CN110245858A - A kind of micro-capacitance sensor reliability estimation method containing electric automobile charging station - Google Patents
A kind of micro-capacitance sensor reliability estimation method containing electric automobile charging station Download PDFInfo
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Abstract
The present invention relates to a kind of micro-capacitance sensor reliability estimation method containing electric automobile charging station, comprising the following steps: 1) according to electric car operation characteristic in microgrid, obtain the state-of-charge of each time point electric automobile power battery；2) according to micro-capacitance sensor internal power interactive tactics, interactive response power calculation model is established；3) Interruption performance is switched according to the position of network switching and different type, region division is carried out to micro-capacitance sensor；4) according to the difference of internal fault point region when micro-capacitance sensor isolated operation, different switch motion modes is taken to carry out Fault Isolation；5) the micro-capacitance sensor operational reliability containing electric automobile charging station is assessed using sequential Monte Carlo simulation.Compared with prior art, the present invention agree at this stage and the development trend of following electric automobile charging station access power grid, consider comprehensively, be widely used.
Description
Technical Field
The invention relates to the field of power distribution network planning, in particular to a micro-grid reliability evaluation method with an electric vehicle charging station.
Background
With the rapid development of economic society, electric automobiles are vigorously developed in recent years by using electric power to replace petroleum as a main power energy source, and the characteristics of no carbon emission, environmental friendliness and the like are achieved. As a novel power load, if the electric vehicle is charged in an unordered manner on a large scale, great impact is certainly brought to the safety stability and the economical efficiency of a power distribution system. Particularly, charging is carried out in the peak period of the power grid load, so that the peak is added to the peak of the power load, and the power supply burden and the operation risk of the system are increased.
Therefore, there is a need to analyze and study the usage habits of different types of electric vehicles and different vehicle users. Through the analysis of the charging and discharging behavior characteristics of different types of electric automobiles, an electric automobile charging station is established to carry out centralized planning and management on the electric automobiles, so that the charging load of the electric automobiles is controllable. Meanwhile, along with the development and research of a power interaction technology between the electric automobile and a power grid, the electric automobile is connected to the power distribution network as a mobile energy storage, and can be used as a standby power supply to deliver electric energy to the power grid during the peak load period of the power grid through a certain power interaction response strategy.
After the electric automobile is connected to the power grid in a large scale, the structure and the operation mode of the power grid become more complex. There is no evaluation method for evaluating the operational reliability of a microgrid including an electric vehicle charging station.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a microgrid reliability evaluation method comprising an electric vehicle charging station.
The purpose of the invention can be realized by the following technical scheme:
a reliability evaluation method for a micro-grid with an electric vehicle charging station comprises the following steps:
1) acquiring the charge state of the power battery of the electric automobile at each time point according to the running characteristics of the electric automobile in the micro-grid;
2) establishing an interactive response power calculation model according to a microgrid internal power interaction strategy;
3) according to the positions of the network switches and the on-off characteristics of the switches of different types, carrying out region division on the micro-grid;
4) according to the difference of the areas where the internal fault points are located when the micro-grid isolated island operates, different switching action modes are adopted to carry out fault isolation;
5) and evaluating the operation reliability of the microgrid with the electric vehicle charging station by adopting a sequential Monte Carlo simulation method under the condition of considering the internal power interaction and fault isolation of the microgrid.
In the step 1), the state of charge of the power battery of the electric automobile at each time point meets the following constraints:
wherein, T0、T′0Respectively, the departure time points of regular bus and private electric automobile in the morning, and T0＜T′0， T1And T2Time points of access and departure, T, respectively3For the point in time, T ', at which the coach stops at the charging station after returning to the park'3Is the time point of the private electric automobile arriving at home, SOCmin(T0/T′0)、SOCmin(T1)、SOCmin(T2)、SOCmin(T3/T′3) Are respectively at T0Or T'0、T1、T2、T3Or T'3State of charge, S, of an electric vehicle at a point in time1For regular bus at N1、N3Distance traveled in time intervals, S2For private electric automobile at n1、n3Time-interval driving course, N1Time period for the electric regular bus to start from the garden area in the morning and return to the garden area after the electric regular bus is connected with the staff at the fixed station, N2Is electricityTime period when the shift car is parked in the charging station in the park, N3Time period for afternoon bus to transport employees to fixed sites and back to park, N4For time periods when regular bus is parked at park charging station, n1For the time period from home to park when the employee takes the private electric automobile in the morning, n2Time period for a private electric car to stop at a charging station in a park, n3Time period from park to home for employee to take private electric automobile, n4For the time when a private electric vehicle stops at the house of an employee, W is the power consumption per kilometer of the electric vehicle, WedRated electric quantity, SOC, of the power battery of the electric automobilesd·minThe minimum state of charge threshold is set for ensuring a certain service life of the power battery.
The step 2) specifically comprises the following steps:
21) determining an operating period of the microgrid comprising N1、N2、N3And N4A time period;
22) and performing source and load power balance calculation on the fault-free area, wherein the source and load power balance formula is as follows:
Pph(t)＝PWT(t)+PPV(t)-PL(t)
wherein, Pph(t) is the area balance power, PL(t) is the real-time load power within the microgrid; pWT(t) is the total power generation power of the wind turbine generator set at the moment t, PPV(t) is the total power generation power of the photovoltaic generator set at the moment t;
23) when P is presentph(t) > 0 and at N1And N3During the time interval, no electric automobile is connected, the micro-grid only charges the energy storage device, and N is2And N4In time periods, in order to ensure that the energy storage equipment is required to maintain the stability of the system operation when no electric automobile is accessed, the state of charge of the electric automobile is at least SOCESS·sdThen, charging the electric automobile in the electric automobile charging station;
24) when in usePph(t) is less than or equal to 0 and is in the range of N1And N3At time intervals, only the energy storage device is discharged, at N2And N4During the period of time, when the electric vehicle is discharging, if Pph(t)+PEV·dis(t) < 0, the energy storage device participates in the discharging operation at the same time, and if the combined output of the energy storage device, the electric vehicle charging station and the renewable energy cannot meet the load requirement, namely Pph(t)+PEV·dis(t)+PESS·dis(t) < 0, load shedding is performed according to the important level of the load in the network, and if the power supply is insufficient when the output power is reduced to zero, the load in the island region is further shed, wherein PEV·dis(t) discharge power of the charging station at time t, PESS·dis(t) is the discharge power of the energy storage device at the moment t;
25) based on the internal power interaction strategy of the microgrid in the steps 23) and 24), the calculation formula of the charging and discharging power of the energy storage device at different time intervals is as follows:
wherein, PESS·dis(t) discharge power of the energy storage device, PESS·ch(t) charging power of the energy storage device, PESS·dis·maxIs the maximum discharge power, P, of the energy storage deviceESS·ch·maxMaximum charging power for energy storage, SOCESS(t) State of Charge, SOC, of the energy storage deviceESS·sdThe energy is stored in order to maintain the charge state of a subsequent system to be stable when no electric vehicle is in an electric vehicle charging station;
26) in N1、N3The number of electric vehicles in the charging station for the time period is approximately zero, considering that in N2、N4The interactive power condition between the time-period electric vehicle charging station and the microgrid, namely the interactive response power calculation model is as follows:
when P is presentph(t) > 0, charging station charging power:
when P is presentph(t) < 0, charging station discharge power:
PEV·dis·max(t)＝Ncar(t)·Pcar·dis+Nbus(t)·Pbus·dis
wherein, PEV·maxMaximum allowable flow power, P, of a main line connecting a charging station to a microgridEV·dis·max(t) is the maximum power that can be delivered by the charging station at time t.
In the step 3), the specific classification of the area division of the microgrid comprises:
a primary area: the method comprises the following steps that a region without any type of switching device is arranged inside, once an element fault occurs in the region, the region is isolated integrally, and when the fault is enumerated, a primary region is used as a minimum enumeration unit, and the integral fault rate of the region is considered;
and (3) secondary area: the circuit breaker is used as a boundary, a region without the circuit breaker in the region is the same branch region formed by combining a plurality of primary regions.
In the step 4), the fault isolation by adopting different switching action modes specifically comprises:
when a fault occurs in a primary region with an isolating switch as a boundary, all the circuit breakers or intelligent switches in the upstream direction of the region act firstly to cut off the power supply current of all power supplies, the isolating switch in the fault region is cut off to isolate the fault, the circuit breakers and the intelligent switches are superposed, and the fault-free equipment of the micro-grid recovers to normal operation;
when a fault occurs in a primary region with the intelligent switch as a boundary, only the corresponding intelligent switch is switched off;
when a line branch circuit has a fault, the on-off operation of the isolating switch is not needed after the current is blocked, and meanwhile, the circuit breaker and the intelligent switch are not closed any more.
The step 5) specifically comprises the following steps:
51) reading original data, setting an initial value T of an analog clock to be 0, and assuming that all elements of the micro-grid are in a normal working state initially;
52) obtaining a TTF time sequence table and a TTR time sequence table according to the non-fault working time TTF and the fault repairing time TTR of each element in the micro-grid;
53) enumerating faults and selecting the minimum value TTF in the TTF time sequence listiThe corresponding element is a failed element;
54) get from T to T + TTFiIn the simulation time period, the operating conditions of the micro-grid in different time periods whether the electric vehicle charging station is connected or not are added, and the simulation time T is accumulated as T + TTFi；
55) Judging the type and position of the fault and determining a fault influence area;
56) fault isolation is carried out on the micro-grid after the fault;
57) before the fault node returns to normal operation, whether load reduction is needed or not is determined according to the operation condition of the area after fault isolation, if yes, the power failure time of the reduced load and the reduced load power are accumulated, and the simulation time T is accumulated as T + TTRi；
58) Acquiring the power failure time of the affected load nodes;
59) judging whether the time reaches the specified time limit, if not, returning to the step 52); if yes, continuing the next step;
510) and performing reliability evaluation according to reliability evaluation indexes of the microgrid system and the load nodes.
In the step 510), the reliability evaluation indexes include conventional reliability evaluation indexes and microgrid reliability evaluation indexes including electric vehicle charging stations.
The conventional reliability evaluation indexes comprise system annual average power failure frequency SAIFI, system annual average power failure time SAIDI, user annual average power failure duration CAIDI and average power supply availability ASAI.
The micro-grid reliability evaluation indexes comprising the electric automobile charging stations comprise average charging depth ACD, average discharging depth ADD, average load reduction depth ALRD of the charging stations, and load reduction force η caused by reduction of discharging of the electric automobile charging stations when power supply in a fault-free area is insufficient.
The calculation formula of the micro-grid reliability evaluation index containing the electric vehicle charging station comprises the following steps:
wherein,the power of ith charging and jth discharging of the electric vehicle charging station is respectively, CHT and DIST are respectively the total charging and discharging times of the electric vehicle charging station, PGiThe power that the renewable energy source can send out when charging for electric automobile charging station ith time, and the ALR is the total number of times of load reduction in the microgrid, PzThe load power for the z-th reduction.
Compared with the prior art, the invention has the following advantages:
according to the invention, according to the working properties of electric automobile users in a park and the running characteristics of different types of electric automobiles, a power interaction strategy between an energy storage system and a microgrid system in a park microgrid combined network is provided when the park microgrid runs in an isolated island, various actual running conditions (charging, faults, reduction and the like) are considered, and the operational reliability of the microgrid with the electric automobile charging station is evaluated by adopting a sequential Monte Carlo simulation method and combining the evaluation indexes provided by the invention, so that the influence of the electric automobiles participating in V2G on the operational reliability of the microgrid is effectively and intuitively reflected, and a reference value is provided for the subsequent actual operation of the microgrid.
Drawings
FIG. 1 is a flow chart of the present invention.
Fig. 2 shows the driving states of two types of electric vehicles in different periods of a working day.
Fig. 3 is a schematic diagram of an internal power interaction operation strategy of a microgrid.
Figure 4 is an example campus microgrid emulation feeder system.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
Examples
As shown in fig. 1, the present invention provides a method for evaluating operational reliability of a micro-grid including an electric vehicle charging station, comprising the following steps:
s1, calculating the charge state of the power battery of the electric automobile at each time point according to the running characteristics of the electric automobile in the micro-grid;
s2, establishing an interactive response power calculation model according to the internal power interaction strategy of the microgrid;
s3, area division is carried out on the micro-grid according to the positions of the network switches and the on-off characteristics of the switches of different types;
s4, according to the difference of the areas where the internal fault points are located when the micro-grid isolated island operates, different switching action strategies are adopted to carry out fault isolation;
s5, the sequential Monte Carlo simulation algorithm is adopted to evaluate the operation reliability of the micro-grid with the electric vehicle charging station.
In step S1, the state of charge of the electric vehicle power battery at each time point is calculated according to the operating characteristics of the electric vehicle in the microgrid, and the specific steps are as follows:
step S11: according to the working time characteristics of electric vehicle users in a park, the running characteristics of different types of electric vehicles are analyzed, and fig. 2 is a schematic diagram of the running states of the electric vehicles in different periods of a working day. Wherein N is1The time period that the electric duty car starts from the park in the early season and returns to the park after receiving the staff at the fixed station; n is1The time period from home to park for the employee to take the private electric automobile in the morning; n is a radical of2(n2) The time period for the electric regular bus (private electric automobile) to stop in the charging station in the garden area; n is a radical of3Time period for afternoon bus to transport employees to fixed sites and back to park, n3The time period from the park to the home for the employee to take the private electric automobile; n is a radical of4For time periods when regular bus is parked at park charging station, n4The private electric automobile is stopped at the house of the staff for a certain time;
step S12: in order to meet the vehicle using requirements of electric vehicle users, the minimum constraint that the state of charge of the power battery at each time point needs to be met is as follows:
in the formula: t is0、T′0Respectively, the departure time points of regular bus and private electric automobile in the morning, and T0＜T′0； T1And T2Respectively the time points of access (on-duty) and departure (off-duty); t is3Stopping at a charging station after the regular bus returns to the park; t'3A time point of arrival of the private EV; SOCmin(T0/T′0)、SOCmin(T1)、 SOCmin(T2)、SOCmin(T3/T′3) Is at T0Or T'0、T1、T2、T3Or T'3A charge state of each electric vehicle at a time point; s1、S2Respectively as regular bus (private electric automobile) in N1(n1)、N3(n3) Time interval driving route(kM); w is the power consumption per kilometer of the electric automobile, WedThe rated electric quantity is the rated electric quantity of the power battery of the electric automobile; SOCsd·minThe minimum state of charge threshold is set for ensuring a certain service life of the power battery.
In step S2, an interactive response power calculation model is established according to the microgrid internal power interaction strategy, and the specific steps are as follows:
step S21: determining microgrid operating period, i.e. N1,N2,N3,N4；
Step S22: and performing source and load power balance calculation on the fault-free area, wherein the source and load power balance formula is as follows:
Pph(t)＝PWT(t)+PPV(t)-PL(t)
in the formula: pL(t) is the real-time load power within the microgrid; pWT(t) is the total power generated by the wind turbine generator at the moment t, PPVAnd (t) is the total power generation power of the photovoltaic generator set at the moment t.
Step S23: if Pph(t) > 0. In N1And N3In time periods, no electric vehicle is connected, and the microgrid will only charge the energy storage battery. In N2And N4In time interval, in order to ensure that the energy storage equipment is required to maintain the stability of the system operation when no electric automobile is accessed, the state of charge of the energy storage equipment is kept to a certain limit SOCESS·sd. Secondly, charging the electric automobile in the electric automobile charging station;
step S24: if Pph(t) is less than or equal to 0. In N1And N3And in the time interval, only the energy storage battery is discharged. In N2And N4In the time period, the electric automobile is firstly arranged to discharge. If Pph(t)+PEV·dis(t) < 0, the energy storage battery also participates in the discharging operation. If the energy storage battery, the electric vehicle charging station and the renewable energy source cannot meet the load requirement, namely Pph(t)+PEV·dis(t)+PESS·disWhen (t) < 0, load reduction is performed according to the importance level of the load in the network. Wherein P isEV·dis(t) discharge power of the charging station at time t, PESS·disAnd (t) is the discharge power of the energy storage battery at the moment t. Meanwhile, the variation of the output power of the electric vehicle charging station should be considered. When the output power is reduced to zero, the power supply is still insufficient, and the load in the island region is further reduced.
Step S25: based on the power interaction strategy, the calculation model of the charging and discharging power of the energy storage device at different time intervals is as follows:
in the formula: pESS·dis(t) discharge power of the energy storage device, PESS·ch(t) charging power of the energy storage device, PESS·dis·maxIs the maximum discharge power, P, of the energy storage deviceESS·ch·maxMaximum charging power for energy storage, SOCESS(t) State of Charge, SOC, of the energy storage deviceESS·sdThe energy is stored in the state of charge which is required to be kept for maintaining the stability of a subsequent system when no electric vehicle is in the electric vehicle charging station.
Step S26: in N1、N3The number of electric vehicles in the charging station is substantially zero during the time period. Therefore, consider only N2、N4The interactive power condition between period electric vehicle charging station and little electric wire netting:
when P is presentph(t) > 0, charging station charging power:
when P is presentph(t) < 0, charging station discharge power:
PEV·dis·max(t)＝Ncar(t)·Pcar·dis+Nbus(t)·Pbus·dis
in the formula: pEV·maxThe maximum allowable flow power of a main line connected with the micro-grid for the charging station is constrained by line parameters; pEV·dis·max(t) the maximum power which can be sent out by the charging station at the moment t, and the number N of various electric vehicles which can participate in discharging in the station at the momentcar(t)、Nbus(t) and discharge power P of single electric vehiclecar·dis、Pbus·disOf (3) is performed.
In step S3, according to the positions of the network switches and the on-off characteristics of the switches of different types, the microgrid is divided into regions, which are specifically classified as:
a primary area: there is no area inside any switching device of any kind. The area will be isolated as a whole regardless of which element fails. Therefore, when enumerating faults, the primary region is taken as the minimum enumeration unit, and the overall fault rate of the region is considered.
And (3) secondary area: the circuit breaker is taken as a boundary, and the region no longer contains the circuit breaker. Generally, the same branch region is formed by combining a plurality of primary regions.
In step S4, according to the difference of the areas where the internal fault points are located in the micro grid island operation, different switching action strategies are adopted to perform fault isolation, and the specific steps are as follows:
step S41: when a fault occurs in a primary region with an isolating switch as a boundary, the circuit breakers or intelligent switches in all upstream directions of the region act firstly to cut off the power supply current of all power supplies, the isolating switch in the fault region is cut off to isolate the fault, the circuit breakers and the intelligent switches are superposed, and the fault-free equipment of the micro-grid recovers to normal operation;
step S42: when a fault occurs in a primary region with the intelligent switch as a boundary, the corresponding intelligent switch is only needed to be disconnected;
step S43: when a line branch fails, the disconnecting switch is not required to be switched on or off after the current is blocked, and the circuit breaker and the intelligent switch can not be switched on again.
In step S5, a sequential monte carlo simulation algorithm is used to evaluate the reliability of the operation of the microgrid including the electric vehicle charging station, and the specific steps are as follows:
step S51: reading original data, setting an initial value T of an analog clock to be 0, and assuming that all elements are in a normal working state initially;
step S52: calculating the Time To Failure (TTF) and the Time To Repair (TTR) of each element in the network to obtain a time sequence table: TTF, TTR;
step S53: the faults are enumerated. Selecting the minimum TTF of TTFsiThe corresponding element is a fault element;
step S54: analyzing simulation time T to T + TTFiIn the time period, the running conditions of the system in different time periods of whether the electric vehicle charging station is connected or not are added, and the accumulated simulation time T is T + TTFi；
Step S55: judging the type and position of the fault, and determining a fault influence area;
step S56: fault isolation is carried out on the micro-grid after the fault;
step S57: and before the fault node recovers to normal operation, analyzing the operation condition of the area after the fault is isolated. It is determined whether load shedding is required. If yes, accumulating the power failure time of the reduced load and the reduced load power. And accumulating the simulation time T as T + TTRi；
Step S58: calculating the power failure time of the affected load nodes;
step S59: judging whether the simulation time reaches a specified simulation time limit, if not, returning to the step S62; if yes, continuing the next step;
step S510: and calculating the reliability evaluation indexes of the system and the load nodes.
The reliability evaluation index specifically includes:
the power supply reliability evaluation index in the isolated island state of the micro-grid can adopt the reliability evaluation index (the average annual power failure frequency SAIFI of the system, the average annual power failure time SAIDI of the system, the average annual power failure duration CAIDI of a user and the average power supply availability ASAI) of the traditional power distribution network. Meanwhile, considering the power interaction condition between the accessed EV charging station and the microgrid system, the invention also provides the following indexes to analyze the influence on the operation reliability of the microgrid after the access of the EV charging station on the basis of the traditional indexes:
(1) firstly, the intimacy between the EV charging station and the microgrid is analyzed by counting the charging and discharging times (CHT and DIST) of the EV charging station in a simulation period, and parameters such as Average Charging Depth (ACD) (kW/time), Average Discharging Depth (ADD) (kW/time) and the like of the charging station. Wherein:
in the formula:power for ith charging and jth discharging of the EV charging station respectively; PG (Picture experts group)iAnd when the EV power station is charged for the ith time, the renewable energy can generate power.
(2) The method comprises the steps of calculating the number of times (times/year) of load reduction in the microgrid and the Average Load Reduction Depth (ALRD) (kW/times), analyzing the microgrid with the access of EV charging stations and the microgrid without the access of the EV charging stations, and further analyzing the influence of the access of the EV charging stations on the power supply reliability of the microgrid. Wherein:
in the formula: pzThe load power for the z-th reduction.
(3) When the power supply in the non-fault area in the network is insufficient, the EV charging station participates in discharging, the power supply shortage in the network is reduced, the reduced load power is reduced, and therefore the number of users with power failure is reduced. The effect can be represented by the following formula:
fig. 4 shows a network structure diagram of an embodiment, which is based on a network structure of an IEEE power distribution system reliability evaluation test system RTBS Bus 6, and an area where load nodes LP13-LP23 are located is used as a microgrid and is connected to a power distribution network through a PCC switch.
The micro-grid is partitioned, the partitioning conditions are shown in table 1, 11 load primary regions are totally used, a photovoltaic power generator set and a wind power generator set are used as two power source primary regions and are respectively connected into No. ① secondary region regions and No. ③ secondary region regions, wherein the photovoltaic installed capacity is 1.5MW, the wind power generator set is composed of 3 fans of 0.8MW, the cut-in wind speed of each fan is 4m/s, the rated wind speed is 12.5m/s, the cut-out wind speed is 25m/s, an energy storage battery ESS is used as a single primary region and is connected into No. ③ secondary region, the capacity is 5000 kW.h., cables are adopted by distribution lines in the micro-grid region, and table 2 is corresponding reliability parameters of the micro-grid.
TABLE 1 microgrid zoning scenario
TABLE 2 reliability parameters
For the charging stations EV1 and EV2 in fig. 4, 50 private electric vehicle charging piles and 5 electric regular bus charging piles are respectively arranged, the private electric vehicles are assumed to be unified to be of a biedi E5 vehicle type, the electric regular bus is of an aerospace E8 vehicle type, and configuration parameters of the two types of electric vehicles are shown in table 3. Time node T0(T0‘)、T1、T2、T3(T3') were taken as 7:00(7:30), 9:00, 17:00, 19:00(18:30), respectively.
TABLE 3 configuration parameters of two types of electric vehicles
In the present embodiment, the calculation of the related reliability index is performed for two situations, i.e., the access state of the EV charging station and the non-EV charging station, respectively, and the results are shown in table 4 below. In this example, the load nodes LP13, LP17, and LP19 are set to have a low importance level and can be reduced preferentially, and the subsequent reduction of the corresponding loads is determined by the electrical distance between the load node and the power supply node, and the distances are reduced in order from far to near.
TABLE 4 associated reliability index
| Reliability index | EV-free charging station | EV-contained charging station |
| SAIFI (time/family, year) | 2.449 | 2.212 |
| SAIDI (h/family-year) | 14.298 | 12.103 |
| ASAI | 0.99634 | 0.9986 |
| ACD (kW/times) | -- | 0.2062 |
| ADD (kW/times) | -- | 0.1983 |
| ALR (time/year) | 1577 | 676 |
| ALRD (kW/times) | 0.3842 | 0.2763 |
| η | -- | 0.4178 |
As can be seen from the calculation results in table 4, in the isolated island operation state of the microgrid, considering the power interaction situation between the electric vehicle charging station and the microgrid, the average power failure time of the microgrid system is reduced by 0.237 (times/household/year), the average power failure frequency is reduced by 15.35%, the average load shedding depth (ALRD) is reduced by about 28.1%, the load shedding frequency (ALR) is reduced by 57.1%, and the improvement of the power supply quality of the microgrid to the load in the isolated island operation state is effectively reflected. The charging depth index (ACD) of the electric automobile also reflects, the V2G technology of the electric automobile charging station is fully utilized, the charging requirement of the electric automobile is met, and the consumption capacity of the system to distributed energy is increased. When the generated power in the microgrid is abundant, the electromobile is charged, and the wind and light abandoning rate in the system can be effectively reduced.
Claims (10)
1. A reliability evaluation method for a micro-grid with an electric vehicle charging station is characterized by comprising the following steps:
1) acquiring the charge state of the power battery of the electric automobile at each time point according to the running characteristics of the electric automobile in the micro-grid;
2) establishing an interactive response power calculation model according to a microgrid internal power interaction strategy;
3) according to the positions of the network switches and the on-off characteristics of the switches of different types, carrying out region division on the micro-grid;
4) according to the difference of the areas where the internal fault points are located when the micro-grid isolated island operates, different switching action modes are adopted to carry out fault isolation;
5) and evaluating the operation reliability of the microgrid with the electric vehicle charging station by adopting a sequential Monte Carlo simulation method under the condition of considering the internal power interaction and fault isolation of the microgrid.
2. The method for evaluating reliability of the microgrid comprising an electric vehicle charging station as claimed in claim 1, wherein in the step 1), the state of charge of the power battery of the electric vehicle at each time point satisfies the following constraints:
wherein, T0、T′0Respectively, the departure time points of regular bus and private electric automobile in the morning, and T0＜T′0，T1And T2Time points of access and departure, T, respectively3For the point in time, T ', at which the coach stops at the charging station after returning to the park'3Is the time point of the private electric automobile arriving at home, SOCmin(T0/T′0)、SOCmin(T1)、SOCmin(T2)、SOCmin(T3/T′3) Are respectively at T0Or T'0、T1、T2、T3Or T'3State of charge, S, of an electric vehicle at a point in time1For regular bus at N1、N3Distance traveled in time intervals, S2For private electric automobile at n1、n3Time-interval driving course, N1Time period for the electric regular bus to start from the park in the morning and return to the park after the staff is connected to the fixed station, N2Time period for parking electric duty car in park to charge station, N3Time period for afternoon bus to transport employees to fixed sites and back to park, N4For time periods when regular bus is parked at park charging station, n1For the time period from home to park when the employee takes the private electric automobile in the morning, n2Time period for a private electric car to stop at a charging station in a park, n3Time period from park to home for employee to take private electric automobile, n4For the time when the private electric automobile stops at the house of the staff, W is the power consumption of the electric automobile per kilometer, WedRated electric quantity, SOC, of the power battery of the electric automobilesd·minThe minimum state of charge threshold is set for ensuring a certain service life of the power battery.
3. The method according to claim 2, wherein the step 2) specifically comprises the following steps:
21) determining an operating period of the microgrid comprising N1、N2、N3And N4A time period;
22) and performing source and load power balance calculation on the fault-free area, wherein the source and load power balance formula is as follows:
Pph(t)＝PWT(t)+PPV(t)-PL(t)
wherein, Pph(t) is the area balance power, PL(t) is the real-time load power within the microgrid; pWT(t) is the total power generation power of the wind turbine generator at the moment t, PPV(t) is the total power generation power of the photovoltaic generator set at the moment t;
23) when P is presentph(t) > 0 and at N1And N3During the time interval, no electric automobile is connected, the micro-grid only charges the energy storage device, and N is2And N4In time periods, in order to ensure that the energy storage equipment is required to maintain the stability of the system operation when no electric automobile is accessed, the state of charge of the electric automobile is at least SOCESS·sdThen, charging the electric automobile in the electric automobile charging station;
24) when P is presentph(t) is less than or equal to 0 and is in the range of N1And N3At time intervals, only the energy storage device is discharged, at N2And N4During the period of time, when the electric vehicle is discharging, if Pph(t)+PEV·dis(t) < 0, the energy storage device participates in the discharging operation at the same time, and if the combined output of the energy storage device, the electric vehicle charging station and the renewable energy cannot meet the load requirement, namely Pph(t)+PEV·dis(t)+PESS·dis(t) < 0, load shedding is performed according to the important level of the load in the network, and if the power supply is insufficient when the output power is reduced to zero, the load in the island region is further shed, wherein PEV·dis(t) discharge power of the charging station at time t, PESS·dis(t) is the discharge power of the energy storage device at the moment t;
25) based on the internal power interaction strategy of the microgrid in the steps 23) and 24), the calculation formula of the charging and discharging power of the energy storage device at different time intervals is as follows:
wherein, PESS·dis(t) discharge power of the energy storage device, PESS·ch(t) charging power of the energy storage device, PESS·dis·maxIs the maximum discharge power, P, of the energy storage deviceESS·ch·maxMaximum charging power for energy storage, SOCESS(t) State of Charge, SOC, of the energy storage deviceESS·sdThe energy is stored in order to maintain the charge state of a subsequent system to be stable when no electric vehicle is in an electric vehicle charging station;
26) in N1、N3The number of electric vehicles in the charging station for the time period is approximately zero, considering that in N2、N4The interactive power condition between the electric vehicle charging station and the microgrid in the time period, namely the interactive response power calculation model is as follows:
when P is presentph(t) > 0, charging station charging power:
when P is presentph(t) < 0, charging station discharge power:
PEV·dis·max(t)＝Ncar(t)·Pcar·dis+Nbus(t)·Pbus·dis
wherein, PEV·maxMaximum allowable flow power, P, of a main line connecting a charging station to a microgridEV·dis·max(t) is the maximum power that can be delivered by the charging station at time t.
4. The method as claimed in claim 1, wherein the step 3) of specifically classifying the microgrid into regions comprises:
a primary area: the method comprises the following steps that a region without any type of switching device is arranged inside, once an element fault occurs in the region, the region is isolated integrally, and when the fault is enumerated, a primary region is used as a minimum enumeration unit, and the integral fault rate of the region is considered;
and (3) secondary area: the circuit breaker is used as a boundary, a region without the circuit breaker is arranged in the region, and the same branch region is formed by combining a plurality of primary regions.
5. The method according to claim 1, wherein the step 4) of performing fault isolation by adopting different switching actions specifically comprises:
when a fault occurs in a primary region with an isolating switch as a boundary, all the circuit breakers or intelligent switches in the upstream direction of the region act firstly to cut off the power supply current of all power supplies, the isolating switch in the fault region is cut off to isolate the fault, the circuit breakers and the intelligent switches are superposed, and the fault-free equipment of the microgrid recovers to normal operation;
when a fault occurs in a primary region with the intelligent switch as a boundary, only the corresponding intelligent switch is switched off;
when a line branch circuit has a fault, the on-off operation of the isolating switch is not needed after the current is blocked, and meanwhile, the circuit breaker and the intelligent switch are not closed any more.
6. The method according to claim 1, wherein the step 5) specifically comprises the following steps:
51) reading original data, setting an initial value T of an analog clock to be 0, and assuming that all elements of the micro-grid are in a normal working state initially;
52) obtaining a TTF time sequence table and a TTR time sequence table according to the non-fault working time TTF and the fault repairing time TTR of each element in the micro-grid;
53) enumerating faults and selecting the minimum value TTF in the TTF time sequence listiThe corresponding element is a failed element;
54) get from T to T + TTFiIn the simulation time period, the operating conditions of the micro-grid in different time periods whether the micro-grid is connected to the electric vehicle charging station or not are added, and the simulation time T is accumulated as T + TTFi；
55) Judging the type and position of the fault and determining a fault influence area;
56) fault isolation is carried out on the micro-grid after the fault;
57) before the fault node recovers to normal operation, whether load reduction is needed or not is determined according to the operation condition of the area after fault isolation, if yes, the reduced load is accumulatedThe power off time of the load and the power of the load are reduced, and the simulation time T is accumulated to be T + TTRi；
58) Acquiring the power failure time of the affected load nodes;
59) judging whether the time reaches the specified time limit, if not, returning to the step 52); if yes, continuing the next step;
510) and performing reliability evaluation according to reliability evaluation indexes of the microgrid system and the load nodes.
7. The method as claimed in claim 6, wherein in step 510), the reliability evaluation indexes include a conventional reliability evaluation index and a microgrid reliability evaluation index including an electric vehicle charging station.
8. The method of claim 7, wherein the general reliability assessment indicators 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.
9. The method of claim 7, wherein the microgrid reliability evaluation indexes of the charging stations comprise an average charging depth ACD, an average discharging depth ADD, an average load reduction depth ALRD, and a load reduction intensity η when the power supply of the fault-free area is insufficient.
10. The method according to claim 9, wherein the calculation formula of the reliability evaluation index of the microgrid including the electric vehicle charging station comprises:
wherein,the power of ith charging and jth discharging of the electric vehicle charging station is respectively, CHT and DIST are respectively the total charging and discharging times of the electric vehicle charging station, PGiThe power that the renewable energy source can send out when charging for electric automobile charging station ith, and the ALR is the total number of times of load reduction in the microgrid, PzThe load power for the z-th reduction.
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