A new energy power grid active control method and device considering voltage support capability

Abstract

The application discloses a new energy power grid active control method and device considering voltage support capability and belongs to the technical field of power system stability analysis and control. By constructing a reactive power capacity new energy multi-station short-circuit ratio index, the voltage support strength of a high proportion new energy power grid is accurately evaluated; after a power grid fault, a power source homophonic grouping constraint is established according to a multi-type power source grouping result, and a voltage support strength constraint of an islanded sub-system is constructed; the optimal solution section search model of active control is established by comprehensively considering the homophonic grouping constraint and the voltage support strength constraint, and the optimal solution section and the islanded sub-system control scheme are obtained by solving the model. The defects that the traditional active solution section control method does not consider the voltage support capability are overcome, the short-circuit ratio index is taken as a constraint and is integrated into the control model, the islanded sub-system has sufficient voltage support strength before and after active control is ensured, and the safe and stable operation level of the high proportion new energy power grid is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of power system stability analysis and control technology, specifically to an active control method and device for a new energy power grid that considers voltage support capability. Background Technology

[0002] Guided by the "dual carbon" goals, building a new power system with new energy sources as the mainstay has become an urgent task for promoting the clean and low-carbon transformation of energy, and an important measure to ensure national energy security. As the proportion of new energy connected to the grid using maximum power point tracking (MPPT) continues to rise, the equivalent short-circuit capacity of the power grid decreases, significantly weakening the system's ability to withstand disturbances, with voltage stability being particularly prominent. The short-circuit ratio, as a key indicator for measuring the voltage support strength of the system, directly affects the stable operation of the new energy grid-connected system. Accurately assessing the voltage support strength of high-proportion new energy grids and isolated subgrids after disconnection is of great significance for the large-scale sustainable development of new energy.

[0003] While traditional short-circuit ratio indices applicable to single-infeed renewable energy grid-connected systems can still roughly reflect the voltage support strength of the grid, their accuracy is reduced because they do not consider the influence of other renewable energy sources. Weighted short-circuit ratios and composite short-circuit ratios proposed for multi-infeed renewable energy grid-connected systems treat all renewable energy sources as a whole, roughly estimating the interaction between each infeed branch through weighting or summation, resulting in low accuracy. Short-circuit ratio indices for multiple renewable energy plants calculated based on capacity and voltage are best suited for analyzing the voltage support strength of multi-infeed renewable energy systems, but are difficult to directly apply in active disconnection control. The search for the optimal disconnection section is the core of active disconnection control after instability in renewable energy grids. Currently, optimization methods are commonly used to search for the optimal disconnection section. The core idea of ​​this method is to solve the optimal disconnection section search problem for active control by establishing a mathematical programming model when the grid power source grouping results are known. However, in practical applications of high-proportion renewable energy power grids, the aforementioned active disconnection control methods have the following shortcomings: First, they do not take into account the voltage support capacity of the renewable energy power grid, making it difficult for traditional active disconnection control methods to meet the requirements for safe and stable operation of high-proportion renewable energy power grids before and after control; second, the traditional short-circuit ratio index for multiple renewable energy power plants does not take into account the non-functional capacity of renewable energy power plants, making it difficult to accurately assess the voltage support strength of high-proportion renewable energy power grids; finally, most current active control methods focus on issues such as frequency security, while neglecting other stability issues in high-proportion renewable energy power grids.

[0004] Therefore, researching how to propose active control methods suitable for high-proportion renewable energy power grids based on actual safe operation requirements and considering voltage support strength constraints is of great significance for the safe and stable operation of power systems. Summary of the Invention

[0005] The purpose of this invention is to provide a method and apparatus for active control of new energy power grids that takes into account voltage support capability, so as to solve the problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] An active control method for a new energy power grid considering voltage support capability, the method includes the following steps:

[0008] Step S100: Based on the short-circuit capacity of the AC system and the equivalent grid-connected capacity of new energy sources, and combined with the reactive power characteristics of new energy power plants and reactive power compensation devices, construct a short-circuit ratio index for multiple new energy power plants that considers reactive power capacity.

[0009] Step S200: Based on the short-circuit ratio index of the new energy multi-station, establish the voltage support strength constraint of the new energy power grid, construct a new energy carrying capacity assessment model that considers the voltage support strength, and determine the initial operating state of the new energy power grid before active control, including the active power output of the power source and the active power flowing through the line before disconnection.

[0010] Step S300: Determine the grouping results of multiple types of power sources based on the relative movement trend of power sources after the fault in the new energy grid, and calculate the number of islanded subsystems after active disconnection control;

[0011] Step S400: Establish power coherence grouping constraints based on the results of multi-type power grouping, and construct voltage support strength constraints for the islanded subsystem considering the non-functional capacity of the new energy power station.

[0012] Step S500: Construct an optimal disconnection profile search model for active control by combining disconnection constraints. The disconnection constraints include power source coherence grouping constraints, voltage support strength constraints of the islanded subsystem, linearized AC power flow constraints, power flow constraints after line disconnection, internal connectivity constraints of the island, and island power balance constraints, to obtain the optimal disconnection profile and active control results of the islanded subsystem.

[0013] As a preferred embodiment of the active control method for new energy power grids that considers voltage support capability in this invention, the expression for the short-circuit ratio index of multiple new energy power plants considering reactive power capacity is as follows:

[0014] ;

[0015] In the formula: To consider the short-circuit ratio of multiple new energy power plants in terms of reactive power capacity; Let be the short-circuit capacity at the grid connection point corresponding to node i; These are the active power output values ​​of new energy sources at nodes i and j, respectively; The voltage interaction factor between nodes j and i; Let be the reactive power capacity of the new energy power station at node i.

[0016] As a preferred embodiment of the active control method for new energy power grids considering voltage support capability in this invention, the establishment of voltage support strength constraints for the new energy power grid includes:

[0017] Based on the short-circuit ratio index of multiple new energy power plants, voltage support strength constraints for the new energy power grid are established, including:

[0018] ;

[0019] ;

[0020] ;

[0021] ;

[0022] In the formula: A collection of capacitor banks; A collection of static var compensator groups; Let be the unit reactive power of capacitor b; The number of capacitor banks put into use; The maximum number of capacitor banks that can be put into use; These are the upper and lower limits for reactive power dispatching by the static reactive power compensator, respectively; CSCR is the critical short-circuit ratio. The scheduling value for the static var compensator s.

[0023] As a preferred embodiment of the active control method for new energy power grids considering voltage support capacity in this invention, the new energy carrying capacity assessment model considering voltage support strength takes the maximum grid-connected power of new energy as the optimization objective, and combines the active and reactive power balance constraint equations at nodes, the linearized AC power flow equations, line power constraints, generator output constraints, and the short-circuit ratio index of multiple new energy power plants to constrain the optimization objective; specifically including:

[0024] Based on the voltage support strength constraint of the renewable energy power grid, a renewable energy power grid carrying capacity assessment model is established with the optimization objective of maximizing renewable energy grid-connected power. The expression is as follows:

[0025] ;

[0026] In the formula: A collection of new energy power stations; The active power contribution for the i-th renewable energy power station.

[0027] As a preferred embodiment of the active control method for new energy power grids that considers voltage support capability in this invention, the node active and reactive power balance constraint equations, linearized AC power flow equations, line power constraints, generator output constraints, and the short-circuit ratio index for multiple new energy power stations include:

[0028] The expression for the active and reactive power balance equations at the nodes is:

[0029] ;

[0030] In the formula: , These are the receiving-end busbar and the sending-end busbar of the transmission line, respectively. , These represent the active power output and reactive power output of the generator during normal operation, respectively. These represent the active and reactive power of branch (i,j), respectively. These represent the active and reactive loads of node i, respectively. This is the reactive power dispatch value for capacitor bank c; For node i, the reactive power output of the new energy power station;

[0031] The linearized AC power flow model is expressed as follows:

[0032]

[0033]

[0034] In the formula: Let (i,j) be the conductance and susceptance of the branch. , Let be the voltage magnitudes at nodes i and j, respectively. and These are the voltage phase angles of nodes i and j, respectively.

[0035] The expression for the power constraint through the line is:

[0036]

[0037] In the formula: These represent the maximum and minimum values ​​of the active power flowing through the line, respectively. These represent the maximum and minimum values ​​of reactive power flowing through the line, respectively.

[0038] The active and reactive power output constraint expressions for the renewable energy power station are as follows:

[0039]

[0040] The constraint expressions for the active and reactive power outputs of the generator are as follows:

[0041]

[0042] In the formula: These represent the maximum active power output of the new energy power station and the generator, respectively. These represent the minimum and maximum reactive power output of the new energy power station, respectively. These are the minimum and maximum reactive power outputs of the generator, respectively.

[0043] As a preferred embodiment of the active control method for new energy power grids that considers voltage support capability in this invention, the specific implementation process of establishing power source coherence grouping constraints based on the results of multi-type power source grouping and constructing voltage support strength constraints for islanded subsystems considering the non-functional capacity of new energy power stations in islanded subsystems includes:

[0044] Based on the grouping of co-operating generating units among various power sources, the power grid system is decomposed into... An isolated subsystem In this system, each node corresponds to only one isolated subsystem; For node i, partition it into 0-1 variables. =1, then node i belongs to a point within island k. =0, then node i does not belong to any point within island k;

[0045] To determine whether nodes i and j belong to the same isolated subsystem, an auxiliary variable is introduced. By establishing power source homology grouping constraints, a linear expression is obtained:

[0046]

[0047]

[0048] In the formula: The decision variable is a 0-1 variable for line partitioning; It is an auxiliary variable, specifically an auxiliary 0-1 variable; Partition node j with 0-1 variables; A set of branches;

[0049] To limit the active power output of renewable energy plants within each islanded subsystem after disconnection and ensure it meets the critical short-circuit ratio requirement, a short-circuit ratio constraint is defined for the islanded subsystem after active disconnection control, and a voltage support strength constraint is constructed for the islanded subsystem:

[0050]

[0051] In the formula: These represent the active power output values ​​of renewable energy power plants at nodes i and j in the isolated subsystem k power grid; These represent the power changes of renewable energy power plants at nodes i and j in the isolated subsystem k power grid; The voltage interaction influence factor between nodes j and i in the isolated subsystem k-grid; Let i be the short-circuit capacity at node i in the isolated subsystem k-grid. Let J be the reactive power capacity of the renewable energy power station at node J in the isolated subsystem k power grid.

[0052] As a preferred embodiment of the active control method for new energy power grids considering voltage support capability in this invention, the specific implementation process of constructing the optimal solution section search model for active control by combining the solution constraint conditions includes:

[0053] Combining the separation constraints, an optimal separation section search model for active control is constructed with the objectives of minimizing both comprehensive power flow impact and load shear. The objective function is:

[0054]

[0055] In the formula: The penalty coefficient for the impact of trends; This is the load shedding penalty factor; Let i be the load shedding amount at node i; Let be the decision variable, representing the opening / closing state of branch (i,j). If , it means that branch (i,j) is broken. If , it means that branch (i,j) is connected; The active power of branch (i,j) during stable operation of the system before islanding; D is the set of all loaded nodes in the system;

[0056] A commercial optimization solver is used to solve the optimal solution cross-section search model to obtain the optimal solution cross-section and the active control results of the island subsystem.

[0057] As a preferred embodiment of the active control method for new energy power grids that considers voltage support capability in this invention, the isolation constraints include power source coherence grouping constraints, voltage support strength constraints of islanded subsystems, linearized AC power flow constraints, power flow constraints after line disconnection, internal connectivity constraints of islands, and island power balance constraints.

[0058] The node power balance constraint considers the active and reactive power balance of load shedding and power generation changes at each node, limiting the range of generator and load shedding at each node. The constraint formula is as follows:

[0059]

[0060]

[0061]

[0062] In the formula: To provide power output for wind farm dispatch during normal operation; This is the reactive power dispatch value for capacitor bank c; The scheduling value for the static var compensator s; These represent the changes in the generator's active and reactive power output, respectively. This refers to changes in wind farm dispatching. These represent the maximum values ​​of the changes in active and reactive power of the generator, respectively. The maximum load that can be removed;

[0063] The power flow constraints of the line include a linearized AC power flow model, the model formula of which is:

[0064]

[0065]

[0066] In the formula: It is a positive number. As an auxiliary variable, , Let be the voltage magnitudes at nodes i and j, respectively. and Let be the voltage phase angles at nodes i and j, respectively. For line conductance, For line susceptance;

[0067] The connectivity constraint, after the power grid is divided into islands, ensures that the nodes within the islands are connected, but the islands are not connected to each other. This connectivity within the islands is guaranteed by constructing a virtual active power balance, the formula for which is:

[0068]

[0069] In the formula: The active power of the virtual branch; For the active power output of the virtual generator;

[0070] The unbalanced power selection constraint for the isolated subsystem allows the unbalanced power generated during active disconnection control to be represented by either a power surplus or a power deficit. A power surplus indicates that the power generation of the isolated subsystem exceeds its load, while a power deficit indicates that the power generation of the isolated subsystem is less than its load. An isolated subsystem cannot simultaneously have both a surplus and a deficit, and both must be non-negative. The constraint formula is as follows:

[0071]

[0072]

[0073] In the formula: Let k be the magnitude of the unbalanced power of the isolated subsystem. δ represents the power surplus and deficit of the islanded subsystem k, respectively; δ is a binary variable representing the selection relationship between the power surplus and deficit within the islanded subsystem. The two cannot coexist in an islanded subsystem.

[0074] A new energy grid active control device considering voltage support capability, the device includes an initial state determination module, a clustering result determination module, and a breakup control decision module;

[0075] The initial state determination module is used to establish the voltage support strength constraint of the new energy power grid based on the short-circuit ratio index of the new energy multi-station, and to construct a new energy carrying capacity assessment model that considers the voltage support strength, so as to determine the initial operating state of the new energy power grid before active control.

[0076] The clustering result determination module is used to determine the clustering results of multiple types of power sources and the number of islanded subsystems after active disconnection control based on the relative movement trend of power sources after a fault in the new energy power grid, and to construct voltage support strength constraints for each islanded subsystem.

[0077] The decoupling control decision module is used to construct an optimal decoupling profile search model for active control based on the homogeneity grouping constraint and the voltage support strength constraint of the islanded subsystem, and obtain the optimal decoupling profile and the active decoupling control results of each islanded subsystem by solving the optimal decoupling profile search model.

[0078] Compared with existing technologies, the beneficial effects achieved by this invention are as follows: In the active control method and device for a new energy power grid considering voltage support capability provided by this invention, based on multi-type power source grouping, this invention considers the reactive power capacity and voltage support strength constraints of new energy power plants, constructs an optimal cross-section search model for active control, and obtains active control that satisfies the voltage support strength constraints by limiting the active power output of new energy power plants before and after active control. The short-circuit ratio index of new energy multi-power plants considering reactive power capacity proposed in this invention can accurately and effectively evaluate the voltage support strength of high-proportion new energy power grids. This invention limits the active power output of new energy power plants by constructing short-circuit ratio constraints, ensuring that the voltage support strength of high-proportion new energy power grids is within a reasonable range before and after active control. Compared with existing active control methods that do not consider short-circuit ratio constraints and the reactive power support capability of new energy power plants, this invention can be applied to actual high-proportion new energy power grids, enabling the controlled islanded subsystems to have sufficient voltage support capability, which is of great significance for ensuring the safe and stable operation of high-proportion new energy power grids. Attached Figure Description

[0079] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0080] Figure 1 This is a flowchart illustrating an active control method for a new energy power grid that considers voltage support capability in an embodiment of the present invention.

[0081] Figure 2 This is a modified IEEE 39-node system topology diagram in an embodiment of the present invention;

[0082] Figure 3 This is a node voltage phase angle diagram in an embodiment of the present invention;

[0083] Figure 4 This is a diagram showing the active power output and short-circuit ratio of the wind farm before active control in this embodiment of the invention.

[0084] Figure 5 This is the active power output diagram of the generator before active control in this embodiment of the invention;

[0085] Figure 6 This is a diagram showing the change in active power output and short-circuit ratio of a wind farm after active control in an embodiment of the present invention.

[0086] Figure 7 This is a diagram showing the change in active power output of the generator after active control in an embodiment of the present invention;

[0087] Figure 8 This refers to the change in generator output in this embodiment of the invention. Detailed Implementation

[0088] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0089] Please see Figures 1-8 In this embodiment, a new energy grid active control method considering voltage support capability is provided. The method includes the following steps:

[0090] Step S100: Based on the short-circuit capacity of the AC system and the equivalent grid-connected capacity of new energy sources, and combined with the reactive power characteristics of new energy power plants and reactive power compensation devices, construct a short-circuit ratio index for multiple new energy power plants that considers reactive power capacity.

[0091] Step S200: Based on the short-circuit ratio index of the new energy multi-station, establish the voltage support strength constraint of the new energy power grid, construct a new energy carrying capacity assessment model that considers the voltage support strength, and determine the initial operating state of the new energy power grid before active control, including the active power output of the power source and the active power flowing through the line before disconnection.

[0092] Step S300: Determine the grouping results of multiple types of power sources based on the relative movement trend of power sources after the fault in the new energy grid, and calculate the number of islanded subsystems after active disconnection control;

[0093] Step S400: Establish power coherence grouping constraints based on the results of multi-type power grouping, and construct voltage support strength constraints for the islanded subsystem considering the non-functional capacity of the new energy power station.

[0094] Step S500: Construct an optimal disconnection profile search model for active control by combining disconnection constraints. The disconnection constraints include power source coherence grouping constraints, voltage support strength constraints of the islanded subsystem, linearized AC power flow constraints, power flow constraints after line disconnection, internal connectivity constraints of the island, and island power balance constraints, to obtain the optimal disconnection profile and active control results of the islanded subsystem.

[0095] In summary, the embodiments of the present invention achieve active disconnection control of high-proportion renewable energy power grids through the above steps S100-S500, so that the power grids before and after control have sufficient voltage support capabilities to ensure the stable operation of the system.

[0096] The specific process is as follows: construct a linearized short-circuit ratio index for multiple new energy power plants; further construct a new energy carrying capacity assessment model that considers voltage support strength; determine the power plant grouping results based on the relative motion trend of power sources after a fault; further consider the non-functional capacity of new energy power plants in islanded subsystems to construct voltage support strength constraints for islanded subsystems; construct an optimal disconnection section search model for active control, and obtain the active disconnection control results by solving the above model.

[0097] Specifically, the expression for the short-circuit ratio index of new energy multi-stations considering reactive power capacity is as follows:

[0098] ;

[0099] In the formula: To consider the short-circuit ratio of multiple new energy power plants in terms of reactive power capacity; Let be the short-circuit capacity at the grid connection point corresponding to node i; These are the active power output values ​​of new energy sources at nodes i and j, respectively; The voltage interaction factor between nodes j and i; Let be the reactive power capacity of the renewable energy power station at node i. Here, node i is a system node.

[0100] 1) In high-proportion renewable energy grid-connected systems, the short-circuit ratio is commonly used to measure the strength of voltage support. Its expression is:

[0101] (1)

[0102] In the formula: Let be the short-circuit capacity at the grid connection point corresponding to node i; Let be the rated capacity of the new energy power station at the grid connection point corresponding to node i.

[0103] The short-circuit ratio index in equation (1) is only applicable to single-infeed systems and cannot take into account the influence of renewable energy sources at other infeed points. Therefore, the short-circuit ratio index for multiple renewable energy power plants is established by using the ratio of the AC system short-circuit capacity to the equivalent grid-connected capacity of renewable energy. :

[0104] (2)

[0105] In the formula: Let i be the equivalent grid-connected capacity of new energy at node i; These represent the installed capacity of new energy power plants at nodes i and j, respectively. These are the voltages at nodes i and j, respectively. These are the self-impedance and mutual impedance of nodes i and j, respectively; This is a conjugate operation.

[0106] The embodiments of this invention mainly focus on the evaluation of the short-circuit ratio on the grid voltage support strength during the operation phase. Therefore, the equivalent short-circuit ratio of the system power nodes is calculated using the actual output of new energy sources at the grid connection point. The calculation of the short-circuit ratio shown in equation (2) is simplified as shown in equation (3):

[0107] (3)

[0108] (4)

[0109] In the formula: These are the active power output values ​​of new energy sources at nodes i and j, respectively; The voltage interaction factor between nodes j and i; These represent the voltage changes at nodes i and j, respectively. These are the system's self-impedance and mutual impedance, respectively.

[0110] 2) The short-circuit ratio index for multiple new energy power plants mentioned above only considers the active power of the new energy power plants, while ignoring the reactive power characteristics of the new energy power plants and their corresponding reactive power compensation devices. Figure 2This explains the concept of non-functional capacity in renewable energy power plants, because renewable energy power plants can operate at their rated capacity. Within the range, reactive power will be reduced from Change to Therefore, renewable energy power plants can provide reactive power at their rated active power level, and their reactive power capacity is:

[0111] (5)

[0112] In the formula: Let i be the reactive power capacity of the new energy power station at node i; Let be the power factor constant of the renewable energy power station at node i. Let be the rated power of the new energy power station at node i.

[0113] To address the inability of traditional short-circuit ratio indicators to reflect this characteristic, this invention proposes constructing a short-circuit ratio indicator for multiple renewable energy power plants that considers reactive power capacity. As shown in equation (6):

[0114] (6)

[0115] From equation (6), we can see that the reactive power capacity It has the function of increasing short-circuit capacity, so the reactive power provided by the new energy power station can increase the strength of the system.

[0116] Specifically, the new energy carrying capacity assessment model considering voltage support strength takes the maximum grid-connected power of new energy as the optimization objective, and combines the active and reactive power balance constraint equations at nodes, the linearized AC power flow equations, line power constraints, generator output constraints, and the short-circuit ratio index of the new energy multi-stations to constrain the optimization objective; specifically including:

[0117] 1) In high-proportion renewable energy power grids, the system voltage strength is relatively weak. Considering the impact of the capacity of capacitor banks and static reactive power compensation devices of renewable energy power plants on the system voltage support strength, the short-circuit ratio of multiple renewable energy power plants, which takes into account reactive power capacity, is further added to the renewable energy power grid carrying capacity assessment model:

[0118] (7)

[0119] (8)

[0120] (9)

[0121] (10)

[0122] In the formula: A collection of capacitor banks; A collection of static var compensator groups; Let be the unit reactive power of capacitor b; It is an integer variable between 0 and 1, representing the number of capacitor banks put into use. This represents the maximum number of units that can be invested. These represent the upper and lower limits of reactive power dispatching by the static reactive power compensator; CSCR is the critical short-circuit ratio.

[0123] 2) Further construct a new energy carrying capacity assessment model that considers voltage support strength as follows:

[0124] A new energy grid carrying capacity model is established with the goal of maximizing the grid-connected power of new energy sources, as shown in Equation (11):

[0125] (11)

[0126] In the formula: A collection of new energy power stations; The active power contribution for the i-th renewable energy power station.

[0127] The active and reactive power balance equations at the nodes are shown in equation (12):

[0128] (12)

[0129] In the formula, , These are the receiving-end busbar and the sending-end busbar of the transmission line, respectively. , These represent the active and reactive power outputs of the generator, respectively. Contribute to the dispatching of new energy power plants; These represent the active and reactive power of branch (i,j), respectively. These represent the active and reactive loads of node i, respectively. This is the reactive power dispatch value for capacitor bank c; The scheduling value for the static var compensator s; This represents the active power flowing through the line. For node i, the reactive power output of the new energy power station; This represents the active power flowing through the line.

[0130] The linearized AC power flow model is shown in equations (13) and (14);

[0131] (13)

[0132] (14)

[0133] In the formula, Let (i,j) be the conductance and susceptance of the branch. , Let be the voltage magnitudes at nodes i and j, respectively. and These are the voltage phase angles of nodes i and j, respectively.

[0134] The power constraint for the line current is shown in equation (15):

[0135] (15)

[0136] In the formula: These represent the maximum and minimum values ​​of the active power flowing through the line, respectively. These represent the maximum and minimum reactive power flowing through the line, respectively.

[0137] The active and reactive power output constraints of the new energy power station are shown in Equation (16), and the active and reactive power output constraints of the generator are shown in Equation (17):

[0138] (16)

[0139] (17)

[0140] In the formula: These represent the maximum active power output of the new energy power station and the generator, respectively. These represent the minimum and maximum reactive power output of the new energy power station, respectively. These are the minimum and maximum reactive power outputs of the generator, respectively.

[0141] Specifically, the implementation process of establishing power coherence grouping constraints based on the results of multi-type power source grouping, and constructing voltage support strength constraints for islanded subsystems considering the non-functional capacity of renewable energy power plants includes:

[0142] Based on the relative movement trends of power sources after a fault in the renewable energy grid, the grouping results of various power sources are determined, and the number of islanded subsystems after active disconnection control is determined. ;

[0143] Based on the grouping of co-operating generating units among various power sources, the power grid system is decomposed into... There are isolated subsystems, where Equation (18) means that one node corresponds to only one isolated subsystem; For node i, partition it into 0-1 variables. If the value is 1, then node i belongs to a point within the island subsystem k. =0, node i does not belong to the point within the island subsystem k;

[0144] Equation (19) determines whether nodes i and j belong to the same isolated subsystem, thereby deciding whether to open or close the branch. Since it involves the multiplication of two binary variables, an auxiliary variable is introduced. As shown in equation (20), after linearization, a linear expression is obtained.

[0145] (18)

[0146] (19)

[0147] (20)

[0148] In the formula: The decision variable is a 0-1 variable for line partitioning; As an auxiliary variable, it is an auxiliary 0-1 variable. For node j, partition the variable into 0-1. The number of isolated subsystems; A set of branches;

[0149] To limit the active power output of renewable energy plants within each islanded subsystem after disconnection and ensure it meets the critical short-circuit ratio requirement, a short-circuit ratio constraint is defined for islanded subsystem k after active disconnection control, and the voltage support strength constraint of the islanded subsystem is constructed as shown in equation (21):

[0150] (twenty one)

[0151] In the formula: These represent the active power output values ​​of renewable energy power plants at nodes i and j in the isolated subsystem k power grid; These represent the power changes of renewable energy power plants at nodes i and j in the isolated subsystem k power grid; The voltage interaction influence factor between nodes j and i in the isolated subsystem k-grid; Let i be the short-circuit capacity at node i in the isolated subsystem k-grid. Let J be the reactive power capacity of the renewable energy power station at node J in the isolated subsystem k power grid.

[0152] Specifically, the implementation process of constructing the optimal solution cross-section search model for active control includes:

[0153] Combining the separation constraints, an optimal separation section search model for active control is constructed with the goal of minimizing the combined power flow impact and shear load. The objective function is shown in equation (22):

[0154] (twenty two)

[0155] In the formula: A set of branches; The penalty coefficient for the impact of trends; This is the load shedding penalty factor; Let i be the load shedding amount at node i; Let be the decision variable, and represent the opening / closing state of branch (i,j). This means that the branch is disconnected. , where branch (i,j) is connected; The active power of branch (i,j) during stable operation of the system before islanding; D is the set of all loaded nodes in the system. Loaded nodes are a subset of system nodes. They are the same type of nodes, only the set range is different.

[0156] In this embodiment of the invention, the following settings are provided: During the disconnection process, priority is given to the disconnection method with less power flow impact in order to improve the transient stability of each island after disconnection.

[0157] The optimal solution cross-section search model can be solved using the commercial optimization solver Cplex to obtain the optimal solution cross-section and the active control results of the isolated subsystem.

[0158] Specifically, the decoupling constraints include power source coherence grouping constraints, voltage support strength constraints of islanded subsystems, linearized AC power flow constraints, power flow constraints after line disconnection, internal connectivity constraints of islands, and island power balance constraints.

[0159] The node power balance constraint takes into account the active and reactive power balance of load shedding and power generation changes at each node, as shown in equations (23) and (24); equation (25) limits the range of shedding capacity and load at each node.

[0160] (twenty three)

[0161] (twenty four)

[0162] (25)

[0163] In the formula: To provide power output for wind farm dispatch during normal operation; This is the reactive power dispatch value for capacitor bank c; The scheduling value for the static var compensator s; These represent the changes in the generator's active and reactive power output, respectively. This refers to changes in wind farm dispatching. This represents the maximum value of the changes in active and reactive power of the generator. The maximum load that can be removed.

[0164] The power flow constraints of the line include a linearized AC power flow model, the model formula of which is:

[0165] (26)

[0166] (27)

[0167] In the formula: For a sufficiently large positive number, As an auxiliary variable, , Let be the voltage magnitudes at nodes i and j, respectively. and Let be the voltage phase angles at nodes i and j, respectively. For line conductance, For line susceptance;

[0168] The connectivity constraint ensures that after the power grid is divided into islands, the nodes within the islands are connected, but the islands are not connected to each other, thus avoiding isolated nodes and unstable islands. The connectivity within the islands is guaranteed by constructing a virtual active power balance, as shown in equation (28).

[0169] (28)

[0170] In the formula: The active power of the virtual branch; The active power output of the virtual generator is greater than or equal to 1 to ensure that there are no isolated generator nodes in the island.

[0171] The unbalanced power selection constraint of the isolated subsystem allows the unbalanced power generated during the active disconnection control process to be represented by power surplus or deficit, as shown in equations (29)-(30). Power surplus indicates that the power generation of the isolated subsystem is greater than the load, while power deficit indicates that the power generation of the isolated subsystem is less than the load. Equation (30) ensures that a single isolated subsystem cannot simultaneously have both surplus and deficit, and that both must be non-negative. The constraint formula is as follows:

[0172] (29)

[0173] (30)

[0174] In the formula: Let k be the magnitude of the unbalanced power of the isolated subsystem. These represent the power surplus and deficit of the islanded subsystem, respectively; δ is a binary variable representing the selection relationship between the power surplus and deficit within the island, and the two cannot coexist in an island.

[0175] In summary, the embodiments of the present invention can realize the islanding of a high proportion of new energy power grids through the above steps, and ensure that each islanded subsystem can operate safely and stably after the islanding is separated.

[0176] A new energy grid active control device considering voltage support capability, the device includes an initial state determination module, a clustering result determination module, and a breakup control decision module;

[0177] The initial state determination module is used to establish the voltage support strength constraint of the new energy power grid based on the short-circuit ratio index of the new energy multi-station, and to construct a new energy carrying capacity assessment model that considers the voltage support strength, so as to determine the initial operating state of the new energy power grid before active control.

[0178] The clustering result determination module is used to determine the clustering results of multiple types of power sources and the number of islanded subsystems after active disconnection control based on the relative movement trend of power sources after a fault in the new energy power grid, and to construct voltage support strength constraints for each islanded subsystem.

[0179] The decoupling control decision module is used to construct an optimal decoupling profile search model for active control based on the homogeneity grouping constraint and the voltage support strength constraint of the islanded subsystem, and obtain the optimal decoupling profile and the active decoupling control results of each islanded subsystem by solving the optimal decoupling profile search model.

[0180] The following example illustrates an active control method for new energy power grids that considers voltage support capability, as proposed in this invention. Simulation analysis and verification are performed using a modified IEEE-39 node system as an example. The topology of the modified IEEE-39 node system is shown below. Figure 2 As shown below, see the description for details:

[0181] The modified IEEE 39-node system topology is as follows: Figure 3 As shown, the simulation includes 6 generator sets, 4 wind farms, and 46 branches. Generators at nodes 32, 34, 35, and 37 are replaced with wind farms with a rated power of 600 MW. Using generator G2 as the reference generator, a scenario is simulated that causes the system to collapse after a disturbance: At 0s, a three-phase permanent fault is introduced on an AC branch between nodes 16 and 17 near node 17. The fault lasts for 0.3s, after which the faulty line is disconnected. The entire simulation lasts for 5s. During this period, the relative movement trend of the bus voltage phase angle is shown in the figure. Figure 4As shown, based on the relative movement trend of the power sources, the generators and wind farms are ultimately divided into two groups: {G1-G2, G6, W1, W4} and {G3-G5, W2-W3}. The critical short-circuit ratio is set to 1.5. To verify the effectiveness of the proposed renewable energy carrying capacity assessment model considering voltage support strength constraints and the optimal cross-section search model for active disconnection control, two examples are set up for analysis and simulation: Example 1, the islanding active disconnection control method without considering voltage support strength constraints; Example 2, the active disconnection control method considering voltage support strength constraints and renewable energy participation in regulation.

[0182] During the assessment of the renewable energy grid's carrying capacity before proactive disconnection control, the active power output and short-circuit ratio of the wind farm under two different calculation scenarios are as follows: Figure 5 As shown, the active power output of the generator is as follows: Figure 6 As shown. Without considering voltage support strength constraints, the wind farms are in a state of high active power output. The short-circuit ratios of wind farms W1, W2, W3, and W4 are 1.35, 1.48, 1.34, and 1.31, respectively, all of which are less than the critical short-circuit ratio of 1.5. After considering the voltage support strength constraints, wind farms W1 and W3 reduce their output power by 98.75MW and 117.81MW, respectively, and the short-circuit ratios of wind farms W1, W2, W3, and W4 increase to 1.5, 1.71, 1.5, and 1.5, respectively, meeting the grid voltage support strength requirements. The active power output of the generators and wind farms at this time, as well as the active power flowing through the lines, are used as the initial operating conditions before the grid's active disconnection control.

[0183] In the active disconnection control phase following grid instability in the renewable energy power grid, the optimal cross-section search model was optimized. The search results for disconnection cross-sections in Examples 1 and 2 are shown in Table 1. These include: disconnection cross-section, unbalanced power, power generation change, and load shedding.

[0184] Table 1 Search Results for the Separation Section

[0185]

[0186] The power output change and short-circuit ratio of wind farms in Examples 1 and 2 are as follows: Figure 7As shown, in Scenario 1, without considering the short-circuit ratio constraint, the active power of wind farms W2 and W3 increases by 59.67MW to compensate for the power deficit in island 1, resulting in a decrease in the short-circuit ratios at the grid connection points of wind farms W2 and W3 to 1.12 and 0.98, respectively. Simultaneously, wind farms W1 and W4 in island 2 reduce their active power by 58.08MW and 119.47MW, respectively, to reduce the power surplus in island 2, with their grid connection point short-circuit ratios at 1.32 and 1.28, both below the critical short-circuit ratio. In Scenario 2, considering the short-circuit ratio constraint of the island subsystem, the wind farms all implement varying degrees of wind curtailment to improve the voltage support strength of the island subsystem. In Island 1, wind farms W2 and W3 reduce their active power by 141.28MW and 116.6MW respectively, increasing their grid connection point short-circuit ratios to 1.72 and 1.5. Simultaneously, in Island 2, wind farms W1 and W4 reduce their active power by 82.51MW and 119.47MW respectively, increasing their grid connection point short-circuit ratios to 1.5 and 1.51, thus meeting the voltage support strength requirements of the isolated power grid. However, because this embodiment of the invention does not consider transmission line losses, there is a situation where the two islands have the same unbalanced power.

[0187] The changes in generator output in Examples 1 and 2 are as follows: Figure 8 As shown, in islanded subsystem 1, compared to Example 1, generator G3 increases its active power by 20.95MW in Example 2 to reduce the load shedding in islanded subsystem 1. In islanded subsystem 2, to meet the voltage support strength of the grid, the wind curtailment of wind farm W1 increases, and to meet power balance, the active power of generators G2 and G6 decreases to 0 and 5.02MW, respectively. Meanwhile, in Example 2, to meet the power balance of islanded subsystem 1, an additional 356.27MW of load needs to be shedding, of which 160MW, 59.27MW, and 137MW are shedding at nodes 15, 18, and 21, respectively. Through the comparative analysis of the above examples, the active control method for new energy grids considering voltage support strength constraints proposed in this embodiment can maintain the voltage support strength of the grid above the threshold before and after active disconnection control, which is more conducive to the safe and stable operation of high-proportion new energy grids.

[0188] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0189] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for active control of a new energy power grid considering voltage support capability, characterized in that, The method includes the following steps: Step S100: Based on the short-circuit capacity of the AC system and the equivalent grid-connected capacity of new energy sources, and combined with the reactive power characteristics of new energy power plants and reactive power compensation devices, construct a short-circuit ratio index for multiple new energy power plants that considers reactive power capacity. Step S200: Based on the short-circuit ratio index of the new energy multi-station, establish the voltage support strength constraint of the new energy power grid, construct a new energy carrying capacity assessment model that considers the voltage support strength, and determine the initial operating state of the new energy power grid before active control, including the active power output of the power source and the active power flowing through the line before disconnection. Step S300: Determine the grouping results of multiple types of power sources based on the relative movement trend of power sources after the fault in the new energy grid, and calculate the number of islanded subsystems after active disconnection control; Step S400: Establish power coherence grouping constraints based on the results of multi-type power source grouping, and construct voltage support strength constraints for the islanded subsystem considering the non-functional capacity of the renewable energy power station. Specifically, this includes: Based on the relative movement trends of power sources after a fault in the renewable energy grid, the grouping results of various power sources are determined, and the number of islanded subsystems after active disconnection control is determined. ; Based on the grouping of co-operating generating units among various power sources, the power grid system is decomposed into... An isolated subsystem In this system, each node corresponds to only one isolated subsystem; For node i, partition it into 0-1 variables. =1, then node i belongs to a point within island k. =0, then node i does not belong to any point within island k; To determine whether nodes i and j belong to the same isolated subsystem, an auxiliary variable is introduced. By establishing power source homology grouping constraints, a linear expression is obtained: In the formula: The decision variable is a 0-1 variable for line partitioning; It is an auxiliary variable, specifically an auxiliary 0-1 variable; Partition node j with 0-1 variables; A set of branches; To limit the active power output of renewable energy plants within each islanded subsystem after disconnection and ensure it meets the critical short-circuit ratio requirement, a short-circuit ratio constraint is defined for the islanded subsystem after active disconnection control, and a voltage support strength constraint is constructed for the islanded subsystem: In the formula: These represent the active power output values ​​of renewable energy power plants at nodes i and j in the isolated subsystem k power grid; These represent the power changes of renewable energy power plants at nodes i and j in the isolated subsystem k power grid; The voltage interaction influence factor between nodes j and i in the isolated subsystem k-grid; Let i be the short-circuit capacity at node i in the isolated subsystem k-grid. Let J be the reactive power capacity of the renewable energy power station at node j in the isolated subsystem k power grid; Let be the unit reactive power of capacitor b; The number of capacitor banks put into use; s is the scheduling value of the static var compensator s; CSCR is the critical short-circuit ratio; Step S500: Construct an optimal disconnection profile search model for active control by combining disconnection constraints. The disconnection constraints include power source coherence grouping constraints, voltage support strength constraints of the islanded subsystem, linearized AC power flow constraints, power flow constraints after line disconnection, internal connectivity constraints of the island, and island power balance constraints, to obtain the optimal disconnection profile and active control results of the islanded subsystem.

2. The active control method for a new energy power grid considering voltage support capability according to claim 1, characterized in that, The expression for the short-circuit ratio index of new energy multi-stations considering reactive power capacity is as follows: ； In the formula: To consider the short-circuit ratio of multiple new energy power plants in terms of reactive power capacity; Let be the short-circuit capacity at the grid connection point corresponding to node i; These are the active power output values ​​of new energy sources at nodes i and j, respectively; The voltage interaction factor between nodes j and i; Let be the reactive power capacity of the new energy power station at node i.

3. The active control method for a new energy power grid considering voltage support capability according to claim 2, characterized in that, The voltage support strength constraints for establishing a new energy power grid include: Based on the short-circuit ratio index of multiple new energy power plants, voltage support strength constraints for the new energy power grid are established, including: ； ； ； ； In the formula: A collection of capacitor banks; A collection of static var compensator groups; Let be the unit reactive power of capacitor b; The number of capacitor banks put into use; The maximum number of capacitor banks that can be put into use; These are the upper and lower limits for reactive power dispatching by the static reactive power compensator, respectively; CSCR is the critical short-circuit ratio. The scheduling value for the static var compensator s.

4. The active control method for a new energy power grid considering voltage support capability according to claim 3, characterized in that, The new energy carrying capacity assessment model considering voltage support strength takes the maximum grid-connected power of new energy as the optimization objective. It combines the active and reactive power balance constraint equations at nodes, the linearized AC power flow equations, line power constraints, generator output constraints, and the short-circuit ratio index of multiple new energy power plants to constrain the optimization objective; specifically, it includes: Based on the voltage support strength constraint of the renewable energy power grid, a renewable energy power grid carrying capacity assessment model is established with the optimization objective of maximizing renewable energy grid-connected power. The expression is as follows: ； In the formula: A collection of new energy power stations; The active power contribution for the i-th renewable energy power station.

5. The active control method for a new energy power grid considering voltage support capability according to claim 4, characterized in that, The node active and reactive power balance constraint equations, linearized AC power flow equations, line power constraints, generator output constraints, and the short-circuit ratio index for multiple new energy power stations include: The expression for the active and reactive power balance equations at the nodes is: ； In the formula: , These are the receiving-end busbar and the sending-end busbar of the transmission line, respectively. , These represent the active power output and reactive power output of the generator during normal operation, respectively. These represent the active and reactive power of branch (i,j), respectively. These represent the active and reactive loads of node i, respectively. This is the reactive power dispatch value for capacitor bank c; For node i, the reactive power output of the new energy power station; The linearized AC power flow model is expressed as follows: In the formula: For the conductance and susceptance of branch (i,j), , Let be the voltage magnitudes at nodes i and j, respectively. and Let be the voltage phase angles of nodes i and j, respectively; The expression for the power constraint through the line is: In the formula: These represent the maximum and minimum values ​​of the active power flowing through the line, respectively. These represent the maximum and minimum values ​​of reactive power flowing through the line, respectively. The active and reactive power output constraint expressions for the renewable energy power station are as follows: The constraint expressions for the active and reactive power outputs of the generator are as follows: In the formula: These represent the maximum active power output of the new energy power station and the generator, respectively. These represent the minimum and maximum reactive power output of the new energy power station, respectively. These are the minimum and maximum reactive power outputs of the generator, respectively.

6. The active control method for a new energy power grid considering voltage support capability according to claim 5, characterized in that, The specific implementation process of constructing the optimal solution section search model for active control by combining the solution constraint conditions includes: Combining the separation constraints, an optimal separation section search model for active control is constructed with the objectives of minimizing both comprehensive power flow impact and load shear. The objective function is: In the formula: The penalty coefficient for the impact of trends; This is the load shedding penalty factor; Let i be the load shedding amount at node i; Let be the decision variable, representing the opening / closing state of branch (i,j). If , it means that branch (i,j) is broken. If , it means that branch (i,j) is connected; The active power of branch (i,j) during stable operation of the system before islanding; D is the set of all loaded nodes in the system; A commercial optimization solver is used to solve the optimal solution cross-section search model to obtain the optimal solution cross-section and the active control results of the island subsystem.

7. The active control method for a new energy power grid considering voltage support capability according to claim 6, characterized in that, The constraints for decoupling include power source coherence grouping constraints, voltage support strength constraints of islanded subsystems, linearized AC power flow constraints, power flow constraints after line disconnection, internal connectivity constraints of islands, and power balance constraints of islands. The node power balance constraint considers the active and reactive power balance of load shedding and generation changes at each node, limiting the range of generator and load shedding at each node. The constraint formula is as follows: In the formula: To provide power output for wind farm dispatch during normal operation; These represent the changes in the generator's active and reactive power output, respectively. This refers to changes in wind farm dispatching. These represent the maximum values ​​of the changes in active and reactive power of the generator, respectively. The maximum load that can be removed; The active-reactive coupling coefficient; Line power flow constraints include a linearized AC power flow model, the model formula of which is: In the formula: It is a positive number. As an auxiliary variable, For line conductance, For line susceptance; Connectivity constraints arise after the power grid is divided into islands, where the nodes within the islands are connected, but the islands are not connected to each other. Virtual active power balance is constructed to ensure connectivity within the islands, and the formula for this construction is as follows: In the formula: The active power of the virtual branch; For the active power output of the virtual generator; The unbalanced power selection constraint for islanded subsystems, during active disconnection control, represents the unbalanced power as either a power surplus or a power deficit. A power surplus indicates that the power generation of the islanded subsystem exceeds its load, while a power deficit indicates that the power generation of the islanded subsystem is less than its load. An islanded subsystem cannot simultaneously have both a surplus and a deficit, and both must be non-negative. The constraint formula is: In the formula: Let k be the magnitude of the unbalanced power of the isolated subsystem. These represent the power surplus and deficit of the isolated subsystem k, respectively. It is a binary variable representing the choice between power surplus and deficit within an islanded subsystem. The two cannot coexist in an islanded subsystem.

8. A new energy grid active control device considering voltage support capability, using the new energy grid active control method considering voltage support capability as described in any one of claims 1-7, characterized in that, The device includes an initial state determination module, a clustering result determination module, and a disengagement control decision module; The initial state determination module is used to establish the voltage support strength constraint of the new energy power grid based on the short-circuit ratio index of the new energy multi-station, and to construct a new energy carrying capacity assessment model that considers the voltage support strength, so as to determine the initial operating state of the new energy power grid before active control. The clustering result determination module is used to determine the clustering results of multiple types of power sources and the number of islanded subsystems after active disconnection control based on the relative movement trend of power sources after a fault in the new energy power grid, and to construct voltage support strength constraints for each islanded subsystem. The decoupling control decision module is used to construct an optimal decoupling profile search model for active control based on the homogeneity grouping constraint and the voltage support strength constraint of the islanded subsystem, and obtain the optimal decoupling profile and the active decoupling control results of each islanded subsystem by solving the optimal decoupling profile search model.

Images