Photovoltaic accessible capacity evaluation method and device considering network-forming type energy storage

Abstract

The invention provides a photovoltaic accessible capacity evaluation method and device considering network construction type energy storage, and relates to the technical field of power system analysis and new energy grid connection. The method comprises the following steps: constructing a power grid model, and constructing a system impedance matrix based on a network topology structure of the power grid model; a Thevenin equivalent model of the network construction type energy storage device is established, after the Thevenin equivalent model is connected to a power grid node, the system impedance matrix is corrected, a corrected equivalent system impedance matrix is obtained, and the power grid node comprises at least one photovoltaic load access node; when a three-phase short-circuit fault occurs in a target node, the short-circuit ratio and the photovoltaic permeability of the target node are calculated based on the corrected equivalent system impedance matrix, and the target node is any node in the power grid nodes; and determining the increased maximum accessible capacity of the target node according to the short-circuit ratio and the photovoltaic permeability of the target node. The transmission efficiency and reliability of the power grid can be improved.

Description

Technical Field

[0001] This application relates to the fields of power system analysis and new energy grid connection technology, and in particular to a method and device for assessing the grid-connectable capacity of photovoltaic power that takes into account grid-connected energy storage. Background Technology

[0002] As the penetration rate of distributed renewable energy sources such as photovoltaic power generation in the power system continues to increase, the system's short-circuit capacity is gradually decreasing, and the problem of insufficient short-circuit ratio is becoming increasingly prominent. The short-circuit ratio, as an important indicator of grid strength, directly affects the stability and security of photovoltaic power plant grid connection. When the short-circuit ratio is too low, photovoltaic inverters are prone to control instability or even shutdown, thus limiting the scale of photovoltaic grid connection. Summary of the Invention

[0003] This application provides a method and apparatus for assessing the grid-connectable capacity of photovoltaics that takes into account grid-connected energy storage, in order to solve the problem that existing photovoltaic grid-connectable capacity assessment methods are mostly based on complex electromechanical transient models and do not fully take into account the short-circuit current support effect of grid-connected energy storage.

[0004] In a first aspect, this application provides a method for assessing the grid-connectable capacity of photovoltaic systems that takes into account grid-connected energy storage, including: Construct a power grid model, and based on the network topology of the power grid model, construct the system impedance matrix; A Thevenin equivalent model of a grid-connected energy storage device is established, and the system impedance matrix is ​​corrected after the Thevenin equivalent model is connected to a grid node to obtain the corrected equivalent system impedance matrix. The grid node includes at least one photovoltaic load connection node. When a three-phase short-circuit fault occurs at the target node, the short-circuit ratio and photovoltaic penetration rate of the target node are calculated based on the corrected equivalent system impedance matrix. The target node is any node in the power grid. Based on the short-circuit ratio and photovoltaic penetration rate of the target node, the maximum increase in the connectable capacity of the target node is determined.

[0005] Secondly, this application provides a photovoltaic grid-connectable capacity assessment device that takes into account grid-connected energy storage, comprising: A construction module is used to build a power grid model and, based on the network topology of the power grid model, construct a system impedance matrix; The correction module is used to establish the Thevenin equivalent model of the grid-type energy storage device, and after the Thevenin equivalent model is connected to the grid node, the system impedance matrix is ​​corrected to obtain the corrected equivalent system impedance matrix. The grid node includes at least one photovoltaic load access node. The calculation module is used to calculate the short-circuit ratio and photovoltaic penetration rate of the target node based on the corrected equivalent system impedance matrix when a three-phase short-circuit fault occurs at the target node. The target node is any node in the power grid. The determination module is used to determine the maximum increase in gridable capacity of the target node based on the short-circuit ratio and photovoltaic penetration rate of the target node.

[0006] This application provides a method and apparatus for assessing the grid-connectable capacity of photovoltaic (PV) energy storage. The method involves constructing a grid model and, based on the network topology, building a system impedance matrix. A Thevenin equivalent model of the grid-connected energy storage device is established, and after connecting the Thevenin equivalent model to grid nodes, the system impedance matrix is ​​corrected to obtain a corrected equivalent system impedance matrix. Each grid node includes at least one PV load connection node. When a three-phase short-circuit fault occurs at a target node, the short-circuit ratio and PV penetration rate of the target node are calculated based on the corrected equivalent system impedance matrix. The target node can be any node in the grid. Based on the short-circuit ratio and PV penetration rate of the target node, the maximum increase in grid-connectable capacity of the target node is determined. This application, by constructing a power grid model and system impedance matrix and analyzing the impact of grid-connected energy storage, provides a clear understanding of the electrical characteristics of different nodes in the power grid. This helps planners optimize the power grid topology based on evaluation results during power grid construction, improving transmission efficiency and reliability. Furthermore, when a three-phase short-circuit fault occurs at a target node, calculating the short-circuit ratio based on the corrected equivalent system impedance matrix more accurately reflects the dynamic characteristics of the power grid under fault conditions. This helps operators promptly identify weak points in the power grid and take corresponding measures to strengthen grid stability, such as adjusting generator output and configuring reactive power compensation devices, preventing grid collapse during faults. Simultaneously, by establishing a Thevenin equivalent model of the grid-connected energy storage device and correcting the system impedance matrix after connecting it to a power grid node, the impact of grid-connected energy storage on the power grid can be intuitively analyzed. This contributes to a deeper understanding of the operating characteristics and effects of grid-connected energy storage devices in the power grid, providing a theoretical basis for further research and application of grid-connected energy storage technology. Attached Figure Description

[0007] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0008] Figure 1 This is a flowchart illustrating the photovoltaic grid-connectable capacity assessment method provided in the embodiments of this application, which takes into account grid-connected energy storage. Figure 2 This is a schematic diagram of the network topology of the power grid model provided in the embodiments of this application; Figure 3 This is a control block diagram of the grid-type energy storage provided in the embodiments of this application; Figure 4 This is a schematic diagram of the power grid model structure considering equivalent grid-type energy storage access provided in the embodiments of this application; Figure 5 This is a schematic diagram of the photovoltaic grid-connectable capacity assessment device provided in the embodiments of this application, which takes into account grid-connected energy storage. Detailed Implementation

[0009] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0010] To make the objectives, technical solutions, and advantages of this application clearer, the following description will be provided in conjunction with the accompanying drawings and specific embodiments.

[0011] Due to the high proportion of photovoltaic (PV) grid integration, the power system faces challenges such as decreased short-circuit current and limited renewable energy capacity. Accurate assessment of PV capacity is difficult when grid-connected energy storage is integrated. Grid-connected energy storage, with its voltage source characteristics and current limiting capabilities, can provide short-circuit current support during grid faults or weak grid scenarios, and is considered a key means to improve the system's short-circuit ratio and enhance renewable energy integration capabilities. However, existing PV capacity assessment methods are mostly based on the electromechanical transient model of grid-connected energy storage, failing to fully consider the supporting role of energy storage in short-circuit current. This application discloses a method for assessing PV capacity that considers grid-connected energy storage. It establishes a grid model including nodes, lines, loads, infinite power sources, and distributed PV, and constructs a system impedance matrix. Based on this, the grid-connected energy storage device is equivalent to a Thevenin equivalent model of a voltage source connected in series with a series impedance. A virtual impedance control strategy is introduced to correct the system impedance matrix, resulting in an equivalent system impedance matrix that takes into account the impact of energy storage. Then, under grid fault scenarios, the short-circuit current of the fault node is calculated based on the corrected equivalent system impedance matrix. Simultaneously, the contribution of multiple energy storage devices connected to the grid to the short-circuit current is considered, yielding the short-circuit ratio taking into account grid-connected energy storage. Finally, dual threshold constraints of short-circuit ratio and photovoltaic penetration rate are set. By gradually increasing the installed capacity of individual or multiple photovoltaic systems, the maximum accessible capacity for a single power station or the entire system is obtained. Based on the above steps, this application can take into account the equivalent effect of grid-connected energy storage, balance the constraints of short-circuit ratio and photovoltaic penetration rate, and solve the problems of limited photovoltaic access and uncertainty in the maximum accessible capacity considering grid-connected energy storage. It can provide effective technical support for the planning and operation of new energy grid connection while ensuring system safety and stability.

[0012] Figure 1 The implementation flowchart of the photovoltaic grid-connectable capacity assessment method considering grid-connected energy storage provided in the embodiments of this application is described in detail below: In step 101, a power grid model is constructed, and a system impedance matrix is ​​constructed based on the network topology of the power grid model.

[0013] In this embodiment, a power grid model is established, including nodes (Bus), lines (Lines), loads (Loads), power sources, and distributed photovoltaic (PV) generators (Sgens). A complete network topology is constructed through the connection relationships of these modules, as detailed below. Figure 2 As shown. Then, based on the network topology of the power grid model, the system impedance matrix is ​​constructed. .

[0014] Specifically, based on the network topology of the power grid model, the admittance matrix of the power grid model is calculated. ,Right now:

[0015] Then the system impedance matrix corresponding to this power grid model Simultaneously, the active power of each distributed power station is acquired. ,load Location and voltage level of photovoltaic load connection nodes As a subsequent short-circuit ratio With photovoltaic penetration rate Input for the calculation.

[0016] Reference Figure 3 As shown, this application embodiment also requires obtaining the rated capacity of the grid-type energy storage device. and its control parameters, including virtual impedance. Virtual potential Grid-type energy storage output voltage and current limit value .

[0017] This application's embodiments, by constructing a power grid model and system impedance matrix, and analyzing the impact of grid-connected energy storage, provide a clear understanding of the electrical characteristics of different nodes in the power grid. This helps planners optimize the power grid topology based on evaluation results during power grid construction, such as rationally selecting the routing and connection methods of transmission lines, thereby improving the power grid's transmission efficiency and reliability.

[0018] In step 102, a Thevenin equivalent model of the grid-type energy storage device is established. After the Thevenin equivalent model is connected to the grid node, the system impedance matrix is ​​corrected to obtain the corrected equivalent system impedance matrix. The grid node includes at least one photovoltaic load connection node.

[0019] In this embodiment, an equivalent Thevenin model of a grid-connected energy storage device is established and connected to a grid node. After connection, the system impedance matrix constructed in step 101 is corrected to obtain a corrected equivalent system impedance matrix.

[0020] This application's embodiments establish a Thevenin equivalent model of a grid-based energy storage device and, after connecting it to a grid node, correct the system impedance matrix, allowing for a direct analysis of the impact of grid-based energy storage on the power grid. This contributes to a deeper understanding of the operating characteristics and effects of grid-based energy storage devices in the power grid, providing a theoretical basis for further research and application of grid-based energy storage technology.

[0021] In one possible implementation, establishing a Thevenin equivalent model of a grid-type energy storage device can include: Under the condition of open circuit at the grid connection point of a grid-connected energy storage device, Kirchhoff's current law and voltage law are used to solve for the port open-circuit voltage, and the port open-circuit voltage is used as an equivalent voltage source. With the voltage source set to zero, calculate the equivalent impedance of the port and treat the equivalent impedance of the port as the series impedance; Thevenin equivalent model of a grid-type energy storage device is established using an equivalent voltage source and series impedance.

[0022] Optionally, the Thevenin equivalent model of the grid-type energy storage device in this application embodiment includes an equivalent voltage source and a series impedance. The specific construction process is as follows: Under the condition of open circuit at the grid connection point, the open circuit voltage at the port is solved using Kirchhoff's current law and voltage law or the nodal voltage method, and is used as the equivalent voltage source; under the condition of zero voltage source, the equivalent impedance at the port is calculated, which is used as the series impedance in the Thevenin equivalent model.

[0023] For example, refer to Figure 4 As shown, the grid-type energy storage device is equivalent to an equivalent voltage source using the Thevenin equivalent. With series impedance A series Thevenin equivalent model is constructed and connected to a power grid node. Among these, Figure 4 In , , , These are the mutual impedances between node 1 and node 2, and between node 2 and node 2, respectively. Mutual impedance between nodes, node 1 and node The mutual impedance between nodes and the connection impedance between node 1 and the power grid side.

[0024] In one possible implementation, after the Thevenin equivalent model is connected to the grid node, the system impedance matrix is ​​corrected to obtain the corrected equivalent system impedance matrix, which may include: Based on the principles of impedance matrix formation and correction, the system impedance matrix is ​​corrected to obtain the equivalent system impedance matrix; The virtual impedance is introduced into the equivalent system impedance matrix to correct the equivalent system impedance matrix, resulting in the corrected equivalent system impedance matrix.

[0025] Optionally, in the embodiments of this application, the impedance matrix when calculating the short-circuit ratio of grid-type energy storage considers the equivalent impedance of the equivalent grid-type energy storage, that is, the modified equivalent system impedance matrix.

[0026] The Thevenin equivalent model of a grid-connected energy storage device consists of an equivalent voltage source and a series impedance. This model is used to connect the grid-connected energy storage device to the corresponding grid node. Then, based on the principles of impedance matrix formation and correction, the system impedance matrix is... After correction, the equivalent system impedance matrix is ​​obtained. The calculation formula is:

[0027] in, The equivalent system impedance matrix, Here is the system impedance matrix. The system impedance matrix is ​​the first row vectors The system impedance matrix is ​​the first Transpose of a row vector For power grid nodes Self-impedance.

[0028] Then, when the current limit is reached, the grid-type energy storage device will limit the output current by adjusting the virtual impedance, which is:

[0029] in, For virtual impedance, For virtual potential, For grid-type energy storage output voltage, This is the current limiting value.

[0030] At this point, the virtual impedance will be... Introducing this into the equivalent system impedance matrix, we further modify the equivalent system impedance matrix to obtain the modified equivalent system impedance matrix, i.e.:

[0031] in, This is the corrected equivalent system impedance matrix.

[0032] From the formula for calculating the corrected equivalent system impedance matrix, we can see that the corrected equivalent system impedance matrix... The Okay, number The elements of the column are:

[0033] in, For the first Okay, number The corrected equivalent system impedance matrix of the column. Before the equivalent grid-type energy storage is connected, the first impedance matrix of the system is... Okay, number Column elements, The impedance matrix of the system before grid connection of energy storage is the first Okay, number Column elements, The impedance matrix of the system before grid connection of energy storage is the first Okay, number The elements of the column.

[0034] The embodiments of this application can reflect the impact of energy storage on short-circuit current and system impedance at the impedance matrix level through Thevenin equivalent and virtual impedance correction, making the modeling process simpler and the calculation efficiency higher.

[0035] In step 103, when a three-phase short-circuit fault occurs at the target node, the short-circuit ratio and photovoltaic penetration rate of the target node are calculated based on the corrected equivalent system impedance matrix. The target node is any node in the power grid.

[0036] In this embodiment of the application, when a three-phase short-circuit fault occurs at the target node, the short-circuit ratio and photovoltaic penetration rate of the fault node (i.e., the target node) are calculated using the corrected equivalent system impedance matrix obtained in step 102.

[0037] The short-circuit ratio is a crucial indicator for measuring the strength and stability of a power grid. In this application, when a three-phase short-circuit fault occurs at the target node, the short-circuit ratio is calculated based on the corrected equivalent system impedance matrix, which more accurately reflects the dynamic characteristics of the power grid under fault conditions. This helps operators promptly identify weak points in the power grid and take corresponding measures to strengthen its stability, such as adjusting generator output and configuring reactive power compensation devices, to prevent grid collapse during faults.

[0038] Furthermore, with the large-scale integration of distributed energy sources such as photovoltaics, the photovoltaic penetration rate has an increasingly significant impact on the safe and stable operation of the power grid. This application's embodiments, by calculating the photovoltaic penetration rate of target nodes and comprehensively considering its relationship with the short-circuit ratio, can reasonably control the proportion of photovoltaics integrated into the power grid. This avoids problems such as voltage fluctuations and frequency instability caused by excessively high photovoltaic penetration rates, ensuring the safe and stable operation of the power grid under various energy source integration scenarios.

[0039] In one possible implementation, when a three-phase short-circuit fault occurs at the target node, the short-circuit ratio and photovoltaic penetration rate of the target node are calculated based on the corrected equivalent system impedance matrix, which may include: Using the system short-circuit current, the first short-circuit current, and the second short-circuit current, the target short-circuit current when a three-phase short-circuit fault occurs at the target node is calculated. The first short-circuit current is the short-circuit current provided by the grid-connected energy storage device at the target node, and the second short-circuit current is the sum of the short-circuit currents provided by the grid-connected energy storage devices at all nodes in the power grid except the target node to the target node. Calculate the short-circuit ratio of the target node based on the target short-circuit current; The photovoltaic penetration rate of the target node is calculated using the photovoltaic active power and load active power of the target node.

[0040] Optionally, in embodiments of this application, when a three-phase short-circuit fault occurs at the target node, the modified equivalent system impedance matrix is ​​used. Calculate the target node The target short-circuit current provided by the design and equivalent grid-type energy storage Among them, the target short-circuit current It includes the following three components: (1) Calculate the system short-circuit current provided by the system. .

[0041] (2) Calculate the target node The first short-circuit current provided by the equivalent grid-type energy storage device is connected at the location. Utilizing the target node The equivalent voltage source of the Thevenin equivalent model of the grid-connected energy storage device. and series impedance Calculate the first short-circuit current. Specifically: At the target node When a three-phase short-circuit fault occurs at the target node, The theoretical value of the fault current provided by the grid-connected energy storage device can be expressed as: However, due to the current limiting characteristics of the energy storage converter, the actual injected short-circuit current cannot exceed the set maximum limit value. Therefore, the target node The first short-circuit current provided by the equivalent grid-type energy storage at the connection point for:

[0042] in, This is the first short-circuit current. The first part is the equivalent system impedance matrix after correction for equivalent grid-type energy storage access. Line number The elements of the column, i.e., the target node Self-impedance; For the target node Current limit value for the equivalent grid-type energy storage connected to the site.

[0043] (3) In the embodiments of this application, when calculating the target short-circuit current, the contribution of the grid-type energy storage device connected to other nodes (i.e., the first node) to the target short-circuit current of the target node is considered. That is, the contribution of the equivalent grid-type energy storage device connected to each first node to the target node is calculated. The short-circuit current contribution value, i.e., the second short-circuit current. ,Right now: For each first node, the short-circuit current provided by the grid-type energy storage device connected at the first node to the target node is calculated using the equivalent voltage source and series impedance of the Thevenin equivalent model of the grid-type energy storage device connected at the first node. The first node is any node in the power grid other than the target node. The sum of the short-circuit currents provided to the target node by all grid-type energy storage devices connected at the first node is taken as the second short-circuit current.

[0044] For a grid-type energy storage device with multiple nodes connected in the system, each node is equivalent to a voltage source. Series equivalent impedance The corresponding node for grid connection is The fault occurred at the target node. At that time, the equivalent grid-type energy storage connected to each node is related to the target node. The short-circuit current contribution can be calculated by superimposing the corrected equivalent system impedance matrix. The short-circuit current injected by each equivalent grid-connected energy storage unit into the connected node is:

[0045] in, For each equivalent grid-connected energy storage unit, the connected nodes Injected short-circuit current, The first part is the equivalent system impedance matrix after correction for equivalent grid-type energy storage access. Line number The elements of a column, i.e., nodes Self-impedance; For nodes Current limit value for the equivalent grid-type energy storage connected to the site.

[0046] The equivalent grid-type energy storage connected to other nodes is calculated using the corrected equivalent system impedance matrix, with nodes as the basis. For example, it targets the node. The formula for calculating the contribution of short-circuit current is:

[0047] in, For nodes For the target node The contribution of short-circuit current, The first part is the modified equivalent system impedance matrix after introducing a virtual impedance control strategy through equivalent grid-type energy storage. Line number Column elements, The first part is the modified equivalent system impedance matrix after introducing a virtual impedance control strategy through equivalent grid-type energy storage. Line number The elements of the column.

[0048] Therefore, the sum of the short-circuit currents provided to the target node by the equivalent grid-type energy storage connected to other nodes (i.e., all first nodes) is the second short-circuit current. for:

[0049] in, This is the second short-circuit current. This represents the total number of the first node.

[0050] Therefore, the target node Target short-circuit current when a three-phase short-circuit fault occurs for:

[0051] The embodiments of this application can take into account the contribution of each energy storage device to the short-circuit current of the fault node when multiple energy storage devices are connected to the grid, thereby improving the accuracy and applicability of the short-circuit ratio assessment.

[0052] After determining the target short-circuit current, the short-circuit ratio of the target node is calculated by combining the node voltage amplitude, the target short-circuit current, and the photovoltaic injected power. Calculate the product of the target short-circuit current and the rated voltage of the target node when a three-phase short-circuit fault occurs at the target node, and use this product as the first power. Calculate the equivalent injected power of all distributed photovoltaic power stations at the first node to the target node, and use the sum of the equivalent injected power and the photovoltaic active power of the target node as the second power. The ratio of the first power to the second power is used as the short-circuit ratio of the target node.

[0053] Optionally, the formula for calculating the short-circuit ratio of the target node is:

[0054] in, For the target node The short-circuit ratio, For the target node Rated voltage, For the target node The active power generated by the new energy power station For the target node Self-impedance, For the target node Connection nodes with other new energy power stations Mutual impedance between them The second power refers to the power output of all distributed photovoltaic power stations (i.e., other renewable energy power stations) at the first node relative to the target node. Equivalent injection power and target node The sum of the photovoltaic active power of a distributed photovoltaic power station (i.e., other new energy power stations).

[0055] Then, obtain the target node. Photovoltaic active power in the area (i.e., target node) (Active power of distributed photovoltaic power stations at the location) and load active power (i.e., target node) (Active power of the load at the distributed photovoltaic power station) The formula for calculating the photovoltaic penetration rate of the target node is:

[0056] in, For the target node Photovoltaic penetration rate.

[0057] In step 104, the maximum increase in grid capacity of the target node is determined based on the short-circuit ratio and photovoltaic penetration rate of the target node.

[0058] In this embodiment, the short-circuit ratio and photovoltaic penetration rate of the target node calculated in step 103 are used to determine the maximum available capacity of the target node. This embodiment can reasonably determine the maximum available capacity of the photovoltaic power station and the system as a whole under the premise of ensuring the safe and stable operation of the system, and effectively alleviate the problem of uncertain photovoltaic access capacity.

[0059] In one possible implementation, determining the maximum increase in grid-connectable capacity for the target node based on the short-circuit ratio and photovoltaic penetration rate of the target node may include: Determine whether the short-circuit ratio of the target node meets the short-circuit ratio threshold, and whether the photovoltaic penetration rate of the target node meets the penetration rate threshold; If the short-circuit ratio of the target node meets the short-circuit ratio threshold and the photovoltaic penetration rate of the target node meets the penetration rate threshold, then the installed capacity of the photovoltaic power station of the target node is uniformly increased by a preset number. After the increase, the network topology based on the power grid model is returned, the system impedance matrix is ​​constructed and the process continues. If the short-circuit ratio of the target node does not meet the short-circuit ratio threshold, and / or the photovoltaic penetration rate of the target node does not meet the penetration rate threshold, then the installed capacity of the target node at the previous moment will be used as the maximum connectable capacity to be added to the target node.

[0060] Among them, whether the short-circuit ratio of the target node meets the short-circuit ratio threshold is considered to be satisfied if the short-circuit ratio of the target node is greater than the short-circuit ratio threshold, otherwise it is not satisfied.

[0061] Whether the photovoltaic penetration rate of the target node meets the penetration rate threshold, that is, if the photovoltaic penetration rate of the target node is lower than the penetration rate threshold, it is considered to meet the threshold; otherwise, it is considered not to meet the threshold.

[0062] Optionally, the grid-accessible capacity assessment determined in this application embodiment is based on dual constraints of short-circuit ratio and photovoltaic penetration rate. During the grid-accessible capacity assessment, the installed capacity is first uniformly increased at one or more photovoltaic power station nodes at the target node. After each increase, the short-circuit ratio of each node is compared. Compared with the set short-circuit ratio threshold and the photovoltaic penetration rate at each node With the set penetration threshold When the minimum short-circuit ratio at any node is lower than the short-circuit ratio threshold, and / or the maximum photovoltaic penetration rate exceeds the penetration rate threshold, the increase in installed capacity is stopped. This achieves photovoltaic grid-connectable capacity assessment based on dual-indicator constraints, obtaining the maximum grid-connectable capacity for a single node or the entire system. .

[0063] The specific evaluation process is as follows: Step 1, set the short-circuit ratio threshold. and penetration threshold This serves as a constraint for assessing accessibility capacity.

[0064] Step 1.1, Selection of the short-circuit ratio threshold. The short-circuit ratio is an important indicator for evaluating the short-circuit capability and voltage stability of a power grid after the integration of new energy sources or energy storage. In capacity assessment, the short-circuit ratio threshold can be used to limit the connected capacity and ensure the system's short-circuit capability and voltage stability. In this embodiment, an empirical value of 3 can be used as the short-circuit ratio threshold, i.e. This value ensures the safe and stable operation of the power grid under typical access conditions, while also facilitating capacity assessment and planning.

[0065] Step 1.2, Calculation of the penetration threshold. Photovoltaic penetration rate. It is a key indicator for measuring the impact of photovoltaic power generation on the power grid within a region. Specifically, it represents the ratio of photovoltaic active power to the active power of the load in a certain region, expressed by the formula... calculate.

[0066] The penetration rate threshold is calculated by deriving the relationship between photovoltaic penetration rate and reverse load rate. Reverse load rate refers to the phenomenon in a distribution network where the power flow direction is opposite to that of the traditional power grid due to the integration of distributed generation, resulting in reverse power flow in the distribution network equipment. The formula for calculating reverse load rate is:

[0067] in, For reverse load rate, The equivalent electrical load at any given moment is the load minus the output of power sources other than distributed generation. These are the actual operating limits for transformers or lines.

[0068] Set a coefficient ,according to Then we have:

[0069] Lianlide:

[0070]

[0071] When reverse load rate When the value is 0.8, the calculated permeability threshold is:

[0072] Actual operating limits of actual power grid transformers , and take The calculated penetration threshold is:

[0073] Step 2, at the target node The installed capacity of one or more photovoltaic power stations is increased uniformly, and the target node is calculated in real time after each increase in installed capacity. short-circuit ratio and photovoltaic penetration rate Determine the target node short-circuit ratio Does it meet the short-circuit ratio threshold? (i.e., whether the minimum short-circuit ratio is greater than the short-circuit ratio threshold), and photovoltaic penetration rate Does it meet the penetration threshold? (i.e., whether the maximum value of photovoltaic penetration is lower than the penetration threshold), when the target node short-circuit ratio Short-circuit ratio threshold not met and / or photovoltaic penetration rate Penetration threshold not met When the time comes, stop increasing the installed capacity and use the installed capacity from the previous moment as the target node. Increased maximum access capacity If all conditions are met, then at the target node... After the photovoltaic power station uniformly increases the installed capacity by a preset number, the process of returning to the system impedance matrix construction process continues.

[0074] This application provides a method for assessing the grid-connectable capacity of photovoltaic (PV) energy storage. The method involves constructing a grid model and, based on the network topology, building a system impedance matrix. A Thevenin equivalent model of the grid-connected energy storage device is established, and after connecting the Thevenin equivalent model to grid nodes, the system impedance matrix is ​​corrected to obtain a corrected equivalent system impedance matrix. The grid nodes include at least one PV load connection node. When a three-phase short-circuit fault occurs at the target node, the short-circuit ratio and PV penetration rate of the target node are calculated based on the corrected equivalent system impedance matrix. The target node can be any node in the grid. Based on the short-circuit ratio and PV penetration rate of the target node, the maximum additional grid-connectable capacity of the target node is determined. This application, by constructing a power grid model and system impedance matrix and analyzing the impact of grid-connected energy storage, provides a clear understanding of the electrical characteristics of different nodes in the power grid. This helps planners optimize the power grid topology based on evaluation results during power grid construction, improving transmission efficiency and reliability. Furthermore, when a three-phase short-circuit fault occurs at a target node, calculating the short-circuit ratio based on the corrected equivalent system impedance matrix more accurately reflects the dynamic characteristics of the power grid under fault conditions. This helps operators promptly identify weak points in the power grid and take corresponding measures to strengthen grid stability, such as adjusting generator output and configuring reactive power compensation devices, preventing grid collapse during faults. Simultaneously, by establishing a Thevenin equivalent model of the grid-connected energy storage device and correcting the system impedance matrix after connecting it to a power grid node, the impact of grid-connected energy storage on the power grid can be intuitively analyzed. This contributes to a deeper understanding of the operating characteristics and effects of grid-connected energy storage devices in the power grid, providing a theoretical basis for further research and application of grid-connected energy storage technology.

[0075] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0076] The following are device embodiments of this application. For details not described in detail, please refer to the corresponding method embodiments described above.

[0077] Figure 5 A schematic diagram of a photovoltaic grid-connectable capacity assessment device considering grid-connected energy storage, provided in an embodiment of this application, is shown. For ease of explanation, only the parts relevant to the embodiment of this application are shown, and are described in detail below: like Figure 5 As shown, the photovoltaic grid-connectable capacity assessment device 5, which takes into account grid-connected energy storage, includes: Module 51 is used to construct a power grid model and, based on the network topology of the power grid model, construct a system impedance matrix. The correction module 52 is used to establish the Thevenin equivalent model of the grid-type energy storage device, and after the Thevenin equivalent model is connected to the grid node, the system impedance matrix is ​​corrected to obtain the corrected equivalent system impedance matrix. The grid node includes at least one photovoltaic load connection node. The calculation module 53 is used to calculate the short-circuit ratio and photovoltaic penetration rate of the target node based on the corrected equivalent system impedance matrix when a three-phase short-circuit fault occurs at the target node. The target node is any node in the power grid. The determination module 54 is used to determine the maximum increase in grid capacity of the target node based on the short-circuit ratio and photovoltaic penetration rate of the target node.

[0078] This application provides a photovoltaic (PV) grid-connected capacity assessment device that considers grid-connected energy storage. It constructs a grid model and, based on the network topology of the grid model, builds a system impedance matrix. A Thevenin equivalent model of the grid-connected energy storage device is established, and after connecting the Thevenin equivalent model to grid nodes, the system impedance matrix is ​​corrected to obtain a corrected equivalent system impedance matrix. The grid nodes include at least one PV load connection node. When a three-phase short-circuit fault occurs at the target node, the short-circuit ratio and PV penetration rate of the target node are calculated based on the corrected equivalent system impedance matrix. The target node can be any node in the grid. Based on the short-circuit ratio and PV penetration rate of the target node, the maximum increase in connectable capacity of the target node is determined. This application, by constructing a power grid model and system impedance matrix and analyzing the impact of grid-connected energy storage, provides a clear understanding of the electrical characteristics of different nodes in the power grid. This helps planners optimize the power grid topology based on evaluation results during power grid construction, improving transmission efficiency and reliability. Furthermore, when a three-phase short-circuit fault occurs at a target node, calculating the short-circuit ratio based on the corrected equivalent system impedance matrix more accurately reflects the dynamic characteristics of the power grid under fault conditions. This helps operators promptly identify weak points in the power grid and take corresponding measures to strengthen grid stability, such as adjusting generator output and configuring reactive power compensation devices, preventing grid collapse during faults. Simultaneously, by establishing a Thevenin equivalent model of the grid-connected energy storage device and correcting the system impedance matrix after connecting it to a power grid node, the impact of grid-connected energy storage on the power grid can be intuitively analyzed. This contributes to a deeper understanding of the operating characteristics and effects of grid-connected energy storage devices in the power grid, providing a theoretical basis for further research and application of grid-connected energy storage technology.

[0079] In one possible implementation, the correction module can be used to: Based on the principles of impedance matrix formation and correction, the system impedance matrix is ​​corrected to obtain the equivalent system impedance matrix; The virtual impedance is introduced into the equivalent system impedance matrix to correct the equivalent system impedance matrix, resulting in the corrected equivalent system impedance matrix.

[0080] In one possible implementation, the device may further include a virtual impedance calculation module, which can be used for: When the current limit is reached, a virtual impedance is obtained based on the output current limitation of the grid-type energy storage device.

[0081] In one possible implementation, the correction module can also be used for: Under the condition of open circuit at the grid connection point of a grid-connected energy storage device, Kirchhoff's current law and voltage law are used to solve for the port open-circuit voltage, and the port open-circuit voltage is used as an equivalent voltage source. With the voltage source set to zero, calculate the equivalent impedance of the port and treat the equivalent impedance of the port as the series impedance; Thevenin equivalent model of a grid-type energy storage device is established using an equivalent voltage source and series impedance.

[0082] In one possible implementation, the computation module can be used for: Using the system short-circuit current, the first short-circuit current, and the second short-circuit current, the target short-circuit current when a three-phase short-circuit fault occurs at the target node is calculated. The first short-circuit current is the short-circuit current provided by the grid-connected energy storage device at the target node, and the second short-circuit current is the sum of the short-circuit currents provided by the grid-connected energy storage devices at all nodes in the power grid except the target node to the target node. Calculate the short-circuit ratio of the target node based on the target short-circuit current; The photovoltaic penetration rate of the target node is calculated using the photovoltaic active power and load active power of the target node.

[0083] In one possible implementation, the computation module can also be used for: The first short-circuit current is calculated using the equivalent voltage source and series impedance of the Thevenin equivalent model of the grid-type energy storage device connected at the target node. For each first node, the short-circuit current provided by the grid-type energy storage device connected at the first node to the target node is calculated using the equivalent voltage source and series impedance of the Thevenin equivalent model of the grid-type energy storage device connected at the first node. The first node is any node in the power grid other than the target node. The sum of the short-circuit currents provided to the target node by all grid-type energy storage devices connected at the first node is taken as the second short-circuit current. The sum of the system short-circuit current, the first short-circuit current, and the second short-circuit current is taken as the target short-circuit current when a three-phase short-circuit fault occurs at the target node.

[0084] In one possible implementation, the computation module can also be used for: Calculate the product of the target short-circuit current and the rated voltage of the target node when a three-phase short-circuit fault occurs at the target node, and use this product as the first power. Calculate the equivalent injected power of all distributed photovoltaic power stations at the first node to the target node, and use the sum of the equivalent injected power and the photovoltaic active power of the target node as the second power. The ratio of the first power to the second power is used as the short-circuit ratio of the target node.

[0085] In one possible implementation, the computation module can also be used for: The ratio of photovoltaic active power to load active power in the area where the target node is located is used as the photovoltaic penetration rate of the target node.

[0086] In one possible implementation, determining the module's specific purpose can be used for: Determine whether the short-circuit ratio of the target node meets the short-circuit ratio threshold, and whether the photovoltaic penetration rate of the target node meets the penetration rate threshold; If the short-circuit ratio of the target node meets the short-circuit ratio threshold and the photovoltaic penetration rate of the target node meets the penetration rate threshold, then the installed capacity of the photovoltaic power station of the target node is uniformly increased by a preset number. After the increase, the network topology based on the power grid model is returned, the system impedance matrix is ​​constructed and the process continues. If the short-circuit ratio of the target node does not meet the short-circuit ratio threshold, and / or the photovoltaic penetration rate of the target node does not meet the penetration rate threshold, then the installed capacity of the target node at the previous moment will be used as the maximum connectable capacity to be added to the target node.

[0087] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0088] Those skilled in the art will recognize that the templates, units, and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0089] If the module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium. When executed by a processor, the computer program can implement the steps of the above embodiments of the photovoltaic grid-connected capacity assessment method considering grid-connected energy storage. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory, a random access memory, an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0090] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for photovoltaic accessible capacity evaluation considering network-type energy storage, characterized in that, The method comprises the following steps: constructing a power grid model, and constructing a system impedance matrix based on the network topology of the power grid model; establishing a Thevenin equivalent model of the grid-connected energy storage device, and correcting the system impedance matrix after the Thevenin equivalent model is connected to a power grid node, to obtain a corrected equivalent system impedance matrix, wherein the power grid node comprises at least one photovoltaic load connection node; when a three-phase short-circuit fault occurs at a target node, calculating the short-circuit ratio and photovoltaic penetration rate of the target node based on the corrected equivalent system impedance matrix, wherein the target node is any node in the power grid node; determining the maximum accessible capacity added by the target node according to the short-circuit ratio and photovoltaic penetration rate of the target node.

2. The method of claim 1, wherein, The step of correcting the system impedance matrix after the Thevenin equivalent model is connected to a power grid node to obtain a corrected equivalent system impedance matrix comprises the following steps: correcting the system impedance matrix according to the formation and correction principle of the impedance matrix to obtain an equivalent system impedance matrix; introducing a virtual impedance into the equivalent system impedance matrix to correct the equivalent system impedance matrix to obtain a corrected equivalent system impedance matrix.

3. The method of claim 2, wherein, Before the step of introducing a virtual impedance into the equivalent system impedance matrix to correct the equivalent system impedance matrix to obtain a corrected equivalent system impedance matrix, the method further comprises the following step: when the current is limited, obtaining the virtual impedance based on the output current limitation of the grid-connected energy storage device.

4. The method of claim 1, wherein, The step of establishing a Thevenin equivalent model of the grid-connected energy storage device comprises the following steps: under the condition that the grid-connected point of the grid-connected energy storage device is open, solving the open-circuit voltage of the port by using the Kirchhoff's current law and the voltage law, and taking the open-circuit voltage of the port as an equivalent voltage source; under the condition that the voltage source is zero, calculating the port equivalent impedance and taking the port equivalent impedance as a series impedance; establishing the Thevenin equivalent model of the grid-connected energy storage device by using the equivalent voltage source and the series impedance.

5. The method of claim 4, wherein, The step of calculating the short-circuit ratio and photovoltaic penetration rate of the target node based on the corrected equivalent system impedance matrix when a three-phase short-circuit fault occurs at the target node comprises the following steps: calculating the target short-circuit current when a three-phase short-circuit fault occurs at the target node by using the system short-circuit current, a first short-circuit current and a second short-circuit current, wherein the first short-circuit current is the short-circuit current provided by the grid-connected energy storage device connected to the target node, and the second short-circuit current is the sum of the short-circuit currents provided by the grid-connected energy storage devices connected to all nodes in the power grid node except the target node; calculating the short-circuit ratio of the target node according to the target short-circuit current; calculating the photovoltaic penetration rate of the target node by using the photovoltaic active power and the load active power of the target node.

6. The method of claim 5, wherein, The step of calculating the target short-circuit current when a three-phase short-circuit fault occurs at the target node by using the system short-circuit current, a first short-circuit current and a second short-circuit current comprises the following steps: calculating the first short-circuit current by using the equivalent voltage source and the series impedance of the Thevenin equivalent model of the grid-connected energy storage device connected to the target node; For each first node, an equivalent voltage source and a series impedance of a Thevenin equivalent model of a grid-forming energy storage device connected to the first node are used to calculate a short-circuit current provided by the grid-forming energy storage device connected to the first node to the target node, the first node being any node in the grid nodes except the target node; a sum of the short-circuit currents provided by all the grid-forming energy storage devices connected to the first nodes to the target node is taken as the second short-circuit current; a sum of the system short-circuit current, the first short-circuit current and the second short-circuit current is taken as a target short-circuit current when a three-phase short-circuit fault occurs at the target node.

7. The method of claim 6, wherein, The calculation of the short-circuit ratio of the target node according to the target short-circuit current comprises: a product of the target short-circuit current when a three-phase short-circuit fault occurs at the target node and a rated voltage of the target node is calculated, and the product is taken as a first power; an equivalent injection power of all the distributed photovoltaic power stations at the first nodes to the target node is calculated, and a sum of the equivalent injection power and a photovoltaic active power of the target node is taken as a second power; a ratio of the first power to the second power is taken as the short-circuit ratio of the target node.

8. The method of claim 5, wherein, The calculation of the photovoltaic penetration rate of the target node using the photovoltaic active power and the load active power of the target node comprises: a ratio of the photovoltaic active power to the load active power in a region where the target node is located is taken as the photovoltaic penetration rate of the target node.

9. The method of claim 1, wherein, The determination of the maximum accessible capacity added by the target node according to the short-circuit ratio and the photovoltaic penetration rate of the target node comprises: it is judged whether the short-circuit ratio of the target node satisfies a short-circuit ratio threshold value and whether the photovoltaic penetration rate of the target node satisfies a penetration rate threshold value; if the short-circuit ratio of the target node satisfies the short-circuit ratio threshold value and the photovoltaic penetration rate of the target node satisfies the penetration rate threshold value, a preset amount of installed capacity of the photovoltaic power station of the target node is uniformly increased, and after the increase, the network topology structure based on the grid model is returned to continue to execute the construction of the system impedance matrix; if the short-circuit ratio of the target node does not satisfy the short-circuit ratio threshold value and / or the photovoltaic penetration rate of the target node does not satisfy the penetration rate threshold value, an installed capacity of the target node at a previous time is taken as the maximum accessible capacity added by the target node.

10. An apparatus for evaluating photovoltaic accessible capacity considering network-type energy storage, comprising: It comprises: a construction module configured to construct a grid model and construct a system impedance matrix based on a network topology structure of the grid model; a correction module configured to establish a Thevenin equivalent model of a grid-forming energy storage device and correct the system impedance matrix to obtain a corrected equivalent system impedance matrix after the Thevenin equivalent model is connected to a grid node, the grid node comprising at least one photovoltaic load connection node; a calculation module configured to calculate a short-circuit ratio and a photovoltaic penetration rate of a target node based on the corrected equivalent system impedance matrix when a three-phase short-circuit fault occurs at the target node, the target node being any node in the grid nodes. A determining module is configured to determine the maximum accessible capacity of the target node according to the short-circuit ratio and the photovoltaic penetration rate of the target node.

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