operation of the power grid.

Contents of the invention

The present invention solves the above-mentioned shortcomings of the prior art, and provides a lower cost and more efficient distribution network expansion planning method including distributed power sources.

The technical solution adopted by the present invention to solve its technical problems: the method for expanding and planning distribution network with distributed power sources, the specific steps are as follows:

(1) Calculate the maximum capacity P _min of the distributed power generation that the existing distribution network can accommodate, and use this as the basis for measuring the maximum bearing capacity of the existing distribution network;

(2) Carry out load forecasting, determine the local load _PL in the planning level year, and determine the planned access distributed power capacity P _DG according to the resource distribution and geographical environment conditions;

(3) Source-load coordination: compare the load _PL with the distributed power capacity P _DG , if P _DG > _PL , it means that the distributed power capacity cannot be completely absorbed by the local load, and go to step (4); if P _DG < P _L , indicating that the capacity of the distributed power generation can be completely absorbed by the local load, and go to step (5);

(4) Source-network coordination: compare the distributed power capacity P _DG with the smaller value P _min , if P _DG <P _min , it means that the existing distribution network can withstand the connected distributed power, go to step (6); if P _DG >P _min , indicating that the distributed power generation capacity exceeds the capacity of the existing distribution network, and it is necessary to increase the capacity of the substation or build a new line;

(5) Load-network coordination: compare the load _PL with the smaller value P _min , if _PL <P _min , it means that the existing distribution network can meet the load growth without expansion; if _PL >P _min , it means that the load The growth of the distribution network exceeds the capacity of the existing distribution network, and it is necessary to increase the capacity of the substation or build a new line;

(6) According to the distribution of natural resources and the geographical environment, determine the candidate locations that allow access to distributed power sources. Under the condition of satisfying the safe operation of the power grid, determine the access locations of distributed power sources according to the load demand and carrying capacity on the line and capacity.

The beneficial effects of the present invention are: the present invention enables effective combination of power supply and power grid, complementary advantages, and coordinated development; in the case of a given planned access capacity of distributed power supply, the specific access location of distributed power supply can be determined, and investment in grid expansion can be saved Cost, in order to minimize the adverse impact of distributed power on the power grid, maximize its benefits, fully consider the coordination of load forecasting, distributed power planning capacity, substation capacity and line current carrying capacity, and adapt to load growth At the same time, it can improve the active consumption capacity of the distributed power supply, which has important practical value.

Description of drawings

Figure 1 is the distribution network expansion planning process including distributed power generation;

Figure 2 is a simplified geographic wiring diagram;

Figure 3 shows the geographical location and candidate access nodes of the distributed power supply.

detailed description

The present invention will be further described below:

The specific steps of this distributed power distribution network expansion planning method are as follows:

(1) Calculate the maximum capacity P _min of the distributed power generation that the existing distribution network can accommodate, and use this as the basis for measuring the maximum bearing capacity of the existing distribution network;

(2) Carry out load forecasting, determine the local load _PL in the planning level year, and determine the planned access distributed power capacity P _DG according to the resource distribution and geographical environment conditions;

(3) Source-load coordination: compare the load _PL with the distributed power capacity P _DG , if P _DG > _PL , it means that the distributed power capacity cannot be completely absorbed by the local load, and go to step (4); if P _DG < P _L , indicating that the capacity of the distributed power generation can be completely absorbed by the local load, and go to step (5);

(4) Source-network coordination: compare the distributed power capacity P _DG with the smaller value P _min , if P _DG <P _min , it means that the existing distribution network can withstand the connected distributed power, go to step (6); if P _DG >P _min , indicating that the distributed power generation capacity exceeds the capacity of the existing distribution network, and it is necessary to increase the capacity of the substation or build a new line;

(5) Load-network coordination: compare the load _PL with the smaller value P _min , if _PL <P _min , it means that the existing distribution network can meet the load growth without expansion; if _PL >P _min , it means that the load The growth of the distribution network exceeds the capacity of the existing distribution network, and it is necessary to increase the capacity of the substation or build a new line;

(6) According to the distribution of natural resources and the geographical environment, determine the candidate locations that allow access to distributed power sources. Under the condition of satisfying the safe operation of the power grid, determine the access locations of distributed power sources according to the load demand and carrying capacity on the line and capacity.

After the distributed power supply is connected to the distribution network, it will affect the grid node voltage, line flow, short-circuit current, reliability, etc., and the degree of influence is closely related to the access location and capacity of the distributed power supply. Location and capacity are very important. Given the planned access capacity of distributed power, determine the specific access location of distributed power. Firstly, a distribution network expansion planning model is established, which is described in detail as follows:

①Economic objective function

Distributed power generation access to the distribution network generally aims at the minimum economic cost, which mainly includes three parts: new line construction cost, line loss cost, and power outage loss cost. Therefore, the objective function is:

$\begin{array}{c}\begin{array}{cc}\mathrm{<span\; class="notranslate">\; min</span>}& {\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; u</span>}\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; g</span>}\mathrm{<span\; class="notranslate">\; e</span>}}\end{array}\\ <span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}\mathrm{<span\; class="notranslate">\; l</span>}}{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}\mathrm{<span\; class="notranslate">\; E.</span>}}{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}\mathrm{<span\; class="notranslate">\; i</span>}}\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; E.</span>}\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; S</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}\mathrm{<span\; class="notranslate">\; E.</span>}}\end{array}<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, C _L is the cost of the new line; C _loss is the cost of line loss; C _outage is the cost of outage loss; n _DG is the number of DGs connected to the distribution network; C _DGi is the cost of the i-th DG Investment cost (10,000 yuan); C _Pl is the cost of the unit length line (yuan/km); l _i is the length of the i-th new line (km); C _PE is the unit electricity price (yuan/kW); ΔP _li is the i-th line The active power loss of each line (kW); T is the running time of the line (h); EENS is the power shortage (kWh), which is expressed by the load shedding after the line exceeds the limit.

②Security constraints

The distribution network after the distributed power generation is connected also needs to meet the N-1 criterion, that is, any independent component in the network that is cut off due to a failure should not cause other equipment to be overloaded, so the result of the access scheme must meet the N-1 criterion. test:

m ∈ Ω _N-1 (2)

Among them, m represents the solution of the model; Ω _N-1 represents the set of access schemes that satisfy the N-1 check, which is composed of the power flow balance constraints and equipment quota constraints of the power grid under different faults.

The following is a detailed description through specific calculation examples:

Taking a certain power supply area as an example, this paper gives a scheme for the optimal access location of distributed power when the planned access amount is determined. The simplified geographical wiring diagram is shown in Figure 2, and the voltage level and rated capacity of each substation in this area are listed in Table 1.

Table 1 Substation voltage level and rated capacity

When substations B, C, and D are completely shut down due to a fault, the load is transferred to the adjacent line through the contact switch, and the adjacent A substation continues to supply power to this part of the load. Calculate the load rate and N-1 verification results of the corresponding lines after the three substations are completely shut down and load transfer occurs, and the results are shown in Table 2.

Table 2 Load rate and N-1 verification results of the line after load transfer

It can be seen from Table 2 that when a power outage occurs in substation D, the load will exceed the capacity of substation A after the load is transferred to the third line. If the distributed power supply is connected to the third line, the required distributed power supply capacity will be large, and the investment cost will be high. Considering from the economic point of view , the more appropriate expansion method is to increase the capacity of the substation; when the B substation and C substation have a power outage and the load is transferred, the load rate of the first line and the second line increases rapidly, and it can be considered to connect distributed power to these two lines to increase the line capacity. The thermal stability margin can relieve the current carrying pressure of the line, and at the same time improve the consumption capacity of the distributed power supply.

The wind power is abundant in northern Hebei, and the distributed wind power generation is developing rapidly. In some areas, the installed capacity of wind power can account for more than 80% of the local electricity load. A substation is located in a town, where the power load is relatively small, and distributed power generation is developing rapidly. Therefore, in the next few years, the growth rate of distributed power will be greater than the growth rate of load, that is, the capacity of distributed power that is planned to be connected If it is greater than the local load, the distributed power supply will send power to the grid in reverse. According to historical statistics and load forecast data, according to the annual load growth rate of 1%, the load of substation A will reach 6.08MW by 2020, and the distributed power capacity of the local planning connection is 15MW, but the grid frame in this area can accommodate the maximum The capacity of distributed power generation is only 12.12MW, so the maximum capacity of connected distributed power should be 12.12MW. In order to improve system economy and power supply reliability, it is necessary to optimize the access position of distributed power.

If all the planned distributed power sources are connected to a certain line, there are three situations: only connected to the first line, only connected to the second line or only connected to the third line. Calculate the load rate of the corresponding lines in these three situations respectively, and the results are shown in Table 3:

Table 3 Line load rate after the distributed power supply is connected

It can be seen from Table 3 that after the first line and the second line are connected to the distributed power supply, the load rate of the line changes greatly and exceeds the rated load. The power grid leads to overloading of the line; while the load of the third line is relatively large, the capacity of the connected distributed power supply offsets part of the load, and the active power and reactive power transmitted on the line are reduced, which reduces the load rate. If the distributed power supply is only connected to the first or second line, the line will be overloaded and the wire will be damaged due to overheating. In severe cases, the scope of the accident will be expanded, threatening the safe and stable operation of the entire system. Therefore, it is necessary to reasonably plan the access location of distributed power generation, and to ensure the local increase in load demand while improving the consumption capacity of distributed power generation under the condition of satisfying the safe and stable operation of the distribution network.

According to the above analysis, distributed power generation is more suitable for access to the first or second line. Considering the distribution of local resources and the geographical environment, the location of the distributed power supply is shown in Figure 3. Each of the two lines has four candidate nodes that can be connected to the distributed power supply.

According to the economic model of distributed power access point optimization established above, in order to reduce the cost of new lines, distributed power generally chooses the nearest access line. According to FIG. 3 , the candidate access nodes are node 2 on the first line and node 6 on the second line. This article only considers a distributed power generation with an access capacity of 12.12MW. Assuming that the distance from the location of distributed power generation to node 2 and node 6 is the same, the cost C _L of the new line is also the same. Therefore, it is only necessary to compare the total loss and load shedding of the three lines under the two access schemes, and the results are listed in Table 4.

Table 4 The total loss and load shedding of the three lines at different points of distributed power access

It can be seen from Table 4 that although the two distributed power access schemes meet the N-1 criterion, when connecting to node 2, the line between node 2 and A substation is overloaded and the load on the first line of the line needs to be cut off, while the access to node 2 is overloaded. Node 6 will not experience line overload without load shedding, and the line loss is smaller than that of access node 2. Therefore, from the perspective of economy and security, distributed power is more suitable for access to node 6 on the second line.

According to the above-mentioned distributed power access scheme, without increasing the capacity of substations or building new lines, it can meet the power demand of increasing loads, save investment costs, and have good economic benefits. It is a feasible method in actual projects. implementation plan.

From the perspective of economy and security, a scheme of distributed power access to distribution network considering the maximum consumption capacity of grid frame is proposed. First, a calculation model of the maximum consumption capacity of distributed power generation based on power flow constraints is established, and then the investment cost of distributed power generation, new line construction cost, line loss cost and power outage loss cost are the minimum as the goal, and the node voltage, line load An optimization model of distribution network access to distribution network is established based on constraints such as power flow, power balance, and N-1 verification, and then the optimal access scheme for distributed power generation is obtained. Taking a certain power supply area of Hebei Power Grid as an example, the results show that under the premise of determining the planning capacity of distributed power, using this method can obtain a more reasonable distributed power access location, which has important practical value.

In addition to the above-mentioned embodiments, the present invention can also have other implementations. All technical solutions formed by equivalent replacement or equivalent transformation fall within the scope of protection required by the present invention.

Claims (1)

1. the power distribution network Expansion Planning method containing distributed power source, is characterized in that: specifically comprise the following steps that

(1) the distributed power source heap(ed) capacity P that existing power distribution network can be dissolved is calculated_min, in this, as the foundation weighing existing power distribution network maximum bearing ability；

(2) load prediction is carried out, it is determined that the loading P that planning level year is local_L, determine, according to resource distribution and geographical environment situation, the distributed power source capacity P that planning accesses_DG；

(3) source lotus is coordinated: compare loading P_LWith distributed power source capacity P_DGIf, P_DG>P_L, illustrate that distributed power source capacity can not be dissolved by local load completely, go to step (4)；If P_DG<P_L, illustrate that distributed power source capacity can be dissolved by local load completely, go to step (5)；

(4) source net is coordinated: compare distributed power source capacity P_DGWith smaller value P_minIf, P_DG<P_min, illustrate that existing power distribution network can bear the distributed power source of access, go to step (6)；If P_DG>P_min, illustrate that distributed power source capacity exceedes existing power distribution network ability to bear, it is necessary to increase substation capacity or newly-built circuit；

(5) lotus net is coordinated: compare loading P_LWith smaller value P_minIf, P_L<P_min, illustrate that existing power distribution network disclosure satisfy that the growth of load, it is not necessary to enlarging；If P_L>P_min, what load was described grows beyond existing power distribution network ability to bear, it is necessary to increase substation capacity or newly-built circuit；

(6) according to natural resources distribution and geographical environment situation, determine the position candidate allowing to access distributed power source, when meeting electric power netting safe running, determine on-position and the capacity of distributed power source according to the workload demand on circuit and current-carrying capacity size.