System frequency response analysis method based on electromechanical wave propagation characteristics

Abstract

An electromechanical wave propagation characteristic-based system frequency response analysis method comprises the following steps of: firstly, setting a power vacancy disturbance point, calculating a turning frequency omega ci and a propagation coefficient PC between a disturbance source point and a generator node, and screening out a generator influenced by electromechanical disturbance; and then, according to the propagation coefficient, determining whether the generator node is influenced by electromechanical disturbance, screening out the generator influenced by the electromechanical disturbance, calculating a compound electromechanical distance # imgabs0 # between the disturbance source point and the generator node j influenced by the disturbance, and performing hierarchical clustering on the system according to the compound electromechanical distance # imgabs1 #. According to the method, a power system is divided into a research area (affected by electromechanical disturbance and participating in frequency modulation) and an external area (not affected by electromechanical disturbance and only performing power transmission), parameters of generators in the research area are aggregated, a system equivalent frequency response model is established, and frequency response analysis is performed on the research area. The method provides effective measures for simplifying modeling and analysis of frequency response of a complex power system.

Description

Technical Field

[0001] The present invention relates to the technical field of system frequency response analysis, and particularly to a system frequency response analysis method based on the characteristics of electromechanical wave propagation. Background Art

[0002] Modern power systems are highly complex, dynamically interconnected non-linear power systems, and their operation is always affected by various stochastic disturbances. The disturbances cause electromechanical dynamic phenomena such as rotor angle deviation and frequency fluctuations of generators, and propagate in the system in the form of approximate electromechanical waves. The propagation characteristics of electromechanical waves will affect the frequency security of the power grid. The disturbance energy will exponentially decay with the increase of electrical distance during the propagation process, resulting in an obvious localization characteristic in the spatial distribution of dynamic responses. Research shows that the influence range of electromechanical waves is usually limited to a finite area centered on the disturbance source, and its energy decay can be described by an exponential function. However, the existing system frequency response (SFR) analysis methods have obvious limitations. The traditional SFR model is based on the lumped parameter assumption, lumps the inertia of the whole network equivalently into a single inertia center, and assumes that the frequency dynamics have global consistency. This simplified modeling method cannot accurately reflect the influence of the disturbance source location on the frequency propagation path, nor can it accurately evaluate the transfer characteristics of the frequency support ability between regions.

[0003] In view of the above limitations, it is both technically difficult and practically unnecessary to study the dynamic frequency response characteristics of a complete complex modern power system. Therefore, in modern power systems, considering the spatial characteristics of electromechanical wave propagation, a system frequency response analysis method based on the characteristics of electromechanical wave propagation is particularly important for simplifying the complexity of frequency response analysis and reducing the calculation scale. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a system frequency response analysis method based on the characteristics of electromechanical wave propagation. This method first analyzes the influence degree of the components in the system affected by electromechanical wave disturbances and the response speed to the disturbances, then calculates the corner frequency and the composite electromechanical distance of each node in the system, and performs hierarchical clustering on the system, so as to divide the system into a research area and an external area, and then conducts a system frequency response analysis on the research area. Thus, it effectively simplifies the complexity of system frequency response analysis and reduces the calculation scale.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A system frequency response analysis method based on the characteristics of electromechanical wave propagation includes the following steps:

[0007] Step 1: Set a power deficit disturbance point, and calculate the corner frequency ω ci between the disturbance source point and the generator node

[0008] Step 2: Determine whether the generator node is affected by the electromechanical disturbance according to the propagation coefficient PC;

[0009] Step 3: Screen out the generators affected by the electromechanical disturbance, and calculate the composite electromechanical distance between the disturbance source point and the generator node j affected by the disturbance

[0010] Step 4: According to the composite electromechanical distance Perform hierarchical clustering on the power system, and accordingly divide the power system into a research area and an external area, and aggregate the parameters of each generator in the research area;

[0011] Step 5: Establish a system equivalent frequency response model and calculate the research area frequency.

[0012] In the said Step 1, the power system is regarded as a grid continuum model of unevenly continuously distributed generators, lines and loads. In the grid continuum model, the relationship between the electromechanical wave propagation speed and the inertia:

[0013]

[0014] In Equation (1), v is the electromechanical wave propagation speed; ω is the generator angular frequency; U is the per-unit value of the voltage amplitude; Δx is the distance between two nodes; z is the per-unit impedance of the line; h is the inertia per unit length.

[0015] In a discrete power system, the electromechanical wave exists in a finite frequency range, and this range is related to the generator moment of inertia and the system line impedance. It is represented by the turning frequency ω c as follows:

[0016]

[0017] When the frequency of the electromechanical wave signal is greater than the turning frequency ω c , the amplitude of the electromechanical wave will rapidly decay along the propagation direction; when the frequency of the electromechanical wave signal is greater than 3 times the turning frequency ω c , the amplitude of the electromechanical wave decays to zero, and at this time the disturbance energy will no longer be able to propagate.

[0018] Set the propagation coefficient PC = Δω / ω c , where Δω is the increment of the generator rotor angular frequency. The larger the propagation coefficient PC, the smaller the influence of the generator at this node by the electromechanical disturbance. When the propagation coefficient PC is greater than 3, the generator will not be affected by the electromechanical disturbance. In the said Step 3, based on the absolute quantity of the propagation time of the electromechanical disturbance between any two points, the composite electromechanical distance is defined The composite electromechanical distance represents the increment of the power angle θ that the generator turns through when it makes a uniformly accelerated or decelerated motion with a constant initial acceleration after the disturbance appearsi The required time, i.e.:

[0019]

[0020] In the formula: is the composite electromechanical distance, with the unit of second; w is the error correction factor; M i is the rotor inertia constant of generator node i; B is the transfer susceptance; def represents definition, that is, defining the composite electromechanical distance

[0021] Between generator node i and generator node j, since Bij = Bji, but generally M i ≠M j , so it can be seen that the electromechanical distance is directional. For an actual power system, it is difficult to determine the propagation direction of electromechanical disturbances. Therefore, an electromechanical distance without direction is set That is, the average value of the electromechanical distance between the generator disturbance source node i and generator node j is:

[0022]

[0023] In the formula: represents the average value of the electromechanical distance between node i and node j when the disturbance source point is i; represents the average value of the electromechanical distance between node j and node i when the disturbance source point is j; represents the electromechanical distance between node i and node j when the disturbance source point is i; represents the electromechanical distance between node j and node i when the disturbance source point is j; B ij represents the transfer susceptance between node i and node j when the disturbance source point is i; B ji represents the transfer susceptance between node j and node i when the disturbance source point is j.

[0024] Under the action of the same electromechanical wave disturbance, the larger the inertia M i of the generator, the smaller the rotor acceleration of the generator under the action of the system accelerating power, the greater the obstacle to the propagation of the electromechanical wave, and the greater the electromechanical distance; similarly, when the transfer admittance B ij between the disturbance source point and the generator node is larger, the greater the accelerating power obtained by the generator, the greater the rotor acceleration of the generator, the greater the influence of the generator on the electromechanical wave disturbance, the smaller the obstacle to the propagation of the electromechanical wave, and the smaller the electromechanical distance. When an electromechanical disturbance occurs, the smaller the electromechanical distance, the faster the generator response speed and the closer the connection between the two machines.

[0025] In step 4, the part of the power system in the research area is affected by the electromechanical disturbance and participates in frequency regulation; the part of the power system in the external area is not affected by the electromechanical disturbance and only conducts power transmission;

[0026] Perform hierarchical clustering on the power system, and divide the power system into a research area and an external area according to the hierarchical clustering results, as Figure 4 shown. Before the division, the generators in both the research area and the external area can participate in frequency regulation through tie lines. After the division, the generators in the external area only perform power transmission and do not participate in frequency regulation;

[0027] Perform parameter aggregation on the steam turbines in the research area. The parameter aggregation of the steam turbines in the research area is described by the following equations (5) to (9).

[0028] Among them, the mechanical power increment of the steam turbine-governor model is:

[0029]

[0030] In equation (5): ΔP mT (s) is the mechanical power increment; F H is the proportion of the high-pressure turbine stage power; T R is the reheater time constant; R T is the steam turbine droop coefficient; T C is the air volume time constant; T G is the air chamber time constant; s is the complex frequency domain variable in the Laplace transform; Δω s (s) is the angular frequency increment.

[0031] Suppose there are N synchronous machines in the power system. Since the steam turbine droop coefficient R T is related to the rated capacity S N , the constant gain for multiple steam turbine-governors is:

[0032]

[0033] In equation (6): S Ni is the rated power of synchronous machine i; S sys is the rated power of the entire system; K mi represents the proportion of the rated power of synchronous machine i in the rated power of the entire system;

[0034] The equivalent droop coefficient R of the power system is:

[0035]

[0036] Among them, the equivalent gain is defined as κ i = K mi / R Ti , R Ti is the droop coefficient of the i-th steam turbine.

[0037] As can be seen from Equation (5), the mechanical power increment of the turbine-governor model is affected by T G 、T C 、T R and F H and other four parameters. To simplify the description, Equation (7) defines the normalized gain λ i to represent the comprehensive effect of the turbine-governor of the synchronous machine i;

[0038]

[0039] In step 5, according to Equations (5) to (8), the transfer functions of multiple synchronous machines are aggregated into an equivalent machine transfer function as follows:

[0040]

[0041] According to Equation (9), a power system frequency response aggregation equivalent model of the research area is established. As Figure 5 shown, the parameters of i turbines ( Figure 5 in the upper red frame of the figure) are aggregated and equivalent to 1 turbine ( Figure 5 in the lower red frame of the figure).

[0042] The technical effects of a system frequency response analysis method based on the characteristics of electromechanical wave propagation according to the present invention are as follows:

[0043] 1) For a complete complex modern power system, by applying the method proposed by the present invention, a simplified research area is used to equivalently replace the modern power system, so that the frequency response results of the research area are consistent with the frequency response results of the complex power system. This method provides an effective measure for simplifying the frequency response modeling and analysis of complex power systems.

[0044] 2) In step 1 of the present invention, a power deficit disturbance point is set, and the turning frequency ω ci and the propagation coefficient PC between the disturbance source point and the generator node are calculated, and the generators affected by electromechanical disturbances are screened out, providing a basis for calculating the composite electromechanical distance.

[0045] 3) In step 2 of the present invention, it is determined whether the generator node is affected by electromechanical disturbances according to the propagation coefficient. In step 3, the generators affected by electromechanical disturbances are screened out, and the composite electromechanical distance between the disturbance source point and the affected generator node j is calculated, providing a basis for step 4 to perform hierarchical clustering.

[0046] 4) In step 4 of the present invention, according to the composite electromechanical distance Perform hierarchical clustering on the system, and accordingly divide the power system into a research area (affected by electromechanical disturbances and participating in frequency regulation) and an external area (not affected by electromechanical disturbances and only performing power transmission). Aggregate the parameters of each generator in the research area to provide a basis for establishing a frequency response model in step 5.

[0047] 5) In step 5 of the present invention, an equivalent frequency response model of the system is established, and frequency response analysis is performed on the research area, which can effectively simplify the complexity of the system frequency response analysis and reduce the calculation scale. Brief Description of the Drawings

[0048] The present invention will be further described below with reference to the drawings and embodiments:

[0049] Figure 1 It is a flowchart of an embodiment of the present invention.

[0050] Figure 2 It is a simulation system diagram of an embodiment of the present invention.

[0051] Figure 3 It is a diagram of the hierarchical clustering result.

[0052] Figure 4 It is a schematic diagram of the division of the research area and the external area.

[0053] Figure 5 It is an aggregated equivalent model of the power system frequency response.

[0054] Figure 6 It is a frequency response curve of the research area. Detailed Embodiment

[0055] For the system frequency response modeling method based on the characteristics of electromechanical wave propagation, first set the power deficit disturbance point, and calculate the turning frequency ω between the disturbance source point and the generator node ci and the propagation coefficient PC, and screen out the generators affected by electromechanical disturbances. Then, determine whether the generator node is affected by electromechanical disturbances according to the propagation coefficient, screen out the generators affected by electromechanical disturbances, and calculate the composite electromechanical distance between the disturbance source point and the affected generator node j Then, according to the composite electromechanical distance Perform hierarchical clustering on the system, and accordingly divide the power system into a research area (affected by electromechanical disturbances and participating in frequency regulation) and an external area (not affected by electromechanical disturbances and only performing power transmission). Aggregate the parameters of each generator in the research area, establish an equivalent frequency response model of the system, and perform frequency response analysis on the research area. Finally, the effectiveness of the method and results is verified through the IEEE 10-machine 39-bus test system.

[0056] The flowchart of the present invention is as Figure 1 shown, and includes the following steps:

[0057] Step 1: Set the power deficit disturbance point and calculate the turning frequency ω between the disturbance source point and the generator node ci and the propagation coefficient PC:

[0058] Due to the uneven distribution of the structure and parameters of the actual power system, considering the propagation characteristics of the electromechanical disturbance load, the geographically wide-area distributed power system is regarded as a grid continuum model of unevenly continuously distributed generators, lines and loads. In this grid continuum model, the relationship between the propagation speed and inertia of the electromechanical wave:

[0059]

[0060] In formula (1), v is the propagation speed of the electromechanical wave; ω is the angular frequency of the generator; U is the per-unit value of the voltage amplitude; Δx is the distance between two nodes; z is the per-unit impedance of the line; h is the inertia per unit length.

[0061] However, in a discrete power system, the electromechanical wave can only exist within a limited frequency range, which is related to the generator moment of inertia and the system line impedance, and is represented by the turning frequency ω c as:

[0062]

[0063] When the frequency of the electromechanical wave signal is greater than the turning frequency, the amplitude of the electromechanical wave along the propagation direction will rapidly decay. When the frequency of the electromechanical wave signal is greater than 3 times the turning frequency, the amplitude of the electromechanical wave decays to zero, and at this time the disturbance energy will no longer be able to propagate. Set the propagation coefficient PC = Δω / ω c , where Δω is the increment of the generator rotor angular frequency. The larger the PC, the smaller the influence of the electromechanical disturbance on the generator at this node. When PC is greater than 3, the generator will not be affected by the electromechanical disturbance.

[0064] Step 2: Determine whether the generator node is affected by the electromechanical disturbance according to the propagation coefficient, screen out the generators affected by the electromechanical disturbance, and calculate the composite electromechanical distance between the disturbance source point and the generator node affected by the disturbance

[0065] Based on the absolute quantity of the propagation time of the electromechanical disturbance between any two points, the composite electromechanical distance is defined. This load electromechanical distance represents the work angle increment θ that the generator rotates through when it accelerates (or decelerates) uniformly with a constant initial acceleration after the disturbance appears i required time, that is:

[0066]

[0067] In the formula: def means definition, that is, define the composite electromechanical distance is the composite electromechanical distance in seconds; w is the error correction factor, typically taken as w = 0.9; M i is the rotor inertia constant of generator node i; B is the transfer susceptance.

[0068] Between generator node i and generator node j, since Bij = Bji, but generally M i ≠M j , so it can be seen that the electromechanical distance is directional. For an actual power system, the propagation direction of electromechanical disturbances is difficult to determine. Therefore, an undirected electromechanical distance is set That is, the average electromechanical distance between generator node i (the disturbance source node) and j is:

[0069]

[0070] In the formula: represents the average electromechanical distance between node i and node j when the disturbance source point is i; represents the average electromechanical distance between node j and node i when the disturbance source point is j; represents the electromechanical distance between node i and node j when the disturbance source point is i; represents the electromechanical distance between node j and node i when the disturbance source point is j; B ij represents the transfer susceptance between node i and node j when the disturbance source point is i; B ji represents the transfer susceptance between node j and node i when the disturbance source point is j.

[0071] Under the action of the same electromechanical wave disturbance, the larger the inertia M i of the generator, the smaller the rotor acceleration of the generator under the action of the system acceleration power, the greater the hindrance to the propagation of the electromechanical wave, and the greater the electromechanical distance; similarly, when the transfer admittance B ij between the disturbance source point and the generator node is larger, the greater the acceleration power obtained by the generator, the greater the rotor acceleration of the generator, the greater the influence of the generator on the electromechanical wave disturbance, the smaller the hindrance to the propagation of the electromechanical wave, and the smaller the electromechanical distance. When an electromechanical disturbance occurs, the smaller the electromechanical distance, the faster the generator response speed and the closer the connection between the two machines.

[0072] Step 3: According to the composite electromechanical distance perform hierarchical clustering on the system. Accordingly, divide the power system into a research area (affected by electromechanical disturbances and participating in frequency regulation) and an external area (not affected by electromechanical disturbances and only performing power transmission), and aggregate the parameters of each generator in the research area:

[0073] According to hierarchical clustering, divide the original system into a research area and an external area, and perform parameter aggregation on the research area. For exampleFigure 4 As shown in the figure. Before the division, the generators in both the study area and the external area can participate in frequency regulation through tie lines. After the division, the generators in the external area only perform power transmission and do not participate in frequency regulation. The mechanical power increment of the steam turbine-governor model is as follows:

[0074]

[0075] In Equation (5): ΔP mT (s) is the mechanical power increment; F H is the proportion of the high-pressure turbine stage power; T R is the reheater time constant; R T is the steam turbine droop coefficient; T C is the air volume time constant; T G is the air chamber time constant; s is the complex frequency domain variable in the Laplace transform; Δω s (s) is the angular frequency increment. Suppose there are N synchronous machines in the power system. Since the steam turbine droop coefficient R T is related to the rated capacity S N , the constant gain for multiple steam turbine-governors is:

[0076]

[0077] In Equation (6): S Ni is the rated power of synchronous machine i; S sys is the rated power of the entire system. K mi represents the proportion of the rated power of synchronous machine i in the rated power of the entire system. The equivalent droop coefficient R of the power system is

[0078]

[0079] Among them, the equivalent gain is defined as κ i = K mi / R Ti , and R Ti is the droop coefficient of the i-th steam turbine. It can be seen from Equation (5) that the mechanical power increment of the steam turbine-governor model is affected by T G , T C , T R and F H and other four parameters. For simplicity of description, Equation (7) defines the normalized gain λ i to represent the comprehensive effect of the steam turbine-governor of synchronous machine i.

[0080]

[0081] Step 4: Establish the equivalent frequency response model of the system and conduct frequency response analysis on the study system:

[0082] According to Equations (5) to (8), the transfer functions of multiple synchronous machines are aggregated into the transfer function of an equivalent machine as follows:

[0083]

[0084] Based on Equation (9), a system frequency response aggregation model for the research area is established. As Figure 5 shown, the parameters of i steam turbines ( Figure 5 in the red box in the upper figure) are aggregated and equivalent to 1 steam turbine ( Figure 5 in the red box in the lower figure).

[0085] Step 5: For the system frequency response modeling and characteristic analysis method based on the electromechanical distance established above, its correctness is verified through simulation.

[0086] Build the IEEE 10-machine 39-bus system model as Figure 2 shown on the MATLAB / Simulink simulation platform to verify the effectiveness of the method of the present invention. The detailed data of the model and parameters in the example system can be referred to Table 1 and Table 2. The following settings are made before performing the example verification:

[0087] (1) At t = 100 s, set the sudden increase in load L3 = 700 MW (10% of the total load) to simulate a system frequency disturbance accident.

[0088] (2) Set the following simulation items:

[0089] 1) Calculate the corner frequency and electromechanical distance according to Step 1 and Step 2, and divide the example system into the research area and the external area by hierarchical clustering.

[0090] 2) Establish a system frequency response model, calculate the frequency of the research area, and compare it with the time-domain simulation frequency characteristics of the actual example system to verify the reliability of the classification method of the present invention.

[0091] Table 1 Line parameter values of the example system

[0092]

[0093]

[0094] Table 2 Synchronous machine parameter values

[0095]

[0096] For the system frequency response modeling method based on the characteristics of electromechanical wave propagation of the present invention, the effect verification:

[0097] When t = 100 s is set, the sudden increase in load L3 = 700 MW (located at node 39, accounting for 10% of the total load), the simulated system has a frequency accident and follows Figure 1 the control flow chart for execution.

[0098] Table 3 Calculation results of turning frequencies and propagation coefficients

[0099]

[0100]

[0101] According to Equation (2), the turning frequencies ω of each generator node are calculated c , as shown in Table 3. According to Step 1, since the propagation coefficients PC of G6 and G7 are greater than 3, it indicates that the amplitudes of the electromechanical wave disturbances of G6 and G7 are basically attenuated to zero. At this time, G6 and G7 are not affected by the electromechanical wave disturbances and cannot respond to the electromechanical wave disturbances. Therefore, G6 and G7 are classified into the external region and are not the main research objects.

[0102] Based on the above calculation results of the turning frequencies, the composite electromechanical distances between the disturbance source point G1 and the generators G2, G3, G4, G5, G8, G9, G10 affected by the electromechanical wave disturbances are calculated as shown in Table 4:

[0103] Table 4 Calculation results of composite electromechanical distances

[0104]

[0105] Performing hierarchical clustering on the above composite electromechanical distances can clearly observe the connection strengths between different generator sets. The results are as Figure 3 shown. From Figure 3 the hierarchical clustering results, it can be seen that the connections between the generator sets G1, G2, G3, G4, G8, G9 are very close, forming a relatively concentrated cluster. Therefore, G1, G2, G3, G4, G8, G9 are selected as the research area. The connection between generator G5 and other generator sets in the system is weak. Therefore, G5 is classified into the external region. From the above results, G1, G2, G3, G4, G8, G9, G10 are the research area, and G5, G6, G7 are the external regions. For the example system, the time-domain simulation method is used to calculate the system frequency characteristics and related indicators.

[0106] For the research area, the equivalent inertia constant of the system is aggregated and solved. Combining with the synchronous generator set model of the system, a system frequency response model of the research area can be established, as Figure 5 shown. Calculate the system frequency characteristics and related indicators. By comparing the coincidence degrees of the two frequency dynamic characteristics and related indicators, it can be reflected that the research area can equivalently replace the system frequency response. Compare the simulation calculation frequency response curves and related indicators, asFigure 6 As shown in Table 4. The frequency difference is the largest at t = 112.68 s. The actual frequency is 49.792 Hz, and the frequency in the study area is 49.776 Hz, with a difference of 0.016 Hz.

Claims

1. System frequency response analysis method based on electromechanical wave propagation characteristics, characterized by The following steps are involved: Step 1: Set the power shortage disturbance point and calculate the turning frequency ω between the disturbance source point and the generator node ci and propagation coefficient PC; Step 2: Determine whether the generator node is affected by the electromechanical disturbance based on the propagation coefficient PC; Step 3: Screen out the generators affected by the electromechanical disturbance and calculate the composite electromechanical distance between the disturbance source point and the generator node j affected by the disturbance Step 4: Based on the composite electromechanical distance Perform hierarchical clustering on the power system, divide the power system into the study area and the external area, and aggregate the parameters of each generator in the study area; Step 5: Establish the system equivalent frequency response model and calculate the frequency of the study area.

2. The system frequency response analysis method based on electromechanical wave propagation characteristics according to claim 1, characterized in that: In step 1, the power system is regarded as a grid continuum model of unevenly and continuously distributed generators, lines and loads. In the grid continuum model, the relationship between the electromechanical wave propagation speed and inertia is: In formula (1), v is the propagation speed of electromechanical waves; ω is the angular frequency of the generator; U is the per-unit value of the voltage amplitude; Δx is the distance between the two nodes; z is the per-unit value of the line unit impedance; and h is the inertia per unit length.

3. The system frequency response analysis method based on electromechanical wave propagation characteristics according to claim 2 is characterized by: In discrete power systems, electromechanical waves exist in a limited frequency range, which is related to the generator's rotational inertia and the system line impedance, and is expressed by the transition frequency ω. c express: When the electromechanical wave signal frequency is greater than the turning frequency ω c When the amplitude of the electromechanical wave along the propagation direction will decay rapidly; when the electromechanical wave signal frequency is greater than 3 times the turning frequency ω c When , the amplitude of the electromechanical wave decays to zero, and the disturbance energy can no longer propagate.

4. The system frequency response analysis method based on electromechanical wave propagation characteristics according to claim 3 is characterized by: Set the propagation coefficient PC = Δω / ω c , where Δω is the generator rotor angular frequency increment.

5. The system frequency response analysis method based on electromechanical wave propagation characteristics according to claim 4 is characterized by: In step 2, the larger the propagation coefficient PC is, the less the node generator is affected by the electromechanical disturbance. When the propagation coefficient PC is greater than 3, the generator will not be affected by the electromechanical disturbance.

6. The system frequency response analysis method based on electromechanical wave propagation characteristics according to claim 1 is characterized by: In step 3, the composite electromechanical distance is defined based on the propagation time of the electromechanical disturbance between any two points. Composite electromechanical distance It means that after the disturbance occurs, the generator rotates at a constant initial acceleration and performs uniform acceleration or deceleration, and the power angle increment θ i The time required is: Where: is the composite electromechanical distance, in seconds; w is the error correction factor; M i is the rotor inertia constant of generator node i; B is the transfer susceptance; def means definition, i.e., definition of composite electromechanical distance Between generator node i and generator node j, since Bij = Bji, but in general, M i ≠M j Therefore, it can be seen that the electromechanical distance is directional; for the actual power system, the propagation direction of the electromechanical disturbance is difficult to determine, so the electromechanical distance without direction is set That is, the average electromechanical distance between the generator disturbance source node i and the generator node j is: Where: It represents the average electromechanical distance between node i and node j when the disturbance source point is i; It represents the average electromechanical distance between node j and node i when the disturbance source point is j; It represents the electromechanical distance between node i and node j when the disturbance source point is i; represents the electromechanical distance between node j and node i when the disturbance source is j; B ij represents the transfer susceptance between node i and node j when the disturbance source is i; B ji It represents the transfer susceptance between node j and node i when the disturbance source point is j.

7. The system frequency response analysis method based on electromechanical wave propagation characteristics according to claim 6 is characterized by: Under the same electromechanical wave disturbance, the inertia of the generator M i The larger it is, the smaller the generator rotor acceleration under the system acceleration power, the greater the propagation barrier of the electromechanical wave, and the greater the electromechanical distance; Similarly, when the transfer admittance B between the disturbance source and the generator node ij The larger it is, the greater the acceleration power obtained by the generator, the greater the rotor acceleration of the generator, the greater the impact of the electromechanical wave disturbance on the generator, the smaller the obstacle to the propagation of the electromechanical wave, and the smaller the electromechanical distance; when an electromechanical disturbance occurs, the smaller the electromechanical distance, the faster the generator responds, and the closer the connection between the two machines.

8. The system frequency response analysis method based on electromechanical wave propagation characteristics according to claim 1 is characterized by: In step 4, the power system in the study area is partially affected by electromechanical disturbances and participates in frequency modulation; the power system in the external area is partially not affected by electromechanical disturbances and only performs power transmission; hierarchical clustering is performed on the power system, and the power system is divided into the study area and the external area according to the hierarchical clustering results. Before the division, the generators in the study area and the external area all participate in frequency modulation through the tie line; After the division, the generators in the outer area only perform power transmission and do not participate in frequency regulation.

9. The system frequency response analysis method based on electromechanical wave propagation characteristics according to claim 8, characterized in that: Perform parameter aggregation on the steam turbines in the study area. include: Among them, the mechanical power increment of the turbine-governor model is: In formula (5): ΔP mT (s) is the mechanical power increment; F H is the power proportion of the high-pressure turbine stage; T R is the reheater time constant; R T is the turbine regulation coefficient; T C is the gas volume time constant; T G is the air chamber time constant; s is the complex frequency domain variable in Laplace transform; Δω s (s) is the angular frequency increment; Assume that there are N synchronous machines in the power system; due to the turbine adjustment coefficient R T With rated capacity S N For a multi-turbine-governor, the constant gain is: In formula (6): S Ni is the rated power of synchronous machine i; S sys is the rated power of the entire system; K mi It represents the ratio of the rated power of synchronous machine i to the rated power of the whole system; The equivalent droop coefficient R of the power system is: where the equivalent gain is defined as κ i =K mi / R Ti , R Ti is the regulation coefficient of the i-th steam turbine; From formula (5), we can see that the mechanical power increment of the turbine-governor model is affected by T G 、T C 、T R and F H In order to simplify the description, the normalized gain λ is defined in equation (7): i represents the combined effect of the turbine-governor of synchronous machine i; 10. The system frequency response analysis method based on electromechanical wave propagation characteristics according to claim 9, characterized in that: In step 5, according to equations (5) to (8), the transfer functions of multiple synchronous machines are aggregated into one equivalent machine transfer function: According to formula (9), the frequency response aggregation equivalent model of the power system in the study area is established, and the parameters of i steam turbines are aggregated and equivalent to one steam turbine.

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