CN110210777B - Power distribution network reliability assessment method containing micro-grid and electric vehicle charging station - Google Patents

Power distribution network reliability assessment method containing micro-grid and electric vehicle charging station Download PDF

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CN110210777B
CN110210777B CN201910502082.2A CN201910502082A CN110210777B CN 110210777 B CN110210777 B CN 110210777B CN 201910502082 A CN201910502082 A CN 201910502082A CN 110210777 B CN110210777 B CN 110210777B
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范宏
陈龙超
鲁家阳
郭翔
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Shanghai University of Electric Power
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Abstract

The invention relates to a reliability evaluation method for a power distribution network comprising a micro-grid and an electric vehicle charging station, which comprises the following steps of 1) considering the changes of the electrical structure and the operation mode of the power distribution network after the micro-grid and the electric vehicle charging station are connected, and establishing a power distribution network frame structure taking the micro-grid and the electric vehicle charging station into account; 2) acquiring the operating condition of the power distribution network according to different operating conditions of the grid-connected micro-grid and the charging and discharging characteristics of the electric vehicle charging station; 3) and evaluating the power supply reliability of the power distribution network after the electric vehicle charging station and the grid-connected type microgrid are connected according to different running states of the power distribution network by adopting a sequential Monte Carlo simulation method. Compared with the prior art, the method has the advantages of comprehensive consideration, accurate evaluation and the like.

Description

Power distribution network reliability assessment method containing micro-grid and electric vehicle charging station
Technical Field
The invention relates to the field of power distribution network planning, in particular to a method for evaluating reliability of a power distribution network comprising a micro-grid and an electric vehicle charging station.
Background
With the continuous maturity of the development of the micro-grid technology, the grid-connected micro-grid becomes an organic component of the power distribution network. Due to the technical advantages of the grid-connected micro-grid in the aspect of solving the problem of the connection of the distributed power supply to the power distribution network, the development of the grid-connected micro-grid is promoted greatly. Meanwhile, due to the rapid development of the electric vehicle industry in the modern times and the centralized management of electric vehicles, electric vehicle charging stations have also become important constituent elements of micro-grids and power distribution networks, and the structures and operations of the power distribution networks have become more and more complex. Along with the improvement of the requirement of modern users on the power utilization quality, the evaluation of the power supply reliability of the power distribution network after the access of various novel elements is considered is more important.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a method for evaluating the reliability of a power distribution network comprising a micro-grid and an electric vehicle charging station.
The purpose of the invention can be realized by the following technical scheme:
a reliability evaluation method for a power distribution network containing a micro-grid and an electric vehicle charging station comprises the following steps:
1) considering the changes of the electrical structure and the operation mode of the power distribution network after the micro-grid and the electric vehicle charging station are connected, and establishing a power distribution network frame structure considering the connection of the micro-grid and the electric vehicle charging station;
2) acquiring the operating condition of the power distribution network according to different operating conditions of the grid-connected micro-grid and the charging and discharging characteristics of the electric vehicle charging station;
3) and evaluating the power supply reliability of the power distribution network after the electric vehicle charging station and the grid-connected type microgrid are connected according to different running states of the power distribution network by adopting a sequential Monte Carlo simulation method.
The step 1) specifically comprises the following steps:
11) determining the operation condition of the microgrid according to the type, the geographical position and the internal power supply factors of the grid-connected microgrid;
12) determining the operation condition of the electric vehicle charging station according to the vehicle type and the construction area of the electric vehicle charging station;
13) and constructing a schematic diagram of a power distribution network structure considering the access of the micro-grid and the electric vehicle charging station.
In the step 2), the operation conditions of the power distribution network include a fault-free operation condition and an operation condition that faults occur in different areas, the operation conditions include two sub-conditions of power interaction between the grid-connected micro-grid and the power distribution network and power interaction between the independent operation electric vehicle charging station and the power distribution network under the fault-free operation condition, and the operation conditions that faults occur in different areas include two sub-conditions that a fault occurs in an upstream area of the access point and a fault occurs in a downstream area of the access point.
Under the mutual sub-situation of power between grid-connected microgrid and distribution network, except that the distribution network is in the peak load period, in other time quantum, the distribution network all can regard as microgrid's stand-by power supply, when the power supply is not enough in the microgrid, microgrid purchase the power demand that electric quantity satisfies load user in the microgrid from the external power grid, then have:
when the load of the large power grid system is at a peak value, an interactive power calculation model between the micro power grid and the power distribution network is as follows:
Figure GDA0002938086120000021
wherein, Δ PM→W(t) the power delivered by the microgrid to the distribution network during this period, PDG(t) is the output of the distributed power supply in the microgrid, PL(t) is the load power in the microgrid, PEV·ch(t) is the charging required power of the EV charging station in the microgrid;
when the load of the large power grid system is at an average running level, the micro power grid is in grid-connected running at the moment, and a power calculation model transmitted from the power distribution network to the micro power grid is as follows:
PW→M(t)＝PL(t)+PEV·ch(t)-PESS·dis(t)-PDG(t)
wherein, PW→M(t) the power delivered by the distribution network to the microgrid for this period, PESS·dis(t) is the discharge power of the energy storage device, when PW→MWhen the (t) > 0, the power output in the microgrid is smaller than the load requirement, otherwise, the microgrid transmits power to an external power grid, and the power is | PW→M(t)|；
When the load of the large power grid system is in a valley, the micro power grid is in grid-connected operation, and a power calculation model transmitted to the micro power grid by the power distribution network is as follows:
PW→M(t)＝PL(t)+PEV·ch(t)+PESS·ch(t)-PDG(t)
when P is presentW→MWhen the (t) > 0, the power output in the microgrid is smaller than the load requirement, otherwise, the microgrid transmits power to an external power grid, and the power is | PW→M(t)|。
Under the mutual sub-situation of power between independent operation electric automobile charging station and distribution network, then have:
when the load of the large power grid is at the peak value, the charging station does not charge, and then the power transmitted to the power grid by the charging station is as follows:
Figure GDA0002938086120000031
wherein, PEV→W(t) Power delivered to the grid for the electric vehicle charging station at that time period, N1For the number of electric vehicles that can participate in the discharge in the charging station during this period,
Figure GDA0002938086120000032
discharge power for the ith electric vehicle at time t, N2The number of reserve batteries that can participate in discharging in the charging station for that period,
Figure GDA0002938086120000033
the discharge power of the jth storage battery at the time t is obtained;
when the load of the large power grid is in a flat value and a low valley stage, the charging station does not feed electric energy to the power grid any more, and only serves as the charging load of the power grid, and the charging power of the charging station at the moment is as follows:
Figure GDA0002938086120000034
wherein, PEV·ch(t) is the charging power of the electric vehicle charging station at the moment t, n1 is the number of electric vehicles participating in charging in the charging station,
Figure GDA0002938086120000035
for the charging power of the a-th electric vehicle, n2 is the number of backup batteries participating in charging in the charging station,
Figure GDA0002938086120000036
charging power of the spare storage battery for the station b.
Under the condition that a fault sub-condition occurs in an upstream area of an access point, according to the organization structure and the power supply access condition of the area, the following steps are carried out:
when the island area after fault isolation contains the micro-grid and the distribution network electric load outside the micro-grid, the power balance condition in the area is as follows:
ΔP1(t)＝PDG(t)+PESS·dis(t)+PEv·dis(t)-Pwl(t)-Pl(t)
wherein, Δ P1(t) the balance power of the fault-free zone at this time, PDG(t) is the power output of the regional distributed power supply, PESS·dis(t)、PEv·dis(t) discharge power, P, of the energy storage and electric vehicle charging stations in the microgrid, respectivelywl(t) is the conventional load power in the microgrid, Pl(t) distribution network load in the fault-free region, when Δ P1(t) < 0, performing load reduction operation when power supply in the region is insufficient;
when a plurality of micro-grids are contained in the formed fault-free island region, the power balance condition in the region is as follows:
Figure GDA0002938086120000037
wherein, Δ P2(t) balancing power for this time no fault zone,
Figure GDA0002938086120000038
the surplus power of the kth micro-grid in the area is equal to delta P2When (t) is more than or equal to 0, the output of the power supply in the area can meet the requirement of the load, all the loads normally use power, and when delta P is larger than or equal to 02(t) < 0, and
Figure GDA0002938086120000041
when the load of the partial distribution power grid is reduced, the load of the partial distribution power grid is reduced
Figure GDA0002938086120000042
When the power distribution network is in island operation, all the power distribution network loads in the region are powered off;
when a charging station and a microgrid exist simultaneously, if abundant power exists in the microgrid, the abundant power is transmitted to the distribution network, if the microgrid does not have abundant power, the microgrid is converted into isolated island operation, and at the moment, a discharge power calculation model of the charging station is as follows:
Figure GDA0002938086120000043
PEV·dismax(t)＝PEV→W(t)
wherein, PEV·dis(t) is the discharge power of the charging station, m is the number of micro-grids in the area,
Figure GDA0002938086120000044
for rich power of the Tth microgrid, Pl(t) Power demand of distribution network load in area, PEV·dismax(t) maximum dischargeable power, P, of the charging station for this phaseEV→W(t) power delivered to the distribution network by the charging station, equilibrium power in the fault-free zone
Figure GDA0002938086120000045
When the load is reduced, the load is reduced according to the load priority;
when the island region does not contain a micro-grid and contains an electric vehicle charging station and a power distribution network load which are operated independently, the charging station performs concentrated discharge to supply power for other power loads in the island region, when the discharge power of the charging station is smaller than the load demand of the power distribution network in the region, the loads are reduced according to priority, and when the balance power delta P of the fault-free region is smaller than the balance power delta P of the fault-free region4(t)＝Pl(t)-PEV·dismaxAnd (t) > 0, reducing the load of the distribution network in the region according to the load priority.
When a fault sub-condition occurs in an access point downstream area, fault isolation is performed through a section switch at the moment, the power failure time of loads in a fault area lasts until fault repair, grid-connected operation is performed on a grid-connected micro-grid and an electric vehicle charging station which operates independently without being affected by faults, the operation condition of the grid-connected operation is the same as that of a fault-free condition of a power distribution network, when the faults occur in the grid-connected micro-grid, the micro-grid is converted into isolated island operation, when a power main circuit where the micro-grid or an electric vehicle charging station access point is located breaks down, the micro-grid is converted into isolated island operation, the electric vehicle charging station is also disconnected with the power distribution network and does not perform charging and discharging operation, and at the moment, all power distribution network loads on a.
The step 3) specifically comprises the following steps:
31) acquiring original data of each element of the power distribution network, and determining simulation time limit TlimInitializing the simulation time T of the system to be 0;
32) obtaining the fault-free working time sequence TTF of all elements in the distribution network system, and selecting the element with the minimum fault-free working time as the fault element, namely TTFi＝min[TTF]；
33) At T → T + TTFiIn the time period, the system runs without faults, in the time period, according to the simulation of the fault-free running condition, the number of users with reduced loads and reduced power caused by insufficient power supply in the microgrid during the load peak period of the power grid are counted, and the cumulative simulation time T is T + TTFi；
34) Judging whether the simulation time T reaches the simulation time limit, namely whether T is greater than TlimIf yes, go to step 38), if no, go to step 35);
35) after the fault element is enumerated, a random number is generated to obtain the repair time TTR of the fault elementi；
36) At T → T + TTRiIn a time period, when an element in a system breaks down, firstly, judging the area of the broken element, if the broken point is positioned in the upstream area of an access point of a micro-grid and an electric vehicle charging station or an isolated island area formed after fault isolation is accessed by the micro-grid or the electric vehicle charging station, simulating according to the fault sub-state of the access point upstream area, if the broken point is positioned in the downstream area of the access point of the micro-grid and the electric vehicle charging station, completely cutting off the load in the area, and the power cut time is the time of fault restorationMeta TTRiIf the fault node is located in the micro-grid, the micro-grid is converted into isolated island operation, and the accumulated simulation time T is T + TTRiAnd the power off time of the load user;
37) judging whether the simulation time T reaches the simulation time limit, namely whether T is greater than TlimIf yes, executing step 38), if no, returning to step 32);
38) and acquiring related reliability indexes of each node and each system according to the power failure times and the power failure time of each load point, and finishing reliability evaluation according to the related reliability indexes.
In step 38), the related reliability evaluation indexes include a system annual average outage frequency SAIFI, a system annual average outage time SAIDI, a user annual average outage duration CAIDI, and an average power supply availability ASAI.
Compared with the prior art, the invention has the following advantages:
in order to accurately simulate the structure and the operation turntable of a power distribution network comprising a microgrid and an electric vehicle charging station, the power interaction between a grid-connected microgrid and the power distribution network under a fault-free operation condition and the power interaction between an independently operated electric vehicle charging station and the power distribution network are considered, the corresponding conditions of two sub-conditions of the fault occurrence in the upstream area of an access point and the fault occurrence in the downstream area of the access point under the operation condition of the fault occurrence in different areas are considered comprehensively, and finally, the power supply reliability of the power distribution network after the electric vehicle charging station and the grid-connected microgrid are evaluated by adopting a common sequential Monte Carlo simulation method, so that the evaluation is accurate, and a reference basis is provided for subsequent power distribution network planning and control of each unit.
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FIG. 1 is a flow chart of the method of the present invention.
Fig. 2 is a power distribution network frame structure diagram for taking the micro-grid and electric vehicle charging station into consideration.
Fig. 3 illustrates a power interaction between the distribution network and the microgrid during a fault-free state.
Fig. 4 is a charging and discharging strategy for an independent operation charging station.
Fig. 5 is a flowchart of reliability evaluation.
Fig. 6 is a simulation diagram of the reliability calculation of the power distribution network in the embodiment.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
As shown in fig. 1, the present invention provides a method for evaluating reliability of a power distribution network including a microgrid and an electric vehicle charging station, comprising the following steps:
1) considering the changes of the electrical structure and the operation mode of the power distribution network after the micro-grid and the electric vehicle charging station are connected in a large quantity, and establishing a power distribution network frame structure considering the connection of the micro-grid and the electric vehicle charging station;
2) analyzing the operation condition of the power distribution network by comprehensively considering different operation conditions of the grid-connected micro-grid and the charging and discharging characteristics of the electric vehicle charging station
3) Based on the operation strategy of the novel power distribution network in different working states, the power supply reliability of the power distribution network after the electric vehicle charging station and the grid-connected type microgrid are connected is evaluated by adopting a sequential Monte Carlo method.
Considering the changes of the electrical structure and the operation mode of the power distribution network after the micro-grid and the electric vehicle charging station are connected in a large number in the step 1), establishing the grid structure of the power distribution network connected with the micro-grid and the electric vehicle charging station, and the specific steps are as follows:
step 11: according to different application scenes of the micro-grid, the grid-connected micro-grid has various types such as a residential district type, an industrial park type, a commercial office district type and the like. While the microgrid in remote areas or on islands is essentially operating as an island. Meanwhile, the operation conditions of the micro-grids are determined according to the different geographic positions, the internal power supply composition types and capacities, the corresponding equipment configuration and other factors of the micro-grids, the respective operation conditions are different, and the micro-grids have characteristics according to the types of the grid-connected micro-grids, the geographic positions, the internal power supply and other factors;
step 12: the electric vehicle charging station also has different built areas according to different types of the charging vehicles inside the electric vehicle charging station. The electric bus charging station is generally constructed and managed uniformly by a bus company due to an independent operation management system, and the geographical position is generally the first and last stations of a bus line and only carries out charging and discharging management on the electric bus. The charging sites used by private electric vehicles are residential communities and industrial and commercial office areas, so that the charging stations can be uniformly managed by the micro-grid in the area where the charging station is located, namely the charging stations belong to the internal components of the micro-grid. Therefore, the mode that different types of electric automobile charging stations insert the distribution network can be divided into: the access is realized in two modes, namely micro-grid access and independent access. Determining the running state of the electric vehicle charging station according to the vehicle type, the construction area and the like of the electric vehicle charging station;
step 13: and determining a schematic diagram of a power distribution network structure considering the access of the micro-grid and the electric vehicle charging station, as shown in fig. 2.
The method comprises the following steps of 2), comprehensively considering different operation conditions of a grid-connected micro-grid and the charging and discharging characteristics of an electric vehicle charging station to analyze the operation conditions of the power distribution network, and specifically comprising the following steps:
step 21: performing operation analysis on the power distribution network in a fault-free state, wherein the operation analysis comprises two conditions of power interaction between the grid-connected micro-grid and the power distribution network (as shown in fig. 3) and power interaction between an independently-operated electric vehicle charging station and the power distribution network (as shown in fig. 4);
(1) power interaction between grid-connected microgrid and power distribution network
At this time, the power interaction condition between the micro-grid and the power distribution grid depends on the operation state of the large grid system.
1) When the load of the large power grid system is at a peak value: the electricity price ratio in this period is higher, and the electric quantity purchased from the power distribution network by the micro-grid is reduced as much as possible, so that the operation cost of the micro-grid is reduced. Therefore, on the basis of considering the charging load of the electric automobile in the microgrid, the power generation output of the microgrid is abundant, and at the moment, the microgrid outputs power to the power distribution network, so that the operating pressure of the large power grid is relieved to a certain extent; if the power supply in the microgrid is insufficient, in order to avoid causing the load of the large power grid, namely the load of the peak-to-peak, the microgrid is disconnected from the large power grid and operates in an isolated island mode, the energy storage and electric vehicle charging station in the microgrid participates in discharging operation to meet the power consumption requirement of the conventional load in the microgrid, the microgrid is connected after the load of the power distribution network is over-peak, and the energy storage and the electric vehicle are charged to supplement the electric quantity.
At this time, the interactive power calculation model between the micro-grid and the power distribution network is as follows:
Figure GDA0002938086120000071
in the formula: delta PM→W(t) the power delivered by the microgrid to the power distribution network during the period; pDG(t) the output of the distributed power supply in the microgrid; pL(t) is the load power within the microgrid; pEV·chAnd (t) is the charging required power of the electric vehicle charging station in the microgrid.
2) When the load of the large power grid system is at the average operation level, the micro power grid is in grid-connected operation. The charging load is charged in the period of time by an electric vehicle charging station in the microgrid, when the output of a distributed power supply in the microgrid can meet the requirements of all loads in the microgrid, surplus electricity charges the stored energy, and if the surplus electricity exists, the surplus electricity is transmitted to an external power grid; if the distributed power supply in the microgrid cannot meet the power consumption requirement of the internal load (including the charging load of the electric automobile), the energy storage device in the microgrid jointly uses the external power supply as a supplementary power supply for the load of the microgrid, and the insufficient power is supplemented by the external power supply.
At this moment, the power calculation model of the power distribution network to the microgrid is as follows:
PW→M(t)＝PL(t)+PEV·ch(t)-PESS·dis(t)-PDG(t)
in the formula: pW→M(t) the power transmitted by the distribution network to the microgrid in the period of time; pESS·disAnd (t) is the discharge power of the stored energy. If P isW→MIf the (t) is greater than 0, the output of the power supply in the microgrid is smaller than the load requirement at the moment; otherwise, the micro-grid will deliver power to the external grid with power magnitude | PW→M(t)|。
3) When the load of the large power grid system is in a low-ebb period, the micro power grid is in grid-connected operation, the electricity price is low, therefore, the energy storage equipment and the electric automobile in the micro power grid are in a charging state, and the external power grid is used as powerful supplement for power supply of the micro power grid system.
At this moment, the power calculation model of the power distribution network to the microgrid is as follows:
PW→M(t)＝PL(t)+PEV·ch(t)+PESS·ch(t)-PDG(t)
in the formula: pBat·ch(t) charging power of the energy storage device in the microgrid at the time interval; if P isW→MIf the (t) is greater than 0, the output of the power supply in the microgrid is smaller than the load requirement at the moment; otherwise, the micro-grid will deliver power to the external grid with power magnitude | PW→M(t)|。
According to the analysis, when no fault occurs in both the power distribution network and the micro-grid, the power distribution network can be used as a standby power supply of the micro-grid in other time periods except the peak load period. When the power supply in the microgrid is insufficient, the microgrid purchases electric quantity from an external power grid to meet the power consumption demand of load users in the microgrid. Therefore, the number of power failure users and the average power failure time of a user caused by insufficient power supply in the microgrid are reduced, and the power supply reliability of the power distribution network is integrally improved.
(2) Power interaction between independent operation electric vehicle charging station and power distribution network
1) Analysis of operating conditions
For example, in fig. 2, the charging and discharging strategy of the electric vehicle charging station connected to the power distribution network through the transformer T2 is also dependent on the operating state of the power grid. Because the independently operated electric automobile charging station is generally an electric bus power battery charging station managed and constructed by a bus company, the charging and discharging time is influenced by the driving characteristics of the vehicle. According to analysis, the bus centralized charging time is generally the time when the power grid operation load is in the valley, and at the moment, the bus centralized charging time is only used as the charging load of the power grid, and charging is reasonably arranged according to the charging requirements of the electric vehicles and the storage batteries in the station.
And when the load of the power grid is peak, the mode of changing the battery can be selected for supplementing the electric quantity. And reasonably arranging the replaced battery to participate in discharging operation according to the residual electric quantity of the battery under the requirement of ensuring the minimum state of charge limit value of the battery, feeding power to a power grid to assist the safe operation of the power grid, and arranging charging when the load of the power grid is low. The charging station can ideally be considered not to be charged when the load of the power grid is at the peak value, the charging is properly carried out when the load value is at the flat value, and the centralized charging is carried out in the valley period, so that the safe operation of the power grid is ensured.
2) Electric vehicle charging station charge and discharge power calculation model
During the load peak period of the large power grid, the power transmitted to the power grid by the charging station is as follows:
Figure GDA0002938086120000091
in the formula: pEV→W(t) the power transmitted to the power grid by the electric vehicle charging station in the time period; n is a radical of1For the number of electric vehicles that can participate in the discharge in the charging station during this period,
Figure GDA0002938086120000092
the discharge power of the ith electric automobile at the time t; n is a radical of2The number of reserve batteries that can participate in discharging in the charging station for that period,
Figure GDA0002938086120000093
the discharge power of the jth storage battery at the time t is obtained; wherein i is 1,2, 3. cndot. N1，j＝1,2,3····N2。
And secondly, when the load of the large power grid is in a flat value and a low valley stage, the charging station does not feed electric energy to the power grid any more and only serves as the charging load of the power grid. The charging power of the charging station at this time is:
Figure GDA0002938086120000094
in the formula: pEV·ch(t) is the charging power of the electric vehicle charging station at the moment t; n1 is the number of electric vehicles participating in charging in the charging station,
Figure GDA0002938086120000095
charging power for the a-th electric vehicle; n2 is the number of reserve batteries participating in charging in the charging station,
Figure GDA0002938086120000096
charging power for the backup storage battery of the station b; wherein, a is 1,2, 3. cndot. n1, b is 1,2, 3. cndot. n 2.
Step 22: and analyzing the operation strategy of the power distribution network when faults occur in different areas, wherein the two conditions that the upstream area of the access point has faults and the downstream area of the access point has faults are included.
(1) Failure of access point upstream area
For the operating condition of the fault-free island region formed after fault isolation, analysis can be carried out according to the organization structure of the region and the condition of power supply access:
1) if the isolated island region contains the microgrid and the power load of the power distribution network outside the microgrid, such as the downstream region after fault isolation when the transformer T2 in fig. 2 has a fault, the distributed power supply in the microgrid also bears the power load of the power distribution network outside the microgrid in the isolated island region. Meanwhile, the energy storage device is combined with an electric vehicle charging station in the microgrid to participate in discharging operation according to the power balance condition of the island area. When the total power output of the power supply in the island region is smaller than the total load demand, in order to ensure reliable power utilization of important loads in the microgrid, the load of a power distribution network outside the microgrid is firstly reduced. And if the load electricity consumption in the microgrid cannot be completely met, gradually reducing the load in the microgrid according to the priority. At this time, the power balance condition analysis in the region is calculated as:
ΔP1(t)＝PDG(t)+PESS·dis(t)+PEv·dis(t)-Pwl(t)-Pl(t)
in the formula: pDG(t) is the power output of the distributed power supply in the region; pESS·dis(t)、PEv·dis(t) the discharge power of the energy storage and electric vehicle charging station in the microgrid respectively; pwl(t) is the conventional load power in the microgrid, PlAnd (t) is the load of the power distribution network in the fault-free area. When Δ P1When (t) < 0, the power supply in the area is insufficient, and the load reduction operation is performed.
2) If the formed fault-free island region contains a plurality of micro-grids, each micro-grid can be similarly equivalent to different power supplies. When the microgrid has abundant power, the microgrid can be supplied to loads outside the microgrid itself. When the power supply inside the microgrid is insufficient, the electric energy output from other microgrids with surplus electric quantity can be absorbed. Namely, each micro-grid can not only supply power for the load of the power distribution network in the island region, but also share energy sources with each other. And when the total power output in the fault-free area is smaller than the total load requirement, the load is reduced according to the load priority. And the load priority in the microgrid is higher than the load of the power distribution network outside the microgrid. If all the micro-grids have no abundant electric quantity, each micro-grid is converted into an independent island operation state, the load of the power distribution network in a fault-free area is forced to be completely powered off, and the load power supply condition in the micro-grid is based on the respective island operation condition of the micro-grid. The power balance state analysis in this region is calculated as:
Figure GDA0002938086120000101
in the formula:
Figure GDA0002938086120000102
surplus power of the kth micro-grid in the area is obtained; when Δ P2(t) when the power supply capacity in the region is larger than or equal to 0, the demand of the load can be met, and all loads can normally use electricity; when Δ P2(t) < 0, and
Figure GDA0002938086120000103
when the power grid is in use, the load of the distributed power grid is reduced; when in use
Figure GDA0002938086120000104
Each microgrid is converted into an islandAnd (4) running, and cutting off the load of all the distribution networks in the region.
3) When the charging station and the microgrid coexist: if the surplus power exists in the microgrid, the surplus power is transmitted to the power distribution network; if the microgrid has no abundant power, the microgrid is converted into island operation. At this time, the micro-grid is equivalent to a power supply point in the area. At this time, for a faultless island area, the electric vehicle charging station can be regarded as the energy storage device in the area, and the discharge power of the electric vehicle charging station depends on the difference between the output power of each equivalent power point and the load demand power of the distribution network in the area, and is limited by the maximum discharge power of the charging station at this stage. That is, the discharge power calculation model of the charging station in this case is:
Figure GDA0002938086120000111
wherein, the maximum output power of the charging station in this period is:
PEV·dismax(t)＝PEV→W(t)
in the formula: m is the number of micro-grids in the area,
Figure GDA0002938086120000112
rich power for the τ -th microgrid; pl(t) power demand of distribution network loads within the area; pEV·dismax(t) the maximum dischargeable power of the charging station for this phase.
When in use
Figure GDA0002938086120000113
The load is reduced according to the load priority.
4) If the island region does not contain the micro-grid, but contains electric vehicle charging stations and power distribution network loads which operate independently. At the moment, the charging station reasonably arranges the vehicles and the storage batteries according to the charge state of the vehicles connected into the station and under the condition of ensuring the subsequent driving requirement, so that the concentrated discharging operation is carried out, and power is supplied to other electric loads in the island region. When the discharge power of the charging station is less than that in the areaWhen the load of the power distribution network is required, the load is reduced according to the priority. When Δ P4(t)＝Pl(t)-PEV·dismaxAnd (t) > 0, reducing the load of the distribution network in the region according to the load priority.
(2) Access point downstream area failure
When a fault occurs in a distribution network node downstream of a microgrid access point, such as a user load 3 in fig. 2, the fault isolation is performed through a section switch. Because the downstream isolation area has no access to the distributed power supply, the power failure time of the load in the fault area can be continued until the fault is repaired. And for the grid-connected micro-grid at the upstream of the fault point and the independently operated electric vehicle charging station, the grid-connected operation is not influenced by the fault, and the operation condition can be analyzed according to the fault-free condition of the power distribution network. When the fault occurs in the interior of the grid-connected microgrid, the microgrid is converted into an island operation. The fault processing method in the microgrid is the same as a common microgrid fault isolation method and an operation strategy.
When a power main line where a microgrid or an electric vehicle charging station access point is located breaks down, such as a point P1 or a point P2 in fig. 2 breaks down, the microgrid is converted into an isolated island operation, and the electric vehicle charging station is also disconnected from the power grid and does not perform charging and discharging operations. At this time, the load of the power distribution network on the fault line is completely powered off until the fault is repaired.
In step 3), based on the operation strategy of the novel power distribution network in different working states, the power distribution network power supply reliability of the electric vehicle charging station and the grid-connected microgrid after being connected is evaluated by adopting a sequential Monte Carlo method, and the specific steps are as shown in FIG. 5:
step 31: reading original data of each element of the power distribution network, confirming simulation time limit, and initializing the simulation time T of the system to be 0;
step 32: according to the formula
Figure GDA0002938086120000121
None of all elements within a computing systemTTF, and selecting the element with the minimum fault-free working time as the fault element, namely TTFi＝min[TTF]；
Step 33: at T → T + TTFiAnd in the time period, the system operates without faults. During the period, the operation condition of the power distribution network can be analyzed according to the operation strategy in step S31, and the number of users and the reduced power of load reduction in the microgrid due to insufficient power supply during the peak period of the load of the power distribution network can be counted. Accumulated simulation time T ═ T + TTFi；
Step 34: judging whether the simulation time T reaches the simulation time limit, namely T is more than or equal to TlimIs there a If yes, go to step S8; if not, executing the next step;
step 35: after the defective element i is enumerated, a random number is generated again, and the repair time TTR of the defective element is calculatedi。
Step 36: at T → T + TTRiDuring the time period, the element i in the system fails. Firstly, judging the area where the fault element is located, and analyzing the area if the fault point is located in the upstream area of the access point of the micro-grid and the electric vehicle charging station or the micro-grid or the electric vehicle charging station is accessed in an island area formed after fault isolation; if the fault point is located in a downstream area of the access point of the micro-grid and the electric vehicle charging station, namely the formed island area does not contain other types of distributed power supplies, the load in the area is completely powered off, and the power off time is fault repair time TTRi(ii) a And if the fault node is positioned inside a certain microgrid, the microgrid is converted into an isolated island operation, and the operation strategy of the microgrid is the same as the isolated island microgrid operation strategy. Accumulated simulation time T ═ T + TTRiAnd the outage time of the load user.
Step 37: judging whether the simulation time T reaches the simulation time limit, namely T is more than or equal to TlimIs there a If yes, go to step S8; if not, jumping to S2, and continuing to execute the simulation;
step 38: and calculating the related reliability indexes of each node and the system according to the power failure times and the power failure time of each load point.
Example (b):
the present example is an improvement on the basis of an F4 feeder of an IEEE RBTS BUS6, and as shown in fig. 6, an independently operated Electric BUS charging Station (Electric BUS Station) is added on the basis of an original network, and in the present example, 12 Electric buses are provided in the independently operated Electric BUS charging Station, the power battery capacity of each Electric vehicle is 87kW · h, the rated charge-discharge power in a fast charge mode is 60kW, and the charge-discharge power in a slow charge mode is 12 kW. On the basis that each vehicle loads a power battery, 12 spare power batteries for battery replacement are additionally arranged in the charging station. Meanwhile, two micro-grids W1 and W2 are formed by accessing distributed power sources and energy storage devices in the improved system. The system comprises a W1, a residential community micro-grid, an electric vehicle charging station EV1, a charging and discharging system and a charging and discharging system, wherein the W1 is a residential community micro-grid, the installed photovoltaic power in the residential community micro-grid is 800kW, 50 private electric vehicles with the same vehicle model are arranged in the electric vehicle charging station EV1 in a residential underground parking lot, the power battery capacity of each vehicle is 45 kW.h, and the charging and discharging power under a slow charging mode is 3.5; w2 is the district microgrid, and its inside photovoltaic installed capacity is 1MW, and wind turbine generator system comprises 2 fans of 0.8MW, and the capacity of energy storage system ESS sets up to 500 kW.h. Wherein the cut-in wind speed of the fan is 4m/s, the rated wind speed is 12.5m/s, and the cut-out wind speed is 25 m/s. The number of electric vehicles in the EV2 charging station in W2 was similarly set to 50, and the power battery capacity and the charge/discharge power of the vehicle were the same as those in W1. And simulating the reliability parameters of the power equipment elements such as the transformer, the line and the like in the system. And the peak hours of the load level in the power distribution network system are 7:00-11:00 and 18:00-22:00, the flat hours are 11:00-18:00, and the valley hours are 22: 00-7: 00 of the next day.
For the electric bus charging station, the station is set as a first station of the lines on 2 bus lines in the present embodiment, and each line is provided with 6 buses to operate according to time sequence. The departure time and the outage time of each shift of the vehicle are shown in table 1. During operation, the bus can change the power at the charging station once so as to meet the operation requirement of the whole day. The time characteristics for electric car access within the microgrid are shown in table 2.
TABLE 1 departure and stoppage times for each shift of vehicles
Departure time of line 1 No. 1 line outage time Departure time of line 2 No. 2 line outage time
5:30 20:50 5:40 20:50
5:50 21:10 6:00 21:10
6:10 21:30 6:20 21:30
6:30 21:50 6:40 21:50
6:50 22:10 7:00 22:10
7:10 22:30 7:20 22:30
TABLE 2 time characteristics of electric vehicle access within microgrid
Figure GDA0002938086120000131
According to the driving time characteristics of different types of electric vehicles, the number of electric vehicles connected to each charging station at different time nodes can be known, as shown in table 3. The electric vehicle charging station participates in power dispatching of the power distribution network or the micro-grid, and the total charging and discharging power of the charging station can be determined according to the number of the connected electric vehicles in the station at different time points and the charge state of each vehicle. Meanwhile, considering the operation of the electric automobile and the driving requirements of the automobile owner, when the electric bus is connected to the power grid, the electric bus does not participate in the discharging operation when the charge states of the vehicle-mounted power battery and the standby power battery are lower than 0.65. When the charge state of the private electric automobile is lower than 0.5, the private electric automobile does not participate in the discharging operation.
TABLE 3 number of electric vehicles inserted in each charging station
Figure GDA0002938086120000141
The simulation system is improved on the basis of the original system, wherein a micro-grid W1 system is formed by adding distributed power sources and energy storage in the load node LP18-LP21 areas, a micro-grid W2 system is formed in the node LP36-LP40 areas, and an electric vehicle charging station is connected to a branch line where the LP32 is located. Therefore, the effect of improving the reliability of power consumption to the load node in each area differs depending on the power supply configuration and the operation policy of each area. Table 4 lists the difference comparison between the average annual outage time of typical load nodes before and after system modification in each area to reflect the effect of the reliability change of the load nodes in different areas.
TABLE 4 comparison of differences
Figure GDA0002938086120000142
Figure GDA0002938086120000151
Based on the power interaction strategy of the section for different operation conditions of the power distribution network system, the power supply reliability of the formed novel simulation system is calculated and analyzed according to corresponding evaluation indexes, the evaluation indexes are aligned with the reliability indexes of the original system, and the calculation results are shown in a table 5.
TABLE 5 reliability index benchmarks
Figure GDA0002938086120000152

Claims (8)

1. A reliability assessment method for a power distribution network comprising a micro-grid and an electric vehicle charging station is characterized by comprising the following steps:
1) considering the changes of the electrical structure and the operation mode of the power distribution network after the micro-grid and the electric vehicle charging station are connected, and establishing a power distribution network frame structure considering the connection of the micro-grid and the electric vehicle charging station;
2) acquiring the operating condition of the power distribution network according to different operating conditions of the grid-connected micro-grid and the charging and discharging characteristics of the electric vehicle charging station;
3) according to different running states of the power distribution network, the power supply reliability of the power distribution network after the electric vehicle charging station and the grid-connected type microgrid are connected is evaluated by adopting a sequential Monte Carlo simulation method, and the method specifically comprises the following steps:
31) acquiring original data of each element of the power distribution network, and determining simulation time limit TlimInitializing the simulation time T of the system to be 0;
32) obtaining the fault-free working time sequence TTF of all elements in the distribution network system, and selecting the element with the minimum fault-free working time as the fault element, namely TTFi＝min[TTF]；
33) At T → T + TTFiIn the time period, the system runs without faults, in the time period, according to the simulation of the fault-free running condition, the number of users with reduced loads and reduced power caused by insufficient power supply in the microgrid during the load peak period of the power grid are counted, and the cumulative simulation time T is T + TTFi；
34) Judging whether the simulation time T reaches the simulation time limit, namely whether T is greater than TlimIf yes, go to step 38), if no, go to step 35);
35) after the fault element is enumerated, a random number is generated to obtain the repair time TTR of the fault elementi；
36) At T → T + TTRiIn a time period, when an element in a system breaks down, firstly, judging the area of the broken element, if the broken point is positioned in the upstream area of an access point of a micro-grid and an electric vehicle charging station or an isolated island area formed after fault isolation is accessed by the micro-grid or the electric vehicle charging station, simulating according to the fault sub-state of the access point upstream area, if the broken point is positioned in the downstream area of the access point of the micro-grid and the electric vehicle charging station, completely cutting off the load in the area, and taking the power-off time as the fault restoration time TTRiIf the fault node is located in the micro-grid, the micro-grid is converted into isolated island operation, and the accumulated simulation time T is T + TTRiAnd the power off time of the load user;
37) judging whether the simulation time T reaches the simulation time limit, namely whether T is greater than TlimIf yes, executing step 38), if no, returning to step 32);
38) and acquiring related reliability indexes of each node and each system according to the power failure times and the power failure time of each load point, and finishing reliability evaluation according to the related reliability indexes.
2. The method for evaluating the reliability of the power distribution network comprising the microgrid and the electric vehicle charging station as claimed in claim 1, wherein the step 1) specifically comprises the following steps:
11) determining the operation condition of the microgrid according to the type, the geographical position and the internal power supply factors of the grid-connected microgrid;
12) determining the operation condition of the electric vehicle charging station according to the vehicle type and the construction area of the electric vehicle charging station;
13) and constructing a schematic diagram of a power distribution network structure considering the access of the micro-grid and the electric vehicle charging station.
3. The method as claimed in claim 1, wherein in step 2), the operating conditions of the power distribution network include a fault-free operating condition and a fault-free operating condition in different areas, the fault-free operating condition includes two sub-conditions of power interaction between the grid-connected micro-grid and the power distribution network and power interaction between the independently operated electric vehicle charging station and the power distribution network, and the fault-free operating condition in different areas includes two sub-conditions of a fault in an area upstream of the access point and a fault in an area downstream of the access point.
4. The method of claim 3, wherein under a condition of a power interaction sub-system between the grid-connected microgrid and the power distribution network, the power distribution network can be used as a backup power supply of the microgrid in other time periods except a peak load period, and when power supply in the microgrid is insufficient, the microgrid purchases electric quantity from an external power grid to meet power consumption requirements of load users in the microgrid, and the method comprises the following steps:
when the load of the large power grid system is at a peak value, an interactive power calculation model between the micro power grid and the power distribution network is as follows:
Figure FDA0002938086110000021
wherein, Δ PM→W(t) the power delivered by the microgrid to the distribution network during this period, PDG(t) is the output of the distributed power supply in the microgrid, PL(t) is the load power in the microgrid, PEV·ch(t) is the charging required power of the EV charging station in the microgrid;
when the load of the large power grid system is at an average running level, the micro power grid is in grid-connected running at the moment, and a power calculation model transmitted from the power distribution network to the micro power grid is as follows:
PW→M(t)＝PL(t)+PEV·ch(t)-PESS·dis(t)-PDG(t)
wherein, PW→M(t) the power delivered by the distribution network to the microgrid for this period, PESS·dis(t) is the discharge power of the energy storage device, when PW→MWhen the (t) > 0, the power output in the microgrid is smaller than the load requirement, otherwise, the microgrid transmits power to an external power grid, and the power is | PW→M(t)|；
When the load of the large power grid system is in a valley, the micro power grid is in grid-connected operation, and a power calculation model transmitted to the micro power grid by the power distribution network is as follows:
PW→M(t)＝PL(t)+PEV·ch(t)+PESS·ch(t)-PDG(t)
when P is presentW→MWhen the (t) > 0, the power output in the microgrid is smaller than the load requirement, otherwise, the microgrid transmits power to an external power grid, and the power is | PW→M(t)|。
5. The method of claim 3, wherein under the condition of a power interaction sub-situation between the independently operated electric vehicle charging station and the power distribution network, the following steps are performed:
when the load of the large power grid is at the peak value, the charging station does not charge, and then the power transmitted to the power grid by the charging station is as follows:
Figure FDA0002938086110000031
wherein, PEV→W(t) Power transmitted to the grid by the electric vehicle charging station in a time period, N1The number of electric vehicles that can participate in the discharge in the charging station during the time period,
Figure FDA0002938086110000032
discharge power for the ith electric vehicle at time t, N2To account for the number of backup batteries that may participate in discharging within the charging station during a time period,
Figure FDA0002938086110000033
the discharge power of the jth storage battery at the time t is obtained;
when the load of the large power grid is in a flat value and a low valley stage, the charging station does not feed electric energy to the power grid any more, and only serves as the charging load of the power grid, and the charging power of the charging station at the moment is as follows:
Figure FDA0002938086110000034
wherein, PEV·ch(t) is the charging power of the electric vehicle charging station at the moment t, n1 is the number of electric vehicles participating in charging in the charging station,
Figure FDA0002938086110000035
for the charging power of the a-th electric vehicle, n2 is the number of backup batteries participating in charging in the charging station,
Figure FDA0002938086110000036
charging power of the spare storage battery for the station b.
6. The method according to claim 3, wherein in the event of a fault sub-condition in an area upstream of the access point, the method comprises, based on the organization and configuration of the area and the power access conditions:
when the island area after fault isolation contains the micro-grid and the distribution network electric load outside the micro-grid, the power balance condition in the area is as follows:
ΔP1(t)＝PDG(t)+PESS·dis(t)+PEv·dis(t)-Pwl(t)-Pl(t)
wherein, Δ P1(t) the balance power of the fault-free zone at this time, PDG(t) is the power output of the regional distributed power supply, PESS·dis(t)、PEv·dis(t) discharge power, P, of the energy storage and electric vehicle charging stations in the microgrid, respectivelywl(t) is the conventional load power in the microgrid, Pl(t) distribution network load in the fault-free region, when Δ P1(t) < 0, performing load reduction operation when power supply in the region is insufficient;
when a plurality of micro-grids are contained in the formed fault-free island region, the power balance condition in the region is as follows:
Figure FDA0002938086110000041
wherein, Δ P2(t) balancing power for this time no fault zone,
Figure FDA0002938086110000042
the surplus power of the kth micro-grid in the area is equal to delta P2When (t) is more than or equal to 0, the output of the power supply in the area can meet the requirement of the load, all the loads normally use power, and when delta P is larger than or equal to 02(t) < 0, and
Figure FDA0002938086110000043
when the load of the partial distribution power grid is reduced, the load of the partial distribution power grid is reduced
Figure FDA0002938086110000044
When the power distribution network is in island operation, all the power distribution network loads in the region are powered off;
when a charging station and a microgrid exist simultaneously, if abundant power exists in the microgrid, the abundant power is transmitted to the distribution network, if the microgrid does not have abundant power, the microgrid is converted into isolated island operation, and at the moment, a discharge power calculation model of the charging station is as follows:
Figure FDA0002938086110000045
PEV·dismax(t)＝PEV→W(t)
wherein, PEV·dis(t) is the discharge power of the charging station, m is the number of micro-grids in the area,
Figure FDA0002938086110000046
for rich power of the Tth microgrid, Pl(t) Power demand of distribution network load in area, PEV·dismax(t) maximum dischargeable power, P, of the charging station for this phaseEV→W(t) power delivered to the distribution network by the charging station, equilibrium power in the fault-free zone
Figure FDA0002938086110000047
When the load is reduced, the load is reduced according to the load priority;
when the island region does not contain a micro-grid and contains an electric vehicle charging station and a power distribution network load which are operated independently, the charging station performs concentrated discharge to supply power for other power loads in the island region, when the discharge power of the charging station is smaller than the load demand of the power distribution network in the region, the loads are reduced according to priority, and when the balance power delta P of the fault-free region is smaller than the balance power delta P of the fault-free region4(t)＝Pl(t)-PEV·dismaxAnd (t) > 0, reducing the load of the distribution network in the region according to the load priority.
7. The method of claim 3, wherein in the event of a sub-fault condition in the downstream area of the access point, the fault isolation is performed by a section switch, and the time of the power failure of the load in the fault area continues until the fault is repaired, and for the grid-connected microgrid and the independently operated electric vehicle charging station upstream of the fault point, the grid-connected operation is performed without being affected by the fault, and the operation status is the same as the non-fault status of the distribution network, when the fault occurs inside the grid-connected microgrid, the microgrid is switched to the island operation, when the main power line of the microgrid or the access point of the electric vehicle charging station fails, the microgrid is switched to the island operation, the electric vehicle charging station is also disconnected from the power network without performing charging and discharging operations, and the load of the distribution network on the fault line is completely powered off, until the fault is repaired.
8. The method as claimed in claim 1, wherein the reliability evaluation indexes of the distribution network include a system annual average outage frequency SAIFI, a system annual average outage time SAIDI, a user annual average outage duration CAIDI, and an average power supply availability ASAI in step 38).
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