A method for identification and quantitative remodeling of key converter port admittance of a multi-feed system

Abstract

This invention provides a method for identifying and quantitatively reshaping the port admittance of key converters in multi-infeed systems, belonging to the field of small-signal stability analysis and improvement of multi-infeed systems in new energy sources. The method includes: establishing a small-signal model of the active subsystem; constructing a small-signal model of the passive subsystem; constructing the open-loop transfer function of the multi-infeed system; determining the stability of the multi-infeed system by combining the open-loop transfer function and the generalized Nyquist criterion; calculating the admittance sensitivity for the eigenvalues ​​that cause instability in the multi-infeed system; identifying the port admittance of key converters in the multi-infeed system; quantifying the reshaping value of the key converter port admittance by combining phase compensation and admittance sensitivity values; and quantitatively reshaping the key converter port admittance using voltage feedforward. This invention improves the small-signal stability of multi-infeed systems by identifying and quantitatively reshaping the port admittance of key converters that have the greatest impact on system stability, thereby achieving a quantitative improvement in the phase of system eigenvalues ​​at the oscillation frequency.

Description

Technical Field

[0001] This invention relates to the field of small-signal stability analysis and improvement of new energy multi-infeed systems, and in particular to a method for identifying and quantitatively reshaping the port admittance of key converters in multi-infeed systems. Background Technology

[0002] To achieve the "dual carbon" goals and promote energy transition, new energy sources, represented by wind power and photovoltaics, have been vigorously developed. Converters, due to their high efficiency and flexibility, are widely used at the interface between new energy sources and the power grid. However, their interaction with the grid is prone to small-signal instability due to impedance mismatch. With the continuous expansion of new energy grid integration and the increasing dispersion of integration locations, multi-feed systems for new energy are gradually taking shape. In this scenario, the different capacities and control parameters of new energy converters at different integration locations lead to differences in the impedance / admittance characteristics of converters at different integration points. This makes the source-grid interaction more complex, increases the factors that could cause system instability, and dramatically raises the risk of small-signal instability.

[0003] Existing methods for improving small-signal stability in multi-infeed systems of new energy sources treat each converter equally, failing to consider the differences between converters and their varying degrees of impact on system stability. They add the same active damping control to each converter individually. However, this approach faces significant limitations in engineering practice: real-world multi-infeed systems have a large number of converters, making it difficult to implement additional damping operations on each converter individually, resulting in poor economic efficiency in engineering applications. Summary of the Invention

[0004] To address the aforementioned shortcomings in the existing technology, this invention provides a method for identifying and quantitatively reshaping the port admittance of key converters in multi-feed systems, which solves the problem of small-signal instability caused by the dispersed connection of a large number of differentiated converters to the power grid.

[0005] To achieve the above objectives, the technical solution adopted by this invention is: a method for identifying and quantitatively reshaping the port admittance of a key converter in a multi-feed system, comprising: S1. Based on the voltage and current relationship between the converter and the power supply port in the active subsystem, establish... dq Small-signal model of active subsystems in coordinate system F a ; S2. Eliminate nodes not connected to active components based on the node admittance matrix, and obtain the small-signal model of the passive subsystem characterizing the small-signal characteristics of the line based on the input-output relationship between passive subsystems. F p ; S3, Based on small signal model F a and small signal model Fp Construct the overall open-loop transfer function of the multi-feed system. F ; S4, combined with open-loop transfer function F The generalized Nyquist criterion is used to determine the stability of the multi-feed system. If the system is stable, the process ends; otherwise, proceed to step S5. S5. Calculate the corresponding admittance sensitivity for the characteristic values ​​that cause instability in the multi-feed system; S6. Based on admittance sensitivity, identify the key converter port admittance of the multi-feed system, and combine the phase compensation method to quantify the reshaped value of the key converter port admittance. S7. Based on the reshaping value obtained by quantization, the admittance of the key converter port is quantitatively reshaped using voltage feedforward.

[0006] The beneficial effects of this invention are as follows: By calculating admittance sensitivity, identifying the key converter port admittance of a multi-infeed system, quantifying the reshaping value of the key converter port admittance, and then using voltage feedforward to quantitatively reshape the key converter port admittance, this invention can determine the small-signal stability of a multi-infeed system containing heterogeneous converters, identify the key converter port admittance that has the greatest impact on system stability, and achieve the purpose of quantitatively improving the small-signal stability of the multi-infeed system by quantitatively reshaping the key converter port admittance.

[0007] Furthermore, the relationship between the voltage and current at the converter and the grid power supply port is expressed as follows:

[0008]

[0009] in, and They represent converters The current vector and voltage vector at the grid connection point. T Represents the transformation matrix. and They represent converters In local dq Admittance matrices in the coordinate system and the global coordinate system. Indicates converter The equivalent current source, Represents the transformation matrix T The inverse matrix, Indicates converter local dq Coordinate system and global dq Angular difference between coordinate systems and Representing ports respectively N+j The current vector and voltage vector, Indicates grid power supply j The impedance matrix, Indicates grid power supply j The voltage vector; The small signal model F a The expression is as follows:

[0010] in, This represents the output vector of the active subsystem. This represents the input vector of the active subsystem. Indicates converter N The admittance matrix, N Indicates the total number of converters. Indicates grid power supply M The impedance matrix, M The total number of power sources in the power grid. It represents the equivalent power source in an active subsystem.

[0011] The beneficial effect of the above further scheme is that, based on the relationship between the voltage and current at the converter and the power supply port in the active subsystem, a [system / mechanism] can be established. dq Small-signal model of active subsystems in coordinate system F a This lays the model foundation for establishing the open-loop transfer function of the system.

[0012] Furthermore, the passive subsystem small-signal model F p The expression is as follows:

[0013] in, This represents the output vector of the passive subsystem. This represents the input vector of the passive subsystem. , , and Both represent submatrices of the simplified matrix of the nodal admittance matrix.

[0014] The beneficial effects of the above-mentioned further scheme are: eliminating nodes not connected to active components based on the node admittance matrix, and obtaining a passive subsystem small-signal model characterizing the small-signal characteristics of the line based on the input-output relationship between passive subsystems. F p This lays the model foundation for establishing the open-loop transfer function of the system.

[0015] Furthermore, the open-loop transfer function F The expression is as follows:

[0016] in, This represents the output vector of the active subsystem. E Represents the identity matrix. Indicating the equivalent power source in an active subsystem, F a F p Defined as the open-loop transfer function of the system F .

[0017] The beneficial effect of the above further scheme is: based on the small signal model F a and small signal model F p Construct the overall open-loop transfer function of the multi-feed system. F This information is then used to determine the stability of the system.

[0018] Furthermore, the open-loop transfer function is calculated using the generalized Nyquist criterion. F Eigenvalues λ The expression is as follows:

[0019] in, This indicates the calculation of the rows and columns of a matrix.

[0020] The beneficial effect of the above further scheme is: to plot the open-loop transfer function of the system. F Eigenvalues λ The Nyquist curve is used to determine the stability of a system: if the eigenvalues λ If the Nyquist curves do not enclose the point (-1, j0), the system is stable; otherwise, the system is unstable.

[0021] Furthermore, the expression for the admittance sensitivity is as follows:

[0022] in, Indicates converter ( q , r The admittance sensitivity of the port. Indicates the instability eigenvalue. Representing the small signal model F a The Middle q OK r Column elements, Represent the open-loop transfer function F The first in k 1 left eigenvalue vector This indicates the initial state of the converter admittance. Represent the open-loop transfer function F The first in k A right eigenvalue vector.

[0023] The beneficial effect of the above-mentioned further scheme is that, for the characteristic values ​​that cause instability in multi-feed systems, the corresponding admittance sensitivity is calculated, and the influence of the admittance of each converter port on system stability is quantified.

[0024] Furthermore, the expression for the change in eigenvalues ​​of the key converter port admittance identification is as follows:

[0025] Where, Δ λ k Δ represents the change in eigenvalues. f a_q,r This represents the admittance correction. N Indicates the total number of converters. Represent the open-loop transfer function F The first in k 1 left eigenvalue vector This indicates the initial state of the converter admittance. Representing the small signal model F a The Middle q OK r Column elements, Represent the open-loop transfer function F The first in k A right eigenvalue vector, Indicates converter ( q , r The admittance sensitivity of the port.

[0026] The beneficial effect of the above-mentioned further scheme is that the port with the largest admittance sensitivity amplitude causes the largest eigenvalue shift under the same admittance increment, and has the most significant impact on system stability. Therefore, this port is identified as the key converter port admittance and is the object of admittance reshaping.

[0027] Furthermore, the expression for the phase compensation method is as follows:

[0028] in, K This represents the coefficient related to phase compensation. Indicates the oscillation frequency The change in eigenvalues ​​under the following conditions Indicates oscillation frequency The phase boosted by the lower eigenvalue, where j represents the imaginary unit. Indicates oscillation frequency The multi-feed system k Each feature value.

[0029] Furthermore, the expression for the reshaped value of the key converter port admittance is as follows:

[0030] in, Indicates the oscillation frequency, Δ λ k Indicates the change in eigenvalues. This represents the coefficient related to phase compensation. Indicates oscillation frequency The multi-feed system k 1 eigenvalue, Indicates the converter with the largest amplitude. n ( , The admittance sensitivity of the port. Indicates oscillation frequency f c Next key converter n ( , The required corrected admittance value for the port. and represents the magnitude and phase of the admittance increase, respectively, and j represents the imaginary unit.

[0031] The beneficial effect of the above further scheme is that it increases the phase of the eigenvalues ​​that cause system instability at the oscillation frequency. This improves the stability of the system.

[0032] Furthermore, the key converter n The admittance value increases by matrix Δ Y vscn The expression is as follows:

[0033] in, , , and These represent the oscillation frequencies respectively. f c Next key converter n of dd port, dq port, qd ports and qq The required increase in admittance for the port.

[0034] The beneficial effect of the above-mentioned further scheme is that by quantitatively reshaping the admittance of the key converter port, the phase of the system characteristic value at the oscillation frequency can be quantitatively improved.

[0035] Furthermore, S7 includes: Based on the reshaped values ​​obtained through quantization, voltage feedforward control combined with a second-order bandpass filter with phase compensation is used to control the key converter. n Port admittance is quantitatively reshaped.

[0036] Furthermore, voltage feedforward controller G vi,n The expression for the transfer function is as follows:

[0037] in, Z L,n Represents the filter impedance matrix. K n This represents the proportional gain of space vector pulse width modulation. G d,n Represents the delay matrix, G c,n This represents the current loop PI control matrix. G a3,n This represents the voltage vector correction matrix taking into account the effects of the phase-locked loop, Δ. Y vscn Indicates converter n The admittance value increases with the matrix.

[0038] The beneficial effect of the above-mentioned further scheme is that it utilizes voltage feedforward to reshape the quantitative admittance of the key converter.

[0039] Among them, a second-order bandpass filter with phase compensation is used for the converter. n The admittance value increases by matrix Δ Y vscn The elements in the text are described as follows:

[0040] in, Indicates oscillation frequency f c Next key converter n ( , The required corrected admittance value for the port. and These represent the magnitude and phase of the admittance increase, respectively. s Represents a complex frequency variable. This indicates the angular frequency information of the filter.

[0041] The beneficial effect of the above-mentioned further scheme is that it can quantitatively reshape the port admittance of key converters in practical scenarios by using a bandpass filter with phase compensation. Attached Figure Description

[0042] Figure 1 This is a flowchart of the method of the present invention.

[0043] Figure 2 This is a topology diagram of a new energy multi-infeed system containing 4 converters and 2 grid power sources.

[0044] Figure 3 shows the Nyquist plots of the eigenvalues ​​of the multi-feed system, where Figure 3(a) is... λ 1- λ The Nyquist plot of 6, Figure 3(b) is λ 7- λ 12 The Nyquist plot.

[0045] Figure 4 Admittance sensitivity analysis for multi-feed systems.

[0046] Figure 5 The diagram shows the admittance reshaping method for converter 1 based on voltage feedforward.

[0047] Figure 6 After admittance reshaping λ Nyquist plot of 1.

[0048] Figure 7 Waveforms of the voltage at the grid connection point of converter 1 before and after admittance reshaping. Detailed Implementation

[0049] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0050] Example like Figure 1 As shown, this invention provides a method for identifying and quantitatively reshaping the port admittance of key converters in a multi-feed system, the implementation of which is as follows: S1. Based on the voltage and current relationship between the converter and the power supply port in the active subsystem, establish... dq Small-signal model of active subsystems in coordinate system F a ; In this embodiment, in S1, the active subsystem includes all active components (converter and grid power supply) in the system, based on the relationship between the voltage and current at the converter and grid power supply ports:

[0051]

[0052] in, and They represent converters The current vector and voltage vector at the grid connection point. T Represents the transformation matrix. and They represent converters In local dq Admittance matrices in the coordinate system and the global coordinate system. Indicates converter The equivalent current source, Represents the transformation matrix T The inverse matrix, Indicates converter local dq Coordinate system and global dq Angular difference between coordinate systems and Representing ports respectively N+j The current vector and voltage vector, Indicates grid power supply j The impedance matrix, Indicates grid power supply j The voltage vector.

[0053] Small-signal models of active subsystems can be constructed. F a :

[0054] X a =[ v 1… v N i N+1 … i N+M ] -1 This represents the input of an active subsystem. O a =[ i 1… i N v N+1 … v N+M ]-1 This represents the output vector of the active subsystem. C a =[ I s1 … I sN v g1 … v gM ] -1 This represents the equivalent power source in an active subsystem. Indicates converter N The admittance matrix, Indicates grid power supply M The impedance matrix, i N and v N Representing ports respectively N The current vector and voltage vector, i N+M and v N+M Representing ports respectively N + M The current vector and voltage vector, N Indicates the total number of converters. M This indicates the total number of power sources in the power grid.

[0055] S2. Eliminate nodes not connected to active components based on the node admittance matrix, and obtain the small-signal model of the passive subsystem characterizing the small-signal characteristics of the line based on the input-output relationship between passive subsystems. F p ; In this embodiment, in S2, the passive subsystem is used to describe the small-signal characteristics of passive lines in the network, and the output and input of the passive subsystem are the same as the input and output of the active subsystem. Therefore, based on the node admittance matrix, the small-signal model of the passive subsystem is established using the Kron simplification method and matrix transformation. F p :

[0056] in, , , and Each represents a submatrix of the simplified matrix of the nodal admittance matrix. X p =[ i 1… i N v N+1 … v N+M ]-1 This represents the input vector of the passive subsystem. O p =[ v 1… v N i N+1 … i N+M ] -1 This represents the output vector of the passive subsystem.

[0057] S3, Based on small signal model F a and small signal model F p Construct the overall open-loop transfer function of the multi-feed system. F ; In this embodiment, in S3, by combining the small-signal models of the active and passive subsystems, a small-signal model of the entire multi-feed system can be constructed:

[0058] in, E Represents the identity matrix. F a F p The open-loop transfer function of the system is related to the stability of the multi-feed system and is defined as follows: F .

[0059] S4, combined with open-loop transfer function F The generalized Nyquist criterion is used to determine the stability of the multi-feed system. If the system is stable, the process ends; otherwise, proceed to step S5. In this embodiment, in S4, the open-loop transfer function of the system is calculated using the generalized Nyquist criterion. F Eigenvalues λ :

[0060] in, This indicates the calculation of the rows and columns of a matrix.

[0061] By drawing the system open-loop transfer function F Eigenvalues λ The Nyquist curve is used to determine the stability of the system: if λ If the Nyquist curves do not enclose the point (-1, j0), the system is stable; otherwise, the system is unstable.

[0062] S5. Calculate the corresponding admittance sensitivity for the characteristic values ​​that cause instability in the multi-feed system; In this embodiment, the initial state of the converter admittance is defined as follows:P 0=( f a0_1,1 , f a0_1,2 , f a0_2,1 , f a0_2,2 ,…, f a0_2N, 2N In the case of instability in a multi-infeed system of new energy sources, the characteristic values ​​that lead to system instability are targeted. λ k Calculate the corresponding admittance sensitivity S ak ( q , r ):

[0063] in, Indicates converter ( q , r The admittance sensitivity of the port. Indicates the instability eigenvalue. Representing the small signal model F a The Middle q OK r Column elements, Represent the open-loop transfer function F The first in k 1 left eigenvalue vector This indicates the initial state of the converter admittance. Represent the open-loop transfer function F The first in k A right eigenvalue vector.

[0064] S6. Based on admittance sensitivity, identify the key converter port admittance of the multi-feed system and quantify the remodeling value of the key converter port admittance. In this embodiment, in S6, the first-order Taylor expansion of the eigenvalues, i.e., the expression for the change in eigenvalues, is as follows:

[0065] Where, Δ λ k Δ represents the change in eigenvalues. f a_q,r This represents the admittance correction. N Indicates the total number of converters. q and r They represent the small signal model respectively. F a The row and column indices of the element (converter port admittance) range from 1, 2, ..., 2.N , Represent the open-loop transfer function F The first in k 1 left eigenvalue vector This indicates the initial state of the converter admittance. Representing the small signal model F a The Middle q OK r Column elements, Represent the open-loop transfer function F The first in k A right eigenvalue vector, Indicates converter ( q , r The admittance sensitivity of the port.

[0066] The port with the largest admittance sensitivity amplitude causes the largest eigenvalue shift under the same admittance increment, and has the most significant impact on system stability. Therefore, this port is identified as the key converter port admittance and is the target for admittance reshaping.

[0067] Furthermore, a phase compensation method is employed, which increases the phase of the eigenvalues ​​that cause system instability at the oscillation frequency. This improves system stability.

[0068] in, K This represents the coefficient related to phase compensation. Indicates the oscillation frequency The change in eigenvalues ​​under the following conditions Indicates oscillation frequency The phase boosted by the lower eigenvalue, where j represents the imaginary unit. Indicates oscillation frequency The multi-feed system k Each feature value.

[0069] By increasing the phase of the eigenvalues ​​that cause system instability at the oscillation frequency. This improves the stability of the system.

[0070] By combining admittance sensitivity analysis values ​​and system characteristic value corrections, the key converter port admittance correction is quantified. Assuming the converter... n of( , Port admittance sensitivity If the amplitude is at its maximum, it represents the critical converter port admittance, and its quantized reshaped value is:

[0071] in, Indicates the oscillation frequency, Δ λ k Indicates the change in eigenvalues. This represents the coefficient related to phase compensation. Indicates oscillation frequency The multi-feed system k 1 eigenvalue, Indicates the converter with the largest amplitude. n ( , The admittance sensitivity of the port. Indicates oscillation frequency f c Next key converter n The required corrected admittance value for the port. and These represent the magnitude and phase of the admittance increase, respectively. and These represent the key converters. n The row and column indices of the port admittance, where j represents the imaginary unit.

[0072] By quantitatively reshaping the admittance of key converter ports, a quantitative improvement in the phase of the system characteristic value at the oscillation frequency can be achieved.

[0073] Corresponding key converters n The admittance value increases by matrix Δ Y vscn The expression is as follows:

[0074] Where, Δ f a_2n-1,2n-1 ( f c ), Δ f a_2n-1,2n ( f c ), Δ f a_2n,2n-1 ( f c ) and Δ f a_2n,2n ( f c ) respectively represent in f c Next key converter n of dd port, dq port, qd ports and qq The required increase in admittance for a port is 0 if it is not a critical converter port admittance.

[0075] S7. Based on the reshaping value obtained by quantization, the admittance of the key converter port is quantitatively reshaped using voltage feedforward.

[0076] In this embodiment, in S7, voltage feedforward control combined with a second-order bandpass filter with phase compensation is used to identify the key converter. n Perform admittance reshaping to achieve the expected admittance correction Δ. Y vscn Voltage feedforward controller G vi,n The specific transfer function expression is:

[0077] in, Z L,n Represents the filter impedance matrix. K n This represents the proportional gain of space vector pulse width modulation. G d,n Represents the delay matrix, G c,n Represents the current loop PI control matrix G a3,n This represents the voltage vector correction matrix taking into account the effects of the phase-locked loop, Δ. Y vscn Indicates converter n The admittance value increases with the matrix.

[0078] A second-order bandpass filter with phase compensation is used for Δ Y vscn The elements in the text are described as follows:

[0079] in, Indicates oscillation frequency f c Next key converter n The required correction to the admittance. and These represent the magnitude and phase of the admittance increase, respectively. s Represents a complex frequency variable. This indicates the angular frequency information of the filter. and These represent the key converters. n The row and column indices of the port admittance, where j represents the imaginary unit.

[0080] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0081] Figure 2The diagram shows a new energy multi-infeed system containing four converters and two grid power sources. Different control parameters are set for each converter to reflect their differences. Specific parameter settings for the converters and the system are shown in Tables 1 and 2.

[0082] Table 1 Converter Parameters

[0083] Table 2 System Parameters

[0084] pass Figure 2 The active subsystem model of the multi-feed system is obtained:

[0085] In the passive subsystem, nodes without connections to active components are not reflected in the interaction between the two subsystems. Therefore, the Kron simplification method is first used to eliminate these nodes. Then, based on the connection relationship between the active and passive subsystems, it can be seen that the input and output of the passive subsystem are respectively the output and input of the active subsystem. After matrix transformation, the small-signal model of the passive subsystem shown is obtained. F p :

[0086] in, Y 11 , Y 12 , Y 21 , Y 22 Submatrices that simplify the nodal admittance matrix.

[0087] By combining the small-signal models of the active and passive subsystems, the open-loop transfer function of the multi-feed system can be obtained: F = F a F p .

[0088] Figure 3 shows the Nyquist curves of the eigenvalues ​​of a multi-infeed system according to the present invention's method for identifying and quantitatively reshaping the port admittance of key converters in a multi-infeed system. As can be seen from the figure, the system... λ 2 to λ 12 None of the Nyquist curves enclose the point (-1, j0); λ The Nyquist curve of 1 encloses the point (-1, j0), and the intersection of the Nyquist curve and the unit circle characterizes the oscillation frequency of the system. f cThis indicates that the system is unstable and the theoretical oscillation frequency is... f c The frequency is 319.00 Hz, and the phase margin is -6.12°.

[0089] calculate λ 1 corresponds to admittance sensitivity S ak ( q , r ), Figure 4 The oscillation frequency is given. f c At 319.00 Hz, λ 1. Sensitivity amplitude regarding the port admittance of each converter. (From...) Figure 4 It can be seen that converter 1's qq The port admittance sensitivity amplitude is 0.35, which is significantly greater than the port admittance sensitivity amplitudes of other converters, indicating that converter 1... qq Port admittance has the greatest impact on system stability and is the key to the specific implementation of admittance reshaping of converter port admittance.

[0090] To improve system stability and retain a certain phase margin, the objective of admittance reshaping is set as: to make λ 1 at the oscillation frequency f c The phase at that point is increased by 20°. Combining the eigenvalue correction and admittance sensitivity values, the converter 1's... qq The port admittance remodeling value increases by 1.01e. j(-0.10) Ω is achieved using a second-order bandpass filter with phase compensation:

[0091] Admittance reshaping value Δ of converter 1 Y vsc1 [0 0;0 Δ] f a_2,2 ( f c )],use Figure 5 The voltage feedforward method is used to quantitatively reshape the admittance of converter 1.

[0092] Figure 6 The converter 1 admittance reshaping is given. λ The Nyquist curve of 1. Combined with... Figure 2 and Figure 6 Analysis shows that at 319.00 Hz λ The phase of 1 increased by 13.79° - (-6.12°) = 19.91°, which is consistent with the expected target of 20° for the phase increase of the system's eigenvalues, effectively improving the stability of the system.

[0093] A model of a multi-feed system was built in the HIL hardware-in-the-loop experimental platform, and the port voltage of converter 1 was used as the data for subsequent analysis. Figure 7 The voltage waveforms at the grid connection point of converter 1 before and after admittance reshaping are shown, indicating that the system initially oscillates. When the proposed admittance reshaping strategy is added to converter 1, the voltage and current of converter 1 return to sinusoidal, and the system stability is improved.

[0094] In summary, this invention establishes a synchronous rotating coordinate system based on the voltage and current relationship between the converter and the power grid port in the active subsystem. dq Small-signal model of active subsystems in coordinate system F a Construct a small-signal model of a passive subsystem. F p Combining small-signal models of active and passive subsystems, an open-loop transfer function for a new energy multi-infeed system is constructed. F By combining the system's open-loop transfer function and the generalized Nyquist criterion, the stability of the multi-feed system is determined; for the eigenvalues ​​that cause system instability, the corresponding admittance sensitivity is calculated. S ak ( q , r This invention identifies the key converter port admittances of a multi-infeed system and quantifies their reshaped values. Voltage feedforward is then used to quantitatively reshape the key converter port admittances. By identifying and quantitatively reshaping the key converter port admittances that have the greatest impact on system stability, this invention achieves a quantitative improvement in the phase of the system's eigenvalues ​​at the oscillation frequency, thereby enhancing the small-signal stability of the multi-infeed system.

[0095] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for identifying and quantitatively reshaping the port admittance of a key converter in a multi-infeed system, characterized in that, Includes the following steps: S1. Based on the voltage and current relationship between the converter and the power supply port in the active subsystem, establish... dq Small-signal model of active subsystems in coordinate system F a ; S2. Eliminate nodes not connected to active components based on the node admittance matrix, and obtain the small-signal model of the passive subsystem characterizing the small-signal characteristics of the line based on the input-output relationship between passive subsystems. F p ; S3, Based on small signal model F a and small signal model F p Construct the overall open-loop transfer function of the multi-feed system. F ; S4, combined with open-loop transfer function F The stability of the multi-feed system is determined using the generalized Nyquist criterion; if the system is stable, the process ends. Otherwise, proceed to S5; S5. Calculate the corresponding admittance sensitivity for the characteristic values ​​that cause instability in the multi-feed system; S6. Based on admittance sensitivity, identify the key converter port admittance of the multi-feed system, and combine the phase compensation method to quantify the reshaped value of the key converter port admittance. S7. Based on the reshaping value obtained by quantization, the admittance of the key converter port is quantitatively reshaped using voltage feedforward.

2. The method for identifying and quantitatively reshaping the port admittance of key converters in a multi-feed system according to claim 1, characterized in that, The expression for the relationship between voltage and current at the converter and grid power supply ports is as follows: in, and They represent converters The current vector and voltage vector at the grid connection point. T Represents the transformation matrix. and They represent converters In local dq Admittance matrices in the coordinate system and the global coordinate system. Indicates converter The equivalent current source, Represents the transformation matrix T The inverse matrix, Indicates converter local dq Coordinate system and global dq Angular difference between coordinate systems and Representing ports respectively N+j The current vector and voltage vector, Indicates grid power supply j The impedance matrix, Indicates grid power supply j The voltage vector; The small signal model F a The expression is as follows: in, This represents the output vector of the active subsystem. This represents the input vector of the active subsystem. Indicates converter N The admittance matrix, N Indicates the total number of converters. Indicates grid power supply M The impedance matrix, M The total number of power sources in the power grid. It represents the equivalent power source in an active subsystem.

3. The method for identifying and quantitatively reshaping the port admittance of key converters in a multi-feed system according to claim 1, characterized in that, The passive subsystem small-signal model F p The expression is as follows: in, This represents the output vector of the passive subsystem. This represents the input vector of the passive subsystem. , , and Both represent submatrices of the simplified matrix of the nodal admittance matrix.

4. The method for identifying and quantitatively reshaping the port admittance of key converters in a multi-feed system according to claim 1, characterized in that, The open-loop transfer function F The expression is as follows: in, This represents the output vector of the active subsystem. E Represents the identity matrix. Indicating the equivalent power source in an active subsystem, F a F p Defined as the open-loop transfer function of the system F .

5. The method for identifying and quantitatively reshaping the port admittance of key converters in a multi-feed system according to claim 1, characterized in that, Calculate the open-loop transfer function using the generalized Nyquist criterion. F Eigenvalues λ The expression is as follows: in, This indicates the calculation of the rows and columns of a matrix.

6. The method for identifying and quantitatively reshaping the port admittance of a key converter in a multi-feed system according to claim 1, characterized in that, The expression for the admittance sensitivity is as follows: in, Indicates converter ( q , r The admittance sensitivity of the port. Indicates the instability eigenvalue. Representing the small signal model F a The Middle q OK r Column elements, Represent the open-loop transfer function F The first in k 1 left eigenvalue vector This indicates the initial state of the converter admittance. Represent the open-loop transfer function F The first in k A right eigenvalue vector.

7. The method for identifying and quantitatively reshaping the port admittance of key converters in a multi-feed system according to claim 1, characterized in that, The expression for the characteristic value change of the key converter port admittance identification is as follows: Where, Δ λ k Δ represents the change in eigenvalues. f a_q,r This represents the admittance correction. N Indicates the total number of converters. Represent the open-loop transfer function F The first in k 1 left eigenvalue vector This indicates the initial state of the converter admittance. Representing the small signal model F a The Middle q OK r Column elements, Represent the open-loop transfer function F The first in k A right eigenvalue vector, Indicates converter ( q , r The admittance sensitivity of the port.

8. The method for identifying and quantitatively reshaping the port admittance of a key converter in a multi-feed system according to claim 1, characterized in that, The expression for the phase compensation method is as follows: in, K This represents the coefficient related to phase compensation. Indicates the oscillation frequency The change in eigenvalues ​​under the following conditions Indicates oscillation frequency The phase boosted by the lower eigenvalue, where j represents the imaginary unit. Indicates oscillation frequency The multi-feed system k Each feature value.

9. The method for identifying and quantitatively reshaping the port admittance of a key converter in a multi-feed system according to claim 1, characterized in that, The expression for the reshaped value of the key converter port admittance is as follows: in, Indicates the oscillation frequency, Δ λ k Indicates the change in eigenvalues. This represents the coefficient related to phase compensation. Indicates oscillation frequency The multi-feed system k 1 eigenvalue, Indicates the converter with the largest amplitude. n ( , The admittance sensitivity of the port. Indicates oscillation frequency f c Next key converter n ( , The required corrected admittance value for the port. and represents the magnitude and phase of the admittance increase, respectively, and j represents the imaginary unit.

10. The method for identifying and quantitatively reshaping the port admittance of a key converter in a multi-feed system according to claim 1, characterized in that, S7 includes: Based on the reshaped values ​​obtained through quantization, voltage feedforward control combined with a second-order bandpass filter with phase compensation is used to control the key converter. n Quantitative reshaping of port admittance; Voltage feedforward controller G vi,n The expression for the transfer function is as follows: in, Z L,n Represents the filter impedance matrix. K n This represents the proportional gain of space vector pulse width modulation. G d,n Represents the delay matrix, G c,n This represents the current loop PI control matrix. G a3,n This represents the voltage vector correction matrix taking into account the effects of the phase-locked loop, Δ. Y vscn Indicates converter n The admittance value increases the matrix. , , and These represent the oscillation frequencies respectively. f c Next key converter n of dd port, dq port, qd ports and qq The required increase in admittance for a port is 0 if it is not a critical converter port admittance. Among them, a second-order bandpass filter with phase compensation is used for the converter. n The admittance value increases by matrix Δ Y vscn The elements in the text are described as follows: in, Indicates oscillation frequency f c Next key converter n ( , The required admittance value for the port. and These represent the magnitude and phase of the admittance increase, respectively. s Represents a complex frequency variable. This indicates the angular frequency information of the filter. and These represent the key converters. n The row and column indices of the port admittance, where j represents the imaginary unit.

Images