High-proportion new energy power grid island division method considering frequency constraint

Abstract

The invention discloses a high-proportion new energy power grid island division method considering frequency constraint, and belongs to the technical field of power system stability analysis and control, and the method comprises the steps: calculating a coherence coupling matrix of a generator and a new energy station through point voltage phase angle information; constructing a homology information undirected graph and calculating a normalized Laplacian matrix; performing characteristic value analysis, and determining the number of coherent generator groups and the coordinates of the generator and the new energy station; determining the composition of a coherent generator group through inverse mapping, and obtaining a multi-type power supply grouping result; establishing a coherence grouping constraint and a frequency security constraint according to a multi-type power supply grouping result; and constructing an island division optimal section search model and solving to obtain an optimal splitting section. By the adoption of the method, coherence grouping of multiple types of power supplies is achieved, and the optimal island division scheme is obtained by constructing and solving the island division optimal section search model considering the new energy supporting capacity and the frequency constraint.

Description

Technical Field

[0001] The present invention relates to the technical field of power system stability analysis and control, and in particular to a method for islanding a high-proportion new energy power grid taking frequency constraints into account. Background Art

[0002] With the continuous expansion of high-proportion renewable energy grid connection and regional grid interconnection, the operation mode of the power grid is complex and changeable, and its safety and stability face new challenges. When the power grid suffers extreme situations such as sudden disasters, it is more likely to cause the expansion of local accidents, causing huge losses to society and the economy. The island division after the active decoupling of the power system is the last line of defense to avoid the collapse of the power system. Unreasonable island division methods may lead to a large number of machine and load shedding after decoupling, affecting the dynamic stability of the island, and may cause the new energy station to be disconnected from the grid, causing a secondary shock to the system.

[0003] The multi-type power source grouping of the power system is the primary task to achieve islanding. At present, the model-based and measurement-based coherence identification methods are commonly used to achieve multi-type power source grouping. The model-based coherence group identification method relies on the detailed model and accurate parameters of the system, which makes the model-based coherence group identification method face huge challenges in practical applications. On the contrary, the measurement-based method uses the wide-area synchronous phasor measurement unit data to determine the coherence group. This type of method uses the relevant theories of pattern recognition and data mining to extract the power angle information that can characterize the coherence between generators from the wide-area measured information of the power system to divide the coherence group. Determining a reasonable disconnection section is the core of achieving islanding. At present, the optimization-based method is a common method for searching the optimal disconnection section. The core idea of ​​this method is to solve the optimal section search problem of active disconnection by establishing a mathematical programming model when the generator grouping results are known. However, in the actual application of high-proportion new energy power grids, the above-mentioned islanding division methods have the following shortcomings:

[0004] ① The synchronization mechanism of the current renewable energy stations has not been clarified, and the traditional synchronization grouping method is difficult to apply to power grids with a high proportion of renewable energy. Research on synchronization grouping containing multiple types of power sources still needs to be deepened; ② The supporting capacity of renewable energy stations is not taken into account, and the traditional disconnection section search method is difficult to meet the needs of island division in power grids with a high proportion of renewable energy; ③ Most of the current island division methods focus on studying the solution algorithm for the optimal disconnection section problem and ignore other stability constraints in the power grid.

[0005] Therefore, it is of great significance for the safe and stable operation of the power system to study how to propose an island division method suitable for a high-proportion renewable energy power grid based on the actual demand of the high-proportion renewable energy power grid and taking into account the frequency security constraints. Summary of the invention

[0006] The purpose of the present invention is to provide a method for islanding a high-proportion renewable energy power grid taking into account frequency constraints, which uses node voltage information to achieve coherent grouping of multiple types of power sources, and constructs an optimal section search model for islanding based on considerations of renewable energy support capabilities and frequency constraints. By solving the optimal section search model for islanding, the optimal islanding scheme is obtained.

[0007] To achieve the above object, the present invention provides a method for islanding a high-proportion renewable energy grid taking frequency constraints into account, the steps comprising:

[0008] S1. Based on the wide-area measurement device, the node voltage phase angle information of the generator and the new energy station is collected from the power system and the frequency deviation value is calculated. The cosine similarity between each power node is calculated according to the frequency deviation value to obtain the coherent coupling matrix of each power system generator and new energy station in the high-proportion new energy grid;

[0009] S2. According to the obtained coherent coupling degree matrix of the generator and the new energy station, a coherent information undirected graph of the high-proportion new energy power grid is constructed, a weight matrix of the coherent information undirected graph is calculated, and a normalized Laplace matrix of the coherent information undirected graph is constructed;

[0010] S3. Perform eigenvalue analysis on the normalized Laplace matrix, calculate its eigenvalue and eigenvector, determine the number of synchronous generators in the power system according to the eigenvalue, and obtain the coordinate distribution of the generator and the new energy station in the Euclidean space according to the eigenvector;

[0011] S4. Determine the composition of the coherent cluster through cluster analysis and inverse mapping of spatial coordinates, merge the coherent clusters according to the actual grid operation scale limit, and determine the final multi-type power source grouping result;

[0012] S5. Establish coherent grouping constraints and frequency safety constraints based on the multi-type power grouping results;

[0013] S6. Based on the coherent grouping constraints and frequency constraints, an optimal section search model for island partitioning is constructed, and the optimal section search model for island partitioning is solved to obtain the optimal solution section and the island partitioning result.

[0014] Preferably, step S1 specifically includes:

[0015] The extended dynamic synchronization identification method is used to describe the synchronization characteristics of the new energy station in the power system that are similar to the generator after being disturbed. The frequency deviation value of the generator and the new energy station at a certain moment in the power system is calculated by the voltage phase angle change rate. The formula is:

[0016]

[0017] Where Δf i| t Indicates the frequency deviation between the generator and the new energy station. is the voltage phase angle of node i, ω o represents the rated angular frequency, Δt represents the time interval, and t represents a certain moment;

[0018] Calculate the frequency deviation vector Δf between the generator and the new energy station within a certain period of time i , Δf i It is constructed by the frequency deviation values ​​at different times, and the formula is:

[0019]

[0020] In the formula, N represents the number of generators and new energy station nodes;

[0021] According to the difference in frequency deviation vectors between the generator and the new energy station nodes, the cosine similarity between the power supply nodes is calculated, and then the synchronous group is determined. The formula is:

[0022]

[0023] In the formula, CC ij Represents cosine similarity, CS ij It represents the coherent coupling degree between the power supply of node i and the power supply of node j;

[0024] The coherent coupling degree of each generator and the new energy station is calculated according to the cosine similarity, and the coherent coupling degree matrix C of the system generator and the generator is obtained. The formula is:

[0025]

[0026] Preferably, in step S2, the coherent information undirected graph G=(V,E) of the high-proportion new energy power grid, V represents the vertex set of G, corresponding to the set of generators and new energy stations in the power system; E represents the edge set of G, corresponding to the set of coherent coupling degrees between the generators and new energy stations.

[0027] Preferably, calculating the weight matrix of the homology information undirected graph in step S2 and constructing the normalized Laplace matrix of the homology information undirected graph includes:

[0028] Based on the homology information undirected graph G, the vertex weight and edge weight of the homology information undirected graph G are defined as:

[0029] w ii =CC ii =1;

[0030] w ij =CS ij ;

[0031] In the formula, wii represents the vertex weight, w ij represents edge weight;

[0032] Based on vertex weights and edge weights, the weight matrix of the homology information undirected graph G is obtained;

[0033] The non-normalized Laplace matrix L is constructed according to the weight matrix of the homology information undirected graph G. The construction process includes:

[0034]

[0035] Where, L ij represents the elements in L, d i Represents the weight factor of vertex i in the homology information undirected graph G, d i The expression is:

[0036]

[0037] Combined with the weight factor of vertex i, the normalized Laplacian matrix is ​​further expressed as:

[0038]

[0039] Where D is the vertex weight factor d i The diagonal matrix formed.

[0040] Preferably, step S3 includes:

[0041] The normalized Laplace matrix L N Perform eigenvalue analysis, calculate its eigenvalue and eigenvector, and according to the normalized Laplace matrix L N The maximum characteristic gap is used to determine the number of coherent clusters in the system. The formula is:

[0042] Δλ k =λ k -λ k-1 ;

[0043] Where k is the normalized Laplace matrix L N The maximum characteristic gap Δλ max The corresponding value indicates the number of synchronized clusters;

[0044] Based on the number of coherent machines k, the normalized Laplace matrix L N The first k eigenvectors u of 1 、u 2 、···、u k The elements in are assigned to the elements in the vertex set V in the homology information undirected graph G by row, and the coordinate information of each generator and new energy station in the vertex set V in the k-dimensional Euclidean space is obtained.

[0045] Preferably, in step S5, establishing coherent grouping constraints and frequency safety constraints according to the multi-type power grouping results includes:

[0046] According to the grouping of synchronous units, the power system is divided into N A There are islands, and the same group grouping constraints are constructed based on the islands. The expression is:

[0047]

[0048] In the formula, x i,k Indicates the 0-1 variable of node i partition. If x i,k =1, then node i belongs to the point in island k, otherwise x i,k = 0, node i does not belong to island k, x j,k represents the 0-1 variable of node j partition, if x j,k = 1, then node j belongs to the point in island k, otherwise x j,k = 0, node j does not belong to island k, i and j represent the nodes at both ends of line l, E represents the set of lines, U ij Represents the line partition 0-1 variable, indicating the connectivity status of branch (i, j). If U ij = 0, indicating that branch (i, j) is disconnected by decoupling, otherwise U ij =1, the branch is connected; z ij,k Represents auxiliary 0-1 variables;

[0049] Considering that the lowest frequency point and the highest frequency point are related to the inertia of the power system and the response of the generator speed governor, the frequency constraint is constructed to ensure that the power system has sufficient inertia and primary frequency response backup support after active decoupling to maintain the dynamic stability of the frequency of the island subsystem. The expression is:

[0050]

[0051] In the formula, They respectively represent the upper reserve of the primary frequency response of the generator when a power shortage occurs and the lower reserve of the primary frequency response of the generator when a power surplus occurs; They respectively represent the upper reserve of the primary frequency response of the new energy station when a power shortage occurs and the lower reserve of the primary frequency response of the new energy station when a power surplus occurs; Indicates the lowest frequency point when power shortage occurs; Indicates the highest frequency point when power surplus occurs; c i Indicates the power regulation rate of the generator or new energy station; H * k represents the equivalent inertia of island k, f 0 Indicates the rated frequency of the power system, Respectively represent the power surplus and deficit; f DB represents the dead zone frequency, w represents the new energy station node, Ω k represents the set of generators and new energy stations of island k;

[0052] In order to ensure that the frequency change rate of the island subsystem does not exceed its limit after decoupling, the surplus or shortage in the island is limited. The formula is:

[0053]

[0054] Where, RoCoF max Indicates the maximum frequency change rate allowed for power grid operation.

[0055] Preferably, in step S6, constructing an optimal section search model for island partitioning based on the homology constraint and the frequency constraint includes:

[0056] The objective function of the optimal section search model for power system islanding is established. The objective function takes the total load shedding of the cutting machine and the minimum cost of breaking the line as the objective function, and the expression is:

[0057] min∑ l∈E (1-U ij ) ij +∑ i∈D ΔP Di λ d ;

[0058] Where: ij represents the cost of opening the circuit, λ d Indicates the load shedding penalty coefficient; ΔP Di is the load shedding amount of island node i;

[0059] Considering the active and reactive balance equations of load shedding and power generation changes at each node, as well as the active and reactive output changes and load shedding range of generators and new energy stations, the node power balance constraint is established, and its expression is:

[0060]

[0061] Where P Gi , Q Gi They represent the active and reactive output of the generator during normal operation, P Wi Indicates the dispatching output of new energy stations during normal operation; P l , Q l Respectively represent the active and reactive power of branch l; P Di , Q Di Respectively represent the active and reactive loads of node i; Q c Represents the reactive dispatch value of capacitor bank c; Q srepresents the dispatch value of static VAR compensator s; ΔP Gi , ΔQ Gi Respectively represent the change in active and reactive output of the generator; ΔP Wi Indicates the change in the dispatch of new energy stations; E Ri 、E Oi Respectively represent the receiving end bus and the sending end bus of the transmission line; ΔP Gmax , ΔQ Gmax Indicates the maximum value of the active and reactive power changes of the generator; P Dmax Indicates the maximum load that can be removed; ΔP Wmax Indicates the maximum value of the adjustable range of the new energy station; establishes the line flow constraint, and its expression is:

[0062]

[0063] In the formula, M represents an arbitrarily large number, Represents auxiliary variables, U ij is the line switching variable, P ij represents the active power flowing through branch (i, j), G ij represents the conductance of branch (i, j), B ij The susceptance of the conductance of the path (i, j), V i 、V j Represent the voltage amplitude of node i and node j respectively, δ i and δ j They represent the voltage phase angles of node i and node j respectively;

[0064] Connectivity constraints are established. After the power system is actively decoupled, the islands formed are connected internally, but not connected to each other, and each node can only belong to one island. The expression is:

[0065]

[0066] Where: P l ' represents the active power of the virtual branch; P r ' ef It represents the active output of the virtual generator, and its value is greater than or equal to 1 to ensure that there are no isolated generator nodes in the island;

[0067] Establish the unbalanced power constraint within the island. The unbalanced power within the island is represented by the power surplus or deficit, and the expression is:

[0068]

[0069]

[0070] Where P Gi, P Wi , P Di They represent the output of the generator, new energy station and load power in the isolated island k respectively. It represents the unbalanced power size of island k, and δ is a binary variable, which represents the relationship between the power surplus and deficit in the island. The two cannot exist at the same time in an island.

[0071] Preferably, in step S6, a Cplex solver is used to solve the island partition optimal section search model to obtain the optimal solution section and the island partition result.

[0072] Therefore, the present invention adopts the above-mentioned high-proportion new energy power grid island division method taking into account frequency constraints, which has the following beneficial effects:

[0073] (1) The present invention uses node voltage phase angle information to accurately and effectively evaluate the synchronization characteristics of generators and new energy stations, thereby achieving synchronization grouping of multiple types of power sources;

[0074] (2) The present invention considers the impact of virtual inertia and power support of new energy stations on the optimal section search, ensuring the accuracy of the search results of the optimal section for island division;

[0075] (3) The island division method of the present invention takes into account frequency safety constraints and new energy support capabilities, and can be applied to actual high-proportion new energy power grids. The divided island power grids have sufficient frequency support capabilities to ensure the safe and stable operation of high-proportion new energy power grids.

[0076] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 is a flow chart of a method according to an embodiment of the present invention;

[0078] Figure 2 This is a schematic diagram of a primary frequency response mode of a high-proportion new energy power grid according to an embodiment of the present invention;

[0079] Figure 3 The modified IEEE39 node system topology diagram of the embodiment of the present invention;

[0080] Figure 4 It is a node voltage phase angle diagram of an embodiment of the present invention;

[0081] Figure 5 It is a normalized Laplace matrix eigenvalue graph of an embodiment of the present invention;

[0082] Figure 6 It is a normalized Laplace matrix eigenvalue gap diagram according to an embodiment of the present invention;

[0083] Figure 7 It is a three-dimensional spatial coordinate diagram of the generator and wind farm station according to an embodiment of the present invention.

[0084] Figure 8 This is a schematic diagram of island division without considering frequency safety constraints according to an embodiment of the present invention.

[0085] Fig. 9 This is a schematic diagram of island division in which frequency safety and stability constraints are taken into consideration and new energy sources participate in regulation according to an embodiment of the present invention. DETAILED DESCRIPTION

[0086] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0087] Example

[0088] Reference Figure 1 The present invention provides a method for islanding a high-proportion new energy power grid taking frequency constraints into account, the steps comprising:

[0089] S1. Based on the wide-area measurement device, the node voltage phase angle information of the generator and the new energy station is collected from the power system and the frequency deviation value Δf is calculated. i | t , calculate the cosine similarity CC between each power node according to the frequency deviation value ij , and obtain the coherent coupling matrix C of each power system generator and new energy station in the high-proportion new energy grid. Specifically including:

[0090] The frequency deviation phasor of the traditional generator can be expressed by formula (1):

[0091]

[0092] In the formula, δ represents the generator power angle, f 0 is the rated frequency; ω 0 is the rated angular frequency.

[0093] The extended dynamic synchronization identification method is used to describe the synchronization characteristics of the new energy station in the power system after being disturbed, which is similar to the traditional generator. That is, the node voltage phase angle information is used instead of the generator power angle. The frequency deviation value of the generator and the new energy station at a certain moment in the power system can be calculated by the voltage phase angle change rate. The formula is:

[0094]

[0095] Where Δf i | t Indicates the frequency deviation between the generator and the new energy station. is the voltage phase angle of node i, ω o represents the rated angular frequency, Δt represents the time interval, and t represents a certain moment.

[0096] Calculate the frequency deviation vector Δf between the generator and the new energy station within a certain period of time i , Δf i It is constructed by the frequency deviation values ​​at different times, and the formula is:

[0097]

[0098] Where N represents the number of generators and new energy station nodes in the power system.

[0099] Since there are differences in the frequency deviation vectors between the generator and the new energy station nodes, the cosine similarity is used as the coherent coupling index of the generator and the new energy station to determine the coherent group. The formula is:

[0100]

[0101] In the formula, CS ij Represents the coherent coupling degree between node i and node j.

[0102] According to the cosine similarity formula (4) and formula (5), the coherent coupling degree of each generator and the new energy station is calculated, and the coherent coupling degree matrix C of the system generator and the generator is obtained, which is:

[0103]

[0104] S2. According to the coherent coupling matrix C of the generator and the new energy station, the coherent information undirected graph G of the high-proportion new energy power grid is constructed, the weight matrix w of the coherent information undirected graph is calculated, and the normalized Laplace matrix L of the coherent information undirected graph is constructed. N . Specifically include:

[0105] The coherent undirected graph G = (V, E) is constructed using the coherent coupling degree between each generator and renewable energy station, where V represents the vertex set of G, corresponding to the set of generators and renewable energy stations in the power system; E represents the edge set of G, corresponding to the set of coherent coupling degrees between generators and renewable energy stations.

[0106] Based on the definition of homology information undirected graph G, the vertex weight and edge weight of the homology information undirected graph G are defined as:

[0107] w ii =CC ii =1 (7)

[0108] w ij =CS ij (8)

[0109] In the formula, w ii represents the vertex weight, w ij Represents edge weight; based on vertex weight and edge weight, the weight matrix w of the homology information undirected graph G is obtained.

[0110] According to the weight matrix of the homology information undirected graph G, a normalized Laplace matrix L is constructed to achieve graph segmentation of the homology information undirected graph G. The construction process is as follows:

[0111]

[0112] Where, L ij represents the elements in L, d i Represents the weight factor of vertex i in the homology information undirected graph G, d i The expression is:

[0113]

[0114] According to the non-normalized Laplacian matrix L constructed by formula (9), combined with the weight factor of vertex i, the normalized Laplacian matrix L of the homology information undirected graph G is further constructed: N Expressed as:

[0115]

[0116] Where D is the vertex weight factor d i The diagonal matrix formed.

[0117] S3, normalized Laplace matrix L N Perform eigenvalue analysis, calculate its eigenvalues ​​and eigenvectors, determine the number k of synchronized power system clusters based on the eigenvalues, and obtain the coordinate distribution of generators and new energy stations in k-dimensional Euclidean space based on the eigenvectors.

[0118] Specifically include:

[0119] The normalized Laplace matrix L N Perform eigenvalue analysis, calculate its eigenvalue and eigenvector, and according to the normalized Laplace matrix L N The maximum characteristic gap is used to determine the number of coherent clusters in the system. The formula is:

[0120] Δλ k =λ k -λ k-1 (12)

[0121] Where k is the normalized Laplace matrix L N The maximum characteristic gap Δλ max The corresponding value indicates the number of synchronized clusters;

[0122] Based on the number of coherent machines k, the normalized Laplace matrix L N The first k eigenvectors u of 1 、u 2 、···、u k The elements in are assigned to the elements in the vertex set V in the homology information undirected graph G by row, and the coordinate information of each generator and new energy station in the vertex set V in the k-dimensional Euclidean space is obtained, that is, (u 1i ,u 2i ,···,u ki ).

[0123] S4. Determine the composition of k groups of coherent generators through cluster analysis and inverse mapping of spatial coordinates, merge the coherent generators according to the actual operation scale limit of the power grid, and determine the final multi-type power source grouping result.

[0124] Specifically, in the k-dimensional space, a clustering algorithm is used to cluster the generators and new energy stations in the vertex set V into k categories, realizing the graph segmentation of the coherent information undirected graph G. The coherent clusters are merged according to the actual grid operation scale limit to determine the final multi-type power source grouping result N A .

[0125] S5. Establish coherent grouping constraints and frequency safety constraints based on the results of multi-type power grouping. Specifically:

[0126] Coherence grouping constraints

[0127] According to the grouping of synchronous units, the power system is divided into N A There are islands, and the same group grouping constraints are constructed based on the islands. The expression is:

[0128]

[0129] Among them, formula (13) indicates that each node can only belong to one island, and formula (14) determines whether nodes i and j belong to the same island, thereby determining the disconnection of the branch. Because it is the multiplication of two binary variables, formula (15) introduces the auxiliary variable z l,k After linearization, we finally get a linear expression. i,k Indicates the 0-1 variable of node i partition. If x i,k =1, then node i belongs to the point in island k, otherwise x i,k = 0, node i does not belong to island k, x j,k represents the 0-1 variable of node j partition, if x j,k = 1, then node j belongs to the point in island k, otherwise x j,k = 0, node j does not belong to island k, i and j represent nodes at both ends of line l, l represents line, E represents the set of lines, U ij Represents the line partition 0-1 variable, indicating the connectivity status of branch (i, j). If U ij = 0, indicating that branch (i, j) is disconnected by decoupling, otherwise U ij =1, the branch is connected; z ij,k Represents an auxiliary 0-1 variable.

[0130] Frequency safety constraints

[0131] The generator rotor motion equation considering the virtual inertia and power support of new energy is shown in formula (16):

[0132]

[0133] Where: f(t) is the system frequency; df(t) / dt is the frequency change rate; H * is the system equivalent inertia; P m (t), P w (t), P e (t) are the mechanical power, new energy power and electrical load of the system respectively.

[0134] like Figure 2 As shown in the figure, it is a schematic diagram of the primary frequency response model of a high-proportion renewable energy grid. From the figure, we can see that P m (t)+P w (t)-P e (t), based on this formula, equation (16) is nadir Integrate in the interval, t nadir Represents the moment of the lowest frequency, we can get:

[0135]

[0136] Formula (17) is a formula that converts the lowest frequency point fnadir With the system rated frequency f 0 、Power shortage amount P l , System speed regulator dead time t db And the algebraic expression related to the system climbing rate C, according to which the minimum climbing rate of the power system can be obtained:

[0137]

[0138] Since the speed regulator has a dead zone f db , at the first moment of power shortage, the system frequency is driven only by the system inertia response, so the dead time t db and speed regulator dead zone f db The following relationship exists:

[0139]

[0140] Substituting equation (19) into equation (18), the primary frequency response constraint of a single generator or new energy station is obtained as:

[0141]

[0142] In order to ensure that the system has sufficient inertia and primary frequency response backup support after active decoupling to maintain the dynamic stability of the frequency, the relevant constraints of frequency stability are modeled based on the above derivation conclusions.

[0143] Considering that the lowest frequency point and the highest frequency point are related to the inertia of the power system and the response of the generator speed governor, the sufficient conditions for satisfying the primary frequency response criterion after a fault are obtained according to the inference equations (20) and (21) in the previous text, and the frequency constraint is constructed, which is expressed as follows:

[0144]

[0145] Wherein, equations (22) and (23) ensure that the primary frequency response reserve of each generator or renewable energy station can be provided when or before the lowest or highest frequency point occurs; equations (24) and (25) require that the primary frequency response reserve capacity of the synchronous group should fully cover the surplus or shortage remaining in the island after decoupling. They respectively represent the upper reserve of the primary frequency response of the generator when a power shortage occurs and the lower reserve of the primary frequency response of the generator when a power surplus occurs; They respectively represent the upper reserve of the primary frequency response of the new energy station when a power shortage occurs and the lower reserve of the primary frequency response of the new energy station when a power surplus occurs; Indicates the lowest frequency point when power shortage occurs; Indicates the highest frequency point when power surplus occurs; c iH is the power regulation rate of the generator or new energy station; * k is the equivalent inertia of island k, f 0 Indicates the rated frequency of the power system, Respectively represent the power surplus and deficit; f DB represents the dead zone frequency, w represents the new energy station node, Ω k represents the set of generators and new energy stations of island k;

[0146] After the disturbance of power shortage occurs, the frequency change rate of the system is proportional to the actual shortage and inversely proportional to the system equivalent inertia. In order to ensure that the frequency change rate of the island subsystem does not exceed its limit after decoupling, the surplus or shortage in the island is limited according to equations (26) and (27), as shown below:

[0147]

[0148] Where, RoCoF max Indicates the maximum frequency change rate limit allowed for power grid operation.

[0149] S6. Based on the coherent grouping constraints and frequency constraints, an optimal section search model for island partitioning is constructed, and the optimal section search model for island partitioning is solved to obtain the optimal solution section and the island partitioning result. Specifically, it includes:

[0150] The objective function of the optimal section search model for power system islanding is established. The objective function takes the sum of load shedding and line disconnection cost as the minimum, and the expression is:

[0151] min∑ l∈E (1-U ij ) ij +∑ i∈D ΔP Di λ d (28)

[0152] Where: ij represents the cost of opening the circuit, λ d Indicates the load shedding penalty coefficient; ΔP Di is the load shedding amount of island node i.

[0153] Node power balance constraints

[0154] Considering the active and reactive balance equations of load shedding and power generation changes at each node, as well as the active and reactive output changes and load shedding range of generators and new energy stations, the node power balance constraint is established, and its expression is:

[0155]

[0156] Where P Gi , Q Gi They represent the active and reactive output of the generator during normal operation, P Wi Indicates the dispatching output of new energy stations during normal operation; P l , Q l Respectively represent the active and reactive power of branch l; P Di , Q Di Respectively represent the active and reactive loads of node i; Q c Represents the reactive dispatch value of capacitor bank c; Q s represents the dispatch value of static VAR compensator s; ΔP Gi , ΔQ Gi Respectively represent the change in active and reactive output of the generator; ΔP Wi Indicates the change in the dispatch output of the new energy station; E Ri 、E Oi Respectively represent the receiving end bus and the sending end bus of the transmission line; ΔP Gmax , ΔQ Gmax Indicates the maximum value of the active and reactive power changes of the generator; P Dmax Indicates the maximum load that can be removed; ΔP Wmax Indicates the maximum value of the adjustable range of the new energy station.

[0157] Line power flow constraints

[0158] Establish line flow constraints, the expression is:

[0159]

[0160] In the formula, M represents an arbitrarily large number, Represents auxiliary variables, U ij is the line switching variable, P ij represents the active power flowing through branch (i, j), G ij represents the conductance of branch (i, j), B ij The susceptance of the conductance of the path (i, j), V i 、V j Represent the voltage amplitude of node i and node j respectively, δ i and δ j They represent the voltage phase angles at node i and node j respectively.

[0161] Connectivity constraints

[0162] Connectivity constraints are established. After the power system is actively decoupled, the islands formed are connected internally, but not connected to each other, and each node can only belong to one island. The model can be determined and constructed by the single commodity flow method. Its principle and specific method are as follows: First, a virtual assumption is made on the network, assuming that there is only one generator node in each island, and the other nodes are load nodes with a per-unit value of 1pu. If each island satisfies the virtual active power balance constraint, it means that there is a path from the generator node to all other nodes in the corresponding island, which can ensure the internal connectivity of the island. The expression is:

[0163]

[0164] Where P l ' represents the active power of the virtual branch; P r ' ef It represents the active output of the virtual generator. Its value is greater than or equal to 1 to ensure that there are no isolated generator nodes in the island.

[0165] Unbalanced power constraints within an island

[0166] The unbalanced power constraint in the island is established. The unbalanced power in the island is represented by the power surplus or deficit. The power surplus represents the part where the power generation of the generator and renewable energy in the island is greater than the load, and the power deficit represents the part where the power generation of the generator and renewable energy in the island is less than the load. Formula (35) represents the unbalanced power in the island, and formula (36) ensures that there cannot be a surplus and a deficit in an island at the same time. The expression is:

[0167]

[0168] Where P Gi , P Wi , P Di They represent the output of the generator, new energy station and load power in the isolated island k respectively. It represents the unbalanced power size of island k, and δ is a binary variable, which represents the relationship between the power surplus and deficit in the island. The two cannot exist at the same time in an island.

[0169] Finally, based on the coherent grouping constraints, frequency constraints and other constraints on power system operation, the solver Cplex is used to solve the optimal section search model for island partitioning, obtain the optimal decoupling section, and get the island partitioning result.

[0170] The method of the present invention is verified in combination with a specific example. The modified IEEE-39 node system is used as an example for simulation analysis and verification. The topology diagram of the modified IEEE-39 node system is shown in FIG. Figure 3 Shown

[0171] The modified IEEE39 node system topology is shown in the figure below: Figure 3 As shown in Figure 1, it includes 6 generator sets, 4 new energy stations and 46 branches. The new energy station takes the wind farm station as an example. The generators at nodes 32, 34, 35 and 37 are replaced by wind farms of equal capacity respectively. Generator G2 is used as the reference machine to simulate a situation that causes the system to collapse after a disturbance: at 0s, a three-phase permanent fault is set on an AC branch between nodes 16 and 17 near node 17. The fault lasts for 0.3s. After 0.3s, the fault line is removed. The entire simulation time lasts for 5s. The relative movement trend of the bus voltage phase angle during this period is shown in Figure 11. Figure 4 shown.

[0172] by Figure 4 The voltage phase angle with a time window of 0.3 to 5 s is used as the input of the method proposed in the present invention. The input signal is first standardized. Then, the coherence coupling matrix C of the generator and the wind farm is calculated by equations (4) and (5). The weight matrix w of the coherence information undirected graph G is constructed according to equations (7) and (8) based on the calculated coherence coupling matrix C. Based on the obtained weight matrix w, the unnormalized Laplace matrix L of the coherence information undirected graph G is constructed according to equation (9). Based on the obtained unnormalized Laplace matrix L, the normalized Laplace matrix L of the coherence information undirected graph G is further calculated by equation (11): N . Then perform eigenvalue analysis, and the eigenvalue results are as follows Figure 5 As shown, the eigenvalue gap results are Figure 6 According to the method proposed in step S3, the normalized Laplace matrix L is calculated. N The maximum eigenvalue gap of , and then determine the number of coherent groups. Obviously, by Figure 6 It can be seen that: L N The maximum characteristic gap is Δλ 3 , therefore, the optimal number of coherent clusters k for the system is 3.

[0173] According to the determined optimal number of coherent clusters 3 and L N The corresponding first three eigenvectors determine the geometric coordinate positions of the generator and wind farm in the 3D Euclidean space. The results are as follows: Figure 7 As shown. Further, according to the calculated spatial distribution of each generator, the generators and wind farms are clustered, the number of clusters is 3, and finally three groups of synchronous clusters are obtained. The results are shown in Table 1, which are synchronous cluster 1, which consists of generators G4, G7, G9 and wind farm stations G5 and G6; synchronous cluster 2, which consists of generator G1 and wind farm stations G3 and G8; synchronous cluster 3, which consists of generator G10. Obviously, this result is consistent with Figure 4The observed voltage phase angle change trends of the generator and the new energy station under fault conditions are consistent, which verifies the correctness and effectiveness of the multi-type power grouping method proposed in the embodiment.

[0174] Table 1. Coherent cluster identification results

[0175] Synchronous Cluster unit 1 G4, G5, G6, G7, G9 2 G1, G3, G8 3 G10

[0176] According to the coherent identification results, coherent cluster 3 has only one generator. Due to the size of the power system, it is difficult to maintain stable operation after dividing it into isolated subsystems. Figure 4 It can be seen that the node voltage phase angle variation law of G10 is similar to that of synchronous group 2, so synchronous group 2 is merged with synchronous group 3, and finally the generator and wind farm are divided into two groups, namely: {G1-G3, G8-G10} and {G4-G7, G9}. Further, according to the division results of generators and new energy stations, the optimal decoupling section search in island division is carried out, and the rated frequency of the power grid is set to 50Hz, the lowest frequency point is set to 49.5Hz, and the speed regulator dead zone f db =20mHz, and the maximum value of RoCoF is set to 0.8Hz / s. In order to verify the effectiveness of the proposed optimal split section search model and analyze the impact of the primary frequency response on the optimal split section search results, two examples are set up for analysis and simulation.

[0177] Example 1, the island division method without considering the frequency security and stability constraints; Example 2 considers the frequency security and stability constraints and the island division method of new energy participating in the regulation. Through optimization solution, the search results of the split section of Example 1 and Example 2 are shown in Table 2. Including split section, unbalanced power, power generation change and load shedding.

[0178] Table 2 Search results for the decomposition section

[0179]

[0180]

[0181] In Example 1, the power flow impact caused by system decoupling is 419.96MW. From Table 2, it can be seen that the total power generation of Island 1 is 270.40MW less than the total load, which is an island with power generation shortage. Therefore, it is necessary to cut off the excess load to maintain power balance, that is, it is necessary to cut off 146.65MW and 123.75MW of load at BUS-20 and BUS-23 nodes respectively. Similarly, the total power generation of Island 2 is 270.40MW more than the total load, which is an island with surplus power generation. Therefore, it is necessary to adjust the generator output to maintain power balance, that is, the output of G1 and G10 generators needs to be reduced by 126.13MW and 144.27MW respectively. In Example 2, since the regulating effect of the primary frequency response characteristics of the generator and wind farm on the system frequency is taken into account, under the relevant constraints of system frequency safety, the unbalanced power of island 1 and island 2 is relatively small, and the upper and lower reserves of the primary frequency response of each generator and wind farm can balance the power shortage or surplus of the corresponding island. However, the flow impact caused by the corresponding system decoupling increases to 558.12MW. It can be seen from Table 2 that Island 1 is an island with a power generation capacity greater than the load capacity, with a surplus of 49.6MW of power generation, and the reserve capacity under the primary frequency response of the wind farm G5 on the island reduces this part of the power surplus. In Island 2, there will be an additional 49.6MW of load after the island is divided. The power shortage in the island is jointly supported by the upper reserve capacity of the primary frequency response of G2 and G4 to reduce the load shedding. Since the present invention does not consider the loss of the transmission line, the two islands in Example 1 and Example 2 have the same unbalanced power. Finally, the final island division results of Example 1 and Example 2 are as follows. Figure 8 and Fig. 9 As shown, the effectiveness of the method for islanding the new energy power grid with improved proportions provided by the present invention is verified.

[0182] Therefore, the present invention adopts the above-mentioned method for islanding a high-proportion new energy power grid taking into account frequency constraints. By considering frequency safety constraints and new energy support capabilities, a search model for the optimal section for islanding is constructed, thereby ensuring the accuracy of the search results for the optimal section for islanding.

[0183] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for isolating a high-proportion renewable energy grid taking frequency constraints into account, characterized in that the steps include: S1. Based on the wide-area measurement device, the node voltage phase angle information of the generator and the new energy station is collected from the power system and the frequency deviation value is calculated. The cosine similarity between each power node is calculated according to the frequency deviation value to obtain the coherent coupling matrix of each power system generator and new energy station in the high-proportion new energy grid; S2. According to the obtained coherent coupling degree matrix of the generator and the new energy station, a coherent information undirected graph of the high-proportion new energy power grid is constructed, a weight matrix of the coherent information undirected graph is calculated, and a normalized Laplace matrix of the coherent information undirected graph is constructed; S3. Perform eigenvalue analysis on the normalized Laplace matrix, calculate its eigenvalue and eigenvector, determine the number of synchronous generators in the power system according to the eigenvalue, and obtain the coordinate distribution of the generator and the new energy station in the Euclidean space according to the eigenvector; S4. Determine the composition of the coherent cluster through cluster analysis and inverse mapping of spatial coordinates, merge the coherent clusters according to the actual grid operation scale limit, and determine the final multi-type power source grouping result; S5. Establish coherent grouping constraints and frequency safety constraints based on the multi-type power grouping results; S6. Based on the coherent grouping constraints and frequency constraints, an optimal section search model for island partitioning is constructed, and the optimal section search model for island partitioning is solved to obtain the optimal solution section and the island partitioning result.

2. A method for islanding a high-proportion renewable energy grid taking frequency constraints into account according to claim 1, characterized in that: Step S1 specifically includes: The extended dynamic synchronization identification method is used to describe the synchronization characteristics of the new energy station in the power system that are similar to the generator after being disturbed. The frequency deviation value of the generator and the new energy station at a certain moment in the power system is calculated by the voltage phase angle change rate. The formula is: Where Δf i | t Indicates the frequency deviation between the generator and the new energy station. is the voltage phase angle of node i, ω o represents the rated angular frequency, Δt represents the time interval, and t represents a certain moment; Calculate the frequency deviation vector Δf between the generator and the new energy station within a certain period of time i , Δf i It is constructed by the frequency deviation values ​​at different times, and the formula is: In the formula, N represents the number of generators and new energy station nodes; According to the difference in frequency deviation vectors between the generator and the new energy station nodes, the cosine similarity between the power supply nodes is calculated, and then the synchronous group is determined. The formula is: In the formula, CC ij Represents cosine similarity, CS ij It represents the coherent coupling degree between the power supply of node i and the power supply of node j; The coherent coupling degree of each generator and the new energy station is calculated according to the cosine similarity, and the coherent coupling degree matrix C of the system generator and the generator is obtained. The formula is:

3. A method for islanding a high-proportion new energy power grid taking frequency constraints into account according to claim 2, characterized in that: In step S2, the coherent information undirected graph G=(V,E) of the high-proportion renewable energy power grid, where V represents the vertex set of G, corresponding to the set of generators and renewable energy stations in the power system; E represents the edge set of G, corresponding to the set of coherent coupling degrees between the generators and renewable energy stations.

4. The method for islanding a high-proportion new energy power grid taking frequency constraints into account according to claim 3 is characterized in that: In step S2, the weight matrix of the homology information undirected graph is calculated, and the normalized Laplace matrix of the homology information undirected graph is constructed, including: Based on the homology information undirected graph G, the vertex weight and edge weight of the homology information undirected graph G are defined as: w ii =CC ii =1; w ij =CS ij ; In the formula, w ii represents the vertex weight, w ij represents edge weight; Based on vertex weights and edge weights, the weight matrix of the homology information undirected graph G is obtained; The non-normalized Laplace matrix L is constructed according to the weight matrix of the homology information undirected graph G. The construction process includes: Where, L ij represents the elements in L, d i Represents the weight factor of vertex i in the homology information undirected graph G, d i The expression is: Combined with the weight factor of vertex i, the normalized Laplacian matrix is ​​further expressed as: Where D is the vertex weight factor d i The diagonal matrix formed.

5. A method for islanding a high-proportion renewable energy grid taking frequency constraints into account according to claim 4, characterized in that: Step S3 includes: The normalized Laplace matrix L N Perform eigenvalue analysis, calculate its eigenvalue and eigenvector, and according to the normalized Laplace matrix L N The maximum characteristic gap is used to determine the number of coherent clusters in the system. The formula is: Dl k =λ k -l k-1 ; Where k is the normalized Laplace matrix L N The maximum characteristic gap Δλ max The corresponding value indicates the number of synchronized clusters; Based on the number of coherent machines k, the normalized Laplace matrix L N The first k eigenvectors u1, u2, ···, u k The elements in are assigned to the elements in the vertex set V in the homology information undirected graph G by row, and the coordinate information of each generator and new energy station in the vertex set V in the k-dimensional Euclidean space is obtained.

6. A method for islanding a high-proportion renewable energy grid taking frequency constraints into account according to claim 5, characterized in that: In step S5, establishing coherent grouping constraints and frequency safety constraints according to the multi-type power grouping results includes: According to the grouping of synchronous units, the power system is divided into N A There are islands, and the same group grouping constraints are constructed based on the islands. The expression is: In the formula, x i,k Indicates the 0-1 variable of node i partition. If x i,k =1, then node i belongs to the point in island k, otherwise x i,k = 0, node i does not belong to island k, x j,k represents the 0-1 variable of node j partition, if x j,k = 1, then node j belongs to the point in island k, otherwise x j,k = 0, node j does not belong to island k, i and j represent the nodes at both ends of line l, E represents the set of lines, U ij Represents the line partition 0-1 variable, indicating the connectivity status of branch (i, j). If U ij = 0, indicating that branch (i, j) is disconnected by decoupling, otherwise U ij =1, the branch is connected; z ij,k Represents auxiliary 0-1 variables; Considering that the lowest frequency point and the highest frequency point are related to the inertia of the power system and the response of the generator speed governor, the frequency constraint is constructed to ensure that the power system has sufficient inertia and primary frequency response backup support after active decoupling to maintain the dynamic stability of the frequency of the island subsystem. The expression is: In the formula, They respectively represent the upper reserve of the primary frequency response of the generator when a power shortage occurs and the lower reserve of the primary frequency response of the generator when a power surplus occurs; They respectively represent the upper reserve of the primary frequency response of the new energy station when a power shortage occurs and the lower reserve of the primary frequency response of the new energy station when a power surplus occurs; Indicates the lowest frequency point when power shortage occurs; Indicates the highest frequency point when power surplus occurs; c i Indicates the power regulation rate of the generator or new energy station; H * k represents the equivalent inertia of island k, f0 represents the rated frequency of the power system, Respectively represent the power surplus and deficit; f DB represents the dead zone frequency, w represents the new energy station node, Ω k represents the set of generators and new energy stations of island k; In order to ensure that the frequency change rate of the island subsystem does not exceed its limit after decoupling, the surplus or shortage in the island is limited. The formula is: Where, RoCoF max Indicates the maximum frequency change rate allowed for power grid operation.

7. A method for dividing isolated islands of a high-proportion renewable energy power grid taking frequency constraints into account according to claim 6, characterized in that: In step S6, based on the coherence constraint and the frequency constraint, constructing the optimal section search model for island partitioning includes: The objective function of the optimal section search model for power system islanding is established. The objective function takes the total load shedding of the cutting machine and the minimum cost of breaking the line as the objective function, and the expression is: min∑ l∈E (1-U ij )l ij +∑ i∈D ΔP Di l d ; Where: ij represents the cost of opening the circuit, λ d Indicates the load shedding penalty coefficient; ΔP Di is the load shedding amount of island node i; Considering the active and reactive balance equations of load shedding and power generation changes at each node, as well as the active and reactive output changes and load shedding range of generators and new energy stations, the node power balance constraint is established, and its expression is: Where P Gi , Q Gi They represent the active and reactive output of the generator during normal operation, P Wi Indicates the dispatching output of new energy stations during normal operation; P l , Q l Respectively represent the active and reactive power of branch l; P Di , Q Di Respectively represent the active and reactive loads of node i; Q c Represents the reactive dispatch value of capacitor bank c; Q s represents the dispatch value of static VAR compensator s; ΔP Gi , ΔQ Gi Respectively represent the change in active and reactive output of the generator; ΔP Wi Indicates the change in the dispatch of new energy stations; E Ri 、E Oi Respectively represent the receiving end bus and the sending end bus of the transmission line; ΔP Gmax , ΔQ Gmax Indicates the maximum value of the active and reactive power changes of the generator; P Dmax Indicates the maximum load that can be removed; ΔP Wmax Indicates the maximum value of the adjustable range of the new energy station; Establish line flow constraints, the expression is: In the formula, M represents an arbitrarily large number, Represents auxiliary variables, U ij is the line switching variable, P ij represents the active power flowing through branch (i, j), G ij represents the conductance of branch (i, j), B ij The susceptance of the conductance of the path (i, j), V i 、V j Represent the voltage amplitude of node i and node j respectively, δ i and δ j They represent the voltage phase angles of node i and node j respectively; Connectivity constraints are established. After the power system is actively decoupled, the islands formed are connected internally, but not connected to each other, and each node can only belong to one island. The expression is: Where: P′ l Represents the active power of the virtual branch; P′ ref It represents the active output of the virtual generator, and its value is greater than or equal to 1 to ensure that there are no isolated generator nodes in the island; Establish the unbalanced power constraint within the island. The unbalanced power within the island is represented by the power surplus or deficit, and the expression is: Where P Gi , P Wi , P Di They represent the output of the generator, new energy station and load power in the isolated island k respectively. It represents the unbalanced power size of island k, and δ is a binary variable, which represents the relationship between the power surplus and deficit in the island. The two cannot exist at the same time in an island.

8. The method for islanding a high-proportion renewable energy grid taking frequency constraints into account according to claim 7, characterized in that: In step S6, the solver Cplex is used to solve the optimal section search model for island partitioning, obtain the optimal solution section, and obtain the island partitioning result.

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