Island microgrid reliability evaluation method and device considering hybrid energy storage system

Abstract

The invention discloses an island micro-grid reliability evaluation method and device considering a hybrid energy storage system, and the method comprises the steps: obtaining the operation parameters of an island micro-grid energy storage system, considering the uncertainty of load output, and the charge and discharge and capacity constraints of the energy storage system, building a load output model and an energy storage charge and discharge model, state parameters of the hybrid energy storage system are obtained, a multi-state model of the hybrid energy storage system is established, the state probability is solved, and a reliability index of the hybrid energy storage system is obtained; establishing a minimum load reduction strategy model on the basis of considering the load importance; and according to the hybrid energy storage system multi-state model, the energy storage charging and discharging model, the load output model and the minimum load reduction strategy model, constructing an island photovoltaic micro-grid reliability evaluation program containing the hybrid energy storage system, and outputting a reliability index of the hybrid energy storage system. And reliability evaluation can be carried out on the island photovoltaic micro-grid system containing the wind and light storage.

Description

Technical Field

[0001] The present disclosure relates to the technical field of power systems, and in particular to a reliability assessment method and device for an island microgrid considering a hybrid energy storage system. Background Art

[0002] With the introduction of the concept of smart grid technology and the development of distributed generation and microgrid technology, microgrids can now actively detach from the power system to form an electric "island". The island microgrid is a new type of power system that mainly absorbs renewable energy. It has the advantages of simple structure, small conversion loss, and high power generation and distribution efficiency. However, since the island photovoltaic microgrid lacks the support of the main grid and contains renewable energy such as photovoltaic and wind power as important power sources, its output has strong volatility and randomness. Therefore, when wind and solar resources are abundant, wind and solar power may be abandoned, and when they are insufficient, it will lead to problems such as load shedding. As an important component of the island photovoltaic microgrid, energy storage has a direct impact on the reliability of the power supply of the island photovoltaic microgrid due to its own equipment failure.

[0003] In addition, as an energy storage, the performance of the battery will be reduced due to the impact of high-power loads. As a power storage, the supercapacitor has high power density and low energy density. From the current energy storage technology, a single energy storage method cannot meet the multiple energy storage needs of the microgrid, so it is necessary to combine the two to form a hybrid energy storage system, which is responsible for the steady-state and transient components of the power fluctuation of the isolated photovoltaic microgrid, and complement each other's advantages. Therefore, the hybrid energy storage system is a direction of current energy storage development. Under the reliability requirements of the isolated photovoltaic microgrid, it is important to establish its multi-state reliability model and detailed energy storage system reliability model, deeply analyze the impact of hybrid energy storage on the reliability of the microgrid, which is different from the traditional single type of energy storage system, and explore the reliability configuration of various operating modes of the isolated photovoltaic microgrid, which is of great significance to improving the power supply reliability of the microgrid distribution network.

[0004] In existing research, there have been some studies on the reliability assessment of isolated photovoltaic microgrids, and most of them focus on the analysis of their internal uncertainty parameters, such as the uncertainty of renewable energy output, state modeling of important equipment, and the temporal and spatial randomness of electric vehicles. However, there are still few studies on energy storage reliability, and the diversity within the energy storage system has not been considered. On the other hand, in the state modeling research of energy storage systems, there are few studies on reliability modeling of hybrid energy storage systems. Most of them use multi-state modeling of the output of distributed generation (DG) within the isolated photovoltaic microgrid to derive a multi-state model of a single type of energy storage power, which has the disadvantages of a cumbersome calculation process and certain limitations. Summary of the invention

[0005] In view of the problems in the existing reliability research of isolated photovoltaic microgrids that the topology of hybrid energy storage systems is not fully considered and a detailed multi-state reliability model is not established for them, a reliability assessment method and device for isolated microgrids considering hybrid energy storage systems are proposed. The method fully considers the impact of the multi-topology structure model of the hybrid energy storage system on the reliability, and not only performs more detailed reliability modeling inside the energy storage system, but also expands the scope of application of the reliability assessment method.

[0006] According to a first aspect of the present disclosure, a method for evaluating the reliability of an island microgrid considering a hybrid energy storage system is provided, the method comprising: Step S1: Acquire the operating parameters of the isolated microgrid energy storage system, and establish a load output model and an energy storage charging and discharging model based on the operating parameters, taking into account the uncertainty of load output and the charging and discharging of the energy storage system and its capacity constraints; Step S2: acquiring state parameters of the hybrid energy storage system, analyzing the topological structure of the hybrid energy storage system based on the state parameters, establishing a multi-state model of the hybrid energy storage system, solving the state probability based on the Markov chain, and obtaining a reliability index of the hybrid energy storage system; Step S3: Conduct reliability assessment on the isolated island photovoltaic microgrid of the hybrid energy storage system, and calculate the normal working time and repair time of the internal equipment of the isolated island photovoltaic microgrid; Step S4: establishing a minimum load reduction strategy model based on load importance; Step S5: constructing a reliability assessment program for an isolated photovoltaic microgrid containing a hybrid energy storage system according to the multi-state model of the hybrid energy storage system, the energy storage charging and discharging model, the load output model, and the minimum load reduction strategy model; Step S6: According to the reliability assessment procedure for the isolated photovoltaic microgrid containing the hybrid energy storage system, the reliability index of the hybrid energy storage system is output and evaluated.

[0007] According to the above aspects and any possible implementation, an implementation is further provided, wherein the operating parameters of the isolated microgrid energy storage system include: the peak value of the annual load , Maximum charging power of energy storage , Maximum energy storage capacity , Maximum discharge power of energy storage , minimum energy storage capacity limit .

[0008] According to the above aspects and any possible implementation, an implementation is further provided, which establishes a load output model and an energy storage charging and discharging model based on the operating parameters taking into account the uncertainty of the load output and the charging and discharging of the energy storage system and its capacity constraints, including: Obtain the ratio coefficient of the load peak on a specified date to the load peak of that month, the ratio coefficient of the load peak of that month to the load peak of the whole year, the standard deviation of load fluctuation, and the expected value of load fluctuation; Based on the ratio coefficient of the load peak of the day to the load peak of the month, the ratio coefficient of the load peak of the month to the load peak of the whole year, and the peak value of the load of the whole year , establish the load time series model; Based on the standard deviation of the load fluctuation and the expected value of the load fluctuation, a load output volatility model is established ; Establishing a load output model according to the load time series model and the load output volatility model; Combined with the energy storage system charging and discharging and its capacity constraints, according to the maximum charging power of the energy storage , Maximum energy storage capacity , Maximum discharge power of energy storage , minimum energy storage capacity limit , establish an energy storage charging and discharging model.

[0009] According to the above aspects and any possible implementation, an implementation is further provided, wherein solving the state probability based on the Markov chain to obtain the reliability index of the hybrid energy storage system includes: Define the discrete state space and transition probability matrix of the hybrid energy storage system, and solve the probability of each state according to the Markov process approximation principle and the total probability condition; According to the state probabilities and transition probability matrix, solving the frequency of each state and the average duration of the state; According to the frequency and average duration of each state, the state of the hybrid energy storage system is classified into different operation modes, and the state probability, frequency and average duration of each operation mode are calculated; The state probability, frequency and average duration of each operating mode are taken as reliability indicators of the hybrid energy storage system.

[0010] According to the above aspects and any possible implementation, an implementation is further provided, wherein the reliability assessment of the isolated island photovoltaic microgrid of the hybrid energy storage system is performed, and the normal working time and repair time of the internal equipment of the isolated island photovoltaic microgrid are calculated, including: Calculate the average power outage duration, average power outage frequency and average power supply availability of the system to evaluate the system reliability; Calculate the power outage duration, power outage times, and power outage amount of user nodes to evaluate the reliability of user nodes; The normal working time and repair time of the internal equipment of the isolated island photovoltaic microgrid are calculated based on the failure rate and repair rate of the equipment.

[0011] According to the above aspects and any possible implementation, a further implementation is provided, which establishes a minimum load reduction strategy model based on the load importance, including: Obtain the operation data of the microgrid at time t, where the operation data includes load output, distributed power output, and maximum charging and discharging power of energy storage; Determine whether load reduction is necessary based on load output, distributed power output, and maximum charge and discharge power of energy storage, and reduce loads in order of their importance.

[0012] According to the above aspects and any possible implementation, an implementation is further provided, which constructs a reliability assessment program for an isolated photovoltaic microgrid containing a hybrid energy storage system based on the multi-state model of the hybrid energy storage system, the energy storage charging and discharging model, the load output model, and the minimum load reduction strategy model, including: Initialize data, set system simulation time and years, determine load importance ranking, and record the initial operating status of the equipment.

[0013] Randomly select faulty equipment and its repair time, calculate the DG output and load demand within a specific time period, and solve the energy storage system output and load reduction based on the minimum load reduction strategy.

[0014] Update load reduction information, accumulate power outage times and time, and update the working status and time matrix of each load node.

[0015] The simulation continues until the set simulation period is reached, and finally the reliability evaluation indicators are counted and output.

[0016] According to a second aspect of the present disclosure, a device for evaluating the reliability of an island microgrid considering a hybrid energy storage system is provided, the device comprising: The load output model and energy storage charge and discharge model unit are used to obtain the operating parameters of the isolated island microgrid energy storage system, and establish the load output model and energy storage charge and discharge model based on the operating parameters, taking into account the uncertainty of the load output and the charge and discharge of the energy storage system and its capacity constraints; A reliability index acquisition unit of the hybrid energy storage system is used to acquire state parameters of the hybrid energy storage system, analyze the topological structure of the hybrid energy storage system based on the state parameters, establish a multi-state model of the hybrid energy storage system, solve the state probability based on the Markov chain, and obtain the reliability index of the hybrid energy storage system; An isolated photovoltaic microgrid reliability assessment unit is used to conduct reliability assessment on the isolated photovoltaic microgrid of the hybrid energy storage system and calculate the normal working time and repair time of the internal equipment of the isolated photovoltaic microgrid; A minimum load reduction strategy model building unit is used to build a minimum load reduction strategy model based on the load importance; An island photovoltaic microgrid reliability assessment program construction unit is used to construct an island photovoltaic microgrid reliability assessment program containing a hybrid energy storage system according to the hybrid energy storage system multi-state model, energy storage charging and discharging model, load output model and minimum load reduction strategy model; The reliability index output unit of the hybrid energy storage system is used to output the reliability index of the hybrid energy storage system and perform an evaluation according to the reliability evaluation program of the isolated island photovoltaic microgrid containing the hybrid energy storage system.

[0017] According to a third aspect of the present disclosure, an electronic device is provided, comprising: a memory and a processor, wherein a computer program is stored in the memory, and when the processor executes the program, the method according to the first aspect of the present disclosure is implemented.

[0018] According to a fourth aspect of the present disclosure, a computer-readable storage medium is provided, on which a computer program is stored, and when the program is executed by a processor, the method according to the first aspect of the present disclosure is implemented.

[0019] Compared with the prior art, the present invention achieves the following beneficial effects: The present invention proposes a reliability assessment method for an island microgrid considering a hybrid energy storage system. According to the topological structure of the hybrid energy storage system, a reliability model of its N states is established in combination with Markov theory. The state probabilities of n operating modes are obtained after the states are summarized. On the basis of considering the multi-states of the hybrid energy storage system, with the goal of ensuring the overall load power supply, a minimum load reduction strategy is adopted to conduct reliability assessment on an island photovoltaic microgrid system containing wind, solar and storage, which is of great significance to improving the power supply reliability of the island microgrid.

[0020] It should be understood that the contents described in the summary of the invention are not intended to limit the key or important features of the embodiments of the present disclosure, nor are they intended to limit the scope of the present disclosure. Other features of the present disclosure will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The above and other features, advantages and aspects of the embodiments of the present disclosure will become more apparent with reference to the following detailed description in conjunction with the accompanying drawings. The accompanying drawings are used to better understand the present solution and do not constitute a limitation of the present disclosure. In the accompanying drawings, the same or similar reference numerals represent the same or similar elements, among which: Figure 1 A flow chart of a method for evaluating the reliability of an island microgrid considering a hybrid energy storage system according to an embodiment of the present disclosure is shown; Figure 2 A schematic diagram of a process for evaluating the reliability of a photovoltaic microgrid according to an embodiment of the present disclosure is shown; Figure 3A schematic diagram of an isolated island photovoltaic microgrid reliability test system according to an embodiment of the present disclosure is shown; Figure 4 A schematic diagram of an internal power supply and its output according to an embodiment of the present disclosure is shown; Figure 5 A schematic diagram of energy storage output and adjustable capacity according to an embodiment of the present disclosure is shown; Figure 6 A schematic diagram of a multi-state space transfer model of a hybrid energy storage system according to an embodiment of the present disclosure is shown; Figure 7 A schematic diagram of a Markov state transition density matrix according to an embodiment of the present disclosure is shown; Figure 8 A block diagram of an island microgrid reliability assessment device considering a hybrid energy storage system according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] In view of the problems in the existing reliability research of isolated photovoltaic microgrids that the topology of hybrid energy storage systems is not fully considered and a detailed multi-state reliability model is not established for them, this paper proposes a reliability assessment method for isolated microgrids considering hybrid energy storage systems. According to the topological structure of the hybrid energy storage system and combined with Markov theory, a reliability model of its N states is established, and the state probabilities of n operating modes are obtained after the states are summarized; then, on the basis of considering the multi-states of the hybrid energy storage system, with the goal of ensuring the overall load power supply, a minimum load reduction strategy is adopted to conduct a reliability assessment of the isolated photovoltaic microgrid system containing wind, light and storage, which is of great significance to improving the power supply reliability of the isolated microgrid.

[0024] In the following, in conjunction with the accompanying drawings, a reliability assessment method for an island microgrid considering a hybrid energy storage system provided by the present disclosure is described.

[0025] Embodiment 1 like Figure 1 As shown, the embodiment of the present disclosure provides a flowchart of a method for evaluating the reliability of an isolated microgrid considering a hybrid energy storage system, the method comprising: S1: Obtain the operating parameters of the island microgrid energy storage system, and establish a load output model and an energy storage charging and discharging model based on the operating parameters, taking into account the uncertainty of load output and the charging and discharging of the energy storage system and its capacity constraints.

[0026] The operating parameters of the isolated microgrid energy storage system include: the peak value of the annual load , Maximum charging power of energy storage , Maximum energy storage capacity , Maximum discharge power of energy storage , minimum energy storage capacity limit The state parameters include: the operating state of the internal structure of the hybrid energy storage system (1 indicates normal operation, 0 indicates failure), the number of transfer-in schemes K, the number of transfer-out schemes M, and a certain operating state S belonging to the kth operating mode. d .

[0027] In some embodiments, based on the operating parameters, the uncertainty of load output and the charging and discharging of the energy storage system and its capacity constraints are considered to establish a load output model and an energy storage charging and discharging model, including: Obtain the ratio coefficient of the load peak on the specified date to the load peak of the current month, obtain the ratio coefficient of the load peak of the current month to the load peak of the entire year, the standard deviation of load fluctuation, and the expected value of load fluctuation; Based on the ratio coefficient of the load peak of the day to the load peak of the month, the ratio coefficient of the load peak of the month to the load peak of the whole year, and the peak value of the load of the whole year , establish the load time series model; Based on the standard deviation of the load fluctuation and the expected value of the load fluctuation, a load output volatility model is established ; Establishing a load output model according to the load time series model and the load output volatility model; Combined with the energy storage system charging and discharging and its capacity constraints, according to the maximum charging power of the energy storage , Maximum energy storage capacity , Maximum discharge power of energy storage , minimum energy storage capacity limit , establish an energy storage charging and discharging model.

[0028] Specifically, S1-1: The output calculation formula considering load uncertainty is as follows: (1) Where: and They are respectively the time series model of load output and the volatility model of load output.

[0029] Load timing model It can be expressed as: (2) Where: The ratio of the peak load of the day to the peak load of the month; The ratio of the peak load of the current month to the peak load of the whole year; Load output fluctuation model It can be expressed by normal distribution, and its calculation formula is: (3) Where: is the standard deviation of load fluctuation; is the expected value of load fluctuation.

[0030] S1-2: Based on the charging and discharging of the energy storage system and its capacity constraints, establish its charging and discharging model.

[0031] The charging model calculation formula is: (4) Where: P ch (t) is the charging power of the energy storage at time t; E ESS (t) is the energy stored in the energy storage at time t, For the time scale, this patent recommends setting it to 1h.

[0032] The discharge mode calculation formula is: (5) Where: P disch (t) is the discharge power of the energy storage at time t.

[0033] S2: Obtain state parameters of the hybrid energy storage system, analyze the topological structure of the hybrid energy storage system based on the state parameters, establish a multi-state model of the hybrid energy storage system, solve the state probability based on the Markov chain, and obtain the reliability index of the hybrid energy storage system.

[0034] In some embodiments, the state probability is solved based on the Markov chain to obtain the reliability index of the hybrid energy storage system, including: defining the discrete state space and transition probability matrix of the hybrid energy storage system, and solving the probability of each state according to the Markov process approximation principle and the total probability condition; solving the frequency and average duration of each state according to the state probabilities and transition probability matrix; classifying the state of the hybrid energy storage system into different operating modes according to the frequency and average duration of each state, and calculating the state probability, frequency and average duration of each operating mode; using the state probability, frequency and average duration of each operating mode as the reliability index of the hybrid energy storage system. Specifically, S2-1: The discrete state space of the hybrid energy storage system S={S1, S2, S3, …, S32}, defines the transition probability matrix as: (6) Where: is the one-step transition probability, indicating that arrive The transition probability (i,j=1,2,3,…,32) According to the Markov process approximation principle and the total probability condition, the probability of each state can be solved (i=1, 2, …,32) (7) Where: P is the row vector composed of the probabilities of each state, that is, P = [P1, P2, …, P 32 ]; A is the transfer density matrix of the Markov model, and its calculation formula is: (8) Where: I is the unit matrix.

[0035] S2-2: According to the above step (2-1), the state probabilities Ai and transition probability matrices in the steady state are obtained , its frequency and the average duration of the state can be solved respectively: (9) Where: Status The steady-state frequency of Status The average duration of Indicated by the status Transition to this state The transition probability of Indicated by the status Transfer to another state The transition probability.

[0036] The states are summarized with the four operating modes in the hybrid energy storage system as the target, and the state probability, frequency and average duration of the new state are obtained, that is, the reliability indicators of the four maximum output powers of the hybrid energy storage system: (10) Where: For the The state probability of each operating mode; For the The frequency of each operating mode; For the The average duration of each operating mode.

[0037] S3: Conduct reliability assessment on the isolated island photovoltaic microgrid of the hybrid energy storage system and calculate the normal working time and repair time of the internal equipment of the isolated island photovoltaic microgrid.

[0038] In some embodiments, the reliability evaluation indicators (system and user indicators) and component life calculation method include the following parts: S3-1: System reliability index Average power outage duration of the system : (11) Where: is the total number of nodes; is the number of users of each node; For Node Annual downtime.

[0039] Average power outage frequency of the system : - (12) Where: For Node Annual failure frequency.

[0040] Average power supply availability : (13) Where: The number of hours of electricity required within a specified period of time.

[0041] S3-2: Node reliability index The power outage duration of node i It is the sum of the annual downtime of the node within the simulation period: (14) Where: For Node In the Annual downtime of the year.

[0042] node Number of power outages It is the sum of the annual failure frequency of the node within the simulation period: (15) Where: For Node In the Annual failure frequency for the year.

[0043] node Power shortage It is the sum of the product of the annual outage time and the load of the node within the simulation period: (16) Where: For Node In the Annual load size.

[0044] S3-3: Hypothetical Equipment The failure rate and repair rate are and , its normal working hours and repair time They are: (17) (18) Where: , are random numbers between (0, 1) that follow a uniform distribution.

[0045] S4: Based on the consideration of load importance, a minimum load reduction strategy model is established.

[0046] In some embodiments, the goal of the minimum load reduction strategy is to minimize the load reduction of the entire isolated island photovoltaic microgrid, that is, to ensure that as many loads as possible are powered for a long time. First, the operation data of the microgrid at time t is obtained, wherein the operation data includes load output, distributed power supply output and maximum charge and discharge power of energy storage; Determine whether load reduction is necessary based on load output, distributed power output, and maximum charge and discharge power of energy storage, and reduce loads in order of their importance.

[0047] Specifically, assume that the load importance is: , then the minimum load reduction strategy process of this patent is as follows: S4-1: Confirmed Monitor the status of each unit in the microgrid at all times and obtain the operating data of the microgrid: load output , DG output And the maximum charge and discharge power of energy storage ,calculate Is the value greater than If yes, the microgrid will abandon wind and solar power, otherwise it will proceed to the next step; (4-2) Calculation Is the value greater than If yes, the microgrid performs energy storage discharge operation, otherwise it proceeds to the next step; (4-3) Calculation Is the value greater than If yes, the microgrid will perform energy storage discharge operation, otherwise it will proceed to the next step; (4-4) Calculation Is the value greater than If yes, the microgrid performs electric vehicle + energy storage discharge operation, otherwise proceed to the next step; (4-5) Command (Discharge), after reducing the load according to its importance, the entire minimum load reduction process ends.

[0048] For the convenience of calculation, this patent will The output of each unit of the isolated island photovoltaic microgrid is abbreviated as DG output , load output (l=1, 2, 3, …, n), maximum charge and discharge power of hybrid energy storage system and maximum adjustable capacity , respectively abbreviated as , , , .

[0049] S5: Based on the multi-state model of the hybrid energy storage system, the energy storage charging and discharging model, the load output model and the minimum load reduction strategy model, a reliability assessment program for an isolated photovoltaic microgrid containing a hybrid energy storage system is constructed.

[0050] In some embodiments, Figure 2 As shown in the figure, the reliability assessment process of the hybrid energy storage system based on the sequential Monte Carlo method includes the following parts: S5-1: Data initialization. Set system simulation time , the simulation period is , reduce the load to empty , the remaining load of the isolated photovoltaic microgrid is all loads. Determine the importance ranking of each node load, and record the ranked nodes as , record the operating status of all N devices as normal operating status, that is, =[1,1,…,1].

[0051] S5-2: Extract the faulty equipment and its repair time in the isolated photovoltaic microgrid. According to formula (17), the equipment Normal working hours , recorded as =[ , , …, ] Select the minimum value The device is considered as a faulty device. Its repair time The calculation formula of is shown in formula (18).

[0052] S5-3: Calculation , ]DG output during the time period , Load demand . Based on the minimum load reduction strategy, solve the output of the hybrid energy storage system and load reduction.

[0053] S5-4: Update load reduction , the cumulative number of power outages and power outage duration that reduced load.

[0054] S5-5: Update the normal working time matrix of each load node ,in , move the faulty device in the ST matrix The state of is updated to state 0. At the same time, let .

[0055] S5-6: From the updated normal working time matrix Select the minimum time, , note that this may be the first device to fail, or it may be the first device to be repaired. At the same time, change the state of the ST matrix to Status and normal working hours matrix Update. Order .

[0056] S5-7: If , return to step S4-2, otherwise proceed to the next step.

[0057] S5-8: Count the total number of power outages and total power outage time of each load point, and calculate and output the reliability evaluation index of the isolated island photovoltaic microgrid according to equations (11)-(16).

[0058] S6: According to the reliability assessment procedure of the isolated photovoltaic microgrid containing the hybrid energy storage system, the reliability index of the hybrid energy storage system is output and evaluated.

[0059] According to the embodiments of the present disclosure, the following technical effects are achieved: (1) The impact of the multi-topology structure model of the hybrid energy storage system on reliability is fully considered. Not only is a more detailed reliability modeling of the internal energy storage system performed, but the scope of application of the reliability assessment method is also expanded.

[0060] (2) The calculation process in the reliability assessment process is simplified, making the use of reliability assessment more flexible, which is of great significance for the reliability assessment of isolated island photovoltaic microgrids.

[0061] Embodiment 2 The following is a practical example of the method of the present invention. Figure 3 The reliability test system of the isolated photovoltaic microgrid shown in the figure is used as an example for simulation calculation.

[0062] Disconnect S1 to form an island-type microgrid with four internal power sources: wind, solar, storage and diesel. The island photovoltaic microgrid contains a total of five loads (L1~L5), and their importance is ranked as follows: , the photovoltaic and wind power capacity are both 1000kW, the diesel generator capacity is 350kW, the hybrid energy storage system capacity is 400kW·h, and the maximum output power is 300kW. In order to delay the battery life loss, the power distribution parameters are shown in Table 1: Table 1

[0063] The simulation period is set to 8000 years. The microgrid user load curve is predicted based on the weather and user behavior on a typical day, and the output curve of each DG is obtained according to the output model solved in step (1). Figure 4 As shown; Based on the internal power supply and load output, the output curve and adjustable capacity of the hybrid energy storage system can be determined, as shown in Figure 5 As shown in Table 2, the failure rate, repair rate and repair time of isolated island photovoltaic microgrid equipment are shown in Table 2: Table 2

[0064] In order to fully analyze the reliability of the above example system, this patent establishes a multi-state Markov model of the hybrid energy storage system, which is divided into five sub-modules: lithium battery, DC / DC converter, supercapacitor, emergency power supply circuit and device-level module. The failure rates are set as , the repair rates are set to ,The reliability parameters of each part are shown in Table 2.

[0065] Combined with the hybrid energy storage multi-state space transfer model, such as Figure 6 As shown, establish its Markov state transition density matrix, see Figure 7 According to step S2, the state probability, frequency and average duration of the hybrid energy storage system can be obtained, see Table 3: Table 3

[0066] Based on the above 400kW·h hybrid energy storage system reliability model, the minimum load reduction strategy is adopted according to step S4. Figure 3 The isolated photovoltaic microgrid reliability test system shown in FIG. 1 starts the evaluation process according to step S5, and calculates the reliability index of each load node and the system according to step S3, as shown in Table 4 and Table 5: Table 4

[0067] Table 5

[0068] From Table 4 and Table 5, we can see that: (1) The number of power outages. The number of power outages at the five load points was within 200 to 320. , priority guarantee ~ Therefore, the number of load outages increases as the importance of the load decreases, but the overall difference is small; (2) Duration of power shortage and amount of power shortage. The duration of power shortage is similar to the number of power outages, but since the number of power outages and duration of power shortages between load points are relatively small, the amount of power shortage is mainly related to the load size of each load point.

[0069] According to the embodiments of the present disclosure, the following technical effects are achieved: (1) The impact of the multi-topology structure model of the hybrid energy storage system on reliability is fully considered. Not only is a more detailed reliability modeling of the internal energy storage system performed, but the scope of application of the reliability assessment method is also expanded.

[0070] (2) The calculation process in the reliability assessment process is simplified, making the use of reliability assessment more flexible, which is of great significance for the reliability assessment of isolated island photovoltaic microgrids.

[0071] It should be noted that, for the aforementioned method embodiments, for the sake of simplicity of description, they are all expressed as a series of action combinations, but those skilled in the art should be aware that the present disclosure is not limited by the described order of actions, because according to the present disclosure, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all optional embodiments, and the actions and modules involved are not necessarily required by the present disclosure.

[0072] The above is an introduction to the method embodiment. The following is a further explanation of the scheme disclosed in the present invention through an apparatus embodiment.

[0073] Figure 8 FIG. 1 shows a block diagram of an isolated microgrid reliability assessment device considering a hybrid energy storage system according to an embodiment of the present disclosure. Figure 8 As shown, the device comprises: The load output model and energy storage charge and discharge model unit 810 is used to obtain the operating parameters of the island microgrid energy storage system, and establish the load output model and energy storage charge and discharge model based on the operating parameters, taking into account the uncertainty of the load output and the charge and discharge of the energy storage system and its capacity constraints; A reliability index acquisition unit 820 of the hybrid energy storage system is used to acquire state parameters of the hybrid energy storage system, analyze the topological structure of the hybrid energy storage system based on the state parameters, establish a multi-state model of the hybrid energy storage system, solve the state probability based on the Markov chain, and obtain the reliability index of the hybrid energy storage system; An isolated photovoltaic microgrid reliability assessment unit 830 is used to perform reliability assessment on the isolated photovoltaic microgrid of the hybrid energy storage system and calculate the normal working time and repair time of the internal equipment of the isolated photovoltaic microgrid; A minimum load reduction strategy model building unit 840 is used to build a minimum load reduction strategy model based on the load importance; An island photovoltaic microgrid reliability assessment program construction unit 850 is used to construct an island photovoltaic microgrid reliability assessment program containing a hybrid energy storage system according to the hybrid energy storage system multi-state model, energy storage charging and discharging model, load output model and minimum load reduction strategy model; The reliability index output unit 860 of the hybrid energy storage system is used to output the reliability index of the hybrid energy storage system and perform an evaluation according to the reliability evaluation program 860 of the isolated photovoltaic microgrid containing the hybrid energy storage system.

[0074] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working process of the described module can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0075] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps recorded in this disclosure can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of this disclosure can be achieved, and this document is not limited here.

[0076] The above specific implementations do not constitute a limitation on the protection scope of the present disclosure. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. A reliability assessment method for an island microgrid considering a hybrid energy storage system, characterized in that: include: Step S1: Acquire the operating parameters of the isolated microgrid energy storage system, and establish a load output model and an energy storage charging and discharging model based on the operating parameters, taking into account the uncertainty of load output and the charging and discharging of the energy storage system and its capacity constraints; Step S2: acquiring state parameters of the hybrid energy storage system, analyzing the topological structure of the hybrid energy storage system based on the state parameters, establishing a multi-state model of the hybrid energy storage system, solving the state probability based on the Markov chain, and obtaining a reliability index of the hybrid energy storage system; Step S3: Conduct reliability assessment on the isolated island photovoltaic microgrid of the hybrid energy storage system, and calculate the normal working time and repair time of the internal equipment of the isolated island photovoltaic microgrid; Step S4: establishing a minimum load reduction strategy model based on load importance; Step S5: constructing a reliability assessment program for an isolated photovoltaic microgrid containing a hybrid energy storage system according to the multi-state model of the hybrid energy storage system, the energy storage charging and discharging model, the load output model, and the minimum load reduction strategy model; Step S6: According to the reliability assessment procedure for the isolated photovoltaic microgrid containing the hybrid energy storage system, the reliability index of the hybrid energy storage system is output and evaluated.

2. The method according to claim 1, characterized in that The operating parameters of the island microgrid energy storage system include: the peak value of the annual load , Maximum charging power of energy storage , Maximum energy storage capacity , Maximum discharge power of energy storage , minimum energy storage capacity limit .

3. The method according to claim 2, characterized in that Based on the operating parameters, the uncertainty of load output and the charging and discharging of the energy storage system and its capacity constraints are considered to establish a load output model and an energy storage charging and discharging model, including: Obtain the ratio coefficient of the load peak on a specified date to the load peak of that month, the ratio coefficient of the load peak of that month to the load peak of the whole year, the standard deviation of load fluctuation, and the expected value of load fluctuation; A load time series model is established based on the ratio coefficient of the load peak of the day to the load peak of the month, the ratio coefficient of the load peak of the month to the load peak of the whole year, and the peak value of the load of the whole year; Based on the standard deviation of the load fluctuation and the expected value of the load fluctuation, a load output volatility model is established; Establishing a load output model according to the load time series model and the load output volatility model; In combination with the charging and discharging of the energy storage system and its capacity constraints, an energy storage charging and discharging model is established according to the maximum charging power of energy storage, the maximum capacity of energy storage, the maximum discharge power of energy storage, and the minimum capacity limit of energy storage.

4. The method according to claim 1, characterized in that: The state probability is solved based on the Markov chain to obtain the reliability index of the hybrid energy storage system, including: Define the discrete state space and transition probability matrix of the hybrid energy storage system, and solve the probability of each state according to the Markov process approximation principle and the total probability condition; According to the state probabilities and transition probability matrix, solving the frequency of each state and the average duration of the state; According to the frequency and average duration of each state, the state of the hybrid energy storage system is classified into different operation modes, and the state probability, frequency and average duration of each operation mode are calculated; The state probability, frequency and average duration of each operating mode are taken as reliability indicators of the hybrid energy storage system.

5. The method according to claim 1, characterized in that The reliability assessment of the isolated photovoltaic microgrid of the hybrid energy storage system is performed to calculate the normal working time and repair time of the internal equipment of the isolated photovoltaic microgrid, including: Calculate the average power outage duration, average power outage frequency and average power supply availability of the system to evaluate the system reliability; Calculate the power outage duration, power outage times, and power outage amount of user nodes to evaluate the reliability of user nodes; The normal working time and repair time of the internal equipment of the isolated island photovoltaic microgrid are calculated based on the failure rate and repair rate of the equipment.

6. The method according to claim 1, characterized in that Based on the load importance, a minimum load reduction strategy model is established, including: Obtain the operation data of the microgrid at time t, where the operation data includes load output, distributed power output, and maximum charging and discharging power of energy storage; Determine whether load reduction is necessary based on load output, distributed power output, and maximum charge and discharge power of energy storage, and reduce loads in order of their importance.

7. The method according to claim 1, characterized in that According to the multi-state model of the hybrid energy storage system, the energy storage charging and discharging model, the load output model and the minimum load reduction strategy model, a reliability assessment procedure for an isolated photovoltaic microgrid containing a hybrid energy storage system is constructed, including: Data initialization, setting system simulation time and years, determining load importance ranking, and recording the initial operating status of the equipment; Randomly select faulty equipment and its repair time, calculate the DG output and load demand within a specific time period, and solve the energy storage system output and load reduction based on the minimum load reduction strategy; Update load reduction information, accumulate power outage times and time, and update the working status and time matrix of each load node; The simulation continues until the set simulation period is reached, and finally the reliability evaluation indicators are counted and output.

8. An island microgrid reliability assessment device considering a hybrid energy storage system, characterized in that: include: The load output model and energy storage charge and discharge model unit are used to obtain the operating parameters of the isolated island microgrid energy storage system, and establish the load output model and energy storage charge and discharge model based on the operating parameters, taking into account the uncertainty of the load output and the charge and discharge of the energy storage system and its capacity constraints; A reliability index acquisition unit of the hybrid energy storage system is used to acquire state parameters of the hybrid energy storage system, analyze the topological structure of the hybrid energy storage system based on the state parameters, establish a multi-state model of the hybrid energy storage system, solve the state probability based on the Markov chain, and obtain the reliability index of the hybrid energy storage system; An isolated photovoltaic microgrid reliability assessment unit is used to conduct reliability assessment on the isolated photovoltaic microgrid of the hybrid energy storage system and calculate the normal working time and repair time of the internal equipment of the isolated photovoltaic microgrid; A minimum load reduction strategy model building unit is used to build a minimum load reduction strategy model based on the load importance; An island photovoltaic microgrid reliability assessment program construction unit is used to construct an island photovoltaic microgrid reliability assessment program containing a hybrid energy storage system according to the hybrid energy storage system multi-state model, energy storage charging and discharging model, load output model and minimum load reduction strategy model; The reliability index output unit of the hybrid energy storage system is used to output the reliability index of the hybrid energy storage system and perform an evaluation according to the reliability evaluation program of the isolated island photovoltaic microgrid containing the hybrid energy storage system.

9. An electronic device, characterized in that: It includes a processor, and a memory and a network interface connected to the processor; the network interface is connected to a non-volatile memory in a server; when the processor is running, it calls a computer program from the non-volatile memory through the network interface, and runs the computer program through the memory to execute the method described in any one of claims 1 to 7.

10. A storage medium, characterized in that: Computer program instructions are stored on the computer storage medium, and when the computer program instructions are executed by the processor, the method according to any one of claims 1 to 7 is implemented.

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