Reliability evaluation method for power distribution network containing energy storage in island and emergency recovery mode

Abstract

The invention discloses a reliability evaluation method for a power distribution network containing energy storage in an island and emergency recovery mode, and relates to the technical field of power distribution network reliability evaluation, and the method comprises the steps: employing a region branching method to isolate a fault region, and dividing the power distribution network containing energy storage into a fault upstream region, a fault interior region and a fault downstream region; according to an interruption time calculation method, the non-power-supply amount ENS of each load point in each fault area is calculated; the method comprises the following steps: for a fault downstream region, considering the condition of recovering power supply by using distributed energy and stored energy in an island and bundled support operation mode, respectively calculating the interruption duration of each load point in the downstream region under each condition, and calculating the non-power-supply ENS by combining the fault rate of the load point; and evaluating the reliability of the energy-storage-containing power distribution network according to the non-power-supply ENS of each load point in the energy-storage-containing power distribution network. According to the method, more realistic, more accurate and more efficient evaluation of the reliability of the energy storage-containing power distribution network can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of reliability assessment of distribution networks, and in particular to a reliability assessment method for distribution networks containing energy storage in isolated island and emergency recovery modes. Background Art

[0002] When a fault affects the power supply from the main substation to the user, the traditional solution is to reconfigure the grid to deliver power from adjacent feeders to unpowered areas, such as turning off the grid-connected switch. However, the distribution network does not always have this function. For this reason, the access of distributed energy (DG) has created a new solution for restoring the load supply of the distribution network, and the deployment of energy storage systems (ESS) has provided a new technical method for dealing with the volatility and intermittency of distributed power sources. Distributed energy DG and energy storage systems ESS provide a variety of options for restoring the supply of the distribution network: one is to supply power to areas that cannot access backup feeders due to fault isolation, that is, island operation; the other is to support recovery from adjacent feeders with emergency relationships but limited transmission capacity, called bundled support operation.

[0003] Reliability is one of the basic parameters that need to be evaluated in distribution network planning. At present, the reliability evaluation of distribution networks mainly includes analytical methods and Monte Carlo simulation (MCS). Among them, MCS helps to introduce timing uncertainty into the evaluation process in a probabilistic framework, but MCS still has certain disadvantages: it has many simulation iterations and long calculation time. Moreover, although MCS has been widely used in energy storage evaluation in distribution system reliability research, existing research has not yet analyzed the contribution of energy storage under the bundled support mode and its impact on the reliability of the distribution network.

[0004] The analytical method is a computationally efficient method to calculate the average value of the reliability index that replaces the MCS. It is analyzed and evaluated by energy storage modeling. However, this energy storage modeling method has the disadvantage of increasing the complexity required to deal with the variability and time evolution of power generation and demand during the fault. To this end, an effective modeling method has been proposed in the prior art, which defines the probabilistic state of stored energy during the fault duration. However, this model does not include the charging and discharging process of energy storage, so it cannot be used to apply energy storage operation strategies to restore supply; moreover, although a variety of analytical methods have been proposed to evaluate the reliability of renewable DG distribution networks in island mode and bundled-support mode, this analytical method is rarely used for energy storage evaluation.

[0005] Therefore, the existing analytical method for evaluating the reliability of distribution networks does not evaluate the contribution of energy storage in the bundled support recovery mode, nor does it consider the need to model the time-sequential charging and discharging process within the fault duration when modeling energy storage. The final reliability evaluation result is inaccurate. Summary of the invention

[0006] To address the deficiencies of the above-mentioned prior art, the present invention provides a reliability assessment method for a distribution network containing energy storage in an island and emergency recovery mode, and adopts an analytical method to assess the impact of energy storage on the reliability of the distribution network, and the impact simultaneously takes into account the fault conditions of DG and ESS in the island repair mode and the bundled support repair mode; the assessment method takes into account the variability and time fluctuations of renewable energy generation and demand during the fault period, establishes a chronological charging and discharging model of energy storage to support power generation shortages and shorten fault duration, and finally incorporates these factors into the calculation of reliability indicators to achieve a more realistic reliability index calculation and ensure the accuracy of the final assessment.

[0007] In a first aspect, the present invention provides a reliability assessment method for a distribution network containing energy storage in an island and emergency recovery mode.

[0008] A reliability assessment method for a distribution network with energy storage in an island and emergency recovery mode, comprising:

[0009] The regional branch method is used to isolate the fault area and divide the distribution network containing energy storage into the upstream, internal and downstream areas of the fault.

[0010] According to the interruption time calculation method, the ENS of each load point in each fault area is calculated respectively; for the downstream area of ​​the fault, the use of distributed energy and energy storage to restore power supply in the island and bundled support operation modes is considered, and the interruption duration of each load point in the downstream area is calculated in each case, combined with the failure rate of the load point, to calculate the ENS of the power outage;

[0011] The reliability of the distribution network with energy storage is evaluated based on the unpowered energy ENS of each load point in the distribution network with energy storage.

[0012] In a second aspect, the present invention further provides an electronic device comprising a memory and a processor, and computer instructions stored in the memory and executed on the processor, wherein when the computer instructions are executed by the processor, the steps of the method described in the first aspect are completed.

[0013] In a third aspect, the present invention further provides a computer-readable storage medium for storing computer instructions, which, when executed by a processor, complete the steps of the method described in the first aspect.

[0014] One or more of the above technical solutions have the following beneficial effects:

[0015] 1. The present invention provides a reliability assessment method for a distribution network with energy storage in an island and emergency recovery mode. The method takes into account the variability and temporal fluctuations of renewable energy generation and demand during a fault, establishes a chronological charging and discharging model for energy storage to support power generation shortages and shorten fault duration, and finally incorporates these factors into the calculation of reliability indicators to achieve a more realistic reliability index calculation and ensure the accuracy of the final assessment.

[0016] 2. The method proposed in the present invention takes into account the fault conditions of DG and ESS in the island repair mode and the bundled support repair mode, and adopts an analytical method to evaluate the impact of energy storage on the reliability of the distribution network. During the evaluation, the probability modeling of the charging and discharging of the energy storage system in chronological order during the fault is performed, and the volatility of DG and demand is considered. A strategy for restoring supply during the fault is formulated, thereby providing a more realistic reliability index calculation.

[0017] 3. The reliability assessment method of a distribution network with energy storage in an island and emergency recovery mode proposed in the present invention can evaluate the impact of energy storage in a grid area operating in an island or recovered by an adjacent feeder with limited transmission capacity, and model the energy storage sequential charging and discharging process during a fault and apply corresponding operation strategies. Finally, by comparing the evaluation results with the sequential MCS calculation results, the effectiveness of the method of the present invention is verified. Compared with the traditional MCS, the method of the present invention can effectively improve the calculation efficiency while maintaining high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0019] Figure 1 It is a flow chart of a reliability assessment method of a distribution network containing energy storage in an island and emergency recovery mode according to an embodiment of the present invention;

[0020] Figure 2 A schematic diagram of different areas after fault isolation and power restoration in an embodiment of the present invention;

[0021] Figure 3 Schematic diagram of the time interval during a downstream area fault in an embodiment of the present invention;

[0022] Figure 4 Calculate the fault duration of DG and energy storage in the embodiment of the present invention Flowchart of

[0023] Figure 5 is a curve diagram of power generation and load during a fault in an embodiment of the present invention;

[0024] Figure 6 A flow chart of a strategy for restoring energy storage performance during a fault in an embodiment of the present invention;

[0025] Figure 7 A schematic diagram of an improved IEEE RTS BUS 6 system in an embodiment of the present invention;

[0026] Figure 8 A comparison chart of evaluation results obtained by using different evaluation methods in an embodiment of the present invention;

[0027] Fig. 9 In the embodiment of the present invention, ENS and ENS * Error comparison chart. DETAILED DESCRIPTION

[0028] It should be noted that the following detailed descriptions are exemplary only, are intended to describe specific embodiments, are intended to provide further explanation of the present invention, and are not intended to limit exemplary embodiments according to the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those of ordinary skill in the art to which the present invention belongs. In addition, it should also be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0029] Embodiment 1

[0030] This embodiment provides a reliability assessment method for a distribution network containing energy storage in an island and emergency recovery mode. Figure 1 As shown, the method comprises the following steps:

[0031] Step S1: Isolate the fault area using the regional branching method, and divide the energy storage distribution network into fault upstream, fault internal, and fault downstream areas;

[0032] Step S2, according to the interruption time calculation method, respectively calculate the power outage ENS of each load point in each fault area; wherein, for the downstream area of ​​the fault, consider the situation of using distributed energy and energy storage to restore power supply in the island and bundled support operation modes, respectively calculate the interruption duration of each load point in the downstream area in each case, and combine the failure rate of the load point to calculate the power outage ENS;

[0033] Step S3: Evaluate the reliability of the distribution network with energy storage according to the unpowered energy ENS of each load point in the distribution network with energy storage.

[0034] The following content introduces in more detail the reliability assessment method of the distribution network containing energy storage in the island and emergency recovery modes proposed in this embodiment.

[0035] It should be clear that the reliability index is used to quantify the impact of distribution network interruptions on load points and load areas. The reliability index (index i) of each load point in the distribution network is the failure rate λ i , Annual average power outage time U i , Annual unusable electricity i and no power supply ENS i , the calculation formula of this parameter is as follows:

[0036]

[0037] ENS i =La i ·U i (2)

[0038] In the above formula, N j is the number of distribution network equipment failures, λ i is the annual average failure rate of load point i, r i,j is the power outage time of load point i caused by fault j, U i is the annual average power outage time of load point i, r i is the annual unavailable power at load point i, La i,j is the average demand of load point i at fault j, ENS i is the unpowered energy at load point i.

[0039] Generally, the system average fault frequency index (SAIFI), the system fault average duration index (SAIDI) and the energy unavailable (ENS) are often used for reliability assessment, and these parameters can be calculated by the above load point reliability index. In this embodiment, the reliability of the distribution network is assessed by calculating ENS.

[0040] In step S1, for the calculation of the reliability index, a regional branching method is used, which simulates the operation of the protection device when a fault occurs and identifies the network areas that have different effects on reliability. Figure 2 As shown in FIG, based on the regional branching method, the distribution network containing energy storage after fault isolation j is divided into three types of areas: the upstream area of ​​the fault (i.e., area 1), the internal area of ​​the fault (i.e., area 2), and the downstream area of ​​the fault (i.e., area 3).

[0041] In steps S2 and S3, for each of the above-mentioned areas, the failure rate and interruption time of each load point in each fault area are calculated respectively, and then the power outage ENS is calculated based on the failure rate and power outage time (i.e., interruption time), so as to evaluate the reliability of the distribution network.

[0042] Specifically, for the failure rate and interruption time, in the divided area, if the fault duration is less than a certain time threshold, the failure rate λi,j is equal to zero, otherwise, the failure rate λ i,j Equal to the failure rate of the component causing the failure, λ j ; The average interruption time of each regional load point is determined by the following formula (3):

[0043]

[0044] In the above formula, tsi j is the time to isolate fault j; tsr j The time to restore supply to the upstream area of ​​fault j; r j is the mean repair time for fault j.

[0045] Based on the above formula, the average failure rate and average interruption time of the load points in the upstream and internal areas of the fault can be calculated to obtain the power outage ENS. The average interruption time of the load points in the downstream area of ​​the fault can be calculated by the following content.

[0046] Before performing the reliability assessment, the following assumptions are made: the operation of the distribution system is radial; only sustained faults are assessed; the protection devices are considered reliable and their faults are ignored; the DGs and ESSs are disconnected when a fault occurs and reconnected after the fault is mitigated and the network is reconfigured; the network is equipped with appropriate island operation protection and control systems; and active power adequacy assessment is performed without considering reactive power.

[0047] like Figure 3 The example of the time interval recorded by the load points in the downstream area during the fault is shown in FIG. 1 . The total interruption duration of a load point in the downstream area is the switching time tsw after the occurrence of fault j. j and fault duration The sum is:

[0048]

[0049] In the above formula, tsw j is the switching time after fault j occurs, which includes the time required to identify the fault, isolate the fault, and prepare for downstream recovery; is the duration of fault j.

[0050] Furthermore, the duration of the fault interruption The calculation of needs to consider the existence of alternative resources, and in addition to considering emergency bundle support and DG, the impact of energy storage must also be considered. In this embodiment, the use of distributed energy and energy storage to restore power supply in the island and bundle support operation modes is considered, and the interruption duration of each load point in the downstream area is calculated in each case. On this basis, the average interruption time of the downstream area is calculated in combination with the above formula (3).

[0051] Specifically, considering various situations of using distributed energy and energy storage to restore power supply, the switching time tsw after fault j occurs is calculated and determined j and fault duration include:

[0052] ① When there is no alternative supply source in the downstream area, the fault isolation time tsi j is the switching time tsw j , the average repair time r of fault j j is the duration of fault j That is: tsw j =tsi j ,

[0053] ② When the downstream area is equipped with an emergency power grid with sufficient transfer capacity, the fault isolation time tsi j and downstream area switch switching time t tie The maximum value in is the switching time tsw j , fault j duration is 0, that is:

[0054]

[0055] ③ When the downstream area is equipped with an emergency power grid with limited transfer capacity in an emergency, the downstream area is combined with distributed energy DG and energy storage system ESS, and the distributed energy is operated in a bundled-support mode. At this time, the fault isolation time tsi j , Downstream area switch switching time t tie , the maximum startup time of DG in case of failure st dg , the maximum startup time of ESS in case of failure st s The maximum value in is the switching time tsw j , and the fault j duration is obtained by probability calculation Right now:

[0056] tsw j =max(tsi j ,t tie ,st dg ,st s ) (6)

[0057] ④ When there is no emergency power grid in the downstream area, the distributed resource island operation is adopted, and the distributed energy DG and energy storage system ESS are used to restore the interrupted power supply. At this time, the fault isolation time tsi j , the maximum startup time of DG in case of failure st dg , the maximum startup time of ESS in case of failure st sThe maximum value in is the switching time tsw j , and the fault j duration is obtained by probability calculation Right now:

[0058] tsw j =max(tsi j , st dg , st s ) (7)

[0059] In the above cases ③ and ④, use Figure 4 The probability calculation process shown in the figure is used to calculate the duration of fault j. Specifically include:

[0060] First, upload the required fault state and representative time interval data, set different fault states, representative time intervals, and time interval lengths in the downstream area to simulate multiple fault scenarios. Among them, the fault state means that the distributed energy DG and energy storage system ESS in the downstream area of ​​the distribution network are in different states when the fault occurs. The probability combination of the different states of the distributed energy DG and the energy storage system ESS forms a combined state, which is the fault state, and the probability of the occurrence of the combined state is the fault state probability.

[0061] Secondly, the adequacy of distributed energy DG and energy storage ESS is evaluated under each fault state, representative time interval, and time interval length, and the fault duration under each simulated fault scenario is calculated.

[0062] Specifically, the selection probability is P cr The fault state cr is used to evaluate its ability to provide interrupted supply. The evaluation is performed under different renewable energy generation and demand conditions during the fault period given in each representative time interval rs. Considering that component failures may occur at different times of the year, the fault is simulated by assuming that a failure may occur in each time length h of the representative time interval rs. The probability of a failure occurring in each time length of each representative time interval is recorded as the failure occurrence time probability p h,rs For each combination of the above specific conditions (fault state cr, representative time interval rs, and time interval length h), a sufficiency evaluation is performed to calculate the fault duration

[0063] Finally, based on the fault duration Combining the fault state probability and the fault occurrence time probability, the fault j duration is calculated

[0064] Specifically, consider the probability condition shown in the following formula (8): Aggregate all values ​​of to get the total fault j duration The calculation formula is:

[0065]

[0066] In order to determine the above probability, the traditional two-state modeling is used for the lines and transformers in the network: the up state represents the normal operation state, and the down state represents the fault state. This two-state model is used for DG and ESS, and the state at each moment is reflected by the fault rate FOR. When a fault occurs, the DG and ESS used to restore the downstream area can be in different states (up and down). The probability combination of these devices and their respective states forms a set of combined states, which is defined as the fault state. Each fault state has a specific recovery capability. The fault state probability p cr The calculation of is shown in the following formula (9):

[0067]

[0068] In the above formula, They are the DG and ESS status respectively, 1 is normal and 0 is faulty.

[0069] Furthermore, the adequacy of distributed energy sources (DG) and energy storage (ESS) is evaluated to assess the operation of energy storage during faults, so as to provide uninterrupted power supply in the case of insufficient power generation. The fault duration under each simulated fault scenario is calculated through evaluation. This is accomplished by:

[0070] (1) Quantify the power generation and power demand in the downstream area and construct the power generation and power load curve. Specifically, quantify the total power profile of the demand and power generation in the downstream area, calculate and construct the power generation and power load curve based on all the fault states of the equipment and the different conditions of renewable energy power generation and the demand within a year. The quantified result can be expressed by the following formula:

[0071]

[0072] In the above formula, are the total power generation and total power demand of the downstream at time length t respectively; is the status of downstream DG and bundled feeder. Among them, the transmission capacity of the feeder It is determined while maintaining network constraints, which takes into account the demand, downstream DG and ESS, and the transmission capacity of adjacent feeders connected through emergency situations.

[0073] like Figure 5 Power generation in the downstream area during the fault is shown and load After the switching time is over, the ability to restore power is evaluated within the restoration evaluation time (from the fault start time t1 to the fault end time tf). If the duration of the representative time intervals is shorter than the fault, these time intervals can be repeated as many times as needed to cover the duration of the fault.

[0074] (2) The charging and discharging process of the energy storage system ESS during the fault is modeled in chronological order to construct an energy storage model.

[0075] Specifically, assuming that the energy storage system is in the initial charging state when the fault occurs, the following equations (12) to (15) are used to model the charging and discharging process of the energy storage system during the fault in chronological order, and the constructed energy storage model is:

[0076]

[0077] In the above formula, Pc s,t , Pd s,t are the energy storage charging and discharging power, η is the efficiency, C s is the energy storage capacity, S O C s are the upper and lower limits of energy storage capacity, are the total power generation and total power demand of the downstream area at time length t, rc s,t ,rd s,t are the energy storage charging and discharging power ratios under time length t respectively.

[0078] Each time the energy storage system ESS is charged or discharged, the ratio of the total power that can be charged by the energy storage device is updated as:

[0079]

[0080] The ratio of the total power required to be released from the energy storage device is:

[0081]

[0082] Regarding the priority use of ESS, in this embodiment, it is assumed that the ESS with a lower state of charge is charged first, and the ESS with a larger state of charge is discharged first (the range of the state of charge is 0 to 1, which measures the ratio of energy storage to energy storage capacity).

[0083] (3) Based on the power generation and power load curves, determine the duration of power shortage, select the time lengths in reverse chronological order, use the energy storage model to evaluate the energy storage capacity for each time length, and calculate the fault duration and the time length s for recovery to start j,j,cr,rs,h .

[0084] Specifically, Figure 6 The calculation shown gives the average outage time and the time length s for recovery to start j,j,cr,rs,h process, the j,j,cr,rs,h In the following formula (21), it is used to calculate the non-energy supply. Through this evaluation method, a specific strategy is adopted when operating energy storage to reduce the duration of the interruption. The evaluation process includes:

[0085] (3.1) During the fault period, based on the power generation and power load curves, the duration of the power shortage is calculated to determine the duration of the power shortage.

[0086] (3.2) Evaluate the energy storage capacity for the duration of power shortage. Select the duration in reverse chronological order, and use the energy storage model to evaluate the energy storage capacity for each duration, such as Figure 4 As shown, the evaluation starts with the last time length ts during which there is a power generation shortage. Once the evaluation is completed, the previous time lengths are selected in reverse chronological order for evaluation.

[0087] (3.2.1) Starting from the last time length ts when there is a power generation shortage, the maximum available SOC value at the time length ts is determined according to the energy storage model. The maximum available energy storage at this time length ts is:

[0088]

[0089] Consider the discharge power Pd s,t Between t1 and ts-1, the SOC value is 0. It is calculated by the above formula (12) and formula (13).

[0090] (3.2.2) Evaluate the maximum available SOC value during the time length ts to tf Including: in each time length, according to the relationship between power generation and power demand, determine the charging and discharging power of the energy storage system, and update the SOC value during the charging and discharging cycle.

[0091] Evaluated between time lengths ts and tf Specifically, at each time length, if the power generation exceeds the demand, the energy storage system calculates the charging power according to formula (14); on the contrary, when all ESS (designed as Pdm t , calculated by the following formula (19)) The maximum power that can be released is sufficient to meet the power shortage, and the energy storage system gives priority to power supply. In this case, the discharge power is calculated by formula (15). During the charge and discharge cycle, SOC is updated by using (12) and formula (13).

[0092]

[0093] (3.2.3) If the ESS fails to supply all the generation during the time interval from ts to tf, then the fault duration is and the time length s for recovery to start j,j,cr,rs,h are all 0, and the next time length (i.e., the previous power generation shortage time length) is evaluated in reverse chronological order; conversely, if the energy storage system ESS does not fully restore all power generation shortage supplies within the time interval from time length ts to tf, the evaluation of the power generation shortage time length is stopped, which means that the power supply has been interrupted from the beginning of the fault until the time length ts, and the fault duration is calculated at this time and the time length s for recovery to start i,j,cr,rs,h .

[0094] (4) Repeat the above calculation step (3) to calculate the next set of fault durations and the time length s for recovery to start i,j,cr,rs,h , until the calculations under all fault scenarios are completed, that is, until all combinations of fault conditions (defined by cr, rs and h) are calculated.

[0095] After the above parameters are calculated, the unpowered energy ENS is calculated based on the failure rate and interruption time for each load point in each fault area of ​​the energy storage distribution network, and the power shortage ENS of the energy storage distribution network is calculated based on the unpowered energy ENS of each load point in each fault area of ​​the energy storage distribution network. i * (which can be called unpowered power) is used to evaluate the reliability of the distribution network containing energy storage.

[0096] Specifically, since the calculation of ENS is for the load point fault downstream in the area, considering the variability of the load interrupted during the fault, this embodiment calculates by using its average load Figure 1 The ENS at the load points (i.e., load points) located in regions 1 and 2 is calculated by the following equations (20) and (21) to calculate the power shortage: Compared with the method based on average value, the method of this embodiment can provide more realistic evaluation results.

[0097]

[0098] In the above formula, La i,j is the average demand of load point i when fault j occurs, pcr is the probability of recovering to state cr; p h,rs is the annual probability of time length h being within the representative time interval rs; is the total electricity demand in the downstream area over time length t.

[0099] Furthermore, in order to verify the evaluation method proposed in this embodiment and verify the contribution of energy storage to reliability, an example analysis is performed using the IEEE RTS BUS6 system, as shown in FIG. Figure 7 The DG reliability parameters are shown in Table 1, and the ESS related parameters are shown in Table 2. A set of control cases without energy storage is set up to compare the impact of energy storage on reliability.

[0100] Table 1DG reliability parameters

[0101] type Failure rate (times / year) Repair time Start-up time (h) DG 2 60 0.25

[0102] Table 2 Energy storage related parameters

[0103]

[0104] To verify the method described in this example, the results of this method are compared with the calculation results of the sequential MCS method under the same scenario, and a variance coefficient of 1.5% is used as the convergence standard of MCS. Figure 8 As shown, the method described in this embodiment is basically consistent with the MCS calculation result, which verifies the effectiveness of this method.

[0105] Combined with the number of calculations shown in Table 3 below, it can be seen that in the energy storage application scenario, the calculation speed of the analysis technology is relatively improved, which verifies the rapidity of the method described in this embodiment; while MCS samples the random occurrence of network faults until the reliability index converges to a solution, which results in the need to evaluate the network faults multiple times, which is inefficient.

[0106] Table 3 Comparison results between the method proposed in this embodiment and the number of MCS calculations

[0107] SMCS Methods DGonly 222.81 201.2 DG+ESS 288.1 246.4

[0108] Table 4 below shows the results of SAIDI (System average interruption frequency index) in the network under two conditions. Figure 8 It is shown that the SAIDI is reduced in the original distribution network without DG, and in the analyzed scenarios, the SAIDI is the same, because the interruption is not avoided, but only the duration is reduced. According to the results, the SAIDI of feeders F3 and F4 is significantly reduced, which is caused by the energy storage support of variable renewable energy generation during island operation. For example, the integration of DG alone improves the SAIDI of feeder F4 by 5.8%. In feeders F3 and F4, the SAIDI improves by 3-4% with the access of energy storage.

[0109] Table 4 SAIDI in the evaluated scenarios (in hours / customer-year)

[0110] F1 F2 F3 F4 total DGonly 0.934 0.925 0.928 8.258 3.798 DG+ESS 0.905 0.906 0.764 6.966 3.277

[0111] The energy storage recovery contribution of feeders F1 and F2 in connected support mode is smaller compared to the isolated feeders (F3 and F4). In the case of F1, the total marginal SAIDI improvement using distributed energy resources is 16%. The penetration of DG alone improved the SAIDI by 6%, while the access of energy storage increased the SAIDI to 9% in the scenario. A similar SAIDI reduction was obtained for energy storage in F2. In summary, although the transmission limitations between feeders F1 and F2 under specific load and fault conditions have a strong impact on the results, energy storage in connected support operation still improves reliability.

[0112] Table 5 below shows the power shortage ENS* calculated using the method proposed in this embodiment. Fig. 9 The difference between ENS* and ENS calculated using equation (2) is shown, i.e., the first method takes into account the time-varying nature of the load during the fault, while the second method uses the traditional method based on the average load value. Fig. 9 The results of each feeder (F1 to F4) and the entire test network (Total) obtained by these two methods are shown.

[0113] Table 5 ENS* (MWh / year) under the assessment scenario

[0114] F1 F2 F3 F4 total DGonly 1.125 1.214 2.012 41.05 45.4 DG+ESS 1.078 1.174 1.739 35.07 39.06

[0115] Obviously, the difference between ENS* and ENS is significant, especially in areas of the network where there is a large amount of unsupplied energy. In addition, installing more energy storage will lead to a reduction in unsupplied energy, so the difference in unsupplied energy calculated by the two methods will also decrease. Fig. 9 As shown, the use of average load values ​​overestimates the ENS in all energy storage scenarios, thus emphasizing the importance of considering fluctuations in the demand profile during the time interval when supply is not restored.

[0116] Embodiment 2

[0117] This embodiment provides an electronic device, including a memory and a processor, and computer instructions stored in the memory and executed on the processor. When the computer instructions are executed by the processor, the steps in the reliability assessment method of a distribution network containing energy storage in an island and emergency recovery mode as described above are completed.

[0118] Embodiment 3

[0119] This embodiment also provides a computer-readable storage medium for storing computer instructions, which, when executed by a processor, complete the steps in the reliability assessment method for a distribution network containing energy storage in an island and emergency recovery mode as described above.

[0120] The steps involved in the above embodiments 2 to 3 correspond to the method embodiment 1. For the specific implementation, please refer to the relevant description part of embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media including one or more instruction sets; it should also be understood to include any medium that can store, encode or carry an instruction set for execution by a processor and enable the processor to execute any method in the present invention.

[0121] Those skilled in the art should understand that the modules or steps of the present invention described above can be implemented by a general-purpose computer device, or alternatively, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0122] The above description is only a preferred embodiment of the present invention. Although the specific implementation mode of the present invention is described in conjunction with the accompanying drawings, it is not a limitation of the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, various modifications or variations that can be made by those skilled in the art without creative work are still within the protection scope of the present invention.

Claims

1. A reliability assessment method for a distribution network with energy storage in an island and emergency recovery mode, characterized in that: include: The regional branch method is used to isolate the fault area and divide the distribution network containing energy storage into the upstream, internal and downstream areas of the fault. According to the interruption time calculation method, the ENS of each load point in each fault area is calculated respectively; for the downstream area of ​​the fault, the use of distributed energy and energy storage to restore power supply in the island and bundled support operation modes is considered, and the interruption duration of each load point in the downstream area is calculated in each case, combined with the failure rate of the load point, to calculate the ENS of the power outage; The reliability of the distribution network with energy storage is evaluated based on the unpowered energy ENS of each load point in the distribution network with energy storage.

2. A reliability assessment method for a distribution network containing energy storage in an island and emergency recovery mode as claimed in claim 1, characterized in that: The interruption duration of each load point in the downstream area is the sum of the switching time after the occurrence of fault j and the duration of fault j; wherein the switching time after the occurrence of the fault includes the time required to identify the fault, isolate the fault and prepare for downstream recovery.

3. A reliability assessment method for a distribution network containing energy storage in an island and emergency recovery mode as claimed in claim 2, characterized in that: Considering various situations of using distributed energy and energy storage to restore power supply, calculate and determine the switching time tsw after fault j occurs j and fault duration include: When there is no alternative supply source in the downstream area, the fault isolation time tsi j is the switching time tsw j , the average repair time r of fault j j is the duration of fault j When the downstream area is equipped with an emergency power grid with sufficient transfer capacity, the fault isolation time tsi j and downstream area switch switching time t tie The maximum value in is the switching time tsw j , fault j duration is 0; When the downstream area is equipped with an emergency power grid with limited transfer capacity in an emergency, the downstream area is combined with distributed energy DG and energy storage system ESS, and the distributed energy is operated in a bundled-support mode. At this time, the fault j isolation time tsi j , Downstream area switch switching time t tie , the maximum startup time of DG in case of failure st dg , the maximum startup time of ESS in case of failure st s The maximum value in is the switching time tsw j , the duration of fault j is obtained by probability calculation When there is no emergency power grid in the downstream area, the distributed resource island operation is adopted, and the distributed energy DG and energy storage system ESS are used to restore the interrupted power supply. At this time, the fault j isolation time tsi j , the maximum startup time of DG in case of failure st dg , the maximum startup time of ESS in case of failure st s The maximum value in is the switching time tsw j , the duration of fault j is obtained by probability calculation 4. A reliability assessment method for a distribution network containing energy storage in an island and emergency recovery mode as claimed in claim 3, characterized in that: The duration of fault j is obtained by probability calculation include: Set different fault states, representative time intervals, and time interval lengths in the downstream area to simulate various fault scenarios; The adequacy of distributed energy DG and energy storage ESS is evaluated under each fault state, representative time interval, and time interval length, and the fault duration under each simulated fault scenario is calculated. Based on the fault duration Combining the fault state probability and the fault occurrence time probability, the fault j duration is calculated 5. A reliability assessment method for a distribution network containing energy storage in an island and emergency recovery mode as claimed in claim 4, characterized in that: The fault state means that when the fault occurs, the distributed energy DG and the energy storage system ESS in the downstream area of ​​the distribution network are in different states, and the probability combination of the different states of the distributed energy DG and the energy storage system ESS forms a combined state, which is the fault state, and the probability of the combined state occurring is the fault state probability; The failure occurrence time probability refers to the probability that a failure may occur in each time length of each representative time interval.

6. A reliability assessment method for a distribution network containing energy storage in an island and emergency recovery mode as claimed in claim 4, characterized in that: Evaluate the adequacy of distributed energy sources (DG) and energy storage (ESS) and calculate the fault duration under each simulated fault scenario include: Quantify the power generation and power demand in the downstream area and construct power generation and power load curves; Model the charging and discharging process of the energy storage system ESS during the fault in chronological order and construct an energy storage model; Determine the length of time that power shortages will exist based on generation and load curves; Select the time lengths in reverse chronological order, use the energy storage model to evaluate the energy storage capacity for each time length, and calculate the fault duration and the time length s for recovery to start j,j,cr,rs,h ; Repeat the calculation steps to calculate the next fault duration and the time length s for recovery to start j,j,cr,rs,h , until the calculations for all fault scenarios are completed.

7. A reliability assessment method for a distribution network containing energy storage in an island and emergency recovery mode as claimed in claim 6, characterized in that: Select the time lengths in reverse chronological order, and use the energy storage model to evaluate the energy storage capacity for each time length, including: The evaluation starts with the last time length ts when there is a power generation shortage, and the maximum available SOC value at the time length ts is determined according to the energy storage model. Evaluate the maximum available SOC value between the time length ts and the fault end time tf Including: in each time length, according to the relationship between power generation and power demand, determine the charging and discharging power of the energy storage system, and update the SOC value during the charging and discharging cycle; If the energy storage system ESS fails to supply all power generation during the time interval from time length ts to the fault end time tf, then the fault duration is and the length of time it takes for recovery to begin are all 0, and the next time length is evaluated in reverse order; on the contrary, if the energy storage system ESS does not restore all power generation shortages within the time interval from the time length ts to the fault end time tf, the evaluation is stopped, and the fault duration is calculated at this time and the length of time it takes for recovery to begin 8. The reliability assessment method of a distribution network containing energy storage in an island and emergency recovery mode as claimed in claim 1, characterized in that: According to the unpowered energy ENS of each load point in the distribution network with energy storage, the reliability of the distribution network with energy storage is evaluated, including: Based on the unpowered energy ENS of each load point in the upstream, internal and downstream areas of the distribution network containing energy storage, the power shortage of the distribution network containing energy storage is calculated. This is used to evaluate the reliability of the distribution network with energy storage; the power shortage is calculated The calculation formula is: Among them, La i,j is the average demand of load point i when fault j occurs, pcr is the probability of recovery state cr; p h,rs is the annual probability of time length h being within the representative time interval rs; is the total electricity demand in the downstream area over time length t.

9. An electronic device, characterized in that: The invention comprises a memory and a processor and computer instructions stored in the memory and executed on the processor. When the computer instructions are executed by the processor, the steps of a reliability assessment method of a distribution network containing energy storage in an island and emergency recovery mode as described in any one of claims 1 to 8 are completed.

10. A computer-readable storage medium, characterized in that: Used to store computer instructions, which, when executed by a processor, complete the steps of a reliability assessment method for a distribution network containing energy storage in an island and emergency recovery mode according to any one of claims 1 to 8.

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